ANALYSIS OF HEAVY PARAFFINIC FISCHER-TROPSCH WAXES
USING GEL PERMEATION CHROMATOGRAPHY
by
HARRY ELLIS JOHNSON
B.S.,
Stanford University
(1981)
Submitted to the Department of
Chemical Engineering
in Partial Fulfillment of the
Requirements of the Degree of
MASTER OF SCIENCE
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
May 1983
@c
Massachusetts Institute of Technology 1983
Signature redacted---
Signature of Author
06e
Certified by
r md nt o femical Engineering
May 1983
1/4
Signature redacted
Professor Charlds N. Satterfield
Thesis Supervisor
Accepted by
Sig iature redacted
Archives
MASSACHUSETTS INSTiTUTE
OF TECHNOLOGY
OCT 2 41983
LIBRARIES
Professor Glenn C. Williams
Chairman, Department Committee
2
ANALYSIS OF HEAVY PARAFFINIC FISCHER-TROPSCH
WAXES USING GEL PERMEATION CHROMATOGRAPHY
by
HARRY ELLIS JOHNSON
Submitted to the Department of Chemical Engineering
on May 1, 1983 in partial fulfillment of the
requirements for the degree of Master of Science in
Chemical Engineering
ABSTRACT
The technique of Gel Permeation Chromatography
(GPC) was
utilized in analysis of paraffinic wax samples generated via
the Fischer-Tropsch synthesis in a slurry reactor.
Chromtograms were obtained by using standard GPC equipment with Waters
100 and 500A Ultrastyragel TM columns.
Differential number
fraction molecular weight distributions were obtained to C70
and C105 for ambient and elevated temperature injections re-
spectively.
Corresponding relation of heavy wax hydrocarbonproduct distributions to Flory plots show chain growth probability factor a value of 0.92 - 0.94.
These values are within
experimental accuracy of results found by previous investigators obtained by vapor-phase gas chromatography analysis.
The
results indicate that GPC may be used successfully in obtaining
quantitative data for heavy solid products formed by slurryreactor operation of the Fischer-Tropsch synthesis.
Thesis Advisor:
Title:
Charles N. Satterfield
Professor of Chemical Engineering
3
MASSACHUSETTS
INSTITUTE OF TECHNOLOGY
DEPARTMENT OF
CHEMICAL ENGINEERING
Room number:
6 6-2 5 0
Cambridge, Massachusetts
02139
Telephone:
253-6546
May 1, 1983
Professor Jack P. Ruina
Secretary of the Faculty
Massachusetts Institute of Technology
Dear Professor Ruina:
In accordance with the regulations of the faculty, I
submit herewith a thesis entitled "Ai1alysis of Heavy Paraffinic
Fischer-Tropsch Waxes Using Gel Permeattion Chromatography," in
partial fulfillment of the requirements for the degree of Master
of Science in Chemical Engineering at the Massachusetts
Institute of Technology.
Respectfully submitted,
,/
Signature redacted
4
ACKNOWLEDGEMENTS
I would like to thank my thesis advisor Professor Charles
Satterfield for his helpful support and critism.
I will remember to "stick to the facts".
I hope that
I also wish to thank
Professor Jeff Tester and Michel Boudart for their constant
encouragement throughout my graduate career.
I wish to thank the GEM program, Shell Development Co.,
Amoco, and Chevron for their financial support.
Thanks are
also extended to the Department of Energy for its support of
the project.
To my collegues in the department, I have unmeasureable
gratitude for all of the assistance offered during my stay at
M.I.T..
Special acknowledgements are given to Harvey Stenger,
Rich Pekela, Al Horn, Lisa Jungherr, and my officemates.
I
also wish to thank all of my friends who suffered with me
through this very trying ordeal.
I am especially grateful for
the friendship and support of Pieter VanderWerf, Brian Smiley,
Westley Spruill, and Scott Slate.
To Eugenia Brown, I offer
the sincerest thanks for her friendship and love.
Thanks also
to Sally Kreuz for the exceptional assistance in production of
this thesis.
And finally to my family,
of thanks.
I offer a thunderous chorus
To my parents I give my love and appreciation for
all they've done.
Thanks for teaching me to believe in myself
and giving me the courage to try and accomplish my goals.
most of all,
thanks for instilling in me a devotion to God.
And
5
TABLE OF CONTENTS
Page
I.
Introduction
11
II.
Objectives
15
III.
Literature Review
16
IV.
Experimental
35
IV.A.
35
35
35
35
49
49
49
IV.B.
Experimental Apparatus
IV.A.l.
Fischer-Tropsch Reactor
IV.A.2.
Ambient Temperature Apparatus
IV.A.3.
Elevated Temperature Apparatus
Experimental Procedures
IV.B.l.
Ambient Temperature Procedures
1.
Sample Preparation
2.
IV.B.2.
Chromatographic Analysis
2a.
Preparation
2b.
2c.
Analysis
Calculation
50
51
52
Elevated Temperature Procedures
1.
Sample Preparation
53
53
2.
Chromatographic Analysis
53
2a.
Preparation
53
2b.
Analysis
54
2c.
Calculation
55
V.
Results
V.A.
Ambient Temperature GPC Results
V.B.
Elevated Temperature GPC Results
VI.
Discussion
103
VII.
Conclusion
113
VIII.
Appendices
114
IX.
References
117
56
56
84
6
LIST OF FIGURES
Figure No.
3-1
Page
Development and Detection of Size Separation by
21
3-2
General Schematic of GPC Equipment.
24
4-1
Slurry Reactor Apparatus.
36
4-2
Waters M6000A Solvent Delivery System, Exploded
View.
38
Waters M6000A Solvent Delivery System, Circuit
Diagram for Hydraulic Components.
39
Injectors:
Injector;
40
GPC.
4-3
4-4
4-5
(1)
Rheodyne Model 7125 Sample
(2) Waters U6K Sample Injector.
Schematic of Waters R401 Refractive Index De-
tector Optical Unit.
42
4-6
Schematic Waters 150C Main Pump.
45
4-7
Schematic Waters 150C Injection System.
47
4-8
Schematic Waters 150C Differential Refractor-
meter.
5-1
5-2
5-3
48
GPC Chromatogram -
Injection 1-4:
Mixture of n-
Hydrocarbon Standards C22, C28, and C38.
59
GPC Chromatogram - Injection 1-7:
Mixture of nHydrocarbon Standards C24, C25, C26, C28, and
C30.
60
GPC Calibration Curve Run 2:
Phase,
Toluene Mobile
1 x 100A Ultrastyragel Column,
22C, and
n-hydrocarbon standards C19, C20, C21, C22, C23,
C24, C25, C26, C28, C30, C32, C36, C38, and C40.
61
5-4
GPC Chromatogram -
62
5-5
GPC Calibration Curve Run 3:
Toluene mobile
phase, 1 x 100A Ultrastyragel column, 24.4C, and
n-Hydrocarbon Standards C19, C22, C26, C28, C36,
and C40.
Injection 2-15:
SS-9A
65
7
Figure No.
5-6
5-7
5-8
5-9
5-10
5-11
5-12
5-13
5-14
5-15
5-16
5-17
5-18
5-19
Page
GPC Chromatogram - Injection 3-11:
SS-9E,
Attenuation 2X, Chart Speed changed to 4 inch/
min @ 5.8 minutes.
67
GPC Chromatogram - Injection 3-12:
uation 2X, Chart Speed 4 inch/min.
68
SS9D, Atten-
Peak Height and Retention Time Distribution:
Injections 3-11 and 3-12.
70
Cumulative Weight Fraction Molecular Weight Distribution:
Injections 3-11 and 3-12.
71
Differential Number Fraction Molecular Weight
Distribution:
Injections 3-11 and 3-12.
72
GPC Calibration Curve Run 4.
Toluene Mobile
Phase, 1 x 100A Ultrastyragel Column, 23C, nhydrocarbon Standards C20, C28, C32, C36, C40
and Polystyrene Standards 800, 1800, and 2000.
74
Peak Height-Retention Time Distribution:
Injec-
tion 4-11.
77
Cumulative Weight Fraction Molecular Weight Distribution:
Injection 4-11.
78
Differential Number Fraction Molecular Weight
Distribution:
Injection 4-11.
79
GPC Calibratiop Curve Run 5.
Toluene Mobile
Phase, 1 x 100A and 1 x 500AO
Ultrastyragel
Columns, 25C, n-Hydrocarbon Standards C20, C24,
C28, C36, C40 and Polystyrene Standard 1800.
81
Area Percent Molecular Weight Distribution:
jections 5-12 and 5-17.
83
In-
Cumulative Weight Fraction Molecular Weight Distribution:
Injections 5-12 and 5-17.
85
Differential Number Fraction Molecular Weight
Distribution:
Injections 5-12 and 5-17.
86
GPC Calibration Curve 0 Run 6:
Trichlorobenzene
Mobile Phase, 1 x 100A and 1 x 50OX Ultrastyragel
Columns,
C28, C38,
50C,
n-Hydrocarbon Standards C20,
and C40.
C24,
88
8
Figure No.
5-20
5-21
Page
GPC Calibration Curve Run 7:
Trichlorobenzene
Mobile Phase, 1 x 100A and 1 x 500l Ultrastyragel Columns, 50C, n-Hydrocarbon Standards Standards C20, C24, C28, C38, C40 and Linear Polyethylene Standard 1800.
91
Area Percent Molecular Weight Distritubion:
jections 7-7, 7-8, 7-9, 7-11, and 7-12.
99
In-
5-22
Cumulative Weight Fraction Molecular Weight Distribution:
Injections 7-7, 7-8, 7-9, 7-11,and 7-12. 100
5-23
Differentioal Number Fraction Molecular Weight
Distribution:
Injections 7-7, 7-8, 7-9,7-11, and7-12. 101
5-24
Weight Percent Molecular Weight Distribution:
Injection 7-13.
102
Form of Flory Plot Postulated for 2-Site Reaction and Accumulation of Products in Liquid
Carrier
104
6-1
6-2
Carbon Number Distribution for Run 9 at 248C and
H2/CO Feed of 1.81.
6-3
Carbon Number Distribution of Liquid Carrier
After Run 9.
6-4
6-6
107
Theoretical Carbon Number Distribution Based on
Flory Equation.
6-5
106
108
Carbon Number Distribution of Heavy Paraffinic
Fischer-Tropsch Wax at Ambient Temperature Using
GPC.
110
Carbon Number Distribution of Heavy Paraffinic
Fischer-Tropsch Waxes at Elevated Temperature
Using GPC.
111
9
LIST OF TABLES
Table No.
3-1
Page
Gel Permeation Chromatography Operating Conditions - Hillman, 1971.
32
Summary of Iun 1.
Operating Conditions:
Solvent - Toluene, Temperature - 25C, Columns
1 x 100A Ultrastyragel, Flowrate - 1 ml/min,
Injection Volume 100 pl, Polarity - Positive.
57
5-2
Summary of Run 2.
58
5-3
Summary of Run 3.
64
5-6
Cumulative and Differential Weight Fraction
Molecular Weight Distribution Data:
Injections
3-11 and 3-12.
69
5-5
Summary of Run 4.
77
5-6
Cumulative and Differential Weight Fraction
Molecular weight Distribution data:
Injection
4-11.
76
5-7
Summary of Run 5.
80
5-8
Cumulative and Differential Weight Fraction Molecular Weight Distribution Data:
Injections 5-12
and 5-17.
82
5-9
Summary of Run 6.
87
5-10
Summary of Run 7.
90
5-11
Fischer-Tropsch Synthesis Operating Conditions.
92
5-12
Cumulative and Differential Weight Fraction
-
5-1
Molecular Weight Distribution Data:
5-13
5-14
5-15
Injection
7-7.
93
Cumulative and Differential Weight Fraction
Molecular Weight Distribution Data:
Injection
7-8.
94
Cumulative and Differential Weight Fraction
Molecular weight Distribution Data:
Injection
7-9.
95
Cumulative and Differential Weight Fraction
Molecular Weight Distribution Data:
Injection
7-11.
96
10
Table No.
5-16
Page
Cumulative and Differential Weight Fraction
Molecular Weight Distribution Data:
Injection
7-12.
97
5-17
GPC Weight Percent Data:
98
6-1
a Values of GPC.
Injection 7-13.
112
11
I.
INTRODUCTION
The production of synthetic fuels to supplement dwindling supplies of natural fuels has directed attention towards
development of processes which utilize abundant resources of
indigenous reserves such as coal.
Fischer-Tropsch synthsis.
One such process is the
In this procedure the indirect
liquefaction of coal to hydrocarbons is accomplished via the
catalytic reaction of synthesis gas, a mixture of carbon monoxide and hydrogen produced by gasifaction of coal in the presence
of oxygen and steam.
The hydrocarbons produced from the
Fischer-Tropsch synthesis are predominantly linear paraffins
and olefins with some oxygenates
(primarily alcohols).
The
overall reaction stoichiometry may be represented as:
Paraffins : nCO +
(2n + 1)H2
2
C H
n 2n+2
+ nH2 0 + 123 kcal
2
(1)
Olefins:
Alcohols:
nCO + 2nH 2
nCO + 2nH
C H
2
+
n 2n
+ nH 0 + 93 kcal
CnH 2n+OH
(2)
2
+
(n -
1)H 20
+ 102 kcal
(3)
where the heat of reaction is based on n=3 at 227C.
Two im-
portant side reactions may also occur:
Water-Gas-Shift:
Boudouard:
H20 + CO = CO2 + H2 + 10 kcal
2CO
-+
C(s)
+ CO2 + 42 kcal
(4)
(5)
The synthesis of hydrocarbons from carbon monoxide and
hydrogen has been known since the classical methane synthesis
12
of Sabatier and Senderens
(1902).
In 1922 Franz Fischer and
Hans Tropsch obtained their first patent on "Synthol", a mixture of oxygen-containing derivatives of hydrocarbons.
developments by Fischer and Tropsch in the 1920's
Further
and 1930's
directed the synthesis to produce predominately hydrocarbons
by using cobalt-based catalysts in fixed-bed, vapor-phase
reactors.
In 1943, Germany optained a peak production of
16,000 bbl per day.
23% diesel fuel,
oil.
The products consisted of 46% gasoline,
23% waxes and detergents, and 3% libricating
With World War II, Germany's supply of cobalt from the
Belgium Congo was severely cut and active search was initiated
to develop iron catalysts.
In the United States during the
1950's a fluidized-bed process using an iron catalyst to convert synthesis gas from then inexpensive natural gas to gasoline was installed by Hydrocol, but it never operated satisfactorily.
And as petroleum supplies became plentiful further
investigation of the Fischer-Tropsch synthesis became uneconomical.
Until recently, South Africa has been the only country
actively pursuing Fischer-Tropsch technology.
Synthetic Oil Limited
At South African
(SASOL), fixed- and fluidized-bed proce-
dures have been developed which utilize iron catalysts at intermediate pressures
(5 -
50,000 bbl per day.
25 amt), with production capacity of
Current expansion is afoot which will
ultimately increase capacity to over 100,000 bbl per day.
The Fischer-Tropsch synthesis is a linear polymerization
process.
The process begins with an adsorbed single-carbon
specie which can either grow in molecular size by addition of
13
another carbon unit or terminate by desorption into the gas
(or liquid) phase as product.
Debate still exists over the
mechanism and nature of this carbon unit.
But this does not
affect the mathematical development of an expression to predict carbon number distribution if the probability of chain
growth is independant of molecular size.
Flory
(1936) statistically derived the basic relation-
ship for any polymerization process where the primary step is
addition of monomer units one at a time onto the terminus of
a growing linear chain.
The chain growth proability factor
* is defined as:
r
=
(r
pt
where r
+ r
(6)
)
a
and rt are the rates of propagation and termination
respectively (a is independant of molecular size).
fraction m
The mole
of molecules in the polymer mixture which contains
n structural units is given by the Flory Equation:
mn
=
(1 - a)
n-
(7-)
If the added weight of each carbon unit is proportional to
chain length n, the weight fraction w
w
=
(l -c )2n
n
is given by:
(n-l)(8
A more covenient form for expressing experimental data is
the logarithmic form of the Flory Equation:
ln
(m )
n
=
n ln (x)
+
ln
(1-)
(9)
14
Therefore a plot of ln
linear with slope ln
(m n)
versus carbon number n should be
(a) and ordinate intercept
(1 - a)
at n = 1.
The products formed in Fischer-Tropsch synthesis depend
on the hydrogen to carbon monoxide ratio in the synthesis gas
as well as on the catalyst and reactor conditions selected.
These products range from methane to high molecular weight
compounds such as heavy paraffinic wax.
Gas chromatography
has been successfully applied in the analysis of most FischerTropsch products.
However utilization of gas chromatography
becomes ineffective in examination of high carbon number products
(C30 +) due to the low volatility of these heavier
hydrocarbons.
For complete analysis, an additional technique is
needed that will provide quantitative data of the heavy
Fischer-Tropsch fractions.
meation Chromatography
One such technique is Gel Per-
(GPC), which involves the separation of
molecules based upon differences in their effective size in
solution.
The size sorting takes place by repeated transfer
of solute molecules between the bulk mobile phase and stagnant
liquid phase within the pores of the packing, allowing sample
characterization by its molecular weight distribution.
15
II.
OBJECTIVES
The present investigation focused on gel permeation
chromatography analysis of heavy paraffinic waxes formed during
the Fischer-Tropsch synthesis in a slurry reactor.
of fundamental and practical importance.
This is
Fundamentally, one
would like to know how high in molecular weight the FischerTropsch synthesis proceeds and if the Flory equation is applicable in this high carbon number product region.
Practically,
it is needed to know how long the reaction can be allowed to
continue before excessive accumulation of heavy hydrocarbons
might occur in the reaction apparatus.
of GPC was sought.
First, an understanding
Then application of GPC analysis to Fischer-
Tropsch wax samples was undertaken.
Finally GPC data were
interpreted and related to other results.
16
III.
LITERATURE REVIEW
attributed to work performed by Michael Tswett.
In 1903
-
Conventional founding of liquid chromatography has been
1906, Tswett recognized chromatography as a general method in
description of separation of
colored vegetable pigments in
petroleum ether on calcium carbonate.
From Tswett's early
findings, a large number of workers continued to develop
liquid chromatography to its present high performance capabilities and it has found application in various forms of
scientific disciplines
(Synder and Kirkland 1974).
The phenomena of gel chromatography were first observed
with adsorption of different sized ions in 1925
(Ungerer 1968).
The term "molecular sieving" was first used in 1926 by McBain
(Porath 1962a).
The crystalline crosslinkages of natural and
synthetic aluminum silicates, known as molecular sieves,
made possible separation of molecules according to size and
shape (Wiegner 1931,
1948).
Tiselius 1934, Claesson and Claesson 1944,
Later, Barrer and Brook established and proved correla-
tions of adsorption and molecular size in molecular sieves
(1953).
Sieving properties were also found during application
of ion exchange resins (Samuelson 1944, Rauen and Felix 1948).
A correlation between the number of crosslinkages, the degree
of swelling,
and the ion exchange capacity of the large ions
was found in the structure of ion exchange resins
Amberlite, Kumi and Myers 1949, Mikes 1958).
(Wofattite,
This property
was used in sepration of numerous compound groups including
17
amino acids, peptides, and proteins
Thompson 1952, Partridge 1952).
(Richardson 1949, 1951,
This experience directed
attention to larger-pored polysaccharide matrices.
Uncharged
crosslinked galactomannane gel was used in the desalting of
colloids (Deuel and Nenkom 1954).
Peptides and proteins
were separated on granulated starch particles
Storgards 1955, Lathe and Ruthuen 1955).
(Lindquist and
Later, it was estab-
lished by Lathe and Ruthuen that the penetration of molecules
into the gel phase depended upon structure and contration of
the gel, and a relationship between molecular size and chromatographic behavior was found
(1956).
The study of electrophoresis played an important role in
the development of gel permeation chromatography.
Preparative
and analytical methods of gel electrophoresis prompted the
examination of macromolecues and biopolymers
(Smithies 1955,
Raymond and Wintraub 1959, Davis and Ornstein 1959, Porath and
Bennich 1962).
The electroosmosis of natural substances and
proteins in dextran, a characteristic polysaccharide,
investi-
gated by Tiselius in Sweden led to the production of a new
semi-synthetic gel (1959).
Sephadex, dextran gel copolymerized
with epichlorhydrin and packed into a column, achieved good
separation even without an electric current.
A closer examina-
tion of Sephadex by Porath and Flodin marked the beginnings
of what may be called an explosive development of gel chromatography
(1959).
Since the properties of natural polysaccarides,
such as
dextran, were difficult to reproduce, application of such
materials were not found wholly suitable for chromatographic
18
uses.
In the early 1960's semi-synthetic and synthetic poly-
mers replaced the natural gel formers
Sehon 1962, Hjerten and Mosback 1962).
(Polson 1961, Lea and
Initially hydrophilic
polyacrylamide gels produced by copolymerization of acrylamide
and methylene bisacrylamide found widest application.
The
examination of gels which swelled in organic solvents began
simultaneously with that of hydrophilic gels, particularly
with attention to polystryene matrices copolymerized with
divinylbenzene.
In 1964 J.C. Moore disclosed the use of cross-linked
polystrene gels for separating synthetic polymers soluble in
organic solvents
(Moore 1964).
It was recognized that with
proper calibration, gel permation chromatography was capable
of providing molecular weight and molecular weight distribution
information for synthetic polymers.
Gel permeation chromatography is used as an analytical
technique for separating small molecules according to size
difference and to obtain molecular weight distribution information of polymers.
(The raw-data GPC curve is a molecular
weight distribution curve.)
With a concentration sensitive
differential refractometer detector, the GPC curve can become
a size distribution curve in weight concentration.
And with
proper calibrating, molecular weight averages can be calculated.
A convenient quantity which measures the average chain
length in a polymer sample is the number-average molecular
weight, Mn,
defined as:
19
Mw
n
W
=
=
EN
W
E()Mw.
(10)
'
EN
M
1
where W
and N
are the weight and number of molecules with
molecular weight Mw , respectively.
M
Ehi
and Mw
(11)
(h /Mw
)
S
where h
From GPC:
is the GPC curve height at the ith volume increment
is the molecular weight of the species eluted at the
ith retention volume, and N is the number of chains present.
Another convenient quantity obtainable from GPC data is the
weight-average molecular weight, Mw,
M
ZN Mw
2
E N__MW
2
N. Mw.
w
given by:
2w
VW. Mw
L~d
1W1(12)
EW.
ll
1
and from GPC:
M
The value of M
w
w
=
Z(h. Mw.)
(13)
Ehi
is always greater than Mn
n
except when the
values are identical in monodisperse systems.
The dispersity,
M /M , is a measure of the broadness of the molecular weight
distribution.
The Z-average molecular weight, Mz,
is related
to a higher moment of the distribution and is defined as:
Mw3
M
z
=
ZN
ENi Mw 1 2
(14)
20
(Dallas and Abbott 1979).
In the
(theoretical) model to describe GPC, the gel is
composed of a porous matrix whose pores are closely controlled
in size.
The separation mechanism involves differences in
ability of molecules to penetrate the pores.
Very large mole-
cules cannot penetrate into the gel pores and thus migrate
down the column through the interstitial volume between particles and emerge first from the column.
Smaller molecules can
to some degree penetrate into the gel pores, and thus they
are slowed in their migration through the column.
Very small
molecules that are able to completely penetrate into the gel
pores will be retained the most,
last
(Lawrence 1981).
and elute from the column
This is represented by the illustration
shown in Figure 3-1.
The retention time,
RT,
is the time required for a peak
to elute from the column following sample injection.
Its
value is sensitive to changes in experimental conditions such
as flow rate and the specific column used.
The retention
volume, RV, accounts for flow rate differences and is defined
as:
RV = F(RT)
where F is the mobile flow rate.
(15)
The peak capacity factor,
k', is a more basic retention parameter.
Physically, k'
represents the ratio of the weight of solute in the stationary
phase to that in the mobile phase.
RT k
T
RV- V
T
0
o
This is defined as,
m
_
m
(16)
21
(A)
TIME
SEQUENCE:
Sample
Injected
(B)
Small
(D) Solutes
Eluted
Large
(C) Solutes
Eluted
Size
Separation
00C>,
C-
.
.
49~K
Refractive
Index Detect
Chromatogram
(Concentration
Elution Curve)
Injection
(A)
(B)
(C)
(D)
RT = RV/F
Figure 3-1:
Development and Detection of Size Separation by
GPC (Yau, Kirkland, and Bly 1979).
22
= RT for an untetained peak and Vm = F(T ) for the
where T
retention volume of unretained solute.
To account for differences in stationary-phase loading,
the solute distribution coefficient, KLC,
is defined as:
k' V
K
LC
=
V
m
(17)
S
where Vs is the equivalent liquid volume for a stationary
phase.
Physically, KLC is the ratio of solute concentration
in the stationary phase to that in the mobile phase.
Transfer between mobile and stationary phases occurs
as solute molecules migrate through the column to continually
redistribute themselves between the phases to satisfy thermodynamic equilibrium.
This implies equivalance of chemical
potential of each solute component in the two phases.
For
dilute solutions at equilibrium, solute distribution can be
related to the standard free energy difference,
AG*, given
by:
AG* =
-
AG* =
AH*
RTlnK
(18)
with
-
TAS*
(19)
where K is the solute distribution coefficient, R is the universal gas constant, T the absolute temperature, and AH0
and
AS* are standard enthalpy and entropy differences between
phases, respectively.
In GPC,
solute distribution is governed
primarily by entropy changes between phases
Therefore,
with AH0
~ 0, KGPC is given by,
(Dawkins 1976).
23
KGPC
eAS/R
(20)
Temperature changes have only a small indirect effect on GPC
retention since they only affect polymer solute molecule size,
which in turn affects AS*.
Large fluctuations of temperature
of GPC experiments should be avoided.
The results of temperature, flow rate, and steric mixing
experiments show that GPC retention is an equilibrium, entropycontrolled,
size-exclusion process.
The diffusion in and out
of the pores of the solute is fast enough with respect to
flow rate to maintain equilibrium solute distribution.
Extensive developments in liquid chromatography have
made available a variety of equipment which can be used in
gel permeation chromatography.
A general schematic for GPC
equipment is shown in Figure 3-2. The instrumentation used in
GPC is needed to function rapidily and reliably.
In the solvent
delivery system a constant, reproducible supply of solvent
to the column is required.
The sample injector must introduce
sharp volumes of sample without disturbing the flow of the
solvent.
High efficiency columns are needed to give maximum
separation capability and provide reproduciable information over
extended periods of time.
Specific detectors with wide sensi-
tivity ranges are used to monitor the separation.
A detailed
description of apparatus used in this study will be presented
in Section IV.A.
Gel permeation chromatography was primarily developed
for measuring molecular size distribution of polymer products.
24
8
7
6
5
3
2
Figure 3-2:
General schematic of GPC equipment:
(1) Solvent
Supply; (2) Solvent Delivery System; (3) Injector;
(4) Sample Syringe; (5) Columns; (6) Differential
Refractometer Detector; (7) Computerized Data
Handling Device; (8) Recorder.
25
A series of narrow molecular weight range fractions of anionic
polystyrene samples were efficiently separated in polystrene
columns with aromatic and chlorinated solvents
(Moore 1964).
Further investigation by Hendrickson and Moore
(1966) found
that by calibrating columns with carefully characterized
polymers, it was possible to prepare a curve relating the
elution volume to the logarithm of the average molecular chain
length
(or effective angstrom chain length) given by:
Angstrom chain length
where C.A.U.
(A)
=
2.5 + 1.25
(C.A.U.)
is the size in carbon atom units.
(21)
These calibra-
tion curves were often linear over a large range of chain
length, and molecular weight distributions of unknown polymer
samples could then be calculated.
Analysis of polystyrene,
polyvinylchloride, and polypropyleneoxide dissolved in THF
showed some deviation from the molecular chain length correlation.
Hendrickson and Moore suggested five basic forces that
might be expected to modify elution volume of compounds in
GPC:
(1) changes in width of the network openings in the column
packing beads,
(2)
solvent -
tion of solute molecules,
(5)
solute association,
(4)
(3)
dimeriza-
intramolecular bonding, and
adsorption of solute onto or into the gel surface.
fore,
There-
simple chain length was an inadequate size parameter in
correlation of elution volumes of some non-normal samples.
Smith and Kollmansberger
(1965) reported on the separa-
tion of a number of alkanes and halogenated aromatic compounds
by GPCalso using THF as the solvent.
They established that
26
the apparant molecular volume is the important parameter influencing the degree of separation,
(where molar volume
(ml/nole)
is defined as molecular weight divided by density at 25C.).
Later, Edwards and Ng
(1968) investigated the use of bulk
molar volume for various compounds (including normal hydrocarbons) and showed that there was a linear relationship between logarithm bulk molar volume and elution volume for normal
hydrocarbons.
The elution behavior of about 100 model com-
pounds was studied to show the effectiveness of GPC as an
analytical tool.
It was found that organic functional groups
exert a systematic influence on GPC elution behavior, reinforcing the theory that such behavior is the result of
solute's association with the solvent, the gel packing, or
itself.
By measuring these effects with model compounds, gen-
eralized observations for characterization of nonfunctional
minor components of lower molecular weight epoxy resins was
accomplished.
Rather than using standards such as polystyrene and
polypropylene glycols to calibrate GPC columns, Sweeney,
Thompson,
and Ford (1970) used normal paraffins and cali-
brated by carbon number.
This calibration was used to deter-
mine relationships between boiling point, carbon number,
elution volume.
and
A limited number of branched hydrocarbons
were also investigated as well as a brief quantitative study
to determine response factors for the normal hydrocarbons.
Lambert
(1970) recommeded that a set of molar volume
values for n-alkanes be used as standards to calibrate GPC
27
columns.
Molar volume is given by:
Molar volume
(ml/mole @ 20C)
= 33.02 + 16.18
+ 0.004
where C.A.U.
(C.A.U.)
(C.A.U.)
(22)
is as previously defined.
Debate still exists over the appropriate parameter to
use in calibration of GPC columns.
Mori and Yamakawa
(1980)
obtained relationships among oligostyrene, n-hydrocarbons,
and oligoethylene glycol in chloroform and tetrahydrofuran.
Different elution behaviors of oligomers in different eluents
made it difficult to use molar volumes or effective chain
lengths as the calibration parameter.
The n-hydrocarbons are
non-polar compounds and were assumed to elute without solutesolvent association or the adsorption on the gel.
Molecular
weight conversion equation for several oligomers based on
molecular weight of oligostryene and n-hydrocarbons were de-
derived, making it possible to use these as reference standards when molecular weights of oligomers are measured.
A wax is a complete mixture of high molecular weight
organic components.
Hatt and Lamberton (1956) defined a wax
as "a thermoplastic of low mean molecular weight and low mechanical strength."
hydrocarbon,
They classified waxes into three categories:
natural
(ester), and synthetic waxes.
Hydrocar-
bon waxes, derived from petroleum, can be further sub-divided
into two groups, the paraffinic and the microcrystalline
waxes.
Paraffinic waxes consist primarily of long chain nor-
mal paraffins, with small amounts of branched chain and
28
cycloparaffin in the approximate range of C18 -
C42.
The
microcrystalline waxes consist mainly of branched chain paraffins of high molecular weight.
The natural
(ester) waxes,
excreted by most animals and plants, are more complex in
composition and consist mostly of mixtures of esters of long
chain
(C18+) fatty acids and alcohols.
of free acids, alcohols, paraffins,
Appreciable amounts
resins, dihydride alcohols,
hydroxy acids, ketones, and sterols are also present.
Syn-
thetic waxes may be entirely synthetic, such as polyethylene
types, be prepared from petroleum waxes, or be prepared from
other natural materials.
Many elaborate procedures have been utilized in complete
analysis of waxes
(Robinson and Johnson 1966).
widespread use of chromatographic techniques,
Prior to
lengthy pro-
cesses of fractional distillation and fractional crystallization were used.
Infra-red spectroscopy has been applied in
the fingerprinting of single wax compounds by comparison with
infra-red spectrums of known waxes.
properties
Investigation of wax
(melting point, inflexions on cooling curves, speci-
fic gravity, penetration hardness, and refective index) have
been used for the quality control of all types of waxes, however, the information given by these methods is not completely
reliable.
Robinson and Johnson noted two problems involved
in complete analysis:
1.
Separation of wax constituents according to their
chemical nature,
etc.
i.e.
ester, alcohols, paraffins,
29
2.
Separation of the fractions into individual single
chemical species must then be identified.
Chromatographic techniques are superior due to, i)
efficiency of separation,
iii)
ii)
simplicity of operation, and
direct indication of the identity of components from
their rention data.
Paper chromatography was used to separate the mercuric
acetate-methanol adducts of the allyl esters of the fatty
acids by Kaufman of Pollenberg
(1957).
Reversed phase paper
chromatography was used to separate even-numbered acids up
the C36
in Beeswax, Carnuba wax, and Montan wax by Kaufmann
and Das
(1963).
The major problem in paper chromatography
is the low solubility of wax acids in solvents at room temperature, and elevation of temperature increases the complexity
of the method.
Gas chromatography of waxes has been largely investigated.
Adlard and Whitham
(1958) separated paraffin hydrocarbons up
to C36 using a silicone coated column at 270C.
Normal paraffins
were removed from kerosine by means of Linde 5A molecular
sieve by Whitham (1958).
O'Connor and Norris (1960 and 1962)
extended this procedure to the higher molecular weight paraffins waxes.
Gas chromatography of separated fractions gave
the ratio of normal to non-normal paraffins, the relative
amounts of each normal paraffin,
and the relative amounts of
total non-normal paraffin of each carbon number in a paraffin
wax.
Unfortunately this separation procedure required long
time periods
(15 days) which minimized the use of this method
30
for routine analysis.
Scheneck and Esima
(1963) used Linde 5A
sieves in conjuction with a gas chromatography column using
silicon stationary phase for paraffins in crude oils and rock
extracts.
Gas-solid chromatography was used by Scott and Rowell
(1960) to separate C15 and C36 paraffins using an alumina
column deactivated with sodium hydroxide at 390C.
co-workers
Levy and
(1961) separated and identified 67 components
pre-
sent in a refined paraffin using mass spectrometry in conjuction with gas chromatography
(8-foot columns packed with 10%
microwax distillation residue on Chromosorb W.
at temperatures
of 300C).
Levy and Paul
(1963) used a dual column, dual flame
ionization, temperature programmed gas chromatograph to obtain
carbon number distributions of C19 to C36 paraffinic waxes
using 12-foot 1/8-inch copper tubing packed with 0.82% microcrystalline wax distillation residue on 80-100 mesh Diatoport
S over the temperature range 140-330C at 2.3C per minute.
Resolution of a homologous series of the even-numbered alkanes
from tetradecane through dopentacontane was accomplished on
6-foot aluminum columns packed with 0.1% Apiezon L on 60-80
mesh glass microbeads over the temperature range 40 to 350C
at 5.6C per minute by Perkins, Laramy, and Lively
(1963).
Hydrocarbon components in the range C25 to C68 of four microsrystalline waxes were resolved on dual 2-foot columns packed
with SE 52 on Chromosorb G using a temperature programmed
dual flame ionization gas chromatograph by Ludwig
(1965).
Column chromatography was found to be rather inefficient
31
in total characterization of waxes.
Cole and Brown
(1960)
used a specially prepared alumina column for separation of
complex waxes into fractions according to their chemical nature, however incomplete separation often occurred.
Wiedenhof
(1959) used column chromatography prior to X-ray diffraction
measurements on wax fractions.
Ion exchange column chromato-
graphy was used in determination of free wax acids, wax soaps,
and total hydrocarbon content in waxes by Presting and Janicke
(1960).
Robinson and Johnson recommended use of ion exchange
column chromatography only as a precursor to gas or thin
layer chromatography
(1966).
With the introduction of GPC by Moore
(1964), column
chromatography became a more useful technique in wax analysis.
Hillman
(1971) found that by selecting the appropriate porosity
range of Styragel column packing, waxes in carbon range C15
to C100 could be closely examined.
By using a series of
Styragel columns it was possible to characterize hydrocarbon
and ester waxes dissolved in organic solvents.
Operating
conditions for study are shown in Table 3-1.
The GPC unit was calibrated using 0.1% solutions of nhydrocarbons (C16, C20, C28, C32, C36, C48)
molecular weight range polystrenes
from Waters Associates).
and narrow
(No. 25168, 26169, 25171
Retention times were plotted versus
carbon number, the carbon number for polystrenes being calculated by effective carbon number
(equation 21).
Calibration
plots were essentially linear over the range interest but
showed marked deviation at high molecular weights where the
TABLE 3-1:
Gel permeation chromatography operating conditions-Hillman, 1971.
I
Column Porosities
(A)
100, 500, 10,
II
100,
100, 100, 500
III
100,
400, 500, 103
3 x 104
Column Temperature
70
30
80
Solvent
Toluene
Tetrahydrofurane
o-Dichlorobenzene
Inhibitor
Nil
Quinol
Stavox CP
1.0
1.0
0.5-1.0
1.0
1.0
1.0
Sample size (ml)
2
2
2
Sensitivity
x2
x2
x2 for fingerprinting
x4 for polyethylene
70
30
80
70
30
80
70
30
80
Flow rate
(*C)
(ml/min)
Sample Concentration
Inlet
heater
Syphon heater
(*C)
(*C)
Detector heater
(*C)
(%)
(5g/gall)
L&J
33
molecular exclusion of the column system was approached.
The
extrapolation of the linear region for the n-hydrocarbons
passed through the point for the lowest molecular weight polystyrene standard.
In the actual hydrocarbon wax analysis,
carbon numbers corresponding to the retention times of the
maxima of the gel permeation chromatograms were read off the
applicable calibration curve.
A correction factor of twice
the standard deviation of the gaussian peak obtained for injection of pure C36 was introduced to account for peak broading
during elution.
Improvements in the efficiency of small pore packing
materials and column preparation advanced the speed and convenience of GPC to that of gas chromatography.
Lack of vola-
tility, or absence of significant differences in polarity,
solubility, or ionic characteristics are not significant problems in GPC analysis.
Krishen and Tucker found that the
high efficiency of the GPC column affords a separation of components as distinct separate peaks, in the short time, and
provided a useful technique for extending the molecular weight
range beyond that covered by gas chromatography
Harmon
(1977).
(1978) used GPC in characterization of hydrocar-
bon waxes, reporting molecular size distribution profiles,
coupled with melting point profiles from differential scanning
calorimetry, as the basis for comparison and selection of
replacement waxes for use by the B.F. Goodrich Company.
Styragel columns were used by Sosa, Lombana, and Petit
in analysis of crude paraffinic waxes
(C16 - C50) waxes
(1978).
34
Molecular weights
(Mn and Mw)
and molecular weight distribu-
tions of waxes containing various amounts of oil were determined.
The method of GPC was choosen because temperatures re-
quired to analyze n-paraffins having chain lengths above C40
are almost at the upper useful limit of routine gas chromatography.
Gas and gel permeation chromatograms were presented
and were found to complement each other well.
35
IV.
A.
EXPERIMENTAL
EXPERIMENTAL APPARATUS
A.
1.
Fischer-Tropsch Reactor
The Fischer-Tropsch synthesis reactions were carried out
in a semi-continuous, slurry-bed catalytic reactor system.
A
schematic of the slurry reactor unit is shown in Figure 4-1.
The stainless-steel, 1-liter autoclave was operated isothermally
in semi-batch mode.
Pre-mixed synthesis gas was feed into the
autoclave by a pneumatically-controlled valve while volatile
products were removed overhead.
The catalyst and inert liquid
carrier remained in the reaction vessel.
were collected in a wax trap
(held at 2C).
(held at 70C)
Condensable products
and a cold trap
A detailed discussion of the reactor system and
procedures followed during operation are found in the Ph.D.
thesis of G.A. Huff and related publications by Satterfield
and Huff.
A.
2. Ambient Temperature Apparatus
Analysis of Fischer-Tropsch wax samples at ambient temperature was performed on two gel permeation chromatographic
apparatuses.
sions:
This equipment may be categorized into five divi-
solvent delivery system, injector, columns, detector,
and data compiling system.
1.
Solvent Delivery System
In both sets of GPC components used at ambient temperature,
Waters Associates Model M6000A pumps were utilized to deliver
a constant flow of solvent.
Diagrams of this pump are shown in
Vant
Ab
PI
P -6
Corriar
Som pla
P
9
-8-
I-
P
10
-11
_
LA~)
a.'
3*
4
1
Wox
Sompla
Figure 4-1:
Oil
Sompla
(1) Gas Cylinder with Premixed CO/H 2 Mixture;
Slurry Reactor Apparatus:
(2) Pressure regulator; (3) Automated Flow controller; (4) Back-Pressure
Regulator; (5) 1-Liter, Mechanically Stirred Autoclave with Thermocouple
at (a) and Turbine Impeller at (b); (6) Pressure Gauge; (7) Wax Receiver;
(8) Ice-Cooled Receiver; (9) Back-Pressure Regulator; (10) Gas Sample
Valve; (11) Soap-Film Flowmeter (Huff 1982).
37
Figures 4-2 and 4-3.
The M6000A is a dual head reciprocating
piston positive displacement pump, in which solvent enters
through an inlet check valve during the first half of the
piston stroke and exits through an outlet check valve during
the second half of the stroke.
Each pump head delivers 100
microliters of solvent per stroke.
A steady flow of solvent
was provided by precise timing of the pistons. The flow rate
of the pump was adjustable in 0.1 ml/minute increments between
0 and 9.9 ml/minute.
2.
Injector
Two types of injectors were used in these experiments,
a Rheodyne Model 7125
(Run 5).
4-4.
(Runs 1 -
4)
and Waters Associates U6K
Schematics of these injectors are shown in Figure
The Model 7125 is a six port sample injection valve.
The sample loop, whose volume corresponds to the injection
volume, is loaded by syringe through a needle port built into
the valve shaft.
While in the load position, solvent from
the pump flows directly to the columns and sample from the
syringe may be loaded into the sample loop.
When flipped to
the inject position, solvent from the pump pushes the samples
from the sample loop into the column.
The U6K has a 2 ml last-in-first-out sample loop into
which any sample amount under 2 ml can be injected.
load, the solvent flows through the restrictor loop.
While on
To in-
ject a sample into the sample loop, the needle port valve is
locked by flipping the injector valve to inject, allowing
solvent flow through the sample loop to carry the sample into
the columns.
I
~Ii I-M~4
~r
1
-
Figure 4-2:
-
-
k
Waters M6000A Solvent Delivery System, Exploded View
Equipment Manuals).
(Waters GPC
W00
39
AC j.L3QA V
-E -- OT 2
IREFERENCE
HIGM CI4OLAASSEMBLY
TRANSEEREA
PUMP
MEA
OUTLET
ACESSORY
EE NOT &I
C.
E
OUTAsETOLO
VALV
FITFILTER
CONNECTION
-414ALs D*asAD UfA
MITLET
LTE-
-XLT
CHIECK
VALVI
ASSEMBLY
LEFT
IS 3 G ME
IU I 04CT
syaPyN
Pump 14EAO
OUTLET
CECK
VALVE
v.4
CMAVS
CI
ASSEMASLY
PUMP'NG
a
141GO4
PUW 04EAO
6--FLAVTA
-FHLI-
wOLET
CHECK
OLET
CHICK
VALVE
sEMBLY
fRACitOft
cC T .
OUTLET PO0-4
ctsE NoE Is)
VALVI
ASSEMBLY
INLE T
MsANIFOLD
ASSErSIBy
PvRG1 iNft TL
14 7O
O WCTM
7-r3 COLL ECT LINE)
"AVTE VALVE
WASTEPORT
FLT
....
m. SOLVENT
IETO
DEsTECT.R
SOLVE.T
PiSOVE4 EOLV ST63)
L
VAV I
L T
SOLVENT PIES 0tvC.11
ASLENTlm PLaSIO IR 0 ME
Figure 4-3:
Waters M6000A Solvent Delivery System, Circuit
Diagram for Hydraulic Components (Waters GPC
Equipment Manual).
40
-,e
LIFJ
Vets
IL
At\/pop
U.I
_J_
Poll
e' ;Kt
ri~~~
j;C~
.2~
PLU
flleneto
INJFCT
(1) Rheodyne Model
Sample
7125
Injector
LJ
(2)
Figure 4-4:
C
Waters U6K Sample Injector
(1) Rheodyne Model 7125 Sample Injector
Injectors:
Manual); (2) Waters U6K Sample
(Rheodyne Injector
(Waters GPC Equipment Manual).
Injector
41
3.
Columns
The columns used were Waters Associates Ultrastyrageltm
Gel Permeation Columns.
As discussed in Section III,
is a cross-linked styrene/divinylbenzene copolymer.
Styragel
The Ultra-
styragel columns are available in a variety of pore sizes
50
ranging from 100 to 10 A.
Ultrastyagel columns have better
resolution that their precursor, Waters
p Stryageltm columns.
Ultrastyagel columns provide the highest resolution per column
of any GPC
column currently used for separation of hydrocarbons,
low to intermediate MW polymers,
synthesis reaction products,
and polymer additives as well as other samples.
produces 10,000 -
15,000 plates per cm column.
Each column
Two sizes of
Q
columns were used in this investigation, 1 x 100A
(Runs 1-4)
0
and 1 x 100A0 in series with 1 x 500A
(Run 5), each 30 cm in
length.
4.
Detector
A Waters Associates R401 refractive index detector was
used in all GPC analyses.
and electronic units.
The detector consists of optical
The optical unit,
a schematic shown in
Figure 4-5, consists of a light source shone through a slit,
lens, and the sample cell to a mirror.
a
It reflects off the mir-
ror, back through the sample cell and the lens, to a rotable
piece of glass used as the zero adjust,
and finally to a cadmium
sulfide detector which measures the position of the beam.
The
beam's deflection is proportional to the refractive index difference between the contents of the sample cell, which contains
flow from the column and flow directly from the pump.
MIRROR
SAMPLE
-
LENS
-
REFERENCE
Figure 4-5:
-
0-TTETL
MASK
-
0PTICAL
ZERO
DETECTOR
LIGHT
SOURCE
AMPLIFIER &
PWRSPL
RECORDER
ZERO
ADJUST
Detector Optical Unit (Waters
Schematic of Waters R401 Refractive Index
GPC Equipment Manual).
43
The cadmium sulfide detector outputs a voltage proportional to the beam deflection.
This signal is sent to the
electronics unit, which amplifies the signal and outputs it as
a voltage between -100 and +100 millivolts.
The amplification
of the signal from the optics unit is controlled with an attenuator switch with settings from 128X (least sensitive)to 1/4X
(most sensitive).
A zero test setting on the attenuator and a
potentiometer labeled RECORDER ZERO allow the zero setting of
the detector to be matched with the zero setting of the recorder.
A polarity switch allows the polarity of the signal to be reversed.
a chart marker switch sends a
small output to the recorder to
allow events to be marked.
5.
Data Compiling
A Houston Instruments 0 -
10 millivolt 2 channel recorder
with friction driven chart speeds variable over a wide range
was used in Runs 1 -
4.
One channel was used to record the out-
put of the differential refractometer, the other channel was
not used.
The output from the detector was passed through a
two resistor voltage divider, which transformed the 100 millivolt
output to a 10 millivolt output.
A Waters Associates M730 Data Module was employed in Run
5 to compile chromtographic data.
The M730 is a versatile
printer-plotter-integrator offering a choice of calculation
methods and baseline corrections, and individual sample calculations with ten calibration files.
Parameters for set-up, peak
integration,
and calculation are entered prior to injection
of samples.
Integration can be controlled by user selection of
timed events.
A typical plot is marked with an injection mark,
44
retention times,
and start and stop integration marks.
The
calculated results, retention time, area, molecular weight, and
area/molecular weight, are printed after plotting of the chromatogram.
For detailed discussion of operation of the M730, con-
sult the Waters Data Module Instruction Manual.
A.
3.
Elevated Temperature Apparatus
The waters Associates 150C ALC/GPC was used in all elevated
temperature runs.
The Model 150C is a fully automated, micro-
processor-based system consisting of all the fundamental GPC
components plus it has capability for precise temperature control.
High temperature control is extremely important when:
1.
The sample is difficult to dissolve at room temperature
2.
The sample is difficult to keep in solution at room
temperature
3.
The viscosity of the sample in solution is high, or
4.
The viscosity of the solvent is high.
Each component of the self-contained Model 150C is designed for
superior system operation.
The 150C operates automatically
under microprocessor control and functions in the same manner
for single or multiple samples.
via the front panel keyboard.
operating commands are entered
The microprocessor stores the
instructions and organizes them into the required sequence of
mechanical operations.
The solvent delivery system,
shown in Figure 4-6, con-
sists of a noncircular, computer-designed gear drive which overlapes piston strokes to provide constant flow for smooth baseline.
A small pre-pump, in-line filter and debubbler ensure
45
TO INJECTOR COMPARTMENT
PRESSURE
TRANSDUCER
OUTLET 1
CHECK
VALVES
INLET
CHECK
VALVES
BUBBLE
I TRAP
0NLN
INE
MANIFOLD
TO REFERENCE
SIDE OF
REFRACTOMETER
Figure 4-6:
FLE
*
LOW PRESSURE
DETECTOR
PURGE VALVE
Schematic of Waters 150C Main Pump
Equipment Manual).
SOLVENT
SUPPLIED
BY PRE-PUMP
(Waters GPC
46
highly accurate,
resetable solvent delivery to the inlet of the
high pressure pump.
Compressibility compensation provides
accurate flow rates fo 0 to 9.9 ml/minute in 0.1 ml/minute increments.
The programmable injection system,
shown in Figure 4-7,
provides automatic spin, filtration, and injection volumes from
10 to 500 -pl for each of sixteen sample vials.
The 150C per-
forms injection of samples just as an operator would manually
with a syringe.
It cleans the syringe, places the needle into
the sample vial, withdraws a specified amount of sample, injects,
and marks the chromatogram.
The column oven accepts up to 10 columns.
designed to operate from ambient to 150C.
This oven was
It maintains samples
and solvent temperatures constant for consistent and reliable
results.
The programmable heating rate reduces thermal shock to
columns.
The columns used were 1 x 100A and 1 x 500A Ultra-
styragel columns.
A sensitive, linear universal refractive index detector,
shown in Figure 4-8, is utilized in the 150C.
Light passes
through the flow cell and is reflected by a mirror behind the
flow cell.
The reflected light then passes through the flow cell
again and is focused on a photodetector sending an output voltage to the recording device.
When a difference between refrac-
tive indices of the two fluids in the cell chambers is detected,
the refracted light beam falls upon a different part of the
photodetector,
causing a change in the photodector voltage out-
put which is indicated by deflection on the chart recorder.
A
47
SYRINGE
SYRINGE
VALVE
(V2)
(OPENED)
HOLDING LOOP
RES
YRI
MOTORl)E
A TUATED
PISTON
TO COLUMN
TSYRINGE
SE
VENT
INJECT
fl
CLOSED)
BYPASS
T7 7771RESTRICTOR
V'11
SOLVENT
FROM
FILTERED
SA!.MPLE
Figure 4-7:
SAM PLE
VIAL
Schematic of Waters 150 Injection System (Waters
GPC Equipment Manual).
PUMP
48
SAMPLE FROM INJECTOR
COLL UMN SET
CL IMIN
COMPART MENT
SAMPLE SIDE
SILICON
PHOTODETEC TOR
TO
_
COLLIMATING LENS
OUTLET
TEE
a
REFERENCE SIDE
-REAR
MIRROR
FROM PUMP+
BUBBLE TRAP
FIBER OPTICS CABLE
REFRACTOMETER
LIGHT SOURCE
INTERNAL
LOW NOISE
SIGNAL CABLE
W WASTE
CONTAINER
TO R.I. ELECTRONICS
PUMP
COMPARTMENT
Figure 4-8:
Schematic of Waters 150C Differential Refractometer (Waters GPC Equipment Manuals).
49
counter-current heat exchanger ensures thermal stability to
0.0005C.
Fiber optics light transmission provides cooler opera-
tion of the light source for sensitive detection and longer
life.
Usage of a quartz halogen light source provides extra
sensitivity by increasing signal to noise ratio.
Rapid and reproducible data recording with automatic
calculation of GPC data was obtained with the Data Module
M730
(as described in Section 4.A.2.5).
For a more complete
description of the 150C and its components, consult the Waters
Model 150C ALC/GPC Instruction Manual.
B.
EXPERIMENTAL PROCEDURES
B.
1.
Ambient Temperature Procedures
The procedure of obtaining a molecular weight distribution using GPC is broken into three parts:
sample preparation
and solvent selection, actual chromatographic analysis to generate chromatograms,
and calculation of molecular weight informa-
tion from the resultant chromatograms.
1.
Sample Preparation
Samples from 0.02 -
0.2 weight% were prepared by dissolving
a known weight of sample in a given volume of solvent.
Larger
concentration of samples could cause "viscous fingering," a
phenomenon in which the sample components being separated reach
a high enough concentration in the column to begin to interact
with each other, causing poor separation.
The solvent used in
all ambient experiments was HPLC grade Toluene supplied by VWR
Scientific.
Toluene was chosen because of its capatibility with
50
the column system, refractive index difference from samples, and
easy accessibility.
Samples were filtered through Millipore
Corporation Millex-GV .22 pm filters.
2.
2a.
Chromatographic Analysis
Preparation
The solvent is vacuum filtered through 1/2 micron Millipore filters to prevent particulate contamination to the columns.
The pump is then primed by drawing solvent through the pump inlet into a syringe.
ensure that
The pump is turned to a high setting to
the pump outputs to a low pressure.
Solvent is
pushed from the syringe into the pump until the pump can operate
on its own.
The M6000A pump will pump the volume to which it
is set immediately once primed.
The reference valve on the pump is positioned at REFERENCE
and the pump is set at 3 ml/minute to purge the reference cell.
A few minutes purging is sufficient.
Flow is then returned to
0 ml/minute and the reference valve is turned to the column
position.
If the Rheodyne injector is used a syringe full of solvent
is used to flush the sample loop.
If the Waters injector is
used, the valve is turned to INJECT and the sample port valve
to UNLOCK, the pump turned back to 3 ml/minute, and the loop
purged for three sample loop volumes.
After purging, the flow
should again be retuned to zero, the sample port valve locked,
and the injection valve to LOAD.
After the injector is flushed, the flow rate can be
brought slowly up to the operating flow rate,
1 ml/minute in
51
all
ambient experiments.
Care must be taken to ensure that the
pressure does not oscillate considerably, which could be due to
failure of the pump inlet check valve.
If this occurs, the pump
must be reprimed with degassed solvent.
The chart recorder is zeroed relative to the refractive
index detector by turning the detector to ZERO TEST and adjusting
the recording zero knob until flipping the polarity switch
produces
little
or
no deflection of the chart recorder pen.
The optics are zeroed by turning the detector to its lowest sensitivity and adjusting the optical zero to the chart recorder
zero,
and repeating this process in the next higher sensitivity
until the desired
sensitivity is reached.
Sensitivities of 4X
and 2X were used in all ambient experiments.
2b.
Analysis
Once the baseline has steadied and the appropriate sensitivity level reached, samples are ready for injection.
The
desired amount of sample is injected into the sample loop with
a clean syringe.
Injection volumes of 100 pl were used in all
ambient experiments.
When using the Rheodyne injector, the
injector must be on LOAD.
Several hundred microliters of air-
free solvent are injected into the loop and around the injection
port to clean the syringe loop.
Injection of the appropriate
amount of air-free sample then follows.
the injector.
The syringe remains in
When the Waters injector is used, the injector
also must be on LOAD and the sample port unlocked.
After the
sample is unlocked in the injector, it is withdrawn and the
sample port locked.
If the sample port is not locked injection
will cause depressurization of the columns.
52
To inject the sample, flip either injector to INJECT.
The Rheodyne injector must be flipped quickly as there is no
flow when the injector is between LOAD and INJECT.
After one
sample loop volume has flowed through the injector, it can be
flipped back to LOAD,
flushed with solvent.
and in the case of the Rheodyne injector
In any case, the syringe should be rinsed
with clean solvent.
The output of the detector, the chromatogram, is recorded
on the chart recorder
(Runs 1-4)
or the Data Module
(Run 5).
Sufficient time should be allowed for complete elution of sample
before injection of another sample.
This time can be approxi-
mated from flow rate values and column lengths.
After all samples have been run,
the flow rate is slowly
returned to zero, and all instrumentation is turned off except
the detector.
The detector is designed to remain on continuously,
and turning it off will decrease its usefullness.
2c.
Calculation
In order to obtain molecular weight data from a chromatogram,
calibration of the column is first required.
If nar-
rowly dispersed standards are available (as is the case in this
investigation)
calibration is quite simple.
Injecting samples
of the standards and determing their retention time is all that
is required to formulate a calibration curve.
A plot of log
molecular weight versus peak retention time yields a linear
calibration curve which conforms to the equation,
log
(MW)
= D
o + D 1 (RT)
(23)
53
where MW is the standard's molecular weight, RT its retention
time, and D
and D
are calibration constants computed from a
linear fit of data from analyses of a series of standards.
Analysis of a chromatogram involves drawing a baseline
and measurement and interpretation
of the detector response.
The magnitude of the detector response is proportional to the
amount of eluting sample at a specific retention time.
This
retention time is related to the corresponding molecular weight
by the calibration curve via Equation
(23).
To calculate molecular weight distributions, the sample
peak is cut into equally spaced slices, each slice has a retention time and an area.
The area of each slice is directly re-
lated to the weight of a particular molecular weight fraction
in the whole sample.
The complete procedure for computation of
molecular weight distribution is found in Appendix I and is
illustrated in Sections
B.
1.
2.
V.A and B.
Elevated Temperature Chromatography
Sample Preparation
Samples are prepared as in the ambient experiments, except
that sample vials supplied with the 150C are to be used and
placed in the rotary carriage prior to analysis.
The same
sample size and solvent considerations are employed.
The sol-
vent used in all elevated temperature experiments was filtered
HPLC grade 1,2,4 - Trichlorobenzene supplied by Fischer Scientific.
2.
Chromatographic Analysis
2a.
Preparation
54
The prepump is primed by forcing solvent into the prepump
via the external supply line with a syringe or by drawing solvent into the prepump through the solvent drawoff valve.
The
main pump is primed by depressing the SYSTEM PURGE button.
The
flow rate should be set to a flow rate consistent with anticipated
use.
Allow the SYSTEM PURGE to operate for three minutes.
The
injector is now purged by depressing the INJ PURGE button to
flush all flow paths within the injector and to cycle the injector syringe one complete cycle.
Since operating at elevated temperature, time must be
allowed for the system to equilibrate and maintain a stable
baseline.
The 150C is automatically zeroed by inputting a zero
to the scale factor.
Auto zero moves the baseline signal to
the 0 millivolt location and holds it there for twenty-four
seconds.
This allows the system to automatically compensate
for any long term drift that might occur over extended periods
of operation.
2b.
Analysis
Operation of the Model 150C for GPC quantitation is very
simple due to the automated nature of this apparatus.
The
general routine is as follows:
1.
Set data,
time, chart speed, plotting mode, pen con-
trols, GPC mode, and calibration mode.
2.
Set integration parameters for standards to detect
standard peaks
(injection volume, sensitivity, polarity,
ect.).
3.
Inject standards of known molecular weight to determine retention times.
55
4.
A calibration
table
of retention
times and molecular
weights is entered.
5.
The coefficients of the equation representing the
calibration curve are internally calculated.
6.
Slice width, integration parameters for analysis,
and timed events to control baseline are set.
7.
A
Samples are injected and results are calculated.
complete discussion of parameters and detailed operational
procedures can be found in the Waters
2c.
150C Instruction Manual.
Calculation
The Data Module M730 was used to record and report chroma-
tographic data obtained from the 150C.
Manual computation
methods described in Section IV.B.l.2c were also employed to
provide continuity between ambient and elevated temperature
runs.
56
V.
V.A.
RESULTS
AMBIENT GPC RESULTS
To gain an understanding and appreciation for gel permeation chromatography fundamentals,
samples of pure and mix-
tures of pure normal paraffin standards in carbon number range
C19 -
C40 were injected in Runs 1 and 2.
are presented in Tables 5-1 and 5-2.
Summarized results
Injections of mixtures
were used to determine whether or not discrete separation by
carbon number could be achieved.
As seen in the chromatograms
shown in Figures 5-1 and 5-2, separation by GPC will not resolve mixtures by carbon number unless wide separation exists
between the components in the mixture.
Separation of Fischer-
Tropsch wax samples will resemble chromatograms like
Figure 5-2,
exhibiting a bell-shaped curve representative of the distribution
of molecular weight fractions.
In order to correlate retention
time and molecular weight data, a calibration curve was constructed using data from Run 2 for C19 - C40 shown in Figure
5-3.
Equation (23) can now be used to estimate molecular weights
from retention times for samples of unknown molecular weight.
The calibration coefficients determined for the operating conditions of Run 2 are,
D
D
0
=
4.71
=
-0.31
The chromatogram from injection of a slurry wax sample from
Huff's Run 9 is shown in Figure 5-4.
The detector response peaks
at a retention time of 6.86 minutes which corresponds to C28 from
57
SolventOperating Conditions:
Summary of Run 1.
Toluene, Temperature-25C, Columns - 1 x 100A
1 ml/min, Injection
Ultrastyragel, Flowrate
Volume - 100 pl, Polarity - Positive.
-
TABLE 5-1:
MW
log MW
WT
C22
310.59
2.49
.0238
7.5
C28
394.74
2.60
.1589
7.2
C38
535.00
2.73
.0261
6.8
1-2
C40
563.06
2.75
.2123
6.6
1-3
C19
268.51
2.43
.2180
7.8
1-4
C22
310.59
2.49
.0114
7.5
C28
394.74
2.60
.0807
7.1
C38
535.00
2.73
.0114
6.7
C20
282.54
2.45
.0500
7.6
C24
338.64
2.53
.0431
7.2
C28
394.74
2.60
.0431
7.0
C36
506.95
2.71
.0431
7.0
C40
563.06
2.75
.0341
6.6
C24
338.64
2.53
.0363
7.3
C25
352.67
2.55
.0465
7.3
C26
366.69
2.56
.0420
7.3
C28
394.74
2.60
.0397
7.3
C30
422.80
2.63
.0409
7.3
C24
338.64
2.53
.0205
7.4
C25
352.67
2.55
.0205
7.4
C26
366.69
2.56
.0205
7.4
C28
394.74
2.60
.0216
7.4
C30
422.80
2.63
.0239
7.4
1-1
1-5
1-6
1-7
Cn
%
Injection
RT
(min)
58
5-2:
Summary of Run 2.
Operating Conditions:
olventToluene, Temperature-22C, Columns - 1 x 100A Ultrastyragel, Flowrate- 1 ml/min, Injection Volume
100 pl, Polarity - Positive.
Inj ection
*
Cn*
MW
log MW
WT
%
-
TABLE
RT
(min)
2-1
C19
268.51
2.43
.1182
7.46
2-2
C20
282.54
2.45
.1136
7.36
2-3
C21
296.52
2.47
.1159
7.29
2-4
C22
310.59
2.49
.1091
7.19
2-5
C23
324.61
2.51
.1114
7.12
2-6
C24
338.64
2.53
.0909
7.06
2-7
C25
352.67
2.55
.1068
7.02
2-8
C26
366.69
2.56
.1114
6.96
2-9
C28
394.74
2.60
.1204
6.86
2-10
C30
422.80
2.63
.1136
6.76
2-11
C32
450.85
2.65
.1159
6.66
2-12
C36
506.95
2.71
.0932
6.52
2-13
C38
535.00
2.73
.1159
6.66
2-14
C40
563.06
2.75
.1114
6.39
2-15
SS-9A
.1840
6.86
2-16
SS-9B
.1102
6.86
Cn -
refers to n-hydrocarbon standard of known molecular
weight.
SS-ni - refers to Huff slurry reactor run-n,
dissolved sample i of unknown molecular weight.
C28
Impurity*
U,
Inj ectic n
C22
C38
i
0
1
I
I
2
3
I
I
4
5
I
6
I
I
I
7
|
8
|I
9
I|
10
1
11
|
12
I|
13
Retention time
Figure 5-1:
GPC Chromatogram -
Injection 1-4
Mixture of n-Hydrocarbon Standards
C22, C28, and C38.
*Represents low molecular weight impurity absorbed on column.
|
14
(Minutes)
Mixture
Imp urity
0
I
I
I
I
i
0
1
2
3
4
Figure
5-2:
GPC Chromatogram -
5
i
I I.
6
Injection 1-7:
C24, C25, C26, C28, and C30.
i
.
7
8
9
I
10
.
.
Inj ection
11
12
13
14
Retention Time (Minutes)
Mixture of n-Hydrocarbon Standards
61
1000
900
800
700
600
500
log MW
400
=
4.69 -
0.31 RT
S
-)
Ye
300
K.
4
200
I-
100
6.0
6.25
6.5
6.75
7.0
Retention Time, RT.
Figure
5-3:
7.25
7.5
7.75
(minutes)
GPC Calibration Curve - Run 2:
Toluene Mobile
Phase, 1 x 100A Ultrastyragel Column, 22C, and
n-Hydrocarbon Standards C19, C20, C21, C22, C23
C24, C25, C26, C28, C38, C32, C36, C38, and C40.
C28
Injection
I
I
I
0
1
2
3
Retention Time
Figure 5-4:
4
6
(minute)
GPC Chromatogram - Injection 2-13:
I
I
5
SS-9A
7
8
63
the calibration
curve.
The
liquid
runs was octocasane, C28, so it
carrier
used in Fischer-Tropsch
is not unlikely that a major portion of
the accumulated waxcomposition would be C28.
The slight build-up
of carbon fractions greater than C28 can be seen to the left
peak.
It
is
also assumed that
the wax is
product is
of the C28
primarily linear,
so no correction factor for methyl branching is incorporated in calibration or analysis.
In previous work by Huff,
analysis
application of gas chromatography in
of Fischer-Tropsch products has given good quantitative
mates to the carbon number disbribution
was proposed in this
estimates
investigation
up to
approximately
estiC30.
It
to use GPC to generate quantitative
of the carbon number distribution
of heavier hydrocarbons.
Amplification of detector response in the region greater than C28
could be attained
by altering
the attentuation
of the differential
refractometer and the chart speed of the recorder during succeeding
runs.
Analysis of the recorder pen deflection
to the left
of the C28
peak gives precise insight into data generated by the heavier
components of the paraffin wax.
Data for Run 3 is summarized in Table 5-3.
C22,
C26,
C28,
C36 and C40
(supplied by PSC)
erate the calibration curve
Standards C]9,
were injected to gen-
shown in Figure 5-5.
The resulting
calibration coefficients are,
D
D
0
=
4.73
=
-0.30
Several slurry samples were injected,
altering attentuation and
chart speed to magnify detector response for carbon numbers C28
and greater
(retention time 6.98 minutes and greater).
Shown in
64
TABLE 5-3:
Summary of Run
3.
Operating Conditions:
Toluene, Temperature-24.4C, Columns -
Injection
Cn
MW
log MW
Wt
%
Ultrastyragel, Flowrate -1 ml/min,
100 l, Polarity-Positive.
Injection Volume-
RT
(min)
3-1
C19
268.51
2.43
.1182
8.17
3-2
C19
268.51
2.43
.1182
7.60
3-3
C19
268.51
2.43
.1182
7.60
3-4
C19
268.51
2.43
.1960
7.60
C26
266.69
2.56
.2111
7.08
C40
563.06
2.75
.1960
6.53
3-5
C40
563.06
2.75
.1114
6.53
3-6
C22
310.59
2.49
.2001
7.37
C36
506.95
2.71
.2379
6.67
.2270
6.97
.1204
6.98
3-7
SS-9C
3-8
C28
3-9
SS-9D
.5018
7.02
3-10
SS-9D
.5018
7.00
3-11
SS-9E
.7789
7.02
3-12
SS-9D
.5018
7.00
3-13*
SS-9D
.5018
10.10
394.74
2.60
* Flowrate changed to 0.7 ml/min.
Solvent-
1 x 10OA
65
I
1000
I
I
I
900
800
700
600
log MW
500
400
=
4.73 -
0.30 RT
I
0
300
Q)
:3:
200
U4
100
i
I
6.24
6.5
i
6.75
a
7.0
Retention Time, RT
Figure 5-5:
7.25
7.5
(minutes)
GPC Calibration Curve-Run 3:
Toluene Mobile
Phase, 1 x 100A Ultrstragel Column, 24.4C, and
n-Hydrocarbon Standards C19, C22, C26, C28, C36,
and C40.
66
Figures 5-6 and 5-7 are chromatograms illustrating the effect of
changing attentuation to 2X and chart speed to 4 inches/minute
Note that the pen deflection goes
for injections 3-11 and 3-12.
off scale in the region of C28 due to altered attenuation.
usual procedure,
As
molecular weights were approximated by correla-
tion of retention time and calibration coefficients.
In GPC the pen deflection, expressed as detector response,
is proportional to amount of substance eluting at a specific retention time.
Computation of area,
cumulative weight,
and
corresponding molecular weight can be accomplished by using the
slicing procedure discussed in Section IV.B.2.2c and Appendix I.
Retention time and molecular weight distribution data are shown
in Table 5-4 for Injections 3-11 and 3-12.
figures can be generated from this data.
versus retention time,
Several interesting
Plots of peak height
cummulative weight versus molecular weight,
and differential weight fraction versus molecular weight are
shown in Figures 5-8,
5-9 and 5-10 respectively.
Linear trends
in cumulative weight and differential weight fraction distribu-
tions are shown for carbon number range C36 - C68.
To validate linear extrapolation of the calibration curve
to the exclusion limit of the column,
standards of polystyrene
(supplied by the Pressure Chemical Company)
4,
were injected in Run
the results of which are summarized in Table 5-5.
The cali-
bration curve for Run 4 is shown in Figure 5-11, with calibration
coefficients,
=
D
5.27
0
D 1= -0.37
67
5.8 minutes
I
I
6.0
5
I
6.25
I
6.50
.
6.75
7
7.0
I
I
7.25
I
I
7.50
Retention Time
Figure
5-6:
I
7.75
I
8.0
(minutes)
GPC Chromatogram-Injection 3-11:
SS-9E, Attenuation
2X, Chart Speed Changed to 4 inch /min @ 5.8 minutes.
68
I
L
6.0
6.25
i
6.50
I
6.75
I
7.0
I
7.25
7.50
7.75
Retention Time
Figure
5-7:
GPC Chromatogram-Injection 3-12:
2X, Chart Speed 4 inch/min.
8.0
8.25
(minutes)
SS-9D, Attenuation
69
TABLE 5-4:
Injection
3-11
3-12
Cumulative and differential weight fraction
molecular weight distribution data.
i
RT.
MW.
1
Cn
h.
1
8
5.83
954.99
68
0.0
7
5.96
874.98
62
16.0
6
6.09
799.83
57
5
6.22
731.14
4
6.35
3
Cum W.
1
X.
1
N.
x 104
.0315
0.33
.95
.0960
1.10
43.0
.87
.1535
1.92
52
46.0
.78
.1995
2.73
668.34
48
58.0
.66
.2426
3.63
6.48
610.94
43
68.5
.52
.2849
4.60
2
6.61
558.47
40
80.0
.36
5.91
1
6.74
510.51
36
92.0
.17
.3300
-----
7
5.67 1071.52
76
0.
.0082
0. 08
6
5.83
954.99
68
2.
.99
.0695
0. 73
5
6.00
851.14
61
14.
.91
.1780
2. 09
5
6.17
758.58
54
27.
.79
.2575
3. 39
3
6.33
676.08
48
36.
.63
.3604
5. 33
2
6.50
602.56
43
47.
.43
.4385
7. 28
1
6.67
537.03
38
54.
.21
1.0
1.0
70
I
1000
I
I
I
I
..
0
Injection 3-11
A
Injection 3-12
7,
0
700
0
I
0
900
800
I
0
600
0
AA
500
400
0'
0
300
;E,
200
,A
100
0
L
-
5.8
5.9
I
6.0
6.1
6.2
Retention Time, RT
Figure 5-8:
6.3
6.4
6.5
6.6
(minutes)
Peak Height and Retention Time Distribution:
Injections 3-11 and 3-12.
6.7
6.8
71
1. p
*
0
I
Injection 3-11
I
I
I
I
J
A Injection 3-12
0.8
.H
0.6
-H
A
0.4
/A
0.2
I
0.0
300
400
500
I
5-9:
I
I1~-
600 700 8009001000
Molecular Weight, MW
Figure
I
1400
(g/mole)
Cumulative Weight Fraction Molecular Weight
Distribution:
Injections 3-11 and 3-12.
72
8.0
7.0
C
.H
-P
Injection
3-11
A
Injection
3-12
6.0
0
*
A
5.0
A
0
4.0
4
0
3.0
A
a)
2.0
0*
1.0
I
300
I
A i
I J
400
500
600
5-10:
Differential
Number Fraction
Distribution:
; a
:
700 800 9001000
Molecular Weight, MW.
Figure
i
_ _
-
0.0
e i
2
1700
(g/mole)
Molecular Weight
Injections 3-11 and 3-12.
73
5-5:
Inj ection
Summary for Run 4.
Operating conditions:
SolventToluene, Temperature -23C, Columns - 1 x 10QA
ultrastyragel, Flowrate -1 ml/min, Injection volume100 -pl, Polarity - Positive*.
Cn
MW
log MW
WT
%
TABLE
RT
4-1
C20
282.54
2.45
.1706
7.68
4-2
C28
394.74
2.60
.1195
7.33
4-3
C28
394.74
2.60
.1195
7.33
4-4
C32
450.85
2.65
.0341
7.13
4-5
C36
506.95
2.71
.0284
7.00
4-6
C40
563.06
2.75
.0570
6.87
4-7
PS 800**
440
2.64
.1479
7.17
4-8
PS 1800
990
3.00
.1593
6.23
4-9
PS 2000
1100
3.04
.1650
6.23
4-10
C20
282.54
2.45
.1700
7.68
C28
394.74
2.60
.1190
7.30
C32
450.85
2.65
.0340
7.10
C36
506.95
2.71
.0283
7.0
C40
563.06
2.75
.0570
7.0
.5018
7.33
4-11
SS-9D
*
Polarity changed to negative for polystyrene standards.
**
Polystyrene standards of given molecular weight, corresponding
hydrocarbon molecular weight given by (0.55) Polystyrene
weight, Corresponding carbon number:
PS 800-C31, PS 1800-C70,
PS 2000-C78
7000
-
6000
-
5000
-
8000
-
10000
9000
-
74
4000
3000
2000
0
1000
900
800
0.37 RT
5.27
log MW
-
700
600
500
400
300
200
100
6.0
6.25
6.50
6.75
Retention Time,
Figure
5-11:
RT
7.0
7.25
7.50
7.75
8.0
(minutes)
GPC Calibration Curve - Run 4:
1 x 100A Ultrastyragel Column,
Toluene Mobile Phase,
23C n-Hydrocarbon
Standards C20, C28, C32, C36, C40 and Polystyrene
Standards 800, 1800, 2000.
75
The linear exclusion limit occurs at a retention time of 6.23
minutes
(approximately C70).
Retention time and molecular
weight distribution data for Injection 4-11 are shown in Table
5-6.
ential
The resulting peak height, cumulative weight, and differweight fraction distributions are shown in Figures 5-12, 5-13,
and 5-14, respectively.
Again-, linear trends cumulative weight and
-
differential weight fraction distributions are seen for C31
C67.
To extend the observed range of heavier molecular weight
fractions, a 500A Ultrastyragel column was added to the GPC
configuration for Run 5.
Table 5-7.
A summary of the results is shown in
In these series of injections,the Data Module M730
was used to record detector response.
As discussed in Section
IV.A.l.5 the Data Module M730 is capabile of calculating pertinent molecular weight information internally.
The generated
calibration curve is shown in Figure 5-15, with calibration co-
efficients,
D
D
0
=5.05
= -0.17
However the exclusion limit of the column apparatus with the
additional column is still approximately C70 at ambient temperature.
Results of slurry
samples
are summarized in Table 5-8
for Injections
5-12 and 5-17
(note inclusion of molecular and area
percent calculations from retention time by the Data Module).
Module).
A
graph of area percent versus molecular weight
based on Data Module calculations is shown in Figure 5-16.
A
76
TABLE 5-6:
Cumulative and differential weight fraction molecular
weight data for Injection 4-11.
i
RT.
MW.
1
C
n
h.
1
Cum W.
x.
N.
x 104
11
6.10
1030.39
73
0.0
1.00
0.0122
0.12
10
6.20
946.24
67
1.4
0.98
0.0367
0.39
9
6.30
868.96
62
3.3
0.94
0.0673
0.77
8
6.40
797.99
57
6.4
0.87
0.0918
1.15
7
6.50
732.82
52
6.9
0.81
0.1102
1.50
6
6.60
672.98
48
817
0.73
0.1286
1.91
5
6.70
618.98
44
10.2
0.63
0.1469
2.38
4
6.80
567.54
40
11.9
0.52
0.1653
2.91
3
6.90
521.19
37
13.2
0.40
0.1776
3.41
2
7.00
478.63
34
13.9
0.27
0.1969
4.09
1
7.10
439.54
31
15.2
0.13
77
18.0
16.0
4
Ci-
14
0
12.0
10.C
0
_H
Ii
0
8.0
S
6.01
4.0
2.0
n.
6.1
6.2
6.3
6.4
6.5
6.6
Retention Time,
Figure
5-12:
6.7
RT
6.8
6.9
(minutes)
Peak Height-Retention Time Distribution:
Injection 4-11.
7.0
7.1
78
1
I
I
1
1
f1
1
1 1
1.o
A
0
0.8
0~'
0
/
0
0.6
4
/
4
4-)
0.4
0
Q)
0.2
4-)
I
0
300
400
500
I
I
600 700
800 900 1000
Molecular Weight, MW.
Figure 5-13:
(g/mole)
Cumulative Weight Fraction Molecular Weight
Distribution:
Injection 4-11.
2000
79
5.0
I
I
I
I
F
I
I
r-T-r-r
z
4.0
0
3.0
-0
.H
-H
2.0
0
0e
-P
1.0
a)
0
-4
0
300
400
500
600 700 800 900 1000
Molecular Weight W
Figure 5-14:
2000
(g/mole)
Differential Number Fraction Molecular Weight
Injection 4-11.
Distribution:
80
Summary of Run 5.
Operating Conditions:
SolventToluene Temperature-24C Columns - 1 x 10OX
1 x 5001 ultrastyragel, Flowrate - lml/min, Injection
Volume - 100pl, Polarity - Positive.*
Inj ection
*
Cn
MW
log MW
WT
%
&
TABLE 5-7:
RT
5-1
C40
563.06
2.75
.1114
13.33
5-2
C40
563.06
2.75
.1114
13.23
5-3
C36
506.95
2.71
.0932
13.48
5-4
C28
394.74
2.60
.1204
14.13
5-5
C24
338.64
2.53
.0909
14.48
5-6
C20
282.54
2.45
.1136
14.95
5-7
PS 1800
990.00
3.00
.1593
12.40
5-8
Ss-
9C
5-9
SS-
9C
.3853
5-10
SS-
9E
.7789
5-11
SS-
9F
------
.1289
5-12
SS-
9H
------
.6458
5-13
Ss-
9C
------
.3853
5-14
SS-
9C
------
.3853
5-15
Ss- 9C
------
.3853
5-16
SS-
9C
------
.3853
5-17
SS-
9C
------
.3853
5-18
SS-
9C
------
.3853
5-19
SS-
9G
------
.1934
------
.3853
Polarity
changed to Negative for Polystyrene Standard
(Injection 5-7).
81
2000
1000
900
800
0
700
K
log MW
5.05
=
-
0.17 RT
600
-p
..c:
500
100
400
300
200
12.0
12.25
12.50 12.75
Retention Time,
Figure 5-15:
13.0
RT
GPC Calibration Curve Run
13.25
13.50 13.75
(minutes)
5.
Toluene Mobile
Phase, 1 x 100A and 1 x 50OX Ultrastyragel
Columns, 25C, n-Hydrocarbon Standards C20,
C24, C28, C36, C40, and Polystyrene
Standard 1800.
Cumulative and differential weight fraction molecular weight data.
Injection
MW.
Cn
h.
Cum W.
11.79
1000.00
71
2.0
1.00
.0787
0.79
3.12x10-2
12.04
904.66
64
3.5
.97
.1312
0.45
0.24
12.29
818.44
58
6.0
.92
.1966
2.40
4.64
12.54
740.40
52
9.0
.84
.2886
3.90
8.32
12.79
669.83
48
13.0
.73
.4066
6.07
13.43
13.04
605.99
43
18.0
.58
.5113
8.44
19.30
13.29
548.21
39
21.0
.42
.6296
11.48
24.95
13.54
495.96
35
27.0
.20
5
12.27
825.05
59
2.0
1.00
.2383
2.89
7. 08x101
4
12.57
731.56
52
3.5
.90
.4107
5.61
7.52
3
12.87
648.73
46
6.0
.74
.6092
09.39
18.12
2
13.17
575.25
41
8.0
.53
.8208
14.27
29.36
1
13.47
510.07
36
11.0
.25
RT.
5-12
5-17
X.1
N.
x 104
Area
%
TABLE 5-8:
35.56
44.16
00
83
45.0
I
* In jectio n
5-12
A In jectio3 n
5-17
A
6NO
AL0
4
Q)
400
I
jI
I
I
I
iA
-j
1000
Molecular Weight, MW.
Figure 5-16:
I
(g/mole)
Area Percent Molecular Weight Distribution:
Injections 5-12 and 5-17.
84
Shown
in Figures
5-17
and 5-18
are
graphs of
cumulative
weight and differential weight fraction versus molecular weight
based on the manual computation scheme used in analysis of previous runs.
The nature of the cumulative weight, differential
weight fraction, and area percent distributions remains linear
out to the highest molecular weight component excluded from
the column.
Quantitative estimates of corresponding molecular
weight distributions up to C70 were possible.
V.B.
ELEVATED TEMPERATURE GPC RESULTS
Lack of sufficient solubility of slurry samples at ambient temperature lead to analysis of samples at elevated temperature.
By using the Waters 150C GPC apparatus,
it was pos-
sible to efficiently and automatically inject and analyze a
series of paraffinic standards and Fischer-Trposch was samples
at reproducible conditions with precise temperature control.
Summarized results for Run 6 are shown in Table 5-9.
The generated calibration curve for injection of paraffinic
standards is shown in Figure 5-19, with the resulting calibration coefficients
D
0
D
=
=
4.67
-0.0996
Further analysis in Run 6 was suspended due to the clogging of
a guard column after injection of an improperly filtered slurry
sample,
SS-lA,
(which demonstrates the overall efficiency of
the 150C in its ability to protect the columns).
The final series of injections of standards and samples
85
I
I
1.0
S
A
I
-
-I
r
Injection
5-12
AInjection
5-17
0.8
-Ii
I
I
0.6
a
a
-H
0.4
.U
0.2
A
0.0
400
---
-~~
500
600
i
.
(g/mole)
Cumulative Weight Fraction Molecular Weight
Distribution:
a
2000
700 800 900 1000
Molecular Weight, MW
Figure 5-17:
1 :
Injections 5-12 and 5-17.
I
16.0
0T
I
I
I
-rI
I
I
I
I
I
I
I
I
I
I
I
I
I
I
i
i
A
14.0
* Injection 5-12
12.0
A Injection
0
0
10.0
a
-Ii
rz4
5-17
8.0
COz
6.0
z
-i
4.0
4
2.0
44i
44i
.rA
I
0.0
500
600
I
-I
I
700
800
I
I
I
I
I
900 1000
Molecular Weight, MW
Figure 5-18:
I
I
(g/mole)
Differential Number Fraction Molecular Weight Distribution:
Injections 5-12 and 5-17.
I
2000
87
Summary of Run 6.
Operating Conditions:
SolventTrichlorobenzene, Temperature - 50C, Columns1 x 100A and 1 x 500A ultrstragel, Flowrate-
0.7 ml/min, injection volume-300pi,.
positive.
Injection
Cn
MW
log MW
Polarity
RT
6-1
C20
282.54
2.45
22.30
6-2
C24
338.64
2.53
21.40
6-3
C28
394.74
2.60
20.80
6-4
C36
506.95
2.71
19.80
6-5
C40
563.06
2.75
19.20
6-6
SS-lA
-
TABLE 5-9:
88
I
I
1000
I
900
800
700
600
500
log MW =
400
0
300
N4
4.67
-
0.0996
RT
-
-,
K
-H
200
0
a
100
9.0
20.0
Retention Time,
Figure 5-19:
21.0
RT
22.0
(minutes)
Trichlorobenzene
GPC Calibration Curve 0 Run 6:
Mobile Phase, 1 x 100A and 1 x 500k Ultrastyragel
Columns, 50C, n-Hydrocarbon Standards C20, C24, C28,
C36, and C40.
235.
89
was completed in Run 7,
5-10.
the results of which are found in Table
The calibration coefficients for the calibration curve
shown in Figure 5-20 are,
D 0=
D
4.82
= -0.0824
From injection of a sample of linear polyethylene
7-6)
(Injection
the exclusion limit of the columns was determined to be
19.5 minutes
ibraton curve
(corresponding to linear extrapolation of the calup to approximately C116).
Several different slurry samples were injected and analysezed in Injections 7-7 to 7-13.
The different slurry samples
represent different time-on-stream for various operating conditions for the Fischer-Tropsch synthesis as discussed by Huff.
These operating conditions are summarized in Table 5-11.
Re-
tention time and molecular weight distribution data for these
injections are presented in Tables 5-12 through 5-17.
Plots
of area percent versus molecular weight based on Data Module
calculations are shown in Figure
tions,
5-21.
From manual computa-
cumulative weight and weight fraction
are plotted in Figures 5-22
tribution,
shown in Figure
and 5-23.
5-24,
distributions
The weight percent dis-
for Injection 7-13 was gen-
erated by application of the special GPC calculation mode of the Data Module.
Weight percent
The linearity of the
molecular weight distribution to fraction as high as C]05 is
illustrated by these figures.
90
5-10:
Summary of Run 7.
Operating Conditions:
SolventTrichlorobenzene, Temperature-50C, Columns
1 x 100A, 1 x 500A ultrstyragel, Flowrate- 6 ml/min,
-
TABLE
Injection volume Run
C
3004A, Polarity-Positive.
MW
log
(MW)
RT
7-1
20
282.54
2.45
28.80
7-2
24
338.64
2.53
27.70
7-3
28
394.74
2.60
27.00
7-4
36
506.95
2.71
25.70
7-5
40
563.06
2.75
25.10
7-6
LPE
1634.56
3.21
19.50
7-7
SS-lA
---------
----
-----
7-8
SS-8A
-------
7-9
SS-91
------------
7-10
SS-91
-------------
7-11
SS-llA
---------
----
7-12
SS-12A
-----------
----
7-13
SS-12A
-----------
----
---------
-----
91
10000
log MW
=
4.82-
0.0824 RT
1000
Cn
Q)
0
100
19.0 20.0 21.0 22.0 23.0 24.0 25.0
Retention Time,
Figure 5-20:
RT.
GPC Calibration CurveoRun
26.0 27.0 28.0 29.0
(minutes)
7:
Trichlorobenzene
Mobile Phase, 1 x 100A and 1 x 500X Ultrastyragel
Columns, 50C, n-Hydrocarbon Standards C20, C24,
C28, C36, C40 and Linear Polyethylene Standard
1800.
Table 5-11:
Run
Catalyst
Total Time
Total
Loading,*
on Stream,
Pressure
hr
kPa
g/cm
*
Fischer-Tropsch Synthesis Operating Conditions
Slurry
Temperature
*C
H 2 /CO
Feed Ratio
1
0.273
258
100-150
225-273
1.42
8
0.142
860
790
232-263
0.69
9
0.139
680
445-1480
11
0.153
---
12
0.198
432
Precipitated Iron catalyst
232-263
0.55-1.18
275-960
248
0.34
790
248-285
1.19
(Fe-P) used in Run 1.
Fused Iron catalyst used in all other runs listed.
Space Velocity,
hr 1
1500-4000
3300
1500-4000
2300
1500-4000
93
TABLE 5-12:
Cumulative and differential weight fraction
distribution molecular weight data for Injection
i
RT.
1
MW.
1
C
n
h.
1
Cum W.
1
N.
1
x 104
Area
%
7-7.
20
20.04
1473.81
105
0.0
1.00
0.02
0.09
19
20.29
1405.47
100
0.4
1.00
0.06
0.15
18
20.54
1340.34
95
0.8
.99
0.10
0.25
17
20.79
1278.22
91
1.0
.99
0.14
0.38
16
21.04
1218.97
87
1.5
.98
9.21
0.63
15
21.29
1162.51
83
2.3
.97
0.32
0.97
14
21.54
1108.60
79
3.2
.96
0.45
1.32
13
21.79
1057.26
75
4.2
.95
0.60
1.76
12
22.04
1008.23
72
5.1
.93
0.83
2.28
11
22.29
961.56
68
7.2
.90
1.14
3.10
10
22.54
917.00
65
9.0
.86
1.56
4.12
9
22.79
874.50
62
12.1
.81
2.13
5.36
8
23.04
833.88
59
15.5
.75
2.80
6.75
7
23.29
795.32
57
19.0
.68
3.44
8.06
6
23.54
758.46
54
21.5
.60
4.10
9.21
5
23.79
723.30
51
24.5
.51
4.72
10.01
4
24.04
689.78
49
26.0
.41
5.25
10.63
3
24.29
657.81
47
27.5
.31
5.76
11.13
2
24.54
627.33
45
28.5
.21
6.29
11.55
1
24.79
598.25
43
29.9
. 11
12.23
94
TABLE
5-13:
Cumulative and differential weight fraction
distribution molecular weight data for
Inj ection 7-8.
RT.
MW.
1
C
n
h.
1
Cum W.
1
N.
x10
1
4
Area
%
i
22
20.04
1473.81
105
1.0
1.0
0.10
0.55
21
20.29
1405.47
100
1.5
0.99
0.13
0.64
20
20.54
1340.34
95
1.8
0.99
0.16
0.74
19
20.79
1278.22
91
2.1
0.98
0.20
0.87
18
21.04
1218.97
87
2.5
0.97
0.25
1.04
17
21.29
1162.51
83
3.0
0.96
0.34
1.28
16
21.54
1108.60
79
4.0
0.95
0.45
1.59
15
21.79
1057.26
75
5.1
0.93
0.59
1.95
14
22.04
1008.23
72
6.0
0.92
0.76
2.31
13
22.29
961.56
68
7.5
0.89
0.99
2.79
12
22.54
917.00
65
9.4
0.86
1.22
3.33
11
22.79
874.50
62
10.5
0.83
1.45
3.93
10
23.04
833.88
59
12.0
0.79
1.83
4.63
9
23.29
795.32
57
15.0
0.74
2.31
5.28
8
23.54
758.46
54
17.5
0.69
2.74
5.97
7
23.79
723.30
41
19.3
0.63
3.23
6.68
6
24.04
689.78
49
22.1
0.56
3.81
7.38
5
24.29
657.81
47
24.5
0.48
4.37
8.11
4
24.54
627.33
45
26.5
0.40
4.99
8.79
3
24.79
598.25
43
29.0
0.31
5.66
9.57
2
25.04
570.52
40
31.0
0.22
6.58
10.49
1
25.29
544.08
39
35.5
0.10
12.08
95
TABLE 5-14:
Cumulative and differentail weight fraction
distribution molecular weight data for
Injection 7-9.
RT.
MW.
24
20.04
1473.81
105
0.0
1.00
0.0
0.34
23
20.29
1405.47
100
0.0
1.00
0.0
0.38
22
20.54
1340.34
95
0.0
1.00
0.01
0.48
21
20.79
1278.22
91
0.1
1.00
0.06
0.55
20
21.04
1218.97
87
0.4
0.99
0.13
0.68
19
21.29
1162.51
83
0.6
0.99
0.21
0.79
18
21.54
1108.60
79
1.0
0.98
0.31
1.07
17
21.79
1057.26
75
1.2
0.97
0.38
1.25
16
22.04
1008.23
72
1.4
0.96
0.45
1.50
15
22.29
961.56
68
1.5
0.94
0.57
1.81
14
22.54
917.00
65
2.0
0.92
0.69
2.13
13
22.79
874.50
62
2.1
0.91
0.90
2.58
12
23.04
833.88
59
3.0
0.88
1.31
3.15
11
23.29
795.32
57
4.0
0.84
1.72
4.01
10
23.54
758.46
54
4.8
0.80
2.21
4.85
9
23.79
723.30
41
6.0
0.74
2.79
5.65
8
24.04
689.78
49
7.0
0.68
3.31
6.46
7
24.29
657.81
47
7.7
0.62
3.75
7.08
6
24.54
627.33
45
8.2
0.55
4.25
7.69
5
24.79
598.25
43
9.0
0.47
4.88
8.21
4
25.04
570.52
41
9.8
0.38
5.52
8.74
3
25.29
544.08
39
10.5
0.29
6.13
9.21
2
25.54
518.87
37
11.0
0.20
6.87
9.88
1
25.79
494.81
35
12.0
0.10
C
n
h
Cum W.
N.
x 104
Area
%
i
11.51
96
TABLE
5-15:
Cumulative and differential weight fraction
distribution molecular weight data for
Injection
i
7-11.
MW.
21
20.04
1473.81
105
0.6
1.0
0.16
0.10
20
20.29
1405.47
100
0.7
0.99
0.19
0.12
19
20.54
1340.34
95
0.8
0.99
0.24
0.16
18
20.79
1278.22
91
1.0
0.98
0.29
0.36
17
21.04
1218.97
87
1.1
0.33
0.48
0.48
16
21.29
1162.51
83
1.2
0.95
0.41
0.58
15
21.54
1108.60
79
1.5
0.94
0.56
1.0
14
21.79
1057.26
75
2.0
0.92
0.72
1.55
13
22.04
1008.23
72
2.3
0.89
0.84
1.87
12
22.29
961.56
68
2.5
0.87
1.01
2.35
11
22.54
917.00
65
3.0
0.84
1.31
3.11
10
22.79
874.50
62
3.8
0.80
1.67
4.02
9
23.04
833.88
59
4.5
0.76
2.08
5.06
8
23.29
795.32
57
5.3
0.70
2.61
6.28
7
23.54
758.46
54
6.5
0.64
3.14
7.29
6
23.79
723.30
51
7.0
0.57
3.66
8.34
5
24.04
689.78
49
8.0
0.49
4.22
9.37
4
24.29
657.81
47
8.5
0.41
4.91
10.11
3
24.54
627.33
45
9.8
0.31
5.62
11.20
2
24.79
598.25
43
10.2
0.22
6.39
12.31
125.04
570.52
41
11.5
0.11
C
n
h
Cum W.
N.
x
104
Area
%
RT.
14.36
97
TABLE 5-16:
i
Cumulative and differential weight fraction
distribution molecular weight data for
Inj ection 7-12.
RT.
MW
21
20.04
1473.81
20
20.29
19
Cum W
105
0.8
1.0
0.08
0.24
1405.47
100
1.0
1.0
0.11
0.33
20.54
1340.34
95
1.2
0.99
0.14
0.47
18
20.79
1278.22
91
1.5
0.99
0.20
0.67
17
21.04
1218.97
87
2.2
0. 93
0.28
0.87
16
21.29
1162.51
83
2.7
0.97
0.39
1.16
15
21.54
1108.60
79
3.9
0.95
0. 55
1.57
14
21.79
1057.26
75
5.0
0.93
0.71
2.05
13
22.04
1008.23
72
6.0
0.)0
0.3 3
2.53
12
22.29
961.56
68
7.0
0.38
1.13
3.12
11
22.54
917.00
65
8.9
0.04
1
3.7b
10
22.79
874.50
62
10.5
0.80
1.60
4.57
9
23.04
833.88
59
12.5
0.76
2.23
8
23.29
795.32
57
14.2
0.7)
2.6.
6.23
7
23.54
758.46
54
17.0
0.63
3.22
7.11
6
23.79
723.30
51
13.7
0.56
3.703
7.92
5
24.04
689.78
49
21.0
0.49
4.32
8.72
4
24.29
657.81
47
22.5
0.40
4.39
9. 47
3
24.54
627.33
45
24.5
0.31
5.53
10.26
2
24.79
598.25
43
26.2
0. 21
6.32
11.09
1
25.04
570.52
41
29.0
0.10
n
x 104
N.
Area
%
h.
C
12.41
98
TABLE 5-17:
Weight percent data -
1500
GPC mode for Injection
i
RT.
MW.
C
n
h.
Amount
Weight
.31
20
20.0
1486.60
106
0.0
9.93
19
20.25
1417.72
101
.2
13.83
.43
18
20.50
1352.04
96
.5
19.74
.62
17
20.75
1289.40
92
1.0
24.03
.76
16
21.0
1229.66
88
1.2
33.63
1.06
15
21.25
1172.69
84
1.9
44.64
1.41
14
21.50
1118.36
80
2.8
58.08
1.83
13
21.75
1066.55
76
3.8
73.68
2.33
12
22.0
1017.13
72
4.7
90.24
2.85
11
22.25
970.01
69
5.9
110.07
3.48
10
22.50
925.07
66
7.5
132.48
4.19
9
22.75
882.21
63
9.1
159.39
5.04
8
23.00
841.34
60
11.0
189.09
5.98
7
23.25
802.36
57
13.0
221.28
7.00
6
23.50
765.18
54
15.5
254.04
8.04
5
23.75
729.73
52
18.0
286.11
9.05
4
24.0
695.92
50
21.5
318.15
10.07
3
24.25
663.68
47
22.0
347.40
10.99
2
24.50
632.93
45
24.0
733.23
11.81
1
24.75
603.61
43
26.0
399.87
12.65
3158.91
99.99
%
7-13.
16
16
--
I
I
- --
16
16
~~-
Injection
Injection
\~
7-11
A7-8
\
S
A
V
7-1,2
*
A
S
V
\
U
. V.
4-1
A
A
ci)
14
1-4
14
U
,
AS
'.0
'.0
A.
U.
'A
U.
i|
0
|
|
U
|
0
400
1000
Molecular Weight, MW.
Figure 5-21:
(g/mole)
2000
1000
400
Molecular Weight, MW
Area Percent Molecular Weight Distribution:
7-8, 7-9, 7-11, and 7-12.
(g/mole)
Injections 7-7,
2000
1.0
1.0
E
/
At 0
AT
7-7
A 7-8
0
Al
y 7-12
4
0
-4
U
//
0
Iniection
U 7-9
*7-11
-4
AV
4
0 40
U
-
Injection
U
4
r-4
e
me
1
ATe
CH
Ave
.
/
)
///i
.H
4-)
.*0
ATIlZ~
U
/
0.0
/
-
-4J
I
0.0
1000
400
Molecular Weight, MW
Figure 5-22:
(g/mole)
2000
400
Molecular Weight, MW.
1000
(g/mole)
Cumulative Weight Fraction Molecular Weight Distribution:
Injections 7-7, 7-8, 7-9, 7-11, and 7-12.
2000
7.01
7.0
Injection
F
InJection
-4
0
7-7
A
7-8
-
-7-9
*7-11
C)
-4
A\
V
x
7-12
.
o
z
4
0
1
.-I
4J
U
A
CL1
"V
0
'-4
*Wy
-1
A
H-
z
0
H-
~A
-41
(U
w
.44
4-4A
44
~
0.0
400
~
1000
Molecular Weight, MW
Figure 5-23:
(g/mole)
2000
0.0
4 00
1000
Molecular Weight,
MW
(g/mole)
Differential Number Fraction Ilolecular Weight
Distribution:
Injections 7-7, 7-8, 7-9, 7-11, and 7-12.
2000
102
14.0
---
-
I
r -'I''''i
0
S
S
00
0.0
1
50 0
Molecular Weight,
Figure 5-24.
1800
MW.
(g/raole)
Weight Percent Molecular Weight
Distribution:
Injection 7-13.
103
VI.
DISCUSSION
As discussed in Section I, chain growth in the FischerTropsch synthesis is characterized as a linear polymerization
process where the chain growth probability factor,
a, is
governed by the Flory Equation:
mn =
with m
(1-a)a n-l
(24)
the mole fraction at each carbon number n.
of a is obtained from the slope of a plot of ln
The value
(mn)
versus n.
Huff found that the product distribution of the FischerTropsch synthesis in a slurry reactor showed a break at about
C10 indicating two types of sites.
illustrated in Figure 6-1.
This distribution is
It was postulated that some growing
chains are strongly adsorbed on the catalyst which produce
higher molecular weight products, while others are weakly bound
and form a lighter products.
A simplified two-site model was
developed where the mole fraction of total products becomes:
mn
=
Xl
(1
1 )a
n-l +
(1-x )
(1 -a2)a2n-l
(25)
where a is the chain growth probability factor for light components
(below C9), x, is the mole fraction of products produced
by site 1,
heavy
and a 2 is the chain growth probability factor for
components.
At the high carbon number limit,
Equation
(24)
reduces to:
mn=
n-l
(i-X)
('-a 2 )a 2
(26)
104
,Total
Site1.-
In( mn)
Drop
-
Observed
Off Due To
Accumulotion
S it a 2
I
10
CARBON
Figure 6-1:
I
20
NUMBER,n
Form of Flory Plot Postulated for 2-Site Reaction
and Accumulation of Products in Liquid Carrier
(Huff 1982).
105
From previous analysis of overhead products by gas chromatography,
a value of a.2 = 0.93 was
calculated.
A carbon number
distribution for Huff's Run 9 is shown in Figure 6-2.
Unfortu-
nately quantitative data was available only up to C30 due to
accumulation of the heavy components in the liquid carrier.
From further highly accurate gas chromatographic analysis of
the liquid by Exxon's Corporate Research Laboratories, Linden,
N.J.,
estimates of weight fraction up to C50 were obtained as
shown in Figure 6-3.
value a2 =
These results reinforced the postulated
0.93 indicating that there were no more changes in
the chain growth probability factor such as that encountered
near C10.
The results. in Section V can be used to generate estimates of the chain growth probability factor for carbon numbers
as high as C100.
The differential number fraction, N.,
defined as the differential weight fraction, X.,
molecular weight, MW..
The quantity N.
is
divided by
describes the way in
which the number of molecules in a sample vary with molecular
weight in the same manner that mn represents the mole fraction
of molecules in a sample which contains n structural units.
Values for a can be obtained from data generated in Section V
if N.
1
and Cn.
1
are plotted in a manner similar to that employed
by Huff for mn and n based on the Flory Equation.
Shown in Figure 6-4 are plots of mn and n for values of
. =
0.92,
tion.
0.93,
0.94, 0.95,
Similar plots
and 0.96 based on the Flory Equa-
for GPC injections at ambient and elevated
temperatures presented in Section V
are shown in Figures 6-5
106
1.0
E7- I I 1
I
I
I
I i
I
I
I
I
I
-1
kP a and SV of 2340hr
X 9- 23 790 kP a and SV of 4220 hrI
-1
-9-22;790
A 9- 24; 790 kP a and SV of 1540 hr1
hr
V9-25;445 kF a and SV of2320
M9-26;1480 kF a and SV of 2300 hr
0.1
2
c
E
0.01
mx
z
Ix
0
x
-xE
U
I
0.001
0
---.
3x
Av
'
LL
14
x
NO
e x
0..-
0,0001
v 0
0.00001
1
iI
II
II
I
I
I
3
5
7
9
11
13
CARBON
Figure
6-2:
I
-I
15 17
N UMBER, n
Carbon Number Distribution for Run
H 2 /CO Feed of 1.81
I
-- I 1
I -- I
19 21 23 25 27 29
(Huff 1982).
9 at 248C and
107
.001
.0005
0
~~-
=0.93
C
.0001
.00005
10
Figure 6-3:
I
I
I
I
I
I
30
II ~
1
40
20
CARBON NUMBER,n
-1
50
-
.00001
Carbon Number Distribution of Liquid Carrier After
Run 9 (Huff 1982).
108
.01
a=0. 96
0.95
0.94
0.93
0.92
.001
0
o
.0001
0
.00001!
I
40
Figure 6-4:
50
60
70
Carbon Number,n
I
80
Theoretical Carbon Nunber Distribution
on Flory Equation.
90
103
Based
109
and 6-6.
Found in Table 6-1 are the a values obtained by
matching Figures 6-5 and 6-6 with the corresponding slopes in
Figure
6-4.
The ambient and elevated temperature results
support the value of a approximately 0.93 for the heavy paraffinic products with no further break in product distribution.
The advantage of elevated temperature GPC analysis is seen by
the extended range of quantifiable carbon numbers from C50 to
C105.
110
.01
Injections
3-11
A 3-12
* 4-11
z
O5-12
V
0
V 5-17
0
.001
I
r%4
0)
V
V
U
a
U
S
fy
V
U
U
A
0
0e
U
.0001
Q)
L44
U A
-H
.000011l
30
40
50
Carbon Number,
Figure 6-5:
70
60
Cn
80
i
Carbon Number Distribution of Heavy Paraffinic
Fischer-Tropsch Wax at Ambient Temperature
Using GPC.
111
.01
I-
I
I
III
I
I
I
I
I
Injections
0A
@ 7-7
A 7-8
87-9
07-11
V 7-12
"-4
z
Euf
-I
0
.ri
-P
I
I
.001
0
* IA
0
It
*Oo
z
0
I
A
U
*V
"-4
a)
4-4
A
.0001
V
-4
.00001
I
35 40 45
50
55
60 65
Carbon Number,
Figure 6-6:
70 75
80 85
I
I
I
90 95 100
105
Cn.
Carbon Number Distribution of Heavy Paraffinic
Fischer-Tropsch Wax at Elevated Temperature
Using GPC.
112
TABLE 6-1:
INJECTION
a Values
from GPC Analysis.
TEMPERATURE (C)
Cn RANGE
a
3-11
24.4
C40-C68
0.93
3-12
24.4
C43-C76
0.94
4-11
23
C34-C73
0.92
5-12
24
C39-C71
0.93
5-17
24
C36-C59
0.94
7-7
50
C45-C105
0.93
7-8
50
C41-C105
0.93
7-9
50
C37-C105
0.93
7-11
50
C43-C105
0.93
7-12
50
C43-C105
0.93
113
VII.
CONCLUSIONS
The technique of GPC was utilized successfully in analysis
of heavy paraffinic wax samples generated via the FischerTropsch synthesis in a slurry reactor.
Although the calibra-
tion technique did not incorporate any methyl-branching effects,
the results are valid since by analysis with GPC the effective
molar volume
is
of separation.
the fundamental quantity
An a-methyl C n-1
in determining the degree
hydrocarbon would elnte approx-
imately at the same time as a Cn hydrocarbon.
The molecular weight distributions obtained at ambient
and elevated temperatures agree well with distributions found
by Huff using vapor-phase gas chromatography and Exxon researchers
using a combination of GC and GPC.
Results obtained at elevated
temperature are superior due to the precise temperature control
of the Waters 150C which helped to eliminate any sample solubility problems and extended the observable carbon number range
well beyond the C50 limit.
It appears that the Fischer-Tropsch synthesis continues
to grow via the postulated linear polymerization process ad
infinitum since differential number fraction molecular weight
distributions were obtained up to C70 and C105 for ambient and
elevated temperature injections respectively.
probability factor a was found to have values
0.92-0.94.
The chain growth
in the range
114
VIII.
APPENDICES
115
APPENDIX I
Manual Method for Computation of Molecular Weight
Distribution.
Explaination of Symbols
i:
Simply an integer to keep track of the number of
collected data points.
RT.:
Retention time at a specific point on chromatograph
expressed in minutes.
RV.:
Corresponding retention volume found by multipling
RT by flow rate F of the ith point millilters.
MW :
Corresponding molecular weight found from calibration
curve equation, log (MW) = D
+ D
(RT), where D
and
D are the calibration coefficienes and MW expressed
in g/mole.
C
:
Carbon number equivalent to approximate molecular
*
weight based on normal hydrocarbon weight
Cn H 2 n+ 2
h.:
Height from baseline to curve expressed in millimeters.
A:
Area, add 1/2 of the incremental change in h.
previously summed h
value.
E(h1+Ah
i
Cum W.:
to the
2
Cumulative weight fraction distribution, divide the
partially integrated areas by the total area total
area under the curve, Cum W. is the weight fraction
of sample having a retention volume greater than RV.
and molecular weight less than MW.
1
X.:
Differential weight fraction moleuclar weight distribution, weight frequency distribution plot given
by:
h.
MW. AV
1
1
Eh
AMW
1
Number fraction molecular weight distribution, describes
the way in which the number of molecules in a sample
varies with molecular weight, given by X.
.
N.:
MW.
Sample Calculations
(Extended Table 5-4
-
h.
:
1
)
116
h.
hi
Eh
-r
T
Average
h./Z
h.1
1
N.
RIn
i
RT.*
1.
ISI. x 10
I
3-11
8
5.83
9.5499
68-
0.0
394.5
532.5
0
.0203
.8001
.1625
.0315
.0033
7
5.96
8.7498
62.2
16.0
394.5
508.5
.95
.0406
.0634
.7515
.1730
.0960
.0110
6
6.09
7.9983
56.9
34.0
378.5
465.5
.87
.0862
.1014
.6869
.1893
.1535
.0192
7.3114
52.0
46.0
344.5
413.5
.78
.1166
.1318
.6280
.2070
.1995
.0273
.66
.1470
.1603
.5740
.2265
.2426
.0363
.2849
.0460
--
.3300
--
.0591
--
5
4
3-12
I
6.22
6.35
6.6834
47.5
1
58.0
i
h.
Cumu W.
I
A
'
C
n
298.5
349.5
1.0
xi
X1-2
X 10
3
6.48
6.1094
43.4
68.5
240.5
275.75
.52
.1736
.882
.5247
.2478
2
6.61
5.5847
39.7
80.0
172
190
.36
1
5.1051
36.3
92
92
92
.17
.2028
.2332
.2180
--
.4796
-
.2711
6.74
7
5.67
10.7152
76.3
0.0
180.0
0
.0056
1.1653
.1373
.0082
.0008
.0445
1.0385
.1637
.0695
.0073
.9256
.1837
.1780
.0209
.0339
6
5
5.83
9.5499
8.5114
6.0
67.9
60.5
2.0
14.0
180.0
178.0
259.50
256.50
236.50
1.0
.99
.91
.0111
.0778
.1139
4
6.17
7.5858
53.9
27.0
164.0
164.0
.79
.1500
.1750
.8250
.1939
.2575
3
6.33
6.7608
48.1
36.0
317.0
111.50
.63
.2000
.2306
.7352
.2312
.3604
.0533
101.0
54.0
.43
.2611
.2806
.6553
.2594
.4385
.0728
.21
.3000
2
1
*
6.50
6.67
RV
6.0256
6.3703
42.8
38.1
47.0
54.0
54.0
is not shown since flow rate was 1
mI/min
making RL and RV
interchangable.
117
IX.
REFERENCES
1.
Adlard, E.R., and Whitham, B.J., Gas Chromatography
1958, 351, edited by Desty, D.H., Butterworths,
(1958).
2.
Barrer, R.M., and Brook, D., Trans. Faraday Soc.,
49, 9 (1953).
3.
Biloen, P., Recueil, J. of the Roy. Neth. Chem.
99 (2), 33, 1980.
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