Partial Hydrogenation of
Vegetable Oil using Membrane
Reactor Technology
Devinder Singh, Brent Dringenberg,
Dr. Peter Pfromm, Dr. Mary Rezac
Department of Chemical Engineering
Kansas State University
Manhattan, Kansas
Trans-Fatty Acids
• "..there is a direct, proven relationship between
diets high in trans fat content and LDL (“bad”)
cholesterol levels and, therefore, an increased
risk of coronary heart disease..."
from FDA web site 10-3-2005, FDA fact sheet dated July 9, 2003
• By January, 2006 trans fat content will be shown
on the Nutrition Facts Panel.
Note: <0.5 g trans fat/14 g serving = label "zero"
Trans-Fatty Acids
USDA/CFSAN
http://www.cfsan.fda.gov/
~dms/transfat.html
10-4-05
• ChE Freshmen class (9-2005): the vast majority
knew trans fats were "bad" for you.
• Switch to butter?
Origin of trans-fatty acids
stearic acid MP 70C
(C18:0)
oleic acid MP 16C
elaidic acid MP 52C
cis (C18:1 9c)
trans (C18:1 9t)
• Except for some animal fats (beef, mutton), natural oils/fats
are cis.
• Trans-fatty acids: by partial hydrogenation (in the rumen: vaccenic
acid; or in technical hydrogenation of plant oils: elaidic acid; C18:1 9t )
• Why technical partial hydrogenation: optimize physical
parameters (melting point), improve stability, reduce
peroxidation
Strategies to avoid/minimize
trans-fatty acid intake
• Use trans fatty acid free fats and oils
• Avoid partial hydrogenation by
changing the composition
(Example: "Crisco® 0 trans fat": sunflower and
soybean oil+waxy fully hydrogenated
cotton seed oil)
• Minimize/avoid formation of trans fatty
acids during hydrogenation
Standard hydrogenation process
• 1809 Sir Humphrey Davy coins the term "hydrogenation"
W. Normann, 1902: liquid/solid/gas for fat hardening
• Generally batch, 5-20 tons of oil. Parameters: pressure, temperature,
agitation, catalyst, catalyst/oil ratio. 15 MM tons/year world wide.
catalyst: Ni
0.05-0.1 wt% Ni on oil
supported catalyst
120-190C
1-6 atm
steam
"selective" conditions:
hydrogenate most highly
unsaturated fatty acids first
H2
http://www.thesoydailyclub.com/SFC/MSPproducts501.asp
Soyfoods Center, from unpublished manuscript by Shurtleff, W., Aoyagi, A.,
(160-205C, low H2 pressure,
more catalyst, less agitation):
~50% more trans
Alleviating mass transfer limitations
of hydrogenation
Conventional
Here: Membrane based
H2 starved
catalyst
boundary
layer
Defect-free integral-asymmetric
polymeric membrane with
metal sputtered surface
ΔP
Oil
ΔpH2
Catalyst
Membrane
H2
H2(dissolved) H2 supplied
solubility is by diffusion
low in oils
H2 flux can be adjusted
self-controlled H2 transport
boundary layers can be controlled
shear can be introduced at the membrane
Approach: supply hydrogen
where catalysis takes place
Pt layer
H
H
H+ H-H
H
H
H+
"skin"
(defect-free
polymer layer)
H-H
100µm
metal layer
defects
Oil
Pt Layer
(10-20 nm)
integral skin
100-500 nm
200-300
µm
hydrogen
porous substructure
(polymeric)
Baker, R. W., Louie, J., Pfromm, P. H., Wijmans, J. G.,
"Ultrathin Metal Composite Membranes for Gas Separation", U.S. Patent 4,857,080,
Integral-Asymmetric Polyetherimide membrane: QA/QC
[casting after US Patent: 4,673,418, Peinemann et. al., 1987]
Gas
Flux (GPU), RT Selectivity
[10-6 cm3 (STP)cm(H2/N2)
2
s-1 (cm Hg)-1 ]
Before Pt Coating
Hydrogen
11.7
Nitrogen
0.18
66
After Pt Coating, before hydrogenation
Hydrogen
8
Nitrogen
0.18
46
After hydrogenation and washing in
hexane
Hydrogen
0.5
Nitrogen
0.04
12
Peinemann et. al., 1987
Hydrogen
68
Nitrogen
1.4
49
base
membrane
OK
(flux
could be
optimized)
Integral-asymmetric membranes:
bridging the gap from nanomaterials to
the macroscopic world
• The selective polymer layer:
– 100-500 nanometers
thick
– absolutely defect-free
– made on a scale of
– square centimeters
to square meters
• The porous support:
– enables usefulness of the
nanomaterial
100µm
If membrane-based hydrogenation shows
benefits, can it be done on a
technical scale? When?
• H2 pressure will be low while maintaining high H2
availability: existing H2 equipment is perhaps OK.
• Sputtering of technical membranes is relatively
simple (flat sheet, hollow fiber)
• Technical scale gas permeation membranes are
available (Air Liquide/Medal and others)
Iodine value, IV
• Measure of the degree of unsaturation of a fat
(one I2/DB, "g Iodine reacting with double bonds/100 g of fat")
• High IV: less stable to oxidative attack
• Soybean Oil IV130, margerine stock soybean
oil IV65 (40%TFA), shortening stock IV80
(32%TFA)
• If the fat composition is resolved
chromatographically, IV can be calculated
Analytical: preparation of Fatty Acid Methyl Ester
(FAME) AOCS method Ce 2-66
add 2 ml
hexane
add 0.1 mL
methanolic KOH
shake
centrifuge
FAME,
hexane
(30 sec.)
K+
MeO-
0.2 g Oil
add 2 drops FAME/hexane
to 2 ml hexane
FAME,
potassium salt of
glycerol , water
potassium salt
of glycerol, water
Inject 1µl
GC w/FID
CP Sill88, 100m x0.25 mm)
170C
50 min
Gas Chromatogram of Unhydrogenated Soybean Oil (Iodine Value = 126)
(oil supplied by MP Biomedicals, LLC, Irvine, CA; analysis FAME, AOCS method Ce 2-66
MeE
C18:2 9c12c
Methyl linoleate
MeE
MeE
6
C18:1 9c
5
FID Response
[pA]
4
MeE
Methyl Oleate
MeE
MeE
MeE
Methyl stearate
MeE
MeE
C18:0
C18:3 9c12c15c
Methyl linoleneate
3
C18:3t
C18:1 11c
30
C18:2 t
35
Time [min]
C20:0
40
C20:1
45
Reactor system
Nitrogen
P
1/8” SS
TC
Oil
1/8” SS
60-62 psig P
TC
Parr reactor
(160 ml)
Oil, 70 °C
Oil
1/8” SS
1/4” SS
Data
Acquisition
~13 ml/min
50-52 psig
P
Membrane Reactor
(Membrane area
12.6 cm2)
1/8” SS
Hydrogen
Membrane-facilitated hydrogenation
60
50
220°C, 2.5 atm H2, 0.18 wt % Ni **
40
Trans Fatty
30
Acid [wt%]
125 hrs
108 hrs
20
Membrane Reactor
70°C, pH2=3.4 atm
64 hrs
Pt/polyimide membrane
10
8 hrs
16 hrs
0 hrs
0
80
90
100
110
120
Iodine Value IV [g iodine/100 g oil]]
**Karabulut, I. Kayahan, M.Yaprak, S. , Determination of changes in some physical and chemical
properties of soybean oil during hydrogenation , Food Chemistry, 81, 453, 2003.
130
140
Non-hydrogenated vs. Partially Hydrogenated Soybean Oil
60
50
40
Trans Fatty
30
Acid, wt. %
20
6
C18:0
C18:1 9c
C18:2 9c12c
10
5
0
80
90
100
110
120
Iodine Value, g Iodine/ 100 g Oil
4
FID Response
[pA]
3
C18:1 t C18:1 11c
C18:2 t
C18:3 9c12c15c
C18:1 12c
C18:3 t
C20:0
30
35
40
C20:1
45
Time [min]
130
Compare H2 consumed vs. supply
through the membrane
0.05
Max. H2 supplied by membrane
(virgin characteristics before hydrog.experiment)
0.045
0.04
H2 consumed
(from experiment)
0.035
0.03
mol
H2
0.025
process upset
(power outage)
0.02
0.015
0.01
Max. H2 supplied by membrane
(characteristics after hydrog.experiment)
0.005
0
0
20
40
60
Time [h]
80
100
120
140
Conclusions
• Hydrogenation was observed with platinumcoated integral-asymmetric gas permeation
membranes
• The membranes appeared physically stable over
120 hours
• Formation of trans fatty acids was observed, but
perhaps can be further reduced
Acknowledgements
• United States Department of Agriculture
Iodine Value (IV) calculation based on
gas chromatographic resolution of oil
IV = 0.8598*(weight % C18:1)+1.7315*(weight % C18:2)+2.6152*(weight % C18:3)
+0.8173*(weight % C20:1)
Note: weight% is relative to combined detected analytes
Discussion
From GC we obtain the relative amount of Fatty Acid in the mixture of their methyl esters.
For free fatty acids the factors for IV can be calculated as
IVfree= (Mol. Wt. of Iodine/Mol. Wt. of Fatty acid)*n
where n=no. unsaturated bonds
In oil we have to take into account the extra molecular weight due to glycerol and we find
IVoil=(Mol Wt. of Iodine/Mol. Wt. of Fatty Acid+12.68 )*n
where 12.68 takes into account the additional molecular weight.
So for example for C18:1 = (253.8/(282.47+12.68))= 0.8598 (see above)