Simulation of Formaldehyde Production Process
Ruhul Amin, Nazibul Islam, Rezwanul Islam, Yusuf Imtiaz, Saeed M., Unaiza M.
Department of Chemical Engineering
Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh
Abstract
Formaldehyde plays a major role in the synthesis of many important compounds. Worldwide production
of formaldehyde is growing day bay day. There are various industrial processes for the production of
formaldehyde. This article starts with an overview of formaldehyde and the history of formaldehyde
production. Subsequently, production of formaldehyde using silver catalyst is simulated with the help of
Aspen Hysys 7.1. Important parameters such as temperature profile, pressure profile, fluid properties etc
were investigated with this simulation process. The effect of temperature in the reaction was also
examined. The simulation process validated that for maximum conversion to take place, the reaction must
occur in 550C. Finally, 74% formaldehyde was obtained as product.
Key Words: Formaldehyde, Oxidation-dehydrogenation, NRTL, Simulation
approximate order of decreasing consumption,
1. Introduction
products generated from formaldehyde include
Formaldehyde was discovered in 1859 by a
urea formaldehyde resin, melamine resin, phenol
Russian chemist named Aleksandr Butlerov.
formaldehyde resin,poly-oxy-methylene plastics,
However it was in 1869, that German chemist
1,4-butane-di-ol, and methylene-di-phenyl-di-
August Hofmann developed a practical method
iso-cyanate.[5]
to synthesis formaldehyde from methanol.
[1]
In
biomedical
industry,
It
formaldehyde is used in vaccines, medicines,
is a colorless gas with a distinctive pungent
plastics and in x-ray machines. The phenolic
order. It is highly flammable with a flashpoint of
molding resins produced from formaldehyde are
0
50 C; the heat of combustion is 134.1kcal/mol
used in appliances, electrical control, telephone
or 4.47kcal/g.[2] Formaldehyde is soluble in a
and wiring devices.
variety of solvents and is miscible in water. [2, 3]
building industries, formaldehyde-based acetal
Formaldehyde is a key chemical component in
many manufacturing processes. It is used as a
building block for the synthesis of more
complex compounds and materials.
[4]
[6]
In the automotive and
resins are used in the electrical system,
transmission, engine block, door panels and
break shoes. [7]
In
1
The total annual formaldehyde capacity in 1998
software which comes along with excellent
was estimated by 11.3 billion pounds. Since then
reference & tutorial manuals for simulating a
and the production capacity around the globe is
process. Hysys does not wait until entering
expanding exponentially reaching a world’s
every
production of 32.5 million metric tons by 2012.
calculation. It calculates as much as it can at all
[7, 8]
There are two main routes for formaldehyde
time and results are always available, even
production: oxidation-dehydrogenation using a
during calculation. Any changes that one makes
silver catalyst involving both the complete or
to the data are automatically propagated
incomplete conversion of methanol; and the
throughout the program to anywhere that entry
direct oxidation of methanol to formaldehyde
appears and all necessary recalculations are
using metal oxide catalysts.
oxidation-dehydrogenation
[9,
10]
route,
Formaldehyde
catalyst
is
at
formed
hydrogenation of methanol.
about
by
[11, 12]
condition
before
beginning
In the
instantly carried out. It tends to be a lot easier to
vaporized
catch errors as one gradually converge the
methanol with air is passed over a thin bed of
silver-crystal
process
process simulation.
6500C.
the
de-
The other
route involves the oxidation of methanol over a
catalyst of molybdenum and iron at 3500C. [13]
The Fluid package used in this simulation is
NRTL. The non-random two-liquid model is
known as NRTL equation in short[14]. NRTL is
an activity coefficient model that correlates
the activity coefficients of a compound i with
This article deals with the detailed study of the
its mole fractions in the liquid phase concerned.
simulation of formaldehyde production from
The concept of NRTL is based on the hypothesis
methanol. Simulation has been done with the
of Wilson that the local concentration around a
help of Aspen Hysys v7.2. Although simulation
molecule
does not give the real world performance or the
concentration. This difference is due to a
real life production environment but if the basic
difference between the interaction energy of the
process is known and related data are available,
central molecule with the molecules of its own
it is the best way by which an individual can get
kind Uii and that with the molecules of the other
ideas of an industrial process without conducting
kind Uij. The energy difference also introduces a
any experiment.
non-randomness at the local molecular level.
is
different
from
the
bulk
The NRTL model belongs to the so-called local-
2. Methodology
The process of producing formaldehyde from
methanol is simulated in Simulation software
Aspen Hyssy 7.1. Aspen Hysys is a simulation-
composition models. Other models of this type
are the Wilson model, the UNIQUAC model,
and the group contribution model UNIFAC.
These
local-composition
models
are
not
2
thermodynamically
the
separation of recycle methanol overhead, the
assumption that the local composition around
bottom stream containing the formaldehyde and
molecule
local
a few percent methanol. The water intake adjusts
composition around molecule j. This assumption
the formaldehyde to 37% strength (marketed as
is not true, as was shown by Flemmer in
formalin). The yield from the reaction is 85 to
1976[15, 16].
90 percent. The catalyst is easily poisoned so
i
is
consistent
independent
due
of
to
the
stainless-steel equipment must be used to protect
the catalyst from metal contamination.
2.1 Process Description
Formaldehyde results from the exothermic
oxidation and endothermic hydrogenation of
methanol.
These
two
reactions
occur
simultaneously in commercial units in a
balanced reaction, called auto thermal because
2.2 Simplified Block Diagram
the oxidative reaction furnishes the heat to cause
the dehydrogenation to take place. About 50 to
60 percent of the formaldehyde is formed by the
exothermic reaction. The oxidation requires
1.6m3 of air per kilogram of methanol reacted, a
ratio that is maintained when passing separate
streams of these two materials forward. Fresh &
recycled methanol are vaporized, superheated
and
passed
into the methanol-air
mixer.
Atmospheric air is purified, compressed and preheated to 540C in a finned heat exchanger. The
Figure 1: Block diagram of the total process
products leave the converter at 620oC and at 34
to 69 KPa absolute. The converter is a small
water-jacketed vessel containing the silvercatalyst. About 65 percent of the methanol is
converted per pass. The reactor effluent contains
about 25% formaldehyde, which is absorbed
with the excess methanol and piped to the make
tank. The latter feeds the methanol column for
3
2.3 Set Stoichiometry and Rate of
Where,
Reaction
As mentioned earlier, Formaldehyde results
𝑙𝑛𝐾1 = 16.9 −
12500
T
𝑙𝑛𝐾2 = 25.0 −
15724
T
And
from the exothermic oxidation and endothermic
de-hydrogenation of methanol.
CH3OH + 1/2 O2
CH3OH
CH2O + H2O;
CH2O + H2;
H = -156 KJ
For all the equations, T is in Kelvin. [8]
H = +85 KJ
2.4 The Simulation Environment
So the stoichimetry for Methanol in the 1st and
1. First Methanol and feed air are delivered
to a mixer and later preheated to 55⁰ C
2nd reaction would be -1
and delivered to the reactor.
For Formaldehyde it would be +1 for the both
2. In the first step of the reaction, methanol
reactions.
reacts with oxygen to give formaldehyde
For Oxygen it would be -0.5 in the 1st reaction
and water
3. In the 2nd stage some of the methanol
And for water and Hydrogen it would be +1 for
breaks
the 1st and 2nd reaction respectively.
hydrogen.
The rate of reaction for the first reaction will be:
up
to
formaldehyde
and
4. The vapor from the reactor outlet is
cooled to 10⁰ C and delivered to a
mole
k1pm
gcatalyst
−rm1[
]=
hr
1 + k2pm
separator.
5. The Hydrogen is separated from the
mixture.
Where,
6. The remaining mixture is heated to 100⁰
8774
𝑙𝑛𝑘1 = 12.50 −
T
And
C and fed to the distillation column.
7. From the distillation column, we get the
liquid product of 83.2% formaldehyde
𝑙𝑛𝑘2 = −17.29 +
7439
T
The rate of reaction for the second reaction will
be:
and
a
vapor
product
of
44.1%
formaldehyde.
8. The vapor product is heated to 35⁰ C
and delivered to a storage tank.
𝑚𝑜𝑙𝑒
K1√pm
𝑔𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡
𝑟𝑚2[
]=
ℎ𝑟
1 + K2√pm
4
2.5 Importance of Temperature in
3.1 Temperature Profile of Distillation
the Simulation
Column

The heated feed that is delivered to the
200
first reactor is heated to a temperature of
100
55° C by delivering the feed to a heater.
optimum temperature of reactor inlet.

The
final
top
product
from
the
distillation column is delivered to a
0
Temperature
It is heated to 55° C because this is the
0
5
10
15
-100
-200
-300
Number of Tray
heater before it is stored in the storage
tank. The outlet from the heater is
heated to a temperature between 35-45°
C. At temperatures below 35° C, the
product forms formaldehyde polymer
which
is
not
desired. Storage
at
temperatures between 35-45° C further
inhibits the formation of formaldehyde
polymers[2].
Figure 2: Graphical representation of
Temperature vs Tray position from top
From figure 2 we can see that the condenser
temperature
is
around
-2500C.
The
temperature rises rapidly from the condenser
and reaches near 1000C at stage 2 that is first
tray after the condenser. From tray 2, the
temperature rise is linear and is around
3. Results and Discussions
1100C in the reboiler.
Final composition of Formaldehyde obtained is
74.8%.
Different parameters of the distillation
column are shown in different graphs below-
5
3.2 Pressure profile of Distillation column
Here, we see that there is a slight rise of mole
fraction of the light liquid from condenser to
tray 1. After that up to tray 7 this value remains
somewhat constant. From tray 7, which is the
20
Pressure(psia)
feed tray we again see a perfect linear increase
15
in light liquid mole fraction right up to the
10
reboiler.
5
3.4 Flow rate vs. Tray Position
0
-2
3
8
Number
of Tray
13
Figure 3: Graphical representation of
Temperature vs Tray position from top
From this graph we can visualize the pressure
profile of the distillation column. Here we see
that the pressure profile is almost linear. The
linear equation for this curve is,
Net molar flow(lbmole/hr)
8.00E+03
7.00E+03
6.00E+03
5.00E+03
Vapor
4.00E+03
3.00E+03
Liquid
2.00E+03
1.00E+03
0.00E+00
0
Y=0.6081X+10.551
5
10
Tray position
15
With, R2= 0.9946
3.3 Light Liquid Composition
Figure 5: Graphical representation of flow vs
Tray position from top
In the case of molar flow, we see that the
1E+27
1E+24
1E+21
1E+18
1E+15
1E+12
1E+09
1000000
1000
1
vapor flow starts from zero at tray 1 and
Light liquid
increases rapidly up to tray 3. From tray 3
this increase in flow is much sluggish. For
the liquid however, there are rapid increases
in flow from reboiler to tray 1 and also in
0
5
10
Tray Number
15
Figure 4: Graphical representation of light
liquid (mole fraction) vs Tray position from top
tray 7 which is the feed tray. In between
these rapid increases, the flow is somewhat
6
constant. Finally there is a drastic drop in
the flow of liquid at the reboiler.
3.6 Heavy Liquid Compositon vs. Tray
Position
3.5 Light Liquid Composition vs. Tray
Position
0.8
0.7
Formaldehyde
0.6
0.5
0.7
Mole
0.8
0.4
Mole Fraction
Formaldehyde(Light)
H2O
0.3
0.6
0.2
0.5
0.1
H2O(Light)
0.4
0
0
0.3
5 Tray
10
15
0.2
0.1
Figure 7: Graphical representation of
composition (vapor) vs Tray Position from top
0
0
5
10
Tray Position
15
Here we also see that starting from zero in the
Figure 6: Graphical representation of
composition (light liquid) vs Tray position from
top
condenser; the composition of formaldehyde
For the light liquid, we see that water
from there it gradually decreases.
gradually increases. In the case of water, the
composition reaches its maximum at tray 2 and
composition is higher than Formaldehyde in the
condenser. But from the condenser a gradual
3.7 K-values vs tray position
increase in Formaldehyde composition takes
water composition decreases from the condenser
to reboiler.
1.00E+05
1.00E-03
0
1.00E-11
1.00E-19
1.00E-27
1.00E-35
1.00E-43
1.00E-51
1.00E-59
1.00E-67
Hydrogen
5 Water 10
15
K Value
place right up to the reboiler. Evidently the
Tray position
Figure 8: Graphical representation of k-values
vs Tray position from top
7
And, R2=0.9981
In the case of k-values (Distribution Coefficient), we see that the distribution co-
The heat capacity increases with the linear
efficient of hydrogen (present in the feed)
equation:
remains constant with respect to water and
formaldehyde. The k-values for the letter two
Y=0.0643X+3.698
increase dramatically up to tray 2 from where
And, R2=0.8865
they decrease a little and remain perfectly
constant.
3.9 Effect of Temperature on Feed
3.8 Transports Properties of the
Distillation Column
Heat flow (kJ/h)
20
120
Surface Tension
Column Properties
100
80
60
60
-1.25E+08
-1.30E+08
-1.35E+08
-1.40E+08
40
40
-1.20E+08
Temperature of heated feed (°C)
Molecular weight
20
Heat capacity
Figure 10: Graphical representation of heated
0
5 Tray
0
10
15
Figure 9: Graphical representation of column
properties vs tray position from top
flow vs temperature of heated feed
In case of the heated feed, the heat flow keeps
increasing with the increase of temperature of
the heated feed. After 45° C the heat flow does
If we analyze the properties of the light liquid in
not increase too much with the change in
the distillation column, we find that the surface
temperature and becomes constant. So the
tension decreases dramatically from condenser
heated feed is heated to a temperature of 55° C.
to tray 2 and from there, this decrease in surface
tension is gradual.
4. Conclusion
The molecular weight increases linearly with the
The simulation developed by AspenHYSYS is
equation:
useful to understand the detailed environment of
Y=0.2622X+23.182
the production process of formaldehyde. The
8
tray-by-tray characteristics of the distillation
11.
column can be visualized using simulation.
Similarly the products of the reactors can be
anticipated. Thus using this simulation, one can
easily calculate the material and energy feed
12.
13.
required for the production of any specific
amount of product. This in turn will help to
14.
calculate the cost required to operate a
formaldehyde production plant.
15.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
CECIL H. , Frank B., JOHN W., PETER P.
Formaldehyde Fixation The Journal of
Histochemistry and Cytochemistry
1985. 33(8): p. 845-853.
Inc. S.A., Formaldehyde, Material Safety
Data Sheet version 1.10. 2007: Missouri,
USA.
NCDOL, A Guide to Formaldehyde.
North Carolina Dept. of Labor: 1101
Mail Service Center Raleigh, NC 276991101.
Robert C., CRC Handbook of Chemistry
and Physics 62 ed. 1981.
Jacqueline I., Seidel A., Encyclopedia of
Chemical Technology. 1997, John Wiley
and Sons.
Natz B., FORMALDEHYDE: FACTS AND
BACKGROUND INFORMATION. 2007:
Arlington.
Bizzari S.N., Formaldehyde. Chemical
Industries Newletter 2007.
Sanhoob M A., Sulami A., Shehri F.,
Rasheedi S., Production of
Formaldehyde from Methanol
Integrated Final Report. 2012, KFUPM.
Austin T.G., Shreve's Chemical Process
Industries. 5th ed. Chemical Engineering
Seris. 1984, United States: McGraw-Hill
Book Company.
Perry R.H., Green D.W., Perry’s chemical
engineers’ Handbook. 7th ed. 1997:
McGraw-Hill.
16.
Dryden.C.E., Outlines of Chemical
Technology for 21st Century. 1997, New
York press.
Ketta Mc., Encyclopedia of Chemical
Technology,. 1997.
Mccabe W. L., Smith J.C., Harriot P.,
Unit Operations in Chemical
Engineering. 6th ed. 2001: McGraw Hill.
Renon H. Prausnitz J. M., Local
Compositions in Thermodynamic Excess
Functions for Liquid Mixtures. AIChE
Journal, 1968. 14(1): p. 135-144.
Flemmer, Collection of Czechoslovak
Chemical Communications. 1976. p.
3347.
McDermott C.M., Fluid Phase
Equilibrium 1ed. Vol. 33. 1977.
9