Operation and control of reactive distillation for synthesis of methyl formate

Article abstract of DOI:10.14233/ajchem.2013.13701a

Esterification of formic acid and methyl alcohol in reactive distillation column is an effective process for synthesis of methyl formate. Operation and control of reactive distillation for synthesis of methyl formate is studied. First, the thermodynamic properties and reaction kinetics are analyzed, then the comparison of the three operation methods of reactive distillation are studied and at last the operation method with formic acid fed at top column is researched. The results show that it works quite well for this synthesis process.

Full text of DOI:10.14233/ajchem.2013.13701a

Asian Journal of Chemistry; Vol. 25, No. 8 (2013), 4177-4182
http://dx.doi.org/10.14233/ajchem.2013.13701A
Operation and Control of Reactive Distillation for Synthesis of Methyl Formate
*
JIE YANG, PENG BAI and KUN YIN
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P.R. China
*
Corresponding author: Tel: +86 22 27406369; E-mail: yjay007woai@163.com; yj_tju@hotmail.com
Received: 9 March 2012; Accepted: 4 February 2013)
(
AJC-12922
Esterification of formic acid and methyl alcohol in reactive distillation column is an effective process for synthesis of methyl formate.
Operation and control of reactive distillation for synthesis of methyl formate is studied. First, the thermodynamic properties and reaction
kinetics are analyzed, then the comparison of the three operation methods of reactive distillation are studied and at last the operation
method with formic acid fed at top column is researched. The results show that it works quite well for this synthesis process.
Key Words: Methyl formate, Synthesis, Reactive distillation, Operation.
of temperatures favourable for reaction and separation. A
number of chemical systems have been studied in the literature
using reactive distillation columns, most common applications
INTRODUCTION
Methyl formate, HCOOCH , is an important chemical
3
intermediate that has many applications in food, chemical and
pharmaceutical industries. Methyl formate can be made of a
series of downstream products such as fromic acid, acetic acid,
ethylene glycol, dimethyl carbonate and formylation agent.
In china coal is the main energy and people pay great attention
to the research and development of C-1 chemicals in academia
and industry. Recently methyl formate has gradually developed
into a new starting material and structural unit in C-1 chemicals
7-10
are etherification and esterification . Eastman company success-
fully applies reactive distillation technology to the industrial
production of methyl acetate and uses only a reactive distillation
column instead of the complex flow sheet. As a result, the
reaction conversion rate is over 99.8 % and the purity of methyl
acetate is higher than 99.5 %.
In this work, the operation and control of reactive distilla-
tion for the synthesis of methyl formate is presented. First, the
thermodynamic properties and reaction kinetics are analyzed;
then the comparison of the three modes of reactive distillation
operations is studied and at last the optimization and control
of operation method with formic acid fed at top column is
researched.
1
following methane, synthesis gas and methanol . It is one of
the important intermediates in the C-1 chemicals.
There are three main methods in production of methyl
formate. The first one is the direct esterification of formic acid
and methanol. The second one is dehydrogenation of methanol,
2
and the last one is carbonylation of methanol .
EXPERIMENTAL
Esterification is used very early. However, it is limited to
chemical balance and there are several azeotrope in the reacting
mixtures. As a result, the traditional process is complex and it
Thermodynamic properties:Table-1 isAntoine equation
parameters of water, reactants and products.
3,4
needs many reactor and distillation column .
Reactive distillation offers some advantages over conven-
tional processes where reaction and purification are carried
Antoine equation (log P = A-B/t+C) is used to calculate
the saturation vapour pressure of each component in the
reactive distillation mixtures (Table-2). The saturation vapour
pressure is used to calculate the relative volatility and the results
are list in Table-3.
5
out separately . Combining reaction and separation in a single
unit can reduce both operating and capital costs. The direct
removal of products or intermediates in reactive distillation
columns often results in higher reaction conversion. However,
the interaction of equilibrium phase separation and reaction
Reaction kinetics experiment: The esterification is a
reversible reaction, the reaction in this experiment has been
taken place to the direction of formation of methyl formate.
As a result, the reverse reaction is neglected, only the positive
reaction is considerated. The reaction equation is shown as
below.
6
increases the complexity of the operation and control problem .
Applications of reactive distillation are limited to systems in
which the reaction rates are fairly high and there is no mismatch

4
178 Yang et al.
Asian J. Chem.
TABLE-1
ANTOINE EQUATION PARAMETERS
reflux in the distillation process is exported in a tank and then
returns to the still. The amount of formic acid flowing into the
tank is controlled with the pH meter in the tank.
Compounds
Methanol
A
B
C
Temp. (K)
175-279
275-338
338-487
453-513
283-384
279-305
305-443
280-441
7.4182
1710.2
-22.25
The experimental reagents is shown in Table-4 and the
experimental set up are shown in Fig. 1.
7
.23029
.09498
.18215
1595.671 -32.245
7
8
1521.23
2546.019
1563.28
-39.18
83.019
-26.09
TABLE-4
REAGENT SPECIFICATION AND PARAMETERS
Formic acid
6.5028
Methyl formate
6.225963 1088.955 -46.675
.39684 1196.323 -32.629
Reagent
Formic acid
Methanol
6
Formula
HCOOH
88.0 %
CH CH OH
3
Water
7.074056 1657.459
-46.13
2
Purity (mass fraction)
Specification
Source
99.5 %
AR
AR
TABLE-2
SATURATION VAPOUR PRESSURE (UNITS: kPa)
Temp. (ºC) Formic acid Methanol Methyl formate
Chemical reagent
company of Tianjin
Jiangtian
46.06
Chemical reagent
company of Tianjin
Jiangtian
Water
2.3
20
40
60
80
4.5
11.4
25.8
52.8
99.6
175.3
13.0
35.7
84.6
181
63.7
136.9
261.7
462.5
764
Molecular
32.04
7.4
Boiling point (ºC)
3
Density/(g/cm )
101.4
64.5
19.9
47.3
101.3
198.5
1.214
0.978
1
00
20
353.6
641.9
1
1196
4
8
TABLE-3
RELATIVE VOLATILITY
Temperature Methyl formate/
methanol
Methanol/
formic acid
Water/
methanol
(ºC)
12
2
0
0
0
0
4.91
2.94
3.12
3.23
3.45
3.57
3.70
3.33
5.56
4
6
8
3.82
4.76
3.09
4.17
5
2.55
3.85
1
00
20
2.16
3.45
1
1.86
3.23
Average α
3.07
4.00
6
7
7
HCOOH + CH
3
3 2
OH→HCOOCH + H O
Reaciton rate is expressed in eqn. 1.
α
β
r = -dc /dt = kc Ac (1)
B
A
where c
A
-the concentration of formic acid; c -the concentration
B
of methanol; α-the reaction order of formic acid; β-the reaction
order of methanol.
3
We assume the reaction order of formic acid and methanol
is 1, i.e., α = 1, β = 1.
Arrhennius equation is shown in eqn. 2.
13
14
7
15
-
Ea/RT
7
K = Ae
log k = log A-E
(2)
(3)
a
/2.303RT
According to the experiment and date analysis, we can
get that activation energy E = 27.1 kJ/mol, pre-exponential
10
9
a
11
3
actor A = 4.51E-04 m /(s*mol).
1
2
Operation methods: The esterification reaction of metha-
nol and formic acid is an autocatalytic reaction without the
need of using an additional catalyst and considering neither
the problems with catalyst separation and recovery nor the
special requirements for equipment. In this reaction, acid
usually is the heaviest component. Once falls into the still, it
always stays here. However, there will be a lot of water at the
still in the later period of the reaction. This will reduce the
conversion rate of the esterification reaction. Consequently,
study on the operation methods of reactive distillation is of
practical significance. In this work, there are three ways to
operate the reactive distillation process.
1
-distillation kettle; 2-heating package; 3-glass packed tower;
4-condenser; 5-product collection tank; 6-formic acid storage tank;
7-vavle; 8,9-thermometer; 10-sampling port; 11-u-tube manometer;
12-electromagnet; 13-shunt device; 14-pH meter; 15-tank
Fig. 1. Experimental set up of esterification distillation with acidity control
The specific parameters of the experimental equipment
are shown in Table-5.
Experiment processes: 400 mL methanol is added into
the still (1) and 350 mL formic acid is added into the storage
tank (6). After the liquid in the bottle (1) is heated to boiling,
Operation with pH control: In this operation method, a
shunt device is installed on the tower up of the still and the

Vol. 25, No. 8 (2013)
Operation and Control of Reactive Distillation for Synthesis of Methyl Formate 4179
total reflux operation is carried out for 10 min. And then
methanol is full-mined. 40 mL methanol condensate is formed
in 30 min and the average velocity of methanol rising steam is
the tower to make the esterification reaction shift the reaction
equilibrium toward the product side in reaction zone.
Experimental equipments: The experimental setup is
shown in Fig. 3.
1
.33 mL/min. The molar ration of methanol and formic acid
is 1:1, so the flow rate of formic acid is 1.5 mL/min. After 20
min of esterification reaction, reflux ratio is setted as 10 and
the reaction product methyl formate is carried out to break the
reaction equilibrium. When the top temperature rises suddenly
and methyl formate is almost all recovered, the experiment
ends.
4
8
12
TABLE-5
EXPERIMENTAL EQUIPMENT AND TYPE
5
Equipment
Three-necked flask
Glass distillation tower Height: 1.2 + 0.3 m, internal
diameter: 29/32 mm
Description
Volume: 500 mL
Number
1
1
Conderser
Having two ports and liquid
distributor
Range: 0-150 ºC
1
3
6
7
7
Thermometer
Glass packing
Sampling needle
Electric heating
package
3 mm × 3 mm θ net ring
Range: 0-5 um
Heating power controlled by
adjusting voltage
1
1
Product collection tank 200 mL
Formic acid tank
pH buffer tank
1
1
1
500 mL
200 mL
3
10
9
1
2
11
RESULTS AND DISCUSSION
The results are shown in Fig. 2.
MF
Methanol
1
- distillation kettle; 2- heating package; 3- glass packed tower;
1
00
4
- condenser; 5- product collection tank; 6- formic acid storage tank;
7
- vavle; 8,9- thermometer; 10- sampling port; 11- u-tube
manometer; 12-electromagnet;
8
6
4
2
0
0
0
0
0
Fig. 3. Experimental set up of esterification distillation with formic acid
fed at top column
The experimental equipment is very similar with that
described earlier (Fig. 1) which includes a distillation kettle,
two-sectioned packed column (the reactive zone and the
rectifying zone), formic acid storage tank, product tank, con-
densate and reflux system and measuring instruments. And
the specific parameters is shown as below.
5
0.
100
150
200 250
Time (min)
300
350
400
TABLE-6
EXPERIMENTAL EQUIPMENT AND TYP
Fig. 2. Component content at top vs. time
Equipment
Description
Number
The concentration of methyl formate in top product is
more than 90 % after the reaction starts and stays at above
Three-necked flask
Glass distillation
tower
Volume: 500 mL
1
1
Height: 1.2 + 0.3 m, internal
diameter: 29/32 mm
Having two ports and liquid
distributor
95 % soon later. In this reaction process, content of formic
acid in tank (15) is controlled by pH meter (14). When the pH
value is lower than a given value, formic acid is stopped feeding.
Then the content of methyl formate at the top decreases and
the content of methanol increases, shown as 200 min-300 min
in the figure. This is because that as content of formic acid
deceasing, part of methanol rises to the top of the tower. When
the reaction finishes, the formic acid conversion rate is 94.3 %.
Operation with formic acid fed in tower: This operation
is that formic acid is stored in the feed tank and added in to
Conderser
1
3
Thermometer
Glass packing
Sampling needle
Electric heating
package
Range: 0-150 ºC
3 mm × 6 mm glass spring packing
Range: 0-5 um
1
1
Heating power controlled by
adjusting voltage
Experiment processes: The processes and conditions are
the same as described earlier and the results are as below.

4
180 Yang et al.
Asian J. Chem.
From Fig. 4, we can see that the content of methyl formate
The experimental equipment is very the same as that
in experiment 3.2 which includes a distillation kettle, two-
sectioned packed column (the reactive zone and the rectifying
zone), product tank and condenser.
in the top product is over 90 % soon after the feeding and
stabilizes above 95 % later. With the reaction being carried
out, methanol in the distillation kettle is consumed and reaction
product water gradually accumulates at the bottom by gravity.
When the reaction ends, the content of water at the bottom is
up to 80 % while the content of formic acid is less than 10 %
and methyl formate has the lowest content, less than 1 %. The
formic acid conversion rate is 91.5 %.
Experiment processes: 400 mL methanol solution and
350 mL formic acid solution are added into the distillation
kettle. After total reflux operation for 30 min, the reflux ratio
is adjusted to 10. Three hours later, the reaction almost
finishes. Samples are taken from the product storage tank every
20 min to be measured the content of each component. And
the experiment results is described in Fig. 6.
MF
Methanol
100
MF
Methanol
100
80
60
40
20
0
8
0
0
6
40
20
5
0.
100
150
200
Time (min)
250
300
350
0
Fig. 4. Component content at top vs. time
2
0
40 60 80 100 120 140 160 180 200 220
Time (min)
Operation with directly adding of reactants: The reac-
tants of formic acid and methanol are directly adding into the
distillation kettle in this operation. Methyl formate which has
the smallest relative volatility is steamed out by distillation so
as to shift the reaction equilibrium toward ester generation
side and is collected at the top with high purity.
Fig. 6 Component content at top vs. time
After total reflux operation, methyl formate whose purity
is over 90 % is collected quickly at the top. And the content of
methyl formate is up to 95 % soon later. At the beginning of
the reaction, a part of methanol of about 6 % concentration
can be getted at the top. The content of methanol is very low
as the reaction proceeded.
Experimental equipments: The experimental set-up is
shown as below (Fig. 5).
The residual liquid at the bottom is collected. And we
calculate the conversion of formic acid is 78.7 % by chromato-
graphy and sodium hydroxide titration.
4
TABLE-7
CALCULATION OF ACID QUALITY WITH RAW
MATERIAL FED AT BOTTOM
6
10
5
Produced Methanol Methaol
fluid content in quality in
quality (g) produced produced
fluid (%) fluid (g)
Reactor Methanol Methanol
liquid
quality
(g)
content in quality in
reactor reactor
liquid (%) liquid (g)
15.6 54.2
3
245.7
3.6
8.8
347.6
Comparison of the three operation method
8
7
Conversion rate: The conversion rate of formic acid is
listed in Fig. 7. Because all in the three operation methods,
methanol content is 400 mL and formic acid content is 350 mL,
the difference of the conversion rate is caused by the different
operation methods.
9
1
2
1
-distillation kettle; 2-heating package; 3-glass packed tower; 4-
From the figure, we can see that the formic acid conversion
rate in operation with raw material fed is lower than that in the
other two operations. That's because operation with raw
material fed accumulates a lot of water at the bottom and it
condenser; 5-product collection tank; 6-formic acid storage tank; 6,7-
thermometer; 8-sampling port; 9-u-tube manometer; 10-electromagnet;
Fig. 5. Experimental facility of esterification distillation with directly
adding of reactants

Vol. 25, No. 8 (2013)
Operation and Control of Reactive Distillation for Synthesis of Methyl Formate 4181
prevents the reaction shifting toward the positive side. The
formic acid conversion rate in the third operation is a little
higher than that in the second operation. In the third operation,
the content of formic acid is controlled by pH meter and the
formic acid falls into the distillation kettle is less than that in
the second operation, so the conversion rate is correspondingly
higher.
The figure shows that the quality of acid at bottom under
operation with raw material fed at bottom is 90.6 g which is
much larger than that under the other two operations. That's
because the raw material is directly added into the bottom and
positive reaction is inhibited gradually with the reaction
proceeding. The quality of acid under the third operation is
less than that under the second operation dut to the control of
formic acid reflux by pH meter.
1
00
Reaction time: The operation time with raw material fed
at bottom is relatively short and it is about 4 h. The other two
operation times negatively correlates to the adding speed of
formic acid. In the operation with acidity control, when the
pH value reaches a certain value, the acid is stopped adding,
so the operation time is even longer.
9
0
8
7
6
5
4
0
0
0
0
0
Optimal control of operation with fomic acid fed at
top: Also many papers discussed about methyl acetate
mixtures, study on methyl formate mixtures is significant and
helpful for the production and application. The optimal control
of operation with fomic acid fed at top is researched.
Reflux ratio influence with the separation: Experi-
mental equipment and processes is the same previously
described. The reflux ratio is 1:1, 3:1, 5:1 and the other condi-
tions unchange. The influence of reflux ratio are shown in
Figs. 9 and 10.
3
2
1
0
0
0
0
1
2
3
Different operation methods
1
-operation with raw material fed; 2-operation with formic acid fed at top
column; 3-operation with acidity control
Fig. 7. Comparison of formic acid conversion rate under different operation
110
Top product: High purity product is obtained in the three
operation methods and the content of methyl formate is over
9
5 %. It indicates that the esterification reaction is a self-
100
catalytic reaction which can get high purity product without
catalyst.
9
8
0
0
In the operation with raw material fed, the content of
formic acid is over 90 % at the beginning of the reaction. And
in the other operations the content is not very high, which is
less than 90 %. That's because at the beginning, methanol is
heated only and when methanol is full of the tower, formic
acid is added to be reacted. In the end of the reaction, the
content of methyl formate suddenly decreases and it indicates
that most of methyl formate is steamed out.
70
0
2
4
6
8
10
12
Reflux ratio
Fig. 9. Reflux ratio vs. methyl formate concentration at top
Reactor liquid: In the end of the reaction, there are a lot
of water and a little of methanol in the distillation kettle. And
the quality of acid at bottom is shown in Fig. 8.
9
9
9
4
2
0
1
00
9
0
88
86
84
82
8
7
6
5
4
0
0
0
0
0
8
7
7
0
8
6
3
2
1
0
0
0
0
0
2
4
6
8
10
12
Reflux ratio
Fig. 10. Reflux ratio vs. conversion rate of formic acid
1
2
3
Fig. 9 showed that methyl formate concentration at top
Different operation methods
1
-operation with raw material fed; 2-operation with formic acid fed at top
column; 3-operation with acidity control
hardly changes. That may be because a lot of internal reflux
exists in the tower and it counteracts the influence of the
reflux ratio.
Fig. 8. Quality of acid at bottom under different operation

4
182 Yang et al.
Asian J. Chem.
Fig. 10 shows that the conversion rate of formic acid rapid
100
increases and then falls slowly with the reflux ratio increasing.
When reflux ration increases, the driving force of the vapour-
liquid transfer changes larger and the tower separation perfor-
mance improves, more and more methyl formate enrichments
at the top. And this make the reaction equilibrium shifts to the
right, more product is getted. However, if reflux ratio reaches
a certain value, the formic acid conversion rate decreases
gradually. That's because the increasing of methyl formate
reflux make the hydrolysis of methyl formate easily. Mean-
while, a large reflux ratio leads to large energy consumption
and long operation time. So when chose reflux ratio, after meet
the requirement of top product purity and conversion rate, a
small value is considerated to reduce operating costs.
9
9
8
6
94
9
9
8
2
0
8
8
8
8
6
4
2
80
Fluence of formic acid feeding speed: Experimental
equipment and processes is the same as the experiment 3-2.
The feeding speed of formic acid changes and the molar ratio
of formic acid and methanol is 0.5:1, 1.5:1, 2:1 and 2.5:1. The
other conditions unchange. The results are shown as below.
Fig. 11 indicates that methyl formate content at top
changes a little with different reaction molar ratio. However,
when the reaction molar ratio is relatively small, the methyl
formate content is also low. It may be because a lot of methanol
remains in reactive distillation section and it goes up to the
top, collected with the methyl formate product together. So
the methyl formate content decreases.
0
0.5
1.0
1.5
2.0
2.5
3.0
Molar ratio
Fig. 12. Different reaction molar ratio vs. conversion rate of formic acid
Conclusion
In the three operation of reactive distillation for synthesis
of methyl formate, the operation with raw materials fed has
low conversion rate that is 78.7 %. However the operation
time is shortest. The conversion rate under operation with
formic acid fed at top column is higher than that under the
former and it is 91.5 %. The operation time is almost 4 h.
Under the operation with acidity control, the conversion rate
is even larger, which is up to 94.3 %. And the operation time
is even longer than that of the other two operations. The diffe-
rent reflux ratio and reaction molar ratio have influences on
the esterfication reactive distillation process. In the operation
with formic acid fed at top column, a small reflux ratio is
considerated to reduce operating costs when the top product
purity and conversion rate meet the requirement. And a small
reaction molar ratio is chosen when the concentration of
methyl formate at the top meets the product requirements.
1
00
98
9
9
9
9
6
4
2
0
88
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8
8
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