The Optimal Production of Methyl Acetate Using a Microreactor

Summer Research Program 2007

Elizabeth LeitnerValerie PiazzaMaria del Mar RojasAlex KitayevPedro CuacuasGrace BrockCorinna Wang

Table of Contents

Page Section

3 Abstract

4 Introduction

6 Experimental

9 Results & Discussion

19 Conclusion

20 Recommendations

21 Works Cited

22 Acknowledgements

23 Appendix I – Reaction Diagram

24 Appendix II - Calculations

2

Abstract

The purpose of this experiment was to find the optimal condition for producing

methyl acetate. Methyl acetate is made by the esterification of methanol and acetic acid

with an addition of a catalyst, sulfuric acid. Several runs were carried out under different

conditions. Different catalyst amounts were tried with different temperatures and

different pump settings to find the ideal conditions in which the yield of methyl acetate

would be the highest. Using the conversion rate of methanol, the production rate of

methyl acetate was determined. The optimal settings for producing the maximum

conversion of methanol to methyl acetate was 1.0mL catalyst at 40˚C at a pump setting of

15%/35%, which produced a yield of 87.6%.

3

Introduction

Methyl acetate is a commonly used chemical in industry around the world.

Methyl acetate is a component in such items as nail polish removers, glues and used as a

substitute for acetone [1-2]. Methyl acetate is a product of an esterification reaction

involving methanol and acetic acid. Sulfuric acid must be added as a catalyst in order for

the reaction to significantly take place. This is because the catalyst lowers the activation

energy, allowing the sulfuric acid to increase the rate of the reaction without being

consumed. Various conditions can be changed to produce different yields of methyl

acetate. By changing the temperature, flow rate of reactants and amounts of catalyst

used, the amount of methyl acetate produced will vary. To analyze the final product, a

gas chromatograph was used. A sample of the final product was injected into the gas

chromatograph and the results were displayed on the integrator, which included

information such as the retention times for each component as well as the area.

There are two methods that are used to produce methyl acetate. One method uses

reactive distillation and the other method requires the use of a microreactor. Liquid

phase reactions commonly use reactive distillation. Methanol is placed in a container

with acetic acid and sulfuric acid where they are heated. Since methyl acetate (the

product) has the lowest boiling point (56.9˚C) compared to methanol (64.7˚C), acetic acid

(118.7˚C) and the sulfuric acid catalyst (338˚C), which have higher boiling points, it will

be the first compound to vaporize [3-6]. The methyl acetate vapors flow through the

distillation column into a separate container where the methyl acetate is then condensed

back into its liquid phase. According to Le Chatelier’s Principle, if the product is

4

removed from the reaction, the reaction shifts to the product side to compensate for the

lost products [7].

The other method involves the use of a microreactor. For the experiment, the

microreactor was used to mix methanol with acetic acid within narrow channels to

produce methyl acetate. There were inlet tubes for both methanol and acetic acid and a

tube dedicated for the heat exchange fluid to alter the temperature if necessary, as well as

an outlet tube to collect the effluent. These narrow conditions better helped the

substances to mix for a more optimal product.

Reactive distillation and the microreactor both provide a way to produce methyl

acetate. The benefit of using the microreactor in comparison with reactive distillation is

that the microreactor is far safer than distillation. Since the reaction process is confined

into a smaller space, it is easier to both operate and service. Due to its small size, the

microreactor is more easily detected for malfunctions. Also once the malfunctions are

detected they are easier to fix. Since reactive distillation is a large process, it would be far

more difficult to repair. Part of the research was to determine if an array of

simultaneously working microreactors would create the same yield of methyl acetate as a

reactive distillation column under the most optimal conditions.

5

Experimental

The goal of the project was to find the optimal settings for the best production of

methyl acetate using methanol, acetic acid and a catalyst, sulfuric acid. In order to

accomplish this goal various experiments were run. The whole project was separated into

three stages. The first area of experimentation involved the gas chromatograph (GC).

The GC separates and identifies the substances involved in the reaction. Each substance

injected into the GC passes through a column and, in the process, was slowed down

depending on its volatility. As a result, the various substances leave the GC at distinct

rates based on their retention times. A connected Hewlett-Packard 3395 Integrator

served to express the information recognized by the GC through a unique curve for each

substance injected. In addition, it states the retention time of each substance next to its

corresponding curve as well as the areas of each peak. Although it is not immediately

apparent which curve corresponds to which substance, repeated experimentation served

to identify the specific peak and retention time of each compound injected into the GC.

Initially, each substance was run separately through a Gow-Mac Series 580 Gas

Chromatograph in order to ascertain the characteristics: total area, percent area and

retention time. Next, a mixture of the three substances was run through the GC to see if

three different peaks would appear. However, it was imminently apparent that the

methanol and methyl acetate had similar peaks and therefore it was necessary to adjust

the settings. Originally the column temperature was at 110˚C, the detector temperature

was at 185˚C and the injection temperature was at 170˚C. This was problematic due to

the fact that the substances were being processed too quickly, primarily caused by high

temperatures. As a result, the machine could not distinguish between the methanol and

6

methyl acetate. The temperatures needed to be reduced in an effort to slow down the

process. After thorough experimentation it was revealed that the most effective

temperatures were a column temperature of 41˚C, a detector temperature of 128˚C and an

injection port temperature of 127˚C. Furthermore, it was established that the methanol

peak was detected first by the integrator, followed by the methyl acetate and the acetic

acid.

After the GC settings were modified for their ideal use, the pump settings for each

substance needed to be calibrated. The pumps used were Index Corporation Model

#701C Micropumps. A series of processes of methanol and acetic acid was completed in

order to establish the proper calibration settings for each substance. First, an empty

beaker was weighed and recorded on a Denver Instrument APX-2001 balance. Once the

mass was observed, the settings of the methanol pump were tested. Beginning with zero

percent, methanol was run for fifteen seconds into a waste beaker to establish a constant

flow. Then it was moved into the empty beaker for the next fifteen to twenty seconds.

After the pumps were shut the beaker was then weighed again to determine how much

methanol had been collected. This same process was repeated with pump settings

ranging from five percent to forty percent in increments of five percent. The same

calibration process was used for the acetic acid.

In order to analyze samples of methyl acetate and its reactants, methanol and

acetic acid were processed through a microreactor at room temperature without the

presence of a catalyst. A steady state of two seconds was established during which the

sample was not collected. This was done in order to allow time for the reaction to take

place. Then the sample was collected in a beaker for two seconds. This was the sample

7

used to analyze the yield of methyl acetate. The beaker that contained the effluent was

placed in a beaker of ice water. The procedure was repeated at various pump settings,

starting at 20%/20% (methanol pump setting/acetic acid pump setting) at increasing

intervals of five percent until 40%/40%. Then, the procedure was repeated at 35%/15%

and 15%/35%. This was done in an effort to see the impact using different amount of

methanol and acetic acid had on the final results.

In order to determine whether a catalyst would affect the outcome, the reaction

was repeated using 1mL of sulfuric acid. Then the amount of sulfuric acid used was

increased by half a milliliter after each set of runs up to three milliliters. The pump

setting did not differ between the reaction conducted without a catalyst and the reaction

conducted with a catalyst. These reactions were conducted at room temperature.

Another factor involved in the experiment was temperature. The reaction was

conducted at temperatures of 28˚C (room temperature), 40˚C and 50˚C using the same

pump settings. The temperatures were altered using a Corning Stirrer/Hot Plate and

monitored using an Extech RTD thermometer. After the reaction was completed for the

specific pump settings and temperatures, the product of the reaction was collected and

transported to the GC in an ice bath. This was done in an effort to stop the reaction

altogether. This specific reaction is a reversible reaction, so icing the product will

prevent the reverse reaction. Using a syringe, a sample of 0.5μL was extracted and

injected into the GC. Then the attached integrator identified the peaks and retention

times for each substance.

8

Results & Discussion

Initially, the calibration curves for methanol (Figure 1) and acetic acid (Figure 2)

were computed. The results are shown below.

Calibration Curve of Methanol

y = 0.1008x - 0.5423R2 = 0.9873

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20 25 30 35 40 45

Pump Setting (%)

Flow

Rat

e (g

/sec

)

Figure 1 - Calibration curve of methanol

Calibration Curve of Acetic Acid

y = 0.1319x - 0.7931R2 = 0.9508

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20 25 30 35 40 45

Pump Setting (%)

Flow

rate

(g/s

ec)

Figure 2 - Calibration curve of acetic acid

It was necessary to calibrate both the pumps and the GC in order to compute the

flow rate and determine how much of each component was being released from the

microreactor at different time settings. Also, the factor of human error had to be taken

9

into consideration because the amount of the mixture being inserted could have been off

by a fraction of a microliter, which would change the results entirely.

The GC was calibrated using different amounts of pure methanol to find an

average area and number of moles calibrated, which can be observed in Figure 3. The

area computed by the integrator was not able to be used mainly because of human error.

The areas printed out were scattered due to the fact that 0.5μL was not always injected,

sometimes it was a little more and at other times it was a little less. The percentages were

always accurate because no matter how much was injected the same percentage would

always be calculated. Therefore, the percentages were more accurate and were better to

use. Additionally, it was necessary to find the average area for a 0.5μL injection because

the average area would be used as a constant once the calculations were completed. As a

result, all the computation would be accurate. The pumps were calibrated so that the

flow rate could be calculated, and so that the amount of each substance released from the

microreactor could be determined at particular time settings.

10

GC Calibration of Methanol

y = 8E+09x + 23175R2 = 0.9869

0

100000

200000

300000

400000

500000

600000

0 0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007

Number of Moles

Aver

age

Area

Figure 3 - GC calibration of methanol

The conversion of methanol is directly related to the setting in which it is being

pumped. The higher the pump setting, a higher percent of conversion yielded. As shown

in the “calibration calculations,” the pump setting was increased from 20% to 25%,

which raised the average methanol conversion from 24.43845% to 25.91316%. At room

temperature, the optimal condition found was at 35% acetic acid and 15 % methanol,

which yielded an average of 87.6% and was the highest conversion of methanol recorded.

The same correlation was true at 40˚C and 50˚C, as demonstrated in figure 5 and figure 6,

respectively. This result is due to the fact methanol is consumed more rapidly when there

is a smaller amount present in comparison with that of acetic acid.

11

Average Methanol Conversion at Room Temperature

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35 40

Pump Setting (%)

Ave

rage

Con

vers

ion

(%)

Figure 4 - Average methanol conversion with varying pump setting (Room Temp)

Average Methanol Conversion at 40˚C

0

5

10

15

20

25

30

0 10 20 30 40 50

Pump Setting (%)

Ave

rage

Con

vers

ion

(%)

Figure 5 - Average methanol conversion with varying pump setting (40˚C)

12

Average Methanol Conversion at 50˚C

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50

Pump Setting (%)

Ave

rage

Con

vers

ion

(%)

Figure 6 - Average methanol conversion with varying pump setting (50˚C)

In addition to the role of the pump settings, temperature was also a large factor in

the rate of collision of the particles. The higher the temperature was, the higher the rate of

collision. In this experiment the temperature never exceeded 50ºC because the boiling

point of methyl acetate was 56.9ºC and this could potentially have an impact on the

outcome of the experiment.

13

Average Conversion of Methanol (Temperature)

28

29

30

31

32

33

34

35

0 10 20 30 40 50 60

Temperature (˚C)

Aver

age

Conv

ersi

on (%

)

Figure 7 - Average conversion of methanol with varying temperature

Another factor that was thought to have an affect on the reaction, along with

pump settings and heat, was sulfuric acid, the catalyst. A catalyst was necessary for the

reaction to occur because without it the acetic acid and methanol cannot produce methyl

acetate. This can be observed in Table1.

Pump Setting

Conversion of Methanol

20%/20% 1.60593595125%/25% 2.42050928730%/30% 7.22344031135%/35% 4.12228632135%/15% 8.57467769

Table 1 – Conversion of methanol without a catalyst

In theory, a catalyst is supposed to speed up a reaction [8]. Therefore; increasing

the amount of catalyst should also make the reaction occur more rapidly.

When all the trials were completed, the results were recorded and the methanol

conversions were calculated, as seen in Figure 8. The 0mL catalyst runs yielded the least

14

conversion of methanol while the 3.0mL trials yielded the greatest conversion of

methanol. Most of the results correspond with the fact that the greater the concentration

of the catalyst the greater the conversion of methanol. However, there was a break in this

trend between 1.0mL of catalyst and 1.5mL of catalyst. Instead of an increase in

conversion of methanol there was a decrease between these two points. While the source

of the error is unknown, it is likely that there was a problem with the pumps or the

general procedure when conducting the experiment with 1.5mL and 2.0mL of catalyst.

Although the conversions of methanol began to increase after 1.5mL catalyst, the

conversion at 2.0mL and 2.5mL catalyst was relatively the same as the conversion at

1.0mL. This could be due to the fact that the change in the amount of catalyst was

recognizable, but not as significant until a more drastic change occurred, from 1.0mL to

3.0mL for instance.

When analyzing Figure 8, it became apparent that, while the presence of a catalyst

is essential for the reaction to occur, the amount of catalyst present appears to be

insignificant. This is so because the average conversion for each amount of catalyst used,

disregarding the conversion value for 1.5mL catalyst, only varied by less than 2%. This

percentage is within the experimental error. With each step taken in this experiment there

were many opportunities for error, including measuring the wrong amount of substance

into the beaker. Also, while transporting the mixture to the lab to be analyzed by the GC,

the ice water bath could possibly not have been cold enough, which would not prevent

the product from continuing to react.

15

Average Methanol Conversions (Catalyst Experiment)

0

5

10

15

20

25

30

35

0 0.5 1 1.5 2 2.5 3 3.5

Catalyst (mL)

Ave

rage

Con

vers

ion

(%)

Figure 8 - Average methanol conversion with varying amounts of catalyst

To see the effect that the amount of methanol and acetic acid had in relation to

each other, different pump settings of 35%/15% and 15%/35% were tested. According to

Table 2, the average conversion of methanol was lower at 35%/15% than at 15%/35%.

This is because there was a lower amount of acetic acid to react with a greater amount of

methanol. Consequently, the conversion of methanol was much higher at 15%/35%

because there was a greater quantity of acetic acid reacting with a smaller quantity of

methanol.

Pump Settings

Average Conversion of Methanol

35%/15% 15.1386252315%/35% 73.952639

Table 2 – Average conversion of methanol for different pump settings ratios

16

When conducting any lab experiment, results may sometimes be skewed due to

human and inherent errors. Such human errors in this particular lab include the different

mixtures of sulfuric acid that were produced. Graduated cylinders were used to make sure

the right amount of chemicals was mixed together. However, eyes can only see to a

certain degree of accuracy. There were human errors with the pump settings for the

methanol and acetic acid. Sometimes the pumps were set to the incorrect settings, which

produced odd results. After evaluating the results produced by the integrator was it

apparent that the pump settings were not set properly. Those runs had to be done again.

There was also the issue of how the syringe was inserted into the gas chromatograph. At

times the syringe was not inserted properly and got stuck halfway through the injection

port. The syringe then had to be pulled out and inserted once again. The proper injection

technique was to stand and inject the syringe directly. If errors still occurred, the septum

was checked and the injection port was tightened. As a result of improper injections,

some of the mixture may have evaporated, which would produce smaller peaks and areas

than expected. Additionally, the gas chromatograph was very hot, so if the syringe was

not inserted correctly, the mixture would heat up and would therefore react. This would

completely defeat the purpose of keeping the mixture in an ice bath.

There were also inherent errors such as the precision of the graduated cylinder

that was used to create various mixtures of sulfuric acid. That graduated cylinder was

only so accurate. As with the gas chromatograph, the machine needed to be set to certain

conditions in order for there to be a clear separation between all the peaks. However, like

the graduated cylinders, the machine was only so accurate because after multiple

injections of the mixture, the percent area of each peak varied slightly.

17

Additionally, residue contained in the columns of the GC could have led to

inaccurate areas. This could be due to residual water or acetic acid that did not

completely exit the column. Also, the pumps of the microreactor could not have been set

exactly at the desired settings because they did not have many tick marks for them to be

set precisely.

18

Conclusion

Several trends were observed to occur as different variables were tested. As the

pump settings increased, so did the average conversion of methanol. Additionally, when

there was no presence of a catalyst the average conversion was very low and when the

catalyst was present, the conversion was much higher. However, as long as there was the

presence of catalyst, the average conversion did not change much between varying

amounts of catalyst. Also, as the temperature increased the average conversion appeared

to increase exponentially. The average conversion of methanol was greatest when there

was excess amount of acetic acid to react with a limited amount of methanol.

The optimal conditions for producing the greatest conversion of methanol to

methyl acetate appeared to be at a high temperature, with more acetic acid than methanol,

and with the presence of a catalyst. From the experiments conducted, the optimal settings

for producing the maximum conversion of methanol to methyl acetate was 1.0mL

catalyst at 40˚C at a pump setting of 15%/35%, which produced a yield of 87.6%.

19

Recommendations

After completing the experiment, it was recognized that there should be more

experimentation with a higher range of catalyst, possibly starting at 0.1mL and going up

to 10mL. Also, while this experiment concluded at 50ºC, a higher range of temperature

settings could be more effective. In addition, one could experiment with different

combinations of pump settings. Since the 15%/35% and 35%/15% settings were so

significant in the experimental trials, one could try using pump settings in which the ratio

of methanol and acetic acid are in different proportions. Furthermore, additional

investigation of GC settings could provide for a more distinct separation in the peaks of

methanol and methyl acetate. Lastly, more runs could be conducted in order to establish a

more precise average for the collected data.

20

Works Cited

[1] “Methyl Acetate.” Chemicalland21. Arokor Holdings, Inc. 2000 (http://www.chemicalland21.com/industrialchem/solalc/METHYL%20ACETATE.htm).

[2] “Methyl Acetate is offered as a replacement for acetone.” ThomasNet. ThomasNet. 2006 (http://news.thomasnet.com/fullstory/459580).

[3] “Methyl Acetate.” W ikipedia . Wikimedia Foundation, Inc. 2 July 2007 (http://en.wikipedia.org/wiki/Methyl_acetate).

[4] “Material Safety Data Sheet.” Iowa State University. Iowa State University. 14 March 2001 (http://avogadro.chem.iastate.edu/MSDS/methanol.htm).

[5] “Safety Data for Acetic Acid.” University of Oxford. University of Oxford. 6 January 2006 (http://physchem.ox.ac.uk/MSDS/AC/acetic_acid.html).

[6] “Safety Data for Sulfuric Acid.” University of Oxford. University of Oxford. 31 August 2005 (http://physchem.ox.ac.uk/MSDS/SU/sulfuric_acid_concentrated.html).

[7] Clark, Jim. “Le Chatelier’s Principle.” Chemguide. Chemguide. 2002 (http://www.chemguide.co.uk/physical/equilibria/lechatelier.html).

[8] Clark, Jim. “The Effect of Catalysts on Reaction Rates.” Chemguide. Chemguide. 2002 (http://www.chemguide.co.uk/physical/basicrates/catalyst.html).

21

Acknowledgements

A special thanks to:

Con Edison, Sponsor

Professor Okorafor, Chemical Engineering Advisor

Kemi Adeyeba & Albert Wang, Teaching Assistants

Mike Westbrook, Lab Technician

Susan Dorsey, Program Director

The Cooper Union, Program Site

22

Appendix I - Reaction Diagram

Reaction of Methanol and Acetic Acid

ON

OFF

50

0

25ON

OFF

50

0

25ON

OFF

50

0

25

AceticAcid

Methanol

Heater and Stirrer

23

Appendix II – Calculations

Acetic Acidm b

0.1319 -0.7931

Pump Setting (%)

Flow Rate (g/sec)

Flow Rate (mL/sec)

# of moles after 2 sec

Concentration (mol/mL)

20 1.8449 1.758722593 0.061445462 0.00848711825 2.5044 2.387416587 0.156329588 0.01600051230 3.1639 3.016110582 0.197496879 0.01605571335 3.8234 3.644804576 0.23866417 0.01609207740 4.4829 4.27349857 0.279831461 0.01611784115 1.1854 1.130028599 0.073995006 0.00754927235 3.8234 3.644804576 0.23866417 0.024506112

Methanolm b

0.1008 -0.5423

Pump Setting (%)

Flow Rate (g/sec)

Flow Rate (mL/sec)

# of moles after 2 sec

Concentration (mol/mL)

20 1.4737 1.861202324 0.091991261 0.02541247825 1.9777 2.497726699 0.123451935 0.02527089330 2.4817 3.134251074 0.154912609 0.02518756135 2.9857 3.770775448 0.186373283 0.02513266440 3.4897 4.407299823 0.217833958 0.0250937735 2.9857 3.770775448 0.186373283 0.03802912415 0.9697 1.224677949 0.060530587 0.012430599

CombinedPump

Setting (%)Flow Rate (mL/sec)

Amount collected in 2 sec (mL)

20 3.619924917 7.23984983425 4.885143286 9.77028657230 6.150361655 12.3007233135 7.415580024 14.8311600540 8.680798393 17.36159679

35/15 4.900804047 9.80160809415/35 4.869482525 9.73896505

24