1) A student team designed and tested a simple distillation process to purify methacrylic acid (MAA) by removing inhibitor and polymer contaminants. 2) Through 6 trials, the team optimized the process by improving insulation, operating at steady state longer, and maintaining precise temperature and pressure control. 3) The best trial achieved the process goals of over 125g/hour production rate and less than 300ppm polymer content through longer run times and steady operation.

1. Distillation and Characterization of Methacrylic Acid 12/21/2016
Department of Chemical Engineering
Presented by: Tom Ignaczak, Daisy Jin, Megan Johnston, & Vito Martino
Background
Design
Experiments
Analytical Methods
Results
There was a big improvement from trial 2 to 3 in terms of runtime as a result of a new condenser that captured
more vapor. In hindsight, insulation also could have been used to minimize reflux. Significant improvements were
also seen in yield and production rate between trials 4 and 5. These improvements can be attributed mainly to the
system being able to operate at steady state for a longer period of time. Trial 5 achieved all process goals with a
production rate greater than 125 g/hour and a polymer content of at most 300 ppm. Trial 6 was able to achieve
high purity product, but production rate suffered due mainly to the trial being run at a higher pressure. Production
of purified MAA completely stopped twice during trial 6 and the temperature of the distillation flask had to be
increased to get production started again. Even with a working vacuum pump, it is likely that the production rate
for trial 6 would have still been lower than that of trial 5 do to boiling point elevation effects.
“In the production of contact and IOL lenses, [methacrylic acid (MAA) and other] hydrophilic
monomers are used to provide a wettable, biocompatible surface. One issue is that vendors frequently supply
these monomers containing inhibitors which must be removed prior to use in the polymerization process.
Another complication is that there may also be present polymer contamination which will cause the final lens
to be cloudy in appearance.” - Acuity Polymers (Sponsor Company). It was the goal of this project to
develop a simple process for separating MAA from both its inhibitor and polymer. Process goals included a
product impurity content of less than 100 ppm and a production rate of 125g of product per hour. In order
that the product produced may be tested for purity, a standard procedure by which the purified distillate may
be characterized was also developed.
Solubility:
The use of hexanes for solubility testing provided a quick and cheap
way to test for the presence of polymer in the product solution. After
optimizing the test by changing multiple variables, 1 mL of distillate
in 2 mL of hexanes was able to detect down to a 300 ppm
contamination level.
A simple distillation unit can be built following the
PID shown in Figure 4. To achieve process goals,
system pressure and temperature need to be carefully
controlled.
Pressure Control:
System pressure can be controlled by running the
vacuum pump during the process to obtain a
constant pressure of -29.5 inHg.
Team Lynx would like to extend thanks to all those who have helped make this project possible. Robbie Harding
for insight into group development and equipment usage; Mark Juba for invaluable knowledge into the processes
involved throughout the experiment; Acuity Polymers for the opportunity to work on a real life problem; and the
faculty and professors in the Chemical Engineering department.
UV Spectroscopy:
Liquid Chromatography/Mass Spectroscopy:
With background research and some thermodynamic
approximations figure 1 was generated to compare MAA
to its inhibitor, MEHQ. The graph clearly shows that the
two can be effectively separated using vacuum distillation.
It was assumed that this technique would also work for
separating MAA from its polymer. With a little additional
math concerning the number of theoretical equilibrium
stages, it was calculated that single stage distillation would
be an effective purification method. The effect of MEHQ
buildup during distillation on the distilling solution’s
vapor pressure was also considered and modeled. In the
end, a gradual-feed, simple vacuum distillation apparatus
was constructed.
As is the industry standard, UV spectroscopy was used for the detection
of MEHQ. According to research, increasing MEHQ in solution would
increase the absorbance of light at around 290 nm. The expectations for
our results was that the distillates would have lower absorbances than
bulk MAA. Due to inconclusive results upon analysis of products 5 and
6, accurate detection of MEHQ was not obtained.
Since the solubility test did not have a sensitivity of 100 ppm the bulk
MAA and products 5 and 6 were run through a LC/MS. This test plots
the various masses in solution by intensity. The higher peaks indicate a
higher presence of a particular molecular weight. Any smaller peaks could
be ignored as “background noise”. The expected peaks were around 86
and 124 for MAA and MEHQ as those are their respective molecular
weights.
Temperature Control:
1) Distillation flask:
The distillation flask was submerged in a near
constant temperature water bath controlled by a
hot plate. A thermocouple measuring the water
temperature was wired to a measurement
computing board. Then a LabVIEW program was
made to monitor temperature changes in the water
bath. If the temperature went below or beyond the
desired range, the hot plate was turned on and off
manually to control the temperature.
Acknowledgements
2) Collection flask:
To prevent unnecessary polymerization, the temperature
of the collection flask needed to be kept low enough to
freeze MAA. To achieve this an ice water bath was
employed to bring the temperature of the collection
down to a steady 0 °C.
Recommendations for Implementation
● Distillation flask temperature to be controlled to within 1o of 65oC
● Condenser temperature to be controlled to within 1o of 20oC
● Collection flask temperature to be 0oC - exact temperature easy to achieve with ice bath
● System pressure to be controlled to within 0.1 inHg of -29 inHg gauge, 0.45 ± 0.05 psi absolute
● Condenser geometry should minimize reflux into the distillation flask. Insulation of the glass leading to the
condenser will also aid in vapor capture.
● Analysis of MAA solutions:
○ A simple hexane solubility test will determine if polymer content has exceeded 300 ppm
○ UV spectrum analysis is industry standard for detecting MEHQ in solution
3) Condenser:
The cold water circulated through the condenser was
produced using a constant temperature circulating
pump, which pumped water at a constant temperature (
20°C ± 1°C), in order to condense but not freeze the
monomer.
Figure 8: Mass Spectroscopy of Bulk MAA Figure 9: Mass Spectroscopy of Product 5
Table 1: Results Table for 6 Distillation Runs
Figure 8 shows the MS for bulk MAA with inhibitor. There are distinct peaks at 171 and 257, the dimer and
trimer of MAA, respectively. This is due to the sample not being diluted before being run, but it is still all
monomer. The peak at 285 is two MEHQ molecules with a potassium ion.
Figure 9 is the MS of of Product 5. Both the MS of Products 5 and 6 (not pictured) were not diluted and had
peaks at 173 and 257-259. The two major results are the lack of peak at 285 and no large peaks up to 500. The
first implies that the inhibitor was successfully removed. The second shows a lack of polymer with a weight of
up to 500 g/mol. In combination with the solubility test, it is unlikely that any appreciable amount of polymer
forms during this distillation process.
Figure 2
Figure 1
Figure 4
Figure 3
Figure 6: Comparison of contaminated MAA
solution (left) to a pure hexane control (right)
Figure 7: Absorbance Spectrum of MeHQ in
Acrylonitrile (Credit: Applied Analyitcs, 2013)
1) Identification of Most Favorable Operating Conditions
Different distillation temperature settings were tested in order to find the optimal operating condition. 20°C was
identified as an effective temp for our condenser as MAA’s normal freezing point is 16°C and the collection flask
was kept at a constant 0°C. Also, there was no harm in keeping the system pressure low as long as the distillation
temperature was kept low enough as to avoid vaporizing inhibitor. These three variables were kept constant for
every test. 10g samples of MAA were run through the system with different distillation temperature set points.
2) Mid-Scale MAA experiment + Slow feed
This experiment aimed to verify the optimal conditions found from small scale testing. These conditions were:
distillation flask temperature 65°C, condenser 20°C, collection flask 0°C, pressure -29 inHg. 44g bulk MAA was
added to the feed, and the flow rate was monitored so that around 10 mL of MAA was in the distillation flask at
any point in time.
3) System Capacity Production
This experiment was conducted to test how the system would perform during a large scale production. A 210g,
maximum capacity, test run was performed with the parameters laid out in experiment 2. Unfortunately, the there
were complications with vacuum pump, and this test was run at a gauge pressure of -28.75inHg. The distillation
temperature had to be increased correspondingly in an attempt to achieve an acceptable runtime. The distillation
temperature was varied over the course of the experiment, and the highest temperature reached was 77°C.
Figure 5: Actual apparatus built for prototyping