(314b) Esterification and Transesterification of Propylene Glycol Methyl Ether Using Heterogeneous Catalyst in Simulated Moving Bed Reactor

Reactive chromatography is a process that combines reaction and separation in a single unit that leads to a higher productivity^[1]. This process is especially advantageous when the reaction is equilibrium limited where in-situ separation of product shifts the equilibrium in the direction of conversion increase^[2]. A continuous reactive separation process, simulated moving bed reactor (SMBR), utilizes this principle in a train of multiple chromatographic columns that is packed with an adsorbent that also acts as a catalyst.

This study focuses on the catalytic synthesis of propylene glycol methyl ether acetate (DOWANOL™ PMA glycol ether acetate) through two separate types of reactions: transesterification and esterification. Both reactions are equilibrium limited, where conversion can be increased by using porous catalysts that act as both adsorbent and catalyst inside a chromatographic column. Esterification is performed with an acidic catalyst, AMBERLYST^TM 15, which has high activity and stability. On the other hand, transesterification is performed with a basic catalyst, AMBERLITE™ IRA-904, which shows high activity for the transesterification at low temperatures. Esterification has an advantage of enhanced stability of the catalyst, while the transesterification has an advantage of better separation (absence of water) and lower operating temperatures^[3]. The benefits of each reaction and catalyst are discussed with comparisons throughout the study.

Case studies of process development for the ester product are discussed for the transesterification and the esterification reactions. The dynamics of batch reaction and the fixed-bed adsorptive reaction are investigated by carrying out batch reaction experiments and chromatographic pulse tests using porous catalysts. Stirred batch reactor experiments were conducted at various temperatures and different mass transfer resistances. Reaction equilibria and kinetic parameters together with their dependence on temperature were determined by fitting the model to the experimental data. Estimation of the adsorption equilibrium constants and reaction parameters were conducted from pulse tests using a single chromatographic column. Catalytic deactivation of basic catalyst and its influence on the process performance were analyzed.

For the above two production routes, SMBR processes were designed utilizing the mathematical models. Mini plant tests were performed to validate the process concepts, and operations were optimized.  The two processes were compared in terms of productivity, solvent usage, and energy requirement.

References

[1] V. Gyani, S. Mahajani, Reactive Chromatography for the Synthesis of 2-Ethylhexyl Acetate. Separation Science and Technology, 43: 2245-2268, 2008.

[2] A. Rodigues, C. Pereira, J. Santos. Chromatographic Reactors. Chemical Engineering & Technology 2012, 35, No7, 1171-1183

[3] J. Oh, G. Agrawal, B. Sreedhar, M.E. Donaldson, A.K. Schultz, T.C. Frank, A.S. Bommarius, Y. Kawajiri, Conversion Improvement for Catalytic Synthesis of Propylene Glycol Methyl Ether Acetate by Reactive Chromatography: Experiments and Parameter Estimation, Chemical Engineering Journal  2015 (397-409)