Simulated Moving Bed Reactor for Enhancing the Productivities of Equilibrium Limited Reactions

Equilibrium-limited reactions are ubiquitous in the chemical industry. Those with highly unfavorable equilibrium constants face very energy intensive operations for conversion and recovery of the product, often needing extensive recycle. Chances are also that such severely equilibrium-limited reactions using conventional reactors are written off at an early stage and are never scaled up to production.

In this work, we demonstrate the potential of simulated moving bed reactor (SMBR) in increasing the productivity of strongly equilibrium-limited reactions and possibly rendering them economically feasible. In an SMBR, in-situ chromatographic separation of the products aids in shifting the equilibrium, thereby improving the conversion.

Liquid phase transesterification of propylene glycol methyl ether (DOWANOL™ PM) to propylene glycol methyl ether acetate (DOWANOL™ PMA) using a homogeneous catalyst [1] is considered as a case study to compare the performance of SMBR with that of a conventional batch reactor. Here, DOWANOL™ PM is used both as a reactant and desorbent for the chromatographic separation inside the SMBR. In the SMBR process, an anion exchange resin, AMBERLITE™ IRA904 in chloride form is used as a non-catalytic adsorbent, while sodium alkoxide of PM is supplied as a homogeneous catalyst in the desorbent. Using model based optimization, we demonstrate the advantage of employing a non-catalytic adsorbent in the SMBR for the homogeneously catalyzed reaction. With the ability to independently tune the separation of the product in the SMBR, it is demonstrated that the productivity of the process increases with increasing separation factor. Presence of an optimal product separation factor is observed with respect to the amount of DOWANOL™ PM used for reaction and separation. At a fixed conversion of 95%, SMBR outperforms a batch reactor by increasing the productivity by 85% and reducing DOWANOL™ PM usage to 50% of what is required by the batch reactor.

[1] J. Oh, B. Sreedhar, M. E. Donaldson, A. K. Schultz, T. C. Frank, A. S. Bommarius, Y. Kawajiri, "Transesterification of Propylene Glycol Methyl Ether in Chromatographic Reactors Using Anion Exchange Resin as a Catalyst," J. Chromatography A  2016, 1466, 84-95; DOI:10.1016/j.chroma.2016.08.072

™Trademark of The Dow Chemical Company