(81b) Membranes for Olefin Paraffin Separations

Propylene is among the most important chemical feedstocks of the petrochemical industry. A significant amount of this olefin is found in petrochemical product streams and must be separated. Already much work has been done with pure polymer, to increase the permeability and selectivity of propylene/propane separations.

This research has primarily two goals. 1) Keep the efficiency (selectivity) high at higher pressure by suppressing plasticization. 2) Increase the selectivity and permeability with the use of Mixed Matrix membranes for commercial use.

Burns and Koros have identified the so-called ?propylene/propane upper bound curve? in 2001. We have identified and successfully synthesized 6FDA-6FpDA polyimide for Propylene/Propane separation. Our pure polymer selectivity is 19 at 35ºC. Propylene has shown a trend of plasticization above 2 atm. pressure with pure polymer. We have been able to suppress the plasticization occurrence by performing the experiment at 70ºC and synthesizing very high molecular weight and narrow PI polymer. Under these conditions, plasticization does not occur till 4.35 atm.. High molecular weight appears to reduce segmental free volume and mobility in the polymer.

Our next step is to disperse molecular sieves in a polymer to create a hybrid material with superior properties. We are able to see permeability and selectivity enhancements with more than one dense film pure gas permeations. Currently we are trying to verify our positive results with available mathematical models (Cussler and Maxwell). Once successful, we will focus on high temperature and pressure permeations to approximate industry application.