Date of Award

January 2019

Document Type


Degree Name

Master of Science (MS)


Chemical Engineering

First Advisor

Ali S. Alshami


The current processes used for natural gas separation and purification are considered energy intensive which could potentially be substituted by membrane technology. Aromatic polyimides are considered one of the most viable types of polymers used for the fabrication of membranes for gas separation mainly due to their outstanding properties. Moreover, aromatic polyimides could be thermally rearranged to form another class of polymers called polybenzoxazoles which are characterized by having enhanced gas separation properties. This research aimed to (1) synthesize and characterize three different aromatic polyimides via polycondensation reaction of a diamine (BisAPAF) with three different dianhydride precursors (PMDA, ODPA, BTDA), (2) fabricate free-standing polyimide membranes, and thermally rearrange them to polybenzoxazoles and (3) compare the gas separation properties (permeabilities and selectivities) of the membranes before and after the thermal rearrangement and compare the results to Robeson upper bounds. The tested gas pairs tested were CO2/CH4, N2/CH4 and CO2/N2. All the objectives of this research were successfully achieved, and it was found that chemical structure of the starting monomers plays a key role in the physicochemical properties of the synthesized polyimides which, consequently affected the gas separation properties. Among the three polyimides, APAF-BTDA showed the superior performance followed by APAF-PMDA and finally APAF-ODPA. This is believed to be due to the stability of the BTDA pendant group which resulted in high conversion and, hence, the best separation performance where they surpassed the Robeson upper bound for all gas pairs.