Effect of nonsolvent additive on the surface morphology and the gas separation performance of poly(2,6-dimethyl-1,4-phenylene)oxide membranes

Abstract Integrally skinned asymmetric membranes were prepared from poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) using different nonsolvent additives. These nonsolvent additives consisted of branched and linear alcohols ranging from C 3 to C 10 . Permeation data of these membranes were obtained from a constant pressure permeation system for pure gases of CO 2 , CH 4 , O 2 and N 2 . An empirical correlation relating the pure gas permeance ratio of CO 2 /CH 4 and the structural components of the nonsolvent additives has been proposed. The membranes were characterized by atomic force microscope (AFM) and intrinsic viscosity measurements. It was observed that there were two types of surface morphologies: merged nodules and discrete nodules. The appearance of the nodules were reflected in the mean roughness data, R a . It was revealed that membranes with smaller and merged nodules resulted in higher pure gas permeance ratios for O 2 /N 2 and CO 2 /CH 4 with the exception of 3,5,5-trimethyl-1-hexanol and 3-ethyl-2,2-dimethyl-3-pentanol. The microscopic studies showed that the membranes containing discrete nodules resulted in lower pure gas permeance ratios for O 2 /N 2 and CO 2 /CH 4 . It was observed that nonsolvent additives that possess a long straight hydrocarbon chain such as 2-ethyl-1-hexanol, 1-octanol and 2-decanol produced the highest pure gas permeance ratios.