Effect of plasticizers on the formation of silver nanoparticles in polymer electrolyte membranes for olefin/paraffin separation

Abstract

The effect of plasticizers such as dioctyl phthalate, diphenyl phthalate, dioctyl terephthalate, ethylene carbonate, glycerol, and sucrose on the performance and stability of polymer electrolyte membranes consisting of AgBF4 and poly(vinylpyrrolidone) (PVP) or poly(2-ethyl-2-oxazoline) (POZ) has been investigated for the separation of propylene/propane gas mixtures. The mixed gas permeances and selectivities for propylene over propane on AgBF4-PVP and AgBF4-POZ membranes without a plasticizer continuously decreased with time due to the reduction of silver ions in the membrane. Reduction of silver ions to silver nanoparticles in AgBF4-PVP membrane was confirmed by transmission electron microscopic (TEM) analysis. Among the plasticizers tested, the presence of dioctyl or diphenyl phthalate was found to improve the stability and performance of the membranes significantly. On the other hand, the performance of the membranes containing glycerol or sucrose as a plasticizer rapidly deteriorated even faster than that of the membranes without a plasticizer. TEM analysis of the membranes shows that the rate of silver nanoparticle formation is greatly reduced by the addition of a phthalate, but accelerated by the presence of glycerol.