Experimental and theoretical studies of biopolymers on the efficient CO2/CH4 separation of thin-film Pebax®1657 membrane

Abstract

Modified polymeric membranes consisting of a polyethersulfone (PES) support layer and a thin selective Pebax®1657 layer blended with biopolymers (sodium alginate and sodium carboxymethylcellulose) were developed to increase the separation efficiency of CO2 from CH4. The experimental and theoretical investigations were carried out to evaluate the influence of biopolymers loading on the gas separation performance of modified membranes. High CO2 solubility of biopolymers and their proper compatibility with Pebax®1657 were confirmed by Monte Carlo and molecular dynamics simulation, respectively. The double-layer structure of the membranes, biopolymer effect on crystalline phase, and thermal properties of the selective layer were investigated by FE-SEM, XRD, and TGA-DTG-DSC analysis, respectively. The use of alginate and carboxymethylcellulose in the Pebax layer increased CO2 permeability from about 21 Barrer to about 37 and 52 Barrer at 4 bar, respectively. In this regards, the CO2/CH4 ideal selectivity improved from 22 to 31 around and 47. Also, the gas permeability increased in all membranes by increasing feed pressure in the rage of 4-7 bar. For the alginate-modified membrane, the CO2/CH4 ideal selectivity showed an ascending trend by increasing pressure and reached 40.6 at 7 bar while the ideal selectivity of the carboxymethylcellulose-modified membrane decreased by increasing feed pressure.