Separation of ethylene/ethane and propylene/propane by cellulose acetate–silica nanocomposite membranes

The separation of olefin–paraffin mixtures is one of the most important and expensive processes in petrochemical industries. In this research, the performance of cellulose acetate–silica nanocomposite membranes in the separation of ethylene/ethane and propylene/propane has been studied. Silica nanoparticles were prepared via hydrolysis of tetraethoxysilane (TEOS). Membranes were prepared by the solution-casting method. The prepared membranes were characterized using FT-IR, SEM and TGA analyses. Pure gas permeation experiments were performed by the constant volume/variable pressure method at 2 bar feed absolute pressure and 35 °C. The results showed the permeability of ethylene and propylene increased from 0.052 barrer and 0.046 barrer in pure cellulose acetate to 0.11 and 0.098 barrer in the composite membrane containing 30 wt% silica particles, respectively. The comparison of the selectivities of C2H4/C2H6 and C3H6/C3H8 indicates an increase from 2.16 and 2.55 in pure cellulose acetate to 4.07 and 6.12 in composite membrane containing 30 wt% silica particles. The diffusion coefficients of prepared hybrid membranes were determined by the time lag method. The solubility coefficient was calculated indirectly from permeability and diffusivity coefficients. The results showed an increase in the solubility coefficient and a decrease in the diffusion coefficient of gases while increasing the silica mass fraction. To investigate the possible plasticization phenomena, the effect of feed pressure on gas permeability and O2/N2 selectivity, before and after exposure of membranes with propylene, was studied. The results showed no plasticization effects up to 8 bar feed pressure.