Polyalkylmethylsiloxanes composite membranes for hydrocarbon/methane separation: Eight component mixed-gas permeation properties

Abstract The separation of an eight component mixture of saturated and unsaturated hydrocarbons C1-C4 was studied for the first time using dense and composite membranes based on polyhexylmethylsiloxane (PHexMS), polyoctylmethylsiloxane (POMS), and polydecylmethylsiloxane (PDecMS). Dense and composite membranes based on PDMS were also prepared for comparison. Composite membranes were formed on two supports of ultra- and microfiltration type (UFFK and MFFK-1, respectively). Membranes with MFFK-1 support demonstrated a higher C2+/CH4 separation selectivity. An increase of the separation selectivity was observed for both dense and composite membranes with an increase in the length of the polyalkylmethylsiloxane side chain. The selectivity for n-butane/methane gas pair rises from 15.5 to 18.2 with the transition from hexyl to decyl substituent which is more than twice the separation selectivity for this gas pair for PDMS (7.6). An insignificant decrease of selectivity was observed with the transition from dense to composite membranes. For instance, n-butane/methane selectivity of the PDecMS/MFFK composite membrane didn’t exceed 17.0 and was reduced to 16.3 with the decrease of n-butane activity from 0.13 to 0.06 (a drop of the feed mixture pressure from 3 to 1 atm (gauge)). The separation of the gas mixture on MDK-3 (ZAO STC “Vladipor”, Russia) and POMS (HZG, Germany) commercial membranes was investigated. It was shown that PDecMS/MFFK exhibits a 40% higher selectivity for n-butane/methane gas pair (16.7) in comparison with MDK-3 (10.1) and a 20% higher selectivity in comparison with POMS–HZG (13.9).