Comparative performance of various plasma polysiloxane films for the pervaporative recovery of organics from aqueous streams

Thin SiOxCyHz film membranes were deposited from two different organosilicon precursors, one cyclic and one linear, in a low-frequency plasma polymerisation process. The ability of the films for effective recovery of various organic contaminants from aqueous waste was tested using the process of pervaporation. Four separate organic components, phenol, chloroform, pyridine and methylisobutylketone (MIBK), each representative of an industrially significant family of chemicals, were chosen for evaluation. Trends between the pervaporation performances of plasma polysiloxane membranes and the composite plasma parameter V/FM (V: input voltage; F: monomer flow rate; M: monomer molecular weight) were found. Pervaporation measurements reveal that polysiloxane membranes synthesised by the plasma deposition process are sufficiently permeable for the mass transfer boundary layer above the membrane to be dominant. The permeability of plasma membranes formed from cyclic octamethylcyclotetrasiloxane were up to an order of magnitude more permeable than those formed from linear hexamethyldisiloxane. Future work should involve vapour permeation.