Membrane separation of cyclic siloxanes from silicone fluid

Conventional techniques for the removal of silicone oils from small siloxane molecules (either cyclic species, such as D4 or linear siloxanes, known as L2-L6) include stripping and adsorption. Membrane separations could serve as low-energy alternatives or complements to these industrial separation techniques to reduce the overall process energy demand since they do not involve a phase change. This paper presents polymeric membranes as materials for purifying D4 (octamethylcyclotetrasiloxane) rich feed of 90% D4 from a silicone fluid mixture. The transport properties (diffusion, sorption, and permeation) are studied experimentally to understand the driving force and mechanism for the separation related to the properties of the penetrant molecules, such as molecular size. These parameters are utilized in the solution-diffusion model to predict the permeation rates and separation performance of PDMS membranes for the siloxane-silicone fluid mixtures that are rich in the small siloxane. The results presented here suggest that PDMS membranes may serve as an industrially scalable low-cost alternative to small siloxane purification.