Membrane Separation of Cyclic Siloxanes from Silicone Fluid

Abstract

Conventional techniques for the removal of small siloxane molecules (either cyclic species, such as D4 or linear siloxanes, known as L2-L6) from silicone oils include air stripping and volatilization. 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 achieving high-purity separation of D4 (octamethylcyclotetrasiloxane), 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. The results presented here suggest that PDMS membranes may serve as an industrially scalable low-cost alternative to silicone fluid purification.

Keywords: cyclic siloxanes, silicone fluid mixture, solution-diffusion model, PDMS membrane