Mixed Matrix Silicone and Fluorosilicone/Zeolite 4A Membranes for Ethanol Dehydration by Pervaporation

Abstract

The ability of homogeneous and mixed matrix membranes prepared using standard silicone rubber, poly(dimethylsiloxane) (PDMS), and fluorosilicone rubber, poly(trifluoropropylmethylsiloxane) (PTFPMS), to dehydrate ethanol by pervaporation was evaluated. Although PDMS is generally considered to be the benchmark hydrophobic membrane material in pervaporation, water/ethanol molar permselectivity of a pure PDMS membrane was found to be 0.89 for a feed containing 80/20 w/w ethanol/water at 50°C, indicating a slight selectivity for water. Fluorinated groups in PTFPMS improved the water-ethanol permselectivity to 1.85, but decreased the water permeability from 9.7 × 10⁻¹² kmol · m/m² · s · kPa in PDMS to 5.1 × 10⁻¹² kmol · m/m² · s · kPa (29,000 and 15,200 Barrer, respectively). These water permeabilities are attractive, particularly since the rubbery materials should not experience the steep declines in water permeability observed with most standard dehydration membranes as water concentration in the feed decreases. However, the water selectivity is lower than desired for most applications. Particles of hydrophilic zeolite 4A were loaded into both PDMS and PTFPMS matrices in an effort to boost water selectivity and further improve water permeability. Water-ethanol permselectivities as high as 11.5 and water permeabilities as high as 23.2 × 10⁻¹² kmol · m/m² · s · kPa were observed for the PTFPMS/zeolite 4A mixed matrix membranes−6 times higher than for the unfilled PTFPMS membrane.

Keywords:

• dehydration
• fluorosilicone
• mixed matrix
• pervaporation

ACKNOWLEDGEMENTS

GL thanks the U.S. National Research Council for the postdoctoral research work at EPA, Cincinnati. The authors thank Yonggui Shan, Vasudevan Namboodiri, Franklin Alvarez, Raghuraman Venkatapathy, and Richard Meier for analytical/material characterization assistance and helpful discussions.

Notes

*as reported by the manufacturer.