Pervaporation study for the dehydration of tetrahydrofuran-water mixtures by polymeric and ceramic membranes

Abstract

Pervaporation technology can effectively separate a tetrahydrofuran (THF) solvent-water waste stream at an azeotropic concentration. The performance of a Sulzer® 2210 polyvinyl alcohol (PVA) membrane and a Pervatech BV® silica membrane were studied, as the operating variables feed temperature and permeate pressure, were varied. The silica membrane was found to exhibit a flux of almost double that of the PVA membrane, but both membranes had comparable separation ability in purifying the solvent-water mixture. At benchmark feed conditions of 96 wt% THF and 4 wt% water, 50°C and 10 torr permeate pressure, the silica membrane flux was 0.276 kg/m²hr and selectivity was 365. For both membranes, flux was found to increase at an exponential rate as the feed temperature increased from 20 to 60°C. The flux through the silica membrane increases at a 6% faster rate than the PVA membrane. Flux decreased as permeate pressure was increased from 5 to 25 torr for both membranes. The amount of water in the permeate decreased exponentially as the permeate pressure was increased, but increased linearly with increasing temperature. Optimum conditions for flux and selectivity are at low permeate pressure and high feed temperature. When a small amount of salt is added to the feed solution, an increase in flux is observed. Overall models for flux and permeate concentration were created from the experimental data. The models were used to predict scale-up performance in separating an azeotropic feed waste to produce dehydrated THF solvent for reuse and a permeate stream with a dilute THF concentration.

Keywords:

• Pervaporation
• solvent dehydration
• tetrahydrofuran
• polyvinyl alcohol membrane

Acknowledgments

Partial support for this research has been provided by a grant from the U.S. Environmental Protection Agency (NP 97257006-0). Support and advice of our industrial partners at Bristol-Myers Squibb, Drs. San Kiang, Thomas LaPorte, Lori Spangler, and Stephen Taylor are also acknowledged. The following students are thanked for their assistance with the experimental studies; Scott Barnes, Daniel Duffield and John Hekl.