(653c) Modeling Multicomponent Gaseous Diffusion for Membrane Vapor Extraction

A novel separation process, membrane vapor extraction (MVE), has recently been proposed to separate dilute biosolutes from broth exiting a fermenter [1].  In MVE, volatile aqueous biosolutes in the broth vaporize at the upstream side of a membrane, diffuse through the membrane pores, and subsequently dissolve into a nonpolar solvent highly favorable to the solutes but not to water. For successful MVE design and implementation, vapor phase transport of biosolutes and water through the membrane pores must be understood physically.

Previously, we modeled gaseous flow in membrane pores of an MVE separation unit for recovering biobutanol from water using the traditional binary convective diffusion model (CDM) assuming a completely nonvolatile, and aqueous insoluble solvent [1,2]. Neither assumption is rigorous. Unfortunately, CDM is inapplicable for ternary and higher component systems.  Here we extend the binary analysis to a ternary system including finite solvent volatility and finite aqueous solubility using a modified dusty gas model (DGM) [3,4].  First, we establish that modified DGM for the binary system (i.e., nonvolatile solvent) is in accord with CDM for the butanol/water system. Next, we show that with finite solvent volatility butanol (and water) pore fluxes are impeded duty to collision with stagnant solvent vapor. Incorporating, in addition, solvent aqueous solubility in an MVE process leads to a countercurrent flux of solvent that further reduces butanol (and water) fluxes. For the solvent dodecane, little effect is found on the MVE unit performance. However, for strongly volatile and aqueous-soluble solvents, unit efficiency is compromised.

1. Liu, DE; Cerretani, C; Telles, R; Scheer, AP; Sciamanna, S; Bryan, PF; Radke, CJ; Prausnitz, JM. Analysis of Countercurrent Membrane Vapor Extraction of a Dilute Aqueous Biosolute. AIChE Journal, Accepted, 2015.
2. Bird, RB; Stewart, WE; Lightfoot, EN. Transport Phenomena. 2nd ed. New York, NY:Wiley, 2006; Chapter 17.
3. Veldsink, JW; van Damme, RMJ; Versteeg, GF; van Swaaij, WPM. The use of the dusty-gas model for the description of mass transport with chemical reaction in porous media. The Chemical Engineering Journal. 1995; 57:115-125.
4. Weber, AZ; Newman, J. Modeling gas-phase flow in porous media. International communications in heat and mass transfer. 2005; 32:855-860.