(154f) Experimental Validation of Membrane-Vapor-Extraction Separation Process

Our group recently proposed a novel separation process called membrane vapor extraction (MVE), to separate dilute (bio)solutes from an aqueous fermentation broths [1]. In MVE, semi-volatile aqueous solutes vaporize at the upstream side of a membrane, diffuse in through the membrane pores, and subsequently dissolve into a nonpolar solvent highly favorable to the solutes but not to water. Since the two liquids are not in contact, MVE avoids formation of difficult to separate microemulsions.

Design analysis of a 1.5-m long, 30-m² membrane-area countercurrent MVE unit for processing 2-wt. % aqueous butanol by a prototype solvent (dodecane) at 40 °C demonstrated over 90 % recovery of the feel butanol with essentially no water loss [1]. The separation factor is well over 1000. Our initial design study, however, gave no experimental evidence for the calculated MVE-unit performance [1].

The present study experimentally validates the MVE process. A 6-cm wide by 10-cm long Teflon channel-flow cell with 0.1 mm gap thicknesses permits countercurrent (or concurrent) extraction studies. The flow cell is operated in the transient mode since axial concentration changes are minimal. 0.2-µm pore-diameter VersaporeR membranes (Pall Corporation, New York) are both hydrophobic (water contact angle = 128°) and oleophobic (dodecane contact angle = 105°). Accordingly, VersaporeR membranes are nonwetting to both feed and solvent, as required for MVE.

Figure 1 shows a typical result for extraction of 2-wt. % aqueous butanol into dodecane at 40 °C. Filled triangles illustrate loss of butanol from the aqueous feed stream, whereas filled circles demonstrate absorption of butanol into the countercurrent dodecane solvent stream. Solid lines represent a priori predictions using mass transfer coefficients from the Graetz-Lévéque analysis for laminar channel flow. The excellent agreemen confirms that vapor-phase diffusion resistance is negligible in the MVE-membrane pores. We present similar results for different operating conditions in MVE including feed concentration, temperature, and flow rate. In consort with the initial design analysis [1], our new experimental results confirm the viability of MVE to remove and recover dilute aqueous (bio)solutes with minimal energy expenditure.

1.  D.E. Liu, C. Cerretani, R. Telles, A.P. Scheer, S. Sciamana, P.F. Bryan, C.J. Radke, and J.M. Prausnitz, “Analysis of Countercurrent Membrane Vapor Extraction of a Dilute Aqueous Biosolute,” AIChE Journal, 61(9), 2795-2809 (2015).

Figure 1. Transient extraction of 2-wt % aqueous butanol (filled triangles) into dodecane (filled circles) using countercurrent MVE at 40 °C. Solid lines are predicted a priori with Graetz-Lévéque mass transfer resistances and a measured partition coefficient.