Removal of volatile organic compounds from aqueous solutions applying thermally driven membrane processes. 2. Air gap membrane distillation

Abstract

Air gap membrane distillation technique (AGMD) was applied for removal of ethanol, butanol and acetone–butanol–ethanol mixture from water. The influence of various parameters (feed temperature, cooling wall temperature) on pure water transport in AGMD was determined and the efficiency of organic solvents removal from water through two porous membranes (PTFE and PP) was investigated in the detail.Selectivity of organic components recovery did not change significantly with an increase of feed temperature from 41°C to 63°C in case of AGMD applied for ethanol and butanol recovery, however significantly higher fluxes were obtained at higher feed temperature. Slightly higher fluxes were obtained during experiments performed with PTFE membrane comparing with PP one.It was found that both PTFE and PP membranes are wetted during AGMD process of water–butanol feed mixture if organic concentration exceeds 2.5wt% (PTFE) and 1wt% (PP) at 63°C feed temperature. This fact limits the possibility of wider AGMD application in organic solvent recovery.The comparison of the efficiency of AGMD with the efficiency of thermopervaporation (TPV) was also performed. In case of 1wt% ethanol feed mixture it was found that AGMD seems to be more suitable due to higher process separation index value (PSI in the range of 6kgm−2h−1) than in the case of TPV (PSI in the range of 3kgm−2h−1). On the contrary, in the case of water–butanol or water–ABE systems TPV is much more efficient method for organics recovery from aqueous mixtures than AGMD. In contact with 3wt% ABE mixture PSI is equal to 28 and 9kgm−2h−1 for TPV and AGMD processes, respectively.