This paper reported on an extensive study of pervaporation, with the goal of establishing this membrane technology as a clean process for the recovery of volatile organic solvents from wastewater. A synthetic mixture containing n-butanol, dichloromethane and sodium chloride was studied, representing a discharge from the fine chemical sector. This investigation suggests that, by applying subsequent pervaporation stages of hydrophobic followed by hydrophilic membranes, this hazardous and complex wastewater can be transformed into a resource. With the two-stage process the quarternary mixture was separated into a concentrate of organic solvents, brine and an aqueous system.
The reported work indicated that the removal of n-butanol and dichloromethane from mixtures containing sodium chloride was better conducted at high temperatures. The pervaporation of the mixtures using PERTHESE® 500-1 membrane resulted in permeates more enriched in the organic solvents compared to the pervaporation using CMX-GF-010-D. However, the latter exhibited higher fluxes. This work also concluded the existence of the salting out phenomena when the PERTHESE® 500-1 membrane was used.
The dehydration of the organic solvents using the PVA-TiO2 membrane was best conducted at a feed temperature of 49 °C and at the following initial feed concentrations: water 6.64 wt%, dichloromethane 41 wt% and n-butanol 52.4 wt% in order to obtain a permeate with the minimum amount of VOCs.
The stream containing the organic solvents may be further separated by distillation, as n-butanol and dichloromethane have different boiling points, to be re-used internally or by another factory. Additional processes could be considered for the treatment of the resulting brine and aqueous system, so the recovered water may be further utilized for industrial processes or environmental applications.
While further investigation would be needed to establish the applicability of this proposed process in industrial scale applications, the results achieved in laboratory scale experiments demonstrated the potential of pervaporation as a viable wastewater management option for the recovery of VOCs. The amount of effluent to be treated and the high volatility of dichloromethane may limit the large-scale use of this technology. Yet we would like to reiterate the key notion that there is a place and need for a paradigm change in viewing even hazardous wastes as potential resources.