From waste treatment to resource efficiency in the chemical industry: recovery of organic solvents from waters containing electrolytes by evaporation

Organic solvents in chemical industry wastewaters are not only a pollution and health problem but also a sign of inefficient use of resources. This paper reports a methodology based on pervaporation, using first hydrophobic then hydrophilic membranes, for the separation of n-butanol and dichloromethane from sodium chloride containing aqueous mixtures into water, brine and a concentrate of organic solvents. The aim of this research was to study the efficiency of two hydrophobic and one hydrophilic membranes for the recovery of the organic solvents.

The separation of organic solvents from aqueous mixtures was conducted using CMX-GF-010-D (Celfa AG, Switzerland) and PERTHESE® 500-1 (Perouse Plastic, France) membranes, and was promoted by high temperatures. The addition of sodium chloride did not affect the permeation of the organic solvents through the CMX-GF-010-D membrane while the salting out phenomena was observed when the PERTHESE® 500-1 membrane was used.

The dehydration was conducted using a polyvinyl alcohol and titanium dioxide membrane on a support of polyacrylonitrile and polyphenylene sulfide (supplied by Helmholtz-Zentrum Geesthacht Zentrum für Material und Küstenforschung GmbH, Germany). The membrane showed impermeable features towards dichloromethane in the studied conditions. At the optimal dehydration conditions the concentration of water was 97.6 ± 0.1 %wt and the n-butanol content was 2.42 ± 0.13 %wt.

Finally the article calls for a paradigm change, to view organic solvents in wastewaters as resources to be recovered, rather than pollutants to be treated as such.