Effects of emulsion properties on recovering butyl acetate from wastewater of penicillin plant by solvent sublation

The separation efficiency of butyl acetate (BA) from the wastewater of penicillin plant can be improved by solvent sublation. The mechanism of enrichment of BA at the air–water interface is important to the separation process. The predicted adsorption isotherm from BA solution showed that a molecular adsorption mechanism of BA on the air–water interface alone could not elucidate the high sublation efficiency. The physicochemical properties of the wastewater should be considered to be different from those of BA solution. The stability and microstructure of the wastewater emulsion were studied by both optical microscopy and freeze fracture transmission electron microscopy (FFTEM). The agitated wastewater was relatively an unstable emulsion. It could be mainly stratified into three layers with different microstructures: the upper cream layer, the middle layer and the bottom layer. The upper cream layer was a BA-enriched layer verified by FTIR and gas chromatography. In combination of the physicochemical properties, the emulsion properties played an important role in improving the sublation efficiency. The emulsified BA droplets could be effectively enriched into the organic layer by different mechanisms during the sublation.