Optimization of multicomponent pervaporation for removal of volatile organic compounds from water

Abstract

Optimal operation of a hollow fiber membrane module for pervaporative removal of multicomponent volatile organic compounds (VOCs) from wastewater was studied. A shell-and-tube heat-exchange ttype of hollow fiber module was considered for treatment of a wastewater containing toluene, trichloroethane (TCE) and methylene chloride. Three kinds of membranes, i.e., poly (dimethylsiloxane) (PDMS), polyether- block-polyamides (PEBA) and polyurethane (PUR) membranes, were studied. A mathematical model of the module was developed. The flux equations of the model were derived using mass transfer coefficient as described in our previous study. A cost model of the system was used to study the effect of different process and design variables on annual treatment cost. The effects of multicomponent feed mixtures, liquid boundary layer mass transfer resistance, and downstream pressure on the module performance and process economics were studied. A multidimensional optimization technique was used to determine the operation conditions for minimum cost. The sensitivity of the operation cost with respect to different process variables was also studied. The annual treatment cost was found to be relatively insensitive to the downstream pressure in the low pressure iange (for example, 0–2000 Pa for toluene removal, 0–3000 Pa for TCE removal and 0–1500 Pa for methylene chloride removal). The optimal downstream pressure increased with the increase of Henry's law constant of the compounds. The capital cost was found to be dominant in the total treatment cost at laminar flow regime, while the operating cost is diminant cost at turbulent flow regime.