OPTIMIZATION OF MULTICOMPONENT PERVAPORATION FOR REMOVAL OF VOLATILE,ORGANIC-COMPOUNDS FROM WATER

Optimal operation of a hollow fiber membrane module for pervaporative removal of multicomponent volatile organic compounds (VOCs) from waste water was studied. A shell-and-tube heat-exchanger type of hollow fibe r module was considered for treatment of a wastewater containing tolue ne, trichloroethane (TCE) and methylene chloride. Three kinds of membr anes, 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 we re derived using mass transfer coefficient as described in our previou s study. A cost model of the system was used to study the effect of di fferent process and design variables on annual treatment cost. The eff ects of multicomponent feed mixtures, liquid boundary layer mass trans fer resistance, and downstream pressure on the module performance and process economics were studied. A multidimensional optimization techni que was used to determine the operation conditions for minimum cost. T he 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 range (for example, 0-2000 Pa for toluene removal, 0-3000 Pa for TCE removal and 0-1500 Pa for methylene chloride removal). The optimal dow nstream pressure increased with the increase of Henry's law constant o f the compounds. The capital cost was found to be dominant in the tota l treatment cost at laminar flow regime, while the operating cost is d ominant cost at turbulent flow regime.