ENERGY EFFICIENT MEMBRANE SEPARATION PROCESS FOR CONCENTRATION OF AN AQUEOUS SOLUTION

Abstract

In a Mcmbr,=4ne Separation Process, membrane is used as a barrier which separates two fluids. It permits transfer of some compcnants end not of other through it. Transfer through membranes tk(-S piece by diffusion, e tor cL.ss -)f mass transfer which occurs es (-2 movement.of individuol molecule. This mov,,„ nt may be accelerated by an clectirc field, concentration, thermal or pressure gradient or by othk r means. Technological advances developed over the last twenty yesrs enable engineers to perform the venous membrane separation process like reverse osmsi a (RO) electrodialysi s (ED) and ultrafiltration (UF). These three technologies :involve:- no phase change and thir energy consumption is very low. For excrnple to ev7-porati.:, water in at‘simpie,1:single—effect evaporater 1.,cluiris an energy, input of approximately 2260 KJ/kg. In contrast, a osmosAs system operating at 68 atm. with 23 KJ electric input/kg perm ate which is about 1/100.6f energy input in a single effect evaporator and 1/10 of the energy required by the more complex enc,,roy efficient evaporations schemes of multiple effect and vapour recompression single effect evaporator. A mathematical model is digitilly simulated to study the effect of concentration, pressure and temperature on membrane permeation with rccirculation of permeate using stepwise numerical integration technique for NaC1 solution using cellusole acetate membrane. Simulated digital )arogram has bern executed on a large mEmory computer, DEC 20 SYSTEM. In this study,' feed concentration changes from .002 gm-mol/cm3 to .004 gm-mol/cm3,prossurc changes from 10 atm. to 40 atm. and te,,perFture changes from 25°C to 40°C. From the study it is found that the separation through membrane is effected by inital feed concentration and pressure. It can be concluded from the results of • this study that in case the aim is to get potable water fromk:ifacidsh or sea water the permeate is the desirable product where pure water with negligible quanitity of solute is obtained. However, if the aim is to concentrat-an aqueous solution the fed side beco,ncs the desirable product as there is large amount of water rejection through membrane to permeate side with very small amount of solute going in the pormepte. From this study it is also found that it may be adventagecus to oper-,+e low feed concentration, higher pressure and at room temperature.