Modeling and optimization of sweeping gas membrane distillation

Abstract

A central compositional orthogonal design has been applied for modeling and optimization of sweeping gas membrane distillation process. The effects of the operational parameters, liquid temperature, gas temperature, liquid flow rate and gas flow rate and their binary interactions on the membrane distillate flux (i.e. permeate flux) have been investigated. The developed model has been statistically validated by analysis of variance and further used to predict the distillate flux. The optimum operating conditions have been determined by Monte Carlo method finding a liquid inlet temperature of 71.6 degrees C, a gas inlet temperature of 17.3 degrees C, a water circulation velocity of 0.16 m/s (i.e. flow rate of 165 L/h) and a gas circulation velocity of 211 m/s (i.e. flow rate of 36 L/min). Under these optimal conditions the measured water distillate flux was 2.789 x 10(-3) kg/m(2).s, while the predicted distillate flux was only 2% higher confirming the developed model. Desalination experiments were performed under the optimum conditions using a feed 30 g/L NaCl solution and Mediterranean seawater. The obtained distillate fluxes were 2.31 x 10(-3) kg/m(2).s and 2.05 x 10(-3) kg/m(2).s for NaCl solution and seawater, respectively; and the salt rejection factors were 99.94% for 30 g/L NaCl solution and 99.48% for seawater.