Kinetic analysis of the vacuum membrane distillation of chloroform from aqueous solutions

Abstract

In this work, the vacuum membrane distillation (VMD) technology has been applied to the removal of chloroform from a dilute aqueous stream. Microporous polypropylene hollow fiber membranes were used to immobilize the liquid–vapor interface. The influence of the following operational variables was experimentally studied: (i) initial chloroform concentration in the feed (212–2012 mg/l), (ii) feed flow rate in the laminar flow regime (0.23–0.98 l/min) and in the transition to the turbulent flow regime (2.7–8 l/min), (iii) temperature (5–47.5°C) and vacuum pressure in the permeate side (7 and 14 mm Hg). The mathematical model proposed to describe the kinetic results includes the mass balance to the feed tank and the mass balance to the VMD module. In the laminar regime the solution of the continuity mass conservation equation makes the diffusion coefficient of chloroform in the aqueous phase the only parameter needed to describe the separation rates. In the turbulent flow regime, a macroscopic mass balance including an overall mass transfer coefficient that accounts both for liquid film diffusion and membrane mass transport was developed. It was found that only at higher Reynolds numbers within the turbulent flow regime the resistance to mass transfer in the membrane had influence on the overall mass transfer coefficient.