Essay On Membrane Distillation

- Chapter Two

Theoretical Aspects and Literature Review

2.1 Introduction

Membrane distillation (MD) is considered a promising technology for separations that are accomplished by classical separation processes such as distillation or reverse osmosis (RO). As a common separation process , Membrane distillation has been the subject of global academic studies. It is consider to be a low cost separation process that can utilize poor quality waste and/or different energy sources such as geothermal and solar energy. [El-Bourawi et al., 2006](1)

2.2 Membrane distillation fundamentals:-

MD is a thermally driven process, in which water vapor transport occurs through a non-wetted porous hydrophobic membrane. The driving force for Membrane distillation process is given by the vapor pressure gradient which is created by a temperature difference across the membrane. MD operating at lower temperatures compeered to conventional distillation. Also, the hydrostatic pressure in MD is less than that used in pressure-driven processes such as (RO).[ Alkhudhiri et al.,

On the other hand, to avoid wettability of membrane pores, the pore size must be as small as possible leading to a conflict with the requirement of higher MD permeability. An optimum value is needed to be determined for each MD application depending on the type of the feed solution to be treated [El-Bourawi et al., 2006]1. To prevent wetting phenomenon, the upper bound for the average pore diameter of the membranes used in MD is 0.5µm. On the other hand, from the mass transfer point of view, a bigger pore size is desirable especially for Knudsen diffusion and viscous flow mass transfer dominant systems. Therefore, a sharp pore size distribution between 0.3 and 0.5µm may be set as an objective to be achieved for membranes used in MD[ Bonyadi and Chung,