Desalination using supported liquid membranes

Abstract

In the present work, the supported liquid membrane (SLM) technique has been applied to the desalination of saline water. A simple apparatus designed and constructed in our lab was used to conduct the experiments. Various factors that would affect the degree of desalination were studied and these were: type of organic membrane liquid (ML), quantity of ML (i.e. its thickness), presence of emulsifier or mobile carrier (MC) in the ML, concentration of MC in ML, presence of polyelectrolyte (sequestrant) in the receptor phase and presence or absence of magnetic stirring. The volume ratio of donor phase to receptor phase was kept constant at 4:1 and the concentration of sodium chloride solution in the donor phase (simulated seawater) ranged between 36 and 39 g/L. Cellophane constituted the support for the ML. A previous work on desalination by emulsion liquid membranes (ELMs) has proven to be a successful one stage operation with a percent water recovery of 98% and in which >99% of the salt (equivalent to seawater concentration) is removed in only a few minutes. Accordingly, a preliminary work on desalination using SLM technique was attempted and evaluated and compared to the aforementioned ELM technique. The most important findings emphasized the importance of MC in the ML due to the enhancement of mass transfer through the liquid membrane (LM) and the importance of stirring in promoting mass stransfer by minimizing the boundary layer adjacent to the cellophane support. In addition, an optimum concentration of MC existed in the LM. However, desalination using SLMs is much slower than ELMs due to a much lower surface mass transfer area of the former compared with the ELMs. On the other hand, SLMs enable various factors that would affect the process of desalination to be conducted by simple means with a target of optimizing the process.