Membrane processes energy saving

Pervaporation is a membrane separation process where the liquid feed mixture is in contact with the membrane in the upstream under atmospheric pressure and permeate is removed from the downstream as vapor by vacuum or a swept inert gas. Most of the research efforts of the pervaporation have concentrated on the separation of alcohol-water system [1-20] but the separation of acetic acid-water mixtures has received relatively little attention [21-34]. Acetic acid is an important basic chemical in the industry ranking among the top 20 organic intermediates. Because of the small differences in the volatility s of water and acetic acid in dilute aqueous solutions, azeotropic distillation is used instead of normal binary distillation so that the process is an energy intensive process. From this point of view, the pervaporation separation of acetic acid-water mixtures can be one of the alternate processes for saving energy. 

Solvent-resistant nanofiltration and pervaporation are undoubtedly the membrane processes needed for a totally new approach in the chemical process industry, the pharmaceutical industry and similar industrial activities. This is generally referred to as process intensification and should allow energy savings, safer production, improved cost efficiency, and allow new separations to be carried out. 

Source Adapted from Pressurized ozone membrane ultrafiltration/nanofiltration methodology for TDS removal in the paper mill process water for energy saving, production efficiency, and environmental benefits. Available at http /www.recycle.com/linpac-nice3/documents/doefinalreport.pdf. 

Liquid membrane separation combines the solvent extraction and stripping processes (re-extraction) in a single step. The great potential for energy saving, low capital and operating cost, and the possibility to use expensive extractants, due to the small amounts of the membrane phase, make SLMs an area deserving special attention. 

A new process using ion exchange membranes has recently gained wide acceptance in the chlor-alkali industry from the viewpoint of energy saving and environmental control. One of the important breakthroughs for this process was to develop a membrane of high performance. 

Membrane-based separation processes are today finding widespread, and ever increasing use in the petrochemical, food and pharmaceutical industries, in biotechnology, and in a variety of environmental applications, including the treatment of contaminated air and water streams. The most direct advantages of membrane separation processes, over their more conventional counterparts (adsorption, absorption, distillation, etc.), are reported to be energy savings, and a reduction in the initial capital investment required. 

The current efficiency of acid/base generation and the purity of the acid and base made with bipolar membranes drops off as concentrations increase, because Donnan exclusion diminishes with increasing solution concentrations. Further, the production rate is limited by the rate of diffusion of water into the bipolar membrane. Nevertheless, there are substantial advantages to the process. Since there are no gases evolved at the bipolar membranes, the energy associated with gas evolution is saved, and the power consumption is about half that of electrolytic cells. Compared to the electrodes used in conventional electrolytic cells, the bipolar membranes are inexpensive. Where dilute (e.g., 1 N) acids or bases are needed, bipolar membranes offer the prospect of low cost and minimum unwanted by-products. 

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