Application of Bipolar Membranes

One interesting application of bipolar membranes is the production of caustic soda. Currently, caustic soda is produced as a co-product of the products of chlorine by electrolysis of salt. The worldwide demand for polyvinyl chloride and other chlorinated hydrocarbons has led to the development of a large market for chlorine. Because of environmental problems caused by chlorinated hydrocarbons and the disposal of polyvinyl chloride wastes, the demand for chlorine is steadily decreasing, however, and it can be expected that the demand for caustic soda will soon exceed that produced in the chlorine alkaline electrolysis. Thus interest in alternative processes for obtaining caustic soda is increasing. Electrodialytic water dissociation with bipolar membranes is one of the more promising techniques for the future large scale economic production of caustic soda. However, today's bipolar membranes produce caustic soda with some salt contamination. The production of NaOH and H2SO4 from the corresponding salts has been investigated in great detail. Test results obtained in laboratory studies are shown in Figure 4. These tests were carried out with a 1 molL"1 solution Na2SO4 feed at room temperature and an applied current density of 0.1 A cm"2. The test results indicate that up to three normal acid and base solutions can be achieved with a current utilization of 60-70%. However the produced acid and base are contaminated by salt and the salt contamination increases with increasing acid and base concentrations due to decreasing selectivity of the bipolar membrane with increasing acid or base concentrations. Salt concentration can reach values in excess of 0.03 mol at 4 molar base or acid concentrations. To improve the overall efficiency of the electrodialytic dissociation processes and to obtain less salt contamination in the acids and base produced, better proton-blocking membranes have to be developed in addition to more selective bipolar membranes.

Fortunately, there are a large number of other potential applications of the electrodialytic water dissociation where the purity of the product, i.e. the produced acid or base, is not critical and traces of salts can be tolerated. Typical applications of bipolar membranes with large industrial relevance are:

• Recovery of acids and bases such as sulfuric, hydrochloric or hydrofluoric acid and sodium hydroxide from the salts generated in neutralization reactions

• The recovery of organic acids such as formic, acetic, citric, lactic and itaconic acid or certain amino acids from fermentation broths

• Adjustment of pH values in fermentation or chemical production processes without increasing the ion potential

• Regeneration of H2SO4 and NaOH from Na2SO4 obtained in industrial effluents, for example, in the production of viscose or regenerated cellulose

• Regeneration of acids and bases from scrubbers used to remove SO2, NOx from contaminated air streams.

This list of potential applications of the elec-trodialytic water dissociation with bipolar membranes is not complete and as more efficient bipolar membranes become available, more applications will certainly be identified. In this outline three typical examples for the use of bipolar membranes are described in more detail.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment