by David Genders
Salt splitting is a relatively new technology dependent on the availability of modern membranes. Its development has usually been driven by one of two major factors, both environmentally based. The first is the desire to produce caustic soda without the co-production of chlorine, and the second is the increased cost of disposing of heavily laden salt solutions.
Caustic is in Demand
Caustic soda is produced in the USA at a rate of 14 million tons per year, almost entirely by the electrolysis of brine. In this process chlorine is produced at the anode and caustic soda at the cathode in stoichiometric quantities. There is a growing awareness of the need for new processes for the manufacture of high purity sodium hydroxide that do not lead to co-production of chlorine. This requirement exists because the chlorine and sodium hydroxide markets are rarely in balance.
Despite the high demand for chlorine in the last two years, it is still expected that environmental pressures on chlorine will lead to an increased demand for caustic over the coming decade. Predictions are for a long-term trend in which the demand for sodium hydroxide will outstrip that for chlorine.
Several present markets for chlorine are expected to experience significant downturns due to environmental pressures or concerns about health hazards; these include pulp and paper bleaching, fluorocarbons, water treatment and chlorinated hydrocarbons. At the same time, the demand for sodium hydroxide is predicted to continue to grow.
Another trend is towards modular plants that allow the manufacture of chemicals on various scales including generation on a relatively small scale at the site of use.