Originally published 21 April 2015 on IHS Engineering360.
The term “chlor-alkali” refers to the manufacturing of chlorine (chlor) and a strong base, typically sodium hydroxide (alkali), two chemicals that are simultaneously produced by the electrolysis of brine (a solution of salt in water). These two chemicals are the main products of the chlor-alkali industry. Both are produced in a fixed stoichiometric ratio: for each unit of chlorine produced, 1.13 units of sodium hydroxide are produced.
In terms of chlor-alkali production, energy consumption has always been a strong driver to cost. It is among the highest energy consuming processes due to its dependency on energy intensive electrochemical technology. The cost of electricity makes up around 40-60% of the operating cash costs, and therefore has an influence in the production cycle.
IHS Quarterly recently reported that, “one plant can consume as much electricity as a small country” and energy can account for up to 70% of chlor-alkali variable costs. As a result, engineers have been trying to lower that figure while maintaining production requirements in order to increase overall profit.
Membrane cell technology was found to lower operating costs by an average of around 6%. However, additional caustic soda conccentration steps must be provided, leading to additional energy (steam) requirements.
During the last half of the 19th century, chlorine was almost solely used in the textile and paper industry. Today, that industry amounts to roughly 3% of chlorine demand. The main end-use is for chlorinated compounds such as PVC that account for roughly 34% of the market. Further uses are in water treatment, chlorinated intermediates, inorganic and organic chemicals, among others.
“The ratio of chlorine demand between end users varies greatly between regions,” says George Eisenhauer, Director at IHS Chemicals. “Unlike chlorine, sodium hydroxide (also known as caustic soda) has multiple end uses, with none dominant like PVC.”
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IHS Engineering360, April 2015.