Example – the chlor‑alkali process

Generic product activity or name
chlor-alkali process.

Cl2, NaOH, chlorine, sodium hydroxide.

Context and background
The chlor-alkali industry uses brine (salt water) to produce chlorine, sodium hydroxide (NaOH or caustic soda), and hydrogen. An electric current is passed through the brine, to form hydrogen gas at the negative electrode and chlorine gas at the positive electrode, leaving a solution of sodium hydroxide.

The balanced process looks like this:
 2NaCl +2H2O => 2NaOH + Cl2 + H2

Presentation of example
The above activity has only one product without an alternative production route, namely chlorine, which cannot be easily stored and is typically sold locally, and for which the chlor-alkali process is the practically exclusive production route. While sodium hydroxide is currently also produced exclusively from the chlor-alkali process, it is a more flexible product that can be stored and transported over long distances and there are both a well-known substitute (namely sodium carbonate, applicable in pulp and paper, water treatment, and certain chemical sectors where it is used as a neutralising agent) and an alternative production route (the caustification process, where NaOH is produced from lime and soda, which however is currently uneconomical due to the ample supply of NaOH caused by the current global increase in demand for chlorine). When market conditions change, the existence of the two alternatives (substitution and caustification) will provide both a floor and a ceiling on the price of NaOH (Wesnæs and Weidema 2006).

The third co-product, hydrogen, is produced by the activity in relatively small quantities (27 g for every kg of chlorine) providing only approximately 3% of the world market for hydrogen. The main production route for hydrogen is steam reforming of natural gas and this is the most competitive process to cover a change in demand for hydrogen.

Thus, we can conclude that both sodium hydroxide and hydrogen are dependent co-products for the chlor-alkali process.

Information sources used
To thoroughly investigate the markets for chemical products Wesnæs and Weidema (2006) contacted one of the world’s leading marketing consultancies specializing in the bulk chemicals of petrochemicals and plastics industries.

Wesnæs M, Weidema B P (2006). Long-term market reactions to changes in demand for NaOH. Study for Novozymes. Copenhagen: 2.‑0 LCA consultants. http://lca-net.com/p/1014

Author of this example
Bo Weidema


How to reference this
Weidema B P (2014), Example –the chlor-alkali process. Version:  2014-10-08  www.consequential-lca.org