A Comparison of Caustic Soda and Soda Ash

Caustic soda and soda ash are used as a source of alkalinity in SO2 liquid scrubbing in exhaust gas produced from crude oil steam generators. It is used in thermally enhanced oil recovery. It was found that caustic was used more efficiently, thus allowing SO2 scrubber to run on a lower pH with higher SO2 removal capacity. Also, pH with higher So2 transfer capacity. Also, the overall economy likes the use of soda in this scouring application.  You can also buy caustic soda for making various products used in our daily activities such as soaps and detergents.


This study compared caustic soda and soda ash for scrubbing sulfur dioxide in flue gas streams from steam generators used in thermally enhanced oil recovery. Reaction products were measured and the scrubber chemistry was identified. Mass balances were made by varying chemical feed rates in order to determine SO2 recovery efficiencies and economics.

While different differences between caustic soda and ash soda were observed, both SO2 recovery and the economy supported the use of caustic soda, even though the cost per kilogram was higher. This is mainly due to differences in chemical reaction kinetics and the characteristics of handling two chemicals.

Scrubber chemistry

On the basis of pure stoichiometric, one kilogram of caustic soda is equivalent in alkalinity to 1.33 kilograms of soda. However, observed chemical consumption rates are non-stoichiometric. In reality, about two kilograms of soda ash are necessary to do the job of one kilogram of caustic. To understand this phenomenon, scrubber chemistry must be analyzed.