Sulfur Trioxide Liquid or Gas

Both 25% and 65% oleum were introduced into chemical processing in search of stronger sulfonating agents. However, with the sulfonation process SO3 was used and the weak sulfuric acid by-product required disposal as a waste product. Enviromnental consideration led to large effluent treatment plants (ETPs) with consumption of lime in large quantities. As a result, heaps of waste gypsum were formed and posed solid waste disposal problem. 

Due to environmental and economic considerations, the use of pure sulfur trioxide in gaseous or liquid form was investigated. The main consideration was to tame the exothermic reaction and avoid unwanted co-products. 

In 1960 in India, the production of liquid sulfur trioxide was less than 100 tonnes per annum (TPA). Today there are plants in India which produce more than 100 TPD of liquid or gaseous sulfur trioxide with purity of 99-99.5%. The total production of pure sulfur trioxide in India can be estimated as about 300,000 MTs in the year 2003 60% of the production is for captive use. 

The manufacture of liquid or gaseous SO3 is carried out by boiling 25-32% oleum as in the case of manufacturing 65% oleum. The sulfur trioxide can be liquefied by condensing at 43-45 °C. Care should be taken to prevent any moisture ingress in the plant as it may cause serious operating problems. 

The liquefied SO3 is then taken to a product storage tank from which tankers are filled using intermediate lorry filling tanks. 

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