Development of soapstock processing technology to ensure waste-free and safe production

Abstract

Soapstock is a large-tonnage waste of the oil and fat industry, the disposal of which is environmentally hazardous. Processing of soapstock into industrially valuable products, in particular, fatty acids, is promising. The method for producing fatty acids, which consists in sequential saponification of soapstock with sodium hydroxide solution, salting out with sodium chloride and decomposition with sulfuric acid solution has been investigated. The feature of this work is the study of the effect of salting out conditions of saponified soapstock on the yield and neutralization number of fatty acids. As an experimental sample, sunflower soapstock was used, the indicators of which correspond to DSTU 5033 (CAS 68952-95-4): mass fraction of total fat – 67.3 %, fatty acids – 61.8 %, neutral fat – 5.5 %. Soapstock was subjected to preliminary saponification under the following conditions: duration 85 min., concentration of sodium hydroxide solution 45 %. After that, the saponified mass was subjected to salting out. The obtained core soap was decomposed with the sulfuric acid solution under the following conditions: temperature 90 °C, duration 40 min. Rational salting out conditions were determined: duration (80 min.) and sodium chloride concentration (16%). Under these conditions, the fatty acid yield is 95.0 %, the neutralization number is 194.8 mg KOH/g. The resulting fatty acids comply with DSTU 4860 (CAS 61788-66-7): the mass fraction of moisture and volatiles is 0.85 %, the mass fraction of total fat is 98.9 %, cleavage depth is 94.2 % oleic acid. This method of soapstock processing increases the fatty acid yield by 3.5 % compared to the method with saponification and decomposition, by 20.3 % compared to the method of soapstock decomposition with sulfuric acid. At the same time, the neutralization number increases by 4.1 % and 8.2 %, respectively. The improved method for fatty acids producing from soapstock provides high- quality fatty acids with increased yield.