Proposal of complete utilization system of soapstock by electrolysis

Abstract

In deacidification during vegetable oil refinery, a large amount of soapstock, mainly sodium salt of fatty acid, are generated and wasted. We propose an innovative system for the complete utilization of soapstock by Kolbe electrolysis. In conventional Kolbe electrolysis, only water-soluble carboxylic acid with short alkyl chain such as acetic acid and butyric acid are decarboxylated and dimerized to produce hydrocarbons such as ethane and butane. Although fatty acid salts have long alkyl chains, they are soluble in water, and Kolbe electrolysis can be applied to them. Soapstock will be converted by electrolysis into long-chain hydrocarbons used as biofuels and, sodium hydroxide used in vegetable oil refinery. As a result of applying Kolbe electrolysis to an aqueous solution of caprylic acid sodium salt, the formation of hydrocarbons, tetradecane, and sodium hydroxide was observed. When the generated hydrocarbons were used for power generation, the generated energy was almost the same as the energy input in the electrolysis. This means that the soap stock can be reused without any external energy input. Therefore, it is suggested that this electrolysis system will be both carbon-negative and profitability.