Kolbe Electrolysis for Recycling Non-Aqueous Fatty Acid Salts

Abstract

AbstractSoapstock, mainly composed of organic acid salts, is generated in large quantities during the vegetable oil refining process. However, there are serious environmental and economic problems with conventional treatment, and a new approach for effective utilization is required. Our research explored the application of Kolbe electrolysis, a process typically reserved for water-soluble organic acids with low carbon number, to water-insoluble organic acids. We discovered that the reaction can occur effectively with the water-insoluble organic acids when they are in salt form, producing dimerized hydrocarbons and sodium hydroxide. These produced hydrocarbons can be used as alternative biofuels, such as combustion aids for power generation or as boiler fuel. Simultaneously, the caustic soda can be upcycled. We also examined various operating factors and clarified that Kolbe electrolysis proceeded efficiently at high temperatures, low voltages, and high concentrations. Interestingly, the heating values of the dimerized product increased with the length of the carbon chain of the organic acid, although the product yield in Kolbe electrolysis decreased slightly. Therefore, the Kolbe electrolysis treatment of organic acid salt is an upcycling system that produces more energy than it consumes, thereby achieving a positive energy balance.

Keywords

• Biofuel
• Kolbe electrolysis
• Fatty acid salt
• Up-recycle
• Wastewater treatment