Synthesis of KOH-activated carbon through sonication for adsorption in soap production from used cooking oil

Used cooking oil (UCO) is a waste generated from frying processes in both household and industrial sectors. One way to utilize UCO is by processing it into soap. However, before being used as a raw material, purification is required because UCO contains reaction products formed during frying. This study aims to purify UCO using corn cob–based activated carbon (AC), which was activated with KOH and assisted by ultrasonic irradiation, and to evaluate its feasibility as a raw material for liquid soap production. The purification process of UCO was carried out in several stages, including degumming, neutralization, and adsorption using AC. The AC was carbonized and activated with varying KOH concentrations (10% to 60%) under ultrasonic irradiation times of 20, 40, and 60 minutes, followed by characterization using FTIR, XRD, SEM, and BET. The results showed that AC prepared with 40% KOH and 40 minutes of ultrasonic irradiation exhibited the highest iodine adsorption capacity of 1065 mg/g. The purification process from degumming to adsorption successfully reduced the free fatty acid content to 0.144%, peroxide value to 9.8 meQ O₂/kg, and moisture content to 0.07%. The purified UCO was then applied as a raw material to produce high-quality liquid soap.