Synthesis and characterization of biodiesel produced from restaurant waste frying oil based on acidic pretreatment

Abstract

The high demand for energy resources and the exaggeration of fossil fuel-related problems in the environment encouraged researchers to find other energy resources that can achieve sustainability. Waste frying oils (WFOs) are promising feedstock for biodiesel production as an alternative eco-friendly energy resource. However, the higher content of free fatty acids (FFA) and acid value are the major drawbacks of utilizing WFOs in biodiesel production. In this project, two approaches were compared to reduce acid value and FFA content in WFOs, acidic pretreatment and metallic pretreatment. Hydrochloric, sulfuric, and phosphoric acids were tested on the same esterification reaction conditions. Hydrochloric acid succeeded to reduce the acid value from 6.45 to 0.38±0.01 mg KOH/g and FFA content from 3.22% to 19%. In contrast, calcium, manganese, and ferric chlorides were tested as metallic catalysts to reduce the acid value and FFA of the WFO sample on unified reaction conditions. The best result was obtained by calcium chloride where it reduced the same WFO sample into 1.2±0.15 mg KOH/g and 0.6% for acid value and FFA, respectively. Biodiesel fuel was synthesized from acidic pretreated WFO based on optimized transesterification as 1:9, 1.5 w/w%, 65 ℃, and 1.5 h for oil to methanol molar ratio, catalyst ratio, reaction temperature, and reaction time, respectively. The highest biodiesel yield was 95.50% which complied with biodiesel standards of ASTM D6751, EN 14214, and MS2008:2008 with the exception of cloud and pour points. This study project conducted that acidic pretreatment is superior to reducing the acid value and FFA of WFOs toward sustainable biodiesel production..