Techno-Environmental Assessment of Biodiesel Production from Acid Oil via One-Step and Two-Step Esterification

This study aims to evaluate the techno-environmental impacts of biodiesel production from acid oil using a one-step acid catalyst and a two-step immobilized enzyme and acid catalyst esterification. Acid oil was obtained by purifying crude glycerol with pure glycerol and salt as by-products. The experiment was performed to optimize the conversion of the acid oil to biodiesel. The one-step process involves 4% sulfuric acid, a methanol-to-oil molar ratio of 26:1, and a reaction time of 3.4 h. The two-step esterification comprised two stages: the first stage employed immobilized lipase on chitosan. The optimal conditions of the first stage were a 5:1 methanol-to-oil molar ratio, 37 wt % enzyme loading, and a reaction time of 17 h. The second stage of the two-step process involved 3% sulfuric acid with a methanol-to-oil molar ratio of 15:1 for 4 h. Then, a techno-environmental assessment was performed to compare the midpoint impacts of the one-step and two-step esterification. The study generated 7 cases to investigate the significant environmental effects of glycerol (case 1), particularly on global warming potential. It examined the impact of different electricity sources, natural gas (cases 2, 3, and 6) and hydropower (cases 4, 5, and 7), on biodiesel production. Comparing SC-1 (one-step esterification with an acid catalyst) and SC-2 (two-step esterification with an enzyme and acid catalyst), the study found that SC-2 was technically feasible due to lower energy consumption, less chemical use, and less wastewater, but SC-1 was more environmentally friendly. Due to enzyme preparation, SC-2 has had a higher impact on terrestrial ecotoxicity, human noncarcinogenic toxicity, global warming, and land use. The study suggested that biodiesel factories should purify crude glycerol to minimize its environmental effects and enhance biodiesel production's ecological benefits and sustainability.