Abstract:Currently the large surplus of glycerol formed as a by-product during the production of biodiesel offered an abundant and low cost feedstock. Researchers showed a surge of interest in using glycerol as renewable feedstock to produce functional chemicals. This Minireview focuses on recent developments in the conversion of glycerol into valueadded products, including citric acid, lactic acid, 1,3-dihydroxyacetone (DHA), 1,3-propanediol (1,3-PD), dichloro-2-propanol (DCP), acrolein, hydrogen, and ethanol etc. The versatile new applications of glycerol in the everyday life and chemical industry will improve the economic viability of the biodiesel industry.

Looking back at the literature for enzymatic biodiesel, it is evident that the research has been focused on using immobilized lipase to enable re‐use of the enzyme due to price constraints on lipases used for catalyzing the transesterification process. The use of liquid formulations of lipase for biodiesel has recently been implemented in the industry. Technology for using liquid formulated lipases for enzymatic biodiesel production is new and, since enzyme prices have been reduced, it is now possible to simplify the process considerably and apply it for very low‐quality oils. In this paper, the use of liquid lipase formulations for enzymatic biodiesel will be described along with a general proposal for an industrial‐scale enzymatic biodiesel process with >95 % yield.

Currently, the biodiesel industry is investigating non-food crops with high oil content. The industry is also evaluating oil sources from deeper into the industrial or commercial waste streams. Spent coffee grounds could be a feedstock that qualifies for both as a non-food crop and a waste product. The purpose of this study is to evaluate the feasibility of using coffee oil extracted from spent coffee grounds as raw material to produce ASTM standard biodiesel. The two biodiesel production methods that were used are acid-catalyzed esterification followed by alkali-catalyzed transesterification and lipase catalyzed transesterification. It was found that the high level of free fatty acids (FFA) in the coffee oil was reduced from 16.3% to 2.64% by acid-catalyzed esterification with 40/1 molar ratio of methanol to FFA in the presence of 5% (v/v, based on FFA) hydrochloric acid. However, poor conversion was obtained for the further alkali-catalyzed transesterification. In comparison, 98.5% conversion was achieved by using enzymatic catalysis, demonstrating the feasibility of using this approach to process low quality coffee oil from spent coffee grounds for biodiesel production.

Biodiesel, as renewable and biological origin alternative diesel fuel, has been receiving a lot of concern throughout the world due to the energy needs and environmental awareness. However, at present, it is not economically feasible to use food-grade vegetable oils to produce biodiesel because of the surge in feedstocks price. Much attention has been devoted to the application of lower-cost feedstocks to produce biodiesel. This paper provided a comprehensive review of biodiesel production from lower-cost non-edible oil sources, such as waste cooking oil (WCO), grease, soapstock, Jatropha oil, and algae. The engine performances of biodiesel produced from these feedstocks were further evaluated. This review also investigated the various applications for the value-added products from glycerol, the byproduct of biodiesel. Moreover, the challenges in terms of different feedstocks and by-product applications were further pointed out.

Biodiesel, as renewable and biological origin alternative diesel fuel, has been receiving a lot of concern throughout the world due to the energy needs and environmental awareness. However, at present, it is not economically feasible to use food-grade vegetable oils to produce biodiesel because of the surge in feedstocks price. Much attention has been devoted to the application of lower-cost feedstocks to produce biodiesel. This paper provided a comprehensive review of biodiesel production from lower-cost non-edible oil sources, such as waste cooking oil (WCO), grease, soapstock, Jatropha oil, and algae. The engine performances of biodiesel produced from these feedstocks were further evaluated. This review also investigated the various applications for the value-added products from glycerol, the byproduct of biodiesel. Moreover, the challenges in terms of different feedstocks and by-product applications were further pointed out.