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.

The global shortages of fossil fuels, significant increase in the price of crude oil, and increased environmental concerns have stimulated the rapid growth in biodiesel production. Biodiesel is generally produced through transesterification reaction catalyzed either chemically or enzymatically. Enzymatic transesterification draws high attention because that process shows certain advantages over the chemical catalysis of transesterification and it is "greener." This paper reviews the current status of biodiesel production with lipase-biocatalysis approach, including sources of lipases, kinetics, and reaction mechanism of biodiesel production using lipases, and lipase immobilization techniques. Factors affecting biodiesel production and economic feasibility of biodiesel production using lipases are also covered.

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.

Enzymatic biodiesel production shows a very high potential to be an eco‐friendly process compared with traditional chemical processes, which could pose downstream processing problems. As an environmentally benign green approach, enzymatically catalyzed biodiesel production avoids the generation of wastewater and eases the recovery of high purity glycerol. This article discusses the benefits of using enzymatic approach. Both the opportunities and challenges are covered.

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.

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