Biodiesel, defined as the mono-alkyl esters of vegetable oils or animal fats, is an environmentally attractive alternative to conventional petroleum diesel fuel (petrodiesel). Produced by transesterification with a monohydric alcohol, usually methanol, biodiesel has many important technical advantages over petrodiesel, such as inherent lubricity, low toxicity, derivation from a renewable and domestic feedstock, superior flash point and biodegradability, negligible sulfur content, and lower exhaust emissions. Important disadvantages of biodiesel include high feedstock cost, inferior storage and oxidative stability, lower volumetric energy content, inferior low-temperature operability, and in some cases, higher NO x exhaust emissions. This review covers the process by which biodiesel is prepared, the types of catalysts that may be used for the production of biodiesel, the influence of free fatty acids on biodiesel production, the use of different monohydric alcohols in the preparation of biodiesel, the influence of biodiesel composition on fuel properties, the influence of blending biodiesel with other fuels on fuel properties, alternative uses for biodiesel, and value-added uses of glycerol, a co-product of biodiesel production. A particular emphasis is placed on alternative feedstocks for biodiesel production. Lastly, future challenges and outlook for biodiesel are discussed.

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Field pennycress (Thlaspi arVense L.) oil is evaluated for the first time as a feedstock for biodiesel production. Biodiesel was obtained in 82 wt % yield by a standard transesterification procedure with methanol and sodium methoxide catalyst at 60 °C and an alcohol to oil molar ratio of 6:1. Acid-catalyzed pretreatment to reduce the acid value of crude field pennycress oil resulted in a yield after methanolysis of 94 wt %. Field pennycress oil had high contents of erucic (13(Z)-docosenoic; 32.8 wt %) and linoleic (9(Z),12(Z)-octadecadienoic; 22.4 wt %) acids with other unsaturated fatty acids comprising most of the remaining fatty acid profile. As a result, the methyl esters (biodiesel) obtained from this oil exhibited a high cetane number of 59.8 and excellent low temperature properties, as evidenced by cloud, pour, and cold filter plugging points of -10, -18, and -17 °C, respectively. The kinematic viscosity and oxidative stability (Rancimat method) of field pennycress oil methyl esters were 5.24 mm 2 /s (40 °C) and 4.4 h (110 °C), respectively. Other fuel properties such as acid value, lubricity, free and total glycerol content, surface tension, as well as sulfur and phosphorus contents were also determined and are discussed in light of biodiesel standards such as ASTM D6751 and EN 14214. Also reported for the first time are cetane numbers of methyl esters of erucic and gondoic (methyl 11(Z)-eicosenoate) acids, which were found to be 74.2 and 73.2, respectively. In summary, field pennycress oil appears to an acceptable feedstock for biodiesel production. † Disclaimer: Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.

Single, binary, ternary, and quaternary mixtures of canola (low erucic acid rapeseed), palm, soybean, and sunflower (high oleic acid) oil methyl esters (CME, PME, SME, and SFME, respectively) were prepared, and important fuel properties were measured, such as oil stability index (OSI), cold filter plugging point (CFPP), cloud point (CP), pour point (PP), kinematic viscosity (40 °C), lubricity, acid value (AV), and iodine value (IV). The fuel properties of SME were improved through blending with CME, PME, and SFME to satisfy the IV (<120) and OSI (>6 h) specifications contained within EN 14214, the biodiesel standard from the European Committee for Standardization. SME was satisfactory according to ASTM D6751, the American biodiesel standard, with regard to OSI (>3 h). The CFPP of PME was improved by up to 15 °C through blending with CME. Statistically significant relationships were elucidated between OSI and IV, OSI and saturated fatty acid methyl ester (SFAME) content, OSI and CFPP, CFPP and IV, and CFPP and SFAME content. However, the only relationship of practical significance was that of CFPP versus SFAME content when SFAME content was greater than 12 wt %. † Disclaimer: Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.

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Camelina (Camelina sativa L.) is a promising sustainable alternative energy crop belonging to the Brassicaceae (mustard) family. Camelina has several favorable agronomic characteristics which give it potential to significantly enhance domestic biofuels production. With high seed oil content as well as high yield of oil per hectare, camelina can be efficiently processed into high quality renewable fuels such as biodiesel (fatty acid methyl esters) as well as renewable diesel and jet fuels using existing technologies. This review summarizes the attributes of camelina along with conversion of the lipid fraction into advanced renewable biofuels.

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