Animal fats like beef tallow and chicken fat are by­products from the meat industry and stand for cheap feedstock for biodiesel production. The key fatty acids found in beef tallow were oleic (47.2 wt%), palmitic (23.8 wt%), and stearic (12.7 wt%) acids. The prime fatty acids contained in chicken fat include oleic (40.9 wt%), palmitic (20.9 wt%), and linoleic (20.5 wt%) acids (Wyatt et al., 2005). Due to very low concentration of polyunsat­urated fatty acid in beef tallow, the corresponding methyl esters illustrate excellent oxidative stability, as evidenced by an oil stability index (OSI) value of 69 h at 110 °C. In addition, other physical properties of beef tallow methyl esters include kinematic viscosity (40 °C) of 5.0 mm2/s, a flash point (FP) of 150 °C, and CP, PP and cold filter plugging point (CFPP) values of 11, 13, and 8 °C respectively (Moser, 2009). In chicken fat, due to high polyunsaturated fatty acid content, the corresponding methyl esters display poor oxidative sta­bility, as evidenced by an OSI value of 3.5 h at 110 °C. Burning the B20 blends of beef tallow and chicken fat methyl esters results in NOx exhaust emissions of only 2.4% versus 6.2% of B20 blend of soybean methyl esters (SME) (Wyatt et al., 2005).

PORK LARD

Pork lard is a by-product of the food industry and symbolizes a low-cost feedstock for biodiesel produc­tion. The main fatty acids in pork lard includes stearic (121 wt%), linoleic (127 wt%), oleic (44.7 wt%), and pal­mitic (26.4 wt%) acids (Jeong et al., 2009). Due to high saturated fatty acid content in pork lard, the correspond­ing methyl esters exhibit quite high CFPP value of 8 °C and a relatively low iodine value (IV) of 72, along with a typical kinematic viscosity (40 °C) of 4.2 mm2/s. Another study determined that pork lard methyl esters have a kinematic viscosity (40 °C) of 4.8 mm2/s, FP of 160 °C, OSI value of 18.4 h at 110 °C, and CP, PP, and CFPP values of 11, 13, and 8 °C, respectively (Wyatt et al., 2005). Furthermore, combustion of B20 blends of pork lard methyl esters results in NOx exhaust emis­sions of only 3.0% versus 6.2% for a B20 blend of SME.

Other Waste Cooking Oils

Waste oils may include a variety of low-worth mate­rials such as used cooking or frying oils, acid oils, tall oil, vegetable oil soapstocks, and other waste materials.

Waste oils are usually characterized by relatively high FFA and water contents and potentially contain a variety of solid materials that must be removed by filtration prior to conversion to biodiesel (Moser, 2009). In the case of used cooking or frying oils, hydrogenation to in­crease the useful cooking lifetime of the oil may result in the introduction of relatively high-melting trans constit­uents, which influence the physical properties of the resulting biodiesel. Used frying or cooking oil is mainly acquired from restaurants and may cost between free to 50% less expensive than commodity vegetable oils, depending on the source and the availability (Predo — jevic, 2008). The physical properties of methyl esters pre­pared from used cooking or frying oils include kinematic viscosities (40 °C) of 4.23 (Meng et al., 2008), 4.79, and 4.89 mm2/s; FP of 171 °C; cetane number of 55, IV of 125, CFPP values of 1 and —6 °C (Cetinkaya and Karaosmanoglu, 2004), CP values of 9 and 3 °C, and PP values of —3 and 0 °C (Phan and Phan, 2008). The disparities in the physical property data among the various studies may be a result of feedstock origin or due to differences in product purity.