## 5 Developments in Improving Biodiesel Production from Animal Fats
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Animal Feedstock** & **Particular Conditions** & **Catalyst** & **Biodiesel Characteristics** & **References** \\ \hline \multirow{3}{*}{Lard oil, tallow oil, fish oil,} & Hydrocooxygenation and & & & Mixture of C14 to C18 paraffins \\  & hydrodisomerization of the oil in & & & having a ratio of iso to normal \\  & & & component & paraffins of 2 to 8; less than 5 ppm \\  & & & & sulfur; and acceptable habiticity \\ \hline \multirow{3}{*}{Animal oil, fish oil, lard, rendered fats, tallow} & Unwanted water removed by & & Separation of formed crude \\  & & & & biodiesel and crude glycerol from \\  & & & & the second reaction medium by \\  & & & & using a fourth cross-flow filtration \\  & & & & cassette \\ \hline \multirow{3}{*}{Animal fats} & Degumming: physical refining & & & Possibility of using various starting \\  & (heating and vacuum pulling); & & & feed stocks with heat integration to \\  & & & and glycerolysis & minimize operating costs \\ \hline \multirow{3}{*}{Animal fats incl. 10–20\% free  fatty acids} & & & & \\  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \hline \multirow{3}{*}{Animal fats} & \multirow{3}{*}{Animal fats} & \multirow{3}{*}{Exterification reaction of free fatty acids if higher than a set value} & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \cline{1-1} \cline{3-3}  & & & & \\ \hline \multirow{3}{*}{Beef oil, pork oil, animal fats such as fish oil} & & & Reducing costs by producing \\ \cline{1-1} \cline{3-3}  & & & & glycerin and glycerin derivatives in \\ \cline{1-1} \cline{3-3}  & & & & high yield and purity \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Selected patents for biodiesel production from animal fat waste. Technologies for process intensification like ultrasonic and microwave have been developed to be applied in transesterification and improve biodiesel production. The goal is to improve the miscibility of oils and methanol and thus increase the yield of the transesterification [73; 117]. Immiscible liquids can be emulsified at an industrial scale through the use of low frequency ultrasonic irradiation. In the case of microwave irradiation, reactants can be efficiently and rapidly heated to the target temperature [118]. Other process intensification technologies like static mixers [119], capillary reactors [120; 121], microreactors [122; 123] or oscillatory flow reactors [124] are also intended to accelerate the reaction rate and enhance biodiesel production. The use of microwave heating for animal fats containing up to 20% free fatty acids allowed for a decrease in the required time for free fatty acid reduction and increased the final yield [66]. Another alternative was the use of supercritical methanol with temperatures of 300 \({}^{\circ}\)C-400 \({}^{\circ}\)C, pressures up to 41.1 MPa, alcohol to fat ratios of 3:1 and 6:1, and short time (between 2-6 min) that gave 88% conversion for chicken fat [125]. The yield of biodiesel obtained with refined lard could also be obtained with waste lard containing fatty acids and water with no need for pretreatment [72]. Supercritical processes give faster reaction rates with no catalyst and avoid the need for pretreatment even in the presence of free fatty acids and water associated with the use of animal fats [30]. Other authors have assayed the transesterification with immobilized lipase in supercritical CO\({}_{2}\) and reported its contribution in reducing the interaction between methanol and enzyme, reducing its toxicity [75] and immediately separating CO\({}_{2}\) from the product. New heterogeneous catalysts that can be easily recovered, regenerated and reused have been developed for biodiesel production. Such catalysts include alkaline earth metal oxides such as CaO and MgO, hydrolcite, acid zirconia and alumina-based catalysts and immobilized lipase [20].