Continuous production of biodiesel from fat extracted from lamb meat in supercritical CO ₂ media

Waste animal fat is considered a promising cheap alternative feedstock for biodiesel production that does not compete with food stock. In addition, using waste animal fat as a feedstock is considered a waste management process. In this work, an integrated process for a continuous fat extraction from lamb meat followed by enzymatic production of biodiesel in supercritical CO ₂ has been developed and tested. The system simultaneously produces two valuable products, namely biodiesel and healthy low-fat lean lamb meat (HLFLM). For the enzymatic process to be feasible, lipase is preferred to be used in immobilized form, which allows easy reuse. The continuous system was operated at 200bar and a SC-CO ₂ flow of 0.5mlmin ^-1, with extraction and transesterification temperatures of 45°C and 50°C, respectively. The effects of methanol:fat (M:F) molar ratio and enzyme stability were investigated. It was found that with fresh enzyme, a M:F molar ratio of 10:1 gave the highest biodiesel production rate of 0.37mgmin ^-1g-enzyme ^-1 compared to only 0.09mgmin ^-1g-enzyme ^-1 using a M:F molar ratio of 5:1. However, when a M:F molar ratio of 10:1 was used, the activity of the enzyme in the third meat replacement cycle drastically dropped to 18% of its original value, compared to 79% using a M:F molar ratio of 5:1.