Waste fatty acids, conversion

Biodiesel is produced on the industrial scale by methanolysis of vegetable oUs (usually rape or soybean) or waste fat, particularly using frying oils. Methanolysis proceeds with modest amounts of base catalyst, provided the levels of free fatty acid and water in the oil are low (24, 25). The fatty acid content may be reduced by physical or chemical treatment before methanolysis but for waste fats, alternative processes that do not use base catalysis may be preferred. Lipase catalyzed methanolysis is less sensitive to fatty acid and water in the oil and has been tested in batch (26) and fixed-bed reactor (27) conversion of waste oil and grease to biodiesel. 

Numerous catalysts have been used in the production of CLA. We have found that hydroxides of lithium, sodium, and potassium are all capable of generating CLA in various solvents. As fatty acids neutralize the catalyst, it is necessary to add at least one mole of catalyst for every mole of fatty acid in the reaction to ensure soap is generated. We have found that, on a molar basis, potassium hydroxide has proven to be a more effective catalyst than sodium hydroxide, with lithium hydroxide the least effective and not suited for industrial CLA production. On a weight basis, sodium and potassium hydroxide have similar efficiency of conversion. Although sodium hydroxide is much less expensive than potassium hydroxide, the disposal costs for the waste neutralized alkali should also be considered. Potassium salts are easily used as fertilizer and can be applied to fields, whereas sodium salts cannot be disposed of in a similar fashion. 

Transesterification of oil from waste oilseed fiuits with methanol was studied in both homogeneous and heterogeneous catalyzed systems. Potassium loaded on lTQ-6 (Delaminated zeolite lTQ-6) by ionic exchange was found to be an efficient base catalyst, which produced 87% biodiesel. The optimum conditions were found to be 1 20 ratio of oil to MeOH at 180° C with 5% catalyst with reaction time of 48 h. Though potassium leaching was observed, which led to deactivation of the catalyst, its regeneration and reusability were easy to perform [82], The catalyst was also reported to be active in the conversion of oil containing free fatty acids (5.58%) without any soap formation and functions as acid ase catalyst. 

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