Recent Strategy of Biodiesel Production from Waste Cooking Oil and Process Influencing Parameters: A Review

Table 1

Various methods used for production of biodiesel from waste cooking oil through transesterification.

Methods	Catalyst	Advantages	Disadvantages	References
Alkali homogenous catalyst	(1) NaOH; (2) KOH; (3) Sodium methoxide; (4) Potassium methoxide	(1) Fastest reaction; (2) Higher yield; (3) Mild reaction condition; (4) Low cost	(1) Formation of soap; (2) Difficult to separate it from the final product, water interferes with reaction	[10, 14–26]
Alkali heterogeneous catalyst	CaO, CaTiO3, CaZrO3, CaO–CeO2, CaMnO3, Ca2Fe2O5, Al2O3/KI, ETS-10 zeolite, alumina/silica-supported K2CO3	(1) Separation of catalyst from product is easy; (2) Formation of soap is avoided; (3) Less corrosive, less toxicity, less environmental problem	(1) High methanol to oil ratio is required to reach the highest possible conversion	[10, 14, 19, 27–29]
Acid homogenous	Concentrated H2SO4, sulfonic acid	(1) Suitable for high free fatty acid feed stock; (2) Yield is high	(1) Slow reaction; (2) Need extreme pressure and temperature conditions; (3) Difficult to separate; (4) More corrosive	[10, 14, 18, 21, 30]
Acid heterogeneous	ZnO/I2, ZrO2=SO2, Sr/ZrO2TiO2=SO2, carbon-based solid acid catalyst, carbohydrate-derived catalyst, Vanadyl phosphate, niobic acid, sulphated zirconia, Amberlyst-15, Nafion-NR50	(1) Less corrosive; (2) Less toxicity; (3) Less environmental problem	(1) Low acid concentration; (2) High cost; (3) Diffusion limitation	[10, 17, 27, 31]
Enzyme	Candida antarctica fraction B lipase, Rhizomucor mieher lipase,  E. aerogenes lipase, lipase immobilized on hydrotalcite and zeolites	(1) By product of process can be easily removed; (2) Free fatty acid can be completely converted into methyl esters, regeneration and reuse of immobilized enzyme catalyst are possible	(1) High reaction time required; (2) Expansive, activity loss, agglomeration of enzyme	[10, 16, 20, 21, 32–38]