The most effective catalyst for the production of biofuels from waste vegetable oil using the catalytic cracking process is typically a solid acid catalyst. Among the various solid acid catalysts, zeolites, particularly H-ZSM-5, have shown great potential in catalytic cracking of waste vegetable oil to produce biofuels. Other catalysts that have been used include sulfated zirconia, sulfated tin oxide, and heteropolyacids.The concentration of the catalyst plays a crucial role in the yield and quality of the resulting biofuel. The catalyst concentration affects the reaction rate, selectivity, and conversion of waste vegetable oil to biofuel. An optimal catalyst concentration is necessary to achieve a balance between the desired conversion and selectivity.At low catalyst concentrations, the reaction rate may be slow, leading to low conversion and yield of biofuel. On the other hand, at high catalyst concentrations, the reaction rate may be too fast, causing side reactions and the formation of undesired by-products, such as coke, which can lead to catalyst deactivation and lower biofuel quality.Therefore, it is essential to determine the optimal catalyst concentration for a specific catalytic cracking process to maximize the yield and quality of the biofuel produced from waste vegetable oil. This can be achieved through experimental studies and optimization techniques, considering factors such as the type of waste vegetable oil, reaction temperature, and catalyst properties.