Question

why do basic heterogeneous catalysis require an alchol:oil molar ratio up to 15:1, higher than acid heterogeneous catalysis and base homogeneous catalysis

in biodiesel production

Answer 1

The process here talked about is Transesterification.This process is similar to hydrolysis ,except that alcohol is employed instead of water.The rate of transesterificatin can be accelerated by using catalysts.

Many researchers have reported an alcohol to oil molar ratio of 6:1 to be the optimal ratio ,while some reported that maximum bio-diesel production was obtained at a molar ratio of 7:1 in transesterification of used frying oil. In bio-diesel production using waste cooking oils as raw materials, the main cost of materials are the cost of alcohol and catalyst.Since the catalyst is required only in minute amounts ,the primary cost would be the alcohol.Therefore if the use of alcohol can be reduced without significantly reducing the production of bio-diesel ,the production cost would be lowered and the process would be more cost effective . so it is suggested that a higher methanol to oil molar ratio was better than lower ratio in terms of soap formation as other combinations ratios produced low output.And hence we can say that the theoretical optimal amount is ranging from 6:1 to 15:1