NOVELTY - Production of biodiesel involves converting free fatty acids from oil containing 1-90% of free fatty acids into glycerides by esterification with glycerin using a solid super acid catalyst, silica supported sulfated zirconia catalyst; production of biodiesel by trans-esterifying the mixture of oil and glycerides free from free fatty acids with methanol in presence of a base catalyst; purifying the biodiesel; and purifying the glycerin followed by removal of methanol by vacuum distillation.    USE - For production of a biodiesel (claimed).    ADVANTAGE - The process is simple, efficient and easy to work out; and avoids the formation of water in the process thus eliminating the step of water separation.    DETAILED DESCRIPTION - Production of biodiesel involves converting free fatty acids from oil containing 1-90% of free fatty acids into glycerides by esterification with glycerin using a solid super acid catalyst, silica supported sulfated zirconia catalyst, at 65-250 degrees C followed by separation of catalyst by filtration, decantation to obtain a biphasic reaction mixture comprising a top layer of a mixture of oil, small concentration of unreacted free fatty acids and glycerides and a bottom layer of excess/unreacted glycerin; and followed by removal of small concentration of unreacted free fatty acids from the mixture of the top layer by chemisorption by passing the layer through a column containing macro-porous/macro-reticular weak base resin to obtain a mixture of oil and glycerides free from free fatty acids; production of biodiesel by trans-esterifying the mixture of oil and glycerides free from free fatty acids with methanol in presence of a base catalyst at 30-76 degrees C to give biphasic reaction mixture comprising top layer of mixture of biodiesel, dissolved methanol, inorganic salts and the base catalyst and a bottom layer comprising glycerin, methanol, inorganic salts and the base catalyst; purifying the biodiesel by passing the top layer through a column containing macro-porous/macro-reticular strong acid cation exchange resin to obtain biodiesel free from the base catalyst, the inorganic salts, followed by removal of methanol by vacuum distillation and purifying the glycerin by passing the bottom layer through a column containing macro-porous/macro-reticular strong acid cation exchange resin to obtain glycerin free from the base catalyst, the inorganic salts, followed by removal of methanol by vacuum distillation.