A PILOT PLANT TO PRODUCE BIODIESEL FROM HIGH FREE FATTY ACID FEEDSTOCKS

Abstract

Biodiesel is an alternative diesel fuel consisting of the alkyl monoesters of fatty acids from vegetable oils or animalfats. Currently, most biodiesel is made from soybean oil, methanol, and an alkaline catalyst. However, there are large amountsof fats and oils that are unsuitable for human consumption that could be converted to biodiesel at lower cost. The problemwith processing these waste oils is that they often contain large amounts of free fatty acids that cannot be converted to biodieselusing an alkaline catalyst. These free fatty acids react with the alkaline catalyst to produce soaps that inhibit the separationof the biodiesel, glycerin, and wash water. Previous research has developed a process for pretreating these high free fatty acidfeedstocks using acid catalysts, which do not form soaps. The objective of this study was to construct a pilot plant to producebiodiesel from a wide variety of feedstocks including those with high free fatty acids. A 190 L batch pilot plant has been builtthat can process high free fatty acid feedstocks using an acidcatalyzed pretreatment followed by an alkalinecatalyzedtransesterification. Case studies of pilot plantscale production of biodiesel from soybean oil, yellow grease with 9% free fattyacids, and brown grease with 40% free fatty acids are presented. The effect of varying the reaction parameters is discussed,and the separation and washing processes are described. Estimates of the fuel cost using different feedstocks are alsoprovided.