Used frying oils and fats and their utilization in the production of methyl esters of higher fatty acids

Abstract

From the point of view price and available capacity used frying oils or fats (UFO) represent an attractive raw material for the production of methyl esters (ME) of higher fatty acids as alternative fuels for diesel engines. If they are treated such that the required quality, with an acidity number up to 3.0mgKOH/g and a water content up to 0.1wt%, is achieved they can be processed to ME using standard techniques of alkali-catalysed transesterification with methanol which are utilized for production of the ME from new oils/fats. The problematic waste can thus be converted to an ecologically friendly fuel. Vacuum distillation of free fatty acids in a film evaporator is an effective method for simultaneously decreasing the content of FFA and water in UFO. Final distillation of raw ME in a film vacuum evaporator results in practically all parameters required by the standard, in the final ME being achieved. Undesirable low-temperature properties of ME derived from UFO, due to higher fraction of saturated acyls, can be adjusted by the addition of depressants—flow improvers for winterization. Some simplified methods for the quality control of UFO and ME are discussed. The conversion of acylglycerols to ME is monitored by GLC with a packed column, where the peak areas of ME in the sample before and after the reaction with an effective methylation agent are compared. The method for the determination of the water content in esters utilizes the reaction of calcium carbide with water, the volume of acetylene being measured.