Improving biodiesel yield of animal waste fats by combination of a pre-treatment technique and microwave technology

Abstract

Recently, due to its low cost there has been increased attention on Animal Waste Fats (AWFs) as a feedstock for biodiesel production. Advanced microwave technology has also been reported by many researchers to enhance the transesterification in biodiesel production. However, esterification of free fatty acids in the feedstock reported here has not attracted so much attention. AWFs come with its challenges namely, high free fatty acid (FFA) content and high water content. This study utilizes AWFs (tallow) containing very large amount of FFA; (25 wt%, 18 wt%, and 9.4 wt% FFA/AWFs) as feedstock for fatty acid methyl ester (FAME) production. A simple thermal pre-treatment technique followed microwave assisted esterification with methanol (MeOH) was conducted in a batch process to reduce the FFA content to as low as 1 wt% FFA, which is then suitable for the alkaline transesterification process. The pre-treatment of AWFs at 88 °C to first reduce water and decrease viscosity, followed by an operating microwave power of 70 W producing a power density 1.147 mW/m3, achieved a 15% increase in reduction of FFA over 30 W microwave power and conventional thermal method. Under optimum conditions, using 2.0 wt.wt% sulphuric acid catalyst/AWFs and 1:6 M ratio AWF/MeOH, the FFA conversion of 93 wt % was achieved. The results indicated that the pre-treatment and microwave application provided a faster route to high FFA reduction of AWFs during esterification process. The proposed technology is promising for the potential scale up industrial application.