Tea Waste Derived Heterogeneous Acid Catalyst for Esterification of Free Fatty Acids in Biodiesel Production

Abstract

When the amount of free fatty acids (FFA's) in oils used for transesterification in biodiesel production is high, they react with the base catalysts (KOH or NaOH) used in the reaction forming soap. To avoid this soap formation, FFA level of the oils needs to be reduced by esterification of FFA with a short chain alcohol with the presence of an acid catalyst. Homogeneous acid catalysts are efficient in operation but cannot be reused. Therefore, heterogeneous acid catalysts are a better option, and a novel heterogeneous acid catalyst was synthesized from a low cost waste material; used tea powder for the pre-treatment of free FFA. It was prepared by direct sulfonation of tea waste powder followed by carbonization in the presence of nitrogen gas. The modified tea waste acid catalyst was characterized using Scanning Electron Microscopy (SEM), elemental analysis (EDAX) and Fourier Transform Infrared Spectroscopy (FT-IR). High porosity and acidity (5.2 mmol/g) were observed in the developed catalyst, which showed repeated usability with more than 80% FFA conversion even after 4 cycles at catalyst loading of 5 wt.%.