Biodiesel production from fats extracted from coffee husks: esterification with H2SO4 and transesterification with KOH

Abstract

 The search for non-food feedstocks is one of the main challenges in the production of biofuels. For biodiesel, research is oriented towards the use of non-conventional crops, as well as towards residues or wastes with a high content of fats and oils. Coffee grounds contain a good proportion of fats and are a commercial and domestic waste. In this work, the production of biodiesel using fats extracted from coffee grounds was evaluated in a two-step process. The fats extracted from coffee grounds with boiling to reflujo with hexane as solvent presented high acidity, 32.07 ± 0.01% (70.24 ± 0.03 mg KOH/ g fat), indicating a high content of free fatty acids (FFA). First, the fats were esterified at 60°C and 100 rpm, varying the reaction conditions. At the best conditions, 0.7% H₂SO₄ concentration, 1:6 GMR:MeOH for 120 min, the acidity decreased below 1%, with 94.92% FFA conversion to methyl esters. They were subjected to a transesterification process with KOH (1.5% m/v) in the presence of methanol (RMG:MeOH of 1:15) at 60°C and 100 rpm for 30 min. The biodiesel was separated by decantation and purified by successive washes with acidified water, which resulted in a mixture of methyl esters of linoleic (48.40%), palmitic (36.21%), stearic (8.69%) and oleic (6.69%) acids, whose properties conform to the requirements of ASTM D 6751 and EN 14214.