Palm fatty acid distillate (PFAD) is a non-desired by-product from the crude palm oil refinery process. Thus, the present study aims to synthesize an acid catalyst from spent ground coffee and to apply it in the esterification reaction of PFAD for biodiesel production, as well as to optimize the reaction conditions. The spent ground coffee was carbonized in a tubular oven at 600 °C for 1 h, with nitrogen flow of 80 mL min-1. The obtained biochar (BC) was sulfonated using 1.0 g of BC and 10 mL of concentrated H2SO4 (ratio 1:10), at 200 °C for 4 h. After, the solid was washed with deionized water to neutral pH and kiln-dried at 60 °C for 24 h to obtain the catalyst with a total acid density of 5.54 mmol H+ g-1. The response surface methodology was based on an experimental design of Box & Behnken and it was used to obtain the best reaction conditions. The coefficient of determination (R2) has showed adequate (0.91608), indicating the percentage of experimental variance explained by the proposed regression equation. The conversion of reaction products was determined by the evaluation of acid values, according to AOCS Cd 3d-63 standard. The best reaction conditions obtained in the optimization for time, temperature and catalyst concentration were 2 h, 120 °C and 3.5%, respectively, with a conversion of 97.2%. The reaction between methanol and PFAD without catalyst shows a conversion of 16.9%, while the reaction uses only BC as a catalyst was 19.7%, what demonstrate the high catalytic performance of this type of (acid) catalyst. According to the pareto diagram and response surface methodology, temperature is a factor that considerably influences the conversion rates of FFA to methyl ester.1 In the studied levels of temperature (60–120 °C) and time (0,5–2,5 h), the best values for biodiesel conversion are obtained for the highest points. In this way, low concentrations of catalyst (around 3%) are capable of promoting high conversion rates (>90%) for times from 2 h and for temperatures from 100 °C. The catalyst remained highly efficient at its first reuse: 89.6% (conversion). Thus, the results revealed a promising utilization for spent ground coffee as a sustainable feedstock for the synthesis of a heterogeneous acid catalyst in the biodiesel production from PFAD.

  1 .ALHASSAN, Fatah H. et al. Applied Catalysis A: General, v. 456, p.182-187, 2013.