Hydrothermal carbonization of acerola (Malphigia Emarginata. D.C.) waste pretreated with supercritical CO2 and zinc chlorine as an additive

This study investigates the application of supercritical CO2 (SC-CO2) in acerola waste pretreatment for hydrothermal carbonization, examining the impact of ZnCl2 as an additive. Quantified response variables included hydrochar yield, high heat value, energy yield and oxygenated functional groups. Four equations were proposed to correlate the independent variables-additive concentration (C), temperature (T) and residence time (t)-with each response. Subsequently, a multiple-response optimization study was conducted to determine the best conditions, considering all responses. Utilizing SC-CO2 pretreatment and ZnCl2 additive resulted in hydrochar with the highest values for all responses. The optimum conditions obtained were T = 161.4°C, t = 105.5 min, and C = 1.43%. The hydrochar obtained under optimal conditions demonstrated that the supercritical CO2 pretreatment associated to the use of ZnCl2 additive increased the process yield in 11.02% and the energy yield in 13.02%, confirming the potential application of the hydrochar as a solid fuel.