Biochar from waste coffee husk as a thermal conductivity enhancer in palm stearin BPCMs

Abstract

Bio-based phase change materials (BPCM) integrate natural sources like vegetable oils. While they typically have lower phase-change enthalpy than synthetic options, they are valued for their low toxicity and environmental impact. BPCMs provide a biodegradable alternative, but their low thermal conductivity limits efficiency in heat transfer applications. This study investigates the use of biochar derived from coffee husks as an additive to enhance thermal conductivity of palm stearin Biochar, characterized by stable chemical properties, high porosity, and significant adsorption capacity, is produced via pyrolysis, which also addresses waste management in the coffee industry and promotes renewable energy solutions, converting coffee husks into biochar effectively captures carbon that would be lost during combustion. In this way, the sample was characterized through proximate analysis, higher calorific value, crystallographic structure, and thermogravimetric analysis (TGA) to evaluate its thermal decomposition under pyrolysis conditions. Results indicate that coffee husk is an ideal candidate for pyrolysis applications; thus, biochar was produced from coffee husk in a 125 mL reactor, with a heating rate of 50 °C/min, from room temperature up to a maximum of 600 °C. TGA and differential scanning calorimetry (DSC) were employed to evaluate both palm stearin and the produced biochar, focusing on their thermal decomposition profiles. Results show that incorporating even small amounts of biochar (as low as 0.013 wt. %) significantly improves the thermal conductivity of the PCM. This study highlights the different pyrolysis temperature zones of coffee husks and compares them with the thermal behavior of palm stearin. Overall, this work underscores the potential of biochar as a sustainable additive to enhance the thermal properties of organic PCMs, contributing to the circular economy while mitigating greenhouse gas emissions from coffee waste.