Physical Properties of Biochar Produced from Pyrolysis of Arabica Coffee Pulp: The Effect of Pre-Washing Process

Abstract

Coffee pulp is a potential source of biomass which abundantly available in coffee exporter countries such as Brazil, Colombia, Indonesia etc. It is necessary to develop technologies to convert coffee pulp into value-added products. This study aims to investigate the slow pyrolysis process of arabica coffee pulp in a pilot scale reactor and evaluate the properties of resulting biochar. Prior to pyrolysis experiment, some of coffee pulp were soaked in tap water for 20 h with a ratio of water to coffee pulps of 1:5. As comparison, another set of pyrolysis experiment was carried out without soaking and washing of feedstock. The pyrolysis process was carried out in a batch reactor at temperatures within the range of 400 to 420°C. During the run, the reaction temperature versus time was recorded and products yield were quantified. Characterization of biochar product was performed under proximate, bomb calorimeter and density analyses. The yield of biochar and pyrolytic oil, respectively were 33% and 36%. Biochar characterization results suggested a significant decrease in the ash content when washing pretreatment was applied. Increases in the calorific value and bulk density were also observed from pre-washed coffee pulp sample.