Chemical and physical characterization of spent coffee ground biochar treated by a wet oxidation method for the production of a coke substitute

Abstract

Coke production relies on the availability, cost and quality of coking coal. Depleting coking coal resources and environmental pressure force the metallurgical industry to search for alternative methods to produce coke. Waste spent coffee grounds (biomass) treated via hydrothermal liquefaction (HTL) is an energy-efficient method to produce biochar. In this study the use of HTL biochar as feedstock for the production of a coke substitute was investigated. Wet oxidation treatment of the prepared biochar samples was done with different wet oxidant hydrogen peroxide concentrations (5, 15, 30%). The biochar was treated for different time durations (0.5, 1, 2, 6 and 24 h) and at different temperatures (room temperature and 80 °C). Thereafter, the various samples were characterized and pyrolysed to obtain a coke substitute. Characterization of the various samples before and after thermal treatment was done using Fourier-transform infrared spectroscopy (FTIR), free swelling index, ultimate and proximate analysis, gross calorific value and compressive strength determination. The investigated characteristics of the produced coke substitute obtained from the pyrolysed biochar treated for 24 h with 30 vol% H₂O₂ at room temperature, showed the most promising results when compared to blast furnace coke.

Keywords: Biochar; Biomass; Coke production; Hydrothermal liquefaction; Spent coffee grounds; Wet oxidation.