Characterization of the thermal and mechanical properties of briquettes from coffee husks (Coffea arabica) with crude glycerin as binder

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Abstract
Given the growing demand for sustainable energy sources, the search for alternatives to fossil fuels has intensified, with particular emphasis on the reuse of agro-industrial waste. Among these, coffee husk (Coffea arabica), widely produced in Brazil, presents high energy potential and availability. A strategy for the valorization of this residue is briquetting, a compaction process that transforms biomass into a solid biofuel with high energy density, good combustion efficiency, and ease of transport and storage. In this context, the aim of this study was to propose a renewable fuel option and evaluate its energy potential, by means of the production and carbonization of briquettes made from coffee husks and different binder concentrations (crude glycerin). Cold briquetting was performed in a mold machined for this study. The effects of the binder concentration (0 % to 25 % w/w) on moisture, volatiles, fixed carbon and ash contents, the heating value, bulk density of briquettes, diametrical compression strength, diametral expansion, longitudinal expansion and carbonization yields was assessed, using a completely randomized design with three replicates in each treatment. Carbonization was carried out at 450 ºC. The addition of 5% (w/w) binder in the briquettes resulted in a higher compressive strength (78.99 kPa). Increases in glycerin concentration reduced the fragmentation of compacted material, but resulted in a reduction in the calorific value, increase in moisture and volatile contents, and expansion of the briquettes. The gravimetric yields were not significantly affected (p>0.05) by the addition of glycerin, but the charcoal produced from briquettes with the binder showed less fragmentation. The briquettes and charcoal produced showed potential for use in the generation of energy, and production of activated carbon and biochar.

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