Materials Science Forum Vol. 1177

Abstract: The depletion of fossil fuels and the environmental burden of biomass residues have driven interest in hydrothermal carbonization as a sustainable pathway for energy and material production. This study investigates the valorization of coffee parchment, an underutilized by-product of coffee processing, through microwave-assisted hydrothermal carbonization with liquid fraction recirculation. The primary aim was to evaluate how operating conditions and liquid reuse affect hydrochar properties and process efficiency. Experiments were conducted at temperatures between 70 and 110 °C and residence times from 60 to 180 minutes, using a modified microwave reactor. Hydrochar samples were characterized for surface acidity, functional groups, iodine number, and morphology, while the recirculated liquid fraction was monitored for its influence on subsequent reactions. Results show that total acid density increased with temperature and time, peaking at 3.39 mmol g⁻¹ at 110 °C and 180 minutes, while sulfonic and weak acid densities remained unchanged. Liquid fraction recirculation enhanced surface acidity but reduced iodine number and porosity due to pore blockage from soluble organics. FTIR analysis confirmed enrichment of oxygenated groups, and SEM images revealed cavity formation and pore collapse across recirculation cycles. These findings highlight the potential of liquid fraction recirculation to tailor hydrochar properties for catalytic rather than adsorptive applications, advancing sustainable strategies for coffee waste utilization.

Abstract: Evaporation of a saline solution from a porous medium often leads to the formation of salt efflorescence at the surface of the medium. We look at the special case where the medium is formed by the assembly of fine and coarse medium vertical columns perpendicular to the evaporation surface and where there is a continuous wicking of the solution into the medium in combination with evaporation. Experiments lead to distinguish two main cases depending on the development or not of the efflorescence at the surface of the coarse medium. On the contrary, the presented analysis suggests that the coarse medium surface colonization occurs when the evaporation flux is sufficiently high no matter what the type of efflorescence is on the fine medium surface. In addition, the analysis suggests that the colonization will always occur when the supersaturation is close to the solubility.

Abstract: This work focuses on the design and the study of mechanical behavior of new adobe clay bricks material made from local ecological materials for use in construction. The hydraulic binder used is a clay mineral material from the Sibang district in Gabon, and the biomass consists of sawdust from tropical wood species (okoume) combined with additives such as sugar cane molasses and cassava starch. The sawdust comes from okoume, where the selected protocol is based on their availability and widespread use locally. Preleminary tests done on clay show detailed analyses using laser granulometry, chemical analysis of major elements in total rock, X-ray diffraction on total rock and oriented samples (normal and heated to 550°C and ethylene glycol), infrared spectroscopy, cation exchange capacities, and scanning electron microscopy. The mixture of sawdust from okoume, padouk, azobe specie and 85% Sibang clay allowed for the design of bricks with quality facades. The respective compression strength tests resulted in 6.44 MPa, 3.15 MPa and 3.13 MPa, where the mixture containing the okoume sawdust showed a resistance, of 6.44 MPa, two times higher than the others. The adobe bricks incorporating sawdust from okoume, padouk and azobe woods are in compliance with the French standard for compressed earth blocks. The sawdust-wood mixture combined with clay is an ecological material and an alternative to the use of traditional concrete blocks in Gabon.