Hydrothermal Liquefaction of Biomass

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

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.

White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis

In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst.