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Valorization of hemp stalk waste through thermochemical conversion for energy and electrical applications

Marrot L., Candelier K., Valette J., Lanvin C., Horvat B., Legan L., DeVallance D.B.. 2021. Waste and Biomass Valorization : 19 p..

DOI: 10.1007/s12649-021-01640-6

The presented research aimed at finding new ways to value hemp by-products (stalks) from the cannabidiol industry through thermochemical conversion. Chemical and elemental composition of hemp biomass was investigated by successive chemical extractions and Scanning Electron Microscopy along with Energy-dispersive X-ray Spectroscopy. Proximate and elemental analyses completed the chemical characterization of the hemp biomass and its biochar. Thermogravimetric analysis of the hemp biomass allowed to understand its kinetic of decomposition during thermal conversion. The carbon structure and porosity of the biochar were assessed by Raman spectroscopy and CO2 gas adsorption. Properties of interest were the energy production measured through calorific values, and the electrical conductivity. Two ways of valorisation of the hemp biomass were clearly identified, depending mainly on the chosen pyrolysis temperature. Hemp biochar carbonized at 400¿600°C were classified as lignocellulosic materials with a good potential for solid biofuel applications. Specifically, the resulting carbonized biochar presented low moisture content (below 2.50%) favourable for high fuel quality, low volatile matter (27.1¿10.4%) likely to show lower particle matter emissions, limited ash content (6.8¿9.8%) resulting in low risk of fouling issues during the combustion, high carbon content (73.8¿86.8%) suggesting strong energy density, associated with high higher heating values (28.45¿30.95 MJ kg-1). Hemp biochar carbonized at 800¿1000 °C displayed interesting electrical conductivity, opening opportunities for its use in electrical purposes. The electrical conductivity was related to the evolution of the biochar microstructure (development of graphite-like structure and changes in microporosity) in regard with the thermochemical conversion process parameters.

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