Upgrading of flax powder and short fibers into high value-added products

Lignocellulosic materials have great potential to be valorized into new products. Flax by-products such as powder and short fibers are used in the present study to identify plausible potential applications for the products obtained from their hydrothermal treatment. The as-received industrial flax by-products are subjected to hydro thermal carbonization (HTC) in a wide range of severity, an operating parameter combining time and temperature. In this way, the yield and characteristics of the resulting HTC products: hydrochars, carbon quantum dots (CQDs) and organics such as 5-hydroxymethylfurfural (5-HMF) and furfural (FU), are determined. Likewise, pyrolysis of the hydrochars and the starting flax by-products at 900 degrees C is also carried out, leading to carbon materials with developed surface areas, higher than 950 m(2/g), and CO2 capture values of up to 4.8 mmol/ g at 1 bar and 0 degrees C. In the overall process, severities above 4.9 were found to be optimal in terms of higher calorific value (around 27 MJ/kg) of the obtained hydrochars, production of organic products (0.22 and 0.06 g/L of 5-HMF and FU, respectively), photoluminescence quantum yield of the CQDs fraction (4.7%) and CO2 capture (up to 4.8 mmol/g) by the hydrochar-derived carbons.