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.

Automated summary

In this study, flax by-products were subjected to hydrothermal treatment to identify potential applications for the resulting products. It was found that severities above 4.9 were optimal in terms of calorific value, production of organic products, photoluminescence quantum yield of carbon quantum dots, and CO2 capture by the resulting carbons.