Lignocellulosic materials. A promising hydrothermal route to biorefinery products

Abstract

Hydrothermal conversion (HTC) has emerged as a viable alternative to traditional crude oil. In this study, the hydrothermal liquefaction process of a hybrid herbaceous biomass species (Pennisetum sp) was investigated to understand the most appropriate operating conditions and the properties of the obtained materials. The yields of biocrude and light biocrude (referred to as maltoid oils) were optimized and various wastes available from agriculture, urban areas and industries were tested at the optimal HTC variables. At 647±5 K, the biocrude yield reached 22.55% dafb, when a potassium carbonate solution of 1.10 eq/L was used. As the catalyst concentration increased to 1.78 eq/L, the biocrude yield decreased, leading to a higher proportion of aqueous phase and gases, thus facilitating the development of new water-soluble materials. Increasing the water:biomass ratio from 4:1 improved the overall conversion but reduced the bio-crude yield. The same effect was observed when the reaction time was increased from 60 to 120 minutes with the increase of charred materials (solid waste), indicating a repolymerization of HTC products that could have been involved in useful biocrude. The repolymerization and solidification of the biocrude during storage observed both in the FTIR spectroscopy study and in the 1H NMR study highlights the instability of this material. This high reactivity also detected by TGA-MS in thermal decomposition is mainly due to the oxygen content but also to the nitrogen content present in the biocrude (O = 11.02%, N = 2.46%). Furthermore, biocrude products were obtained from different types of biomasses and it was found that there is a low critical micelle concentration for the light biocrude in aliphatic fuel mixtures (4.12% w/v).

Keywords

• Biomass-based materials
• Hydrothermal conversion
• Pennisetum (glaucum x purpureum)
• Bio-crude
• Chemical feedstocks
• Chars