Kinetic study of lignocellulosic biomass transformation into glycols
Résumé
Glycols cover a wide range of applications, in particular for the polymer industry or as synthesis
precursors. To date, these compounds are produced from fossil resources (ethane/ethylene). The
possibility to obtain polyols on a large scale from renewable biomass, in particular from
lignocellulosic biomass such as wood, is therefore of particular importance in the context of the
development of biorefineries. Thus, the project aims at understanding reaction pathways from
lignocellulosic biomass to produce ethylene glycol (EG) and propylene glycol (PG) with an
innovative multifonctionnal catalyst.
The formation of EG or PG from cellulose has been studied on supported bifunctional catalysts
involving acid sites (for hydrolysis of polysaccharides and retro-aldol condensation (RAC) of
sugars) as well as metal sites (for hydrogenation of low carbon number polyols). The reactions are
typically carried out in water at 200-250°C, under 60-100 bar of H2, giving yields between 40 to
80% of glycols using catalysts based on carbon supported nickel tungsten carbides Ni-W xC/AC.
Depending on the preparation method of catalyst and on the loading of metal, various metallic
species (W, W 2C, WC, Ni) can be obtained. The selective W 2C phase with the presence of a
Ni17W 3 alloy, noted 5%Ni-30%W 2C/AC, was found as the most effective for the transformation of
cellulose to EG and PG due to the catalytic synergy between both sites [1].
Three consecutive reactions are required to obtain EG and PG: (1) hydrolysis of polysaccharides
to sugars, (2) RAC of sugars and (3) hydrogenation of intermediates. Glycolaldehyde and
hydroxyacetone (from RAC of glucose or fructose) are respectively main intermediates for EG and
PG. In addition, a series of parallel side reactions compete the main pathway leading to by-
products like mannose and fructose (from glucose isomerization), sorbitol (from glucose
hydrogenation), erythritol (from erythrose that comes from incomplete RAC of glucose) and
glycerol (from dihydroxyacetone hydrogenation that comes from fructose) [2].
To better understand the reaction pathways involved in the transformation of lignocellulose to
glycols, the monitoring of the reaction is required starting from glucose up to more complex
matrices (cellobiose, cellulose and lignocellulose). So far, the catalytic conversion of glucose in the
presence of 5%Ni-30%W 2C/AC was done with regular sampling over time and the main
intermediates compounds were identified and quantified by HPLC-RID-UV. The variation of
experimental parameters (temperature, pressure, concentration) and the replacement of glucose
substrate by intermediates will be performed to validate the reaction pathway and to develop a
robust kinetic model. This model will integrate reaction and diffusion for different stages of the
reaction allowing the understanding of the mechanisms involved in the transformation of
lignocellulosic biomass to polyols.
[1] F. Goc, PhD Thesis, Université Claude Bernard Lyon 1 (2022).
[2] Ji et al., Angew. Chem. Int. Ed., 47 (2008) 8510-8513 ; Ooms et al., Green Chem., 16 (2014) 695-707.