Liquefaction of wood in two successive steps: solvolysis in ethylene-glycol and catalytic hydrotreatment

The purpose of this paper is to describe a process of wood liquefaction in two steps: a first step of wood solvolysis in acidified ethylene-glycol or in some recycled solvent; a second step of catalytic hydrogenation at high pressure of the solvolysis liquid product. For the solvolysis step, the liquefaction yield is limited by the acidity of reactant media and by the formation of a coke-like residue. A kinetic model of solvolysis is proposed accounting for the production of the coke-like residue. When using recycled solvolytic oil instead of fresh ethylene-glycol, the conversion into liquid is also reduced and the viscosity of the solution strongly increases. The step of hydrogenation was investigated by varying different parameters, i.e., the nature of the catalyst, the initial hydrogen pressure (30-60-90 MPa), the maximal temperature of plateau (from 330 to 400 °C) and the ratio tetralin/solvolytic oil. A slightly better deoxygenating rate is obtained by using a Ni-Mo bi-functional catalyst. The deoxygenation rate increases with the tetralin/solvolytic oil ratio and a minimum value of 0.5 for this ratio is necessary to prevent the unwanted formation of a solid residue. After hydrogenation, an upgraded oil is obtained with a heating value similar to that of a usual petroleum fuel.