Catalytic liquefaction and hydrodeoxygenation, the case of a real feed: Wheat straw soda lignin
Résumé
Nowadays, lignin, one of the main biomass components, is co-produced in quite large quantities in pulp industry and only used as a low-value fuel to afford energy. The valorization of lignin is highly desirable since its macromolecular aromatic structure makes it a perfect precursor for aromatic and phenolic compounds. Additionally, it can be planned that the lignin co-production will dramatically increase in the near future in the biorefineries processes with the use of cellulose for the production of bio-ethanol. A way to valorize the lignin is the depolymerization by thermochemical processes as pyrolysis, hydroconversion, hydrothermal conversion, solvolysis and cracking. All these processes must be catalytically assisted to obtain acceptable liquid yields and decrease the solid residues. On the other hand, in the coal liquefaction process, the use of H-donor solvent was found very efficient to avoid solid formation. We present here a study on the hydroconversion of lignin in tetralin, with a NiMoP alumina supported catalyst. This work allowed us to obtain very high liquid yield from a wheat-straw soda lignin (up to 74 wt% based on initial ash-free lignin) and with an excellent mass and carbon balance. A product recovery protocol was implemented and the gases, liquids and solid fractions were separated, quantified and deeply characterized. The solids were separated in two fractions: a partially converted lignin called lignin residue soluble in THF and the THF-insolubles. Several analytic techniques were undertaken to characterize deeply the different fractions: mGC-MS to identify the gas components; CHONS, Gel-permeation chromatography and NMR were used to characterize the liquids and solids. Two-dimensional GC with MS and FID detectors was successfully used to respectively identify and quantify the different monomers of the liquid phase.