Catalytic hydrogenation of coniferyl alcohol as a stabilisation process for lignin monomers : correlation between the catalytic performance and the physico-chemical properties of Ni/TiO2 catalysts

Details

Supervisors

Debecker, Damien P. ; Cybulska, Iwona

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries

Abstract

Nowadays, with the depletion of fossil fuels as main source of energy and chemicals, strong alternatives are more than ever required. Among them, the biorefinery concept has emerged since a few years. A biorefinery is a network of facilities that process the different components of biomass to produce biofuels, energy and chemicals. Currently, few industries (paper, 1st generation biofuels, etc.) that use lignocellulosic biomass as feedstock valorise the carbohydrate fraction while the lignin fraction is burned for energy leaving aside the potential of lignin for high-value applications. In order to valorise the carbohydrate and the lignin fractions, a new process, the reductive catalytic fractionation, was imagined a few years ago. This process, which mainly focuses on lignin valorisation, allows the separation of both fractions without generating intermediate technical lignin and is divided in three distinct parts occurring simultaneously. The solubilisation of lignin, the depolymerisation of lignin into unstable phenolic monomers and finally the stabilisation of these monomers. In order to study the stabilisation step, which takes place in the presence of a heterogeneous catalyst, Ni/TiO2 catalysts with different loadings and different TiO2 supports were synthesised by incipient wetness impregnation method. As lignin polymer is a complex matrix, a model compound (coniferyl alcohol) was used rather than biomass to investigate the catalytic hydrogenation. A series of characterisation studies were done on these catalysts: N2 physisorption, XRD, TEM, NH3 physisorption and CO chemisorption. The efficiency of the catalysts was investigated by comparing the conversion, the selectivity and the yield values of the lignin monomer stabilisation reaction. Then, the role of H2 during the reaction was also studied by changing the initial pressure of hydrogen or testing other solvents. The catalysts supported on P25 stand out high performance as compared to other supports. The latter were affected by the strong metal support interaction effect that decreases the surface of available Ni on the catalyst. It was also shown that the hydrogenation of coniferyl alcohol can be performed with good performance with reduced amount of hydrogen but also without external source of hydrogen if a hydrogen-donor solvent such as isopropanol is used