Hydrodeoxygenation of methyl heptanoate and phenol over sulphided supported NiMo and CoMo catalysts

Abstract

Biomass-based energy sources are under intensive study for replacing fossil fuels with environmentally friendly alternatives. Bio-oils, intended for use as such or mixed with fossil fuels, need to be upgraded by hydrodeoxygenation (HDO) due to the high oxygen-content of the molecules, which causes unwanted fuel properties. This thesis describes oxygen removal reactions of methyl heptanoate and phenol over sulphided NiMo/γ-Al2O3 and CoMo/γ-Al2O3 catalysts. These two components were chosen as representative model reactants of the complex bio-oils. Reaction schemes for the HDO of methyl heptanoate and phenol are presented. Reaction steps were justified with acid-catalysed reactions (hydrolysis, dehydration, esterification), reductive reactions and decarbonylation. Reactivity of the reactants individually and as a mixture and their product distributions were explored with and without a sulphur additive as sulphur is needed to keep the catalyst in the sulphided form. Sulphur-containing components were formed during the HDO reactions even without sulphur addition during the experiments. The source of the sulphur is the sulphur species attached to the catalyst surface. Possible active sites are also discussed. Reduction reactions were proposed to occur on coordinatively unsaturated sites (CUS), whereas acid-catalysed reactions and decarbonylation need sulphur-saturated sites. The vapour-liquid equilibrium (VLE) of methyl heptanoate and solvent, in this case m-xylene, was measured to improve composition analysis of the multi-phase system. The Predictive Soave-Redlich-Kwong (PSRK) model was shown to be a good tool for simulation of the gas phase of a non-ideal system with polar components. The findings give new insights into the HDO reactions by describing the reaction pathways of two different types of model components and how the sulphur species affect those pathways. Moreover, the performance of the sulphided catalyst and simulation of a non-ideal system are presented.