Studies on lignin model compounds upgrading with in-situ glycerol aqueous phase reforming and the application for upgrading of ligneous material

Lignin and glycerol, residues of renewable biomass processing, have significant potential as fuels and chemicals. Lignin is a polymer of phenylpropanoids monomers and is a promising source of renewable hydrocarbons due to its relatively high C/O ratio compared to carbohydrates. However, it also requires hydrogenation for further valorization. Unfortunately, hydrogen currently comes primarily from petroleum, natural gas, and coal. Aqueous phase reforming (APR) of glycerol is a renewable source of hydrogen. This relatively low temperature reforming reaction is thermodynamically possible due to the presence of a C-O bond on every carbon of glycerol. This thesis explores the possibility of lignin depolymerization and fast pyrolysis oil (FPO) hydrogenation using renewable hydrogen from glycerol. This study was conducted with phenol as a model compound. Upgrading more complex materials such as FPO and native lignin from crushed mixed spruce, pine, and fir (SPF) pellets was also tested. Operating conditions were varied in order to understand reaction mechanisms. First, glycerol APR was conducted with Raney Ni® and it was found that glycerol APR occurred via parallel reactions of 1,2-propylene glycol and ethylene glycol. During glycerol APR, CO₂ and CH₄ were the dominant gaseous products while the produced hydrogen tended to react with glycerol, glycerol intermediates (direct methanation) or CO₂ (Sabatier) to form CH₄. The presence of phenol during glycerol APR increased the glycerol reaction rate and CO₂/CH₄ ratio due to the consumption of hydrogen, and produced cyclohexanol, cyclohexanone, and benzene. Phenol hydrogenation during in-situ glycerol aqueous phase reforming and phenol hydrogenation (IGAPH) occurred without the formation of molecular hydrogen as the hydrogen produced by glycerol APR was consumed by phenol before molecular hydrogen could form and desorb from the catalyst surface. The mechanism of phenol hydrogenation during IGAPH is hypothesized to follow the Langmuir-Hinshelwood mechanism. Hydrodeoxygenation (HDO) of phenol could be achieved using the combination of hydrogenation (Raney Ni® and Pt/C) and acid catalysts (Amberlyst-15 and H-ZSM-5). During FPO and SPF upgrading with Pt/C and H-ZSM-5, n-decane was used to separate nonpolar deoxygenated products from very reactive carbohydrates derivatives to prevent condensation reactions. Gasoline-like compounds were obtained from FPO and SPF upgrading.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat

Lignin depolymerization and monomeric evolution during fast pyrolysis oil upgrading with hydrogen from glycerol aqueous phase reforming

A novel approach to Fast Pyrolysis Oil (FPO) upgrading with hydrogen from glycerol aqueous phase reforming (APR) was conducted in a biphasic solution. FPO contains both monomer and polymer compounds which rich in oxygen, giving high acidity and low stability. Hydrogen demanding reaction of depolymerization and hydrodeoxygenation (HDO), often called upgrading, is required to improve FPO properties by converting these compounds to hydrocarbon monomers. APR reaction of glycerol where glycerol is reacted with water to produce hydrogen is one of the renewable choices to obtain hydrogen. Prior to upgrading of FPO, catalyst screening and reaction optimization were studied using phenol as a model compound. Upgrading of FPO with in situ glycerol APR was conducted with Pt/C, facilitating hydrogen production (APR) and utilization (hydrogenation), and H-ZSM-5, facilitating dehydration reaction. n-Decane was added to the reaction as a co-solvent to prevent the condensation of the non-polar fragments of FPO which led to coke formation. Upon upgrading the weight average molecular weight (Mw), polydispersity index (PDI), and oxygen to carbon (O/C) ratio of FPO decreased. The highest hydrocarbon yield (7.7 FPO basis or 34.6 lignin basis) was obtained by combining Pt/C and H-ZSM-5 catalysts with n-decane as a co-solvent. Evidence of progressive depolymerization and sequential demethoxylation, hydrogenation, and deoxygenation during upgrading were observed in the products. © 2022 Elsevier Lt