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G+PS regularly provides virtual sessions that focus on admission requirements and procedures and tips how to improve your application.
Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - May 2021)
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.
Pulp and paper facilities are transforming into innovative biorefineries producing chemicals and materials in order to enhance competitiveness and environmental performance. Hemicellulose fractionation and its integration with the pulp mill are crucial to successful biorefinery processes. Fundamental insight is needed to support technology growth.Hemicellulose oligomers were extracted by hydrolysis of softwood chip fines using hot water; conditions were optimized for high yield and high molar mass. Comprehensive characterization of hydrolysate and hydrolyzed solids is reported. A two-dimensional calibration method enabled measurement of oligomer molar mass and concentration simultaneously by size exclusion chromatography. A population balance model describing evolution of hemicellulose molar mass during hydrolysis was posed. The model describes the full evolution of oligomers from initial softwood solubilization, depolymerization to ever-smaller molecules until final generation of degradation products. A maximum yield and corresponding treatment condition for a specific molar mass could be predicted. Likely modes of hemicellulose bond breaking within the wood matrix and bulk solution are proposed and physical insights are explained. This work provides fundamental insights into the relative reactivity of hemicellulose intermediates to facilitate future conversion technologies.Two hemicellulose hydrolysis integration methods to kraft pulping are proposed. First, adsorption of locust bean gum (LBG, model compound) to Northern Bleached Softwood Kraft (NBSK) pulp was shown to improve paper tensile and burst strength and lower refining time by strengthening inter-fibre bonding. LBG adsorption to NBSK pulp fibre is dependent on electrostatic forces, and high salt addition at low pH facilitates adsorption. The adsorption followed pseudo-second-order kinetics and the Langmuir adsorption isotherms, indicating a reversible, monolayer, homogenous adsorption to a finite number of sites on the fibre surface with chemisorption as the rate determining step. Second, mild hydrolysis was combined with kraft pulping as pre-treatment to produce hemicellulose oligomer and kraft pulp. Particle size effects on hydrolysis and subsequent kraft pulping were assessed. Kraft pulping of pre-hydrolyzed softwood chips enhances delignification, reduces fibre yield and chemical consumption, producing fibres with decreased fibre dimension but increased water retention value. The advantages and disadvantages of pre-hydrolysis integration to kraft pulping and associated challenges and future recommendations are discussed.
Ethanol produced from lignocellulose is one of the most promising biofuels. However, the technology to produce lignocellulosic ethanol is still under development and needs to be improved to become economically viable. Enzymatic hydrolysis is one of the most expensive process stages, primarily due to high enzyme costs. Consequently, two cost reduction strategies were studied: optimization of hydrolysis conditions and enzyme recycle by adsorption. To optimize enzymatic hydrolysis, the changes in concentration of cellulases during the reaction must be determined. Protein concentration changes under hydrolysis conditions for Celluclast 1.5L and Novozyme 188, were studied in the absence of substrate. Novozyme 188 protein concentration decreased by 55 to 64% at 50°C after 92 h. A model describing Novozyme 188 protein concentration changes was developed and used to determine free and adsorbed cellulases concentrations. Glucose and xylose yields (58 to 89% conversion) during enzymatic hydrolysis were modeled as a function of enzyme loading, time, lignin content and solids concentration. The proposed model successfully describes hydrolysis of substrates with different lignin contents, linking pretreatment and hydrolysis. The effect of lignin content, enzyme loading and hydrolysis time on enzyme recovery was evaluated, achieving 0 to 35% cellulases recycled. A mass balance of the enzyme recovery process was built and used to achieve a uniform production of sugar. Based on experimental data and the proposed models, the production of ethanol with and without enzyme recycling was simulated in AspenPlus. The ethanol production process at different operating conditions was economically evaluated. The economic analysis showed that raw material expenses determine production costs, where biomass, caustic and enzyme expenses are the major contributors to the operating cost. The lowest production costs ($1.86 and $2.13/ kg ethanol) were obtained at low enzyme loadings and mild pretreatment conditions. Sugar losses at severe pretreatment conditions have a significant negative effect on production costs: severe conditions increased production cost by 18 to 23%. Therefore, optimal hydrolysis conditions must be determined considering the entire process. The implementation of the enzyme recycling process decreased production costs up to 14% depending on operating conditions, demonstrating the potential benefits of the enzyme recycling technology.
Master's Student Supervision (2010 - 2020)
Non-renewable fossil fuels and the dangers of climate change have drawn significant research into the forest biorefinery. The pulp and paper industry is positioned to lead the implementation of new technologies from such research.Northern Bleached Softwood Kraft (NBSK) pulp is one of the chief products of the pulp and paper industry in British Columbia (B.C). It is primarily used as reinforcing pulp. Hemicellulose present in mill waste streams such as hog fuel, primary sludge, and chip fines, can be separated and utilized as a strength additive to improve physical strength properties of NBSK pulp, and reduce refining energy.This study investigated the influence of operating variables on the separation of hemicellulose oligomers from these lignocellulosic waste streams, and the adsorption of these oligomers onto NBSK pulp. Reaction temperature and residence time were studied for the separation of hemicellulose, while adsorption temperature, time, fibre consistency, oligomer-to-pulp percentage, and weight average molar mass Mw, were studied for the adsorption of hemicellulose onto NBSK pulp. Hog fuel and primary sludge were found to contain 58.98% and 67.90% polysaccharides respectively. Hemicellulose oligomer yields greater than 90% were obtained from hog fuel via liquid hot water treatment, and from primary sludge via dilute acid hydrolysis. A maximum total oligomer mass of 3.25g was obtained from 25g oven-dry hog fuel. Oligomer-to-pulp percentage and fibre consistency showed a linear effect on the adsorption yield, while adsorption temperature showed a nonlinear effect. The results are encouraging, and suggest the potential of these waste streams to produce a green hemicellulose-based paper strength additive.
The challenges of upgrading pyrolysis oil to transportation fuel limit the economic viability of biomass pyrolysis. Therefore, this dissertation investigated partial oxidation of pyrolysis oil to produce value-added chemicals. Two model compounds, acetic acid (AcOH) and acetaldehyde (AcH) were selected for gas phase oxidation trials. Thermal oxidation of AcOH emphasized AcOH’s refractory nature as the maximum conversion of AcOH was less than 6% at 350 ⁰C at 1 atm with GHSV of 2000 h-¹. AcH was more reactive; conversion of AcH was approximately 40% under identical conditions. Thermal oxidation of both compounds produced only carbon dioxide (CO₂). Although the true reaction mechanism of AcH thermal oxidation could not be determined, the activation energy was calculated to be between 47.1±0.55 kJ/mol and 55.2±0.6 kJ/mol. Catalytic partial oxidation (CPO) of AcOH and AcH was examined using vanadium pentoxide supported by titanium oxide (V₂O₅/TiO₂). Conversion of CPO of AcOH was slightly higher than thermal oxidation but produced only CO₂. CPO of AcH generated AcOH, a desirable product, as well as formic acid (FA), carbon monoxide (CO) and CO₂, suggesting that multiple reactions occurred. However, the selectivity to AcOH was relatively low (43% at 175 ⁰C, GHSV=20000 h-¹, 2.4V/TiO₂). The selectivity of AcH to AcOH was improved by adjusting temperature, adopting higher vanadium (V) loading catalysts, and increasing oxygen (O₂) concentration. At 200 ⁰C, GHSV=20000 h-¹, and using 6.9V/TiO₂, the selectivity to AcOH increased to 70%. Constant selectivity of all products with respect to residence time indicates the reactions are likely parallel. The rate constant for AcH CPO was calculated assuming an overall 1st order reaction. The linearized Arrhenius law yielded an activation energy of 43.9 kJ/mol for the overall AcH CPO reaction. Simultaneous CPO of AcH and AcOH was also examined. The conversion of AcH in the mixture was similar to the conversion of CPO of AcH alone. This study demonstrated the feasibility of producing AcOH via CPO of AcH. The viability of partial oxidation of pyrolysis oil must be confirmed using model compounds with more complex functional groups and pyrolysis oil.