Hydrothermal liquefaction of lignocellulosic biomass using water and hydrogen-donor solvent mixtures to produce energy-dense heavy oil

  • Author / Creator
    Das, Snehlata
  • Energy transition from non-renewable to renewable energy is required to confront rising levels of greenhouse gas emissions responsible for increasing global temperatures and disrupting weather patterns. Switching to renewable energy sources for energy generation also resolves the issues related to depletion of fossil fuels and promises sustainable growth of the country. Lignocellulosic biomass are renewable sources of energy that can be converted into fuels and platform chemicals, proving to be effective alternative sources of energy generation. Agricultural and forest wastes that are underutilized and abundant in Canada, are carbon-rich sources of energy that have the potential to be used as feedstock in bio-industries. Thermochemical conversion technologies can convert these carbon-rich lignocellulosic biomass into valuable transportation fuels.

    Hydrothermal liquefaction (HTL) is a thermochemical conversion technology that allows high-moisture content lignocellulosic biomass feedstocks to be converted into energy-dense heavy oil, along with hydrochar, aqueous phase fraction and gases as by-products. Present study involves the use of corn stover, wheat straw and hardwood as biomass feedstock for HTL conversion process operated at 300°C, final pressure range 2200 psi to 2450 psi, and zero min retention time. HTL experiments will focus on selecting biomass of varying composition of polymers and inorganic content and their effect on yield and quality of heavy oil and hydrochar. Experiments will also extend towards the study of addition of alcoholic Co-solvents to water on heavy oil and hydrochar yield and quality, as a means of initial upgrading step necessary for HTL operation.
    HTL experiments were conducted in a 250 mL, T316-T high pressure-high temperature autoclave bench top reactor, with reactions taking place in nitrogen gas environment. Product separation and recovery was conducted through detailed procedure provided in later chapter, heavy oil and hydrochar was obtained separately for analysis. Characterization tests on heavy oil such as CHNS, GC-MS, TAN and TGA, and for hydrochar CHNS and SEM analysis were conducted.
    Among agricultural and forest biomass, highest heavy oil yield obtained was 42.0 wt.% and hydrochar content of 14.6 wt.% when hardwood was the feedstock for HTL experiment, at reactor temperature of 300°C, final pressure of 2200 psi and 0 min retention time. HTL experiments performed on agricultural feedstocks, have shown relatively lesser yield and quality of heavy oil as compared to that obtained by using forest biomass as feedstock, and present HTL experiments using water and Co-solvent mixtures have been conducted on primarily corn stover and wheat straw. Heavy oil derived from wheat straw showed the highest energy content of 32.86 MJ/kg, lowest oxygen content of 17.99 wt.%, highest light naphtha fraction of 20.66 % and lowest middle distillate fraction of 22.56 %, using water-2-propanol mixture. Therefore, addition of alcoholic Co-solvent with water eases the conversion of biomass polymers to valuable chemicals and produces heavy oil resembling gasoline or diesel. Further work is required to understand the interaction of Co-solvents with small constituents of biomass such as extractives and inorganic matter, which would determine the selectivity of certain compounds necessary for producing useful chemicals and fuels. Also, the effect of adding alkali catalyst with water-Co-solvent mixture needs to be explored, in order to understand their performance on heavy oil yield and quality.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.