Hydrothermal liquefaction of lignocellulosic biomass to produce biofuels

  • Author / Creator
    Mathanker, Ankit
  • There is an increasing need of clean renewable energy sources to address the growing problems of greenhouse gas emission, global warming and climate change. The rapid consumption of fossil fuel resources has also contributed to toxic emissions and raised a question on sustainability of present fuels. Hence, alternative renewable fuels such as biofuels have been considered as a promising low pollution source. Biomass is composed of the green carbon i.e. carbon that belongs to the present biological cycle, making it a cleaner fuel. Biomass has an inherent energy that comes from the sun and has possibility to regrow in a short period of time. Lignocellulosic biomass mainly derived from agricultural and forest can be processed through pyrolysis, gasification, steam reforming and hydrothermal liquefaction to obtain high energy density biofuels. Predominantly, all biomass materials contain high moisture, which makes the hydrothermal liquefaction as the most effective technique for conversion of biomass to biofuels such as bio-oil, hydrochar and gases. In this work, hydrothermal liquefaction process was used for conversion of lignocellulosic biomass (corn stover) into liquid, solid and gaseous fuels at moderate temperature in the range of 250 – 375 °C, final pressure (Pf) in range of 1100 – 3400 psi and retention time (tr) in range 0 – 60 min. The key focus of this research work is to understand feedstock properties, develop experimental methodology for hydrothermal liquefaction and apply it for conversion of biomass to biofuels. The study also attempts to optimize the process parameters with an aim to obtain quantitatively and qualitatively better biofuels. The experiments were performed in a 250 mL, high pressure autoclave batch reactor having temperature and pressure upper limit of 500 °C and 5000 psi (34.47 MPa) respectively. An inert nitrogen environment was maintained. The final recovered slurry was processed through a detailed separation procedure in order to obtain the bio-oil and hydrochar separately for analysis. In order to understand the properties of products, characterization tests such as elemental analysis and GC-MS was performed on bio-oil and elemental analysis, FTIR and SEM were carried out on hydrochar. The quantitative results obtained at different operation conditions gave a highest yield of heavy oil (29.25 wt.%) obtained at 300 °C, final pressure, Pf, of 2200 psi and 0 min retention time. The highest yield of hydrochar (30.21 wt.%) was obtained at 350 °C, Pf of 3150 psi and soak period, tr, of 15 min. Based on elemental analysis and energy calculation, highest carbon content and higher heating value for heavy oil was 76.32 wt.% and 35.13 MJ/kg at 375 °C, Pf of 600 psi and tr of 15 min; and for hydrochar it was 68.23 wt.% and 24.7 MJ/kg at 350 °C, Pf of 3150 psi and tr of 15 min. The GC-MS results for heavy oil indicated that majority of the compounds were phenolic in nature. FTIR results confirmed the decomposition of protein and carbohydrate and formation of new aromatic bonds in hydrochar during HTL. The morphology results for different hydrochar indicates the breaking of fibrous structure and formation of a more porous material. Even though, quality of oil obtained in this study was good, more studies need to be carried out in a direction to upgrade oil by reducing the oxygen content and increasing the higher heating value; moreover, developing better understanding by analyzing viscosity and total acid number value.

  • Subjects / Keywords
  • Graduation date
    Spring 2020
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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