Evaluation of Solvent Extraction of Lignite for Production of Transportation Fuels

• Author / Creator

  Adesanwo, Toluwanise I J

• Previous studies on the extraction of liquid products from coals have focused mainly on increasing the yield, with very little emphasis on the quality of the liquid products. The main goal of this study is to achieve a balance between the yield and quality of the coal derived liquids. The first part of the study focused on characterizing four fractions of coal liquid produced from thermal liquefaction, comparing the properties with those of specification fuels, and identifying refining pathways to produce on-specification fuels. The second part of the research focuses on studying the effects of liquefaction conditions on coal liquid quality. The quality was assessed by different analytical techniques including gas chromatography-mass spectrometry, high-performance liquid chromatography, and nuclear magnetic resonance.

  In the first part of the study, Coal liquids were produced by solvent extraction of Bienfait lignite at 415 °C and 4 MPa H2 for 1 h with a hydrotreatedcoal tar distillate in 2:1 solvent to coal ratio. Detailed characterization was performed on four straight run distillation fractions of the coal liquids in the 120-370 °C boiling range. Potential refining challenges were indentified by comparing the properties of the derived liquids with on- specifications of gasoline, jet and diesel fuel. Results indicate that coal-derived naphtha can be refined to an aromatic motor-gasoline blending component by mild hydrotreating to remove the heteroatoms present in the naphtha. Similarly, coal-derived kerosene can be converted into a jet fuel blending component, but does not meet standard specifications for jet fuel. Coal derived distillate; however, is a poor feed material for diesel fuel production.

  The second part of the study seeks to understand the impact of liquefaction conditions on the molecular composition of coal derived liquids and in particular on the aromatic hydrocarbon composition. A sensitivity analysis is analysis is carried out to study the effects of temperature and residence time on the quality of the liquid products. Thermal digestion of a Canadian lignite coal was performed in an autoclave reactor. An industrial hydrogenated coal tar distillate was used as solvent with a coal to solvent ratio of 1:2. Digestion was carried out under initial hydrogen pressure of 4MPa at different temperatures and for different lengths of time. The reaction time was divided into two periods: heat-up time; the time required to heat the reactor from 25 oC to the operating temperature, and hold time; the time at the operating temperature before being cooled down. The tetrahydrofuran (THF)-soluble portion of the product was collected for analysis. The micro carbon residue (MCR) content of the THF-soluble liquids suggest an increases in the concentration of heavier molecules in the liquids as the reaction temperature and hold time increases. High performance liquid chromatography (HPLC) analysis revealed that the mono-aromatic and di-aromatic content decreased as the reaction temperature increased from 350 to 450 oC. This was accompanied with an increase in heavier polyaromatic hydrocarbons as well as the formation of new species of heavier polyaromatic hydrocarbons. Given that homolytic bond cleavage increases as reaction temperature increases, heavy polyaromatic hydrocarbon content is expected to decrease as reaction temperature increases. However, preliminary results indicate an increase in free radical recombination reactions and hydrogen disproportionation reactions as the liquefaction temperature increased from 350 to 450 oC. In a typical experiment, a 1.6 wt% reduction liquid yield was observed as the hold time increased from 15 minutes to 30 minutes at 450 oC. An increase in heavy aromatics content would be understandable if liquid yield increased, as this will imply a trade-off between yield and quality. However, increasing the severity and time of thermal digestion of lignite coal resulted in lower quality coal liquids, without an increase in liquid yield.

• Subjects / Keywords

  • Coal liquid
  • Lignite
  • Transportation fuels
  • Refining
  • Solvent extractions
  • Coal

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3637D

• 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.