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Evaluation of Solvent Extraction of Lignite for Production of Transportation Fuels Open Access


Other title
solvent extraction
Coal liquid
transportation fuels
Type of item
Degree grantor
University of Alberta
Author or creator
Adesanwo, Toluwanise I J
Supervisor and department
Dr Arno De Klerk (Chemical and Materials Engineering)
Dr Rajender Gupta (Chemical and Materials Engineering)
Examining committee member and department
Dr Joao Soares (Chemical and Materials Engineering)
Dr Arno De Klerk (Chemical and Materials Engineering)
Dr Rajender Gupta (Chemical and Materials Engineering)
Dr Petr Nikrityuk (Chemical and Materials Engineering)
Department of Chemical and Materials Engineering
Chemical Engineering
Date accepted
Graduation date
Master of Science
Degree level
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.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Adesanwo, T.; Rahman, M.; Gupta, R.; de Klerk, A. Characterization and Refining Pathways of Straight-Run Heavy Naphtha and Distillate from the Solvent Extraction of Lignite. Energy & Fuels 2014, 28 (7), 4486-4495

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