Steam pretreatment for coal liquefaction.
Item
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Title
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Steam pretreatment for coal liquefaction.
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Identifier
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AAI9732931
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identifier
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9732931
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Creator
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Ivanenko, Olga.
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Contributor
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Adviser: Robert A. Graff
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Date
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1997
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Chemical | Energy
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Abstract
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The objectives of this work are to test the application of steam pretreatment to direct coal liquefaction, to investigate the reaction of model compounds with water, and to explore the use of zeolites in these processes.;Previous work demonstrated the effectiveness of steam pretreatment in a subsequent flash pyrolysis. Apparently, subcritical steam ruptures nearly all of the ether cross links, leaving a partially depolymerized structure.;It was postulated that very rapid heating of the pretreated coal to liquefaction conditions would be required to preserve the effects of such treatment. Accordingly, a method was adopted in which coal slurry is injected into a hot autoclave containing solvent. Since oxygen is capable of destroying the pretreatment effect, precautions were taken for its rigorous exclusion.;Tests were conducted with Illinois No. 6 coal steam treated at 340{dollar}\sp\circ{dollar}C, 750 psia for 15 minutes. Both raw and pretreated samples were liquified in deoxygenated tetralin at high severity (400{dollar}\sp\circ{dollar}C, 30 min.) and low severity (a: 350{dollar}\sp\circ{dollar}C, 30 min., and b: 385{dollar}\sp\circ{dollar}C, 15 min.) conditions under 1500 psia hydrogen. Substantial improvement in liquid product quality was obtained and the need for rapid heating and oxygen exclusion demonstrated. Under low severity conditions, the oil yield was more than doubled, going from 12.5 to 29 wt%.;Also chemistry of the pretreatment process was studied using aromatic ethers as model compounds. {dollar}\alpha{dollar}-Benzylnaphthyl ether ({dollar}\alpha{dollar}-BNE), {dollar}\alpha{dollar}-naphthylmethyl phenyl ({dollar}\alpha{dollar}-NMPE), and 9-phenoxyphenanthrene were exposed to steam and inert gas at pretreatment conditions and in some cases to liquid water at 315{dollar}\sp\circ{dollar}C. {dollar}\alpha{dollar}-BNE and {dollar}\alpha{dollar}-NMPE showed little difference in conversion in inert gas and in steam. Hence, these compounds are poor models for coal in steam pretreatment. Thermally stable 9-phenoxyphenanthrene, however, was completely converted in one hour by liquid water at 315{dollar}\sp\circ{dollar}C. At pretreatment conditions mostly rearranged starting material was obtained. Therefore, 9-phenoxyphenanthrene, though less reactive, is a model for ether linkages in coal.;Application of 5A zeolite suppressed isomerization of {dollar}\alpha{dollar}-BNE improving the yield of thermolysis products in steam and in inert gas. Pretreatment and liquefaction of mixtures of coal and zeolites increased yields of asphaltenes and preasphaltenes under both high and low severity conditions.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
