New Direction to Preconversion Processing for Coal Liquefaction

Nishioka, Masaharu; Laird, Wallace; Bendale, P.G.; Zeli, Ronald A.

doi:10.1021/ef00045a020

Cited by 11 publications

(9 citation statements)

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“…For experiments with added water, the ratio of coal to water was kept at 2, based on earlier work of Song et al with Wyodak coal . Reaction temperatures in the range 200−350 °C have been shown by many investigators to be appropriate for pretreatment of low-rank coals. − , The pressure of the gas charged (H 2 or N 2 ) was 1000 psi at room temperature. The reactor pressure increased to ∼1500 psi at 330 °C for reactions in the absence of water and ∼2150 psi for reactions in the presence of water.…”

Section: Methodsmentioning

confidence: 99%

“…As examples of such pretreatment methods, heating under molecular hydrogen with or without added solvent or catalyst, − heating in CO−H 2 O in the presence of basic catalysts or with steam, − and solvent swelling of coals − were reported to be effective in enhancing conversion and improving the quality of liquid products in liquefaction reactions. Steam treatment was also found effective in the improvement of extraction , and pyrolysis yields. ,− In solvent-swelling pretreatment, coal exposed to an effective swelling solvent has been considered to be more accessible to catalyst, molecular hydrogen, and donor solvent. − Depending on the conditions and the type of additives, combinations of the cleavage of relatively weak bonds, an increase of the labile hydrogen content in coal, and some extent of defunctionalization and depolymerization reactions may be anticipated in the former case.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Water and Molecular Hydrogen on Heat Treatment of Turkish Low-Rank Coals

et al. 1998

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Two low-rank Turkish coals, Tunçbilek (TB) subbituminous and Göynük (GN) lignite, were subjected to low-severity heat treatment with or without added water, under N2 or H2 atmospheres at 285−330 °C, both as original coals and after demineralization with HCl(aq)/HF(aq) treatment. The samples processed in H2−H2O combination seemed to be more dissociated or decomposed than those processed in N2−H2O or under H2 without water. Gas analyses and spectroscopy of samples clearly indicated an effect of water in enhancing decarboxylation reactions and that oxygen rejection from the coals was mainly due to CO2 formation. Water also enhanced the cleavage of aryl−ether bonds. These cleavage reactions are more pronounced in GN coal than in TB coal, probably due to a higher concentration of activated ether structures in the former coal. The disruption of noncovalent interactions is considered mainly responsible for the extensive depolymerization of TB coal. The role of H2 in these heat treatment conditions is considered to be predominantly hydrogenation of polyaromatic sites with the help of mineral matter and scavenging radicals, which arose from cleavage of weak aliphatic ether bonds. The coal samples treated in H2−H2O donated more hydrogen to anthracene during their co-pyrolysis, attributed mainly to a reduced tendency of the treated samples to undergo radical-generating reactions.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Water and Molecular Hydrogen on Heat Treatment of Turkish Low-Rank Coals

et al. 1998

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“…The design of the next generation of coal liquefaction processes will require a deeper understanding of coal's intrinsic properties and the ways in which it is chemically transformed under process conditions. 25,26 Coal properties such as the chemical form of the organic material, the types and distribution of organics, and the nature of the pore structure must be determined for coals of different ranks in order to use each coal type most effectively.…”

Section: Coal Structurementioning

confidence: 99%

“…The first type of pretreatment methods is heat treatment. 25,[130][131][132] The low temperature treatment could allow time both for solvent penetration and hydrogen transfer. Preheat treatment at 200 C 130 and 277-322 C 131 has been shown to increase conversions for the noncatalytic liquefaction of bituminous coals.…”

Section: Nonradical Reactionsmentioning

confidence: 99%

Clean liquid fuels from direct coal liquefaction: chemistry, catalysis, technological status and challenges

Vasireddy

Morreale

Cugini

et al. 2011

Energy Environ. Sci.

344

209

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Increased demand for liquid transportation fuels coupled with gradual depletion of oil reserves and volatile petroleum prices have recently renewed interest in coal-to-liquids (CTL) technologies. Large recoverable global coal reserves can provide liquid fuels and significantly reduce dependence on oil imports. Direct coal liquefaction (DCL) converts solid coal (H/C ratio z 0.8) to liquid fuels (H/C ratio z 2) by adding hydrogen at high temperature and pressures in the presence or absence of catalyst. This review provides a comprehensive literature survey of the coal structure, chemistry and catalysis involved in direct liquefaction of coal. This report also touches briefly on the historical development and current status of DCL technologies. Key issues, challenges involved in DCL process and directions for the future research are also addressed.

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“…Soaking coal in a coal liquid at a temperature between 350 and 400 °C prior to coal liquefaction is a very effective conversion method, which does not make use of hydrogen. − It has been found that the addition of small amounts of peroxides for this procedure provides further conversion. This communication reports results which may be useful in thedevelopment of an economical liquefaction process.…”

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confidence: 99%

Effect of Peroxides during Pretreatment for Coal Liquefaction

Nishioka

2003

Energy Fuels

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Soaking coal in a coal liquid at a temperature between 350 and 400°C prior to coal liquefaction is a very effective conversion method, which does not make use of hydrogen. 1-3 It has been found that the addition of small amounts of peroxides for this procedure provides further conversion. This communication reports results which may be useful in thedevelopment of an economical liquefaction process.Coal molecules are strongly associated with each other, resulting in difficult solubilization. 1,4 This in turn produces only a portion of coal that is extracted with good solvents. 5 Since intra-and intermolecular interactions stronger than hydrogen bonds and dispersion forces are significant in coal, higher temperatures are necessary to overcome these interactions. 1 Temperatures above 300°C may be required to provide the sufficient solvation of coal. 2 If temperatures are lower than 300°C, coal may associate more at higher temperatures because coal tends to reach a stable conformation due to molecular mobility at such temperatures. 1,6,7 Solvation will result in more swelling, dissolution, and reduction in particle sizes as schematically shown in Figure 1. A better reactivity is expected for more dissociated coal ( Figure 1c) during coal liquefaction. From a structure point of view, the following suggestions are made to solvate coal before liquefaction:(1) coal should be treated at as low concentrations as possible, 4,8 (2) coal should be treated at temperatures higher than 300°C, 2 (3) raw coal should be used rather than dried coal, 9 (4) demineralized coal should be used if a catalytic effect of mineral is negligible. 9 These optimal conditions must be determined from a processing point of view. As for observations regarding the effect of temperature, higher temperature soaking at between 350 and 400°C led to significantly effective conversion. 2 Coal liquefaction that followed generated a 30% increase in the oil yield and a 15-20% decrease in the gas yield compared with results obtained using conventional methods. 3 Additionally, it is helpful to develop economical liquefaction if a further step is available for dissociated coal before liquefaction. It was reported that light fractions were formed from coal and petroleumderived heavy ends by reactions using radical initiators such as hydrogen peroxide (H 2 O 2 ) 10 and cumene hydroperoxide (CHP) 11 at temperatures of 120-350°C. A coalderived sample was heated in cyclohexane at 350°C in the presence of H 2 O 2 (0.3%). 10 The sample before and after heating was analyzed by gas chromatography, and it was found that n-alkanes and polycyclic aromatic hydrocarbons were newly produced in quantities 10-20 times more than the abundance in the original sample. The atmospheric residue of crude oil was heated at 120 and 300°C in the presence of CHP (2%). 11 The heating caused a ∼16% increase in the fraction boiling in the range 100-540°C. For the above reasons, the effect of these additives at a pretreatment stage of coal liquefaction was studied in this communicatio...

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New Direction to Preconversion Processing for Coal Liquefaction

Cited by 11 publications

References 0 publications

Effects of Water and Molecular Hydrogen on Heat Treatment of Turkish Low-Rank Coals

Effects of Water and Molecular Hydrogen on Heat Treatment of Turkish Low-Rank Coals

Clean liquid fuels from direct coal liquefaction: chemistry, catalysis, technological status and challenges

Effect of Peroxides during Pretreatment for Coal Liquefaction

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