Liquefaction of subbituminous coals under apparently non-hydrogenative conditions

Mochida, Isao; Iwamoto, Kenjiro; Tahara, Tsutomu; Korai, Yozo; Fujitsu, Hiroshi; Takeshita, Kenjiro

doi:10.1016/0016-2361(82)90004-7

Cited by 31 publications

(13 citation statements)

References 13 publications

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“…So far, there are two distinct molecular mechanisms that have been proposed. The first is a stepwise mechanism, in which the hydrogen atom in H-donor is abstracted, forming hydrogen radical, then it unites with free radical produced from coal pyrolysis. , The other is a concerted mechanism, which suggests that C–H bond cleavage in H-donor is assisted by coal radicals . For our knowledge, a systematical theoretical mechanism study with a state of the art method is still absent.…”

Section: Introductionmentioning

confidence: 99%

Rational Design of Hydrogen-Donor Solvents for Direct Coal Liquefaction

Hou

Zhou

Guo³

et al. 2018

Energy Fuels

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Facing the challenge of processes in direct coal liquefaction (DCL), it is vital to develop optimal hydrogen-donor solvent (H-donor) to dramatically moderate coal liquefaction conditions. Here, we propose an approach for rational design of optimal H-donor candidates based on density functional theory (DFT) calculations combining reverse searching algorithm. First, the mechanism of hydrogen transfer from H-donor to coal radical was investigated by using common model compounds. DFT calculations show that the concerted hydrogen transfer route promoted by coal radicals is the dominant pathway. The C−H bond dissociation enthalpies (BDEs) show strong correlation with intrinsic reaction barriers and rate constants (in log scale), which allow us to define a cheap metric for comparing the hydrogen-donation ability of different H-donors. Then the framework for rational design of H-donor candidates is established to seek molecules with low C−H BDEs based on inverse molecular design strategy. In the searching procedure, the chemical structure of parent molecule is varied by appropriate substituent from a predefined library (15 substituents). To reduce searching space, four empirical rules are proposed to guide the structural modifications. Finally, the H-donor candidates designed are validated by transition state calculations. It is confirmed that the inverse molecular design approach is effective for seeking candidate H-donors with lower reaction barriers and potentially higher rate of hydrogenation, which open a window for the rational design of optimal H-donors to improve the yields of the liquid products from coal under mild conditions.

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Section: Introductionmentioning

confidence: 99%

Rational Design of Hydrogen-Donor Solvents for Direct Coal Liquefaction

Hou

Zhou

Guo³

et al. 2018

Energy Fuels

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“…Considering the fact that tetralin is a common hydrogen donor solvent and also widely used industrially in the coal liquefaction processes by virtue of its hydrogen-donating efficiency, the mechanism of hydrogenation of the benzyl radical is first analyzed considering tetralin as the counterpart. It is assumed that the mechanism of hydrogenation may proceed through two different plausible pathways: (1) stepwise and (2) concerted. ,− Schematic representations of the likely mechanisms are outlined below where M–H: hydrogen donor and X • : coal radical. In the first stepwise mechanism as depicted above, the transfer of hydrogen to the coal free radical occurs in two distinct steps.…”

Section: Resultsmentioning

confidence: 99%

Deciphering the Differential Influence of Organic Additives on Coal Fluidity Development: A First-Principles Investigation

et al. 2021

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Formation of high-quality coke is essentially controlled by the development of the extended stability of the coal fluid phase during industrial carbonization processes. Stabilization of coal free radicals through hydrogenation leads to this development of coal fluidity. The donatable hydrogens are usually supplied by the donor hydrogen species formed through the thermal decomposition of a coal macromolecular network. In view of the limited reserve of the donor hydrogen species within a coal system, organic additives with characteristic hydrogen-donating ability are conventionally added to the system to maintain the desirable coal fluidity. However, the choice of compounds requires a clear understanding of their chemistry and associated reaction features. In this context, factors controlling hydrogen-donating properties of some organic donor hydrogen compounds are investigated herein within the framework of density functional theory. A mechanistic interpretation of the reaction of the compounds with the coal radical is offered. In addition to structural modification, the influence of the functional group, namely, the phenolic hydroxyl group, on the hydrogen-donating efficiency of the systems is validated through our calculations. The key role of molecular orbitals in facilitating the release of hydrogens from them is also elucidated. Thus, the work features an advanced understanding of a fundamental industrial process combining a detailed electronic description of the systems. The efficiency of a new compound to act as a superior hydrogen donor candidate is identified. The insights obtained are believed to help derive a rational understanding of the systems and structure−property relationships, which, in turn, can inspire future studies to engineer desired compounds with improved properties. The relevance of our findings to practical carbonization processes is also illustrated in the present work.

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“…The objectives of this project are to: (1) study the scope of hydrothermal pretreatment of coal on subsequent conversion, (2) identify and study the chemical or physical causes of this effect, and (3) attempt to elucidate the chemistry responsible for any coal-resid synergisms. This project is divided into three tasks.…”

Section: Discussionmentioning

confidence: 99%