Authors: I.Y. Petrov, K.Y. Ushakov, A.R. Bogomolov, Tryasunov

Title of the article: Catalytic liquefaction of coals - a promising way to produce motor fuels and valuable chemical compounds. Part 2. Coal structures and chemistry of their direct liquefaction processes

Year: 2020, Issue: 5, Pages: 33-46

Branch of knowledge: 05.17.07 Chemical technology of fuel and high-energy substances

Index UDK: (66.092.094.25.097+66.061):552.57

DOI: 10.26730/1999-4125-2020-5-33-46

Abstract: This review considers the main objectives, conceptual features and chemical aspects of direct coal liquefaction processes. The modern concepts of coal compositions and structures, reactions occurring during their thermal transformations, as well as the problems to be solved by researchers in the development of these processes are discussed. Direct coal liquefaction is often described as a pyrolytic free radical process. Direct liquefaction and pyrolysis share an identical initial step  the thermal generation of radicals from coal by homolytic bond cleavages. During the pyrolysis, these radicals are either capped by an internally transferred hydrogen or they combine with carbon to form material of heavier molecular weight (char or coke) in the course of so-called retrograde (or reverse) reactions. Unlike the pyrolysis process, when coal is liquefied, the split off carbon fragments (radicals), as a rule, are covered with hydrogen and dissolve with a solvent. From a chemical point of view, the main goals of coal liquefaction process are as follows: 1) converting coal into a soluble form (to ensure the disintegration of macromolecules); 2) reducing the size of the primary coal molecules formed, making them accessible for penetration into pores of the catalyst; 3) cleavage of "key" aromatic-aliphatic and aromatic-aromatic bonds (including hydrogenation of aromatics and ring opening of saturated rings), as well as various carbon-heteroatomic bonds (i.e., bonds of carbon with nitrogen, oxygen, and sulfur) within the coal with the formation of smaller fragments; 4) increase in the atomic H/C ratio to about 2:1 to obtain a liquid product comparable in composition to traditional crude oil, gasoline or bitumen.

Key words: coal structures and compositions direct coal liquefaction processes pyrolysis radicals hydrogen hydrogen donor solvent

Receiving date: 24.11.2020

Publication date: 23.12.2020

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