Study On Characteristics Of Some Potential Coal Liquefaction Solvents And Their Effect On Coal Liquefaction

In advanced direct coal liquefaction(DCL)process,solvent plays an important role.In addition to its function of "coal powder conveyor",it can improve coal liquefactionefficiency.Many studies have shown that tetralin,dihydrophenanthrene or dihyroanthrancene type solvents can increase coal conversion and oil yield significantly.Their proper aromaticity and hydroaromatic structure can be of benefit to dispersion,dissolution and hydrogen addition of coal radicals and liquefaction products.Nevertheless,in practice,the solvent used in DCL is mainly from the process derived-oil.Additional solvent may be the products or hydrotreating products of petroleumrefining or coking process.The solvent used in DCL process should be characterized with complex chemical composition and structure.Its function in DCL process depends on its composition as well as the treatment condition.Based on the requests of the projects from Chinese Academy of sciences and Synfuel China,eighteen solvents were selected as the potential DCL process solvent.The comparison study was made on solvents'chemical and physical properties and theireffect on coal liquefaction.The solvents are included in three series(YLA?YLB and YLC).YLA is petroleum based aromatic oil,including four samples with the differenthydrotreating extent.YLB is coal tar based hydrotreating oil,including one full cut sample and seven narrow cut samples.YLC is DCL process derived mix oil,including six samples with the differenthydrotreating extent.In order to collect basic data for solvent and solvent preparation condition selection of the pilot plant test project,the objective of this study are to understanding the characteristics of these candidate solvents.It has been foundthat the characteristics of samples withinthe same seriesare similar,in general.The significant difference can be observed among the samples in the differentseries.The parent sample of the YLA series was appeared with the higher boiling temperature distribution.The boiling temperature distributionprofile of YLA seriesmoves to low boiling temperature regionas the increaseof hydrogenationruns.The boiling temperaturedistributionprofile of narrow cut samples of YLB series was apparently narrowed,although the boiling temperature of neighbor fractionsis still significantly overlapped.The parent sample of the YLC series was appeared with the lower boiling temperature distribution.The boiling temperature distribution profile ofYLC seriesmoves to low boiling temperature region as the decrease of hydrogenationspace velocity.Furthermore,the(H/C)atomicratio of YLA,YLBandYLCseries are in the range of 1.3-1.47,1.40-1.53 and 1.47-1.72,respectively.The group composition distributions of samples are complex.The YLA samples contain a larger amount of high condensed aromatics which is agreed with theirhigher boiling temperature distribution.As the increase of hydrogenation extent,the high condensed aromatics decreased significantly.In general,with the increase of hydrogenation extent,the high condensed aromatics decreased and 1-ringaromatics,2-ring aromatics and cycloparaffinicsincreased.It can be speculated that hydroaromatics are intermediate products of the related hydrogenation reaction.In YLC series,the lower boiling temperature fractions contain more 1-ring aromatics and the higher boiling temperature fractions contain more paraffinics.Under a comparable condition,the different solvents appeared with the different influence on coal liquefaction.The conversion rates of HM coal in three seriessolvents range from 77%to 86%.Unfortunately,the group composition data of solvent is hardly to be used as a main parameter for evaluating and predicting the effect of solvent on coal liquefaction.