The Detection Of Oxygen-containing Functional Groups Of Low Rank Bituminous Coal And Its Conversion Behavior In Direct Coal Liquefaction Process

There are many influencing factors in the direct liquefaction of coal,such as coal rank,hydrogen donor solvent,reaction temperature,reaction time,reaction pressure,the type of catalyst,oxygen-containing groups and so on.The oxygen content of low rank coal is about 10-20%.The main existing forms are phonetic hydroxyl groups and ether linkages,as well as furans and carbonyl,etc.We know that the oxygen content have a significant effect on the direct liquefaction of coal,while the research in the area is scarce.In this paper,in order to explore the influence of the oxygen functional groups on the direct liquefaction of low rank coal,three kinds of low rank bituminous coals(386,387,388)were used.Firstly the three coals were floated by zinc chloride solution,and washed by Hydrochloric acid and HF acids according to GB/T212-2001 up to the ash content less than 2%.Then the raw coals and washed coals were analyzed by Infrared Spectroscopy.We can see that the main structure of organic macromolecules change very little,while inorganic components have large change.The oxygen-containing functional groups of the washed coals were determined by chemical analysis methods.Three kinds of low rank bituminous coals mainly include the following oxygen functional groups:carboxyl,hydroxyl,carbonyl,ether and methoxyl.Among them,the contents of phonetic hydroxyl and ether are high,carboxyl and carbonyl is less,methoxyl is almost disappearing.The two washed coals(386,388)were liquefied using an autoclave(WHf,Weihai)with a volume of 0.3L,the liquefaction yield of coals was calculated,and the liquefied products were analyzed.Among them,the N-hexane solubles was analyzed by GC-MS,the asphaltene,former asphaltene,and liquefaction residue,were analyzed by FTIR and chemical methods.The washed coals and liquefied products of asphaltene,former asphaltene,and liquefaction residue were compared through FTIR and chemical analysis.The results can be obtained:(1)Ether C-O stretching vibration absorption peak disappeared in the liquefaction residues,asphaltene and former asphaltene.That means that the ether content in the liquefaction residues,asphaltene,and former asphaltene were greatly reduced compared with the coals.The above analysis shows that ether bonds in the coals during the direct liquefaction process fractured,and combined with the hydrogen donor solvent,and then transferred to the liquid products.(2)The carbonyl and carboxyl content in the liquefied products were lower than the coals.That means the liquefaction process of coals caused decarboxylation radical reactions.(3)Comparison of the carboxyl and methoxyl content in the coal sample and the liquefaction products of asphaltene and former asphaltene.We found a significant increase in the hydroxyl content in the latter,while methoxyl has almost disappeared.From this we conclude that,the bridge bond fracture in direct coal liquefaction process,especially fracture between the ether bonds between the C-O and CH3-O,can generate hydroxyl groups under donor solvent.The mechanism investigation of the coal containing oxygen functional groups on direct liquefaction needs to be more advanced equipments and more analysis.