Study Of The Oxygen Fate And Separation Technology In Direct Liquefaction Of Lignite

Direct coal liquefaction a kind of coal conversion process with highest utilization.In last 100 years,strict conditions and single product are not varied,which makes its production cost high and hinder its commercialization.As a result,high efficiency of coal direct liquefaction and lower cost of separation process are expected.Oxygen(O)is the most abundant impurity atoms in coal and coal liquid,which is generally not less than 20%in low rank coal.Particularly phenol's reaction is a issue:some studies shows that phenolics increase of coal conversion while it reduces the oil yield;Some studies shows that phenolics lead the crosslinking reaction of coal conversion and the oil yield is reduced.The reaction mechanism of phenol is the key to solve the direct coal liquefaction process's problems.This paper is aimed at the phenolics' mechanism of reaction in the direct coal liquefaction process.Protection mechanism of phenolic hydroxyl group and the separation of coal liquid are studied too.In conclusion there are mainly three parts:a.The phenolics' reaction mechanism in the direct coal liquefaction;b.The Fe catalyst's effection on phenolics;c.The effective separation of the coal liquid distillatePhenolics' influence in the process of direct coal liquefaction is very complex:they can provide H free radicals and also form polymers;different phenolics have different reaction path,which affect direct coal liquefaction process differently.Phenolics are hydrogen solvents whose hydroxyls release H atoms easily,and form phenoxyl radicals at the same time.In abundant H free radicals conditions,phenoxyl radicals can get H atom and keep the stability of phenolic hydroxyl groups;In insufficient system,they will polymerize with other radicals.Higher H free radical concentration leads to greater stability of phenolic hydroxyl.Lower H free radical concentration can cause crosslink reactions in the direct coal liquefaction process.FeS catalyst under the condition of coal direct liquefaction process,m-cresol by polycondensation was 24.76%,2-naphthol polycondensation by 37.58%Hydrogen-donor system in direct coal liquefaction process include hydrogen-donor solvent,hydrogen and surful and Fe catalyst.H atom is transferred from hydrogen by catalyst,and then enters into the solvent to stable the free radicals.High active catalyst can providing more hydrogen atom and keep H radical concentration at a higher level.In order to eliminate the crosslinking reactions caused by phenolic hydroxyl,Fe7S8 catalyst is prepared.Furthermore Fe7S8 catalyst is applied to keep phenolic hydroxyl group's stability.The experiment result shows that it can reduce the polycondensation of m-cresol and 2-naphthnol by 57.35%and 58.06%respectively.Different construction plays different reactions.M-cresol just condenses with each other while 2-naphthnol not only condenses but also can be hydrogenated.The effection of catalyst on phenolic compounds is detailed as follow.The catalyst can improve the phenolic compounds to release their H atom on the phenolic hydroxyl group,and leaves more phenoxy radicals,which can receive H atoms from catalyst or other solvent molecular and get back to phenolic forms.Otherwise these phenoxy radicals will be condensed to form large molecular.As following Fe7Ss catalyst is applied in direct lignite liquefaction process.The experiment result means that it can keep O element in the oil and prevent them to form asphaltene and preasphaltene which have more large molecular.Compared with FeS,it can increase coal conversion by 15.27%,and oil yield significantly by 210.15%,while gas+water and asphaltene yield reduced by 64.38%and 25.04%respectively.At the same time,the oxygen content of asphaltene,preasphaltene,and the tetrahydrofuran insolubles are deduced by:75.09%,41.54%,75.81%respectively.These results show that the phenolic hydroxyl group is an important factor of secondary/crosslinking reaction,and Fe7S8 catalyst can prevent them from secondary or crosslinking reaction by more hydrogen-donating abilityThe separation of coal liquid is a main problem to hinder the direct coal liquefaction process The coal liquid distillate is an azeotropic mixture of aromatics,alkanes and phenolics.On the basis of the intermolecular forces between different compounds,DMSO is selected as the solvent to eliminate the old intermolecular forces.The vapor-liquid equilibrium experiments show that:DMSO can complex with phenolic hydroxyl by 1:1 mole ratio,and with aromatics by ? hydrogen bond or ?-? forces,and with alkanes by weak van der waals forces.Different forces lead to their different distillate behavior,and more solvent ratio benefits the separation process.Finally the 150-180? coal liquid distillate is separated via batch distillation into three fractions:150-160? fraction(containing 79.17 wt%aromatics and 20.25 wt%alkanes),160-185? fraction(containing 81.30 wt%alkanes and 17.69 wt%aromatics)and a bottom product(containing 27.95 wt%phenolics and 72.05 wt%DMSO).