Study On Pretreatment Technology Of Medium-Low Temperature Coal Tar And Removal Of Nitrogen Compounds

The preparation of clean and light fuel oil by hydrogenation of medium-low temperature coal tar is of great significance to alleviate the current shortage of oil in China.During the hydrogenation process,iron and nitrogen heteroatoms in coal tar easily cause a series of problems such as equipment corrosion and catalyst poisoning inactivation.In particular,coal tar is rich in a large number of complex nitrogen compounds,and its occurrence form and removal regularity are still unclear.Therefore,coal tar needs to be pretreated to remove these impurity components before hydrogenation.Firstly,the coal tar was pretreated by acid refining method,and the removal rule of iron and nitrogenheteroatomsincoaltarwasstudiedemphatically.Secondly,acid neutralization-column chromatography was used to enrich the basic nitrogen and non-basic nitrogen compounds in the coal tar of<360?distillate,and characterized by gas chromatography-mass spectrometry?GC-MS?.The effect of acid concentration on the enrichment of nitrogen compounds was studied,a method for enrichment of nitrogen compounds in the<360?distillate was explored.Based on this,the occurrence form and removal regularity of nitrogen compounds in the<360?distillate before and after pretreatment were studied.Finally,electrospray ionization?ESI?combined with Fourier transform ion cyclotron resonance mass spectrometry?FT-ICR MS?was used to study the occurrence form and removal regularity of basic and non-basic nitrogen compounds in>360?distillate before and after pretreatment.The conclusions were as follows:?1?The best pretreatment conditions of coal tar are as follows:adding 5 wt%H₂SO₄ solution in coal tar,the mass ratio is 0.5:1,then adding 200?g/g of P₂ demulsifier,stirring at 80?for60 minutes and standing at 60?for 120 minutes.Under these conditions,the removal rates of iron and nitrogen can reached 70.29%and 72.16%,respectively.The pretreatment technology had a good effect on removing iron and nitrogen from coal tar.?2?The ratio of basic nitrogen content such as aniline,quinoline and pyridine in<360?distillate was about 1:4:1,and the ratios of non-basic nitrogen content such as indole,pyrazole and pyrrole was 5:8:1.After pretreatment,the removal rate of total nitrogen in<360?distillate was 74.54%,and the difficulty of removal of basic nitrogen and non-basic nitrogen compounds were:quinoline>pyridine>aniline,indole>pyrrole>pyrazole.A large amount of basic nitrogen which is easy to cause catalyst deactivation is removed,and the removal rates of aniline,pyridine and quinoline compounds were 93.75%,83.70%and80.95%,respectively.Non-basic nitrogen compounds were also removed to a certain extent,such as the removal rate of pyrazole compounds up to 73.91%.?3?The basic and non-basic nitrogen in>360?distillate were mainly N₁,N₂,N₃ and N₄.The relative abundance order of basic nitrogen was N₁>N₂>N₃>N₄,of which N₁ was mainly pyridine and quinoline compounds.The relative abundance order of non-basic nitrogen was N₄>N₂>N₁>N₃,of which N₄ was mainly pyrazole compounds.After pretreatment,the removal rate of total nitrogen in>360?distillate was 70.35%,and the relative abundance order of basic nitrogen ranged from high to low was N₁>N₂>N₄>N₃,of which N₁ was mainly oxazine compounds,mainly NOS compounds,and the major nitrogen removal compounds were quinoline,pyridine-alcohols,piperidine thiamine,pyrazine and pyrimidine compounds.The relative abundance of non-basic nitrogen compounds was N₂>N₄>N₁>N₃ from high to low after pretreatment,of which N₂ was mainly indole and pyrazole compounds,indole,carbazole and pyrazole were the main components in non-basic nitrogen compounds.The above research results provide theoretical basis for coal tar hydrogenation process,and provide reference for the removal of miscellaneous atomic compounds,which is of great significance for the processing and utilization of coal tar.