Study On Hetero-atomic Types And Hydroconversion Rule Of Medium/Low Temperature Coal Tar Asphaltenes

In view of the energy situation of rich coal and poor petroleum in China,it is very important to develop coal clean utilization.In 2019,the production of medium/low temperature coal tar(LCT)reached 9 million tons.LCT is mainly used for the hydrogenation of clean fuel oil,thus relieving the supply and demand gap of crude oil in China.Eespecially,LCT asphaltenes contain many oxygen,nitrogen,sulphur hetero-atoms(O,N,S)with complex structure and different polarity,which limits the processing and utilization of LCT.Therefore,fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)combined with electrospray ionization source(ESI),were used in this thesis.The type distribution of O,N and S in LCT asphaltenes was characterized at the molecular level.In addition,the effects of hydrogenation conditions on the composition of LCT hydrogenation products,the asphaltenes'structure and removal rule of hetero-atoms were investigated.Firstly,LCT asphaltenes were characterized by ESI FT-ICR MS.In negative-ion ESI,it was found that the acidic oxygen in asphaltenes was mainly O₄types,it is different O₂type naphthenic carboxylic acid oxygen in asphaltenes of crude oil.The non-basic nitrogen are mainly N₁and N₄types,in which the parent structure of N₁type is mainly pyrrole derivatives with high degree of condensation.Its condensation degree is higher than crude asphaltenes,and more difficult to process.In positive-ion ESI,the results showed that the neutral oxides in LCT asphaltenes were mainly O₁and O₂types,in which the maternal structure of O₁type may be consisted of 3-7 aromatic rings and 1 furan ring,or 3-8aromatic rings and 1 keto group.The basic nitrogen are mainly pyridine derivatives,its condensation degree is higher than that of pyridines in asphaltenes of crude oil.The neutral sulfur are mainly S₁and S₂types.The S₁type is mainly thiophene sulfides,which is different from the sulfur ether in asphaltenes of crude oil.At the same time,in positive-ion ESI FT-ICR MS,more complex hetero-atomic compounds were detected,such as N₁O₁,N₁O₂,S₁O₁,S₁O₂,etc.Secondly,the effects of different reaction pressure and catalyst-to-LCT ratio on the hydrogenated oil composition,asphaltenes conversion rate and asphaltenes composition were investigated.The experimental results showed that when the reaction pressure increases from 6 MPa to 12 MPa,the LCT system becomes lighter and lighter.The conversion rate of asphaltenes increased from 32.13%to 58.24%and the sulfur removal rate increased from 35.52%to 57.38%.When the catalyst-to-LCT ratio increases from 1:25to 1:10,the content of toluene insoluble substance increases from 1.81%to 2.36%,and the conversion rate of asphaltenes increases first and then decreases.In the end,the effect of different reaction pressures and catalyst-to-LCT ratio on the asphaltenes structure and the hetero-atoms occurrence forms were investigated.The results demonstrated that as the increase of reaction pressures,the interaction between asphaltenes unit sheet weakened,and interlamellar spacing(d_m)and interchain spacing(d_?)increased;While layer diameter(L_a)and cell height(L_c)decreaseed;Aromaticity(f _A)decreased from0.71 to 0.69;Single bond oxygen,ketone oxygen,thioethers and sulfones are mainly removed.With the increase of catalyst-to-LCT ratio,d_m,d_?,L_aand L_cdecreased,resulting in the decrease of molecular size of asphaltenes;f _Aincreased from 0.692 to 0.72,naphthenic ring number(R_n)decreased from 5.8 to 4.53,which indicated that the ring-opening rate of naphthenic rings was slightly higher than that of aromatic rings hydrogenation.The results of this paper provide a theoretical basis for the study of the removal of hetero-atoms in LCT asphaltenes.At the same time,it can provide valuable guidance for the hydrotreating of LCT and help to optimize the hydrotreating process of LCT.