The Study On Chemical Composition Characteristics And Slurry-bed Hydrocracking Technology Of Coal Tar

With the emergence of the poor and heavy quality oil continuously,the method of using coal tar to produce light fuel oil was paid widespread attention.So,the research of coal tar chemical composition characteristics and highly efficient processing technology has been an emergency work.The components of middle/low temperature coal tar was separated and identified by modified chromatographic separation experiment.The process optimization experiment and pilot scale test of medium/low temperature coal tar heavy fraction(AR,>350℃ fraction)hydrocracking was inspected in magnetic-stirred autoclave and slurry-bed hydrocracking pilot plant with 3000 m L loop reactor under the best conditions,respectively.In addition,the properties,structure parameters and microstructure of C7-asphaltene,toluene insoluble(TI)and coke were analyzed with the help of ultimate analysis,average molecular weight determination(VPO),1H-NMR,XRD,FT-IR,SEM,and XPS.Furthermore,the relevance of coking and these structures and the coke formation mechanisms of coal tar heavy fraction in slurry-bed hydrocracking reaction was speculated.The result shows that the contents of paraffin,cycloparaffin,arene,polar components and asphaltene in full-range fraction of coal tar were 10.72%,9.11%,38.93%,22.30% and 18.94%.The saturates were maily made up with paraffin and cycloparaffin,aromatics were arene with 1~3 rings,polar components and asphaltene were polycyclic aromatics.The content of CTAR in coal tar was more than 40% and the most remarkable hydrogenation result in hydrocracking experiment appeared when the reaction temperature was 425℃,initial hydrogen pressure was 9MPa(reaction pressure was 12.5 MPa),reaction time was 60 min,dosage of oil soluble Mo-Ni bimetallic catalyst,additive(SDBS)and sulfur was 150 μg·g-1,200 μg·g-1and 400 μg·g-1,respectively.In addition,the ideal effect of CTAR slurry-bed hydrocracking pilot scale test was obtained under this condition.The yield of naphtha,diesel and wax oil was 88.26% and the light oil yield per unit of coke could be up to 48.13 and the CTAR slurry-bed hydrocracking technology have advantages of high light oil yield,little coke,almost no coke on the surface of reactor.C7-asphaltene units are mainly composed of polycyclic aromatics linked with naphthene rings,side few and short aliphatic chains(mainly n-alkanes less than 3 C atoms).The asphaltene units have small average molecular weights and there is no aromatic sheet stacking structures existing.Furthermore,short chains are not easy to break and fewer polycyclic aromatics radicals generated in the hydrocracking process.O atoms in asphaltene are mainly distributed in epoxyalkane or ethers(C-O-C).The main surface functional groups were C-C,C-H and C-O,and the relative concentration of neutral functional groups was 7.9%,acid functional groups was 0.01%,and the basic functional groups was 1.47%,and the surface properties of asphaltene suggested tend to its alkaline.The stabilization effect rest with the acid-base interaction and hydrogen-bond interaction between asphaltene surface functional groups and additives and the acid-base interaction was the most important factor.Furthermore,amphiphile with acidic groups such as SDBS was the optimal additives in CTAR hydrocracking process.TI was made up with the carbonaceous,mineral particles and polycyclic aromatic hydrocarbons originated from the production process of coal tar and it has obvious layered stack structure which was easily broken as smaller carbonaceous and mineral particles(several microns)with larger specific surface area and adsorption capacity under the physical forces and These particles could provide coke centers with sulfurized catalyst and adsorbed macromolecular radicals to reduced coking on the surface of reactor in slurry-bed hydrocracking process.Ca,Si,Al,Na of TI are derived from minerals that exist in CTAR and C and O mainly existed in C-C,C-H,C-O-C,C-OH,N-containing groups appeared mainly as pyrrole and amine and aliphatic sulfur was perceived as the main S-containing group.The coking of reaction system has the characteristic of “two coke center(catalyst and micro grain)and a adsorption center(carbonaceous particles)” and the coke is the aggregate(about 10 μm)distributed in the liquid phase steadily formed by globular particles(about 1 μm)adsorbing on the surface of carbonaceous particles.The formation of coke is a process of radical condensation,adsorption and adsorption happened at the same time.