Thermal Simulation Experimental Study On The Evolution Of Hydrocarbon Generation In Coal Vitrinite

In order to study the hydrocarbon generation process,closed-system thermal simulation experiment?with controlled water?was performed.In these experiments,the pyrolysis gas samples and solid char samples were obtained.Through the anlysis results of those pyrolysis gas,hydrocarbon generation kinetics of the vitrinite samples under different temperature were calculated.In addition,the macromolecular structure of the coal vitrinite samples was also characterized through experimental and numerical methods to help understand to the mechanism of the hydrocarbon generation process.The results domenstrated that during the process of hydrocarbon generation,the reflectance of vitrinite samples,the content of elemental composition and the loss rate of mass all changed regularly.In the early stage of coalification,non hydrocarbon components occuypied a relatively large proportion of the total.With an increase in maturity of coal vitrinite,the proportion of the hydrocarbon components increase continously.In hydrocarbon products,the order of yield value is:C₁>C₂>C₃>C₄>C₅.In addition,the yield of normal alkanes is much larger than that of isomers,and a small amount of olefin gas also exists.According to the kinetic characteristics of hydrocarbon generation,hydrocarbon generation process can bedivided into three stages:250-350??350-450?and 450-550?,and the activation energy required in the second stage is the largest.According to the experimental results,macromolecular structure of the coal vitrinite samples has been modeled and optimization were also performed based on the molecular mechanics and dynamics theory.During the energy minimization process,non bonding energydecrease significantly,and this is mainly because the fat structure contains more macromolecules in the torsion and bending.The order of stability of different functional groups,from large to small,is as follows:polycyclic aromatic hydrocarbons,aromatic hydrocarbons,aliphatic ring,aliphatic side chains and methyl,hydroxyl,carbonyl and carboxyl,ether oxygen bond,which directly influences reaction order of different parts of the vitrinite samples in hydrocarbon generation process.During the hydrocarbon generation process,the chemical structure of coal samples changes regularly.The infrared spectra data revealed that with pyrolysis temperature increasing,the area of absorbed peak of aromatic C=C bond relative gradually decreases,aromatic rate increases and the fat structure parameters show a downward trend.The laser Raman experimentla results show that the distance between the G peak and the peak peak of D increases continously.Meanwhile,the results of X ray diffraction showed that the interlayer spacing(D₀₀₂)decreases with an increase in pyrolysis temperature and while the stacking heights?Lc?and average diameter?La?increase.Several hydrocarbon generation jumps exist in the hydrocarbon generation process which correspond to the vitrinite reflectance of 0.7%,1.5%and 3.68%respectively and in the vicinity of the transition point,the evolution of the molecular structure has changed markedly.Thus,the hydrocarbon generation process can be divided into four stages:side chain,aromatization,polycondensation and stacking process.The aromatization and polycondensation process is the main hydrocarbon generation stage of the vitrinite.The vitrinite molecular structure is constantly increased because of the pyrolysis of the hydrocarbon substances.