Study Of Coal Vitrinite Macromolecular Structure Evolution And Control Mechanism Of The Energy Barrier In Hydrocarbon Generation

Superimposed basins were affected by multi-stages tectonisms, which leads to un-continuously thermal history of coal bed. The secondary hydrocarbon generation of coal should be given more attention. This work aims at investigating vitrinite secondary hydrocarbon generation and hysteresis to obtain Energy Barrier and coalification. In addition, the kinetic model and parameters were used to get hydrocarbon generation in geological history. Based on the separation of vitrinite in different coal ranks, high purity vitrinite was obtained. The characteristics of coal petrology were obtained by coal macerals and vitrinite reflectance test experiments. Five vitrinite samples were characterized by proximate analyses, ultimate analyses, and rock-eval. Vitrinite samples inserted into a furnace at room temperature and heated at a rate of 10 and 30 °C/h were subjected to X-ray diffraction analysis(XRD), Fourier transform infrared spectroscopy(FTIR) and solid-state 13 C nuclear magnetic resonance spectroscopy(13C NMR) to characterize the macromolecular structure of vitrinite of different ranks of coal. The activation energy and its frequency factor were calculated by Kinetic 2000 software and kinetic model. The structure models of vitrinite were built for molecular simulation and quantum chemistry calculation. From molecular structure evolution and organic matter pyrolysis hydrocarbon generation kinetics, the relationship between hydrocarbon phase and macromolecular structure was used to analyzed an energy barrier mechanism exists in the hydrocarbon generation of vitrinite. The results were shown as follow.(1) We took high purity vitrinite in different coal ranks through the separation experiment. Five samples with different hydrocarbon generation potentials represented different coal ranks and parent materials.(2) The yield of methane and C2-5 at heating rate(10 and 30 °C/h) was obtained and cumulative formation of methane and C1-5 continuously increases with increasing temperature of pyrolysis. The activation energies of vitrinite in different coal rank with various frequency factors were also calculated by kinetic model.(3) The contents of each functional group in the FTIR spectra were analyzed systematically, and the related structural parameters of vitrinite were calculated. The structural features of vitrinite were discussed with the ultimate observation of a pattern of changes in the macromolecular structure of vitrinite with changes in the rank of coal. Geometry optimized structural conformations of M1 V during pyrolysis were put forward.(4) Two macromolecular structural models were constructed. The final structural models were the basis of the hydrogen saturation simulations using Materials Studio 4.0 software to conduct molecular mechanics and molecular dynamics computations to obtain the minimum energy configuration of these models. The activity of the macromolecular structure can be qualitatively described in terms of the bond length.(5) Control of the molecular structure evolution on the hydrocarbon energy barrier was found. The energy barrier phenomenon exists in the second hydrocarbon generation. The meaning of the energy barrier is that organic matter evolution requires a much higher temperature than the last termination temperature to continue. More activation energy can spur further maturation of organic matter.Conclusions are useful for the developing of secondary hydrocarbon generation theory of sedimentary organic matter. These results are also important and practical for the coalification theory and coal gas, shale gas and other unconventional gas.