煤的原子分子结构及吸附甲烷机理研究进展

STUDY ON STRUCTURE OF COAL AND ADSORPTION MECHANISM OF METHANE ON IT

总结了煤的原子径向分布与微晶结构、稠环芳烃的电子光谱规律与煤的颜色间的关系、煤与 CH4分子的相互作用、无烟煤及其炭化样吸附 /解吸甲烷的热力学和动力学过程等内容的研究与发展 .结果表明 :( 1 )低阶煤的微晶参数 d0 0 2 ,Ic和 Ia随含碳量呈阶段性变化 ,其微晶结构特征与纤维素的结构有关 ,并可用煤化度 p定量描述煤化过程中煤的微晶结构变化 .( 2 )煤中存在1 3个苯环以上稠环芳香结构单元 .( 3)甲烷分子与煤表面的相互作用各向异性 ,最大作用势 (吸附势 )为 2 .65 k J/mol,旋转势垒为 1 .34k J/mol,预计吸附振动光谱的跃迁基频为 5 3cm-1.( 4 )煤对甲烷的饱和吸附量几乎不随温度变化 ,炭化样与活性炭的饱和吸附量则随温度的降低而线性增大 ;从煤制备的炭化样 ,以及活性炭的吸附热都接近甲烷液化热 ,而煤的吸附热则高出近一倍 .( 5 )煤层 (粒 )吸附解吸甲烷的动力学过程可用通用的一级组合模型和实用的吸附 (解吸 )扩散控制模型来描述 ,其三常数动力学公式中的初始吸附 (解吸 )率 Q0 /Qmax可作为煤与瓦斯突出预测指标 .( 6)甲烷在无烟煤中的扩散系统为～ 1 0 -10 cm2 /s,扩散活化能为 1 4.3k J/mol;

The atomic radial distribution microcrystal structure,condensed aromatic structure of coal,and the interaction between the coal surface and the mehtane molecular,adsorption(desorption) characteristic and kinetics of methane on coal and its char are studied by using X-ray diffraction(XRD),ultraviolet-visible(UV-Vis) diffuse reflection and low temperature in situ (FT-IR) spectroscopy,quantum chemical ab initio and discrete variation(DV) Xα methods,adsorption volumetry,and so on.The following results have been concluded.The microcrystal structure characteristic of low rank coal results from the structure of cellulose(plants).It is suggested that the coalification degree p can be used to quantitatively describe the microcrystal structure change of coal in coalification process.DV-Xα calculation shows that the coal has a condensed aromatic structure unit more that 13 benzene rings,which has λ _ max =537 nm.Quantum chemical ab initio calculation indicates that this interaction between the coal surface and the methane molecule is anisotropic and the maximum interaction potential(adsorption potential)is 2.65 kJ/mol,rotation potential barrier is 1.34 kJ/mol.The calculated transition fundamental frequency in vibration spectrum of corresponding adsorption state is 53 cm -1 .These results have shown that the adsorption of methane on coal should be a physical process(that is ,freezing at surface).Adsorption experiments with varying temperature in -21 ℃-50 ℃ have shown that the adsorption relationships of methane in anthracite,char,and active carbon accord with the Langmuir and D-A equations.Two models to describe the kinetic process of the adsorption/desorption of methane on coal are proposed,which are the general combined one oreder model and the practical adsorption/desorpption-diffusion determinating model.A three constants kinetic formula is concluded.It is suggested that the initial adsorption/desorption ratio Q _0/ Q _ max could be used as the index predicted the outburst of coal and gases.The diffusion coefficient and activated energy is ～10 -10 cm 2/s and 14.3 kJ/mol.respectively,which indicates that the diffusion of methane in coal is in fact the flow through micropores.