层柱粘土吸附甲烷的模拟和参数优化研究

Simulation and Optimization of Model Parameters for Adsorption of Methane on Pillared Clay

用巨正则系综MonteCarlo方法(GCMC)来模拟ZrO2柱撑粘土对天然气主要成分甲烷的吸附.为了更好地反映甲烷与层柱粘土无机层板的相互作用,对墙势模型中的尺寸参数σfw和能量参数εfw取值进行了优化.我们系统地改变甲烷在蒙脱土晶体结构中的位置,建立起一系列甲烷与层板相互作用的Lennard-Jones势能曲线,通过最小二乘法拟合这些Lennard-Jones势能曲线得到一系列的σfw和εfw值,利用拟合得到的σfw和εfw算术平均值作为墙势模型中两个交互作用参数的取值进行分子模拟,模拟结果与文献实验值符合较好.在此基础上,进一步模拟了3种不同孔率,层间距为0.64nm的ZrO2柱撑粘土(ZPC)在245K下对临界态甲烷的吸附,发现3～4MPa是ZPC材料吸附甲烷较适合的压力范围,而且孔率大的ZPC有利于甲烷的吸附.

A grand canonical Monte Carlo （GCMC） method was carried out to simulate the adsorption of methane being a main component in natural gas on ZrO2 pillared clay. In the simulation, wall potential model and optimized model parameters, αfw and εfw, were employed to make simulation results reflect very well the real interaction between methane molecules and inorganic layered boards in pillared clay. In the optimization of wall model parameters, firstly, positions of methane were changed systemically in montmorillonite crystal structure, and then a series of Lennard-Jones potential curves reflecting the interaction between methane molecules and layered boards were obtained; secondly, those Lennard-Jones potential curves were simulated through the least squares method, so a series of values of two cross-interaction parameters were obtained; finally, the even values of σfw and εfw were introduced into the formula of wall potential model, which was proved to be very effective because the simulation result was in good agreement with the experimental data. Based on optimized parameters, the adsorptions of methane on three different porosity ZrO2 pillared clays （ZPC） with the layer distance of 0.64 nm at 245 K have been simulated. It was thought that the proper pressure of methane molecules adsorbed on ZPC materials was in the range 3-4 MPa, and the larger the porosiw of ZPC materials, the more the amount of the methane adsorbed on ZPC materials.