甲烷在活性炭上吸附平衡模型的研究

摘要

比较吸附模型分析甲烷在活性炭上吸附平衡的适用性,为吸附式天然气(ANG)的工程应用提供准确的预测模型.基于在温度268.15 ～338.15 K、压力0～12.5 MPa测试的甲烷在Ajax活性炭上的吸附平衡数据,选择Langmuir、Langmuir-Freundlich和Toth方程,应用非线性回归拟合方程参数后,确定绝对吸附量和甲烷吸附相态,并比较方程在不同压力区域内的预测精度.结果表明,甲烷吸附相密度随平衡温度和压力变化；由绝对吸附量确定的甲烷在Ajax活性炭上的平均等量吸附热为15.72 kJ/mol,小于由过剩吸附量的标绘结果；Langmuir、Langmuir-Freundlich和Toth方程预测结果在0～0.025 MPa的累积相对误差为6.449 8％、7.9184％和0.9100％,在1～10 MPa为0.491 1％、0.161 3％和0.369 4％.Toth方程在整个压力范围内的预测结果最为准确,但Langmuir-Freundlich方程在较高压力区域内具有较高的预测精度.%Comparisons of accuracies of adsorption models in predicting adsorption data of supercritical methane on activated carbon were carried out for practical application of adsorption of natural gas (ANG). Ajax activated carbon was selected as an adsorbent, six isotherms of excess adsorption amount of methane were measured at temperature from 268. 15 K to 338. 15 K and pressure up to 12. 5 MPa. Parameters of Langmuir, Langmuir-Freundlich and Toth equations were firstly set by the linear fit of adsorption data, absolute amounts and densities of the adsorbed phase of supercritical methane were then determined by the modified models. Isosteric heats of methane adsorption on Ajax activated carbon were determined by adsorption isosteres on the absolute amounts. Comparisons were made between experimental data and those predicted by models. Results showed that the adsorbed phase densities of supercritical methane on the activated carbon varied with equilibrium temperatures and pressures, the mean value of isosteric heat of adsorption set by absolute amounts was 15.72 kJ/mol, which was smaller than that plotted from the excess amounts. The relative errors between the experimental data and those predicted by Langmuir, Langmuir-Freundlich and Toth equations varied with the pressure, The accumulated relative errors were respectively 6. 449 8%, 7. 918 4% and 0. 910 0% at lower pressure range from 0 to 0.025 MPa, but will respectively be 0.491 1% , 0. 161 3% and 0. 369 4% while pressure was in range of 1 ~ 10 MPa . Toth equation performed well in predicting the equilibrium data in the whole pressure range, but the results from Langmuir-Freundlich equation had higher prediction accuracies while the pressure got higher.