超临界甲烷在活性炭上的吸附平衡分析

为分析由吸附平衡时的热力参数确定吸附量、吸附模型和等量吸附热精度的影响因素,选择在温度268.15~338.15 K和压力0~13.5 MPa测试的甲烷在Ajax活性炭上的吸附平衡数据,通过引入甲烷分子可进入活性炭吸附空间内的容积和可以不考虑甲烷在孔内吸附的临界孔宽的概念,依据甲烷在吸附平衡前后的总量守恒,确定甲烷在吸附池内的总量、绝对吸附量和过剩吸附量三者之间的关系式。结果表明,在引入吸附质分子可进入吸附空间内的容积和临界孔宽后,经由活性炭的孔径分布(PSD),可以准确计算甲烷在活性炭上的过剩吸附量;应用实验数据非线性回归Toth方程参数后,可由Gibbs关于吸附的定义确定甲烷在活性炭上的绝对吸附量。比较结果时发现,由于未考虑本体相中甲烷分子对吸附甲烷分子的影响,采用过剩吸附量的等量吸附线标绘确定的等量吸附热数值偏高,工程应用时应由绝对吸附量来确定等量吸附热。

Adsorption equilibrium of supercritical methane on activated carbon

Equilibrium adsorption data of methane on Ajax activated carbon were volumetrically measured under a temperature of 268.15~338.15 K and a pressure up to 13.5 MPa.Accessible volumes for methane molecules and critical pore width for methane effective adsorption were introduced;on the basis of these concepts,the mass balance of the adsorbate confined within the adsorption cell was used to determine the relationship among the total amount,excess adsorption amount and absolute adsorption amount.By considering the accessible volume and critical pore width,the excess adsorption amount was obtained by the pore size distribution(PSD) determined by Nonlocal Density Functional Theory(NDFT) calculation.The equilibrium adsorption data were fitted by Toth model through nonlinear regression,which was verified the accuracy in predicting the absolute adsorption amount.The isosteric heat of methane adsorption on activated carbon was over-estimated by using the excess amounts,but underestimated by using the total amounts.The isosteric heat of adsorption should be determined from the adsorption isosteres of absolute adsorption amount when considering the thermal effect in adsorption process.