甲烷在页岩上的吸附等温过程

Adsorption isotherms process of methane on gas shales

为了从热力学角度研究页岩吸附甲烷的机理,通过容积法测定35,50和65℃时,0~12MPa下甲烷在页岩上的吸附等温线,采用考虑吸附相体积的修正Langmuir模型处理实验数据,并根据Clausius-Clapeyron方程和vant Hoff方程计算甲烷在页岩上吸附时的等量吸附热和极限吸附热。结果表明：甲烷在页岩上的吸附等温线具有Ⅰ型吸附等温线特征,修正Langmuir吸附模型较好地拟合了吸附数据,拟合的平均相对误差小于4.1%。根据等量吸附线计算的等量吸附热为11.67~16.62 kJ/mol,平均14.58 kJ/mol,说明页岩对甲烷的吸附为物理吸附,并且等量吸附热随甲烷吸附量的增大而非线性递减,表明页岩表面能量的不均匀性,甲烷分子优先吸附在页岩表面的高能吸附位。由vant Hoff方程计算甲烷在页岩上的极限吸附热为23.91 kJ/mol。

In order to investigate the thermodynamics mechanism of methane adsorption on shales, adsorption isotherms of CH4 on shales were measured under 35,50 and 65 ℃ and 0-12 MPa by volumetric method. Experiment data were treated by modified Langmuir equation. The isosteric adsorption heat and limit isosteric adsorption heat of methane on shale were calculated to study the adsorption behavior according to the Clausius-Clapeyron equation and rant Hoff equation. The research results show that adsorption isotherms of methane in shale is characterized by the type I ad- sorption isotherm, and modified Langmuir adsorption model fits well with the adsorption data, while the average relative error is less than 4. 1%. The isosteric adsorption heat, calculated from the adsorption isotherms, is from 11.67 to 16.62 kJ/rnol with an average of 14. 58 kJ/mol, which indicates the adsorption performance may be dominant by phys- ical adsorption. The isosteric adsorption heat of methane on shale decreases nonlinearly with the increasing of adsorp- tion, which reflects the energetically heterogeneous surface of shale, and methane preferentially adsorb on the high en- ergetic adsorption sites. The limit isosteric adsorption heat of methane on shale is 23.91 kJ/mol calculated from vant Hoff equation.