【摘要】 为了明晰煤层气中CH₄和N₂在吸附剂上的平衡吸附、热力学和动力学扩散机制,以实验室制备椰壳活性炭为吸附剂,基于体积法测量了298～338 K,0～0.1 MPa下CH₄/N₂在制备活性炭上的吸附等温线,采用经典Langmuir和Sips模型拟合平衡吸附数据获得模型参数、热力学参数以及平均相对偏差。基于重量法分别测量了298 K,0～1.0 MPa下单组份和不同配比的CH₄-N₂二元组分的吸附等温线,评价了其分离性能和竞争吸附机制。采用电子天平测量了动态吸附速率曲线,利用W-M内扩散模型、Lagergren准一阶动力学模型和Makay二阶动力学模型对动态吸附数据拟合,从动力学的角度研究温度和压力对甲烷和氮气吸附的影响机制,探讨甲烷和氮气在活性炭吸附过程中的扩散控制步骤。研究结果表明:Langmuir和Sips模型对甲烷和氮气在活性炭上的平衡吸附结果均匹配性良好。相较而言,Sips模型考虑了活性炭表面非均一性,拟合效果更佳;通过计算吸附热发现CH₄/N₂在活性炭上的吸附为物理吸附过程且甲烷吸附热大于氮气。二元混合气体在活性炭表面存在竞争吸附,CH₄吸附起主导作用;混合气吸附量介于甲烷和氮气纯组分吸附量之间,且与纯组分吸附量不呈简单比例加和关系;吸附剂分离比达4.21,分离性能较好。表观动力学模型拟合结果说明CH₄和N₂在活性炭表面的动力学吸附过程受外扩散主要控制,其次为表面吸附过程,内扩散不是主要控制步骤;温度降低和压力增加有利于内扩散,不利于外扩散过程,升高温度和压力对扩散和吸附控制作用有不同程度的影响。更多还原

【Abstract】 In order to clarify the equilibrium adsorption, thermodynamic and kinetic diffusion mechanism of CH₄/N₂ on the adsorbent, using activated carbon prepared in the lab as adsorbent, the adsorption isotherms of CH₄/N₂ on the activated carbon were measured by volumetric method at 298～338 K and 0～0.1 MPa. The model parameters, thermodynamic parameters and average relative deviation were obtained by using classical Langmuir and Sips model fitting equilibrium adsorption data. Adsorption isotherms of single component and CH₄-N₂ binary component with different proportions were measured based on the gravimetric method respectively. The separation performance and competitive adsorption mechanism were evaluated. The dynamic adsorption rate curves were measured by electronic balance, W-M internal diffusion model, Lagergren quasi-first-order kinetic model and Makay second-order kinetic model were used to fit the dynamic adsorption data, the influence mechanism of temperature and pressure on the adsorption of methane and nitrogen was studied from the perspective of dynamics, and the diffusion control steps of methane and nitrogen in the adsorption process of activated carbon were discussed. The results show that the two equilibrium adsorption models match well while Sips model has the better fitting effect since Sips model takes the surface heterogeneity of activated carbon into consideration. It was found that the adsorption process of CH₄/N₂ on the activated carbon is a physical adsorption process and the adsorption heat of methane is greater than that of nitrogen by calculating. There exists a competitive adsorption of binary mixed gas, and CH₄ adsorption plays a dominant role, the adsorption capacity of the mixture gas is between the adsorption capacity of methane and that of nitrogen. The equilibrium separation coefficient is up to 4.21. The kinetic adsorption process of CH₄ and N₂ on the surface of activated carbon is mainly controlled by external diffusion, followed by surface adsorption process, and internal diffusion is not the main control step. The decrease of temperature and increase of pressure are favorable to internal diffusion, but unfavorable to external diffusion. Increasing temperature and pressure have different effects on diffusion and adsorption control.更多还原