Prediction of Multicomponent Adsorption Equilibrium in Industrial Microporous Adsorbents

本研究从理论和实验两个方面研究了多孔固体的平衡物理吸附过程，重点研究了吸附剂孔道的多分散性对吸附过程的影响。理论上，将在大正则系综中进行蒙特卡罗模拟，在分子水平上研究多组分流体混合物在碳固相中狭缝状孔隙中的吸附过程。在模拟中，流体分子之间的相互作用将用Lennard-Jones势来表示，而流体分子和吸附剂之间的相互作用将用9-3势来考虑。对于类似流体分子之间的相互作用，相互作用参数将通过将纯组分模拟的液体密度和蒸汽压的预测值与实验值进行匹配来获得。将使用一组组合规则来从相似相互作用的参数中获得不同的流体相互作用参数。模拟将建立纯组分和混合组分等温线作为温度和压力的函数。除了蒙特卡罗模拟外，还将发展一个基于理想吸附溶液理论(IAS)的吸附理论。在实验上，将使用石墨化碳和甲烷、乙烷、乙烯、二氧化碳和丙烯等小分子在开流装置中进行平衡吸附测量。在该装置中，所需组成的气体混合物通过吸附剂，并对流出气体进行监测，直到其组成与进料的组成相同。此时，系统关闭，测量压力，通过加热吸附剂并允许解吸的物质流动到先前真空的解吸罐来启动解吸。通过测量脱附罐中的压力和组成，可以计算出吸附在吸附剂上的物质的量和组成。除了吸附测量外，还将通过氮气吸附来测量孔径分布。对吸附结果的解释将利用基于密度泛函理论的新的孔内氮吸附统计力学模型，该模型适用于微孔(20A及以下)和中孔(20-5000A)。理论中将考虑孔尺寸分布，并将理论预测与实验进行比较。

This research studies, theoretically and experimentally, the process of equilibrium physical adsorption onto porous solids, particularly focusing on the effect of polydispersity of the adsorbent pores. Theoretically, Monte Carlo simulations in the Grand Canonical Ensemble will be undertaken to study the adsorption process of multicomponent fluid mixtures at a molecular level, in slit shaped pores within a solid phase of carbon. In the simulation, interactions among fluid molecules will be represented by a Lennard-Jones potential, and interactions among the fluid molecules and the adsorbent will be accounted for using a 9-3 potential. For the interactions between like fluid molecules, interaction parameters will be obtained by matching the predictions of pure component simulations for the liquid density and vapor pressure with experimental values. A set of combining rules will be used to obtain the unlike fluid interaction parameters from those of the like interactions. The simulations will establish pure and mixed component isotherms as a function of temperature and pressure. In addition to the Monte-Carlo simulations, an adsorption theory will be developed which will be based on the Ideal Adsorbed Solution theory (IAS). Experimentally, equilibrium adsorption measurements will be undertaken using graphitized carbon and small molecules such as methane, ethane, ethylene, carbon dioxide and propylene in an open flow apparatus. In this apparatus, a gas mixture of desired composition is passed over the adsorbent, and the effluent gas is monitored until its composition is identical to that of the feed. At that point, the system is closed, the pressure is measured, and desorption is initiated by heating the adsorbent and allowing the desorbed material to flow to a previously evacuated desorbate tank. The pressure and composition in the desorbate tank is measured, and from these measurements the amount of material which had been adsorbed onto the adsorbent, and its composition, can be calculated. In addition to the adsorption measurements, pore size distributions will be measured by nitrogen adsorption. The interpretation of the adsorption results will utilize a new statistical mechanical model for nitrogen adsorption in a pore which is based on density functional theory and which is valid for micropores (20 A and smaller) as well as mesopores (20-5000 A). The pore size distribution will be factored into the theory, and theoretical predictions will be compared with experiments.