Collaborative Research: Adsorption Equilibration of Binary Mixtures on Planar and Porous Sorbents

在将两种气体的混合物引入到放置有吸收材料的容器中之后，由于特定的分子结合到吸收表面上，所以容器内的混合物的压力和两种气体的比率随时间而变化。 经过足够的时间后，气体的压力和组成达到恒定值，并且在表面上形成与气相平衡的冷凝相。 该项目研究吸附的动力学，即从引入气体混合物直到达到平衡的过程的演变，以及它如何取决于参数，如起始气体混合物的成分和温度，每个气体分子附着在吸附剂上的强度，以及不同分子达到最终状态的速度。 虽然这是一个非常复杂的过程，有许多方面还没有很好地理解，但吸附的大多数实际应用（如气体分离或气体储存）要么取决于这些动力学，要么受到这些动力学的限制。 对混合物吸附动力学的更全面的理解将允许更好地控制该过程和更有效的实际应用。 通过对模型系统进行计算机模拟，并将结果与通过确定压力和组成的实验获得的结果作为时间的函数进行比较，来研究吸附的动力学。 计算机模拟提供了对该过程的微观理解，实验是对模拟有效性的测试。参与该项目的研究生和本科生可以从更广泛的角度来研究这种伙伴关系的实验理论特征所提供的现象。 特别努力招聘和保留的学生从代表性不足的群体，通过暑期课程为当地高中生和一对一的辅导计划，提供关键的学生support.Technical AbstractThis项目解决的问题，如何混合气体的方法吸附平衡，因为它与各种固体表面和/或被限制在小孔内。这是通过结合一系列涉及理论，实验和模拟的研究结果来实现的。关于单一组分平衡的信息（对于许多系统来说，这本身往往很难找到）不足以理解混合物的吸附动力学，其中物种之间的相互作用具有独特的定义作用。理解和充分利用吸附剂的吸附特性时，两个不同的物种竞争成为吸附到其表面上，需要进一步和明确的调查的动力学过程中存在的混合物，最终导致最终的平衡状态的吸附相。这些现象的三个主要方面进行了研究：a）如何吸附率的二元混合气体（及其个别组件）取决于分压和温度？（实验和模拟）; B）平衡过程中的竞争涉及哪些基本过程，它们如何影响吸附速率？（理论和模拟）; c）表面上每个组分的空间分布如何随时间变化？（理论与模拟）。这些问题是针对两种吸附剂（平面和多孔）和两种吸附物（球形和线性），重点是分子相互作用的作用（特别是不同的物种之间），吸附物的取向自由度的影响和，那些施加的多孔吸附剂的限制。实验是在一个专门建造的设置，允许体积吸附测量以及通过质谱法确定的气体混合物的组成作为系统接近平衡，并允许控制温度在延长的时间段。建模和模拟研究通过使用动力学蒙特卡罗方法模拟吸附动力学来探索实验中研究的相同系统和行为。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估而被认为值得支持。

Non-Technical AbstractAfter a mixture of two gases is introduced into a container where an absorbing material has been placed, the pressure and the ratio of the two gases of the mixture inside the container change with time, as particular molecules bind to the absorbing surface. After enough time elapses, the pressure and the composition of the gas reach constant values, and a condensed phase forms on the surface, in equilibrium with the gas phase. This project studies the kinetics of adsorption, that is, the evolution of this process from the introduction of the gas mixture until equilibrium is reached, and how it depends on parameters such as the composition and temperature of the starting gas mixture, how strongly each of the gas molecules attaches to the sorbent, and how fast the different molecules reach their final state. While this is a very complex process, with numerous aspects that are not well understood, most practical applications of adsorption (such as gas separation or gas storage) either depend on, or are limited by, these dynamics. A more complete understanding of the mixture adsorption dynamics will allow for better control of the process and more efficient practical applications. The kinetics of adsorption is studied by performing computer simulations for model systems, and comparing the results with those obtained through experiments in which pressure and composition are determined, as a function of time. The computer simulations provide a microscopic understanding of the process, and the experiments are a test for the validity of the simulations. Graduate and undergraduate students participating in the project can gain a broader perspective of the investigated phenomena provided by the experimental-theoretical character of this partnership. Special efforts are made towards recruitment and retention of students from underrepresented groups, through summer programs for local high school students and one-on-one mentoring programs that provide critical student support.Technical AbstractThis project addresses the question of how a mixture of gases approaches adsorption equilibrium as it interacts with various kinds of solid surfaces and/or is confined within small pores. This is achieved by combining results from a series of studies that involve theory, experiments and simulations. Information on the equilibration of a single component (which is itself often difficult to find for many systems) is not sufficient to understand the sorption kinetics of mixtures, where the interplay between the species has a distinct and defining role. Understanding and taking full advantage of the adsorption characteristics of a sorbent when two distinct species compete to become adsorbed onto its surfaces requires further and explicit investigation of the kinetic processes present in the mixture that eventually lead to the final equilibrium state of the adsorbed phase. Three main aspects of these phenomena are investigated:a) How does the adsorption rate of a binary mixture of gases (and of its individual components) depend on the partial pressures and temperature? (experiments and simulations); b) What are the elementary processes involved in the competition during equilibration, and how do they affect the adsorption rates? (theory and simulations); c) How does the spatial distribution of each component on the surface change with time? (theory and simulations). These questions are addressed for two kinds of sorbents (planar and porous) and two kinds of adsorbates (spherical and linear), with a focus on the role of molecular interactions (especially between the distinct species), the effects of the orientational degrees of freedom of the adsorbates and, those of the confinement imposed by the porous sorbents. The experiments are conducted in a specially built setup that allows for volumetric adsorption measurements as well as for the determination of the composition of the gas mixture through mass spectrometry as the system approaches equilibrium, and which allows control of the temperature over extended periods of time. The modeling and simulation studies explore the same systems and behavior studied in the experiments by using a Kinetic Monte Carlo approach to simulate adsorption dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.