Prediction of Sorption and Diffusion in Zeolite Catalysts

本文对碳氢化合物在五元沸石中的吸附和扩散现象进行了探索性研究。这是开发从微观结构和化学成分定量预测这些现象的可靠方法的第一步。以甲烷/硅沸石和丁烷/硅沸石为实验对象进行了深入的研究。强大的计算技术(构型积分计算、分子动力学、巨正则系综蒙特卡罗)被用来在原子水平上模拟这些体系，推导出平衡吸附等温线和自扩散系数，并扩展了对潜在分子机制的基本理解，远远超出了其现状。理论预测将与现有的实验证据相对照。此外，还将启动一项实验工作，以制备表征良好的大晶体硅石样品，并用重量法直接测量吸附和扩散。在这项初步研究中开发的分子模拟方法是相当通用的。一旦它们的预测能力在定义良好的测试系统中建立起来，它们在各种沸石和吸附树脂中的应用将是直截了当的。这项研究的长期目标是得到一幅自洽的吸附和扩散的微观图像，这对用于分离和催化应用的沸石系统的分子工程设计是有用的。

This is an exploratory study of the phenomena of sorption and diffusion of hydrocarbons in pentasil zeolites. It is undertaken as a first step towards the development of reliable methods for the quantitative prediction of these phenomena from microscopic structure and chemical constitution. The systems methane/silicalite and butane/silicalite are investigated in depth, as test cases. Powerful computational techniques (evaluation of configurational integrals, molecular dynamics, grand canonical ensemble Monte Carlo) are employed to simulate these systems at an atomistic level, deduce equilibrium sorption isotherms and self-diffusion coefficients, and extend the fundamental understanding of underlying molecular mechanisms far beyond its present status. Theoretical predictions will be checked against available experimental evidence. In addition, an experimental effort will be initiated for the preparation of well characterized, large crystal silicalite samples and the direct measurement of sorption and diffusion by gravimetric techniques. The molecular simulation methods developed in this preliminary study are quite general. Once their predictive power is established in well defined test systems, their application to a wide variety of zeolites and sorbates will be straightforward. The long range objective of this research is to arrive at a self- consistent microscopic picture of sorption and diffusion, useful for the molecular engineering design of zeolite systems for separations and catalytic applications.