(572g) Modeling and Simulation of Multicomponent Adsorption Columns

Adsorptive separation of a multicomponent gaseous mixture in a suitable nanoporous material is a non-hazardous, inexpensive, sustainable, and environmentally benign process. The present work focuses on developing a comprehensive theoretical approach to separate methane and carbon dioxide from other gases such as nitrogen using packed-beds filled with nanoporous adsorbent. Previous work by this group considered binary mixtures, and isothermal as well as isobaric conditions. Here, emphasis is given in multicomponent mixtures and temperature and pressure effects. The adsorption of gaseous species onto the surface of a porous solid is simulated using kinetic Monte Carlo methods on a square lattice. Species from the gas phase deposit onto the sites of the surface thus forming a monolayer of adsorbed species. The parameters required in the rate expressions of the different molecular micro-processes are estimated from experimental pure-component adsorption data. Adsorptive separation of the components of a multicomponent gaseous mixture is achieved in fixed-beds filled with porous adsorbent. As the gas stream flows through the column, the species deposit onto the porous solid at different degrees. The objective of the modeling is the calculation of the concentrations at the column outlet in terms of time (breakthrough analysis). Modeling of the column comprises conservation statements for the species (mass balances) that contain the amounts adsorbed. As already emphasized, the present work considers non-isothermal conditions and pressure losses. The resulting conservation equations can be solved numerically using a finite difference/element technique in which the equations are discretized in space. The system of equations is advanced in time by calculating the amount adsorbed from kinetic Monte Carlo simulations using parameters that correspond to the condition (concentrations, temperature, and pressure) of the gas phase at each node. The model will be tested and used in the sweetening (separation of sour gases) and inert rejection (separation of nitrogen) of natural gas.