Year: 2003
Type: dissertation
Abstract: Increasingly the recovery of hydrogen from refinery gases represents an important operation in the oil & gas industry, particularly as hydrogen is being seen as an energy of the future.Membrane separations are an economic alternative to either pressure swing adsorption separations or cryogenic separations.Transport across thin membranes can produce chemical and physical separations at a relatively low cost.Thus, the diffusion of gas mixtures inside a porous material is an important factor in membrane separations.This research involves the mathematical modelling of adsorption and diffusion in microporous carbon membranes and particularly the Selective Surface Flow (SSF) carbon membranes developed by Air Products and Chemicals, Inc.Molecular simulations are used to predict the performance of the SSF membranes for hydrogen/hydrocarbon mixture separation under realistic conditions of temperature, pressure and bulk-gas composition.Non-Equilibrium Molecular Dynamics (NEMID) gives a fully rigorous account of the dynamics of adsorption and diffusion at an atomic level, by integrating the equations of motion of adsorbed molecules interacting with each other, and with the surface, according to specified intermolecular potentials.In our NEMD simulations, it is assumed that all the pores in the membranes are identical, unconnected and open to the surface.However, this single-pore assumption is unlikely to occur in a real material.A real membrane contains pores of different sizes, connected together in a pore network, allowing the possibility of connectivity effects that are not accommodated by a single-pore model.Thus, critical path analysis (CPA) is used to characterise the pore network structure.The CPA shows that species are selectively transported through essentially distinct sub-networks within the pore network of the membrane.The simulation results are compared with experimental permeabilities, obtained from the Air Products, for a mixture of hydrogen/methane relevant to e.g. the recovery of hydrogen from catalytic reformer offgas.I would like to thank my supervisor Nigel Seaton for all his excellent advice, trust and for his continued encouragement throughout all these years and for the highly challenging technical discussions relating to this thesis.Thanks are also due to Tim C. Golden, James M. D. MacEiroy and Madhukar B. Rao for useful discussions.I would like to thank Tim Golden and Catherine Golden for their
Source: ERA
Authors: Vieira Linhares, Alexandre Manual
Language: English
Subfield: Filtration and Separation
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
Funders: Strong, Royal Academy of Engineering
OpenAlex ID: W2141041347