Discovery of novel zeolites for natural gas purification through combined material screening and process optimization

Abstract

in Wiley Online Library (wileyonlinelibrary.com) An efficient computational screening approach is proposed to select the most cost-effective materials and adsorption process conditions for CH 4 /CO 2 separation. The method identifies eight novel zeolites for removing CO 2 from natural gas, coalbed methane, shale gas, enhanced oil recovery gas, biogas, and landfill gas sources. The separation cost is minimized through hierarchical material screening combined with rigorous process modeling and optimization. Minimum purity and recovery constraints of 97 and 95%, respectively, are introduced to meet natural gas pipeline specifications and minimize losses. The top zeolite, WEI, can recover methane as economically as $0.15/MMBTU from natural gas with 5% CO 2 to $1.44/MMBTU from natural gas with 50% CO 2 , showing the potential for developing natural gas reservoirs with higher CO 2 content. The necessity of a combined material selection and process optimization approach is demonstrated by the lack of clear correlation between cost and material-centric metrics such as adsorption selectivity. V C 2014 American Institute of Chemical Engineers AIChE J, 60: 1767-1785, 2014 Keywords: zeolites, adsorption/gas, process synthesis, optimization, computational screening IntroductionThere are vast reserves of natural gas worldwide that are uneconomical to develop due to high CO 2 content, which can be as high as 70% by volume.1 About 10% of natural gas in the United States contains significant quantities of CO 2 that must be removed prior to pipeline transportation to meet the typical specification on CO 2 of 3%.2,3 Typical specifications on composition for U.S. pipelines are provided in Table 1. Even for natural gas sources with low to moderate CO 2 content that is separated before pipeline transport, the CO 2 is often vented into the atmosphere, which contributes to global climate change. In fact, natural gas production is the second-largest source of CO 2 emissions in the United States (after fossil fuel consumption). 5 Even more of an environmental concern is methane, which is the most potent greenhouse gas (GHG) with about 21 times the GHG warming potential than CO 2 . It is, therefore, important to minimize methane losses during natural gas purification for both economic and environmental reasons.Major methane sources in the United States that may require CO 2 separation are illustrated in Figure 1. Shale gas sources typically contain 0-10% CO 2 , but the CO 2 content can increase during the life of a well to up to 30%. 6 Coalbed methane is a type of natural gas found in unmineable coal areas, which is typically extracted through the addition of CO 2 that is selectively adsorbed in the coal bed. As a result, coalbed methane typically contains 30-50% CO 2 . 7 The gases resulting from enhanced oil recovery may contain 20-80% CO 2 in addition to CH 4 . 8 Biogas is the result of anaerobic decomposition of organic waste, such as animal products (e.g., manure), agricultural residues, municipal solid waste, and municipal wastewat...

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