Sweetening Natural Gas

graph showing top-performing zeolite structures

Natural gas often contains contaminants. “Sour” gas is natural gas that contains a significant amount of hydrogen sulfide, H2S. Not only is H2S toxic enough to be fatal at concentrations as low as 1,000 ppm, but it is also very corrosive and can damage the pipelines, so it must be reduced to acceptable levels before the natural gas can be used. This is usually done with an amine-based absorption method that is costly and energy-intensive, in particular for highly sour gas mixtures. An alternative to the amine-based process involves the pretreatment with sorbent materials such as zeolites, which have a porous structure and are part of a class of materials known as “molecular sieves.” They can be used to selectively separate specific molecules, such as H2S, from natural gas.

MSI PIs Michael Tsapatsis (professor, Chemical Engineering and Materials Science) and J. Ilja Siepmann (professor, Chemistry; Chemical Theory Center) and Ph.D. candidate Mansi Shah (the study’s first author) recently published a paper in Angewandte Chemie International Edition that describes a hierarchical screening approach using Monte Carlo simulations to determine the best sorbent materials to “sweeten” natural gas (i.e., remove a significant fraction of H2S and other contaminants). The authors successfully identified zeolitic sorbents that were able to selectively remove H2S and CO2. The computational results point the way to further experimental work to synthesize these zeolite materials and to refine the process. The paper can be found on the journal website: Mansi S. Shah, Michael Tsapatsis, and J. Ilja Siepmann. 2016. Identifying optimal zeolitic sorbents for sweetening of highly sour natural gas. Angewandte Chemie - International Edition 55: 5938-42. DOI: 10.1002/anie.201600612.

Professor Tsapatsis and his research group use MSI for computational modeling that supports their studies of zeolites, especially zeolite nanosheets. Professor Siepmann and his group develop and use computational-chemistry tools on the supercomputers in support of projects that investigate a variety of complex chemical systems and processes. Ms. Shah’s research focuses on several gas and liquid separations relevant to the chemical and energy industries, both computationally and experimentally; she is co-advised by Professors Tsapatsis and Siepmann.

Image description: Selectivity (left axis) and partial molar adsorption enthalpies (right axis) in top-performing zeolite structures at mole fraction = 0.50, temperature = 343 K, and pressure = 50 bar. H2S/CH4 selectivity, cyan triangles; H2S/C2H6 selectivity,  magenta squares; and partial molar adsorption enthalpies (for the H2S/CH4 mixture), green bars. Image and description adapted from Angewandte Chemie International Edition, 55(20), 5938-5942 (2016), DOI: 10.1002/anie.201600612.

posted on December 8, 2016

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