Adsorption of H2S from Hydrocarbon Gas Using Doped Bentonite: A Molecular Simulation Study.

Matthew Lasich

doi:10.1021/acsomega.0c02934

Abstract

Hydrogen sulfide is a commonly occurring impurity in hydrocarbon gases such as natural gas or landfill gas. Apart from its toxicity, H2S can cause problems in downstream processing because of corrosion of piping in the presence of moisture. Removing this contaminant using a cost-effective and energy-efficient technique such as adsorption using commonly occurring adsorbents would be beneficial both for processing and refinement of hydrocarbon gases and for their use as an energy source. In this work, grand canonical Monte Carlo simulations were performed using an ab initio forcefield to predict adsorption isotherms for methane, hydrogen sulfide, and nitrogen in bentonite doped with K+, Li+, and Na+ cations with a view to aiding the development of low-cost pressure-swing adsorption systems for the targeted removal of H2S from landfill gas or natural gas. Pure species simulations were done, in addition to considering mixtures at conditions approximating real-world natural gas fields. Highly selective targeted adsorption of hydrogen sulfide was achieved for all three doped bentonites, with the adsorbed phase consisting of almost pure H2S, although the volume of gas adsorbed differed between adsorbents. The results suggest the following ranking for the three doped bentonite adsorbents in terms of their overall performance: K+ > Li+ > Na+. By considering both the composition of the adsorbed phase and the total quantity of adsorbed gas, there may be an interplay between the gas–gas and gas–solid interactions that becomes somewhat noticeable at low pressures.

Highlights

Natural or other gases containing significant quantities of hydrogen sulfide as an impurity are described as being “sour” gases, whereas gases that contain acidic gases such as carbon dioxide or hydrogen sulfide are described as “acid” gases
Natural gas, and landfill gas to remove hydrogen sulfide in particular is important for downstream processing, and this is typically achieved using either absorption, adsorption, cryogenic distillation, or membrane processes
Note that while the gas consists of methane, ethane, carbon dioxide, nitrogen, and hydrogen sulfide, only methane, hydrogen sulfide, and nitrogen adsorbed into the nanoporous bentonite crystal

Summary

Introduction

Natural or other gases containing significant quantities of hydrogen sulfide as an impurity are described as being “sour” gases, whereas gases that contain acidic gases such as carbon dioxide or hydrogen sulfide are described as “acid” gases. Hydrogen sulfide is especially problematic as it toxic, but in the presence of water, it can damage piping via sulfide stress cracking. This can add to maintenance costs in downstream processing or refinement of natural or landfill gas. Natural gas deposits naturally contain some hydrogen sulfide, with some wells producing gas with over 10 percent H2S content.[1] Coal and biomass gasification to produce syngas typically produces gases with substantial hydrogen sulfide content by way of sulfur content conversion. Natural gas, and landfill gas to remove hydrogen sulfide in particular is important for downstream processing, and this is typically achieved using either absorption, adsorption, cryogenic distillation, or membrane processes. The well-known amine and Claus processes are commonly used to sweeten sour gases in refineries, natural gas processing plants, or in gasification or syngas plants

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Conclusion