Removal of Carbon Dioxide from Natural Gas Using an Amine-Functionalized Metal-Organic-Framework

Raw natural gas contains methane as its major component, but it also contains considerable amounts of light and heavier hydrocarbons along with other contaminants such as CO₂ and H₂S (i.e. acid gas in general) that cause corrosion and fouling of the pipeline and equipment during transportation and liquefaction. To achieve the specifications for liquefied natural gas (LNG), the acid gas levels must to be controlled to ≤ 50 ppmv CO₂ and ≤ 4 ppmv H₂S. Amine-based acid gas removal processes have been employed in the gas industry, but these processes have disadvantages including high regeneration energy requirements and inefficiencies; these issues have not been adequately solved to date. Currently, adsorptive acid gas removal technologies have received significant interest because of the simplicity of adsorbent regeneration by thermal or pressure variation1). Numerous micro- and mesoporous adsorbents including zeolites [2-3], titanosilicates[4], activated carbons[5-6], metal-organic-framework (MOF) [7], and silica-alumina materials[8-9] were studied for this type of application. However, the CO₂/CH₄ selectivity of the aforementioned adsorbents was not high enough for commercial applications.

In this study, an amine-functionalized MOF was synthesized, physicochemically characterized, and tested for thermal swing adsorption (TSA) applications. The effect of various TSA operating conditions including the purge flow rate and regeneration temperature on the breakthrough capacity for a binary mixture of CO₂ and CH₄ were elucidated. The cyclic breakthrough experiments for TSA using the extrudate were performed to assess its performance and stability. The CO₂/CH₄ selectivity of the amine-functionalized MOF were estimated and compared with that of commercial adsorbents.

References

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