Mitigating phase changes in the gas-phase that disrupt CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system

Date published

2024-06-01

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Elsevier

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Article

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2772-4212

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Citation

Luqmani B, Nayak V, Brookes A, et al., (2024) Mitigating phase changes in the gas-phase that disrupt CO2 capture in membrane contactors: CO2-NH3-H2O as a model ternary system. Journal of Membrane Science Letters, Volume 4, Issue 1, June 2024, Article number 100076

Abstract

Solid and liquid products can form in the gas phase of membrane contactors applied to reactive ternary systems for CO2 absorption, which poses a critical barrier for carbon capture applications. The mechanism initiating these unwanted phase changes in the gas phase is unclear. This study therefore systematically characterises CO2 absorption in distinct regions of the vapour-liquid equilibrium (VLE) within an illustrative ternary system (CO2-NH3-H2O), to provide an explanation for the formation and mitigation of these solid and liquid products in the gas-phase. Unstable CO2 absorption and increased pressure drop indicated product formation within the gas-phase, which occurred at high CO2 capture ratios. Temporal analysis of gas-phase composition enabled gas-phase products to be related to the relative ternary composition. This was subsequently correlated to distinct regions of the VLE. Consequently, mitigation strategies can be developed with recognition for where products are least likely to form. Pressurisation was proposed to modify the relative gas-phase ammonia composition to reposition conditions within the VLE. The commensurate increase of CO2 into the solvent shifts the ammonia-ammonium equilibrium towards ammonium to indirectly reduce vapour pressure. This synergistic strategy allows sustained operation of membrane contactors for CO2 separation within reactive ternary systems which are critical to delivering carbon capture economically at scale.

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Github

Keywords

HFMC, CO2 capture, Carbon capture and storage, Chilled ammonia process, Crystallisation

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Attribution 4.0 International

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We are grateful for the financial and technical support offered by Anglian Water, Northumbrian Water and Severn Trent Water. We also acknowledge the funding and training resources provided to Benjamin Luqmani from the Engineering and Physical Sciences Research Council through the STREAM Industrial Doctorate Centre (EP/L015412/1).