CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration

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dc.contributor.authorBavarella, S.
dc.contributor.authorLuqmani, Ben
dc.contributor.authorThomas, Navya
dc.contributor.authorBrookes, Adam
dc.contributor.authorMoore, A.
dc.contributor.authorVale, P.
dc.contributor.authorPidou, Marc
dc.contributor.authorMcAdam, Ewan J.
dc.date.accessioned2022-03-30T14:51:50Z
dc.date.available2022-03-30T14:51:50Z
dc.date.issued2022-03-16
dc.description.abstractSolids formation can substanitally reduce the energy penalty for ammonia solvent regeneration in carbon capture and storage (CCS), but has been demonstrated in the literature to be difficult to control. This study examines the use of hollow fibre membrane contactors, as this indirect contact mediated between liquid and gas phases in this geometry could improve the regulation of solids formation. Under conditions comparable to existing literature, NH4HCO3 was evidenced to primarily crystallise in the gas-phase (lumen-side of the membrane) due to the high vapour pressure of ammonia, which promotes gaseous transmission from the solvent. Investigation of solvent reactivity demonstrated how equilibria dependent reactions controlled the onset of NH4HCO3 nucleation in the solvent, and limited ‘slip’ through transfomation of ammonia into its protonated form which occurs prior to the phase change. Crystallisation in the solvent was also dependent upon ammonia concentration, where sufficient supersaturation must develop to overcome the activation energy for nucleation. However, this has to be complemented with a reduction in solvent temperature to offset vapour pressure and limit the risk of gas-phase crystallisation. While changes to the solvent chemistry were sufficient to shift from gas-phase to liquid phase crystallisation, wetting was observed immediately after nucleation in the solvent. This was explained by a local region of supersaturation within the coarse membrane pores that promoted a high nucleation rate, altering the material contact angle of the membrane sufficient for solvent to breakthrough into the gas phase. Adoption of a narrower pore size membrane was shown to dissipate wetting after crystallisation in the solvent, illustrating membrane contactors as a stable platform for the sustained separation of CO2 coupled with its simultaneous transformation into a solid. Through resolving previous challenges experienced with solids formation in multiple reactor configurations, the cost benefit of using ammonia as a solvent can be realised, which is critical to enabling economically viable CCS for the transition to net zero, and can be exploited within hollow fibre membrane contactors, eliciting considerable process intensification over existing reactor designs for CCS.en_UK
dc.identifier.citationBavarella S, Luqmani B, Thomas N, et al., (2022) CO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regeneration. Separation and Purification Technology, Volume 290, June 2022, Article number 120786en_UK
dc.identifier.issn1383-5866
dc.identifier.urihttps://doi.org/10.1016/j.seppur.2022.120786
dc.identifier.urihttp://dspace.lib.cranfield.ac.uk/handle/1826/17715
dc.language.isoenen_UK
dc.publisherElsevieren_UK
dc.rightsAttribution 4.0 International*
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/*
dc.subjectChilled ammoniaen_UK
dc.subjectCarbon capture and storage (CCS)en_UK
dc.subjectMembrane crystallisationen_UK
dc.subjectAmmonium bicarbonate solid formationen_UK
dc.subjectAmmonium bicarbonate crystallisation/precipitationen_UK
dc.titleCO2 absorption into aqueous ammonia using membrane contactors: Role of solvent chemistry and pore size on solids formation for low energy solvent regenerationen_UK
dc.typeArticleen_UK

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