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Projeto de investigação
Carbon dioxide removal from anaesthetic gas circuits using an Integrated Enzymatic Reactor/Membrane Contactor with Task Specific Ionic Liquids
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CO2 removal from anaesthesia circuits using gas-ionic liquid membrane contactors
Publication . Martins, Carla Maria Figueiredo; Crespo, João; Coelhoso, Isabel; Neves, Luísa
Inhalational anaesthesia is delivered through assisted ventilation and is typically composed by 65-70% of anaesthetic gas (nitrous oxide or xenon), 30% of oxygen and 1-3% of halogenated hydrocarbons (HHCs). Due to the elevated costs of the anaesthesia agents, the remaining anaesthetics present in exhalation are recycled and reused, to minimize the amount of fresh anaesthesia and thus reduce the costs. An alkali hydroxide mixture, commonly called by soda lime, is used to remove CO2from the exhalation, to allow the rebreathing of the anaesthetics. However, some controversy is associated to the use of soda lime, due to the toxic compounds that can be formed in contact with HHCs.The present dissertation concerns the development of a membrane device to replace soda lime, based on two membrane contactors and a biocompatible ionic liquid as a safer strategy for the CO2removal in anaesthesia circuits. The work is divided in three main topics. The first topic focuses on the study of different cholinium-based ionic liquids affinity towards CO2, enhanced by the addition of carbonic anhydrase enzyme. The ionic liquids were tested with different water activities to assess the optimum water amount for the enzyme activity. The results showed an increased affinity towards CO2, when compared with most used ILs. The presence of a very low amount of carbonic anhydrase (0.1 mgCA/gIL) enhanced the CO2transport with a maximum increase of 63%.The second topic involved the understanding of the equilibrium and kinetics of CO2absorption in a cholinium lysinate ionic liquid solution. CO2absorption was monitored through pH measurements and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). A comprehensive model based on chemisorption thermodynamics and absorption kinetics is proposed and validated experimentally. Also,it is demonstrated the potential of using ATR-FTIR as a monitoring tool for absorption of CO2in aqueous solutions of cholinium lysinate.Finally, the third topic focuses on the evaluation of the performance of two distinct membrane contactors with cholinium-based ionic liquids: a microfluidic contactor with a dense polydimethylsiloxane membrane and a porous polytetrafluoroethylene capillary membrane contactor. The characterisation of the systems involved the determination of the mass transfer parameters, i.e. CO2flux across the membrane, overall mass transfer coefficients, selectivity and CO2loadings. Both configurations showed high performance for the capture of CO2, considering either nitrous oxide or xenon as inhalation anaesthetic agents. Aiming an extended shelf-life, a regenerating unit for the ionic liquid solution wasconsidered. The results showed that the use of ion-exchange resins is suitable to revert the chemisorption of CO2in these ionic liquids, avoiding the use of thermal regeneration.The major outcome from the work developed in this Ph.D. is that membrane contactors combined with cholinium-based ionic liquids are suitable for CO2removal from anaesthesia circuits and the recycling of anaesthetics with reuse of ionic liquid significantly reduces the cost per operation, leaving space for a widespread use of better performing, although more expensive, gases like xenon.
Impact of Ionic Liquid Structure and Loading on Gas Sorption and Permeation for ZIF-8-Based Composites and Mixed Matrix Membranes
Publication . Ortiz-Albo, Paloma; Ferreira, Tiago J.; Martins, Carla F.; Alves, Vitor; Esteves, Isabel A. A. C.; Cunha-Silva, Luís; Kumakiri, Izumi; Crespo, João Goulão; Neves, Luísa A.; DQ - Departamento de Química; LAQV@REQUIMTE; MDPI AG
Carbon dioxide (CO2) capture has become of great importance for industrial processes due to the adverse environmental effects of gas emissions. Mixed matrix membranes (MMMs) have been studied as an alternative to traditional technologies, especially due to their potential to overcome the practical limitations of conventional polymeric and inorganic membranes. In this work, the effect of using different ionic liquids (ILs) with the stable metal–organic framework (MOF) ZIF-8 was evaluated. Several IL@ZIF-8 composites and IL@ZIF-8 MMMs were prepared to improve the selective CO2 sorption and permeation over other gases such as methane (CH4) and nitrogen (N2). Different ILs and two distinct loadings were prepared to study not only the effect of IL concentration, but also the impact of the IL structure and affinity towards a specific gas mixture separation. Single gas sorption studies showed an improvement in CO2 /CH4 and CO2 /N2 selectivities, compared with the ones for the pristine ZIF-8, increasing with IL loading. In addition, the prepared IL@ZIF-8 MMMs showed improved CO2 selective behavior and mechanical strength with respect to ZIF-8 MMMs, with a strong dependence on the intrinsic IL CO2 selectivity. Therefore, the selection of high affinity ILs can lead to the improvement of CO2 selective separation for IL@ZIF-8 MMMs.
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Fundação para a Ciência e a Tecnologia
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OE
Número da atribuição
SFRH/BD/111128/2015