Mass transfer analysis of CO2 capture by PVDF membrane contactor and ionic liquid

Post-combustion processes based on ionic liquids (ILs) and membrane contactors are attractive alternatives to traditional systems. Here, a gas stream composed of 15% CO2 and 85% N2 flowed through the lumen side of a hollow-fiber membrane contactor containing poly(vinylidene fluoride)-IL (PVDF-IL) fibers. The IL 1-ethyl-3-methylimidazolium acetate [emim][Ac] served as an absorbent due to its high chemical absorption and CO2 solubility. The overall mass transfer coefficient (Koverall), activation energy (Ea), and resistances of the hollow-fiber membrane were quantified. The Koverall value was one order of magnitude higher than those reported in previous works with conventional solvents, and the Ea was lower than formerly stated values for other solvents. A theoretical simulation was conducted to estimate the operational parameters required for 90% CO2 capture and to quantify intensification effects related to CO2 absorption in a packed column.This research was funded by the Spanish Ministry of Economy and Competitiveness (Projects CTQ2013-48280-C3-1-R and CTQ2016-76231-C2-1-R). The authors thank Dr. J. C. Remigy (Laboratoire de Genie Chimique, UPS, Toulouse, France) for the preparation of 1AQ2-PVDF fibers

CO2 separation applying ionic liquid mixtures: the effect of mixing different anions on gas permeation through supported ionic liquid membranes

In order to increase flexibility in tailoring the permeability and selectivity of supported ionic liquid membranes (SILMs) for flue gas separation and natural gas purification, this work explores the use of ionic liquid mixtures. For that purpose, gas permeation properties of CO2, CH4 and N-2 in several binary ionic liquid mixtures based on a common cation ([C(2)mim](+)) and different anions such as bis(trifluoromethyl-sulfonyl) imide ([NTf2](-)), acetate ([Ac](-)), lactate ([Lac](-)), dicyanamide ([DCA](-)) and thiocyanate ([SCN](-)) were measured at 293 K using a time-lag apparatus. In addition to gas permeation results, the thermophysical properties of those mixtures, namely viscosity and density, were also determined so that trends between the two types of properties could be evaluated. The results show that mixing [Ac](-) or [Lac](-) with [NTf2](-) promotes the decrease of gas permeability and diffusivity of the SILMs based on those binary mixtures, essentially due to their high viscosities. The pure ionic liquids containing anions with nitrile groups, [DCA](-) or [SCN](-), and also their mixtures with [C(2)mim][NTf2] exhibit permselectivities ranging from 19.1 to 23.0 for CO2/CH4, and from 36.6 to 67.8 for CO2/N-2, as a consequence of a reduction in the CH4 and N-2 permeabilities, respectively. Furthermore, it is shown that mixing anions with different chemical features allows variations in ionic liquid viscosity and molar volume that impact the gas permeation properties of SILMs, offering a clear pathway for the optimization of their CO2 separation performances

Ionic liquids in the electrochemical valorisation of CO2

The development of electrochemical processes for using captured CO2 in the production of valuable compounds appears as an attractive alternative to recycle CO2 and, at the same time, to store electricity from intermittent renewable sources. Among the different innovative attempts that are being investigated to improve these processes, the application of ionic liquids (ILs) has received growing attention in recent years. This paper presents a unified discussion of the significant work that involves the utilisation of ILs for the valorisation of CO2 by means of electrochemical routes. We discuss studies in which CO2 is used as one of the reactants to electrosynthesise value-added products, among which dimethyl carbonate has been the focus of particular attention in the literature. Approaches based on the electrochemical reduction of CO2 to convert it into products without the use of other carbon-based reactants are also reviewed, highlighting the remarkable improvements that the use of ILs has allowed in the CO2 electroreduction to CO. The review emphasises on different aspects related to process design, including the nature of IL anions and cations that have been used, the working conditions, the electrocatalytic materials, the electrode configurations, or the design of electrochemical cells, as well as discussing the most relevant observations, results and figures of merit that the participation of ILs has allowed to achieve in these processes. Several conclusions are finally proposed to highlight crucial challenges and recommendations for future research in this area.The financial support from the Spanish Ministry of Economy and Competitiveness Project CTQ2013-48280-C3-1-R is gratefully acknowledged. J. Albo particularly thanks Juan de la Cierva program (JCI-2012-12073)

CO₂ capture using alkanolamine/room-temperature ionic liquid blends : absorption, regeneration, and corrosion aspects

Le réchauffement climatique, résultant essentiellement des émissions anthropiques de dioxyde de carbone, demeure un sujet de grande préoccupation. Le captage et la séquestration du dioxyde de carbone est une solution viable permettant de prévoir une baisse des émissions de CO2 issues des importantes sources ponctuelles qui impliquent la combustion des carburants fossiles. Dans cette perspective, les systèmes aqueux d’alcanolamines offrent une solution prometteuse à court terme pour la capture du CO2 dans les installations de production d'électricité. Cependant, ces systèmes sont confrontés à divers accrocs opératoires tels que les limitations d’équilibre, les grandes quantités d’énergie requises pour la régénération, les pertes en solvant et la corrosion prononcée des installations, pour ne citer que ces quelques inconvénients. L’eau étant la principale cause de ces complications, une mesure à prendre pourrait être le remplacement de la phase aqueuse par un solvant plus stable. Les liquides ioniques à température ambiante, dotés d’une haute stabilité thermique et pratiquement non-volatils émergent en tant que candidats prometteurs. De plus, grâce à leur nature ajustable, ils peuvent être apprêtés conformément aux exigences du procédé. La substitution de la phase aqueuse dans les processus utilisant l’alcanolamine par les liquides ioniques à température ambiante ouvre une opportunité potentielle pour une capture efficace du CO2. Un aspect remarquable de ces systèmes serait la cristallisation du produit résultant de la capture du CO2 (c-à-d, le carbamate) au sein même du liquide ionique qui non seulement déjouerait les contraintes d’équilibre mais également pourvoirait une opportunité intéressante pour la séparation des produits. Étant donné le peu d’information disponible dans la littérature sur la viabilité des systèmes utilisant la combinaison d’amine et de liquide ionique, l’étude proposée ici a pour but d’apporter une meilleure compréhension sur l’efficacité à séparer le CO2 d’un mélange de type postcombustion à travers une approche plus systématique. À cet effet, des liquides ioniques à base d’imidazolium ([Cnmim][Tf2N], [Cnmim][BF4], [Cnmim][Otf]) ont été choisis. Deux alcanolamines, à savoir, le 2-amino-2-methyl-1-propanol (AMP) et le diéthanolamine (DEA) ont été examinées en détail afin d’explorer la capture du CO2 et les possibilités de régénération qu’offre un système amine-liquide ionique. Les résultats ont révélé l’intérêt de la combinaison DEA-liquide ionique étant donné que ce système pourrait aider à réduire de manière significative l’écart entre les températures d’absorption et de régénération, promettant ainsi une perspective attrayante en termes d’économie d’énergie. En outre, les liquides ioniques ont également été scrutés du point de vue de leur nature hydrophobe/hydrophile afin d’étudier le comportement corrosif du mélange amine-liquide ionique au contact d’échantillons d’acier au carbone. Bien que l’utilisation des liquides ioniques hydrophiles ait aidé à abaisser la vitesse de corrosion jusqu’à concurrence de 72%, l’emploi de liquides ioniques hydrophobes s’avère plus efficace, car annulant quasiment le phénomène de corrosion même dans un environnement riche en CO2. Dans le cas des mélanges immiscibles comme DEA-[hmim][Tf2N], une agitation continue s’avère nécessaire afin d’assurer une dispersion prolongée des gouttelettes d’amine émulsifiées au sein de liquides ioniques et ainsi atteindre une vitesse de capture optimale.Global warming, largely resulting from anthropogenic emissions of carbon dioxide, continues to remain a matter of great concern. Carbon capture and storage (CCS) is a viable solution to ensure a prevised fall in CO2 emissions from large point sources involving fossil fuel combustion. In this context, aqueous alkanolamine systems offer a promising near-term solution for CO2 capture from power generation facilities. However, these face several operational hitches such as equilibrium limitations, high regeneration energy requirement, solvent loss, and soaring corrosion occurrence. The main culprit in this respect is water and, accordingly, one feasible practice may be the replacement of aqueous phase with some stable solvent. Room-temperature ionic liquids (RTILs), with high thermal stability and practically no volatility, are emerging as promising aspirants. Moreover, owing to the tunable nature of ionic liquids, RTIL phase can be adapted in accordance with the process requirements. Replacing aqueous phase with RTIL in case of alkanolamine based processes provided a potential opportunity for efficient CO2 capture. The most striking aspect of these schemes was the crystallization of CO2-captured product (carbamate) inside the RTIL phase that not only helped evade equilibrium constraints but also rendered a worthy opportunity of product separation. Since there is little information available in the literature about the viability of amine-RTIL systems, the proposed research was aimed at better understanding CO2 separation proficiency of these fluids through a more systematic approach. Imidazolium RTILs ([Cnmim][Tf2N], [Cnmim][BF4], [Cnmim][Otf]) were chosen for this purpose. Two alkanolamines, 2-amino-2-methyl-1-propanol (AMP) and diethanolamine (DEA) were examined in detail to explore CO2 capture and regeneration capabilities of amine-RTIL systems. The results revealed the superiority of DEA-RTIL combination as this scheme could help significantly narrow the gap between absorption and regeneration temperatures thus promising a sparkling prospect of attenuating energy needs. Furthermore, ionic liquids were scrutinized in reference to their hydrophobic/hydrophilic nature to study the corrosion behaviour of carbon steel in amine-RTIL media. Though hydrophilic ionic liquids helped decrease corrosion occurrence up to 72%, hydrophobic RTIL appeared to be the most effective in this regard, virtually negating the corrosion phenomenon under CO2 rich environment. In case of immiscible blends like DEA-[hmim][Tf2N], continual agitation appeared to be a necessity to ensure a prolonged dispersion of amine in the RTIL phase and, thereby, to attain an optimal capture rate

CO2 CAPTURE USING ALKANOLAMINE/ROOM-TEMPERATURE IONIC LIQUID BLENDS Absorption, Regeneration, and Corrosion Aspects

Le réchauffement climatique, résultant essentiellement des émissions anthropiques de dioxyde de carbone, demeure un sujet de grande préoccupation. Le captage et la séquestration du dioxyde de carbone est une solution viable permettant de prévoir une baisse des émissions de CO2 issues des importantes sources ponctuelles qui impliquent la combustion des carburants fossiles. Dans cette perspective, les systèmes aqueux d‟alcanolamines offrent une solution prometteuse à court terme pour la capture du CO2 dans les installations de production d'électricité. Cependant, ces systèmes sont confrontés à divers accrocs opératoires tels que les limitations d‟équilibre, les grandes quantités d‟énergie requises pour la régénération, les pertes en solvant et la corrosion prononcée des installations, pour ne citer que ces quelques inconvénients. L‟eau étant la principale cause de ces complications, une mesure à prendre pourrait être le remplacement de la phase aqueuse par un solvant plus stable. Les liquides ioniques à température ambiante, dotés d‟une haute stabilité thermique et pratiquement non-volatils émergent en tant que candidats prometteurs. De plus, grâce à leur nature ajustable, ils peuvent être apprêtés conformément aux exigences du procédé. L

CO₂ Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration

One of the major drawbacks of aqueous alkanolamine based CO₂ capture processes is the requirement of significantly higher energy of regeneration. This weakness can be overcome by separating the CO₂-captured product to regenerate the corresponding amine, thus avoiding the consumption of redundant energy. Replacing aqueous phase with more stable and practically nonvolatile imidazolium based room-temperature ionic liquid (RTIL) provided a viable approach for carbamate to crystallize out as supernatant solid. In the present study, regeneration capabilities of solid carbamates have been investigated. Diethanolamine (DEA) carbamate as well as 2-amino-2-methyl-1-propanol (AMP) carbamate were obtained in crystalline form by bubbling CO₂ in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([hmim]­[Tf₂N]), was used as aqueous phase substituent. Thermal behavior of the carbamates was observed by differential scanning calorimetry and thermogravimetric analysis, while the possible regeneration mechanism has been proposed through ¹³C NMR and FTIR analyses. The results showed that decomposition of DEA-carbamate commenced at lower temperature (∼55 °C), compared to that of AMP-carbamate (∼75 °C); thus promising easy regeneration. The separation of carbamate as solid phase can offer two-way advantage by letting less volume to regenerate as well as by narrowing the gap between CO₂ capture and amine regeneration temperatures

CO₂ Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration

One of the major drawbacks of aqueous alkanolamine based CO₂ capture processes is the requirement of significantly higher energy of regeneration. This weakness can be overcome by separating the CO₂-captured product to regenerate the corresponding amine, thus avoiding the consumption of redundant energy. Replacing aqueous phase with more stable and practically nonvolatile imidazolium based room-temperature ionic liquid (RTIL) provided a viable approach for carbamate to crystallize out as supernatant solid. In the present study, regeneration capabilities of solid carbamates have been investigated. Diethanolamine (DEA) carbamate as well as 2-amino-2-methyl-1-propanol (AMP) carbamate were obtained in crystalline form by bubbling CO₂ in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([hmim]­[Tf₂N]), was used as aqueous phase substituent. Thermal behavior of the carbamates was observed by differential scanning calorimetry and thermogravimetric analysis, while the possible regeneration mechanism has been proposed through ¹³C NMR and FTIR analyses. The results showed that decomposition of DEA-carbamate commenced at lower temperature (∼55 °C), compared to that of AMP-carbamate (∼75 °C); thus promising easy regeneration. The separation of carbamate as solid phase can offer two-way advantage by letting less volume to regenerate as well as by narrowing the gap between CO₂ capture and amine regeneration temperatures