129 research outputs found
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)
COâ capture using alkanolamine/room-temperature ionic liquid blends : absorption, regeneration, and corrosion aspects
Le rĂ©chauffement climatique, rĂ©sultant essentiellement des Ă©missions anthropiques de dioxyde de carbone, demeure un sujet de grande prĂ©occupation. Le captage et la sĂ©questration du dioxyde de carbone est une solution viable permettant de prĂ©voir une baisse des Ă©missions de CO2 issues des importantes sources ponctuelles qui impliquent la combustion des carburants fossiles. Dans cette perspective, les systĂšmes aqueux dâalcanolamines offrent une solution prometteuse Ă court terme pour la capture du CO2 dans les installations de production d'Ă©lectricitĂ©. Cependant, ces systĂšmes sont confrontĂ©s Ă divers accrocs opĂ©ratoires tels que les limitations dâĂ©quilibre, les grandes quantitĂ©s dâĂ©nergie requises pour la rĂ©gĂ©nĂ©ration, les pertes en solvant et la corrosion prononcĂ©e des installations, pour ne citer que ces quelques inconvĂ©nients. Lâeau Ă©tant la principale cause de ces complications, une mesure Ă prendre pourrait ĂȘtre le remplacement de la phase aqueuse par un solvant plus stable. Les liquides ioniques Ă tempĂ©rature ambiante, dotĂ©s dâune haute stabilitĂ© thermique et pratiquement non-volatils Ă©mergent en tant que candidats prometteurs. De plus, grĂące Ă leur nature ajustable, ils peuvent ĂȘtre apprĂȘtĂ©s conformĂ©ment aux exigences du procĂ©dĂ©. La substitution de la phase aqueuse dans les processus utilisant lâalcanolamine par les liquides ioniques Ă tempĂ©rature ambiante ouvre une opportunitĂ© potentielle pour une capture efficace du CO2. Un aspect remarquable de ces systĂšmes serait la cristallisation du produit rĂ©sultant de la capture du CO2 (c-Ă -d, le carbamate) au sein mĂȘme du liquide ionique qui non seulement dĂ©jouerait les contraintes dâĂ©quilibre mais Ă©galement pourvoirait une opportunitĂ© intĂ©ressante pour la sĂ©paration des produits. Ătant donnĂ© le peu dâinformation disponible dans la littĂ©rature sur la viabilitĂ© des systĂšmes utilisant la combinaison dâamine et de liquide ionique, lâĂ©tude proposĂ©e ici a pour but dâapporter une meilleure comprĂ©hension sur lâefficacitĂ© Ă sĂ©parer le CO2 dâun mĂ©lange de type postcombustion Ă travers une approche plus systĂ©matique. Ă cet effet, des liquides ioniques Ă base dâimidazolium ([Cnmim][Tf2N], [Cnmim][BF4], [Cnmim][Otf]) ont Ă©tĂ© choisis. Deux alcanolamines, Ă savoir, le 2-amino-2-methyl-1-propanol (AMP) et le diĂ©thanolamine (DEA) ont Ă©tĂ© examinĂ©es en dĂ©tail afin dâexplorer la capture du CO2 et les possibilitĂ©s de rĂ©gĂ©nĂ©ration quâoffre un systĂšme amine-liquide ionique. Les rĂ©sultats ont rĂ©vĂ©lĂ© lâintĂ©rĂȘt de la combinaison DEA-liquide ionique Ă©tant donnĂ© que ce systĂšme pourrait aider Ă rĂ©duire de maniĂšre significative lâĂ©cart entre les tempĂ©ratures dâabsorption et de rĂ©gĂ©nĂ©ration, promettant ainsi une perspective attrayante en termes dâĂ©conomie dâĂ©nergie. En outre, les liquides ioniques ont Ă©galement Ă©tĂ© scrutĂ©s du point de vue de leur nature hydrophobe/hydrophile afin dâĂ©tudier le comportement corrosif du mĂ©lange amine-liquide ionique au contact dâĂ©chantillons dâacier au carbone. Bien que lâutilisation des liquides ioniques hydrophiles ait aidĂ© Ă abaisser la vitesse de corrosion jusquâĂ concurrence de 72%, lâemploi de liquides ioniques hydrophobes sâavĂšre plus efficace, car annulant quasiment le phĂ©nomĂšne de corrosion mĂȘme dans un environnement riche en CO2. Dans le cas des mĂ©langes immiscibles comme DEA-[hmim][Tf2N], une agitation continue sâavĂšre nĂ©cessaire afin dâassurer une dispersion prolongĂ©e des gouttelettes dâamine Ă©mulsifiĂ©es 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 rĂ©chauffement climatique, rĂ©sultant essentiellement des Ă©missions anthropiques de dioxyde de carbone, demeure un sujet de grande prĂ©occupation. Le captage et la sĂ©questration du dioxyde de carbone est une solution viable permettant de prĂ©voir une baisse des Ă©missions de CO2 issues des importantes sources ponctuelles qui impliquent la combustion des carburants fossiles. Dans cette perspective, les systĂšmes aqueux dâalcanolamines offrent une solution prometteuse Ă court terme pour la capture du CO2 dans les installations de production d'Ă©lectricitĂ©. Cependant, ces systĂšmes sont confrontĂ©s Ă divers accrocs opĂ©ratoires tels que les limitations dâĂ©quilibre, les grandes quantitĂ©s dâĂ©nergie requises pour la rĂ©gĂ©nĂ©ration, les pertes en solvant et la corrosion prononcĂ©e des installations, pour ne citer que ces quelques inconvĂ©nients. Lâeau Ă©tant la principale cause de ces complications, une mesure Ă prendre pourrait ĂȘtre le remplacement de la phase aqueuse par un solvant plus stable. Les liquides ioniques Ă tempĂ©rature ambiante, dotĂ©s dâune haute stabilitĂ© thermique et pratiquement non-volatils Ă©mergent en tant que candidats prometteurs. De plus, grĂące Ă leur nature ajustable, ils peuvent ĂȘtre apprĂȘtĂ©s conformĂ©ment aux exigences du procĂ©dĂ©. L
CO<sub>2</sub> Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration
One of the major drawbacks of aqueous alkanolamine based
CO<sub>2</sub> capture processes is the requirement of significantly
higher
energy of regeneration. This weakness can be overcome by separating
the CO<sub>2</sub>-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 CO<sub>2</sub> in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium
bisÂ(trifluoromethylsulfonyl)Âimide ([hmim]Â[Tf<sub>2</sub>N]), 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 <sup>13</sup>C NMR and FTIR analyses. The results showed that
decomposition of DEA-carbamate commenced at lower temperature (âŒ55
°C), compared to that of AMP-carbamate (âŒ75 °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 CO<sub>2</sub> capture and
amine regeneration temperatures
CO<sub>2</sub> Capture in Alkanolamine-RTIL Blends via Carbamate Crystallization: Route to Efficient Regeneration
One of the major drawbacks of aqueous alkanolamine based
CO<sub>2</sub> capture processes is the requirement of significantly
higher
energy of regeneration. This weakness can be overcome by separating
the CO<sub>2</sub>-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 CO<sub>2</sub> in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium
bisÂ(trifluoromethylsulfonyl)Âimide ([hmim]Â[Tf<sub>2</sub>N]), 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 <sup>13</sup>C NMR and FTIR analyses. The results showed that
decomposition of DEA-carbamate commenced at lower temperature (âŒ55
°C), compared to that of AMP-carbamate (âŒ75 °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 CO<sub>2</sub> capture and
amine regeneration temperatures
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