CO2 Capture Kinetics Research Articles

Quaternary functionalized mesoporous adsorbents for ultra-high kinetics of CO2 capture from air

Obstacles to widespread deployments of direct air capture of CO2 (DAC) lie in high material and energy costs. By grafting quaternary ammonium (QA) functional group to mesoporous polymers with high surface area, a unique DAC adsorbent with moisture swing adsorption (MSA) ability and ultra-high kinetics was developed in this work. Functionalization is designed for efficient delivery of QA group through mesopores to active substitution sites. This achieved ultra-high kinetics adsorbent with half time of 2.9 min under atmospheric environment, is the highest kinetics value reported among DAC adsorbents. A cyclic adsorption capacity of 0.26 mmol g−1 is obtained during MSA process. Through adsorption thermodynamics, it is revealed that adsorbent with uniform cylindrical pore structure has higher functional group efficiency and CO2 capacity. Pore structure can also tune the MSA ability of adsorbent through capillary condensation of water inside its mesopores. The successful functionalization of mesoporous polymers with superb CO2 adsorption kinetics opens the door to facilitate DAC adsorbents for large-scale carbon capture deployments.

Influence of the initial CH4-hydrate system properties on CO2 capture kinetics

Recovering methane from natural gas hydrate deposits using carbon dioxide injection is currently of great environmental and energetic interest as it shows potential for producing an energy resource while mitigating CO2 emissions through CO2 sequestration. This work investigates the exchange kinetic between CH4 and CO2 (or CO2-N2(v)) in synthetic hydrates, with an emphasis on the impact of CH4 hydrate formation conditions (e.g. driving force Δp) on the subsequent exchange reactions. Different driving forces Δp are utilized and show that the exchange kinetic is improved by a factor of ~3 when the exchange is performed with low Δp CH4 hydrates, for which there is a higher relative amount of free H2O(liq) (277 K); the kinetic is further improved when stirring is applied. Isobaric CH4 hydrates exhibit a fast primary hydrate dissociation and CH4 release, followed by a slower exchange kinetic, possibly limited by solid-state exchange diffusion or secondary CO2-rich hydrate formation within the stability field of CH4 hydrates. Upon exposure to a mixed CO2-N2(v) gas stream, secondary hydrate production is governed by the effective Δp remaining after dissolution of the gas mixture, and results in an even slower exchange reaction rate. These results may help optimizing recovery processes in field trial experiments, where both hydrates and liquid water coexist, and aid in predicting the risk of geo-hazards induced by unstable secondary hydrate formation. Furthermore, the exchange kinetic dependencies highlighted here are important as they affect the overall energy efficiency and energy cost of CH4 recovery processes in gas hydrate field trials.

Understanding and Improving the Kinetics of Bulk Carbonation on Sodium Carbonate

Slow kinetics of CO2 capture on sodium carbonate (Na2CO3) restricts its application in CO2 capture from flue gas despite advantages of low cost, high abundance, and economical retrofitting of extan...

K-doping effect in the kinetics of CO2 capture at high temperature over lithium silicates obtained from rice husks: In situ/operando techniques

K-doped lithium silicates were synthesized as CO2 sorbents using rice husks as silica source. Two different doping methods were used to prepare the solids, incipient wetness impregnation and co-impregnation. Noticeable differences were observed between the sorbents obtained by each route. Unlike the co-impregnated sample, a KLi3SiO4 phase was detected by XRD in the doped-samples prepared by incipient wetness impregnation. This phase was associated with a porous layer deposition over the sorbent particle surface, which was observed by SEM. The effect of CO2 partial pressure and sorption temperature was evaluated for the solids. A remarkable improvement of the capture efficiency was observed in the doped-samples, especially at low temperature and CO2 partial pressure. The kinetics of the samples was studied using the double exponential model and operando Raman and DRIFT spectroscopies. Different reactivity properties were found depending on the synthesis method employed. The complete analysis of the results allowed us to propose a transformation mechanism for the solids during the sorption step, highlighting the improvement of surface reaction and volumetric diffusion processes in the CO2 capture step.

Kinetic and heat duty study of aprotic heterocyclic anion-based dual functionalized ionic liquid solutions for carbon capture

Due to its excellent and reversible CO2 uptake, the novel aprotic heterocyclic anion-based dual functionalized ionic liquid solution ([DETAH][AHA]) presented as an efficient candidate for CO2 capture. The kinetics of CO2 capture into [DETAH][AHA] solutions, e.g., [DETAH][Im] and [DETAH][Tz], was studied by using a double-stirred cell, with concentrations ranging from 0.25 to 1.0 mol/L and temperatures from 303 to 333 K. The overall first-order reaction rate constants (kov) and the secondary-order reaction rate constants (k2, FIL) of CO2 capture into this two [DETAH][AHA] solutions were obtained, and they all increased as the temperature increased. The relationship between k2, FIL and reaction temperature was determined by Arrhenius equation, which expressed as k2=1.0365×1012exp-5873.67T and k2=3.5361×1012exp-6380.60T, respectively. The calculated activation energies of such two solutions were 48.83 kJ/mol and 53.05 kJ/mol, respectively. From the heat duty evaluation, the total CO2 regeneration energy consumption of [DETAH][Im] and [DETAH][Tz] were respectively 2.94 and 2.84 GJ·mol−1 CO2, which were all less than that of traditional MEA solution due to their lower desorption reaction heat. A fast absorbent rate, a lower activation energies and regeneration energy consumption of [DETAH][AHA] solutions indicate greater potential and application prospects.

Amine-containing nanogel particles supported on porous carriers for enhanced carbon dioxide capture

Amine-containing nanogel particles with a lower cooling and heating cycles (303–348 K), which is beneficial to limit the degradation and volatile of amine, has been developed as promising absorbents for CO2 capture. It is extremely important to understand the CO2 capture kinetics and mechanisms for design and operation of corresponding processes. In present work, poly tetra fluoroethylene and carbon paper were used to support the GPs by filtering and loading method. The CO2 uptake and release performance of poly tetra fluoroethylene and carbon paper supported nanogel particles was measured. It was found that carbon paper as supporter shows higher CO2 capacity and desorption rate. A comparison of three different kinetic models shows that carbon paper as supporter gives a more enhanced kinetic behavior. Avrami’s fractional order model presents the best fit to experimental data. To further investigate the mechanism of CO2 uptake on absorbents, interparticle diffusion model, intraparticle diffusion model and Boyd’s film diffusion model were also applied. Film diffusion resistance governed the mass transfer rate of CO2 uptake on studied absorbents at the initial CO2 uptake stages. In the following stages, intra-particle diffusion resistance plays a major role until the equilibrium is reached. The sensible heat of carbon paper as supporter is about 25% lower than that of poly tetra fluoroethylene as supporter. The desorption activation energy obtained from the Arrhenius equation is 18 kJ/mol for carbon paper as supporter, which is 84% lower than that of the typical aqueous MEA solvent.

A Carbide Slag-Based, Ca12Al14O33-Stabilized Sorbent Prepared by the Hydrothermal Template Method Enabling Efficient CO2 Capture

Calcium looping is a promising technology to capture CO2 from the process of coal-fired power generation and gasification of coal/biomass for hydrogen production. The decay of CO2 capture activities of calcium-based sorbents is one of the main problems holding back the development of the technology. Taking carbide slag as a main raw material and Ca12Al14O33 as a support, highly active CO2 sorbents were prepared using the hydrothermal template method in this work. The effects of support ratio, cycle number, and reaction conditions were evaluated. The results show that Ca12Al14O33 generated effectively improves the cyclic stability of CO2 capture by synthetic sorbents. When the Al2O3 addition is 5%, or the Ca12Al14O33 content is 10%, the synthetic sorbent possesses the highest cyclic CO2 capture performance. Under harsh calcination conditions, the CO2 capture capacity of the synthetic sorbent after 30 cycles is 0.29 g/g, which is 80% higher than that of carbide slag. The superiority of the synthetic sorbent on the CO2 capture kinetics mainly reflects at the diffusion-controlled stage. The cumulative pore volume of the synthetic sorbent within the range of 10–100 nm is 2.4 times as high as that of calcined carbide slag. The structure of the synthetic sorbent reduces the CO2 diffusion resistance, and thus leads to better CO2 capture performance and reaction rate.

Synthesis of hierarchical Li4SiO4 nanoparticles/flakers composite from vermiculite/MCM-41 hybrid with improved CO2 capture performance under different CO2 concentrations

Li4SiO4 is a type of very promising high-temperature CO2 sorbent, but suffers from poor cycling stability and low CO2 uptake under relatively low CO2 concentrations. In this contribution, we synthesized hierarchical Li4SiO4 nanoparticles/flakers composite from vermiculite/MCM-41 hybrid precursor and demonstrated these hybrid-type sorbents possess improved CO2 capture performance under different CO2 concentrations. The structural and morphological properties of synthesized n-(VER/MCM-41) (n = 1, 2, 3) precursors and the resulting Li4SiO4-based sorbents n-(VER/MCM-41)-Li4SiO4 were carefully characterized using XRD, SEM, BET, and XRF. Then the CO2 uptakes and CO2 sorption kinetics of n-(VER/MCM-41)-Li4SiO4 were evaluated at different temperatures (500–650 °C). We also found that the n-(VER/MCM-41)-Li4SiO4 is much less affected by CO2 concentration. Finally, the regenerative property and thermal stability of n-(VER/MCM-41)-Li4SiO4, VER-Li4SiO4, and MCM-41-Li4SiO4 were compared. In all, we demonstrated this new Li4SiO4 possesses the merits of both MCM-41-Li4SiO4 and VER-Li4SiO4 including high CO2 uptake, less effected by CO2 concentration, fast CO2 capture kinetics, and excellent cycling stability.

Toward Understanding the Kinetics of CO2 Capture on Sodium Carbonate.

Sodium carbonate (Na2CO3) has been widely studied as a promising candidate for CO2 capture from humid flue gas because of its low cost, high abundance, reusability, and moderate operating temperatures. However, the slow kinetics of CO2 capture on unmodified Na2CO3 make it an unacceptable choice for practical applications. If the reaction kinetics could be dramatically improved, then Na2CO3 could be a viable material for large-scale carbon capture applications. The first step to systematic improvement of kinetics is to understand the rate-limiting steps in the uncatalyzed system. We have therefore investigated the structural, mechanistic, and energetic properties of CO2 capture on the (001) and (-402) surfaces of Na2CO3 using density functional theory to identify the origin of the slow kinetics observed in experiments. We have identified reaction pathways for co-adsorbed CO2 and H2O that lead to bicarbonate formation on the (001) and (-402) surfaces having activation energies of 0.40 and 0.34 eV, respectively. We modeled surface carbonation reactions under conditions of high surface loading of water by performing ab initio molecular dynamics simulations at typical operating temperatures. Multiple reactions were observed on picosecond time scales. Our results indicate that the Na2CO3 carbonation reaction is not controlled by the kinetics of the reaction at the surface but is likely by diffusion limitations. We propose two possible scenarios that could result in diffusion control of the reaction rate.

Absorption characteristics and kinetics of CO2 capture into N-methyldiethanolamine aqueous solution catalyzed by the immobilized carbonic anhydrase

Carbonic anhydrase (CA) is the most effective CO2 hydratase catalyst, but the poor storage stability and repeatability of CA limit its development. Therefore, CA was immobilized on the epoxy magnetic composite microspheres to enhance the CO2 absorption into N-methyldiethanolamine (MDEA) aqueous solution in this work. In the presence of immobilized CA, the CO2 absorption rate of MDEA solution (10 wt%) (0.63 mmol·min−1) was greatly improved by almost 40%, and their reaction equilibrium time was shortened from 150 min to 90 min compared with that into MDEA solution. The results indicated that the absorption of CO2 into MDEA solution had been significantly enhanced by using CA. After the 7th reuse recycle, the activity of the immobilized CA was still closed to its initial value at 313.15 K. Moreover, enzyme catalytic kinetics of immobilized CA was investigated using the p-nitrophenyl acetate (p-NPA) as substrate. The values of Michaelis–Menten constant (Km) and the maximum velocity (Vmax) of the immobilized CA were calculated to be 27.61 mmol/L and 20.14 × 10−3 mmol·min−1·mL−1, respectively. Besides, the kinetics of CO2 reaction into MDEA with or without CA were also compared. The results showed that CO2 absorption into CA/MDEA aqueous solution obeyed the pseudo first order regime and the second order kinetics rate constant (k2) was calculated to be 929 m3·kmol−1·s−1, which was twice higher than that of MDEA aqueous solution without immobilized CA (k2=414 m3·kmol−1·s−1) at 313.15 K.

Review of liquid nano-absorbents for enhanced CO2 capture.

Liquid nano-absorbents have become a topic of interest as a result of their enhanced mass-transfer performance for CO2 capture. They are believed to have revolutionized the conventional CO2 chemisorption process by largely improving CO2 capture kinetics and reducing the energy requirement for solvent regeneration. Two classes of nanomaterial-based CO2 capture absorbents, amine-based nanoparticle suspensions (nanofluids) and nanoparticle organic hybrid materials (NOHMs), have been developed, with significant progress achieved in recent decades. This review addresses two key questions for these two state-of-the-art nanomaterials: how are the physical and chemical properties of the prepared liquid nano-absorbents transformed relative to those of the base fluids? And how does the transformation of the properties affect the CO2 capture behavior? While the current synthesis procedure for liquid nano-absorbents is quite straightforward, more advanced synthesis methods for long-term nanoparticle stability have been suggested for the future. Nanofluids have been shown to increase the CO2 uptake by over 20% and the CO2 capture rate by 2-93% compared with the values observed with neat amine solvents. Nanoparticles with catalytic effects on CO2 capture can significantly increase the CO2 desorption rate by as high as 4000%. NOHMs exhibit the interesting feature of enhanced mass transfer in CO2 capture because of the unique pathway network that is created in them for CO2 to reach specific functional groups. NOHMs promise an effect of combined CO2 capture and conversion, and can be used especially as electrolytes for CO2 electro-reduction. However, there are still some challenges for the application of these materials in real life, such as poor stability and high viscosity. Therefore, efficient CO2 capture processes using these solvents need to be urgently developed and studied in the future.

Hydroquinone clathrate based gas separation (HCBGS): Application to the CO2/CH4 gas mixture

Hydroquinone (HQ) clathrates have recently been identified as promising candidates for selective gas capture and storage processes. This study evaluates the effectiveness of HQ clathrates in the separation of CO2 from CO2/CH4 gas mixtures, through direct gas/solid reactions in a fixed-bed reactor. The influence of the process operating parameters (i.e. reaction time, pressure, temperature and feed gas composition) on the CO2 capture kinetics, selectivity towards CO2, and transient storage capacity were investigated. The experiments were performed using either pure HQ or HQ-based composite materials, with temperatures ranging from about 283 to 343 K, pressures from 3.0 to 9.0 MPa, and CO2 mole fraction in the gas mixture ranging from 0.2 to 1. The experimental results show that over the range of gas composition investigated, the enclathration reaction is selective to CO2. This preferential CO2 capture is enhanced at high CO2 mole fractions, low temperatures and high pressures. Regarding gas capture kinetics, it was confirmed that the composite material is much more efficient than pure HQ crystals. The CO2 enclathration rate increases with temperature, pressure and CO2 fraction in the feed gas. For the first time, the feasibility of such gas separation techniques using HQ clathrates was demonstrated at bench scale.

Molecular Modeling Analysis of CO2 Absorption by Glymes.

The properties of diglyme + CO2 systems were analyzed through density functional theory and molecular dynamics methods with the objective of inferring the microscopic properties of CO2 capture by glyme-based solvents and the effect of ether group regarding solvents affinity toward CO2. Calculations of diglyme + CO2 molecular clusters using density functional theory allowed accurate quantification and characterization of short-range intermolecular forces between these molecules, whereas the molecular dynamics simulation of diglyme + CO2 liquid mixtures, for different CO2 contents, were the means to infer the properties and dynamics of bulk liquid phases upon CO2 absorption. Likewise, liquid diglyme + CO2 gas interfaces were also studied using molecular dynamics methods to examine the kinetics of CO2 capture, adsorption at the gas-liquid interface, and the mechanism of interface crossing, which is of pivotal importance for the design of CO2 capturing units.

CO2 adsorption/regeneration kinetics and regeneration properties of amine functionalized SBA-16

The adsorption/regeneration kinetics of CO2 capture by amine-functionalized SBA-16 was presented to understand the potential mechanism of adsorption of CO2 by adsorption column. Three adsorption kinetic models were used to simulate the isothermal CO2 adsorption data. Based on the value of the correlation coefficient R 2, the fractional order model is considered to be the most suitable model for the CO2 adsorption performance at different temperatures and CO2 concentrations. The results of kinetic analysis show that the adsorption process follows the pseudo second order reaction, and the higher concentration of CO2 or operating temperature will promote the diffusion of CO2 into the adsorbent. Steam stripping and VTSA regeneration were carried out to study the behavior of adsorbent regeneration. Results show that both regeneration methods can achieve rapid regeneration of the adsorbent, and temperature is a major factor in the regeneration of adsorbent due to the chemical bond between CO2 and adsorbents. The Avrami fractional-order models simulates the experimental data well. The absolute value of the activation energy obtained from the Arrhenius equation for CO2 desorption was 59.05 kJ/mol.

Fundamentals in CO2 capture of Na2CO3 under a moist condition

Capacity and kinetics of CO2 capture of Na2CO3 were studied to determine the mechanism for CO2 sequestration under ambient conditions. Bicarbonate formation of Na2CO3 was examined by a thermogravimetric analysis (TGA) under various CO2 and water vapor concentrations and the accompanying structural changes of Na2CO3 were demonstrated by X-ray diffraction (XRD). Morphological variations were observed during the reaction of CO2 capture through scanning electron microscope (SEM). Structural changes and morphological variations, which occurred during the course of the reaction, were then connected to the kinetic and exothermic properties of the CO2 capture process from the XRD and SEM measurements. The results showed that the bicarbonate formation of Na2CO3 has two different pathways. For higher CO2 and H2O concentrations, the bicarbonate formation proceeded effectively. However, for lower CO2 and H2O concentrations, the reactions were more complicated. The formation of Na2CO3•H2O from Na2CO3 as the first step, followed by the subsequent formation of Na5H3(CO3)4, and then the bicarbonate formation proceeds. To understand such fundamental properties in CO2 capture of Na2CO3 is very important for utilization of Na2CO3 as a sorbent for CO2 capture.

Determination and analysis of CO2 capture kinetics and mechanisms on the novel graphene-based adsorbents

Some graphene-based adsorbents such as mesoporous graphene oxide/TiO2 nanocomposite, thermally treated graphene nanosheets, holey graphene frameworks and 3-D graphene-based porous adsorbent have recently been introduced as promising adsorbents for post-combustion CO2 capture while, their CO2 adsorption kinetics and mechanisms have not sufficiently been reported by the scholars. To begin, in this study, CO2 capture kinetics of these adsorbents are investigated by different adsorption kinetic models including pseudo-first order model, pseudo-second order model, Avrami model, and the fractal-like exponential kinetic model. Subsequently, the Eyring and Arrhenius equations are used to determine the activation parameters related to the CO2 adsorption on these adsorbents. Furthermore, a mechanism is proposed to describe the negative activation energy assessed for CO2 adsorption on the studied adsorbents. Eventually, the rate-limiting kinetic models including interparticle diffusion model, intraparticle diffusion model and Boyd’s film diffusion model are applied to determine CO2 capture mechanisms on the mentioned graphene-based adsorbents.

Kinetics of Carbon Dioxide Absorption by Nonaqueous Solutions of Promoted Sterically Hindered Amines

The mechanism and kinetics of CO2 capture using piperazine (PZ) promoted nonaqueous solutions of 2-amino-2-methyl-1,3-propanediol (AMPD) and 2-amino-2-ethyl-1,3-propanediol (AEPD) were investigated by stopped-flow technique. The termolecular mechanism was used to model the kinetics of the reactions. AMPD or AEPD like other sterically hindered amines absorbs CO2 in an equimolar ratio that is significantly higher than that of monoethanolamine (MEA). However, the steric hinderance results in decreased reaction rate as in the case of AMPD and AEPD. The reaction can be promoted by addition of small amounts of cyclic polyamines, such as PZ or its derivatives. Our results show clearly that nonaqueous solutions of AMPD and AEPD can achieve reaction rates comparable to commercial systems by the addition of small amounts of PZ.

Creating innovative composite materials to enhance the kinetics of CO2 capture by hydroquinone clathrates

This study addresses both the preparation of a reactive medium composed of porous particles impregnated with hydroquinone (HQ), an organic compound capable of forming gas clathrates, and an evaluation of the kinetic performance of these composite materials for CO2 capture. Two types of porous silica particles of different sizes and pore diameters were tested. The porous particles were impregnated with HQ by a dry impregnation (DI) method in a fluidized bed, and by a wet impregnation (WI) method. The impregnation effectiveness of the two methods is discussed, and the reactivity of the composite materials formed in terms of CO2 capture and storage capacity is studied experimentally. The experimental results showed that the HQ adheres well on the silica without any chemical modification of the deposit’s structure. We demonstrated that the impregnation technique plays a very important role in the kinetics of CO2 capture. A series of experiments performed using a magnetic suspension balance at 3.0MPa and 323K showed that the silica-based impregnated particles reversibly capture and store CO2, and that the CO2 capture kinetics are significantly enhanced compared to the results obtained with pure powdered HQ. Finally, we demonstrated that CO2 capture is faster with dry-impregnated particles.

Mechanism and Kinetics of CO2 Absorption into an Aqueous Solution of a Triamino-Functionalized Ionic Liquid

A novel ionic liquid (1-aminoethyl-3-methylimidazolium lysinate, [C2NH2MIm][Lys]) functionalized with three amino groups had been developed for carbon dioxide (CO2) capture in this work. The CO2 absorption loading of [C2NH2MIm][Lys] solution was found to be 1.59 mol CO2/mol IL with a concentration of 0.5 mol/L at 313.15 K, which was much higher than that of the most existing dual functionalized ILs. Besides, [C2NH2MIm][Lys] also owned a good regenerability even after 6 regeneration cycles. According to the results of 13C nuclear magnetic resonance (13C NMR), CO2 absorption into [C2NH2MIm][Lys] solution could be divided into two stages, which began with the formation of carbamate, and followed by the hydration of CO2 to form carbonate/bicarbonate. Meanwhile, the desorption of the saturated [C2NH2MIm][Lys] was proven to be a reverse process of the adsorption. Based on the mechanism results, the kinetics of CO2 capture into [C2NH2MIm][Lys] solution was investigated by using a double stirred-cell absorber at ...

Carbon steel corrosion in piperazine-promoted blends under CO2 capture conditions

Aqueous amine promoter blends have improved CO2 absorption capacity and uptake. Tertiary (3°) and sterically-hindered (SH) amines are favoured for their molar absorption ratio, (i.e. CO2 absorption capacity). With a promoter, namely piperazine (PZ), the ordinarily slow reaction kinetics of a 3°/SH amine is accelerated. Amine blends of 30 and 50% by weight, MDEA+PZ and AMP+PZ, were tested using immersion corrosion techniques at 120°C. In all cases, a siderite (FeCO3) product layer was formed on the surface of the carbon steel coupons. Aqueous PZ solutions produced thin layers with comparatively lower Fe ion concentrations than blended solutions. The fast CO2 capture kinetics of PZ, and therefore carbonate formation, makes the rapid reaction possible due to readily available Fe ions oxidised on the surface. The replacement of PZ content in a blend, by MDEA or AMP, resulted in slower formation of siderite and variably poorer corrosion protection. Critically, the use of AMP in the blend offers better protection against corrosion, shown by lower concentration of Fe ions in the bulk solution than parallel MDEA solutions. This can be attributed to the faster formation of carbonate species by AMP, as a SH amine, which also results in more imperfect crystals.