Effects of alumina phases on CO2 sorption and regeneration properties of potassium-based alumina sorbents

A range of potassium-based alumina sorbents were fabricated by impregnation of alumina with K₂CO₃ to examine the effects of the structural and textural properties of alumina on the CO₂ sorption and regeneration properties. Alumina materials, which were used as supports, were prepared by calcining alumina at various temperatures (300, 600, 950, and 1,200 °C). The CO₂ sorption and regeneration properties of these sorbents were examined during multiple tests in a fixed-bed reactor in the presence of 1 vol% CO₂ and 9 vol% H₂O. The regeneration capacities of the potassium-based alumina sorbents increased with increasing calcination temperature of alumina. The formation of KHCO₃ increased with increasing calcination temperature during CO₂ sorption, whereas the formation of KAl(CO₃)(OH)₂, which is an inactive material, decreased. These results is due to the fact that the structure of alumina by the calcination temperature is related directly to the formation of the by-product [KAl(CO₃)(OH)₂]. The structure of alumina plays an important role in enhancing the regeneration capacity of the potassium-based alumina sorbent. Based on these results, a new potassium-based sorbent using δ-Al₂O₃ as a support was developed for post-combustion CO₂ capture. This sorbent maintained a high CO₂ capture capacity of 88 mg CO₂/g sorbent after two cycles. In particular, it showed a faster sorption rate than the other potassium-based alumina sorbents examined.     

Preparation and performance of potassium-based sorbent using SnO<Subscript>2</Subscript> for post-combustion CO<Subscript>2</Subscript> capture

Potassium-based sorbents using γ-Al₂O₃ or TiO₂ as a support or an additive material have disadvantages in terms of their thermal stability and cyclic CO₂ capture. To overcome the shortcomings of these sorbents, a novel potassium-based sorbent (KSnI30) using SnO₂ was developed in this study. The KSnI30 sorbent formed only K₂CO₃ and SnO₂ phases without any inactive alloy species even after calcination at high temperatures (500–700 °C), indicating the good thermal stability of the KSnI30 sorbent regardless of the calcination temperature. Furthermore, the KSnI30 sorbent has an excellent regeneration property (above 98 %), as well as high CO₂ capture capacities (89–94 mg CO₂/g sorbent). Its excellent regeneration property is due to the formation of a KHCO₃ phase without by-products during CO₂ sorption. These results of the present study demonstrate that the SnO₂ shows promise as a new support or an additive material to replace TiO₂ and γ-Al₂O₃ in the preparation of a regenerable potassium-based sorbent for post-combustion CO₂ capture with good thermal stability and excellent regeneration property.     

Sorption of Carbon Dioxide from Wet Gases by K2CO3-in-Porous Matrix: Influence of the Matrix Nature

In a fixed-bed absorber at 40°C, the dynamics of carbon dioxide sorption over composite sorbents prepared by impregnation of potassium carbonate in various porous matrixes is studied. The dynamic capacity of the synthesized sorbents is shown to reach 0.12 g CO₂ per 1 g of the sorbent. The composite dynamic capacity depends on the nature of the host matrix and decreases in the sequence alumina > activated carbon > vermiculite > silica gel. For K₂CO₃-on-alumina, the sorption capacity decreases considerably after the first cycle of «absorption and regeneration under 200–350°C», whereas the sorbents based on active carbons could be reversibly restored. The findings are discussed within the idea on a chemical interaction between the host matrix and the impregnated salt.     

Sorption of carbon dioxide by the composite sorbent “potassium carbonate in porous matrix”

Sorption of CO₂ in the presence of water vapor by the K₂CO₃—-Al₂O₃ composite sorbent was studied by IR spectroscopy in situ, X-ray diffraction analysis, and the differentiating dissolution method and reasons for a decrease in its dynamic capacity are given. The samples containing K₂CO₃·1.5H₂O in pores are characterized by the maximal dynamic capacity. A mechanism for CO₂ sorption was proposed, which qualitatively explains the obtained dependence of the capacity on the water content in the composite sorbent. A high dynamic capacity can be maintained by regeneration of the sorbents by water vapor at 170 °N. The capacity of the sorbents decreases during the first 10 sorption—regeneration cycles due to the formation of an inactive phase of potassium aluminum carbonate.     

FT-IR study on CO<Subscript>2</Subscript> adsorbed species of CO<Subscript>2</Subscript> sorbents

The stability of amine-functionalized silica sorbents prepared through the incipient wetness technique with primary, secondary, and tertiary amino organosilanes was investigated. The prepared sorbents were exposed to different gaseous streams including CO₂/N₂, dry CO₂/air with varying concentration, and humid CO₂/air mixtures to demonstrate the effect of the gas conditions on the CO₂ adsorption capacity and the stability of the different amine structures. The primary and secondary amine-functionalized adsorbents exhibited CO₂ sorption capacity, while tertiary amine adsorbent hardly adsorbed any CO₂. The secondary amine adsorbent showed better stability than the primary amine sorbent in all the gas conditions, especially dry conditions. Deactivation species were evaluated using FT-IR spectra, and the presence of urea was confirmed to be the main deactivation product of the primary amine adsorbent under dry condition. Furthermore, it was found that the CO₂ concentration can affect the CO₂ sorption capacity as well as the extent of degradation of sorbents.     

CO_2 capture over molecular basket sorbents: Effects of SiO_2 supports and PEG additive

The objective of this work is to study the influences of silica supports and PEG additive on the sorption performance of molecular basket sorbent(MBS) for CO_2 capture consisting of polyethylenimine and one of the following supports: SBA-15(2-D structure), TUD-1(3-D sponge-like structure) and fumed silica HS-5(3-D disordered structure). Effects of the supports regarding pore structures and pore properties, the PEI loading amount as well as the sorption temperature were examined. Furthermore, polyethylene glycol(PEG) was introduced as an additive into the sorbents and its effect was investigated at different PEI loadings and sorption temperatures. The results suggest that the pore properties of MBS(after PEI loading) play a more important role in the CO_2 sorption capacity, rather than those of the supports alone.MBS with 3D pore structure exhibits higher CO_2 sorption capacity and amine efficiency than those with 2D-structured support. Among the sorbents studied, fumed silica(HS-5) based MBS showed the highest CO_2 sorption capacity in the temperature range of 30-95 °C, probably due to its unique interstitial pores formed by the aggregation of polymer-loaded SiO_2 particles. It was found that the temperature dependence is directly related to the PEI surface coverage layers. The more PEI surface coverage layers, the higher diffusion barrier for CO_2 and the stronger temperature dependence of CO_2 capacity. 3D MBS exceeds 2D MBS at the same PEI coverage layers due to lower diffusion barrier. Adding PEG can significantly enhance the CO_2 sorption capacity and improve amine efficiency of all MBS, most likely by alleviating the diffusion barrier within PEI bulk layers through the inter-molecular interaction between PEI and PEG.     

MgO/CaO-loaded porous carbons for carbon dioxide capture

Nanoporous carbons loaded with both MgO and CaO were prepared by a simple heating of mixtures consisting of poly(ethylene terephthalate) and natural dolomite. Preparations were carried out at temperatures ranging from 850 to 1,000 °C that ensured complete thermal decomposition of the dolomite contained in the mixtures to the oxides. An influence of the PET/dolomite weight ratio and temperature of the preparation process on the porosity of the obtained composite products and on CaO and MgO crystallite sizes are discussed using the results of nitrogen adsorption/desorption at 77 K and X-ray diffraction analyses, respectively. Performances of the hybrid materials as sorbents for carbon dioxide were examined using thermogravimetric analyses. Finally, possibility of regeneration of the spent sorbent materials together with a side—effect accompanying this process are discussed on the basis of thermogravimetric measurements. As found, a part of CO₂ captured by the hybrid sorbents gets adsorbed weakly and another portion is fixed strongly. During thermal regeneration, the strongly fixed CO₂ reacts with carbon material. In this way small fraction of a sorbent is lost.     

Dry Potassium-Based Sorbents for CO<Subscript>2</Subscript> Capture

Dry potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, CaO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property of various sorbents were measured in the presence of H₂O in a fixed bed reactor, during multiple cycles at various temperature conditions (CO₂ absorption at 50–100 °C and regeneration at 130–400 °C). The KAlI30, KCaI30, and KMgI30 sorbents formed new structures such as KAl(CO₃)₂(OH)₂, K₂Ca(CO₃)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely convert to the original K₂CO₃ phase at temperatures below 200 °C, during the CO₂ absorption process in the presence of 9 vol.% H₂O. In the case of KACI30, KTiI30, and KZrI30, only a KHCO₃ crystal structure was formed during CO₂ absorption. The formation of active species, K₂CO₃·1.5H₂O, by the pretreatment with water vapor and the formation of the KHCO₃ crystal structure after CO₂ absorption are important factors for absorption and regeneration, respectively, even at low temperatures (130–150 °C). In particular, the KTiI30 sorbent showed excellent characteristics with respect to CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (87 mg CO₂/g sorbent) without the pretreatment with water vapor, unlike KACI30, and a fast and complete regeneration at a low temperature condition (1 atm, 150 °C). In addition, the higher total CO₂ capture capacity of KMgI30 (178.6 mg CO₂/g sorbent) than that of the theoretical value (95 mg CO₂/g sorbent) was explained through the contribution of the absorption ability of MgO support. In this review, we introduce the CO₂ capture capacities and regeneration properties of several potassium-based sorbents, the changes in the physical properties of the sorbents before/after CO₂ absorption, and the role of water vapor and its effects on CO₂ absorption.     

Properties and Application of a Chelating Sorbent Prepared by Modification of LiChroprep-NH<Subscript>2</Subscript> with Calcon

A new chelating sorbent for metal ions was prepared by modification of chemically modified silica – LiChroprep-NH₂ with Calcon. The molecular mechanism of binding this reagent to the surface of the applied carrier is presented. The properties of this sorbent were compared to analogous sorbents with a plain silica carrier and chemically modified silicas – LiChroprep-RP containing Calcon. The advantages of the new sorbent compared to the silica and LiChroprep-RP chelating sorbents are demonstrated. The sorbent obtained was applied as stationary phase in solid-phase extraction (SPE) for separations of some chosen mixtures of metal ions and for additional purification of aqueous solutions of salts of alkali metals from trace amounts of heavy metals. The multiple use of the sorbent based on LiChroprep-NH₂ in sorption-desorption processes of metal ions without deterioration of its sorption capacity is demonstrated.     

Gas generation during Cypris clay expansion

Blast furnace slag was leached using HCl to prepare lithium-based sorbents for CO₂ capture, and chemical composition and phase of the acid leaching slag were determined by X-ray fluorescence analysis. The microstructure and morphology of both sorbents were characterized by scanning electron microscope and X-ray diffraction. The absorption capacity of both sorbents was observed non-isothermally and isothermally using thermogravimetric analysis, and 12 carbonation and calcination cycles were conducted to observe cycling stability. Controlling step of absorption process was determined by fitting the isothermal graphs using a double exponential model. The results show that 98.33% amorphous SiO₂ can be obtained when the blast furnace slag was treated at 373 K for 10 h. Purified lithium-based sorbent by acid leaching slag (LBS-ALS) shows dense polyhedral particles with particle size between 25 and 120 μm. LBS-ALS shows similar absorption capacity with pure Li₄SiO₄ (P-Li₄SiO₄), but narrower absorption temperature range at non-isothermal absorption condition. The double exponential model fits well with the isothermal graphs for LBS-ALS and P-Li₄SiO₄, and diffusion of CO₂ is the controlling step of the absorption process at lower temperature. LBS-ALS shows different controlling mechanism for desorption process compared with P-Li₄SiO₄. LBS-ALS maintains higher absorption capacity after 12 cycles in 100% CO₂ flow.     

Sorption-desorption of radiocesium on various sorbents in presence of humic acid

In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm^–3 NaCl was in order zeolite > NiFeCN–SiO₂ > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN–SiO₂ was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN–SiO₂ and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN–SiO₂ > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.     

Sorption of phosphorus(V) by polymeric sorbents based on aminopolystyrene and 4-amino-<Emphasis Type="Italic">N</Emphasis>-azobenzenesulfamide

Phosphorus(V) sorption on sorbents based on aminopolystyrene and 4-amino-N-azobenzenesfulamide from aqueous solutions is studied. The following sorption parameters are determined: the optimum acidity, pH_opt; 50% sorption pH, pH₅₀; optimal time τ, min; quantitative-sorption temperature; and phosphorus(V) sorption capacity of the sorbent (SCS). Sorption isotherms are plotted.     

Kinetics of carbon dioxide sorption by the composite material K2CO3 in Al2O3

The kinetics of the CO₂ sorption by a composite sorbent K₂CO₃ in Al₂O₃ was studied in a gradientless adsorber at 295 K. The order of the sorption rate with respect to the CO₂ concentration was found to be n = 1.04 ± 0.07. The sorption rate constants were evaluated for sorbent grains of various sizes between 0.25 and 2.1 mm. It was shown that the rate constant is proportional to the grain reciprocal radius. The dynamic capacity was obtained as a function of the CO₂ concentration. The maximum sorption capacity was found to be 83 mg of CO₂ per 1 g of the sorbent. This revised version was published online in August 2006 with corrections to the Cover Date.     

聚乙烯亚胺修饰的氧化硅纳米管基吸附剂的制备及其CO_2吸附应用

以P123为模板,1,2-二(三甲氧基硅基)乙烷(BTME)为硅源合成了介孔氧化硅纳米管(E-SNTs).将ESNTs经过聚乙烯亚胺(PEI)修饰后制得吸附剂用于捕捉CO2.对吸附剂进行了透射电镜(TEM)、物理吸附、傅里叶变换红外(FTIR)光谱、热重分析(TGA)等表征.E-SNTs-PEI吸附剂的最佳CO2吸附温度为75°C.吸附剂的CO2吸附量随着PEI负载量的增加呈现先增大后减小的趋势,其中50%为最佳负载量,此时吸附剂的吸附量最大为3.32 mmol·g-1.相比较SBA-15基吸附剂,E-SNTs基吸附剂具有更优异的吸附性能.在有水汽的存在下,吸附剂E-SNTs-50的CO2吸附量达到3.75 mmol·g-1.经过四次循环吸脱附实验测试E-SNTs-PEI吸附剂的稳定性能,结果表明其CO2吸附量基本不变,该吸附剂表现出较好的稳定性和可再生能力.     

Lithium silicate nanosheets with excellent capture capacity and kinetics with unprecedented stability for high-temperature CO2 capture

An excessive amount of CO₂ is the leading cause of climate change, and hence, its reduction in the Earth''s atmosphere is critical to stop further degradation of the environment. Although a large body of work has been carried out for post-combustion low-temperature CO₂ capture, there are very few high temperature pre-combustion CO₂ capture processes. Lithium silicate (Li₄SiO₄), one of the best known high-temperature CO₂ capture sorbents, has two main challenges, moderate capture kinetics and poor sorbent stability. In this work, we have designed and synthesized lithium silicate nanosheets (LSNs), which showed high CO₂ capture capacity (35.3 wt% CO₂ capture using 60% CO₂ feed gas, close to the theoretical value) with ultra-fast kinetics and enhanced stability at 650 °C. Due to the nanosheet morphology of the LSNs, they provided a good external surface for CO₂ adsorption at every Li-site, yielding excellent CO₂ capture capacity. The nanosheet morphology of the LSNs allowed efficient CO₂ diffusion to ensure reaction with the entire sheet as well as providing extremely fast CO₂ capture kinetics (0.22 g g⁻¹ min⁻¹). Conventional lithium silicates are known to rapidly lose their capture capacity and kinetics within the first few cycles due to thick carbonate shell formation and also due to the sintering of sorbent particles; however, the LSNs were stable for at least 200 cycles without any loss in their capture capacity or kinetics. The LSNs neither formed a carbonate shell nor underwent sintering, allowing efficient adsorption–desorption cycling. We also proposed a new mechanism, a mixed-phase model, to explain the unique CO₂ capture behavior of the LSNs, using detailed (i) kinetics experiments for both adsorption and desorption steps, (ii) in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy measurements, (iii) depth-profiling X-ray photoelectron spectroscopy (XPS) of the sorbent after CO₂ capture and (iv) theoretical investigation through systematic electronic structure calculations within the framework of density functional theory (DFT) formalism.

Capturing CO₂ before its release. Lithium silicate nanosheets showed high CO₂ capture capacity (35.3 wt%) with ultra-fast kinetics (0.22 g g⁻¹ min⁻¹) and enhanced stability at 650 °C for at least 200 cycles, due to mixed-phase-model of CO₂ capture.     

Sorbents based on calix[4]arenes for extraction of technetium(vii) from acidic and alkaline media

Sorption of Tc^VII from solutions of various compositions with new sorbents prepared by the noncovalent immobilization of (thia)calix[4]arenes on the Amberlite XAD-7™ support was studied. The sorbents studied efficiently extract technetium(vii) from both acidic and alkaline media. The sorption capacity of the sorbent with thiacalix[4]arene groups is superior to that of the sorbents with calix[4]arene groups and several times higher than that of the sorbents previously proposed for the sorption of Tc^VII. Technetium(vii) is sorbed by this sorbent as 1: 1 and 1: 2 thiacalix[4]arene—NH₄TcO₄ and 1: 1 and 1: 2 thiacalix[4]arene—NaTcO₄ complexes.     

Chelating tendencies in the rows of polymeric sorbents and their copper(II) and lead(II) complexes

The physicochemical properties of chelating polymer sorbents (CPSs), derivatives of poly(styrene-2-hydroxy-〈1-azo-1′〉-2′-hydroxybenzene), are studied with respect to copper and lead ions. The following sorption parameters are determined: the optimum acidity, temperature, and duration; the sorption capacity of the sorbent (SCS); and stability constants of polychelates. Quantitative correlations are found between the dissociation constants (pK′ _a) of the analytical functional group (AFG) of the sorbent, and the pH₅₀ of chelation of the tested metals; between p K′ _a and the stability of the complexes (logβ); and between pK′_a and the charge of the oxygen atom of the complexing group (z); these correlations are intended for use in elucidating the effect of the structural features and acid-base properties of the AFG on the chemisorption parameters of copper(II) and lead(II). These correlations predict the physical-chemical properties of sorbents and the sorption parameters of trace elements for preconcentrating and separating them from biological, natural, and technical objects     

Encapsulated Ionic Liquids for CO2 Capture: Using 1‐Butyl‐methylimidazolium Acetate for Quick and Reversible CO2 Chemical Absorption.

The potential advantages of applying encapsulated ionic liquid (ENIL) to CO₂ capture by chemical absorption with 1‐butyl‐3‐methylimidazolium acetate [bmim][acetate] are evaluated. The [bmim][acetate]‐ENIL is a particle material with solid appearance and 70 % w/w in ionic liquid (IL). The performance of this material as CO₂ sorbent was evaluated by gravimetric and fixed‐bed sorption experiments at different temperatures and CO₂ partial pressures. ENIL maintains the favourable thermodynamic properties of the neat IL regarding CO₂ absorption. Remarkably, a drastic increase of CO₂ sorption rates was achieved using ENIL, related to much higher contact area after discretization. In addition, experiments demonstrate reversibility of the chemical reaction and the efficient ENIL regeneration, mainly hindered by the unfavourable transport properties. The common drawback of ILs as CO₂ chemical absorbents (low absorption rate and difficulties in solvent regeneration) are overcome by using ENIL systems.     

Intramolecular Hydrogen Bonds Enhance Disparity in Reactivity between Isomers of Photoswitchable Sorbents and CO2: A Computational Study

Reducing the emission of greenhouse gases, such as CO₂, requires efficient and reusable capture materials. The energy for regenerating sorbents is critical to the cost of CO₂ capture. Here, we design a series of photoswitchable CO₂ capture molecules by grafting Lewis bases, which can covalently bond CO₂, to azo‐based backbones that can switch configurations upon light stimulation. The first‐principles calculations demonstrate that intramolecular hydrogen bonds are crucial for enlarging the difference of CO₂ binding strengths to the cis and trans isomers. As a result, the CO₂–sorbent interaction can be light‐adjusted from strong chemical bonding in one configuration to weak bonding in the other, which may lead to a great energy reduction in sorbent regeneration.     

Effect of amine double-functionalization on CO<Subscript>2</Subscript> adsorption behaviors of silica gel-supported adsorbents

Amine double-functionalized adsorbents were fabricated using silica gel as supports and their capabilities for CO₂ capture were examined. Aminopropyltrimethoxysilane (1N-APS), and N¹-(3-trimethoxysilylpropyl)diethylenetriamine (3N-APS) were used as grafted amine compounds, and tetraethylenepentamine and polyethyleneimine were used as impregnated species. The influence of double-functionalization method on the CO₂ adsorption performance and textural properties of adsorbents was investigated. The adsorption capacity, the amine efficiency, and the thermal stability of double-functionalized sorbents depend strongly upon molecular variables associated with two different functional states (i.e., chemically grafted and physically impregnated amines). The temperature dependence of adsorption isotherms reveals that the CO₂ adsorption behavior in the double-functionalized adsorbents follow the diffusion limitation model proposed by Xu et al. (Energy Fuels 16:1463–1469, 2002) where the CO₂ adsorption is helped by the diffusion of impregnated amines. It is also found that the adsorption isotherm in the double-functionalized sorbent system with a proper choice for grafted and impregnated amines is nearly independent of temperature, which may offer a novel means to fabricate practically useful sorbents that can be used in a wide range of temperature without loss of CO₂ adsorption capacity.