CO2 Sorption Capacity Research Articles

RETRACTED: Mixed-ligand coordination polymers: Catalytic CO2 fixation and treatment activity on the intestinal polyps by inducing the intestinal epithelial cells apoptosis

Abstract By virtue of a dual-ligand strategy, two transition metal coordination polymers of {[Ni2(NDC)2(L1)(H2O)2(H2O)]·(DMF)2(H2O)}n (1, L1 = 3,3′-azobis pyridine) and [Mn(NDC)(L2)(H2O)]n (2, L2 = 1,4-bis(1H-benzo[d]imidazol-1-yl)butane) have been synthesized via the corresponding metal salts reacting with the 1,4-naphthalene dicarboxylic acid (H2NDC) in the existence of distinct nitrogen-donor co-ligands. Given the permanently microporous nature, moderate CO2 sorption capacity as well as high density of the open metals positions, the activated 1 revealed the chemical fixation of the cyclic carbonates and carbon dioxide or an efficient activity of catalysis in the existence of the cocatalyst under the mild and solvent-free conditions. To evaluate the activity of the compound against intestinal polyps, following experiments were conducted. The Cell Counting Kit-8 (CCK-8) method was implemented to evaluate the inhibitory effects of these two compounds against the intestinal epithelial cells. Next, the western blotting was conducted and the apoptotic protein Bcl-2 expression levels was determined as well.

Preparation of CaO-SiO<sub>2</sub> Adsorbent for Potential CO<sub>2</sub> Capture via Dry Mixing Method

Calcium-looping technology is defined as one of the most desirable methods of carbon capture, utilization and storage (CCUS). However, because of sintering, rapid deactivation of CaO-sorbents is currently a major barrier to this technology. The stability of calcium based sorbent may be enhance by incorporating them with inert support materials such as MgO, Al2O2, ZrO2 and SiO2. For this study, calcium based sorbent has been incorporate with silica obtained from rice husk ash. CaO-SiO2 sorbents are prepared using physical dry mixing method which is much simpler compared to other available methods. The prepared CaO-SiO2 sorbents were then characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). New crystalline phase, larnite (Ca2SiO4) was detected in XRD patterns and this phase possess good chemical durability and may help to prevent sintering effect of calcium based sorbents and enhance their cyclic capability. CaO-SiO2 sorbent calcined at 700 oC with different grinding times have highest intensity of XRD peak at (104) with element of calcite. Sorbents with different weight composition of CaCO3-RHA were observed to have different surface morphology. SEM images of the sorbent (90wt% CaCO3-RHA) before calcination showed bigger particle size with irregular shape and more porosity. Then, SEM analysis was conducted for samples with different grinding times after calcination. CaO-SiO2 sorbents with 20minutes grinding time exhibited small size of particles with some porosity. Besides that, the particles are well distributed without agglomeration occured. The CaO-SiO2 sorbent calcined at 700 oC sorbents were tested for 20 consecutive carbonation and calcination cycles using Thermogravimetric Analysis (TGA). CaO-SiO2 sorbent treated with 700 oC calcination temperature and 20 minutes of grinding shows better cyclic CO2 sorption capacity.

A kinetic study of CO2 sorption/desorption of lithium silicate synthesized through a ball milling method

Lithium silicates show high CO2 sorption capacity and excellent cyclic stability at high temperatures. Lithium orthosilicate was synthesized through a planetary ball milling route from LiOH and silica powder and was characterized for its structural and morphological features using TG, DSC, XRD, FTIR and FESEM techniques. Thermogravimetry was employed to study the CO2 sorption capacity of the synthesized sorbent under dynamic, isothermal and cyclic conditions. The material absorbed 30.5 % CO2 and retained its sorption capacity even after 10 cycles. The CO2 sorption and desorption kinetics of the synthesized sorbent were studied using Avrami–Erofeev method and Kissinger–Akahira–Sunose method respectively. The sorption of CO2 on lithium silicate took place by surface chemisorption and diffusion and activation energies required are 79 kJ mol−1 and 109 kJ mol−1 respectively. The activation energy for CO2 desorption increases with the progress in desorption from 91 kJ mol−1 to 146 kJ mol−1.

Sorption equilibria, kinetics, and temperature-swing adsorption performance of polyethyleneimine-impregnated silica for post-combustion carbon dioxide capture

The sorption equilibria and kinetics of CO2, N2, and H2O on polyethyleneimine (PEI)-impregnated silica (PEI–silica) were studied to determine CO2 capture by temperature-swing adsorption (TSA). The experimental isotherms of CO2 were correlated well by the dual-site Langmuir (DSL) model while those of H2O were well-predicted by the Brunauer–Emmett–Teller (BET) model. The amounts of the components adsorbed at equilibrium were in the order of qH2O>qCO2≫qN2. The isosteric heat of adsorption (Qst) of CO2 on PEI–silica changed from 70 to 55 kJ/mol along the sorption amount. The highly enhanced adsorption affinity of PEI–silica for CO2 resulted in chemisorption, while the adsorptions of H2O and N2 exhibited typical physisorption. PEI–silica exhibited higher selectivity than KOH-treated activated carbon (KOH–AC) for the simulated flue gases, i.e., the mixture of CO2 and N2. Although PEI–silica became hydrophobic, the H2O molecules were expected to affect the CO2 capture process because of their high adsorption amount and rate. The variation in the non-isothermal kinetic behavior of CO2 caused by pressure differed from that of H2O because of the difference between chemisorption and physisorption. PEI–silica exhibited a high CO2-sorption capacity of 2.3 mmol/g (pure CO2 at 70 °C) with a high sorption rate (>90% of saturation within 1 min). Compared with the cyclic test that employs desorption in hot N2, the working capacity decreased more when the desorption was conducted in hot CO2 flow.

In-situ pyrolysis of Taihu blue algae biomass as appealing porous carbon adsorbent for CO2 capture: Role of the intrinsic N

An environment-friendly, cost-effective, and facile N self-doping porous carbon (NC) were prepared through in-situ pyrolysis of nitrogen abundant Taihu blue algae biomass for CO2 uptake. It was found that the CO2 sorption capacity of porous carbon prepared through carbonization at 800 °C with KOH activation (N-C-800) exhibit higher CO2 uptake capacity of 4.88 (1 bar and 0 °C) and 2.76 mmol/g (1 bar and 25 °C) respectively, with the CO2/N2 selectivity of N-C-800 attaining 39.3. Besides, the adsorption capacity of N-C-800 remained stable even after 7 repeated cycles, with a slight loss of nearly 6%. Moreover, total graphitic N (Ntg) sources from the intrinsic N in N-C-800 is not only higher than other agro-sourced porous carbon materials, but the graphitic N performed a sound correlation with the CO2 uptake capacity. Combining experiments with Density Functional Theory (DFT) calculations, higher adsorption energy of N-C-800 (−13.6 kJ/mol, comparing with −6.9 kJ/mol of N-free carbon framework) would render the efficient adsorption of CO2 molecular onto the graphitic N site. The current study not only provides a new option for the reclamation of Taihu blue algae biomass as N self-doping material, but a proof-of-concept investigation employing NC materials as an appealing candidate for CO2 capture.

Hypercrosslinked Polymers as a Photocatalytic Platform for Visible-Light-Driven CO2 Photoreduction Using H2 O.

The design of robust, high‐performance photocatalysts is key for the success of solar fuel production by CO2 conversion. In this study, hypercrosslinked polymer (HCP) photocatalysts have been developed for the selective reduction of CO2 to CO, combining excellent CO2 sorption capacities, good general stabilities, and low production costs. HCPs are active photocatalysts in the visible light range, significantly outperforming the benchmark material, TiO2 P25, using only sacrificial H2O. It is hypothesized that superior H2O adsorption capacities facilitate access to photoactive sites, improving photocatalytic conversion rates when compared to sacrificial H2. These polymers are an intriguing set of organic photocatalysts, displaying no long‐range order or extended π‐conjugation. The as‐synthesized networks are the sole photocatalytic component, requiring no added cocatalyst doping or photosensitizer, representing a highly versatile and exciting platform for solar‐energy conversion.

Heterojunction of Pores in Granola‐Type Crystals of Two Different Metal–Organic Frameworks for Enhanced Formaldehyde Removal

Metal–organic frameworks (MOFs) have introduced heterogeneity in their homogeneous matrix to create new functions that cannot be realized by each MOF individually. In this study, we chemically combined two different MOFs (UiO‐66 and HKUST‐1) in granola‐type granules (termed as HKUST‐1∧UiO‐66) to create a heterojunction of pores in nanocrystalline particles. The structure, morphology, elemental composition, and pore environment were characterized to confirm that two types of pores are in conjunction all over the HKUST‐1∧UiO‐66 granules. We found that the HKUST‐1∧UiO‐66 granules showed an enhanced CO2 sorption capacity than its constituents due to the complexity and the heterojunction of pores inside. Moreover, the HKUST‐1∧UiO‐66 granules present four and two times higher formaldehyde removal capacity than those of the HKUST‐1 and UiO‐66 samples, respectively.

Cellulose macromolecule as a source for advanced materials preparation

Cellulose is the most abundant, biopolymer on Earth. It has numerous applications in many industries and can be engineered into fibers, films, sponges, beads, and other cellulosic materials. Of special interest, cellulose aerogels with high surface area and better pore characteristics have attracted considerable attention due to their properties such as biodegradability, biocompatibility, etc. In this paper, we present two main applications of cellulose-based materials for CO2 absorption and dye removal. The current CO2 capture, storage, and utilization technologies include absorption, adsorption, membrane and cryogenic processes. Among those, the adsorption processes on solid adsorbents have been regarded as the most attractive technique due to their high CO2 sorption capacity, low cost, low energy, and reusability. In this regard, solid sorbents prepared from cellulose are promising because of their relative abundance, sustainability, biodegradability, non-toxicity, renewability, thermal stability and good sorption properties. Activated carbons possess high surface areas and low chemical reactivity, therefore, they have been widely used as adsorbents at low and ambient temperatures. Data for the CO2 capture by CO2-activated cellulose aerogels with enhanced surface area and microporosity showed 383% and 311% increase in CO2 absorption respectively at 0 °C and 25 °C. Furthermore, cationic functionalization of cellulose aerogels resulted in 99.6% removal of negatively charged dye molecules.

A diamino-functionalized silsesquioxane pillared graphene oxide for CO2 capture.

In the race for viable solutions that could slow down carbon emissions and help in meeting the climate change targets a lot of effort is being made towards the development of suitable CO2 adsorbents with high surface area, tunable pore size and surface functionalities that could enhance selective adsorption. Here, we explored the use of silsesquioxane pillared graphene oxide for CO2 capture; we modified silsesquioxane loading and processing parameters in order to obtain pillared structures with nanopores of the tailored size and surface properties to maximize the CO2 sorption capacity. Powder X-ray diffraction, XPS and FTIR spectroscopies, thermal analysis (DTA/TGA), surface area measurements and CO2 adsorption measurements were employed to characterize the materials and evaluate their performance. Through this optimisation process, materials with good CO2 storage capacities of up to 1.7/1.5 mmol g−1 at 273 K/298 K in atmospheric pressure, were achieved.

Mixtures of Cellulose Fibers from Pineapple Leaves, Ionic Liquid, and Alkanolamines for CO2 Capture

Researchers around the world are looking for ways to improve or develop new technologies to mitigate the emissions of CO2 present in greenhouse gases. Amines are currently the most used substances to capture CO2. The ionic liquids (ILs), however, have also been considered promising materials. Recently, mixtures of ILs and amines have been studied for this purpose. The ILs are also being supported in solid matrices (polymers, zeolites, cellulose, and membranes) to obtain stable, easy to handle, and reusable materials. Cellulose fibers make a promising matrix, considering their affinity with CO2, renewable feature, and thermal, mechanical, and chemical stability. To improve the CO2 capture capacity by using cellulose and the mixture of ILs and amines, we prepared mixtures of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] and monoethanolamine or triethanolamine. Then, we dropped the mixtures on natural cellulose fibers from pineapple leaves. This paper reports the characterization of the composite materials by FTIR, XRD, XPS, FESEM, and TGA-FTIR in order to evaluate their structure, composition, morphology, and thermal behavior. We also report the CO2 sorption capacity at 25 °C and 25 bar as determined by the pressure-decay technique as well as the CO2 selectivity using a CO2/CH4 mixture. We found that the fiber with an alkaline treatment containing 35 % of IL and 35 % of TEA captures the highest amount of CO2 (141 mg of CO2/g of fiber) and that the mixture TEA/IL is more selective for CO2.

New polysulfone microcapsules containing metal oxides and ([BMIM][NTf2]) ionic liquid for CO2 capture

CO2 emission from flue gas is one of the main sources of global warming. The development of new materials with enhanced CO2 adsorption is crucial to foster sustainable development. In this work, 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf2]) ionic liquid (IL) was synthesized and combined to metal oxides (Fe2O3, CuO and TiO2) for further encapsulation in polysulfone (PSF) using emulsification method. Computational study using “ab initio” method was also performed. Scanning electron microscopy evidenced the uniform formation of the IL/metal oxide encapsulated polysulfone microcapsule. Transmission electron microscopy (TEM) and Scanning electron microscopy indicates the formation of microcapsules of around 1.0 μm containing a dense core (IL/metal oxide) when Fe2O3 was encapsulated by a polymer shell presenting better CO2 sorption compared to microcapsule containing CuO and TiO2. Thermogravimetric analysis (TGA) presents microcapsule thermal behavior indicating microcapsule lower degradation temperature when compared to neat PSF. IL encapsulation capacity was determined using acetone immersion test. Results indicated around 40 % of encapsulation capacity. Differential scanning calorimetry shows the complete disappearance of the IL (at -3.14 ℃) characteristic peak after the acetone immersion test confirming IL removal by the method. The residue wt.% calculated by TGA in air atmosphere was used to determine the metal oxide amount incorporated in the microcapsules. The CO2 sorption capacity of microcapsule with Fe2O3 shows an enhancement of around 47 % as compared to the neat-PSF. Here we reported the development of an effective solvent-free adsorbent for CO2 capture fostering industrial application.

Carbon dioxide and methane sorption characteristics of Damodar Valley and Upper Assam shale, India

Shale gas has become one of the most significant unconventional hydrocarbon resources. The gas is adsorbed in shale micropores, more precisely in the pores of clay minerals and organic matter. In this work, studies were done on the shale samples of Damodar valley and Upper Assam Basin. High pressure adsorption isotherms of methane (CH4) and carbon dioxide (CO2) were analysed to assess the gas storage capacity. The organic geochemistry, thermal maturity and mineralogy are analysed by Rock-Eval pyrolysis, petrographic study and XRD study respectively. The purpose of this study was to understand the factors controlling the variations in the nature of high pressure CH4 and CO2 sorption capacities. The factors include organic-inorganic constituents, and pore characteristics. Results show that the shale samples have a higher CO2 sorption capacity compared to that of methane. However, the CO2 sorption capacity shows a sharp decrease after 70 bar. Under similar temperature and pressure condition CO2: CH4 ratio increases with increasing pressure up to a pressure of 70 bar and then shows a sharp decrease. Petrographic study shows that vitrinite is the most dominant maceral group. Unlike clay minerals, organic matter shows a robust control over gas sorption in the studied shale samples. Sorption potential of carbon dioxide and methane increases positively with vitrinite content but, decreases with rising mineral matter and thermal maturity. Vitrinite content also controls the CO2: CH4 ratio, and the ratio bears no relation with thermal maturity. Micropores, rather than mesopores, mostly influence the gas sorption.

In Situ Investigation of CO2 Separation in Macrocyclic and Porous Ionic Liquids

With the continued rise in atmospheric CO2 levels and the potential impact on climate, carbon capture and storage has gained prominence as a potential technological solution to reduce CO2 emissions, resulting in increased interest in advanced materials to facilitate the removal of CO2 from energy-related emissions. While a number of approaches have been explored to separate CO2 from mixed streams, ionic liquids are promising materials due to their negligible vapor pressure, high thermal stability, and the ability to tune physicochemical properties such as CO2 solubility. The incorporation of free volume into ionic liquids through appropriate development of bulky cation/anion pairs or through the creation of porous ionic liquids can impact both gas transport and solubility. Macrocyclic ionic liquids where the bulky cation consists of a nitrogen heterocycle connected by ether linkages can selectively remove CO2 from mixed gas streams and offer a potential avenue for CO2 capture. Porous ionic liquids are emerging materials that combine the attributes of porous materials within a nonvolatile liquid matrix. Permanent porosity is incorporated into the ionic liquid by adding a framework material (zeolitic imidazolate framework) where the cations and anions are too large to diffuse into the host. We investigated the selective absorption of CO2 in both macrocyclic and porous ionic liquids and examined the effect of porosity on CO2 sorption capacity and gas transport. Relevant physical and chemical properties of these unique materials such as solubility, density, viscosity and structure were measured. In addition, analysis of the vibrational modes of both the ionic liquid and the CO2 through in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements was used to better understand the mechanisms of CO2 interaction with the ionic liquids and the impact on solubility and transport. Moreover, we find that certain of these ionic liquids exhibit a unique binding and release of CO2 which could open new avenues for CO2 capture and storage.

Equilibrium curve of carbon dioxide adsorption–desorption using potassium carbonate on gamma-alumina in fluidized bed reactor

At present, global warming becomes a major problem affecting the world in many ways. The main cause is the releasing of large amounts of carbon dioxide (CO2) into the atmosphere. The reduction of CO2 is thus a tremendous challenge. The CO2 capture processes then are invented to account this problem. One of the essential basic information for designing and operating of these separation processes is the adsorption–desorption equilibrium. In this study, the equilibrium isotherms on potassium carbonate on gamma-alumina (K2CO3∕γ-Al2O3) solid sorbent were correlated with Langmuir, Freundlich, Sips and Toth models. The CO2 sorption capacities were measured with pressures at different system temperatures (45–90 °C). From the result, it was found that Sips isotherm was the suitable model (R2 ranged between 0.91–0.99 with an error of less than 2.09%). When comparing the CO2 capture capacity with pure K2CO3, the obtained CO2 capture capacities were improved by impregnating K2CO3on the γ-Al2O3 support.

Characterization of Modified Natural Minerals and Rocks for Possible Adsorption and Catalytic Use.

This study focused on natural materials such as clinoptilolite (CLI), metakaolin (MK), marlstone (MRL) and phonolite (PH). Clinoptilolite is one of the most known and common natural minerals (zeolites) with a unique porous structure, metakaolin is calcined kaolin clay, marlstone is a sedimentary rock and phonolite is an igneous rock composed of alkali feldspar and other minerals. These natural materials are mainly used in the building industry (additions for concrete mixtures, production of paving, gravels) or for water purification, but the modification of their chemical, textural and mechanical properties makes these materials potentially usable in other industries, especially in the chemical industry. The modification of these natural materials and rocks was carried out by leaching using 0.1 M HCl (D1 samples) and then using 3 M HCl (D2 samples). This treatment could be an effective tool to modify the structure and composition of these materials. Properties of modified materials were determined by N2 physisorption, Hg porosimetry, temperature programmed desorption of ammonia (NH3-TPD), X-ray fluorescence (XRF), X-ray powder diffraction (XRD), diffuse reflectance infrared Fourier transform (DRIFT) and CO2 adsorption using thermogravimetric analysis (TGA). The results of N2 physisorption measurements showed that that the largest increase of specific surface area was for clinoptilolite leached using 3M HCl. There was also a significant increase of the micropore volume in the D2 samples. The only exception was marlstone, where the volume of micropores was zero even in the leached sample. Clinoptilolite had the highest acidity and sorption capacity of CO2. TGA showed that the amount of CO2 adsorbed was not significantly related to the increase in specific surface area and the opening of micropores. Hg porosimetry showed that acid leaching using 0.1 M HCl and 3 M HCl resulted in a significant increase in the macropore volume in phonolite, and during leaching using 3M HCl there was an increase of the mesopore volume. From the better properties, cost-efficient and environmental points of view, the use of these materials could be an interesting solution for catalytic and sorption applications.

Porosity and hydrophilicity modulated quaternary ammonium-based sorbents for CO2 capture

Quaternary ammonium (QA)-based polymeric sorbents are known to be effective for CO2 capture, especially from ultradilute streams like air. In this work, we address two major challenges in QA sorbent design for application in moisture-swing processes, porosity control and hydrophilicity modulation. Facilely substituting porous CO2-active components for non-porous ones can enhance the sorption kinetics by 4-fold compared to the state-of-art, and micro–mesoporous structures are identified as optimal porous structures. A method to modulate the hydrophilicity of QA-based sorbents is developed using controlled radical polymerization, incorporating fluorine-containing monomers. The CO2 sorption capacity and the tolerance towards moisture are simultaneously enhanced via adjustment of the structure and the content of fluorine-containing blocks. We postulate that porosity and hydrophilicity optimization can make QA-based sorbents adaptive to deployment of scalable moisture-swing processes in varied and complex atmospheric circumstances.

Performance and dynamic behavior of sorption-enhanced water-gas shift reaction in a fluidized bed reactor for H2 production and CO2 capture

A multi-scale dynamic model for a sorption-enhanced water-gas shift (SE-WGS) fluidized bed reactor was developed and the reactor performance in terms of hydrogen production and carbon dioxide capture was analyzed. K2CO3-promoted hydrotalcite sorbent was used as a reference in the SE-WGS fluidized bed reactor and steam methane reforming gas was used as the feed. The sensitivity analysis of the performance was carried out by varying the temperature, pressure, and sorbent circulation rate. The CO conversion achieved at low pressures in the SE-WGS fluidized bed reactor was much higher than the catalytic equilibrium conversion. However, the advantages of the SE-WGS reactor were lost at pressures of over 7 bar. The desired sorption capacity and rate of the CO2 sorbent were suggested to enhance the performance of the SE-WGS fluidized bed reactor at 30 bar. At a five-time higher sorption capacity, the CO conversion and carbon capture efficiencies could be achieved to 95.0% and 86.4%, respectively. In addition, with a simultaneous increase of 1.5 times in the sorption rate, the CO conversion and carbon capture efficiency could be achieved to 99.3% and 98.2%, respectively. Because the CO2 sorption capacity is mainly determined in the mixing zone, the operating conditions need to be finely controlled for the maximum utilization of the sorbent capacity. The study demonstrates the advantages of the SE-WGS fluidized bed reactor for simultaneous H2 production and CO2 capture. In addition, the optimization of the sorption capacity and rate of the CO2 sorbent can provide guidance for the development of high-performance sorbents for application in SE-WGS fluidized bed reactors.

Synthesis of Discrete CHA Zeolite Nanocrystals without Organic Templates for Selective CO2 Capture.

Small-pore zeolites such as chabazite (CHA) are excellent candidates for the selective separation of CO2 ; however, the current synthesis involves several steps and the use of organic structure-directing agent (OSDA), increasing their cost and energy requirements. We report the synthesis of small-pore zeolite crystals (aluminosilicate) with CHA-type framework structure by direct synthesis in a colloidal suspension containing a mixture of inorganic cations only (Na+ , K+ , and Cs+ ). The location of CO2 molecules in the host structure was revealed by 3D electron diffraction (3D ED). The high sorption capacity for CO2 (3.8 mmol g-1 at 121 kPa), structural stability and regenerability of the discreate CHA zeolite nanocrystals is maintained for 10 consecutive cycles without any visible degradation. The CHA zeolite (Si:Al=2) reaches an almost perfect CO2 storage capacity (8 CO2 per unit cell) and high selectivity (no CH4 was adsorbed).

Synthesis of Discrete CHA Zeolite Nanocrystals without Organic Templates for Selective CO2 Capture

AbstractSmall‐pore zeolites such as chabazite (CHA) are excellent candidates for the selective separation of CO2; however, the current synthesis involves several steps and the use of organic structure‐directing agent (OSDA), increasing their cost and energy requirements. We report the synthesis of small‐pore zeolite crystals (aluminosilicate) with CHA‐type framework structure by direct synthesis in a colloidal suspension containing a mixture of inorganic cations only (Na+, K+, and Cs+). The location of CO2 molecules in the host structure was revealed by 3D electron diffraction (3D ED). The high sorption capacity for CO2 (3.8 mmol g−1 at 121 kPa), structural stability and regenerability of the discreate CHA zeolite nanocrystals is maintained for 10 consecutive cycles without any visible degradation. The CHA zeolite (Si:Al=2) reaches an almost perfect CO2 storage capacity (8 CO2 per unit cell) and high selectivity (no CH4 was adsorbed).

Facile reactivation of used CaO-based CO2 sorbent via physical treatment: Critical relationship between particle size and CO2 sorption performance

Herein we report a new and facile mechanical approach for maximizing the CO2 sorption performance of CaO sorbents, and also for recovering the sorption performance of the used (or deactivated) sorbent. We compared the physicochemical properties of CaO-based sorbents, which could change depending on their preparation methods, and determined that the CaO particle size was the most critical factor that affected their CO2 sorption performance. The CO2 sorption performance of CaO-based sorbents could be maximized via the simple physical reduction of their particle size, and this was experimentally demonstrated using ball-milling. The CO2 sorption uptake of CaO prepared using the conventional solid-state method was significantly increased to the highest ever reported level after ball-milling, and it reached 98.0% of the theoretical maximum CO2 sorption capacity. The most important application of the particle-size-dependency of CaO-based sorbents on their CO2 sorption uptake is the reactivation of used sorbents via reducing the size of the aggregated or sintered bulky particles that form after cyclic usage. The CO2 sorption uptake of the used CaO (~32.9 wt% after 10 alternative sorption–regeneration cycles) was successfully recovered (almost doubled) to ~64.7 wt% after ball-milling. This is the first time a facile mechanical-grinding-based reactivation method, which appeared to be highly efficient and directly applicable to the continuous calcium looping technology, has been developed and used.