Highest CO2 Sorption Capacity Research Articles

Pressure swing adsorption of Li exchange hierarchical X zeolite for pure hydrogen from binary gas mixture

This study reports the separation of pure hydrogen (H2) employing pressure swing adsorption (PSA). The Li-X and Li-hierarchical X (Li–H-X) zeolite were prepared by an ion exchange process. The sorbents were evaluated through several experiments including, breakthrough, empty bed contact time (EBCT), single-bed, and two-bed PSA with different steps. The effect of pressure, purity, and recovery relationship was developed. The high-pressure PSA study was performed at 4, 6, and 10 bar with varying feed flow rates to assess their efficacy in pure H2 separation using binary gas stream (H2/CO2, 75/25 vol.%). The breakthrough adsorption capacity of Li–H-X exhibited 3.4 mmol g−1 and 0.212 mmol g−1 of CO2 and H2, respectively. Li–H-X shows ∼8% higher CO2 sorption capacity than the Li-X sorbent at 1 bar and 300 K due to the large meso-microporous structure of the sorbent. The two-bed PSA purity and recovery were found higher than single-bed PSA. Using two-bed PSA, the Li–H-X achieved a 99.5% of purity, 92.9% of recovery, and 10.4 mL min−1 g−1 of productivity, which was ∼16% higher recovery and productivity than single-bed PSA at a flow rate of 1200 mL min−1 at 6 bar. With increasing the pressure and flow rate, the recovery of Li–H-X was enhanced up to 93.7% with 99.1%–99.9% H2 purity. The long-term PSA was run using Li–H-X sorbent for 7.5 h with 230 cycles with H2 purity between 98.5 and 99.5% at 6 bar. Interestingly, the adsorbent shows the scalability of PSA for efficient H2 separation for a binary mixture of H2/CO2.

Scalable and Highly Porous Membrane Adsorbents for Direct Air Capture of CO2.

Direct air capture (DAC) of CO2 is a carbon-negative technology to mitigate carbon emissions, and it requires low-cost sorbents with high CO2 sorption capacity that can be easily manufactured on a large scale. In this work, we develop highly porous membrane adsorbents comprising branched polyethylenimine (PEI) impregnated in low-cost, porous Solupor supports. The effect of the PEI molecular mass and loading on the physical properties of the adsorbents is evaluated, including porosity, degradation temperature, glass transition temperature, and CO2 permeance. CO2 capture from simulated air containing 400 ppm of CO2 in these sorbents is thoroughly investigated as a function of temperature and relative humidity (RH). Polymer dynamics was examined using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS), showing that CO2 sorption is limited by its diffusion in these PEI-based sorbents. A membrane adsorbent containing 48 mass% PEI (800 Da) with a porosity of 72% exhibits a CO2 sorption capacity of 1.2 mmol/g at 25 °C and RH of 30%, comparable to the state-of-the-art adsorbents. Multicycles of sorption and desorption were performed to determine their regenerability, stability, and potential for practical applications.

CO2 capture using silica-immobilized dicationic ionic liquids with magnetic and non-magnetic properties

The need to find alternative materials to replace aqueous amine solutions for the capture of CO2 in post-combustion technologies is pressing. This study assesses the CO2 sorption capacity and CO2/N2 selectivity of three dicationic ionic liquids with distinct anions immobilized in commercial mesoporous silica support (SBA- 15). The samples were characterized by UART-FTIR, NMR, Raman, FESEM, TEM, TGA, Magnetometry (VSM), BET and BJH. The highest CO2 sorption capacity and CO2/N2 selectivity were obtained for sample SBA@DIL_2FeCl4 [at 1 bar and 25 °C; 57.31 (±0.02) mg CO2/g; 12.27 (±0.72) mg CO2/g]. The results were compared to pristine SBA-15 and revealed a similar sorption capacity, indicating that the IL has no impact on the CO2 sorption capacity of silica. On the other hand, selectivity was improved by approximately 3.8 times, demonstrating the affinity of the ionic liquid for the CO2 molecule. The material underwent multiple sorption/desorption cycles and proved to be stable and a promising option for use in industrial CO2 capture processes.

Modulated synthesis of hcp MOFs for preferential CO2 capture.

We herein show that the μ2-OH bridging groups in the double M12O8(OH)14 clusters of hcp UiO-66 could act as a preferential CO2 sorption site, compared to fcu UiO-66. As such, hcp-UiO-66-0.015 shows a high binary CO2 sorption capacity of 0.31 mmol g-1 and CO2/N2 (15/85) mixture selectivity of 87 at 298 K and 1 bar, which holds great potential for post-combustion CO2 capture.

Structure-Property Relationships of CO2 Absorbing Core-Shell Microparticles with Encapsulated Ionic Liquid.

The demand for new ionic liquid (IL)-based systems to selectively sequester carbon dioxide from gas mixtures has prompted the development of individual components involving the tailored design of IL themselves or solid-supported materials that provide excellent gas permeability of the overall material as well as the ability to incorporate large amounts of ionic liquid. In this work, novel IL-encapsulated microparticles comprising a cross-linked copolymer shell of β-myrcene and styrene and a hydrophilic core of the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) are proposed as viable materials for CO2 capture. Water-in-oil (w/o) emulsion polymerization of different mass ratios of β-myrcene to styrene (i.e. 100/0, 70/30, 50/50, 0/100) yielded IL-encapsulated microparticles, where the encapsulation efficiency of [EMIM][DCA] was dependent on the copolymer shell composition. Thermal analysis using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that both thermal stability and glass transition temperatures depend on the mass ratio of β-myrcene to styrene. Images from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the microparticle shell morphology as well as measure the particle size perimeter. Particle sizes were found to be between 5 and 44 μm. CO2 sorption experiments were conducted gravimetrically using TGA instrumentation. Interestingly, a trade-off between CO2 absorption capacity and ionic liquid encapsulation was observed. While increasing the β-myrcene content within the microparticle shell increases the amount of encapsulated [EMIM][DCA], the observed CO2 absorption capacity did not increase as expected due to reduced porosity compared to microparticles with higher styrene content in the microparticle shell. [EMIM][DCA] microcapsules with a 50/50 weight ratio of β-myrcene/styrene showed the best synergistic effect between spherical particle diameter (32.2 μm), pore size (0.75 μm), and high CO2 sorption capacity of ∼0.5 mmol CO2/g sample within a short absorption period of 20 min. Therefore, core-shell microcapsules composed of β-myrcene and styrene are envisioned as a promising material for CO2 sequestration applications.

Fruit waste (pomelo peels)-derived activated carbons for biogas upgradation and capture of green house gases from flue gas and low concentration coalbed methane

Rising emissions of greenhouse gases, such as CO2 and CH4, due to anthropogenic activities cause several adverse environmental impacts and encourage technological development for their effective capture and separation. The present work addresses a facile hydrothermal approach to impregnate K2CO3 and K2C2O4 into pomelo peels (fruit waste), followed by thermochemical activation for preparing activated carbons, i.e., PKC and PKOX, respectively, as adsorbents for biogas upgradation (CO2/CH4) and capture of greenhouse gases from flue gas (CO2/N2) and low concentration coalbed methane (CH4/N2). The high CO2 sorption capacity of PKC (4.67 mmol.g-1) and PKOX (3.96 mmol.g-1) at 298 K and 1 bar is attributed to their high surface area (1224–1371 m2.g-1), excellent microporosity, nitrogen-based functionalities, and turbostratic structural features. The ideal adsorbed solution theory (IAST) model is applied to estimate separation selectivity for binary gas mixtures, i.e., CO2/N2 (15:85), CO2/CH4 (45:55), and CH4/N2 (30:70) using PKC and PKOX adsorbents. The adsorption selectivity of PKC and PKOX for CO2/CH4 is found to be 143% and 296% higher compared to a widely used commercial activated carbon, signifying the potential of PKOX for biogas upgradation via adsorptive separation of CO2. The adsorption selectivity of PKC and PKOX for CO2/N2 is estimated to be 124% and 119% higher than commercial activated carbon, revealing the potential of both PKC and PKOX for capturing CO2 from flue gas to minimize its release in the atmosphere.

Catalyst-free upcycling of crosslinked polyethylene foams for CO2 capture

Recycling of crosslinked plastics is an intractable challenge due to their very limited amenability to mechanical reprocessing. While a variety of chemical recycling methods have been recently reported, these systems primarily focus on deconstructing or depolymerizing plastics to monomers and liquid fuels, which their subsequent use likely involves additional energy consumption and greenhouse gas emission. In this work, we present a simple, scalable, and catalyst-free method for directly converting crosslinked polyethylene (PE) foams into porous carbon materials. This process is enabled by sulfonation-based crosslinking, allowing the conversion of PE to become efficient carbon precursors, while retaining the high porosity feature from the foam precursors. Through two steps of sulfonation and carbonization, derived carbons contain a relatively high surface area and sulfur-doped framework. As a result, these materials can exhibit high CO2 sorption capacity and CO2/N2 selectivity. This work presents a viable pathway to address two grand-scale environmental challenges of plastic wastes and greenhouse gas emissions.Graphical abstract

Fabrication of porous Li4SiO4 ceramic sorbent pebbles with high CO2 sorption capacity via the simple freeze-drying method

At present, the Li4SiO4 ceramic sorbents have displayed a great prospect for CO2 gas removal in the atmosphere owing to their high sorption capacity and stable sorption-desorption property. In this paper, a simple method combining the wet method and freeze-drying method is initially employed to fabricate Li4SiO4 sorbent with rich porosity and direction arrangement channels, which overcomes the dense interior structure, barren porosity, inferior adsorption stability, and costly production described in the previous literature. The effects of freeze way and temperature on the interior structure of Li4SiO4 sorbent were studied respectively. In the freeze-drying process, only the freeze-drying Li4SiO4 cylinder (FSC) green sorbents have columnar ice crystals in the interior owing to the temperature gradient, and the unidirectional alignment of pore channels can be obtained after the vacuum drying process due to the sublimation of ice crystals, which will improve CO2 capture capacity. Moreover, it can be seen from the optical image that the sorbent pebbles have a uniform distribution of diameter and sorbent samples of OSF (fabricated without the freezing process), FSP (fabricated with the freezing process), and FSC show excellent mechanical strength of 37.5 N, 22.5 N, and 0.43Mpa, respectively. Compared with OSP and FSP samples, the FSC sorbent performed superior CO2 sorption capacities (0.305 g CO2/g sorbent) and outstanding stability after 40 times cycles due to its optimal pore microstructure. Therefore, the prominent capture capacity and the satisfying crushing load of the FSC sorbents fabricated via the Freeze-drying method in this paper have promising prospects for CO2 removal.

High efficient pre-combustion CO2 capture by using porous slurry formed with ZIF-8 and isoparaffin C16

Integrated gasification combined cycle (IGCC) power generation has drawn more and more attention because of the increasing demand for zero CO2 emission. H2/CO2 mixture with middle/higher pressure like IGCC gas is usually separated by using low energy consumption physical absorption approach. Here, for upgrading traditional physical absorbents, we report a new porous slurry formed with ZIF-8 and isoparaffin C16 to raise CO2 capture capacity and selectivity. The properties and sorption behaviors of this slurry have been experimentally investigated, and the content of ZIF-8 is optimized as 20 wt%. The optimized slurry exhibits low viscosity (11.02–2.75 mPa·s when temperature ranges from 273.15 to 303.15 K), sufficiently high sorption speed, low CO2 sorption heat (9.39–18.47 kJ/mol, decreasing with increasing CO2 loading). More importantly, the slurry exhibits much higher CO2 sorption capacity (e.g., 3.39 mol/L/MPa at 0.1 MPa and 273.15 K, vs. 2.48 mol/L/MPa for dimethyl ethers of polyethylene glycol (DEPG) and 2.22 mol/L/MPa for propylene carbonate (PC)) and selectivity over H2 (17.4–205, which could be one time higher than DEPG and three times higher than PC). The recyclability of this slurry system is also excellent. The 98% sorption capacity is recovered by vacuuming for 5 min without heating, showing that the easy sorption-desorption cycle can be completed only via pressure swing. We believe ZIF-8/isoparaffin C16 slurry would be a promising alternative to existing commercial CO2 absorbent for separating IGCC gas with higher efficiency and lower energy cost.

Lotus seed pot-derived nitrogen enriched porous carbon for CO2 capture application

The rapid rise in anthropogenic carbon dioxide (CO2) concentration forces humanity for development of efficient carbon capture and storage approaches. Among many approaches, the adsorption of CO2 within the solid adsorbents is considered a feasible approach. In the present study, the lotus seed pot biomass was converted into a N-rich porous carbon adsorbent. The adsorbent preparation strategy is based on the pre-carbonization of lotus seed pot, melamine treatment and the subsequent KOH activation at elevated temperatures. The sorbents prepared here showed high surface areas up to the 2040 m2/g along with 0.88 cm3/g of pore volume after KOH etching. Up to 6.58 wt% nitrogen incorporated thanks to the melamine precursor. The optimized sample (LPM-650–2) presents 4.02 and 6.20 mmol/g CO2 uptake at 25 and 0 °C at 1 bar, respectively. We postulated that high N content and narrow pore size are the dominant factors for the high CO2 sorption capacity. Moreover, these lotus seed pot-derived carbons display great uptake reversibility, optimal heat of adsorption, rapid carbon uptake kinetics and high CO2/N2 selectivity. This study depicts a general approach to produce N-doped porous adsorbents from the lotus seed pot and offers potential for various environmental applications including CO2 capture.

One-step synthesis of porous Li4SiO4 pellets by polyvinyl alcohol (PVA) method for CO2 capture

Li4SiO4 has shown great prospects for cyclic high-temperature CO2 capture due to its excellent stability, high capacity and low regeneration temperature. However, dense morphology and attrition problem are the main obstacles that lie in its way to the practical applications. This work, for the first time, proposed a simple polyvinyl alcohol (PVA) technique for the one-step preparation of porous spherical Li4SiO4 pellets. The produced pellets exhibited a uniform diameter distribution of 2.5–3.5 mm and high capacity of 0.320 g CO2/g sorbent. Besides, the PVA method-derived Li4SiO4 pellets also presented excellent cyclic stability in the extended sorption/desorption operations of 30 cycles. It has been indicated that the enhancement of CO2 sorption capacity is ascribed to the formation of abundant pore channels and cavities resulted from the burning out of the well-dispersed polyvinyl alcohol. Moreover, the influence of CO2 presence at desorption stage on the sorbent performance was also investigated. It was indicated that the existence of CO2 at desorption stage caused sintering, which in turn resulted in the reduction of CO2 sorption capacity. In addition, the mechanical property of the pellets was tested. The weight loss was lower than 9 wt% over 2400 rotations in the anti-attrition ability test. In general, the high CO2 sorption capacity and satisfying mechanical property of the Li4SiO4 pellets via PVA route endows this method with promising prospects for the granulation of Li4SiO4 sorbents for realistic CO2 removal.

Upcycling Mask Waste to Carbon Capture Sorbents: A Combined Experimental and Computational Study

Massive plastic pollution and grand scale emission of CO2 into the atmosphere represent two major and deeply connected societal challenges, which can have adverse impacts on climate, human health, and marine ecosystems. In particular, the COVID-19 pandemic led to substantially increased production, use, and discarding of disposable masks, a problem that requires urgent and effective technological solutions to mitigate their negative environmental impacts. Furthermore, over the years significant research efforts have sought to address the challenges of plastic waste and CO2 emission, such as development of chemical upcycling methods and low-cost CO2 capture sorbents at scale, respectively. In this work, we introduce a simple and scalable method for directly converting surgical polypropylene mask waste into sulfur-doped carbon fibers, which can exhibit a high CO2 sorption capacity of ≤3.11 mmol/g and high selectivity (>45) against N2 gas. This excellent performance is attributed to the high affinity between sulfur heteroatoms in the carbon framework and CO2 gas molecules, confirmed by combined experimental and simulation investigations. This work provides an industrially viable approach for upcycling plastic waste into carbon-based products with increased value, which can then be employed to address the environmental challenges of CO2 remediation.

Single-step fabrication of templated Li4SiO4-based pellets for CO2 capture at high temperature

The present study proposes a novel single-step method for the fabrication of macro-porous K2CO3-doped Li4SiO4 pellets for carbon dioxide capture at high temperature and low concentration of CO2. Cylindrical pellets were directly prepared by mechanical compression of precursors and then calcination at high temperature. The pellets characterization evidenced that, during the calcination process, both the synthesis of Li4SiO4 and the development of macro-porosity into pellets occurred due to the release of decomposition gases. The obtained pellets were tested for CO2 capture at 580 °C and CO2 partial pressure of 0.04 atm, and the long-time stability was evaluated by multiple sorption/desorption cycles operating at moderate Li4SiO4 conversions. This single-step pelletization method allowed to produce a sorbent with high CO2 sorption capacity (253.2 mg CO2/g sorbent) even at low concentration of CO2. Moreover, the single-step pellets displayed a good cyclic stability over 200 adsorption/desorption cycles, making them suitable for CO2 capture in industrial applications in a fixed bed reactor.

Enhancement of carbon dioxide adsorption performances by hydrazinolysis of poly(n-vinylformamide) grafted fibrous adsorbent

Abstract Emission of carbon dioxide (CO2) becomes a main concern in battling issues of global warming. The strategy to reduce the concentration of CO2 could be achieved by implementing carbon capture and storage (CCS) technology such as adsorption by solid adsorbents. In this work, hydrazone containing adsorbent was prepared by radiation induced grafting of N-vinylformamide (NVF) onto polyethylene coated polypropylene (PE/PP) fibrous sheets and subsequent hydrazinolysis for CO2 capture. Hydrazinolysis of the amide group to hydrazone moieties was accelerated by the addition of ammonium salts. These newly prepared adsorbent was characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The adsorption tests of pure CO2 and N2, and their mixture were carried using the gravimetric method. The result revealed that the obtained adsorbent was highly CO2 selective and attained remarkably higher CO2 sorption capacity of 3.1 mmol/g at 30 bar and room temperature compared to 0.3 mmol/g for amide-containing sample. The new adsorbent could be used for few repeated cycles with negligible loss in sorption capacity. Overall, the hydrazone-containing adsorbent has storing potential for CO2 capture, and more studies need to be conducted for further development.

Ni-CaO dual function materials prepared by different synthetic modes for integrated CO2 capture and conversion

Dual-functional materials (DFMs) present broad prospects in CO2 capture and in-situ conversion to value-added products using renewable energy. Herein, we proposed and demonstrated three different synthetic modes for preparing Ni-CaO DFMs using carbide slag as calcium precursor. CO2 sorption and in-situ hydrogenation performance of the Ni-CaO DFMs was evaluated using a fixed-bed reactor. Results indicated that CO2 sorption capacity and CO productivity of the synthesized Ni-CaO DFMs depended on the synthetic modes. The desired Ni/CS-P30-C synthesized by acid pretreatment of carbide slag followed by citric acid complex exhibited a high CO2 sorption capacity (13.28 mmol/g DFMs) and a great CO productivity (5.12 mmol/g DFMs) under the isothermal testing temperature of 650 °C. The sample also showed stable CO2 uptake and CO productivity within 17 cycles. The good CO2 sorption and in-situ hydrogenation performance were associated with the better textural properties, smaller particle size and more uniform dispersion of Ni species, which were resulted from propionic acid pretreatment and citric acid complex processes. In addition, Ni-CaO pellet with high mechanical strength (2.88 MPa) and abrasion ability (weight loss of 2.36% after 3000 rotations). had also been prepared by the extrusion-spheronization method. The pelletization process adversely affected the CO2 sorption and in-situ hydrogenation performance, but the pellet exhibited good stability in cyclic operations.

Insights into the Solubility of Carbon Dioxide in Grafted Mesoporous Silica for the Catalytic Synthesis of Cyclic Carbonates by Nanoconfinement.

Gas solubility can go beyond classical bulk-liquid Henry's law saturation under the nanoconfinement of a liquid phase. This concept establishes the foundation of the current study for developing a novel catalytic system for transformation of carbon dioxide to cyclic carbonates at mild conditions with major emphasis on application for CO2 capture and utilization. A series of mesoporous silica-based supports of various pore sizes and shapes grafted with a quaternary ammonium salt is synthesized and characterized. CO2 sorption in styrene oxide, either in bulk or nanoconfined state, as well as catalytic reactivity for CO2 transformation into styrene carbonate, are experimentally evaluated. The family of mesoporous catalysts with aligned cylindrical pores (MCM-41 and SBA-15) with pore sizes ranging from 3.5 to 9 nm exhibit enhanced sorption of CO2 in nanoconfined styrene oxide with maximum sorption capacity taking place in MCM-41 with the smallest pore size. The catalysts with interconnected cylindrical pores (KIT-6) with pore sizes ranging from 4.5 to 8.7 nm showed CO2 solubilities almost equal to the bulk solubility of styrene oxide. Monte Carlo simulations revealed that the oversolubility in styrene oxide confined complex is directly related to the density of adsorbed solvent in the nanopore, which is less than its bulk density. Catalytic reactivities correlate with CO2 sorption enhancement, showing higher turnover frequencies for catalysts having higher CO2 sorption capacity. The turnover frequency is increased by a factor of 7.5 for grafted MCM-41 with the smallest pore size with nanoconfined styrene oxide in comparison to the homogeneous reaction implemented in bulk.

CO2 sorption using encapsulated imidazolium-based fluorinated ionic liquids

The development and testing of new sorbents for the efficient removal of CO2 from flue gases is essential. Encapsulated room-temperature ionic liquids (RTILs) can be potentially employed in CO2 capture. In this work, we report the preparation and characterization of encapsulated imidazolium-based fluorinated RTILs for CO2 capture. [Emim][TF2N], [Bmim][TF2N], and [Hmim][TF2N] RTILS were encapsulated in polysulfone (PSF) using an emulsification method and characterized by several techniques. The pressure-decay technique was used to assess the CO2 sorption capacity and reusability. Encapsulated RTILs showed improved utility for CO2 capture processes compared with non-encapsulated RTILs, including higher CO2 sorption capacity and faster CO2 sorption/desorption. The CO2 absorption/desorption cycles demonstrated the reuse capacity of all microcapsules under mild conditions. The highest CO2 sorption capacity was noted for encapsulated [Emim][TF2N] (39.5 mg CO2 g−1 at 298.15 K and 1 bar; 62.7 mg CO2 g−1 at 298.15 K and 10 bar). It is worth emphasizing that the encapsulated [Emim][TF2N] contained a lower ionic liquid (IL) content (37.5. ± 0.6) when compared to other encapsulated samples. Moreover, encapsulated [Emim][TF2N] presented a higher CO2 affinity than the encapsulated ILs reported in the literature.

Stabilization of CO2 Capture Performance Using Natural Modified CaO-Based Pellets Prepared by Extrusion Granulation

CaO-based materials have a high commercialization potential to be used as Calcium-Looping (CaL) sorbents for CO2 capture, owing to their high CO2 sorption capacity and the lowcost raw materials. The present work focuses on the comparative study of two natural CaO-based sorbents (limestone and wastes of marble powder) with and without alumina incorporation, tested under CaL conditions for CO2 capture. The incorporation of alumina in CaO-based pellets was performed by extrusion followed by calcination at 800 oC and granulation, using different CaO/Al2O3 ratios (50/50, 60/40 and 70/30) and MethocellTM as pore forming agent. The experiments were carried out in a laboratory scale fixed bed reactor unit along 10 carbonation-calcination cycles using a gas mixture with a CO2 concentration of 25% to mimic the real flue gases in the cement industry, and the calcination was performed under industrial realistic conditions (80% of CO2; 930 oC) foreseen for the subsequent CO2 utilization. During the CaL tests a fraction of CaO was converted to calcium aluminate due to its exposure to the process high temperatures. Anyway, the use of modified natural CaO-based pellets containing Al2O3 as structural agent is attractive, since higher CaO conversion values were achieved. The enhanced performance of pellets can be justified by the higher specific surface area and stabilization of CaO crystallite sizes along the cycles promoted by the formation of calcium aluminates. The highest CaO conversion was achieved for the case of 60/40 CaO/Al2O3 pellets, allowing the reduction of the CaO make-up frequency along the time as well as the associated costs.

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.