CO2 Diffusion Resistance Research Articles

From low-cost mineral to high-performance Li4SiO4 for solar energy storage and CO2 capture

The huge consumption of fossil fuels results in excessive CO2 emissions and its reduction has become a common concern. The combination of renewable energies (i.e., solar energy) and carbon capture, utilization, and sequestration are well recognized as two major routes to achieving carbon neutrality. Lithium orthosilicate (Li4SiO4) has been identified as one of the most promising candidates for solar energy storage and CO2 capture. However, the cost reduction and performance enhancement remain to be the main obstacles for its practical application. In this work, high-performance Li4SiO4 heat carriers have been synthesized using low-cost mineral as silicon source for solar energy storage and CO2 capture. Li4SiO4 derived from diatomite exhibited cyclic energy storage densities above 500 kJ/kg. The performance was further improved by doping alkali carbonates, particularly doping 3 wt% K2CO3 (LD-P-3K), which exhibited high and stable energy storage density of approximately 700 kJ/kg in the tested 10 cycles. Then, the mechanism of alkali doping was revealed through experiments and DFT calculations. The DSC results demonstrated that the improved performance was attributed to the formation of a eutectic melt which reduced the CO2 diffusion resistance. The DFT calculations showed that K-doped Li4SiO4 had lower adsorption energy and more significant charge migration, which meant stronger interaction. Additionally, diatomite-derived Li4SiO4 material is also a promising candidate for high-temperature CO2 capture, evidenced by its relatively high cyclic CO2 capture capacity (∼0.25 g/g). In general, satisfactory density/capacity and stability endows diatomite-derived Li4SiO4 with great prospects for both thermochemical energy storage and high-temperature CO2 capture.

Effect of hydrothermal pH values on the morphology of special microspheres of lignin-based porous carbon and the mechanism of carbon dioxide adsorption

The study reports the economic and sustainable syntheses of a lignin-based porous carbon (LPC) for CO2 capture application. The pH values of hydrothermal solution affected the polymerization and aromatization of spheroidization, with morphological changes from blocky to microsphere. In addition, the reliable mechanisms of CO2 adsorption were proposed by combining experiments with Gaussian16 simulations based on DFT. The electrostatic attraction of oxygen-containing functional groups and the diffusivity resistance of CO2 in the pores are the key factors for the CO2 adsorption. ​The carboxyl groups have the strongest electrostatic attraction to CO2. LPC-pH 1 has the highest carboxyl group content, possessing a CO2 adsorption capacity of up to 5.10 mmol/g at 0℃, 1 bar. Furthermore, CO2 diffusion resistance became a main factor as the adsorption temperature increases. The innovative combination of quantum chemical calculations and microscopic properties provides a viable pathway for an insight into the future control of lignin-based carbon formation.

Direct air CO2 capture using coal fly ash derived SBA-15 supported polyethylenimine

Designing an amine modified silica derived from coal fly ash (CFA) towards direct air CO2 capture (DAC) provides an economic way to manage increasing atmospheric CO2 concentration utilizing solid wastes. In this work, rod-like SBA-15 (SBA-15-R) and wheat-like SBA-15 (SBA-15-W) with distinct pore lengths are synthesized from CFA by controlling the synthesis conditions and then modified by PEI via the wet impregnation method. Their CO2 adsorption behaviors under sub-ambient conditions are investigated to explore their feasibility under aggressive conditions. The adsorbents with various silica morphologies exhibit distinctive CO2 adsorption performance under ambient and sub-ambient conditions. At 35°C under dry conditions, the CO2 adsorption capacity increases with amine loading. The CO2 adsorption capacity (qe) of SBA-15-W-PEI with long channels reaches the highest qe of 1.92 mmol/g with 70 wt.% PEI loading due to a large amount of strong chemisorption sites. Under the sub-ambient conditions (-20°C, 400 ppm), SBA-15-R-PEI30 with short channels having weaker CO2 diffusion resistance exhibits promising CO2 uptake of 0.83 mmol/g. These findings indicate that the ultra-dilute CO2 adsorption at ambient temperature requires an adsorbent with large amounts of adsorption sites, whereas the adsorbents for cold temperature application should reconcile amine loading with CO2 diffusion resistance inside pores. The co-adsorption of H2O and CO2 significantly improves CO2 capacity from 0.83 mmol/g and 1.92 mmol/g to 1.81 mmol/g and 3.48 mmol/g for SBA-15-R-PEI30 (-20°C, 400 ppm) and SBA-15-W-PEI70 (35°C, 400 ppm), respectively. Furthermore, the CFA derived SBA-15-PEI shows good cyclic stability during five consecutive TSA cycles. Preparing the amine silica adsorbents from coal fly ash potentially reduces the adsorbent cost of DAC devices. Moreover, the systematic exploration of amine silica adsorbents at a wide range of temperatures guides the design of high-performance CO2 adsorbents employed under various climatic conditions.

Surface oxidation modification of nitrogen doping biochar for enhancing CO2 adsorption

The purpose of this paper is to demonstrate a surface oxidation modification strategy of nitrogen doping biochar for enhancing CO2 adsorption. The porous structure and surface group distribution of nitrogen doping biochars before and after modification (remarked as TF and OTFs) were characterized. Then the thermodynamic and kinetic characteristics of CO2 adsorption such as adsorption capacity, selectivity and activation energy were systematically investigated. The results indicated that the modified biochars OTFs exhibited high adsorption capacity of CO2 between 5 and 8 mmol·g-1 at 100 kPa and 273 K. The oxidation modification affected CO2 adsorption behaviors by the ways of adjusting surface pore size and surface group distributions. The former decreased the mass transfer diffusion resistance of CO2 from gas phase to biochar surface by transforming some micropores to the mesopores. And the later improved the adsorption selectivity of CO2 to the other gases such as N2 based on the interaction difference enhancement by those oxygen-containing (OFGs) and nitrogen-containing functional groups (NFGs). When the molar ratios of CO2/N2 in gas mixture were 1:1 and 15:85, the modified biochar OTF-10 exhibited the better selectivity, and the maximum selectivities of CO2 to N2 at 273 K were 44.7 and 69.4, respectively. Furthermore, the behavior of CO2 adsorption on the biochars well conformed to the quasi-first-order dynamical model, accompanied by the higher adsorption rate of CO2 and activation energy. The obtained activation energies for TF and OTF-10 were 12.98 and 16.62 kJ·mol-1, respectively. The higher activation energy for OTF-10 meant that the adsorption temperature had a stronger effect on adsorption rate of CO2.

Hierarchical porous AlOOH hollow microspheres for efficient CO2 capture

In order to reverse the trend of increasing carbon dioxide (CO2) emissions, the development of efficient and economical CO2 trapping agents is an urgent necessity for the sustainable development of industry. In this paper, hierarchical porous hydroxyl aluminum oxide (AlOOH) hollow microspheres with controllable structure and morphology were prepared by conventional hydrothermal synthesis using malonic acid as a structure guiding agent. Then, potassium carbonate (K2CO3) based adsorbents were prepared using AlOOH hollow microspheres as supports, and their CO2 trapping performance was assessed by simulating industrial flue gas flow in a fixed bed. The results show that the loading of K2CO3, the pore structure, and the surface basic site of the adsorbent have a significant influence on the trapping performance of CO2. Among the prepared K2CO3/AlOOH adsorbents, 30 wt% K2CO3/AlOOH adsorbent has the best CO2 capture ability, which is about 2.15 times higher than that of K2CO3/C–Al2O3 adsorbent prepared from commercial alumina (C–Al2O3). There may be two explanations for this. Firstly, it may be due to the nanostructured shell and hierarchical porous structure of the adsorbent, which reduces the intra-particle diffusion resistance of CO2, and secondly, it may be due to the suitable surface basic sites of the adsorbent. In addition, the adsorbent was regenerated at 120 °C after trapping CO2, and then CO2 was captured in a cycle. It was found that the CO2 capture capability of the adsorbent did not decrease significantly after 10 cycles. In this work, an excellent technique for preparing porous honeycomb adsorbents with suitable surface basic sites has been devised, which provides a creative strategy for capturing and utilizing CO2.

Organolithium-derived alkali-doped highly durable Li4SiO4 heat carrier for solar thermochemical energy storage

Thermochemical energy storage (TCES) technology plays a vital role in utilizing solar energy to produce electricity. However, traditional TCES technologies such as calcium looping route suffer from unsatisfactory long-term durability. Lithium looping has demonstrated excellent cyclic stability, but it has been rarely employed for energy storage. In this work, organolithium-derived Li4SiO4 heat carrier was synthesized and further decorated with alkali doping. The porous microstructures and wrinkled surfaces of organolithium-derived Li4SiO4 were demonstrated, with alkali doping facilitating the formation of low-temperature eutectic materials and reducing CO2 diffusion resistance, thereby enhancing its cyclic energy storage performance. Li4SiO4 doped with 3 wt% K2CO3 shows energy storage density of as high as 638.23 kJ/kg, equal to a high conversion of 81.41% over long storage/release tests of 15 cycles. The high energy density and excellent cyclic durability of Li4SiO4 were attributed to its porous microstructures and formed eutectic melts. Furthermore, for practical application, the carbonation (or heat release) temperature for Li4SiO4 looping TCES system was optimized. To sum up, Li4SiO4 exhibits great potential as a candidate for thermochemical energy storage in solar energy utilization due to its excellent long-term cyclic durability.

Capturing CO2 by ceria and ceria-zirconia nanomaterials of different origin.

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO2 capture. Two commercial cerias and two home-prepared samples, CeO2 and CeO2-ZrO2 (75% CeO2) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N2-adsorption, XPS, H2-TPR, Raman and FTIR spectroscopy. Static and dynamic CO2 adsorption experiments were applied to assess the CO2 capture performance. The type of surface species formed and their thermal stability were evaluated by in situ FTIR spectroscopy and CO2-TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO2 adsorption and, consequently, demonstrated almost identical CO2 capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO2 increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO2 sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO2-adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO2 diffusion resistance. Having the same surface area as the synthesized CeO2, the mixed CeO2-ZrO2 oxide exhibited the highest CO2 capture capacity of 136 μmol g-1 under dynamic conditions. This was related to the highest concentration of CO2 adsorption sites (including defects) on this sample. The CeO2-ZrO2 system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.

Resolving high potential structural deterioration in Ni-rich layered cathode materials for lithium-ion batteries operando

LixNi0.90Co0.05Al0.05O2 (NCA) extracted from an automotive battery cell is studied using a combination of in-house operando techniques to understand the correlation between gas evolution and structural collapse when NCA is cycled to high potentials in a lithium-ion battery configuration. The operando techniques comprise X-ray diffraction (XRD) and online electrochemical mass spectrometry (OEMS), and cycled using intermittent current interruption (ICI). The ICI cycling protocol is used to assess the dynamic change in resistance as well as to provide a validation of the operando setups. Both gas evolution and structural collapse have previously been observed as degradation mechanisms of Ni-rich electrodes including NCA, however, their causal link is still under debate. Here our presented results show a correlation between the decrease of the interlayer distance in NCA with both an increase in CO2 evolution and diffusion resistance above 4.1 V. Additionally, particle cracking, which is a mechanism often correlated with gas evolution, was found to be reversible and visible before gas evolution and Li diffusion resistance increase. The ICI technique is shown to be useful for the correlation of operando experiments on parallel setups and evaluation of mass transport dependent processes.

Leaf anatomical alterations reduce cotton's mesophyll conductance under dynamic drought stress conditions.

Drought stress significantly affects cotton's net photosynthetic rate (A) by restraining stomatal (gs ) and mesophyll conductance (gm ) as well as perturbing its biochemical process, resulting in yield reductions. Despite the significant progress in dissecting effects of drought on photosynthesis, the variability observed in cotton's gm , and the mechanisms contributing to that variability under dynamic drought stress conditions are poorly understood. For that reason, a controlled-environment experiment with two cotton genotypes (Dexiamian 1, Yuzaomian 9110), three water levels (soil relative water content: control [75 ± 5]%, moderate drought [60 ± 5]%, severe drought [45 ± 5]%), and two drought durations (10 and 31 days) were conducted. The results indicated that the cotton boll biomass was significantly decreased under 10-day severe drought and 31-day moderate and severe drought. Decreases in gs were later accompanied by decreases in gm and further combined with reductions in electron transport rate, as drought stress progressed in duration and severity, ultimately resulting in significant reductions in A of subtending leaf. Stomatal and mesophyll conductance constraints were the primary factors limiting photosynthesis, while biochemical constraints decreased, as drought stress progressed. Considering gm , its decline was ascribed to increases in the diffusion resistance of CO2 through cytoplasm (rcyt ), under short- or long-term drought, as well as to increases in leaf dry mass (LMA), and decreases in the chloroplast surface area exposed to intercellular air space (Sc /S), under long-term drought. It was concluded that A could be enhanced, under dynamic drought stress conditions, by increasing gm through increasing Sc /S and reducing LMA and rcyt .

High CO2 adsorption on amine-functionalized improved macro-/mesoporous multimodal pore silica

In recent years, amine functionalized materials have attracted great interest as prospective solid adsorbents for CO2 capture. However, the amine functionalization of traditional supports (such as SBA-15, etc.) can lead to a decrease in the pore volume and specific surface area of the adsorbent, which significantly affects the CO2 adsorption–desorption kinetics. To overcome this problem, the macro-/mesoporous multimodal pore silica was quickly synthesized using a ternary nonionic surfactant as a template through a partitioned collaborative self-assembly method, and impregnated with TEPA. The prepared support HMS-4 h has bimodal pores (pore size of 9.41 nm and 90 nm), which can not only improve the dispersibility of the loaded TEPA, but also effectively reduce the diffusion resistance of CO2. At the same time, the high surface area (838 m2/g) and large pore volume (2.34 cm3/g) of HMS-4 h can further improve the adhesion and quantity of amine-based active sites. The highest adsorption capacity reaches 6.04 mmol/g for HMS-4 h-75%TEPA at 90 ℃ and 1 bar. The adsorption capacity for HMS-4 h-75%TEPA was steady after 10 adsorption–desorption cycles. BET, XRD, FT-IR, SEM, TG-DTG were used to characterize the performance of the adsorbent. The CO2 adsorption mechanism and the effects of organic amine loading, adsorption temperature and CO2 concentration on CO2 adsorption performance were systematically studied. The research shows that HMS-4 h-75%TEPA is an excellent adsorbent with high adsorption capacity in a wide temperature range, and low energy. This provides a reference for the design of high-performance solid amine CO2 adsorbents in the future.

Li4SiO4 pellets templated by rice husk for cyclic CO2 capture: Insight into the modification mechanism

Li4SiO4 stands out among various solid sorbents for CO2 capture. The commonly used mechanical granulation process for Li4SiO4 sorbents causes the destruction of the microstructures. Therefore, with the characteristics of huge production and low cost, an agricultural waste (rice husk) was employed as a pore former to improve the structures of Li4SiO4 pellets and, thus, enhance the cyclic CO2 sorption performance. The rice husk templating greatly enhanced the CO2 sorption capacity of Li4SiO4 pellets. Especially, 20 wt% rice husk-templated Li4SiO4 exhibited the capacity of 0.21 g/g, which was nearly twice that of the unmodified sorbent. The quick release of the combustion gases from burning rice husk could create porosity for the sorbents. In addition, the alkaline compositions in rice husk promoted the CO2 sorption due to the decreased CO2 diffusion resistance by the formation of molten phases. Moreover, the ashes of rice husk after high-temperature combustion were found to block the pores of the sorbents, leading to the capacity reduction. The comprehensive function of rice husk templating for Li4SiO4 pellets was the tradeoff between the positive effects of pore creation and alkaline doping and the negative effects of pore blockage by the ashes.

Influence of surfactant on CO2 adsorption of amine-functionalized MCM-41

ABSTRACT Concerning the increasing greenhouse effect, the development of efficient CO2 adsorbents is very important. In this study, the influence of surfactant on the adsorption performance of amine-functionalized MCM-41 was analysed. The results showed that the residual amount of surfactant in MCM-41 was gradually decreased with the increase of calcination temperature which improved the pore structure. The maximum adsorption capacity (5.495 mmol/g) appeared at PEI-MCM-41-100°C indicated that the adsorption capacity could be improved under the function of surfactant. By calculating the diffusion coefficient of CO2 adsorption process in PEI-MCM-41-100/200/300/400/550°C, the diffusion resistance of CO2 was the lowest in PEI-MCM-41-100°C, which directly proved that the synergism of surfactant and organic amine could reduce the diffusion resistance of CO2 in the pore.

CaO/Ca(OH)2 heat storage performance of hollow nanostructured CaO-based material from Ca-looping cycles for CO2 capture

A hollow nanostructured CaO-based material fabricated from calcined limestone and glucose by hydrothermal carbonization method was proposed to be used in the process coupled Ca-looping for CO2 capture and CaO/Ca(OH)2 heat storage. The effects of hydrothermal temperature and interval in the preparation process on CO2 capture and heat storage capacities of the hollow CaO were studied. The interaction effect of Ca-looping and heat storage on the performance of the hollow CaO was determined. The hollow nanostructure of CaO decreases the diffusion resistance of CO2 and steam in its inner. The CO2 capture capacity of the hollow CaO reaches 0.45 g/g after 20 Ca-looping cycles, which is 1.7 times as high as that of limestone. The hollow CaO (hydrothermal temperature of 170 °C for 6 h) after 10 Ca-looping cycles achieves a heat storage capacity of 0.85 mol/mol during the subsequent heat storage cycles, which is 1.3 times as high as that of limestone. A few heat storage cycles improve pore structure of the sintered hollow CaO after Ca-looping cycles, so its CO2 capture capacity in the following Ca-looping cycle is enhanced by 94%. Thus, the hollow nanostructured CaO seems promising in the process coupled Ca-looping and CaO/Ca(OH)2 heat storage.

Acclimation of mesophyll conductance and anatomy to light during leaf aging in Arabidopsis thaliana.

Mesophyll conductance (gm ), a key limitation to photosynthesis, is strongly driven by leaf anatomy, which is in turn influenced by environmental growth conditions and ontogeny. However, studies examining the combined environment × age effect on both leaf anatomy and photosynthesis are scarce, and none have been carried out in short-lived plants. Here, we studied the variation of photosynthesis and leaf anatomy in the model species Arabidopsis thaliana (Col-0) grown under three different light intensities at two different leaf ages. We found that light × age interaction was significant for photosynthesis but not for anatomical characteristics. Increasing growth light intensities resulted in increases in leaf mass per area, thickness, number of palisade cell layers, and chloroplast area lining to intercellular airspace. Low and moderate-but not high-light intensity had a significant effect on all photosynthetic characteristics. Leaf aging was associated with increases in cell wall thickness (Tcw ) in all light treatments and in increases in leaf thickness in plants grown under low and moderate light intensities. However, gm did not vary with leaf aging, and photosynthesis only decreased with leaf age under moderate and high light, suggesting a compensatory effect between increased Tcw and decreased chloroplast thickness on the total CO2 diffusion resistance.

Enhanced Adsorption of Carbon Dioxide from Simulated Biogas on PEI/MEA-Functionalized Silica.

A series of efficient adsorbents were prepared by a wet-impregnation method for CO2 separation from simulated biogas. A type of commercially available silica, named as FNG-II silica (FS), was selected as supports. FS was modified with a mixture of polyethyleneimine (PEI) and ethanolamine (MEA) to improve the initial CO2 adsorption capacity and thermal stability of the adsorbents. The influence of different adsorbents on CO2 adsorption performance was investigated by breakthrough experiments. Scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and N2 adsorption–desorption isotherm were used to characterize the silica before and after impregnating amine. Additionally, the thermal stability of adsorbents was measured by differential thermal analysis (TDA). Silica impregnated with mixtures of MEA and PEI showed increased CO2 adsorption performance and high thermal stability compared with those obtained from silica impregnated solely with MEA or PEI. With a simulated biogas flow rate of 100 mL/min at 0.2 MPa and 25 °C, FS-10%MEA-10%PEI exhibited a CO2 adsorption capacity of ca. 64.68 mg/g which increased by 81 % in comparison to FS-20%PEI. The thermal stability of FS-10%MEA-10%PEI was evidently higher than that of FS-20%MEA, and a further improvement of thermal stability was achieved with the increasing value of PEI/MEA weight ratio. It was showed that MEA was able to impose a synergistic effect on the dispersion of PEI in the support, reduce the CO2 diffusion resistance and thus increase CO2 adsorption performance. Additionally, if the total percentage of amine was the same, FS impregnated by different ratios of PEI to MEA did not exhibit an obvious difference in CO2 adsorption performance. FS-15%PEI-5%MEA could be regenerated under mild conditions without obvious loss of CO2 adsorption activity.

Synthesis and characterization of MSU-2 synthesized by using tetraethylorthosilicate and Triton X-100

Adsorption technology is one of the well-established gas separation techniques as it can minimize cost and energy requirement for CO2 separation. Mesoporous silicas such as MSU-2 appears to be a good adsorbent as it comprises of three-dimensional (3D) wormhole framework structures that are highly interconnected which minimize the diffusion resistance of CO2 through its pore structure. Current study focus on the preparation of MSU-2 and investigation on the CO2 adsorption on the synthesized MSU-2. In this study, MSU-2 was prepared by using tetraethylorthosilica (TEOS) as a source of silica in the presence of non- ionic polyethyleneoxide (PEO)-based surfactants under an acidic condition where the pH is 2 at 55 °C for 48 hours via the fluoride-assisted two-step synthesis process. The two main steps involved are hydrolysis of TEOS and condensation of silica. The morphology, crystallinity, functional groups and pore characteristics of MSU-2 were investigated by using characterization method of Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray (EDX) Spectrometry, X-ray Diffractometer (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET). The synthesized MSU-2 was well crystallized and possessed a uniform monodisperse microspherical morphology with BET surface area, pore volume and pore size of 964 m2/g, 0.98 cm3/g and 4.1 nm, respectively. All the characterization results showed that MSU-2 was successfully synthesized via solution precipitation method. In conclusion, the high BET surface area of the synthesized MSU-2 shows that MSU-2 is a very potential candidate as a good adsorbent for gases.

Using lantern Zn/Co-ZIF nanoparticles to provide channels for CO2 permeation through PEO-based MMMs

To reduce the diffusion resistance of CO2 and enhance its permeability in mixed matrix membranes (MMMs), lantern Zn/Co-ZIF nanoparticles were loaded in-situ into semi-interpenetrating cross-linked poly(ethylene oxide) (XLPEO) membranes to provide efficient channels for CO2 permeability. TEM and SEM results showed that the Zn/Co-ZIF nanoparticles (diameter 490–550 nm) treated at 145 °C possessed a lantern structure with hollow cores (diameter 380–450 nm) and thin shells (thickness 20–85 nm). XRD and BET results indicated that the nanocrystal structure and porosity of the Zn/Co-ZIF remained intact after etching at 145 °C. Peaks shifts in the infrared spectra confirmed that the Zn/Co-ZIF nanoparticles were well integrated with the XLPEO membrane through hydrogen bonds. Therefore, doping 15 wt% lantern Zn/Co-ZIF nanoparticles into the membrane dramatically increased CO2 permeability by 72% to 761.9 ± 3.0 barrers, while the CO2/N2 selectivity was above the upper bound established by Robeson in 2008.

CO2 adsorption of MSU-2 synthesized by using nonionic polyethyleneoxide (PEO)-based surfactants

Adsorption technology is a well-established technology for CO2 removal. MSU-2 mesoporous silica appears to be very potential adsorbent for efficient CO2 gas adsorption due to its three-dimensional (3D) wormhole framework structures that are highly interconnected which is able to minimize the diffusion resistance of CO2. So far, there is no previous study reported on the CO2 adsorption of MSU-2. Thus, the current study focuses on the investigation on the synthesis of MSU-2 by using different surfactants (Triton X-100, Igepal CA-720 or Tergitol NP-9) and followed by the CO2 adsorption studies on the synthesized MSU-2. The morphology, crystallinity, functional groups, pore characteristics and pore structure of the MSU-2 synthesized were investigated. FESEM images showed that MSU-2 synthesized by using Igepal CA-720 possessed the most uniform and defined microspherical morphology compared to the MSU-2 synthesized by using the other surfactants. Besides, the MSU-2 synthesized by using Igepal CA-720 displayed the highest BET surface area of 938 m2/g and CO2 adsorption capacity of 0.57 mmol/g compared to the other MSU-2 samples. The obtained results showed that Igepal CA-720 is the most suitable surfactant for MSU-2 synthesis compared to the other surfactants in the current study.

Mesocellular silica foam supported polyamine adsorbents for dry CO2 scrubbing: Performance of single versus blended polyamines for impregnation

Siliceous foams with three-dimensional mesoporous structures were synthesised and used to prepare polyethyleneimine (PEI) and tetraethylenepentamine (TEPA)-functionalised sorbent materials for CO2 capture, with a particular focus on the performance of impregnated amine blends versus single amine sorbent systems. Using thermal gravimetric analysis supported by other characterisations, the obtained results demonstrated that compared to the impregnated mono-component PEI and TEPA sorbent systems, the binary PEI-TEPA blend sorbents all achieved significantly higher CO2 capacities and faster adsorption kinetics, due to the enhanced formation of micro-cavities within the supported amine layers that led to reduced CO2 diffusion resistance and increased accessibility of the amines to CO2. It was found that at 70 °C and 15% CO2 in N2, the CO2 adsorption capacity of the silica-supported PEI–TEPA (3:2) at 70 wt% amine loading increased by 40% compared to the supported PEI at the same level of amine impregnation, whilst the time to achieve 80% and 90% of the equilibrium adsorption capacity was reduced by 70% and 35%, respectively. Extended cyclic adsorption-desorption tests showed that the TEPA-blended PEI sorbents all exhibited considerably higher thermal stability than both the supported PEI and TEPA sorbents, being indicative of the suppressed urea formation even in the pure and dry CO2 gas stream used in the desorption cycles. Calculations indicated that compared to the silica-supported PEI sorbents, the higher adsorption capacities achieved by the binary PEI-TEPA sorbent systems could lead up to 10% reduction in the energy requirement for sorbent regeneration, highlighting the suitability of using amine blending as a facile effective strategy to promote the overall performance of polyamine-based adsorbents for CO2 separation.

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.