Amine Loading Research Articles

Enhancing adsorbent performance for direct air capture of CO2 by in-situ amine-grafting of layered double hydroxides

The development of efficient and cost-effective CO2 adsorbents is crucial for carbon capture from ultradilute conditions. Amine-grafted mesoporous materials prepared by silane chemical reactions are well-known CO2 adsorbents with high thermal stabilities, but their capacities for direct air capture (DAC) are usually restricted by low amine loadings and CO2 capture capacity. Herein, we present an in-situ amine grafting method that enables high amine loadings by in-situ grafting initial ultrathin LDHs nanosheets in an organic solvent. For in-situ triamine grafted Mg2Al-CO3 LDH (IN-TRI-LDH) amine loading is boosted to 5.91mmol N g−1 and ultimately achieving a remarkable adsorption capacity of 0.98 mmol g−1 at 25°C and 400 ppm CO2, nearly double that of the amine-LDHs grafted through a conventional two-step process. A further 22 % enhancement of the CO2 capacity is observed under 20 RH%. In addition, IN-TRI-LDH maintains a working capacity of 0.85 mmol g−1 at a low desorption temperature of 70 °C. A 50 adsorption–desorption cyclic test under simulated humid DAC conditions shows minimal performance degradation. Such a sufficient working capacity and low desorption temperature reduces the thermal energy consumption to 2.27 GJ t−1 at a desorption temperature of 40 °C.

Multiple-amine functionalized γ–Al2O3 for post-combustion CO2 capture: Performance, mechanism, and kinetics

High-efficiency and cost-effective adsorbents are crucial to dry capture of carbon dioxide (CO2). The polyethyleneimine (PEI) was co-impregnated with tetraethylenepentamine (TEPA) on γ-alumina (Al2O3) to synthesize the adsorbent and enhance the capture process. The influence of amine loading and operating parameters on CO2 adsorption was investigated, and the process parameters were modeled. The results depict that the optimal loading is 50 % when functionalized either PEI or TEPA individually, which is 3.7 and 4.6 times higher than γ–Al2O3. The CO2 capacity of γ–Al2O3 functionalized with multiple amines (30 %PEI+20 %TEPA) is 2.65 mmol/g, due to the synergies of the two amines to increase the chance of CO2 binding to the sites. Regeneration performance illustrates that the adsorbent remains at 90.2 % of the initial capacity after seven tests. The maximal capacity of 2.70 mmol/g occurs at 70 °C. Modeling results indicate the kinetics can be evaluated by the Avrami model (R2 > 0.990) with the activation energy of 5.65 kJ/mol. The process is controlled by physical–chemical adsorption, influenced by intraparticle diffusion, as described by the deactivation model. Finally, a comparison and assessment were conducted for their techno-economic performances, and the pathway to applications was also proposed in engineering practice.

Investigating the Corrosion Inhibition Performance of a Novel Coconut Oil-Based Poly(urethane-urea) Hybrid Coating on Carbon Steel in 3.5% NaCl Solution

Polyurethane has been used for years as an anti-corrosion coating due to its intrinsic hydrophobic properties. However, its hydrophobicity is not enough to inhibit the permeation of corrosive agents; thus, incorporating it with polyurea would further enhance its hydrophobic properties. In this study, coconut oil, a saturated, low molecular weight vegetable oil, was employed as an eco-friendly precursor for synthesizing a novel poly(urethane-urea)- based hybrid coating. The synthesis process involved the utilization of a coconut oil-based polyol blend, triethanolamine (TEA) as an amine source, and hexamethylene diisocyanate (HDI). The resulting hybrid coating on carbon steel demonstrated remarkable anticorrosion performance in a 3.5 wt. % NaCl solution, owing to the intrinsic hydrophobic characteristics of coconut oil and polyurea. Significant corrosion rate reduction was observed with increasing amine content, accompanied by an enhancement in mechanical properties. Notably, an amine loading of 4% consistently exhibited superior corrosion resistance and mechanical performance in the hybrid coating. Chemical structural analysis revealed a hydrogen-bonding network in polyurea coatings, reducing porosity, enhancing barrier properties, and improving mechanical characteristics, highlighting its potential for sustainable corrosion protection.

Amine-impregnated cellulose aerogels prepared from old corrugated containers: Microstructure characterization and CO2 capture performance

Here, five different amines (MEA, DETA, TEPA, PEI, and PEPA) were immobilized onto a mesoporous cellulose aerogels (CAs) support prepared from old corrugated containers (OCCs) using the impregnation method, and the thermal stabilities, pore structures, and CO2 adsorption capacities of the resulting amine loaded materials were investigated. The results showed that the thermal stabilities and pore textures of the materials decreased relative to the unmodified CAs support. Additionally, the addition of high molecular weight amines improved the thermal stability of the resulting materials, in the order of PEI>PEPA>TEPA>DETA>MEA. The adsorption capacities of the five Amine40@CAs materials tested ranged from 111.76 to 62.48 mg.g−1 and were in the order of DETA>PEI>MEA>TEPA>PEPA. Considering both thermal stability and CO2 adsorption capacity, PEI is the most suitable for physical immobilization in the CAs support. Consequently, the sample loaded with 30 % PEI exhibits a maximum CO2 capture capacity of 136.84 mg.g−1 material. However, a loading above 30 % results in pore blockage due to amine infiltration into the pore structure, leading to a decrease in the specific surface area and hence the CO2 adsorption capacity. This indicates that there is a balance to be struck between amine loading and CO2 uptake in the solid amine adsorbents using the physical impregnation method, and it is necessary to choose an appropriate method for improving the pore structure in order to maximize the amine loading and thus enhance the CO2 capture capacity.

Amine/vermiculite composite aerogels fabricated by polyethyleneimine-induced vermiculite nanosheet gelation for efficient direct air capture

Direct air capture (DAC), being able to remove the accumulated CO2 in atmosphere and CO2 carbon emission from discrete sources, is a promising technology for mitigating the global greenhouse effect and achieving carbon neutrality. However, achieving high-capacity, low-cost DAC of CO2 through simple methods remains a significant challenge. In this study, a simple, cost-effective, and environmentally friendly method for fabricating amine/vermiculite composite aerogels is proposed for capturing CO2 from ambient air. Natural two-dimensional material, vermiculite nanosheets with exposed surface and intrinsic negative charge, was utilized as the the building blocks for fabricating aerogel as solid amine adsorbents, via the fast gelatin between vermiculite and amine, significantly reducing the cost of adsorbent preparation while achieving promising CO2 capture capability. The effects of amine loading, amine molecular weight, and porosity on CO2 capture capacity and amine efficiency were investigated. It is found that the amine with larger molecular weights endows more stable amine anchoring in the composite aerogel, the aerogels using amine with higher molecular weights demonstrated higher residual amine ratios under vacuum conditions during the aerogel adsorbent synthesis, consequently enhancing the CO2 capture capacity of the adsorbents. By optimizing synthesis strategy and the amine loading of the composite aerogels, the highest CO2 capture capacity (0.72 mmol/g) and amine efficiency (0.29) were achieved. The monolithic structure of the aerogels ensures low pressure drop of 0.35 hPa during gas flow-through, enhancing their integration and applicability in adsorption devices. The vermiculite-based adsorbents exhibit unique advantages in practical DAC processes, including lower cost, higher amine efficiency, and stable cyclic performance. These findings hold significant promise for the application and advancement of DAC technologies.

Amine-impregnated as-synthesized silicas for CO2 capture: Experimental study and mechanism analysis

Porous silicas have been extensively investigated as amine carriers for the production of CO2 adsorbents, while few studies demonstrated that as-synthesized silicas (without template removal) can also serve as good amine carriers for efficient CO2 capture. This raises a fundamental question of whether the time-consuming and energy-intensive process of removing the template from as-synthesized silicas is still necessary. More importantly, a reasonable mechanism is quite needed to explain the as-synthesized silicas as effective amine carriers. To this end, in this study, four types of as-synthesized silicas were compared together with their corresponding porous silicas as amine carriers for CO2 capture. Experimental results show that as-synthesized silicas exhibit comparable or even better performance at medium amine loadings (50 ∼ 60 wt%), including larger CO2 adsorption capacities and better cyclic stability, while porous silicas predominate at high amine loadings (70 wt%). Molecular simulation results indicate that the amine species are located in the interparticle cavities in the silicas rather than in the structural pores. This work provides important guidance for the future design of practical solid-amine CO2 adsorbents.

Prediction of CO2 absorbing performance of amine aqueous solution using random forest models

Designing an amine(s) solution for the chemical absorption of CO2 for carbon capture, utilization and storage is a significant challenge. To accelerate the development of high-performance amine solutions, a method for predicting the CO2 loading of amine(s) solution is studied. Available literature data are curated (45 amines, 3151 data points), and random forest regression is conducted using the data with descriptors calculated using HSPiP or RDkit software. The CO2 loadings of single amine aqueous solutions are regressed with high accuracy (R2 = 0.943, RMSE = 0.072–0.073 for the validation data). Feature importance analysis suggests that the partial charge of atoms in the amine is an important descriptor, as well as process parameters such as CO2 partial pressure and temperature. Based on the analysis, a simpler descriptor list is developed with temperature, CO2 partial pressure, and partial charges of N atoms calculated by density functional theory. CO2 loading of a single amine solution is regressed with an accuracy comparable to that of the above models (R2 = 0.931, RMSE = 0.079) with only 5 descriptors. Moreover, data including both single and blended amine solutions are regressed with high accuracy (R2 = 0.944, RMSE = 0.073) with only 8 descriptors. The generalization performances of the models are evaluated using the leave-one-group-out procedure. Although some outliers exist, the overall trend of almost all amines can be predicted using the procedure in this study.

Utilizing silica fume and synthetically produced mesoporous silicas for simulated flue gas CO2 adsorption

ABSTRACT Carbon capture and storage (CCS) is crucial in mitigating greenhouse gas emissions. Solid adsorbents, notable for their reusability and corrosion resistance, are gaining attention in CO2 gas separation. This study uses Silica fume as an adsorbent and silica source for SiO2 and MCM-41 silica-based adsorbents. Silica was extracted via an alkaline dissolution method, and adsorbents were synthesized using a CO2-induced precipitation method, chosen for its shorter synthesis time and CO2 utilization. The effects of pore volume, average pore diameter, and specific surface area on amine loading and CO2 adsorption capacity were investigated using CTAB surfactant in SiO2 synthesis, resulting in MCM-41. The synthesized adsorbents were modified with TEPA and DEA amines due to their high affinity for CO2. After determining optimal amine loading, the impact of combining TEPA with DEA was examined. The highest CO2 adsorption capacity under simulated flue gas conditions (15% volume CO2 and 85% volume N2) was 198 milligrams per gram of adsorbent for the SiO2 adsorbent functionalized with 50% by weight amine (28% TEPA and 22% DEA). Variations in CO2 adsorption over time, the influence of adsorbent quantity on adsorption capacity, the affinity of the adsorbent for N2 adsorption, and the adsorption–desorption cycle were investigated. The 28%TEPA-22%DEA-SiO2 adsorbent emerged as the optimal choice due to its large total volume and average pore diameter, absence of a template in its structure, excellent performance in CO2 adsorption, lack of affinity for N2, and robust adsorption–desorption stability.

Synergistic enhancement of CO2 capture via amine decorated hierarchical MIL-101(Cr)/SBA-15 composites

Synthesis of amine incorporated hierarchical metal organic framework (MOF) MIL-101(Cr)/SBA-15, meso/micro-porous composites, with tailored properties for CO2 capture is reported. The synthesized composites were characterized in terms of their crystallinity, morphology, functional groups, and textural properties. Isothermal adsorption of CO2 from concentrated sites as well as ambient conditions were evaluated by gravimetric and volumetric measurements. The optimized composite i.e., MIL-101(Cr)/SBA-15/PEI-25 showed improved pseudo-equilibrium adsorption capacity of 3.2 mmol/g at 303 K and 1 bar, compared to nascent SBA-15 (0.8 mmol/g) and the MOF, i.e., MIL-101(Cr) (1.3 mmol/g). Such adsorption performance can be attributed to the basic sites of the impregnated polyethyleneimine (PEI), unsaturated Cr(III) metal sites, and the hierarchical pore structure of the composite which imparts chemical as well physical adsorption forces towards CO2 uptake. Interestingly, lower amine loading of 25 wt% in the composite resulted in facile CO2 desorption at much lower temperature of 65 °C. This guaranteed energy-efficiency and good reusability of the composite, after ten cycles, are evident from their structural and morphological studies.

Mild preparation of structured solid amine adsorbent pellets with the assistance of alginate for efficient and stable CO2 adsorption

The industrialization of solid amine adsorbents requires the molding of the adsorbents, and the blockage or collapse of the pore structure caused by the molding process will inevitably affect the CO2 adsorption performance. Herein, the structured solid amine adsorbent pellets (SA-T/M) were fabricated based on the crosslinking of alginate and Ca2+ under mild conditions. The pelletized SA-T/M well preserved the pore structure of the original support, with only a 26.8 % diminution in specific surface area, which profited to a more uniform loading and dispersion of amine. Benefitting from the influence of pore structure on amine dispersion, SA-T/M achieved a pretty CO2 adsorption capacity of 2.49 mmol g−1. The hydroxyl group of alginates can form hydrogen bonds with the amines, which greatly improved the amine stability of the adsorbent and enabled SA-T/M to exhibit excellent cyclic stability. After 30 adsorption-desorption cycles, the adsorption capacity of SA-T/M merely decreased by 15.6 %. Considering the adsorption capacity and stability of structured adsorbents, the molding strategy with the assistance of alginate provides a potential path for the industrial application of solid amine adsorbent molding technique.

Understanding the effect of density functional choice and van der Waals treatment on predicting the binding configuration, loading, and stability of amine-grafted metal organic frameworks.

Metal organic frameworks (MOFs) are crystalline, three-dimensional structures with high surface areas and tunable porosities. Made from metal nodes connected by organic linkers, the exact properties of a given MOF are determined by node and linker choice. MOFs hold promise for numerous applications, including gas capture and storage. M2(4,4'-dioxidobiphenyl-3,3'-dicarboxylate)-henceforth simply M2(dobpdc), with M = Mg, Mn, Fe, Co, Ni, Cu, or Zn-is regarded as one of the most promising structures for CO2 capture applications. Further modification of the MOF with diamines or tetramines can significantly boost gas species selectivity, a necessity for the ultra-dilute CO2 concentrations in the direct-air capture of CO2. There are countless potential diamines and tetramines, paving the way for a vast number of potential sorbents to be probed for CO2 adsorption properties. The number of amines and their configuration in the MOF pore are key drivers of CO2 adsorption capacity and kinetics, and so a validation of computational prediction of these quantities is required to suitably use computational methods in the discovery and screening of amine-functionalized sorbents. In this work, we study the predictive accuracy of density functional theory and related calculations on amine loading and configuration for one diamine and two tetramines. In particular, we explore the Perdew-Burke-Ernzerhof (PBE) functional and its formulation for solids (PBEsol) with and without the Grimme-D2 and Grimme-D3 pairwise corrections (PBE+D2/3 and PBEsol+D2/3), two revised PBE functionals with the Grimme-D2 and Grimme-D3 pairwise corrections (RPBE+D2/3 and revPBE+D2/3), and the nonlocal van der Waals correlation (vdW-DF2) functional. We also investigate a universal graph deep learning interatomic potential's (M3GNet) predictive accuracy for loading and configuration. These results allow us to identify a useful screening procedure for configuration prediction that has a coarse component for quick evaluation and a higher accuracy component for detailed analysis. Our general observation is that the neural network-based potential can be used as a high-level and rapid screening tool, whereas PBEsol+D3 gives a completely qualitatively predictive picture across all systems studied, and can thus be used for high accuracy motif predictions. We close by briefly exploring the predictions of relative thermal stability for the different functionals and dispersion corrections.

A general Energy-Efficient strategy for optimizing CO2 Capture: Designing and harnessing the rapid adsorption kinetics of Amine-Impregnated adsorbents

This study aims to optimize the performance of amine-impregnated CO2 adsorbents for both direct air capture (DAC) and point source CO2 capture (PSC) applications. The main objective of this study is to investigate the relationship between the weight fraction of amine loading and the efficiency of CO2 uptake on the designated support, aiming to find a straightforward method to design effective amine support materials. To this end, a composite material denoted as PEI/CNT@ZIF-8 has been developed. This composite is comprised of polyethylenimine (PEI), multi-walled carbon nanotubes (CNTs), and zeolitic imidazolate frameworks (ZIF-8). CNTs offer several advantages for enhancing CO2 uptake, including rearranging the ZIF-8 particles to facilitate PEI loading, creating strong electrostatic interaction for amine anchoring, and establishing CO2 diffusion channels to improve CO2 capture kinetics. In DAC scenarios, with a CO2 concentration of 400 ppm balanced with N2, the 25.0 wt% PEI/CNT(1)@ZIF-8(5) demonstrates superior CO2 uptake, achieving 4.08 mmol g−1 within a one-hour interval by harnessing the rapid kinetic region and exhibiting a low desorption energy of 55.8 kJ mol−1 for releasing CO2. In PSC scenarios, with a CO2 concentration of 15 vol% under both dry and wet conditions, the 37.5 wt% PEI/CNT(1)@ZIF-8(5) exhibits excellent CO2 uptake of 2.21 and 2.58 mmol g−1, respectively, at 50 ℃. The findings suggest that adjusting the balance between CO2 uptake and adsorption kinetics by considering the amine weight fraction can optimize the performance of solid amine CO2 adsorbents across diverse operational conditions. Furthermore, rather than relying on a single support material, this study reveals the potential of combining CNTs with materials such as SiO2 nanoparticles, Al2O3, or metal–organic frameworks (MOFs) to enhance CO2 capture performance. This approach holds promise as an effective and straightforward strategy.

Minimizing usage of silane coupling agent for amine-grafted mesoporous silica CO2 adsorbent

Amine-grafted adsorbents are promising CO2 adsorbents; however, the excessive addition of an amino silane coupling agent during their synthesis increases their production cost. Thus, using low amounts of silane, we synthesized 3-aminopropyltrimethoxysilane (APTMS)-grafted SBA-15 mesoporous silica and evaluated its CO2 adsorption performance. APTMS-grafted SBA-15 samples were prepared using either impregnation or heating–filtration method (grafting). The obtained samples were characterized by X-ray diffraction spectroscopy, transmission electron microscopy, N2 adsorption/desorption, scanning electron microscopy, magic-angle spinning nuclear magnetic resonance, and elemental analysis. The results revealed that the micropores of SBA-15 were preferentially blocked, and APTMS increasingly occupied the mesopores with increasing amine loading. The CO2-adsorption performance of the adsorbents was measured by thermogravimetric analysis under dry conditions. Both synthesis methods achieved high amine immobilization efficiency (78.3–92.2%), as estimated from the amount of silane coupling agents used in the synthesis and that immobilized on the support. The adsorbents prepared by the two methods adsorbed similar amounts of CO2 of approximately 0.5 mmol g− 1 in 400 ppm CO2 and ~ 1.0 mmol g− 1 in 5 vol% CO2. The adsorption amounts attained in this study are comparable to those of previously reported silane-coupling-agent-modified adsorbents that were prepared with more silane. In contrast, the adsorption rate of the samples was affected by the synthesis method, even with similar amine loadings. Nonetheless, the results revealed that even with a low amount of the silane coupling agent, high-performance amine-grafted CO2 adsorbents could be synthesized.

Experimental testing and mechanism investigation of amine-functionalized layered vermiculite for CO2 capture

Solid amine adsorbents have attracted significant attention due to their low energy consumption, high selectivity, and environmental friendliness, positioning them as the most promising technology for CO2 capture. However, current adsorbent carrier materials commonly encounter challenges such as expensive costs and inadequate stability. In this study, acid-activated expanded vermiculite carrier (AEV) with a large pore volume and hierarchical pore structure was prepared. Subsequently, a series of functionalized polyethyleneimine (PEI) adsorbents were synthesized and employed in CO2 capture experiments to investigate the impact of PEI loading and temperature on adsorption characteristics. The results showed that the acid-modified expanded vermiculite with a large pore volume structure significantly increased amine loading, while the layered structure network promoted amine dispersion. Under the conditions of 50 wt% PEI loading, the CO2 capture capacity of AEV reached 3.29 mmol/L at 75 ℃. Furthermore, density functional theory was utilized to calculate the adsorption energy and Gibbs free energy change of CO2 and polyethyleneimine molecules. The HOMO and LUMO distributions of CO2 molecules with different polyethyleneimine chains were determined using frontier orbital theory, combined with infrared spectroscopy results confirming the conversion of CO2 into carbamate. Additionally, AEV-PEI50 adsorbent exhibited good stability during 8 cycles of the adsorption process. The obtained results demonstrate that the utilization of layered mesoporous scaffolds offers notable benefits in terms of efficient CO2 capture.

Use of Ball Drop Casting and Surface Modification for the Development of Amine-Functionalized Silica Aerogel Globules for Dynamic and Efficient Direct Air Capture.

Amine-functionalized silica aerogel globules (AFSAGs) were first synthesized via a simple ball drop casting method followed by amine grafting. The effect of grafting time on the structure and CO2 adsorption performance of the AFSAGs was investigated. The CO2 adsorption performance was comprehensively studied by breakthrough curves, adsorption capacity and rates, surface amine loading and density, amine efficiency, adsorption halftime, and cyclic stability. The results demonstrate that prolonging the grafting time does not lead to a significant increase in surface amine content owing to pore space blockage by superabundant amine groups. The CO2 adsorption performance shows obvious dependence on surface amine density, determined by both the surface amine content and specific surface area, and working temperature. AFSAGs with a grafting time of 24 h (AFSAG24) with a moderate surface amine density have optimal CO2 adsorption capacities, which are 1.78 and 2.14 mmol/g at 25 °C with dry and humid 400 ppm CO2, respectively. The amine efficiency of AFSAG24 with low CO2 concentrations, 0.38-0.63 with dry 400 ppm-1% CO2, is the highest among the reported amine-functionalized adsorbents. After estimation with different diffusion models, the CO2 adsorption process of AFSAG24 is governed by film diffusion and intraparticle diffusion. In the range of 1-4 mm, the ball size does not affect the CO2 adsorption capacity of AFSAG24 obviously. AFSAG24 offers significant advantages for practical direct air capture compared with its state-of-the-art counterparts, such as high dynamic adsorption capacity and amine efficiency, excellent stability, and outstanding adaptation to the environment.

Composite Molecular Sieve ZSM-5/MCM-48-Based Impregnation Modification for Efficient Adsorption of CO2

Micro/mesoporous materials are low-cost functional materials with the potential for CO2 adsorption. Modifying micro/mesoporous materials is significant for enhancing CO2 adsorption and their high-value utilization. Herein, the micro/mesoporous material of composite molecular sieve ZSM-5/MCM-48 (ZM) was synthesized by a two-step crystallization method using cetyltrimethylammonium bromide as a template, tetraethyl orthosilicate as a silicon source and ZSM-5 seed as part of silicon aluminum source. Tetraethylenepentamine (TEPA) and polyethyleneimine (PEI) were used as impregnation modifiers to modify ZM with amine groups. The results showed that with the increase of amine loadings, both ZM-T60 (Impregnated with TEPA) and ZM-P60 (Impregnated with PEI) functionalized adsorbents exhibited the best adsorption capacities of [Formula: see text] and [Formula: see text] at 60, respectively, when the loading of ZM sample was 60%. The adsorption kinetic analysis showed that the adsorption of CO2 by ZM-T60 and ZM-P60 was a chemisorption-dominated process accompanied by physical adsorption. After 10 adsorption/desorption cycles, the CO2 adsorption capacity of ZM-T60 and ZM-P60 decreased by 8.7% and 2.6%, respectively. This work demonstrates that impregnation modification of the composite molecular sieve to achieve efficient CO2 adsorption has practical application significance.

Amine-functionalized porous silica production via ex- and in-situ method using silicate precursors as a selective adsorbent for CO2 capture applications

A comparison of the amine-modified silica particle’s characteristics via ex- and in-situ routes and their application as a CO2 gas adsorbent is reported. Modifying silica particles via ex-situ involves two separate steps: forming porous silica particles with sodium lauryl sulfate (SLS) as a template and impregnation using ultrasound assistance. In contrast to ex-situ modification, in-situ modification of silica particles is carried out in one step by mixing directly between the silica source and the modifying agent. Controlling the characteristics of modified silica particles via in-situ is carried out by adding an SLS template removed simultaneously with particle formation to increase the surface area and porosity. Increasing the SLS template concentration shows a linear relationship between increasing particle surface area and amine loading. However, two different modification routes exert a direct influence on aminopropyl distribution. Silanization via in-situ which involves a simultaneous condensation reaction produces a higher amine loading reaching 1.2845 mmol/g of silica than via ex-situ which is only 0.9610 mmol/g of silica. The amount of aminopropyl that can be grafted on the silica surface shows a linear relationship to the quantity of CO2 gas adsorption capacity. Amine-modified silica particles obtained the highest adsorption capability via the in-situ route with an SLS 3 CMC template of 2.32 mmol/g silica at an operating pressure of 6 bar.

Physicochemical synergistic adsorption of CO2 by PEI‐impregnated hierarchical porous polymers

AbstractAmine‐functionalized porous polymers have been considered as a prominent chemical adsorption material for carbon capture and storage (CCS) process, because of their large adsorption capacity and high selectivity. By comparison, the low energy‐consumption for desorption and high recyclability are the advantages of the physical adsorption approach. In this work, an amine‐functionalized hierarchical porous polymer was prepared by HIPE (high internal phase emulsions) template and amine impregnation strategy, and applied as CO2 adsorbent to realize chemical adsorption and physical adsorption simultaneously. First, a hierarchical porous matrix of poly(styrene‐glycidyl methacrylate) was prepared by the HIPE method. The formed meso/micropores in the typical porous polymer matrix could attract CO2 molecules, where the physical adsorption was achieved. Subsequently, PEI (polyethyleneimine) was impregnated into the porous polymer with abundant macropores, and the numerous of amino groups provided the reaction sites, where the chemical adsorption was achieved. As a result, an effective CO2 adsorption material was obtained via controlling the porous structure by changing the volume fraction of dispersive phase, impregnation condition and amine loading. Aided by the chemical adsorption of amino groups, the CO2 adsorption capacity of the obtained adsorbent reached 3.029 mmol/g. Moreover, the CO2 adsorption thermodynamics confirmed the physicochemical synergistic adsorption, and then the Qst reduced to 31–42 kJ/mol and a good cyclic stability was obtained. As conclusion, the porous adsorbent showed a good industrial application prospect. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Thickness dependent CO2 adsorption of poly(ethyleneimine) thin films for direct air capture

Mesoporous silica impregnated with polyethyleneimine (PEI) has been shown to be a suitable material for the direct air capture (DAC) of CO2. Factors such as CO2 concentration, temperature, and amine loading impact overall capture capacity and amine efficiency by altering diffusional resistance and reaction kinetics. When studied in the impregnated 3-dimensional sorbent material, internal diffusion impacts the evaluation of the reaction kinetics at the air/amine interface. In this work, we designed a novel tandem quartz crystal microbalance with dissipation (QCM-D) and polarization modulation infrared reflective absorption spectroscopy (PM-IRRAS) instrument. CO2 adsorption kinetics of the PEI-based amine layer in a 2-dimensional geometry were studied at a variety of film thicknesses (10 nm to 100 nm), temperatures (25 °C to 80 °C), and CO2 concentrations (5 % and 0.04 % by mole fraction). Total CO2 capture capacity increased with film thickness but decreased amine efficiency, as additional diffusional resistance for thicker films limits access to available amine sites. The capture capacity of thick films (>50 nm) is shown to be limited by amine availability, while capture of thin films (<50 nm) is limited by CO2 availability. A 50 nm PEI film was shown to be optimal for capture of 0.04 % (400 ppm) CO2. The adsorption profiles for these conditions were fitted to pseudo-first order and Avrami fractional order models. The reaction process switches between a diffusion limited reaction to a kinetic limited reaction at 80 °C when using 5 % CO2 and 55 °C when using 0.04 % CO2. These results offer accurate analysis of adsorption of CO2 at the air/amine interface of PEI films which can be used for the design of future sorbent materials.

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.