Enhancement Of CO2 Uptake Research Articles

CO2 Uptake and Stability Enhancement in Vinyltrimethoxysilane-Treated SBA-15 Solid Amine-Based Sorbents.

Silica-supported amine absorbents, including materials produced by tethering aminosilanes or infusion of poly(ethyleneimine), represent a promising class of materials for CO2 capture applications, including direct air and point source capture. Various silica surface treatments and functionalization strategies are explored to enhance stability and CO2 uptake in amine-based solid sorbent systems. Here, the synthesis and characterization of novel vinyltrimethoxysilane-treated Santa Barbara Amorphous-15 (SBA-15) supports and the corresponding enhancement in CO2 uptake compared to various SBA-15-based control supports are presented. The relationship between CO2 diffusion and amine efficiency in these systems is explored using a previously reported kinetic model. The synthesized materials are characterized with CO2 and H2O isotherms, diffuse reflectance infrared Fourier transform spectroscopy, 1H T1-T2 relaxation correlation NMR, and rapid thermal cycling experiments. The novel support materials are shown to enable high amine efficiencies, approaching a fourfold improvement over standard SBA-15-supported amines, while simultaneously exhibiting excellent stability when cycled rapidly under humid conditions. As the poly(ethyleneimine) loadings are held constant across the various samples, enhancements in CO2 uptake are attributed to differences in the way the poly(ethyleneimine) interacts with the support surface.

Amphipathic Solvent-Assisted Synthetic Strategy for Random Lamellae of the Clinoptilolites with Flower-like Morphology and Thinner Nanosheet for Adsorption and Separation of CO2 and CH4.

The random lamellae of the synthetic CP were synthesized with a hydrothermal approach using o-Phenylenediamine (OPD) as a modifier. The decreases in the order degree of the CP synthesized in the presence of the OPD resulted from the loss of long-range order in a certain direction. Subsequently, the ultrasonic treatment and washing were conducive to further facilitate the disordered arrangements of its lamellae. The possible promotion mechanism regarding the nucleation and growth behaviors of the sol-gel particles was proposed. The fractal evolutions of the aluminosilicate species with crystallization time implied that the aluminosilicate species became gradually smooth to rough during the crystallization procedures since the amorphous structures transformed into flower-like morphologies. Their gas adsorption and separation performances indicated that the adsorption capacity of CO2 at 273 K reached up to 2.14 mmol·g-1 at 1 bar, and the selective factor (CO2/CH4) up to 3.4, much higher than that of the CPs synthesized without additive OPD. The breakthrough experiments displayed a longer breakthrough time and enhancement of CO2 uptake, showing better performance for CO2/CH4 separation. The cycling test further highlighted their efficiency for CO2/CH4 separation.

Improving the Separation of CO2/CH4 Using Impregnation of Deep Eutectic Solvents on Porous Carbon

The separation of CO2/CH4 using porous carbon can be increased by the presence of a functional group of nitrogen on the carbon surface. This study explores the potential of porous carbon derived from the palm kernel shell (C-PKS) impregnated with a deep eutectic solvent (DES), which is one of the chemicals containing a nitrogen element. The DES was composed of a quaternary ammonium salt of choline chloride (ChCl) and a hydrogen bond donor of alcohol. Three alcohols of 1-butanol (-ol), ethylene glycol (-diol), and glycerol (-triol) were employed to study the effects of a number of hydroxyl groups in the separation performance. The research steps included (i) the preparation of DES-impregnated porous carbon synthesized from the palm kernel shell (DES/C-PKS), (ii) characterization of the material, and (ii) a separation test of CO2/CH4 with a breakthrough system. Materials were characterized using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDX), N2-sorption analysis, and Fourier transform infrared (FTIR) spectroscopy. SEM images showed a significant morphological difference of pristine carbon and DES/C-PKS. There was a significant decrease in the range of 67–73% of a specific surface area with respect to pristine carbon, having initially 800 m2/g. However, the N element on the carbon surface increased after impregnation treatment, which was shown from the intensity of the FTIR graphs and EDX analysis. Adsorption isotherm revealed that DES/C-PKS could enhance up to 1.6 times the adsorption capacity of CO2 at 1 atm and 30 °C while increasing the selectivity of CO2/CH4 up to 125%. The breakthrough experiment showed that all DES/C-PKS materials displayed a better performance for the separation of CO2/CH4, indicated by a longer breakthrough time and enhancement of CO2 uptake. The best separation performance was achieved by DES/C-PKS using glycerol as a hydrogen bond donor with 15.4 mg/g of CO2 uptake or equivalent to 95% enhancement of the uptake capacity compared to pristine porous carbon. Also, the cycling test revealed that DES/C-PKS can be used repetitively, which further highlights the efficiency of the material for the separation of CO2/CH4.

Structural Dynamism-Actuated Reversible CO2 Adsorption Switch and Postmetalation-Induced Visible Light Cα-H Photocyanation with Rare Size Selectivity in N-Functionalized 3D Covalent Organic Framework.

The impact of dimensionality and flexibility on anticipated properties has prompted major research focus to three-dimensional covalent organic frameworks (3D COFs), where astute functionalization of porous channels for dynamic CO2 adsorption as well as size-exclusive C-H activation under eco-friendly condition are the most intriguing advanced applications. Herein, we report an imine-based, diamondoid COF that embraces one-dimensional porous channels in spite of ninefold interpenetration. A combination of intrinsic microporosity and pore wall decoration with accessible N atoms from linear strut renders this 3D COF display reasonable CO2 affinity with decent selectivity (CO2/N2: 64.2; CO2/CH4: 10.5) alongside worthy multicyclic CO2 uptake-release recurrence. Interestingly, the COF undergoes solvent-assisted alteration to a pore-stretched structure via -C═N- "pedal" motion with a concomitant enhancement in CO2 uptake, where steady reversibility of such structural dynamism instigates unprecedented CO2 adsorption switch up to seven consecutive cycles. Integration of 2,2'-bipyridyl units benefits anchoring of homogeneous catalyst to device first-ever Ru(Bpy)22+ hooked diamondoid COF (Ru-COF), which performs visible-light-triggered oxidative cyanation of tertiary amines at room temperature, using molecular oxygen as a selective oxidant in green solvent H2O. The photocatalyst-engineered COF manifests excellent recyclability and comparable activity to that of homogeneous catalyst. To the best of Ru-COF, atom-economic photocyanation is realized via in situ generated iminium ion, wherein larger-sized substrates exhibit insignificant conversion of α-aminonitriles and validate rarest size selectivity in oxidative Strecker reaction. This study not only demonstrates potential of 3D COF as next-generation dynamic CO2 adsorbent but also sheds light on tailor-made fabrication of smart functional material for promising catalytic applications through an environmentally benign route.

Water Based Synthesis of ZIF-8 Assisted by Hydrogen Bond Acceptors and Enhancement of CO2 Uptake by Solvent Assisted Ligand Exchange

The aim of this work was to synthesize zeolitic imidazolate framework-8 (ZIF-8) by an alternative method and then modify the surface properties for enhancing the CO2 adsorption performance. The ZIF-8 was synthesized by a water based synthesis method using 2-methyl imidazole (2-MeIM) as a hydrogen bond donor and quaternary ammonium salts (QAS) as a hydrogen bond acceptor. The optimal synthesis conditions were investigated by varying (i) the order of precursor mixing during the synthesis process (ii) different QAS (tetrabutyl ammonium bromide (TBAB), tetraethyl ammonium bromide (TEAB) and trimethyl phenyl ammonium bromide (TMPAB)) and (iii) the ratio between 2-MeIM and QAS. The results show that the optimal synthesis condition was using TMPAB as the hydrogen bond acceptor with the ratio between 2-MeIM and TMPAB of 8:2 and in the order of first mixing both hydrogen bond donor and acceptor before adding Zn(NO3)2⋅6H2O solution. TMPAB can provide uniform size distribution with the smallest particle sizes of ZIF-8. This can be explained by the higher hydrogen bond strength between hydrogen bond donor (2-MeIM) and hydrogen bond acceptor (TMPAB) when compared with that of the rest of two QAS. The synthesized ZIF-8 was modified by solvent-assisted ligand exchange methods. The organic linker of ZIF-8 (2-MeIM) was exchanged by 2-aminobenzimidazole (2-NH2bZIM) and 2-phenylimidazole (2-PhIM). The CO2 uptake of modified ZIF-8 was enhanced upon exchanging with 2-NH2bZIM. The increase in CO2 uptake was due to an additional interaction between CO2 and exchanged imidazole linker and an increase in surface properties (higher surface area, pore size and pore volume).

Enhancement of CO2 Uptake and Selectivity in a Metal-Organic Framework by the Incorporation of Thiophene Functionality.

The complex [Zn2(tdc)2dabco] (H2tdc = thiophene-2,5-dicarboxylic acid; dabco = 1,4-diazabicyclooctane) shows a remarkable increase in carbon dioxide (CO2) uptake and CO2/dinitrogen (N2) selectivity compared to the nonthiophene analogue [Zn2(bdc)2dabco] (H2bdc = benzene-1,4-dicarboxylic acid; terephthalic acid). CO2 adsorption at 1 bar for [Zn2(tdc)2dabco] is 67.4 cm3·g–1 (13.2 wt %) at 298 K and 153 cm3·g–1 (30.0 wt %) at 273 K. For [Zn2(bdc)2dabco], the equivalent values are 46 cm3·g–1 (9.0 wt %) and 122 cm3·g–1 (23.9 wt %), respectively. The isosteric heat of adsorption for CO2 in [Zn2(tdc)2dabco] at zero coverage is low (23.65 kJ·mol–1), ensuring facile regeneration of the porous material. Enhancement by the thiophene group on the separation of CO2/N2 gas mixtures has been confirmed by both ideal adsorbate solution theory calculations and dynamic breakthrough experiments. The preferred binding sites of adsorbed CO2 in [Zn2(tdc)2dabco] have been unambiguously determined by in situ single-crystal diffraction studies on CO2-loaded [Zn2(tdc)2dabco], coupled with quantum-chemical calculations. These studies unveil the role of the thiophene moieties in the specific CO2 binding via an induced dipole interaction between CO2 and the sulfur center, confirming that an enhanced CO2 capacity in [Zn2(tdc)2dabco] is achieved without the presence of open metal sites. The experimental data and theoretical insight suggest a viable strategy for improvement of the adsorption properties of already known materials through the incorporation of sulfur-based heterocycles within their porous structures.

Improvement of CO2 uptake of activated carbons by treatment with mineral acids

Three commercial activated carbons (ACs) supplied by Carbon, Norit and Desotec were modified by acid treatments. A significant CO2 capacity improvement of up to 36% was achieved. It was found that higher CO2 uptakes were related to removal of inorganic impurities i.e. mineral matter and increase of the submicropores volume i.e. smaller than 0.8nm. Sorbents were thoroughly characterized in terms of texture and chemical composition. CO2 uptake was determined by BET isotherm measurement carried out at 273K and pressure of up to 0.95 bar. The enhancement of CO2 uptake was observed especially for ACs with the highest initial mineral matter content. It was found that mineral matter in ACs plays the role of a ballast and additionally blocks adsorption places and submicropores volume thus lowers CO2 uptake. On the other hand it was proven that mineral matter may prevent the structure from collapsing and thus can stabilize high SSA. The AC surface oxidation effect on CO2 uptake was determined by comparison of ACs treated with HCl and HNO3. Both acids remove mineral matter content to the same degree, but detailed X-ray photoelectron spectroscopy (XPS) study revealed that in case of HNO3 treatment, AC surface was more oxidized which correlated with higher CO2 uptake. However observed uptake increase was attributed to increase of the submicropores volume.

On the potential use of quarry waste material for CO2 sequestration

The use of solid wastes rich in Ca2+, Mg2+ and Fe2+ for the ex situ sequestration of CO2 could provide an economically and technologically viable option for the reduction of anthropogenic CO2 emissions. Here, we investigate for the first time the potential use of waste materials from mafic rock quarries as a feedstock for the sequestration of CO2 by ex situ mineral carbonation. The experimental procedure was performed on a waste material from a dolerite quarry operating in the Troodos ophiolite (Cyprus). The ball milling process was applied to this quarry waste in order to create nanomaterials with enhanced CO2 adsorption capacity. Through CO2 chemisorption followed by temperature-programmed desorption (CO2-TPD) experiments, the optimum ball milling conditions were found (20h of wet ball milling with 50wt% ethanol as process control agent), leading to an enhancement of the CO2-storage capacity of the waste material by a factor of ∼120. This enhancement of CO2 uptake is closely related to (i) the reduction of particle size to the nanoscale, (ii) the structural disordering of the constituent silicate minerals, and (iii) the presence of augite nanocrystals after ball milling. The experimental results suggest that waste materials from dolerite quarries may indeed be used as feedstock for the ex situ mineralization of CO2. They also strongly demonstrate that ball milling is a very promising technique for optimizing the ex situ carbonation of this waste material; thus the proposed methodology could be a fundamental part of a future carbon sequestration strategy.

Hierarchical Mesoporous Metal-Organic Frameworks for Enhanced CO2 Capture.

Hierarchical porous materials are promising for catalyst, separation and sorption applications. A ligand-assisted etching process is developed for template-free synthesis of hierarchical mesoporous MOFs as single crystals and well-intergrown membranes at 40 °C. At 223 K, the hierarchical porous structures significantly improve the CO2 capture capacity of HKUST-1 by more than 44 % at pressures up to 20 kPa and 13 % at 100 kPa. Even at 323 K, the enhancement of CO2 uptake is above 25 % at pressures up to 20 kPa and 7 % at 100 kPa. The mesoporous structures not only enhance the CO2 uptake capacity but also improve the diffusion and mass transportation of CO2 . Similarly, well-intergrown mesoporous HKUST-1 membranes are synthesized, which hold the potential for film-like porous devices. Mesoporous MOF-5 crystals are also obtained by a similar ligand-assisted etching process. This may provide a facile way to prepare hierarchical porous MOF single crystals and membranes for wide-ranging applications.

Enhanced CO2 capture by biomass-templated Ca(OH)2-based pellets

Biomass-templated Ca(OH)2-based pellets were synthesized for high-temperature post-combustion CO2 capture. Four types of biomass-derived materials were used for sorbent templating: cardboard, maple leaves, date seeds, and white soft wood. After calcination at 850°C in air, composite pellets with leaves exhibited a high pore volume of 0.11cm3/g, compared to that of 0.07cm3/g for pellets without biomass addition. The alteration in porosity was attributed to the release of combustion gases during the combustion of biomass. After 20 capture cycles with no steam, these pellets captured 0.24g CO2/g calcined pellets, compared to 0.18g/g for biomass-free pellets. The highest CO2 uptake was achieved with pellets containing 10% leaves. This enhancement in CO2 uptake allowed the possibility of doubling the binder content, thus improving the mechanical strength of the pellets. The introduction of steam to the carbonation environment resulted in relatively high uptakes of 0.53 and 0.41g/g for the first and 20th cycles, respectively. In general, all composite pellets modified with biomass displayed better performance than their counterpart pellets, indicating the benefits of biomass addition. The dispersed biomass ash also appears to have helped stabilize the morphology of these pellets as well as acting as a doping agent assisting CO2 capture via enhanced diffusion. Considering the fact that such biomass materials are readily available and cheaper than synthetic organic materials by at least an order of magnitude, their utilization should not significantly increase the cost of the templated sorbent.

Ligand Functionalization and Its Effect on CO2 Adsorption in Microporous Metal–Organic Frameworks

We report two new 3D structures, [Zn3(bpdc)3(2,2'-dmbpy)] (DMF)x(H2O)y (1) and [Zn3(bpdc)3(3,3'-dmbpy)]·(DMF)4(H2O)0.5 (2), by methyl functionalization of the pillar ligand in [Zn3(bpdc)3(bpy)] (DMF)4·(H2O) (3) (bpdc=biphenyl-4,4'-dicarboxylic acid; z,z'-dmbpy=z,z'-dimethyl-4,4'-bipyridine; bpy=4,4'-bipyridine). Single-crystal X-ray diffraction analysis indicates that 2 is isostructural to 3, and the power X-ray diffraction (PXRD) study shows a very similar framework of 1 to 2 and 3. Both 1 and 2 are 3D porous structures made of Zn3(COO)6 secondary building units (SBUs) and 2,2'- or 3,3'-dmbpy as pillar ligand. Thermogravimetric analysis (TGA) and PXRD studies reveal high thermal and water stability for both compounds. Gas-adsorption studies show that the reduction of surface area and pore volume by introducing a methyl group to the bpy ligand leads to a decrease in H2 uptake for both compounds. However, CO2 adsorption experiments with 1' (guest-free 1) indicate significant enhancement in CO2 uptake, whereas for 2' (guest-free 2) the adsorbed amount is decreased. These results suggest that there are two opposing and competitive effects brought on by methyl functionalization: the enhancement due to increased isosteric heats of CO2 adsorption (Q(st)), and the detraction due to the reduction of surface area and pore volume. For 1', the enhancement effect dominates, which leads to a significantly higher uptake of CO2 than its parent compound 3' (guest-free 3). For 2', the detraction effect predominates, thereby resulting in reduced CO2 uptake relative to its parent structure 3'. IR and Raman spectroscopic studies also present evidence for strong interaction between CO2 and methyl-functionalized π moieties. Furthermore, all compounds exhibit high separation capability for CO2 over other small gases including CH4, CO, N2, and O2.

Fine-tuning the balance between crystallization and gelation and enhancement of CO2 uptake on functionalized calcium based MOFs and metallogels

The synthesis, structure, gas adsorption and catalytic properties of a new 3D porous, crystalline metal–organic framework (Ca-5TIA-MOF) as well as stable viscoelastic metallogels (Ca-5TIA-Gel) are reported. Remarkably, the preparation of both types of materials can be carried out starting from the same organic ligand (i.e. 5-(1,2,4-triazoleyl)isophthalic acid (5TIA)), divalent metal ion (i.e. Ca(II)) and organic solvent (i.e. DMF). In this particular case, the presence of water in the solvent system favors the formation of a crystalline MOF, whereas a pure organic solvent induces gelation. The characterization of the materials was carried out using a series of techniques including XRD, FT-IR, TGA, TEM, SEM, SAXS and dynamic rheology. Experimental PXRD peaks of both Ca-5TIA-xerogel and Ca-5TIA-MOF matched reasonably well with simulated PXRD, suggesting the presence of, at least, some common structural elements in the 3D networks of both xerogel and crystalline phases. Moreover, the nature of the metal counteranion was found to have a critical influence on the gelation phenomenon. To the best of our knowledge, this report describes unprecedented Ca-based LMW-metallogels, as well as the first porous Ca-based MOF, which shows adsorption capacity for CO2 at 1 atm pressure. Interestingly, Ca-5TIA-xerogel presented 20% higher CO2-uptake than the crystalline Ca-5TIA-MOF at 1 atm and 298 K. Both Ca-5TIA-MOF and Ca-5TIA-Gel also displayed a modest catalytic activity towards the hydrosilylation of benzaldehyde, with slightly better performance for the gel phase material.

Experimental and Computational Study of Functionality Impact on Sodalite–Zeolitic Imidazolate Frameworks for CO2Separation

This study deals with the enhancement of CO2 uptake by ligand functionalization of zeolitic imidazolate framework (ZIF) materials. The ligand dipole moment could be considered as one of the main criteria for CO2 adsorption enhancement. To verify this hypothesis, an experimental–computational study was performed on an isoreticular ZIF series with sodalite (SOD) topology using published structures (ZIF-8, ZIF-90, and ZIF-Cl) as well as hypothetical structures (ZIF-COOH and ZIF-NO2) designated using DFT calculations. An analysis of structural and adsorptive properties was proposed for these materials used to separate CO2 from CH4, CO, or N2 gas. The accuracy of the calculated results was validated by comparison with our own experimental results. An exponential relationship between the ligand dipole moments and the isosteric heat of adsorption of CO2 was highlighted. Modifying the nature of the linker (dipole moment) allows a 5- to 7-fold improvement in CO2 selectivity for CO2/CH4, CO2/N2, and CO2/CO mixtures.

Chemical Engineering Challenges and Investment Opportunities in Sustainable Energy

The chemical and energy industries are transforming as they adjust to the new era of high-priced petroleum and severe global warming. As a result of the transformation, engineering challenges and investment opportunities abound. Rapid evolution and fast growth are expected in cathode and anode materials as well as polymeric electrolytes for vehicular batteries and in high-performance polymer-ceramic composites for wind turbines, fuel-efficient aircraft, and lighter and safer cars. Unique process-engineering opportunities exist in sand-oil, coal, and possibly also shale liquefaction to produce transportation fuel; and also in genetic engineering of photosynthesizing plants and other organisms for their processing into high-performance biodegradable polymers and high-value-added environmentally friendly chemicals. Also, research on the feasibility of mitigation of global warming through enhancement of CO(2) uptake by the southern oceans by fertilization with trace amounts of iron is progressing. Because chemical engineers are uniquely well trained in mathematical modeling of mass transport, flow, and mixing, and also in cost analysis, they are likely to join the oceanographers and marine biologists in this important endeavor.