Low-pressure CO2 Research Articles

Guanidine-functionalized basic binuclear poly(ionic liquid)s for low partial pressure CO2 fixation into cyclic carbonate

The direct conversion of low partial pressure (10–15 %) from industrial waste gas into high value-added chemicals provides a favorable solution to global climate change. However, developing high-efficient catalysts for the conversion of low partial pressure CO2 under mild conditions is still a major challenge. Here, guanidine-functionalized basic binuclear poly(ionic liquid)s (P-DBTMGH) were prepared by free radical copolymerization. With the introduction of guanidine ionic liquids into the framework of GB-PILs, the alkalinity in the structure was improved, and thus enhancing CO2 surface adsorption and activation ability. Meanwhile, bromide containing binuclear sites help to increase the ion density of bromide and promote the occurrence of ring opening. Using epichlorohydrin as a probe substrate, P-DBTMGH could efficiently catalyze the cycloaddition reaction of the simulated flue gas (15 vol% CO2 + 85 vol% N2) without any co-catalyst or solvent, and chloropropene carbonate (CPC) with a selectivity and yield of 99 % and 96 % was obtained, which was better than or equivalent to the results reported previously. Moreover, the theoretical studies deeply understood the synergetic effect of guanidine basic sites and bromide containing binuclear sites on CO2 activation and ring-opening of epoxides, which provides a better choice for high-value utilization of low partial pressure CO2 from flue gas.

DESAIN DAN PEMBUATAN MESIN EKSTRAKSI SUPERKRITIS BERBASIS CO2 CAIR UNTUK MENGEKSTRAKSI SENYAWA BIOAKTIF

Bioactive compounds in animal and plant cells have many benefits for human health, such as antioxidants, antibacterial, anti-inflammatory, and anticancer. Extraction and separation of bioactive compounds from other compounds is an important step, and commonly, conventional methods are used, but these methods have disadvantages, like producing unwanted compounds. Alternative methods can be conducted using supercritical fluid extraction, but this equipment is expensive and has a small capacity. So, this study aims to produce functional and structural designs and manufacture supercritical fluid extraction machines using carbon dioxide solvents (CO2) operating with a semi-continuous system. This research succeeded in designing and manufacturing a supercritical fluid extraction machine using carbon dioxide (CO2) solvent that operates in a semi-continuous system for the extraction of bioactive compounds, with main components including cover frames, supercritical extractor chamber, low and high-pressure CO2 tubes, compressors and boosters, pipelines, direct valves, manometers, heating, cooler, and expanders, result from reservoirs and automatic control. Moreover, the preliminary simulation test studies revealed that the supercritical extractor chamber could withstand an absolute pressure of 1000 bar, a temperature of 300°C, and a work capacity of 1 L. It indicated that the supercritical CO2 fluid extractor system was performing well for the conditioning of the extractor chamber, which is generated using a booster and controlled by a one-way valve. Then, the extract is transferred to the separation chamber to separate the CO2 gas. Then, CO2 gas is returned to the low-pressure CO2 tubes for recycling and reuse for the following process.

A comprehensive study on the effect of rock corrosion and CO2 on oil-water interfacial tension during CO2 injection in heavy oil reservoirs

This study is focused on addressing issues related to the interaction mechanism between reservoir rocks and fluids during CO2 injection in heavy oil reservoirs. The results indicate that the carbonated water formed after high-pressure CO2 injection is causing corrosion in the core structure. Furthermore, the average corrosion rate increases from 0.358% as pressure increases from 8 MPa to 16 MPa to 0.742%. The core slices exhibit corrosion pits and cracks on their surface, as well as surface particles flaking and dissolving. The dynamic IFT between decyl trimethyl ammonium bromide solution and crude oil exhibited slower stabilization and less change without CO2 injection. However, with increasing pressure post CO2 injection, the dynamic IFT decreased at a more rapid rate. Furthermore, positive correlation between equilibrium IFT and temperature was observed with low-pressure CO2. In contrast, the surfactant played a more dominant role in reducing IFT with high-pressure CO2. The findings of this study can help for better understanding of the mechanism of microscopic action on reservoir rock and oil-water interface after CO2 injection, and offer theoretical basis and reference for CO2 injection in heavy oil reservoirs to enhance the recovery rate.

One-pot growth of metal-organic frameworks on polymers for catalytic performance enhancement in the CO2 cycloaddition to epoxides

A novel approach is reported to prepare 3D-printed polymers that incorporate metal-organic frameworks (MOFs) through a one-pot growth process, involving covalent grafting and growth onto 3D polymeric surfaces. The resulting hybrid materials were subjected to comprehensive characterization using techniques such as SEM, XRD, FTIR, Raman, and XPS. The findings demonstrated an excellent dispersion of the inorganic units on the polymer matrix while preserving their metal-organic structure. The hybrid materials exhibited the presence of Lewis acid and basic groups within the MOF. The catalytic performance of these hybrid materials was evaluated in the mild cycloaddition reaction of carbon dioxide (CO2) to epoxides. Notably, the polymers incorporating UiO-67 MOFs displayed remarkable activity, even at low CO2 pressures and in the absence of auxiliary co-catalysts or additives. The catalytic activity of these hybrid materials exhibited a significant improvement, up to two orders of magnitude higher than analogous bulk MOFs. This observation highlights the superior performance of the 3D-printed polymer/MOF hybrids in this catalytic transformation.

Breaking barriers: Unleashing CO2 selectivity with ultrathin poly(1,3-dioxolane) composite membranes produced by continuous assembly of polymers

Carbon dioxide (CO2) emissions have continued to rise with the sustained reliance on fossil fuels. One leading solution to capturing CO2 emissions is ultrathin film composite (UTFC) membranes due to their cost-efficiency and relatively low environmental impact. On-going efforts to overcome the challenges of practical membrane technology have included increased gas selectivity and robustness toward the low partial pressure of CO2 emitted from coal-fired power stations. Poly(1,3-dioxolane) (PDXL) has been discovered to have exceptional CO2/N2 selectivity outperforming similar high-polar polymers including poly(ethylene oxide) (PEO), PolyActive™, and Pebax®. However, designing as a composite membrane with PDXL has never been accomplished due to a vital challenge of poor interlayer adhesion, and this has restricted its further advancements. The surface-confined Continuous Assembly of Polymers (CAP) technology can be used to overcome the issue of poor interlayer adhesion; however this strategy needs to be modified to ensure all layers are covalently linked. In this study, we synthesized crosslinkable poly(1,3-dioxolane) dimethacrylate (PDXLDMA) and fabricated UTFC membranes via a revised CAP process. The resulting PDXL-based UTFC membrane demonstrated the highest CO2/N2 selectivity (71.3) ever achieved under dry conditions, while maintaining a gas permeance of above 1000 GPU. The modified CAP process preserved PDXL's inherent properties in the UTFC membrane and demonstrated excellent chemical and mechanical strength through crosslinked layers and covalent bonding of the multilayer structure.

Research on coal matrix pore structure evolution and adsorption behavior characteristics under different thermal stimulation

The technique of thermal stimulation for coalbed methane extraction is considered an important approach for increasing coalbed methane production capacity in the future. This study focuses on the impact of the thermal evolution of pore structure in coal on gas adsorption characteristics. The low-pressure CO2 and N2 physical adsorption data were analyzed using classical thermodynamic methods and density functional theory. The results showed a decrease in pore volume and an increase in average pore size. The fractal dimensions obtained from the Frenkel-Halsey-Hill and Sierpinski fractal models indicate that the micro-scale spatial structure of coal becomes simpler, and the surface becomes smoother. The high-pressure volumetric method was employed to determine the gas adsorption parameters of the coal, and a comparison was made between the calculated gas adsorption parameters based on the micro-pore structure parameters of the coal samples. It was found that the variation pattern of micro-pores in the coal samples correlated highly with the methane adsorption capacity. The decrease in adsorption capacity increases the proportion of free-phase methane, which helps enhance the early-stage methane extraction rate. Improving gas migration pathways avoids the limitation imposed by diffusion in the later stages of coalbed methane extraction.

CeO2 nanorods with bifunctional oxygen vacancies for promoting low-pressure photothermocatalytic CO2 conversion with CH3OH to dimethyl carbonate

The direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol is a kind of highly-attractive route for CO2 conversion to high value-added chemicals. However, a key core problem is how to more effectively activate CO2. Here, we adopt simple template-free hydrothermal method to prepare CeO2 nanorods with oxygen vacancies and introduce light energy into the thermal catalysis system for promoting low-pressure photothermalcatalytic CO2 with methanol direct conversion to DMC. The SEM, HRTEM, XRD, XPS, N2 adsorption-desorption isotherm, CO2-TPD, EPR, Raman, photoluminescence spectra and UV-Vis-IR DRS characterizations are carried out to analyze the microscopical properties including the crystal phases, chemical states, structural features, optical properties for building up the intrinsic relationship with macroscopic performance. Our findings reveal that oxygen vacancies can not only act as photo-produced charge trapping center to prevent the recombination of photoinduced electrons and holes, but also promote CO2 adsorption and activation abilities through Lewis acid-base interaction. Finally, the detailed action mechanism for photothermalcatalytic CO2 conversion with methanol to DMC is proposed. This work should provide new ideas and insights for achieving the CO2 conversion into high value-added long-chain chemicals.

Study on the Influence of Gas Desorption Characteristics of Different Coal Bodies under Hydraulic Permeability Enhancement

To investigate the influence of hydraulic permeability enhancement on the gas desorption and accumulation characteristics of water-bearing coal bodies and deeply implement hydraulic fracturing measures to prevent and control gas disasters in coal seams, isothermal adsorption/desorption tests, low-pressure CO2 adsorption tests, and X-ray diffraction (XRD) tests were performed on anthracite from Anbao Coal Mine in Guizhou and bituminous coal from Huainan Pan’er Coal Mine. The study results showed that the gas desorption by kinds of water-bearing coal samples (anthracite) and bituminous coal (PE) was evidently promoted by stress. After each stress path, differences were observed between coal samples in gas desorption, which, however, presented similar variation trends. The gas desorption of the AB coal samples was greater than that of PE coal samples, and the increment of the limiting gas desorption by the AB coal samples was greater than that by the PE coal samples. The specific surface area of the AB coal samples was larger than that of the PE coal samples, and they both contained hydrophilic minerals and moisture. It was found through field observation that after hydraulic permeability enhancement acted upon water-bearing coal, the desorbed gas passively migrated under the stress action. When the coal body was free from the hydraulic stress action, gas started flowing back. The study results reveal the influence of hydraulic permeability enhancement on the accumulated gas desorption characteristics of water-bearing coal, and will be of theoretical and practical engineering significance for the prevention and control of gas disasters in coal seams using hydraulic measures.

CO2 Adsorption Behavior of Nanosized CHA Zeolites Synthesized in the Presence of Barium or Calcium Cations

AbstractAlkaline‐earth metal cations impact the rate of crystallization and the adsorption of N2 and CO2 on nanosized chabazite zeolites. In this study, either calcium or barium is added to precursor mixtures containing alkali‐metal cations (Na+, K+, Cs+) to prepare chabazite (labeled Ca‐CHA and Ba‐CHA), and are compared to a reference sample (Ref‐CHA) synthesized using exclusively Na+, K+, and Cs+. Partial substitution of the Na+ and the pore‐blocking Cs+ extra‐framework cations is observed for Ca‐CHA depending on the molar ratio of K2O used in the synthesis, while a change to the amount of Na+ cations only is observed for Ba‐CHA. The type of alkaline‐earth metal cation affects the crystallization rate; slower in the presence of Ca2+ (10 h to full crystallinity) and similar rates in the presence of Ba2+ (4 h to full crystallinity); the crystallite size and morphology remained similar. The presence of Ca2+ or Ba2+ extra‐framework cations leads to N2 uptake values of 290 and 169 mmol g−1 (−196 °C, 100 kPa), respectively, while at low CO2 pressure (<1 kPa, 25 °C), the physisorbed CO2 capacity for Ref‐CHA, Ca‐CHA, and Ba‐CHA zeolites is 0.63, 0.66, and 0.59 mmol g−1, respectively. Interestingly, an opposite effect is observed for the amount of chemisorbed CO2 species.

Expulsion of small molecule hydrocarbons and expansion of nanopores effect in tectonically deformed coal evolution

This work aimed to investigate the impact of the evolution of small molecular structures during the deformation of coal on the constraints imposed on nanoscale pores and adsorption behaviors. Both undeformed and tectonically deformed coal (TDC) from the Huaibei mining area in China were collected for analysis. The pyridine was employed for the extraction of small molecules from coal, which was further complemented by Fourier-transform infrared spectroscopy (FTIR) and low-pressure CO2 and N2 adsorption experiments (LP-CO2/N2AD). The study yielded the following results: (1) Intense tectonic stresses facilitate the removal and recombination of small molecular side chains within the basic structural units (BSU) of coal. As deformation occurs, hydroxyl groups, aliphatic hydrocarbons, C=O, C=C, aromatic hydrocarbons, and 'C' structures tend to accumulate, resulting in an enhanced extraction rate. (2) The deformation process of the coal demonstrates a significant pore-expansion effect, with the most substantial increase observed in micropores (surface area increased by over 70 %), followed by mesopores and macropores. This enlargement facilitates the aggregation of small molecules and gas storage. (3) Intense deformation stages involving shear slip, ductile deformation, and maceral fragmentation result in small molecular fractures and an increased number of micropores. The removal and recombination of I, DOC, and CH2/CH3 within BSUs lead to the formation of larger interconnected pores accompanied by the aggregation of hydroxyl groups (OH–), C=O, C=C, aliphatic hydrocarbons, and 'C' structures. (4) The adsorption capacity of residual coal is lower than that of the raw coal before extraction, indicating that small molecular structures contribute to increased adsorption. This likely plays a significant role in the higher gas content observed in structurally deformed coal. The removal of small molecular structures effectively diminishes the adsorption capacity, providing novel perspectives for coalbed methane development and gas extraction in TDC areas.

Zn,N co-doped 3D carbon frameworks constructed by in-situ polymerization-pyrolysis of fluid precursors and their applications in boosting atmospheric CO2 capture and fixation

Through the rational design of 1-butyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide ([Bmim][NTf2])-based multi-component fluid precursors, we present a novel and sustainable strategy for preparing Zn,N co-doped 3D carbon frameworks (Zn@CTDPOP-IL) via in-situ polymerization-pyrolysis of fluid precursors, and explore their applications in atmospheric CO2 capture and clean conversion into cyclic carbonates. The structure and performance of Zn@CTDPOP-IL frameworks were optimized by preparing them under different pyrolysis temperatures and fluid precursor compositions. It was found that the in-situ polymerization of aldehyde and amine components in fluid precursors was crucial for achieving a high specific surface area of carbon frameworks; [Bmim][NTf2] was used as both the solvent and catalyst for in-situ polymerization, as well as the soft template agent during subsequent pyrolysis process. The carbon frameworks also possess multiple Lewis acid/base active sites, exhibiting excellent CO2 adsorption (3340 μmol/g) and conversion performance under mild (40 °C, 0.1 MPa) and solvent-free conditions. The cyclic carbonate yield reaches up to 94 % with a selectivity of 99 %, which is attributed to the superior activation abilities of Lewis acid/base sites towards epoxide and CO2 respectively. The reusability and universality of the catalyst were further investigated, revealing its exceptional structural stability and satisfactory versatility. Finally, we elucidated a proposed cycloaddition mechanism catalyzed by multiple active sites in Zn@CTDPOP-IL. Compared to other reported porous carbon materials, the Zn@CTDPOP-IL frameworks developed herein are simple and environmentally friendly in preparation while exhibiting excellent dual functionality for CO2 adsorption and catalytic conversion, making them highly promising for cleaner treatment of low-pressure waste CO2 resource.

Assessing the environmental impacts of flow and batch syntheses of hypercrosslinked polymers for low-pressure CO2 adsorption

The microporosity of hypercrosslinked polymers (HCPs) renders such materials ideal adsorbents for carbon capture. We recently showed that the CO2/N2 selectivity of HCPs synthesised by internal crosslinking of poly-α,α′-dichloro-p-xylene (p-DCX) in continuous flow synthesis was 850 % higher than those produced in batch reactions. We hypothesised that this could potentially reduce the amount of HCP adsorbents required for delivering the same carbon capture performances, hence improving the environmental impacts of carbon capture. This was evaluated here where we analysed the environmental impacts of using both batch- and flow-synthesised HCPs for adsorbing 40 mg of CO2 with the life-cycle assessment method. We also deployed this approach to evaluate HCPs synthesised via post-crosslinking of polystyrene crosslinked with DCX (p-PS-DCX) and externally crosslinking of polystyrene with formaldehyde dimethyl acetal (FDA) crosslinker (p-PS-FDA). Amongst all HCPs studied in this work, the changes in environmental impact of deploying internally crosslinked HCPs for carbon capture were the worst. This was mostly attributed to its low product yield (7 %), which had a larger influence on the environmental impacts than its adsorption performance as verified by sensitivity analysis. To offset the adverse effects of low product yield, the product yield from flow synthesis of HCPs should ideally reach 25 %. By identifying that product yield is key for promoting environmental sustainability in carbon capture using flow-derived HCPs, future work should focus on optimising continuous flow synthesis to deliver ideal product yield. Hypercrosslinked polymers (HCPs) can be deployed adsorbents for carbon capture. Here we hypothesise that one can use HCPs with better CO2/N2 selectivity to deliver the same carbon capture performances, hence improving the environmental impacts of carbon capture. This was evaluated here using batch- and flow-synthesised HCPsvia internal, external and post-crosslinking strategies with the life cycle assessment method. The environmental impacts of internally crosslinked HCPs were worst due to a low product yield of 7 % Sensitivity analyses indicated that this limitation can be overcome when HCP yield from flow synthesis reach 25 %. Future work should focus on optimising continuous flow synthesis to deliver ideal product yield for minimising environmental impacts of deploying HCPs in carbon capture.

CO2-diffusion controlled mesophase formation in poly(l-lactic acid) and its effect on cold-crystallization

A mild CO2-treatment of a poly(l-lactic acid) PLLA disk with tailored geometry allowed to compare cold crystallization of PLLA containing α"-mesophase, with cold-crystallization of fully amorphous PLLA, both coexisting within a single sample. The use of PLLA disks with 0.5 mm thickness, low CO2 pressure (3.0 MPa) and short treatment time (5 min) at 25 °C, led to only partial diffusion of the gas into the polymer. CO2-induced mesophase developed in surface-near regions of the disks, where CO2 penetrated, whereas the core of the samples was not reached by the gas and remained amorphous. Cold-crystallization of CO2-treated PLLA was analyzed after full desorption of the gas, using different heating rates. Slow heating allowed to identify two cold-crystallization events: low-temperature cold-crystallization in the outer parts of the sample treated with CO2, promoted by prior formation of the α"-mesophase, and high-temperature cold-crystallization, occurring at similar temperatures as in case of non-CO2-treated amorphous PLLA. In both cases, cold-crystallization led to formation of conformationally disordered α′-crystals, as revealed by temperature-resolved wide-angle X-ray scattering. This study confirms that formation of α′-crystals is mainly controlled by the crystallization temperature, also when crystallization is promoted by the prior presence of a mesophase.

Design and synthesis of ZnGlu MOF/SBA-16 nanocomposite, and its performance as an environmentally friendly nanocomposite for solvent-free chemical fixation of CO2 to epoxides for high-yield synthesis of cyclic carbonates

In this study, ZnGlu MOF has been immobilized into hexagonal mesoporous silica SBA-16 to fabricate ZnGlu MOF/SBA-16 hybrid material. The prepared hybrid material was introduced as a sustainable green nanocomposite for CO2 epoxidation to cyclic carbonates under solvent-free conditions at low pressure of CO2 (5 bar). The structure of the obtained nanocomposites is authenticated using various analytical techniques like FT-IR, XRD, SAXRD, CO2-TPD, NH3-TPD, BET, TEM, FE-SEM, EDX, EDX-mapping, and ICP-OES. For making a greener process, ZnGlu MOF/SBA-16 nanocomposite showed remarkable catalytic activity for converting CO2 with diverse epoxides toward five-membered cyclic carbonates prepared without using any toxic metals and reagents. The presence of the mesoporous silica SBA-16 has improved reactants diffusion and molecular accessibility for suitable interactions in Lewis acid centers, which led to MOFs outperforming in the efficient chemical fixation of CO2. Also, the essential role of free amino groups in ZnGlu MOF was shown as base sites and H-bonding groups when suggesting a possible reaction mechanism. This efficient, and convenient catalytic system can be separated by filtration, and its original activity was maintained for five successive cycles under the same reaction conditions. The above nanocomposite, with great potential, can be used to catalyze different chemical reactions for industrial purposes.

Significance of particle size and lithotype on adsorption equilibrium in low pressure N2 and CO2 adsorption of coal: Implications for abnormal phenomenon of adsorption in N2 adsorption of semianthracite

Low pressure N2 and CO2 adsorption was conducted on different lithotypes (vitrain and clarain) with ten different particle sizes ranging from 2.8-2.0 mm to 0.045–0.020 mm of semianthracite (Ro, max = 2.06%) having the abnormal phenomenon of adsorption in N2 adsorption. The effects of particle size and lithotype on adsorption equilibrium in N2/CO2 adsorption and associated pore structure were systematically analyzed to explore the possible reason for the abnormal phenomenon of adsorption and propose the suitable particle size for N2/CO2 adsorption. Decreasing particle size in vitrain and clarain shortens the gas flow paths and removes the constrictions, which facilitates the complete adsorption equilibrium in CO2 adsorption and improves the degree of adsorption equilibrium in N2 adsorption. For different lithotypes with the same particle size, clarain achieves complete adsorption equilibrium easier and quicker in CO2 adsorption and has higher degree of adsorption equilibrium in N2 adsorption than vitrain. The abnormal phenomenon of adsorption in N2 adsorption is resulted from the combined effect of extremely low degree of adsorption equilibrium and elastic deformation of coal. The abnormal phenomenon of adsorption is more pronounced in vitrain than in clarain and gradually disappears with decreasing particle size in both vitrain and clarain. Particle sizes of <0.075 mm (>200 mesh) and <1.0 mm (>18 mesh) are recommended as the suitable particle sizes in N2 adsorption and CO2 adsorption to accurately characterize pore structure for the coals having the abnormal phenomenon of adsorption, respectively.

A new microcellular foaming strategy to develop structure-gradient thermoplastic polyurethane foams with enhanced elasticity

Functionally graded polymer foams are advanced materials that exhibit great potential for applications in energy absorption, electromagnetic interference shielding, and high-elasticity due to the graded cellular structure for mechanical performance and functional properties enhancements. However, producing polymer foams with tailored gradient structures remains a significant challenge. Herein, a new microcellular foaming strategy with two-step adsorptions was developed to prepare thermoplastic polyurethane (TPU) foams with gradient cellular structures. The TPU samples were saturated with low-pressure CO2 in the first sorption stage and partially saturated with high-pressure CO2 in the second sorption stage. By regulating CO2 pressure in the first stage and adsorption duration in the second stage, TPU samples with gradient CO2 concentrations were achieved, thereby leading to structure-gradient TPU foams. Finally, a prospective microcellular-macrocellular gradient foam with a cell size range of 30 μm to 400 μm was successfully prepared. The energy loss coefficient of structure-gradient TPU foam can be reduced by 21.5% compared to that of the foam with uniform cellular structure. Structure-gradient TPU foams show significantly enhanced mechanical performance and elasticity, and the underlying mechanism was clarified. The super-elastic TPU foams with tailored gradient structures hold significant promise for broaden applications requiring lightweight, flexibility, and elasticity.

Volumetric and viscometric properties of aqueous choline chloride + methyldiethanolamine deep eutectic solvents

Amine-based deep eutectic solvents have the advantages of easy preparation, extremely low vapor pressure, stable biodegradation and high CO2 loading, which has become the most potential CO2 absorbent. In this work, the amine-based functionalized DES of choline chloride + methyldiethanolamine with different molar ratios were successfully prepared, and the densities and viscosities of DES aqueous solutions were measured from 303.15 K to 333.15 K. The effects of DES composition, water content and temperature on the excess molar volume, partial molar volume, apparent molar volume, limiting partial molar volume and viscosity deviation were investigated. The hydration and intermolecular interaction in DES solution were analyzed. The critical concentration of water in solution was determined under the premise of maintaining DES hydrogen bond network.

Role of interaction between molding pressure and CO2 pressure in carbonating cement block

To improve the mechanical performance and boost the carbonation reaction, varying molding (casting) pressures (10, 15, and 20 MPa) and CO2 pressures (0.1, 0.25, 0.5, and 1 MPa) were applied to produce cement blocks, which were then subjected to 1 h of carbonation curing and subsequent 28 d of water curing. The results showed that higher CO2 pressure promoted both the hydration and carbonation processes regardless of molding pressure after 1 h of carbonation and thereby densifying the microstructure, which translated into improved compressive strength of the cement block. Cement blocks fabricated with a higher molding pressure showed a negative effect on the carbonation reaction, resulting in a similar strength between the 10 and 20 MPa samples after carbonation for 1 h under the same CO2 pressure. However, a higher molding pressure exerted a positive impact on the subsequent hydration reaction, resulting in a 324.9% increase in the compressive strength of the 20 MPa sample after a further 28 d of water curing. Overall, a 15 MPa molding pressure coupled with a higher CO2 pressure (≥1 MPa) was found to be the optimal regime for carbonation curing. In contrast, a combination of a higher molding pressure (≥20 MPa) with a relatively lower CO2 pressure (≤0.5 MPa) was conducive to the strength gain under further water curing after carbonation.

Ultrasound-promoted metal-free homogenous olefins epoxidation and direct conversion of alkenes to cyclic carbonates using catalytic TAIm[X] (X = WO42-, HSO5-) recyclable ionic liquid under mild conditions

TAIm[WO4] and TAIm[HSO5] ionic liquids were prepared and used as efficient solvent and recyclable catalysts for the mild epoxidation of olefins and the domino preparation of cyclic carbonate from alkenes under ultrasound irradiation. H2O2 was used as an oxidant. The physical properties and structure of the ionic liquids were studied by various analytical methods including FTIR, EDX, viscosity, and density measurements. High to excellent yields were obtained for a wide variety of olefins whether aliphatic or aromatic types for the epoxides as well as the conversion of cyclic and terminal olefins to cyclic carbonates at low CO2(g) pressure (∼1 atm.). Moderate CO2(g) solubility in the ionic liquids was found. Also, excellent epoxide-selectivity was obtained for all olefins. Scalability of the method demonstrated a direct scalability for the promising gram scale epoxidation of olefins with at least efficiency loss. The TAIm[WO4] and TAIm[HSO5] ionic liquids could be recycled from the homogenous mixture by a simple solvent-solvent extraction, and reused for at least several times with insignificant activity loss.

Hydroxybenzoic acid derived porous carbons for low pressure CO2 capture

There is an urgent need to mitigate CO2 emissions released into the atmosphere from coal-fired power plants. 4-Hydroxybenzoic acid (HBA) is a cost-effective small organic molecule (SOM) that has been used in this study as a molecular precursor for CO2-philic and affordable solid sorbent production. Many pore development strategies and comprehensive characterization techniques were employed. It is found that pyrolysis of HBA (H-800) without any additives allows reaching a capacity of 1.09 mmol g−1 at 0.15 bar, 298 K or 0.86 mmol g−1 at 0.15 bar, 313 K, which shows that simple carbonization of appropriate SOM may yield competitive results over well-known carbonization methods. Several carbonization techniques were employed on the SOM, including CO2, ZnCl2, KOH activations, or potassium salt thermolysis, and zinc salt thermolysis. Starting from zinc salt ends up with very low carbon yield (3 wt%) and high meso-macro pore volume, which is in the range of 2.78 cm3 g−1. KOH activation or potassium salt thermolysis results are comparable to the CO2 capture performance of H-800, though higher micropore volumes up to 0.55 cm3 g−1 were achieved. Additionally, CO2 activation resulted in similar CO2 capture capability and micropore volume as in the case of H-800. Finally, it was found that ultramicropores are the effective pore range for low pressure CO2 adsorption (0.15 bar) at 298 K or 313 K.