Journal of CO2 Utilization最新文献

This study investigates the effect of synthesis and operating parameters on the adsorption of CO₂ and N₂ and the CO₂/N₂ selectivity of a hypercrosslinked adsorbent based on waste-expanded polystyrene. Six factors were examined, including synthesis time, crosslinker and catalyst amounts, adsorption temperature and pressure, and CO₂ percentage in the mixture. The response surface methodology (RSM) and ideal adsorbed solution theory (IAST) were employed to design the experiment. After synthesizing 19 adsorbents under different conditions, characterization tests were conducted. Results indicate that the specific surface area and micropore volume initially increase and then decrease with increased synthesis time, crosslinker, and catalyst amounts. The highest specific surface area and micropore volume were 803.84 m²/g and 0.1355 cm³/g, respectively. CO₂/N₂ selectivity and the adsorption of CO₂ and N₂ also increase and decrease with increased synthesis parameters. Furthermore, it was observed that CO₂ adsorption and CO₂/N₂ selectivity increased with an increase in pressure and CO₂ percentage and a decrease in temperature, while N₂ adsorption decreased. The adsorbents were optimized using RSM to maximize CO₂ adsorption and CO₂/N₂ selectivity with a target of 15 % CO₂ in the gas mixture. The optimal synthesis parameters for the hypercrosslinked adsorbent, including synthesis time, crosslinker, and catalyst amounts, were determined to be approximately 13 hours, 30 mmol, and 30 mmol, respectively. Under optimal conditions for flue gas applications (CO₂:N₂/15:85), the adsorbent demonstrated a CO₂/N₂ selectivity of 11.05, making it suitable for flue gas capture.

CuOx/LaCoO₃ systems have been studied for the rWGS reaction under thermal assisted photocatalytic conditions within low temperature range of 180–330 ºC. CuOx species deposited from chemical reduction method over LaCoO₃ homogeneously covered the perovskite surface. The reduction pretreatment before reaction leads to the partial Co reduction and the complete reduction of Cu. A significant improvement on CO production has been attained upon Cu incorporation. In addition, upon UV–vis irradiation the CO production is also enhanced. Best results have been obtained for 5 wt% Cu. The highest synergistic effect was observed for the lowest temperature, for which catalytic contribution is negligible. Thus, a good compromise is attained at 300 ºC for which a CO production of 5.45 mmol/h·g and 92 % selectivity, showing a good synergistic effect between thermo and thermo-photocatalytic activity.

Efficient and affordable adsorbents for CO₂ capture are essential in implementing carbon capture technology to mitigate the negative impact of greenhouse gas emissions. This study focuses on synthesizing new nanoporous adsorbents from industrial waste slag using a simple and cost-effective coprecipitation method. In this method, raw slag was milled for 48 h and used as a benchmark for comparing two newly synthesized adsorbents. Selectivity and pure gas isotherm experiments were conducted for all adsorbents in the 25–65°C temperature range and under harsh industrial conditions of 65°C and 15 % CO₂. This study utilized the response surface methodology (RSM) to optimize the CO₂ adsorption parameters. Specifically, the optimized adsorption conditions were determined for the 15/85 % CO₂/N₂ condition, and the optimal values for pressure and temperature were found to be 5 bar and 45°C, resulting in CO₂/N₂ selectivity of 5.65. The NH₃-slag adsorbent was identified as the superior choice based on its selectivity and maximum adsorption capacity. The maximum adsorption capacity and cyclic efficiency were determined to be 4.15 mmol/g and 98.1 %, respectively, at a temperature, pressure, and composition of 45°C, 5 bar, and 15 % CO₂. Isotherm and thermodynamic models were employed to further investigate the adsorption process. The isotherm results indicated that the adsorption of CO₂ by adsorbents occurred heterogeneously in patch-wise sites. Meanwhile, the thermodynamic parameters showed that the process was exothermic and spontaneous, with ΔH° falling below 20 (kJ/mol), showing physisorption phenomena.

There is a limited number of systematic CO₂ conversion studies that provide a clear understanding of the effect of the active sites of catalysts. Hence, this work examines the catalytic activity of 24 organic salts consisting of chloride, bromide or iodide anions and imidazolium, ammonium, or phosphonium-based cations, in the synthesis of hexylene and styrene carbonates from CO₂, resulting in a diverse range of yields. The findings revealed that high yields depend heavily on catalyst solubility in the reaction medium, but solubility alone does not guarantee reaction success. This finding supports the new hypothesis that catalyst dissociation, reliant on solubility, is a critical factor in defining the catalytic activity. A strong correlation was observed between carbonate yields and the dissociation constants of catalysts, calculated using the COSMO-RS method. This suggests that greater dissociation, reflecting weaker cation-anion interactions, facilitates the anion nucleophilic attack on the epoxide. Also, the relationship between calculated dissociation constant and experimental ionic conductivity was successfully validated. This highlights the significance of organic salt dissociation on catalytic performance and validates the use of computational tools to predict key operational parameters, enhancing the understanding and optimization of CO₂ conversion into cyclic carbonates.

To enhance the CO₂ adsorption of almond shell-derived activated carbon (AC) samples treated with cold oxygen plasma, the samples were impregnated with cholinium-amino acid ionic liquids ([Cho][AA] ILs) using the vacuum-assisted impregnation method. The physicochemical and textural properties of the resulting composites (ILs@AC) were characterized using various techniques, including Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) spectroscopy, and Brunauer-Emmett-Teller (BET) surface area measurement. The CO₂ adsorption performance of the samples was evaluated using a quartz crystal microbalance (QCM) over a temperature range of 288.15–308.15 K and gas pressures up to 1 bar. The IL@AC composite materials exhibited notably improved CO₂ adsorption capacities compared to pristine AC. The CO₂ adsorption isotherms onto the IL@AC composite samples closely conformed to the Langmuir isotherm model, indicating the dominant involvement of strong intermolecular interactions, particularly driven by amine functionalities. Meanwhile, the results revealed that [Cho][His]@AC showed lowered CO₂ adsorption capacity compared to [Cho][Pro]@AC and [Cho][Gln]@AC. Among the studied ionic liquids, [Cho][Pro]@AC showed the highest absorption capacity (2.332 mmol·g⁻¹ at 288 K and 1 bar). This was due to the obstruction of internal pores within the AC structure caused by excessive amine incorporation into its porous framework. In the meantime, for a deeper insight into the impregnation process of ILs onto the AC surfaces and their potential interactions with CO₂ molecules, we conducted density-functional theory (DFT) calculations using the ωB97XD/6-31 + G(d,p) method. The calculated interaction energies, ranging from − 1.19 to − 1.44 eV, along with calculated quantum chemical descriptors, indicated a notable stabilization of IL species on the AC surfaces, with high affinity toward CO₂ molecules.

This study concerns wet carbonation of β-C₂S (Ca₂SiO₄) in a closed system at 23 °C. The progress of carbonation was detected by quantitative X-ray diffraction (QXRD) and thermogravimetric analysis (TGA). Further measurements of pH and ion concentrations as well as modelling carbon species and saturation indices were done. Additionally, stable carbon isotope ratios (δ¹³C) in CO₂, dissolved inorganic carbon (DIC) and carbonate phases were measured. The aim of this study was to investigate δ¹³C isotope values during C₂S carbonation. If a systematic fractionation of carbon isotopes occurs during the reaction, it can help to quantify the carbonation reaction. During the carbonation process over 48 h, we found carbon isotope distributions from the gaseous phase to the solution and ultimately to the solid phase. Calculations confirm the direct relation of δ¹³C values to the carbonation progress. With this, stable isotope measurements offer a promising tool to monitor the reaction progress in-situ.

Lime mud (LM) is a highly alkaline solid waste generated during the papermaking process, and its direct application in cement-based materials can result in insufficient material properties. Pre-carbonation can reduce the alkalinity of LM and improve its ability as a supplementary cementitious material. This study explored the potential of pre-carbonated lime mud (CLM) to partially replace Portland cement under normal and carbonation curing. It was found that CLM absorbed some CO₂ and reduced a small amount of alkalinity after pre-carbonation treatment. Under normal curing conditions, LM can promote the hydration reaction at an early age but inhibit subsequent cement hydration due to its alkalinity. In contrast, CLM significantly alleviated the negative impacts of directly incorporating LM into Portland cement. Under carbonation curing conditions, a significant improvement in the compressive strength of cement-based materials containing LM and CLM was observed. The alkaline properties and nucleation effects of CLM and LM enhanced CO₂ sequestration efficiency. Especially after 14 days of carbonation curing, the sample with CLM exhibited higher CO₂ uptake and better mechanical properties than the sample with LM. This study provides a new solution to improve the resource utilization of LM and mitigates the negative impacts of LM on cement-based materials.

This study investigates the long-term stability and performance in chemical looping reverse water-gas shift reaction (rWGS) of a 50 wt% Fe₂O₃-MgAl₂O₄ material produced using an industrial method. While prior research predominantly focuses on short-term deactivation of lab-scale materials, this research explores the complex relationship between the cycle duration, material performance and stability of an upscaled material. Through comprehensive analyses, successful upscaling is demonstrated. Performance tests on the upscaled material reveal that shorter cycle durations lead to superior CO space-time yield, with a steady-state deactivation rate of 0.07 %/h over 28 days on stream. During the first 225 h of redox time, the equilibrium CO₂ conversion for catalytic rWGS is exceeded. Characterization post-cycling identifies key deactivation mechanisms, underscoring the challenge of maintaining stability over extended cycles. Rietveld refinement and STEM-EDX mapping indicate the formation of Fe_xMg_1-xAl₂O₄ and MgFe₂O₄ phases, the former of which contributes to reduced redox capacity, as indicated by temperature-programmed reduction measurements before and after cycles. Optimal performance was observed with shorter cycles despite lower material utilization, emphasizing the trade-offs between performance and stability. This research provides comprehensive insights for optimizing chemical looping CO₂ utilization processes, vital for advancing scalable and economically viable solutions to combat carbon emissions.

Accurate understanding and quantitative characterization of the microscopic distribution and mobilization mechanisms of remaining oil are crucial for further enhancing oil recovery during CO₂ flooding. In this study, miscible CO₂ flooding experiments after water flooding were performed to investigate the mass transfer and microscopic distribution characteristics of remaining oil and CO₂ using micro-computed tomography technique. Additionally, the distribution characteristics of multiphase fluids (oil, water and CO₂) in the pores were comprehensively investigated. Furthermore, the mass transfer effects during the miscible CO₂ flooding process, as well as the CO₂ sequestration ratio (SR) and sequestration factor (SF) were systematically examined. The experimental results show that the ultimate oil recovery factor after miscible CO₂ flooding were 80.9 %, 70.7 %, and 64.7 %, respectively. During the water flooding stage, the produced oil mainly consisted of light hydrocarbons (C₅–C₁₆), followed by medium hydrocarbons (C₁₇–C₂₇). The remaining oil was mainly in cluster and network pattern, followed by multiple and oil film pattern. After miscible CO₂ flooding, the produced gas mainly consisted of CO₂ and CH₄, with a significant increase in the mass fraction of light hydrocarbons (C₅–C₁₆) in the produced oil. The remaining oil was mainly in multiple and singlet pattern, followed by network and film pattern, with a small portion in cluster pattern. The higher the displacement rate, the smaller the SR, but most of the injected CO₂ (SR > 70 %) was retained in the porous media, demonstrating the feasibility of CO₂ geological sequestration during the miscible flooding process.

The mechanism of early age accelerated carbonation cured ordinary Portland cement mixtures is evaluated using experimental and thermodynamic modeling. This study considered three early precuring conditions, two carbonation curing periods, four CO₂ concentrations, and a 0.5 w/c ratio. The investigation was conducted using phase profiling of mixtures based on QXRD results and developed a thermodynamic model that simulated the experimental conditions. The mechanical characteristics of carbonation-cured mortar specimens, including compressive strength, elastic modulus, shrinkage, and mass change, were evaluated. The results revealed that short precuring durations hindered carbonation, resulting in lower CO₂ uptake, strength, elastic modulus and higher shrinkage. Increasing the precuring period from six-hours to one or three days resulted significant amount of CaCO₃ precipitation on the surface of the specimen and appropriate mechanical properties. One day precuring followed by one day carbonation with a 10 % CO₂ exposure resulted in a higher calcite precipitation on the surface with less depth of penetration. It was found that a balance between drying-induced degradation and microstructure densification due to calcite precipitation is crucial. An appropriate precuring duration, for each binder type and mix proportion, should be applied to achieve desired properties and CO₂ uptake in carbonation-cured cementitious materials.