Search Results (4,217)

Cupriavidus necator can produce single-cell proteins (SCPs) using electrons produced by hydrogen as energy, oxygen as electron acceptors, and CO₂ as carbon sources. Gas fermentation is a process of microbial fermentation that uses gas substrates (such as hydrogen, carbon dioxide, etc.) which faces several challenges, mainly including the low solubility of gas substrates, the danger of hydrogen and oxygen mixing, and the optimization of fermentation conditions. To overcome these challenges, this article explores a variety of strategies—including the design of a self-developed bioreactor—to reduce the risk of static electricity. Without the addition of filler material, the results showed that the maximum cell dry weight (CDW) of 30% secondary seed inoculation was 20.41% higher than that of 10% secondary seed inoculum, and 5.99% higher than that of 20% secondary seed inoculum. Combined with the filler material and with the use of high-efficiency continuous fermentation technology, the average yield of continuous fermentation was 23.31 g/day, while the average yield of batch fermentation was 14.33 g/day. The daily yield of continuous fermentation is 1.63 times that of batch fermentation. These efforts are aimed at improving the efficiency and safety of gas fermentation. Full article

Ensuring long-term wellbore integrity is critical for carbon dioxide geological storage. Ordinary Portland cement (PC) is usually used for wellbore primary cementing and plug operation, and set cement is easily corroded by acidic fluids, such as carbon dioxide, in underground high-temperature and high-pressure (HTHP) environments, resulting in a decrease in the mechanical properties and an increase in permeability. In order to achieve long-term wellbore integrity in a CO₂-rich environment This study introduces materials such as thermosetting vinyl ester resin (TSR), filler composite resin (FCR), and low-cost resin cement (RC). Corrosion experiments were conducted using four materials in 28 days under supercritical carbon dioxide gas and water phase conditions of 60 °C and 10 MPa. The samples were characterized through mechanical property testing machines, core permeability measuring instruments, FTIR, XRD, and SEM. The results proved that after corrosion, PC mechanical properties decreased, the permeability increased, and the microscopic composition and morphology changed greatly. Penetrating corrosion occurs in the sample in the gas phase environment, and propulsive corrosion from outside to inside occurs in the water phase environment. However, TSR, FCR, and RC materials all maintain excellent resistance to carbon dioxide corrosion in gas and water environments. They have higher compressive strength and extremely low permeability compared to ordinary Portland cement. These three materials’ compressive strengths can be maintained around 131, 99, and 58 MPa, and permeability can be stabilized at <6 × 10⁻⁷, <6 × 10⁻⁷, and 0.16 mD levels. In summary, the above three materials all show better performance than ordinary Portland cement and are promising alternative materials that can be used in primary cementing and plug operations of carbon dioxide geological storage wells. Full article

Understanding the behavior of carbon dioxide (CO₂) under varying thermodynamic conditions is essential for optimizing processes such as Carbon Capture and Storage (CCS) and supercritical fluid extraction. This study employs molecular dynamics (MD) simulations with the EPM2 and TraPPE-small force fields to examine CO₂ phase behavior, structural characteristics, and transport properties across a temperature range of 228–500 K and pressures from 1 to 150 atm. Our findings indicate a good agreement between simulated and experimental liquid–vapor coexistence curves, validating the capability of both force fields to model CO₂ accurately in a wide range of thermodynamical conditions. Radial distribution functions (RDFs) reveal distinct interaction patterns in liquid and supercritical phases, while mean squared displacement (MSD) analyses show diffusivity increasing from $5.2\times {10}^{-9}$ m²/s at 300 K to $1.8\times {10}^{-8}$ m²/s at 500 K. Additionally, response functions such as the heat capacity effectively capture phase transitions. These findings provide quantitative insights into CO₂ phase behavior and transport properties, enhancing the predictive reliability of simulations for CCS and related industrial technologies. This work bridges gaps in the CO₂ modeling literature and highlights the potential of MD simulations in advancing sustainable applications. Full article

The interactions among water molecules, coal beds, and gases during the process of coal bed methane mining are highly complex. The water and methane (CH₄)/carbon dioxide (CO₂) molecules compete for adsorption and undergo a series of reactions that affect gas diffusion. In this study, Monte Carlo and molecular dynamics methods were used to investigate the microscopic mechanism of CH₄/CO₂ competitive adsorption and diffusion during CO₂-enhanced coal bed methane mining (ECBM) under different moisture contents, and the geological storage potential of CO₂ was predicted. The results showed that when the CO₂ and water binding sites were independent of each other, the water molecules changed the electrostatic potential around the coal molecules, resulting in enhanced CO₂ adsorption performance, as verified by the surface electrostatic potential. When the water molecules formed a water molecule layer, the adsorption capacity of the secondary adsorption sites provided was larger than that of the surface of the coal molecules, so the CO₂ molecules were preferentially adsorbed on the secondary adsorption sites. However, the number of secondary adsorption sites available was not as large as that on the surface of the coal molecules. The interaction energies revealed that when the displacement effect of CH₄ in the process of CO₂-ECBM and the sequestration effect of CO₂ were considered comprehensively, the best CO₂ sequestration effect and a good CH₄ displacement effect were obtained at a 3% moisture content. The worst CO₂ sequestration effect was found at a 5% moisture content. After CO₂ injection, the main adsorption layer of CH₄ shifted from X = 5 and X = 9 to X = 8.7 and X = 12.5, respectively, and obvious detachment and diffusion occurred. The distribution of the molecular motion and diffusion coefficient revealed the considerable displacement and dispersion of the gas molecules. The distribution of the gas molecular velocity and diffusion coefficient indicated that a 3% moisture content was the ideal condition for CO₂ displacement of CH₄, and the CO₂ sequestration effect was good. Full article

A good quantitative knowledge of regional sources and sinks of atmospheric carbon dioxide (CO₂) is essential for understanding the global carbon cycle. It is also a key prerequisite for elaborating cost-effective national strategies to achieve the goals of the Paris Agreement. However, available estimates of CO₂ fluxes for many regions of the world remain uncertain, despite significant recent progress in the remote sensing of terrestrial vegetation and atmospheric CO₂. In this study, we investigate the feasibility of inferring reliable regional estimates of the net ecosystem exchange (NEE) using column-averaged dry-air mole fractions of CO₂ (XCO₂) retrieved from Orbiting Carbon Observatory-2 (OCO-2) observations as constraints on parameters of the widely used Vegetation Photosynthesis and Respiration model (VPRM), which predicts ecosystem fluxes based on vegetation indices derived from multispectral satellite imagery. We developed a regional-scale inverse modeling system that applies a Bayesian variational optimization algorithm to optimize parameters of VPRM coupled to the CHIMERE chemistry transport model and which involves a preliminary transformation of the input XCO₂ data that reduces the impact of the CHIMERE boundary conditions on inversion results. We investigated the potential of our inversion system by applying it to a European region (that includes, in particular, the EU countries and the UK) for the warm season (May–September) of 2021. The inversion of the OCO-2 observations resulted in a major (more than threefold) reduction of the prior uncertainty in the regional NEE estimate. The posterior NEE estimate agrees with independent estimates provided by the CarbonTracker Europe High-Resolution (CTE-HR) system and the ensemble of the v10 OCO-2 model intercomparison (MIP) global inversions. We also found that the inversion improves the agreement of our simulations of XCO₂ with retrievals from the Total Carbon Column Observing Network (TCCON). Our sensitivity test experiments using synthetic XCO₂ data indicate that the posterior NEE estimate would remain reliable even if the actual regional CO₂ fluxes drastically differed from their prior values. Furthermore, the posterior NEE estimate is found to be robust to strong biases and random uncertainties in the CHIMERE boundary conditions. Overall, this study suggests that our approach offers a reliable and relatively simple way to derive robust estimates of CO₂ ecosystem fluxes from satellite XCO₂ observations while enhancing the applicability of VPRM in regions where eddy covariance measurements of CO₂ fluxes are scarce. Full article

There are limited studies in the literature on the surface characterization of modified graphene and graphene oxide and the impact of these modified adsorbents on adsorption performance. In addition, the amine group essentially has a promising affinity for carbon dioxide (CO₂). Therefore, chitosan was used in this study to be grafted onto graphene and graphene oxide respectively. This study examines the effects of graphene, graphene oxide, and chitosan-modified graphene oxide thin films on the removal of carbon dioxide (CO₂). Thin films of graphene, graphene oxide, and their chitosan-modified counterparts were prepared via the methods of precipitation and grafting. The differences in the chemical structure, surface properties, and surface morphology of the films were evaluated, and their effect on the adsorption performance of CO₂ is discussed herein. The micrographs from a scanning electron microscope (SEM) show that the surface of graphene oxide appeared to be more porous than graphene, and the amount of grafted chitosan on graphene oxide is higher than that on graphene. An analysis of atomic force microscope (AFM) finds that the surface of chitosan-modified graphene oxide is rougher than that of chitosan-modified graphene. The results of energy-dispersive X-ray spectroscopy (EDS) spectra reveal that the composition of oxygen in graphene oxide is greater than that in graphene and confirm that the oxygen and nitrogen contents of chitosan-modified adsorbents are greater than those of the pristine materials. An analysis of Fourier-transform infrared spectroscopy (FTIR) shows that most of the oxygen-containing groups are reacted or covered by amide or amine groups due to modification with chitosan. The adsorption isotherms for CO₂ adsorbed by the prepared graphene and graphene oxide presented as type I, indicating great adsorption performance under low pressure. The appropriate amount of chitosan for modifying graphene oxide could be found based on the change in surface area. Although the breakthrough times and the thicknesses of the mass transfer regions for graphene oxide modified with 0.9% and 1.2% chitosan were similar, the modification of graphene oxide with 0.9% chitosan was appropriate in this study due to a significant decrease in surface area with 1.2% chitosan dosage. The adsorption uptake difference between chitosan-modified graphene oxide and graphene was greater than that without modification with chitosan due to more chitosan grafted on graphene oxide. The Toth adsorption isotherm model was used to fit the adsorption uptake, and the average deviation was about 1.36%. Full article

Rapid industrialization and the indiscriminate use of fossil fuels have generated an impact that is affecting the climate worldwide. Among the substances that are causing climate change are several gases such as carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O) and sulphur hexafluoride (SF₆), among others. Particularly, carbon dioxide is one of the substances that has attracted the most attention from researchers, as it is responsible for more than three quarters of greenhouse gases. Because of this, many efforts have been directed towards the capture of CO₂, its separation, adsorption and transformation into products that are less harmful to the environment or that even have added value in the industry. For this purpose, the use of different types of macrocycles has been explored mainly in the last 5 years. This review seeks to present the advances that have occurred in recent years in the capture and transformation of CO₂ by different methods, to finally focus on the capture and transformation through macrocycle systems such as azacompounds, heterometallic macrocycles, calixpyrrols, modified cyclodextrins and metallic porphyrins, among others. Full article

Converting carbon dioxide (CO₂) into solar fuels through photocatalysis represents an appealing approach to tackling the escalating energy crisis and mitigating the greenhouse effect. In this study, using melamine–formaldehyde (MF) nanospheres as a nitrogen source, a N element was simultaneously doped into the TiO₂ nanoparticle structure supported by carbon hollow spheres using a one-step carbonization method to form a heterojunction N-CHS@N-TiO₂ (marked as (N-(CHS@TiO₂)). The composite showed superior photocatalytic activity in reducing CO₂ compared with TiO₂ and N-CHS: after 6 h of visible light irradiation, the CO yield was 4.3 times that of N-CHS and TiO₂; 6 h of UV irradiation later, the CO yield reached 2.6 times that of TiO₂ and 7 times that of N-CHS. The substantial enhancement in photocatalytic activity was attributed to the nitrogen simultaneously doped carbon hollow spheres and TiO₂, mesoporous structure, small average TiO₂ crystal size, large surface areas, and the heterostructure formed by N-CHS and N-TiO₂. The UV-vis diffuse reflectance spectra (DRS) exhibit a significant improvement in light absorption, attributed to the visible-light-active carbon hollow sphere and the N element doping, thereby enhancing solar energy utilization. Full article

Combustion is the most advanced and proven method on the market for using agricultural by-product residues and waste from the agri-food industry. Currently, a wide range of combustion technologies is used to produce heat and electricity in low-power heating devices (>50 kW) using various types of biofuels from biomass (woody biomass, herbaceous biomass, waste and residues from the agri-food industry). Combustion of biomass fuels, especially those of wood origin, causes lower carbon dioxide (CO₂) and sulfur oxides (SO_x) emissions into the atmosphere compared to coal combustion. The growing interest in solid biofuels has contributed to intensive activities on improving the combustion process and energy devices enabling effective and economic conversion of chemical energy contained in biomass into other usable forms such as heat, electricity. Having good quality fuel, it is necessary to ensure an appropriate, clean combustion technique, which allows to achieve the highest thermal efficiency of the heating device and at the same time the lowest emission of pollutants. The article presents issues related to the theory, characteristics of the combustion process and problems related to the formation of harmful chemical compounds nitrogen oxides (NO_x), SO_x, carbon monoxide (CO), particulate matter (PM) emitted to the atmosphere during the combustion process in low-power heating devices. The analysis indicates the possibility of minimizing undesirable phenomena during the combustion of these biofuels related to ash sintering, the formation of deposits, corrosion and improving the amount of condensable solid particles formed and therefore reducing the emission of gaseous products to the environment. Full article

In energy conservation and low-carbon environmental protection, separating and capturing CO₂ from blast furnace gas is a crucial strategy for the steel industry to achieve its dual carbon goals. This study conducts an experimental study on the phase change absorption of carbon dioxide for the low-energy capture of carbon dioxide in blast furnace gas in iron and steel enterprises. The experiment used 30%wt monoethanolamine (MEA) and 30%wt 1-(2-aminoethyl)piperazine (AEP) as a reference to blend different absorbents, and the CO₂ absorption effect of the absorbents was tested. The results indicated that the MEA system phase change absorbents have the best absorption effect when the mass ratio of additives to water is 5:5, and the AEP system has the best absorption effect at 7:3. The absorption effect of different phase separators is as follows: n-propanol > sulfolane > isopropanol. AEP/n-propanol/H₂O (7:3) has a maximum absorption load of 2.03 molCO₂·mol⁻¹ amine, a relatively low rich phase ratio of 0.46, and low regeneration energy consumption. The load capacity of different absorbents was calculated based on the load experiment results, and it was found that the loading capacity of the MEA system was greater than that of the AEP system, with the maximum load capacity of MEA/n-propanol/H₂O (5:5) being 4.02 mol/L. Different types of absorbents exhibited an increase in rich phase density with the increase in additive quality. The regeneration performance of the absorbent indicated that at a temperature of 393.15 K, the desorption load of n-propanol aqueous solution rich phase in the absorbent was high, and the desorption speed was the fastest. Full article

Mushrooms are a raw material rich in many nutritional compounds, and that is why a number of them are widely known as functional food. They contain fatty acids, carbohydrates, lycopene, sterols, lovastatin, trace elements, and other valuable compounds that show a wide range of properties, such as hepatoprotective, anticancer, antiviral, etc. For more efficient utilisation of mushrooms’ biologically active substances, widespread supercritical carbon dioxide extraction (Sc-CO₂) was used as an efficient way to isolate the high-value phytoconstituents from this type of raw material. Using Sc-CO₂, the extracts of five types of edible mushrooms—Lycoperdon saccatum, Pleurotus ostreatus, Craterellus cornucopioides, Russula Cyanoxantha and Cantharellus cibarius—were obtained. During the Sc-CO₂ process, the extraction time was reduced to 4 h compared to the prolonged process time applied in the typical traditional techniques (6–24 h). The extraction pressure (30 MPa) and temperature (40 °C) were constant. Fatty acids and the compounds of steroid structures were determined in the obtained extracts using GC–MS and GC–FID methods of analysis. The dominant compounds identified in the lipid extracts were fatty acids (linoleic, oleic, palmitic and stearic) and sterols (ergosterol, 7,22-ergostadienone and 7,22-ergostadienol). For complete insight into the process and to obtain the value of the extracts, chemometric analysis is provided. Principal component analysis (PCA) and hierarchical cluster analysis (HCA), as well as k-means clustering, showed that Craterellus cornucopioides was distinguished based on the extraction yield results. Full article

The electrocatalytic reduction of carbon dioxide (CO₂RR) into high-value-added products is considered to be a promising way to mitigate carbon emissions. However, it remains a challenge to design an efficient catalyst with an excellent performance. In this work, we synthesized a metal azole framework (MAF) by changing 2-methylimidazole ligands into 5-mercapto-1-methyltetrazole (MMT) for use as organic linkers and mercaptan groups as anchoring sites for the Ag nanoparticles. The Ag NPs@ MAF-MMT material displayed a wide potential window from −0.6 to −1.2 V vs. RHE, with a maximum CO Faradaic efficiency (FE_CO) over 90.5%, and a current density of 18 mA cm⁻² at −1.1 V vs. RHE for 11 h in an H-cell. This work provides a new option to immobilize Ag nanoparticles in MAFs material for the exploration of carbon dioxide reduction catalysts. Full article

The co-production of BHD with other renewable fuels (i.e., using a novel process involving carbon dioxide utilization to achieve the global sustainability goal) is presented. The three configurations of BHD production from refined bleached deodorized palm oil (RBDPO), including (1) the conventional BHD process with hydrogen recovery (BHD process), (2) the BHD process coupled with the Fischer–Tropsch process (BHD-FT process), and (3) the BHD process coupled with the bio-jet fuel and methanol processes (BHD-BIOJET-MEOH process) are investigated using the process model developed in Aspen Plus. The effect of the operating parameters is studied, and the condition of each process offering the highest BHD yield is proposed. Then, the pinch analysis and heat exchanger network (HEN) design of each proposed process are performed to find the highest energy-efficient configuration. The economic and environmental analysis is later performed to investigate the sustainability performance of each configuration. The conventional BHD process requires less hydrogen and consumes less energy than the others. The BHD-BIOJET-MEOH process is the most economically feasible, offering the highest net present value (NPV) of USD 7.93 million and the shortest payback period of 3 years and 1 month. However, it offers the highest carbon footprint of 0.820 kgCO₂ eq./kg of BHD, and it presented the highest potential environmental impact (PEI) in all categories. Full article

The electrochemical conversion of CO₂ into high value-added carbon materials by molten salt electrolysis offers a promising solution for reducing carbon dioxide emissions. This study focuses on investigating the influence of molten salt composition on the structure of CO₂ direct electroreduction carbon products in chloride molten salt systems. Using CaO as a CO₂ absorber, the adsorption principle of CO₂ in LiCl-CaCl₂, LiCl-CaCl₂-NaCl and LiCl-CaCl₂-KCl molten salts was discussed, and the reasons for the different morphologies and structures of carbon products were analyzed, and it was found that the electrolytic efficiency of the whole process exceeded 85%. Furthermore, cathode products are analyzed through Scanning Electron Microscope (SEM), X-Ray Diffractometer (XRD), Thermal Gravimetric Analyzer (TGA), Raman Spectra and Fourier Transform Infrared (FTIR) techniques with a focus on the content and morphology of carbon elements. It was observed that the carbon content in the carbon powder produced by molten salt electrochemical method exceeded 99%, with most carbon products obtained from electrolysis in the Li-Ca chloride molten salt system being in the form of carbon nanotubes. In contrast, the Li-Ca-K chloride system yielded carbon nanospheres, while a mixture was found in the Li-Ca-Na chloride system. Therefore, experimental results demonstrate that altering the composition of the system allows for obtaining the desired product size and morphology. This research presents a pathway to convert atmospheric CO₂ into high value-added carbon products. Full article

This study investigated the application of supercritical carbon dioxide (CO₂) for the extraction of essential oils from plant materials with anxiolytic potential, focusing on the leaves of burrito (Aloysia polystachya) and the seeds of sucupira-preta (Bowdichia virgilioides). The supercritical extraction technique was chosen for its ability to produce high-purity extracts without residual solvents and to reduce the environmental impact. This study evaluated the influence of temperature (40 °C, 50 °C, and 60 °C) and pressure (22 MPa, 25 MPa, and 28 MPa) on extraction efficiency using a 2² factorial design with triplicates at the central point. The maximum yields were 1.2% for burrito leaves and 4.2% for sucupira-preta seeds. Despite their relatively low yields, the extracts contained a diverse range of chemical compounds, including fatty acids (oleic, linoleic, and palmitic acids), squalene, β-carotene, vitamin E, and other bioactive molecules with antioxidant, anti-inflammatory, and immunomodulatory properties. Statistical analysis demonstrated that pressure was the most influential factor affecting yield, whereas temperature played a secondary role. The Sovová kinetic model provided a good fit for the extraction curves, with determination coefficients (R²) above 0.95, thus validating the efficiency of the method. These results highlight the pharmaceutical potential of these extracts, particularly for therapeutic and anxiolytic purposes. Full article