CO2 utilization: Turning greenhouse gas into fuels and valuable products

Graphene Oxide-Arginine Composites: Efficient Dual Function Materials for Integrated CO2 Capture and Conversion

The "on-demand" capture and utilization of CO2 is effectively realized with a readily accessible dual function organic composite. The covalent and controlled derivatization of graphene oxide (GO) surface with naturally occurring arginine led to a "smart" material capable of capturing (chemisorption) CO2 from high-purity flue-gas as well as low-concentration streams (i. e. direct air capture) and concomitant chemical activation toward the incorporation into cyclic carbonates. The overall integrated CO2 capture and conversion (ICCC) strategy has been fully elucidated mechanistically via dedicated computational, spectroscopic and thermal analyses.

Impact of Sr Addition on Zirconia-Alumina-Supported Ni Catalyst for COx-Free CH4 Production via CO2 Methanation

Zirconia-alumina-supported Ni (5Ni/10ZrO2+Al2O3) and Sr-promoted 5Ni/10ZrO2+Al2O3 are prepared, tested for carbon dioxide (CO2) methanation at 400 °C, and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, surface area and porosity, infrared spectroscopy, and temperature-programmed reduction/desorption techniques. The CO2 methanation is found to depend on the dispersion of Nickel (Ni) sites as well as the extent of stabilization of CO2-interacted species. The Ni active sites are mainly derived from the reduction of 'moderately interacted NiO species'. The dispersion of Ni over 1 wt % Sr-promoted 5Ni/10ZrO2+Al2O3 is 1.38 times that of the unpromoted catalyst, and it attains 72.5% CO2 conversion (against 65% over the unpromoted catalyst). However, increasing strontium (Sr) loading to 2 wt % does not affect the Ni dispersion much, but the concentration of strong basic sites is increased, which achieves 80.6% CO2 conversion. The 5Ni4Sr/10ZrO2+Al2O3 catalyst has the highest density of strong basic sites and the highest concentration of active sites with maximum Ni dispersion. This catalyst displays exceptional performance and achieves approximately 80% CO2 conversion and 70% methane (CH4) yield for up to 25 h on steam. The unique acidic-basic profiles composed of strong basic and moderate acid sites facilitate the sequential hydrogenation of formate species in the COx-free CH4 route.

Synergistic sustainability: Future potential of integrating produced water and CO2 for enhanced carbon capture, utilization, and storage (CCUS)

Produced water (PW) and carbon dioxide (CO2) are traditionally considered waste streams the oil and gas industry and other sectors generate. However, these waste products are examples of "waste to wealth" products with a dual nature of being valuable products or disposable byproducts. PW contains various elements and compounds that can be extracted and used in the manufacturing or chemical processing industry. Concentrated brine is generated from PW and can be used as feedstock in chemical processes. On the other hand, excess CO2 produced in various industrial processes needs to be sequestered either through non-conversion processes, such as enhanced oil recovery and storage in geological formations, or through CO2 conversion processes into fuels, polymers, and chemicals. While there is growing interest in reusing these products individually, no studies have explored the opportunities for producing additional chemicals or valuable products by combining CO2 and PW waste streams (CO2-PW). This study identifies the potential resources that can be generated by combining the beneficial reuse of PW and CO2 conversion processes. CO2-PW chemical conversion presents an opportunity to expand the carbon capture, utilization, and storage (CCUS) mix while reducing the environmental impact of disposing of these byproducts. The advantages of utilizing these waste streams for diverse applications are linked with the sustainable management of PW and decarbonization, contributing positively to a more responsible approach to resource management and climate change mitigation.

Carbon dioxide reduction to high-value chemicals in microbial electrosynthesis system: Biological conversion and regulation strategies

Large emissions of atmospheric carbon dioxide (CO2) are causing climatic and environmental problems. It is crucial to capture and utilize the excess CO2 through diverse methods, among which the microbial electrosynthesis (MES) system has become an attractive and promising technology to mitigate greenhouse effects while reducing CO2 to high-value chemicals. However, the biological conversion and metabolic pathways through microbial catalysis have not been clearly elucidated. This review first introduces the main acetogenic bacteria for CO2 reduction and extracellular electron transfer mechanisms in MES. It then intensively analyzes the CO2 bioconversion pathways and carbon chain elongation processes in MES, together with energy supply and utilization. The factors affecting MES performance, including physical, chemical, and biological aspects, are summarized, and the strategies to promote and regulate bioconversion in MES are explored. Finally, challenges and perspectives concerning microbial electrochemical carbon sequestration are proposed, and suggestions for future research are also provided. This review provides theoretical foundation and technical support for further development and industrial application of MES for CO2 reduction.

Experimental Study on the Effect of CO2 Injection Pressure on the Migration Characteristics and Extraction Effects of Replacement CH4

To study the effect of CO2 injection pressure on gas migration characteristics and coalbed methane (CBM) extraction, a platform for the experimental replacement of CH4 with CO2 was used to conduct experiments on the replacement of CH4 under different CO2 injection pressures and analyze the gas transport characteristics and CH4 extraction during the experiment. The results reveal that the rate of gas migration out of the coal seam accelerates with increasing gas injection pressure, as determined by comparisons of the migration rates between adjacent monitoring points. The change trend of the CH4 desorption rate under different gas injection pressures is divided into slow decline, sharp decline, and stability stages, and the maximum value of the effective diffusion coefficient increases from 2.3 × 10-5 to 3.4 × 10-5 and 4.6 × 10-5 cm2/s as the gas injection pressure increases from 0.6 to 0.8 and 1.0 MPa. Similarly, the change pattern of coal seam permeability can be divided into slow decline, sharp decline, and stability stages. After the gas injection pressure was increased from 0.6 to 0.8 and 1.0 MPa, the CH4 desorption volume increased from 90.2 to 94.1 and 97.8 L, whereas the coal seam CO2 sequestration volume increased from 269.2 to 274.2 and 322.8 L, respectively. In contrast, the CH4 extraction efficiency increased from 76.9 to 80.2 and 82.9%, respectively. The research results have important reference value and practical significance for optimizing the CO2 injection pressure and improving the CBM extraction.

Effect of glucose pretreatment on Cu-ZnO-Al2O3 catalyzed CO2 hydrogenation to methanol

A series of Cu-ZnO-Al₂O₃ catalysts (CZA) were prepared by glucose pretreatment and applied for methanol synthesis from CO₂ hydrogenation. The advantages of the glucose pretreatment and the effects of glucose content were investigated by XRD, N₂ physisorption, SEM, N₂O chemisorption, CO₂-TPD, H₂-TPR, TG, and XPS characterization techniques. The influence of glucose pretreatment on the average Cu particle size and the interaction between different components, as well as the effects of the amount of glucose on the Cu specific surface area, the ratio of Cu⁰/Cu⁺ and the performance of the catalysts were discussed. The results showed that the catalysts prepared by glucose pretreatment increased the number of basic sites and had a significant advantage in methanol yield. The optimum content of glucose was beneficial to improve the catalytic performance of the CZA catalyst. The maximum space-time yield of methanol was obtained by 2 wt% glucose pretreatments at 200 °C, which was 57.0 g kg^-1 h^-1.

Functionalization of nitrogen-doped graphene quantum dot: A sustainable carbon-based catalyst for the production of cyclic carbonate from epoxide and CO2

A series of organic compounds were successfully immobilized on an N-doped graphene quantum dot (N-GQD) to prepare a multifunctional organocatalyst for coupling reaction between CO₂ and propylene oxide (PO). The simultaneous presence of halide ions in conjunction with acidic- and basic-functional groups on the surface of the nanoparticles makes them highly active for the production of propylene carbonate (PC). The effects of variables such as catalyst loading, reaction temperature, and structure of substituents are discussed. The proposed catalysts were characterized by different techniques, including Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy/energy dispersive X-ray microanalysis (FESEM/EDX), thermogravimetric analysis (TGA), elemental analysis, atomic force microscopy (AFM), and ultraviolet-visible (UV-Vis) spectroscopy. Under optimal reaction conditions, 3-bromopropionic acid (BPA) immobilized on N-GQD showed a remarkable activity, affording the highest yield of 98% at 140°C and 10⁶ Pa without any co-catalyst or solvent. These new metal-free catalysts have the advantage of easy separation and reuse several times. Based on the experimental data, a plausible reaction mechanism is suggested, where the hydrogen bonding donors and halogen ion can activate the epoxide, and amine functional groups play a vital role in CO₂ adsorption.

Recent Applications and Strategies to Enhance Performance of Electrochemical Reduction of CO2 Gas into Value-Added Chemicals Catalyzed by Whole-Cell Biocatalysts

Carbon dioxide (CO2) is one of the major greenhouse gases that has been shown to cause global warming. Decreasing CO2 emissions plays an important role to minimize the impact of climate change. The utilization of CO2 gas as a cheap and sustainable source to produce higher value-added chemicals such as formic acid, methanol, methane, and acetic acid has been attracting much attention. The electrochemical reduction of CO2 catalyzed by whole-cell biocatalysts is a promising process for the production of value-added chemicals because it does not require costly enzyme purification steps and the supply of exogenous cofactors such as NADH. This study covered the recent applications of the diversity of microorganisms (pure cultures such as Shewanella oneidensis MR1, Sporomusa species, and Clostridium species and mixed cultures) as whole-cell biocatalysts to produce a wide range of value-added chemicals including methane, carboxylates (e.g., formate, acetate, butyrate, caproate), alcohols (e.g., ethanol, butanol), and bioplastics (e.g., Polyhydroxy butyrate). Remarkably, this study provided insights into the molecular levels of the proteins/enzymes (e.g., formate hydrogenases for CO2 reduction into formate and electron-transporting proteins such as c-type cytochromes) of microorganisms which are involved in the electrochemical reduction of CO2 into value-added chemicals for the suitable application of the microorganism in the chemical reduction of CO2 and enhancing the catalytic efficiency of the microorganisms toward the reaction. Moreover, this study provided some strategies to enhance the performance of the reduction of CO2 to produce value-added chemicals catalyzed by whole-cell biocatalysts.

Response of aquatic plant decomposition to invasive algal organic matter mediated by the co-metabolism effect in eutrophic lakes

The decomposition of aquatic plant residues changes by the invasive algal organic matter in eutrophic lakes, however, the driving mechanisms of these biogeochemistry processes are still far from clear. In this study, a series of microcosms was constructed to simulate the mixed decomposition processes of aquatic plant residues with invasive algae as long as 205 days. Three aquatic plants (Potamogeton malaianus, Nymphoides peltatum, and Phragmites australis) and algae were collected from a typical eutrophic lake. The addition of algae promoted the decomposition of three plant residues based on the mass loss, and the positive co-metabolism effect was produced. The co-metabolism intensity was 8%-25% on the water surface and 19%-45% on the water-sediment interface, respectively. In addition, the response of three aquatic plant residues to the algal organic matter was different with their co-metabolism intensities in the order of P. australis > P. malaianus > N. peltatum on both the water surface and water-sediment interface. The phylum number of bacteria attached to the surface of plant residues increased from 27 to 52. The abundance of Bacteroidetes, which had the function of decomposing refractory organic matter, increased most significantly at the final incubation. At present, shallow lakes are under the double pressure of eutrophication and global warming, and the intensity and duration of algal blooms are increasing. Therefore, the co-metabolism effect of the residue decomposition process described here may change the carbon cycle strength and increase the greenhouse gas emissions of lakes and need to be taken into account in future lake management.

A 3D Printed Membrane Reactor System for Electrochemical CO2 Conversion

Nowadays, CO₂ electroreduction is gaining special interest as achieving net zero CO₂ emissions is not going to be enough to avoid or mitigate the negative effects of climate change. However, the cost of CO₂ electroreduction is still very high because of the low efficiency of conversion (around 20%). Therefore, it is necessary to optimize the reaction conditions. Thus, a miniaturized novel membrane reactor was designed and manufactured in this study, with a shorter distance between the electrodes and a reduced volume, compared with CNC-manufactured reactors, using novel stereolithography-based 3D printing. The reduced distance between the two electrodes reduced the electrical resistance and therefore lowered the overpotential necessary to trigger the reaction from -1.6 V to -1.2 V, increasing the efficiency. In addition, the reduction in the volume of the reactor increased the catalyst area/volume ratio, which also boosted the concentration of the products (from FE 18% to FE 21%), allowing their better identification. Furthermore, the smaller volume and reduced complexity of the reactor also improved the testing capacity and decreased the cost of experimentation. The novel miniaturized reactor can help researchers to perform more experiments in a cost/time-effective way, facilitating the optimization of the reaction conditions.

Protonated Porphyrins: Bifunctional Catalysts for the Metal-Free Synthesis of N-Alkyl-Oxazolidinones

The protonation of commercially available porphyrin ligands yields a class of bifunctional catalysts able to promote the synthesis of N-alkyl oxazolidinones by CO₂ cycloaddition to corresponding aziridines. The catalytic system does not require the presence of any Lewis base or additive, and shows interesting features both in terms of cost effectiveness and eco-compatibility. The metal-free methodology is active even with a low catalytic loading of 1 % mol, and the chemical stability of the protonated porphyrin allowed it to be recycled three times without any decrease in performance. In addition, a DFT study was performed in order to suggest how a simple protonated porphyrin can mediate CO₂ cycloaddition to aziridines to yield oxazolidinones.

Using greenhouse gases in the synthesis gas production processes: Thermodynamic conditions

The work concerns the thermodynamic analysis of CH₄ reforming with various oxidants (CO₂, H₂O, O₂) in the technological variants DRM (Dry Reforming of Methane) and TRM (Tri-reforming of Methane) technological variants. Both processes of synthesis gas production (raw material for the production of value-added products) are problematic in terms of environmental protection. In the process, two components of greenhouse gases are used as a substrate: CO₂ and CH₄. The influence of temperature, pressure, and the molar ratio of oxidants to methane on the efficiency of both processes was analyzed using the deterministic method: raw material conversion, product efficiency and selectivity - H₂ and CO, and the value of the H₂/CO ratio characterizing the suitability of the synthesis gas for various syntheses. The problem of carbon deposition tendency in DRM was minimized through the selection of operational process conditions, and in the case of TRM, it was fully reduced. The deterministic method of non-linear programming by defining the objective function with constraints helped formulate allowed one the values of TRM parameters: complete reduction of the coking problem, maintaining the H₂/CO ratio at the desired level - 2 and CO₂ conversion equal to 90%, led to a hydrogen efficiency of over 90%. This efficiency can be obtained at the process temperature T = 273 K, with a pressure of 1 atm, and the molar ratios of oxidants to methane: CH₄/CO₂/H₂O/O₂ = 1/0.36/0.77/0.01.

Insight into the comprehensive effect of carbon dioxide, light intensity and glucose on heterotrophic-assisted phototrophic microalgae biofilm growth: A multifactorial kinetic model

Heterotrophic-assisted photoautotrophic microalgae biofilm cultivation was an alternative way to realize CO₂ reduction and wastewater treatment. Growth kinetics supplied a channel to better understand how the cultivation conditions affect microalgal growth and CO₂ reduction. However, the two growth modes (heterotroph and photoautotroph) have different needs for organic and inorganic nutrients. Thus, combining the threshold theory and multiplication theory, an integral multifactorial kinetic model that looking insight into the comprehensive effect of glucose, CO₂, light intensity, and nitrate was developed for heterotrophic-assisted photoautotrophic microalgae biofilm growth in this study. R² between model and experiment was 0.99. It predicted the maximum specific growth rate and maximum CO₂ consumption rate of heterotrophic-assisted photoautotrophic microalgae biofilm was 1.868 h^-1 and 1.02 h^-1, respectively. This model fully explained the influence of the main factors on microalgae biofilm growth and reasonably predicted the growth rate of microalgae biofilm under different growth conditions.

A Review on Green Hydrogen Valorization by Heterogeneous Catalytic Hydrogenation of Captured CO2 into Value-Added Products

The catalytic hydrogenation of captured CO2 by different industrial processes allows obtaining liquid biofuels and some chemical products that not only present the interest of being obtained from a very low-cost raw material (CO2) that indeed constitutes an environmental pollution problem but also constitute an energy vector, which can facilitate the storage and transport of very diverse renewable energies. Thus, the combined use of green H2 and captured CO2 to obtain chemical products and biofuels has become attractive for different processes such as power-to-liquids (P2L) and power-to-gas (P2G), which use any renewable power to convert carbon dioxide and water into value-added, synthetic renewable E-fuels and renewable platform molecules, also contributing in an important way to CO2 mitigation. In this regard, there has been an extraordinary increase in the study of supported metal catalysts capable of converting CO2 into synthetic natural gas, according to the Sabatier reaction, or in dimethyl ether, as in power-to-gas processes, as well as in liquid hydrocarbons by the Fischer-Tropsch process, and especially in producing methanol by P2L processes. As a result, the current review aims to provide an overall picture of the most recent research, focusing on the last five years, when research in this field has increased dramatically.

Recent Application of Core-Shell Nanostructured Catalysts for CO2 Thermocatalytic Conversion Processes

Carbon-intensive industries must deem carbon capture, utilization, and storage initiatives to mitigate rising CO₂ concentration by 2050. A 45% national reduction in CO₂ emissions has been projected by government to realize net zero carbon in 2030. CO₂ utilization is the prominent solution to curb not only CO₂ but other greenhouse gases, such as methane, on a large scale. For decades, thermocatalytic CO₂ conversions into clean fuels and specialty chemicals through catalytic CO₂ hydrogenation and CO₂ reforming using green hydrogen and pure methane sources have been under scrutiny. However, these processes are still immature for industrial applications because of their thermodynamic and kinetic limitations caused by rapid catalyst deactivation due to fouling, sintering, and poisoning under harsh conditions. Therefore, a key research focus on thermocatalytic CO₂ conversion is to develop high-performance and selective catalysts even at low temperatures while suppressing side reactions. Conventional catalysts suffer from a lack of precise structural control, which is detrimental toward selectivity, activity, and stability. Core-shell is a recently emerged nanomaterial that offers confinement effect to preserve multiple functionalities from sintering in CO₂ conversions. Substantial progress has been achieved to implement core-shell in direct or indirect thermocatalytic CO₂ reactions, such as methanation, methanol synthesis, Fischer-Tropsch synthesis, and dry reforming methane. However, cost-effective and simple synthesis methods and feasible mechanisms on core-shell catalysts remain to be developed. This review provides insights into recent works on core-shell catalysts for thermocatalytic CO₂ conversion into syngas and fuels.

Plasma-Catalytic CO2 Hydrogenation over a Pd/ZnO Catalyst: In Situ Probing of Gas-Phase and Surface Reactions

Plasma-catalytic CO₂ hydrogenation is a complex chemical process combining plasma-assisted gas-phase and surface reactions. Herein, we investigated CO₂ hydrogenation over Pd/ZnO and ZnO in a tubular dielectric barrier discharge (DBD) reactor at ambient pressure. Compared to the CO₂ hydrogenation using Plasma Only or Plasma + ZnO, placing Pd/ZnO in the DBD almost doubled the conversion of CO₂ (36.7%) and CO yield (35.5%). The reaction pathways in the plasma-enhanced catalytic hydrogenation of CO₂ were investigated by in situ Fourier transform infrared (FTIR) spectroscopy using a novel integrated in situ DBD/FTIR gas cell reactor, combined with online mass spectrometry (MS) analysis, kinetic analysis, and emission spectroscopic measurements. In plasma CO₂ hydrogenation over Pd/ZnO, the hydrogenation of adsorbed surface CO₂ on Pd/ZnO is the dominant reaction route for the enhanced CO₂ conversion, which can be ascribed to the generation of a ZnO _x overlay as a result of the strong metal-support interactions (SMSI) at the Pd-ZnO interface and the presence of abundant H species at the surface of Pd/ZnO; however, this important surface reaction can be limited in the Plasma + ZnO system due to a lack of active H species present on the ZnO surface and the absence of the SMSI. Instead, CO₂ splitting to CO, both in the plasma gas phase and on the surface of ZnO, is believed to make an important contribution to the conversion of CO₂ in the Plasma + ZnO system.

Ultra-Cheap Renewable Energy as an Enabling Technology for Deep Industrial Decarbonization via Capture and Utilization of Process CO2 Emissions

Rapidly declining costs of renewable energy technologies have made solar and wind the cheapest sources of energy in many parts of the world. This has been seen primarily as enabling the rapid decarbonization of the electricity sector, but low-cost, low-carbon energy can have a great secondary impact by reducing the costs of energy-intensive decarbonization efforts in other areas. In this study, we consider, by way of an exemplary carbon capture and utilization cycle based on mature technologies, the energy requirements of the “industrial carbon cycle”, an emerging paradigm in which industrial CO2 emissions are captured and reprocessed into chemicals and fuels, and we assess the impact of declining renewable energy costs on overall economics of these processes. In our exemplary process, CO2 is captured from a cement production facility via an amine scrubbing process and combined with hydrogen produced by a solar-powered polymer electrolyte membrane, using electrolysis to produce methanol. We show that solar heat and electricity generation costs currently realized in the Middle East lead to a large reduction in the cost of this process relative to baseline assumptions found in published literature, and extrapolation of current energy price trends into the near future would bring costs down to the level of current fossil-fuel-based processes.

Determination of photoautotrophic growth and inhibition kinetics by the Monod and the Aiba models and bioenergetics of local microalgae strain

The usage of fossil fuels results in a high amount of greenhouse gas (GHG) emissions and renewable green energy requirements entail saving ecological balance. Therefore, microalgae cultivation is widespread as a suitable raw material to produce renewable and sustainable fuel. Mathematical models are useful tools for the estimation of different conditions of a system. In this study, mathematical models were developed for monitoring the cultivation of local species of microalgae based on the chlorophyll-a and biomass concentration. Coefficients that were calculated from the Monod kinetic model were μmax; 0.03 day^-1, K_S, C_i; 0.53 mM with an R² value of 0.93 and from the Aiba inhibition kinetic model was μmax and K_S, C_i 1.48 day^-1 and 0.08 mM with an R² value of 0,73. According to the literature, there was no model was developed for the determination of kinetic coefficients based on chlorophyll-a production due to the inorganic carbon consumption. While both growth and inhibition models were developed for the inorganic carbon consumption, chlorophyll-a concentration was used for the growth model and biomass concentration was used for the inhibition model which caused and directly affected by the decrease of light penetration. The maximum biomass and chlorophyll-a concentrations were found as 1.2 g/L and 27.8 mg/L respectively with 10.24 mg/L. day^-1 nitrogen and 1.19 mg/L.day^-1 phosphorus uptake rate.

Research Progress and Reaction Mechanism of CO2 Methanation over Ni-Based Catalysts at Low Temperature: A Review

The combustion of fossil fuels has led to a large amount of carbon dioxide emissions and increased greenhouse effect. Methanation of carbon dioxide can not only mitigate the greenhouse effect, but also utilize the hydrogen generated by renewable electricity such as wind, solar, tidal energy, and others, which could ameliorate the energy crisis to some extent. Highly efficient catalysts and processes are important to make CO2 methanation practical. Although noble metal catalysts exhibit higher catalytic activity and CH4 selectivity at low temperature, their large-scale industrial applications are limited by the high costs. Ni-based catalysts have attracted extensive attention due to their high activity, low cost, and abundance. At the same time, it is of great importance to study the mechanism of CO2 methanation on Ni-based catalysts in designing high-activity and stability catalysts. Herein, the present review focused on the recent progress of CO2 methanation and the key parameters of catalysts including the essential nature of nickel active sites, supports, promoters, and preparation methods, and elucidated the reaction mechanism on Ni-based catalysts. The design and preparation of catalysts with high activity and stability at low temperature as well as the investigation of the reaction mechanism are important areas that deserve further study.

Reducing the Environmental Impacts of Desalination Reject Brine Using Modified Solvay Process Based on Calcium Oxide

In this research, the influence of a variety of operational factors such as the temperature of the reaction, gas flow rate, concentration of NaCl, and the amount of Ca(OH)2 for reducing the environmental impacts of desalination reject brine using the calcium oxide-based modified Solvay process were investigated. For this purpose, response surface modeling (RSM) and central composite design (CCD) were applied. The significance of these factors and their interactions was assessed using an analysis of variance (ANOVA) technique with a 95% degree of certainty (p < 0.05). Optimal conditions for this process included: a temperature of 10 °C, a Ca(OH)2/NaCl concentration ratio of 0.36, and a gas flow rate of 800 mL/min. Under these conditions, the maximum sodium removal efficiency from the synthetic sodium chloride solution was 53.51%. Subsequently, by employing the real brine rejected from the desalination unit with a 63 g/L salinity level under optimal conditions, the removal rate of sodium up to 43% was achieved. To investigate the process’s kinetics of Na elimination, three different kinds of kinetics models were applied from zero to second order. R squared values of 0.9101, 0.915, and 0.9141 were obtained in this investigation for zero-, first-, and second-degree kinetic models, respectively, when synthetic reject saline reacted. In contrast, according to R squared’s results with utilizing real rejected brine, the results for the model of kinetics were: R squared = 0.9115, 0.9324, and 0.9532, correspondingly. As a result, the elimination of sodium from real reject brine is consistent with the second-order kinetic model. According to the findings, the calcium oxide-based modified Solvay method offers a great deal of promise for desalination of brine rejected from desalination units and reducing their environmental impacts. The primary benefit of this technology is producing a usable solid product (sodium bicarbonate) from sodium chloride in the brine solution.

Constructing Schottky junctions via Pd nanosheets on DUT-67 surfaces to accelerate charge transfer

The separation, transfer and recombination of charge often affect the rate of photocatalytic reduction of CO₂. Schottky junctions can promote the rapid separation of space charge. Therefore, in this paper, Pd nanosheets were grown on the surface of DUT-67 by a hydrothermal method, and a Schottky junction was constructed between DUT-67 and Pd. Under the action of the Schottky junction, the CO yield of 0.3-Pd/DUT-67 reached 12.15 μmol/g/h, which was 17 times higher than that of DUT-67. Efficient charge transfer was demonstrated in photochemical experiments. The large specific surface area and the increased light utilization rate also contributed to the increase in the CO₂ reduction efficiency. In addition, the mechanism of Pd/DUT-67 photocatalytic reduction of CO₂ was proposed.

Application of Porous Materials for CO2 Reutilization: A Review

CO2 reutilization processes contribute to the mitigation of CO2 as a potent greenhouse gas (GHG) through reusing and converting it into economically valuable chemical products including methanol, dimethyl ether, and methane. Solar thermochemical conversion and photochemical and electrochemical CO2 reduction processes are emerging technologies in which solar energy is utilized to provide the energy required for the endothermic dissociation of CO2. Owing to the surface-dependent nature of these technologies, their performance is significantly reliant on the solid reactant/catalyst accessible surface area. Solid porous structures either entirely made from the catalyst or used as a support for coating the catalyst/solid reactants can increase the number of active reaction sites and, thus, the kinetics of CO2 reutilization reactions. This paper reviews the principles and application of porous materials for CO2 reutilization pathways in solar thermochemical, photochemical, and electrochemical reduction technologies. Then, the state of the development of each technology is critically reviewed and evaluated with the focus on the use of porous materials. Finally, the research needs and challenges are presented to further advance the implementation of porous materials in the CO2 reutilization processes and the commercialization of the aforementioned technologies.

Environmental and energetic analysis of coupling a biogas combined cycle power plant with carbon capture, organic Rankine cycles and CO2 utilization processes

Greenhouse gas emissions from power plants that use fossil fuels cause a serious impact to the environment, for this reason the use of renewable energy technologies is an important alternative as a way of combatting climate change. The production of power via biomass is considered as a carbon neutral energy resource, but it is well known that the non-fossil CO₂ emitted from this type of processes can also be captured. In order to do so, in this work it is proposed a match between a Biogas combined cycle power plant and postcombustion carbon capture process, to capture the CO₂ produced by the biogas combustion, and also it considered a match with an organic Rankine cycle that uses the wasted energy of the combustion gases. Additionally, it is considered that the captured carbon is used to produce some value-added chemicals and fuels. Environmental and energetic evaluations were carried out for the coupling of those technologies. The implementation of the carbon capture plant, results on a diminution of the 87% of the emission of the combined cycle power plant. The life cycle analysis results show that the study case of Syngas production via dry reforming of methane, presents the lower global warming potential (0.088 CO₂-eq kg/kg) and it was also found that the global warming potential has a reduction with the help of the mass integration between the different alternatives of CO₂ utilization. Finally, it was found an annual reduction of 0.055 CO₂-eq t for the system with mass integration compared with the cases without mass integration.

Stepping Stones in CO2 Utilization: Optimizing the Formate to Oxalate Coupling Reaction Using Response Surface Modeling

One of the crucial steps for the conversion of CO₂ into polymers is the catalytic formate to oxalate coupling reaction (FOCR). Formate can be obtained from the (electro)catalytic reduction of CO₂, while oxalate can be further processed toward building blocks for modern plastics. In its 175 year history, multiple parameters for the FOCR have been suggested to be of importance. Yet, no comprehensive understanding considering all those parameters is available. Hence, we aim to assess the relative impact of all those parameters and deduce the optimal reaction conditions for the FOCR. We follow a systematic two-stage approach in which we first evaluate the most suitable categorical variables of catalyst, potential poisons, and reaction atmospheres. In the second stage, we evaluate the impact of the continuous variables temperature, reaction time, catalyst loading, and active gas removal within previously proposed ranges, using a response surface modeling methodology. We found KOH to be the most suitable catalyst, and it allows yields of up to 93%. Water was found to be the strongest poison, and its efficient removal increased oxalate yields by 35%. The most promising reaction atmosphere is hydrogen, with the added benefit of being equal to the gas produced in the reaction. The temperature has the highest impact on the reaction, followed by reaction time and purge rates. We found no significant impact of catalyst loading on the reaction within the ranges reported previously. This research provides a clear and concise multiparameter optimization of the FOCR and provides insight into the reaction cascade involving the formation and decomposition of oxalates from formate.

Assessment of optimal conditions for the performance of greenhouse gas removal methods

In this study, a comparative literature-based assessment of the impact of operational factors such as climatic condition, vegetation type, availability of land, water, energy and biomass, management practices, cost and soil characteristics was carried out on six greenhouse gas removal (GGR) methods. These methods which include forestation, enhanced weathering (EW), soil carbon sequestration (SCS), biochar, direct air capture with carbon storage (DACCS) and bioenergy with carbon capture and storage (BECCS) were accessed with the aim of identifying the conditions and requirements necessary for their optimum performance. The extent of influence of these factors on the performance of the various GGR methods was discussed and quantified on a scale of 0-5. The key conditions necessary for optimum performance were identified with forestation, EW, SCS and biochar found to be best deployed within the tropical and temperate climatic zones. The CCS technologies (BECCS and DACCS) which have been largely projected as major contributors to the attainment of the emission mitigation targets were found to have a larger locational flexibility. However, the need for cost optimal siting of the CCS plant is necessary and dependent on the presence of appropriate storage facilities, preferably geological. The need for global and regional cooperation as well as some current efforts at accelerating the development and deployment of these GGR methods were also highlighted.

Environmental impacts and greenhouse gas emissions assessment for energy recovery and material recycle of the wastewater treatment plant

This study investigated the environmental burdens concerning the recycling/recovery process of a wastewater treatment plant's construction material waste and biogas. Detailed data inventories of case studies were employed in several scenarios to explore the role of end-of-life treatment methods. The ReCiPe 2016 and the Greenhouse gas Protocol life cycle impact methods were conducted to measure the impact categories. The construction and demolition phases were considered for recycling potential assessment, while the operational phase was examined for assessing the advantages of energy recovery. Metal and concrete recycling show environmental benefits. Increasing the reprocessing rate requires more water consumption but results in: firstly, a decrease of 18.8% in total damage; secondly, reduces problematic mineral scarcity by 3.9%; and thirdly, a shortfall in fossil fuels amounting to 11.6%. Recycling concrete helps to reduce the amount of GHG emissions 1.4-fold. Different biogas treatment methods contribute to various outcomes. Biogas utilization for on-site energy purposes has more advantages than flaring and offsite consumption. Electricity and heat generation originating from biogas can provide 70% of the energy requirement and replace 100% natural gas usage. Biomethane production from biogas requires extreme power and more resources. Meanwhile, producing heat and electricity can offset 102.9 g of fossil CO₂, and manufacturing biomethane contributes the equivalent of 101.2 g of fossil fuel-derived CO₂. Reducing 10% of recovered electricity creation could rise 19.19% global warming indicator of the wastewater treatment plant.

Assessment of potential, cost, and environmental benefits of CCS-EWR technology for coal-fired power plants in Yellow River Basin of China

As an effective emission reduction approach, CO₂ capture and storage (CCS) combined with enhanced water recovery (EWR) technology can not only reduce CO₂ emissions, but can also recover deep saline water resources to relieve pressure on regional water resources, and can ensure the energy supply and both social and economic development. However, the environmental benefits and application costs of CCS-EWR are uncertain, and are determined by the technology level, geological conditions, and other physical factors. In this study, an optimal source-sink matching model and a techno-economic assessment model were developed to evaluate the contributions of CCS-EWR to carbon emission reduction and the increase of the water supply by considering various uncertain factors, as well as the corresponding costs. In addition, the Yellow River Basin (YRB) in China was selected as the research region because, while there are abundant coal-fired power plants (CFPPs) in the YRB, the water resources are scarce. The results revealed the following. (1) The maximum CO₂ capture capacity of the 236 CFPPs in the YRB is about 738.77 Mt/a, and nearly 13.14 Gt of fresh water could be provided until the 236 CFPPs in the YRB retire, which can partially relieve the pressure on the supply of water resources. (2) With the consideration of the CCS-EWR benefits, the average cost of the 236 CFPPs in the YRB in their residual lifetime to reduce their CO₂ emissions by 90% will be no more than 180 CNY/t. (3) The incentive effect of the increase of the industrial water price on the profits of CCS-EWR projects is not significant. CCS-EWR technology has better application prospects in China under the dual constraints of carbon-neutral targets and water shortages, and more policy support is required for its deployment.

Enzymes for Efficient CO2 Conversion

The accumulation of carbon dioxide in the atmosphere as a result of human activities has caused a number of adverse circumstances in the world. For this reason, the proposed solutions lie within the aim of reducing carbon dioxide emissions have been quite valuable. However, as the human activity continues to increase on this planet, the possibility of reducing carbon dioxide emissions decreases with the use of conventional methods. The emergence of compounds than can be used in different fields by converting the released carbon dioxide into different chemicals will construct a fundamental solution to the problem. Although electro-catalysis or photolithography methods have emerged for this purpose, they have not been able to achieve successful results. Alternatively, another proposed solution are enzyme based systems. Among the enzyme-based systems, pyruvate decarboxylase, carbonic anhydrase and dehydrogenases have been the most studied enzymes. Pyruvate dehydrogenase and carbonic anhydrase have either been an expensive method or were incapable of producing the desired result due to the reaction cascade they catalyze. However, the studies reporting the production of industrial chemicals from carbon dioxide using dehydrogenases and in particular, the formate dehydrogenase enzyme, have been remarkable. Moreover, reported studies have shown the existence of more active and stable enzymes, especially the dehydrogenase family that can be identified from the biome. In addition to this, their redesign through protein engineering can have an immense contribution to the increased use of enzyme-based methods in CO₂ reduction, resulting in an enormous expansion of the industrial capacity.

Do public-private partnerships in energy and renewable energy consumption matter for consumption-based carbon dioxide emissions in India?

The present study explores the effect of renewable energy consumption and public-private partnership investment in energy on consumption-based carbon dioxide emissions for India from 1990Q1 and 2015Q4 whilst controlling technology innovation and economic growth. The study employs the Maki cointegration, Bayer-Hanck cointegration, fully modified ordinary least squares, dynamic ordinary least squares, and frequency-domain causality tests to explore these dynamics. The outcomes of the present study reveal that (i) there is a long-run cointegration equation between consumption-based carbon dioxide emissions and its possible determinants; (ii) whilst renewable energy consumption is beneficial for lowering consumption-based carbon dioxide emissions, public-private partnership investment in energy makes a positive contribution to consumption-based carbon dioxide emissions in the long-run; and (iii) public-private partnership investment in energy and renewable energy consumption also significantly causes consumption-based carbon dioxide emissions at different frequency levels in India. The present study recommends that policymakers in India should apply a series of policies to discourage the use of non-renewable energy and raise the share of renewable energy in order to reduce consumption-based carbon dioxide emissions in the country. The present study also recommends that public-private partnership investment in renewable energy should increase to achieve cleaner production processes.

Technoeconomic and Life Cycle Analysis of Synthetic Methanol Production from Hydrogen and Industrial Byproduct CO2

CO₂ capture and utilization provides an alternative pathway for low-carbon hydrocarbon production. Given the ample supply of high-purity CO₂ emitted from ethanol and ammonia plants, this study conducted technoeconomic analysis and environmental life cycle analysis of several systems: integrated methanol-ethanol coproduction, integrated methanol-ammonia coproduction, and stand-alone methanol production systems, using CO₂ feedstock from ethanol plants, ammonia plants, and general market CO₂ supply. The cradle-to-grave greenhouse gas emissions of methanol produced from the stand-alone methanol, integrated methanol-ethanol, and integrated methanol-ammonia systems are 13.6, 37.9, and 84.6 g CO₂-equiv/MJ, respectively, compared to 91.5 g CO₂-equiv/MJ of conventional methanol produced from natural gas. The minimum fuel selling price (MFSP) of methanol ($0.61-0.64/kg) is 61-68% higher than the average market methanol price of $0.38/kg, when using a Department of Energy target renewable hydrogen production price of $2.0/kg. The methanol price increases to $1.24-1.28/kg when the hydrogen price is $5.0/kg. Without CO₂ abatement credits, the H₂ price needs to be within $0.77-0.95/kg for the MFSP of methanol to equal the average methanol market price. With a CO₂ credit of $35/MT according to tax credit per metric ton of CO₂ captured and used, the methanol price is reduced to $0.56-0.59/kg.

The Effect of Si on CO2 Methanation over Ni-xSi/ZrO2 Catalysts at Low Temperature

A series of Ni-xSi/ZrO2 (x = 0, 0.1, 0.5, 1 wt%, the controlled contents of Si) catalysts with a controlled nickel content of 10 wt% were prepared by the co-impregnation method with ZrO2 as support and Si as a promoter. The effect of different amounts of Si on the catalytic performance was investigated for CO2 methanation with the stoichiometric H2/CO2 molar ratio (4/1). The catalysts were characterized by BET, XRF, H2-TPR, H2-TPD, H2-chemisorption, CO2-TPD, XRD, TEM, XPS, and TG-DSC. It was found that adding the appropriate amount of Si could improve the catalytic performance of Ni/ZrO2 catalyst at a low reaction temperature (250 °C). Among all the catalysts studied, the Ni-0.1Si/ZrO2 catalyst showed the highest catalytic activity, with H2 and CO2 conversion of 73.4% and 72.5%, respectively and the yield of CH4 was 72.2%. Meanwhile, the catalyst showed high stability and no deactivation within a 10 h test. Adding the appropriate amount of Si could enhance the interaction between Ni and ZrO2, and increase the Ni dispersion, the amounts of active sites including surface Ni0, oxygen vacancies, and strong basic sites on the catalyst surface. These might be the reasons for the high activity and selectivity of the Ni-0.1Si/ZrO2 catalyst.

Carbon dioxide capture and use in photobioreactors: The role of the carbon dioxide loads in the carbon footprint

This research evaluated the carbon dioxide capture and use by Scenedesmus obliquus in a photobioreactor under different CO₂ loads. Performance indicators, carbon and energy balances, sustainability indicators, and carbon credits on the photobioreactor were assessed. The results expressed that the CO₂ loads of 384.9 kg/m³/d (15% CO₂) provide the best trade-off for the process. For this condition, maximum biomass productivities of 0.36 kg/m³/d, carbon dioxide conversion rates of 0.44 kgCO₂/m³/d, and oxygen release rates of 0.33 kgO₂/m³/d were observed, reaching maximum CO₂ removal efficiencies of 30.76%. Volatile organic compounds were the major products generated (>80%). However, only <3% was fixed in biomass. From the environmental and economic point of view, the net energy ratio was 3.44, while the potential carbon credit was of 0.04 USD per m³ of culture. Finally, the use of adequate CO₂ loads was also proven to be determinant to improve the global performance of the system.