Search Results (16)

Transforming H₂O and CO₂ into solar fuels like syngas is crucial for future sustainable transportation fuel production. Therefore, the MgFe₂O₄/CO₂ splitting cycle was thermodynamically scrutinized to estimate its solar-to-fuel energy conversion efficiency in this investigation. The thermodynamic data required to solve the modeling equations were obtained using the HSC Chemistry program. The reduction non-stoichiometry was assumed to be equal to 0.1 for all computations. One of the study’s primary goals was to examine the impact of the inert sweep gas’s molar flow rate on the process parameters related to the MgFe₂O₄/CDS cycle. Overall, it was understood that the effect of the inert sweep gas’s molar flow rate on the thermal reduction temperature was significant when it increased from 10 to 40 mol/s compared to the rise from 40 to 100 mol/s. The energy needed to reduce MgFe₂O₄ increased slightly due to the surge in the inert sweep gas’s molar flow rate. In contrast, the energy penalty for heating MgFe₂O_4-δred from the re-oxidation to thermal reduction temperature significantly decreased. Including gas-to-gas heat exchangers with a gas-to-gas heat recovery effectiveness equal to 0.5 helped reduce the energy demand for heating the inert sweep gas. Overall, although the rise in the inert sweep gas’s molar flow rate from 10 to 100 mol/s caused a drop in the thermal reduction temperature by 180 K, the total solar energy needed to drive the cycle was increased by 85.7 kW. Accordingly, the maximum solar-to-fuel energy conversion efficiency (13.1%) was recorded at an inert sweep gas molar flow rate of 10 mol/s, which decreased by 3.7% when it was increased to 100 mol/s. Full article

In the present work, inexpensive and commercially available diethyltriamine pentaacetic acid (DTPA) was used as an initiator to catalyze the N-formylation reaction of CO₂ with amines via the construction of C-N bonds in the presence of xanthone as the photosensitizer and PhSiH₃ as the reducing agent. After a systematic study of various factors, the optimal conditions for the photocatalytic reaction were obtained: 2.5 mmol of amine, 2.5 mmol of PhSiH₃, 10 mol% of DTPA, 20 mol% of xanthone, 1 mL of dimethylsulfoxide (DMSO), atmospheric pressure, and 35 W UV lamp irradiation for 48 h. Under the optimal conditions, the catalyst system afforded high performance for the N-formylation of amines (primary and secondary amines) and CO₂, and the yields of the N-formylated products of dialkylamines were above 70%. Further studies exhibit that the catalytic system has a wide scope of substrate applications. For various alicyclic secondary amines, heterocyclic secondary amines, aliphatic primary amines, and aromatic primary amines, the corresponding N-formylation products can be obtained efficiently. In addition, the catalyst can be recycled by simple precipitation and filtration. After five cycles of recycling, there was no significant change in the catalytic and structural properties of DTPA. Finally, a possible reaction mechanism is proposed. Full article

Photocatalytic carbon dioxide conversion is a promising method for generating carbon fuels, in which the most important thing is to adjust the catalyst material to improve the photocatalytic efficiency and selectivity to conversion products, but it is still very challenging. In order to enhance the efficiency of CO₂ photoreduction, it is important to develop an appropriate photocatalyst. The present study focuses on developing a simple and effective hydrothermal reaction treatment to improve the catalytic efficiency of transition metal cobalt (Co) and organophosphonates. Photoexcited charge carriers are separated and transferred efficiently during this treatment, which enhances CO₂ chemisorption. Under visible light exposure, the best performing catalyst, CoP-4, showed 2.4 times higher activity than Co₃O₄ (19.90 μmol h⁻¹ g⁻¹) for reducing CO₂ into CO, with rates up to 47.16 μmol h⁻¹ g⁻¹. This approach provides a viable route to enhancing the efficiency of CO₂ photoreduction. Full article

For the direct reduction of CO₂ and H₂O in solid oxide electrolysis cells (SOECs) with cermet electrodes toward methane, a fundamental understanding of the role of elemental carbon as a key intermediate within the reaction pathway is of eminent interest. The present synchrotron-based in situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) study shows that alloying of Ni/yttria-stabilized-zirconia (YSZ) cermet electrodes with Cu can be used to control the electrochemical accumulation of interfacial carbon and to optimize its reactivity toward CO₂. In the presence of syngas, sufficiently high cathodic potentials induce excess methane on the studied Ni/yttria-stabilized-zirconia (YSZ)-, NiCu/YSZ- and Pt/gadolinium-doped-ceria (GDC) cermet systems. The hydrogenation of carbon, resulting from CO activation at the triple-phase boundary of Pt/GDC, is most efficient. Full article

Carbon capture and storage (CCS) is an established and verified technology that can implement zero emissions on a large enough scale to limit temperature rise to below 2 °C, as stipulated in the Paris Agreement. However, leakage from CCS sites must be monitored to ensure containment performance. Surface monitoring of carbon dioxide (CO₂) concentrations at onshore CCS sites is one method to locate and quantify CCS site leakage. Employing soil accumulation chambers, we have established baseline data for the natural flux of CO₂ as a threshold alert to detect CO₂ leakage flux to ensure the safety of onshore CCS sites. Within this context, we conducted on-site CO₂ measurements at three different locations (A, B, and C) on the INAS test field at the Ito campus, Kyushu University (Japan). Furthermore, we developed a specific measurement system based on the closed-chamber method to continuously measure CO₂ flux from soil and to investigate the correlation between CO₂ flux from the soil surface and various parameters, including environmental factors and soil sample characteristics. In addition, gas permeability and the effect of different locations on soil CO₂ flux are discussed in this study. Finally, we present an equation for estimating the soil CO₂ flux used in the INAS field site that includes environmental factors and soil characteristics. This equation assists in defining the threshold line for an alert condition related to CO₂ leakage at onshore CCS sites. Full article

In order to select the best mixed amines in the CO₂ capture process, the absorption of CO₂ in mixed amines was explored at the required concentrations by using monoethanolamine (MEA) as a basic solvent, mixed with diisopropanolamine (DIPA), triethanolamine (TEA), 2-amino-2-methyl-1-propanol (AMP), and piperazine (PZ). Here, a bubble column was used as the scrubber, and a continuous operation was adopted. The Taguchi method was used for the experimental design. The conditional factors included the type of mixed amine (A), the ratio of the mixed amines (B), the liquid feed flow (C), the gas-flow rate (D), and the concentration of mixed amines (E). There were four levels, respectively, and a total of 16 experiments. The absorption efficiency (E_F), absorption rate (R_A), overall mass transfer coefficient (K_Ga), and scrubbing factor ($\varphi$) were used as indicators and were determined in a steady-state by the mass balance and two-film models. According to the Taguchi analysis, the importance of the parameters and the optimum conditions were obtained. In terms of the absorption efficiency (E_F), the absorption rate (absorption factor) (R_A/$\varphi$), and the overall mass transfer coefficient (K_Ga), the order of importance is D > E > A > B > C, D > E > C > B > A, and D > E > C > A > B, respectively, and the optimum conditions are A1B4C4D3E3, A1B3C4D4E2, A4B2C3D4E4, and A1B1C1D4E1. The optimum condition validation results showed that the optimal values of E_F, R_A, and K_Ga are 100%, 30.69 × 10⁻⁴ mol/s·L, 1.540 l/s, and 0.269, respectively. With regard to the selection of mixed amine, it was found that the mixed amine (MEA + AMP) performed the best in the CO₂ capture process. Full article

Impurities in carbon dioxide can affect several aspects of the carbon capture and storage process, including storage capacity, rock erosion, accuracy of flow meters, and toxicity of potential leaks. There is an industry need for guidance on performing purity analysis before carbon dioxide is transported and stored. This paper reviews selected reports that specifically provide threshold amount fraction limits for impurities in carbon dioxide for the purpose of transport and storage, with rationales for these limits. A carbon dioxide purity specification is provided (including threshold amount fractions of impurities) on the basis of the findings, as well as recommendations on further work required to develop a suitable gas metrology infrastructure to support these measurements including primary reference materials, sampling methods, and instruments for performing purity analysis. These recommendations provide important guidance to operators and gas analysis laboratories for performing quality assurance. Full article

We compare different approaches for the preparation of carbon monoxide-rich synthesis gas (syngas) for Fischer–Tropsch (FT) synthesis from carbon dioxide (CO₂) using a self-consistent design and process simulation framework. Three alternative methods for suppling heat to the syngas preparation step are investigated, namely: allothermal from combustion (COMB), autothermal from partial oxidation (POX) and autothermal from electric resistance (ER) heating. In addition, two alternative design approaches for the syngas preparation step are investigated, namely: once-through (OT) and recycle (RC). The combination of these alternatives gives six basic configurations, each characterized by distinctive plant designs that have been individually modelled and analyzed. Carbon efficiencies (from CO₂ to FT syncrude) are 50–55% for the OT designs and 65–89% for the RC designs, depending on the heat supply method. Thermal efficiencies (from electricity to FT syncrude) are 33–41% for configurations when using low temperature electrolyzer, and 48–59% when using high temperature electrolyzer. Of the RC designs, both the highest carbon efficiency and thermal efficiency was observed for the ER configuration, followed by POX and COMB configurations. Full article

Development of a practicable artificial photosynthesis process has been considered today as one of the top-most research priorities to address the problems related to the global warming and the associated social cost of carbon, and to develop the renewable fuels employable in place of fossil fuels. For this purpose, a simple and inexpensive route has been devised to synthesize a high-purity bmim[BF₄] to employ as a helper catalyst to promote the electrochemical CO₂ reduction (ECR) to CO formation over Sn and MoSi₂ cathodes. The rates of CO₂ reduction over Sn and MoSi₂ cathodes have been determined to be >110 mA/cm² during cyclic voltammetry. The CO formation at a current density of >100 mA/cm² in the ECR reaction is very essential to consider this reaction for industrial practice when the required electricity derived from sunlight is available at an affordable price. The bmim[BF₄] mediated ECR reaction over Sn and MoSi₂ cathodes has been identified to be a revere reaction of CO oxidation in air. The experiments with isotopic ¹³CO₂ confirmed that CO₂ is the only source of CO formation in the ECR reaction. The underlying reaction mechanism in bmim[BF₄] mediated ECR reaction over Sn has been presented and discussed in this article. Full article

New methods in lowering energy consumption costs for evaporation and concentration are needed in many commercial chemical processes. Pervaporation is an underutilized, low-energy processing method that has a potential capability in achieving lower energy processing costs. A recently developed new electrochemical process that can generate a 5–25 wt% pure formic acid (FA) from the electrochemical reduction of CO₂ requires a low-energy process for producing a more concentrated FA product for use in both on-site and commercial plant applications. In order to accomplish this, a 25 cm² membrane area pervaporation test cell was constructed to evaluate the FA-H₂O system separation performance of three distinct types of membrane candidates at various FA feed concentrations and temperatures. The selection included one cation ion exchange, two anion ion exchange, and two microporous hydrophobic membranes. The permeation flux rates of FA and H₂O were measured for FA feed concentrations of 10, 20, 40, and 60 wt% at corresponding temperatures of 22, 40, and 60 °C. The separation performance results for these particular membranes appeared to follow the vapor liquid equilibrium (VLE) characteristics of the vapor phase in the FA-H₂O system as a function of temperature. A Targray microporous hydrophobic high-density polyethylene (HDPE) membrane and a Chemours Nafion^® N324 membrane showed the best permeation selectivities and mass flux rates FA feed concentrations, ranging from 10 to 40 wt%. The cation and anion ion exchange membranes evaluated were found not to show any significant enhancements in blocking or promoting the transport of the formate ion or FA through the membranes. An extended permeation cell run concentrated a 10.12% FA solution to 25.38% FA at 40 °C. Azeotropic distillation simulations for the FA-H₂O system using ChemCad 6.0 were used to determine the energy requirement using steam costs in processing FA feed concentrations ranging from 5 to 30 wt%. These experimental results indicate that pervaporation is a potentially useful unit process step with the new electrochemical process in producing higher concentration FA product solutions economically and at lower capital costs. One major application identified is in on-site production of FA for bioreactors employing new types of microbes that can assimilate FA in producing various chemicals and bio-products. Full article

This paper argues that electrification and gasification go hand in hand and are crucial on our pathway to a carbon-neutral energy transition. Hydrogen made from renewable electricity will be crucial on this path but is not sufficient, mainly due to its challenges related to its transport and storage. Thus, other ‘molecules’ will be needed on the pathway to a carbon-neutral energy transition. What at first sight seems a contradiction, this paper argues that carbon (C) will be an important and required chemical element in many of these molecules to achieve our carbon neutrality goal. Therefore, on top of the “Hydrogen Economy” we should work also towards a “Synthetic Hydrocarbon Economy”, implying the needs for lots of carbon as a carrier for hydrogen and embedded in products as a form of sequestration. It is crucial that this carbon is taken from the biosphere or recycled from biomass/biogas and not from fossil resources. Due to efficiency losses in capturing and converting atmospheric CO₂, the production of renewable molecules will increase the overall demand for renewable energy drastically. Full article

There is currently quite a lot of scientific interest in carbon dioxide (CO₂) capture and valorization with ionic liquids (ILs). In this manuscript, we analyze the influence of the potential applied, the nature of the cathode and the electrolyte using different organic mediators, such as nitro or cyano aromatic derivatives, to promote the electrochemical activation of CO_2. An electrocatalytic process using a homogeneous catalysis is seen when nitroderivatives are used, yielding to oxalate in organic electrolytes and ILs. Turnover frequency (TOF) values and Farafay efficiencies were slightly higher in N,N’-dimethylformamide (DMF) than in ILs probably due to the viscosity of the electrolyte. The use of cyano derivatives allows to tune the electrochemical reactivity in function of the reduction potential value applied from electrocarboxylated products (via a nucleophile-electrophile reaction) to oxalate. These electrochemical reactions were also performed using three different cathodes, organic electrolytes and ionic liquids. The use of copper, as a cathode, and ionic liquids, as electrolytes, would be a cheaper and greener alternative for activating carbon dioxide. Full article

This paper is a review on the application of imidazolium-based ionic liquids tethered to polymer backbones in the electrochemical conversion of CO₂ to carbon monoxide and formic acid. These tethered ionic liquids have been incorporated into novel anion ion exchange membranes for CO₂ electrolysis, as well as for ionomers that have been incorporated into the cathode catalyst layer, providing a co-catalyst for the reduction reaction. In using these tethered ionic liquids in the cathode catalyst composition, the cell operating current increased by a factor of two or more. The Faradaic efficiencies also increased by 20–30%. This paper provides a review of the literature, in addition to providing some new experimental results from Dioxide Materials, in the electrochemical conversion of CO₂ to CO and formic acid. Full article

Methane is the second most important greenhouse gas. Natural methane emissions represent 35–50% of the global emissions budget. They are identified, measured and categorized, but, in stark contrast to anthropogenic emissions, research on their mitigation is largely absent. To explain this, 18 problems are identified and presented. This includes problems related to the emission characteristics, technological and economic challenges, as well as problems resulting from a missing framework. Consequently, strategies, methods and solutions to solve or circumvent the identified problems are proposed. The framework covers definitions for methane source categorization and for categories of emission types and mitigation approaches. Business cases for methane mitigation are discussed and promising mitigation technologies briefly assessed. The importance to get started with methane mitigation in the different areas is highlighted and avenues for doing so are presented. Full article