A 4E analysis of renewable formic acid synthesis from the electrochemical reduction of carbon dioxide and water: studying impacts of the anolyte material on the performance of the process

Carbon dioxide (CO2) utilization alternatives for manufacturing formic acid (FA) such as electrochemical reduction (ER) or homogeneous catalysis of CO2 and H2 could be efficient options for developing more environmentally-friendly production alternatives to FA fossil-dependant production. However, these alternatives are currently found at different technological readiness levels (TRLs), and some remaining technical challenges need to be overcome to achieve at least carbon-even FA compared to the commercial process, especially ER of CO2, which is still farther from its industrial application. The main technical limitations inherited by FA production by ER are the low FA concentration achieved and the high overpotentials required, which involve high consumptions of energy (ER cell) and steam (distillation). In this study, a comparison in terms of carbon footprints (CF) using the Life Cycle Assessment (LCA) tool was done to evaluate the potential technological challenges assuring the environmental competitiveness of the FA production by ER of CO2. The CF of the FA conventional production were used as a benchmark, as well as the CF of a simulated plant based on homogeneous catalysts of CO2 and H2 (found closer to be commercial). Renewable energy utilization as PV solar for the reaction is essential to achieve a carbon-even product; however, the CF benefits are still negligible due to the enormous contribution of the steam produced by natural gas (purification stage). Some ER reactor configurations, plus a recirculation mode, could achieve an even CF versus commercial process. It was demonstrated that the ER alternatives could lead to lower natural resources consumption (mainly, natural gas and heavy fuel oil) compared to the commercial process, which is a noticeable advantage in environmental sustainability terms.

The future of carbon dioxide utilisation (CDU) processes, depend on (i) the future demand of synthesised products with CO2, (ii) the availability of captured and anthropogenic CO2, (iii) the overall CO2 not emitted because of the use of the CDU process, and (iv) the economics of the plant. The current work analyses the mentioned statements through different technological, economic and environmental key performance indicators to produce formic acid from CO2, along with their potential use and penetration in the European context. Formic acid is a well-known chemical that has potential as hydrogen carrier and as fuel for fuel cells.This work utilises process flow modelling, with simulations developed in CHEMCAD, to obtain the energy and mass balances, and the purchase equipment cost of the formic acid plant. Through a financial analysis, with the net present value as selected metric, the price of the tonne of formic acid and of CO2 are varied to make the CDU project financially feasible. According to our research, the process saves CO2 emissions when compared to its corresponding conventional process, under specific conditions. The success or effectiveness of the CDU process will also depend on other technologies and/or developments, like the availability of renewable electricity and steam.

Carbon Dioxide as Chemical Feedstock

CO2 capture and utilization from supercritical coal direct chemical looping combustion power plant – Comprehensive analysis of different case studies

Hydrogen is deemed as a crucial component in the transition to a carbon-free energy system, and researchers are actively working to realize the hydrogen economy. While hydrogen derived from renewable energy sources is a promising means of providing clean energy to households and industries, its practical usage is currently hindered by difficulties in transportation and storage. Due to the extreme operating conditions required for liquefying hydrogen, various hydrogen carriers are being considered, which can be transported and stored at mild operating conditions and provide hydrogen at the site of usage. Among various candidates, green hydrogen carriers obtained via carbon dioxide utilization have been proposed as an economically and environmentally feasible option.Herein, the potential of using methanol and formic acid as green hydrogen carriers are evaluated regarding various production and dehydrogenation pathways, within a hydrogen distribution system including the recycle of carbon dioxide. Recent progress in carbon dioxide utilization processes, especially conversion of carbon dioxide captured in amine solutions, have demonstrated promising results for methanol and formic acid production. This study analyzes seven scenarios that consider carbon dioxide utilization-based thermocatalytic and electrochemical methanol and formic acid production, as well as different dehydrogenation pathways, and compares them to the scenario of delivering liquefied hydrogen. The scenarios are thoroughly analyzed via techno-economic analysis and life cycle assessment methods. The results of the study indicate that methanol-based options are economically viable, reducing the cost up to 43% compared to liquefied hydrogen delivery. As for formic acid, only the electrochemical production method is profitable, retaining 10% less cost compared to liquefied hydrogen delivery. In terms of environmental impact, all of the scenarios show higher global warming impact values than liquefied hydrogen distribution. However, results show that in an optimistic case where wind electricity is widely used, electrochemical formic acid production is competitive with liquefied hydrogen distribution, retaining 39% less global warming impact values. This is because high conversion can be achieved at mild operating conditions for the production and dehydrogenation reactions of formic acid, reducing the input of utilities other than electricity. This study suggests that while methanol can be a short-term solution for hydrogen distribution, electrochemical formic acid production may be a viable long-term option.

Increasing levels of carbon dioxide in the atmosphere and the growing need for energy necessitate a shift toward reliance on renewable energy sources and the utilization of carbon dioxide. Thus, producing carbonaceous fuel by the electrochemical reduction of carbon dioxide has been very appealing. We have focused on addressing the principal challenges of poor selectivity and poor energy efficiency in the electrochemical reduction of carbon dioxide. We have demonstrated here a viable pathway for the efficient and continuous electrochemical reduction of CO2 to formate using the metal-independent enzyme type of formate dehydrogenase (FDH) derived from C andida boidinii yeast. This type of FDH is attractive because it is commercially produced. In natural metabolic processes, this type of metal-independent FDH oxidizes formate to carbon dioxide using NAD+ as a cofactor. We show that FDH can catalyze the reverse process to generate formate when the natural cofactor NADH is replaced with an artificial cofactor, the methyl viologen radical cation. The methyl viologen radical cation is generated in situ, electrochemically. Our approach relies on the special properties of methyl viologen as a "unidirectional" redox cofactor for the conversion of CO2 to formate. Methyl viologen (in the oxidized form) does not catalyze formate oxidation, while the methyl viologen radical cation is an effective cofactor for the reduction of carbon dioxide. Thus, although the thermodynamic driving force is favorable for the oxidized form of methyl viologen to oxidize formate to carbon dioxide, the kinetic factors are not favorable. Only the reverse reaction of carbon dioxide reduction to formate is kinetically viable with the cofactor, methyl viologen radical cation. Binding free energy calculated from atomistic molecular dynamics (MD) simulations consolidate our understanding of these special binding properties of the methyl viologen radical cation and its ability to facilitate the two-electron reduction of carbon dioxide to formate in metal-independent FDH. By carrying out the reactions in a novel three-compartment cell, we have demonstrated the continuous production of formate at high energy efficiency and yield. This cell configuration uses judiciously selected ion-exchange membranes to separate the reaction compartments to preserve the yields of the methyl viologen radical cation and formate. By the electroregeneration of the methyl viologen radical cation at -0.44 V versus the normal hydrogen electrode, we could produce formate at 20 mV negative to the reversible electrode potential for carbon dioxide reduction to formate. Our results are in sharp contrast to the large overpotentials of -800 to -1000 mV required on metal catalysts, vindicating the selectivity and kinetic facility provided by FDH. Formate yields as high as 97% ± 1% could be realized by avoiding the adventitious reoxidation of the methyl viologen radical cation by molecular oxygen. We anticipate that the insights from the electrochemical studies and the MD simulations to be useful in redesigning the metal-independent FDH and alternate artificial cofactors to achieve even higher rates of conversion.

Carbon dioxide utilization—Electrochemical reduction to fuels and synthesis of polycarbonates

Chemical looping combustion (CLC) is an encouraging technology for hydrogen and power co-generation with efficient CO2 capture. Utilization of the captured CO2 is a much more important task to realize negative CO2 emissions. The objective of the work is to explore a case study of carbon dioxide utilization (CDU) in the form of formic acid synthesis using the captured CO2 and co-generated H2 from coal direct chemical looping (CDCL) power plant. Steady-state simulations are performed on the power and H2 co-generation CDCL plant integrated with formic acid synthesis and presented a comparison of overall performance of the CDCL plants with and without CDU integration. The simulation results revealed that the formic acid synthesis integrated CDCL plant avoids release of 62.49 kg.CO2/GJ of fuel input into the environment and utilizes the captured CO2 completely with the net electrical efficiency penalty of 5.8%.

In this paper, full repowering of a 320 MW steam power plant was investigated in Bandar Abbas. Due to unavailability of natural gas in the winter, LNG, Diesel, and Heavy fuel were examined as alternative fuels. The energetic, exergetic, exergoeconomic, and exergoenvironmental (4E) analyses were performed for old and repowered cases. The exergoenvironmental analyses were done based on the Life Cycle Assessment in SimaPro software. The net power, fuel consumption, costs, and environmental impacts were calculated by considering different fuels for each season. To better demonstrate the plant performance, the exergy destruction level (EDL) and the exergy cost destruction level (ECDL) were defined and applied as EDL/ECDL. To perform this analysis, a computer program was developed that could predict the base cycle and repowered cycle behaviors for different operating conditions with relative errors of less than 1.85%. Results demonstrated a 16% increase in the overall cycle efficiency, a 12% decrease in the methane consumption, and a 3% elevation in the net power using the LNG fuel.

The use of metal-impregnated polytetrafluoroethylene-bonded carbon gas-diffusion electrodes for the electrochemical reduction of carbon dioxide in aqueous solution has been investigated over a wide range of pH (1 to 5). High rates of reduction of carbon dioxide to formic acid were demonstrated. Lead-impregnated electrodes operated at 115 mA cm−2 in an aqueous acidic electrolyte (pH 2) selectively produced formic acid with a current efficiency of nearly 100% at aniR-corrected potential of approximately −1.8V versus saturated calomel electrode. Electrodes impregnated with either indium or tin produced formic acid at rates comparable with those containing lead. However, in addition to formic acid, small quantities of carbon monoxide were also produced and the simultaneous production of hydrogen by the reduction of water was more significant. Thus, it appears that the electrocatalytic activity for the electrochemical reduction of carbon dioxide to formic acid is lead>indium∼tin.

Electrochemical reduction of carbon dioxide to useful chemical has been studied as a promising method to utilize CO2. This method can selectively produce a variety of useful chemicals (e.g. carbon monoxide, formic acid, methane, and other hydrocarbons) according as reaction condition such as types of electro-catalysts, electrolytes, operation voltage, and so on [1,2]. In this study, we selected formate as a target product because it has various advantages as a feed stock chemical. Formate is produced by the electrochemical reduction of the CO2 and the formate, after treatment to form formic acid, will be used as fuel for Direct Formic Acid Fuel Cell. Particularly in the case of CO2-based unitized re-generative fuel cell, the inter-conversion reaction between CO2-C1 fuels is important. Therefore, we develop a catalyst that can be used in both sides reaction; the electrochemical conversion of CO2 to formate and the oxidation of formic acid [3]. In this case, it is most important to develop bi-functional catalysts that have activities for both reactions. In addition, high selectivity and activity to CO2 reduction as well as reduced amounts of noble metal loading for the formic acid oxidation reaction are also desired. The catalysts were made by co-electrodeposition of noble metal and post-transition metal to form binary alloy catalysts. Electrodeposition was performed at a constant deposition potential in a 3-electrode cell containing metal precursors, supporting electrolyte, and complexing agent. For some cases, thermal annealing was performed to enhance the characteristics of the fabricated catalysts. The alloy catalysts were characterized with EDS, SEM and XRD. The electrochemical reduction of carbon dioxide was performed and the produced amounts of formate were measured with HPLC. Formic acid oxidation was also performed with CV using the same catalysts. The activities to both reactions were characterized according to the alloy composition, morphologies, and other physic-chemical properties. In conclusion, certain composition of the alloy catalysts exhibited the significant activities to both reactions simultaneously.

To meet the global climate goals agreed upon regarding the Paris Agreement, governments and institutions around the world are investigating various technologies to reduce carbon emissions and achieve a net-negative energy system. To this end, integrated solutions that incorporate carbon utilization processes, as well as promote the transition of the fossil fuel-based energy system to carbon-free systems, such as the hydrogen economy, are required. One of the possible pathways is to utilize CO2 as the base chemical for producing a liquid organic hydrogen carrier (LOHC), using CO2 as a mediating chemical for delivering H2 to the site of usage since gaseous and liquid H2 retain transportation and storage problems. Formic acid is a probable candidate considering its high volumetric H2 capacity and low toxicity. While previous studies have shown that formic acid is less competitive as an LOHC candidate compared to other chemicals, such as methanol or toluene, the results were based on out-of-date process schemes. Recently, advances have been made in the formic acid production and dehydrogenation processes, and an analysis regarding the recent process configurations could deem formic acid as a feasible option for LOHC. In this study, the potential for using formic acid as an LOHC is evaluated, with respect to the state-of-the-art formic acid production schemes, including the use of heterogeneous catalysts during thermocatalytic and electrochemical formic acid production from CO2. Assuming a hydrogen distribution system using formic acid as the LOHC, each of the production, transportation, dehydrogenation, and CO2 recycle sections are separately modeled and evaluated by means of techno-economic analysis (TEA) and life cycle assessment (LCA). Realistic scenarios for hydrogen distribution are established considering the different transportation and CO2 recovery options; then, the separate scenarios are compared to the results of a liquefied hydrogen distribution scenario. TEA results showed that, while the LOHC system incorporating the thermocatalytic CO2 hydrogenation to formic acid is more expensive than liquefied H2 distribution, the electrochemical CO2 reduction to formic acid system reduces the H2 distribution cost by 12%. Breakdown of the cost compositions revealed that reduction of steam usage for thermocatalytic processes in the future can make the LOHC system based on thermocatalytic CO2 hydrogenation to formic acid to be competitive with liquefied H2 distribution if the production cost could be reduced by 23% and 32%, according to the dehydrogenation mode selected. Using formic acid as a LOHC was shown to be less competitive compared to liquefied H2 delivery in terms of LCA, but producing formic acid via electrochemical CO2 reduction was shown to retain the lowest global warming potential among the considered options.

The electrochemical CO2 reduction (ECR) to produce value-added fuels and chemicals using clean energy sources (like solar and wind) is a promising technology to neutralize the carbon cycle and reproduce the fuels. Presently, the ECR has been the most attractive route to produce carbon-building blocks that have growing global production and high market demand. The electrochemical CO2 reduction could be extensively implemented if it produces valuable products at those costs which are financially competitive with the present market prices. Herein, the electrochemical conversion of CO2 obtained from flue gases of a power plant to produce diesel and formic acid using a consistent techno-economic approach is presented. The first scenario analyzed the production of diesel fuel which was formed through Fischer-Tropsch processing of CO (obtained through electroreduction of CO2) and hydrogen, while in the second scenario, direct electrochemical CO2 reduction to formic acid was considered. As per the base case assumptions extracted from the previous outstanding research studies, both processes weren’t competitive with the existing fuel prices, indicating that high electrochemical (EC) cell capital cost was the main limiting component. The diesel fuel production was predicted as the best route for the cost-effective production of fuels under conceivable optimistic case assumptions, and the formic acid was found to be costly in terms of stored energy contents and has a facile production mechanism at those costs which are financially competitive with its bulk market price. In both processes, the liquid product cost was greatly affected by the parameters affecting the EC cell capital expenses, such as cost concerning the electrode area, faradaic efficiency, and current density.

A techno-economic evaluation approach to the electrochemical reduction of CO2 for formic acid manufacture

In carbon dioxide utilization by cyclometalated five-membered ring products, the following compounds are used in four types of applications:1. 2-Phenylpyrazole iridium compounds, pincer phosphine iridium compounds and 2-phenylimidazoline iridium compounds are used as catalysts for both formic acid production from CO2 and H2, and hydrogen production from the formic acid. This formic acid can be a useful agent for H2 production and storage for fuel cell electric vehicles.2. Other chemicals, e.g., dimethyl carbonate, methane, methanol and CO, are produced with dimethylaminomethylphenyltin compounds, pincer phosphine iridium compounds, pincer phosphine nickel compound and ruthenium carbene compound or 2-phenylpyridine iridium compounds, and phenylbenzothiazole iridium compounds as the catalysts for the reactions with CO2.3. The five-membered ring intermediates of cyclometalation reactions with the conventional substrates react with carbon dioxide to afford their many types of carboxylic acid derivatives.4. Carbon dioxide is easily immobilized at room temperature with immobilizing agents such as pincer phosphine nickel compounds, pincer phosphine palladium compounds, pincer N,N-dimethylaminomethyltin compounds and tris(2-pyridylthio)methane zinc compounds.