Electrochemical conversion of carbon dioxide: effect of the cell and of the operating parameters on the performances of the process.

Recycling technologies of CO2 allow to introduce renewable energy in the chemical and energy chain, storing a renewable energy in the chemical form. In this context, electrochemical conversion of CO2 is considered one of the more interesting approaches, using excess electric energy from intermittent renewable sources. (1) Furthermore, products can be selectively controlled by changing the operating conditions of electrolysis. In particular, in the last years, an increasing attention has been devoted to the electrochemical conversion of CO2 to formic acid or formate in water. (2,3,4) The main hurdle of the reduction of CO2 from water solution is the low CO2 solubility in water. In this work,…

ELECTROCHEMICAL CONVERSION OF CARBON DIOXIDE TO FORMIC ACID IN A PRESSURIZZED FILTER PRESS CELL

To limit the negative effect of carbon dioxide as a greenhouse gas, an interesting approach is the utilization of Carbon Capture and Conversion (CCC) methodology, which is focused on the use of CO2 waste as a feedstock to produce added-value product by using the excess electric energy from renewable source [1]. In this framework, an increasing attention has been devoted in the electrochemical conversion of carbon dioxide to formic acid in water [2,3], which is considered one of the more attractive pathway to convert CO2. Since the main hurdle of the CO2 reduction from aqueous solution is the low CO2 solubility in water, in this work, the effect of some operating parameters, including pressu…

Catalytic hydrothermal liquefaction of municipal sludge assisted by formic acid for the production of next-generation fuels

Abstract Hydrothermal liquefaction (HTL) of municipal sludge (MS) was studied at 325 °C and 30 min at 10 and 30% w/w concentration of MS using formic acid (FA) as a green liquid hydrogen donor both in the absence and in the presence of heterogeneous catalysts. Pellets of commercial NiMo/Al2O3, CoMo/Al2O3 and felt of activated carbon ACF 1600 were used as catalysts. The addition of FA at high MS loading allowed to increase the yields in BC from 41 to 62% and its H/C ratio from 1.80 to 2.01 leading to energy recovery (ER) higher than 100%.When heterogeneous catalysts were used together with FA, a marked improvement of BC yields and quality was obtained at 10% MS loading. This behavior was not…

STUDY OF ELECTROCHEMICAL PROCESSES FOR THE CONVERSION OF CARBON DIOXIDE TO ADDED-VALUE PRODUCTS

Pressurized CO2 Electrochemical Conversion to Formic Acid: From Theoretical Model to Experimental Results

To curb the severely rising levels of carbon dioxide in the atmosphere, new approaches to capture and utilize this greenhouse gas are currently being investigated. In the last few years, many researches have focused on the electrochemical conversion of CO2 to added-value products in aqueous electrolyte solutions. In this backdrop, the pressurized electroreduction of CO2 can be assumed an up-and-coming alternative process for the production of valuable organic chemicals [1-3]. In this work, the process was studied in an undivided cell with tin cathode in order to produce formic acid and develop a theoretical model, predicting the effect of several operative parameters. The model is based on …

Electrochemical Treatment of Synthetic Wastewaters Contaminated by Organic Pollutants at Ti 4 O 7 Anode. Study of the Role of Operative Parameters by Experimental Results and Theoretical Modelling

In the last years, an increasing attention has been devoted to the utilization of anodic oxidation (AO) technologies for the treatment of wastewater polluted by recalcitrant organics. Recently, Ti4O7 was proposed as a promising anode for AO for the treatment of various organics. Here the potential utilization of commercial Ti4O7 anodes has been evaluated considering the electrochemical treatment of synthetic wastewater contaminated by three very different organic molecules (namely, oxalic acid, phenol and Acid Orange 7), all characterized by a very high resistance to AO. The performances of Ti4O7 were compared with that of two largely investigated anodes: Boron-doped diamond (BDD), which is…

Electrochemical conversion of CO2 to HCOOH at tin cathode in a pressurized undivided filter-press cell

Abstract The electrochemical reduction of carbon dioxide to formic acid was performed for the first time in a pressurized filter-press cell with a continuous recirculation of the electrolytic solution (0.9 L) at a tin cathode. It was shown that the performances of the system are comparable or slightly better than that of a batch system with a smaller volume (0.05 L). The selection of proper values of both current density and CO2 pressure allowed to achieve quite high values of faradaic efficiencies. Long-time electrolyses have shown that the system is stable and that it can allow to generate quite high concentrations of HCOOH (about 0.4 M).

Electrochemical treatment of paper mill wastewater by electro-Fenton process

Abstract The electrochemical oxidation of organics in paper mill wastewater belonging to Halfa industries (Tunisia) was performed by galvanostatic electrolyses using electro-Fenton (EF) process. The effect of several operating parameters, such as applied current density, electrodes material, air pressure and the presence of sodium chloride (NaCl) was evaluated. In particular, carbon felt (CF), modified carbon felt (MCF) and gas diffusion electrode (GDE) were used as cathode while Ti/IrO2-Ta2O5 and Boron Doped Diamond (BDD) as anode. Total Organic Carbon (TOC) measure was chosen as reference parameter to assess the extent of the treatment. The experimental results show that, by adopting the …

High-pressure synthesis of CO and syngas from CO2 reduction using Ni-N-doped porous carbon electrocatalyst

Abstract Electrochemical conversion of CO2 to CO or syngas (CO/H2 mixture) is considered one of the most promising approaches to valorise waste-CO2. To develop the process on industrial scale, it would be necessary to use selective and inexpensive electrodes and to obtain high productivities with low energy consumption. In this frame, Ni−NC catalysts are considered among the most interesting ones because of their relatively low cost, high faradaic efficiency in CO ( F E C O ), and high stability. However, up to now, quite low productivities were obtained as a result of low current densities achieved in aqueous electrolytes. In this work, we have evaluated the performances of a Ni−NC electro…

Electrochemical Conversion of CO2 to HCOOH at Tin Cathode: Development of a Theoretical Model and Comparison with Experimental Results

The electrochemical reduction of pressurized carbon dioxide at tin cathode is considered a very promising process for the production of formic acid. Here, the process was studied in an undivided cell with the aim of developing a simple theoretical model. First, a large series of polarization and electrolyses was performed in order to evaluate the kinetic of the process. According to the literature, experimental results can be described by a simple reaction mechanism, which involves the following key stages: (i) mass transfer of CO2 to the cathode; (i) its adsorption described by a Langmuir equation; (iii) the reduction of adsorbed CO2. A simple model was developed based on the cathodic conv…

Electrochemical Treatment of Wastewater by ElectroFenton, Photo-ElectroFenton, Pressurized- ElectroFenton and Pressurized Photo ElectroFenton: A First Comparison of these Innovative Routes

In the last few years increasing attention has been devoted to the utilization of electroFenton (EF) and EF based technologies for the treatment of wastewater polluted by recalcitrant organics. It has been shown that the performances of EF can be strongly improved using ultraviolet (UV) irradiation, e.g., by the photo-electroFenton (PEF) method, or pressurized air or oxygen, e.g., by the pressurized-electroFenton (PrEF) one. Although several studies were carried out on the degradation of many organic pollutants using EF, PEF or PrEF, a systematic comparison between PEF and PrEF was never reported as well as the possibility to couple the irradiation with pressurized air. In this study the pe…

Removal of Phenol from Water in the Presence of NaCl in Undivided Cells Equipped with Carbon Felt or Ni Cathodes: Effect of Air Pressure

Recently, the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides was shown to be significantly improved adopting proper operative conditions such as suitable anodes and cathodes and low current density. In particular, the use of suitable cathodes such as carbon felt or silver could increase the removal of TOC and reduce the formation of chlorinated by-products. In this study, attention was focused on the utilization of carbon felt cathodes with the main aim to evaluate the effect of air pressure on the process using phenol as model organic pollutant. It was shown that, in the presence of carbon felt cathode, the use of pressurized air allows b…

Assisted reverse electrodialysis for CO2 electrochemical conversion and treatment of wastewater: A new approach towards more eco-friendly processes using salinity gradients

Abstract In this paper, the utilization of assisted reverse electrodialysis (A-RED), recently used for pre-desalination, is proposed as a general method to reduce the energy requirements of electrolysis processes and evaluated for two model processes: (i) the cathodic conversion of carbon dioxide to formic acid; (ii) the anodic treatment of water contaminated by organics. In A-RED, two solutions with different salt content and an external potential difference, applied in the direction of the natural salinity gradient, are both used to drive redox processes. It was shown, for the first time, that the cathodic conversion of CO2 to formic acid can be performed by both reverse electrodialysis (…

Treatment of aqueous solutions of oxytetracycline by different electrochemical approaches: anodic oxidation, pressurized electro-Fenton and oxidation by electrogenerated active chlorine

The tetracycline group (TCs) includes the most common antibiotics for treatment of both human and animal infections. TCs are resistant to biological degradation; hence, conventional wastewater treatments are unable to remove these contaminants. Here, the utilization of different electrochemical processes, such as electro-Fenton (EF), direct anodic oxidation (AO) and indirect oxidation by electrogenerated active chlorine (EAC), for the treatment of aqueous solutions of oxytetracycline (OTC), which is one of the TCs, was studied. The effect of various operating conditions was evaluated to optimize the selected processes. EAC gave the fastest abatement of OTC, but the lowest removal of TOC and…

Towards the electrochemical conversion of CO2 to formic acid at an applicative scale: technical and economic analysis of most promising routes

In the last decade, the electrochemical conversion of CO 2 to formic acid, FA, using Sn‐based cathodes, was widely investigated. In this work, the technical feasibility and economic viability of this process were evaluated considering the most promising electrochemical routes reported in the literature. Five case studies, based on the utilisation of GDE technologies or high CO 2 pressures, were analysed. The cost for producing FA by the electrochemical route was compared with that of the conventional chemical route. Several scenarios were envisioned finding the target figures of merit, the potential bottlenecks (including low FA concentration, GDE cost and high energy consumption) of each t…

ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE TO FORMIC ACID AT TIN CATHODE IN DIVIDED AND UNDIVIDED CELLS: EFFECT OF OPERATING PARAMETERS

The electrochemical reduction of carbon dioxide is considered a relevant topic for both the synthesis of chemicals and the decrease of global warming. Electrochemical processes could utilize excess energy from intermittent renewable sources to convert carbon dioxide in various products such as CO, formate and formic acid, methane and ethylene in water and oxalic acid, formic acid, CO as well as carboxylic acids (by reaction with suitable reagents such as aromatic ketones or benzylic halides) in aprotic solvents [1-3]. It has been shown that the selectivity of the process dramatically depends on the nature of the cathode. Four distinct classes of metal catalysts have been identified on the b…

Electrochemical conversion of CO2 to formic acid using a Sn based cathode: Combined effect of temperature and pressure

Electrochemical conversion of CO2 in the aqueous electrolyte into value-added chemicals is considered one of the most promising strategies to valorize waste-CO2. In the last decade, high attention was focused on the electro- chemical synthesis of formic acid (FA) via CO2 reduction using Sn cathodes. To improve the final concentration of FA in aqueous electrolytes, several approaches, including the utilization of different technologies (i.e. pressurized CO2 reactor, a gas diffusion electrode, divided cell etc...) and different operative conditions (i.e. pH, current densities, temperature, mixing rate, etc...) were investigated in detail. To date, the effect of temperature (T) on the electroc…

Electrochemical production and use of chlorinated oxidants for the treatment of wastewater contaminated by organic pollutants and disinfection

Abstract In the last years, an increasing attention has been devoted to the use of electrogenerated chlorinated oxidants for the treatment of wastewater polluted by recalcitrant organics and/or for the disinfection of water contaminated by pathogen microorganisms. In this review, more recent and relevant findings were presented and critically discussed. The main advantages and disadvantages of this technique were commented, including the potential formation of toxic chlorinated organic specie and of chlorate and perchlorate or the difficult selection of proper operative parameters, as well as the key points that should be addressed to enhance the use on an applicative scale.

Electrochemical conversion of CO2 to formic acid using a Sn based electrode: A critical review on the state-of-the-art technologies and their potential

Abstract The electrochemical conversion of carbon dioxide is considered one of the most promising strategies to convert waste-CO2 into value-added chemicals. This review focuses on the synthesis of formic acid/formate in aqueous electrolyte using Sn-based cathodes; this material is considered relatively cheap and shows promising results in terms of faradaic efficiency. In order to be suitable at an industrial scale, the process should present simultaneously high current densities, faradaic efficiencies close to 100%, high concentrations of formic acid and long-term stability. Analysing the main results reported in the literature, it was observed that to date further studies are necessary to…

Electrochemical treatment of wastewater contaminated by organics and containing chlorides: Effect of operative parameters on the abatement of organics and the generation of chlorinated by-products

Abstract In the last years, large attention has been devoted to the electrochemical treatment of wastewater polluted by recalcitrant organics and containing chlorides. However, the utilization on an applicative scale of this route is limited by the fact that usually it is not possible to achieve high removals of organics without the generation of significant amounts of chlorinated by-products. Here, the role of several operative parameters on the performances of the process was systematically evaluated using phenol as a model organic pollutant. It was shown that the removal of phenol and TOC and the generation of many by-products including chlorophenols, chloroacetic acids, chlorate and per…

Electrochemical reduction of carbon dioxide to formic acid at a tin cathode in divided and undivided cells: effect of carbon dioxide pressure and other operating parameters

Abstract The reduction of carbon dioxide to formic acid at a tin cathode was studied in both divided and undivided cells. In the first stage of the study, the effect of some operating parameters, including the working potential and the nature of the supporting electrolyte and of the cathode, on both the cathodic reduction of CO2 and the anodic oxidation of formic acid was investigated in a divided cell. In a second stage, the reduction of carbon dioxide was performed in an undivided cell with the aim of studying the effect on the generation of formic acid of various operating parameters such as current density, cathode to anode area ratio, mixing rate and nature of the anode and of the supp…

Effect of Pressure on the Electrochemical Conversion of CO2 to CO

To minimize the negative effect of carbon dioxide as a greenhouse gas and introduce renewable energy in the chemical and energy chain, an interesting approach is the Carbon Capture and Conversion. In this context, one of more appealing conversion strategies is the el Ectrochemical reduction of CO2, which could combines the utilization of excess electric energy from intermittent renewable sources with CO2 (1). Furthermore, CO2 can be selectively converted into various useful chemicals by changing the operating conditions of electrolysis. In particular, an increasing attention has been devoted to the electrochemical conversion of carbon dioxide to carbon monoxide (2,3). The main obstacle of t…

Electrochemical conversion of carbon dioxide to formic acid: on the road to applicative scale

In this context, electrochemical reduction of CO2 is considered one of the more attractive pathway to convert CO2, because the products can be selectively controlled by changing the operative conditions of the electrolysis. In the last years, an increasing attention has been devoted on the electrochemical conversion of CO2 to formic acid in water [2,3]. The main hurdle of the reduction of CO2 from water solution is the low CO2 solubility in water. In this work, the effect of some operating parameters, including pressure, current density, and flow rate, on the conversion of CO2 at tin flat cathodes to formic acid was studied using a pressurized filter-press cell with a continuous recirculati…

Cathodic reduction of CO2 to formic acid: Effect of the nature of the cathode for pressurized systems

Electrochemical conversion of CO2 into formic acid (FA) in an aqueous electrolyte is considered a promising strategy to valorise waste-CO2. Some studies, mainly performed using Sn cathodes, have shown that the performance of the process can be strongly improved using pressurized systems. On the other hand, other studies, usually carried out in non-pressurized systems, have indicated that the nature of the cathode can strongly affect the process. Hence, in this work, we have investigated the coupled effect of nature of the cathode and CO2 pressure (PCO2 ) on the electrochemical conversion of CO2 to FA. Four electrodes (Sn, Sn/C-NP, Bi, Bi/C-NP) have been used as model cathodes. The results o…

System Design Rules for Intensifying the Electrochemical Reduction of CO 2 to CO on Ag Nanoparticles

Electroreduction of CO2 (eCO2RR) is a potentially sustainable approach for carbon-based chemical production. Despite significant progress, performing eCO2RR economically at scale is challenging. Here we report meeting key technoeconomic benchmarks simultaneously through electrolyte engineering and process optimization. A systematic flow electrolysis study - performing eCO2RR to CO on Ag nanoparticles as a function of electrolyte composition (cations, anions), electrolyte concentration, electrolyte flow rate, cathode catalyst loading, and CO2 flow rate - resulted in partial current densities of 417 and 866 mA/cm2 with faradaic efficiencies of 100 and 98 % at cell potentials of −2.5 and −3.0 …

Electrochemical Abatement of Organic Pollutants in Water by Electro- Fenton with Natural Heterogeneous Catalysts Under Pressure

In recent decades, electrochemical advanced oxidation processes (EAOPs) have proved as alternative technologies to conventional processes. Indeed, EAOPs can often allow to treat wastewater containing toxic and POPs. Among them, electro-Fenton (EF) is considered particularly promising for the treatment of recalcitrant organics, since it presents various advantages, including high abatements for many organic pollutants, simplicity of equipment and operations, relatively low cost and low consumption of chemicals. Recently, the utilization of some natural heterogeneous catalysts was proposed in order to avoid some disadvantages of the conventional EF process. In this frame, in this work EF proc…

Effective Removal and Mineralization of 8-Hydroxyquinoline-5-sulfonic Acid through a Pressurized Electro-Fenton-like Process with Ni−Cu−Al Layered Double Hydroxide

Ni−Cu−Al layered double hydroxide (Ni−Cu−Al LDH) was proposed as an electro‐Fenton‐like catalyst for 8‐hydroxyquinoline‐5‐sulfonic acid (8‐HQS) removal in water. The properties of the prepared catalysts were characterized by using X‐ray, SEM and EDAX analyses. The effect of numerous operative parameters on the removal of 8‐HQS and total organic carbon (TOC) was studied. Very high level removal of both 8‐HQS and TOC (87 and 79 %, respectively) were obtained by using a pressurized electro‐Fenton‐like process (PrEFL‐LDH) at P=10 bars, using a Ti/IrO2‐Ta2O5 anode for 6 h. The process presented good performances in a large range of pH (3–10) and gave better removals of 8‐HQS and TOC with respect…

Electrochemical conversion of Carbon Dioxide: effect of operating parameters and of the reactor on the performances of the process.

Electrochemical treatment of aqueous solutions of organic pollutants by electro-Fenton with natural heterogeneous catalysts under pressure using Ti/IrO2-Ta2O5 or BDD anodes

The treatment of toxic organic pollutants by electro-Fenton (EF) presents some drawbacks such as the necessity to work at low pH and the low solubility of oxygen in water contacted with air or oxygen at room pressure that results often in slow and relatively low abatements. Here, the coupled adoption of natural heterogeneous catalysts and of relatively high pressure was proposed in order to improve the performances of EF for the treatment of organic pollutants. Caffeic acid (CA) and 3-chlorophenol were used as model resistant organic pollutants. EF process was performed using both conventional homogeneous FeSO4 and natural heterogeneous catalysts (pyrite, chalcopyrite, Fe2O3 and Fe3O4) as i…

Premio di Laurea “Ametek Scientific Instruments”: Electrochemical Conversion of Carbon Dioxide to Formic Acid. Study of the Effect of the Operating Parameters

Electrochemical conversion of CO2 is considered one of the more appealing approaches to introduce renewable energy in the chemical and energy chain and to mitigate the greenhouse gases effect. In this work, the reduction of carbon dioxide was performed in undivided electrochemical cell to produce formic acid, which is one of the highest value-added chemicals and economically feasible for large-scale applications (1). It is well known that the main hurdle of the reduction of CO2 from water solution is the low CO2 solubility in water. In order to overcome this obstacle, a specific investigation on the effect of the CO2 pressure and other operating parameters at tin flat cathodes was carried o…

Cover Feature: System Design Rules for Intensifying the Electrochemical Reduction of CO 2 to CO on Ag Nanoparticles (ChemElectroChem 9/2020)

Electrochemical conversion of pressurized CO2 at simple silver-based cathodes in undivided cells: study of the effect of pressure and other operative parameters

Abstract Electrochemical reduction of pressurized CO2 is proposed as an interesting approach to overcome the main hurdle of the CO2 electrochemical conversion in aqueous solution, its low solubility (ca. 0.033 M), and to achieve good faradaic efficiency in CO using simple sheet silver cathodes and undivided cells, thus lowering the overall costs of the process. The effect on the process of CO2 pressure (1–30 bar), current density, nature of the supporting electrolyte and other operative conditions, such as the surface of the cathode or the mixing rate, was studied to enhance the production of CO. It was shown that pressurized conditions allow to improve drastically the current efficiency o…

Liquefazione idrotermica di fanghi di depurazione dalle acque reflue in presenza di acido formico come co-solvente

A causa del progressivo impoverimento delle risorse di combustibili fossili e dell’impatto negativo che il loro utilizzo ha sull'ambiente, la produzione di carburanti da fonti alternative, come le biomasse, ha ricevuto negli ultimi anni una notevole e crescente attenzione. Questo studio è incentrato sulla liquefazione idrotermica (HTL) dei fanghi provenienti dalla depurazione delle acque reflue civili. Tale tipo di biomassa oltre ad avere un alto tasso di umidità, ha un elevato contenuto organico e per essere smaltita è necessario che gli impianti di depurazione investano un ingente capitale [1]. L’HTL tradizionale prevede l’utilizzo dell’acqua, in parte già contenuta nella biomassa, come s…

Electrochemical treatment of wastewater containing NaCl. Methods to increase the removal of organic pollutants and minimize the formation of toxic by-products

In many cases, wastewater can contain both organic pollutants and NaCl. Electrochemical methods allow to treat very effectively organic pollutants in the presence of NaCl. However, the utilization on an applicative scale of this route is limited by the fact that usually the high removals of organics is coupled with the generation of significant amounts of chlorinated by-products. The role of several operative parameters on the performances of the process was systematically evaluated using phenol as a model organic pollutant. It was shown that the removal of phenol and TOC and the generation of many by-products including chlorophenols, chloroacetic acids, chlorate and perchlorate dramaticall…