1,721,182 research outputs found
Effect of Pressure on the Electrochemical Conversion of CO2 to CO
Full text linkTo 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 that conversion from water solution is the low CO2 solubility in water. In this work, a methodical study on the effect of the CO2 pressure and of other operating parameters on the conversion of CO2 at flat cathodes to carbon monoxide was performed. In detail, the reduction of CO2 was studied in different kind of electrochemical cells to evaluate the effect of various operating parameters, including the nature of the supporting electrolyte and the nature of cathode (Ag and Au), the current density, the pH and the pressure of CO2 . It was shown that an increase of the pressure
leads to an improvement the stability of the electrode
Electrochemical conversion of carbon dioxide: effect of the cell and of the operating parameters on the performances of the process.
Full text linkRecycling 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, a systematic study on the effect of the CO2 pressure and of other operating parameters on the conversion of CO2 at tin flat cathodes to formic acid was performed to overcome this obstacle. The reduction of CO2 was first studied in a glass undivided cell at atmospheric pressure to evaluate the effect of various operating parameters, including the nature of the anode and of the supporting electrolyte, the mixing rate, the current density and cathode to anode area ratio. Subsequently, in order to improve the performance of the process, a series of electrolysis was performed in a batch stainless steel undivided cell in a wide range of pressure of CO2 and current density. It was shown that an increase of the pressure leads to a drastic enhancement of the final formic acid concentration. Indeed, the utilization of relatively high CO2 pressures (15–30 bar) allowed to achieve high concentrations of formic acid (up to 0.46 mol L-1) at high current density (up to 90 mA cm-2) and with cheap and simple undivided cell. (5) Several researchers have discussed the economic feasibility for large-scale design of the CO2mitigation electrochemistry system, by suggesting that could be operationally profitable. Therefore, in the last stage, the process was performed in a pressurized filter-press cell, suitable for scale-up on applicative scale. The goal of this research is to provide an electrochemical process sustainable at applicative point of view characterized by a high yield and selectivity of the product. Long-term stability has also to be acquired in order to obtain an interesting alternative at commercial level for the conversion of carbon dioxide
Conversion of CO2 to formic acid in a microfluidic electrochemical cell with and without supporting electrolyte
Full text linkElectrochemical reduction of carbon dioxide to formic acid or formate (FA) is considered an interesting route to
valorize CO2 effluents. Here, we have performed the conversion of CO2 to FA in an undivided microchannel
electrochemical reactor characterized by very small inter-electrode distances (75–250 μm) using Na2SO4 as
supporting electrolyte (SE). It was found that the use of the microfluidic cell allows to work both in the presence
and in the absence of SE with lower cell potentials with respect to conventional cells and to obtain significant
conversions per pass of CO2 to FA. The effect of many parameters, such as distance between electrodes, flow rate,
current density, concentration of Na2SO4 and pH, was studied. In particular, it was shown that the production of
FA increases by reducing the concentrations of Na2SO4 and it presents the maximum value in the absence of it
Devolopment of a process for the treatment of synthetic wastewater without energy inputs using the salinity gradient of wastewaters and a reverse electrodialysis stack
No full textElectrochemical processes are considered very effective methods for the treatment of wastewater contaminated by organics resistant to conventional biological processes and various inorganic pollutants. Large sites that treat wastewaters usually deal with a large number of waters often characterized by different salinity contents, that could be potentially used to provide the energy necessary for the electrochemical remediation. Hence, in this work a reverse electrodialysis (RED) process for the treatment of synthetic wastewaters contaminated by organics, without energy inputs, using the salinity gradient of different wastewaters, was studied, for the first time. It was found that two synthetic wastewaters with different NaCl content can be effectively used in a RED system to drive anodic and cathodic processes for the removal of their organic contents without external energy supplies. The effects of salinity gradient, external resistance and set-up of the process was evaluated. Under optimized operating conditions, a fast and high removal of TOC (about 70% every hour) in the anodic compartment and a good stability of operating conditions for all the monitored time (10 h) were achieved. In addition, about 67% of the solution with high salinity used in the stack to provide the salinity gradient was effectively treated in the anodic compartment of the stack
Electrochemical incineration of oxalic acid at boron doped diamond anodes: Role of operative parameters
No full textThe electrochemical incineration of oxalic acid (OA) at boron doped diamond (BDD) anodes was investigated both theoretically and experimentally in order to find the influence of the operative parameters on the performances of the process. Polarization curves and chronoamperometric measurements indicate the probable occurrence of a direct electrochemical oxidation of OA at the surface of the BDD anode at low pH and of a hydroxyl radical-mediated reaction at high pH. When incineration electrolyses are performed at low pH with potentiostatic alimentation, a dramatic influence of the potential is observed. In amperostatic incineration, high CE are obtained when most part of the process was under charge transfer controlled kinetics, i.e., when low current densities and high flow rates are imposed. Under these conditions no significant effect of current densities or flow rates is observed. The results obtained at low pH are in good agreement with the previsions of a model based on the assumption that, under adopted experimental conditions, the performances of the process are mainly determined by the competition between the direct oxidation of oxalic acid and the water discharge. The effect of the pH and of the supporting electrolyte was further investigate
Carbonization of waste organic matrices in zinc-based molten salts
No full textMolten salt driven catalytic carbonisation offers a new and emerging technology approach for treating organic wastes to achieve negative CO2 emissions and a circular
carbon economy by converting the low-value carbon content of the waste into high value solid carbon materials which can be reused, and also converting the hydrogen content of the waste into a low-carbon hydrogen-rich fuel gas. In the work herein, a methodology to handle pure ZnCl2 (and load it into batch reactors) was built. The ZnCl2 used to this purpose was provided by VWR Chemicals (>97% of purity). Pellets of HDPE were provided by polymer testing laboratory. After that, some experimental trials on molten salts assisted pyrolysis using ZnCl2 in mixture with HDPE were conducted. Then the HDPE pellets were milled to obtain filaments with dimensions of 1mm x 2mm. The preliminary collected outcomes showed that, when the reaction temperature increased from 300 to 380 °C for 30 min, the gaseous products yield increased from values below 1%w/w to 3%w/w. In both experiments hydrogen was the main component (90 % mol). With an increase of the reaction time from 30 min to 3 h an enhancement in the production of light olefins in the place of hydrogen was observed. TGA analyses were conducted of ZnCl2, of HDPE and of HDPE in the presence of ZnCl2 and the catalytic activity of ZnCl2 was demonstrated by an improvement of the mass loss rate
Electrochemical production and use of chlorinated oxidants for the treatment of wastewater contaminated by organic pollutants and disinfection
Full text linkIn 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 CO2to HCOOH at tin cathode in a pressurized undivided filter-press cell
No full textThe 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 CO2pressure 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)
Effect of mode of operation, substrate and final electron acceptor on single-chamber membraneless microbial fuel cell operating with a mixed community
Full text linkWaste minimization and circular thinking are to be achieved in order to cope with the limited amount of resources of our planet. In this perspective, bio-electrochemical systems (BESs) can contribute to the global balance with their ability to extract chemical residual energy from wastewater and transform it directly into electrical current. BESs development has been limited by the cost connected to reactor design, in which membranes and cathode catalyst constituted a major drawback. In this paper we report the optimization process of a simple reactor without membranes or precious catalyst that produced 47.1 mW mâ2, which is more than what achieved with configurations including membranes, operating in similar conditions (glycerol as substrate and hydraulic retention times of 3 days). In opposition to what is usually reported for conventional divided microbial fuel cells (MFCs), we have found that in this kind of reactor fermenting substrates (mainly glycerol) can give higher current density than non-fermentable ones (acetate). Feeding modality and proper electrode orientation were confirmed to have a dramatic impact on power output. Finally, a possible niche for the exploitation of our single chamber membraneless MFC was pointed out to exist in bio-refinery industry
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