Browsing by Author "Sousa, Miguel M."
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- Electrochemical CO2 reduction at room temperature and mild pressuresPublication . Messias, Sofia; Sousa, Miguel M.; Ponte, Manuel Nunes; Rangel, C. M.; Pardal, T.; Machado, AnaABSTRACT: Carbon capture and utilization technologies (CCU) and electrolytic hydrogen production are closely interconnected technologies and necessary for a sustainable energy system. This work describes the development of a process for room temperature co-electrolysis of CO2 and water to produce syngas, at mild pressures. The influence of several parameters in the performance of the process is reported.
- Electrochemical production of syngas from CO2 at pressures up to 30 bar in electrolytes containing ionic liquidPublication . Messias, Sofia; Sousa, Miguel M.; Ponte, Manuel Nunes; Rangel, C. M.; Pardal, T.; Machado, AnaABSTRACT: Electrochemical CO2 reduction in a reactor that can operate up to 100 bar and 80 degrees C, with a configuration similar to that of an alkaline electrolyser, for hydrogen production suitable to be used industrially is reported for the first time. The effect of pressure on the co-electrolysis of CO2 and water was studied. The successful scale-up from a previously reported batch process to electrodes of ca. 30 cm(2) geometrical area (30-fold factor) that combines the use of pressure and an ionic liquid-based electrolyte is presented. Also for the first time, the potential of the system under study to achieve high conversions of CO2 to avoid a purification step of syngas from unreacted CO2 is shown. An inexpensive commercial foil of the common metal zinc was employed. A semi-continuous operation yielded syngas productivities in the range of 0.02-0.04 mmol cm(-2) h(-1) at ca. -1.2 V vs. QRE Ag/Ag+. When an electrolyte consisting of 90 wt% H2O and 10 wt% 1-ethyl-3-methylimidazolium trifluoromethanesulfonate was used, selectivities for CO in the range of 62% to 72% were obtained at 10 bar pressure, whereas selectivities of 82% were obtained at 30 bar pressure. H-2/CO ratios in the range of 1/1 to 4/1 at 10 bar pressure suitable for the synthesis of a variety of fuels, such as hydrocarbons, methanol, methane and chemical building blocks, were observed. An energy efficiency of 44.6% was calculated for a H-2/CO ratio of 2.2 suitable for the synthesis of methanol.
- Pressurized electrochemical process for syngas production [Resumo]Publication . Messias, Sofia; Sousa, Miguel M.; Rangel, C. M.; Pardal, T.; Ponte, Manuel Nunes; Machado, AnaABSTRACT: Carbon Capture and Utilisation (CCU) comprise technologies that capture carbon dioxide and convert it into chemical products, such as fuels, chemicals and building materials that can replace the same products derived from fossil resources. These technologies can thus contribute to reach the ambitious 2030 targets set by the European Union for decarbonisation of the economy of 40% CO2 reduction, introduction of 27% renewable energies in the energy mix and 27% energy efficiency. CCU technologies are at different stages of maturity and some are already commercially deployed. One of these commercial technologies is the production of methanol by CO2 hydrogenation at high temperature using hydrogen produced by water electrolysis. Another CCU technology that is still at laboratory stage is electrochemical CO2 reduction. In this process carbon dioxide is co-electrolyzed with water near room temperature. Hydrogen is produced in situ. Depending on process conditions and catalysts CO2 reduction originates a series of products, such as CO, formic acid, hydrocarbons, alcohols etc. at the cathode. Oxygen is produced at the anode resulting from water oxidation reaction. Figure 1 illustrates the process. Electrochemical CO2 reduction presents several technological challenges that have not been surpassed yet, such as low CO2 conversions, poor stability of electrodes and low energy efficiencies. This work reports not yet published results of the development of a pressurized electrochemical process for producing syngas (CO + H2) by electrochemical reduction of carbon dioxide. Green syngas produced using renewable energy can be an important platform for introducing renewable energy in the chemical industry. The development of a process that works at pressures higher then atmospheric pressure seems promising to circumvent the aforementioned challenges, namely low conversions and low energy efficiencies.