Solid Polymer Electrolyte Reactor Research Articles

Novel Electrocatalytic Hydrogenation Using a Solid Polymer Electrolyte (SPE) Reactor

Organic electrosynthetic reactions, which are driven by electricity, can generally be carried out under mild conditions (room temperature and ambient pressure). In addition, they do not require any hazardous reagents and produce less waste than other conventional chemical syntheses. Therefore, electrosynthesis is known to be a mild and clean method for organic synthesis and there has recently been renewed interest in its development. However, electrosynthesis also has some disadvantages. Ordinary chemical reactions are homogeneous, while the reaction field of electrolysis is a heterogeneous interface, therefore electrosynthesis has a productive drawback. In addition, a large amount of supporting electrolyte is usually required. Therefore, the availability of solvents is limited by the necessity for dissolution of a supporting electrolyte. The presence of the supporting electrolyte might also cause separation problems in the reaction workup. Moreover, in an ordinary electrolysis system, solution resistance is generated between the working and counter electrodes, resulting in a decrease in energy efficiency. To overcome these problems, we focused on a solid polymer electrolyte (SPE) reactor which was originally developed for fuel cell technologies and demonstrated various electrocatalytic hydrogenations in a SPE reactor (Figure 1) [1-5].As shown in Figure 1, a SPE membrane such as a proton exchange membrane (PEM) is integrated into the central part of the reactor, and is sandwiched between a pair of catalyst layers on the anode and cathode sides. For this reason, the substrate solution does not require a supporting electrolyte and the cell resistance can be minimized. The anode and cathode have highly porous 3D structures in order to conduct an efficient electrochemical reaction. Moreover, the reaction can be carried out in a flow operation. Thus, the SPE reactor system possesses many characteristics designed to overcome the disadvantages of conventional electrosynthetic processes.In a series of studies we have conducted, in this presentation, we will discuss two topics such as diastereoselective reduction of cyclic ketones and electrocatalytic hydrogenation of pyridines.The authors gratefully acknowledged support by JST CREST Grant No. 18070940, Japan.[1] A. Fukazawa, M. Atobe, et al. ACS Susutain. Chem. Eng. 2019, 7, 11050.[2] S. Nogami, M. Atobe, et al. J. Electrochem. Soc. 2020, 167, 155506.[3] A. Fukazawa, M. Atobe, et al. Org. Biomol. Chem. 2021, 19,7363.[4] S. Nogami, M. Atobe, et al. ACS Catalysis, 2022, 12, 5430.[5] Y. Shimizu, M. Atobe, et al. ACS Energy Lett., 2023, 8, 1010. Figure 1

Platinum supported on reduced graphene oxide as a catalyst for the electrochemical hydrogenation of soybean oils

Platinum nanoparticles anchored over graphene nanocomposites (Pt/Gr) were synthesized and used for the investigation of the electrochemical hydrogenation of soybean oils. By exploiting Pt/Gr nanocomposites as cathode catalysts of a membrane electrode assembly, a promising solid polymer electrolyte (SPE) reactor was fabricated. The obtained Pt/Gr nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy, which can definitely show that Pt nanoparticles successfully formed on graphene and were well-distributed on the surface of graphene sheets. The further electrochemical characterizations demonstrated that Pt/Gr has undoubtedly higher electrocatalytic activity and stability compared to the commercial Vulcan XC-72 supported Pt nanoparticles; this outcome will lead to further application as a new electrode material in the SPE reactor. The trans fatty acid content of the obtained hydrogenated soybean oil (IV: 111.3 g I2/100 g oil) using Pt/Gr as the cathode catalyst in the SPE reactor was only 1.53%. To achieve a similar IV, the usage of Pt was much less when graphene was selected as a catalyst carrier compared to Vulcan XC-72. The changes in the fatty acid components and the hydrogenated selectivity of octadecenoic acids were also discussed.

Synthesis and Evaluation of Copper-Supported Titanium Oxide Nanotubes as Electrocatalyst for the Electrochemical Reduction of Carbon Oxide to Organics

Carbon dioxide (CO2) is considered as the prime reason for the global warming effect and one of the useful ways to transform it into an array of valuable products is through electrochemical reduction of CO2 (ERC). This process requires an efficient electrocatalyst with high faradaic efficiency at low overpotential and enhanced reaction rate. Herein, we report an innovative way of reducing CO2 using copper-metal supported on titanium oxide nanotubes (TNT) electrocatalysts. The TNT support material was synthesized using alkaline hydrothermal process with Degussa (P-25) as a starting material. Copper nanoparticles were anchored on the TNT by homogeneous deposition-precipitation method (HDP) with urea as precipitating agent. The prepared catalysts were tested in a home-made H-cell with 0.5 M NaHCO3 aqueous solution in order to examine their activity for ERC and the optimum copper loading. Continuous gas-phase ERC was carried out in a solid polymer electrolyte (SPE) reactor. The 10% Cu/TNT catalysts were employed in the gas diffusion layer (GDL) on the cathode side with Pt-Ru/C on the anode side. Faradaic efficiencies for the three major products namely methanol, methane, and CO were found to be 4%, 3%, and 10%, respectively at −2.5 V with an overall current density of 120 mA/cm2. The addition of TNT significantly increased the catalytic activity of electrocatalyst for ERC. It is mainly attributed to their better stability towards oxidation, increased CO2 adsorption capacity and stabilization of the reaction intermediate, layered titanates, and larger surface area (400 m2/g) as compared with other support materials. Considering the low cost of TNT, it is anticipated that TNT support electrocatalyst for ECR will gain popularity.

Preparation of the Pt/CNTs Catalyst and Its Application to the Fabrication of Hydrogenated Soybean Oil Containing a Low Content of Trans Fatty Acids Using the Solid Polymer Electrolyte Reactor.

Pt/CNTs were synthesized with an ethylene glycol reduction method, and the effects of carboxyl functionalization, ultrasonic power and the concentration of chloroplatinic acid on the catalytic activity of Pt/CNTs were investigated. The optimal performance of the Pt/CNTs catalyst was obtained when the ultrasonic power was 300 W and the concentration of chloroplatinic acid was 40 mg/mL. The durability and stability of the Pt/CNTs catalyst were considerably better compared to Pt/C, as shown by cyclic voltammetry measurement results. The trans fatty acids content of the obtained hydrogenated soybean oil (IV: 108.4 gl2/100 g oil) using Pt/CNTs as the cathode catalyst in a solid polymer electrolyte reactor was only 1.49%. The IV of hydrogenated soybean oil obtained using CNTs as carrier with Pt loading 0.1 mg/cm2 (IV: 108.4 gl2/100 g oil) was lower than carbon with a Pt loading of 0.8 mg/cm2 (IV: 109.9 gl2/100 g oil). Thus, to achive the same IV, the usage of Pt was much less when carbon nanotubes were selected as catalyst carrier compared to traditional carbon carrier. The changes of fatty acid components and the hydrogenated selectivity of octadecenoic acid were also discussed.

Enhanced nitrate reduction with copper phthalocyanine-coated carbon nanotubes in a solid polymer electrolyte reactor

Research on nitrate removal has drawn more attention because of the increasing nitrate contamination in ground and surface water. In this work, copper phthalocyanine supported on functionalised multiwalled carbon nanotubes (CuPc/CNT) prepared using the impregnation method was characterised and tested for their electrocatalytic behaviour towards nitrate reduction. Cyclic voltammetry, rotating disc electrode and chronoamperometry techniques were employed for the electrochemical characterisation. The CuPc/CNT electrocatalyst showed higher catalytic activity towards nitrate reduction than CuPc supported on carbon black (CuPc/C). From kinetic studies, the order of reaction and the reaction rate constant were found to be 0.78, 15.03 and 0.81, 0.46 s−1 for CuPc/CNT and CuPc/C, respectively. Electrolysis studies in an H-cell at 24 h showed the percentage of nitrate removal up to 76 and 45 % for CuPc/CNT and CuPc/C, respectively. Furthermore, nitrate reduction in a solid polymer electrolyte reactor with membrane electrode assemblies designed using supported CuPc cathode showed a maximum faradaic efficiency of 41 % for CuPc/CNT and 38 % for CuPc/C.

Tungsten carbide-supported Pd electrocatalysts for triglyceride hydrogenation in a solid polymer electrolyte reactor

Noble metals are often used for the electrochemical hydrogenation of organics, however, substitutes are being sought due to their high cost. Research described in this paper compared the performance of tungsten carbide-supported Pd (Pd/W 2C) catalysts to those of W 2C, Pd and other noble metals for the hydrogenation of triglycerides in a solid polymer electrolyte reactor. Rates for the Pd/W 2C catalysts increased with increasing Pd loading. The 6 wt.% Pd/W 2C catalyst exhibited the highest activity, and was more active than the Pd or W 2C catalysts, indicating a possible synergy. Hydrogenation rates for all of the catalysts were functions of the applied potential, suggesting that the rate-determining step was electrochemical.

Low Temperature Electrochemical Production of Hydrogen from the Hybrid Copper-Chlorine Thermochemical Cycle

Electrolysis of cuprous chloride is a critical step in the copperchlorine thermochemical cycle for hydrogen production, a novel process with the advantage of mild operating conditions and capability of recovery of low grade heat from nuclear reactors. This step can be achieved in solid polymer electrolyte reactor with either Nafion membrane or anion exchange membrane. In this paper, cell polarization experiments show that the reactor with Nafion 115 has a higher thermal stability than that of the AMX membrane for the bulk electrolysis. In the anode half cell reaction, effects of catalysts and mass transfer were studied on the thin film electrode on the rotating disk electrode (RDE). It was found that the active carbon Vulcan XC 72 has comparable activity towards the cuprous chloride oxidation with conventional electro- catalysts, such as Pt black, Pt/C and RuO2. Also, mass transfer was serious in the rate process in the anode.

Electrochemical treatment of aqueous oxalic acid solution by using solid polymer electrolyte (SPE) reactor

In this study, the feasibility of electrochemical oxidation of the aqueous oxalic acid solution has been investigated in an electrochemical reactor with SPE and simultaneous hydrogen production has been observed. Experiments were conducted to examine the effects of applied current density, flow rate of solution, pH of the solution, the concentration of supporting electrolyte, the temperature of the solution, types of the electrode and membrane material on removal efficiency. As a result of the studies oxalic acid as COD at the original pH can be treated to meet discharge limits at ambient temperature without any pH adjustment with low energy consumption. COD removal efficiency of 97% has been achieved by using titanium oxide coated with iridium oxide as anode. Since there is no need to use liquid electrolyte in this type of reactor, aqueous oxalic acid solution can be oxidized without adding any supporting electrolyte such as Na2SO4.

Application of a solid polymer electrolyte reactor to remove nitrate ions from wastewater

The application of a zero gap solid polymer electrolyte (ZGSPE) reactor to deminealise nitrate ions in aqueous wastewater is described. The following performance data for the reduction of a simulated alkaline solution with 16.1 mM nitrate ions under galvanostatic operation were achieved: percentage of nitrate removal up to 100%, rates of nitrate removal up to 0.057 mol cm−2 h−1, space–time yields up to 5.4 kg m−3 h−1, current efficiencies up to 24.5% and energy consumption between 40.1 and 63.3 kW h kg−1. The beneficial effects of higher temperatures and nitrate ion concentrations and using a suitable electrolyte flow rate on the activity, selectivity and efficiency is reported. PdRh1.5/Ti mini-mesh electrode used in the study was stable after a cumulative use of 1000 h.

Paired electrolysis in a solid polymer electrolyte reactor—Simultaneously reduction of nitrate and oxidation of ammonia

Abstract Simultaneous reduction of nitrates and oxidation of ammonia in aqueous solutions have been carried out in a zero gap solid polymer electrolyte (ZGSPE) reactor, operated galvanostatically in a batch recycle mode. Complete removal of 16.1 mM nitrate and 9.4 mM ammonia was achieved within 45 h with removal rates of 0.057 mol NO 3 − cm −2 h −1 and 0.017 mol NH 3 cm −2 h −1 . Space–time yields of 5.4 kg NO 3 m −3 h −1 and 0.17 kg NH 3 m −3 h −1 , current efficiencies for nitrogen formation of 24.5% in the nitrate reduction and 1.4% in the ammonia oxidation and energy consumptions of 40.1 kWh (kg NO 3 − ) −1 were obtained during nitrate reduction, no nitrite was formed and N 2 was the main product under the best conditions. However, an improvement in the selectivity for the ammonia oxidation towards nitrogen is required. Effects of reactant concentrations, temperature and flow rate have been investigated. Use of the ZGSPE reactor could treat a wide range of wastes containing nitrate and ammonia, including those with very low levels of nitrate ions and ammonia.

Fundamental and applied studies on the electrochemical hydrodehalogenation of halogenated phenols at a palladised titanium electrode

In situ Fourier transform infrared studies have shown that the electrochemical hydrodehalogenation (HDH) of a wide range of halogenated phenols to give the phenolate anion was observed through a common adsorbed intermediate at a palladium catalysed titanium electrode. The mechanism of the reduction may be represented as a sequence of electron additions and halide expulsions leading, via the intermediate radical, to product. The electrochemical HDH of halogenated phenols in aqueous solution was studied at ambient temperature and atmospheric pressure in a two-compartment H-cell reactor and a solid polymer electrolyte reactor, as well as with in situ Fourier transform infrared (FTIR) spectroscopy. Complete dehalogenation of 10mM halogenated phenol solutions was observed with current efficiencies up to 90% in the H-cell, whilst current efficiencies up to 50% were observed using the solid polymer electrolyte reactor.

Design and operation of a solid polymer electrolyte reactor for electrochemical hydrodehalogenation

A solid polymer electrolyte reactor is designed for the electrochemical hydrodehalogenation (HDH) of halogenated organic compounds in oil and/or aqueous solutions. The reactor has been evaluated at 0.05, 0.1, 0.2, 1 and 2 dm 3 scales under various conditions and its effectiveness has been demonstrated experimentally using the HDH of 2,4-dichlorophenol (DCP) and 2,4-dibromophenol (DBP) as model reactions of environmental interest. The HDH of low concentration DCP and DBP in oil solutions in the reactor achieved conversions up to 35% within 3–4 h with current efficiencies up to 26%, space–time yields up to 0.70 (kg DCP or DBP) m −3 h −1 and energy consumptions of 4.7 kW h (kg DBP or DCP) −1. With the concentrated DCP or DBP–oil solutions, the performances were significantly improved, i.e. current efficiencies of 60–85%, space–time yields of 1.5–5.6 (kg DCP or DBP) m −3 h −1 and energy consumptions of 1.5–2.4 kW h (kg DCP or DBP) −1. The HDH of DCP and DBP in the aqueous solutions was compared to the paraffin oil media and the reactor stability was evaluated for operating times of up to 170 h.

Electrochemical hydrodehalogenation of 2,4-dichlorophenol in paraffin oil and comparison with aqueous systems

Electrochemical hydrodehalogenation (HDH) of 2,4-dichlorophenol (DCP) has been carried out in paraffin oil solutions using a solid polymer electrolyte reactor in a batch recycle mode with a dilute H 2SO 4 aqueous solution as the anode feed and source of hydrogen. The technology expands the application ranges of the electrochemical HDH from aqueous systems to non-conductive media. The influence of current density, reactant concentration and temperature is evaluated. The data are compared with those achieved in aqueous solutions. The HDH, in the paraffin oil, has been demonstrated in operation periods of up to 170 h.

Engineering aspects of electrochemical hydrodehalogenation of 2,4-dichlorophenol in a solid polymer electrolyte reactor

A solid polymer electrolyte reactor is designed for the electrochemical hydrodehalogenation (HDH) of 2,4-dichlorophenol (DCP) in paraffin oil. The reactor has been evaluated at 0.05, 0.1, 0.2, 1 and 2 dm 3 scales in terms of cathode materials and structure and ratio of the cathode surface area to the solution volume. A cathode of titanium mini mesh with a palladium electrocatalyst produced by electrodeposition was particularly effective. Current efficiencies of up to 80%, percentage of DCP removal of up to 50%, space-time yields of up to 5.0 kg DCP m −3 h −1 and energy consumption as low as 1.5 kW h (kg DCP) −1, were achieved. The reactor showed stable operation for periods of up to 170 h.

Electrochemical hydrodehalogenation of 2,4-dibromophenolin paraffin oil using a solid polymer electrolyte reactor.

A new technology for remediation of halogenated organics-oil systems, which can cause serious environmental problems, has been demonstrated using the electrochemical hydrodehalogenation of 2,4-dibromophenol (DBP) in paraffin oil in a solid polymer electrolyte reactor. The reactor has been evaluated in terms of cathode materials and structure and the ratio of the cathode surface area to the solution volume. A cathode of titanium minimesh with a palladium electrocatalyst produced by electrodeposition was particularly effective. Current efficiencies of up to 85% and percentage of DBP removal of up to 62%, space-time yields of up to 7.6 kg DBP m(-3) h(-1), and energy consumption as low as 1.6 kW h (kg of DBP)(-1) were achieved. The reactor showed stable operation for periods of up to 170 h. The results demonstrated that electroreduction could be an alternative technology to electrooxidation forthe treatment of wastes and toxic halogenated compounds, making the process simpler in comparison to electrooxidation.

Feasibility study of electrochemical hydrodehalogenation of 2,4-dibromophenol in a paraffin oil

The feasibility of electrochemical hydrodehalogenation (HDH) of 2,4-dibromophenol (DBP) in paraffin oil has been evaluated for short or long operation periods of up to 170 h. HDH has been performed successfully using a solid polymer electrolyte reactor in a batch recycle mode with a dilute H 2SO 4 aqueous solution as the anode feed and source of protons. The work reported in this paper expands the application of electrochemical HDH from aqueous systems to non-conductive media. The effect of the operating conditions, including current density, reactant concentration and temperature, is evaluated. The results are compared with those achieved in the aqueous solutions.

Electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. Sensory and compositional characteristics of low Trans soybean oils

AbstractSoybean oils were hydrogenated either electrochemically with Pd at 50 or 60°C to iodine values (IV) of 104 and 90 or commercially with Ni to iodine values of 94 and 68. To determine the composition and sensory characteristics, oils were evaluated for triacylglycerol (TAG) structure, stereospecific analysis, fatty acids, solid fat index, and odor attributes in room odor tests. Trans fatty acid contents were 17 and 43.5% for the commercially hydrogenated oils and 9.8% for both electrochemically hydrogenated products. Compositional analysis of the oils showed higher levels of stearic and linoleic acids in the electrochemically hydrogenated oils and higher oleic acid levels in the chemically hydrogenated products. TAG analysis confirmed these findings. Monoenes were the predominant species in the commercial oils, whereas dienes and saturates were predominant components of the electrochemically processed samples. Free fatty acid values and peroxide values were low in electrochemically hydrogenated oils, indicating no problems from hydrolysis or oxidation during hydrogenation. The solid fat index profile of a 15∶85 blend of electrochemically hydrogenated soybean oil (IV=90) with a liquid soybean oil was equivalent to that of a commercial stick margarine. In room odor evaluations of oils heated at frying temperature (190°C), chemically hydrogenated soybean oils showed strong intensities of an undesirable characteristic hydrogenation aroma (waxy, sweet, flowery, fruity, and/or crayon‐like odors). However, the electrochemically hydrogenated samples showed only weak intensities of this odor, indicating that the hydrogenation aroma/flavor would be much less detectable in foods fried in the electrochemically hydrogenated soybean oils than in chemically hydrogenated soybean oils. Electrochemical hydrogenation produced deodorized oils with lower levels of trans fatty acids, compositions suitable for margarines, and lower intensity levels of off‐odors, including hydrogenation aroma, when heated to 190°C than did commercially hydrogenated oil.

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. II. Hydrogenation selectivity studies

AbstractSoybean oil has been hydrogenated electrochemically in a solid polymer electrolyte (SPE) reactor at 60°C and 1 atm pressure. These experiments focused on identifying cathode designs and reactor operation conditions that improved fatty acid hydrogenation selectivities. Increasing oil mass transfer into and out of the Pd‐black cathode catalyst layer (by increasing the porosity of the cathode carbon paper/cloth backing material, increasing the oil feed flow rate, and inserting a turbulence promoter into the oil feed flow channel) decreased the concentrations of stearic acid and linolenic acid in oil products [for example, an iodine value (IV) 98 oil contained 12.2% C18:0 and 2.3% C18:3]. When a second metal (Ni, Cd, Zn, Pb, Cr, Fe, Ag, Cu, or Co) was electrodeposited on a Pd‐black powder cathode, substantial increases in the linolenate, linoleate, and oleate selectivities were observed. For example, a Pd/Co cathode was used to synthesize an IV 113 soybean oil with 5.3% stearic acid and 2.3% linolenic acid. The trans isomer content of soybean oil products was in the range of 6–9.5% (corresponding to specific isomerization indices of 0.15–0.40, depending on the product IV) and did not increase significantly for high fatty acid hydrogenation selectivity conditions.

The electrochemical hydrogenation of edible oils in a solid polymer electrolyte reactor. I. Reactor design and operation

AbstractA new electrochemical method has been devised and tested for the moderate temperature/atmospheric pressure hydrogenation of edible oils, fatty acids, and fatty acid methyl esters. The method employed a solid polymer electrolyte (SPE) reactor, similar to that used in H2/O2 fuel cells, with water as the source of hydrogen. The key component of the reactor was a membrane‐electrode‐assembly, composed of a RuO2 powder anode and either a Pt‐black or Pd‐black powder cathode that were hot‐pressed as thin films onto the opposing surfaces of a Nafion cation‐exchange membrane. During reactor operation at a constant applied current, water was back‐fed to the RuO2 anode, where it was oxidized electrochemically to O2 and H+. Protons migrated through the Nafion membrane under the influence of the applied electric field and contacted the Pt or Pd cathode, where they were reduced to atomic and molecular hydrogen. Oil was circulated past the back side of the cathode and unsaturated triglycerides reacted with the electrogenerated hydrogen species. The SPE reactor was operated successfully at a constant applied current density of 0.10 A/cm2 and a temperature between 50 and 80°C with soybean, canola, and cottonseed oils and with mixtures of fatty acids and fatty acid methyl esters. Reaction products with iodine values in the range of 60–105 were characterized by a higher stearic acid content and a lower percentage of trans isomers than those produced in a traditional hydrogenation process.

Current efficiency for soybean oil hydrogenation in a solid polymer electrolyte reactor

Soybean oil has been hydrogenated electrocatalytically in a solid polymer electrolyte (SPE) reactor, similar to that in H2/O2 fuel cells, with water as the anode feed and source of hydrogen. The key component of the reactor was a membrane electrode assembly (MEA), composed of a precious metal-black cathode, a RuO2 powder anode, and a Nafion® 117 cation-exchange membrane. The SPE reactor was operated in a batch recycle mode at 60°C and one atmosphere pressure using a commercial-grade soybean oil as the cathode feed. Various factors that might affect the oil hydrogenation current efficiency were investigated, including the type of cathode catalyst, catalyst loading, the cathode catalyst binder loading, current density, and reactant flow rate. The current efficiency ordering of different cathode catalysts was found to be Pd>Pt>Rh>Ru>Ir. Oil hydrogenation current efficiencies with a Pd-black cathode decreased with increasing current density and ranged from about 70% at 0.050Acm−2 to 25% at 0.490Acm−2. Current pulsing for frequencies in the range of 0.25–60Hz had no effect on current efficiencies. The optimum cathode catalyst loading for both Pd and Pt was 2.0mgcm−2. Soybean oil hydrogenation current efficiencies were unaffected by Nafion® and PTFE cathode catalyst binders, as long as the total binder content was ≤30wt% (based on the dry catalyst weight). When the oil feed flow rate was increased from 80to 300mlmin−1, the oil hydrogenation current efficiency at 0.100Acm−2 increased from 60% to 70%. A high (70%) current efficiency was achieved at 80mlmin−1 by inserting a nickel screen turbulence promoter into the oil stream.