The electrochemical synthesis of aminonitriles I. H-cell studies with adiponitrile and azelanitrile

Adiponitrile and azelanitrile were electrochemically hydrogenated to their corresponding aminonitriles in a divided H-cell using Raney nickel powder as the cathode material. The effects of current, temperature, and solvent/supporting electrolyte composition on product selectivities were investigated. Syntheses of the fully hydrogenated diamine by-product increased with increasing current and solution temperature. When a 0.8 M adiponitrile/alcohol/water/ammonium actetate electrolyte was hydrogenated at temperatures of 35–45°C, 6-aminocapronitrile selectivities in the range of 79–97% and current efficiencies of 50–60% were obtained. The optimum applied current was 60 mA for each 2.5 g of catalyst (an apparent current density of 4.8 mA cm^–2). For the case of azelanitrile, reaction selectivities for the partially hydrogenated 9-aminononanenitrile product ranged from 80–93%.     

Electrocatalytic hydrogenation of soybean oil in a radial flow-through Raney nickel powder reactor

Soybean oil has been hydrogenated electrocatalytically on Raney nickel powder catalyst at atmospheric pressure and moderate temperatures in a novel undivided packed bed radial flow-through reactor. The reactor consisted of a single anode/cathode tubular element, where Raney nickel catalyst powder was contained in the annular space between two concentric porous ceramic tubes and the flow of the reaction medium (a dispersion of oil in a water/t-butanol/tetraethylammonium p-toluenesulfonate electrolyte) was either in the inward or outward radial direction. The innovative design of this reactor allows for a thin nickel bed and a high anode/cathode interfacial area without the normal problems associated with electrolyte flow distribution. The total size of the reactor can be increased without changing the relative anode/cathode position and the electrolyte flow pattern by simply increasing the length and/or number of anode/cathode elements in a single common shell (similar to a shell-and-tube heat exchanger). For the brush hydrogenation of soybean oil, current efficiencies of 90–100% were achieved with a single element reactor when the electrolyte oil content was 10 or 25 wt/vol %, the apparent current density was 10 or 15 mA cm^–2, the temperature was 75 °C, and the electrolyte flowed in the inward radial direction. The electrohydrogenated oil product was characterized by a high stearic acid content and low concentrations of linolenic acid and trans fatty acid isomers, as compared to the traditional high temperature chemical catalytic oil hydrogenation route with hydrogen gas.     

The paired electrochemical synthesis of sorbitol and gluconic acid in undivided flow cells. I

The strategy of paired electrochemical synthesis for the production of organic chemicals, in which the reactions at both the anode and cathode simultaneously contribute to the formation of the final product(s), could result in as much as a 50% reduction in energy consumption as compared to conventional electro-organic syntheses. In order to evaluate this hypothesis the electrochemical oxidation of glucose to gluconic acid and the reduction of glucose to sorbitol were paired in undivided flow-through parallel plate and packed bed cells.To date, the optimum electrode materials and operating conditions for the paired synthesis are: an amalgamated zinc cathode, a graphite anode, an initial glucose concentration of 0.8 mol dm^–3, a 0.8 mol dm^–3 NaBr supporting electrolyte, an electrolyte flow rate of 0.81 min^–1 and an electrolyte pH of 7. Under these conditions the current efficiencies for sorbitol and gluconic acid were 26% and 68%, respectively at 0.25 F mole^–1. Current losses are believed to be due to hydrogen evolution and the reduction of-gluconolactone (an intermediate in the formation of gluconic acid) to glucose.     

Electrohydrogenation of 4-amino-5-nitrosodimethyluracil with a foamed nickel cathode

The hydrogenation of 4-amino-5-nitrosodimethyluracil as an intermediate of commercially synthesized caffeine is generally carried out using iron powder reduction or Raney nickel catalyst. However, the iron powder results in serious pollution and the Raney nickel catalyst needs an expensive hydrogen supply system operated under severe conditions. A green chemical technology using an electrohydrogenation process with a foamed nickel cathode was studied experimentally in a filter-press cell to eliminate the pollution and the unsafe conditions. The results showed that the electrohydrogenation process mainly depended on the pH of the catholyte, the current density and the temperature. All conversions for the pH range 2–8 were over 98%, but the current efficiency gradually decreased with increasing pH. For the current density range 84–420 A m^–2 the conversion was over 98%, but the current efficiency decreased with increasing current density. The current efficiency improved with increasing temperature. The results show that to obtain a conversion of over 98% and a current efficiency of nearly 100%, the operating conditions should be pH 3–4, 84–168 A m^–2 and 20–30 °C. The conversion and the current efficiency of the electrohydrogenation process were improved by using a foamed nickel cathode with a three-dimensional reticulated structure.     

Material properties and processing in the production of fuel cell components: I. Hydrogen anodes from Raney nickel for lightweight alkaline fuel cells

The production steps of Raney nickel based, PTFE bonded hydrogen anodes for alkaline fuel cells are examined. The Raney nickel catalyst has been made by leaching the nickel aluminium alloy and additional stabilization. The electrode is fabricated by mixing the catalyst with copper oxide for enhancing electronic conductivity and aqueous PTFE emulsion as a hydrophobic binder. Each process step, starting from the nickel aluminium alloy is described and the physical properties of catalyst and electrode are evaluated. At an overpotential of 100 mV the optimized hydrogen anode exhibits at negligable excess hydrogen pressure (1·02bars) a current density of nearly 400 mA cm^–2 at 80°C in 30 wt% KOH. Long term performance test shows that electrode overpotential of more than 60 mV should be avoided. A life time of 5000 hrs at 50°C and a current density of 100 mA cm^–2 has been proven.     

阴极电还原合成甘露醇和山梨醇的研究

采用电化学方法 ,在弱碱性条件下 ,对阴极电还原葡萄糖合成甘露醇和山梨醇进行了研究 ,得到了最佳电解条件 :RaneyNi做阴极 ,电流密度为 4 0A/dm2 ,pH =12 ,温度为 5 0℃ ,葡萄糖的起始浓度为 0 8mol/L ,支持电解质Na2 SO4 的浓度为 0 45mol/L。在此条件下 ,葡萄糖的转化率达 77 1% ,产物组成中甘露醇和山梨醇的质量分数分别为 2 1 3%和 78 7%。     

The role of supporting electrolyte during the electrocatalytic hydrogenation of aromatic compounds

The electrocatalytic hydrogenation of benzene, aniline, and nitrobenzene was investigated at a Raney nickel powder cathode. The single phase electrolyte consisted of t-butanol, water, and a hydrotropic salt, either sodium or tetraethylammoniump-toluenesulphonate (TEATS). The hydrogenation of benzene was achieved only in the latter case; the only product detected was cyclohexane. The highest current efficiency (73%) was obtained at 50° C, 1.0m benzene, 2.5m TEATS, and at an apparent current density of 4.0 mA cm^–2. Aniline was electrocatalytically hydrogenated to cyclohexylamine only in the presence of a quaternary ammonium ion supporting electrolyte (containing either Br^– orp-toluenesulphonate anions), with product current efficiencies of 40%. When nitrobenzene was hydrogenated with a sodiump-toluenesulphonate supporting electrolyte, only nitro group reduction was observed. When the supporting electrolyte was TEATS, both nitro group reduction and aromatic ring hydrogenation occurred.     

Electrochemical hydrodechlorination of 4-chlorobiphenyl in aqueous solution with the optimization of palladium-loaded cathode materials

The electrochemical hydrodechlorination of 4-chlorobiphenyl (4-MCB) in aqueous solution containing methanol (MeOH), sodium acetate, acetic acid and bromide of hexadecyltrimethylammonium (CTAB) was investigated under constant current electrolysis at ambient temperature by using a membrane-separated flow-through cell operated in batch-recycle modes. The effects of catalyst type, cathode substrate, cathode recycle, and catalyst loading on the conversion of 1 mM 4-MCB were evaluated. Convention hydrogenation catalysts including Pd, Pt, and Ni and several types of cathode substrates such as metallic mesh/foam and activated carbon material, were tested. It was found that the palladium-loaded nickel foam was most suitable to be used as cathode for the treatment of 4-MCB due to its high performance and stability, which could rapidly dechlorinate 4-MCB to biphenyl with 94.3% conversion and 91.5% yield under constant current of 15 mA after 3 h electrolysis. During the electrolysis, the current efficiencies and energy consumptions were in range of 5.5-20% and 2.1-7.9 kWh kg⁻¹, respectively.     

Hydrogen evolution reaction on Ni-Al electrodes

The hydrogen evolution reaction (h.e.r) was studied in alkaline solutions on two types of electrodes: (1) obtained by alloying Raney nickel without or with nickel and (ii) by pressing Raney nickel and nickel powders at room temperature. The obtained electrodes are usually very active for the h.e.r. The most active electrode was obtained by pressing Raney nickel with nickel powder (50 wt %). It was characterized by a large roughness factor, R 10 000 and a very low overpotential at the current density of 250 mA cm^–2, ₂₅₀ = 56 mV. The mechanism of the h.e.r. was studied using a.c. impedance measurements. The high electrode activity is connected with the increase in the intrinsic activity of the porous electrode surface.     

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.     

Electrochemical regeneration of ceric sulphate in an undivided cell

Ceric sulphate (0–0.5 m) was generated electrochemically from cerous sulphate slurries (0.5–0.8 m total cerium) in 1.61 m sulphuric acid, at 50 °C, using a bench scale differential area undivided electrochemical cell with an anode to cathode ratio of eleven. A cell current efficiency for Ce(IV) of 90% was obtained at an anode current density of 0.25 A cm^–2. An empirical model illustrates an increase in overall current efficiency for Ce(IV) with an increase in electrolyte velocity, an increase in total cerium concentration, and a decrease in the cell current. From separate kinetic studies on rotating electrodes, both, anode and cathode kinetics were found to be affected by cerium sulphate adsorption processes. Anode adsorption of cerous sulphate species leads to inhibited mass transfer and negatively affected current efficiencies for Ce(IV). Cathode adsorption of cerium sulphate is thought to be responsible for high cathode current efficiencies for hydrogen (93–100%). The dissolved cerous sulphate concentration increased with increasing ceric sulphate and total cerium sulphate concentrations resulting in slurries with a stable dissolved cerous sulphate concentration of as high as 0.851 m in 1.6 m H₂SO₄ at room temperature.     

Ni and Mo coatings as hydrogen cathodes

The catalytic activity of hydrogen cathodes based on Ni/Mo coatings prepared in different ways has been investigated under conditions of advanced alkaline water electrolysis in 10m KOH at 100°C, in the current density range 0.05–1.0 A cm^–2. The activity of electrodeposited Ni/Mo and Ni/Mo/V coatings was quite low, apparently due to their low effective surface area. The activity of all thermally deposited Ni/Mo coatings, electrodeposited Ni/Mo/Cd coatings and of Raney nickel-Mo alloys has been found to be high. When accompanied by some current interruptions of various durations, however, it successively decreased during long-time electrolysis, especially when the residual potential of the electrode, after the current interruption, approached a certain threshold value. The rate of electrode deactivation depends on its mode of preparation as well as on electrolysis conditions, particularly on conditions during the current interruptions. The Mo content in the coating decreased quickly by a factor of 2–10 under operating values of both Tafel constants. The addition of Mo to the expressed as an increase in the absolute values of both Tafel constants. The addition of Mo to the Raney nickel improves its catalytic efficiency as long as Mo is not dissolved. The enhancing of catalytic activity by Mo in Raney nickel is partly caused by synergetic effects between Ni and Mo, as follows from their electronic structure, and partly by material stabilization as follows from comparison with the Raney nickel (Zn).     

Influence of frequency of alternating current on the electrochemical dissolution of mild steel and nickel

The electrochemical dissolution of mild steel and nickel in hydrochloric acid and sulphuric acid has been studied with alternating current of varying frequencies. For both mild steel and nickel the current efficiency decreases exponentially with increasing frequency. With increasing current density (32 to 100 mA cm^–2) and increasing acid concentration (0.5 to 2.0 N), the current efficiency increases. Mild steel is dissolved more efficiently in sulphuric acid than hydrochloric acid but the reverse is true for nickel.     

Scale-up of the perforated bipole trickle-bed electrochemical reactor for the generation of alkaline peroxide

This paper reports work on the scale-up of a perforated bipole trickle-bed electrochemical reactor for the electro-synthesis of alkaline peroxide. The reactor uses a relatively simple cell configuration in which a single electrolyte flows with oxygen gas in a flow-by graphite felt cathode, sandwiched between a microporous polyolefin diaphragm and a nickel mesh/perforated Grafoil anode/bipole. Both one and two-cell reactors are scaled-up from cathode dimensions 120 mm high by 25 mm wide and 3.2 mm thick (reactor-A) to 630 mm high by 40 mm wide and 3.2 mm thick (reactor-B). The scale-up is achieved by the use of constrictions that prevent segregation of the 2-phase flow in the larger cell, combined with switching from a polypropylene to a polyethylene diaphragm with improved transport properties and raising the electrolyte feed concentration from 1 to 2 M NaOH.For the one-cell reactor-B with a polypropylene diaphragm, operating on a feed of 1 M NaOH and oxygen at 900 kPa(abs)/20 °C, the peroxide current efficiency at a superficial current density of 5 kA m⁻² increases from 27% (un-constricted cathode) to 57% with a constricted cathode. The corresponding current efficiencies at 3–5 kAm⁻² for reactor-A and the constricted reactor-B are respectively 69–64% and 66–57%. Under similar conditions at 3–5 kA m⁻² the one-cell constricted reactor-B with a polyethylene diaphragm gives current efficiencies of 88–64%, and changing to an electrolyte of 2 M NaOH raises this range to 90–80%. At 3–5 kA m⁻² the equivalent two-cell (bipolar) constricted reactor-B shows current efficiencies of 82–74% and at 5 kA m⁻² obtains 0.6 M peroxide in 2 M NaOH with specific energy 6.5 kWh per kg H₂O₂.     

Electrochemical conversion of 2,3-butanediol to 2-butanone in undivided flow cells: a paired synthesis

A procedure has been developed for converting 2,3-butanediol inca. 10% aqueous solution to 2-butanone by passing it through a porous anode at which it is selectively oxidized to acetoin by electrogenerated NaBrO and then pumping to a porous cathode at which it is reduced to 2-butanone. The not fully optimized yields and current efficiencies are 75% and 60%, respectively. The procedure employs: Pb/Hg or Zn/Hg cathodes, graphite anodes, pHca. 7, ambient temperature, current density of 2 mA cm^–2, five minute residence time outside the cell, packed bed electrodes, and parallel electrolyte and current flow.     

贮氢合金电极在山梨醇制备中的应用

用贮氢合金作催化还原电极恒电位电解葡萄糖 ,得出合金的表面处理及电极的活化可提高山梨醇电流效率至 80 %以上的结论。同时贮氢电极与Pb电极及发泡Ni电极作了对比 ,发现电解葡萄糖制备山梨醇过程中 ,贮氢电极是较好的还原电极。用贮氢电极 (2 )做阴极 ,30℃ ,电流密度为 80 0mA/dm2 ,葡萄糖溶液及硫酸钠支持电解质浓度均为 0 .5mol/L ,pH =8的条件下 ,电解葡萄糖制山梨醇电流效率高达 94% ,葡萄糖转化率达 80 %以上。     

葡萄糖催化加氢制山梨醇的动力学研究

本文进行了葡萄糖在拉内镍(Raney nickel)存在下的加氢反应动力学研究,反应温度383～413K,反应压力2.0～6.OMPa.根据实验结果筛选出一个合适的反应模型,即为吸附在催化剂表面上的葡萄糖分子和氢分子间进行的反应,产物山梨醇的脱附为速度控制步骤.本征动力学方程为;r=kK_Gc_GaK_Hp_H/(1+K_Gc_G+aK_Hp_H)     

Transformation of Glucose into Sorbitol on Raney Nickel Catalysts in the Absence of Molecular Hydrogen: Sugar Disproportionation vs Catalytic Hydrogen Transfer

Topics in Catalysis - Raney nickel catalysts have been tested in the transformation of glucose into sorbitol through a hydrogen transfer pathway in the presence of short chain alcohols. Comparison...     

DDQ cathodes for seawater cells

A positive electrode containing 2,3-dichloro-5,6-dicyano-p-quinone (DDQ) as the cathode active material was discharged in a magnesium seawater cell at room temperature. Analysis of the dissolved species of DDQ in water and potential sweep voltammetry studies were also carried out. The open circuit voltage of the DDQ-Mg cell was as high as 2.2 V and the single cell could be discharged at current densities greater than 50 mA cm^–2. However, the current efficiencies for the DDQ cathodes in a three-cell immersion-type battery were not high enough for high drain applications, probably due to a high leak current through the common electrolyte.     

Structured Raney Nickel Catalysts for Liquid‐Phase Hydrogenation

Structured catalysts consisting of metal sheets on which Raney nickel was deposited by the thermal spraying method were tested for the liquid‐phase hydrogenation of glucose to sorbitol and 2‐nitrotoluene to 2‐methylaniline, used as model reactions. Catalytic tests performed in a bench‐scale (1 L) reactor showed that the catalytic activity of Raney Ni sheets is significantly higher than the one of the pellets used for fixed‐bed applications, but lower than the activity of the powder catalyst used in slurry mode. The activity could be significantly improved when applying a two‐phase co‐current flow through a monolith. In this case, the activity was superior to the one obtained with the slurry catalyst. These results confirm the potential of Raney Ni monoliths as structured catalysts.