硝基苯电还原制备对氨基苯酚工艺过程

采用固定床电解槽还原硝基苯制备对氨基苯酚,并对其工艺条件进行了优化。以铜网组成固定床电解槽阴极,镀铱钛网(DSA)作为阳极,在电流密度为1000 A·m^-2,阴极电解槽内流速为4.28 cm·s^-1,铜网厚度为10 mm,温度为85℃条件下,硝基苯还原的电流效率接近100%,对氨基苯酚的选择性可达到83%。电解液可循环套用5次,硫酸和氨水的消耗量降至原来的25%,硫酸铵和废水的排放量也减少了75%。采用扩散渗析法回收废弃电解液中的硫酸,以APS为阴离子交换膜,模拟液的流量为0.01 ml·min^-1、温度为20℃时,酸回收率达到61%,且对氨基苯酚和苯胺的透过率分别仅为1.4%和1.6%。     

Hydroxylamine production by electroreduction of nitric oxide in a trickle bed cell

Hydroxylamine was produced in a trickle bed cell by passing nitric oxide gas and sulphuric acid catholyte co-currently downward through a cathode bed of tungsten carbide particles. The dependence of hydroxylamine concentration and current efficiency on cathode activity and particle size, flow rate and composition of gas and catholyte, bed height, and reactor temperature and pressure are reported. Hydroxylamine concentrations of up to 0.18 mol/L were produced at 62% current efficiency in a single pass through a 0.375 m high cell operated at atmospheric pressure and a current density of 213 A/m². The hydroxylamine concentration increased with cell pressure, gas flow rate and decreases in catholyte flow and could be raised to 0.4 mol/L by recycling the catholyte. The process appears to be controlled by mass transfer at current densities over 400 A/m² and by electrochemical reaction below about 300 A/m².     

Chlorate Transport through Ion-Exchange Membranes

A laboratory scale chlor-alkali membrane cell was used to measure the chlorate concentration in the outlet NaOH as a function of current density, temperature, film thickness, brine strength and various membrane properties. The chlorate concentration in the NaOH increased with increasing anolyte chlorate spiking level and temperature and decreasing current density and carboxylate film thickness and was strongly dependent on the type of ion-exchange membrane used. In addition, the presence or absence of sacrificial fibers in the membrane did not measurably influence the resultant chlorate concentration. Chlorate ions were transported to the catholyte side by diffusion and electroosmotic convection and transported toward the anolyte side by migration. This balance between the three modes of transport dictates the chlorate concentration present in the NaOH product.     

Anodic oxidation of aniline for waste water treatment

The electro-oxidation of dilute aqueous solutions of aniline was studied on a lead dioxide packed bed anode. The anolyte consisted of 400 ml of 5.5 mM aniline in dilute sulphuric acid. The anolyte was recirculated through a packed bed electrochemical reactor with an anode compartment volume of 5.0, at various flowrates. The concentrations of aniline, benzoquinone, maleic acid and carbon dioxide were measured against time for experiments ranging from 0.5 to 5.0h in duration. The effects of applied current, pH, flowrate and initial aniline concentration on the percentage of aniline oxidized and carbon dioxide produced are discussed. Aniline in the solution oxidized readily, but further oxidation of intermediates to carbon dioxide was more difficult. The percentage of aniline oxidized increased with increasing current density, while it decreased with increasing initial aniline concentration and pH. Current efficiencies ranged from 15 to 40% for complete oxidation of aniline to CO₂.     

Recovery of metals from complexed solutions by electrodeposition

Electrolytic recovery of metals from aqueous solutions containing complexing chelating agents such as EDTA, NTA, and citrate was studied in a two-chamber cell separating with a commercial cation-exchange membrane (CEM). Equimolar solutions of metal and a chelating agent as a catholyte and NaNO₃ as an anolyte were used; the effect of current densities, initial catholyte and anolyte pH, metal concentration and the type of the CEM, chelating agent and metal on the recovery of metals was determined. The recovery of metal increased with higher initial anolyte pH, concentration and current density, whereas it decreased with lower initial catholyte pH. The results show that electrodeposition seems to be an applicable method for the recovery of metals under appropriate conditions.     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

Analysis of molar flux and current density in the electrodialytic separation of sulfuric acid from spent liquor using an anion exchange membrane

Separation of sulfuric acid from a dilute solution involved a plate and frame type electrodialysis unit using a commercial anion exchange membrane. Experiments were conducted in batch with catholyte concentrations ranging from 1 to 5 wt%. Effect of applied current density, initial catholyte concentration and initial concentration difference of catholyte and anolyte on the molar flux was studied extensively. The maximum molar flux was estimated to be 10.52×10^-8 mol cm^-2s^-1 at 4.45 wt% catholyte concentration and applied current density of 30 mA cm^-2. Current efficiencies were observed to be 75 to 85% at lower current density, which rose to more than 100% at 20 and 30mA cm^-2, at equal initial concentration of catholyte and anolyte. Diffusive flux and flux due to membrane potential contributed very less compared to total flux in presence of applied electric current. An equation was developed to predict the practical molar fluxes, which fitted satisfactorily with minor standard deviation. Pristine and used membrane specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM).     

The electroreduction of oxygen to hydrogen peroxide on fluidized cathodes

The cathodic reduction of oxygen to hydrogen peroxide on fluidized beds of graphite has been studied. The cathodes were fluidized by an oxygen saturated solution of 0.1M NaOH, or by the simultaneous introduction of oxygen gas and hydroxide solution. With increasing current density, the current efficiency always decreased while the product peroxide concentration went through a maximum. In the two-phase system the maximum peroxide concentration increased with bed height. Both current efficiency and the rate of peroxide production generally decreased with catholyte flowrate. For the three-phase fluidized cathode the rate of peroxide production and the current efficiency increased with both catholyte and oxygen flowrate. Possible rate controlling steps are discussed. Current densities for both two phase and three phase fluidized beds were too low to be of commercial use.     

填充床电极二维模型的逼近解析

建立了填充床电极普遍化二维数学模型,用以描述电极内超电势、浓度以及电流密度的分布。该模型包含了填充床电极内横向返混和纵向对流传质的影响,为非线性的椭圆和抛物线形耦联偏微分方程组。用Adomian分解法求解模型获得其逼近解析解,简要介绍了求解方法并给出了两维分布计算结果的图形实例。本文对填充床电极二维模型的分析不仅能为该类电极的设计、优化操作提供理论依据,也可为其他催化反应工程系统的理论分析所借鉴。     

Evaluation of Elution Parameters for Cesium Ion Exchange Resins

Abstract

Cesium ion exchange is one of the planned processes for treating and disposing of waste at the U.S. Department of Energy Hanford Site. Radioactive supernatant liquids from the waste tanks will undergo ultrafiltration, followed by cesium ion exchange using a regenerable organic ion exchange resin. Two resins, SuperLig^®644 and a resorcinol‐formaldehyde resin, are being evaluated for cesium removal and cesium elution characteristics. The main purpose of this study is to optimize the cesium elution to provide a resin that, after undergoing elution, would meet the U.S. Department of Energy/Office of River Protection Project‐Waste Treatment Plant processing and resin disposal criteria. Columns of each resin type were loaded to greater or equal to 90% breakthrough with a Hanford waste stimulant and eluted with nitric acid. The temperature, flow rate, and nitric acid concentration were varied to determine the optimal elution conditions. Temperature and eluant flow rate were the most important elution parameters. As would be predicted based upon kinetic consideration alone, decreasing the eluant flow rate and increasing the temperature provided the optimal elution conditions. Varying the nitric acid concentration did not have a significant effect on the elution completion; however, elutions performed using both high acid concentration (1 M) and elevated temperature (45°C) resulted in resin degradation, causing gas generation and resin bed disruption.     

Electrochemical membrane reactor: In situ separation and recovery of chromic acid and metal ions

An electrochemical membrane reactor with three compartments (anolyte, catholyte and central compartment) based on in-house-prepared cation- and anion-exchange membrane was developed to achieve in situ separation and recovery of chromic acid and metal ions. The physicochemical and electrochemical properties of the ion-exchange membrane under standard operating conditions reveal its suitability for the proposed reactor. Experiments using synthetic solutions of chromate and dichromate of different concentrations were carried out to study the feasibility of the process. Electrochemical reactions occurring at the cathode and anode under operating conditions are proposed. It was observed that metal ion migrated through the cation-exchange membrane from central compartment to catholyte and OH⁻ formation at the cathode leads to the formation of metal hydroxide. Simultaneously, chromate ion migrated through the anion-exchange membrane from central compartment to the anolyte and formed chromic acid by combining H⁺ produced their by oxidative water splitting. Thus a continuous decay in the concentration of chromate and metal ion was observed in the central compartment, which was recovered separately in the anolyte and catholyte, respectively, from their mixed solution. This process was completely optimized in terms of operating conditions such as initial concentration of chromate and metal ions in the central compartment, the applied cell voltage, chromate and metal ion flux, recovery percentage, energy consumption, and current efficiency. It was concluded that chromic acid and metal ions can be recovered efficiently from their mixed solution leaving behind the uncharged organics and can be reused as their corresponding acid and base apart from the purifying water for further applications.     

Copper Recovery from EDTA − Chelating — Copper Wastewater in a Fluidized Bed

Copper recovery from ethylenediaminetetraacetic acid (EDTA)‐chelating‐Cu wastewater was conducted by means of electrochemical process using a Cu cathode and a PbO₂ anode. In this study, the effects of operating parameters including current density, initial pH, and electrolytic‐cell mode on the quality of copper deposit and current efficiency were studied. It was found that the key factors influencing deposit quality and current efficiency are current density and electrolytic cell mode as well as interactions between them. A better quality of copper deposit with high current efficiency can be obtained at lower current density (2.5 mA/cm²) in this fluidized packed‐bed electrolytic cell.     

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate

Simultaneous electrosynthesis of alkaline hydrogen peroxide and sodium chlorate in the same cell was investigated. The alkaline hydrogen peroxide was obtained by the electroreduction of oxygen in NaOH on a fixed carbon bed while the chlorate was obtained by the reaction of anodic electrogenerated hypochlorite and hypochlorous acid in an external reactor. An anion membrane, protected on the anode side with an asbestos diaphragm, was used as the separator between the two chambers of the cell. The trickle bed electrode of dimensions 0.23 m high ×0.0362 m wide × 0.003 m thick was used on the cathode side. The anolyte chamber of the cell, 0.23 m high × 0.0362 m, wide × 0.003 m thick was operated at a fixed anolyte flow of 2.0 × 10^–6 m³ s^–1 while the oxygen loadings in the trickle bed was kept constant at 0.102 kg m^–2 s^–1. Other operating conditions include inlet and outlet temperatures of 27–33°C (anode side), 20–29°C (cathode side), cell voltages of 3.0–4.2 V (at current density of 1.2–2.4 kAm^–2) and a fixed temperature of 70°C in the anolyte tank.The effects of superficial current density, NaOH concentration (0.5–2.0 M) and catholyte liquid loadings (0.92–4.6 kg m^–2 s^–1) on the chlorate and peroxide current efficiencies were measured. The effect of peroxy to hydroxyl mole ratio on the chlorate current efficiency was also determined.Depending on the conditions, alkaline peroxide solution and sodium chlorate were cogenerated at peroxide current efficiency between 20.0 and 86.0%; chlorate current efficiency between 51.0 and 80.6% and peroxide concentration ranging from 0.069 to 0.80 M. The cogeneration of the two chemicals was carried out at both concentrated (2.4–2.8 M) and dilute (0–0.5 M) chlorate solutions. A relative improvement on the current efficiencies at concentrated chlorate was observed. A chloride balance indicated a less than 0.4% chloride loss to the catholyte. The results are interpreted in terms of the electrochemistry, chemical kinetics and the hydrodynamics of the cell.Nomenclature C _i concentration of speciesi (mol m^–3) - F Faraday constant (96 500 C mol^–1) - I current (A) - Q catholyte flow rate (m³s^–1) - total time of cell operation (s) - _i current efficiency of speciesi (%)     

A feasibility study of mercury deposition in a lead fluidized bed electrode

Following previous work on the recovery of copper from very dilute solutions using a copper fluidized bed electrode, the behaviour of a lead fluidized bed electrode (FBE) is described, for the recovery of mercury from chloride solutions, as typified by chlor-alkali plant effluent.Injection of known quantities of Hg(II) into the FBE catholyte and integration of the current vs time response followed by chemical analysis, allowed mean current efficiencies for mercury deposition to be determined as a function of:feeder electrode potential, Hg(II) concentration, flow rate, bed depth, particle size range, and reservoir volume. By judicious choice of these experimental variables, particularly by limiting bed depths to 20 mm, (potentiostatic) current efficiencies for Hg(II) deposition of 99% could be achieved.Nomenclature a cross sectional area of FBE cell (1.26×10^–3 m²) - A area per unit volume of FBE electrode (m^–1) - c(x) concentration at distancex from feeder electrode (mol m^–3) - c ₀ inlet concentration (mol m^–3) - c _XL outlet concentration (mol m^–3) - D diffusion coefficient (m²s^–1) - I current density (A m^–2) - L static bed length (mm) - t time (s) - T catholyte temperature (K) - u electrolyte superficial linear velocity (mm s^–1) - V electrolyte volume (m³) - XL expanded bed length (mm) - diffusion layer thickness (m) - characteristic length (u/DA) (m) - (lead) density (11.4×10⁶ g m^–3)     

Microbial fuel cells operated with iron-chelated air cathodes

The use of non-noble metal-based cathodes can enhance the sustainability of microbial fuel cells (MFCs). We demonstrated that an iron-chelated complex could effectively be used as an aerated catholyte or as an iron-chelated open air cathode to generate current with the use of MFCs. An aerated iron ethylenediaminetetraacetic acid (Fe-EDTA) catholyte generated a maximum current of 34.4 mA and a maximum power density of 22.9 W m⁻³ total anode compartment (TAC). Compared to a MFC with a hexacyanoferrate catholyte, the maximum current was similar but the maximum power was 50% lower. However, no replenishment of the Fe-EDTA catholyte was needed. The creation of an activated carbon cloth open air cathode with Fe-EDTA–polytetrafluoroethylene (PTFE) applied to it increased the maximum power density to 40.3 W m⁻³ TAC and generated a stable current of 12.9 mA (at 300 mV). It was observed that the ohmic loss of an open air cathode MFC was dependent on the type of membrane used. Moreover, increasing the anode electrode thickness of an open air cathode MFC from 1.5 to 7.5 cm, resulted in a lowering of the power and current density.     

Effect of Drag–Reducing Polymers on the Rate of Liquid-Solid Mass Transfer in Fixed Beds of Spheres under Forced Convection Conditions

The effect of drag–reducing polymers on the rate of liquid – solid mass transfer in a packed bed reactor under forced convection conditions was studied by measuring the rate of diffusion–controlled dissolution of copper spheres in acidified chromate solutions. The variables investigated were superficial liquid velocity, sphere diameter, bed height, and polymer concentration. The mass transfer coefficient was found to increase with increasing superficial liquid velocity. Increasing both sphere diameter and bed height were found to decrease the mass transfer coefficient. Polymer addition was found to decrease the rate of mass transfer by an amount ranging from 29.2 to 56.9% depending on superficial liquid velocity and polymer concentration. Mass transfer data were correlated in absence and in the presence of drag–reducing polymer, using the following equations, respectively: J_d = 3.71Re^–0.54 and, J_d = 2.5 Re^–0.61where J_d is mass transfer J-factor and Re is the Reynolds number.     

Electrodeionization 1: Migration of Nickel ions absorbed in a rigid, Macroporous Cation-exchange Resin

The removal of nickel ions from a packed bed of ion-exchange material under an applied potential is studied. This process involves the use of an electrodialysis type cell in which the centre compartment is filled with a packed bed of ion-exchange particles. The bed width, concentration of nickel in the resin and electrolyte concentration were varied. Emphasis was placed on the rate of nickel migration, current efficiency and the effective mobility of nickel in the system. The purpose of the study is to aid in the development of a system for the continuous removal of heavy metal ions from dilute solutions.     

Simultaneous phenol removal and biological reduction of hexavalent chromium in a packed‐bed reactor

BACKGROUND: Phenol and hexavalent chromium are considered industrial pollutants that pose severe threats to human health and the environment. The two pollutants can be found together in aquatic environments originating from mixed discharges of many industrial processes, or from a single industry discharge. The main objective of this work was to study the feasibility of using phenol as an electron donor for Cr(VI) reduction, thus achieving the simultaneous biological removal/reduction of the two pollutants in a packed‐bed reactor. RESULTS: A pilot‐scale packed‐bed reactor was used to estimate phenol removal with simultaneous Cr(VI) reduction through biological mechanisms, using a new mixed bacterial culture originated from Cr(VI)‐reducing and phenol‐degrading bacteria, operated in draw–fill mode with recirculation. Experiments were performed for feed Cr(VI) concentration of about 5.5 mg L^?1, while phenol concentration ranged from 350 to 1500 mg L^?1. The maximum reduction/removal rates achieved were 0.062 g Cr(VI) L^?1 d^?1 and 3.574 g phenol L^?1 d^?1, for a phenol concentration of 500 mg L^?1. CONCLUSION: Phenol removal with simultaneous biological Cr(VI) reduction is feasible in a packed‐bed attached growth bioreactor. Phenol was found to inhibit Cr(VI) reduction, while phenol removal was rather unaffected by Cr(VI) concentration increase. However, the recorded removal rates of phenol and Cr(VI) were found to be much lower than those obtained from previous research, where the two pollutants were examined separately. Copyright © 2008 Society of Chemical Industry     

Hydrogen peroxide production in trickle-bed electrochemical reactors

A trickle bed electrochemical reactor has been developed for the production of dilute alkaline peroxide solutions by reduction of oxygen. Oxygen gas and sodium hydroxide flow concurrently downward through a cell which consists of a thin packed cathode bed of graphite particles separated from the anode plate by a porous diphragm. Current flows perpendicular to the flow of electrolyte. The effects of current density, oxygen pressure and flow rate, electrolyte concentration and flow rate, graphite particle size, bed thickness and length were investigated. In 2 M NaOH peroxide solutions of 0.8 M have been produced at 60% efficiency with current densities of 1200 A m^–2 and cell voltages of 1.8 V. A bipolar cell stack consisting of five cells has been tested.     

Electrosynthesis of sodium dithionite in a trickle-bed reactor

Sodium dithionite was generated by electroreduction of sulphur dioxide on a graphite fibre mat cathode in a continuous ‘flow-by’ trickle-bed electrochemical reactor. Reactor performance was measured with respect to variation of the feed catholyte NaOH concentration [0.5-1.0 mol/L], feed gas SO₂ concentration [4-40 vol%], product catholyte pH [2.4-12.0] and applied current [10-50 A (0.4-2.0 kA/m²)]. Product catholyte temperature was in the range 18 to 30°C. With product catholyte pH between 2.4 and 6.9, dithionite was generated at current efficiency from 42 to 100%, concentration from 0.05 to 0.78 mol/L, yield from SO₂ up to 69% and specific energy from about 2 to 5 kWh/kg Na₂S₂O₄. Current efficiency fell with increasing current and rose with increasing gas load. High levels of thiosulphate [0.07-0.3 mol/L] and sulphide [0.01-0.13 mol/L] measured in the product catholyte would compromise the use of this process in commercial applications such as brightening wood pulp.