Macrokinetic Study of the Electrochemical Synthesis Process of Sodium Dichromate

In order to address the problems existing in the traditional production techniques for sodium dichromate, a new green technology for producing sodium dichromate using an electrochemical synthesis method was studied. Using a self‐made electrosynthesis reactor composed of pure titanium and stainless steel, with a multiple‐unit metal oxide combination anode, a stainless steel cathode, and a reinforcing combination cation exchange membrane, the kinetic experiments were carried out on the direct electrochemical synthesis reaction of sodium dichromate from sodium chromate. The kinetic data were experimentally measured at different temperatures and different initial sodium chromate concentrations of anolyte. The results show that the electrochemical synthesis process presents complicated zero‐order reaction kinetic characteristics, with the reaction rate constant depending on the initial sodium chromate concentration. The macrokinetic equation of the electrochemical synthesis reaction was established, and some kinetic parameters were calculated. The apparent activation energy is less than that of the ordinary chemical reaction, and this shows that the electrochemical synthesis of sodium dichromate has great development potential.     

铬酸酐电合成过程中工作电压的变化

引言 铬酸酐主要用于电镀、作氧化剂、水溶性木材防腐剂、制铬盐、着色玻璃等,是一种重要的化工产品,近年发展相当迅速[1].其传统生产工艺中的Na2Cr2O7-H2SO4间歇熔融法、外热连续法、 自热连续法、湿法等技术[2],都不可避免地存在NaHSO4污染产品、铬流失、污染环境等问题.发展前景看好的是有绿色技术之称的电合成法[3, 4],正在竞相研发中[5],其基础研究亟待进行.本文从工程角度研究了铬酸酐电合成过程中工作电压的变化规律.     

电化学合成重铬酸钠阳极稳态极化及交流阻抗法研究

针对重铬酸钠传统生产技术存在问题,提出电化学合成重铬酸钠的绿色新技术,阳极为自制钛基多元金属氧化物复合电极,所用阳极液为铬酸钠水溶液.阳极既是电催化合成过程的催化剂,又是电催化反应进行的场所.根据电催化合成重铬酸钠体系的特点,运用稳态极化曲线和交流阻抗技术研究了阳极反应动力学及电化学行为.实验测得阳极反应活化能等电极反...     

铬酸酐电化学合成中阳极液在钛基多元金属氧化物复合电极上的电化学研究

针对铬酸酐传统生产技术中存在问题,开发了电化学合成铬酸酐的绿色新技术. 本技术所用阳极液为重铬酸钠水溶液,阳极为自制钛基多元金属氧化物复合电极. 作为该技术系列基础研究的一部分,本文用循环伏安法研究了重铬酸钠水溶液在钛基复合电极上的电化学性能. 通过160个循环的电氧化反应,表明该电极具有很稳定的电化学性能. 实验测得不同温度、不同扫描速度v、不同浓度重铬酸钠溶液即重铬酸钠存在下水在电极上的氧化峰峰电流ip和峰电位Ep,建立了i_p～v^1/2和E_p～lnv方程,表明电极反应是主要受扩散控制的不可逆反应. 求得电极反应的动力学参数和反应活化能,初步讨论了温度的影响.     

重铬酸钠溶液分解碳酸钙制取铬酸钙

介绍了一种制取铬酸钙的新方法,利用重铬酸钠溶液分解碳酸钙,可以得到高纯度的铬酸钙. 实验表明,温度和浓度是影响碳酸钙分解的关键因素,当重铬酸钠浓度大于60%、重铬酸钠与碳酸钙摩尔比大于1.05:1时,常压沸腾条件下即可完全分解碳酸钙,制得纯度99.5%的铬酸钙,收率接近100%. 分解过程中产生的二氧化碳气体可用于碳化分离铬酸钙后的铬酸钠溶液再生重铬酸钠,循环利用. 新方法工艺简单、产品纯度和收率都较高,无环境污染.     

电解法制取红矾钠的研究

介绍了用离子膜电解槽电解工业铬酸钠溶液合成重铬酸钠的过程。考察了电流密度、电解温度、阳极液初始浓度、阴极液初始和最终浓度对电流效率和直流耗电量的影响。得出了电解反应的最佳条件     

一种新的芒硝制碱法实验室研究

The purpose of this work is to find a new way for utilizing the rich sodium sulfate resource to produce soda ash. A novel process is proposed which uses aqueous dichromate solution as working medium through decomposition of calcium carbonate in aqueous sodium dichromate, complex decomposition of aqueous sodium sulfate and calcium chromate, regeneration of sodium dichromate and production of sodium bicarbonate from carbonation of aqueous sodium chromate solution, processing and utilization of byproduct calcium sulfate, and production of sodium carbonate from sodium bicarbonate. The process has the features of less corrosion and pollution and low energy consumption.     

芒硝制纯碱和硫酸新工艺探讨

我国芒硝储量世界第一,大部分位于欠发达的西部地区,芒硝还是许多工业过程的副产物,大多含有环境污染物.芒硝本身利用价值低,市场容量小,开发新的利用途径具有重要意义.提出了一种芒硝制纯碱和硫酸的新工艺,它是以氧化钙和重铬酸钠水溶液为转化介质,硫酸钠先和氧化钙在重铬酸钠水溶液中反应,得到硫酸钙沉淀和铬酸钠水溶液,前者高温还原分解再生氧化钙,同时得到二氧化硫和二氧化碳,二氧化硫经转化吸收得硫酸;后者和二氧化碳反应再生重铬酸钠水溶液,同时得到碳酸氢钠沉淀,碳酸氢钠经脱铬处理制得纯碱.该工艺借鉴了工业上成熟的石膏分解制硫酸技术和铬酸钠碳化制重铬酸钠技术,具有成本低、腐蚀轻、无废物排放等特点,有望为我国丰富的芒硝资源开辟新的应用途径.     

Electrochemical production of lead chromate and sodium hydroxide in a two-compartment cell

This paper describes the application of an anode-support system (AS) and a cationic permselective membrane to the electrolytic production of yellow lead chromate pigment and sodium hydroxide solution in a two-compartment cell. The authors have determined that it is possible to utilize in the process an AISI-316 stainless steel or a titanium mesh basket loaded with lead granules. Under the operating conditions used both the AISI-316 stainless steel and the titanium remain passive and act only as electrical contact between the lead anodic pieces and the external current source. A Nafion^® 901 bimembrane (Dupont, USA) is utilized to separate both compartments. Good quality yellow lead chromate and sodium hydroxide solution (50–150 g dm^–3) are obtained, with a power requirement of 0.41 kWh (kg PbCrO₄)^–1.     

使用钛涂钌电极作为阳极电解法制备次磷酸的研究

研究了以钛涂钌电极作为阳极,不锈钢作为阴极,采用四室电渗析槽电解法制备次磷酸的最佳工艺条件(如电解电流、电解时间、原料室次磷酸钠浓度等)。测量了电解过程中钛涂钌电极的阳极电位。结果显示钛涂钌电极在硫酸介质中,具有高的电催化活性和低的析氧电位,是非常省电的阳极材料,在最佳条件下制得的产品纯度高,各项指标都达到了分析纯的标准。该方法没有废物产生,不污染环境,符合清洁生产。     

Kinetic study of hydrogen peroxide decomposition at high temperatures and concentrations in two capillary microreactors

On the background of the direct adipic acid synthesis from cyclohexene and H₂O₂, a kinetic model was derived for the H₂O₂ decomposition catalyzed by sodium tungstate at high H₂O₂ concentrations and high temperatures. A perfluoroalkoxy (PFA) and a stainless steel micro‐flow capillary match commonly used microreactor materials. In the PFA capillary, the decomposition of hydrogen peroxide increased with residence time, reaction temperature and catalyst loading. The reaction order with respect to hydrogen peroxide and sodium tungstate was zero and one, respectively. Simulated data fit well with experimental data in the PFA capillary. While showing a similar trend as that in the PFA capillary, the stainless steel capillary exhibited much higher reaction rates. The steel surface participated in the decomposition process as a heterogeneous catalyst. Key influencing factors of the H₂O₂ decomposition provided some clues on the reaction mechanism of the adipic acid synthesis and its process optimization. © 2016 American Institute of Chemical Engineers AIChE J, 63: 689–697, 2017     

The influence of zinc surface pretreatment on the adhesion of epoxy coating electrodeposited on hot-dip galvanized steel

The adhesion and electrochemical properties of epoxy coatings electrodeposited on hot-dip galvanized steel with and without passive films were investigated during exposure to 3% NaCl. The passive films were formed in hot air, in boiling water and by chromating. Adhesion was measured both by a standardized pull-off method and by swelling in N-methyl pyrrolidone. Pretreatment of hot-dip galvanized steel with passive film formed in hot air increases both dry and wet adhesion strength of the epoxy coating compared to pretreatment with passive film formed in boiling water and chromate coating. The overall increase of wet adhesion for this sample was maintained throughout the whole investigated time period. It was shown that the change in adhesion of epoxy coating on a chromate coating is smallest of all investigated samples, although the initial value of adhesion on this surface had the lowest value. The corrosion stability of coated Zn samples pretreated by different methods, was investigated by electrochemical impedance spectroscopy and in the initial time of exposure to NaCl the highest values of pore resistance were also obtained for the epoxy coating on Zn pretreated in hot air, whereas the epoxy coating on a HDG steel with a chromate coating showed the smallest change in electrochemical properties (pore resistance, coating capacitance, charge-transfer resistance) during prolonged exposure time.     

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.     

硫酸盐还原菌诱导腐蚀的电化学噪声分析

基于电化学噪声(EN)和信号处理研究硫酸盐还原菌(SRB)对304不锈钢诱导的腐蚀。将304不锈钢电极分别置于硫酸盐还原菌接种前后的培养基中,利用电化学工作站分别对2种试样的腐蚀进程进行电化学噪声测量,将测得的噪声数据去除直流漂移,再对这些数据进行时域、频域和小波分析。结果表明:通过时域分析得到的标准偏差和噪声电阻可表征腐蚀速率,局部因子则可以区分腐蚀类型。通过频域分析得到的功率谱密度曲线,能表征304不锈钢腐蚀的程度。小波分析则能从不同尺度下分解信号,更加直观、清晰地表征腐蚀进程。利用电化学噪声技术能很好地监测SRB对不锈钢的腐蚀影响,根据不同的需求采用不同的分析方法进行电化学噪声数据分析,才能准确表征腐蚀类型、腐蚀速率以及腐蚀程度。     

Application of superporous magnetic cationic cryogels for persistent chromate (toxic chromate and dichromate) uptake from aqueous environments

Poly((3‐Acrylamidopropyl)trimethylammonium chloride) (p(APTMACl)) cryogels were prepared with cryopolymerization technique and employed for the removal of toxic chromate and dichromate anions from aqueous media. The maximum adsorption capacities of 94 mg/g and 135 mg/g for chromate and dichromate anions, respectively, were determined with the application of the Langmuir isotherm. These values are very close to the experimental values of about 77 and 128 mg/g from 100 mL, 100 ppm chromate, and dichromate solutions using 0.03 g cryogel. The removal efficiency of chromate and dichromate anions were increased with the increase in the amount of cryogel and the removal percentage of chromate and dichromate toxic anions were estimated as 99.21 and 93.61%, respectively, for 0.15 g of p(APTMACl) cryogels used in 100 mL, 100 ppm chromate, and dichromate solutions. Furthermore, magnetic p(APTMACl) cryogels were also prepared and used in the removal of chromate and dichromate, and the maximum adsorption capacities were 30 mg/g and 40 mg/g, respectively. Additionally, the adsorption of these anions were investigated from different media such as drinking water, tap water, seawater, and creek water; and the maximum adsorption amounts in drinking water were 65.5 ± 15, and 125.5 ± 11 mg/g for chromate and dichromate anions, respectively. The reusability of p(APTMACl) cryogels for the removal of chromate and dichromate anions was also investigated, and it was found that the adsorption capacity for chromate anions decreased to 71.23 ± 4.3 from 97.37 ± 4.5 mg/g, whereas the adsorption capacity of dichromate anions only decreased to 123.69 ± 3.5 mg/g from 129.9 ± 7 mg/g at the end of five adsorption‐desorption cycles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43438.     

电合成重铬酸钠用析氧阳极的研究进展

铬盐行业一直是重污染行业,传统的铬盐生产技术是造成严重污染的原因之一。重铬酸钠作为铬盐的母系产品,其生产技术的改进对于整个铬盐行业的清洁化生产尤为重要。在介绍电合成重铬酸钠技术的基础上,重点介绍了该工艺使用的阳极材料的研究进展、存在的问题以及发展前景。     

不锈钢在氟硼酸清洗剂中的腐蚀行为研究

通过X-射线衍射仪（XRD）对经过不同表面处理的两种不锈钢（1Cr18Ni9Ti）表面进行物相分析,采用失重法测定其在氟硼酸清洗剂中的腐蚀速度,同时借助扫描电镜及电子扫描探针观测浸泡过程中不锈钢的表面腐蚀形貌及其表面粗糙度的变化特征。结果表明：不锈钢在沸腾的浓硝酸中形成一层氧化物后作为模拟污染物相对于未处理前表面含有较...     

流动腐蚀介质中双相不锈钢的电化学阻抗谱

测定了流动氯化物体系中双相不锈钢电极的电化学阻抗谱,发现在单相流中,当流速低于临界值时,阻抗谱为直径较大的容抗弧;一旦流速超过临界值,阻抗谱特征为2个容抗弧.流动介质中加入固体颗粒之后,阻抗谱在低流速下高频区为容抗弧,低频区为直线段,而高流速下低频区则出现实部收缩现象.根据腐蚀电化学理论,提出了流动体系中双相不锈钢电极反应过程动力学模型,较好地解释了流动体系中双相不锈钢电极的电化学阻抗谱,进一步揭示了电化学腐蚀在双相不锈钢流动腐蚀过程中的主导作用机理.     

容量法快速测定煤中全硫

针对称量法测定煤中全硫含量耗时长,介绍了一种快速测定方法。煤中全硫与艾士卡试剂在高温条件下反应生成硫酸钠,硫酸钠与铬酸钡在盐酸介质中反应生成硫酸钡沉淀和重铬酸钠,中和后过滤除去硫酸钡沉淀和过量的铬酸钡,滤液酸化又得到重铬酸钠,加入碘化钾作用定量地析出碘,用硫代硫酸钠标准溶液滴定。方法容易掌握,准确度高。     

Formation of Zeolite (MFI) Layers on Gauze Wire and Arranged Packing Segment

MFI‐type zeolite binderless coating were grown over stainless steel (gauze wire and arranged packing segment) and copper substrates (gauze wire). The kind of preparation and the surface structure (different preliminary treatments of the stainless steel by way of corrosive action) were varied. Four different ZSM‐5‐preparations were selected in consideration of the following aspects: hydrothermal synthesis versus atmospheric pressure, using TPABr as organic template versus template‐free, alkali‐free versus Na₂O or sodium dihydrogenphosphate, variation of Si/Al‐ratio. In addition, silicalite syntheses were carried out for comparison. The catalytic activity was determined via liquid‐phase hydrogenation reactions. Reactions of interest were the hydrogenation of toluene and the catalytic hydrogenation of dissolved oxygen.