Dissolution kinetics of iron oxides in clay in oxalic acid solutions

Clay samples containing 8.15% iron oxides and 27.49% alumina were leached in oxalic acid. Leaching experiments were per-formed in aqueous solutions of oxalic acid of 0.2-2 mol/L at 40-80 C for up to 90 min. The mixed kinetic mechanism, i.e., t/τ=[（1 2X/3） （1 X）2/3 ]＋b[ 1 （1 X）1/3], seemed to be the most appropriate one to fit the kinetic data of leaching iron oxides contained in clay in the aqueous oxalic acid solutions. The Arrhenius activation energy for leaching in the 1.8 mol/L oxalic acid was found to be 41.035 kJ/mol.

Removal of Vand Fe from spent denitrification catalyst by using oxalic acid:Study of dissolution kinetics and toxicity

The selective dissolution of V and Fe from spent denitrification catalyst(SDC)with oxalic acid was investigated to minimise their environmental effects.The dissolution kinetics of different elements from SDC by using 0.1–1.5 mol L^(-1) oxalic acid concentration was studied at 60℃–90℃.V and Fe were preferentially released(65%and 81%)compared with Al,Ti and W within 5 min due to the redox reactions of oxalic acid.The dissolved fractions of Fe,V,Al,Wand Ti increased with the increase of oxalic acid concentration and reaction temperature.The dissolution kinetic experiments were analysed and controlled diffusion with n<0.5 according to the Avrami dissolve reaction model(R^(2)>0.92).The Arrhenius parameters of the Ea values of Ti,W,V,Fe and Al from SDC with oxalic acid were 30,26,20,19 and 11 kJ mol^(-1),respectively.The obtained Avrami equation of V and Fe was successfully used to predict their leaching behaviour in oxalic acid.Toxicity characteristic leaching procedure revealed that the toxicity risk of Vand Fe metals from SDC after leaching with oxalic acid decreased to below 5 mg kg^(-1) residua.Overall,the leaching residua by oxalic acid indicated its safety for the environment.

Insights into kinetics and reaction mechanism of acid-catalyzed transesterification synthesis of diethyl oxalate

The catalytic performance of different acidic catalysts for diethyl oxalate synthesis from the one-step transesterification of dimethyl oxalate and ethanol was evaluated.The effects of different factors(e.g.,acidity,electron accepting capacity,cations type and crystalline water)on the catalytic activity of acidic catalysts were investigated respectively.It was proposed and confirmed that the transesterification reaction catalyzed by a Lewis acid(FeCl3)and a Bronsted acid(H2SO4)follows a first-order kinetic reaction process.In addition,the Lewis acid-catalyzed transesterification processes with different ester structures were used to further explore and understand the speculated reaction mechanism.This work enriches the theoretical understanding of acid-catalyzed transesterification reactions and is of great significance for the development of highly active catalysts for diethyl oxalate synthesis,diminishing the industrial production cost of diethyl oxalate,and developing downstream bulk or high-value-added industrial products.

Oxalic Acid Promoted Hydrolysis of Sodium Borohydride for Transition Metal Free Hydrogen Generation

We reported an inexpensive and high-efficiency hydrogen generation method from NaBH4 hydrolysis promoted by oxalic acid.NaBH4 and H2C2O4 were premixed and hydrogen generation was initiated by adding water into the solid mixture.H2C2O4 was selected as the acid promotor due to its solid state and low mass per proton.The effect of reactant ratio on the hydrogen yield and hydrogen storage density was investigated.With optimized reactant ratio,high gravimetric hydrogen storage up to 4.4wt%based on all the reactants can be achieved with excellent hydrogen generation kinetics.

Oxalic Acid Promoted Hydrolysis of Sodium Borohydride for Transition Metal Free Hydrogen Generation

We reported a low cost,high efficiency hydrogen generation method from NaBH4 hydrolysis promoted by oxalic acid.NaBH4 and H2C2O4 were premixed and hydrogen generation was initiated by adding water into the solid mixture.H2C2O4 was selected as the acid promotor due to its solid state and low mass per proton.The effect of reactant ratio on the hydrogen yield and hydrogen storage density was investigated.With optimized reactant ratio,high gravimetric hydrogen storage up to 4.4wt% based on all the reactants can be achieved with excellent hydrogen generation kinetics.

Kinetics of Manganese Oxides Dissolution in Sulphuric Acid Solutions Containing Oxalic Acid

The kinetics of the interaction of MnO2, Mn2O3, and Mn3O4, with sulphuric acid solutions and the effect of oxalic acid on this process are studied. As the sulphuric acid concentration is increased from 0.1 to 5 N, the dissolution rate of Mn2O3, Mn3O4 to MnO2 and Mn2+ ions decreases, whereas it increases with the concentration of Mn2+ ions. Upon the addition of H2Ox, the complete dissolution of Mn3O4 occurs more quickly. The reaction order with respect to the H+ and O x2- ions is +0.5 ± 0.1. A mechanism of MnO2 dissolution promotion by?O x2- is proposed. The dissolution rate was found to depend on the concentrations of?MnHOx - ions and was highest at pH 1.6 ± 0.2. A rate law and mechanism are suggested for manganese oxides dissolution.

Synthesis of Diethyl Oxalate by a Coupling-Regeneration Reaction of Carbon Monoxide

This article describes a process for the synthesis of diethyl oxalate by a coupling reaction of carbon monoxide, catalyzed by palladium in the presence of ethyl nitrite. The kinetics and mechanism of the coupling and regeneration reaction are also discussed. This paper presents the results of a scale-up test of the catalyst and the process based on an a priori computer simulation.

Radiation-Chemical Degradation of Oxalic Acid in Water Solutions

Co60 gamma ray radiolysis of aqueous oxalic acid solution （1 × 10-2 M） was investigated within the dose range up to 80 kGy. The value of pH increases from 2.0 to 4.0 and approximately 90% of oxalic acid and its derivatives are degraded at the dose of 80 kGy. Dissolved O2 affects to the degradation of oxalic acid at the initial stage due to total consumption of O2 at the dose of 2 kGy. Formation of CO2 occurs at a higher rate at the initial stage until the dissolved 02 is fully consumed. The kinetic model of oxalic acid degradation in aqueous solution under the gamma irradiation was tested. The suggested mechanism complies with the experimental data both of our own and of that reported earlier.

High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process.In this study,a new method for leaching NdFeB waste with oxalic acid was developed.The high-efficiency,simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit.Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90℃ for 6 h in the aqueous solution of oxalic acid(2 mol/L) with a liquid-solid ratio of60 mL/g,the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%,respectively.Rare earth oxalate and Fe(C_(2)O_(4))3^(3-) were left in the residue and the leaching solution,respectively.The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction(XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDS).Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model,and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction.The leaching residue was calcined at 850℃ for 3 h and then decomposed into rare earth oxide,which can be directly used to prepare rare earth alloy via molten salt electrolysis.For the leaching solution,ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate(FeC_(2)O_(4)-2H_(2)O).

Catalytic performance of Fe_3O_4-CoO/Al_2O_3 catalyst in ozonation of 2-(2,4-dichlorophenoxy) propionic acid,nitrobenzene and oxalic acid in water

Fe3O4-CoO/Al2O3 catalyst was prepared by incipient wetness impregnation using Fe（NO3）3.9H2O and Co（NO3）2.6H2O as the precursors, and its catalytic performance was investigated in ozonation of 2-（2,4-dichlorophenoxy）propionic acid （2,4-DP）, nitrobenzene and oxalic acid. The experimental results indicated that Fe3O4-CoO/Al2O3 catalyst enabled an interesting improvement of ozonation efficiency during the degradation of each organic pollutant, and the Fe3O4-CoO/Al2O3 catalytic ozonation system followed a radical-type mechanism. The kinetics of ozonation alone and Fe3O4-CoO/Al2O3 catalytic ozonation of three organic pollutants in aqueous solution were discussed under the mere consideration of direct ozone reaction and OH radical reaction to well investigate its performance. In the catalytic ozonation of 2,4-DP, the apparent reaction rate constants （k） were determined to be 1.456 × 10^-2 min-1 for ozonation alone and 4.740 × 10^-2 min^-1 for O3/Fe3O4-CoO/Al2O3. And O3/Fe3O4-CoO/Al2O3 had a larger Rot （6.614 × 10^-9） calculated by the relative method than O3 did （1.800 x 10-9）, showing O3/Fe3O4-CoO/Al2O3 generated more hydroxyl radical. Similar results were also obtained in the catalytic ozonation of nitrobenzene and oxalic acid. The above results demonstrated that the catalytic performance of Fe3O4-CoO/Al2O3 in ozonation of studied organic substance was universal to a certain degree.

不同浓度草酸溶液下AlN的水解性能研究

氮化铝作为一种新型先进陶瓷材料,应用领域广阔,但是氮化铝在潮湿的空气中易水解,本文探讨了草酸的浓度对AlN粉体抗水解性能的影响,在85 ℃水浴加热下。采用SEM和XRD等方法对样品进行了测试表征,结果表明在低浓度(0.01 M、0.02 M、0.03 M)草酸溶液中,随着草酸浓度增加,氮化铝水解程度减弱,水解主要固相产物为三羟铝石;高浓度草酸溶液中(0.04M、0.05M),氮化铝未水解,其表面微观结构比较光滑。随着反应时间延长,0.05M草酸作用下样品中也有三羟铝石形成样品,表面粗糙。这表明在一定的浓度和反应时间下,草酸溶液中AlN粉体不易水解,这为AlN粉体的存储、水基成型和工业化应用提供一种新思路。

铅铋合金中铅铋分离制备草酸铅工艺研究

针对铅铋在熔炼、吹炼过程极易形成互溶相,难分离,导致产出的铅铋合金堆存或低价外售。通过冷水喷射冲散金属液进行制粒-氧化酸浸回收铅铋的湿法分离工艺,并在浸出液中加入草酸制备草酸铅,优化了影响铅铋浸出率的主要因素,反应温度80~90℃,反应时间120 min,搅拌速率250 r/min,醋酸初始浓度500 g/L时,Pb、Bi的浸出率分别达到了96%、93%,按理论量加入草酸制备的草酸铅产品纯度达到了99.3%,实现了铅铋合金湿法回收。

草酸二甲酯水解制草酸工艺技术探究

分析了草酸在当前和未来市场中的前景,并探讨其生产技术的发展。草酸是一种具有重要化学应用的关键化学品,其在多个领域拥有广泛的使用,深入探究草酸生产制造工艺具有十分重要的意义。首先对草酸生产工艺技术路线进行介绍,探讨了羰化合成草酸二甲酯再与水发生水解反应制草酸的工艺技术,分析了该工艺技术的优劣性,在环保性、中间产物多样性、工艺复杂性和能源消耗等方面得出见解。

煤浆法烟气脱硫中草酸和紫外线强化煤砷浸出过程

以N_(2)、O_(2)、SO_(2)三种气体模拟烟气,在1 L的光反应器中,研究了主要因素对煤砷浸出、As(Ⅲ)氧化以及SO_(2)脱除的影响规律,分析了过程机理,确定了浸出过程速率控制步骤。结果表明,紫外线照射和草酸均能有效提高砷浸出率,180 min时,在遮光和pH为2.5的条件下,加入1.0 mmol/L草酸能使砷浸出率提高32.9%,在紫外线照射下,可使砷浸出率再提高21.3%,且浸出液中的As(Ⅲ)占总砷之比小于13%,还能提高SO_(2)脱除率。低pH有利于煤中砷的浸出,但对SO_(2)的脱除不利。煤砷浸出率和SO_(2)脱除率均随温度的提高而显著增大。动力学分析计算得出煤砷浸出过程的表观活化能为4.9 kJ/mol,说明砷浸出过程受已反应固体层内的扩散过程控制。自由基猝灭实验表明,硫酸根自由基和羟基自由基是紫外线照射下草酸强化煤砷浸出体系中的主要自由基。ATR-FTIR与XPS表征结果进一步证实了浸出液的测定结果。

乙二醇选择性电氧化用于涤纶树脂的回收利用

聚对苯二甲酸乙二醇酯(涤纶树脂,简称PET)作为一类常见的塑料制品,其回收再利用可以有效减少环境污染和能源消耗,目前主要分为机械与化学两类回收方式。但目前化学回收法仍存在不足,并未广泛应用,主要问题之一是水解产物分离提纯困难。因此,以可再生能源为驱动力,将电催化与PET回收转化相结合,利用镍泡沫作为工作电极使氢氧化钠溶液中的乙二醇逐步氧化为乙醇醛、乙醇酸钠,最终生成易于沉淀分离的草酸钠,从而避免能源大量消耗,提高经济效益。本新创实验实现学科交叉,涉及多种基础实验操作,提升学生综合专业素养。有助于学生了解绿色化学与可持续发展理念,拓展专业视野,激发科学探索兴趣。

CO气相催化偶联合成草酸二乙酯动力学

以工业应用为背景,研究了CO在钯系双金属催化剂上气相催化偶联合成草酸二乙酯的动力学特性。得出其速率控制步骤为CO吸附控制,并且认为在催化剂表面上存在烷氧羰基中间体COOR,进一步缔合生成草酸二乙酯,提出了机理型的动力学方程,并据此对反应历程做了探讨。

草酸二乙酯水解宏观动力学研究

在 65～ 80℃对草酸二乙酯水解生成草酸的反应宏观动力学进行了研究 ,得到的草酸二乙酯水解反应速率方程可表示为r C=dccdt=kc0 .5A c1 c- kc1 .5Ck=2 .1 1 7× 1 0 5exp(- 3.479× 1 0 4 /RT) k=5.2 73× 1 0 2 exp(- 1 .398× 1 0 4 /RT)并用实验数据对模型进行了检验。

草酸水解甜高粱秸秆渣的Saeman动力学模型

利用草酸作为催化剂水解甜高粱秸秆渣制备木糖,测定了不同温度下的木糖收率和副产物糠醛产量;依据半纤维素水解的Saeman模型,计算得到了木聚糖水解和木糖降解的动力学数据,其活化能分别为5.89×104,1.38×104J/mol。分析结果表明:木聚糖水解反应速度快,但是生成的木糖容易发生降解;模型最优化反应条件为125℃和77min,实验得到的木糖收率为52.11%。草酸作为一种有机酸,能够用于催化半纤维素水解制备木糖,副产物糠醛的产率较低。

La,Pr,Nd掺杂对纳米TiO_2光催化性能的影响

采用水解共沉淀法制备了稀土元素(La,Pr,Nd)掺杂量为0.5wt%～1.5wt%的TiO2光催化剂样本,并对其进行了XRD、TG-DTA、TEM、BET和UV-Vis表征。结果表明,所制备的TiO2光催化剂是以锐钛矿晶型为主的纳米颗粒,掺杂抑制了TiO2晶型由锐钛矿向金红石的转变,同时减小了晶粒尺寸、增大了比表面积、提高了吸光度,且使TiO2半导体的吸光范围发生了红移。将制得的TiO2光催化剂应用于溶液中草酸的降解反应,用K2MnO4滴定法分析降解效率,发现经掺杂改性后的TiO2样本光催化效率均有提高。其中,以掺杂量为1.0wt%的La掺杂样本具有最高的降解效率,与纯TiO2样本相比对草酸的降解率提高了近45%。

表面活性剂增敏阻抑动力学光度法测定痕量草酸

在稀盐酸介质中 ,微量草酸对H2 O2 氧化靛红的褪色反应有显著的阻抑作用 ,非离子表面活性剂TritonX 1 0 0对此体系有强烈的增敏作用 ,据此建立了表面活性剂增敏阻抑动力学光度分析测定微量草酸的新方法。方法的线性范围是 0 .0 0 5～ 0 .5 0mg L ,检出限为 0 .0 0 5mg L。方法简便 ,快速 ,灵敏度高 ,用于菠菜和尿样中草酸含量的测定 。