Cr～（3+）电化学氧化生成Cr₂O₇～（2-）过程研究

【作者】 陈昌平；

【导师】 许文林；

【作者基本信息】 扬州大学 ， 物理化学， 2003， 硕士

【摘要】 本文研究了Cr³⁺在硫酸介质中电化学氧化生成Cr₂O₇^2-的过程，提出了Cr³⁺电化学氧化生成Cr₂O₇^2-的反应历程。采用循环伏安法和稳态法测定了该体系的循环伏安曲线和稳态极化曲线；恒电流条件下，在两电极体系中采用整体电解法，研究了操作电流密度、Cr³⁺浓度、温度、硫酸浓度以及超声对Cr³⁺电化学氧化生成Cr₂O₇^2-过程电流效率的影响，实验结果验证了提出的反应历程的正确性。本文还研究了自制的Ti/SnO₂+Sb₂O₃/PbO₂电极对Cr³⁺硫酸溶液阳极氧化过程电流密度和Cr³⁺电化学氧化生成Cr₂O₇^2-过程电流效率的影响。并针对以Cr₂O₇^2-/Cr（3+）为媒质间接电化学氧化蒽制蒽醌过程，采用整体电解法研究了活性炭吸附、超声和电极材料对Cr³⁺循环液电化学氧化生成Cr₂O₇^2-过程电流效率的影响，为实现该过程的工业化提供理论指导和技术参数。研究表明： （1）硫酸介质中Cr³⁺电化学氧化生成Cr₂O₇^2-经过下列反应历程： 其中反应②为电化学反应控制步骤，反应③是Cr³⁺氧化生成Cr₂O₇^2-的反应，其中OH_ad与Cr³⁺的反应是Cr³⁺氧化生成Cr₂O₇^2-过程的速率控制步骤，反应④是O₂的生成反应。由上述反应历程推导可得Cr³⁺氧化过程的反应速率r₃、电流效率η和反应选择性β的表达式：陈吕平:cr3十电化学氧化生成crZo户过程研究几=d【er3+=k3厚裔ICr’‘’ 几巧+残 :_r户₃+，=入3L、IJ=k3[Cr3+]k3[Cr，+]+k4[oHod]，，。。₃+1.{不不丁 “，卜‘”V一币不叭A飞(Eor、fer，+1一=下，一exPI一二云.厅二丁了一万r4 A4\Kl/IUnadJ一一一一nn尸 （2）操作电流密度、反应温度、超声及cr3+、H十、50互一的浓度均对cr3+电化学氧化过程的电流效率有影响。提高操作电流密度和50且一的浓度，cr，‘电化学氧化过程的电流效率减小;提高反应温度、增大Cr3十和H十的浓度，过程的电流效率会增大;超声的存在亦使Cr3+硫酸溶液电解时的电流效率增大。 （3）用聚合前驱体通过热分解法自制的Ti/SnOZ+SbZO3lPbO:电极比PbO:电极的抗剥蚀性好，使用寿命长，可以提高Crs+硫酸溶液阳极氧化过程的电流密度和Cr3+电化学氧化过程的电流效率。 （4）cr，十循环液电解时的电流效率低于纯cr3+硫酸溶液电解时的电流效率:cr，+循环液经活性炭吸附后进行电解，或Cr3+循环液在超声下电解，均可提高其电化学氧化过程的电流效率。以自制的Ti/s n02+sbZO3?bo:电极为阳极电解cr，十循环液时的电流效率也低于用该电极电解纯Cr3+硫酸溶液时的电流效率。更多还原

【Abstract】 The electrochemical oxidation of Cr3+ to Cr2O72- in sulfuric acid solution was studied. The formation mechanism of Cr2O72- in sulfuric acid solution was theoretically analyzed. The cyclic voltammograms and steady-state polarization curves of the electrochemical oxidation of Cr3+ in sulfuric acid solution were determined using three-electrode cell. The influences of operation current density, the concentration of Cr3+ and sulfuric acid, temperature as well as ultrasound on the current efficiency of the electrochemical oxidation of Cr3+ to Cr2O72- in sulfuric acid solution were studied. The effects of electrode materials on the current density and the current efficiency of the electrochemical oxidation of Cr3+ were also studied. The influences of active carbon, ultrasound and electrode materials on the current efficiency of the electrochemical oxidation of the contaminated Cr3+ solution in the process of indirect oxidation of anthracene to anthraquinone by Cr2O72- were investigated too.(1) The theoretical analysis and experimental results showed that the formation mechanism of Cr2O72- in sulfuric acid solution wasIn the above mechanism, the reaction (2) was electrochemical reaction determining step, the reaction (3) which was the oxidation of Cr3+ to Cr2O72- and thereaction (4) which was the evolution of oxygen reaction proceeded simultaneously. The reaction of OHad with Cr3+ was considered to be the rate-determining step of the oxidation of Cr3+to Cr2072-.According to the above mechanism, the relation of the rate of the oxidation of Cr3-to Cr2O732- with the concentration of Cr3+ and H+ as well as temperature in sulfuric acid solution was represented as follows:3+The current efficiency of the electrochemical oxidation of Cr3+ to Cr2072- in sulfuric acid solution can be described as:The relation of the selectivity of the reaction (3) and (4) with the operation current density, temperature as well as the concentration of Cr3+ can be expressed as:(2) The experimental results showed that the current efficiency of the electrochemical oxidation of Cr3+ to Cr2O72- in sulfuric acid solution increased with decreasing operation current density or the concentration of SO42- . The current efficiency increased with increasing temperature or the concentration of Cr3+ or the concentration of H+ at the same reaction condition. The current efficiency also increased when the electrolytic oxidation of Cr3+ was carried out in the presence of the ultrasound.(3) The experimental results also showed that the current density and the current efficiency of the electrochemical oxidation of Cr3+ in sulfuric acid solution with Ti/SnO2+Sb2O3/PbO2 as an anode were much higher than that with PbO2 at the same reaction condition. The Ti/SnO2+Sb2O3/PbO2 electrode had a better resistance to denudation and a longer lifetime than PbO2 electrode in the electrochemical oxidation process of Cr3+(4) The current efficiency of the electrolytic oxidation of the contaminated Cr3+ solution was lower than that of the un-contaminated Cr3+ solution with PbO2 as an anode or Ti/SnO2+Sb2O3/PbO2 as an anode. The current efficiency of the electrochemical oxidation of the contaminated Cr3+ solution was improved when the contaminated Cr3+ solution was treated by activated carbon before electrolysis. The current efficiency also increased when the electrolytic oxidation of the contaminated Cr3+ solution was carried out in the presence of the ultrasound.更多还原