Electrodialysis Catalytic Oxidation Purification Of Low Concentration SO₂ In Liquid Phase To Produce Sulfuric Acid

SO₂ as a toxic and harmful pollutant is found in the exhaust gases emitted by many industrial production,if the low concentration of SO₂ can be converted into sulfuric acid while flue gas desulfurization,then the resource utilization of sulfur can be realized.In the traditional sulfuric acid process,contact oxidation system by SO₂ to SO3 process under high temperature and catalyst is required,the SO₂ gas phase oxidation require high energy and cost,and in the liquid phase catalytic oxidation of SO₂ can make the transformation greatly reduce the energy loss and process significantly shorter.In the method of industrial flue gas desulfurization,the most used limestone gypsum method,this method is cheap,but the byproduct gypsum is low and difficult to be used,and it can form secondary pollution.In the present absorption SO₂ process of sulfuric acid,contact oxidation is used more,but must be done in high temperature and catalyst,the energy and cost of SO₂ gas phase oxidation are high.Electrodialysis technique catalytic oxidation SO₂ in liquid phase at room temperature,at the same time,the selection of ion-exchange membrane is used to separate the products from the solution,simultaneous realization of SO₂ absorption oxidation and sulfuric acid concentration enrichment.Compared with pure liquid catalytic oxidation of SO₂,it has the following advantages:?1?The oxygen in the anode can effectively solve the problem of low oxygen content and low oxidation efficiency.?2?The catalytic oxidation,effective separation of products and enrichment of sulfuric acid can be achieved synchronously.?3?The electropositive electrode can oxidize SO₂ effectively,and the catalyst can further improve the effect.In addition,electrodialysis technology covers an area of small,less investment,easy maintenance,good implementation,unlike distillation processes consume a large amount of fuel,without high pressure pump is a semipermeable membrane of reverse osmosis pressure,without ion exchange as frequently regeneration,also do not discharge of acid and alkali waste liquid to pollute the environment,it is an advantage and promising technology.In this paper,talk about the process of producing sulfuric acid by elecrtodialysis catalytic oxidation purification in low concentration SO₂ in liquid phase,several studies have been carried out to explore this new process.Firstly,this paper introduces the significance and content of this research,summarizes the relevant research situation and progress,and explains the equipment materials and analysis methods used in the experiment.Then,from the study of ion exchange membrane,to the research of anodic materials with electrocatalytic properties,the test and analysis of two core materials of electrodialysis are described in detail.After that,deep into the electrodialysis process itself,A series of experimental procedures and the reasons behind the experiment were analyzed to explore the optimal reaction conditions,key influencing factors,and the process of reaction.Finally,on the basis of these works,the principle,law of ion change and catalytic oxidation mechanism of electrodialysis purification SO₂ for sulfuric acid was studied,a model of influence factors was established,the equation of reaction dynamics is derived,the total reaction efficiency equation is proposed,this provides a theoretical basis for further study.The following results and conclusions are obtained through experiment and research:?1?The catalytic oxidation of low concentration of SO₂ can achieve good purification and concentration effect.The maximum removal rate was 83.63%and the highest acid concentration was 41.6%;After adding 40%of O2,0.05mol/L Mn2-,the highest purification rate reached 99.08%,and the highest sulfuric acid concentration reached 43.64%.The optimal reaction conditions as follows:the current density of 40 mA/cm2,the electrolyte flow rate of 100mL/min,SO₂ gas velocity 50mL/min,SO₂ concentration of 3135mg/m3,reaction temperature 40? Sulfuric acid root anti-seepage and water molecular admixture are major obstacles to the improvement of acid concentration.Ion exchange membrane and anode material are the key influencing factors.?2?The reaction process and mechanism are analyzed,SO₂ absorption rate is:JSO₂=GSO₂/A?KG?P-P*??KL?C*-C?,The kinetics equation of electrochemical oxidation is:i=K0Exp?-?E/RT?[SO₂]?f,The total reaction efficiency equation is:J=0.57 + 0.087A + 0.0095B +0.28AB-0.022A2-0.25B2?A:electrochemical oxidation rate,B:liquid phase absorption?.The principle of SO₂ absorption oxidation is discussed;The concentration and equilibrium potential of SO32-and SO42-different pH value in solution are deduced.Two different viewpoints of Mn2+catalysis and Fe3+ distribution free radical theory are discussed.The function relation between the total efficiency and the single factors is calculated.The reaction kinetics and total reaction efficiency of SO₂ liquid phase absorption and electrochemical oxidation were studied.?3?The effect of the existing ion exchange membrane was tested,and two kinds of new ion-exchange membrane were developed,the QPPO-PVDF anion exchange membrane has good performance and low cost.The main parameters and practical effects of three kinds of typical commercial electrodialysis ion exchange membrane are studied.PTFE-Nafion compound ion exchange membrane and QPPO-PVDF anion exchange membrane were developed,the results of test and characterization indicate that:the ULTREX film in the finished product has good performance,it's concentration of sulfuric acid electrodialysis was 51.79%.In the new-developed membrane,PTFE-Nafion composite membrane can obtain the similar effect of the domestic product membrane;the concentration of sulfuric acid of QPPO-PVDF was 42.81%,with the performance of 15%of the existing ionic membrane in China,at the same time,the cost of PPO is 40 yuan/kg is 1/6 of Nafion resin,which has a great cost advantage.?4?Five kinds of anode materials with catalytic oxidation for electrodialysis were developed,the electrodeposition of Ti/MnO2 and Ti/PbO2/MnO2 electrode has the best catalytic oxidation activity and electrochemical properties.The five electrodes of thermal sintering Ti/MnO2,electrodeposition Ti/MnO2,electrodepositing Ti/PbO2,thermal sintering Ti/PbO2/MnO2,electrodeposition Ti/PbO2/MnO2 were respectively produced.The surface morphology,coating structure,element valence state,interface resistance,electrode impedance,oxygen potential,service life,practical effect and catalytic oxidation mechanism were tested and characterized.The results showed that:The electrode of Ti/MnO2 and Ti/PbO2/MnO2 by electrodeposition method were characterized by low resistance,high oxygen overpotential,high activity,corrosion resistance and long service life.Ti/MnO2 electrode surface was compact and more resistant to corrosion.The surface roughness of Ti/PbO2/MnO2 electrodes enhances catalytic oxidation and purification properties of SO₂.The MnO2 coating on each electrode surface showed good catalytic activity for the electrochemical oxidation of SO₂.The electrodialysis liquid phase catalytic oxidation technology can purify SO₂ and synchronize the sulfuric acid,according to the actual demand,the reaction equipment and the setting reaction conditions can be used to achieve good effect.