Knowledge Management System Of Institute of process engineering,CAS
废脱硝催化剂是能源行业产生的典型难处理多金属危险废物，国内年排放量达到50万立方米，其回收处置利用已成为当前研究的热点和重点。本文针对废脱硝催化剂金属资源高效回收的迫切需求，提出草酸净化提钒及稀碱调控回收钛钨载体的工艺路线，实现了废催化剂中杂质脱除、钒金属回收和钛钨载体的可控制备。重点研究了草酸体系下钒铁浸出过程机理，考察了饱和草酸（H2C2O4）浸出液分步氧化水解沉淀回收钒钨工艺过程，分析了稀碱调控过程钛钨载体的孔结构变化规律等，形成废催化剂回收钒钨钛制备偏钒酸铵及钛钨载体的全流程工艺，并对总体工艺过程物质流和经济性进行了系统分析。主要研究内容和结论如下：（1） 开展了预处理高效脱尘和酸浸深度净化除杂过程研究，明晰了还原酸浸钒铁杂质元素的反应机理。研究表明，筛分和45 ℃超声水洗过程有效降低了废催化剂中石英和莫来石相的积灰含量；脱尘废催化剂粉体采用H2C2O4深度净化浸出V和Fe杂质元素，在90 ℃和1.0 mol/L浓度下，浸出率分别为84.22%和96.66%。采用UV-vis全谱扫描和显色反应研究发现，H2C2O4浸出液中V和Fe元素以VO2+和Fe2+价态存在，浸出过程中V3+、V5+及Fe3+经溶解、配位和氧化还原反应，形成稳定配合物VO(C2O4)22-和Fe(C2O4)22-，从而促进了废催化剂中V和Fe元素的浸出。H2C2O4浸出液循环浸出3次后通过减压蒸发-结晶过程分离H2C2O4，回收率为87.67%，回收晶体杂质含量低于500 mg/kg。回用H2C2O4晶体浸出V和Fe元素浸出率为83.52%和95.15%，循环浸出特性良好。（2） 针对饱和H2C2O4浸出液中杂质元素种类多、钒钨元素浓度低的问题，提出了H2O2分步氧化水解沉淀回收V和W的工艺路线。通过一级氧化水解过程的工艺条件优化，在一级氧化摩尔比为0.85、H2C2O4分解度为70%、90 ℃下W元素沉淀率为72.37%，添加Cinc助剂后增加至97.10%，W和V元素分离因数为2957，精制得到WO3含量98.41%的钨酸产品；一级氧化液在摩尔比为2.2和100 ℃的二级氧化水解工艺条件下，V元素沉淀率达到99.89%，精制得到V2O5含量高达99.07%的偏钒酸铵产品。分步氧化水解过程表明，饱和H2C2O4浸出液中TiO(C2O4)22-和WO2(C2O4)22-离子在一级氧化过程中随着H2C2O4氧化分解生成TiO2+和WO22+离子，水解为锐钛型TiO2和H2WO4，在Cinc助剂下促进H2WO4转化为H54N10O48W12；一级氧化液中VO(C2O4)22-和Fe(C2O4)22-离子在二级氧化过程被氧化为VO2+和Fe3+离子，水解为V2O5∙0.5H2O和Fe0.12V2O5。（3） 针对废催化剂比表面积低、夹杂铝硅成型助剂等问题，开展了稀碱浸出铝硅、同步调控孔结构制备多孔钛钨载体的研究。通过热力学计算和碱体系浸出实验，筛选NaOH作为浸出体系，建立了反应条件和载体孔结构调控关系，在160 ℃、2.5 mol/L碱浓度下Al和Si元素浸出率分别为59.51%和71.38%，洗涤后多孔钛钨载体的比表面积、孔容和平均孔径为92.57 m2/g、0.41 cm3/g和17.78 nm，相应指标及K、Na和Fe等杂质元素含量均达到商用要求。进一步开展了钛钨载体制备催化剂及其催化性能评价研究，催化剂在300~500 ℃条件下脱硝活性达到90%以上，同时在350 ℃具有良好的抗硫抗水性。（4） 提出废脱硝催化剂回收钒钨钛的整体工艺路线，开展了百公斤级的全流程工业扩试实验。废催化剂通过预处理脱尘分离18wt.%的飞灰杂质，得到粒径小于75 μm的粉体；酸浸深度净化过程中3次循环浸出V和Fe元素的浸出率均在75%以上，循环浸出液经减压蒸发-结晶过程回收得到81%的H2C2O4。分步分离钨钒过程分离因数达到1501，分离后溶液中W和V浓度仅为0.007和0.004 g/L，环境风险得到有效抑制；稀碱浸出制备得到锐钛型钛钨载体，TiO2和WO3总含量达到95.24%，比表面积为81.11 m2/g，杂质含量符合要求。基于上述结果，对废脱硝催化剂回收利用全流程工艺进行了物质流和经济性分析，吨废催化剂可制备得到0.71 t钛钨载体、V2O5含量4.82 kg的偏钒酸盐和WO3含量3.28 kg的钨酸，整体工艺实现了危险废物的资源化利用，同时具有良好的经济效益。;As a typical refractory muti-metal hazardous waste from energy industry, the annual emission of spent denitration catalyst reaches to 500,000 m3 in China. Its recycling, disposal and utilization processes become increasingly attractive in past years. In order to meet the urgent demand for the recovery of metal resources from spent denitration catalyst, this thesis proposes a new recycling process to achieve the removal of impurities in the spent catalyst, recovering of vanadium using oxalic acid, and regulation of TiW carrier by dilute alkali. This thesis focuses on the mechanism of leaching vanadium and iron by oxalic acid, the process of stepwise oxidation hydrolysis precipitation to recovery of vanadium and tungsten from saturated oxalic acid leachate, the regulation process for the pore structure of TiW carrier by dilute alkali. The full flowsheet for recovery vanadium, tungsten, and titanium from spent catalyst, preparation of ammonium metavanadate and TiW carrier is proposed. The material flow and economy of flowsheet are studied. The main research contents and conclusions are as follows:(1) Pretreatment and deep purification process by acid leaching for removing of impurities are studied, and the reaction mechanisms of leaching vanadium and iron using oxalic acid are clarified. After sieving and ultrasonic washing at 45 ℃, the amount of fly ash impurity with quartz and mullite phases in spent catalyst is significantly reduced. The spent catalyst powder is leached by oxalic acid to remove the impurities of V and Fe elements. The leaching efficiencies of V and Fe are respectively 84.22% and 96.66% under the conditions of 90 ℃ and 1.0 mol/L H2C2O4. The UV-vis full spectrum scanning and color reaction results show that valences for V and Fe elements in the leachate are VO2+ and Fe2+, respectively. These results suggest that V3+, V5+ and Fe3+ in the spent catalyst be transformed into stable VO(C2O4)22- and Fe(C2O4)22- complex via dissolution, coordination and redox reactions, thus promoting the leaching of V and Fe. The leachate is circulated for three times and separated by the process of vacuum evaporation-crystallization to recycle H2C2O4. The recovery rate of H2C2O4 reaches at 88%. The impurity content of H2C2O4 is less than 500 mg/kg. The circulating efficiencies of V and Fe elements are kept at 83.52% and 95.15% respectively, indicating that H2C2O4 shows a good leaching cycle characteristic.(2) In order to solve the problems of diversified of impurity elements and low concentrations of vanadium and tungsten elements in saturated oxalic acid leachate, a stepwise oxidation hydrolysis precipitation process by H2O2 is proposed to recovery of vanadium and tungsten from saturated oxalic acid leachate. Under the optimal conditions including a molar ratio of 0.85 and 90 ℃, the precipitation efficiency of W element is 72.37%. After the addition of Cinc, the precipitation efficiency of W increased to 97.10%. The decomposition rate of H2C2O4 in this process is 69.88% and separation factor of W/V element reaches 2957. After refining process, the tungstic acid product including 98.41% WO3 is obtained. Through the condition optimization of second oxidation hydrolysis precipitation process, the precipitation efficiency of V element reaches to 99.89% with a molar ratio of 2 at 100 ℃. The ammonium metavanadate product including 99.07% V2O5 is obtained after refining process. The mechanism of the stepwise oxidation hydrolysis precipitation process is studied. It shows that the TiO(C2O4)22- and WO2(C2O4)22- ions in saturated oxalic acid leachate are oxidatively hydrolyzed to form anatase TiO2 and H2WO4 with the decomposition of H2C2O4, then H2WO4 is converted to H54N10O48W12 with Cinc additive, which promoting precipitation of W. In second oxidation hydrolysis precipitation process, VO(C2O4)22- and Fe(C2O4)22- ions undergo oxidation reaction to generate VO2+ and Fe3+ ions, and eventually hydrolyze and precipitate in V2O5∙0.5H2O and Fe0.12V2O5.(3) Aiming at the problems of low specific surface area in spent catalyst and containing aluminum silicon elements from promoter, the leaching of Al, Si and the regulation process for the pore structure of TiW carrier by dilute alkali are studied. Through thermodynamic calculation and alkali leaching experiments, NaOH solution is selected as the leaching system. The relationship between reaction conditions and pore structure in the carrier is investigated. The leaching efficiencies of Al and Si elements under the condition of 160 ℃ and 2.5 mol/L NaOH are 59.51% and 71.38%, respectively. The specific surface area, pore volume and average pore diameter of TiW carrier were 92.57 m2/g, 0.41 cm3/g and 17.78 nm. The content of K, Na and Fe in the recovered TiW carrier after acid washing arrives the limitation of commercial carrier. Then resynthesized catalyst is prepared using recovered TiW carrier and its catalytic performance is studied. The denitration activity of the catalyst is higher than 90% at 300-500 ℃. The resynthesized catalyst shows a good resistance of sulfur and water at 350 ℃.(4) The full flowsheet for recovery vanadium, tungsten, and titanium from spent catalyst is put forward. The industrial scale experiments of full flowsheet are carried out. 18wt.% of fly ash impurities are removed by pretreatment process. The powder catalyst with a particle size of less than 75 μm is obtained. The leaching efficiencies of V and Fe elements in three cycles of acid leaching process are all above 75%. About 81% oxalic acid crystal is recovered from cycled leachate through the vacuum evaporation-crystallization process. The separation factor of vanadium and tungsten in the stepwise separation process reaches 1501. After recovering of vanadium and tungsten, the concentrations of W and V are respectively 0.007 and 0.004 g/L, indicating that the environmental risk from leachate is effectively suppressed. The anatase TiW carrier is obtained by the dilute alkali leaching process. The total content of TiO2 and WO3 in carrier is up to 95.24%, meanwhile concentration of impurity contents the limitation requirement. In addition, the specific surface area of carrier is 81.11 m2/g. Based on material flow analysis of recovery process for spent denitration catalyst, it can be concluded that there are 0.71 t TiW carrier, 4.82 kg V2O5 and 3.28 kg WO3 from per ton spent catalyst. The process shows a good economic benefit and realizes the utilization of hazardous waste.
|武文粉. 废脱硝催化剂回收钒钨及载体循环利用过程基础研究[D]. 中国科学院大学,2020.|
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