撞击流反应：沉淀法制备氧化镧超细粉体及热分解动力学研究

发布时间：2018-05-04 16:28

本文选题：撞击流反应器 + 沉淀法　；参考：《武汉工程大学》2011年硕士论文

【摘要】：稀士元素具有独特的4f电子结构,被誉为新材料的宝库,在工业及新材料制备上得到广泛的应用。氧化镧超细粉体具有许多独特的性质,在许多领域具有广泛的应用,如在汽车废气的处理,气体催化剂载体,甲烷氧化耦合催化剂,光学玻璃,陶瓷,电极的制备中有着应用。但目前的制备技术还存在一些未解决的问题,如产品质量、纯度、粒径等问题,此外,开发氧化镧超细粉体制备技术,可以增加高丰度稀土元素镧的工业应用,解决镧的积压问题。因此非常有必要对制备氧化镧超细粉体的工艺进行细致研究。本论文采用撞击流反应-沉淀法制备氧化镧前驱体,然后将前驱体进行焙烧得到氧化镧超细粉体,考察碳酸氢铵、草酸铵、氨水等不同沉淀剂对氧化镧前驱体粒径的影响因素,并对草酸铵制备的氧化镧前驱体进行热分解动力学研究,拟合出动力学模型,并得到相关动力学参数。 (1)在浸没循环撞击流反应器中以碳酸氢铵为沉淀剂,以硝酸镧为镧源,加入少许表面活性剂作分散剂制备氧化镧前驱体,再经过焙烧得到氧化镧超细粉体。通过正交试验考察了浓度比n(NH4HCO3):nLa(NO3)3·6H2O、反应时问、反应温度、PEG用量、螺旋桨转速、焙烧时间及焙烧温度对氧化镧超细粉体粒径的影响,方差分析结果表明,在F值为0.1,0.05,0.01情况F,焙烧温度、反应时问、浓度比均具有显著性。结合正交及单因素试验,优化工艺参数为：浓度比nNH4HCO3:nLa(NO3)3·6H2O=6:1、反应时间为30 mmin、反应温度30℃、加入PEG用量为4%、螺旋桨转速1000r/min、焙烧温度800℃焙烧时间3 h。SEM表明所得产品粒径为100 nm。 (2)在撞击流反应器中以草酸铵为沉淀剂制备氧化镧超细粉体,并通过单因素实验对制备过程进行优化,得到优化工艺参数为：浓度比n(NH4)2C2O4:nLa(NO3)3·6H2O=6:1、反应时间为30 min、反应温度30℃、加入PEG用量为4%、螺旋桨转速1000r/min、焙烧温度800℃、焙烧时间3 h。SEM表明所得产品为球状颗粒,粒径约为200 nm。 (3)在撞击流反应器中以氨水为沉淀剂制备氧化镧超细粉体,通过对制备过程的单因素优化,得到优化工艺参数为：氨水加入量为25 mL、反应时间为15 min、反应温度45℃、加入PEG用量为10%、螺旋桨转速2000 r/min、焙烧温度800℃、焙烧时间2 h。通过SEM观察,所得产品为球状颗粒,粒径约为100 nm。 (4)对草酸铵沉淀法制备的氧化镧前驱体进行热分解动力学研究,结合热重(TG-DSC)及红外光谱(IR)分析,得到氧化镧前驱体为十水草酸镧,其热分解主要分为五个阶段,第一个阶段失去6个结晶水,第二、三阶段分别失去2个结晶水,第四阶段产生中间体La2O2CO3,最后为氧化镧的生成。通过使用Flynn-Wall-Ozawa (FWO)法和Kissinger-Aksahira-Sunose(KAS)法对十水草酸镧的热分解过程进行分析,结果表明,两种方法得到的活化能E均随转换率α的变化而变化,说明十水草酸镧的热分解不是简单的一步反应,而是多步反应。由于model-free的特点,多步反应无法求得动力学模型及相关参数,此时的活化能一般采用平均值法求得,动力学模型及相关参数需使用多元非线性拟合求取。通过FWO法得到草酸镧的热分解的五个阶段的平均活化能分别为：68.94,116.76,144.31,181.43,179.24kJ/mol。通过KAS法得到草酸镧的热分解的五个阶段的平均活化能分别为：65.60,114.28,141.49,179.01,171.79 kJ/mol。 (5)采用多元非线性拟合对十水草酸镧的热分解机理进行拟合,得到热分解机理符合g(α)=[1-(1+α)1/3]2模型,五个阶段的动力学参数为第一阶段：E=65.47 kJ/mol,lgA=-1.6 S-1；第二阶段：E=106.9 kJ/mol,lgA=-0.1 S-1；第三阶段：E=120.9 kJ/mol,lgA=-0.183 S-1；第四阶段：E=177.68 kJ/mol,lgA=2.27 S-1；第五阶段：E=156.4 kJ/mol,lgA=-2.54 S-1。拟合TG曲线能很好的匹配原始TG曲线。
[Abstract]:The dilute element has a unique 4f electronic structure known as the treasure house of new materials. It has been widely used in industry and new material preparation. The ultrafine lanthanum oxide powder has many unique properties and has been widely used in many fields, such as the treatment of automobile exhaust gas, gas catalyst carrier, methane oxidation coupling catalyst, optical glass, There are some applications in the preparation of ceramics and electrodes, but there are still some unsolved problems, such as product quality, purity, particle size and so on. In addition, the development of lanthanum oxide ultrafine powder preparation technology can increase the industrial application of lanthanum rich in rare earth elements and resolve the backlog of lanthanum. Therefore, it is very necessary to prepare lanthanum oxide. The process of ultrafine powder is studied in detail.
Lanthanum oxide precursor was prepared by impinging flow reaction precipitation method, and the precursor was roasted to ultrafine lanthanum oxide powder. The influence factors of ammonium bicarbonate, ammonium oxalate, ammonia and other precipitant on the particle size of lanthanum oxide precursor were investigated, and the thermal decomposition kinetics of lanthanum oxide precursor prepared by ammonium oxalate was studied. The kinetic model is obtained and the related kinetic parameters are obtained.
(1) the lanthanum oxide precursor was prepared with lanthanum nitrate as the lanthanum source in the immersion cycle impingement reactor with lanthanum nitrate as the lanthanum source. The lanthanum oxide precursor was prepared by a few surface active agents and then roasted. The concentration ratio n (NH4HCO3), nLa (NO3) 3. 6H2O, reaction temperature, PEG dosage, snails were investigated through orthogonal test. The effect of rotating speed, roasting time and calcination temperature on the particle size of lanthanum oxide superfine powder. The analysis of variance analysis showed that the F value of 0.1,0.05,0.01 F, roasting temperature, reaction time, concentration ratio were all significant. Combined orthogonal and single factor test, the optimization process parameters were as follows: concentration ratio nNH4HCO3:nLa (NO3) 3. 6H2O=6:1, reaction time was 3 0 mmin, reaction temperature 30 centigrade, adding PEG dosage 4%, propeller speed 1000r/min, calcination temperature 800 centigrade roasting time 3 h.SEM showed that the product diameter was 100 nm.
(2) the ultrafine lanthanum oxide powder was prepared in the impingement reactor with ammonium oxalate as precipitant and optimized by single factor experiment. The optimized process parameters were as follows: concentration ratio n (NH4) 2C2O4:nLa (NO3) 3. 6H2O=6:1, reaction time 30 min, reaction temperature 30, PEG dosage 4%, propeller speed 1000r/min, calcination temperature The product was spherical at 800 degrees C and calcined at 3 h.SEM. The particle size was about 200 nm..
(3) the ultrafine lanthanum oxide powder was prepared in the impinging flow reactor with ammonia as precipitant. Through the single factor optimization of the preparation process, the optimized process parameters were obtained: the ammonia water addition amount was 25 mL, the reaction time was 15 min, the reaction temperature was 45, the dosage of PEG was 10%, the rotation speed of the screw propeller was 2000 r/min, the roasting temperature was 800, and the calcination time 2 h. passed. SEM observation showed that the product was spherical particles with a particle size of about 100 nm..
(4) the thermal decomposition kinetics of lanthanum oxide precursor prepared by ammonium oxalate precipitation method was studied. The lanthanum oxide precursor was ten lanthanum oxalate with TG-DSC and IR analysis. The thermal decomposition of lanthanum oxalate precursor was divided into five stages, the first stage lost 6 crystalline water, and the second, third stage lost 2 crystalline water and fourth stages respectively. The intermediate La2O2CO3 was produced and finally the generation of lanthanum oxide. The thermal decomposition process of lanthanum ten water lanthanum was analyzed by using the Flynn-Wall-Ozawa (FWO) method and Kissinger-Aksahira-Sunose (KAS) method. The results showed that the activation energy E obtained by the two methods all changed with the conversion of conversion rate alpha, indicating that the thermal decomposition of lanthanum oxalate ten was not simple. The one step reaction is a multistep reaction. Because of the characteristics of model-free, the dynamic model and the related parameters can not be obtained by the multistep reaction. The activation energy is generally obtained by mean value method. The dynamic model and the related parameters need to be obtained by multivariate nonlinear fitting. The average activity of the five stages of the thermal decomposition of lanthanum oxalate is obtained by the FWO method. The average activation energy of the five stages of thermal decomposition of lanthanum oxalate by KAS method, respectively, is 65.60114.28141.49179.01171.79 kJ/mol., respectively, by the 68.94116.76144.31181.43179.24kJ/mol. method.
(5) using multivariate nonlinear fitting to fit the thermal decomposition mechanism of lanthanum oxalate ten, the thermal decomposition mechanism conforms to the G (alpha) =[1- (1+ alpha) 1/3]2 model. The kinetic parameters of the five stages are the first stage: E=65.47 kJ/mol, lgA=-1.6 S-1, and the second stage: E=106.9 kJ/ mol, lgA=-0.1 lgA=-0.1; third stage: Third 1; fourth stage: E=177.68 kJ/mol, lgA=2.27 S-1; fifth stage: E=156.4 kJ/mol, lgA=-2.54 S-1. fitting TG curve can very well match the original TG curve.

【学位授予单位】：武汉工程大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TB383.3

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