反胶团法制备二氧化锆超细粉末的工程放大研究
文献类型：学位论文
| 作者 | 王浩然 |
| 学位类别 | 博士 |
| 答辩日期 | 1999-12 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 刘会洲 ; 陈家镛 |
| 关键词 | 超细粉末 二氧化锆 反胶团 喷雾－搅拌混合器 反问题法 Monte-Carlo 模拟 群体平衡公式 |
| 其他题名 | Scale-up studies on Preparation of Ultrafine Zirconium Oxide with Reverse Micelle Method |
| 学位专业 | 化学工艺 |
| 中文摘要 | 纳米材料由于其特殊的物理化学性质而成为21世纪十分重要的一种材料，近二十年来这种材料的合成方法引起了科学工作者浓厚的兴趣，并发展了许多种合成方法。尽管在实验室中纳米材料的制备方法有很大进展，但工业应用仍存在放大效果问题。反胶团法制备二氧化锆超细粉末可以控制颗粒尺寸，得到大小均匀的产品。对该方法传质过程的研究发现：二氧化锆前驱物的形貌决定了产品的性质。由于沉淀反应相对传质过程是一个极快速的过程，两相混合的效果决定了前驱物的形貌。良好的传质要求两相微观混合，然而由于两相不相混溶，无法实现微观混合，因此需要采用新型的混合方式促进两相的传质，得到较好的产品。文中设计了喷雾－搅拌混合器，先将水分散成细小的液滴，再与煤油混合同时采用搅拌控制液滴之间的作用，减少液滴间的凝并，尽量避免液滴的长大。研究了不同搅拌速度、不同搅拌桨类型、不同相比对液滴分布的影响。由于液滴的大小与两相的接触面积直接相关，而接触面积决定了传质的效果，本文着重讨论了液滴尺寸的变化，进而分析两相的传质效果。实验发现搅拌速度的提高在一定范围内减弱了液滴的长大速率，但是搅拌速度的进一步提高加剧了液滴的凝并，促进了液滴的长大。径向流搅拌桨由于会产生较强的最大剪切力，可以得到尺寸很小的液滴，但是液滴的分布范围很大；轴向流搅拌桨使液滴经历了更长的流程，使混合器内液滴的分布很均匀。分散相体积的增加促进了液滴的凝并，导致液滴体积增加。混合器内挡板的数目增加改善了混合效果，但是过多的挡板数目会减少总体流动并把混合局限在局部范围，导致不良的混合性能，而且挡板数目的增加提高了两相混合的能量消耗。文中采用群体平衡模型研究了液滴分布的变化。由于液－液两相混合中液滴具有自我维持的特性，本文利用实验得到的初始40秒的液滴分布利用反问题的方法求取了液滴的凝并频率，然后采用Monte-Carlo模拟的方法模拟出液滴分布随时间的变化。将模型得到的结果与实验结果比较，两者十分吻合，因此该方法可以对喷雾－搅拌混合器内液滴的分布进行模拟。不混溶的液液两相间混合时传质的广泛应用要求对传质过程的理论研究。针对两相快速反应，本文研究了喷雾－搅拌混合器中苯甲酸从水相向煤油的传质，采用电导法测量两相的传质效率。研究了搅拌强度对平均传质效率以及传质均匀性的影响，认为搅拌强度的提高促进了两相的传质，但是当搅拌强度达到一定程度后，继续增加搅拌强度对传质影响不大，而且适当的搅拌强度才会实现均匀传质。文中采用群体平衡模型对两相的传质过程进行了模拟，结果与实验结果吻合很好。然后，使用喷雾－搅拌混合器利用反胶团法得到粒度分布均匀的二氧化锆超细粉末。利用上文的模型预测了不同转速和不同相比下得到的产品。然后用实验验证了模型的准确，认为该模型可以进行反胶团法制备超细粉的放大研究。最后对使用该混合器得到的二氧化锆粉末进行表征，分析了放大后产品的性能不如小试的原因，为以后的研究做好准备。 |
| 英文摘要 | Nanosized particulate materials have been considered as one of the most important materials in the 21~(st) century due to their quite attractive properties. Synthesizing of this kind of material has attracted much attention of research worker during the past twenty years and various techniques have been developed accordingly. Nanosized ZrO_2 can be obtained by reversed micellar method. However, very few work has been focused on the scale-up of different processing techniques. It is rather difficult for rapid disperse a small volume of aqueous phase into bulk organic phase, and is often encountered in practice. A new reactor---spray and rotating mixer is set up, so aqueous phase can be dispersed into tiny drops first, then two phase are mixed. By this method, the difficulty referred before can be diminished. The variation of water drops in kerosene was studied with water as the dispersed phase and kerosene as the continuous phase. The effects of drop size distribution under different impeller speeds, type of impeller and different phase ratios were also studied. Because drop size distribution is closely related to the mass transfer area, the rate of mass transfer in the mixer and the variation of drop size distribution were also studied. By increasing the impeller speed, the rate of enlargement of drop size was slow down. With the increase of impeller speed,it enhances the coalescence of drops, resulting to the increase of drop volume. Rushton blades used for agitation can lead to stronger cutting force, to obtain smaller liquid drops with a wide drop size distribution. Propeller blades used for agitation cause drops to experience a long flow path, so the drops in mixer could be more uniformly dispersed. The higher phase ratio of organic phase to aqueous phase enhances the coalescence of drops, the volume of drops is increased. The results showed that, the variation of drop distribution for samples taken at different positions in the mixer becomes large with decreasing the number of baffles. Four baffles are enough to reach the uniform drop size in short time. A population balance equation(PBE) was used to simulate the variation of drop size distributions. As breakage frequency is known, the coalescence frequency is the key function to be studied. Because there distributions are self-similar, inverse problem method was used to extract coalescence frequency from experimental data. After breakage and coalescence frequencies have been obtained, Monte-Carlo simulation was used to solve PBE. When the simulation result was compared with experimental results, the effectiveness of this model is manifested. Mass transfer process is also considered in the experimental work when benzoic acid is dissolved in water, and conductivity method was used. The effect of impeller speed on mass transfer efficiency is studied. It showed that, high impeller speed enhances the mass transfer to some extents, and for rotational speed is higher than 420 rpm, impeller speed has little effect on mass transfer. And it is also sound that appropriate impeller speed can lead to uniform mass transfer. Compared with experimental results, population balance model can lead to satisfactory fit. To carry out research on the scale-up of this method, theoretical simulation must be done to study the factors which will influence the preparation of nanosized ZrO_2 powder. In this paper, mass transfer is added to the model of the variation of drop distribution with time in the mixer, and the effect of operating factors on the simulation result is obtained. Spraying and rotating mixer is used to attain the ultrafine powder, and size distribution of it is measured by Coulter Particle counter. The mass transfer efficincy was increased with the increasing of phase ratio, but higher phase ratio leads to more different mass transfer result at different position in the mixer. Therefore, uniform particle distribution needs low phase ratio. Finally, zirconium oxide prepared by this method is characterized. The reason that result obtained by scale-up is not as good as the lab test is analyzed, so it pointed out that research work has to be required to be carried out for industrial application of the work. |
| 语种 | 中文 |
| 公开日期 | 2013-09-27 |
| 页码 | 108 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/2005]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 王浩然. 反胶团法制备二氧化锆超细粉末的工程放大研究[D]. 中国科学院研究生院. 1999. |
入库方式： OAI收割
来源：过程工程研究所
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