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气升式内环流反应器中反应结晶过程的实验研究
曹天荣
学位类型硕士
导师张伟鹏 ; 杨超  
2017-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词反应结晶 环流结晶器 氢氧化镍 机制
摘要

气升式内环流反应器混合性能好,传热传质效率高,被广泛应用在生物技术、废水处理等领域。相较搅拌结晶器,其内部剪切力小,剪切场均匀,且无机械传动部件,因此在结晶领域受到越来越多的关注。然而,对于环流反应器中的液液反应结晶过程,尚未有人对其进行过研究。本文以氢氧化镍沉淀反应为模型反应,对环流反应器中的反应结晶过程进行了研究。首先采用正交实验,在气升式内环流结晶器中制得了类球形的氢氧化镍颗粒,并在搅拌结晶器中进行对比实验。通过对两类结晶器中所得颗粒进行XRD、SEM、粒径大小、振实密度、显微镜图像等的分析,完善了氢氧化镍颗粒的生长机制,即:溶液中析出的微晶在流体中运动时,随机碰撞团聚在一起,形成氢氧化镍颗粒,这个过程决定了颗粒的粒径大小;新生成的颗粒中,微晶间空隙较大,在适当的反应条件下,组成颗粒的微晶可以继续生长,填补微晶间的空隙,使得颗粒密度上升。在此基础上,依次探索了初始氨水添加量VN、pH、加料方式、导流筒长度Hd和气体流量qg等操作条件对氢氧化镍颗粒内微晶生长的影响规律,主要成果如下:(1)氢氧化镍颗粒的微晶大小随VN、pH以及Hd的增加,均呈现先增大而后降低的规律,当VN=300mL,pH=11.4,Hd=250mm时,所制备氢氧化镍颗粒的微晶最大,产品质量最佳。(2)环流结晶器顶部气液分离区的微观混合最佳,当加料位置选在此处时,所制备氢氧化镍颗粒的微晶最大。(3)qg对环流结晶器内所制备氢氧化镍颗粒的微晶大小影响显著。随着qg的增加,微晶大小也逐渐变大。 

其他摘要

Airlift loop reactors (ALR) are widely used in biotechnology and wastewater treatment, because of their efficient mixing and good mass/heat transfer characteristics. Comparing with the stirred crystallizer, there are no moving mechanical parts in ALR, and the shear rate is moderate and relatively uniform throughout the reactor volume. In view of these excellent properties, ALR has been considered as a new prospective crystallizer. However, few reports have been found in the literature for the study on liquid-liquid reactive crystallization.The objective of this work is to study the reactive crystallization in an ALR using the precipitation of Ni(OH)2 as a model reaction. Firstly, the spherical Ni(OH)2 particles are prepared by orthogonal experiments in an ALR. Then, the growth of Ni(OH)2 particles in an ALR and a stirred tank was quantified by scanning electronic microscope (SEM), X-ray diffraction (XRD), laser particle analyzer, tap densitometer and optical microscope, and the growth process of Ni(OH)2 particles is analyzed. It is found that the growth of Ni(OH)2 particle tap density mainly depends on the size of crystallites: the bigger the size of crystallites, the bigger the tap density is. Based on these, the growth process of Ni(OH)2 particles in ALR is elaborated. Crystallites precipitated from solution aggregate to form large particles with much void. These constituting crystallites continue to grow up, that takes up the void inside particles and makes the tap density increase.Then, the influence of the volume of ammonium hydroxide (VN), pH, feeding methods, the height of draft tube (Hd) and gas flow (qg) on the growth of crystallites in an ALR is explored. The main conclusions are as follows:(1) The size of Ni(OH)2 crystallites increases firstly and then decreases with the rising of VN, pH and Hd. When VN=300mL, pH=11.4, Hd=250mm, the size of Ni(OH)2 crystallites get to the maxium value.(2) The micro-mixing in gas disengagement zone is most efficient. The crystallites grow up quicker when feeding position is located here.(3) Gas flow has an important effect on the growth of crystallites. The Ni(OH)2 crystallites grow up bigger with the increasing of gas flow. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/24211
专题研究所(批量导入)
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曹天荣. 气升式内环流反应器中反应结晶过程的实验研究[D]. 北京. 中国科学院研究生院,2017.
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