【作者】 向阳；

【导师】 陈建峰；

【作者基本信息】 北京化工大学 ， 化学工程， 2009， 博士

【摘要】 典型的反应沉淀过程是两种液体混合后,反应产生过饱和度,然后发生成核、生长和团聚。如果沉淀动力学的时间尺度远长于混合时间,两股液体的混合过程快于反应,此时最后产物特性主要依靠物化参数,而不是混合条件。实际上,沉淀过程通常非常快,导致了在反应器内达到均匀过饱和度之前,成核、生长和团聚就已经开始了,这种不均匀过饱和度场产生不同的推动力,反过来影响了产物最后的特性,即产物粒子的形貌及粒度分布受到流体力学和混合过程控制。因此,为了改善产品特性以获得最大的经济效率,需要结合流体力学和混合机制来研究化学反应器的反应沉淀过程。因此本文研究了超重力旋转填充床反应器和微通道反应器内的混合-反应沉淀过程。基于前人对旋转填充床中可视化研究及微观混合的研究结果,本论文首先建立了能描述旋转填充床反应器(RPB)内液相反应沉淀过程(包括流体流动、混合、反应、成核及晶体生长)的数学模型。同时就BaCl2与Na2SO4反应生成BaSO4为沉淀体系,实验考察了旋转填充床的反应沉淀过程及各操作条件对产物粒子粒度分布的影响规律,这些工作为旋转填充床的工业应用及结构优化设计提供了理论基础。本文还对多种混合形式的微通道反应器内混合效率进行了研究,建立了CFD模型,考察了在微尺度下不同混合形式及操作参数对混合效率的影响；同时还实验考察了包括混合通道尺度、流量等操作条件对产物颗粒粒度分布的影响规律。最后,基于液相反应沉淀过程的实验和理论研究结果,开展了用超重力法(RPB为核心反应设备)制备纳米药物吉非罗齐的应用研究工作。本论文主要工作如下：1、在前人对RPB内流体流动的可视化观察结果和混合特征研究结果的基础上进行合理假设,结合物料衡算方程、粒度衡算方程及结晶动力学方程,采用聚并-分散模型(Coalescence-Redispersion Model)建立了旋转床内描述流体流动、混合、反应、成核及晶体生长的数学模型,提出了表征填料内液相微观混合强度的模型参数—聚并概率,并根据填料结构与液体微元间混合机制计算给出不同径向填料位置的聚并概率大小。2、设计了一台可实现沿填料径向取样的旋转填充床(RPB)进行BaSO4沉淀的实验研究,首次从实验上证实了RPB填料端效应区对液相反应沉淀过程的重要性。RPB的反应沉淀实验结果表明：提高转速可改善微观混合,使BaSO4产物颗粒粒径减小、粒度分布变窄；反应物流量的增加也会使粒度下降、分布变好,但当流量达到一定数值后这种下降趋势明显减缓；反应物初始浓度增加,粒度变小、分布变窄；在恒定的BaSO4产物浓度下,随反应物体积流量的增大,粒径稍有增大、分布变差。3、基于上面建立的旋转填充床中液相反应沉淀的数学模型,分析计算了聚并概率p、过饱和度、体积比及成核动力学对产物颗粒粒度分布的影响规律。模拟结果表明：成核级数越大,粒径及方差越大,所需填料层厚度增大；随晶核尺度增加,粒径及方差增大；提高反应物初始浓度或体积比,粒径及方差减小。模型的计算结果和实验结果基本吻合,能够正确反映操作参数(流量、转速等)对产物颗粒粒径的影响规律。这些研究结果,为进一步的研究以及旋转填充床的优化设计提供了理论基础。4、基于计算流体力学知识,从湍动理论出发,建立CFD模型并对多个混合形式的微通道反应器内流动情况及混合效率进行了数值计算。模拟结果表明：流动处于层流,物质间混合只能依靠分子扩散进行,通道内流体几乎处于完全离集的状态,流速加快后,辅以湍动扩散,混合效率迅速增大；物料流量增大,混合效率增加；进口物料体积流量比增大,混合效率加快；交叉点两流体混合角度越大,混合强度越高。基于对微通道反应器混合效率的研究结果,在Y型和线型微通道反应器中考察了各操作参数对粒度大小及分布的影响规律。实验结果表明：随混合通道尺度下降,产物颗粒平均粒径及无因次方差减小；提高反应物流量,粒径及方差下降,但是当流量提高到一定数值后这种下降趋势减缓；反应物浓度增大,过饱和度增加,粒径及方差下降,反应物体积流量比增大,粒径及方差下降。上述研究结果对于微通道反应器用于纳米颗粒的制备等相关领域具有一定的指导价值。5、基于对旋转填充床反应沉淀过程的理论及实验研究结果,利用超重力法制备出了具有窄粒度分布、平均粒径约80 nm纳微吉非罗齐颗粒,同时对纳微粉化药物进行了表征,开发出了超重力法制备纳米吉非罗齐的新工艺。更多还原

【Abstract】 Precipitation is a very important unit operation which is widely used in chemical industry in the production of fine solids. Typically, precipitation occurs after the mixing of two liquid streams to create supersaturation, followed by nucleation, particle growth and (very often) agglomeration. If the time scale of precipitation kinetics is much longer than that of mixing, the mixing of two liquid streams is faster than the reaction. In this case, precipitation process is often controlled by physicochemical characteristics, and not the mixing conditions. In fact, precipitation process is so fast that nucleation, growth and agglomeration have started prior to the achievement of a homogeneous supersaturation level in a reactor. The heterogeneous supersaturation field generates different driving forces, which in turn drastically affects the final product properties. Therefore, the modeling of precipitation process in chemical reactors is required by combining fluid and mixing mechanics to improve the product quality. This dissertation had a detailed research on the mixing-precipitation process of nanoparticles in a rotating packed bed and microchannel reactors. Based on the previous research results of visualization and micromixing in a rotating packed bed (RPB), a mixing-precipitation model was firstly presented to describe the flow, mixing, nucleation and growth process in RPB. The validity of this model was verified experimentally with BaSO4 precipitated from the reaction of Bal2 and Na2SO4 in RPB. Furthermore, the mixing efficiencies of various microchannel reactors were investigated by CFD technology, and exploring the effects of operational conditions on particle size distribution was experimentally carried out. Finally, on the basis of the above-mentioned researches, gemfibrozil (GEM) nanodrug was prepared in RPB. The main contents and findings are summarized as follows:1. On the basis of the previous research results of liquid flow and mixing mechanism in RPB, a coalescence-redispersion model is built to describe flow, mixing, reaction, nucleation and growth by reasonable hypothesis and combination with population balance, mass balance and crystallization kinetics for precipitation process in RPB. The mixing intensity of liquid-liquid on cages in RPB can be characterized by the coalescence probability (p), which is defined as the percentage of droplets participating in coalescence-redispersion process. Moreover, coalescence probability at different radial positions of packing was calculated by wire packing structure and mixing mechanism.2. A RPB, which is allowed sampling at radial position, is specially designed to investigate the precipitation of BaSO4 nanoparticles The important effect of inlet region of the RPB on the whole precipitation process was experimentally confirmed for the first time, which has a significant impact on the design of industrial RPB for the precipitation of sparing soluble material, especially the radial thickness (i.e.,40-50 mm in our experimental conditions). The effects of operating conditions on particle size distribution were also investigated. The results showed that the BaSO4 mean particle size and corresponding size distribution decreased with the increase of rotational speed and liquid flow rate, while increased with the increase of volumetric ratio and the decrease of reactant concentrations.3. Based on the above model, the effects of coalescence probability, supersaturation, volumetric ratio and crystallization kinetics on particle number density, supersaturation and mean particle size were explored. The predicted results indicated that mean particle size and variance decreased with the increase of coalescence probability, nucleation order, supersaturation and volumetric ratio, while increases with the increase of the nucleus size. This model has a good agreement between the experimental and predicted results, providing a theoretical base for further investigation and.optimization design of RPB.4. The mixing efficiencies (Is) of various microchannels were investigated by CFD model at different operational conditions. The calculated results showed that the mixing efficiency increased with the increase of liquid flow rate. The bigger two inlet cross angle of micrchannels is, the higher the mixing efficiency. However, the mixing efficiency only slightly increases with the increase of liquid flow rate and volumetric ratio at the higher volumetric flow rate. In addition, the precipitation of BaSO4 nanoparticles was carried out in Y-type and line-type microchannel reactors, respectively. The effects of various operational conditions on particle size distribution of precipitates were studied as well. The results showed that the mean particle size and dimensionless variance decreased with the increase of liquid flow rate, initial concentration and volumetric ratio of reactants, as well as the decrease of the microchannel size.5. On the basis of the above theoretical and experimental results in RPB, the RPB structure was further optimized for the preparation of gemfibrozil (GEM) nanodrug. The results indicated that GEM nanosized particles with a near-spherical shape, a mean particle size of about 80 nm and a narrow PSD could be successfully prepared in RPB. The as-prepared GEM powder was also characterized by XRD and BET.更多还原