【作者】 叶新权；

【导师】 包永忠；

【作者基本信息】 浙江大学 ， 化学工艺， 2003， 硕士

【摘要】 针对四氟乙烯（TFE）分散聚合气-液传质过程对聚合过程影响明显、乳胶粒子易凝聚等特点，采用高效卧式釜代替传统立式釜成为一种发展趋势，而国内对卧式气液搅拌釜的研究相对缺乏。本文对不同搅拌形式卧式釜的气-液传质、功率特性和气泡分布进行了研究，重点讨论了搅拌桨结构的影响，为TFE分散聚合用卧式釜的工业放大提供理论基础。 采用透射和扫描电镜观察了国外和巨化公司PTFE分散树脂的初级粒子和次级粒子形态，发现巨化公司PTFE分散树脂初级粒子以棒状结构为主、粒子尺寸小、粒径分布宽，次级粒子中初级粒子形态不清晰、存在粘并现象，与国外树脂存在较大差别。进行聚合釜结构和搅拌条件的优化是改进PTFE分散树脂颗粒特性的主要途径。 采用纯水—纯氧体系，在常温常压条件下，分别采用直叶桨和变型桨，进行卧式釜传质特性和搅拌功率研究，发现随液含量（液深）增加，容积传质系数k_Lα增大并出现峰值。回归得到k_Lα与弗洛德数（F_r）、桨径（D_i）、桨宽（W_i）、叶片数（n_b）、层间距（l）等的关联式： 直叶桨：k_Lα=6.42Fr^1.32（D_i／D_t）^2.90（W_i／D_t）^1.78（l／L）^-0.3n_b^0.8+2.1Fr 变型桨：k_Lα=4.11Fr^1.12（D_i／D_t）^1.91（B_i／D_t）^1.3n_b 研究了搅拌功率（P）与桨型、转速、液含量、桨径、桨宽、叶片数、叶片宽之间的关系，并得到关联式： 直叶桨：P=9.43×10^-5N^3.72（D_i／D_t）^5.0（W_i／D_t）^1.21（n_b）^0.92 变型桨：P=7.32×10^-5N^1.94（D_i／D_t）^3.4（B_i／D_t）^1.62n_b 采用拍照方法，定性讨论了直叶桨、变形桨和透平桨卧式釜的气泡分布，发现变型桨气泡分布均匀，没有明显死角。 通过以上研究，并结合TFE分散聚合的特点，认为采用变型桨是TFE分散聚合卧式釜较佳的搅拌形式。更多还原

【Abstract】 Concerning with the significant influence of gas-liquid mass transfer on the emulsion polymerization of tetrafluoroethylene (TFE) and the easy coagulation of latex particles in the emulsion polymerization process, it is tended to use the horizontal agitated vessel with high mass transfer efficiency to substitute for the vertical self-suctioning agitated vessel. But studies on the gas-liquid mass transfer of horizontal agitated vessel were lack in our country. The mass transfer, agitation power and bubble distribution of horizontal vessel equipped with different agitators were investigated in the present thesis, with emphasis on the influences of agitator structure. The present work will give theoretical instruction to the scaling up of horizontal vessel in industry.The morphology of primary and secondary particles of Dupont and Juhua Company’s polytetrafluoroethylene (PTFE) was observed by using TEM and SEM. It found that there were many rod-like primary particles in Juhua PTFE, and the mean size of primary particles was relatively smaller and particles size distribution was broader compared with Dupont PTFE. The shape of primary particles in secondary particles of Juhua PTFE was unclear and the "coalescence" of primary particles was obvious, which was quite different from that of Dupont PTFE. The optimization of the reactor structure and agitation conditions was the main method to improve the particle properties of PTFE resin.The mass transfer and agitation power of the horizontal vessel were studied under the normal temperature and pressure, applying pure water-O2 system and using vertical blade turbine impeller and mended turbine impeller. It found that volumetricmass transfer coefficients (kLa) increased and maximum values appeared as theliquid hold-up (liquid depth) increased. The relations between kLa and Fred number (Fr), impellers diameter (Dl), width of impeller (Wi), blade number (nb), distancebetween impellers of two layers (l) were multiply regressed and showed as follows: Vertical-blade turbine impeller:Mend turbine impeller: The influences of agitator type, agitation speed, liquid hold-up, impellers diameter, width of impeller, blade number and width of blade on the agitation power were studied and the following relationship were obtained as follows:Vertical-blade turbine impeller: P = 9.43 10-5 N3.72 (Di / Dl )5.0 (Wt / D, )1.21 (nb )0.92Mend turbine impeller: P = 7.32 x 1(T5 N1’94 (D, I D, )3’4 (5, / D, )’’62 nbDue to the character of high mass transfer, it was very difficult to make quantitative analysis of bubble distribution. Influences of liquid hold-up and agitated speed on bubble distribution were investigated in qualitative analysis. Result shows that the mended turbine had no obvious dead section.It was concluded that the mended turbine impeller was the optimal agitator based on the above studies and the features of TFE dispersion polymerization.更多还原