Studies On Gas-Liquid Mass Transfer And Agitation Characteristics Of Horizontal Vessel

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.