Study On The Influence Of Reactor Micro-mixing Performance On The Preparation And Properties Of Nano BaSO₄

Micromixing and chemical reactions both occur at the molecular scale and thus reactor micromixing has a great influence on chemical reactions.Especially for instantaneous and rapid reactions,micromixing will determine the quality of the product.As a typical rapid reaction,the particle size and particle size distribution（PSD）of precipitated products largely depend on the micromixing effect of reactors.BaSO₄ is an inorganic chemical material which has been applied in many fields.And its application value has much to do with its particle size.Therefore,in this work,stirring tank reactors were constructed by using electric agitator,beaker and peristaltic pump,and micro-impinging stream reactors were constructed by using stainless steel capillary tubes,flat-flow pumps and commercial T-tees,in order to study the effect of the micromixing performance of reactors on the preparation of nano-BaSO₄.The main research contents and results are as follows:（1）Iodide-iodate parallel competitive reaction system was used to study the micromixing of MISR and STR under different structure and operating conditions,and the micromixing time（t_m）was estimated.The experiment showed that in MISR,the segregation index X_S in different pipe diameters decreased with the increase of feed flow rate,and would not change further after the feed flow rate reached a certain value.The smaller the pipe diameter,the smaller the X_S;and X_S was minimum when R was equal to 1.In STR,the X_S in beakers of different volumes decreased with the increase of stirring speed,and would not change when the stirring speed reached a certain value.Factors of a smaller beaker,the stirring paddle positioned at the bottom of the beaker,the closer the feed to the center of the beaker and the faster the drop acceleration would result in smaller X_S.Overall,the micromixing performance of MISR is better than that of STR.（2）BaSO₄ was prepared by MISR and STR under different structure and operating conditions,respectively,and the induced nucleation timeτwas estimated.It was found that the morphology and particle size of BaSO₄ were affected by the micromixing condition of the reactors.The BaSO₄ prepared under the condition of smaller tm had narrower PSD and smaller average particle size.And the particle size and PSD of BaSO₄ were similar when the micromixing time was similar in the reactors with different structures.Sinceτ>t_m in MISR andτ<t_m in STR,the effect of microscopic mixing plays a significant role in the preparation of BaSO₄.It was found that the quality of BaSO₄ prepared in MISR was obviously better than that prepared in STR.（3）BaSO₄ prepared in 0.6mm/1.0mm MISR and 100 mL/250 mL STR were used to prepare inorganic composite ceramic diaphragm.The effect of micromixing on the pores of composite diaphragm was studied.Results showed that the smaller the t_m,the higher the porosity of the composite diaphragm.The porosity of composite diaphragm was similar when the reactor had different structure but similar t_m.In general,the membrane porosity obtained by MISR was higher than that obtained by STR.