Mixing Characteristics Of DLM/S Mixer And Its Application In Rapid Reaction

For the rapid reaction such as the competitive reaction,polymerization reaction and precipitation reaction,the composition of product is controlled by the reaction kinetics and micro-mixing effect.Therefore,these reaction systems have higher micro-mixing requirements for mixing equipment.Due to the limited application of existing mixing equipment in the rapid reactions,it is necessary to carry out research on new and efficient mixing equipment.DLM/S dynamic mixer is a novel inline stator-rotor mixer.The high-speed rotation of the rotor will promote the micro-mixing effect between fluids by strong turbulence,shearing,stretching and crushing.Therefore,this mixer shows great potential for applications in production operations with high micro-mixing requirements.In this thesis,systematic research on the flow characteristics and micro-mixing characteristics of the fluid in the DLM/S dynamic mixer was carried out using fluorescence online detection,computational fluid dynamics(CFD)simulation methods and micro-mixing experimental methods.Further explored the applications of this mixer in the one-step synthesis of polyurea copolymer and the liquid-phase precipitation of Barium Sulfate(BaSO4)particles.Achieved results are as follows:(1)A solution system with different viscosities was established by introducing hydroxyethyl cellulose(HEC),and then the flow characteristics of viscous fluid in the DLM/S dynamic mixer were studied using the residence time distribution(RTD)measurements and CFD simulations.The results show that the flow characteristics in DLM/S dynamic is closer to plug while the fluid will be backmixed due to the entrainment of the rotors near the two ends.Under the same flow rate,increasing the rotation speed has no appreciable impact on the degree of fluid backmixing which will decrease with the increase of the HEC concentration.(2)The modified Villermaux/Dushman reaction system was used to characterize the micro-mixing effect of DLM/S dynamic mixer in the viscous system,and the corresponding relationship between the micro-mixing time and the separation coefficient was solved according to the agglomeration model.In the 1.0%HEC solution system,the micro-mixing time of the DLM/S dynamic mixer is between 4-50 ms,which is much shorter than the micro-mixing time of the traditional stirring mixer,indicating that DLM/S dynamic mixer has better micro-mixing performance.Increasing the rotation speed will cause the shear-thinning of the HEC solution system and increase the fluid turbulence,which will further shorten the micro-mixing time.(3)The one-step synthesis of polyurea copolymer using 4,4’-diphenylmethane diisocyanate(MDI),polyetheramine(D2000/D230)and m-phenylenediamine(MPD)was studied in the DLM/S type dynamic mixer.The results show that in the MDI/D2000(D230)/MPD(1/1/1)competitive reaction system,increasing the speed will enhance the micro-mixing effect,promote the end-capping effect of MPD,inhibit the growth of the MDI-D2000 chain segment,and decrease the molecular weight of the product,increase the MPD content.In the polymerization reaction system of MDI/D2000/MPD(1/0.5/0.5),as the reaction rate of MDI and D2000 is faster,increasing the rotation speed can promote this reaction to generate MDI-D2000-MDI which further react with MPD to produce polyurea with aliphatic-aromatic alternating structure.(4)BaSO4 particles were prepared by liquid-phase precipitation method in the DLM/S dynamic mixer.The results show that increasing the rotation speed has no significant effect on the size of BaSO4 particles,but can inhibit the agglomeration of crystal nuclei during the growth process,prevent the formation of large particles,and therefore lead to a uniform size distribution of the product particles.Compared with the traditional stirred reactor,the BaSO4 particles produced by the DLM/S dynamic mixer have a smaller particle size and a more uniform particle size distribution.