Research On Process Intensification Of Liquid-liquid Heterogeneous Micromixing And Reaction By High-gravity Technology

The liquid-liquid heterogeneous reactions such as saponification,nitration,sulfonation,alkylation and lotion polymerization widely exist in the chemical industry.Due to the poor solubility of reactants,the concentration field inside the reactor varies greatly,resulting in poor mixing and mass transfer efficiency,which limits the apparent reaction rate and leads to a decrease in reaction conversion rate and product selectivity.In order to improve the conversion of raw materials,it is necessary to extend the residence time in the reactor,which will lead to the scale up of device size and further occurrence of side reactions.Therefore,improving the efficiency of liquid-liquid heterogeneous reactions is an urgent need in industry.Liquid-liquid mixing is a premise for liquid-liquid reactions to take place,and the realization of uniform and rapid mixing on the macroscopic and microscopic scales is expected to enhance the efficiency of liquid-liquid reactions.In practice,it is difficult to realize efficient mixing on the microscopic scale.Due to the excellent micromixing and mass transfer performance,the rotating packed bed(RPB)reactors have been widely used for intensifing heterogeneous reactions such as gas-liquid,liquid-liquid homogeneous,and liquid-solid.It can be foreseen that due to the small size of dispersion droplet and strong turbulence of liquids,RPB can also be used to intensify the liquid-liquid heterogeneous reactions.However,there is no quantitative evaluation of the intensification effect of RPB for liquid-liquid heterogeneous reactions,and there is a lack of theoretical and modeling research to guide the scale up design.Therefore,this study focuses on the industrial demand of improving the conversion rate and selectivity of liquid-liquid heterogeneous reactions.The key scientific issue is that the apparent reaction rate is limited by the mixing and mass transfer rate.Thus,a novel chemical probe system was developed to charecterizing the liquid-liqiud mixing efficiency.RPB is developed as intensified reactor for liquid-liquid heterogeneous reactions.The main research content is as follows:1.For the first time,a novel chemical probe system for assessing liquidliquid micromixing efficiency has been developed,which is based on the consecutive-competitive reaction system about aspirin and sodium hydroxide.By changing the solvent properties of the reactants,the system can characterize both liquid-liquid homogeneous and heterogeneous mixing.It fills the research gap of chemical probe system for liquid-liquid heterogeneous mixing and provides a consistent new tool for the comparative study of liquidliquid homogeneous and heterogeneous mixing processes.2.The development guidelines and validation criteria for novel chemical probe systems are systematically clarified.Based on decades of research on chemical probe systems,the authors propose a rigorous calibration logic from kinetic validation to molecular mixing experimental validation to molecular mixing model validation,which ensures the scientifity,sensitivity and reliability of the developed chemical probe systems.3.A new method for quantitative characterization of liquid-liquid heterogeneous micromixing has been developed.Based on the above new system,the quantitative description of liquid-liquid heterogeneous macromixing and micromixing efficiencies in terms of the segregation index has been successfully achieved,and the liquid-liquid heterogeneous micromixing efficiencies of the standard stirred tank and the rotor-stator reactor have been sensitively characterized under different operating conditions.4.A new model has been developed to accompany the new method,which can be mathematically decoupled to obtain the intrinsic quantities of micromixing efficiency based on the experimentally obtained saggregation indexes,realizing the comparison of the reactor characterization results obtained from different experimental conditions.The combination of the system and the model allows quantitative comparison of the efficiency of liquid-liquid heterogeneous mixing in different reactors,providing a new tool for reactor screening.5.Based on the above new system,method and model,the liquid-liquid heterogeneous mixing efficiency of the RPB reactor was quantitatively evaluated for the first time.The results show that under the better operating conditions,the liquid-liquid heterogeneous macroscopic mixing in the reactor is instantaneously uniform.The micromixing characteristic time is in the order of 0.01 s,which is more than one order of magnitude faster than that of the conventional stirred tank reactor.The results indicate that RPB has an excellent potential to be developed as an intensification reactor for liquidliquid heterogeneous mixing.6.In order to facilitate the reactor design and scale-up studies of RPB reactors for liquid-liquid reactor reaction,an universal equation for calculating the size of dispersed-phase droplets in a RPB reactor were obtained for the first time through experimental and modeling analyses:And a suitable model for calculating the mass transfer coefficient was chosen.The above laws were substituted into the model developed above,and the error between the predicted and experimental results was within 20%,which proved the reliability of the aforementioned series of studies.7.Taking the important liquid-liquid heterogeneous reaction of saponification of trichloroethane to vinylidene chloride as an example,a general methodology for the intensification of liquid-liquid heterogeneous reaction was established.That is,firstly,an apparent kinetic model is established based on the intrinsic kinetic results of the reaction system to be investigated;then the matching relationship between the intrinsic reaction rate and mass transfer rate is obtained based on the analysis of the apparent kinetic model to guide the selection interval of the intensified reactor.Finally,a suitable intensified reactor is selected based on the characterization results of the chemical probe system.Based on the above ideas,a RPB reactor was selected in this thesis to enhance the saponification reaction of trichloroethane,which realized the matching of mass transfer rate with the intrinsic reaction rate,and the reaction time was shortened by more than half compared with that of the traditional reactor.8.Through a similar methodology,the saponification reaction of dichloropropanol was carried out in a RPB reactor,and the reactant conversion,product selectivity and yield all increased with the increase of rotational speed.More than 90% product selectivity was achieved under the better conditions.