Study And Application On Mixing Performance For Polymer Solutions In Microreactors

Controllable polymer synthesis with microreactor technology has been a hot research topic while little attention is focused on the mixing process.In this work,the mixing performance for polymer solutions was investigated using hydroxyethyl cellulose solutions as working systems.Further,gas-liquid two-phase flow was applied as a process intensification method to enhance the micromixing performance for polymer solutions in microchannels.At the end,the preparation of sulfonated polystyrene and phenylhydrazine hydrochloride was achieved in microreactors based on the mixing principles obtained earlier.In the mixing experiments,the high-speed camera firstly was applied to record the reaction belts.However,the mixing performance was improved by strengthening the shear effect,reducing the capillary inner diameter and arranging the capillary in a helical form.The mixing time was within the range of 0.1-8.0 ms calculated by a modified stretching efficiency model considering the shear effect and the drag reduction under experimental conditions.It was proven that the good mixing performance for polymer solutions could be obtained in the microchannel even at low Reynolds numbers due to the shear effect.Later,the mixing performance for polymer solutions in microchannels with the gas-liquid two-phase flow operation as a process intensification method was studied.The micromixing performance was largely improved by introducing the inert nitrogen.Operating mode and operating range with regard to gas and liquid volumetric flow rates should be carefully considered in order to avoid unstable process operation zones.The unique side-by-side slug flow pattern in gas-polymer solution two-phase slug flow was found with the use of the high-speed camera.The side-by-side slug flow pattern was described by a simplified model to depict its velocity field and to emphasize the shear effect on the micromixing performance for polymer solutions in the microchannel.Based on the mixing principles obtained,sulfonated polystyrene was prepared with the gas-liquid two-phase flow operation in microreactors.The degree of sulfonation for polystyrene was promoted from 0.42 to 0.575 with the increasing gas fraction from 0 to 0.4.These results demonstrated the effectiveness of such a mixing intensification strategy for reaction processes involving polymer solutions.Furthermore,the phenylhydrazine hydrochloride was synthesized in microreactors at room temperature at the attempt of the simplification of the preparation for diazo salts polymer soulutions in mixing experiments.Experimental conditions,such as the length of microchannel,the flow rate and the temperature for the diazotization reaction were optimized.80% yield for phenylhydrazine hydrochloride could be obtained when the diazotization reaction was operated in 1 m long capillary microreactor with 0.5mm inner diameter at the Reynolds number of 400 and at the room temperature.