| In recent years,engineering technology is rapidly developing towards miniaturization.Micro-chemical technology has become the frontier and hot spot of chemical engineering research.It has the advantages of green,safety,high efficiency and controllability,which has good application prospects in chemical synthesis,biochemical analysis,material preparation and other fields.Taking gas-liquid micro-dispersion technology as the research object,this paper realized the controllable preparation of micro-dispersed bubbles in the micro-reactor and carried out the basic research on the gas-liquid two-phase flow behavior in the microchannel.Using computational fluid dynamics(CFD)methods to simulate and analyze the segmented flow and bubbly flow systems,the effect of the disturbance of microbubbles(air columns)on the enhancement of mass transfer and mixing in the liquid phase was investigated.The characteristics of homogeneous flow,segmented flow and bubbly flow in terms of flow field distribution,convective mixing and selective amplification were compared.The characteristic photochemical microfluidic synthesis system was selected to verify the CFD simulation results.Experimental results showed that the introduction of inert microbubbles to form a micro-dispersion system effectively reduced the thickness of the liquid layer,improved the selectivity of the target product,and avoided the adverse effects of excessive light.Compared with homogeneous flow system and segmented flow system,bubbly flow system had the highest degree of similar amplification.By increasing the channel size from 0.6 mm to 4 mm,the output can be increased by 41 times while maintaining the micro-scale effect.Using simulation data and experimental research results,a prediction formula for mixing time tm was established,which can be used to evaluate the mixing effect and amplification potential of different flow strategies in the microchannel.It also provided a theoretical reference for quantifying the effect of microbubble(column)disturbance on mass transfer and mixing.Aiming at the problems of slow speed,low efficiency and many by-products in the traditional cumene oxidation process,the microchannel reactor was used to strengthen the liquid phase non-catalytic oxidation process of cumene.The effects of reaction residence time,reaction temperature,oxygen partial pressure,initiator content,pipe material and pipe winding method on the experimental results were investigated,and the process conditions were optimized.Experimental results showed that using oxygen as the oxidant,at 130℃,0.8 MPa,and 5 wt%cumene hydroperoxide as the initiator,the conversion rate can reach more than 60%in the PFA tube for 2 hours.Mass transfer and mixing were further enhanced by improving the pipe winding method.The experiment was carried out using the coiled flow inverter,and finally a conversion rate of 66.24%,a selectivity of 91.95%and a yield of 60.91%were obtained,which were significantly better than the experimental results in traditional batch reactors.The reaction conversion rate was doubled while still maintaining a high selectivity of more than 90%,and the reaction time is shortened to 1/4 of the original,greatly improving the oxidation efficiency. |
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