Micro-mixing Characteristics In Novel Jet Loop Reactor

In this paper,a novel jet loop reactor was proposed for the production of butyl rubber.The mixing of the initiator and the monomer could be promoted due to the excellent micro-mixing performance of the jet mixer part.The reaction heat could be quickly removed from the reactor due to the good heat transfer performance of the loop reactor part,which could avoid local hot spots affecting product quality.Compared with traditional butyl rubber polymerization reactor,the novel reactor have good micro-mixing performance,simple structure and enable to achieve products with adjustable molecular weight distribution.In order to grasp the characteristics and design method of this reactor,a chemical probe method(iodate-iodide test system)was adopted to study the micro-mixing characteristics of a small jet mixer and a jet loop reactor,respectively.The change rule of segregation index were found,then the micro-mixing characteristic time was calculated based on the incorporation model.By comparing the micro-mixing characteristic time of the jet loop reactor and the reaction characteristic time of the butyl rubber polymerization,it was proved that the jet loop reactor could be used for the polymerization of butyl rubber.The effects of the flow velocity in nozzle exit and entrainment entrance on the pressure ratio,axial pressure distribution,radial pressure distribution,and energy dissipation rate of the jet mixer were investigated to reveal the flow regularity of the jet loop reactor.Finally,a scaling model was revised to correlate the micro-mixing characteristic time and operating conditions in the jet mixer,which was expected to provide theoretical guidance for the optimal design of the reactor.The main research and conclusions were as follows:(1)A small experimental device of jet mixer with a 9 mm diameter throat tube and 1.3 area ratio was established,where the effects of the flow velocity in nozzle exit(8.40 m/s?16.81 m/s),the flow velocity in entrainment entrance(0.002 m/s?0.04 m/s),the distance between throat tube and nozzle(4 mm?9 mm)and the injection position of entrained fluid on the segregation index and micro-mixing characteristic time in liquid-liquid system were studied by the chemical probe technique(iodate-iodide test system).The study indicated that the micro-mixing characteristic time becomes smaller with the increase of the flow velocity in nozzle exit.What's more,it becomes bigger firstly then smaller with the increase of the flow velocity in entrainment entrance,and the critical flow ratio qc is about 0.015.On the contrary,the micro-mixing characteristic time get smaller firstly then bigger with the increase of the distance between throat tube and nozzle.The optimum distance between throat tube and nozzle Lc,opt is about 0.8 times of throat tube diameter.The mixing effect while entrained fluid injected from the inlet in the throat tube is better than that from the bottom of suction chamber.The results of incorporation model show that the micro-mixing characteristic time of the small jet mixer experimental device is 0.4?5 ms under the experimental conditions.(2)The abovementioned jet mixer was magnified by 3.67 times and combined with a 50 mm diameter loop tube to form a cold model experimental device of jet loop reactor.The pressure ratio,axial pressure distribution(x/d3-0.61?10.30),radial pressure distribution(r/R=0?1)and average energy dissipation rate of the jet mixer were examined by pressure gauge under different flow velocities in nozzle exit(8.42 m/s?16.83 m/s)and entrainment entrance(0.020 m/s?0.203 m/s).It was found that there were two kinds of axial pressure distribution rules in the jet mixer during different flow velocity in nozzle exit.When the flow velocity is lower(v1=8.42 m/s),the pressure decreases firstly and then increases along the flow direction,and the pressure reach lowest at the inlet of the throat tube.When the flow velocity is higher(v1=12.62 m/s),the pressure decrease turn to increase,then decrease turn to increase again along the flow direction.There are two pressure minimum points.The first minimum point is located at the entrance of the throat tube,while the second minimum point is located in the back end of the throat tube(x/d3=4.09).The experimental results also show that the pressure at the wall is higher than the pressure at the center.The mixing section is transferred from the section which hold 2/3 throat tube radius to the section which hold 1/3 throat tube radius from the central axis of the nozzle,finally transferred to the section in the central axis of the nozzle.At x/d3=4.09,the pressure has reached a stable state along radial direction.In addition,the average energy dissipation rate increases with the increase of the flow velocity in nozzle exit and the flow velocity in entrainment entrance.(3)In the jet loop reactor,iodide-iodide test system was adopted to reveal the influence of operating conditions on the micro-mixing characteristics(Xs and tm),including the flow velocity in nozzle exit(8.42 m/s?16.83 m/s)and entrainment entrance(0.02 m/s?0.07 m/s).The study indicated that the micro-mixing characteristic time becomes smaller with the increase of the flow velocity in nozzle exit and becomes bigger firstly then smaller with the increase of the flow velocity in entrainment entrance.The critical flow ratio is 0.02.A revised function of scalingmodelwas established(?)to estimate the micro-mixing characteristic time.The relative deviation between the calculated value and experimental data were less than 20%.When the flow velocity in nozzle exit keeps constant,the calculated critical flow ratio is 0.017,which is in agreement with the experiments.The micro-mixing characteristic time of the jet loop reactor(0.02-0.06 ms)is less than the reaction time of butyl rubber(70 ms),which could meets the requirements of the synthesis reaction of butyl rubber.