Study On The Continuous Process Of Preparing Porous Polymer Microspheres By Foam Phase Separation

Porous polymer microspheres are widely used in drug carriers,catalysts,ion exchange resins,sewage treatment and other fields,because of their low density,high specific surface area and adjustable pore structure.Batch operation was usually used in the traditional methods to prepare porous polymer microspheres.These methods are non-continuous,complicated and inefficient.Therefore,it is significant to develop a simple,continuous and efficient method to prepare porous polymer microspheres,which can be used for industrial production of porous polymer microspheres.In this paper,the method to prepare porous polymer microspheres in foam phase which was developed in our research group,was developed to a continuous process;and then the continuous process was used to prepare porous po lymer microspheres.Firstly,the method to prepare porous polymer microspheres in foam phase was developed to a continuous process and then porous [P(MMA-BA)] polymer microspheres were prepared by using the continuous process to verify its feasibility;and then the effects of four processing parameters including the oil feed rate,the reaction temperature,the concentration of polyvinyl alcohol and the stirring rate,on the yield of microspheres,the amount of foams,the size and morphology of microspheres,and the quality of products were investigated;At last,based on the material balance and heat balance in the system,the reasonable feeding rate of aqueous solution in the continuous process was calculated and it was verified by experimental results.Bas ed on the theoretical and experimental results,feedback was used to improve the continuous process.The main conclusions of this paper include:(1)According to the characters of foam phase preparation of porous microspheres,we designed a continuous reaction device including three parts which were the feeding system(continuous feeding system),reaction system and post-treatment part.The continuous feeding system consisted of tanks for raw materials,metering pumps and pipelines.The reaction part was mainly composed of a constant temperature water bath,a stirring device and a reactor with a foam outlet.Washing and filtering system for microspheres constituted the post-processing part.By using the continuous process device,the continuous preparation o f porous polymer microspheres was verified through experiments.The experimental results showed that when the stirring rate,the reaction temperature,the feed rate of the oil phase and aqueous phase,the concentration of PVA and the mass ratio of P(MMA-BA)? DCM? HT are 500 r/min,45?,30 g/min,1.0 wt.%,10:53:6 respectively,the reactor can discharge continuously at the same time of continuous feeding.Finally,porous P(MMA-BA)microspheres were successfully prepared.Observed by an optical microscope and a scanning electron microscope,the microspheres had full spherical shape and porous structure existing in the interior and on the surface of microsphere.The average particle size of microspheres was 130 ?m and the size distribution was wide.(2)In the continuous process,the yield of the porous polymer microspheres was investigated as a function of the experimental conditions including the reaction temperature,the feed rate of the oil phase,the concentration of PVA and the stirring rate.And the heat demand in reactor was increasing with the raise of feeding quantity of oil phase which was regard as the cold fluid.Then,it affected the foam quantity and the yield of microspheres.With the increase of the feed rate of the oil phase,the yield of microspheres increased at first and then decreased gradually.When the feed rate of oil phase was 30 g/min,the yield of microspheres was the highest,up to 92%±4%.With the increase of the reaction temperature,the rate of solvent migration and volatilization was accelerated.However,owing to the relatively inadequate replenishment of aqueous solution,foam quantity and the yield of microspheres had rised at first and then decreased gradually.When the reaction temperature was 45?,the yield of microspheres was the highest,up to 93%±3%.At the same time,the number of microspheres' holes increased and the pore size of microspheres decreased gradually.Because polyvinyl alcohol had great influence on the viscosity of foam phase,the viscosity of foam phase increased when the concentration of polyvinyl alcohol was higher than 1.0 wt.%.It had contributed to the decreases of foam quantity and the yield of microspheres.In addition,the average particle size of microspheres decreased with the increase of the polyvinyl alcohol's concentration.When the concentration of PVA was 1.0 wt.%,the yield of microspheres was the highest,up to 91.8±6%.With the increase of the stirring rate,the yield of microspheres increased at first and then decreased gradually.Meanwhile,the average particle size of microspheres gradually decreased.And the particle size distribution was much more wide.When the stirring rate was 500 r/min,the yield of microspheres was the highest,up to 91%±4%.(3)Based on the material balance and heat balance,the equilibrium equation was established by regarding the reactor of continuous process unit as the core.When the feed rate of oil phase was constant,the suitable feed rate of water phase was calculated for a steady operation.Based on the established material and heat balance,the optimum feed rate of water phase was c alculated which was 67 g/min under the conditions that the feed rate of the oil phase,the stirring rate,the reaction temperature,the concentration of PVA are 30 g/min,500 r/min,45?,1.0 wt.% respectively.The experimental results showed that the reaction system can't maintain the stable operation for a long time under these conditions.It was shown that the theoretical equilibrium model can't completely reflect the actual supplying and demanding of material and heat in the reactor.So the accuracy of the calculation results of the model was not very good.Based on the theoretical and experimental results,a tank was installed for water phase solution replenishment on the reactor,so that the liquid level can remain basically constant to realize the steady operation.