Thermal Depolymerization Of Poly (Methyl Methacrylate) And Polystyrene To Monomers With A Rotating Bed Reactor

Poly（methyl methacrylate）（PMMA）and polystyrene（PS）are important polymers,which are used in large quantities.However,after use,polymer materials are discarded freely,which not only causes environmental problems,but also causes the waste of polymer resources,therefore,the recycling of polymer materials has become critical.Thermal depolymerization is an effective method to recycle waste polymer materials.But fixed-beds have poor heat transfer and severe carbon accumulation,fluidized-bed reactors require large amounts of inert gas to fluidize and the bed is prone to collapse.Both thermal depolymerization methods have fatal defects.In this paper,the method of preparing monomer by pyrolysis polymerization of waste PMMA and PS in a rotating bed reactor is proposed.The slow rotation of a rotating bed reactor ensures the effective mixing between a hot medium and a raw material,and does not require a large amount of inert gas for fluidization,which does not lead to bed collapse and has a better heat transfer effect and is conducive to continuous thermal depolymerization reactions.A rotating bed reactor was designed in our laboratory and the law of preparing monomers by pyrolysis of these two polymers in this reactor was explored.The motion and mixing of the particles in a rotating bed reactor were simulated.The main research contents and findings of the thesis are as follows:First,the thermal depolymerization of poly（methyl methacrylate）was carried out in a rotating bed reactor,The effects of temperature,N₂flow rate,rotating velocity,filling medium,and filling rate on the thermal depoly-merization of poly（methyl methacrylate）were investigated.The results indicated that the yields of liquid products and monomer methyl methacrylate could be improved with increasing the flow rate of nitrogen,rotating velocity and filling rate at the conditions investigated.The maximum yield of the liquid product was obtained when silicon dioxide particles was used as the filling medium.The highest yield of the liquid product after the thermal depolymerization was 96.2 wt%and the highest yield of monomer methyl methacrylate was 91.2 wt%.The optimum pyrolysis temperature of poly（methyl methacrylate）was 400°C.However,the yields of the liquid product and monomer methyl methacrylate gradually decreased during continuous pyrolysis,and the yield of the liquid product was finally kept at 89wt%.The yield of monomer was kept at 79 wt%.Second,the pyrolysis of polystyrene in a rotating bed reactor was performed.The effects of temperature,N₂flow rate,rotating velocity,filling medium,and filling rate on the thermal depolymerization of polystyrene were investigated.The results indicated that the yields of liquid phase products and styrene could be increased with increasing nitrogen flow rate,rotating velocity and the filling rate of a rotating bed.Silicon dioxide particles as the filling medium could obtain higher yields of monomer and liquid phase products than other filling mediums.The optimum pyrolysis temperature of polystyrene is475°C and the dominant product was the liquid phase product containing styrene.The maximum yield of liquid phase product was 92.0 wt%and the maximum yield of monomer styrene was 64.4 wt%.Last,the mixing and motion of the particles inside a rotating bed were simulated in cold state using the discrete element software EDEM.The number of flights inside a rotating bed increased from 0 to 12,The mixing effect of particles gradually increases and tends to be stable,and the best mixing motion of particles was found at 8 flights.When silicon dioxide particles and iron particles were used together as the filling heat medium,The particle size between them changed from 2 mm:2 mm to 2 mm:1.5 mm and then to 3 mm:1.5 mm,which reduced the relative particle size of iron particles.The mixing effect of the two particles becomes worse,and the mixing effect of the two particles is better when their particle sizes are equal.