Study On Pyrolysis Behavior Of Organic Solid Wastes

Organic solid waste is a kind of waste which can’t be recycled and thus discarded.With the continuous growth of population and higher living demands of residents,the amount of organic solid waste is increasing year by year,and the annual output of municipal solid waste has exceeded 2billion tons.Traditional methods such as landfill,incineration and composting not only result in pollution of water and soil,but also cause a large loss of resources.How to deal with solid waste is a big problem in today’s society.Pyrolysis is a kind of solid waste disposal method and complex organic matter can be broken into fragments with solid residues,eventually formed three kinds of products,coke,oil and gas.These products have a good industrial application prospect.Therefore,pyrolysis of organic solid waste can not only realize efficient utilization of resources,achieve sustainable development,but also reduce pollution to the environment,which is a hotspot of current research.Based on previous studies on the pyrolysis of plastics and biomass,this study focuses on the microwave pyrolysis of urban solid waste in a non-catalytic environment,which has more economic benefits.PET,PP,PE and waste carton from municipal organic solid waste were selected as raw materials.Appropriate reaction conditions were found by investigating the liquid product yield and product properties under different experimental conditions.The raw materials and pyrolysis products were characterized by elemental analysis,infrared,Raman and mass spectrometry.The main conclusions are as follows:（1）PET bottles are mainly composed of C,H and O with O content of 33.7%.The O exists in the form C-O and C=O bonds.Its volatilize accounts for more than 90%.Thermogravimetric（TG）analysis shows that the main weight loss of PET bottle is 370-480℃.The higher the heating rate,the higher the initial decompose and end temperatures.The pyrolysis experiment of PET bottle in tubular furnace shows that the content of wax condensate increases first and then decreases with the increase of temperature（450-600℃,temperature interval 50℃）.The reaction time（30-60 min,with an interval of 10 min）has little influence on the reaction,but the increase of carrier gas flow rate（40-160 m L/min,flow rate interval40 m L/min）will increase the content of condensate.GC/MS,NMR and IR analysis to the products indicated that the condensate is mainly benzene and its derivatives,among which the benzoic acid content is the highest10%.The gas product is mainly CO and CO₂ with a small amount of H₂and aliphatic hydrocarbon.The proportion of CO and CO₂ is more than 90%and CO₂ content decreases with increasing temperature.（2）The element composition of waste cartons is also C,H,O with O content of 54%.The volatile matter and water account for 76.72%and7.39%,respectively.The O exists mainly as O-H,C=O and C-O bonds.TG analysis shows that the waste carton is dehydrated at 50-250℃and decomposes mainly at 250-370℃.The maximum decomposition rate is at350℃.Pyrolysis experiment in tube furnace shows that increasing the temperature（300-450℃,temperature interval 50℃）promotes formation of gas products and decreases the coke yield.The oil product increases firstly and then decrease.Microwave-aided-pyrolysis can produce more oil than tube furnace.Pyrolytic oils are mainly oxygen-containing compounds,including carboxylic acids,ketones,esters,phenols,alcohols and dehydrated sugars.Most of them exist in a five-member or six-member ring structure,and the distillation range is concentrated at 70-250℃.The gas from waste carton pyrolysis is mainly CO₂,CO,H₂ and CH₄.（3）Co-pyrolysis of waste carton and plastic（PP and PE）was investigated.TG analysis indicates two weight loss ranges,300-400℃for waste carton weight loss and 470-510℃for plastic weight loss.Compared with single pyrolysis,co-pyrolysis will make the pyrolysis temperature of waste carton move towards high temperature.The oil yield of co-pyrolysis increases with the increase of plastic content and the decrease of temperature.Waste carton and plastic have synergistic effect in microwave co-pyrolysis.The synergistic effect of waste carton/PP is stronger than that of waste carton/PE.The co-pyrolysis oil product consists of oxygen-containing compounds and aliphatic hydrocarbons,which are produced from waste cartons and plastics,respectively.Addition of plastics can effectively reduce the content of O in the pyrolysis oil,and the distillation range of the oil is concentrated at 200-500℃.The pyrolysis gases are mainly CO₂,CO and C₁-C₅ hydrocarbons,among which CO₂ and CO are from waste cartons,and C₁-C₄ hydrocarbons are mainly from plastics.The co-pyrolysis experiment with CO₂ as carrier gas has less oil yield and more pyrolysis gas yield than that with N₂ as carrier gas,and CO₂ as carrier gas also inhibits the production of CO₂ in pyrolysis gas.