Characteristics Analysis And Equipment Design Of Polyethylene Pyrolysis In Molten Salt/Alkali

Renewable energy has gained great attention and interests in recent years due to growing energy consumption and greater environmental concerns.Pyrolysis oil of waste plastic is a promising renewable energy,which is regarded as a candidate for replacing fossil-derived products and source of chemicals.However,in the traditional thermal cracking process,there are problems such as uneven heat transfer and low product yield,due to low thermal conduction of plastic.For this reason,the molten salt/alkali are used as heat carrier for HDPE plastic pyrolysis study at cracking temperature of 500? in this thesis.Firstly,the effect of salt/alkali on the pyrolysis characteristics of plastic is studied by thermogravimetric experiment,and the pyrolysis mechanism of plastic is analyzed.Then,the pyrolysis experiment of plastic in salt/alkali was carried out in self-made reactor and the related products are analyzed.Finally the reactor for the waste plastic pyrolysis in molten salt is designed based on the experimental study.The specific work of this thesis is as follows:?1?The pyrolysis characteristics of HDPE plastic particles in salt/alkali are studied by thermogravimetric analyzer,and the effects of NaOH,KOH,NaOH-Na₂CO₃,ZnCl₂,ZnCl₂-KCl on the pyrolysis process are investigated.The kinetic laws of thermal cracking under various conditions and the kinetic parameters are studied by Coats-Redfern integral method.The results show that the pyrolysis reactions under different conditions are in accordance with the first-order reaction kinetics.Compared with individual HDPE pyrolysis,the range of weight loss temperature were narrowed when HDPE pyrolysis in the salt/alkali medium,namely from 405⁴90? to 435⁴85?.The temperature of maximum weight loss rate is reduced by 5¹0? and the activation energy is also reduced.?2?The slow and fast pyrolysis of HDPE in NaOH,KOH,NaOH-Na₂CO₃,ZnCl₂ and ZnCl₂-KCl is studied experimentally by using self-made reactor.The effects of different pyrolysis methods in the same medium and different medium with the same pyrolysis methods on pyrolysis process and product yield are investigated at the same crack termination temperature.Qualitative and quantitative analyses of the product components is carried out by FT-IR,¹H NMR and GC-MS.The results show that the addition of salt/alkali medium can increase the yield of pyrolysis oil and reduce the amount of solid residue.In the same medium,the pyrolysis oil yields in fast pyrolysis is higher than that in slow pyrolysis,the components of heavy oil is increased and the content of alkenes is higher than alkanes.The main components of the pyrolysis oil are paraffins and alkenes between C₁₂^C₂₀.The pyrolysis oil obtained by thermal cracking in NaOH and KOH is a complex mixture of hydrocarbons,but when pyrolysis in NaOH-Na₂CO₃,ZnCl₂ and ZnCl₂-KCl,they give a simpler product mix.?3?According to the given parameters of waste plastics which need to be disposed,the amount of molten salt and the compensation heat for the thermal cracking process are determined.And the main parts of the stirring pyrolysis reactor,which is used for waste plastic pyrolysis at high temperature in molten salts are designed,including the design of the shell of reactor,the heating coil,the stirring paddle,the pipes and the heat insulation layer and the selection of the flange and the motor rack.