Experimental Study On Pyrolysis Characteristics And Catalytic Pyrolysis Of Typical Electronic Waste Plastics

The continuous innovation of science and technology has accelerated the upgrading of electronic and electrical products,shortened their service life,and led to the accumulation of a large amount of electronic waste.How to efficiently and cleanly dispose of electronic waste has attracted widespread attention.As an important component of electronic waste,plastic is difficult to degrade naturally under natural conditions.It is often disposed by incineration,which causes serious harm to the environment and wastes its important chemical components.Plastics are mainly derived from petrochemical production and can be converted into fuels or other important chemical raw materials through thermochemical disposal technology to alleviate the increasingly serious oil energy crisis.At present,pyrolysis technology is considered to be a reliable way to dispose of plastic waste,which can efficiently and cleanly dispose of waste while recycling it.However,the products recovered by pyrolysis technology have problems such as complex products and low content of high-quality components.Especially for the pyrolysis recovery of heteroatom-containing plastics such as ABS in electronic waste plastics,the pyrolysis products contain a large amount of nitrogen-containing compounds,which seriously hinders the further utilization of pyrolysis products.Therefore,in this paper,the typical plastic components ABS and PC in electronic waste are selected to achieve the goal of recycling high-quality components.Based on the study of their pyrolysis characteristics,the effects of acidic molecular sieve catalysts with different pore structures on the distribution of pyrolysis products are further studied.The reaction mechanism of the main products in the pyrolysis process of ABS and PC plastics is summarized,which provides theory and reference for the clean and resource utilization of ABS and PC waste plastics.The pyrolysis characteristics of ABS,PC and their blends at different heating rates（5,10,15 and 20°C/min）were studied by thermogravimetric experiments.The results show that under the condition of high heating rate,the pyrolysis interval of each raw material tends to shift to high temperature.ABS contains two thermogravimetric peaks at415°C and 425°C,respectively,corresponding to the pyrolysis of polybutadiene and styrene acrylonitrile copolymer in ABS.PC has a main pyrolysis range of 463-608°C.The thermogravimetric curve of ABS/PC blends has two pyrolysis intervals,corresponding to the main pyrolysis interval of ABS and PC plastics,respectively.The comparison results show that after injection molding,the main pyrolysis interval of ABS component in ABS/PC blends moves to high temperature,and the PC component moves to low temperature.According to the thermogravimetric data,four isoconversional methods:Friedman,Flynn-Wall-Ozawa,Kissinger-Akahira-Sunose and Starink were used to calculate the kinetic and thermodynamic parameters such as activation energy,pre-exponential factor,enthalpy change,entropy change and Gibbs free energy.It provides reference data and theoretical basis for the design of waste plastic pyrolysis reactor and the best reaction conditions of pyrolysis.Three kinds of acidic molecular sieve catalysts with different pore structures（Micro hole ZSM-5,Full holeβ,Mesoporous Hy）were selected to study the catalytic pyrolysis of ABS in tubular furnace.Firstly,the three catalysts were characterized by scanning electron microscopy（SEM）,specific surface area and pore size analysis（BET）,ammonia-temperature programmed desorption（NH₃-TPD）and pyridine infrared spectroscopy（Py-IR）to characterize their morphological appearance and acidic structure.In the tube furnace catalytic pyrolysis experiment of ABS,the effects of different catalysts on the three-phase yield of pyrolysis and the yield of monocyclic aromatic hydrocarbons and nitrogen compounds in pyrolysis oil were studied.The results showed that the addition of catalyst reduced the yield of ABS pyrolysis oil,while the mesoporous Hy zeolite catalyst had the least effect on the yield of ABS pyrolysis oil,and it had the best effect on the quality of pyrolysis oil.The yield of monocyclic aromatic hydrocarbons in pyrolysis oil increased from 40.87%to 54.33%,and the yield of BTX（benzene,toluene and xylene）increased significantly,while the yield of nitrogen-containing compounds decreased from 36.04%to22.66%.The effect of catalyst/raw material ratio on the quality of pyrolysis oil was further studied.The results showed that when the catalyst/raw material ratio was 2,the quality of pyrolysis oil was further improved,the yield of monocyclic aromatic hydrocarbons was further increased,and the yield of nitrogen-containing compounds was further reduced.In addition,the deactivation and regeneration characteristics of Hy molecular sieve catalyst in the process of recycling were also studied.The results showed that the catalyst was seriously deactivated after three times of recycling,and the catalyst could be regenerated by calcination to be similar to the catalytic performance of fresh catalyst.Based on the above results,the formation pathways of the main products of ABS pyrolysis and catalytic pyrolysis were proposed according to the experimental results and relevant literature conclusions.The catalytic pyrolysis experiment of oxygen-containing PC was carried out.It was found that theβmolecular sieve catalyst promoted the cleavage of isopropylidene in the PC structure and promoted the formation of monocyclic phenols such as phenol in the pyrolysis products.At the same time,the catalyst will promote the isomerization reaction of PC primary cracking products and promote the formation of o-methylphenol.ZSM-5catalyst is beneficial to the dehydroxylation and cyclization of phenolic compounds,and promotes the formation of polycyclic aromatic hydrocarbons such as naphthalene and fluorene.