Study On Pyrolysis Properties Of Non-metallic Fractions From Waste Printed Circuit Boards And Bromine Fixation By Co-pyrolysis With Red Mud

Pyrolysis has been proved to be an alternative technology to realize the reduction of non-metallic fractions?NMFs?from waste printed circuit boards?WPCBs?.However,brominated fractions such as brominated epoxy resin of NMFs would generate contaminants containing bromine in pyrolysis process.Alkaline additives could alter the distribution of bromine in NMFs'pyrolytic products.Thus the aim of this study was to fix more bromine in pyrolytic residue by co-pyrolysis with red mud?RM?which is an industrial solid waste with strong alkalinity.The mechanisms of catalytic pyrolysis and bromine fixation by RM have been clarified.1.Thermochemical properties and kinetics study of NMFsThermochemical properties and pyrolysis kinetics of NMFs have been studied by Thermogravimetric?TG?analysis.Results showed that the rapid weight loss stage is300⁵00°C corresponding to the decomposition of epoxy resin.And the weight loss of this stage is 51.29 wt%.According to the TG curves,the pyrolysis of NMFs can be divided into three stages:20¹00°C is the water evaporation stage;100⁵70°C is the organic decomposition stage and 570⁸00°C is the residual char decomposition stage.The rate of weight loss in N₂ atmosphere was higher than that in air atmosphere.The increment of heating rate would promote NMFs'pyrolysis.SKAS model was used to simulate the main reaction stage.The initial reaction kinetic model and apparent activation energy curve was obtained from the simulation.The average value of apparent activation energy was 170.45 kJ/mol.2.Pyrolysis study of NMFs and bromine distributionThe pyrolysis experiments were carried out on a tubular furnace under N₂ atmosphere at300,400,500,600 and 700°C.The study of the products yields showed that:solid yield continuously increased with the increment of pyrolysis temperature then maintained at around52 wt%at 500°C;liquid yield increased with the increment of pyrolysis temperature then decreased,gas yield continuously rise with the increment of pyrolysis temperature.The solid residue at 500°C and thereafter is mainly glass fiber.The bromine in the gas product mainly existed as bromomethane and other brominated alkanes,the bromine in liquid product presented in the form of brominated phenols,and the bromine in solid product mainly existed as organic matter High temperature made more bromine in the NMFs enter into the gas and liquid products.The pyrolysis liquid products mainly consisted of aromatic compounds,phenol and phenolic substances.In addition,the study of pyrolysis experiments under different pyrolysis atmospheres found that the solid phase yield in the CO₂ atmosphere was higher that that in N₂ atmosphere and the yield of the liquid product was lower.3.Bromine fixation in the pyrolysis of NMFs by RMThe co-pyrolysis of NMFs with different content RM were carried out at 500°C under N₂ atmosphere.The results showed that RM could fix bromine in the pyrolysis residue.The ratio of bromine in solid residue to total bromine showed a upward trend,from 36.42 wt%with no additives to 78.59 wt%with 15 wt%RM.The effect of RM on the activation energy of NMFs during pyrolysis was studied by using SKAS model.It was found that RM could reduce the activation energy in the early stage of pyrolysis,which would promote the pyrolysis of NMFs and improve the tar yield.4.Tar upgrading in the pyrolysis of NMFs by RMAnalysis of composition in pyrolysis tar showed that the increment of temperature led to secondary cracking of tar and increase the low carbon content.The addition of RM could elevate the content of low-carbon materials in tar,facilitating the cleaning and detoxification of pyrolysis products from NMFs.The results of this study suggest that bromine could fixed in pyrolysis residue by co-pyrolysis of NMFs with RM,which can provide the theoretical basis for the harmless treatment of NMFs.