【作者】 张翼；

【导师】 杨家宽； 梁莎；

【作者基本信息】 华中科技大学 ， 环境工程， 2017， 硕士

【摘要】 热解技术可以实现废弃印刷电路板(Waste printed circuit boards,简称WPCBs)非金属组分(Non-metallic fractions,简称NMFs)的减量化,但是含溴组分(如溴化环氧树脂)的裂解所释放的含溴污染物会引起二次污染。碱性添加剂在NMFs热解过程中可改变溴的分布。因此,本文的研究目的是将强碱性的工业固废赤泥(Red Mud,简称RM)作为一种添加剂与NMFs共热解实现热解过程溴的固定,考察其对NMFs热解的催化与固溴作用。主要研究内容如下:1.NMFs的热化学特性以及热解动力学研究利用热重分析,采用非等温的方式对NMFs的热化学特性进行研究。根据热重曲线将NMFs的热解分为三个阶段:20~100°C为水分蒸发阶段;100~570°C为有机物分解阶段;570~800°C为残余焦炭的分解阶段。其快速失重阶段为300~500°C,该阶段总失重为51.29 wt%,原料中的环氧树脂在此阶段发生热解。对比了空气气氛下NMFs的失重特性,发现氮气气氛下NMFs失重速率大于空气气氛。提高升温速率可以促进NMFs的热解反应。运用等转化率模型中的SKAS方法(Starink-Kissinger-Akahira-Sunose model)进行动力学分析,得到NMFs主反应阶段活化能变化规律,其平均活化能为170.45 kJ/mol。2.NMFs的热解实验及溴分布研究开展了氮气气氛下热解温度为300、400、500、600以及700°C下NMFs的热解实验。其三相产物产率分布规律为:固相产率随温度升高不断下降,500°C时维持在52 wt%左右基本保持不变;液相产率先上升后下降;气相产率不断上升。对热解产物进行分析,在500°C之后此时残渣中主要为以玻璃纤维为主的惰性氧化物,气体产物中的溴主要以溴代甲烷及其它溴代烷烃的形式存在,液体中的溴主要以溴代苯酚类物质的形式存在,固体的中的溴主要以有机物的形式存在。高温使得原料中的溴更多地进入到气体和液体产物中去。液体产物主要为含有苯环的芳香族化合物,以苯酚及苯酚类物质为主。另又进行了不同热解气氛的热解实验,发现在二氧化碳气氛下NMFs热解的固相产率较惰性气氛高,液相产物产率较低。3.赤泥与NMFs共热解及固溴实验在热解温度为500°C氮气气氛的实验条件下以不同掺量的赤泥掺入NMFs中进行共热解实验。结果证明当赤泥掺量为15 wt%时固体残渣中的溴占总溴的比从没有添加赤泥时的36.42 wt%增加到78.59 wt%。赤泥对NMFs热解过程中的溴具有一定的固定作用,会使更多的溴存留在固体残渣中。利用SKAS模型研究赤泥对NMFs热解过程中活化能变化趋势的影响发现赤泥在反应前期可以降低NMFs热解反应的活化能,促进NMFs的热解反应,提高焦油产量。4.赤泥对NMFs裂解焦油轻质化研究对热解过程中生成的焦油成分进行分析,温度的提高会使得焦油发生二次裂解,增加其中的低碳物质含量。赤泥的加入也可以提高焦油中低碳物质的含量,有利于NMFs热解产物的清洁化和无害化。本论文发现赤泥与NMFs共热解可实现热解过程中的固溴作用,为NMFs无害化处理处置提供理论依据。更多还原

【Abstract】 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.更多还原