PVC热解过程中HCl的生成及其影响因素

采用热重分析仪(TG)对聚氯乙烯(PVC)的热解特性进行研究.在不同条件下进行PVC热解制取氯化氢(HCl)实验,研究载气流量、入料量、热解时间和热解温度对氯化氢产率的影响,得出最佳热解条件;采用离子色谱(IC)、气相色谱(GC)、气质联用仪(GC-MS)对热解产物进行化学分析,揭示PVC热解制取HCl过程的反应机理.结果表明:PVC热解制取氯化氢的最佳热解条件为载气流量100mL/min、热解时间30min、入料量1.2g和热解温度400℃;PVC热解存在2个失重阶段,即260~320 ℃和390~600 ℃;随热解温度升高,焦油产率由0.95%升高到20.29%、HCl产率由25.69%升高到53.76%,而半焦产率则由54.39%下降到11.27%、气体产率变化范围为9.09%~18.97%;当热解温度低于400 ℃时,气体组分仅检测到H2、C2H4、C3H6;当热解温度高于400 ℃时,检测到的气体组分为H2、CH4、C2H4、C2H6、C3H6、C3H8;随着热解温度的升高,焦油组分中不稳定组分逐渐转化为稳定组分.PVC热解制取HCl的第1反应阶段主要是脱除HCl的链式反应,同时生成少量的苯等芳香族化合物及环烷烃等有机化合物;第2反应阶段主要为少量HCl生成、焦油的结构重整、分子重排、脱苯环和同分异构化等.

HCl generation reaction and its influence factors during PVC pyrolysis

The pyrolysis characteristic of poly vinyl chloride (PVC) was investigated by thermogravimetric analysis (TG). The effect of sample amount, pyrolysis time and temperature on the yield of hydrogen chloride (HCl), tar, gas and char during the production of HCl by PVC pyrolysis was studied. The pyrolysis products were analyzed by ion chromatography (IC), gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and the mechanism of HCl production from PVC pyrolysis was revealed. An optimal result could be obtained when 1.2g PVC was pyrolyzed at 400℃ for 30min when the carrier gas flow was 100mL/min. PVC pyrolysis included two decomposition stages, at the temperature of 260~320℃ and 390~600℃, respectively. With temperature increasing, tar yield enhanced from 0.95% to 20.29%, HCl yield raised from 25.69% to 53.76%, while char yield decreased from 54.39% to 11.27% and gas yield varied from 9.09% to 18.97%. H2, C2H4 and C3H6 were detected in the gas product when the temperature was below 400℃, while CH4, C2H6 and C3H8 were also found when the temperature was higher than 400℃. The unstable components converted to stable types when the temperature increased. In the first thermal decomposing stage, chain reactions for the removal of HCl were the main reactions, while in the second stage, the main reactions were tar reforming, molecular rearrangement, benzene removal and isomerization.