PVC与氧化铁氧化硅混合氧化物共热解过程解析

Study on Pyrolysis of PVC and Fe2O3&SiO2 Mixtures

研究了二氧化硅及氧化铁的混合物(SiO2含量20%)与PVC体系共热解的反应过程。利用TG-DSC监测不同质量比((Fe2O3+SiO2)∶PVC=1∶9~3∶1)的混合物在加热过程中的失重情况,升温速率为10~50 K/min。利用XRD和SEM-EDS表征各反应阶段的固相产物。结果表明,在升温至1273 K过程中,混合物失重过程分为3个阶段:第一阶段(室温~673 K),Fe2O3被氯化还原生成FeCl2;第二阶段(673~793 K),Fe2O3被还原成Fe3O4后,部分Fe3O4及FeCl2被还原成Fe;而SiO2以石英相存在,不参与任何反应,这两个阶段与纯PVC的裂解温度区间相对应;第三阶段(793~1273 K),Fe3O4被PVC裂解产物碳逐级还原成FeO与Fe,直至Fe3C,在这一反应阶段SiO2与FeO反应生成铁橄榄石,说明当FeO不存在时,SiO2几乎不影响Fe2O3与PVC之间的反应。可以用廉价的赤铁矿替代氧化铁处理含氯废塑料。

Pyrolysis process of(Fe2O3+SiO2)and PVC mixtures was studied.Weight loss of samples((Fe2O3+SiO2)∶PVC=1∶9 to 3∶1)was monitored with TG-DSC at constant heating rate ranged from 10 to 50 K/min.Solid residues of different reaction stages were characterized by XRD and SEM-EDS.The results show that pyrolysis process can be divided into three stages from room temperature(R.T.)to 1273 K according to weight-loss.Ferric oxide is chlorinated and reduced to ferrous chloride at the first stage(R.T.to 673 K).After reduction of Fe2O3 to Fe3O4,part of FeCl2 and Fe3O4 are reduced to iron metal at the second stage(673 K to 793 K).These two stages are in accordance with pyrolysis of PVC.However,quartz does not change during these two stages.When temperature further rises,Fe3O4 is reduced by carbon to FeO,iron metal and Fe3C consequently at the third stage(793 K to 1273 K),while SiO2 reacts with FeO resulting in fayalite.Therefore,it is assured that SiO2 hardly affects co-pyrolysis process Fe2O3 and PVC mixtures if FeO is not present.It is possible to recycle waste plastic with hematite instead of Fe2O3 to cut cost.