超临界苯类溶剂对聚苯乙烯降解的影响

在高压间歇反应器中,温度340~370℃,以苯、甲苯、乙苯和对二甲苯为超临界溶剂研究了聚苯乙烯(PS)的降解特性.苯类物质是聚苯乙烯的优良溶剂,在超临界条件下其优异的传质、传热性能使聚苯乙烯快速降解.聚苯乙烯在不同超临界溶剂中降解转化率相近,而降解产物组成差别很大,分析了不同超临界溶剂对聚苯乙烯降解过程的影响.结果表明超临界甲苯对降解过程影响最小,苯乙烯收率最高.聚苯乙烯降解过程中,高分子链断裂和解聚同时进行,结合连续分布理论建立了聚苯乙烯降解的动力学模型,得到在超临界甲苯中聚苯乙烯链端解聚活化能为138.4 kJ.mol-1.

EFFECT OF DIFFERENT SUPERCRITICAL SOLVENTS ON THE DEGRADATION OF POLYSTYRENE

The degradation properties of polystyrene in supercritical benzene,toluene,ethylbenzene and p-xylene were studied between 340～370℃ using a quick process.Benzene hydrocarbons are the fine solvents of polystyrene.All the solvents have unique properties such as excellent heat transfer and mass transfer at supercritical conditions,and the degradation conversions of polystyrene were similar using different solvents.The conversion of polystyrene was close to thorough degradation when the temperature reached 370℃.Supercritical degradation of polystyrene in toluene improved the liquid product yield close to 97% while reducing the gas and residue oil less than 1% and 3%,respectively.The products are mainly composed of benzene,ethylbenzene,xylene,styrene,α-methylstyrene etc.But it is noted that the yield of styrene was quite different in different supercritical solvents.The experiments showed that the yield of styrene was much higher using supercritical toluene as solvent than that with other solvents.The yield of styrene obtained from polystyrene in supercritical toluene at 350℃ for 30 min reached a value of 75.5 wt%.The reaction mechanism consists of depolymerization of polystyrene and secondary reactions.The result showed that supercritical solvents affected the secondary reaction differently,because the styrene obtained from degradation could not separate out from the system quickly.Moreover,among the solvents employed in our work,toluene was founded to be the most effective supercritical solvent to recovery styrene from polystyrene.Based on the continuous distribution kinetics,the model of polystyrene degradation was developed at the mechanistic level using population balance equations formulated via the method of moments.The activation energy of polystyrene degradation in supercritical toluene obtained from Arrhenius equation is 138.4 kJ·mol~(-1).