【作者】 周茜；

【导师】 王玉忠；

【作者基本信息】 四川大学 ， 材料学， 2003， 博士

【摘要】 聚烯烃催化裂解研究是近年来人们一直关注和不断研究的一个重要课题，对于资源利用及环境保护具有重大意义。国内外已对通过催化裂解的方式进行废旧聚烯烃的回收进行了大量的研究，取得了大量的成果，也有相应的装置建成投产。然而，时至今日，塑料的回收技术并没有得到广泛的推广和应用，我国的情况更是如此。目前存在的主要问题可归纳为如下几点： ①油品质量不高、收率低；裂解工艺要求仍然较高(如温度很高)，使成本偏高。 ②催化剂的活性较低、催化剂成本高。 ③裂解体系主要集中在对单一聚烯烃裂解行为的研究上，而对混合聚烯烃的研究较少。特别是对在催化剂作用下混合聚烯烃裂解机理及裂解行为的研究，少有涉猎。 ④含有聚氯乙烯(PVC)废旧塑料裂解时产生氯化氢气体，严重腐蚀设备；同时也会产生含氯的有机化合物，从而使其裂解生成的液体作为燃料使用时会生成有毒气体，因而无法作为燃料使用。对于该体系催化裂解的研究，需要同时考虑脱氯与催化裂解两方面的效果。但目前的研究只集中于前者，而对总体的效果没有考虑。 总之，目前采用催化裂解的方法回收废旧塑料在技术及经济上仍具有不可行性的特点。因此，对聚烯烃催化裂解机理进行深入的研究，进而研制出新型催化剂，并对聚烯烃催化裂解过程进行系统的研究，在获得更高的液体产品质量的同时，控制裂解过程中产生的潜在的有害的副产物，是当前废旧聚烯烃催化裂解回收研究领域的重要课题。这一课题的解决，不仅具有理论意义，而且还具有应用价值。 本论文采用间歇式反应器，对城市固体垃圾中废旧塑料主要成分，包括聚乙烯(PE)、聚丙烯(PP)、聚苯乙烯(PS)及聚氯乙烯(PVC)催化裂解行为及催化裂解机理进行了系统的研究，为通过催化裂解回收废旧塑料提供坚实的理论基础。 对单一聚烯烃催化裂解行为的研究表明，沸石分子筛对LDPE和PP体系的催化裂解反应比热裂解反应具有高的裂解活性。对LDPE的催化裂解反应，其主要影响因素是催化剂的酸性，而对于PP，则是催化剂的孔径。 对聚苯乙烯体系，在不同催化剂作用下表现出不同的催化裂解行为。与热裂解相比，碱性催化剂表现出了正催化的作用，而酸性催化剂表现出了负催化的作用。聚苯乙烯在不同催化剂作用下所表现出的不同的催化裂解行为是由不同的裂解机理决定的。其中，在使用酸催化剂时，裂解行为主要受催化剂的酸性影响，同时催化剂的孔道结构对聚苯乙烯的裂解行为也具有重要的影响。 另一方面，聚苯乙烯催化裂解时，温度具有重要的影响。随着温度的提高，液体收率增加，残渣减少，苯乙烯单体收率大幅度增加，液体生成速率迅速增加。 以上述研究为基础，针对当今催化裂解中存在的由于催化剂的活性较低，使裂解温度偏高问题，首次设计制备出具有更强反应活性的新型改性催化剂D-eLaZSM一5。与ZSM一5相比，DeLaZSM一5具有相似的晶体结构及表面性质，但孔容增加，弱酸数目及强度以及总酸量显著增加，而强酸数目减少。 进一步的研究发现:对于LDPE，新型催化剂DeLaZSM一5比ZSM一5具有更高的催化裂解活性。对于LDPE与PP体系，新型催化剂DeLaZSM一5表现出明显的择形催化裂解作用。这种择形作用除与催化剂孔道结构有关外，还与催化剂的酸性及反应温度有关。 目前大量废旧聚烯烃是以混合物的形式存在，因此对混合聚烯烃的催化裂解行为进行研究更具有意义。对不含PVC的混合聚烯烃，主要进行了各种催化剂对混合聚烯烃裂解活性的比较，并对混合聚烯烃混合前后不同的催化裂解行为进行了深入的分析。研究发现，不同棍合聚烯烃体系表现出不同的催化裂解行为。对于LDPE/PP混合物，所采用的各种催化剂使裂解活性均增加，裂解活—1-~了飞，性大小顺序为:DeLaZSM一5>ZSM一5>USY>热裂解。对于LDPE/PS的混合物，不同的催化剂对裂解活性的影响不同:与热裂解相比，ZSM一5和DeLaZSM一5使裂解活性增加，USY使裂解活性降低;裂解活性大小顺序为:DeLaZSM一5>ZSM一5>热裂解>USY。对于PP用S的混合物，不同的催化剂对裂解活性的影响也不同:与热裂解相比，USY使裂解活性增加，25协5和DeLaZSM一5使裂解活性降低;裂解活性大小顺序为:USY>热裂解>DeLazSM一5>ZSM一5。对于LDPE户P用S三元混合物，加入催化剂后对裂解行为的影响并不十分明显:与热裂解相比，加入ZSM一5或DeLaZSM一5后，裂解活性先降低，后增加;加入USY后裂解活性降低。总体上裂解活性大小顺序为:DeLaZSM一5>ZSM一5>热裂解>USY。 另一方面，由于混合聚烯烃混合前后各自的裂解行为不同，因此对不同的聚烯烃混合物产生的混合效应进行了研究。对于LDPE/PP混合物，热裂解时表现出“正”的混合效应，混合物比单一聚合物裂解活性更高;对催化裂解，ZSM一5和DeLaZSM一5两种催化剂均使体系表现出“正”的混合效应，且DeLaZSM一5具有更大的混合效应;催化剂USY表现出“负”的混合效应，混合后催化活性降低。对于LDPE/PS混合物，热裂解时从总体上表现出“正”的混合效应，混合更多还原

【Abstract】 Recently the recycling of waste plastics has received much attention all over the world because of serious environmental problems caused by waste plastics as well as their potential for use as resources. Among the four plastics recycling methods defined by ASTM, the tertiary recycling, in which waste plastics is converted into useful chemicals, is thought to be the most promising method. In particular, tertiary recycling of polyolefin, which in quantity terms represents the largest group of plastics, has attracted much work from many researchers. However, because of chemical and technical problems as well as economic and legal factors, all processes for tertiary recycling of polyolefin have not been cost effective until now.Large-scale tertiary recycling of plastic waste will require efficient catalytic degradation of waste polyolefin. Therefore, detailed knowledge of catalytic degradation mechanism is necessary. In this dissertation we systematically studied the behaviors and mechanism of catalytic degradation of polyolefin in a stirred batch reactor, including polyethylene (PE), polypropylene(PP), polystyrene(PS) and Polyvinyl chloride(PVC), which are main components in municipal waste plastics. It aims to improve their catalytic degradation ability and at the same time control potential harmful products produced during catalytic degradation. Furthermore, It expects to provide strong theoretical basis for recycling waste polyolefin.First, the catalytic degradation of single polyolefin was investigated. ForLDPE and PP, improved activities were observed using Zeolite (ZSM-5 and USY) as catalysts. The order of activities observed suggested that the main factor influencing the PE degradation was the acidity rather than the pore size of the catalysts. For PP, however, the main factor influencing degradation was the pore size of the catalysts.For polystyrene, it was concluded that different catalysts had different effects on its degradation behaviors. Solid bases (BaO) were more effective catalysts than solid acids (ZSM-5 and USY), which could be explained by their different catalytic degradation mechanism. When using acid catalysts, the degradation behavior was mainly affected by the acid properties. Besides, the pore structure also had certain effect on the degradation behavior. On the other hand, the degradation temperature was also important. With the increase of the temperature, the degradation rate, styrene yield, and liquid yield increased, and the residue yield decreased.Next, a new modified catalyst, DeLaZSM-5, was synthesized. This catalyst was characterized by SEM, XRD, NH3-TPD, ICP and SBET, it was observed that the structures and surface properties were similar with those of ZSM-5, but the pore volume and the number and strength of weak acid sites increased, and the strong acid sites decreased.Further study revealed that for LDPE, DeLaZSM-5 showed much higher catalytic activity than ZSM-5; For LDPE and PP, DeLaZSM-5 exhibited obvious shape-selective effect. The pore structure, acid properties of the catalyst and the reaction temperature are key to this shape-selective effect.To date, most waste streams contain a mixture of polymers, which are costly to segregate, therefore catalytic degradation of polyolefin mixtures were studied in this dissertation. For the mixtures without PVC, their catalytic degradation behaviors using different catalysts were compared. It was found that different polyolefin mixtures had different catalytic degradation behaviors. For LDPE/PP, degradation activities were improved when using catalysts, and the order of activities was: DeLaZSM-5 > ZSM-5 > USY > no catalyst. For LDPE/PS, different catalysts showed opposite catalytic effects: ZSM-5 and DeLaZSM-5 increased its degradationactivity, while USY decreased its degradation activity. The order of activities was: DeLaZSM-5 >ZSM-5 >no catalyst>USY. For PP/PS, different catalysts also had opposite catalytic effects. However, the order of activities was different from that of LDPE/PS: USY > no cataly更多还原