【作者】 黄凯；

【导师】 李伯耿；

【作者基本信息】 浙江大学 ， 化学工程与技术， 2018， 硕士

【摘要】 早期聚丙烯反应器内合金化方法为序贯聚合法,在聚合过程中可以直接制备高性能、高附加值的聚丙烯合金,相较于机械共混有很大的优势。但是在聚合过程中,易受到停留时间分布及扩散/聚合动力学的影响,存在颗粒内及颗粒间结构的不均匀问题,影响最终产品的性能。多区循环反应器技术(MZCR)的开发则极大程度地消除了上述问题,使固体颗粒在快速流态化的提升管和沉降态的下降管两种不同的“单体氛围”中循环反复运动,只要循环速率足够大,经过多次循环便可形成具有多层类似“洋葱”的结构,产品的性能得到大幅度提高。为制备具有类似颗粒结构的聚丙烯合金,田洲等[5]提出了气氛切换聚合方法(ZJU-ASP技术),即将催化剂/聚合物颗粒静止,通过脉冲引入乙烯,在设定的切换频率下周期性地改变单体组成,制备了刚-韧平衡性能优异的聚丙烯/乙丙弹性体(iPP/EPR)合金。另一方面,由于来源于C4馏分的大量的1-丁烯生产能力被闲置,可利用1-丁烯来改性聚丙烯,制备聚丙烯/丙丁共聚物合金。考虑到采用两段序贯聚合法制备丙丁合金也可能存在颗粒内及颗粒间结构的不均匀问题,其机械性能有提高的空间。因此,本文采用单体组成周期性切换聚合工艺制备聚丙烯/1-丁烯合金,并与序贯聚合法制备的合金性能进行比较,并考察了单体组成周期性切换聚合工艺参数-切换频率对丙烯/1-丁烯多相共聚物的组成及结构和机械物理性能的影响,将不同组成的丙烯/1-丁烯合金进行溶剂萃取分级,采用差式扫描量热法(DSC),高温凝胶渗透色谱法(GPC),13C NMR等对各级分进行表征分析。结果表明单体组成周期性切换法制备的合金刚-韧平衡性能优异,表现出典型的“强而韧”的应力应变曲线,其内部的含量较高的丙丁嵌段共聚物起到相容剂的作用。SEM显示合金颗粒的球形度好,很好地复制了 DQ催化剂的颗粒形态,粒径均匀,有良好的流动性。同时,随着切换频率的增加,其聚合活性显著提高,熔融温度及熔融焓有规律地增加,共聚物中丁烯含量降低,沸腾乙醚可溶级分所占的比例逐渐降低,而沸腾正庚烷可溶级分和不溶级分所占的比例有规律地增加,嵌段共聚物中[PPP]含量增加,长序列PP链段增加,合金的结晶度提高;不同单体组成的聚合时间比(Pro Ⅱ/Pro Ⅰ)增加时,其聚合活性有所下降,熔融及结晶温度降低,共聚物中丁烯含量增加。基于单体组成周期性切换聚合工艺建立了丙丁共聚的动力学模型,借助于Aspen Plus的sensitivity模块对液相浓度进行动态分析。对于动力学参数的估算中,对聚合速率进行模拟,结果显示模型能很好预测动力学曲线。而且,关联了单体组成周期性切换聚合工艺的特征参数-切换频率对聚丙烯多相共聚物的组成与结构的影响,通过调节工艺参数来有效调节聚合活性,各级分比例及1-丁烯含量等。另外,该催化剂所生成的聚合物分子量分布曲线接近于正态分布。更多还原

【Abstract】 The early polypropylene reactor alloying method is the sequential polymerization method,and the polypropylene alloys with high performance and high added value were prepared directly in the polymerization process.Compared with mechanical blending,the performance of reactor alloy technology is outstanding.But in the process of polymerization,it is easily affected by the residence time distribution and diffusion/polymerization kinetics,and there is an inhomogeneous problem in the particle and intergranular structure,which affects the performance of the final product.The development of the multi zone cycle reactor technology(MZCR)greatly eliminates the above problem,making solid particles circulate repeatedly in two different"monomer atmosphere" of fast fluidization pipe and settling tube.As long as the circulation rate is large enough,the polymer can only form extremely thin within a single polymerization cycle.The polymer layer(up to the micron level),after many cycles,can form a multilayer structure,and the performance of the product has been greatly improved.In order to prepare the polypropylene alloy with similar particle structure,Tian Zhou and other[5]proposed an atmosphere switching polymerization(ZJU-ASP Technology).The catalyst/polymer particles were static,the ethylene was introduced through the pulse and the monomer composition was periodically changed under the set switching frequency,and the iPP/EPR alloy.with excellent stiffness and toughness was prepared.Both MZCR and ZJU-ASP technology show that the iPP/EPR prepared by this method is better than the two sequential polymerization method.On the other hand,because a large number of 1-butene production capacity from the C4 fraction is idle,1-butene can be used to modify polypropylene.It was considered that alloys prepared by two-stage sequential polymerization may also have the problem of inhomogeneous particles and intergranular structure,and the mechanical properties of the alloy can be improved.In this paper,polypropylene/1-butene alloy was prepared by two-stage sequential polymerization and periodic switching polymerization of monomers.The performance difference of polypropylene alloy containing a small amount of butene prepared by sequential polymerization and periodic switching polymerization of monomers was compared in the supported Ziegler-Natta catalytic system.The effect of the periodic switching polymerization process on the composition and structure of alloys was studied.The solvent extraction and classification of alloys were carried out by differential scanning calorimetry(DSC),high temperature gel permeation chromatography(GPC)and 13C NMR.The results show that the equilibrium performance of the stiffness and toughness of the alloy prepared by monomer composition switching method are excellent,and the relatively high content of block copolymer acts as compatibilizer.SEM shows that the sphericity of the particles is good,the particle shape of the DQ catalyst is well replicated,the particle size is uniform and the fluidity is good.At the same time,with the increase of switching frequency,the polymerization activity increased significantly,the melting temperature and melting enthalpy increased regularly,the content of butene in the copolymer decreased,the proportion of the soluble grade of boiling ethyl ether decreased gradually,while the proportion of the soluble and insoluble fractions of the boiling n-heptane increased regularly,and the block copolymer was increased.The content of[PPP]increased,the long sequence PP segment increased,the crystallinity of the alloy increased,and the polymerization activity decreased,the melting and crystallization temperature decreased,and the butene content in the copolymer increased when the time ratio of polymerization I segment/polymerization Ⅱ segment increased.Based on the monomer composition switching process,a kinetic model of propylene/1-butene multiphase copolymer was established,and the dynamic analysis of liquid phase concentration was carried out with the help of the sensitivity module of Aspen Plus.For the estimation of kinetic parameters,the polymerization rate is simulated,and the results show that the model can predict the kinetic curve very well.Moreover,the influence of switching frequency on the composition and structure of polypropylene multiphase copolymers was related to the composition and structure of heterophasic polypropylene copolymers.By adjusting the process parameters,the polymerization activity,the proportion of different fractions and the content of 1-butene were adjusted effectively.In addition,the molecular weight distribution curve of the catalyst is close to the Gauss distribution.更多还原