【作者】 魏舸裔；

【导师】 阳永荣； 王靖岱；

【作者基本信息】 浙江大学 ， 化学工程， 2011， 硕士

【摘要】 宽／双峰相对分子质量分布聚乙烯(双峰PE)是指相对分子质量分布曲线呈现2个峰值或1个相对较宽峰值的聚乙烯树脂。目前反应器新技术发展迅速,使得双峰聚乙烯的生产得以工业化。现有工艺通常是将二至三个反应器串联,通过改变反应器的气体组成及反应条件,使反应产物具有不同的分子量分布。但反应器串联工艺生产的产品颗粒间或颗粒内部不均匀,且在共混时容易形成凝胶或鱼眼。同时,工艺中第一个反应器的气体无法彻底隔绝,会进入下一个反应器,影响其气体组成,导致产品的双峰分布较窄,无法生产出宽分布的双峰聚乙烯。本文首先针对目前生产双峰聚乙烯的反应器技术及工艺存在的问题,设计了三种不同的反应器：分离分凝反应器、多温区内循环反应器和多区循环反应器。结合实际工业生产数据,计算了分离分凝反应器和多温区内循环反应器在一定规模下的尺寸结构及操作条件,并提出了工艺条件的确定原则,使设计方案更具有工业参考价值。其次,本文针对所设计的多区循环反应器进行了系统的流体动力学研究,考察了鼓泡流化床床、快速流化床、分布板和旋风分离器等部分的压力分布,并研究了静床高和表观气速对压降、提升段内固体循环量、气阻效果的影响。主要结论如下：反应器内的压降主要以分布板和颗粒的静压头为主,增加气速和器内固体量均导致床层压降的增大；鼓泡流化床的压力梯度较大,而提升段的压力基本不变；淘洗作用的引入,有效地实现颗粒在循环反应器内的自动筛分和物料转移；利用声发射检测手段,结合小波分解和PLS建立的固体颗粒流量回归模型,能准确预测高速流态化下的颗粒流量；通过气相色谱检测气流阻隔前后的CO2浓度发现,在气提段,采用气体阻隔方法,能有效维持不同反应器的反应气氛,确保生产分子量呈双峰／宽峰分布的聚乙烯。最后,基于Z-N催化剂下的乙烯配位聚合及其动力学模型,本文从微尺度、中尺度到宏观尺度建立了多区循环反应器内乙烯气相聚合的多颗粒模型。该模型适用于反应器从开车到平稳运行状态中分子量及其分布、产品颗粒粒径和产量的模拟计算。通过对反应器的模拟,得到以下结论：从反应器开车到平稳运行的过渡期,产品的数均聚合度及平均分散指数在反应开始时瞬间提高,在短时间内达到峰值,随后稍微降低并趋于平稳；产量达到平衡耗时较长,在开车后运行4小时后,反应器的总产量才保持在较平稳的状态；单体浓度对产品分子量及其分布影响最大；氢气对高分子量部分的反应影响较为明显,在实际反应中,要严格控制低氢反应区中的氢气浓度；循环比R的增大,会降低聚合物颗粒在反应区内的单次停留时间,导致分子量降低,不利于低氢反应区的反应进行；高活性的催化剂能缩短活聚物所需的单次停留时间,更适用于该反应装置。更多还原

【Abstract】 Bimodal polyethylene is a kind of engineering thermoplastic with extensively expanded properties. It is now mainly produced by a two-step or multi-step sequential polymerization process, in which the first step is ethylene polymerization and the second step is ethylene-hydrogen copolymerization. The problem with two-step process is that the polymer has low homogeneity and lead to the formation of fish-eyes in the production of films. Meanwhile, if the reacting gas can not be isolated and flows to next reactor, it will influence the polymerization in the next reactor, and the molecular weight distribution of the final product will become lower.First of all, in this article, three new reactors are designed and three patents have been applied, which are separating and recondensing reactor, multi-temperature reacting zone reactor and multizone circulating reactor. Calculations have been made to figure out the size and operating parameters of the separating and recondensing reactor and multi-temperature reacting zone reactor. Besides, the principle of selecting technological conditions is established according to the actual production data.Secondly, the multizone circulating reactor has been researched deeply. The fluid hydrodynamics of multizone circulating reactor is investigated. The influences of different superficial gas velocity and static bed height on the pressure distribution, circulating solid flow rate and the effect of gas barrier in both the bubbling bed and the riser have been investigated. The main achievements are as follows:(1) Besides the gas distributor, the pressure drop in reactor is mainly affected by the solid particle concentration. (2) Both the increase of superficial gas velocity and the polymer mass quantity in reactor will cause the increase of pressure drop. (3) Pressure drops faster in the bubbling bed than in the riser. (4) Employment of elutriation in this design successfully realizes the solid material transportation among the reacting zones. (5) Based on single-channel AE measurement, a regression model of particle mass flowrate in high-speed fluidization is built up by the use of wavelet packet transformation and partial least square(PLS) method. Results show that PLS method based on multi-scale analysis of A E signals is feasible for the detection of particle mass flowrate in high-speed fluidization. (6) Gas chromatography is used to detect the concentration of tracer gas CO2 both in the location of before and after the feeding position of barrier gas. Results show that the adoption of barrier gas can effectively create two different reacting conditions, making it possible to produce bimodal polyethylene.Last but not the least, based on the kinetic mechanism of polyethylene polymerization and the multigrain model, a mathematic model of gas phase polyethylene polymerization in multizone circulating reactor is presented. This model can be used in both the dynamic state and the steady state of the reactor. It can predict the important parameters of product, such as molecular weight and molecular weight distribution, particle size distribution and the reactor production, and so on. After the simulation of the reactor, there are some conclusions as follows:(1) The molecular weight, exponent index and particle size can reach their balance soon, but the production of the reactor causes a long time, which is 4 hours in the simulation. (2) Monomer concentration has the greatest impact on the molecular weight and the molecular weight distribution of product. (3) Concentration of hydrogen takes an obvious effect on the low hydrogen reacting zone, which means it’s important to control the hydrogen concentration in this zone strictly. (4) The increase of recycle rate R, will lower the product molecular weight, which goes against of the production of bimodal PE. (5) Catalysts with high activation are more suitable for this reactor.更多还原