环管工艺生产聚丙烯过程细粉产生的原因分析

Spheripol环管工艺占我国聚丙烯生产能力的一半以上,该工艺具有转化率高、生产能力大等优点.然而,我国大多数环管装置均不同程度上存在生产过程中经常性出现细粉,影响产品质量以及造成生产不正常的缺陷.结合笔者多年相关的研究,对相关工艺细粉产生的原因进行分析,并提出了一些改进措施.     

双峰聚乙烯的生产

介绍了双峰聚乙烯的生产技术和工艺，生产用催化剂和投资情况，以及双峰聚乙烯的主要生产厂家。     

LDPE细粉产生的原因及控制措施

分析了低密度聚乙烯(LDPE)细粉产生的可能原因:LDPE在生产过程中挤出切粒不良,颗粒脱水干燥,气力输送碰撞摩擦,颗粒外观不良等。通过加强相关设备管控,控制LDPE颗粒外观,选择合适的气力输送系统,增加除尘设备等措施,可以减少和降低最终产品中的细粉含量,对LDPE质量提升有一定借鉴意义。     

双峰聚乙烯的生产技术及市场前景

介绍双峰聚乙烯的性能特点和用途,阐述双峰聚乙烯的生产工艺、催化剂的研究开发进展以及国内外生产概况,提出了发展我国双峰聚乙烯生产的一些建议。     

双峰聚乙烯的生产技术及市场前景

介绍双峰聚乙烯的性能特点和用途,阐述双峰聚乙烯的生产工艺、催化剂的研究开发进展,以及国内外生产概况,提出了发展我国双峰聚乙烯生产的一些建议。     

我国双峰聚乙烯生产发展迅速

上海石化公司25万t/a全密度双峰聚乙烯装置生产的双峰聚乙烯树脂不仅使产品有优良的物理机械性能，而且大大改善了其加工性能，在强度、稳定性、低收缩性、抗开裂性等方面有着其他产品不可替代的优点。该装置可生产薄膜、吹塑、挤出涂层、管材、电缆护套料和注塑等六大类的高性能塑料专用料。其中第三代聚乙烯管材料PE100是国内惟一能制造高压燃气管道的聚乙烯专用料，在充分保证强度的同时，可大大降低管道的壁厚，节约大量材料。该装置生产的电缆护套料加工生产的电缆无故障，工作时间比传统产品提高4倍以上。     

聚丙烯装置细粉产生的原因分析

从催化剂和工艺操作2方面分析了聚丙烯装置生产中细粉产生的原因,以及细粉过多时对生产的危害。结果表明,催化剂细粉含量高、运输、制备、破碎,汽蒸系统、干燥系统操作不当,反应器出口没加或少加失活剂是细粉产生的主要原因;细粉产生的过多,干燥效果差、风送系统运转困难、引起工艺系统的堵塞、影响设备的使用寿命。提出了相应解决办法及注意事项。     

双峰聚乙烯的生产技术及工艺

简要介绍了聚乙烯树脂技术发展历程和对产品性能的要求,国内外石化企业双峰聚乙烯生产技术进展概况及生产双峰聚乙烯产品所使用的３种方法,重点介绍了串联反应釜生产工艺,并以ＵｎｉｐｏｌⅡ和Ｂｏｒｓｔａｒ技术为例,对其工艺流程、技术特性作了论述。     

双峰聚乙烯生产技术的优化

分析了双峰聚乙烯装置运行中存在的主要问题,根据双峰工艺技术特点,从流化床参数控制、产品牌号切换、催化剂切换、在线色谱分析等方面采取了优化措施。严格控制流化床的乙烯分压和乙烯分压的增长速率、1-丁烯的加入速率、流化密度、流化速率、气相反应器入口温度以及反应温度变化率,并对在线色谱进行改造,增加了一个旋风分离器。通过优化,提高了流化床参数控制的稳定性,避免了块料的产生,实现了长周期运行的目标。     

Crosslinking of bimodal polyethylene

Two bimodal polyethylenes, differing only in polymerisation order, were investigated with respect to crosslinking behaviour and network properties. The crosslinked materials were examined using size exclusion chromatography (SEC), gel-content measurements, and calculations of the network density. Dynamic mechanical analyses in the melt were performed to monitor the crosslinking and to provide another measure of the network density. The experiments were performed to investigate any potential influence of the polymerisation order on the crosslinking as well as to study the network formation in the crosslinked polymers. The bimodal polyethylenes were also compared to two monomodal polyethylenes representing the short chain branched, high molecular weight fraction, and the linear, low molecular weight fraction, respectively. The SEC measurements clearly showed how the crosslinking starts with the consumption of the high molecular weight fraction. The gel-content measurement showed the importance of a high molecular weight material for the gel formation. The network density calculations demonstrated how long chains can give rise to apparent networks which are mainly due to chain entanglements. The experiments showed that the polymerisation order for the bimodal polyethylenes has no effect on the crosslinking.     

Simulation study of production of fine ceramic powders in a cyclone reactor

A numerical simulation study of production of fine ceramic powders in an innovative vapor-phase aerosol reactor is described. Arrangement is typical of reverse-flow cyclone equipment; no similar device is present in current scientific literature and industrial technology. The cyclone reactor has a potential technological application as it realizes process intensification by two simultaneous operating advantages: (i) curly flow reduces recirculation of as-synthesized particles towards flame region, and (ii) cyclone arrangement segregates large particles. As a result, ceramic powders with narrower particle size distribution can be produced with regard to traditional equipment. The study is based on the re-modeling of an existing industrial reactor for production of fine TiO₂ according to a cyclone configuration; particle size distributions from simulation and plant are compared.     

双金属中心双峰聚乙烯催化剂研究进展

双峰聚乙烯因兼具优良的加工性能和优异的力学性能,被广泛应用于PE100、PE100RC等高等级管材的生产,其在聚乙烯市场中的地位越来越重要。目前工业上基本采用双釜串联工艺生产双峰聚乙烯,该工艺设备投资及能耗较高,且均被国外公司垄断。相比之下,单釜双峰工艺因采用双金属中心催化剂在单一反应器中生产双峰聚乙烯,其设备投资和操作费用更低,且更加绿色环保,因而成为近年来国内外研究的热点。综述了本课题组近期基于铬系催化剂开发的新型双金属中心双峰聚乙烯催化剂,同时对其他双金属中心聚乙烯催化剂进行了介绍,并对该领域的未来发展进行了展望。     

双峰PE树脂的结构与性能

研究了国产催化剂和进口催化剂分别生产的同一牌号双峰聚乙烯树脂的结晶性能和流变行为,表征了其相对分子质量及其分布.2种树脂的力学性能差异可归结为其相对分子质量及其分布和结晶性能的不同:国产催化剂生产的树脂要达到同进口催化剂生产的树脂一样的流变行为,模头温度必须达到200℃以上.     

Hopper-valve for fine powders in a moving-bed standpipe

In this paper, a new valve for Geldart-A powder, so-called hopper-valve, is presented. The method of its design, the range of operation, and the method of monitoring are also discussed in detail.     

基于催化剂颗粒停留时间分布的双峰聚乙烯牌号切换优化

针对环管-流化床串联的Borstar双峰聚乙烯工艺,建立了包括催化剂切换在内的双反应器串联牌号切换模型,使产品牌号的切换时间最短、过渡料数量最少。同时,推导了双反应器串联工艺中,存在催化剂切换时各反应器内聚合物的瞬时与累积性能指标（熔融指数与密度）的模型。研究表明,对于涉及催化剂切换的牌号切换,最优策略是采用催化剂分步进料方式,综合考虑新旧催化剂对操作参数的不同要求及各反应器内残留原催化剂比重对最终产品性能的影响,从而达到明显缩短切换时间、有效抑制操作变量急剧变化、平缓产品性质变化轨迹的优化目的。     

双峰PE生产工艺对其结晶行为和力学性能的影响

采用高温液相凝胶渗透色谱仪、广角X射线衍射仪和拉力机,研究了双峰聚乙烯(PE)生产中环管反应器和气相反应器的工艺参数对双峰PE产品的结晶行为和力学性能的影响。结果表明:环管反应器聚合产物的结晶度随停留时间的延长而减小,气相反应器产物的结晶度随n(H2)/n(C2H4)下降、n(1-C4H8)/n(C2H4)增大和床层分配率增加而减小,双峰PE的拉伸屈服应力和拉伸弹性模量随其结晶度和相对分子质量增加而减小。     

Simulations of vibrated fine powders

During the past few decades, several studies have been conducted to understand the behaviour of powders in vibrated beds. This paper introduces a technique of incorporating the agglomeration and deagglomeration phenomena in the simulation of vibrated fine powders. Two-dimensional direct simulations are performed using 300 spheres 2.99 mm in diameter in a trapezoidal container vibrated vertically at an amplitude of 2.5 mm and 20 Hz frequency as preliminary conditions. Under non-cohesive conditions, the results are in agreement with those found in the literature. As a preliminary effort to predict the behaviour of cohesive fine powders under vibrated conditions, agglomeration and deagglomeration processes are modelled as the formation and destruction, respectively, of interparticle bonds during particle collisions. Two parameters used to model agglomeration and deagglomeration are the ease of cohesion and cohesivity of the powder. Dependencies of these parameters on certain physical properties of cohesive powders have been suggested. Simulation results reveal two aggregate populations, one with uniform size aggregates and another population with multi-sized aggregates. The former aggregates were more prevalent in weakly cohesive powders while the latter in highly cohesive powders. Interesting macroscopic bed behaviour such as alternating cycles of agglomeration and deagglomeration were also observed. Further work is needed in which the aerodynamic forces are taken into account and cohesion mechanisms at the particle surface are modelled.