国外聚乙烯催化工艺研究进展

聚乙烯(PE)以其性优、价廉的优势,成为通用合成树脂中产量最大的品种,主要包括低密度聚乙烯(LDPE)、线性低密度聚乙烯(LLDPE)、高密度聚乙烯(HDPE)、中密度聚乙烯(MDPE)、以及一些具有特殊性能的专用料树脂。催化剂是聚烯烃工业的核心,通过调控活性中心和改善聚合工艺,提高了催化剂活性,完善了所得聚烯烃的性能,推动了聚乙烯工业的蓬勃发展。研发特殊性能或优异性能聚烯烃树脂的催化剂,是目前聚烯烃领域关注的焦点。本文对近年来国外聚乙烯催化剂的研究进展进行了综述,重点阐述了目前研究开发中的催化工艺,涵盖了Ziegler-Natta催化剂、铬催化剂、茂金属催化剂、过渡金属催化剂以及制备双峰或宽峰分布聚烯烃的复合催化剂等;对各类新型催化剂的制备方法和工艺特点进行了总结,同时指明了相关工艺的研发公司,以便国内相关研究部门借鉴。     

淤浆法双峰聚乙烯工艺及催化剂的研究进展

分子量分布呈双峰或宽峰的聚乙烯具有良好的物理机械性能和加工性能,是聚乙烯高性能化的发展方向之一。在制备双峰聚乙烯方面,两个或多个反应器的串联工艺是目前最为成熟和经济的生产方式。本文介绍了用于生产双峰聚乙烯的Basell公司的Hostalen工艺、三井化学公司的CX工艺和INOES公司的Innovene-S工艺,比较了三种工艺装置的特点,重点指出了三种工艺装置在生产双峰聚乙烯产品方面的优势和缺点,为国内引进该类工艺装置提出了建议。此外,本文还对应用于三种工艺的催化剂的研究发展情况进行了述评,对催化剂的性能特点进行了分析比较,并指出了目前双峰聚乙烯催化剂的开发方向。     

汽车用聚烯烃材料单一化关键技术研究

介绍了我们在聚丙烯釜内合金的催化剂制备、聚合工艺、结构性能关系和加工应用等方面的研究成果。以新型给电子体Ziegler-Natta催化剂和Ziegler-Natta/茂金属复合催化剂为基础,在中国石油自己的聚丙烯中试装置上成功制备出从高刚到高韧的三个釜内合金基础树脂,以此开发出系列汽车用聚丙烯专用料,并对专用料的成型与汽车制件的应用进行了研究。本研究成果为聚丙烯釜内合金树脂在汽车塑料中的广泛应用奠定了技术和产业基础。     

一种新型MAO改性的高活性铬基气相聚乙烯催化剂

制备了一种新型的CrO3／SiO2／MAO(／EtOAlEt2)乙烯聚合催化剂，在微机控制的自动评价装置上进行了乙烯气相聚合评价试验，研究了催化剂制备中有机铝化合物对催化剂的改性作用．结果表明，MAO作为还原剂可以明显提高催化剂的聚合活性，显著影响乙烯聚合反应动力学，得到的聚乙烯树脂融体流动速率较低．同时采用MAO和EtOAlEt2作为还原剂制备催化剂时，二者具有显著的协同效应，催化剂聚合活性高，临氢效应敏感高，树脂的融体流动速率高．     

高分子负载钯催化剂对丙烯酸甲酯加氢反应的研究

制备了商品化的强碱阴离子交换树脂D296,D261,弱碱阴离子交换树脂D370,螯合树脂D401,强酸阳离子交换树脂D61,D72,D001-CC,干氢催化树脂及交联聚丙烯腈,聚N-乙烯基吡咯烷酮负载钯催化剂,考察了它们对丙烯酸甲酯加氢反应的催化性能。实验结果表明,它们都能以较高的催化活性将丙烯酸甲酯完全转化为丙酸甲酯,是制备高纯丙酸甲酯的优良催化剂。     

高结晶聚丙烯(HCPP)的研发和产业化进展

高结晶聚丙烯一般采用高等规度聚丙烯加入成核剂制备。本文较全面地综述了制备高结晶度聚丙烯的催化剂体系及其制备技术。高等规度聚丙烯可以通过传统Ziegler-Natta聚丙烯催化剂与合适的外给电子体搭配制备,也可以通过选取具有合适结构的茂金属化合物制备。目前,聚丙烯工艺主要使用传统Ziegler-Natta催化剂。本文介绍了生产高结晶度聚丙烯的主要生产厂家、牌号和生产工艺,如Spheripol环管/气相工艺、Unipol气相工艺、Novolen气相工艺I、nnovene气相工艺、Hypol釜式本体工艺等,展望了高结晶度聚丙烯的应用前景,认为高结晶聚丙烯是PP新产品开发及高性能化的重要途径之一,具有非常广阔的市场前景,对于我国高结晶度聚丙烯牌号的开发具有较大的意义。     

乙烯反应中的铁配合物催化剂：从概念到产业化

聚烯烃的核心是催化剂,地球上丰度最高的过渡元素铁的配合物在催化乙烯反应中展示了优异性能,本文综述了用于乙烯低聚与聚合的铁配合物催化剂的最新进展.通过调控所用配体的电子效应和空间位阻可以实现乙烯催化性能与所得聚合物微观结构的控制;铁催化剂具有独特的优势,不仅实现α-烯烃制备,而且可以制备高度线性聚乙烯包括制备窄分布的聚乙烯蜡.铁催化剂未来将在高附加值聚乙烯有巨大应用潜力.     

镍配合物催化乙烯低聚/聚合的研究进展

催化乙烯低聚或聚合的镍配合物催化剂研究,不仅帮助提供探索乙烯配位聚合机理的催化剂模型,更为重要的帮助探讨不同催化剂模型下的催化剂活性和选择性,为工业界寻找具有潜在应用价值的高效催化剂奠定基础.同时,利用镍配合物催化剂容易导致所得聚烯烃树脂产生支链的特点,有望制备具有优异性能的支化聚烯烃树脂.本文综述了近年来镍配合物在乙烯低聚或聚合催化剂研究方面的进展,并特别强调了催化剂结构和催化性能之间的内在规律.     

磺酸型树脂固定床连续催化二壬基酚烷基转移反应的研究

以壬基酚装置精馏塔釜底液为原料,以磺酸型聚苯乙烯阳离子交换树脂为催化剂,采用常压固定床连续工艺,开展二壬基酚与苯酚的烷基转移反应研究制取壬基酚。分别采用红外光谱、差热热重分析、催化剂颗粒强度测试等表征方法对催化剂的组成、热稳定性及力学性能进行研究。考察了反应温度、原料配比、质量空速和反应时间等因素对催化性能的影响。结果表明,所制备的树脂具有良好的热稳定性和耐压强度,适用于180℃以下的固定床连续反应工艺。在反应温度为160℃、原料质量空速为1h~(-1)、苯酚与二壬基酚质量比为3:1的条件下,二壬基酚转化率达85.9%~90.6%,壬基酚收率达56.8%~67.2%,催化剂稳定性好,连续反应200h催化性能仍保持稳定。     

载镍炭化树脂催化剂的制备──树脂预处理及交换对炭化树脂表面性能的影响

球形炭化树脂作为催化剂载体具有许多独特的优点，为炭素材料催化剂开拓了新的前景。在诸多炭化树脂催化剂的制备方法中，离子交换－炭化法具有许多优点，是重要的制备方法之一。本文从Ｄ１５２大孔弱酸阳离子交换树脂为前驱载体，用不同的预处理方法先制成钙型Ｄ１５２树脂（Ｃａ／Ｄ１５２），然后同Ｎｉ的ＮＨ３－ＮＨ４＋水溶液、乙醇水溶液进行离子交换，再经炭化后制成了高分散度、高强度的栽体镍炭化树脂（Ｎｉ／Ｃ）催化剂。本文对各种制备条件与（Ｎｉ／Ｃ）催化剂的结构性能的关系进行了讨论。     

Strain hardening test on the limits of Slow Crack Growth evaluation in high resistance polyethylene resins: Effect of comonomer type

Long term performance assessment of polyethylene pipes is an issue that has greatly increased in importance in recent years due to the incorporation in the market of high resistance to crack polyethylene grades (PE100RC), where established Slow Crack Growth (SCG) evaluation using traditional tests such as Full Notch Creep Test (FNCT) or Pennsylvania Notch Tensile (PENT) Test is insufficient. The development in recent years of fast evaluation techniques such as Strain Hardening (SH) modulus has opened an important alternative for quick SCG evaluation since it correlates well with other conventional tests such as FNCT and PENT. In this work, a large number of commercial and experimental polyethylene pipe resins with different comonomer types were evaluated in order to define their SH values to rank the resins as PE100 or PE100RC. A relationship is proposed that utilizes SH test results to estimate the SCG resistance of PE pipes. 1-Butene copolymer resins display threshold SH values of 38 and 53 MPa that have been assigned to PE100 and 100RC grades, respectively. Moreover, dependence of the SH values on comonomer type used has been demonstrated. The experimental results show that 1-hexene copolymer resins exhibit higher SH values than 1-butene comonomer based resins.     

Prediction of the remaining lifetime of polyethylene pipes after up to 30 years in use

Plastics pipes made of polyethylene (PE) play an outstanding role in gas and water supply. While for modern pipe grades typical lifetimes of 50 years are taken for granted and service times of 100 years are discussed, pipes made of PE with a lower performance have been used for decades. As the repair and rehabilitation of existing pipe systems involve immense costs, the question of their qualitative condition has to be considered. In this paper, four different pipes used in the gas and water distribution in Austria with an age up to 30 years have been investigated. After a morphological and mechanical study, particular attention was paid to material stabilization, which is essential for long-term applications. Fracture mechanics tools have been used to gain information on the resistance to crack initiation and slow crack growth. Furthermore, a fracture mechanics extrapolation procedure has been applied to predict the remaining lifetime of the pipes. The results have indicated that all the pipes investigated are still in a very good condition and are likely to be sufficiently safe to remain in use.     

Using developed creep constitutive model for optimum design of HDPE pipes

Unlike metal pipes, high density polyethylene (HDPE) pipes are not susceptible to erosion and corrosion. However, the most important mechanical feature of the HDPE pipes is that this material creeps even at room temperature. Therefore, it is essential to study the creep behavior of this material in order to develop a model. In this paper, creep behavior of HDPE at different temperature and stress levels has been experimentally studied to obtain the creep constitutive parameters of the material. These parameters are used to predict the creep behavior of different structures such as HDPE pipes. For this purpose, a number of specimens have been machined from industrial manufactured pipe walls. Uniaxial creep tests have been carried out and creep strain curves with time for each test were recorded. Then, a constitutive model is proposed for HDPE based on the experimental data and optimization methods. The results of this model have been compared with the test data and good agreement is observed. The developed constitutive model and reference stress method (RSM) were used to produce graphs which provide optimum creep lifetime and design conditions for HDPE pipes that are subjected to combined internal pressure and rotation. These graphs can facilitate the design process of HDPE pipes.     

Multi-Layer Pipes for Hydrocarbons Conveyance

The replacement of metals with plastics in piping systems is a well established practice in a vast range of public and industrial applications. However, difficulties still exist, mainly related to the limited chemical resistance of the polymers commonly used in pipe manufacturing to some conveyed fluids. This prevents using plastic pipes in important applications such as the transport of liquid hydrocarbons, particularly in oil fields. The use of chemically resistant polymers, such as fluorinated polyolefins, is precluded by high cost and poor mechanical properties. Co-extrusion of multi-layer pipes carrying an internal chemically resistant liner can be a viable alternative capable to extend the use of plastic pipes to refining and chemical industries. An experimental PE/PA multi-layer pipe has been developed whose resistance to diffusion and mechanical properties have been tested. Tests in real oil fields confirm the good performance of the new pipes.     

Classifying formulations of crosslinked polyethylene pipe by applying machine‐learning concepts to infrared spectra

Crosslinked polyethylene (PEX‐a) pipes are emerging as promising replacements for traditional metal or concrete pipes used for water, gas, and sewage transport. Understanding the relationship between pipe formulation and performance is critical to their proper design and implementation. We have developed a methodology using principal component analysis (PCA) and the machine learning techniques of k‐means clustering and support vector machines (SVM) to compare and classify different PEX‐a pipe formulations based on characteristic infrared (IR) spectroscopy absorbance peaks. The application of PCA revealed that a large percentage (89%) of the total variance could be explained by the first three principal components (PC1‐PC3), with distinct clustering of the data for each formulation. By examining the contribution of the individual IR bands to the PCs, we determined that PC1 could be attributed to different peroxide crosslinkers, whereas PC2 and PC3 could be attributed to differences in the additives. Using the PCA results as input to k‐means clustering and SVM resulted in very high accuracy of classifying the different pipe formulations. Our approach highlights the advantages of using PCA and machine learning techniques to characterize different formulations of PEX‐a pipes, which is important to achieve a detailed understanding of the pipe formulation and manufacturing process. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1255–1262     

NMR imaging of polyethylene pipes

¹H nuclear magnetic resonance (NMR) imaging techniques have been used to image the extrusion aid (EA) in polyethylene (PE) pipe samples. The resulting two-dimensional images show the distribution of EA within the pipe. EA is found to be uniformly distributed in a normal pipe. Examples of degraded pipes, due to exposure to extreme conditions, show migration of EA to the pipes' wall surfaces. NMR images of a normal pipe and two examples of damaged pipes are presented. The imaging technique and the results are discussed. © 1995 John Wiley & Sons, Inc.     

固体酸催化醇酸树脂的分子量分布及其与性能关系的研究

本文用HPGPC法等研究了固体酸催化醇酸树脂合成中MWD及其与性能的关系。结果表明,固体酸催化醇酸树脂化过程的MWD等物性变化规律与未加催化剂的相似,logM_w和logd与p、M_w与分散度d及logη_G与M_w之间均呈线性关系。然而在达到同样M_w和MWD时,催化新工艺所需时间大大缩短,所需温度也有较大下降,而所得树脂粘度较低,贮存稳定性更好,其成膜干性更好,漆膜硬度也较高。     

A survey of methods for the detection of thermal oxidation in high-density polyethylene pipes

Seven methods for the detection of thermal oxidation of the inner wall surface of high-density polyethylene (HDPE) pipes are presented. The methods presented include infrared spectroscopy, polarized light microscopy, differential scanning calorimetry, scanning electron microscopy, gloss measurements and uniaxial creep tests. These tests have been developed on the basis of earlier reported data for a large number of PE pipes. The tests are compared with each other and with the internal pressurizing test with respect to reliability of results, the time taken to determine whether or not a pipe is oxidized, the experimental difficulties, costs, etc.     

Residual stress in polyethylene pipes

This paper deals with residual stress in polyethylene (PE) pipes as an important factor that influences their lifetime. Residual hoop stress distribution in a PE pipe was determined using a methodology previously carried out by the authors on polypropylene pipes. Axial residual stress magnitude was determined by comparison of experimental data and finite element modelling. Based on the obtained results, a new simplified methodology for determining the residual hoop stress is proposed. The method needs only one circular specimen made of pipe, but, unlike older methods, provides a more precise estimation of residual hoop stress distribution taking into account its exponential shape. Some older results from literature are recalculated using this method and residual hoop stress of various PE pipe grades and dimensions are then compared. To provide an idea of residual hoop stress influence on lifetime of a pipe, a lifetime estimation is carried out for the examined pipe.     

Deterioration of polyethylene pipes exposed to water containing chlorine dioxide

Chlorine species used as disinfectants in tap water have a deteriorating effect on many materials including polyethylene. There are only very few scientific reports on the effect on polyethylene pipes of water containing chlorine dioxide. Medium-density polyethylene pipes stabilized with hindered phenol and phosphite antioxidants were pressure tested with water containing 4 ppm chlorine dioxide at 90 °C and pH = 6.8 as internal medium. The stabilizers were rapidly consumed towards the inner pipe wall; the rate of consumption was four times greater than in chlorinated water (4 ppm, pH = 6.8) at the same temperature. The depletion of stabilizer occurred far into the pipe wall. A supplementary study on a polymer analogue (squalane) containing the same stabilizer package showed that the consumption of the phenolic antioxidant was 2.5 times faster when exposed water containing chlorine dioxide than on exposure to chlorinated water. The subsequent polymer degradation was an immediate surface reaction. It was confirmed by differential scanning calorimetry, infrared spectroscopy and size exclusion chromatography that in the surface layer which came into contact with the oxidising medium, the amorphous component of the polymer was heavily oxidized leaving a highly crystalline powder with many carboxylic acid chain ends in extended and once-folded chains. Scanning electron microscopy showed that propagation of cracks through the pipe wall was assisted by polymer degradation.