共查询到19条相似文献,搜索用时 343 毫秒
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结合DQ型高效催化剂在液相本体法聚丙烯装置中的应用情况,分析了产品中产生过多细粉的原因.主要包括催化剂的粒径分布、催化剂的活化程度、预聚合程度、聚合反应速率、牌号切换、原料丙烯质量等.提出了选择合适的催化剂、优化催化剂预接触罐和反应器的操作、提高原料丙烯质量等改进措施. 相似文献
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在淤浆聚合条件下采用新型负载型非茂金属催化剂(SSTU)制备了超高相对分子质量聚乙烯(UHMWPE),考察了聚合温度、预聚合、助催化剂用量等聚合条件对催化剂活性、UHMWPE堆密度、粒径分布、粘均相对分子质量、力学性能、结晶性能和微观形貌等的影响.结果表明,提高聚合温度和助催化剂用量有利于催化剂活性发挥,而降低聚合温度和不预络合时可以得到高粘均相对分子质量的UHMWPE.由SSTU聚合得到的UHMWPE粒径分布均匀,细粉含量低(质量分数小于0.5%),结晶性能和力学性能好,在微观形貌上与齐格勒-纳塔催化剂制备的UHMWPE有显著区别. 相似文献
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研究了丙烯淤浆预聚合对聚丙烯(PP)性能的影响,试验过程中采用Ziegler-Natta催化剂,并使用三乙基铝作为助催化剂。结果表明,与不预聚相比,经过预聚PP的等规度、结晶度、熔点、结晶温度都有所提高,但熔体流动速率下降。预聚时加入外给电子体。可以提高PP的熔点和结晶度。在铝钛物质的量比为3/1~10/1范围内增加预聚合过程中的烷基铝用量。也可以提高PP的熔点和结晶度。提高预聚合温度。PP的结晶温度不下降。 相似文献
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据TaikabutsuOverseas报道,铝镁浇注料中有海水镁砂细粉,铝尖晶石浇注料中有烧结尖晶石细粉。两种浇注料均采用电熔刚玉作骨料,氧化铝水泥作结合剂。制备TC/S比为4和8的两种渣,抗渣试验在1650C下进行,保温4h。结果表明:(l)对于相同的MgO含量,铝镁浇注料的抗渣性比铝尖晶石浇注料好;(2)对于C/S为4和8的两种渣,铝尖晶石的浇注料的抗渣性随尖晶石加人量的增加只有很少的提高;(3)铝镁浇注料对C/S比高的渣,其抗渣性随ugo含量的增加有明显提高。铝镁浇注料和铝尖晶石浇注料的抗渣性比较@李荔寅… 相似文献
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针对环管工艺聚丙烯生产过程中出现的细粉较多,分析了预聚合的作用以及细粉含量增加的主要原因,对预聚合工艺提出了改进措施,达到降低聚合物中的细粉的目的,解决细粉对生产的影响. 相似文献
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中国石油化工股份有限公司(简称中国石化)开发出一种制备细粉含量少的聚乙烯催化剂新方法。该方法以铬金属化合物为活性组分,无机氧化物为载体,将浸渍好的催化剂前体用热风和红外组合干燥处理,再依次进行高温焙烧,还原,干燥,得到细粉含量少的聚乙烯催化剂。该方法克服了热风干燥的不均匀性,制备的催化剂平均粒径大且规整,极大减少了细粉含量,有利于高密度聚乙烯的生产。 相似文献
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The slurry prepolymerization of ethylene using TiCl4/MgCl2 as a catalyst was investigated. A 23‐factorial experimental design method was employed to study the effects of the temperature, hydrogen, and active cocatalyst‐to‐catalyst molar ratio (Al/Ti) on the catalyst activity, prepolymer melt flow index, and powder bulk density. All dependent variables increased when the active Al/Ti ratio increased from 1 to 2. The hydrogen–Al/Ti interaction had a significant effect on the prepolymer melt flow index and catalyst activity. The hydrogen (partial pressure ranging from 0.5 to 1.5 bar) and temperature (ranging from 60 to 80°C) variables as well as the hydrogen–temperature and hydrogen–temperature–Al/Ti interactions increased the prepolymer powder bulk density, which ranged from 0.11 to 0.373 g/cc. To find the reason for the prepolymer powder bulk density variation with the operating conditions, the particle size distribution and crystallinity of the prepolymers were determined. The increasing catalyst activity, ranging from 132 to 660 g of polyethylene/mmol of Ti, enhanced the weight percentage of fines, which ranged from 3 to 60, and decreased the average particle size, which ranged from 562 to 120 μm. This was the reason for the increasing prepolymer powder bulk density and could be due to the breakup of the prepolymer particles during prepolymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
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The initial state polymerization of propylene with Ziegler–Natta catalysts has been investigated and discussed at very low polymerization yields under adiabatic industrial prepolymerization conditions in diluted slurry regarding the effects of significant process parameters like monomer pressure, aluminum alkyl, and donor kind and concentration including the morphology of the catalyst/polymer particles formed. A sharp temperature increase in the first minutes of the initial state polymerization is followed by a temperature maximum and a slow decrease. With cocatalyst triethyl aluminum (TEAL), high prepolymerization yields were already achieved at a molar ratio TEAL/Ti of 3.0, remaining about constant until ratios of at least 300. The external donor dicyclopentyl dimethoxy silane leads to higher polymerization yields than the donor cyclohexyl dimethoxymethyl silane in the initial state polymerization too; however, both show a remarkable decreasing effect on polymerization yield above a specific molar ratio donor/Ti obviously correlated with the bulkiness of the alkyl groups. The particle size of the catalyst and the catalyst/prepolymer particles is increasing with polymerization yield until about 22 g PP/g Cat with particles almost perfectly spherical. The particle size distribution is rather broad at lower prepolymerization stages but unifying with lower polymerization rates at higher polymerization times. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
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Mehrdad Seifali Abbas-Abadi 《Designed Monomers and Polymers》2017,20(1):524-531
In the previous studies, the several halocarbons (HC) were tested as promoters for a Ti-based Ziegler–Natta (ZN) catalyst at different polymerization conditions. The Results showed that chloro cyclohexane has the best operation in catalyst activity, polymer particle size growth, hydrogen responsibility and wax reduction too. For the first time in this study, the effect of Al/Ti ratio on the optimum HC/Ti ratio has been considered and the results showed that the optimum HC/Ti ratio depends on the Al/Ti ratio directly. In the optimum HC/Ti ratio, the catalyst activity and hydrogen responsibility ratio of the catalyst increase up to 125 and 55% respectively. The acceptable growth of polymer powder up to 46%, lower flow rate ratio (FRR) up to 19% and decrease of wax amount up to 12%, completed the promotion results. Furthermore, in the next part of this study and as key note, a little dose of halocarbon was used in the catalyst preparation to produce the special catalysts with dual active sites. In the catalyst preparation, the concentration of each active sites depends on the halocarbon amount and it can control the molecular weight distribution of the produced polyethylene; because each active sites have different response to hydrogen. The halocarbon based catalysts showed the remarkable effect on the catalyst activity, the molecular weight and especially molecular weight distribution (MWD). The flow rate ratio and MWD could be increased up to 77 and 88% respectively as the main result of halocarbon addition during the catalyst preparation. 相似文献
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The prepolymerization effect on propylene polymerization in the presence of a TiCl3‐based catalyst, modified by di‐n‐buthyl ether, was studied. The influence of prepolymerization on the electron spin resonance spectra and morphology of the catalyst, as well as the properties and the morphology of both prepolymer and regular polymerization products, was investigated. The polymer morphology was evaluated through scanning electron microscopy, polymer bulk density, and particle size distribution. Some evidence of the enhancement effect of prepolymerization on the catalyst activity and stereospecificity was obtained. No influence from prepolymerization was observed on molecular weight and its distribution, melting point, and crystallinity of polypropylene. These findings, when discussed in connection with the morphology results of the catalyst and prepolymer, showed that the prepolymerization performed at mild reaction conditions prevents fast and extensive “fragmentation” of the original catalyst agglomerates. The more controlled breakup of the catalyst particles in the course of slowed growth of prepolymer exposes the occluded catalyst fragments with uniform size and prevents their reagglomeration. Resulting from the above, catalyst homogeneity, catalyst activity, and polymer morphology are improved. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 353–359, 1999 相似文献
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The bulk polymerization of propylene in liquid monomers with Ziegler‐Natta catalyst at 95°C is studied, using alkyl aluminum as the cocatalyst and dicyclopentyldimethoxysilane as the external donor. The highest catalyst activity is shown at the cocatalyst/Ti molar ratio of 300, which keeps relatively constant with the molar ratio increasing from 300 to 800. Besides, the catalyst activity is up to 65 kgPP/(gCat*h) in the range of cocatalyst/donor molar ratio from 12 to 16. The polymerization reaction rate curves with and without catalyst precontacting are similar, while the activity with catalyst precontacting are higher than that without precontacting. Furthermore, the kinetics of polymerization with and without prepolymerization are investigated in the range of the polymerization temperature from 70 to 95°C. It shows that at the high temperature, the polymerization rate increases with prepolymerization. Finally, the influence of prepolymerization at 95°C on the polymerization kinetics and particle properties is also described. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41816. 相似文献
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Liquid propylene was polymerized in a 5‐L autoclave batch reactor using a commercially available TiCl4/MgCl2/Al(ethyl)3/DCPDMS Ziegler–Natta catalyst, with a phthalate ester as internal electron donor. The powders from these polymerizations were characterized using laser diffraction particle size distribution (PSD) analysis, scanning electron microscopy (SEM), and bulk density measurements. These characteristics were analyzed as a function of the process conditions, including hydrogen and monomer concentration, polymerization temperature, and the prepolymerization method. It was shown that polymerization temperature influences the powder morphology to a large extent. At low temperatures, high‐density particles were obtained, showing regular shaped particle surfaces and low porosities. With increasing temperature, the morphology gradually was transferred into a more open structure, with irregular surfaces and poor replication of the shape of the catalyst particle. When using a prepolymerization step at a relatively low temperature, the morphology obtained was determined by this prepolymerization step and was independent from conditions in main polymerization. The morphology obtained was the same as that observed after a full polymerization at temperature. Even when using a short polymerization at an increasing temperature, the morphology was strongly influenced by the initial conditions. The effect of variation in hydrogen concentration supported the conclusion that the initial polymerization rate determines the powder morphology. In the absence of hydrogen, high bulk densities, and regularly shaped particles were obtained, even at high temperatures. With increasing hydrogen concentration, the reaction rates increased rapidly, and with that changed the morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1421–1435, 2003 相似文献
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采用溶胶凝胶法制备了一系列CuZnAlTi催化剂,采用X射线粉末衍射、N2吸附、H2程序升温还原、NH3程序升温脱附等方法对催化剂进行了表征,并将催化剂用于固定床CO加氢催化反应中,考察了钛铝比对催化剂结构和性能的影响。结果表明,催化剂中Al和Ti组分均以无定形或高度分散的形式存在;在CuZnAl催化剂中引入Ti组元,可以提高催化剂中CuO的分散度和催化剂的表面积和表面酸含量,减小催化剂的平均孔径,降低催化剂中CuO的被还原能力,从而改变了催化剂上CO加氢反应的产物分布。随着Ti/Al比增加,催化剂中CuO晶粒和平均孔径呈现先减小后增大的趋势,而催化剂的比表面积和还原峰顶温度呈现先升后降的趋势,CO转化率与Ti/Al比间没有一定的顺变关系。 相似文献
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以TiCl4/Al(i-Bu)3为引发体系,用本体预聚合法引发1-十二烯聚合,制备高减阻性能的油溶性减阻剂。研究了二苯基二甲氧基硅烷(DDS)、预聚与后聚单体体积比、预聚温度和预聚时间对聚合物减阻性能的影响。结果表明,在优化的合成工艺条件下,能够合成减阻率为50.67%,增输率为48.1%的聚合物(添加量为10 mg/L)。通过IR、GPC和1H-NMR分析表明:转化率接近100%,重均相对分子质量Mw为3.58×106、相对分子质量分布宽度指数Mw/Mn为4.44。采用预聚工艺较本体直接聚合可以节省主催化剂用量达40%以上。 相似文献