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聚合反应

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Polymerization 聚合反应 - 搅拌技术
 

Polymerization comprises a vast field of applications. EKATO has specialized in optimizing existing mixing solutions as well as in Joint Developments from Laboratory to Industrial Scale.
        聚合反应有大量的应用领域。 EKATO专业于现有搅拌技术方案的优化和从实验室到工业规模装置的联合开发。

We have decades of experience in designing based on Licensor's engineering specification including comprehensive documentation, too.
        几十年来, w88优德官网有按专利商的工程规范进行设计和编制综合文件的经验。

EKATO has a wide range of experience in emulsion-, solution- and suspension polymerization and can support with process and engineering know-how. The range goes from well-known polymers like HDPE, PET, PP or PVC to specialties or still to be commercialized Green Polymers. 
        EKATO在乳液聚合、溶液聚合和悬浮聚合方面有广泛的经验, w88优德官网可以提供工艺和工程专用技术的支持, 品种从众所周知的如 HDPE、 PET、PP 和PVC 到一些特殊的品种或还在商业开发中的绿色聚合物。

 

Emulsions polymerization 乳液聚合

In emulsion polymerization, the water-insoluble monomer is predispersed in an aqueous phase. In contrast to bead polymerization, the dispersion is not stabilized physically by turbulence, but chemically using emulsifiers. Polymerization does not take place in the dispersed monomer droplets, whose diameter is 10–1000 μm, but in the much smaller latex particles with diameters of about 0.3–0.8 μm. These contain both polymer and monomer molecules and are surrounded by emulsifier molecules that stabilize them against the aqueous phase. Owing to the small particle size, the heat of reaction can easily be dissipated into the aqueous phase. Heat transfer between the vessel wall and the aqueous phase is very good on account of the low viscosity of the emulsion and the high thermal conductivity of water.


在乳液聚合中,水不溶性单体预分散在水相中。 与珠粒聚合相反,分散体不是通过湍流物理稳定,而是使用乳化剂化学稳定。 聚合不发生在直径为10-1000μm的分散的单体液滴中,而是在直径为约0.3-0.8μm的小得多的胶乳颗粒中发生。 它们含有聚合物和单体分子,并被乳化剂分子包围,乳化剂分子使它们相对于水相稳定。 由于粒径小,反应热可以很容易地消散到水相中。 由于乳液的低粘度和水的高导热性,容器壁和水相之间的传热非常好。


Solvent Polymerization 溶液聚合

In homogeneous solvent polymerization, the viscosity is lowered by adding a chemically inert solvent. Both the monomer and the polymer are present in solution during the entire process. In many cases, heat removal is improved by simultaneous evaporative cooling induced by boiling off the solvent.


在均相溶剂聚合中,通过添加化学惰性溶剂降低粘度。 在整个过程中单体和聚合物都存在于溶液中。 在许多情况下,通过煮沸溶剂引起的同时蒸发冷却来改善除热。


Suspension Polymerization 悬浮聚合

There are two different types of suspension polymerization:

  • Pearl polymerization: neither the polymer nor the monomer are soluble in the carrier liquid so that polymerization takes place inside the monomer droplets (diameter 10–1000 μm).
  • Precipitation polymerization: the monomer is dissolved in the carrier liquid, whereas the polymer is not soluble and thus precipitates during polymerization.

Primary polymer particles usually have a diameter of approx. 1 μm. These particles agglomerate to porous secondary particles with a diameter of 100–200 μm. The solid particles have a tendency to stick together (coagulate) in certain polymerization phases and thus have to be separated again by shear forces in a flow field. 

 

有两种不同类型的悬浮聚合:

        珍珠聚合:聚合物和单体都不溶于载液,因此在单体液滴(直径10-1000μm)内发生聚合。
        沉淀聚合:单体溶解在载液中,而聚合物不溶,因此在聚合过程中沉淀。
        初级聚合物颗粒通常具有约的直径。 1微米。 这些颗粒聚集成直径为100-200μm的多孔二级颗粒。 固体颗粒具有在某些聚合相中粘在一起(凝结)的趋势,因此必须通过流场中的剪切力再次分离。


HIPS (High Impact Resistant Polystyrene) 高抗冲聚苯乙烯

Equipment to produce high-impact polystyrene (HIPS) generally consists of a cascade of three to five reactors, divided into pre-polymerization and post-polymerization stages. In the pre-polymerization stage, the target morphology and particle size are already essentially predefined. The reaction is generally carried out at 100–150 °C with yields of up to 15–30 %. During post-polymerization, the polymerization reaction is continued to give higher yields with correspondingly higher viscosities. Post-polymerization is usually carried out at temperatures of 140–190 °C.
        生产高抗冲聚苯乙烯(HIPS)的设备通常由三至五个反应器的级联组成,分为预聚合和后聚合阶段。 在预聚合阶段,目标形态和粒度已基本预定义。 反应通常在100-150℃下进行,产率高达15-30%。 在后聚合期间,继续聚合反应以获得更高的产率和相应更高的粘度。 后聚合通常在140-190℃的温度下进行。

In the reactor cascade, the heat of polymerization is removed by evaporating the styrene monomer. The gaseous monomer is then condensed and fed back into the reactor. This type of heat removal requires high homogeneity and good surface entrainment. For this reason, these reactors are often equipped with the Ekato Paravisc. Temperature homogeneity is the key variable influencing the molecular weight distribution and thus the attainable product quality. 
        在反应器级联中,通过蒸发苯乙烯单体除去聚合热。 然后将气态单体冷凝并送回反应器。 这种类型的散热需要高均匀性和良好的表面夹带。 出于这个原因,这些反应堆通常配备有Ekato Paravisc。 温度均匀性是影响分子量分布的关键变量,因此影响可达到的产品质量。


橡胶Rubber

Polybutatien(丁基橡胶)Polybutatien (Butyl Rubber)

Polybutadiene (butyl rubber) is used as a synthetic rubber, particularly for the treads of car tyres. It is almost exclusively produced by solution polymerization using Ziegler-Natta catalysts. Toluene is the most commonly used solvent.
The mixing requirements for the reaction are good homogenization and axial flow to ensure rapid equalization of concentration and temperature gradients.
聚丁二烯(丁基橡胶)用作合成橡胶,特别是用于汽车轮胎的胎面。 它几乎完全由使用齐格勒 - 纳塔催化剂的溶液聚合制备。 甲苯是最常用的溶剂。
反应的混合要求是良好的均质化和轴向流动,以确保浓度和温度梯度的快速均衡。

 

 

IIR(异丁烯 - 异戊二烯橡胶)IIR (Isobutene-Isoprene Rubber)

Isobutylene-isoprene rubber (IIR) is a copolymer of isobutylene and isoprene. This material is used for high-performance, long-distance car tyres.
To achieve a high molecular weight, the strongly exothermic reaction must be carefully controlled at very low temperatures as low as –90 °C to –100 °C. The most commonly used process for synthesising IIR is low-temperature cationic polymerization.

This type of polymerization involves generating a suspension of very fine rubber particles in methyl chloride. Because the reaction is very exothermic, the reactor is designed as a draft tube with very high axial flow rates. The cylindrical chamber of the reactor is equipped with tube bundle heat exchangers. In addition, the extremely fast reaction necessitates fast homogenization of the material feeds. The impeller is introduced from below, which requires the corresponding submerged seal with flushing device. 
 

        异丁烯 - 异戊二烯橡胶(IIR)是异丁烯和异戊二烯的共聚物。 该材料用于高性能长途汽车轮胎。
        为了获得高分子量,必须在低至-90°C至-100°C的极低温度下小心控制强放热反应。 最常用的合成IIR的方法是低温阳离子聚合。

        这种类型的聚合包括在氯甲烷中产生非常细的橡胶颗粒的悬浮液。 因为反应是非常放热的,所以反应器设计成具有非常高的轴向流速的引流管。 反应器的圆柱形腔室配备有管束式热交换器。 此外,极快的反应需要快速均质化进料。 叶轮从下方引入,这需要相应的浸没式密封和冲洗装置。


聚酯和PET(聚乙烯对苯二甲酸酯)Polyester und PET (Polyethylenterephthalat)
 

Polyesters are synthesised by condensation polymerization (or polycondensation) of polyfunctional carboxylic acids with polyfunctional alcohols. Polycondensation, in which water is always a product, is endothermic, in contrast to other classical polymerization reactions. Shifting the chemical equilibrium of the reversible reaction to the side of the polyester requires that the water produced by the condensation reaction is continuously removed from the reaction mixture. At high viscosities, water can only be removed by evaporation from the surface of the reaction mixture. This means that the contents of the reactor must be efficiently circulated using axial pumping impellers with a small wall clearance to achieve high degrees of polymerization. Whereas a purely radial pumping agitator produces high polymerization degrees only close to the surface, this can be achieved throughout the reaction vessel if there is also axial exchange. The axial flow can be improved significantly by using a draft tube.

Thermoplastic polyesters, especially polyethylene terephthalate, are economically important materials that are used to manufacture fibres and bottles. One group of polycondensates, the polycarbonates, are gaining importance as high-performance plastics. 

 

        通过多官能羧酸与多官能醇的缩聚(或缩聚)合成PPolyesters。与其他经典聚合反应相比,其中水总是产物的缩聚是吸热的。将可逆反应的化学平衡转移到聚酯侧需要从反应混合物中连续除去由缩合反应产生的水。在高粘度下,水只能通过从反应混合物表面蒸发除去。这意味着必须使用具有小壁间隙的轴向泵送叶轮有效地循环反应器的内容物以实现高聚合度。尽管纯径向泵送搅拌器仅在靠近表面处产生高聚合度,但如果还存在轴向交换,则可在整个反应容器中实现。通过使用引流管可以显着改善轴向流动。

        热塑性聚酯,特别是聚对苯二甲酸乙二醇酯,是用于制造纤维和瓶子的经济上重要的材料。一组缩聚物,即聚碳酸酯,作为高性能塑料越来越重要。


HDPE  (High-Density Polyethylen 高密度聚乙烯)

Precipitation polymerization of HDPE is carried out at low pressures in an autoclave. Unimodal HDPE is produced in parallel reactors, whereas bimodal HDPE is produced in series reactors. Current reactors have a volume of up to 300 m3 and capacities of up to 500 kt/a.
The catalyst is prepared batchwise in a vessel, diluted in another vessel and then added to the reactor. The continuously operating reactor is also fed with monomer, hydrogen and hexane. The exothermic reaction takes place at a pressure of 5–10 bar and a temperature of 75–85 °C. Heat is removed with an external heat exchanger. The molecular weight, molecular weight distribution and density of the product are controlled by adjusting the type and concentration of the catalyst and co-monomer as well as the quantity of hydrogen.

The processing chain ends with the post-reactor in which the monomer reaches a conversion rate of 99%. The resulting suspension is fed to a receiver and then centrifuged, dried in a fluidised bed with hot nitrogen and finally sieved. Stabilisers and additives are mixed in before it is extruded.

Due to the the tall shape of these polymerization reactors the main mixing task is to achieve very short blend times. In addition, high wall velocities must prevent scaling on the vessel walls.

EKATO developed the ISOJET VDT concept to carry out these tasks efficiently. The flow mechanics induced by the multiple Isojet stages stacked on top of each other act as a virtual draft tube (VDT) that accelerates the downward axial flow. This allows extremely short blend times, even in very thin and tall vessels. The special design of this mixing system quickly equalises any concentration or temperature gradients, thus leading to high product qualities. The flow pattern close to the walls shows correspondingly high upward flow velocities that prevent incrustations and deposits.

        HDPE的沉淀聚合在高压釜中在低压下进行。单峰HDPE在并联反应器中生产,而双峰HDPE在串联反应器中生产。目前的反应堆容积高达300立方米,容量高达500千吨/年。
        催化剂在容器中分批制备,在另一容器中稀释,然后加入反应器中。连续操作的反应器也加入单体,氢和己烷。放热反应在5-10巴的压力和75-85℃的温度下进行。用外部热交换器除去热量。通过调节催化剂和共聚单体的类型和浓度以及氢的量来控制产物的分子量,分子量分布和密度。

        加工链以后反应器结束,其中单体的转化率达到99%。将得到的悬浮液加入接收器中,然后离心,在流化床中用热氮气干燥,最后过筛。在挤出之前将稳定剂和添加剂混合。

        由于这些聚合反应器的高形状,主要的混合任务是实现非常短的混合时间。此外,高壁速度必须防止容器壁上的结垢。

        EKATO开发了ISOJET VDT概念,以有效地执行这些任务。由彼此堆叠的多个Isojet级引起的流动力学充当虚拟引流管(VDT),其加速向下的轴向流动。即使在非常薄且高的容器中,这也允许非常短的混合时间。该混合系统的特殊设计可快速平衡任何浓度或温度梯度,从而实现高产品质量。靠近壁的流动模式显示出相应高的向上流动速度,以防止结壳和沉积物。

  

EPS, PMMA, PVC

Some of the most common polymers, such as Polyvinyl Chloride, Expanded Polystyrene and Polymethyl Methacrylate, are synthesized using pearl polymerization. Pearl polymerization is characterized by the monomer being present in an insoluble form at the start of polymerization. The monomer droplets are dispersed in the aqueous phase and act as "small water-cooled reactors".

Key parameters governing the product quality during pearl polymerization are the particle size distribution and often also the porosity of the end product. As a general rule, the material with the narrower particle size distribution is more attractive to the market. This goal means demanding requirements for the mixing system:

  • narrow droplet size distribution of the monomer in water
  • small temperature and concentration gradients
  • Avoiding of a separate monomer phase on the surface (pooling)
  • Homogeneous suspending of the polymer beads
  • Good heat transfer

Pearl polymerization is generally carried out with simple, usually single-stage radial-pumping impellers. Particularly in tall vessels, however, their mixing efficiency is limited in the upper regions. The advantages of the Ekato Viscoprop agitator over these traditional mixing systems are discussed below. 

 

        一些最常见的聚合物,如聚氯乙烯,膨胀聚苯乙烯和聚甲基丙烯酸甲酯,是用珍珠聚合法合成的。珍珠聚合的特征在于单体在聚合开始时以不溶形式存在。单体液滴分散在水相中并起“小水冷反应器”的作用。

        控制珍珠聚合期间产品质量的关键参数是粒度分布,通常还有最终产品的孔隙率。作为一般规则,具有较窄粒度分布的材料对市场更具吸引力。该目标意味着对混合系统的苛刻要求:

单体在水中的窄液滴尺寸分布
温度和浓度梯度小
避免在表面上形成单独的单体相(合并)
均匀悬浮聚合物珠粒
良好的传热
珍珠聚合通常用简单的,通常是单级径向泵送叶轮进行。然而,特别是在高容器中,它们的混合效率在上部区域受到限制。下面讨论Ekato Viscoprop搅拌器相对于这些传统混合系统的优点。

 
 
 

The CFD simulation of the flow velocities for the Viscoprop clearly shows that the flow currents near the agitator shaft and close to the impellers are fast and directed downwards in an axial direction. This is achieved by the optimized shape of the Viscoprop impellers and tailoring of the mixing system, including baffles, to the reaction vessel. Close to the reactor wall there is a corresponding flow profile directed upwards that provides high wall speeds which reduces deposits forming at the wall.

Another benefit of a axial pumping, multi-stage set up is a more narrow particle size distribution. 

 

        Viscoprop的流速的CFD模拟清楚地表明,搅拌轴附近和叶轮附近的流动是快速的并且沿轴向向下指向。 这通过Viscoprop叶轮的优化形状和将混合系统(包括挡板)定制到反应容器来实现。 靠近反应器壁的是相应的向上流动轮廓,其提供高壁速,这减少了在壁处形成的沉积物。

        轴向泵送,多级设置的另一个好处是更窄的粒度分布。

ABS  (Acrylonitrile-Butadiene-Styrenecopolymer 丙烯腈 - 丁二烯 - 苯乙烯共聚物)

The synthesis of ABS is generally carried out in two steps. In the first step, the butadiene monomer undergoes emulsion polymerization to produce a polybutadiene dispersion (PBL). This is then reacted in the second step with the styrene-acrylonitrile (SAN) copolymer in an emulsion to achieve the target rubber concentration. Before continuing processing with styrene-acrylonitrile, it is important to adjust the particle size of the PBL dispersion to the desired value. Larger particles produce a greater impact toughness in the final product, but a lower surface gloss. The optimum size range of the PBL particles is approx. 0.3–0.5 µm.

Loading of the latex particles in the shear field of the agitator increases with increasing particle size. If the emulsifier envelope of two neighbouring particles is destroyed by high local shear introduced by an unsuitable agitator system, they will coagulate to even larger latex particles. This results in substantial changes to the mechanical properties of the end product. It also leads to the formation of thicker wall deposits that inhibit the dissipation of heat generated by the reaction. As a consequence, frequent cleaning cycles with considerable loss of productivity must be accepted. The Ekato Isojet B, a very low shear impeller, is ideal for PBL reactors, particularly as a multi-stage version. At the same time, using baffles as additional heat exchangers provides very efficient cooling.

 

        ABS的合成通常分两步进行。在第一步中,丁二烯单体经历乳液聚合以制备聚丁二烯分散体(PBL)。然后在第二步中将其与乳液中的苯乙烯 - 丙烯腈(SAN)共聚物反应以达到目标橡胶浓度。在继续用苯乙烯 - 丙烯腈处理之前,重要的是将PBL分散体的粒度调节至所需值。较大的颗粒在最终产品中产生较大的冲击韧性,但表面光泽度较低。 PBL颗粒的最佳尺寸范围是约。 0.3-0.5μm。

        在搅拌器的剪切场中加载胶乳颗粒随着粒度的增加而增加。如果两个相邻颗粒的乳化剂包膜被不适合的搅拌器系统引入的高局部剪切破坏,它们将凝结成甚至更大的胶乳颗粒。这导致最终产品的机械性能的显着变化。它还导致形成较厚的壁沉积物,其抑制反应产生的热量的消散。因此,必须接受频繁的清洁循环,同时显着降低生产率。 Ekato Isojet B是一种极低剪切叶轮,是PBL反应器的理想选择,特别是作为多级反应器。同时,使用挡板作为额外的热交换器提供非常有效的冷却。



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