聚氯乙烯乳液聚合生产工艺介绍

聚氯乙烯乳液聚合工艺简介

工艺路线选择

3.1.1 PVC工艺介绍

聚氯乙烯（PVC）是由氯乙烯在引发剂存在下聚合而成的热塑性树脂，也是世界上最早工业化生产的塑料之一。在世界上众多塑料品种中，PVC以其综合性能优异、价格低廉、与氯碱工业关系密切等优点，自20世纪30年代工业化以来，受到各工业国家的广泛重视，并保持了长期的发展势头。它是世界第二大塑料品种，仅次于聚乙烯。

目前，世界上生产PVC的聚合工艺主要有悬浮法、本体法、乳液法、微悬浮法和溶液聚合法五种。其中，悬浮聚合工艺一直是工业生产的主要工艺，绝大多数均聚和共聚产品采用悬浮聚合工艺。以美国为例，在PVC生产过程中，悬浮聚合占87.8%，本体聚合占4.4%，乳液和微悬浮聚合占6.4%，溶液聚合占1.4%。与美国相比，西欧乳胶和本体聚合的比例较大，而日本悬浮聚合的比例较大。

3.1.2各种生产工艺介绍

（1） 本体聚合。第一阶段称为预聚。当氯乙烯在62-75℃强搅拌下转化率为8%时，输送至聚合釜。当加入等量的低效引发剂单体时，在60℃左右缓慢搅拌，继续聚合，直至转化率达到80%，反应停止。在本体聚合中，氯乙烯单体不加介质，只加引发剂。结构规则、孔隙率高、质量好的PVC树脂。然而，PVC树脂的聚合操作难以控制，分子量分布较宽。

（2） 悬浮聚合。通过添加适量的分散剂和引发剂，将液态氯乙烯单体分散在水中，分散剂和引发剂不溶于水，但易溶于单体，然后在一定温度下搅拌，使其悬浮在水相中形成聚合珠。经过碱洗、汽提、离心、干燥，得到白色粉末状PVC树脂。通过选择不同的分散剂，可以得到两种不同颗粒结构和形貌的树脂。国产品牌分为SG松（棉球）树脂和XJ紧（乒乓球）树脂。本实用新型吸油性好，易塑化，成型时间短，加工操作方便，适合粉末直接成型。因此，一般选用悬浮法聚合的松散树脂作为PVC硬质制品成型的基本原料。目前，各树脂厂生产的悬浮式PVC树脂基本上是松散的。

（3） 乳液聚合。在乳化剂的作用下，将氯乙烯单体分散在水中形成乳液，再用水溶性引发剂引发聚合。用盐将乳液与聚合物分离，再经洗涤、干燥得到PVC树脂粉末。乳液型PVC树脂粒径很细，乳化剂含量高，电绝缘性差，成本高。这种树脂常用于制备PVC糊。

（4） 微悬浮聚合。以油为引发剂，将乳化剂分散稳定的小氯乙烯单体液滴聚合制得PVC乳液，经破乳、洗涤、干燥得到PVC树脂粉末。该法生产的PVC树脂加工性能好，能满足大多数加工的需要。

（5） 溶液聚合。以甲醇、甲苯、苯、丙酮为溶剂，氯乙烯单体在该溶剂中聚合。由于溶剂具有链转移剂的作用，聚合物的分子量和聚合速率都不高。由于溶剂不断沉淀，树脂不溶。这种PVC树脂不适用于一般的成型，而只能用作涂料和粘合剂。是目前各种聚合方法中产量最少的方法之一。

就以上五种主要的聚合工艺而言，通过几种方法的比较，悬浮法是最成熟的工艺，在世界PVC生产中占有绝对份额，转化率最高，产品品种最多，因此，悬浮法是目前最成熟的工艺

Introduction of polyvinyl chloride emulsion polymerization process

Selection of process route

3.1.1 introduction of PVC process

Polyvinyl chloride (PVC) is a thermoplastic resin polymerized by vinyl chloride in the presence of initiator, and it is also one of the earliest industrialized plastics in the world. Among many kinds of plastics in the world, PVC, with its excellent comprehensive properties, cheap price and close relationship with chlor alkali industry, has been widely valued by various industrial countries since its industrialization in the 1930s, and has maintained a long-term development momentum. It is the second largest plastic variety in the world, which is only inferior to polyethylene.

Up to now, there are mainly 5 kinds of polymerization processes for PVC production in the world: suspension, bulk, emulsion, micro suspension and solution polymerization. Among them, suspension polymerization process has always been the main process of industrial production, and the vast majority of homopolymerization and copolymerization products adopt suspension polymerization process. Take the United States as an example, in the PVC production process, suspension polymerization accounted for 87.8%, bulk polymerization accounted for 4.4%, emulsion and micro suspension polymerization accounted for 6.4%, and solution polymerization accounted for 1.4%. Compared with the United States, the proportion of latex and bulk polymerization in Western Europe is larger, while the proportion of suspension polymerization is larger in Japan.

3.1.2 introduction of various production processes

(1) Ontology aggregation. The first stage is called prepolymerization. When the conversion of vinyl chloride is 8% under strong stirring at 62-75 ℃, it is transported to the polymerizer. When the same amount of monomer with low efficiency initiator is added, it is slowly stirred at about 60 ℃ and continues to polymerize until the conversion reaches 80%, the reaction stops. In bulk polymerization, no medium was added to vinyl chloride monomer, only initiator was used. The PVC resin with regular structure, high porosity and high quality. However, it is difficult to control the polymerization operation and the molecular weight distribution of PVC resin is wide.

(2) Suspension polymerization. The liquid vinyl chloride monomer was dispersed in water by adding appropriate dispersant and initiator which was insoluble in water but soluble in monomer, and then was stirred at a certain temperature to make it suspended in water phase as beads for polymerization. After alkali washing, stripping, centrifugation and drying, white powdered PVC resin was obtained. Two kinds of resins with different particle structure and morphology can be obtained by selecting different dispersants. Domestic brands are divided into SG loose (cotton ball) resin and XJ tight (table tennis) resin. The loose resin has the advantages of good oil absorption, easy plasticization, short molding time, convenient processing and operation, and is suitable for direct molding of powder. Therefore, the loose resin polymerized by suspension method is generally selected as the basic raw material for molding of PVC hard products. At present, the suspension PVC resins produced by various resin factories are basically loose.

(3) emulsion polymerization. Under the action of emulsifier, vinyl chloride monomer is dispersed in water to form emulsion, then water soluble initiator is used to initiate polymerization. The emulsion can be separated from the polymer by salt, and then the PVC resin powder can be obtained by washing and drying. Emulsion PVC resin has a very fine particle size, high emulsifier content, poor electrical insulation and high cost. The resin is often used in the preparation of PVC paste.

(4) Microsuspension polymerization. Using oil initiator, PVC emulsion produced by polymerization of small vinyl chloride monomer droplets dispersed and stabilized by emulsifier was obtained by demulsification, washing and drying to obtain PVC resin powder. The PVC resin produced by this method has good processability and can meet the needs of most processing.

(5) Solution polymerization. Using methanol, toluene, benzene and acetone as solvents, vinyl chloride monomer was polymerized in the solvent. Because the solvent has the function of chain transfer agent, the molecular weight and polymerization rate of the polymer are not high. The resin is insoluble due to the continuous precipitation of solvent. This kind of PVC resin is not suitable for general molding, but only used as coating and adhesive. It is one of the methods with the least output among all kinds of polymerization methods at present.

In terms of the above five main polymerization processes, through the comparison of several methods, the suspension process is the most mature process, which occupies an absolute share in the world's PVC production, and has the highest conversion rate and the most varieties of products, so it is easy to adapt to the market. Emulsion method is a method of producing paste resin. The process is complex, the cost is high and the quality of resin is poor.

Suspension polymerization is the most mature technology in various production methods of PVC, so suspension polymerization is adopted in this design.

聚氯乙烯乳液聚合生产工艺介绍

工艺路线的选择

3.1.1PVC工艺简介

聚氯乙烯(PVC) 是由氯乙烯在引发剂作用下聚合而成的热塑性树脂，也是世界上最早实现工业化的塑料品种之一。在世界众多的塑料品种中，PVC 以其优良的综合性能，便宜的价格以及与氯碱工业关系密切，自30 年代工业化以来，一直受到各工业国的普遍重视，保持着长盛不衰的发展势头，是目前世界上仅次于聚乙烯的第二大宗塑料品种。

到目前为止，世界上PVC 生产的聚合工艺主要有5 种，即悬浮、本体、乳液、微悬浮及溶液聚合工艺。其中悬浮聚合工艺一直是工业生产的主要工艺，绝大部分均聚及共聚产品都是采用悬浮聚合工艺。就拿美国为例，聚氯乙烯生产工艺中，悬浮聚合占87.8%，本体聚合占4.4% ，乳液和微悬浮聚合占6.4% ，溶液聚合占1.4%。与美国相比，西欧乳液和本体聚合的比例较大，而日本则悬浮聚合占的比例较大。

3.1.2各种生产工艺介绍

   (1)本体聚合。一般采用两端本体聚合法，第一段称为预聚合，采用高效引发剂，在62～75℃下强烈搅拌下使氯乙烯聚合的转化率为8%时，输送至聚合釜中，在加入低效引发剂的等量单体，在约60℃下，慢度搅拌，继续聚合至转化率达80%时，停止反应。本体聚合时在氯乙烯单体中不加入任何介质，只有引发剂。生产的PVC树脂纯度较高，质量较好，结构规整，孔隙率高而均匀。但聚合操作控制难度大，PVC树脂分子量分布较宽。

(2)悬浮聚合。液态氯乙烯单体以水为分散介质，兵加入适当的分散剂和不溶于水但溶于单体的引发剂，在一定温度下搅拌，使其呈珠粒状悬浮于水相中进行聚合。然后经碱洗、汽提、离心、干燥得到白色粉末状PVC树脂。选取不同的分散剂，可以得到颗粒结构和形态不同的两类树脂。国产牌号分为SG-疏松型（棉花球型）树脂；XJ-紧密型（乒乓球型）树脂。疏松型树脂吸油性好，易塑化，成型时间短，加工操作方便，适用于粉料直接成型，因而一般选用悬浮法聚合的疏松型树脂作为PVC硬质品成型的基础原料。目前各树脂厂生产的悬浮法PVC树脂，基本上都是疏松型的。

（3）乳液聚合。氯乙烯单体在乳化剂作用下，分散于水中形成乳液，再用水溶性的引发剂来引发，进行聚合，乳液可用盐类使聚合物析出，再经洗涤、干燥得到PVC树脂粉末。乳液法PVC树脂粒径极细，树脂中乳化剂含量高，电绝缘性能差，成本高。该树脂常用于PVC糊的制备。

（4）微悬浮聚合。使用油性引发剂，在用乳化剂分散、稳定的细小氯乙烯单体液滴中引发聚合，生成的PVC乳液，经破乳、洗涤、干燥得到PVC树脂粉末。该方法生产的PVC树脂具有良好的加工性能，能满足大多数加工的需要。

（5）溶液聚合。以甲醇、甲苯、苯、丙酮作溶剂，使氯乙烯单体在溶剂中聚合，由于溶剂具有链转移剂的作用，所以聚合物的分子量和聚合速率不高。聚合得到的PVC树脂因不溶于溶剂而不断析出。此种PVC树脂不宜于一般成型用，仅作为涂料、粘合剂，是目前各种聚合方法中产量最少的一种方法。

就以上5种主要聚合工艺来讲，通过几种方法的比较，悬浮法是一种相对最成熟的工艺，在目前世界聚氯乙烯生产中占有绝对的份额，且产品转化率最高，产品品种最多，容易适应市场。乳液法是生产糊树脂的方法，工艺复杂、成本较高且树脂质量较差。

悬浮法工艺在PVC的各种生产方法中技术最为成熟，故本设计采用悬浮法聚合。