Reasons for crude product formation in the 70 polymerization reactor

Periodically, it is due to the accumulation of some impurity in the system. Units for recovering monomers, solid-alkali drying, etc

Are the dispersants for the two lines stored in separate tanks or shared? Are there pipes connecting the two lines? How many reactors are there in each line, and does only one reactor produce the crude product or do all of them? When is the crude product produced?

Exploring the reasons for the formation of coarse PVC particles. Source: Zhongshan Xinlinghang Plastics Co., Ltd. Published on: 2016-07-22 22:17:54. During the production of PVC particles, it is common for coarse particles to appear. So what are the reasons for this phenomenon? As we all know, among all polymer additives, PVC particles have the most stringent requirements regarding their particle shape. This is because modern processing equipment used for PVC particles demands a high standard of particle shape; other polymers are usually processed through granulation or modification before being used as additives, whereas PVC particles are added in their powdered form directly. The most common types are pellets or colored pellets made from materials such as PE, PS, ABS, or PC (polycarbonate). In Europe and the United States, PVC pellets are also blended to create colored masterbatches, thereby producing high-quality PVC pellet products; China has not yet developed advanced processing in this area. 　　Factors affecting the roughness: Many manufacturers attribute it to dispersants, which is a superficial phenomenon. This can be divided into two aspects: First, it is indeed the poor quality of the dispersant (referring here to the dispersant in polyvinyl alcohol systems) and its weak dispersing ability that lead to the formation of coarse particles. We conducted a comparative test between a product with a certain degree of hydrolysis and ALCOTEX7206; the specifications of both products met the required standards. To avoid the formation of coarse material, this product required 2.5 times more of the ingredient than ALCOTEX7206. This is because: as a dispersant for the polymerization of PVC particles, not all products with suitable surface properties can be used as dispersants. In particular, dispersants with a moderate degree of alcoholysis require modification before they can be used. Moreover, all dispersants must be mature products that are ready for industrial use; practical experience in their application is very important, and batch consistency in product quality is also required. Companies such as Japan’s KURARAY, NIPPON GOHSEI, and the UK-based SYNTHOMER all have decades of experience in production and service; their products are highly stable and ensure quality. 　　Second: Indeed, coarse particles were formed, but this was not caused by the dispersant itself; (do not try to shift responsibility by assuming we are dispersant sellers), rather, something damaged the dispersant, rendering it ineffective or partially ineffective, which led to the formation of coarse particles. 　　Usually, there are many possible causes for disrupting the system, and only by examining each one individually can the root cause be identified. However, it is not possible to stop production in order to find the cause; operations must continue. Generally, we recommend increasing the amount of dispersant used in the next batch after processing the crude material by 5-10% to ensure normal production, and then reducing that amount once the cause has been identified. 　　Frequently Asked Questions: 1. Deionized water. We should note that deionized water is the most common dispersion medium for suspension polymerization; a slightly alkaline environment can easily disrupt the polyvinyl alcohol dispersion system. The effect of a slightly acidic environment is that the polymerization of vinyl chloride is an exothermic process, and when the water is acidic, the system becomes even more acidic during the polymerization process, which also affects the crude product. Even in the absence of such a crude product, the particles will remain rough, and this severely impacts the thermal aging and whiteness of the resin. 　　2. Monomers: The international standard for monomers produced by the petroleum method is 99.98%, with approximately 200 ppm of impurities; some domestic calcium carbide-based manufacturers claim that their monomers have a purity of 99.99%, including unknown impurities in that figure, while the acetylene method cannot achieve such a level of purity. The concentration of dispersants is around 700 ppm. These values are in the same order of magnitude, and they have a significant impact. Additionally, crude products tend to form during the startup of new projects. The main reason for this is that the catalyst used in vinyl chloride synthesis requires an activation process; as a result, the formation of monomer isomers or disproportionation products increases significantly, and when this amount reaches a certain level, crude products are produced. One year after driving a vehicle, it is very rare to hear about issues with rough materials from the manufacturer. When restarting after a shutdown for maintenance, since individual impurities settle at the bottom of the storage tank, there is a high likelihood of problems with the material in the first one or two batches; it is generally necessary to add more dispersant, and then reduce the amount once normal operation is resumed. 　　3. Residual initiator radicals. Residual free radicals will graft polymerize with the ester groups on the dispersant, thereby consuming the dispersant and resulting in an coarse product; there are many precedents for this. This tends to occur in tropical regions and is also easily overlooked. 4. Insufficient amount of terminator added. 　　5. Is the new equipment functioning properly? For example, is the measurement accurate and is the pump operating correctly? 6. Under certain conditions, the order in which the dispersant is added also affects the particle structure. 　　7. Has the dispersant lost its effectiveness? Has stratification occurred? 8. In polymerization techniques using a kettle-top condenser, compensatory amounts of dispersant are required, and these amounts need to be high. The hot feeding process also requires more dispersant than the cold feeding process. 　　As mentioned above, the original W control is effective; combined with auxiliary monitoring of the coarse materials, it generally prevents the situation where the production site is filled with waste. 　　From another perspective, as an industrial product based on mature production practices, if dispersants still experience such large fluctuations in their quality, they cannot be sold as commercial products. This is because the production process for dispersants requires continuous batch manufacturing in quantities of over 300 tons, which allows for the production of around 300,000 tons of polyethylene. If there are quality issues with a particular batch, resulting in such a large amount of defective material, it would cause a sensation worldwide.