EPVC

Emulsion Polyvinyl Chloride（EPVC）

1. Polymerization Method
The seeded emulsion polymerization process is adopted for the production of PVC paste resin. In this process, demineralized water, anionic emulsifier, and water-soluble initiator (persulfate) form the aqueous phase. VCM monomer is polymerized within the emulsifier micelles.In the classic non-seeded emulsion process, ultra-fine particles of 0.1–0.3 μm are generated. By preparing small-particle-size seed latex in advance, monomer grows only on the seed surface during the polymerization stage, preventing the formation of new micelles and allowing the particle size to be controlled within the range of 0.3–1.0 μm. This product is mainly used in artificial leather (for shoe uppers and sofas), wallpapers, general rotocast toys, conveyor belt coatings, general foamed products, coated fabrics, general dip-molded products, PVC inks, and other applications.

2. Reaction Mechanism
Reaction equation: 

nCH₂=CHCL→ ~CH₂-CHCL-CH₂-CHCL~

(1) Chain Initiation
The initiator decomposes upon heating to generate primary free radicals:  

I_一^△_→2R

The primary free radicals then attack the double bond of the VCM monomer to form monomer free radicals:

R·+ CH₂=CHCL→ R-CH₂-CHCL

(2) Chain Propagation
Monomer free radicals continuously add VCM monomers, and the molecular chain rapidly lengthens: 

R-CH₂-CHCL+ nCH₂=CHCL → R-(CH₂-CHCL)_n-CHCL

(3) Chain Termination
Two macromolecular free radicals collide and deactivate through two mechanisms: combination and disproportionation. The PVC system predominantly terminates via disproportionation.
(4) Chain Transfer
Macromolecular free radicals can undergo chain transfer to monomers, polymers, solvents, and additives.
Chain transfer to monomer: One macromolecular chain terminates while a new free radical is generated to continue propagation. This directly determines the molecular weight of PVC. In industrial practice, molecular weight is controlled by temperature: higher temperature promotes chain transfer, resulting in lower molecular weight.

~CH₂-CHCL+ CH₂=CHCL → ~CH=CHCL + CH₂=CHCL

Chain transfer to polymer: Branched chains are formed. More branches lead to poorer processing flowability and thermal stability.
The chain transfer constant of VCM radical polymerization is large, making it nearly impossible to control molecular weight by initiator dosage; it is primarily regulated by polymerization temperature.

3. Process Description
Chemical Preparation:Chemicals added to the polymerization system shall be dissolved and prepared in advance in preparation tanks. Except for one catalyst, which shall be dissolved ten minutes before polymerization feeding, all other chemicals shall be prepared in advance in the dissolving tank, N additive storage tank, NA additive storage tank, and D additive storage tank, and then fed to the metering tanks. When required for polymerization, they shall be automatically and accurately added into the polymerization kettle by the program controller through the respective chemical pumps.
Seed Preparation:The seed preparation process for seed emulsion polymerization is generally similar to the product polymerization process. The seed emulsion obtained by polymerization in the polymerization kettle is sent through a filter to the seed storage tank for storage and used as seed during product polymerization. During use, it is sent by the seed transfer pump to the seed metering tank and added into the polymerization kettle quantitatively at fixed times according to the formula. One batch of seed produced can be used for twelve batches of product polymerization. The maximum storage time of the seed emulsion is 7 days.
Polymerization:Demineralized water from the external pipe enters the hot water tank, is heated by steam, and is pumped into the polymerization kettle by the hot water pump. After the hot demineralized water is added into the polymerization kettle, reagents such as buffer and activator are charged through the feeding port. The manhole is then closed, and the air inside the kettle is removed by a vacuum pump to maintain a vacuum in the kettle. After a fixed amount of catalyst is added into the polymerization kettle from the dissolving tank, the vacuum pump is stopped. The seed emulsion is added into the kettle from the seed emulsion metering tank. Vinyl chloride, catalyst, emulsifier, and polymerization degree regulator are continuously added into the polymerization kettle by the respective pumps through flow controllers. The heat of polymerization is removed by jacket cooling water and the reflux condenser to maintain a constant reaction temperature. After a fixed amount of vinyl chloride monomer is added, the bypass operation of the condenser is used to raise the temperature of the materials in the kettle to reach the predetermined conversion rate. After the reaction is completed, the materials pass through the post-mixing tank, where the post-mixing agent is pumped in, and the emulsion in the kettle is then sent to the discharge tank. After the kettle is emptied, the gas is vented, and finally the manhole is opened to clean the polymerization kettle with high-pressure water from the high-pressure water pump. The reflux condenser is flushed with process water (once per kettle).
Degassing and VCM Recovery:After the polymerization reaction is completed, the reaction mixture flows by the kettle's own pressure into the storage tank of the batch degassing system. The gas phase passes through the mechanical defoamer at the top of the foam catcher. After the foam is removed from the vinyl chloride gas by the defoamer, it enters the batch cooling and washing system. After impurities are removed, the vinyl chloride is sent to the gas holder and then to the VCM recovery system. The emulsion is crushed by the emulsion crusher to break up coarse particles in the emulsion, and then sent by the emulsion transfer pump to the intermediate latex storage tank. The residual VCM in the latex is removed by continuous tower stripping and horizontal-tank continuous re-stripping. After the foam is removed from the vinyl chloride gas, it enters the continuous cooling and washing system, and the vinyl chloride is sent by the vacuum pump to the gas holder and then to the VCM recovery system. After VCM recovery from the latex in the horizontal tank is completed, the latex is sent by the emulsion transfer pump to the latex storage tank.
Drying, Pulverizing and Packaging: The latex in the latex storage tank is fed through the latex grinder and drying feed pump into the atomizer. The atomized latex is dried by hot air supplied by the main drying blower and heated by the heater. The dried resin is sent to the bag filter for separation of resin from air. The air is discharged by the exhaust fan through the stack. The resin is fed through the conveyor and pulverizer feed hopper into the pulverizer, where particles agglomerated during drying are broken down. The pulverized resin, together with the air, enters the bag filter, and the air is discharged by the exhaust fan. The finished product enters the storage silo and is automatically weighed and packaged by the packaging machine.
Wastewater Treatment Unit
The VCM tail gas scrubbing wastewater from the unit is treated with steam to remove VCM from the wastewater through the vacuum system. The tail gas is sent to the VCM gas holder. The discharged wastewater requiring primary treatment is collected in the wastewater pit and, together with the polymerization rinsing water, is sent to the primary wastewater treatment unit of the existing plant for flocculation and filter pressing.
DCS automatic control system and SIS emergency shutdown system are adopted to produce P440, P450, R1069, P415, P455, and P460 grade resins.

4. Main Equipment Selection
(1) Polymerization Reactor
Commonly used mainstream polymerization reactors in China include sizes of 16 m³, 24 m³, 30 m³, and 48 m³:
The 24 m³reactor has the largest number of operating cases in China, the most mature process package matching, and the best batch-to-batch stability, with a single-train capacity of 5,000 t/a.
(2) Dryer
The dryer from Niro (Denmark) is the preferred choice, offering reliable and stable operation.

5. Performance Indicators
Product quality: first-grade product rate≥95%
VCM monomer consumption: 1.015 t/t PVC
Demineralized water consumption: 2.5 t/t PVC
Steam consumption: 2.5 t/t PVC
Power consumption: 580 kWh/t PVC

6. Process Block Diagram