The production process and technical route of PVC

The industrial production of polyvinyl chloride (PVC) mainly relies on two routes: the calcium carbide method and the ethylene method. These two processes each have their own characteristics, which determine the resource allocation and industrial patterns in different countries and regions.

I. Calcium carbide method for PVC

The calcium carbide method involves the reaction of calcium carbide (CaC₂) with chlorine gas to produce vinyl chloride monomer (VCM), which is then polymerized to obtain PVC.

Advantages

Relying on China's abundant coal and limestone resources, the self-sufficiency rate of the industrial chain is high.

The investment cost is relatively low, making it suitable for layout in inland areas.

Disadvantage

The energy consumption is high. The comprehensive electricity consumption per ton of PVC far exceeds that of the ethylene method.

The by-products and carbon emissions are large, and the pressure on environmental protection is obvious.

The product quality is slightly inferior to that of the ethylene method in terms of transparency, thermal stability and other aspects.

Ii. Ethylene Method PVC

The ethylene method uses ethylene, a by-product of petrochemicals, as raw material to react with chlorine gas to form VCM, which is then polymerized to produce PVC.

Advantages

The process is mature, with low energy consumption and few by-products.

The product features high purity and stability, making it suitable for high-end applications.

Disadvantage

The investment scale is large and the dependence on the petrochemical industry chain is high.

The prices of raw materials are greatly affected by fluctuations in the international oil and gas market.

Iii. Polymerization Process

Regardless of the raw material route, there are mainly three polymerization methods for PVC:

Suspension polymerization (S-PVC) : accounts for approximately 80%, with uniform particles, suitable for most hard products.

Emulsion polymerization (E-PVC) : Fine particles, suitable for coatings, artificial leather, films, etc.

Bulk polymerization: Less applied, mainly used for transparent products.

Iv. Technological Development Direction

Green and low-carbon: Energy conservation and consumption reduction, recycling and utilization of by-products, and optimization of the calcium carbide process.

New type of catalyst: Enhance conversion rate, reduce by-products, and improve product quality.

High-end applications: Precise aggregation control to meet medical-grade, weather-resistant and other requirements.

Summary

The calcium carbide method is suitable for resource-based countries and regions, while the ethylene method represents the international advanced level. In the future, as carbon reduction requirements increase and high-end applications grow, ethylene methods and high-performance polymerization technologies may gradually become the mainstream in the industry.