Polyvinyl chloride production wastewater treatment technology

As a common chemical raw material, polyvinyl chloride is an important material in organic synthesis.

In recent years, with the rapid development of the construction industry, the market demand for PVC has expanded.

According to the statistics of relevant research institutions: my country currently has more than 200 PVC production enterprises, with an annual production capacity of 15 million tons.

The huge market promotes the development of the PVC industry and its related industries.

In order to make the PVC industry develop green and sustainable, the wastewater treatment in the production process of PVC should be strengthened. For some special heavy metal pollution factors, some professional treatment methods and processes should be adopted to avoid the pollution caused by wastewater discharge. ecological hazards and protect green ecological resources.

Continuous improvement of polymerization formula

1.1 Initiator

In the production of polyvinyl chloride in my country, the initial initiator used is azobisisobutyronitrile (AIBN), which has low initiation activity and long reaction time. After the reaction time ends, a large amount of waste residues will remain in the product. It affects the stability of the product, and because the nitrile group has a certain toxicity, if it enters the wastewater system and is discharged, it will cause huge adverse effects on the surrounding environment.

With the continuous progress of polymerization kettle technology and the improvement of environmental protection requirements, the initiators currently used in the production process of polyvinyl chloride are mainly diethylhexyl peroxydicarbonate (EHP), tert-butyl peroxynecaprate ( TBPND).

In the production process, this kind of initiator with high initiation activity and short initiation time is formulated into a composite state, the heat exchange capacity of the reactor is fully utilized, and the ratio of initiators is adjusted reasonably according to the actual operation of the reactor, so that the The reaction time of the agent is minimized, the residue of the initiator is reduced, and the utilization rate of circulating water in the production process is maximized.

1.2 Dispersant

In the production process of polyvinyl chloride, the function of dispersant is mainly to adjust the liquid surface tension, reduce the droplet aggregation, and the accelerator protects the droplet dispersion, while the single-component dispersant cannot meet the above requirements at the same time.

In the past, traditional polyvinyl chloride was mostly compact, and the dispersant used at that time was gelatin, and gelatin itself is a natural high polymer, and the impurities contained in its own components are difficult to control.

It is easy to absorb water during use, and it is easy to fail under the influence of bacteria. Nowadays, the commonly used dispersants are mainly polyvinyl alcohol (PVA) and cellulose ethers. The products produced by these dispersants have less fine powder, narrow distribution, short gelation time, less additional emissions in the production process, and easy subsequent procedures. production and processing.

Improvement of process equipment technology

2.1 Polymerization kettle

At present, the polyvinyl chloride industry is in a period of rapid development, and advanced polyvinyl chloride production enterprises are accelerating the pace of equipment renewal and production capacity. The production technology transformation of the reaction kettle has become the focus of the production enterprises.

At present, the application ratio of 30m3 polymerization kettles in my country’s polyvinyl chloride production enterprises is gradually shrinking, and is gradually replaced by more than 70m3 polymerization kettles. Development in the direction of more cycles.

At the same time, a baffle plate is set in the polymerization kettle, which increases the turbulent effect in the process of material conveying, and at the same time plays a certain role in reducing the amount of dispersant.

In order to increase the specific heat transfer area of the polymerization kettle, a reflux condenser is set up in the polymerization kettle, and the method of increasing the utilization of circulating water is used to increase the heat transfer coefficient of the polymerization kettle, enhance the heat transfer effect of the polymerization kettle, and reduce the water consumption. The waste of resources greatly improves the performance of the polymerization kettle.

2.2 Stripping equipment technology

In the production process of polyvinyl chloride, the waste water to be treated in the stripping section first enters the stripping tower. The pool is ready for the next process of neutralization, coagulation and sedimentation.

At present, the main tray used in the stripping tower is detachable, so that the material at the top of the tower can be at a lower boiling temperature, saving the amount of steam required for its operation, and adding a flash tank to improve the stripping effect and strengthen the waste water. Treatment capacity, reduce heavy metal organic ions in wastewater, and maximize the recycling rate of circulating water cooling water in the stripping process.

2.3 Drying equipment technology

In the past, the drying equipment used by my country’s polyvinyl chloride production enterprises was mainly air drying and fluidized drying. However, with the continuous progress of modern polymerization technology and the continuous improvement of polymerization degree requirements, traditional drying methods have been unable to meet the requirements of modern industrial society. need.

Therefore, cyclone drying equipment and cooling three-stage drying technology have gradually become the mainstream methods of current PVC production.

This type of drying equipment has simple structure, convenient installation, lower cost than other drying equipment, and good control stability. It can effectively support the separation of chemical centrifugal wastewater in the initiator, dispersant and terminator added in the polymerization reaction, and maximize the value of recycling.

Conclusion

With the continuous progress of PVC production technology and the continuous updating of production equipment, the recycling and recycling technology and method of wastewater in the production process of PVC should also improve accordingly.

Relevant production enterprises and engineering and technical personnel should further explore and study the details of the wastewater generated in each section of PVC in the production process based on the principles of energy conservation, consumption reduction, pollution reduction and efficiency enhancement, and for the purpose of improving production value, so as to achieve enterprise Zero discharge of sewage, and be a resource-saving, ecological and environmental-friendly green enterprise.

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