Method and system for adjusting acidity and alkalinity of water in vinyl chloride rectification process

Abstract

The invention discloses a method and system for adjusting the acidity and alkalinity of water in the vinyl chloride rectification process. The system comprises a compressor, a condenser behind the compressor, a water separator, a crude vinyl chloride monomer storage tank, a vinyl chloride rectification column, a caustic tank and a caustic soda liquid dropwise-adding device. The method comprises the steps that the caustic soda liquid dropwise-adding device sucks caustic soda liquid from the caustic tank, and the caustic soda liquid is continuously added into the water separator from a liquid vinyl chloride outlet pipe and enters the crude vinyl chloride monomer storage tank through the water separator together with liquid vinyl chloride monomers, so that an acidic medium is neutralized and the acidity and alkalinity of the liquid vinyl chloride monomers are adjusted in the crude vinyl chloride monomer storage tank. By means of the method and the system, the effect is very good, the economical and practical properties are achieved, modification is little, and the benefit is high; a low-boiler column is cleared up for once every year, column blocking is not serious, no leakage point of rectification and condensation equipment is found over the past year, the quality of the vinyl chloride monomers is improved, the water content is lowered, and the heat stability of finished pvc (polyvinyl chloride) is significantly improved.

Description

Technical field: [0001] The invention relates to a method and a system for adjusting the pH of water, in particular to a method and a system for adjusting the pH of water in a rectification process of vinyl chloride. Background technique: [0002] In the process of producing polyvinyl chloride by the calcium carbide method, in the presence of water in the vinyl chloride rectification process, the VCM (vinyl chloride) monomer easily absorbs oxygen to generate low-molecular peroxides with an average degree of polymerization lower than 10. The chemical reaction formula is: wxya 2 =CHCl+nO 2 →(CH 2 –CHCl-O-O) n . This peroxide can trigger VCM self-polymerization to generate polyvinyl chloride with a low degree of polymerization. Due to the presence of peroxide chains in this polyvinyl chloride macromolecule, the decomposition temperature of polyvinyl chloride is reduced. Such polyvinyl chloride Under the operating conditions of the rectification system, it is easy to decomp...

AI Technical Summary

Problems solved by technology

Moreover, the presence of iron ions promotes the generation of peroxides between oxygen and VCM in the polymerization system. This peroxide will cause vinyl chloride to accelerate self-polymerization and generate polyvinyl chloride with a lower degree of polymerization. Forced to stop and clean up

In addition, the presence of iron ions will prolong the induction period of the polymerization reaction, slow down the reaction speed, make the thermal stability of PVC products worse, and affect the product quality.

Before the technical transformation, the low boiling tower was cleaned every 3 months, the rectification and condensing equipment such as the total condenser, the tail gas condenser, and the finished product condenser were seriously corroded, and the frequency of maintenance was frequent, and the thermal stability of the PVC finished product was reduced

[0003] At present, the implementation schemes to solve the above problems are: 1. Install solid alkali dryers before and after the compressor, and use 99% solid alkali to dry the vinyl chloride gas to remove the moisture in it. This technology is easy to cause alkali crystallization to block the pipeline , and the operation is frequent and complicated, which brings safety hazards to operators and production, and pollutes the environment at the same time

2. Add a polymerization inhibitor dropwise on the vinyl chloride outlet pipeline of the after-machine condenser to prevent a series of side reactions caused by the hydrolysis of vinyl chloride during the rectification of vinyl chloride. This method will have the following adverse effects on polymerization: 1. 1. The polymerization inhibitor will consume a part of the initiator, thereby prolonging the polymerization reaction time; 2. It is necessary to ensure that the concentration of the polymerization inhibitor in the fresh monomer is stable, so as to ensure the stable production of the polymerization. The amount of polymerization agent is used to adjust the amount of initiator. After the amount of initiator is increased in polymerization, the amount of polymerization inhibitor is reduced or stopped, which will cause overtemperature and overpressure of the polymerization kettle, resulting in unstable production of polymerization; 4. Inhibitors are harmful to the human body ,polluted environment

[0004] In addition, high moisture content will also reduce the whiteness of the finished resin product, increase the content of coarse material in the finished PVC product, and cause the components in the rectification reboiler to easily decompose, cause coking and corrosion of equipment, and affect the normal operation of the device

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