VCM self-polymerization problem

The spray water in the monomer tank is not intended for cooling purposes. Its function is to reduce the temperature of the monomer tank in case of a fire. At ambient temperatures, the tank is safe as long as its fill level does not exceed the specified limits.

1. Recycled monomers tend to self-polymerize. Because the recycled monomer contains active substances. 2. The monomer contains moisture, which facilitates self-polymerization; the presence of water leads to the hydrolysis of the monomer, and the resulting active ions initiate polymerization. 3. It tends to self-polymerize at high temperatures, but there are no quantitative data available. 4. There is a certain relationship between the vapor pressure of the monomer and temperature: lgP = –0.15228 – 1150.9/T + 1.75lgT – 0.002415T. If the temperature is ≥ 35°C, the pressure will exceed 0.53 MPa; in such cases, cooling measures should be considered. Of course, the design temperature for the spherical tank is 55°C, with a pressure of over 0.89 MPa; however, due to the high pressure in the storage tank, distillation cannot be used for direct discharge (except with forced feeding). Higher temperatures accelerate self-polymerization.

Problems with VCM self-polymerization and spray water: 1. Monomer self-polymerization: VCM monomer tends to undergo self-polymerization more easily in the presence of water, especially when Fe(III) is present in the environment. Therefore, it is recommended to use 304 stainless steel pipes for the monomer pipeline, and to implement stricter control over the moisture content in vinyl chloride monomer. 2. Sprinkler water management: Management of the sprinkler cooling water – The activation of the sprinklers is determined primarily based on the pressure in the monomer storage tank; if the pressure is within the specified range, it is not necessary to use sprinkler cooling water.

Then, what are the appropriate levels for moisture and iron content in 4# VCM? Is it generally necessary to add a polymerization inhibitor?

Opinions: 1. The function of spraying: I agree with what was said above, so I won’t repeat it here. 2. Several possibilities for self-polymerization: 1. Insufficient addition of inhibitors in the recycled monomer, leading to residual activity that triggers self-polymerization of the monomer; 2. Excessive water content in the monomer; 3. Inadequate purification of the monomer, resulting in high acidity; 4. Improper control of temperature. 3. Solutions: 1. Enhance the dehydration process of the monomer; 2. Properly control the concentration of the purification alkali; 3. Add inhibitors at the point where moisture is present, etc

Aqueous solutions tend to self-polymerize; in the liquid phase, dehydration should be carried out as much as possible. In the gas phase, polymerization inhibitors can be added. I’ve never seen them being used in the liquid phase, so I’m not sure whether they can be used there

The recycled monomer tends to self-polymerize because it contains initiators and dispersants. The spray water is used for firefighting

1. In the previous steps, the presence of trace amounts of oxygen in the fresh monomer led to the formation of some peroxides. These peroxides undergo redox reactions with ferrous ions, breaking down into free radicals and anions; the free radicals then initiate polymerization, resulting in ‘monomer autopolymerization’. 2. The self-polymerization of recycled monomers occurs because some residual initiator is carried over from the monomers during their recovery from the polymerization reactor; trace amounts of oxygen may be present in the air or steam used in the stripping process, and oxygen can also be present in the water used during compression. All these factors can lead to the self-polymerization of recycled monomers, which is why inhibitors are generally added during the recovery process.

With water present, self-polymerization is more likely if the tank is made of carbon steel. This problem is difficult to avoid; it is recommended to increase the amount of inhibitor added, which can help alleviate this issue.

The liquid phase should be dehydrated as much as possible; an inhibitor can be added to the gas phase. Study hard!