JPH0212963B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for suspension polymerizing vinyl chloride resin using a polymerization vessel equipped with a condenser.

In the production of vinyl chloride resins, condensers are often used to improve productivity and save energy, but suspension polymerization that involves cooling with condensers is known to cause significant foaming in the polymerization system. For example, a method in which a condenser is activated when the polymerization conversion rate reaches 5% or more by opening and closing a valve (Japanese Patent Publication No. 53-38311), a method in which after preliminary stirring, an initiator is charged to start polymerization (Japanese Patent Publication No. 48-29795)
However, in practice, as the viscosity of the polymerization suspension increases after the middle of polymerization, the stirring effect decreases, so the generated air bubbles float to the surface and the hold-up of the suspension increases. In extreme cases, the polymer may enter the conduit or the condenser and polymerize there, forming a lump of scale without being drawn into the suspension system again, making it difficult to operate the condenser normally. Naru et al.
There were problems such as unfavorable quality.

As a result of extensive research in order to solve this problem, the inventor of the present invention found that foaming can be prevented by adjusting the amount of heat removed by the condenser while gradually increasing the polymerization temperature after the middle stage of polymerization (polymerization conversion rate of 50%). The present invention was completed based on the discovery that a controlled polymerization method is extremely effective. The method of the present invention will be explained in detail below.

In recent years, it has been revealed that vinyl chloride monomers pose a risk of causing liver damage, and in order to reduce unreacted monomers remaining in the polymer particles, the suspension after polymerization has been processed under reduced pressure. A method of heating the product while stirring is generally employed, and the steam cost required for this heating accounts for a fairly large proportion of the product.

On the other hand, after the middle of polymerization, the viscosity of the polymerization suspension increases, making it difficult for the generated air bubbles to come out of the suspension, and at the same time, the stirring effect decreases, resulting in a rapid increase in suspension hold-up and extreme In some cases, the suspension may reach the inside of the conduit or condenser, where it may form a lump of polymer, making it difficult to operate the condenser properly and causing unfavorable quality results such as sticking. many.

As the scale of the polymerization reactor increases, this foaming phenomenon becomes more and more noticeable and heat removal becomes difficult. However, according to the present invention, by adjusting the amount of heat removal from the condenser while gradually increasing the polymerization temperature, the foaming phenomenon can be improved after the middle stage of polymerization. By performing polymerization while controlling foaming, it is possible to increase the amount of polymerization charged, increase the polymerization conversion rate, improve productivity, and use the reaction heat of polymerization to heat the suspension, making it suitable for heating. A secondary effect is that steam can be saved. Note that the amount of heat removed from the condenser is generally adjusted by a method of adjusting the amount of cooling water supplied to the condenser, a method of adjusting the temperature of the cooling water, etc., but is not particularly limited. In addition, the larger the ratio of monomer to charging water is, the better from the viewpoint of productivity, but the viscosity of the polymerization suspension increases rapidly from a polymerization conversion rate of 25 to 30%, making stirring difficult. A preferred method is to lower the viscosity of the suspension by pouring water during polymerization in an amount equal to or less than the amount of shrinkage.

Vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride used in the present invention includes:
For example, olefins such as ethylene and propylene; vinyl esters such as vinyl acetate and vinyl stearate; acrylic acid esters such as methyl acrylate and methyl methacrylate; esters and anhydrides of acids such as maleic acid or fumaric acid;
Examples include nitrile compounds such as acrylonitrile and vinylidene compounds such as vinylidene chloride.

The polymerization initiator used in the present invention includes initiators commonly used in vinyl chloride suspension polymerization, such as lauroyl peroxide, 3,5,
5-trimethylhexanoyl peroxide, t
- organic peroxides such as butyl peroxypivalate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and acetylcyclohexylsulfonyl peroxide, and α,α′-azobisisobutyronitrile. and α,α′-azobis2,4-dimethylvaleronitrile, or a mixture of two or more thereof.

The dispersant used in the present invention may be any known dispersant, such as partially saponified polyvinyl alcohol, polyvinylpyrrolidone, vinyl acetate, etc.
Examples include maleic anhydride copolymer, maleic anhydride-styrene copolymer, and methyl cellulose.

The polymerization temperature range in the present invention is usually 40 to 75°C, and the range of increase in polymerization temperature during polymerization is usually 5 to 75°C.
Although the temperature is 20°C, there is no particular limitation.

According to the present invention, when carrying out suspension polymerization of vinyl chloride resin using a polymerization vessel equipped with a condenser, it is possible to increase the amount of polymerization without allowing the suspension to enter the conduit or the inside of the condenser. ,
The present invention prevents the formation of scale and does not cause quality problems such as stickiness, shortens polymerization time, greatly improves productivity, and saves heating steam. It has great industrial value.

Hereinafter, the present invention will be specifically explained using examples.

Example 1 705 kg of pure water, 360 g of di-2-ethylhexyl peroxydicarbonate, and 13.5 g of a 3% partially saponified polypinyl alcohol aqueous solution were placed in a polymerization vessel with an internal volume of 1.5 m ³ equipped with a condenser with a heat transfer area of 5 m ² . was charged, the inside of the polymerization vessel was degassed for 15 minutes while stirring, and 600
Kg of vinyl chloride is charged and the temperature is raised to 58℃ to start polymerization. When the polymerization conversion rate reaches 5%, cooling water is started flowing through the condenser, and the amount of cooling water is gradually increased from 30 minutes onwards. The amount of heat removed from the capacitor is approximately
Polymerization was continued while adjusting the temperature to 50,000 kcal/Hr, and from 3 hours after the start of polymerization (polymerization conversion rate 50%), the cooling water supply to the condenser was stopped, and the polymerization temperature was gradually raised to carry out polymerization. Ta.

After 4 hours, the polymerization temperature reached 75°C, so unreacted monomers were collected and the polymerization was stopped. During stirring, water was continuously added at a rate of 300 c.c./min. After completion of polymerization, no scale formation was observed in the condenser or conduit when inspected. Moreover, the polymerization conversion rate at this time was 83%.

Example 2 Internal volume 10 with a condenser with a heat transfer area of 50 m ²
A ³ m3 polymerization vessel was charged with 4300 kg of pure water, 2.2 kg of di-2-ethylhexyl peroxydicarbonate, and 80 kg of a 3% partially saponified polyvinyl alcohol aqueous solution.
The inside of the polymerization vessel was degassed for 15 minutes while stirring, and 3,600 kg of vinyl chloride was charged and the temperature was raised to 58°C to start polymerization. When the polymerization conversion rate reached 3%, water flow to the condenser was started and gradually The amount of heat removed from the condenser after 30 minutes was increased to approximately 200,000kcal/Hr by increasing the amount of cooling water.
The polymerization was continued while adjusting the temperature to be as follows, and from 3 hours after the start of the polymerization (polymerization conversion rate 50%), the amount of cooling water to the condenser was gradually decreased and the polymerization temperature was gradually raised.

After 4 hours, the polymerization temperature reached 73°C, so the unreacted monomers were collected and the polymerization was stopped. During stirring, water was continuously added at a rate of 2/min. using this method
After repeating 10 batches of polymerization, no scale formation was observed in the capacitor or conduit when inspected. Moreover, the polymerization conversion rate at this time was 83%.

Example 3 A polymerization vessel equipped with the same condenser as in Example 1 was charged with 705 kg of pure water, 220 g of di-2-ethylhexyl peroxydicarbonate, and 13.5 kg of a 3% partially saponified polyvinyl alcohol aqueous solution, and the mixture was poured into the polymerization vessel while stirring. was degassed for 15 minutes, then 600Kg of vinyl chloride was charged and the temperature was raised to 52℃ to start polymerization. When the polymerization conversion rate reached 8%, cooling water was started to flow through the condenser, and the amount of heat removed was approximately 30,000kcal/ The cooling water supply to the condenser was stopped 6 hours after the start of polymerization (polymerization conversion rate 50%), and the polymerization temperature was gradually increased until it reached 68°C at 8.5 hours. Therefore, unreacted monomers were collected and polymerization was stopped. During stirring, 150 c.c./min of water was continuously added. After polymerization was completed, no scale was observed on the condenser or conduit, and the polymerization conversion rate was 85.
It was %.

Comparative Example 1 Polymerization was started in the same manner as in Example 1, and when the polymerization conversion rate reached 5%, cooling water was started flowing through the condenser, and the amount of cooling water was gradually increased. Polymerization was continued at 58° C. while adjusting the amount of heat removed to be about 50,000 kcal/Hr, and at 4 hours, unreacted monomers were collected and polymerization was stopped. After polymerization was completed, an inspection revealed that the condenser and conduit were clogged with overflowing resin. The polymerization conversion rate at this time was 77%
It was hot.

Comparative Example 2 Polymerization was started in the same manner as in Example 3, and when the polymerization conversion rate reached 8%, the flow of cooling water to the condenser was started, and the amount of cooling water was gradually increased.
While adjusting the heat removal amount to approximately 30000kcal/Hr.
Polymerization was carried out at 52°C, and unreacted monomers were collected 8.5 hours after the start of polymerization to stop the polymerization. During stirring, 150 c.c./min of water was continuously added. After polymerization was completed, an inspection revealed that the condenser and conduit were clogged with overflowing resin. Also, the polymerization conversion rate at this time was 78
It was %.

Claims (1)

[Claims] 1. When performing suspension polymerization of vinyl chloride or a vinyl monomer mixture mainly composed of vinyl chloride using a polymerization machine equipped with a reflux condenser (hereinafter referred to as a condenser), the polymerization temperature is gradually increased after the polymerization conversion rate is 50%. A method for producing a vinyl chloride resin, characterized in that foaming is suppressed by adjusting the amount of heat removed in a condenser while increasing the temperature.