CS209874B2 - Method of polymerization the vinylchloride - Google Patents

Abstract

In the process, the vault of the reactor is kept, during the reaction, under a continuous flow of water at a pressure of >/= 15 kp/cm<2> and, after the reaction has taken place, the residual encrustations on the reactor vault are removed mechanically with high-pressure water at >/= 100 kp/cm<2>. As means for carrying out the process, a device comprising a hollow shaft (1) having nozzles (3) and having axial and rotary movement is used. The process is applied in polymerisations of vinyl chloride by itself or as a mixture with other monomers containing 20 % by weight or less of comonomer. <IMAGE>

Description

(54) A process for the polymerization of vinyl chloride

The invention relates to a process which is useful in the suspension polymerization of vinyl chloride, either alone or in admixture with other monomers, for removing incrustations from parts of the reactors in contact with the gas phase.

It is known that one of the greatest problems in the suspension polymerization of vinyl chloride alone or in admixture with other monomers is due to the polymer encrustations deposited thereon. reactor walls and, if not removed, contaminate the product of subsequent polymerization. Removing them, either manually or mechanically using high pressure water, in any case requires opening the reactor and losing one or more hours of time.

Recently, a number of patents have been granted which claim to solve the incrustation problems on the reactor walls in contact with the liquid phase.

In general, these solutions deal with the composition of compositions that prevent the deposition of increments and require cleaning operations after only about ten doses.

The problem of incrustations on the gas-phase portions of the reactor is still unresolved, but the tendency to utilize the reactors to the greatest extent possible (large loading coefficients, intensive mixing, high residual monomer distillation rates and others) has resulted in more intensive formation. foams and splashing strands that cause deposition of polymer on the reactor lid, thereby causing this. the phenomenon has become an even more serious problem. After several batches, the nozzles become clogged and there is a risk of separation of large polymer blocks which prevent the reactor from being discharged and the valve tightness in the bottom of the reactor is broken; thus, the accuracy of the metering and discharging operations is compromised and the reliability of the reactor during polymerization becomes problematic.

Overall, due to incrustations on the reactor lid, the possibility of opening at as long as practicable intervals cannot be influenced by the use of a contamination-preventing mixture.

Now it was found that it is not. .reaktor be opened when each dose for visual inspection lid · and the possible removal of incrustations, when during the 'reaction is carried out continuously in a reactor lid rinsing ^{1 * * * The} dou under a pressure of at least 1.5 MPa, and if after this. the operation is followed by washing (for example, during the discharge of the dose or each time sealing the autoclave) with water. With a pressure of 10 MPa or more.

More specifically, if a rinse at a conversion of between 15 and 25% and at a flow rate of at least 1000 1 / h and a rinse is continued until the conversion reaches at least 40%, only minor incrustations are obtained which can be removed with water below high pressure and that do not cause discomfort or discharge tightness of the drain valve.

Cleaning operations up to a conversion of more than 25% have been included, avoiding the formation of large block incrustations, and premature cleaning is not advantageous because the reduced free volume at conventional industrial batches does not allow the desired water flow rate to be maintained.

Subsequent operations using high pressure water are absolutely necessary in order to prevent minor residual incrustations from further growth during further reactor loading; the water rinse alone during the entire reaction time is capable of permanently preventing polymer deposition only at low charge coefficient batches, with slow agitation, and the like, i.e., in polymerizations of low industrial importance.

The following examples are merely intended to illustrate the need for simultaneous use of the two measures described, but in no way limit the scope of the invention.

Example 1

A 25 m ³ autoclave equipped with a stirrer and a Pfaudler stopper was charged with 70% by-pass water and 1: 1 vinyl chloride and stirred at 120 rpm. The lid was rinsed with a stream of water throughout the reaction. o · Flow rate 1,000 l / h · at pressure 2 MPa. Final performance is 90%. After completion of the reaction, the lid is perfectly clean, as is the case with other doses.

Example 2

The same autoclave as in Example 1 was charged to 90% with a mixture of one part water and one part mixture of 85 parts vinyl chloride and 15 parts vinyl acetate. After rinsing the lid with water at a pressure of 2.5 MPa, where the conversion ranges from 20 to 40%, there are 3 kg of crust on the lid, which are scattered throughout the surface. At subsequent doses, water washing is carried out at a pressure of 30 MPa using orientable nozzles. The lid of the autoclave is perfectly clean and there are no problems with the discharge or leakage of the drain valve.

Example 3

In the same autoclave as in the previous examples, the same loading coefficient and the same water to vinyl chloride ratio were used as in Example 2. After rinsing the lid with water at a pressure of 3 MPa with a conversion of 40 to 65%, 10 kg crusts were collected in the form of rough blocks. At subsequent doses, water washing is carried out under a pressure of 35 MPa, which is sufficient to completely remove contaminants but greatly extends the discharge times, since the polymer clogging the drain valve must be removed manually.

The method described above can be used without limitation for autoclaves of all sizes common in industry and for all mixtures known in the industry, including mixtures patented to reduce pollution.

The invention can be used in the polymerization of vinyl chloride, either alone or in admixture with other monomers, which contains 20% or less of the comonomer; useful comonomers that can be copolymerized with vinyl chloride are known to those skilled in the art. Examples include, but are not limited to, vinylidene chloride, vinyl acetate, vinyl butyrate, methyl acrylates and methacrylates, butylacrylates and methacrylates, isooctylacrylates and methacrylates, diethyl and dipropyl maleate, propylene butylene, propylene butylene, propylene butylene, propylene butylene, propylene butylene, propylene butylene, , vinyl ether, allyl acetate, diallyl phthalate, diallyl maleate, acrylonitrile, methacrylonitrile and others.

In carrying out the above-described method, several minor considerations must be borne in mind that can result in the highest possible use of rinsing and washing water without damaging the proper reaction.

For example, the preferred site of polymermch incrustation could be solid devices protruding into the autoclave, which greatly reduces the rinsing and washing performance.

Therefore, it is preferable to use movable devices of the type shown in the drawing in which water (under low or high pressure) flows through the hollow shaft 11 and is thrown against the cover 2 of the autoclave through nozzles 3 whose diameter and orientation are set to the appropriate value inside the autoclave.

In non-working conditions, the seal 4 between the shaft and the flange 5 and the circumference of the lower part of the flange provide a solid seal without protrusions from the lid into the autoclave.

In addition, the rotational movement of the shaft allows the entire perimeter of the autoclave to be affected by the washing water.

Nozzle diameter and orientation are a function of the operating conditions, i.e. the characteristics of the water used (for rinsing under pressure equal to or greater than 1.5 MPa, for pressure washing equal to or greater than 10 MPa).

The number and location of the devices described depend on the internal configuration of the autoclave, i.e., stops, cooling tubes, agitator shaft, thermocouples, and any components that may come into contact with water jets.

Regardless of the type of gasket and the manner of inducing the necessary movement, the device shown in the drawing is generally characterized by the fact that the water is guided by a hollow shaft 1 axially rotating and flows through nozzles 3 having suitably adjusted dimensions and orientations .

Claims (3)

SUBJECT Process for the polymerization of vinyl chloride, alone or in admixture with other monomers, characterized in that during the reaction, the reactor lid is continuously rinsed with water at a low pressure of at least 1.5 MPa and after completion of the reaction the residual incrustations on the reactor lid are removed mechanically with water under high pressure. at least 10 MPa. 2. The method of claim 1 wherein: OF THE INVENTION The low pressure water rinse is carried out from a conversion value of 15 to 25% to a conversion value of at least 40%, wherein the water flow is at least 1000-1 / h. 3. A method according to claim 1 or 2, characterized in that the water under low and high pressure is injected by a system of orientable nozzles which are protected from possible incrustations in the non-working position.