JPS605604B2 - Method for separating and removing residual monomers from vinyl chloride polymer slurry or cake - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slurry of a vinyl chloride polymer obtained by polymerizing vinyl chloride or a monomer mixture mainly composed of vinyl chloride in an aqueous medium, or a cake obtained by dehydrating the slurry. This invention relates to a method for separating residual monomers.

In the production method of vinyl chloride resin, in which vinyl chloride or a monomer mixture mainly composed of vinyl chloride is polymerized in an aqueous medium, it is occluded in the polymer slurry or cake during the dehydration and drying steps after the completion of polymerization. Since unreacted monomers may be diffused into the atmosphere, it is necessary to separate and remove residual monomers from the slurry or cake as much as possible in advance.

Therefore, in order to separate and remove the residual monomer from this slurry or cake, heating and depressurizing (suction) operation is adopted, but in order to achieve this separation and removal more fully, it is necessary to Since there is a critical step in the rate at which residual monomers are removed from the cake, a relatively long period of high temperature and high vacuum treatment is required. This brings about the disadvantage of causing deterioration.

In particular, when the polymer produced as a result of polymerization has a low average degree of polymerization, it becomes increasingly difficult to separate and remove residual monomers by the heating and depressurizing operation, and in this case, the quality of the polymer may be affected. It has been extremely difficult to remove residual monomers at high removal rates without the disadvantage of deterioration. As a result of extensive research into a method for separating and removing residual monomers from the slurry or cake without such disadvantages, the present inventors have found that the slurry or cake is kept at a relatively high temperature for a short period of time. An extremely effective method is to carry out a treatment process consisting of a process of holding the polymer at a relatively low temperature for a long time at a level that does not cause quality deterioration of the polymer, and repeating this process several times if necessary. They discovered this and completed the present invention.

That is, in the present invention, a slurry or cake of a vinyl chloride-based polymer obtained by polymerizing vinyl chloride or a monomer mixture mainly composed of vinyl chloride in an aqueous medium is used.
A first step of maintaining the slurry or cake at a temperature of 00:00 for 5 to 60 minutes, and a second step of maintaining the slurry or cake after the first step at a temperature of 40:00 to 60:00 for 0.5 to 5 hours. A method for separating and removing residual monomers from a vinyl chloride polymer slurry or cake, which is characterized by performing the treatment multiple times in a treatment step and taking out the separated monomers from the system. In this case, the residual monomer can be separated and removed from the slurry or cake at an extremely high removal rate without deteriorating the quality of the polymer, and the monomer will be released into the atmosphere during the subsequent dehydration or drying process. This has the effect that the risk of being exposed is extremely reduced. Furthermore, when obtaining a vinyl chloride polymer with a relatively low degree of polymerization, this method can be used without deteriorating the quality of the polymer from the slurry after the polymerization operation or the cake obtained by dehydrating the slurry. It is said to be extremely effective in removing residual monomers. To explain the method of the present invention in more detail, the method of the present invention includes a first step of holding the slurry or cake at a relatively high temperature for a short period of time, and a slurry or cake that has undergone this first step. and a second step in which the slurry or cake is held at a relatively low temperature for a long period of time, and the treatment temperature in the first step is such that the monomer remaining in the slurry or cake is easily separated from the slurry or cake as much as possible. From this point of view, a relatively high temperature, i.e., 70 to 100 degrees Celsius, is selected, but if the treatment is carried out for a long time in this temperature range, the quality of the polymer will deteriorate, so the treatment time in this temperature range is 50 degrees. ~60 minutes. However, ``The specific treatment method for this first step is to prepare the slurry in a suitable container (in the case of slurry, the polymerization container itself can be used) equipped with a jacket, heat exchanger, steam blowing device, etc. or by storing the cake and heating it by introducing steam into the container or by other heating means to maintain the temperature at 70 to 100 oo while stirring the cake as appropriate, while reducing the pressure in the container, or This can be carried out by removing the monomer released from the container by blowing in nitrogen gas or the heating steam.The process of removing the monomer remaining in the slurry or cake is carried out from inside the polymer particles. Diffusion of the monomer is the rate-determining step, but maintaining a temperature high enough to obtain a sufficient diffusion rate for a long period of time may have an adverse effect on the quality of the polymer, so it is preferable. do not have.

The second step in the method of the present invention, that is, the step of holding the polymer at a low temperature for a relatively long time without risk of damaging its quality, allows the monomer to diffuse from the inside of the polymer particles to the particle surface within that time. The purpose of this treatment is to create a state in which the monomer easily separates when the temperature is then raised again.
0, and the processing time is 0.5 to 50 hours.

The specific treatment method for this second step is to reduce the temperature to the above 40°C to 40°C after the first step and maintain the same temperature. Accordingly, perform the same depressurization operation or blowing operation of nitrogen gas, etc. as in the first step.In addition, if the object to be treated is a cake, the container is preferably a horizontal dryer type with a stirring function, in addition to the one mentioned above. Things are good.
In the method of the present invention, monomers remaining in the slurry or cake are separated and removed by treating the slurry or cake with the first and second steps described above. It is necessary to repeat the treatment process consisting of the steps described above several times, and thereby the residual monomer can be removed at a high removal rate without deteriorating the polymer. The processed material to which the method of the present invention is applied is, as described above, a slurry obtained by polymerizing vinyl chloride or a monomer polymer mainly composed of vinyl chloride in an aqueous medium, or a slurry obtained by dehydrating this slurry. However, the polymerization in the aqueous medium may be either suspension polymerization or emulsion polymerization, and there is no particular restriction on this point.

Next, examples of the present invention will be given.

Example 1 Slurry obtained by polymerizing vinyl chloride by a normal suspension polymerization method (average degree of polymerization of polypynyl chloride in this slurry: 7
00 unreacted vinyl chloride content (6500 traces), this was heated in a polymerization vessel to 80 qo for a certain period of time, during which time the pressure was reduced to around the saturated water vapor pressure of water at that temperature, and the vinyl chloride monomer released from the slurry was removed. The temperature of the slurry was then lowered to 6530°C and the slurry was left at this temperature for a certain period of time. The vinyl chloride concentration and the quality of the vinyl chloride resin obtained by drying the slurry were as shown in Table 1.

However, Experiments 1 to 5 were based on the present invention, Experiments 6 and 7
shows a comparative example. Processing process: Experiment 1 8
0℃ (15 minutes) - 65℃ (1 hour) - 80qo (15
minute) - 65 o○ (1 hour) - 80 qo (1 flour) -
cooling.

Experiment 2 800 (1 time) - 65q0 (5 hours)
-80oo (15 minutes) -6500 (5 hours) -80q
o (15 minutes) - Cool.

Experiment 3 80oo (15 minutes) - 65oo (1 field time) - 80q○ (15 minutes) - 65q○ (1 field time) -8
000 - (15 minutes) - Cooling.

Experiment 4 80oo (18 minutes) - 65qo (2 hours) - 8'0 (1 powder time) - 65ko0 (2 hours) - Cooling.

Experiment 5 80qC (15 minutes) - 65q○ (5 feeding times) - 8000 (18 minutes) - Cooling. Experiment 6 80qo (
2 hours) - Cooling.

Experiment 7 6500 (2 hours) - Cooling.

Table 1 * 10 parts by weight of pinyl chloride resin powder obtained by drying the slurry, 1 part by weight of lead stearate and 0 parts by weight of stearic acid.
．． 5 parts by weight were blended and kneaded for 5 minutes using two rolls at 170°C to form a sheet, and the degree of initial coloring of this sheet was observed with the naked eye.

○: Almost no initial coloration △: Slight initial coloration ×: Large initial coloration Example 2 A slurry obtained by polymerizing vinyl chloride by a normal suspension polymerization method was dehydrated using a centrifuge, and the resulting cake ( The average degree of polymerization of polyvinyl chloride is 70 and the content of unreacted vinyl chloride is 550.
After holding at OO for a certain period of time, the inside of the dryer was lowered to 60 pm and kept at the same temperature for a certain period of time. This process was repeated several times, and depending on the conditions of the processing process (Experiments 8 to 14), the inside of the cake after the processing was completed. The vinyl chloride concentration and the quality of the vinyl chloride resin (judgment criteria were the same as in the previous example) were as shown in Table 2.

However, Experiments 8 to 12 represent the present invention, and Experiments 13 and 14 represent comparative examples. Treatment process: Experiment 8 80oo (15 minutes) - 60qo (1 hour)
-8000 (15 minutes) -60q○ (1 hour) -80q
o (18 minutes) - Cool.

Experiment 9 80pm 0 (1st class time) - 60qo (5 hours)
-80qo (15 minutes) -60q0 (5 hours) -80q
o (for 1 time) - Cooling.

Experiment 108oo (15 minutes) - 60oo (10 hours)
-80℃ (15 minutes) -60qo (1 wind hour) -80℃
(15 minutes) Cool.

Experiment 11 80oo (18 minutes) - 6020 (24 hours) - 8pi○ (15 minutes) 16bi○ (2 hours) 1 cooling.

Experiment 1280 qo (1 flour) - 60 qo (50 hours) - 8 bi○ (18 minutes) - Cooling. Experiment 1380qo (
2 hours) - Cooling.

Experiment 1460k (2 hours) - Cooling.

From the results shown in Table 2 and above, it can be seen that according to the method of the present invention, unreacted monomers can be removed as much as possible without deteriorating the quality of the vinyl chloride resin.

Claims (1)

[Claims] 1. A first step in which a slurry or cake of a vinyl chloride polymer obtained by polymerizing vinyl chloride or a monomer mixture mainly composed of vinyl chloride in an aqueous medium is held at a temperature of 70 to 100 ° C. for 5 to 60 minutes. step, and the slurry or cake that has passed through the first step is heated to a temperature of 40 to 68°C for 0.5 to
Separation and removal of residual monomers from a vinyl chloride polymer slurry or cake, which is characterized by being treated multiple times in a treatment step consisting of a second step of holding for 50 hours, and removing the separated monomers from the system. how to.