JPS59221335A - Dehydration of vinyl chloride polymer slurry - Google Patents

Abstract

PURPOSE:To obtain a dehydrated cake having low water content, by sucking the slurry of a vinyl chloride polymer with a self-sucking slurry pump placed at a level above the level of the slurry in a vessel, and supplying the slurry to a dehydrator at a specific low ejection pressure to effect the dehydration. CONSTITUTION:For example, the slurry of a vinyl chloride polymer is sucked with a self-sucking slurry pump 2 placed at a level above the liquid level of the slurry in the polymer slurry tank 1, supplied to the dehydrator 3 at an ejection pressure of <=0.8kg/cm<2>G (preferably <=0.5kg/cm<2>G) at the ejection port of the pump, and is dehydrated with the dehydrator.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for dehydrating a vinyl chloride polymer slurry, and the second feature is that the vinyl chloride polymer slurry obtained by suspension polymerization is preferably dehydrated in a state with as little pressure as possible. This provides a method for obtaining a dehydrated cake with a low moisture content by transporting and feeding the dehydrator to a dehydrator at near atmospheric pressure.

Vinyl chloride polymers are generally mass-produced by suspension polymerization, and in the post-treatment process after polymerization in production process C:, unreacted monomers are first recovered from the polymer slurry by vacuum suction. , Next, this polymer slurry is stored in a -tank tank, from where Fll is continuously pumped.
The water is supplied by transport and hung, and the dehydrated polymer cake is transferred to a drying process and dried to produce a product.

A centrifugal separator is commonly used to operate the raw water in the dehydrator. It is advantageous to increase the dehydration efficiency in this raw water tank as high as possible in order to reduce the thermal energy cost in the drying process, but currently the dehydration efficiency is generally set at a water content of 24 to 2.
It is around 6%, and reducing this value to a lower value is difficult because there are problems with the capacity (performance) of the centrifuge and the length of time it takes for trees to mature.

Generally, a centrifugal pump is used to transfer the polymer slurry, and for example, there is a means of pumping up the polymer slurry from the bottom of a tank in which the polymer slurry is stored and supplying it to an IIR water machine via piping. However, in this case, the discharge pressure of the pump is quite high, and is approximately 2 My/crl 0, depending on the size of the tank, the position level of the dehydrator, the condition of the piping, etc.

The present inventors presumed that such pressurization during transfer of the polymer slurry may be detrimental to the improvement of dewatering efficiency (reduction of water content in the polymer cake), and When we investigated the water content of the polymer cake when dewatering was performed by varying the discharge pressure and keeping the operating conditions of the dehydrator constant, we found that the lower the discharge pressure, the lower the water content of the polymer cake. I discovered that. As a result of further research based on this knowledge, the present inventors found that when the discharge pressure reaches around 1.5/adG and becomes smaller than this, the dewatering efficiency of the polymer slurry dehydrator is significantly reduced. improving and using self-priming slurry pump as a pump for polymer slurry transfer,
The present invention was completed by confirming that by installing this pump at a position higher than the liquid level of the polymer slurry, the water content of the polymer cake could be drastically reduced.

That is, the present invention sucks the vinyl chloride polymer slurry with a self-priming slurry pump installed at a position at least higher than the liquid level of the vinyl chloride polymer slurry in the vessel, and discharges the vinyl chloride polymer slurry at the discharge section of the pump. Pressure o, s sand/
The present invention relates to a method for dewatering a vinyl chloride polymer slurry, which is characterized by supplying the slurry to a dehydrator to perform dehydration at crll G or less.

To explain this, vinyl chloride polymers produced by suspension polymerization are generally agglomerates of extremely porous fine particles, and there are many large and small cavities inside the particles. When the unreacted monomers are recovered from the polymer slurry under reduced pressure and the pressure is returned to normal pressure, the pressure balance corresponds to normal pressure, and water enters the cavities of the polymer after the unreacted monomers have escaped. It is estimated that The amount of water that enters this cavity increases as the pressure increases, and even if the pressure is lowered, the water that has entered the cavity will be drained out, making it difficult to increase the dewatering efficiency of the dehydrator. It is estimated that there is.

On the other hand, in the method of the present invention, the polymer slurry is transported by reducing the discharge pressure of the pump to the minimum necessary pressure and supplying the slurry to the dehydrator with as little pressure applied to the slurry as possible. Very water-repellent (-good, nH
It is possible to reduce the moisture content of the dehydrated cake using a water machine significantly lower than before. In this way, the reduction in moisture content in the dehydrated cake directly leads to the saving of thermal energy in the dryer, which improves the steam consumption rate and improves economic efficiency. This will increase processing capacity and help improve productivity.

In order to achieve the above-mentioned advantages, the present invention uses a self-priming slurry pump, but this is because commonly used centrifugal pumps do not have a large suction head, and this centrifugal pump In order to prevent cavitation and vibration, the pump was installed below the slurry level on the suction side, but as long as this centrifugal pump is used, there is a limit to lowering the discharge pressure, and this disadvantage This can be solved by using a self-priming slurry pump.

That is, the present invention uses a self-priming pump instead of a centrifugal pump, and installs it at a position higher than the slurry level in the tank on the suction side of the pump to obtain a cake from the slurry IJ.

The installation position of the self-priming pump is determined by the height of the water column from the bottom of the tank in the case of one tank of atmospheric pressure slurry to the atmospheric pressure and the height of the water column that corresponds to the maximum temperature of the slurry used for transportation. is the limit, and should preferably be set with some margin in mind. If the pressure in a slurry tank is not normal pressure, the pressure in the tank should be taken into consideration when setting.

Invention C: When transporting and supplying polymer slurry to a dehydrator, the discharge pressure of a self-priming slurry pump is adjusted to o, F.
3 Ky/at/l a or less (preferably 0.s
My/crl G or less) is important; if the discharge pressure is higher than this, the efficiency of raw water in the water storage device (:) will decrease, and the objectives and effects of the present invention will not be achieved.

The present invention will be specifically explained below with reference to examples.

Example 1 A dehydration test was conducted using the arrangement shown in FIG. However, the same figure I:
1 is a polymer slurry tank, 2 is a self-priming slurry pump, and 3 is a water storage machine.
1 and h2 are hl=7m and h2=3m, respectively.

The polymer slurry at this time was a 38% by weight slurry of suspension polymerized vinyl chloride polymer (average polymerization IV'1000), and was stored in a tank at a temperature of 55°C and normal pressure.

The self-priming slurry pump 2 is operated at a suction pressure car of 600 m.
mHg, discharge pressure 0.4 ni/cla, flow rate 12r11
I went at 1/hr. A solid ball-type (decanter-type) continuous centrifugal separator was used as the water-squeezing machine 3, and dewatering was carried out with the number of revolutions, cake conveyance speed, dam height, etc. kept constant during the test. .

On the other hand, for comparison, a dehydration test was conducted on the same polymer slurry as above in the arrangement shown in FIG.

However, in the figure, 4 is a centrifugal pump, 5 is a valve, and h3 and h4 indicating the height relationship are b3 =
1m, h4=10m.

By adjusting the valve 5, the discharge pressure of the pump 4 can be adjusted to 1Ky/
ct/l G, 2 Kri/at a or 3s/c
The polymer slurry was controlled and fed to a dehydrator for dehydration. The operating conditions of the dehydrator were the same as above.

For each dehydrated cake obtained in this way, the moisture content and the amount of steam required to dry the volatile content using a fluidized fluidized dryer to 0.2% by weight (wet basis) (in the table, the steam consumption rate is ) were measured and summarized in Table 1.

Table 1 Steam consumption required to obtain 1 ton of combined product Based on the results in Table 1, the relationship between the pump discharge pressure and the corresponding moisture content of the dehydrated cake is shown in a graph as shown in Figure 3. , As can be seen from this result, the discharge pressure is 1.5
The dehydration efficiency improves rapidly when it becomes less than ni/cr/lG.

Example 2 A dehydration test was conducted using the arrangement shown in FIG. The type of polymer slurry, storage conditions, etc. at this time were exactly the same as in Example 1. The operating conditions of the slurry pump 2 are as follows:
0mmHg, discharge pressure 0.4Kg/mG, flow rate 1.5
m'/hr, and a basket-type continuous centrifugal separator was used as the dehydrator 3, and the rotation speed was set at m'/hr.

Dehydration was carried out with the cake conveyance speed etc. kept constant during the test.

On the other hand, for comparison C:, for the same polymer slurry as above,! A dehydration test was conducted using the arrangement shown in Figure J2. However, as the dehydrator 8, the same device as above was used.

As in the previous example, the moisture content of the dehydrated cake and the amount of steam required for drying were measured and summarized in Table 2.

Table 2 Example 3 In Example 1, vinyl chloride was used as the polymer slurry.
A dehydration test was conducted in the same manner as on the same side, except that a 35% slurry of vinyl acetate copolymer (vinyl acetate content: 13 fr%, average degree of polymerization: 500) was used.

For each dehydrated cake obtained in this way, the steam required to dry the moisture content and volatile content to 1.5% (based on humidity) (expressed as steam consumption in the table) was measured. The results were summarized in Table 3 as shown in Table 3.

Table 3

[Brief explanation of the drawing]

Figure 1 shows the arrangement when a self-priming pump is used, Figure 2 shows the arrangement when a centrifugal pump is used, and Figure 3 shows the relationship between pump discharge pressure and dehydrated cake water content based on the data of Example 1. This is a graph. 1... Slurry tank, 2, 4... Pump 3...
Dehydrator. °Patent Applicant: Shin-Etsu Chemical Co., Ltd. Figure 1 Figure 2 Figure 3 Hiroya Gourd (Kg/cm'G) 0 inventions in Shima Factory Author: Shin-Etsu Engineering, 1 Higashiwada, Kamisu-cho, Kashima-gun, Ibaraki Prefecture Kashima Co., Ltd. Office 25

Claims (1)

[Claims] 1. Suction the vinyl chloride polymer slurry with a self-priming slurry pump installed at a position at least higher than the liquid level of the vinyl chloride polymer slurry in the vessel, and reduce the discharge pressure at the discharge part C of the pump. Q, g Ky /cd
A method for dewatering a vinyl chloride polymer slurry, characterized by supplying it to a raw water tank at less than 1 G