JPH0460124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method of extracting unreacted vinyl chloride from suspensions and emulsions (hereinafter collectively referred to as "slurry") of vinyl chloride resin (hereinafter abbreviated as "PVC"). This invention relates to a stripping column for removing monomer (hereinafter abbreviated as "VCM").

PVC is produced by suspension polymerization or emulsion polymerization with VCM alone or with monomers copolymerizable with VCM. After completion of this polymerization, unreacted VCM is removed and recovered by reducing pressure or by blowing inert gas, and then PVC is dried and made into a product.

Incidentally, a tray type stripping tower is used for efficient VCM removal and recovery. In conventional tray-type stripping towers, PVC slurry supplied from the top of the tower comes into countercurrent contact with inert gas and water vapor blown from the bottom of the tower, and VCM in the PVC slurry is removed, and this removed VCM is converted into water vapor. The gas containing VCM is discharged from the top of the tower, and the gas discharged from this tower is subjected to VCM recovery.

Since this stripping tower is a tray type, the VCM removal effect changes depending on the number of trays, and the more the number of trays, the better the effect, but the spacing between the trays needs to be more than a certain level, so It has no choice but to become a device. In addition, there are many brands of PVC,
It is necessary to clean the inside of the stripping tower every time production is changed, but since the stripping tower is of a tray type, there are blind spots for cleaning and it is difficult to clean it completely.

Therefore, the present inventors tried to use a packed tower with fewer blind spots for cleaning as the stripping tower and to use steam as the stripping agent.
Although the VCM removal efficiency was good, there was a problem that the inside of the column was filled with bubbles and PVC slurry bubbles overflowed from the top of the column, making it difficult to continue operation.

The present inventors believe that replacing the packed tower with a stripping tower is better in terms of removing VCM;
It was concluded that the problem was the formation of bubbles, and after further research, the present invention was finally completed.

That is, the present invention relates to a stripping column for removing unreacted vinyl chloride monomer from a vinyl chloride resin suspension or emulsion, and the present invention is a packed column packed with packing material, and the top part of the packed column is A multi-tubular condenser is installed in which the water vapor discharged together with the stripped vinyl chloride monomer is condensed in each tube, separated from the vinyl chloride monomer gas, and directly refluxed to the top of the packed column. This is a stripping column for unreacted vinyl chloride monomer.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a stripping tower of the present invention.

Packed column 1 was stripped at the top of the column.
There is a condenser 2 that condenses water vapor discharged together with VCM, separates it from VCM, and returns the condensed water to the packed column 1.

Next, PVC containing unreacted VCM is placed in the upper space of the packed part (packed part) 3 of the packed column 1.
There is a slurry supply nozzle 4 for introducing slurry, and this slurry supply nozzle 4 has a structure in which the PVC slurry is uniformly distributed and supplied to the cross section of the column.

The filler preferably has a structure that prevents PVC slurry from accumulating or depositing, such as Raschig rings, Berl saddles, Terratte packing, Pall rings, Lessing rings, and Interlock saddles. Among these, terrarette packing is preferred. The size of the packing depends on the size of the tower,
It varies depending on the amount of filling, amount of PVC slurry processed, etc.

The filling amount of the packing is 3 to 50%, preferably 5 to 20% of the internal volume of the packed column. If the amount is less than 3%, no effect will be obtained, and if it is more than 50%, the processing capacity of the stripping column will be poor.

There is a nozzle 5 for blowing water vapor into or just below the lower part of the filling part 3, and normally 2 to 7 kg/cm ² of water vapor is blown during operation. The water vapor blown here rises in the filling section 3, comes into countercurrent contact with the PVC slurry supplied from the slurry supply nozzle 4, and removes VCM from the PVC slurry.

At the bottom of the packed column 1, in countercurrent contact with water vapor,
PVC slurry from which VCM has been removed accumulates, and piping 6 is installed to extract this accumulated PVC slurry.

On the other hand, PVC slurry is sensitive to heat and has a temperature of 90 to 100 for a long time.
PVC decomposes and becomes unusable when exposed to temperatures around ℃, so a pipe 7 is installed at the bottom of the packed column to introduce water or a portion of the extracted and cooled PVC slurry for cooling. is preferred. In addition, as a condition for operation, the temperature at the bottom of the packed column must be constantly lowered to an extent that PVC does not decompose.
Moreover, if the accumulated PCV slurry is immediately extracted and cooled, this piping 7 is unnecessary.

On the other hand, VCM stripped in packed column 1
is separated from entrained water through a condenser 2 directly connected to the packed column 1, and then sent to the VCM recovery process.

Further, the condensed water is refluxed to the packed column 1, and by refluxing this water, the PVC slurry is prevented from foaming. It is desirable that the refluxed water is dispersed throughout the upper part of the packed column, and for this purpose, the condenser 2 is of a multi-type type so that the water condensed in each tube is directly refluxed to the top of the packed column 1. It is desirable to have a structure that allows

The inner diameter of the condenser 2 relative to the inner diameter of the packed column 1 is desirably 1/3 or more and 1 or less, more preferably 2/5.
It is about 7/8.

The operating conditions for the stripping column of the present invention are such that the temperature at the top of the packed column 1 is maintained at 70 to 100°C, preferably 80 to 95°C, and the pressure is maintained at 300 to 760 Torr, preferably 350 to 650 Torr. It is said to be in a boiling state.

At that time, it is preferable that the inside of the tower be operated in a gas dispersion type, and the gas hold up is usually 0.2 to 0.8.
m ³ /m ³ , preferably 0.3 to 0.6 m ³ /m ³ is suitable. If the gas hold up is less than 0.2m ³ /m ³
If VCM removal is not sufficient and the amount exceeds 0.8 m ³ /m ³ , a large amount of steam will be required and the column may deviate from the normal operating range.

If the temperature at the top of packed column 1 exceeds 100℃
causing PVC quality deterioration during VCM removal;
Below 70°C, the efficiency of VCM removal becomes poor. Further, the temperature at the bottom of the column is preferably 100°C or less, and from the viewpoint of operational efficiency of the packed column 1, the temperature difference between the temperature at the top and the top is preferably within 20°C.

The amount of water vapor blown into the packed tower 1 may vary depending on the temperature, pressure, and operating conditions of the packed tower 1, but at 120 to 170°C and 2 to 7 kg/cm ² of water vapor,
A weight ratio of 0.02 to 0.10 for PVC slurry is suitable.

In addition, the residence time of the PVC slurry in the packed tower 1 is determined by the operating conditions of the packed tower 1 and the VCM in the PVC slurry.
Although it varies depending on the concentration and removal rate, etc., it is usually within 30 minutes.

The required tower height of the packed column 1 can be calculated from an experimental formula determined from equilibrium relationships, material balance, etc., determined in advance through preliminary experiments. The effectiveness of removing unreacted VCM depends on various factors such as the operating conditions of the packed column 1 (temperature, pressure, steam injection amount, residence time, etc.), the concentration of the PVC slurry, and the porosity of the PVC resin in the case of a suspension. However, in order to make the unreacted VCM concentration in the PVC slurry exiting the packed tower 1 0.005 times the unreacted VCM concentration in the PVC slurry entering the packed tower 1, the height of the packed section 3 may be within 20 m. That is, by using the packed column 1 of the present invention with a packed section 3 having a height of 20 m, for example, by continuously treating a PVC slurry containing 15,000 ppm of unreacted VCM, the VCM concentration after treatment can be lowered to 75 ppm or less.

The inner diameter of the packed column 1, that is, the empty column cross-sectional area is determined by the amount of PVC slurry to be treated. The stripping column of the present invention has an extremely high removal effect of unreacted VCM, so the stripping column per unit cross-sectional area of the column is
It is preferable to determine the inner diameter of the packed column 1 so that the throughput of the PVC slurry is 10 to 100 ml/min·cm ² .

Since the stripping column of the present invention has a good removal effect of unreacted VCM, it may be used without the conventional batch vacuum degassing method.
Even in that case, the VCM concentration in the PVC slurry after treatment can be adjusted by slightly changing the operating conditions of packed column 1.
It can be reduced to 100ppm or less.

The stripping column of the present invention is highly effective in removing unreacted VCM, requires less steam to be blown into the packed column 1, and is advantageous in terms of energy. Furthermore, since the condensed water is refluxed to the packed column 1, wastewater saturated with VCM is not produced, which is extremely good in terms of environmental hygiene.

The present invention will be explained below with reference to Examples. The examples are for explaining the present invention, and are not intended to limit the technical scope of the present invention.

In addition, unreacted VCM in PVC suspensions and emulsions
was measured by the method described below.

Pour exactly 100 ml of acetone containing 1% by weight of tert-butylcatechol (polymerization inhibitor) into a 300 ml Erlenmeyer flask with a stopper, and add 30 to 50 g of PVC to this.
Add slurry quickly. Accurately measure the amount of this PVC slurry. Next, shake the Erlenmeyer flask containing this sample and acetone for 1.5 hours to extract VCM into a liquid layer, and then quantify the VCM using a gas chromatograph.

Separately, determine the amount of resin in the PVC slurry,
Convert the quantitative value of VCM to the VCM concentration per resin.

VCM contained in PVC slurry is contained in water, but in this specification, all values are calculated per resin.

Example 1 In a polymerization machine, 150 parts by weight of deionized water, 0.03 parts by weight of tert-butyl peroxypivalate, and partially saponified polyvinyl alcohol with a degree of saponification of 80 mol% were added.
0.1 part by weight was charged, and the air inside was removed. Thereafter, 100 parts by weight of VCM was charged and a polymerization reaction was carried out at 57°C. After 11 hours, the pressure decreased to 5 kg/cm ² gauge pressure. Then, while raising the temperature, recovery of unreacted vinyl chloride monomer was started, and recovery was continued at 75° C. until the gauge pressure reached 0 kg/cm ² G, and the obtained PVC slurry was transferred to a raw material slurry storage tank. At this point, the concentration of residual VCM in the PVC chiller was 14,000 ppm. This PVC slurry was subjected to continuous VCM removal treatment using the apparatus shown in FIG. In other words, PVC slurry is taken out from the raw material slurry storage tank, passed through a pump, and then passed through a heat exchanger.
Preheated to 85℃, then filled with 2.5 cm of terrarette packing at a volume ratio of 10%, inner diameter 1 m, filled part 3.
The slurry was continuously supplied from the slurry supply nozzle 4 of the packed column 1 having a height of 10 m at a flow rate of 16 m ³ /hr. Packed tower 1
Steam was blown in from the steam introduction nozzle 5, the temperature at the bottom of the column was maintained at 90°C, the pressure inside the column was reduced, and the inside of the column was brought to a boiling state under conditions of a temperature at the top of the column of 88°C and a pressure of 500 mmHg. Packed tower 1 has a gas hold up
The slurry was brought into countercurrent contact with water vapor by operating in a gas dispersion mode such as 0.45 m ³ /m ³ . The slurry stripped in the packed column 1 was continuously extracted from the pipe 6 at the bottom of the packed column 1 and cooled. A part of it (15% of the total amount) was recycled through pipe 7 at the bottom of packed column 1.
When the concentration of residual unreacted VCM in the slurry stripped in packed column 1 was measured, it was found to be 45 ppm based on resin. The slurry was dehydrated and dried in a conventional manner, and a white resin with no apparent deterioration was obtained. In the packed column 1, the steam introduced into the column reaches the condenser 2 with an inner diameter of 55 cm together with the VCM in the PVC slurry. Here, the water vapor is indirectly cooled by cooling water, becomes condensed water, and returns to the packed tower 1, where it is returned to the VCM.
exits from the top of the concentrator 2 and is sent to the monomer recovery step.

Comparative Example 1 The same operation as in Example 1 was carried out except that the condenser 2 was not activated and the mixed gas of VCM and steam generated in the packed column 1 was completely discharged to the outside of the system. After 10 minutes, the top of packed column 1 was filled with bubbles and could no longer be operated.

Example 2 100 parts by weight of VCM, 150 parts by weight of deionized water, 0.1 parts by weight of sodium lauryl sulfate, 0.2 parts by weight of lauryl alcohol, 2,2'-azobis-2,
0.06 parts by weight of 4-dimethylvaleronitrile was homogenized using a homogenizer and then charged into a polymerization machine.
Thereafter, polymerization was carried out at a temperature of 50° C. until the pressure of the polymerization machine reached 4 kg/cm ² gauge pressure. Next, as an antifoaming agent, manufactured by Diamond Shamlok Co., Ltd.
Add 0.1 part by weight of NOPCOFOAMASTER(TM);
Unreacted VCM was collected at the same temperature until the gauge pressure reached 0 Kg/cm ² G. At this point, residual unreacted VCM in the latex was measured and found to be 12,000 ppm. When the PVC latex thus obtained was treated using the same equipment and operating method as shown in Example 1, the remaining unreacted VCM after treatment was
It was 15ppm.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing an example of a stripping tower of the present invention. 1... Packed tower, 2... Condenser, 3... Packing section,
4...Slurry supply nozzle, 5...Steam introduction nozzle, 6...Slurry take-out piping, 7...Piping for introducing water or cooling slurry.

Claims (1)

[Scope of Claims] 1. A stripping column for removing unreacted vinyl chloride monomer from a vinyl chloride resin suspension or emulsion, which is a packed column packed with packing material, and A multi-tubular condenser is installed that is directly connected to the top of the column and condenses the steam discharged together with the stripped vinyl chloride monomer in each tube, separates it from the vinyl chloride monomer gas, and refluxes it directly to the top of the packed column. A stripping column for unreacted vinyl chloride monomer. 2. The stripping column according to claim 1, wherein the packing is at least one member selected from the group consisting of Raschig rings, Berle saddles, tellerette packings, pole rings, dressing rings, and interlock saddles. 3. The stripping column according to claim 2, wherein the packing is terrarette packing. 4. The stripping column according to claim 1, wherein the amount of packed material is 3 to 50% of the internal volume of the packed column.