JPH01245829A - Gas-liquid contact equipment - Google Patents

Abstract

PURPOSE:To improve the gas-liquid contact efficiency by constituting the title equipment of the plates provided with the reverse directional trays having a plurality of aperture parts in which the aperture faces on the trays passing the raised gas are opened toward the upstream direction of liquid for the flow direction of the liquid on the trays. CONSTITUTION:Slurry introduced on a reverse directional tray 1 is allowed to flow to the direction shown in an arrow A and overflowed over an outlet weir 2 and passed through a downcomer 3 and introduced on the lower-step reverse directional tray 1. On the other hand, steam is blown out toward the direction B reverse to the flow direction of slurry according to the aperture direction of the aperture face and solid substance precipitated on the tray is lifted therewith and distribution width of stagnant time of resin is made narrow and thereby the gas-liquid contact efficiency is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas-liquid contact device, specifically a gas-liquid contact device with good gas-liquid contact efficiency, especially when removing residual monomer from resin slurry after polymerization. The present invention relates to a gas-liquid contacting device suitable for removing unreacted vinyl chloride monomer from a vinyl chloride resin slurry, for example.

[Prior art] Resin produced by suspension polymerization or emulsion polymerization, etc.
After polymerization, the slurry is in a slurry state, and a product is obtained by removing a medium such as water from the slurry and drying it.

Unreacted monomers usually remain in the resin slurry produced by such a manufacturing method. For example, vinyl chloride remains in a vinyl chloride resin slurry. Therefore, if the medium in the resin slurry is immediately separated and dried after polymerization, a significant amount of unreacted monomer remains in the product resin, which poses an environmental health problem.

Therefore, in order to remove as much residual monomer as possible from the resin slurry before drying, a method of bringing the resin slurry into contact with water vapor is adopted.

A countercurrent gas-liquid contacting device is usually used for this steam stripping. For example, Japanese Patent Publication No. 61-11241 discloses the use of a sieve tray as the tray. However, when using sieve trays, the blowing direction of the water vapor blown through the tray and into the slurry is vertically upward, while the flow direction of the slurry is parallel to the tray and toward the outlet ware. In this case, water vapor blown into the slurry from below the tray is entrained in the slurry flow and flows toward the outletware. Therefore, a short path of water vapor is likely to occur on the tray, resulting in a low gas-liquid contact efficiency.

Furthermore, as mentioned above, since the direction of water vapor blowing out from the tray is vertically upward, if the solid content (resin particles) in the slurry is sedimentable, the solid content tends to settle on the tray, and - Once settled, it is difficult to be redispersed in the slurry. Therefore, the residence time distribution width of the solids in the gas-liquid contacting device becomes wide (the term residence time means the time from when the solids are supplied to the device to when they are discharged).

For example, when steam stripping a vinyl chloride resin slurry using the above-mentioned gas-liquid contact device having a sieve tray, a short bath of steam occurs;
Since the slurry cannot be uniformly dispersed due to sedimentation of the resin, the removal efficiency of residual monomer is low, and compensating for this by increasing the number of trays requires a large amount of equipment expense, which increases manufacturing costs. Further, as explained above, since the precipitated resin is difficult to be redispersed in the slurry, it is subjected to a long thermal history, which deteriorates the quality of the vinyl chloride resin.

[Problems to be Solved by the Invention] Therefore, an apparatus that solves the problems of the prior art as described above, that is, has good gas-liquid contact efficiency, and furthermore, when the liquid is a sedimentary slurry, does not cause sedimentation. A gas-liquid contact device that prevents and redisperses settled particles, such as a gas-liquid contact device that can efficiently remove residual monomer from a vinyl chloride resin slurry and perform steam stripping while preventing quality deterioration of vinyl chloride resin due to long-term thermal history. It is an object of the present invention to provide a liquid contacting device.

[Means for Solving the Problems] The above problem is a plate tower type gas-liquid contact device in which the opening surface on the tray through which rising gas passes is oriented in the upstream direction with respect to the flow direction of the liquid on the tray. It has been found that this can be achieved by a gas-liquid contacting device having at least one stage of trays (hereinafter referred to as reverse-direction trays) having a plurality of openings opening toward each other. Here, the term open surface refers to the surface from which rising gas blows out into the liquid (or slurry) on the tray.

The opening surface of the tray of the device of the present invention and the liquid on the plate (
or slurry), the angle formed by the flow direction is approximately 90°.
It is preferable that the flow direction of the slurry is opposite to the blowing direction of the gas blown into the slurry from the tray.

The gas-liquid contact system that can be treated by the apparatus of the present invention is not limited to a specific system, and any system in which good gas-liquid contact is desired can be treated.

As for liquids, remarkable effects are observed especially in slurry systems containing sedimentable solids. Therefore, the apparatus of the present invention will be explained by taking as an example a treatment in which a slurry system, particularly a vinyl chloride resin slurry after polymerization, is brought into contact with water vapor to remove residual monomers.

When removing residual monomer from a vinyl chloride resin slurry using the gas-liquid contacting device of the present invention, the flow direction of the slurry and the blowing direction of water vapor are opposite on the reverse direction tray, so the water vapor is entrained in the flow of the slurry and exits the outlet. This prevents the wear from flowing in the direction of the wear. In addition, the resin that settles on the tray can be rolled up into the slurry by the flow of water vapor to achieve a uniform slurry concentration, improving the removal efficiency of residual monomers, and the resin staying on the tray for a long time, reducing the long thermal history. Since it is possible to prevent this from occurring, the quality of the final product, vinyl chloride resin, is improved.

In the apparatus of the present invention, the angle that the opening surface of the reverse direction tray makes with the flow direction of the slurry can be appropriately changed depending on the physical properties of the gas-liquid system to which it is applied.

Further, the total area of the openings, the area per piece, the shape and arrangement method, the number of trays, etc. can be appropriately selected depending on the system to be applied, operating conditions, etc.

In a generally preferred embodiment of the invention, the ratio of the total area of the open surfaces of the reversible tray to the tray area (hereinafter referred to as the aperture ratio) is between 0.02% and 5%.

Further, the area of each opening surface of the reverse direction tray is preferably 2 x 10 -3 mm' to 2 x 10 "mm".

[Operation and Effect] In the present invention, by using a reverse direction tray as a tray, a short path of water vapor can be prevented, and the gas-liquid contact efficiency between the slurry on the tray and the blown water vapor is improved. That is, water vapor is blown out along the tray from the opening surface of the reverse direction tray in an upstream direction with respect to the flow direction of the slurry, and the solid content that has settled on the upper surface of the tray is rolled up and redispersed in the slurry. Therefore, the residence time distribution width of the slurry, especially the resin therein, becomes narrower, making it possible to uniformly remove residual monomers in the resin.

Next, the apparatus of the present invention will be explained in more detail by way of an example of steam stripping of vinyl chloride resin slurry with reference to the accompanying drawings.

FIG. 1 is an outline of the gas-liquid contacting device of the present invention for removing residual monomer from vinyl chloride resin slurry. The device comprises a reverse direction tray 11 outlet wear 2 and a downcomer 3.

The slurry is supplied from the slurry feed line 4 to the uppermost stage of the apparatus, while the steam is supplied from the steam supply line 5 to the lowermost stage of the apparatus. After the slurry flows down each stage in order to remove residual monomers, it is taken out from the slurry withdrawal line 6 at the bottom stage. On the other hand, the removed residual monomer and water vapor are distilled out from the top stage, the water vapor is condensed and removed in the condenser 7, and the residual monomer is discharged to the outside of the yarn by the vacuum pump 8.

FIG. 2 is a perspective view of the reverse direction tray 1 of the gas-liquid contacting device of the present invention, and FIG. 3 is a sectional view of the reverse direction tray 1. In the figure, arrow A indicates the flow direction of the slurry, and arrow B indicates the direction in which steam is blown out. It will be understood that the flow direction of the slurry and the blowing direction of the steam are opposite, ie, opposite.

In the case of FIG. 3, it can be seen that the angle between the opening surface and the flow direction of the slurry is 90°. However, in another embodiment, the tip C of the opening surface may be further to the right or to the left in the drawing.

FIG. 4 is a schematic diagram showing the internal state of the gas-liquid contact device of the present invention having the reverse direction tray 1 during operation.

As shown in FIGS. 3 and 4, the slurry flowing onto the reverse direction tray 1 flows in the direction of arrow A, overflows the outlet ware 2, passes through the downcomer 3, and flows into the reverse direction tray 1 at the lower stage. flows upward. On the other hand, water vapor is blown out along the surface of the tray in the direction B opposite to the flow direction of the slurry according to the opening direction of the opening surface. Therefore, since the solid content that has settled on the tray is rolled up into the slurry, the residence time distribution width of the slurry, especially the resin therein, is narrowed. Therefore, uniform contact between the slurry and steam becomes possible, and residual monomers can be effectively removed.

[Example] A vinyl chloride resin slurry was stripped with water vapor at a temperature of 70 to IIθ°C and a pressure of 200 to 900 mmHg using the gas-liquid contact device of the present invention shown in Fig. 1 (10 trays, diameter 450 mm). Treatment was performed to remove residual monomer.

The temperature of the slurry in the device was changed by adjusting the degree of vacuum, and the residence time of the slurry was changed by increasing or decreasing the amount of slurry supplied to the device.

The present invention will be explained below with reference to Examples and Comparative Examples.

Examples 1 to 3 Opening ratio 1.0%, area per opening surface 1.5 mm'
The apparatus of the invention of FIG. 1 was used, having a reversible tray of . A vinyl chloride resin slurry containing 200 ppm of residual monomer in the vinyl chloride resin was heated to a predetermined temperature and supplied through a slurry supply line 4, and 110°C steam was supplied through a steam supply line 5. As the slurry flows down, it undergoes repeated vapor-liquid contact with water vapor passing through the counter-directional tray. The processing results are shown in Table 1. The residual monomer in the vinyl chloride resin in the slurry extracted from the bottom stage was 0.09 ppm = 0.05 ppm. The residual monomer in the resin after dehydrating and drying this slurry is 0.
．． It was 0.01 ppm or less.

Table 1 Comparative Examples 1 to 3 The gas-liquid contactor in Figure 1 was replaced with a sieve tray (see Figure 5) instead of the reverse direction tray.The opening ratio and area of each opening were the same as in Examples 1 to 3. ) except for incorporating
Residual monomers were removed from the vinyl chloride resin slurry under the same conditions as in Examples 1-3. The processing results are shown in Table 2.

From the results of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 2, it is clear that the monomer removal efficiency is significantly improved when the gas-liquid contact device of the present invention is used.

The aperture ratio of the χ milk salmon dofutami tray is 0.02%, 1.0% and 5°0%.
Using the same equipment as in Examples 1 to 3, except for
Residual monomer concentration in vinyl chloride resin is 4000ppm
A vinyl chloride resin slurry (average degree of polymerization of 700) was subjected to steam stripping. The processing results are shown in Table 3.

The residual monomer in the resin in the slurry extracted from the bottom stage was 0. After dehydrating and drying this slurry, the residual monomer in the resin was 0.8 ppm. The OI was below ppm.

Comparative Examples 4-5 The same equipment as in Examples 1-3 was used except that a reverse direction tray with an aperture ratio of 0.01% and 8.0% was incorporated, and the residual monomer concentration in the vinyl chloride resin was 4000 ppm. A vinyl chloride resin slurry (average degree of polymerization of 700) was subjected to steam stripping to examine the influence of the aperture ratio. The processing results are shown in Table 4.

Therefore, the aperture ratio of the reverse direction tray is 0.02% to 5°0%.
It can be seen that the removal efficiency of vinyl chloride monomer is good within this range, but the removal efficiency of vinyl chloride monomer decreases even if the aperture ratio of the reverse direction tray is extremely small or large.

This is because if the opening ratio is small, the openings in the tray will be scattered, resulting in insufficient mixing of water vapor and slurry, and the slurry cannot be uniformly dispersed1.On the other hand, if the opening ratio is large, In this case, it is thought that this is because the slurry weaves from the opening to the lower stage, resulting in a short pass of the slurry.

Examples 7 to 9 Opening ratio 1.0%, area per opening surface 2X I
The residual monomer concentration in the vinyl chloride resin was determined using the same equipment as in Examples 1-3, except that it incorporated a reverse directional tray with O-'me'', 1,5 mm', and 2 x lO A vinyl chloride resin slurry containing 500 ppm (average degree of polymerization 800) was subjected to steam stripping. The treatment results are shown in Table 5.

The residual monomer in the resin in the slurry extracted from the bottom stage was 0.06 ppm, and the residual monomer in the resin after dehydrating and drying this slurry was 0.01 ppm or less.◎ Comparative Examples 6 to 7 Opening The ratio is 1.0%, and the area per aperture is I
A residual monomer concentration of 5 oop in the PVC resin was obtained using the same equipment as in Examples 1-3 except that a 10-3 mm', 8 X 10' mm reverse direction tray was incorporated.
pm vinyl chloride resin slurry (average degree of polymerization 800) was subjected to steam stripping and the influence of the area per opening surface was investigated. The processing results are shown in Table 6.

From the results of Examples 7 to 9 and Comparative Examples 6 and 7, the area per opening surface of the reverse direction tray is 2 x 10
If the area is between ``-3 mm'' and 2 x 10 ``mm'', the vinyl chloride monomer removal effect will be good, but if the area per opening surface of the reverse direction tray is too small or too large, the vinyl chloride monomer will be removed. Monomer removal efficiency decreases.

This is because if the area per opening is small, the bubbles of water vapor blown into the slurry will become smaller, making it impossible to uniformly redistribute the settled solids into the slurry. If the area per piece is large,
The bubbles of water vapor blown into the slurry become larger.
This is thought to be due to a decrease in the total contact area between the slurry and water vapor.

[Effects of the Invention] Conventionally, the water vapor on the tray plate was accompanied by the flow of slurry and flowed in the direction of the outlet ware, causing a short path. In addition, sedimentable solids tend to accumulate on the tray plate, making effective contact between the slurry and water vapor impossible. By using the apparatus of the present invention, a short path of water vapor can be prevented, and furthermore, sedimentation can be prevented. By effectively redispersing the solid content into the slurry, uniform mixing is possible, and the contact efficiency with water vapor is higher than with conventional sieve trays, making it possible to narrow the residence time distribution width of the solid content. Become.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the bubble contacting device of the present invention, and FIG.
A perspective view of the reverse direction tray used in the gas-liquid contacting device of the present invention, FIG. 3 is a diagram showing the flow direction of slurry and the blowing direction of steam, and FIG. 4 is a perspective view of the present invention incorporating the reverse direction tray. FIG. 5 is a schematic diagram of the internal state of the gas-liquid contact device, and FIG. 5 is a perspective view of the sieve tray. l... Reverse direction tray, 2... Outlet ware, 3... Downcomer, 4... Slurry liquid feeding line, 5... Steam supply line, 6... Slurry extraction line, 7...・Condenser, death・
- Vacuum pump, 9...Sieve tray, A...Slurry flow direction, B...Steam flow direction, C...Opening surface tip. Patent applicant Kanebuchi Kagaku Kogyo Co., Ltd. Representative patent attorney Haga Aoyama (1 person) Figure 1 Figure 2 θ ρ Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. A tray tower type gas-liquid contact device, which includes a plurality of trays in which the opening surface on the tray through which rising gas passes is opened in the upstream direction with respect to the flow direction of the liquid on the tray. A gas-liquid contact device comprising at least one stage of reverse directional trays having an opening. 2. The angle between the opening surface and the flow direction of the liquid on the tray is 9
2. The device according to claim 1, wherein the angle is 0°. 3. Claim 1, wherein the ratio of the total area of the opening surface of the reverse direction tray to the tray area is 0.02% to 5%.
2. The device according to item 2 or item 2. 4. The area per opening surface of the reverse direction tray is 2×
The device according to any one of claims 1 to 3, which has a size of 10^-^3 mm^2 to 2 x 10^2 mm^2. 5. The device according to any one of claims 1 to 4, wherein the liquid is a slurry containing sedimentable solids. 6. A method for removing residual monomer from a vinyl chloride resin slurry using the gas-liquid contacting device according to claim 5.