JPS598281B2 - Suitable gas-liquid contact column for removing vinyl chloride monomer from vinyl chloride polymer-containing slurry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas-liquid contact column, and more particularly to a gas-liquid contact column involving the use of special trays, the purpose of which is to remove vinyl chloride monomer from a vinyl chloride polymer-containing slurry. To provide a gas-liquid contact tower suitable for

Conventionally used trays for gas-liquid contact include bubble cap trays, sieve trays, valve trays, etc., but when a slurry containing a considerable amount of solids is brought into gas-liquid contact, the solids are removed from the tray and other parts. It tends to settle and accumulate in various parts of the tower, and cleaning is time-consuming and difficult, making it difficult to switch to a different type of slurry, and causing switching, loss, and thermal deterioration.

Therefore, processing settleable slurries in gas-liquid contact columns with conventional trays is not only difficult but also extremely uneconomical. In the present invention, by using a tray with a special structure that has self-cleaning ability in the column, the solid content of the sedimentary slurry, such as the above-mentioned vinyl chloride polymer-containing slurry, is allowed to settle and settle. This enables gas-liquid contact which has many advantages, such as being extremely efficient and economical, and having little pressure loss.

The special tray is constructed by a special type of tray plate and optionally tilting the deck plate and providing holes on the support ring. Typical conventional trays are of the gas dispersion type, which have the function of bringing the gas into contact with the liquid when the gas from below passes through the liquid dammed by an outlet weir. On the other hand, in the tray used in the present invention, gas does not pass through the liquid, and there is no need for a holding assembly for the slurry liquid using outlet wear. The system converts the mixture into a gas-solid-liquid mixed phase state, and if necessary, the mixed phase state is repeatedly collided with several grid-like gas-liquid separation plates provided on the tray to perform gas-liquid separation that also serves as gas-liquid contact. When the gas passes through the separation plate, it turns downward, then turns upward again and enters the upper stage. Hereinafter, the tray used in the present invention will be described in more detail with reference to the accompanying drawings.

FIG. 1 is a plan view of a special tray plate 1 used in the present invention, and FIG. 3 is a longitudinal section of the plate 1.
3 indicates an inclined opening (oblique slit) or an inclined part.
The slit width of the tray plate 1 is preferably about 2 to 5 mm, and the arrangement of these tray plates in the tower is such that the direction of the gas blown out from the inclined slit 2 is relative to the liquid flow direction, as shown in FIG. 2A. For example, it should be about 45 degrees. In addition, tray plate 1 with inclined slits
Although several tray plates are arranged, the tray plates are arranged so that the gas blowing direction is displaced by, for example, about 90 degrees from the adjacent tray plate. When the amount of liquid is small, all of the liquid on the tray is dispersed into droplets by the gas, and when the amount of liquid is large, the gas is dispersed into bubbles in the liquid and at the same time part of the liquid is dispersed, increasing efficiency. Good gas-liquid contact is achieved. At this time, the gas and liquid advance in one direction along the downcomer forming the inclined surface in an integrated mixed phase state, and the liquid increases the driving force of the flow due to the directionality of the gas. Such a contact mechanism eliminates the need for outlet wear for holding or retaining the liquid, and the liquid flow is also propelled by the gas flow, resulting in improved processing efficiency. These things are clear from FIG. 3, in which the gas has an acute orientation with respect to the tray plate 1, and the gas flows from the inclined slit 2 of the tray plate 1 to the inclined slit 2 of the tray plate 1. Liquid flow flowing over part 3 (
The liquid is blown onto the tray plate 1 at a predetermined angle (direction X) with respect to the flow direction Y) to disperse the liquid and form a gas-liquid mixed phase 7. At this time, as shown in FIG. 2B, by providing a gas-liquid separation plate 6 on the tray as required, the gas-solid-liquid mixed phase is caused to collide with the separation plate 6, and entrainment is sufficiently prevented. You can also. Usually, a tray plate made of the same material as the tray plate is used as the gas-liquid separation plate. In addition, the liquid on the tray near the column wall tends to stagnate, but consideration must be given to the arrangement of the tray plate with inclined slits so that the liquid in this area is directed toward the inside of the column. Further, the material of this tray plate with inclined slits may be selected as appropriate depending on the purpose, but metal or plastic is usually conveniently used. It can also be used with commercially available expanded metal tray plates. Up until now, we have talked about a column with a special tray that is extremely suitable for gas-liquid contact with a slurry containing vinyl chloride polymer.
Below, in the production of PVC (vinyl chloride polymer), C
A case in which the gas-liquid contact tower of the present invention is used to remove CM from a PVC slurry containing M (vinyl chloride monomer) residue will be specifically described. During the production of vinyl chloride polymer, VCM in PVC is removed using a distillation column, and VCM in waste water from dehydrators and waste gas from dryers is removed.
It is necessary to prevent pollution caused by VCM.

However, PVC slurry is prone to sedimentation and is susceptible to thermal deterioration;
It is not easy to remove CM by steam stripping, and the valve cap trays or sieve trays conventionally used for distillation have a cap on the tray, and since the tray is flat, PVC is placed on the tray. Slurry tends to stagnate and PVC settles and deposits, making cleaning extremely difficult and time consuming.

On the other hand, in the stripping tower of the present invention, an equivalent amount of V
PVC slurry containing CM was fed to the top of the tower, and sequentially
VCM in PVC can be very efficiently stripped by lowering a tray consisting of a tray plate with inclined slits, and furthermore, PVC slurry does not accumulate on the tray or in various parts of the column and is not subject to thermal deterioration.

Specifically speaking, the stripping procedure is as follows: V
The PVC slurry containing CM is flowed on the inclined part 3 of the tray as shown in FIG. The steam thus oriented accelerates the liquid flow in the direction indicated by Y, i.e. it scatters the slurry as indicated by 7 and does not stagnate on the tray. That's what I do.

Heat transfer and mass transfer between the slurry and the ejected steam are promoted. In this way, the inclined slit 2 gives directionality to the ejected steam and gives fluidity to the PVC slurry during operation.
The part that supports the tray in the column, that is, the support ring, or the lower tray of the downcomer, where the slurry descends from the tray to the lower tray, has no opening, so the solid content in the slurry is improved. To prevent this, small holes are provided in the support ring part to provide fluidity with steam from the bottom, and the downcomer part and its descending lower tray are tilted to prevent the solids from settling. , prevent deposition. Furthermore, when the operation is stopped, since the inclined slit 2 is inclined, the PVC slurry 1 does not descend to the lower part through the slit and the small holes and is deposited, and is therefore easily cleaned, that is, it is used in the present invention. The tray also has self-cleaning properties.
Generally, a distillation column can be used as the gas-liquid contact column of the present invention.

The operating conditions vary depending on the concentration of the slurry, the specifications of the desired product, and various other factors, but VCM in PVC production
In order to remove VCM from the residual PVC slurry by stripping, it is preferable to carry out the stripping at a temperature of about 60 DEG to 100 DEG C. The characteristics of the gas-liquid contact tower of the present invention are summarized as follows.

(1) PVC slurry does not settle or accumulate in the tower,
Continuous operation is possible, and the product PVC does not suffer from thermal deterioration.

(2) Easy to operate and no need for additional personnel
(3) Removes over 90% of ■CM in PVC slurry,
It can be recovered.

(4) Residual CM in dry PVC can be reduced to 10 ppm or less.

(5) Reduce VCM contained in wastewater from the dehydrator.

(6) VCM in PVC drying gas can be extremely reduced.

(7) Since PVC does not remain in the column, it can be easily cleaned.

Therefore, switching to a different type of PVC slurry is easy. (8) Regarding VCM processing after stripping,
You can use the normal collection system as is.

(9) The tray-related equipment is compact and can be installed without interfering with operation.

(0) Construction cost is low compared to other stripping devices.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 (1) A special tray (shaped as shown in FIGS. 1 and 3) consisting of a tray plate with inclined slits used in the present invention and another conventional tray plate as shown in FIG. Each is installed as a tray in the distillation column, and PVC is attached to this.
Slurry was supplied, and its fluidity, in other words, sedimentation properties, were compared under exactly the same conditions for each tray.

The procedure was as follows. In addition, in Figure 4, G is air,
8 is a PVC slurry feed pipe, 9 is an air feed pump, 1
0 indicates a PVC slurry pump, respectively. 30% by weight
PVC slurry (adding water to product PVC to prepare something similar to the actual slurry) is supplied from the top of a model tower made of transparent resin that allows comparison when using various trays, and air is pumped out from the bottom of the tower. The fluidity, ie, sedimentation, on the tray was observed.

The results are shown in Figure 5. As is clear from the figure, among the conventional trays, in the case of bubble caps, PVC accumulates on the cap and wear, resulting in poor fluidity (Fig. 5A), and in the case of valve cap trays and sieve trays, during operation. Although there appeared to be no difference in the PVC, it was observed that the PVC had settled after the operation was stopped (Fig. 5, B and C). On the other hand, no PVC was deposited or deposited on the tray according to the present invention, as shown in FIG. 5D. (2) Next, the PV at the downcomer's descent point and support ring
The fluidity of slurry C was observed by performing the operation shown in FIG. 6A.

In addition, the number 4 in Fig. 6 indicates the downcomer plate,
The plate may be vertical or inclined. The results show that, as shown in Figure 6B, PVC remained at the descent point in the case of only downcomer 5 (indicating space), but on the other hand, in the case of downcomer 1
As shown in Figure C, when a deck plate with an inclined surface was provided at the point of descent of the downcomer, no settling of PVC was observed at the point of descent. The angle of inclination is approximately 10
30° to about 30° is preferred. Further, when small holes 17 were provided in the overlapping portion of the support ring 11 and/or the downcomer plate and the tray plate as shown in FIGS. 7A and 7B, no PVC remained. Although the shape of the hole does not matter, it is preferable that it be provided in close contact with the tower wall. Note that an appropriate gap 18 (for example, 2 m1) is provided between the support ring 11 and the tower wall. Number 19 indicates a weld. Further, the deck plate is usually constructed by slanting a portion of the tray plate at that level. (3) Furthermore, stripping was performed as shown in FIG.

In this stripping, a distillation column with a diameter of 300 fins is equipped with 25 trays consisting of tray plates with inclined slits used in the present invention, with a tray spacing of 300 fins, and 30% by weight PVC slurry is supplied from the top of the column. It is lowered onto the tray and brought into contact with the steam blown in from the bottom of the tower. The inside of the tower is about 60 m
The temperature is maintained at 0-100° C., while the inside of the column is maintained at about 500-60011 Hg by a vacuum pump. In this way, the PVC slurry descending from the top of the column is stripped of its VCM content until it reaches the bottom of the column. The removal rate varied depending on the average degree of polymerization of PVC, but the main results were as shown in the table below. In addition, C from the top of the tower
M and water vapor are condensed in a condenser and refluxed to a distillation column, and VCM is sent to a recovery system. The VCM-free PVC slurry from the bottom of the tower is dried in a drying system to become a product PVC. Furthermore, the quality of the PVC product was such that it was not subject to thermal deterioration.

[Brief explanation of drawings]

FIG. 1 is a partial perspective view of an example of a tray plate with inclined slits used in the present invention, and FIG. 2A is a tray plate with inclined slits shown in FIG. 1 arranged so that gas blows out in the direction of the small arrow. An example of the tray used in the gas-liquid contact tower of the present invention, and FIG. 2B is a part of the longitudinal section of the tower taken along the line AO) L-L in FIG. 2, and FIG. 3 is the tray used in the present invention. Fig. 4 is a schematic diagram of an example of a gas-liquid contact tower used in the fluidity or sedimentation test of PVC slurry, and Fig. 5 A, B, and C show trays of each type. A schematic diagram showing the deposition of PVC in each tray when attached to the tower in FIG. 4 and supplied with PVC slurry,
Furthermore, FIG. 5D is a schematic diagram showing a state in which PVC does not accumulate when the tray plate with inclined slits used in the present invention is attached to the tower of FIG. 4 and PVC slurry is supplied.
Figures 6A, B, and C are model diagrams showing the presence or absence of PVC deposition when the tray at the downcomer first descent point of the tray is left flat and when an inclined surface is provided at the descent point. Figure A is a plan view of the support ring, and Figure 7B is Figure 7A.
O) A partial enlarged view of B and FIG. 8 are model diagrams showing the operation of the gas-liquid contact tower of the present invention in which 25 stages of special trays used in the present invention are installed. 1: Tray plate with inclined slits, 2: Inclined slits in the tray plate, 3: Inclined portion of the tray plate, 4:
Downcomer plate, 5: Downcomer 1, 6: Gas-liquid separation plate, 7: Gas-solid-liquid mixed phase, 11: Support ring, 17
: Small hole provided with support ring number, 18: L distance between column wall and support ring, X: gas flow direction, Y: liquid flow direction.

Claims (1)

[Scope of Claims] 1. A gas-liquid contact tower for removing vinyl chloride monomer from a vinyl chloride polymer-containing slurry having a plurality of trays consisting of a plurality of tray plates and a downcomer, wherein the tray plate has a plurality of inclined surfaces. It is integrally molded to have a slit and an inclined part, and the inclined slit has an acute angle of inclination from the bottom to the top with respect to the liquid flow direction of the tray plate, and has an outlet wear for holding up the liquid. The gas-liquid contact column is suitable for removing vinyl chloride monomer from a vinyl chloride polymer-containing slurry. 2. The plurality of tray plates are arranged so that the direction of the gas blown out from the slit is approximately 45 degrees with respect to the liquid flow direction, and the direction in which the gas is blown out is displaced by approximately 90 degrees with respect to the adjacent tray plate. , a gas-liquid contact tower according to claim 1. 3. The gas-liquid contact tower according to claim 1, wherein the plurality of tray plates are made of expanded metal. 4. The gas-liquid contact tower according to claim 1, wherein the deck plate at the descending point of the downcomer of the tray is tilted to prevent the vinyl chloride polymer-containing slurry from stagnation. 5. The gas-liquid contact tower according to claim 1, wherein holes are provided on the support ring of the tray. 6 The blowing gas cools the slurry to 60° to 100°C.
6. The gas-liquid contact tower according to claim 1 or 5, which is heated to maintain a temperature of .