JPH0575441B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for recovering solvent from a slurry or solution containing polymer, solvent, and high boiling impurities. There are many methods for recovering a solvent from a slurry or solution containing a polymer, and a method in which steam is blown into the solvent and the solvent is recovered by steam stripping is widely used. In order to improve the yield of the solvent, it is well known to carry out the process in multiple stages using a plurality of tanks, and to improve energy efficiency, the method of sequentially blowing the distillate gas from the latter stage into the former stage is well known. However, in these conventional methods, the distillation solvent contains a large amount of water as well as high-boiling impurities (often bp>100° C.) that often form azeotropes with water. Therefore, in order to obtain a solvent with good purity, it is necessary to carry out two stages of rectification, including rectification of high-boiling point impurity cuts and rectification of low-boiling point impurity cuts, after draining. This requires a very large amount of energy and equipment costs are high, resulting in high solvent purification costs. There are various methods for steam stripping, and improvements have been made to improve solvent recovery efficiency, thermal efficiency, and operational management, but basically they can be classified as follows. (1) Batch one-stage stripping This method is suitable for small-scale processing in laboratories, but is not suitable for large-scale industrial processing. (2) Continuous one-stage stripping This method uses simple equipment and is easy to operate and manage, but its thermal efficiency and solvent recovery rate are inferior to other methods. (3) Column-type countercurrent stripping This method uses a tall column-shaped stripping device and has good thermal efficiency and solvent recovery rate, but when processing a slurry or solution containing a polymer, the polymer in the slurry or the solution There are restrictions on the objects that can be processed because the solid polymer that often precipitates from the tray causes problems such as clogging of the tray. (4) Multi-stage co-current stripping This method has a good solvent recovery rate, but the temperature in the latter stages is high and a large amount of impurities are distilled into the recovered solvent. (5) Multistage countercurrent stripping using tanks This method has good solvent recovery rate and thermal efficiency. Looking at the distillation of impurities that form an azeotrope with water, (3) and (5) can lower the gas temperature ultimately sent to the condenser, so the amount of high-boiling point impurities carried into the recovered solvent can be reduced. least. However, even if the stripping temperature in the first stage is lowered in method (5), there is a limit to suppressing the distillation of high-boiling impurities that form an azeotrope with water. The disadvantage is that the amount of impurities is too large. The present invention improves the above problems and suppresses the distillation of water into the recovered solvent by devising a steam stripping process, as well as distilling high-boiling impurities that often form an azeotrope with water. By suppressing emissions, rectification to remove high-boiling impurities from the recovered solvent in the post-process is unnecessary, achieving significant energy savings and solvent cost reductions, and improving equipment stability and versatility. The purpose is to provide a method. In the present invention, when the solvent is continuously taken out and recovered from a slurry or solution containing a polymer, a solvent, and high-boiling point impurities by steam stripping, the steam stripping is performed in multistage countercurrent using a tank, Distillate gas from the latter stage is blown into the former stage one by one, and the distillate gas from the first stage is passed through a plate tower or a packed tower and then cooled and collected in a condenser to form a slurry or solution containing the polymer, water, and high-boiling point impurities. In this method, the solvent is extracted from the last stage of the tank. The number of plates in the tray column (or packed column) may be 15 (equivalent to 15 plates), and depending on the combination of high-boiling point impurities and water, it may be less than 5 plates (equivalent to 5 plates). The azeotrope of can be removed. The solvent that can be recovered by the present invention is not particularly limited as long as its boiling point or azeotropic point with water is 100°C or lower, preferably 90°C or lower, but examples include pentane, hexane, etc. aliphatic hydrocarbons,
Examples include alicyclic hydrocarbons such as methylcyclopentane and cyclohexane, and aromatic hydrocarbons such as benzene. The present invention is particularly effective for high-boiling point impurities that form an azeotrope with water. Forms an azeotrope with water, but the majority of high-boiling impurities that can be removed are
The temperature is 100°C or higher, and the azeotropic point must be higher than the boiling point of the solvent, and the temperature difference therebetween is preferably 5°C or higher. Such high boiling point impurities are extremely common, and are not particularly limited, but examples include alcohols such as butyl alcohol, amyl alcohol, and hexyl alcohol; ethers such as butyl ether, amyl ether, diisoamyl ether, and octyl ether; Esters such as butyl propionate, ethyl caprylate, ethyl benzoate, methyl para-toluate, butyl benzoate, ethyl paraanisate, amines such as dibutylamine, ethylhexylamine, hexylamine, ethylcyclohexylamine, ethylaniline, collidine, etc. chlorodecane, chlorotoluene,
Examples include halides such as 1-bromo-2-ethylhexane. Examples of the polymer in the present invention include olefin polymers, olefin copolymers, and synthetic rubbers, such as polyolefins such as polyethylene, polypropylene, and polybutene, copolymers thereof, and synthetics such as EPR, EPDM, isoprene rubber, butyl rubber, and SBR. There are rubbers with relatively low molecular weights that can be dissolved in hot solvents. The polymer in the present invention may be completely dissolved in the raw material mixture, but may also contain polymer particles. In addition, a dispersant may be used, and examples of the dispersant used include those commonly used such as cationic surfactants, nonionic surfactants, amphoteric surfactants, and anionic surfactants. There are no particular limitations, and they may be used alone or in combination. Next, an example of the process of the present invention will be explained with reference to the drawings. In FIG. 1, a solution or slurry containing solvent, polymer and high boiling point impurities to be treated by the apparatus is continuously introduced into tank 1 through conduit 8. Steam is blown into the tank 1, the solvent is driven out, and the tank 1 is led to a tray column (or packed column) 3 via a conduit 9. In the tray column, the recovered solvent condensed in the condenser 4 is received in the receiver 5, but part of it is returned through the conduit 15 and flows down the column 3, and is brought into contact with the distillate gas in the tank 1 to be distilled off. Removes impurities and water from the gas.
A portion of this impurity, water and solvent is returned to tank 1 via conduit 13. The recovered solvent is sent via a conduit 16 to a recovery tank or to the next process for removing low-boiling point impurities. A solution or slurry containing polymer and high-boiling impurities is withdrawn from tank 1 by pump 6 and sent to tank 2 via conduit 10. In tank 2,
Steam is blown in and kept at a higher temperature than tank 1, and the solvent is almost completely removed. A mixed gas of steam and solvent vapor is transferred to a tank 1 through a conduit 11.
It is returned and blown into the liquid layer. A slurry consisting of water, polymer, high boiling point impurities, dispersant, etc. from which the solvent has been removed is extracted from the tank 2 through a conduit 12.
It is sent to the next process such as polymer separation. A first advantage of the present invention is that high boiling impurities that form azeotropes with water can be removed.
This is not possible with conventional steam stripping equipment, and rectification columns are additionally used to remove high-boiling impurities. This device eliminates the need for this high boiling point removal rectification column, resulting in a significant reduction in equipment costs and running costs. A second advantage of the present invention is that the solvent recovery efficiency is high because the process is carried out in multiple stages using steam stripping. The third advantage of the present invention is that steam stripping is performed in multiple stages using tanks, and the higher temperature gas in the later stage is blown into the tank in the earlier stage, so the heat is effectively utilized. The device itself also consumes less energy. The fourth advantage of the present invention is that the plate column (or packed column)
Since most of the water is removed along with high-boiling point impurities in step 3, there is very little water accumulation in the receiver 5, and there is no need to control the level of the receiver 5 according to the normally used sequence. Example 1 Using the apparatus shown in Figure 1, a mixed solution of 99% by weight n-hexane, 1% atactic polypropylene, and 0.10% amyl ether was prepared, and this was continuously passed through the first stripper at a rate of 12/hr. I fed it. Steam was blown into tank 1 to maintain the temperature at 70 to 75°C to drive out the solvent, and the tank was led to a seven-plate column. The mother liquor in tank 1 was extracted by a pump and continuously sent to tank 2. Blow steam into tank 2 to 85-90℃
The distillate gas was returned to tank 1 and supplied to the liquid phase. The distillate gas from the plate column was cooled in a condenser 5, one part was returned to the plate column, and one part was collected in a receiver. The reflux ratio was kept at 0.5. tank 2
Extraction was carried out intermittently while checking the level. Tanks 1 and 2 were auxiliary heated using heaters to keep them warm. Tank 1 and tank 2 are vertically long 30SUS containers with open windows.
The stirring blades were a combination of inclined fan turbine blades and turbine blades. Example 2 In Example 1, the solvent was replaced with n-hexane, cyclohexane was used, the high boiling point impurity that forms an azeotrope with water was replaced with amyl ether, and ethyl benzoate was used, and the temperatures of tanks 1 and 2 were set to 80°C.
The same experiment as in Example 1 was conducted except that the temperature was maintained at 90-95°C and 85°C and 90-95°C, and the plate column was replaced by a five-stage Raschig ring packed column. Comparative Example 1 In Example 1, tank 1 was
An experiment was conducted in the same manner as in Example 1, except that the distillate gas was directly applied to the condenser and recovered in its entirety. Comparative Example 2 In Comparative Example 1, except that the distilled vapor from Tank 2 was not returned to Tank 1, but collected together with the distilled vapor from Tank 1 through a condenser,
An experiment similar to Comparative Example 1 was conducted. The above test results are shown in Table 1.

[Table] Example 3 The same experiment as in Example 1 was carried out except that the feed liquid contained 3.0% atactic polypropylene and 0.2% n-butyl ether instead of amyl ether. Example 4 Example 3 except that diisoamyl ether was used as a high-boiling impurity in the feed liquid at 0.03%, and methyl p-toluate was added thereto to make the concentration of methyl p-toluate 0.3%. is Example 3
conducted a similar experiment. Example 5 Same as Example 4 except that in Example 3, n-butyl ether was changed to 0.002% as a high-boiling point impurity in the feed liquid, and methyl p-anisate was added to make the concentration of methyl p-anisate 0.05%. I did a similar experiment. Example 6 An experiment similar to Example 1 except that the feed liquid contained 5.0% atactic polypropylene, 0.01% octyl ether instead of amyl ether, 0.003% ethylhexylamine, and 0.01% chlorodecane. Did. Table 2 shows the concentrations of high boiling point impurities in the solvents obtained in Examples 3 to 6.

【table】 [Brief explanation of the drawing]

FIG. 1 shows a flow sheet of an example of an apparatus for carrying out the present invention. In the figure, 1 and 2 are tanks, 3 is a plate column (or packed column), 4 is a condenser, and 5 is a receiver.

Claims (1)

[Claims] 1. When the solvent is continuously taken out and recovered from a slurry or solution containing a polymer, a solvent, and high-boiling point impurities by steam stripping, the steam stripping is performed in a multistage countercurrent flow using a tank. The distillate gas from the latter stage is blown into the former stage one by one, and the distillate gas from the first stage, which is generated in this way and is lower temperature than the distillate gas from the latter stage, is passed through a plate tower with 15 stages or less or a packed tower with the equivalent of 15 stages or less. The method for recovering the solvent, which comprises cooling and recovering the solvent in a condenser, and extracting the slurry containing the polymer, water and high-boiling point impurities from the last stage of the tank. 2. The method according to item 1, wherein the high-boiling point impurity forms an azeotrope with water. 3. Item 1 or 2, characterized in that the contents of the tank to be steam-stripped are stirred.
The method described in section.