JPS6297601A - Process for recovering solvent by steam stripping - Google Patents

Abstract

PURPOSE:To contrive energy saving, by blowing effluent gas from the subsequent stage into the preceding stage to recover the effluent gas of the initial gas by cooling when solvent is recovered from slurry containing polymers by a multistage countercurrent stripping using a tank. CONSTITUTION:Slurry is fed through a pipe 8 into a tank 1 where steam is blown into. Solvent is purged through a pipe 9 to a plate column 3 and further condensed in a condenser 4 to be recovered, while the recovered solvent is received by a receiver 5. Part of the recovered solvent is returned through a pipe 15 to the plate column 3, contacted with effluent gas from the tank 1, where impurities and water in the effluent gas are removed, and returned to the tank 1 through a pipe 13. Slurry in the tank 1 is withdrawn by a pump 6 and sent to a tank 2 through a pipe 10, where steam is blown into to keep said tank 2 at a temperature higher than that of the tank 1, while the solvent is returned to the tank 1 through a pipe 11.

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 of recovering the solvent by steam stripping by blowing steam into the solution 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 at 100 DEG C.) that often form an azeotrope with water. Therefore, in order to obtain a solvent with good purity, it is necessary to perform two stages of rectification, one for removing high-boiling point impurities and the other for removing low-boiling point impurities, after draining. This KU requires a very large amount of energy and equipment costs are high, leading to high costs for solvent purification.

There are various methods for steam stripping, and efforts have been made to improve solvent recovery efficiency, thermal efficiency, and operational management, but basically they can be classified into the following types.

(1) One-stage patch stripping This method is suitable for small-scale processing such as in a laboratory, but is not suitable for large-scale industrial processing.

(2) Continuous one-stage stripping This method uses a simple device 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 to improve thermal efficiency and
Although the solvent recovery rate is good, when processing slurries or solutions containing polymers, problems such as tray clogging may occur due to the polymers in the slurry or solid polymers that often precipitate from the solutions. There are restrictions on what can be processed.

(4) Multi-stage co-current stripping Although this method has a good solvent recovery rate, the temperature in the latter stage 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.

If we look at the distillation of impurities that form an azeotrope with water, (
3), (5>) produces a black gas that lowers the gas temperature ultimately sent to the condenser, so the amount of high-boiling point impurities carried into the recovered solvent is the smallest.

However, even if the first-stage stripping temperature is lowered in method (5), there is a limit to suppressing the distillation of high-boiling impurities that form an azeotrope with water, and the recovered solvent is a solvent used for polymerization, etc. The drawback is that the amount of impurities inside is too large.

The present invention improves the above problems and suppresses the distillation of high-boiling point impurities that are distilled out by steam, thereby increasing the rectification for removing high-boiling point impurities from the recovered solvent in the subsequent process. The objective is to provide a method that eliminates the need for solvents, achieves significant energy savings and solvent cost reductions, and provides stability and versatility of the device.

In the present invention, when the solvent is continuously taken out and recovered from a slurry or solution containing a polymer, a solvent, and a high-boiling point impurity by steam stripping, the steam stripping is performed in a multi-stage countercurrent flow 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 plate column (or packed column) may be 15 plates (equivalent to 15 plates), and may be 5 depending on the combination of high boiling point impurities and water.
An azeotrope of high boiling point impurities and water can be removed even if the stage is less than 5 stages (equivalent to 5 stages).

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,
Aliphatic hydrocarbons such as hexane, methylcyclopentane,
Examples include alicyclic hydrocarbons such as cyclohexane and aromatic hydrocarbons such as benzene.

The present invention is particularly effective for high-boiling point impurities that form an azeotrope with water. An azeotropic mixture is formed with water, but the majority of high-boiling point impurities that can be removed must be at temperatures above 100°C, and the azeotropic point must be higher than the boiling point of the solvent, with a temperature difference of at least 5°C. is preferred.

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; Butyl propionate, ethyl caprylate, ethyl benzoate, methyl-
Esters such as para)ruate, phthyl penzoate, and ethyl caprylate, amines such as diptylamine, ethylhexylamine, hexylamine, ethylcyclohexylamine, ethylaniline, and collidine, chlorodecane, chlorotoluene 1, l-7' romole Examples include halides such as 2-ethylhexane.

Polymers used in the present invention include olefin polymers, olefin copolymers, synthetic rubbers, etc., such as polyolefins such as polyethylene, polypropylene, and polybutene, copolymers thereof, and synthesis of EPR, EPDM, isoprene rubber, butyl rubber, SBR, etc. There are rubbers with relatively low molecular weights that can be commonly understood as thermal solvents. The polymer in the present invention may be completely dissolved in the raw material mixture, but may also contain polymer particles.

Further, 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, the solution or slurry containing solvent, polymer and high-boiling 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 off, and the tank 1 is dedicated to a tray column (or packed column) 3 via a conduit 9. In the tray tower, the condensed melt condensed in the condenser 4 is received in the receiver 5, but a part of it is transferred to the conduit 5 on the way and is transferred to the tower 3.
is allowed to flow down and brought into contact with the distillate gas in tank 1 to remove impurities and water in the distillate gas. A portion of this impurity, water and solvent is returned to tank 1 via conduit 13. The recovered solvent is sent through 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 removed from tank 1 by pump 6 and sent to tank 2 via conduit 10. In tank 2, steam is blown into
Tank 1 is kept at a higher temperature and the solvent #t is completely removed.

The mixed gas of steam and solvent vapor is returned to tank 1 through conduit 11 and blown into the liquid layer.

The slurry consisting of water, polymer, high-boiling impurities, dispersant, etc. from which the solvent has been removed is extracted from the tank 2 through a conduit 12 and sent to the next step (e), 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 apparatus eliminates the need for this high boiling point removal rectification column, resulting in a significant reduction in equipment costs and cleaning costs.

A second advantage of the present invention is that the steam stripping is performed in multiple stages using tanks, so that the solvent recovery efficiency is high.

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 stages is blown into the tanks in the earlier stages, so the heat is effectively used. The device itself also consumes less energy.

The fourth advantage of the present invention is that most of the water is removed along with high-boiling point impurities in the tray column (or packed column) 3, so that the amount of water accumulated in the receiver 5 is extremely small. This eliminates the need for receiver 50 level control using commonly used sequences.

Example 1 Using the apparatus shown in FIG. 1, 99% by weight of n-hexane,
1% atactic polypropylene, 0.0% amyl ether.
A 10% mixed solution was prepared and continuously fed to the first stripper at a rate of 12 J/hr. Blow steam into tank 1 and keep it at 70 to 75°C to drive out the solvent.
He led me to a seven-tier terraced tower. The liquid in tank B was drawn out using a pump and continuously sent to tank 2. Steam was blown into tank 2 to maintain the temperature at 85 to 90°C, and the distilled gas was returned to tank 1 to be supplied to the liquid phase. The distillate gas from the plate column is cooled in a condenser 5, one part is returned to the plate column, and one part is sent to the receiver.
It was collected in The reflux ratio was maintained at 0.5. Removal from Tank 2 was carried out intermittently while monitoring the level.

For tank 1 and tank 2, auxiliary nO heating was performed using a heater to keep them warm. Tanks 1 and 2 were vertically elongated 3018 US containers with slotted windows, and 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 ethyl benzoate, and the temperatures of tanks 1 and 2 were set at 80 to 85°C, respectively. The same experiment as in Example 1 was conducted except that the temperature was maintained at 90 to 95° C. and the plate column was replaced by a Raschig ring packed column equivalent to 5 plates.

Comparative Example 1 An experiment similar to Example 1 was conducted, except that the plate column was not used and the distillate gas from Tank 1 was directly applied to the condenser and the entire amount was recovered.

Comparative Example 2 In Comparative Example 1, distilled vapor from tank 2 was transferred to tank 1.
An experiment similar to Comparative Example 1 was carried out, except that the vapor was collected in a condenser together with the distilled vapor from Tank 1 without being returned.

The above test results are shown in Table 1.

Table 1 Example 3 Same as Example 1 except that the feed liquid contained 3.0% atactic polypropylene and 0.2% n-butyl ether instead of amyl ether. I did an experiment.

Example 4 In Example 3, diisoamyl ether was set to 0.03% as a high-boiling point impurity in the feed liquid, and methyl p-)toluate was added to this to reduce the concentration of methyl p-toluate to 0.
．． An experiment similar to Example 3 was conducted except that the concentration was 3%.

Example 5 In Example 3, n-butyl ether was used as a high-boiling impurity in the feed liquid at O, ob 2%, and methyl p-anisate was added to make the concentration of methyl p-anisate 0.0.
An experiment similar to Example 4 was conducted except that the concentration was 5%.

Example 6 In Example 1, the feed liquid contained 5.0% atactic polypropylene, 0.01% octyl ether in place of amyl ether, and 0.003% ethylhexylamine.
The same experiment as in Example 1 was conducted except that the amount of chlorodecane was 0.01%.

Table 2 shows the concentrations of high boiling point impurities in the solvents obtained in Examples 3 to 6.

Table 2

[Brief explanation of drawings]

FIG. 1 shows a flow sheet of an example of an apparatus for carrying out the present invention. In the figure, 1.2 is a tank, 3 is a plate tower (or packed tower), +r
dxn capacitor, 5 represents the receiver. More than ゛

Claims (2)

[Claims] (1) When using steam stripping to continuously extract and recover the solvent from a slurry or solution containing a polymer, solvent, and high-boiling point impurities, steam stripping is performed in multistage countercurrent flow using tanks, and the subsequent stage The distillate gas of the first stage is sequentially blown into the previous stage, and the distillate gas of the first stage is passed through a plate tower or a packed tower and then cooled and recovered in a condenser, and the slurry containing polymer, water and high boiling point impurities is transferred to the tank. The method for recovering the solvent, characterized in that the solvent is extracted from the last stage. (2) The method according to item 1, wherein the high-boiling point impurity forms an azeotrope with water.