DE1261853B - Process for the production of epsilon-caprolactam - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

Number: File number: Registration date: Display day:

C07d

German class: 12p-5

1261853
J 17047 IV d / 12 ρ
September 30, 1959
February 29, 1968

When working up and processing ε-caprolactam polymers falls under certain Certain circumstances, monomeric e-caprolactam, which for economic reasons again as a starting material should be used for polymerization.

For example, crude polymers of ε-caprolactam contain up to 12% low molecular weight fractions, i. H. monomeric, dimeric and trimeric caprolactam. To obtain a product suitable for spinning, the low molecular weight compounds must be removed as completely as possible from the raw polymer will.

This cleaning can be done e.g. B. by extracting the crushed material with water, by vacuum evaporation the low-boiling components from the melt or by evaporation of the monomers can be made from the solid polymer in vacuo or in an inert gas atmosphere.

An appropriate evaporation process is e.g. B. has been described in Swiss Patent 265 206: Solid f-caprolactam crude polymer is ^{heated in the absence of oxygen and optionally in an inert gas atmosphere to 130 to 200 0} C, whereby the low molecular weight portion of the crude product is distilled off.

Even with the post-condensation of poly- ε- caprolactam (ζ. B. according to the process of the US Pat. 2 557 808 or according to the Belgian patent 551 476) at elevated temperature, monomer ε-caprolactam is obtained from by-product.

In both cases, in the purification of the crude polymer to the spinnable product and in the Post-condensation, of course, preparations are made to restore the c-caprolactam in a pure, polymerizable form To maintain shape.

If the polymer has been treated under a stream of inert gas, efforts are also made to to clean the inert gas and to circulate it. The most obvious method for these purposes consists in the gas flow containing low molecular weight fractions through or over water or to conduct other lactam solvents, the conditions easily being able to be chosen so that the lactam carried along by the gas stream is practically completely absorbed by the solvent. This procedure is simple, but it has economic and technical disadvantages. Be like that on the one hand only get lactam solutions whose work-up requires significant amounts of energy, on the other hand the inert gas is freed from the lactam in this way, but at the same time corresponding to that Vapor pressure of the lactam solvent in the Ab process for the production of ε-caprolactam

Applicant:

Inventa A. G.

for research and patent exploitation,

Lucerne (Switzerland)

Representative:

Dipl.-Ing. F. Weickmann, patent attorney,

8000 Munich 27, Möhlstr. 22nd

Named as inventor:

Dipl.-Ing. Wilhelm Braun, Lucerne;

Walter Zehnder, Ems (Switzerland)

Claimed priority:

Switzerland of November 20, 1958 (66 432)

Sorption temperature saturated with solvent, so that it can be used as a protective or before reuse Purge gas cleaned during evaporation or during post-condensation in a further process stage must become. Another technical disadvantage is that the polymer may contain existing products that can evaporate and are insoluble in the lactam solvent, such as plasticizers or Lubricants, accumulate in solid form when the gas stream is treated with solvents and cause blockages in the absorption system.

Another possibility of removing low molecular weight fractions from the gas stream is available after Swiss Patent 262 206 in that the gas flow is passed through a cooler, in where the volatile components condense. This procedure can be because of the inevitable, periodic necessary removal of the condensate from the cooler only under difficult circumstances perform continuously. In addition, experience has shown that there is a risk of constipation of cooler inlet and outlet.

According to the Belgian patent 567 625, the absorption of the monomer distilling off takes place Caprolactams together with the water contained in the crude polymer in such a way that aqueous Caprolactam solutions are presented and serve for absorption at room temperature. The GE-

809 510/333

recovered e-caprolactam must be used before it can be reused subjected to additional isolation or at least purification of the monomer will.

The invention has for its object to ensure that in the production of the mainly A portion of the polymerization product consisting of monomeric ε-caprolactam, which is volatile at elevated temperature of ε-caprolactam from a hot inert gas stream passed through the polymer Absorption, a largely pure monomeric e-caprolactam is obtained, which is obtained before it is reused does not require additional isolation or at least cleaning.

The object is achieved according to the invention in that liquid ε-caprolactam is used as the absorbent Instead of water or another solvent.

^{An absorption temperature of about 75 °} C., at which the vapor pressure of the ε-caprolactam is still very low (about 0.25 mm mercury column) and there is still no risk of the lactam freezing, has proven to be most favorable. The vaporized lactam is practically completely absorbed; the inert gas flowing through can be reused without cleaning, since it is not contaminated by solvent vapors and, because of the low lactam vapor pressure, contains very little monomeric ε-caprolactam. Nevertheless, it is possible that if the polymer subjected to the evaporation process contains a relatively large amount of water, the water content of the inert gas increases because at the absorption temperature of over 70 ° C the water has such a high vapor pressure that it absorbs only a small part of the lactam will. In this case it is advisable to dewater at least part of the inert gas before it is returned to the evaporation system.

The ε-caprolactam monomers evaporated and absorbed in liquid lactam in the above manner naturally serves as an absorbent after absorption, i. i.e., it just enlarges the amount of the circulating liquid lactam serving as the absorbent. from this constantly increasing amount of lactam becomes the excess corresponding to the amount absorbed withdrawn from lactam and can be returned directly to the polymerization plant, since the Lactam is pure and has a water content of less than 0.1%, even if it was originally the Crude polymer subjected to evaporation process contains up to 2% water in addition to low molecular weight fractions.

The method according to the invention is shown in the description below using the example of cleaning a crude polymer to the spinnable product by evaporation of low molecular weight components and explained on the basis of the figure.

In the evaporation plant 1, low molecular weight fractions and water-containing crude polymer is in heated in a stream of inert gas. The inert gas is fed through the heater 11 and through line 2, loaded with evaporated monomeric ε-caprolactam, passed into the column 3. The column 3 is charged with a filler body layer 4 which increases the contact area. Through the nozzle 5 is injected liquid lactam as an absorption liquid and at the same time as a coolant, which, via the packing layer running down, the countercurrent gas flow cools and therefrom monomeric f-caprolactam absorbed. In the sump 6, all of the lactam, d. H. originally through the Nozzle 5 supplied, together with that absorbed from the inert gas stream, collected and transferred over the line 15, the pump 7 and the cooler 8 are routed to the spray nozzle 5 again. At the same time will from the sump 6 through an overflow pipe 16, which is provided with the tap 14, .continuously or in batches so much lactam withdrawn that the circulated as absorption and cooling liquid Lactam amount remains constant. The amount of lactam withdrawn corresponds to that from the Inert gas stream absorbed. The inert gas largely freed from lactam leaves column 3 through the line 9 and is conveyed by the pump 10 through the heater 11 in the evaporation system 1 returned.

To flush the system, a small stream of fresh gas is constantly introduced through line 12 and through the line 13 a corresponding amount of circulating gas, which water vapor and a little lactam contains, blown off.

This purging can at least partially be replaced by at least a portion of the circulating gas before being returned to the evaporation system 1 after leaving the absorption column by the pump 17, passed through the drying unit 18 and freed from water there will.

example

1000 kg of poly-8-caprolactam in the form of chips with an average diameter of 2.5 mm, a content of monomeric ε-caprolactam of 8.7% and a water content of 1.8% are in the evaporation system 1 for 12 hours 185 ° C heated. Hourly be 250 m ³ in the heater 11 by blowing preheated to 180 ⁰ C nitrogen as recycle gas. The cycle gas loaded with lactam in this way is passed through line 2 into absorption column 3. The vertical column has a diameter of 60 cm and is packed with 15 mm Raschig rings over a length of 400 cm. Every hour, 7 m ^{3 of} ε-caprolactam as a lactam absorbent and coolant are sprayed over the packing from the nozzle. The rising nitrogen, largely freed from lactam and ^{cooled to 76 °} C. in the column, is returned to the evaporation system 1 via line 9 and pump 10 through heater 11.

The sprayed ε-caprolactam collects together with the monomeric or low-molecular ε-caprolactam absorbed by it from the inert gas stream in the sump 6 and is returned to the nozzle via the pump 7 and the water cooler 8, in which it is cooled to 75 ° C 5 out and sprayed again. 88 kg of pure lactam are drawn off through the overflow pipe 16 during the evaporation and absorption. Through line 12, 15 m ^{3 of} fresh nitrogen are fed in every hour, and during the same time an equal amount of circulating gas is blown off through line 13. After the end of the evaporation of monomers, 907 kg of poly-caprolactam chips with an extract content of 1.2% can be withdrawn from the evaporation system.

Claims (2)

Patent claims: 1. Process for the production of the mainly composed of monomeric e-caprolactam, in elevated temperature volatile fraction of the polymerization product of e-caprolactam from a hot inert gas stream passed over the polymer by absorption, characterized in that that liquid ε-caprolactam is used as the absorbent. 2. The method according to claim 1, characterized in that at least part of the im Circulating inert gas before being returned to the evaporation vessel of moisture is released. Considered publications:
Swiss Patent No. 265 206;
announced documents of the Belgian
tents No. 567 625. 1 sheet of drawings