US3335115A - Method of removing monomeric components from polycaprolactam - Google Patents

Description

H. LUDEWIG Aug. 8, 1967 METHOD OF REMOVING MONOMERIC COMPONENTS FROM POLYCAPROLACTAM 2 Sheets-Sheet 1 Filed Sept. 11, 1963 nuooooonodas INVENTOR. HERMANN LUDEWIG 1967 H. LUDEWIG 3,335,115

METHOD OF REMOVING MONOMERIC COMPONENTS FROM POLYCAPROLACTAM Filed Sept. 11, 1963 2 Sheets-Sheet 2 INVENTOR. HERMANN LUDEWIG United States Patent 3,335,115 METHOD OF REMOVING MONOMERIC COMPO- NENTS FROM POLYCAPROLACTAM Hermann Ludewig, Rudolstadt, Germany, assignor to VEB Chemiefaserwerk Schwarza Wilhelm Pieck, Rudolstadt, Germany Filed Sept. 11, 1963, Ser. No. 309,915 5 Claims. (Cl. 260-78) The present invention relates to a process for making products, such as threads, wires, films and the like, from synthetic linear high polymers, especially from polyamides; more particularly, the process relates to making products which are poor in monomers.

The invention also relates to an apparatus for making such polymer products which are poor in monomers.

At present, there are mainly two processes in use for making polyamides, namely (1) the classical grid spinning process, and (2) the direct spinning process.

The grid spinning process comprises subjecting polyamide chips prepared in a polymerization apparatus to a number of operational steps, such as polymerization, comminution, extraction, and drying. The extracted chips are then melted on a grid, and the melt is formed into threads or other shaped products.

In the direct spinning process, the molten polyamide is directly fed from the polymerization apparatus to the spinning head over distribution lines. When in the direct spinning process no additional unit is used, the end product will contain low polymer products in accordance with the chemical equilibrium. For lowering the amount of low polymers in the direct spinning, the following methods are known:

(a) Vacuum stage: in this, the monomeric components are eliminated from the melt by high-vacuum (thin layer evaporation).

(b) Vapor spinning process: This is based on blowing a current of super-heated steam through the polymer melt, said current carrying along all constituents which are undesirable for the spinning operation.

The known processes and the apparatus for carrying them out have certain drawbacks in the production and processing of polyamides. In the grid spinning process, complicated equipment entailing high energy consumption is necessary for lowering the monomeric portions. Furthermore, there is the risk of quality deterioration if polyamide is brought into contact with the atmosphere.

Material obtained by direct spinning has the disadvantage of higher monomer contents which causes difficulties in the processing industry. The use of the vacuum stage for lowering the monomer content requires again complicated apparatus and high energy consumption. The stream spinning process is still under development and there are no reports on the process when used for largescale production.

It is the object of the present invention to provide a method for making shaped articles from high polymers, e.g. polyamides, which are free of the above-mentioned shortcomings. It is another object to provide a method whereby the monomeric, i.e. water soluble portions of the polyamide, are removed in a simple and effective manner.

It is yet another object to provide an apparatus for making the products above-defined.

Other objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

It has now been found unexpectedly that the abovementioned drawbacks can be avoided and the amount of water soluble polymer can be decreased, when the molten polymer, especially polyamide, is treated in an autoclave as a eutectic liquid mixture of polyamide/water or poly- Patented Aug. 8, 1967 amide/organic solvent with application of pressure and elevated temperature.

Thus, according to the invention, the polyamide melt is extracted under pressure in an autoclave partly filled with a solvent, e.g. water, as a eutectic liquid mixture of polyamide and solvent, the extraction taking place above the boiling point of the pure solvent and below the melting point of the pure polyamide; thereby, the soluble (monomeric) portion of the polyamide passes into the solvent which is thereafter removed from the eutectic melt, whereupon spinning takes place in a known manner.

The extraction of the water-soluble portion takes place in an autoclave or a pressure tube under the excess pressure of the solvent or the water. If e-aminocaprolactam is extracted, temperatures will preferably be used in the range of 160 to 180 C. and pressures of about 10 atmospheres excess pressure.

Apart from water, solvents to be used are, e.g. alcoholwater, ketone-water or ketones, and other organic solvents.

vIn some cases, simple stirring of the liquid mixture in water at 160 to 180 C. will be sufficient in order to accelerate extraction and accomplish a thorough elimination of the soluble constituents. One desirable method of operation is to feed the polyamide melt to be extracted under pressure and in the shape of threads or thin sheets into the hot water or other solvent contained within autoclave.

Another method of extracting according to the invention consists in conveying the polyamide melt to be extracted in a thin layer through the hot water or solvent in the autoclave over the guide plates, guide funnels, guide screens, screen inserts or other similar devices.

The extraction may, e.g. be carried out as described below. The polymer melt, e.g. polyamide melt, prepared in a know manner in an autoclave or a tube for fully automatic polymerization of caprolactam is fed by means of a pump or a system of pumps into a container filled with a solvent, e.g. water, maintained at the temperature of about 170 C., and an excess pressure of about 10 atmospheres. The water-soluble portions collect in the water; the liquified polyamide settles at the bottom of the tube and is later, after leaving the container, worked up directly in the eutectic mixture or separated from said mixture, and allowed to solidify in a known manner, re-

' melted, and shaped. In the manner above-described the process may be carried out as a continuous process.

An advantageous embodiment for further processing of the extracted melt consists therein that from the eutectic mixture of polyamide and remaining solvent, the latter is removed in a heated intermediate vessel in a manner known in the polymerization process, namely by degassing, whereafter, the polyamide melt is shaped. The removal of solvent can be enhanced by passing through the melt an inert gas, such as nitrogen, carbon dioxide; and the like, or steam.

In accordance with the invention the melt of the polyamid-solvent mixture is passed into a vessel heated .up to 250 C. and provided with a valve. The solvent con.- tained in the melt escapes over the valve into the open, and the melt free of solvent is spun after degassing in the usual manner. Instead of the vessel, a simple or multiple-stage tube can be used for the degassing. It'is furthermore possible to heat solid polyamide portions together with water or an organic solvent in the autoclave until it liquefies, but not to a point at which depolymerization would occur. Subsequent processing is conventional.

An apparatus for carrying out the process according to the invention is illustrated in the accompanying drawings by way of example. In the drawings: 1

FIG. 1 shows one embodiment of the apparatus in a schematic side view, partly in section, and

FIG. 2 is a similar showing of another embodiment of theapparatus.

Referring now to FIG. 1, designates a U-shaped tube for fully automatic polymerization of a polyamide, known in the art as VK-tube. An inlet opening for admission of lactam is indicated at 7, an outlet opening for escape of steam at 8. The two limbs of the U-tube are surrounded by heating jackets 11 provided with two short pipes 11a used for servicing.

Tube 10 is connected by means of a pumping system schematically indicated at 12 with an elongated vessel 13 in which the extraction is to be performed. Vessel 13 is surrounded by a heating jacket 13a and is partly filled with a solvent, e.g. water which enters at 9a. A short pipe 11b is provided at the bottom of the jacket 13a. From the top of the tube 1.3, an escape valve 9 for solvent, e.g. water leads outside.

A pluarlity of guide plates 14 is arranged throughout the length of the liquid-filled portion of the tube 13 and extending into a sump portion 15 where the mixture of solvent and melt poor in monomers formed in the tube is allowed to collect. The solution above the sump 15 containing the monomers is continuously replaced with fresh water by means of pumps.

Joined to the bottom of tube 13 is a conveyor device with a worm 16 for delivering the liquid mixture of polyamide and remaining water or polyamide and remaining solvent out of the sump to a degassing vessel 17 furnished with a heating jacket 17a and a servicing pipe 11c, from where remaining water or solvent is allowed to escape as steam or vapor through a valve 18, while solvent-free melt collects at the bottom. A spinning device 19 is directly connected to the vessel 17, and the melt is passed through a plurality of spinnerets 19a.

Instead of the spinning device, another shaping device can be provided, when it is desired to produce e.g. film or other sheet material by extrusion of the hot melt.

In the embodiment of the device shown in FIG. 2, 20 designates an autoclave for the polymerization of caprolactam. Inlet and outlet openings at the top are designated by 31 and 32, a heating jacket by 30a and a short pipe at the bottom of the jacket by 28a. The apparatus is designed for working in batches. A valve 21 connects the funnel-shaped bottom of the autoclave 20 with an extraction vessel 23 over line 29. Mounted within the vessel 23 is a stirrer 22 operable by known means (not shown). An escape valve 33 is provided for solvent discharge.

The vessel 23 is surrounded by a heating jacket 30]) which has at the bottom a short servicing pipe 28b.

At the bottom, vessel 23 is connected by a pumping system, schematically illustrated at 24, with a degassing vessel 25. This vessel is equipped with a gas escape valve 34, heating jacket 30c and a servicing pipe 280. Further attached to vessel 25 is a spinning device 27 comprising a plurality of spinnerets for producing filaments or wires 26.

The extraction process according to the invention makes it possible to decrease the monomeric contents of a polyamide containing about 10% thereof down to 1% of monomers and even less.

In the following, the invention will be more fully described in a number of examples, but it should be understood that these are given by way of illustration and not of limitation, and that many modifications may be made without departing from the spirit of the invention.

Example 1 This example of the process is described With reference to FIG. 1.

A melt of caprolactam containing 2% water and acetic acid, namely l/600 mol acetic acid per mol lactam, is

continuously passed through the tube 10. The melt of polyamide which becomes very highly viscous by polymerization, and which contains 10% of water soluble products, is conveyed directly from tube 10 into the elongated extraction or pressure tube 13 by means of the pumping system 12. The pressure tube is filled to /3 with water of C. at an excess pressure of 10 atmospheres. The threads pass through the water at 170 C. over guide plates 14 and collected in the sump 15. While passing through the water at the temperature of 170 C. the content of the water soluble amount decreases from 10% to 0.5%.

From the sump, the melt of polyamide and remaining water is delivered by Worm 16 into the vessel 17 heated up to 250 C., maintained under normal pressure and nitrogen atmosphere. In the vessel degassing takes place by making the water from the melt pass out as steam through the valve 18 into open air. After a degassing period of 15 minutes, the Water-free melt is continuously delivered from the degassing vessel to the spinnerets 19a and is then spun. The threads contain 3 to 4% by weight or less of extract, mainly monomeric components.

The extract-containing water which stands above the sump is continuously replaced by fresh preheated water in a countercurrent stream.

Example 2 This example of the process according to the invention is described with reference to FIG. 2.

A polyamide melt made in a conventional manner from caprolactam in the autoclave 20 is supplied to the extraction vessel 23 in a batch through open valve 21 and line 29.- The extraction vessel is about half filled with hot p-cymol (1-methyl-4-isopropyl-benzene) which has a boiling point of 177 C. at normal pressure. The valve 21 is then closed, and the temperature raised to about 210 C., where it is maintained for about one hour while vigorous stirring is carried out. Thereafter, the stirring is discontinued and separation of the polyamide and the hydrocarbon solvent effected by allowing the mixture to settle. The pumping system 24 then delivers the melt to the degassing vessel 25 maintained at 260 C. where hydrocarbon vapor is allowed to escape through valve 34. After a short heating period, the melt now containing only 2% by weight of monomers or oligomers, is passed on to the spinnerets through which spinning occurs in the conventional manner.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples described which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

By shaped structures it is intended to designate filaments, wires, films, sheets and similar articles made from synthetic high polymers, by spinning and extruding, respectively.

What is claimed is:

1. Method of removing monomeric components from a polycaprolactam containing the same, which comprises contacting said polycaprolactam with a solvent for said monomeric components which solvent at normal pressure has a boiling point below the melting point of said polycaprolactam and which forms a eutectic mixture therewith while maintaining a temperature above the boiling point of the pure solvent and below the melting point of the pure polycaprolactam and as high as the eutectic temperature of said mixture and a pressure which is sufiiciently high so that said solvent is in liquid condition at said temperature, whereby said polycaprolactam is subjected to liquid-liquid extraction by said solvent although at normal pressure said solvent would be in gaseous condition and said polycaprolactam would be in solid condition, so that the major portion of said monomeric components are dissolved by said solvent; and

separating said solvent from said mixture, thereby obtaining a polycaprolactam of low monomeric components content.

2. Method according to claim 1 wherein said solvent is selected from the group consisting of water, alcohol, ketones, alcohol-Water, ketone-Water and cymol.

3. Method according to claim 1 wherein said solvent is water and said temperature is between about 160 C. and 180 C.

4. Method according to claim 1 wherein said solvent is separated from said mixture by degassing.

5. Method according to claim 4 wherein an inert gas is passed through said mixture during degassing.

References Cited UNITED STATES PATENTS 2,361,717 10/1944 Taylor 26078 2,731,081 1/1956 Mayner 26078 6 1/1959 Ludewig 26078 10/1961 Upton et al. 188 1/1962 Kjellmark 26078 4/1962 Monroe 2 60-78 7/1962 Ryffel 26078 7/1962 Braun et a1. 26078 11/1963 Beck 18-8 9/ 1964 Cerutti 260-78 FOREIGN PATENTS 10/ 1962 Canada.

Examiners.

L. S. SQUIRES, H. D. ANDERSON,

Assistant Examiners.

Claims (1)

1. METHOD OF REMOVING MONOMERIC COMPONENTS FROM A POLYCAPROLACTAN CONTAINING THE SAME, WHICH COMPRISES CONTACTING SAID POLYCAPROLACTAN WITH A SOLVENT FOR SAID MONOMERIC COMPONENTS WHICH SOLVENT AT NORMAL PRESSURE HAS A BOILING POINT BELOW THE MELTING POINT OF SAID POLYCAPROLACTAM AND WHICH FORMS A EUTECTIC MIXTURE THEREWITH WHILE MAINTAINING A TEMPERATURE ABOVE THE BOILING POINT OF THE PURE SOLVENT AND BELOW THE MELTING POINT OF THE PURE POLYCAPROLACTAM AND AS HIGH AS THE EUTECTIC TEMPERATURE OF SAID MIXTURE AND A PRESSURE WHICH IS SUFFICIENTLY HIGH SO THAT SAID SOLVENT IS IN LIQUID CONDITION AT SAID TEMPERATURE, WHEREBY SAID POLYCAPROLACTAM IS SUBJECTED TO LIQUID-LIQUID EXTRACTION BY SAID SOLVENT ALTHROUGH AT NORMAL PRESSURE SAID SOLVENT WOULD BE IN GASEOUS CONDITION AND SAID POLYCAPROLACTAN WOULD BE IN SOLID CONDITION, SO THAT THE MAJOR PORTION OF SAID MONOMERIC COMPONENTS ARE DISSOLVED BY SAID SOLVENT; AND SEPARATING SAID SOLVENT FROM SAID MIXTURE, THEREBY OBTAINING A POLYCARPROLACTAM OF LOW MONOMERIC COMPONENTS CONTENT.

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