DE1495187A1 - Method of extracting polyamides - Google Patents

Description

BADISCHE ANILIN- * SODA-FABRIK AG ....

U95187

Our reference: O. Z. 23 157 Buc / Sh Ludwigshafen / Rhein, 30 7.1964

I.7.1968 Process for extracting polyamides

It is known to have low molecular weight fractions, such as monomers and Oligomers to be removed from polyamides by polyamides in lump form, if necessary at elevated temperatures, extracted with extraction agents such as water or low molecular weight monohydric alcohols.

In the case of discontinuous processes, the granulated polyamides are treated with the extractant, e.g. B. by stirring or Injection of inert gases, moving. According to other methods, only the extractant is moved, e.g. by pumping. In all cases the extraction solution is used several times and collected separately depending on the enrichment of the extracted fractions. The extraction solution then becomes preferably the monomers are recovered by evaporation of the extractant. The recovery of the monomers from the extraction-

solutions is technically and economically complex because the

202 / 64BxtraktiorislÖ8ung has only a small content of extract.

90981 1/1190

(Ait7f1Abe.2Nr.1SaU3desAn <ierung8get.v.4.9.19C.

U95-187

It is also known to continuously extract polyamides, by letting the polyamide granulate slide from top to bottom in a vertically arranged tube and the extractant conducts in the countercurrent principle from bottom to top. A part of the extractant can be below the upper The pipe ends are drawn off at different heights in such a way that the amount of extractant flowing through the pipe decreases from bottom to top. Extraction solutions are obtained here with a slightly greater concentration of extract than other methods, but this method is technically complex.

It has now "found that you can get low molecular weight fractions Polylactams by the action of extractants on layered polylactams in lump form at elevated temperature can be advantageously removed by "passing the extractant" from top to bottom through the polylactam layer. According to the method of the invention, the content of lactams in the extraction solution can be increased significantly than this is possible according to known methods «

Suitable extractants are those whose spec. Weight is less than that of the granules to be extracted and smaller than that of the extractable fractions. Water and low molecular weight monohydric alcohols, such as Methanol, ethanol or isopropanol, used as the extractant.

909811/1190 - 3 -

U95187

Polyamides which, according to the invention, can be freed from low molecular weight fractions are those which are produced in the customary manner by polycondensation of cu-aminocarboxylic acids or their polyamide-forming derivatives * Advantageous
the polyamides are in lump form, d. h "in platelet or granular form, used.

The flow rate of the extractant is advantageously chosen so that the liquid flows in a laminar manner. The residence time of the extractant is up to 100 hours on average. The process may be conducted batchwise or% are continuously performed, with the greatest effect is achieved in continuous operation when the granules in countercurrent principle from below is promoted upward.

The inventive method is advantageously carried out at temperatures of from "70 to 120 ⁰ C, whereby it is useful both the Pplylactam and the extraction means to heat,

' i

example 1

A vertically arranged tube with a heating device (2000 mm long, 50 mm diameter) is first _{lycaprolactam with 2370 g of granulated P 0} and. then filled with water from above. Granulate, water and extraction tube are heated to 80 ° C ο Per Stunäs 50 cm ^ extraction solution are now removed from the lower end of the tube and from the upper end of the tube

- 4 _ 90981 1/1190

the missing fresh water, which is heated to 80 ° C, is added. The extract content in percent in the extractant as a function of the extraction time in hours is shown in FIG. 1, curve 1, shown.

Comparative example

The tube described in Example 1, which is filled with polycaprolactam granulate, is filled with water from below, the rate of rise of the water in the column being 1 cm per second. 50 cm 3 of extraction solution are taken per hour at the upper outlet of the tube and the missing ^{water heated to 80 °} C. is added at the lower inlet of the tube. The temperature of the filling is about 8O ⁰ C. The extract content in percent in the extracting agent depending on the extraction time in hours is shown in Figure 1, curve 2 '.

The comparison of curves 1 and 1 shown in FIG clearly shows that the extract content in the extractant, which according to the invention is passed through the column from top to bottom is much greater than the extract content in the extractant, which is passed through the column from bottom to top "became". After 40 hours (point of intersection of curves 1 and 2) in the process according to the invention, about 50 $ oaprolactam is more extracted from the granulate than in the process in which the extractant is directed from the bottom up will.

- 5 -9 0 9 8 11/119 0

- 5 ■ - ■ .. ■ O.Z.

fl ί § ⁷ 1 8 7

Example 2

An apparatus is used as the extraction device in which 10 cylinder tubes are arranged one above the other in such a way that the tapered end of one tube protrudes into the non-tapered end of the other. The two ends are releasably connected to one another by pierced plugs. This extraction battery is arranged vertically and surrounded by a heatable and coolable double-jacket tube (FIG. 2). The cylinder tubes have a volume of 250 cm. The cylinder tube 10 is closed at the lower end by a tap. The cylinder tubes are each filled with 120 g of granulated polycaprolactam, which contains 11.7 extractables, and with 75 g of water. The output from the double-walled tube to the Bxtraktionsbatterie heat energy is dimensioned so that the extraction water is at a temperature of about 90 ⁰ C. Three hours after this temperature has been reached inside the extraction battery, a cylinder tube filled only with polycaprolactam is connected to the lowest cylinder tube 10 in the manner described. After the extraction water has flowed out of the uppermost cylinder tube 1 ″ of the extraction battery, this cylinder tube is removed. 47 ml of extraction solution are then removed from the lowest cylinder tube and the uppermost cylinder tube is filled with fresh water to such an extent that the polycaprolactam filling is completely covered with water.

909811/1190 «" ⁶ ~

The following values are obtained:. ■

Newly set extraction time extract content

Cylinder tubes (hours) in the water in the granules

1 3

2 6

3. 9 4- 12

5 15

6 18

7 21

8 24

9 27

10 30

11 33

12 36

13 39

14 42

15 '45

16 48

As can be seen from the table, after about 30 Hours a balance. With a withdrawal of 47 ecm extraction solution at the lower end of the apparatus with a content $ 26 of caprolactam and oligomers are going this way 12.2 g of extract removed from the system. Together with the 1.8 g of extract that remain in the 120 g of polycaprolactam ($ 1.5),

10 - Start-up
period 19.5 - 22nd - 24.5
25th - 25.5 - 27.5 - 26.5 - 27.7 - 58 28.0 - 52 27.0 - 51 26.5 1, 51 26.0 ' 1, 26.0 1, 25.5 t, 25.5

909811/1190

Γ * '>
Vj *

14 g of extract are found compared to 14.05 B, which, according to the extract determination of 11.7 $>, are introduced into the system with the 120 g of non-extracted granules. The test arrangement with ^fc eliier ten-fold subdivision of the granule column, the continuous process approaches. The total residence time of the granulate in the system is J50 hours, while the extraction water remains in the system for 64 hours.

Example 3

At the lower end of an upwardly conical, widening vessel (opening angle 20 °), which holds a total of 10 1, there is a vertical screw (diameter 25 mm) with which polyamide granules can be pressed into the vessel from below. The vessel (h = 1000 mm; upper diameter = 200 mm) has a heating jacket and is kept at 95 ° C. It contains 5 kg of polycaprolactam granules with an extract content of 11 % and is filled to the top with water at 95 ° C. 100 g of polycaprolactam granules per hour are pressed in at the lower end of the vessel and the equivalent amount of extracted granules are removed from the upper end of the vessel. At the upper end of the vessel, 60 ecm of hot water per hour is run in and the equivalent amount of water which is enriched with caprolactam is withdrawn every hour at the lower end. After JO hours, the balance between the extract content of the extracted granules and the caprolactam content of at the bottom has in the _system: entnommen'wässrigen end caprolactam set. It en'ticontains ± 5 ? ° caprolactam, while the extracted granules am

- 8 909811/1190

at the top of the vessel has an extract content of 1%. By shifting the ratio of polycaprolactam / water in favor of polycaprolactam, even higher caprolactam contents can be achieved in the aqueous solution flowing off.

- 9 -

909811/1190

Claims (2)

- 9 - O.ζ. ο 157 95187 patent claims 1) Process for extracting low molecular weight fractions from polylactams by the action of extractants on layered polylactams in lump form at elevated temperature9, characterized in that the extractant is passed through the polylactam layer from top to bottom. 2) Method according to claim 1, characterized in that the polyamide layer is moved against the direction of flow .des solvent. BADISCHE ANILIN- & SODA-FABRIK AG drawings 90 9811/119 0 Documents (Art. 7, Paragraph 1, Paragraph 2, No. 1, Sentence 3 of the amendment of 4.9.196