DE2403178A1 - Process for the preparation of amine salts - Google Patents

Description

PATENTANWALYSBÜftO 2Λ03178 TlEDTKE - BüHLING "KlNNE TEL. (089) 53 96 53-56 TELEX: 524845 tipat CABLE ADDRESS: Germaniapatent Munich

8000 Munich 2

Bavariaring 4 January 23rd 1974

P.O. Box 202403

B 5815

Imperial 'Chemical Industries Limited
London (Great Britain)

Process for the preparation of amine salts

The invention relates to a process for the preparation of solid salts of amines and organic acids.

Nylon 6,6 (polyhexamethylene adipamide), a used for the production of moldings and for melt spinning too
Polyamide, which is useful for synthetic fibers, is produced by the polycondensation of hexamethylenediamine and adipic acid in
approximately equimolecular proportions produced. An equimolecular mixture of hexamethylene diamine and adipic acid forms the salt hexamethylene diammonium adipate, generally nylon

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Called 6,6 salt. Nylon 6,6 is commonly made in-by an aqueous solution of the nylon 6,6 salt of Subjects to polycondensation. For various reasons it is convenient to use the starting materials for nylon 6,6 as nylon To store, handle and transport 6,6 salt. For example, hexamethylenediamine is more stable in the form of the nylon 6,6 salt, for example against air oxidation than in the form of the free base. Any degradation of the starting materials for nylon 6,6 occurs the polycondensation must be avoided as far as possible, since the impurities formed in the process are often disadvantageous Have an effect on the resulting polyamide by impairing its color or physical properties will.

Nylon 6,6 salt is highly soluble in water. An approximately 50% strength by weight aqueous solution can therefore be prepared at normal temperatures (20 to 25 ^{° C.).} This is very advantageous in the sense that it is possible to start the polycondensation leading to nylon 6,6 with a highly concentrated solution of the starting materials. It is also possible to form such a concentrated solution by mixing aqueous hexamethylenediamine and adipic acid solutions in the appropriate molar ratios. In addition, it is

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half of boundaries possible _9, the nylon 6,6 Sala to .lagern in the form of its aqueous solution _s to handle and transport below. However, nylon 6,6 salt is less stable in the form of an aqueous solution, in particular more susceptible to oxidation, than in the solid state. Since nylon 6,6 salt also weighs about twice as much as the molar equivalent of the solid salt as an aqueous solution, transportation in this form is more expensive. For these reasons, a substantial portion of the nylon 6,6 salt produced is isolated, stored, handled and shipped as a solid material.

Strength Nylon 6.6 salt is expediently prepared by mixing ^one methänolische solutions of hexamethylene diamine and adipic acid. The nylon 6,6 salt, which is sparingly soluble in methanol, crystallizes out and can easily be separated off by filtration or centrifugation. While this approach is viable, it has a number of disadvantages. Methanol is relatively more expensive than water and measures are needed to recover the methanol from time to time by distillation. Since methanol is very flammable, the use of a fire-safe system is necessary, which is complicated and expensive. In addition, during the crystallization, the methanol reacts to a certain extent with the adipic acid to form methyl esters, which results in a lower yield

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Nylon 6,6 salt results.

For these reasons, it would be advantageous to use methanol in the manufacture of nylon 6,6 solid salt to avoid. The methods hitherto attempted for the production of solid nylon 6,6 salt in an aqueous medium have a number of disadvantages. Thus, solid nylon 6,6 salt can be obtained by evaporating the concentrated aqueous solution until the salt separates out. However, this method is thermal because of the large amount of required Energy expensive. Another method is that adipic acid with hexamethylenediamine at elevated temperatures, e.g. at 95 to 100 ° C, neutralized in very strong aqueous solutions, whereby one gets a very strong aqueous solution obtained with up to 70 wt .-% nylon 6,6 salt, which precipitates solid salt on cooling. The high temperatures used however, lead to significant degradation of the nylon 6,6 salt.

We have now found a method for making solid nylon 6,6 salt without these disadvantages. This method is according to the invention characterized in that adipic acid dissolves in an aqueous nylon 6,6 salt solution and the acidic solution neutralized with hexamethylenediamine, solid nylon 6,6 salt separating out. The procedure is too to the production of other water-soluble salts of diamines applicable with dicarboxylic acids, for example on salts with cork

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acid, sebacic acid, dodecanedicarboxylic acid, isophthalic acid as well as with adipic acid, as well as with aze with octamethylenediamine, decamethylenediamine, dodecamethylenediamine, di- (U-aminocyclohexyDmethane or m- or p-xylylenediamine as well as with hexamethylenediamine.

According to the invention a process for the preparation of a solid water-soluble salt of a diamine with a Dicarboxylic acid, especially hexamethylene diammonium adipate, created, which consists in dissolving the dicarboxylic acid in an aqueous solution of said salt, the diamine is added to the aqueous solution obtained and the precipitated solid salt is separated off.

In the case of nylon 6,6 salt, it is preferred to start with an aqueous salt solution of about 50% by weight starch, for example from RO to 60% by weight, and dissolve the adipic acid therein. The temperature should not exceed 80 ⁰ C and preferably in the range of 50 to 65 ° C. At 60 ° C., a solution of 48% by weight nylon 6,6 salt dissolves about 20% by weight adipic acid. The acidic solution is then neutralized with hexamethylenediamine. Since the neutralization is exothermic, this stage is preferably cooled so that the temperature does not exceed 65 ° C. The crystalline

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solid salt begins to precipitate before neutralization is complete. The neutralization is carried out by adding a molar amount of hexamethylenediamine corresponding to the amount of free adipic acid dissolved in the aqueous nylon 6.6 salt solution is equivalent. The completion of the neutralization can be determined by measuring the pH. A pH value of 8.1 is a satisfactory endpoint. After complete neutralization, the aqueous mixture can be cooled for example to a temperature in the range of 20 to 50 ° C, and the crystalline solid salt becomes separated from the mother liquor by filtration, centrifugation or other suitable measures. The wet salt can can usually be dried, for example in a stream of hot nitrogen. The mother liquor, a concentrated one Solution of the nylon 6,6 salt can be reused in the manufacture of further solid nylon 6,6 salt, or it can be used for polycondensation to nylon 6,6. If desired, the mother liquor can before this Further use can be treated with carbon (activated charcoal).

That in the process for the production according to the invention Hexamethylene diamine used by nylon 6,6 salt can be the diamine

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2A03178

be itself or it can conveniently be in the form of a Concentrated aqueous solution, for example a strength of 50 to 90% by weight., can be used.

The invention is illustrated, but not limited, by the following examples. Parts and percentages relate to weight.

example 1

1356 parts of nylon 6,6 aqueous salt solution (48%) were heated to 60 ° C. under a nitrogen atmosphere and 270 parts of adipic acid were added with stirring. When all of the acid had dissolved, hexamethylenediamine (90% strength aqueous solution) was allowed to run in to a pH of 8.1, the temperature being kept at 65 ° C. by cooling. Cooling was continued until the temperature reached 50 ° C. The crystals began to separate out before the addition of diamine was complete, and were separated off by filtration, freed from mother liquor by washing with methanol and ^{dried at 60 °} C. in vacuo. The yield of dry salt was 380 parts in a high quality form suitable for conversion to nylon polymer.

The mother liquor consisted of 1310 parts of a 49.5% nylon 6,6 salt solution and was suitable for reuse.

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Example 2

1356 parts of aqueous nylon 6,6 saline solution (48%) were heated to 60 ° C under a nitrogen atmosphere, and 270 parts of adipic acid were added with stirring. When the acid had dissolved, an aqueous one was left Hexamethylenediamine solution (60%) down to a pH of 8.1 run in, the temperature being kept at 65 ° C. by applied cooling. The cooling was continued until the Temperature had reached 25 ° C. The crystals began to separate out before the end of the diamine addition, were filtered off, freed from the mother liquor and dried. The yield was 370 parts of a high quality, For the conversion to nylon 6,6 salt suitable for NylOnpolymerxsat .

The mother liquor consisted of 1300 parts of a 47% nylon 6,6 salt solution and was after carbon treatment suitable for polymerization to nylon 6,6 or for reuse in the process.

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Claims (2)

Claims 1. A process for the preparation of a solid, water-soluble salt of a diamine with a dicarboxylic acid by Neutralizing the diamine with the dicarboxylic acid, characterized in that the dicarboxylic acid is in an aqueous Dissolves solution of the salt, the diamine is added to the resulting solution and the precipitated solid salt is separated off. 2. The method according to claim 1, characterized in that after separation of the solid salt and optionally mother liquor remaining after treatment with charcoal is reused in the process to dissolve the dirarboxylic acid. 409831/1069 ORIGINAL INSPECTED