DE2729421A1 - Polyamide prodn. from adipic acid and hexa:methylene:di:amine - using aq. monomeric nylon salt soln. made using recycle condensate from the autoclave and evapn. stages - Google Patents

Abstract

Water is added during the salt-forming stage from the diamine and acid, so that the monomeric salt is obtd. as an aq. soln. The aq. soln., together with the usual additives, is concd,in an evapn. stage and the concd. soln. is then subjected to polycondensation under heat and pressure. All the vapours recovered during the concn. and polycondensation stages are condensed and the whole of the condensate from teh polycondensation is mixed with part fo the condensate from the pre-evapn. stage. The combined condensate is then used in the salt-forming stage inplace of fresh water. Process allows recycling of vapours resulting from polycondensation and concn. stages, which contain a number of environmental pollutants, which can no longer legally be released into the atmosphere or drains. These substances are difficult and expensive to remove from theffluent. The process overcomes this problem by recycling these pollutants to the reaction mixt., which has no deleterious effect on the polyamide prod.

Description

Process for the production of polyamide

Description In the discontinuous polycondensation of hexamethylenediamine and adipic acid to polyamide becomes an aqueous solution of monomeric batch Nylon salt first concentrated in an evaporator and then further concentrated in an autoclave, and then polycondensation takes place in the autoclave. This falls in the evaporator and large amounts of steam in the autoclave, around 1.2 t per 1 t of polyamide. This exhaust steam is conventionally blown into the open air, even though it contains pollutants is loaded and the resulting bluish haze is a considerable nuisance represents for residents. According to new legislation, such harassment is not more permissible, and there are technical solutions to hold back the pollutants to accomplish.

A cleaning of the exhaust steam before it is blown off - for example with activated charcoal or by catalytic oxidation - is technically very complex and therefore none economical solution. Withdrawal and cleaning via columns is prohibited the intermittent build-up of steam. One viable option would be to knock down in Condensers, possibly with recovery of heat. However, arises then a sewage problem, since the polluted condensate in the accumulating Form cannot be given into the receiving water. Many methods of reconditioning of the condensate have been intensively investigated, e.g. biological clarification, incineration, Trickling on seepage fields, accumulation of pollutants through electrodialysis or ion exchange or distillation. All efforts failed due to technical reasons Difficulties or at the cost of the proceedings.

The invention is based on the knowledge that a satisfactory Solving the problem of condensate handling only by recycling the condensate, i.e. through recycling - and thus returning the pollutants to the polymerization process - can be searched. This principle is explained in more detail using Table 1.

The subject matter of the invention is defined in the claims.

For the production of a nylon salt solution, the precursor to polycondensation, 80% hexamethylenediamine, adipic acid and water are placed in a reaction vessel brought together with stirring. The process can be carried out continuously or discontinuously will. The resulting monomeric salt is drawn off as approx. 50 filtered, in many cases removed by activated charcoal and finally all in one Storage tank in stock. This salt supply is discontinuous in the subsequent Polycondensation batchwise a weighed amount is taken and the polycondensation subject.

In a typical example (see Table 1) there is an evaporator filling from 2898 kg of a salt solution, i.e. the batch contains 1507 kg of salt and 1391 kg Water. The input of raw materials for this evaporator filling is 837.6 kg of adipic acid, 836.7 kg of 80% diamine and 1223.7 kg of water. In the evaporator is the solution is concentrated, 1016.4 kg of condensate are obtained, and the concentrated salt solution consists of 1505.3 kg nylon salt dissolved in 376.3 kg water. This water and that in the following polycondensation resulting water are then from the Autoclave driven out, so that in addition to the end product polyamide, 1294.9 kg, more 586.7 kg of condensate accumulate. A total of 1016.4 + 586.7 = 1603.1 kg of condensate fall on, the 1014.7 + 582.4 = 1597.1 kg of water contain. The biggest Part of this 1597.1 kg of water, namely 1223.7 kg, is called deionized water Stage of salt production fed. Recycling the condensate now means, related on 1 batch, 1223.7 kg of water as condensate from the salt production stage add and discard the excess. As soon as a certain supply of salt no more deionized water is used for further production needed.

Table 1 Material balance based on 1 batch of starting materials Adipic acid 837.6 kg hexamethylenediamine, 80% aqueous solution 836.7 kg deionized Water 1223.7 kr 2898.0 kg After salt production, nylon salt 1507.0 kg solution water 1391.0 kq 2898.0 kg After the evaporation stage nylon salt 1505.3 kg solution water 376.3 kg evaporator condensate water A 1014.7 kg adipic acid 0.05% = 0.5 kg diamine 0.12 % - ^ 1.2 ka 1016.4 kq 2898.0 kg After the autoclave stage polyamide 1294.9 kg evaporator condensate 1016.4 kg autoclave condensate water 582.4 kg adipic acid 0.12% 5 0.7 kg diamine 0.61% 8 3.6 kq 586.7 kg 2898.0 kg With this driving style and one Salt supply of e.g. 600 t 52% but solution runs a water quantity of 288 t incessantly through the circle: salt supply - evaporator / autoclave - condensers - salt reaction vessel - salt supply. There is a constant renewal of these water menus instead (supply over 80% diamine and over formation during condensation), but the The dilution effect is small, and therefore there is an accumulation of pollutants in the There is a risk of condensate with every passage through the evaporator / autoclave.

The pollutants in the exhaust steam from the evaporator and autoclave consist of Adipic acid and diamine (see Table 1), some of which are available as nylon salts, and from ammonia and other organic ones that have not yet been identified with certainty Links. Adipic acid and diamine understandably do not interfere with recycling. The case is different with ammonia and with organic compounds, by-products the nylon process. One had to expect that their steady accumulation in the Condensate after a short time the nylon process, which is known to be the starting material of the highest purity, would affect it in an inappropriative manner. Surprisingly, really however, such enrichment does not occur. Provided the first indication of this Measurements of ammonia concentrations. A threshold of 70 to 80 mpm NH3 im Condensate is not exceeded. The reason for this is obviously the training of states of equilibrium in the evaporator and autoclave between vapor and liquid phase. Long-term tests led to a corresponding result for the organic by-products.

Here, too, threshold values develop in the mpm range that are not exceeded will. It was only these surprisingly low concentrations of inexperienced compounds made a recycling seem possible, and all technical concerns about the Salt production with condensate and its impurities seemed aUSYR #; UPt ,,,, the practical application under regular production conditions, however, soon leads to serious trouble.

In the case of the nylon salt solution produced, the discoloration decreases, a neuralgic one Point of polyamide production, to such an extent that even that of it produced polyamide is slightly discolored in yellow. A discoloration of the nylon salt solution Activated charcoal initially provides the desired colorless solution again, but the solution is not color-stable, but rather changes color within 1 to 2 days again and therefore does not have the storage capacity required for smooth production.

According to a further feature of the invention, however, this also succeeds Solve a problem. It was found that you cannot get the finished nylon salt solution must treat with activated charcoal, but the (colorless) starting mixture before use for the preparation of the nylon salt solution. With this driving style, a colorless one arises and sufficiently color-stable, i.e. storable nylon salt. It is surprising it is not necessary to additionally treat the saline solution with activated charcoal. the Reactions during dye formation and their suppression are not yet known.

According to a further feature of the invention, a not inconsiderable one occurs Yield increase in polyamide production, which can be seen directly from the Composition of the condensate results (see Table 1). With the previous blow-off 1.2 kg of adipic acid are released from the vapors, i.e. 0.14 8 of the amount of 837.6 used kg lost. For diamine it is 4.8 kg or 0.57%. This is where the bigger losses occur on the autoclave. When recycling is therefore all of the autoclave condensate, but only part of the evaporator condensate reused, i.e. excess condensate is only taken from the evaporator condensate (see Table 2). The losses are falling on 0.2 kg of adipic acid ^ - 0.02 z of the insert, or

0.4 kg diamine - 0.05%. The excess condensate, 374 kg, adjusts close and loading no significant burden for an already existing sewage treatment plant and is discarded.

Table 2 for the salt treatment plant evaporator condensate: Water 641.3 kg 373.4 kg adipic acid 0.3 kg 0.2 kg niamin 0.8 kg 0.4 kg autoclave condensate: Water 582.4 kg - adipic acid 0.7 kg - diamine 3.6 ka - total: water 1223.7 kg 373.4 kg adipic acid 1.0 kg 0.2 kg diamine 4.4 kg 0.4 kg polyamide for textile production is usually not exactly equimolar to achieve a certain stainability narrow hexamethylenediamine and adipic acid are made. Also is often used to control Titanium dioxide is added to the whole of the fiber. The following example takes into account these realities.

For example 2908.0 kg of an aqueous nylon salt solution, produced under Use of condensate from 839.8 kg of adipic acid, 670.2 kg of hexamethylenediamine and 1398.0 kg of water are mixed with 9.7 kg of a 20% aqueous solution in the evaporator Titanium dioxide slurry, 1.05 kg of a 5% aqueous rank hypophosphite solution and 25 g foam eliminator. The mixture therefore contains a total of 1406.8 kg of water, and from the evaporator 1028.8 kg together with 0.5 kg of adipic acid and 1.2 kg hexamethylenediamine evaporated and in a condenser to 1030.5 kg evaporator condensate condensed. The evaporation residue - at around 150 OC above the crystallization limit is held in an oxygen-free, preheated autoclave and the Prevent polycondensation. To do this, the pressure and temperature are gradually increased to about 270 OC and 17 atm increased. The pressure is then released to near atmospheric pressure. Here 581.5 kg of water, 0.7 kg of adipic acid and 3.6 kn hexamethylenediamine escape from the autoclave, and 1302.5 kg of polyamide melt remain. The exhaust steam is in a condenser condensed to 585.8 kg autoclave condensate. The melt is under nitrogen pressure extruded and on a strand granulator to granulate for the melt spinning process processed.

Part of the evaporator condensate - the excess of about 375 kg - discarded, the rest is combined with the autoclave condensate 0, to about 35 C cooled and filtered through activated charcoal.

The filtrate is reused in the production of new nylon salt solution, taking into account the adipic acid and hexamethylenediamine content.

There are no differences in the spinning behavior of the granulate a conventional product, i.e. a product manufactured without recycling. Also the finished one Yarn is no different from conventional material.

End of description.

Claims (2)

Claims 1. Process for the production of polyamide from hexamethylenediamine and adipic acid, wherein in the step of salt formation from hexamethylenediamine and Adipic acid wins the monomeric salt in aqueous solution by adding water, the aqueous solution and additives are concentrated in one evaporation stage, the concentrated Solution in the autoclave at elevated temperatures and pressures of the polycondensation underZ1rft and all exhaust steam condensed, characterized in that one (a) the entire condensate of the autoclave stage and part of the condensate of the evaporation stage combined with one another and (b) the combined condensates of the salt formation stage instead of fresh water. 2. The method according to claim 1, characterized in that the combined condensate with a decolorizing agent before introduction into the salt formation stage, treated like activated carbon.