DD139587A1 - CONTINUOUS METHOD FOR THE PRODUCTION OF POLYAMIDE FROM RHO-CAPROLACTAM - Google Patents

Abstract

The invention relates to the implementation of a continuous process at atmospheric pressure for polyamide production under optimum reaction conditions. The process according to the invention optimizes the product temperature and concentration of the water in such a way that hydrolysis and polyaddition of the * -caprolactam proceed at high reaction rates, whereby the chemical equilibrium in the polymerization of * -caprolactam to polyamide is very soon reached. In the process according to the invention, the average temperature gradient between the product level and the first process-necessary heat transfer between 0.1 and 1.5 grd / cm product depth is selected. The product depth between level and beginning of this heat supply is at least 20 cm. The product temperature in the level is adjusted so that it corresponds to the boiling point of the reaction technically necessary mixture for adjusting the average degree of polymerization of the final polymer. For an average degree of polymerization between 120 and 160, a boiling point of between 200 and 250 ° C is set. By means of the process, polyamide is produced as starting material for silks, fibers and plastic articles.

Description

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Title of the invention

Continuous process for the production of polyamide from ε-caprolactam

Area of application of the invention

The invention relates to the continuous polymerization of ε-caprolactam to polyamide 6 at Atipiosphär endruck, wherein the molten product is transported by the action of gravity.

C harakteristik olutions of the known tech nically en L

It is a Yerfahren for simplified continuous polymerization of s-caprolactam at atmospheric pressure is known in which isothermal process temperature is maintained over the entire reaction time. (DL-PS 55 822).

The reaction rate in the production of polyamide from ε-caprolactam depends crucially on the process parameters of temperature and water content. At high temperatures and high water contents, the reaction rate increases in the start phase of the reaction. In open systems, such as those used for the simplified continuous polymerization of ε-caprolactam, the water is almost completely driven off at high temperatures, which reduces the reaction rate. "At relatively low temperatures, the larger amount of water can be added at relatively low temperatures Start high realizations

speed, but since isothermal ProzeßfUhrung is required, the reaction rate in the subsequent process, especially in the following reaction section with predominant polyaddition reaction is reduced, and also is oriented in this Pail on polyamides with very low average degrees of polymerization because of excessively high in the reaction mixture amount of water, whereby the Polyamide can not be further processed in terms of quality. ,

Consequently, the process mentioned is not optimally designed with respect to the reaction rate, which reduces the space-time yield of polyamide and achieves the equilibrium state of the polyamide after longer reaction times.

Object of the invention

The invention aims to produce polyamide by continuous process at atmospheric pressure or slight overpressure and with the addition of water above the reaction-technically necessary amount, wherein the polymerization under optimal reaction conditions, especially in the hydrolysis of the g-caprolactam and in the polyaddition reaction, should proceed , which increases the space-time yield of polyamide, improves the product quality of the polyamide and reduces energy consumption.

Explanation of the essence of the invention

It is the object to optimize the reaction conditions for the hydrolysis of £ £ -Gaprolaotams to-aminocaproic acid and the polyaddition vonfi-caprolactam £ aminocaproic acid polymer or low so that maximum reaction rates can be achieved depending on the desired Endpolymerisat.

The hydrolysis reaction is "accelerated at high temperatures and high water contents, while the reaction rate in the polyaddition reaction is increased only with increasing temperature." On the other hand, for setting certain average polymerization degrees, a certain amount of water remaining in the product must not be exceeded.

At the beginning of the course of the reaction, the hydrolysis reaction predominates. In the process according to the invention, reaction conditions are set which are characterized by high water content and the possible temperature. This high water content is determined by the fact that, after completion of the hydrolysis, this amount of water remains in the product. including the polymer already reacted in the grafted polymer, which is required for the adjustment of the equilibrium final degree of polymerization. As the reaction progresses, the proportion of the polyaddition reaction in the overall reaction process increases, and the reaction temperatures are set higher, which further accelerates the course of the reaction. It should be noted that with continuous reaction time to the reaction with significant polyaddition, the product temperatures should increase gradually, on the one hand ensures that the optimum amount of water is not expelled and on the other hand, the polyaddition reaction can proceed at high temperatures. Thus, the various temperature settings between the Reaktionsber oak with predominant hydrolysis and significant polyaddition reaction does not affect so that the hydrolysis is heated by Selbstkonvektionsvorgänge in the product too much, is between the product level and the first heat transfer system, in the already clearly polyaddition reaction in addition to decreasing hydrolysis takes place, a minimum distance is included. At predominant polyaddition reaction, which is exothermic, then sets a high reaction temperature. It is polyamide from ξ- caprolactaa, which, if necessary

Chain stabilizers and additives are added, by continuous at atmospheric pressure or low pressure operating method and adding water over the reaction-technically necessary amount, as required in the addition of aqueous suspensions for matting the polyamide prepared. According to the invention, 0.1 to 1.5 grd / cm product depth is selected as the mean temperature gradient between the product level and the first heat input necessary for the process, and the product depth between the level and the beginning of the first heat input necessary for the process is at least 20 cm * as product temperature at or below or above it, the one is set that corresponds to the boiling point of the reaction mixture necessary mixture, consisting mainly of ^ -caprolactam, water, already hydrolyzed and grafted product, for adjusting the average degree of polymerization of the final polymer. It w $ rd "3S: in particular in the production of Endpolymerisaten with Durchschnittspolymerisa- tion degree of between 120 and 160 adjusted to a boiling point or close to the levels in the range 200 to 250 ⁰ C.

embodiment

The invention will be explained with reference to an embodiment.

In a mixing vessel, reaction mixture is prepared. The reaction mixture consists of ε-caprolactam and 0.12 $ acetic acid, which acts as a chain stabilizer. It is polymerized in an operating at atmospheric pressure system by means of the method according to the invention in excess of water. The water is added within the TiOg suspension, the water load of the VK tube is 1.3 %. Since polyamide of the average degree of polymerization 135 is to be produced, the actual amount of water required is only about 0.40 ⁰ Io ₁ so that about 0, 9 $ of water must be evaporated.

Reactions mixture and Ti0 ₂ suspension are distributed at the product level, the upper melt layer is stirred. The ascending vapors are condensed by means of a reflux condenser, whereby vaporizing lactam is retained in the reactor. , ,

At the product surface, the temperature is measured by means of a resistance thermometer approx. 0.5 cm above the product level. This temperature should be 226 ⁰ C and corresponds to the boiling temperature of the product located on the product surface, in which the optimal total amount of water of $ 0.40> remains. The metered reaction mixture is preheated to 219C. As product temperature 253 ⁰ G is regulated directly after the first process-necessary heat supply. At the lactam throughput of 240 kg / h, product temperatures of 226 to 229 ⁰ G are set in the product level under these conditions and with a cooling effect on the reflux condenser of approx. 1000 kcal / h.

The average temperature gradient in the product between level and: completion of the first heat input necessary for the process is adjusted to 0.51 to 0.57 grd / cm product depth and the distance between product level and start of the first process necessary heat supply is 47 cm. In the further course of the polymerization process, the product temperature rises to 275 ° C. in the exothermic reaction phase.

At the beginning of the homogenization phase, in which the polycondensation reaction predominates, the product is cooled to 240 ^° C. At this temperature, the product is homogenized. After a mean Produktverweilseit of 18.5 hours, the polyamide leaves the VK ~ tube with the average degree of polymerization of 135 and an extract content of 8 _? 8 $>. The polyamide is in chemical equilibrium. In contrast to the exemplary embodiment, isothermal Produktteinperaturen between the product level and the completion of the first method, the necessary heat input of 253 ⁰ C set

2 087 4 2

and otherwise unchanged reaction conditions in the homogenization compared to the embodiment complied, we obtain a NaOH a product of 18.5 hours. A polyamide having a Durohschnittspolymerisationsgrad of 135 and a content of Uiederpolymeren of 10.9 #. The polyamide is not in chemical equilibrium.

In contrast to the exemplary embodiment, if the isothermal product temperature of 253 ^° C. is set during the entire process, the average degree of polymerisation falls to 128 and the content of low molecular weight increases to 11.2 $. The polyamide is also not in chemical equilibrium.

In the further processing into textile silks, wherein the polymerization steps following extraction and (drying of the polyamide granules, spinning, stretching and archiving take place under the same process conditions, is for the polyamide, which was prepared according to AusfUhrungsbeispiel by the novel process, compared to the old method produced polyamide, the highest quality content of silks increased by 3.4% and the waste in the silk-making process is reduced by 1.1 % ,

Claims (1)

Invention claim h Continuous process for the preparation of polyamide from ε-caprolactam at atmospheric pressure or slight overpressure, in the case of excess water, wherein water is evaporated off, and optionally with the addition of chain stabilizers in the reaction mixture and, if appropriate, additives characterized by 0.1 to 1.5 grd per cm of product depth is chosen as the mean temperature gradient between product level * and the first process-necessary heat supply, the product depth between level and beginning of this heat supply is at least 20 cm ^ and set the product temperature at or very close to the level is that it corresponds to the boiling point of the reaction-technically necessary mixture consisting mainly of ε-caprolactam, water and .beverly hydrolyzed and anpolyinerisiertem'Produkt, for adjusting the average degree of polymerization of the final polymer, in particular for final polymers with average degree of polymerization between 120 and 160, the boiling temperature between 200 and 250 ⁰ C is set.