FR2930251A1 - Reducing content of caprolactam and oligomers of copolyamide based on epsilon-caprolactam, comprises first washing of copolyamide with aqueous solution comprising epsilon-caprolactam and second washing of copolyamide with aqueous solution - Google Patents

Abstract

Reducing content of caprolactam and oligomers of a copolyamide based on epsilon -caprolactam, whose melting temperature is 80-150[deg] C, comprises: a first washing of copolyamide with an aqueous solution comprising epsilon -caprolactam (20-60 wt.%) for 4-12 hours at 50-75[deg] C; and a second washing of copolyamide with an aqueous solution for 4-8 hours at 40-85[deg] C.

Description

B08 / 2536 GD / VC AM 2514

Société Anonyme known as: ARKEMA FRANCE Process for reducing the content of oligomers and monomers of a copolyamide Invention of: Quentin PINEAU Marie-Françoise LOTTIAU

The present invention relates to a process for reducing the oligomer and monomer content of a ca-caprolactam copolyamide. Poly-caprolactam-based polyamides are widely used today. However, the polymerization of α-caprolactam to homopolyamide PA6 is not complete, it leads to an equilibrium in which the polymer obtained still contains low molecular weight elements, essentially ε-caprolactam, hereinafter referred to as caprolactam and its oligomers, also called 1,8-diazacyclotetradecane, generally of the order of 7 to 12% by weight relative to the weight of the final polyamide. A polycondensation reaction using caprolactam for the synthesis of copolyamides also leads to equilibrium. Thus, it has been observed that a copolyamide made from 40% of caprolactam may contain up to 3.4% by weight of this monomer and 0.2% by weight of its cyclic dimer relative to the weight of the final copolyamide. . However, during the transformation of the copolyamide and during storage of the transformed product, these residual oligomers, and especially the dimer, tend to exude.

In addition, during the transformation of the copolyamide but also during the life of the finished product, the residual caprolactam, which is a volatile organic compound (VOC), causes a phenomenon of "fogging" (condensation phenomenon), as by example described according to the VDA 278 standard.

The literature is abundant on methods for reducing the content of oligomers or caprolactams in homopolyamide PA6. Several processes have been proposed: by continuous or discontinuous extraction with hot water (DE 25 01 348, DE 27 32 328), by vacuum distillation (US 4 376 680) or in a stream of superheated steam ( EP 0 284 968). Improved extraction processes have been developed, such as multi-step hot water extraction against the current, possibly at temperatures above the boiling point of the extraction liquid (EP 0 308 774). . Thus, if it appears easy enough to significantly reduce the residual caprolactam content by the methods mentioned above, it is not the same for its dimer. Indeed, it has much less affinity with water and its physical properties make it more difficult to extract, its sublimation temperature being 210 ° C under 2 torr. The techniques known to date for the homopolyamide, and in particular the methods applying at high temperatures (above 100 ° C.), are not transferable to copolyamides based on caprolactam, that is to say of the type comprising at least two units, one of which is obtained from caprolactam. Indeed, these generally have melting temperatures lower than that of homopolyamide PA6.

For example, the process for extracting caprolactam and / or its oligomers from the homopolyamide PA6 described in document BE 10 08 569 can not be used for the type of copolyamide mentioned above, because it leads to a phenomenon of softening of the copolyamide treated.

Thus, the object of the invention is the provision of a method for washing a copolyamide of the aforementioned type, making it possible to reduce the residual caprolactam contents and its oligomers, and in particular its dimer. The present invention relates to a process for reducing the content of caprolactam and oligomers of a caprolactam-based copolyamide, the melting point of which is between 80 ° C. and 150 ° C., characterized in that it comprises the following successive steps - a first washing of the copolyamide with an aqueous solution comprising caprolactam in a content of between 20 and 60% by weight relative to the total weight of the solution, for a period of between 4 and 12 hours and at a temperature of between 50 and 75 ° C; then - a second washing of the copolyamide with an aqueous solution for a time between 4 and 8 hours and at a temperature between 40 and 85 ° C. Other features, aspects, objects and advantages of the present invention will become more apparent upon reading the description and the examples which follow. The copolyamide, which one seeks to wash according to the method of the invention can comprise at least two distinct reasons and answer the following formula: 6 / Z in which. 6 denotes the unit obtained from ε-caprolactam, and. Z is selected from a unit obtained from an amino acid, a unit obtained from a lactam and a unit having the formula (C-diamine) (Cb diacid), where a represents the number of atoms of carbon of the diamine and b representing the number of carbon atoms of the diacid, a and b each being between 4 and 36. When Z represents an amino acid, it may be chosen from 9-aminononanoic acid (Z = 9 ), 10-aminodecanoic acid (Z = 10), 10-aminoundecanoic acid (Z = 11), 12-aminododecanoic acid (Z = 12) and 11-aminoundecanoic acid (Z = 11) and as its derivatives, especially N-heptyl-11-aminoundecanoic acid. Instead of an amino acid, one could also consider a mixture of two, three, ... or more amino acids. However, the copolyamides formed would then comprise three, four, ... or more, patterns, respectively. When Z represents a lactam, it may be selected from pyrrolidinone, 2-piperidinone, enantholactam, caprylolactam, pelargolactam, decanolactam, undecanolactam, and lauryllactam (Z = 12). Obviously the particular case where the Z motif is caprolactam (Z = 6) is excluded. Indeed, in this particular case, it is in the presence of a homopolyamide, which is strictly excluded from the invention. When the Z motif is a unit corresponding to the formula (diamine in Ca) (diacid in Cb), the unit (diamine in Ca) is of formula H2N- (CH2) a-NH2, when the diamine is aliphatic and linear. Preferably, the monomer (diamine Ca) may be chosen from butanediamine (a = 4), pentanediamine (a = 5), hexanediamine (a = 6), heptanediamine (a = 7), octanediamine (a = 8), nonanediamine (a = 9), decanediamine (a = 10), undecanediamine (a = 11), dodecanediamine (a = 12), tridecanediamine (a = 13), tetradecanediamine ( a = 14), hexadecanediamine (a = 16), octadecanediamine (a = 18), octadecenediamine (a = 18), eicosanediamine (a = 20), docosanediamine (a = 22) and diamines obtained from fatty acids (a = 36).

When the monomer (diamine Ca) is cycloaliphatic, it can be chosen from bis (3,5-dialkyl-4-aminocyclohexyl) methane, bis (3,5-dialkyl-4-aminocyclohexyl) ethane, bis (3 5-dialkyl-4-aminocyclohexyl) propane, bis (3,5-dialkyl-4-aminocyclohexyl) butane, bis- (3-methyl-4-aminocyclohexyl) methane (BMACM or MACM), p-bis (aminocyclohexyl) methane (PACM) and isopropylidenedi (cyclohexylamine) (PACP). It may also comprise the following carbon skeletons: norbornyl methane, cyclohexylmethane, dicyclohexylpropane, di (methylcyclohexyl), di (methylcyclohexyl) propane. A non-exhaustive list of these cycloaliphatic diamines is given in the publication "Cycloaliphatic Amines" (Encyclopaedia of Chemical Technology, Kirk-Othmer, 4th Edition (1992), pp. 386-405).

When the monomer (diamine Ca) is arylaromatic, it can be chosen from 1,3-xylylene diamine and 1,4-xylylenediamine. When the monomer (Cb diacid) is aliphatic and linear, it can be chosen from succinic acid (y = 4), pentanedioic acid (y = 5), adipic acid (y = 6), heptanedioic acid (y = '7), octanedioic acid (y = 8), azelaic acid (y = 9), sebacic acid (y = 10), undecanedioic acid (y = 11) , dodecanedioic acid (y = 12), brassylic acid (y = 13), tetradecanedioic acid (y = 14), hexadecanedioic acid (y = 16), octadecanedioic acid (y = 18) , octadecanedioic acid (y = 18), eicosanedioic acid (y = 20), docosanedioic acid (y = 22) and fatty acid dimers containing 36 carbons. The fatty acid dimers mentioned above are dimerized fatty acids obtained by oligomerization or polymerization of unsaturated monobasic fatty acids with a long hydrocarbon chain (such as linoleic acid and oleic acid), as described in particular in the document EP 0 471 566. When the diacid is cycloaliphatic, it may comprise the following carbon skeletons: norbornyl methane, cyclohexylmethane, dicyclohexylmethane, dicyclohexylpropane, di (methylcyclohexyl), di (methylcyclohexyl) propane. When the diacid is aromatic, it may be chosen from terephthalic acid (noted T), isophthalic acid (noted I) and naphthalenic diacids. Among all the possible combinations for the 6 / Z copolyamides in which Z is a (C 18 diamine) (Cb diacid) unit, copolyamides corresponding to one of the formulas chosen from 6/12, 6 / 11, 6 / 6.10, 6 / 6.9, 6 / 6.18 and 6 / 6.36.

In an advantageous version of the invention, the molar content of Z in the final copolyamide is between 20 and 80% by weight and the molar content of caprolactam in the final copolyamide is between 80 and 20% by weight relative to the weight. final copolyamide.

According to another aspect of the invention, the copolyamide may further comprise at least one third unit and corresponds to the following general formula: 6 / Z / A in which the units 6 and Z are as defined above, and A is chosen from a unit obtained from an amino acid, a unit obtained from a lactam and a unit corresponding to the formula (Cd diamine) (diacid in Ce), with d representing the number of carbon atoms of the diamine and e representing the number of carbons of the diacid, d and e being each between 4 and 36. In the formula 6 / Z / A, reference will be made to what has been previously described for (co) monomers or Z units above. In this same formula, the pattern A has the same meaning as the pattern Z defined above. Of course, the particular case where the unit A is strictly identical to the unit Z is excluded. Among all the possible combinations for the copolyamides 6 / Z / A, particular mention will be made of the copolyamides corresponding to one of the formulas chosen from 6 / 6.6 / 12, 6 / 6.6 / 11, 6 / 6.6 / 6.10, 6 / Pip.12 / 12, 6/11/12, 6 / 6.6 / 6.36, 6 / 6.6 / 11/12 and 6 / 6.6 / 10.10. Preferably, the sum of the molar contents in Z and A units in the final copolyamide 6 / Z / A is between 20 and 80% by weight, the molar content of caprolactam being between 80 and 20% by weight relative to the weight. copolyamide, or terpolyamide 6 / Z / A. The copolyamide, which one seeks to wash, can meet one of the formulas described above, provided that its melting point is between 80 ° C. and 150 ° C., preferably between 85 ° C. and 130 ° C.

According to the process of the invention, the first step consists in washing the copolyamide with an aqueous solution comprising caprolactam in a content of between 20 and 60% by weight relative to the total weight of the solution, for 4 to 12 hours and at a temperature between 50 and 75 ° C.

It is specified that the expression "included between" used in the preceding paragraphs, but also in the remainder of the present description, should be understood as including each of the mentioned terminals.

This first step allows the dissolution of the dimer of caprolactam. According to a preferred embodiment, this step is carried out at a temperature between 60 and 75 ° C, and more particularly at 70 ° C.

Preferably, this first step has a duration of 6 hours. Preferably, the caprolactam content in the aqueous solution is 42%. Preferably, this washing is carried out under an inert atmosphere, for example under a nitrogen sweep.

The process according to the invention is then continued by a second step of washing the copolyamide with an aqueous solution for 4 to 8 hours and at a temperature between 40 and 85 ° C. This step allows the removal of traces of residual monomers from the polycondensation reaction, and also of the first washing step. According to a preferred embodiment, this step is carried out at a temperature between 60 and 80 ° C, and more particularly at 70 ° C. Preferably, this first step has a duration of 5 hours.

Preferably, this washing is carried out under an inert atmosphere, for example under a nitrogen sweep. Depending on the residual content required, it is possible to renew at least once this last washing step with hot water.

This process can be followed by a complementary drying step of the washed copolyamide. This drying can be done for example for 12 hours under a vacuum oven at 50 ° C. It is also possible to perform an intermediate water rinsing step between the first and second washing steps described above. This rinsing can be carried out at room temperature, for 10 to 15 minutes, in order to remove the remains of the aqueous caprolactam solution used in the first step.

The present invention will now be described in the examples below, such examples being given for illustrative purposes only, and obviously not limiting.

EXAMPLES In an autoclave, 120 kg of an aqueous solution of caprolactam 42% and 60 kg of copolyamide granules of formula 6 / 6.6 / 12, the melting point of which is 115 ° C. to be washed, are charged. The mixture is maintained at 70 ° C. for 6 hours with stirring. The solution is then drained.

Then follows a rinsing step with 100kg of water, for 10 minutes at room temperature, then the water is drained. The copolyamide is then washed with water (120 kg) for 5 hours at 70 ° C. The water is then drained. This last washing step is repeated twice.

The polyamide is then dried.

The granules are analyzed by two techniques: The overall rate of caprolactam and dimer can be obtained by NMR (Proton Magnetic Resonance) of the proton after solubilization in a hexafluoroisopropanol / dichloromethane mixture at room temperature overnight. The apparatus used is an Avance 400. The individual levels of caprolactam and dimer can be obtained by gas chromatography (GC). The granules are solubilized for 8 hours at 60 ° C. in a solution of methanol and internal standard. The samples and standards are injected into the Agilent Technologies 6890 WKC 407 chromatograph according to the conditions given below: - Column type: CPSIL 5CB 50m / 0.32mm / 0.12m - Column rate: 2m1 / min in flow mode constant - Split ratio: 50 - FID detector temperature: 320 ° C - Injection mode: autosampler 7683 - Injected volume: 11 1 The results are described in the table below: Treatment GC GC NMR Caprolactam o capro + dimer (%) Dimer (%) (%) before washing 3.29 to 3.19 0.23 to 0.22 3.5 After the first 16.1 to 15.7 0.06 to 0.06 nd * stage wash (caprolactam solution treatment) After rinsing 11.0 to 10.5 0.05 to 0.05 nd After the second 3.96 to 3.71 0.03 to 0.03 nd wash step: hot wash After 2nd 1.58 -1.61 0.02 to 0.02 1.8 hot wash After a third 0.92 to 0.91 0.01 to 0.01 1.0 hot wash * nd signifier not determined treatment with the aqueous solution of caprolactam significantly reduces ent the dimer content. The successive washes with water reduce it still somewhat, but allow to bring the residual caprolactam content to the desired content.

Claims (8)

REVENDICATIONS1. Process for reducing the content of caprolactam and oligomers of a copolyamide based on ε-caprolactam, the melting point of which is between 80 ° C. and 150 ° C., characterized in that it comprises the following successive stages: a first washing of the copolyamide with an aqueous solution comprising α-caprolactam in a content of between 20 and 60% by weight relative to the total weight of the solution, for a time of between 4 and 12 hours and at a temperature between 50 and 75 ° C; then - a second washing of the copolyamide with an aqueous solution for a time between 4 and 8 hours and at a temperature between 40 and 85 ° C. 2. Method according to claim 1, characterized in that the melting temperature of the copolyamide is between 85 ° C and 130 ° C. 3. Method according to claim 1 or 2, characterized in that the copolyamide comprises at least two units corresponding to the following formula: 6 / Z in which: 6 denotes the unit obtained from ε-caprolactam, and. Z is selected from a unit obtained from an amino acid, a unit obtained from a lactam and a unit having the formula (diamine in Ca) (diacid in Cb), where a is the number of carbon atoms in the diamine and b representing the number of carbons of the diacid, a and b being each between 4 and 36. 4. Method according to claim 3, characterized in that the copolyamide comprises at least a third unit and corresponds to the following general formula: 6 / Z / A in which the units 6 and Z are as defined in claim 3, etA is chosen from a unit obtained from an amino acid, a unit obtained from a lactam and a unit corresponding to the formula (Cd diamine) (diacid in Ce), with d representing the number of carbon atoms of the diamine and e representing the number of carbons of the diacid, d and e being each between 4 and 36. 5. Method according to any one of the preceding claims, characterized in that the copolyamide has the formula 6/12, 6/11, 6 / 6.10, 6 / 6.9, 6 / 6.18 and 6 / 6.36, 6 / 6.6 / 12 , 6 / 6.6 / 11, 6 / 6.6 / 6.10, 6 / Pip.12 / 12, 6/11/12, 6 / 6.6 / 6.36, 6 / 6.6 / 11/12 and 6 / 6.6 / 10.10. 6. Method according to any one of the preceding claims, characterized in that the first step is at 70 ° C for 6 hours. 7. Method according to any one of the preceding claims, characterized in that the second step is at 70 ° C for 5 hours. 8. Method according to any one of the preceding claims, characterized in that it comprises at least one additional rinsing step identical to the second step, which follow the latter.