MXPA00008338A - Production of polyamides by reactive distillation - Google Patents

Abstract

The invention relates to a method for producing polyamides, their oligomers or their mixtures, possibly with other reaction products, by reacting aminonitriles (A) and possibly other polyamide-forming monomers and/oroligomers with water (D) by reactive distillation. The reaction product (P) is extracted from the column bottom in the reactive distillation device and resulting ammonia (N), as well as possibly other resulting compounds having a low molecular weight, and water are withdrawn at the head of the column.

Description

PREPARATION OF POLYAMIDES BY REACTIVE DISTILLATION The invention relates to a continuous process for preparing polyamides, their oligomers or mixtures thereof, where appropriate with other reaction products, by the reaction of amino nitplos and, where appropriate, other monomers and / or oligomers forming polyamides with water. Polyamides prepared by direct hydrolytic polymerization of amino nitriles usually contain incompletely hydrolyzed portions of intermediates. These intermediates reduce the increase in molecular weight and can have adverse effects on the quality of the polyamide. Their presence is caused, among others, by the incomplete separation of the ammonia produced in the reaction from the polymer melt. A possible remedy in the case of a continuous or batch reaction is to use the precursor water in amounts that are much greater than stoichiometric to shift the equilibrium of the reaction to the side of the required product and / or increase the reaction times. which is generally an energetically unfavorable process and may increase the proportion of undesired by-products or decomposition products. Another possible measure is to carry out the reaction in various reaction stages, consequently making the process technically elaborated.

A traditional industrial solution is a one-step process for hydrolysis and prepolymerization. However, this requires high operating pressures and pressure equipment suitable for them, in order to keep the volatile components, especially ammonia, in solution. For the heat and mass transfer in the single-phase process, a plurality of separate elements of the apparatus for exchanging heat and mixing are required. The objective of a novel process must be to keep the interval of stay times for the reaction narrow, so that uniform reaction times do not occur, which have an adverse effect on the quality of the product. An object of the present invention is to develop a process for preparing polyamides which, due to the costs of the initial materials and energy are lower and the complexity of the apparatus is reduced, operates with greater efficiency in costs and, at the same time, increases the conversion of the intermediates through an advantageous process control with better separation of substances with low boiling point. We have found that this objective is achieved by a process for preparing polyamides, their oligomers or mixtures thereof, where appropriate with other reaction products, by reacting amino nitriles and, where appropriate, other monomers and / or polyamide-forming oligomers with water in a reactive distillation, where the product of the reaction is discharged from the inner part of the reactive distillation apparatus and the ammonia that is produced and, as appropriate, other low molecular weight compounds that are produced, and water is separates at the top. The preference process is carried out continuously. Reactive distillations per se are well enough known in the area of low molecular weight industrial chemistry. On the contrary, there are few descriptions of these in the area of high viscosity systems, in particular of polymerizations. US 3,900,450 describes, for example, reactive distillation preparing nylon 6,6. The objective is to obtain combining the reaction and the thermal separation technique in a single apparatus (= reactive distillation), characterized by a two-phase process during hydrolysis and polymerization. This process design will be mentioned as reactive distillation onwards. The examples of the equipment used are columns with or without internal elements or bubble columns. In a possible procedure, for example, the amino nitrile and water are fed into the upper half of the column. Substances with low boiling points produced in the reaction (ammonia and water) can then be enriched in the upper part of the column and separated, while the high-boiling substances in the waste product contain the required product of oligomers and polyamide. This integrated process control with continuous separation of the product gives rise to heat transfer and ideal mass, parallel with greater exergy efficiency that is also characterized by rapid heating of the precursors and homogeneous mixing thereof. The reaction can be carried out under autogenous pressure. For the reaction system of the present, the flow, countercurrent of the prepolymer and the ammonia reaction product, combined with the continuous separation of the ammonia through the product of the gases leaving the top from, for example, The column or column of bubble, guarantees very low contents of ammonia in the products of the apparatus that contains amino nitriles practically converted in the required products. It has been found that the process according to the invention gives rise to higher conversions to the required product compared to the continuous separation of ammonia through the product that comes out from the top, which makes the reaction times shorter and reduces the formation of unwanted secondary components. The reaction can be assisted by employing any convenient catalyst that accelerates hydrolysis and / or condensation. Preferred catalysts are those which can be introduced in solid form and consequently easily separated from the required product, or are even present as coatings in parts of the column. The invention relates to a process, preferably continuous, for the hydrolytic conversion of amino nitriles into polyamide and / or its precursors and, as appropriate, other mono- and polyamide-forming oligomers into polyamide. It is possible to use as a reactive distillation apparatus all suitable apparatuses that allow the reactants to react and the ammonia that is produced and, as appropriate, the water to be discharged as gases. The reactive distillation apparatus preferably has a plurality of theoretical separation steps. In a preferred embodiment of the invention, a plate column, bubble column or dividing wall column is used as an apparatus for reactive distillation. If a plate column is used, the amino nitrile is preferably metered into the middle plate at the top of the column. The amino nitrile then flows under gravity down through the apparatus and, during this, reacts continuously with water. The resulting ammonia rises continuously upwards, due to its volatility and is rectified. The precursor or mixture of precursors is preferably dosed as a liquid, or part is fed as a liquid, and the remainder, for example steam, is fed as gas to the apparatus. This last variant has the advantage that the value can also serve as an energy carrier. Steam is often available as an energy carrier at a reasonable cost. The apparatus of preference is designed so that a thermal equilibrium is practically established, depending on the time of stay, of the real or theoretical plates within the column used. If a dividing wall column or an apparatus operating on the principle of a dividing wall column is used as an apparatus, unwanted or desired components may be discharged as intermediate boiling substances and, if required, returned to the device at another point. This procedure can reduce losses of initial materials. The precursors can, if required, be preheated by the condenser in the upper part. A diagram of this type of principle of the process according to the invention are shown in the drawing of Figure 1: Figure 1: Sketch of a reactive distillation process for amino nitriles to polyamide by the use of a plate column. The meanings in this are A: amino nitrile, D: vapor, N: ammonia, P: polyamide prepolymer. In addition, it has been found that bubble columns can be used as an alternative to plate columns, particularly preferably when the viscosity of the polyamide in the waste product is greater than about 150 mPas, since the formation of cake in the Stationary parts of the column can then occur frequently. The feeding of the precursors into the bubble columns should take place at approximately the same positions as in a reactive distillation column, which means that the precursors are dosed at the top of the bubble column.

To reduce reverse mixing within the column, columns may, if required, be equipped with internal elements known to those skilled in the art to reduce reverse mixing. It has also been found that the introduction of catalyst granules into the apparatus gives rise to uniform gas and liquid flow in the column. The reduction of ammonia in the melt can also be assisted by entrainment with inert gas (such as nitrogen). For this purpose, the gas is passed to one or more plates, or in the case of bubble columns, to one or more points by means of suitable devices. It is possible to use as amino nitrile, in principle, all the amino nitplos, which means compounds having at least one amino group and at least one amino group, among these, the? -amino nitriles are preferred, employing from these last in particular? -aminoalkyl nitriles with 4 to 12 carbon atoms, more preferably 4 to 9 carbon atoms in the alkylene radical, or an aminoalkylaryl nitropyl having 8 to 13 carbon atoms, in which case those having an alkyl splitter with at least one carbon atom between the aromatic units and the amino group and cyano group are preferred. Particularly preferred aminoalkylaryl nitriles are those wherein the amino group and the cyano group are relatively in the 1,4 positions. Preference is also given to the use of linear α-aminoalkyl nitriles, such as α-aminoalkyl nitrile, wherein the alkylene radical (-CH 2 -) preferably contains from 4 to 12 carbon atoms, more preferably from 4 to 9 carbon atoms, such as 5-ammo-l-cyanopentane (6-aminocapronitrile), 6-amino-1-cyclohexane, 7-amino-1-cyanoheptane, 8-amino-1-cyanooctane, 9-amino-1-cyanononane, -ÉS-faith ^. particularly preferably 6-aminocapronitrile. 6-Aminocapronitrile is usually obtained by hydrogenation of adiponitrile by known processes, for example, as described in DE-A 836,938, DE-A 848 654 or US 5,151,543. Of course, it is also possible to use mixtures of several amino nitriles or mixtures of an amino nitrile with other comonomers, for example, caprolactam or the mixture defined below. Examples of other polyamide-forming monomers which can be used are dicarboxylic acids such as alkanedicarboxylic acids having from 6 to 12 carbon atoms, in particular from 6 to 10 carbon atoms, such as adipic acid, pimelic acid, suberic acid, azelaic or sebacic acid, and terephthalic acid and isophthalic acid, diamines such as C4-C12 alkyldiamines, in particular having from 4 to 8 carbon atoms, such as hexamethylenediamine, tetramethylenediamine or octamethylenediamine, also m-xylylenediamine, bis (4-) aminophenyl) methane, 2, 2-bis (4-aminophenyl) propane or bis (aminocyclohexyl) -methane, and mixtures of the dicarboxylic acids and diamines, each in any convenient combination with each other, but advantageously in the equivalent ratio. It is also possible to use salts of dicarboxylic acids and diamines, such as adipate •,? 11iMSHft < fe.-wfef "hexamethylenediamonium, hexamethylene diammonium terephthalate or tetramethylene diammonium adipate, hexamethylene diammonium terephthalate, but especially the salt of adipic acid and hexamethylenediamine, hexamethylene diammonium adipate (called AH salt), as a constituent of a mixture with amino nitriles and / or lactams . The dicarboxylic acids which may be used are aliphatic C4-C10 α-dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, preferably adipic acid and sebacic acid, particularly of preference adipic acid, and Cs ~ C12 dicarboxylic acids, aromatics such as terephthalic acid, and C5-C8 cycloalkanedicarboxylic acids such as cyclohexanedicarboxylic acids. It is possible to employ as a, β-diamine having from 4 to 10 carbon atoms tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine and decamethylenediamine, preferably hexamethylenediamine. Aliphatic dinitriles such as 1,4-dicyanobutane (adiponitrile), 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 1,8-dicyanooctane, 1,9-dicyanonane, 1,10-dicyanodecane, particularly preferably adiponitrile, they are used as the C2-C? 2 a,? - dinitriles.

It is also possible if it is desired to use diamines, dinitriles and amino nitriles from alkylen or branched arylenes or alkylarylenes. It is possible to use 5-aminopentanoic acid, aminohexanoic acid, aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanenoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid as acid. preferably 6-aminohexanoic acid. It is also possible to use any of the convenient mixtures of these compounds, diamines and diacids. Other suitable starting materials in the process according to the invention are mixtures with aminocarboxylic acid compounds of the general formula I: H2N- (CH2) m-C (0) RJ (I) wherein R 1 is -OH, -0-C1-C12 alkyl or -NR2R3, where R2 3 and R are, independently of one another, hydrogen, C 1 -C 12 alkyl and C 5 -C 8 cycloalkyl, and m is 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. Particularly preferred aminocarboxylic acid compounds are those in which R is OH, -0-alkyl C1-C4 such as -O-methyl, -O-ethyl, -On-propyl, -Oi-propyl, -On-butyl, -O-sec-butyl, -O-tert-butyl and -NR 2R3 as being -NH2, -NHMe, -NHEt, -NMe-2, and NEt2, and m is 5. Particular preference is given to 6-aminocaproic acid, methyl 6-aminocaproate, ethyl 6-aminocaproate, 6-amino-n -methylcaproamide, 6-amino-n-dimethylcaproamide, 6-amino-n-ethylcaproamide, 6-amino-N, N-diethylcaproamide and 6-aminocaproamide. The starting compounds are available commercially or can be prepared, for example, as described in EP-A-0 234 295 and Ind. Eng. Chem. Process Des. Dev. 17 (1978) 9-16. The preferably used polyamide-forming monomers are amino nitriles as well as water, particularly preferably in a molar ratio in the range from 1: 1 to 20, based on the entire process. Particular preference is given in this regard to aminocapronitrile with an ACN: water ratio of 1: 1 to 6 in the entire process. It is also possible to use, as polyamide-forming monomers, mixtures of: 99, preferably 20 to 99, in particular 50 to 99% by weight, of amino nitriles, 1 to 99, preferably 1 to 80, in particular 1 to 50% by weight. weight of lactams, and 0 to 49% by weight of diamines and / or dicarboxylic acids or salts thereof.

It is also possible to use mixtures of polyamide-forming monomers and oligomers. Preferred polyamide-forming monomers are, in addition to aminocapronitrile, if caprolactam and / or hexamethylenediammonium adipate ("AH salt") is required. The reaction can be carried out in the presence of Bronsted acid catalysts. The heterogenous Brónsted acid catalysts are also preferably used. Suitable catalysts are, in general, in addition to the multiple acid catalysts described in the literature, such as phosphoric acid, etc., in particular heterogeneous catalysts, the Bronsted acid catalysts selected from a beta-zeolite catalyst, lamellar silicate catalyst or a fixed bed catalyst consisting mainly of Ti02 with 70 to 100% anatase and 0 to 30% rutile, in which up to 40% of Ti02 can be replaced by tungsten oxide, preferably they are employed. It is possible, for example, to use the corresponding modifications of Ti02 available from Finnti (type S150). Heterogeneous catalysts may be introduced into the apparatus for example, as a suspension, sintered on packs or as packed or internal elements of randomly ordered or randomly coated catalysts.

- Tase,? & t & Axt- - < "These may also be present coated or distributed on the walls of the apparatus, so that the separation of the reaction mixture is direct. The concentration of water in most of the theoretical or real plates located below the place where the amino nitriles are fed reaches very high concentrations (molar ratio substances of high boiling points: water approximately 1: 4 to 1: 9). so that, even if the components are dosed in stoichiometric amounts in the apparatus, the water may be present in more than the stoichiometric amount within the apparatus itself, which may shift the reaction equilibrium to the side of the products and increase the speed in the which balance is established. The temperature for the reaction should be about 180 ° C to 300 ° C, preferably 200 to 280 ° C, and particularly preferably 220 to 270 ° C in the reaction part of the column, that is, below the feeding of the precursor, depending on the concentration of the water, the time of stay, the use of the catalysts and the composition or concentration of the initial material. In view of the fact that a temperature gradient develops along the column type apparatus, the temperature in the upper part and in the lower part may differ from the mentioned values.

The two-phase process makes it possible to reduce the level of pressure necessary for the reaction since it is not necessary to maintain the gaseous constituents in the liquid phase, as with a one-phase process. It is preferred to simply set the autogenous pressure of the system, depending on the temperature. This is approximately 10 to 60 bar. The complexity of the device is reduced through the integration of technical operations such as heat and mass transfer to one and the same device. With a large number of theoretical plates, the flow profile of the liquid phase in the apparatus approximates the ideal piston type flow, which gives rise to a very uniform interval of stay times in the apparatus. The unwanted or desired precursors or by-products with a boiling point between the ammonia and the polyamide prepolymer can be discharged through a column of dividing walls. The resulting required product has a molecular weight that can be adjusted within wide limits and which differs, and the properties that differ, depending on the time of stay in the apparatus, the process temperatures, the pressure conditions and other parameters of the process . It is possible, if required, to follow the reactive distillation by further processing the product to adjust the desired product properties. The resulting polyamide can, for example, be treated by methods known per se, as described in detail, for example, in DE-A 43 21 683 (page 3, line 54 to page 4, line 3). In a preferred embodiment, the content of the cyclic dimer in the nylon 6 obtained according to the invention can further be reduced by first bringing the nylon with an aqueous solution of caprolactam and subsequently with water and / or by subjecting it to gas phase extraction (described in FIG. EP-A-0 284 968 for example). The low molecular weight constituents resulting from this subsequent treatment, such as caprolactam and its linear and cyclic oligomers, can be returned to the first and / or second and / or third stage. The process according to the invention is distinguished by the performance of the reaction continuously, the energy costs and initial materials reduced and compared to the uncomplicated apparatus. The continuous separation of the product increases the conversion and the reaction rate to obtain the required product by comparison with the batch process and, at the same time, the formation of by-products is reduced. The process can operate more cost effectively and provide a higher quality product than the known processes. ^^^^^? j ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ S ^ jj ^ ^^^^^ The invention is further illustrated by means of the following examples.

EXAMPLES Experiments carried out in a pressure vessel and describing the course of the reaction are described as examples. In addition, examples that indicate the use of convenient columns are mentioned.

Reaction examples Reaction example R1 (continuous degassing): 1400 g of an aminocapronitrile reaction mixture and water in the 1: 4 molar ratio were stirred at 250 ° C in a two liter pressure vessel with heating jacket and anchor stirrer. The established autogenous pressure was 43 bar. During the three hour reaction time, the water was fed continuously to the reactor at a mass flow rate of 100 g / h. In the same way, a mixture of water and ammonia was continuously discharged from the gas phase through an overflow valve.

Reaction example R2 (continuous degassing): 1400 g of an aminocapronitrile reaction mixture and water in a 1: 0.8 molar ratio were stirred at 250 ° C in a two liter pressure vessel with heating jacket and anchor stirrer. The autogenous pressure established was 27 bar. During the three hour reaction time, the water was fed continuously to the reactor at a mass flow rate of 100 g / h. In the same way, a mixture of water and ammonia was continuously discharged from the gas phase through an overflow valve.

Comparative example Cl (batchwise): 1400 g of an aminocapronitrile reaction mixture and water in the molar ratio 1: 4 was stirred at 250 ° C in a pressure vessel with heating jacket and anchor stirrer and with the reactor closed . The established autogenous pressure was 48 bar. The experiment lasted two hours.

Comparative Example C2 (batchwise): 1400 g of an aminocapronitrile reaction mixture and water in the 1: 1 molar ratio was stirred at 250 ° C in a two liter pressure vessel with heating jacket and anchor stirrer and with the reactor closed. The established autogenous pressure was 33 bar. The experiment lasted 200 minutes.

The examples show that the conversion is significantly greater and the proportion of higher oligomers increases even in a one-step separation of the reaction products from lower boiling points by a continuous countercurrent with water. This effect is, of course, even greater in reactive distillation with multiple stages of rectification.

Table 1: Results of the amino nitrile reaction The data for the following substances are percentages in mass as a basis in the complete lot: 5 ACN: aminocapronitrile AC: aminocaproamide AC: aminocaproic acid CL: caprolactam Oligos: oligomers with a degree of polymerization greater than 3 10 tri: trimer di: dimer di -hexa: dimer to hexamer.

Examples of columns (continuous): Example of column 1 A column of plates with 30 bubble plates was operated with a system pressure of 30 bar. 10.1 kg / h of aminocapronitrile were metered into plate 29, the plate below the top plate, at 250 ° C. 2.5 kg / h of the superheated steam at 300 ° C were fed into plate 2. The hydrodynamic residence time of the reaction mixture in the column was 2.3 h. The product in the resulting upper part was ammonia with a content of 0.1% by weight of water at about 70 ° C. The residual product was a nylon 6 prepolymer with a water content of 8.5% by weight. The water content in the plates below the feed point was up to about 50% by weight or, converted, approximately 80% molar.

Example of column 2 A column of plates with 30 bubble plates was operated with a system pressure of 30 bar. A mixture of 8.4 kg / h of aminocapronitrile and 1.5 kg / h of water at 250 ° C was fed to plate 29, the plate below the top. 2 kg / h of superheated steam at 300 ° C were fed onto plate 2. The hydrodynamic residence time of the reaction mixture in the column was 2.8 h. The product in the resulting upper part was ammonia with a content of 2% by weight of water. The residual product was a nylon 6 prepolymer with a water content of 8.7% by weight. An evaporator with forced circulation was located at the foot of the column.

Example of column 3 A mixture of 5 kg / h of aminocapronitrile and 2 kg / h of water was fed below the upper sieve plate into a bubble column which was packed with cylindrical catalyst granulate of 3 mm diameter and length 5 mm and It was divided by plates sieves in 6 zones. A tube with a random packing and a diameter that exceeded the diameter of the column was located as a rectifier above the feed point. A forced circulation evaporator was located at the bottom of the bubble column. The hydrodynamic stay time in the bubble column with random packing was 2.3 h. The pressure established in the column was approximately 32 bar. The residual product was a polyamide prepolymer with a water content of 11% by weight. The superior product was ammonia with 2% by weight of water.

Claims (1)

1. CLAIMS A continuous process of reactive distillation to prepare polyamides, their oligomers or mixtures thereof, as appropriate with other reaction products, by the reaction of the amino nitriles and, as appropriate, other monomers and / or oligomers forming polyamides with Countercurrent water in a reactive distillation apparatus has a plurality of theoretical or real separation steps, wherein the reaction product is discharged from the bottom of the reactive distillation apparatus, and the ammonia that is produced and, as appropriate, other low molecular weight compounds that are produced, and water, are separated at the top. The process as claimed in claim 1, wherein the reaction is carried out under autogenous pressure. The process as claimed in claim 1 or 2, wherein the reaction is carried out in a column of plates, bubble column or column with dividing wall. The process as claimed in any of claims 1 to 3, wherein the amino nitriles, such as the polyamide-forming monomers and water are employed in a molar ratio, based on the entire process, in a range from 1: 1 to 1:20 The process as claimed in any of claims 1 to 3, wherein the mixtures of 1 to 99% by weight of amino nitriles, 99% by weight of lactams, and 0 to 49% by weight of diamines and / or acids dicarboxylics or salts thereof. Polyamide-forming monomers are used as monomers. The process as claimed in any of claims 1 to 5, wherein the reactive distillation is carried out in the presence of Bronsted acid catalysts. The process as claimed in claim 6, wherein heterogeneous Brónsted acid catalysts are employed. The process as claimed in any of claims 1 to 7, wherein water is used in the vapor form. The process as claimed in any of claims 1 to 8, wherein an additional stripping with an inert gas and reactive distillation is carried out.