Continuous process for producing polyamide by polycondensation

Abstract

The present invention relates to a continuous process for the production of polyamides by condensation, comprising the following consecutive steps a) and b) step a) of melting a mixture containing polyamide monomers in an extruder or co-kneader, the monomers being fed to said extruder or co-kneader without the addition of any water, and step b) of carrying out a polycondensation reaction of said mixture obtained after step a) in a horizontal mixer reactor, said steps a) and b) being carried out at close to atmospheric pressure.

Description

[Technical field]

[0001] The present disclosure relates to a continuous process for producing polyamides by polycondensation. [Background technology]

[0002] Polyamides are often produced by the polycondensation of diamines and diacids. These polycondensation reactions are generally carried out in a reactor using a continuous or batch process.

[0003] Generally, in a first step, a salt is formed from the dicarboxylic acid and diamine monomers. This salt, optionally in aqueous solution, is placed in a reactor and heated under pressure until a mixture of sufficient viscosity is obtained. In this step, the water initially added and the water formed during the polycondensation reaction are completely or partially removed from the reactor. The viscosity of the mixture leaving the reactor is generally insufficient, so an additional step is necessary to increase the degree of polymerization and obtain a polyamide, especially intended for extrusion. This is followed by a heat treatment step, often called post-condensation. This can be carried out in a continuous or batch reactor, in the molten or solid state, optionally under reduced pressure.

[0004] These processes not only require relatively long reaction times (on the order of several hours), but also multiple transfers of materials between different reactors for the different steps of the process (synthesis of the salt, polycondensation in the reactor, and post-condensation).

[0005] If the post-condensation step is carried out in the solid state, the molar masses obtained are less uniform and less stable.Finally, under these conditions, the reaction times are very long, leading to high energy costs and therefore high production costs.

[0006] Feeding the monomers in the form of aqueous salt solutions is routinely used, especially to control the stoichiometry, but this solution is economically disadvantageous since a large amount of water needs to be devolatilized in order to obtain sufficient viscosity at the end of the polycondensation step, thus requiring a large amount of energy and large equipment.

[0007] Various alternatives for improving these processes have been described in the literature.

[0008] Some of these alternatives include the preparation of a prepolymer in a reactor, typically using a batch process, followed by a post-condensation step in an extruder under reduced pressure to increase the molar mass of the polyamide. Although optimization of the post-condensation step is possible, these processes are time-consuming and costly, since they require material transport and handling operations that are difficult to implement on an industrial scale. Furthermore, isolating prepolymers with close to isostoichiometric chain ends and stable viscosity and chain end content in each batch is difficult to achieve industrially. In many cases, the solution to this difficulty requires the use of diacid or diamine terminated prepolymers, which require large amounts of fluid monomer to be fed to the extruder, which makes mixing difficult in the extruder, especially when the operation is carried out under reduced pressure, resulting in significant losses of monomer. The above method is specifically described in application EP0410649.

[0009] In a single condensation step in an extruder, by feeding the monomers directly into the input of the extruder, the molar masses obtained remain limited and, due to the short residence times in this type of equipment (typically less than 5 minutes), are often below the molar masses required to convert the product under good conditions, especially by extrusion. Said process is specifically described in application EP0410650, in which the maximum intrinsic viscosity of the obtained solutions is 0.35 dL / g, which corresponds to an Mn value of only 4400 g / mol.

[0010] Application EP2877516 proposes to carry out all the reaction steps from polyamide monomers and the polycondensation step in one and the same extruder with at least two co-rotating feed screws. This requires the use of at least two condensation water devolatilization zones, which makes it difficult to control the monomer losses, either in terms of quantity or variation. Furthermore, the low viscosity of the product at the start of the extruder complicates the management of the conveyance of the material to the first devolatilization zone. Also, to achieve residence times that result in a highly viscous product, it is necessary to use large twin-screw extruders (L / D ≥ 50) or multi-screw extruders with complex maintenance, which in both cases are expensive processes that are difficult to implement on an industrial scale. Finally, the heating efficiency through the extruder barrel is low and a large amount of energy is required for the devolatilization of the water. This is because such equipment is designed to provide most of the energy required for the product through dissipated mechanical energy. However, in the extruder used to carry out all the reaction steps and the polycondensation step, such energy is at a low level, due to the low average viscosity of the product in the equipment.

[0011] The aim of the present disclosure is to propose a process for the production of polyamides which is simple to implement, has low costs in terms of production energy and has short cycle times.

[0012] Summary of the Invention

[0013] The subject of the present invention is therefore a process for the continuous manufacture of polyamides by condensation, comprising the following successive steps a) and b): in step a) a mixture comprising the polyamide monomers is melted in an extruder or co-kneader, to which the monomers are fed without the addition of any water.

[0014] In step b), the polycondensation reaction of the mixture obtained after step a) is carried out in a horizontal mixer reactor, the process being carried out at close to atmospheric pressure. By "pressure close to atmospheric pressure" is meant a pressure between atmospheric pressure and atmospheric pressure +100 mbar, preferably between atmospheric pressure and atmospheric pressure +50 mbar, more preferably between atmospheric pressure and atmospheric pressure +10 mbar.

[0015] Advantageously, the monomers are added to the extruder or co-kneader without adding water. As a result, some steps such as evaporation of water, which is usually added in the prior art processes, can be omitted, thus limiting the heating energy required for this evaporation and thus the cycle time of the process. Furthermore, limiting the entrainment of water vapor allows a reduction in monomer losses.

[0016] Moreover, another advantage is that the entire devolatilization occurs in step b), which contributes to reducing the energy supplied to the melting extruder or co-kneader and to limiting monomer losses.

[0017] Another advantage is that the process is carried out at a pressure close to atmospheric pressure, which, compared with processes carried out under reduced pressure, contributes to reducing the energy required for production, limiting monomer loss during devolatilization, and thus limiting production costs.

[0018] In addition, compared to processes carried out under reduced pressure, it is possible to prevent the polymer from degrading due to oxidation if air enters the polycondensation reactor, limiting reactor fouling. The use of processes carried out under reduced pressure requires many precautions, making them difficult to implement.

[0019] The fact that no additional water is fed together with the monomers and that the operation is carried out at close to atmospheric pressure advantageously allows the installations to be miniaturized and in particular makes it possible to achieve polyamide production rates relative to the capital investments that are more favorable than the solutions proposed in the prior art.

[0020] Also, carrying out the polycondensation reaction in a mixer-reactor, rather than in an extruder, allows for better renewal of the liquid / gas interface and therefore more efficient devolatilization of volatile compounds such as polycondensation water.

[0021] This devolatilization is further aided by the fact that, unlike extruders, mixer-reactors have a continuous gas phase along the screw. Typically, the proportion of liquid phase in a mixer-reactor is 20-75% of the initially available space in the mixer-reactor.

[0022] Also, unlike the polycondensation carried out in an extruder described in EP2877516, the mixer reactor allows better control of the heat input during the polycondensation by limiting the uncontrolled heating of the product through the dissipation of mechanical mixing energy, which reduces the risk of thermal degradation of the polyamide. Moreover, the mixer reactor allows for longer residence times, advantageously more than 5 minutes, preferably more than 15 minutes. As a result, this method advantageously results in a better product quality in terms of quality stability and achievable viscosity.

[0023] This process advantageously gives polyamides with high molar masses without a subsequent additional post-condensation step, such as a post-condensation in the solid state, which is carried out at the discharge from the mixer reactor.

[0024] Other features of the method of the invention are specified below. The polyamides produced in this way are aliphatic, cycloaliphatic, arylaliphatic, aromatic or semi-aromatic polyamides. the polyamide is chosen in particular from among polyamides 11, 11 / B10, 11 / BI / BT, B10, B12, MXD10, MXD.6, 11 / 10T, 11 / BACT / 10T, BACT / 10T. PA11 is a polyamide obtained by polycondensation of 11-aminoundecanoic acid (A11). 11 / B10 is a copolyamide obtained by condensation of 11-aminoundecanoic acid (A11) with bis-(3-methyl-4-aminocyclohexyl)-methane (or 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane) (also called BMACM or MACM) (referred to in this specification as B) and with sebacic acid (10). 11 / BI / BT is a copolyamide obtained by polycondensation of 11-aminoundecanoic acid (A11) and bis-(3-methyl-4-aminocyclohexyl)-methane (or 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane) (also called BMACM or MACM), referred to in this specification as B), with isophthalic acid (I) and terephthalic acid (T). B10 is a homopolyamide obtained by polycondensation of bis-(3-methyl-4-aminocyclohexyl)-methane (or 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane) (also called BMACM or MACM) (referred to in this specification as B) with sebacic acid (10). B12 is a homopolyamide obtained by polycondensation of bis-(3-methyl-4-aminocyclohexyl)-methane (or 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane) (also called BMACM or MACM) (referred to in this specification as B) with dodecanedioic acid (12). MXD10 is a homopolyamide obtained by polycondensation of metaxylylenediamine and sebacic acid (10). MXD6 is a homopolyamide obtained by polycondensation of metaxylylenediamine and adipic acid (6). 11 / 10T is a copolyamide obtained by polycondensation of 11-aminoundecanoic acid (A11) with decanediamine (10) and terephthalic acid (T). BACT / 10T is a copolyamide obtained by polycondensation of bis-(3-methyl-4-aminocyclohexyl)-methane (or 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane) (also called BMACM or MACM), referred to in this specification as B, with decanediamine (10) and terephthalic acid (T). 11 / BACT / 10T is a copolyamide obtained by polycondensation of 11-aminoundecanoic acid (A11) with 1,3-bis(aminomethyl)cyclohexane (BAC), terephthalic acid (T) and decanediamine (10). The mixture in step a) comprises an additive. The additives include at least one catalyst, at least one stabilizer, at least one antioxidant, at least one chain limiter and at least one antifoaming agent. Step a) is carried out in an extruder which preferably has at least two screws, more preferably two screws, in particular co-rotating. In the extruder or co-kneader, the mixture of monomers is melted by heating it so that the discharge temperature of step a) is between 160°C and 300°C. - The mixture obtained in step a) is fed in step b) to a mixer reactor without prior devolatilization. The mixer reactor preferably comprises at least two shafts containing co-rotating stirring elements. - Heat the stirring shaft of the mixer reactor. the polycondensation reaction in step b) is carried out at a temperature of up to 50° C. above the solidification temperature of the polyamide and / or at least 5° C. above this solidification temperature, preferably at a temperature between 240° C. and 310° C. Step b) is carried out under flushing of an inert gas, preferably in countercurrent.

[0025] In another aspect, the present invention also relates to a system for carrying out the method of the present invention, which comprises an extruder or co-kneader connected directly to the input of the mixer reactor, in particular without an intermediate devolatilizer between the mixer reactor and the extruder or co-kneader. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of a system for carrying out the method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Other features, aspects, objects and advantages of the present invention will be more clearly understood from a reading of the following description.

[0028] It is expressly stated that the expressions "from to" and "between" as used herein are to be interpreted as including the limits set forth.

[0029] The method of the present invention comprises at least the two consecutive steps a) and b) as mentioned above. The method may also comprise steps before or after these two steps a) and b), but does not comprise any intermediate steps between steps a) and b).

[0030] The process of the invention is particularly applicable to aliphatic, cycloaliphatic, arylaliphatic, aromatic or semi-aromatic polyamides.

[0031] Step a): Melting a mixture containing polyamide monomers

[0032] In step a), the mixture containing the monomers is brought to a melt temperature in an extruder or co-kneader, said monomers being fed to the extruder or co-kneader without the addition of water.

[0033] In other words, the polyamide monomers fed to the extruder or co-kneader are not dissolved in water, or more generally in a solvent.

[0034] Preferably, therefore, the mixture used in step a) has a very low water content, typically less than 2% by weight, in particular less than 1% by weight, relative to the total weight of the mixture.

[0035] The water that may be present after step a) essentially comes from the possible onset of condensation after melting of the monomers.

[0036] monomer

[0037] Polyamide monomers are monomers suitable for forming polyamides. They may be aliphatic, cycloaliphatic, arylaliphatic or aromatic. These monomers may be in the form of anhydrous salts, or bases or free acids. Regardless of their form, the monomers are introduced into an extruder or co-kneader without the addition of water or solvents.

[0038] One monomer containing both a carboxylic acid functional group and an amine functional group, i.e., only an amino acid-based monomer, may be used, or at least two monomers, one of which has two amine functional groups and the other of which has two carboxylic acid functional groups or their carboxylic anhydrides, may be used, or a C3-C6 lactam-based monomer may be used, or a mixture of these different monomers may be used.

[0039] By amino acid monomer is meant a molecule containing a hydrocarbon chain, generally having from 2 to 40 carbon atoms, bearing an amine functional group and a carboxylic acid functional group.

[0040] Among the amino acid monomers, mention may in particular be made of 6-aminohexanoic acid, 5-aminopentanoic acid, 7-aminoheptanoic acid, 11-aminoundecanoic acid or 12-aminododecanoic acid.

[0041] By diamine monomer is meant a molecule containing a hydrocarbon chain, generally having from 2 to 40 carbon atoms, with two amine functional groups.

[0042] The diamine monomers may be chosen in particular from 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, octane-1-ethylenediamine, decanemethylenediamine, dodecamethylenediamine, m-xylylenediamine, p-xylylenediamine, bis-(4-aminophenyl)methane, bis-(4-aminocyclohexyl)methane, 2,2'-dimethyl-4,4'-methylenebis(cyclohexylamine), 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, metaphenylenediamine, paraphenylenediamine, 2,2,4 or 2,4,4-trimethylhexamethylenediamine, or alternatively from mixtures of these diamines.

[0043] The diamine monomer may preferably be selected from among decane methylene diamine, m-xylylene diamine, p-xylylene diamine, bis-(4-aminocyclohexyl)methane, 2,2'-dimethyl-4,4'-methylenebis(cyclohexylamine), 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, or mixtures of these diamines.

[0044] By dicarboxylic acid monomer is meant a molecule containing a hydrocarbon chain, generally having from 2 to 40 carbon atoms, and having two carboxylic acid functional groups.

[0045] Dicarboxylic acid monomers that can be used include, among others, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, 1,12-dodecanedioic acid, dioleic acid, phthalic acid, terephthalic acid, isophthalic acid, 5-sulfoisophthalic acid, 1,4-cyclohexanedioic acid, 1,3-cyclohexanedioic acid, or mixtures thereof.

[0046] Dicarboxylic acid monomers that can be used preferably include sebacic acid, 1,12-dodecanedioic acid, terephthalic acid, isophthalic acid, or mixtures thereof.

[0047] The C3-C6 lactam monomer refers to an amide contained in a carbocyclic ring having 3 to 6 carbon atoms, for example caprolactam.

[0048] The mixture used in step a) may comprise one or more monomers selected from among amino acids, diacid / diacid monomer pairs, or C3-C6 lactam monomers.

[0049] Before being introduced into the extruder or co-kneader, the monomers are preferably stored under an inert gas atmosphere or flushed with an inert gas, in particular nitrogen gas, to prevent the ingress of oxygen gas into the extruder or co-kneader, thereby reducing the risk of oxidation of the monomers, or oligomers, prepolymers or polymers, throughout the process. Optionally, they may be subjected to a prior devolatilization step.

[0050] The monomers may be fed to the extruder or co-kneader in different states: They may be in solid or liquid state.

[0051] For example, the diamine monomer fed to the reactor may be in a liquid state and the dicarboxylic acid monomer may be in a solid state.

[0052] No pre-preparation step of salt or prepolymer is necessary. The selected monomers may be fed directly into the extruder or co-kneader.

[0053] A solids dosing system, preferably gravimetric, is used to meter the monomer in solid form, typically to within 1%, preferably 0.5%, more preferably 0.1% of the set flow rate.

[0054] They may be used preferably in anhydrous form, under flushing with an inert gas, preferably nitrogen gas.

[0055] They may be loaded into an extruder or co-kneader via a pneumatic loader, optionally followed by an inerting step comprising at least one step using an inert gas, preferably nitrogen gas, preferably in anhydrous form.

[0056] Optionally, they may be inactivated beforehand, especially if they are stored in a container.

[0057] The monomers in solid state may be fed to the extruder or co-kneader via a single input or via different inputs.

[0058] It is also possible to use mixtures of monomers of the same system, for example diacids or diamines, in solid form.

[0059] Liquid dosing systems may be used to meter the monomers in liquid form, typically to within 1% of the set flow rate, preferably 0.5%, more preferably 0.1%, and are preferably loaded using positive displacement pumps equipped with mass flow meters.

[0060] They may be used preferably in anhydrous form, under flushing with an inert gas, preferably nitrogen gas.

[0061] Optionally, they may be inactivated beforehand, especially if they are stored in a container.

[0062] The monomer may be fed in liquid form through a single injection point or through different injection points.

[0063] In particular, it is possible to inject a number of liquid forms of the monomers via a single injection point or, preferably, via different injection points, optionally after the static mixer.

[0064] It is also possible to use mixtures of monomers of the same system, for example diacids or diamines, in liquid form.

[0065] Preferably, the monomers in the solid and liquid states are fed to the extruder or co-kneader via separate inputs.

[0066] The monomers which are in a solid state at room temperature may be premelted and then charged into the extruder or co-kneader, in which case they are heated to a temperature higher than their melting temperature, in particular to a temperature 5° C. higher, in particular to a temperature 10° C. higher.

[0067] A monomer that is in a liquid state at room temperature may be fed to the extruder or co-kneader at room temperature or after heating.

[0068] Extruder or co-kneader

[0069] The terms "extruder" or "co-kneader" are used herein in their normal sense and refer to equipment well known to those skilled in the art.

[0070] In particular, "extruder" means a device that can be used for extrusion, i.e. a (thermo)mechanical process, in which a compressed material is forced through a die to change the material. More specifically, an extruder consists of at least one endless screw that rotates in a cylinder called the extruder body, and a liner that contacts the material, and the extruder body itself consists of several heat conditioning zones. This endless screw ensures a seal between the screw and the wall over the entire length of the screw. In an extruder, each conveying screw is composed of different elements that follow one another in the direction of movement. These different elements are arranged side by side on the axis of rotation. In co-rotating extruders, all conveying screws rotate in the same direction, which often corresponds to a clockwise direction as seen from the discharge of the extruder. These elements are arranged side by side in the same line. The various conveying screws that make up the extruder all have the same diameter, and this diameter generally remains constant along the length of the conveying screw. In most cases, this diameter ranges from 6 to 134 mm. In general, the elements that are arranged in the same plane transverse to the direction of movement are all the same. The rotation speed of the conveying screw depends on the type of extruder, but is the same for all screws constituting the extruder. In general, the rotation speed of the screw is 10 rpm to 1200 rpm depending on the type of extruder.

[0071] Examples of extruders suitable for carrying out the process of the present invention include, inter alia, Clextral's Evolum series, Coperion's ZSK series, or Coperion's STS series.

[0072] A "co-kneader" is also a device well known to those skilled in the art. Unlike an extruder, a co-kneader generally has only one endless screw that moves back and forth while rotating, and only at certain points on the screw does it seal between the screw and the wall.

[0073] Examples of co-kneaders suitable for carrying out the process according to the invention include, in particular, the SJW series from Xinda, the MDK series from BUSS AG or the COMPEO series from BUSS AG.

[0074] The diameter D of the extruder or co-kneader screw varies depending on the flow rate of the raw materials. It is preferably greater than or equal to 40 mm, more preferably greater than or equal to 100 mm.

[0075] The L / D ratio (L designates the length of the extruder or co-kneader screw and D the diameter of the screw) is preferably 30 or more, preferably 40 or more.

[0076] The rotation speed of the screw varies widely depending on the flow rate and the L / D ratio, but is preferably at least 600 rpm, more preferably at least 800 rpm, and even more preferably at least 1000 rpm.

[0077] Preferably, the mixing is carried out in an extruder which preferably comprises at least two screws, more preferably two screws, preferably co-rotating, so that the reaction mixture including the monomers can be efficiently mixed and conveyed along the axis of the screws from the input to the output of the extruder, gradually passing through different temperature zones to melt the mixture of monomers.

[0078] The screw components are selected to form sequences that allow either the primary conveying of material or the primary mixing of the monomer feed. Preferably, these sequences are selected to form a steam-proof plug of continuously renewed material downstream of the final injection point of solid monomer.

[0079] The extruder or co-kneader may comprise heating means such as electrical means or a heat exchange fluid, preferably electrical means, which are provided in addition to the mechanical energy transferred to the mixture in step a) in the form of thermal energy.

[0080] The mixture containing the polyamide monomer is heated in an extruder or co-kneader so that the discharge temperature in step a) is in particular 160°C to 300°C, preferably 200°C to 280°C, thereby melting the mixture.

[0081] Preferably, a temperature gradient is applied along the axis of the screw between the input and the discharge of the extruder or co-kneader.

[0082] Mixing may be carried out under flushing with an inert gas, preferably nitrogen gas, in a countercurrent direction to the direction of movement of the reaction mixture, in particular in an extruder or co-kneader.

[0083] The mixture used in step a) may further comprise additives.

[0084] The additives may be selected from conventional additives used in polyamides, which are well known to those skilled in the art.

[0085] For example, they may be selected from among catalysts, antioxidants, heat stabilizers, UV absorbers, light stabilizers, lubricants, inorganic fillers, flame retardants, nucleating agents, colorants, reinforcing fibers, waxes, and mixtures thereof.

[0086] Advantageously, they are chosen from among catalysts, stabilizers, antioxidants, chain limiters, antifoam agents, and / or mixtures thereof.

[0087] In particular, the catalyst may be orthophosphoric acid, hypophosphorous acid, or phosphorous acid. The stabilizer may be sodium hypophosphite, a phosphite salt, or a phenol. The chain limiter may be acetic acid, stearic acid, or benzoic acid. The antifoaming agent may be silicone oil.

[0088] The additives may be added to the extruder or co-kneader in liquid and / or solid form, in particular via one or more inputs. They may also be added mixed with one or more monomers, either alone or as a mixture.

[0089] In another embodiment, all or part of the additives may be injected in liquid form into the mixer reactor and the remainder fed to the extruder, preferably into the first 2 / 5ths of the mixer reactor, more preferably upstream of the first orifice for discharging the gas phase.

[0090] Injection of liquid additives into the extruder

[0091] Additives in liquid form are added through one or more injection points, preferably using an injector.

[0092] Liquid additives may be injected at room temperature, in a heated but unmolten state, or in a molten state. They may also be added in the form of an aqueous solution.

[0093] Several additives in liquid form may be injected in liquid form at one injection point, optionally after premixing in a static mixer, or preferably they are injected through one or more injection points.

[0094] One or more additives or a portion of the additives in liquid form may be mixed with one or more liquid monomers or a portion of the liquid monomers, optionally premixed in a static mixer, and then added at one or more feed points.

[0095] These liquid forms of the additives may be used under flushing with an inert gas, preferably nitrogen gas, preferably anhydrous, or with a headspace filled with an inert gas, preferably nitrogen gas, preferably anhydrous.

[0096] Loading the solid form of additives into the extruder

[0097] Additives in solid form are fed to the extruder or co-kneader, preferably after metering by a gravimetric solids feed device.

[0098] They are added with an accuracy of within 1%, preferably within 0.5%, and more preferably within 0.1% of the set value.

[0099] These solid form additives may be used under flushing with an inert gas, preferably nitrogen gas, and preferably anhydrous.

[0100] They may be loaded into an extruder or co-kneader via a pneumatic loader, optionally followed by an inerting step comprising at least one step using an inert gas, preferably nitrogen gas, preferably in anhydrous form.

[0101] Optionally, they may be inactivated beforehand, especially if they are stored in a container.

[0102] All or part of the additives in solid form may be premixed with other additives or monomers in solid form before being added to the extruder or co-kneader.

[0103] In one embodiment, all or part of the additives may be mixed with other additives or monomers, preferably in solid form, for addition to an extruder or co-kneader.

[0104] In one embodiment, the additives may be premixed and then added to the extruder or co-kneader via a single feed point.

[0105] In another embodiment, the mixing may occur in a feed line fed by multiple containers each containing an additive or mixture of additives, the mixture being formed in the feed line by one or more static mixers.

[0106] In another embodiment, the additives are added separately to the extruder or co-kneader, in other words, each additive is added to the extruder or co-kneader via a separate feed point.

[0107] Between steps a) and b), during transitional stages of the process such as shutdown or startup, it is possible to direct the flow of material leaving the extruder or co-kneader to a purge before entering the mixer reactor.

[0108] The extruder therefore comprises at its discharge a system of valves, preferably with a minimum of non-renewable volume, or preferably a three-way valve.

[0109] The transfer of materials from the extruder or co-kneader to the mixer reactor may be carried out under gravity or optionally by a gear pump.

[0110] The product obtained after step a) is a mixture of monomers in the molten state, forming a liquid phase.

[0111] Depending on the mixing conditions and the monomers used, the polycondensation reaction may have already started in step a). In this case, the product obtained from step a) may contain a prepolymer with a very low molar mass. The intrinsic viscosity in m-cresol of the prepolymer, measured according to the ISO 307:2019 standard, is generally strictly less than 0.40 dL / g, preferably less than or equal to 0.30 dL / g and more preferably less than or equal to 0.25 dL / g.

[0112] The product obtained after step a) may contain a vapor phase consisting essentially of water vapor, mainly originating from the water of condensation formed in the melting step, if the polycondensation reaction has already been initiated in the melting step.

[0113] Preferably, the extruder or co-kneader does not contain more than two water discharge devices, more preferably none at all, especially for the water produced by the polycondensation reaction. Said device is also called devolatilizer in the remainder of the specification. This prevents the entrainment of monomers that have changed into vapor form in the molten state during the water removal, thereby maintaining the stoichiometry of the monomers when they leave the extruder after step a) and thus in the mixture for the polycondensation reaction in the mixer reactor used in step b). Furthermore, the method is simplified and the product quality is improved, since the management of the material conveyance to the devolatilizer is no longer necessary (this conveyance is made difficult by the low viscosity of the product in the extruder). Finally, the devolatilization of the water in the extruder requires the transfer of a large amount of energy towards the center of the extruder, which has a low heating efficiency by design and, furthermore, due to the low viscosity of the molten product, the mechanical energy transmitted by the screw is very low.

[0114] Advantageously, the stoichiometry and / or conversion of the mixture of monomers can be controlled in the extruder. In particular, the measurement of the chain ends of the product resulting from step a) may be carried out directly on the liquid phase leaving the extruder or co-kneader, without isolation and without a material recycle loop. This is preferably carried out by near infrared spectroscopy (NIR) using a measuring probe placed in the flow of the liquid phase. Depending on the measurement results, the input flow rate of the monomers and / or the flow rate of the additives to the extruder or co-kneader can be adjusted, preferably automatically, to obtain the desired stoichiometry and / or conversion. Preferably, the adjustment is carried out by changing the flow rate of the liquid monomer.

[0115] The residence time of the monomers in the extruder or co-kneader may vary depending on the flow rate, characteristics and / or operating parameters of the extruder or co-kneader, and is preferably equal to or less than 3 minutes, more preferably equal to or less than 2 minutes, and even more preferably equal to or less than 1 minute.

[0116] Step b): Polycondensation

[0117] The material flow, i.e. the product obtained after step a), is fed directly to the mixer reactor, in particular without interrupting the material flow between the extruder or co-kneader and the mixer reactor.

[0118] In particular, the mixture obtained in step a) is fed to the mixer reactor in step b) without prior devolatilization.

[0119] The molten monomers mixed in the extruder or co-kneader continue to react in the mixer reactor.

[0120] The mixer reactors used in step b) are reactors conventionally used in the synthesis of polyamides, in particular as reactor-finishing units (for carrying out the finishing step of the polyamides). Examples of mixer reactors which can be used in the present invention are described in particular in applications EP 1 436 073, US 8 376 607 and EP 0 715 882.

[0121] More specifically, a mixer-reactor is a reactor with a typically horizontal axis, which is generally a horizontal cylindrical reactor or a horizontal reactor with an elliptical cross section.

[0122] The length and diameter of the reactor can be selected and the flow rate of the molten, i.e., liquid, reaction mixture can be adjusted and controlled to adjust the residence time within the reactor and thereby obtain the desired transport rate.

[0123] The length of the mixer reactor may be about three times the inner diameter of the reactor.

[0124] The mixer reactor is partially filled with liquid phase. Typically, the liquid phase filling rate of the mixer reactor is 20-75% of the initially available space in the reactor, in particular to facilitate the renewal of the interface between the liquid and gas phases and thus to remove the water formed during polycondensation.

[0125] The mixer reactor comprises one or more agitators. The agitators are mounted horizontally so that they can rotate in the reactor. They may be, for example, Archimedes screws, cage-type agitators, or continuous disks (with or without openwork) mounted on a shaft. The diameter of the agitator is usually slightly smaller than the inner diameter of the reactor mixer. The axis of the agitator may be offset from the axis of the finishing reactor. This allows circulation of the gas phase in particular in the reactor. This circulation can also be ensured, for example, by drilling holes in the agitator disks. When several agitators are used, their construction may differ from each other.

[0126] The rotation speed of the stirrer may be, for example, 5 to 100 rpm.

[0127] The agitator may include a number of disks that define compartments within the mixer reactor. For example, the agitator may include 5 to 15 disks. The last compartment of the mixer reactor corresponds to the space between the last disk on the shaft and the vertical end wall of the mixer reactor.

[0128] The mixer reactor is preferably self-cleaning. More specifically, it is a reactor that preferably comprises two co-rotating shafts. It may in particular be a mixer reactor of the REACOM type sold by BUSS-SMS-CANZLER or a mixer reactor of the LIST CRP / TCP type sold by LIST TECHNOLOGY AG.

[0129] Step b) is carried out at a temperature above the solidification temperature of the polyamide produced, preferably at least 5° C. above this solidification temperature, more preferably at least 10° C. above this solidification temperature.

[0130] The heating temperature of the polycondensation reactor may be adjusted depending on the specific polycondensation rate of the product being synthesized.

[0131] The polycondensation reaction may in particular be carried out at close to atmospheric pressure and at temperatures between 240°C and 310°C.

[0132] Heating is achieved by heating the wall of the mixer-reactor barrel, preferably its rotating shaft. Preferably, the heating of the mixer-reactor is achieved by a heat exchange fluid. Preferably, the rotating shaft is heated to a temperature equal to or higher than the temperature of the wall of the mixer-reactor barrel.

[0133] The residence time of the molten material in the mixer reactor is at least 5 minutes, preferably at least 10 minutes, more particularly at least 15 minutes. Preferably, the residence time is at most 60 minutes, preferably at most 50 minutes, more particularly at most 40 minutes.

[0134] The level of the liquid phase in the reactor resulting from the product obtained in step a) is preferably 20% greater, more preferably 25% greater, even more preferably 35% greater than the initial free volume in the reactor.

[0135] The level of the liquid phase in the reactor is preferably less than 75%, more preferably less than 65%, even more preferably less than 55%.

[0136] The level of the liquid phase in the mixer-reactor can be measured by visual assessment and / or by direct weighing of the reactor and / or monitored by a level probe and / or gravimetric measurement (mass balance) of the reactor input / output.

[0137] The water of condensation, which is mainly produced in the mixer reactor, but possibly also in the melting step a), is advantageously removed by means of an inert gas stream, preferably countercurrently.

[0138] Preferably, the injection of the inert gas, preferably nitrogen gas, is carried out at one or more feed points. The inert gas may be injected into the gas or liquid phase of the mixer reactor, preferably into the gas phase. Preferably, the internal gas flow occurs in a parallel direction opposite to the flow of the liquid reaction mixture. In this case, the inert gas is preferably injected into the last 4 / 5 of the reactor length, more preferably into the penultimate section of the mixer reactor, and even more advantageously into the last section of the mixer reactor. The inert gas may be heated before injection into the mixer reactor. The humidity content of the inert gas may be adjusted before injection into the mixer reactor.

[0139] The mixer reactor preferably comprises, upstream of the inert gas feed point relative to the direction of flow of the reaction liquid, one or more orifices for discharging the gas phase from the mixer reactor, in which case the orifices for discharging the gas phase are preferably located within the first two-fifths of the reactor, more preferably between the second and third sections of the reactor.

[0140] The flow rate of the inert gas, in particular nitrogen gas, fed to the reactor is defined such that the steam dilution factor F is less than 1.40, preferably less than 1.20, more preferably less than 1.10.

[0141] (Formula 1) TIFF2024546929000001.tif16153

[0142] The gas phase is generally composed of inert gases, water of condensation and residual volatile compounds from the polycondensation, the latter being chosen in particular from among additives, oligomers with a molar mass below 1000 g / mol, amino acids, diamines, cyclic compounds, alone or in mixtures.

[0143] In particular, in the case of polyamide compositions containing only amino acid-based monomers, the compound is composed of a mixture of oligomers, amino acids, cyclic dimers and additives.

[0144] The reactor mixture can be equipped with a device called a devolatilization line, which manages the gas phase at the discharge of the polycondensation reactor, preferably at a pressure close to atmospheric pressure.

[0145] Preferably, the mixer reactor contains a gas phase discharge orifice connected to a devolatilization line at near atmospheric pressure.

[0146] Advantageously, the devolatilization line comprises a device called a control valve, which makes it possible to regulate the pressure in the mixer reactor to a value close to atmospheric pressure.

[0147] Advantageously, the devolatilization line is at a temperature above the softening temperature of the oligomer, preferably above the melting temperature of the oligomer.

[0148] The temperature of the devolatilization line is 120 to 300°C, preferably 180 to 300°C, and more preferably 180 to 250°C.

[0149] Preferably the mixer reactor contains at least two devolatilizers, preferably the same, both connected to the reactor by the same orifice and only one operating at a time so that they can be cleaned without interrupting the process by switching from one to the other.

[0150] The water vapor and other volatile compounds such as monomers or oligomers thus removed can be separated by conventional distillation systems. The monomers and / or oligomers recovered from this separation may be recycled back to the extruder, either alone or in admixture with other non-recycled monomers.

[0151] In the case of the synthesis of polyamides containing one or more diamines, the gas phase leaving the mixer reactor may in particular contain one or more of these diamines.

[0152] Preferably, between the gas phase discharge orifice of the mixer reactor and the devolatilization line, a partial condenser is arranged to separate the diamine or mixture of diamines contained in the gas phase from other compounds. The mass flow rate of the diamine alone or the mixture with other diamines discharged from the partial condenser is 10% or less, preferably 5% or less, more preferably 3% or less, advantageously 1% or less, compared to the total mass flow rate of the diamines fed in step a).

[0153] The recovered diamine or diamine mixture is then directed towards a vessel and, optionally, undergoes further treatment, for example in a rectification column, in order to modify its composition so as to be reused as monomer at the input of step a), preferably as a mixture with the non-recycled diamine or diamine mixture.

[0154] It is also possible to recycle the recovered diamine or diamine mixture to the mixer reactor without further treatment, preferably in the first 2 / 8 of the reactor, more preferably in the first 1 / 8 of the mixer reactor, more advantageously at the same level as the reactor screw used to feed the product obtained from step a).

[0155] The set temperature of the partial condenser is 90°C to 200°C, preferably 95°C to 200°C, more preferably 100°C to 150°C, and even more advantageously 100°C to 120°C.

[0156] Advantageously, a demister or bed droplet separator is inserted between the gas phase discharge orifice of the mixer reactor and the partial condenser.

[0157] The gas phase passing through the devolatilization line is then cooled at the end of the line, where all or part of its components change from the gaseous state to the liquid and / or solid state. This operation may be carried out in a condenser at a temperature lower than the condensation temperature of the most volatile compound contained in the gas phase. Preferably, the scrubbing of the gas phase is carried out with a solvent, preferably water. For this purpose, it is possible to use one or more devices connected in series, such as spray columns, cyclone spray scrubbers, packed bed scrubbers, plate scrubbers, etc., in cocurrent, countercurrent or crossflow.

[0158] The resulting phase may then be treated to separate the compounds colloidally solubilized or dispersed in the solvent and / or to separate the solids from the solvent. Several methods are known to those skilled in the art, such as coagulation, flocculation, electrocoagulation precipitation, adsorption, ion exchange, decantation, centrifugation, filtration, flotation, etc.

[0159] The product may be removed from the mixer reactor by a vertical discharge single or twin screw through an outlet formed in the barrel of the mixer reactor, which may be located in one of the walls at the downstream end of the mixer reactor or in the vertical end wall of the mixer reactor.

[0160] The discharge screws are advantageously heated to a temperature equal to or higher than the temperature of the barrel of the reactor mixer. When twin screws are used, they may be straight or conical and may be positioned one behind the other or at the same height as the reactor outlet.

[0161] The product is then processed by a gear pump to regulate the discharge from the reactor, downstream of which a heated die may be arranged to obtain pellets by direct cutting or by granulation of the rods obtained by cooling the product, advantageously in a water bath.

[0162] Optionally, the granules are dried in-line by an air stream flowing parallel to the rod and opposite the direction of rod movement.

[0163] Measurements of the stoichiometry and / or conversion of the product obtained from step b) may be carried out. In particular, measurements of the chain ends of the product obtained in step b) may be carried out directly on the liquid phase leaving the mixer reactor, without isolation and without a material recycle loop. Preferably, this measurement is carried out by near infrared spectroscopy (NIR) using a measurement probe placed in the flow of the liquid phase.

[0164] It is also possible to carry out this measurement on the solid pellets exiting the mixer-reactor, preferably by near infrared spectroscopy (NIR).

[0165] In order to obtain the desired stoichiometry and / or conversion, the monomer flow rate and / or additive flow rate may be adjusted, preferably automatically, in the feed to the extruder or co-kneader and / or in the mixer reactor, preferably in the first 2 / 8 of the mixer reactor, more preferably in the first 1 / 8 of the mixer reactor, more advantageously at the same screw level of the mixer reactor as the feed point of the product obtained from step a), according to the measurement results. The adjustment is preferably made by changing the liquid monomer flow rate.

[0166] The flow rate and / or the humidity content of the inert gas stream in the mixer reactor may also be adjusted, preferably automatically, according to the measurement results in order to obtain the desired conversion.

[0167] Advantageously, the polyamide obtained after step b) according to the process of the invention has an intrinsic viscosity in meta-cresol solution, measured according to the ISO 307:2019 standard, of at least 0.80 dL / g, preferably at least 1.10 dL / g and more preferably at least 1.30 dL / g.

[0168] Advantageously, the polyamide obtained after step b) according to the process of the invention has an intrinsic viscosity in meta-cresol solution, measured according to the ISO 307:2019 standard, of at most 2.50 dL / g, more preferably at most 2.20 dL / g and even more preferably at most 1.80 dL / g. Working Example

[0169] In the examples below, the following abbreviations are used: A11 corresponds to 11-aminoundecanoic acid. DA10 corresponds to decanediamine. B corresponds to bis-(3-methyl-4-aminocyclohexyl)-methane (or 3,3'-dimethyl-4,4'-diaminodicyclohexyl-methane), also called BMACM or MACM. T corresponds to terephthalic acid. BAC corresponds to 1,3-bis(aminomethyl)cyclohexane, which has a cis-isomer content of 75%.

[0170] A Werner & Pfleiderer co-rotating twin-screw extruder ZSK30 (diameter 30 mm, length 38 mm) was equipped with two gravimetric metering feeders located at the beginning of the feeding zone and two injection points in barrels 4 and 6. The extruder was heated by an electric heating element under the conditions shown in Table 2. No devolatilization sink was provided.

[0171] The discharge of the extruder is connected via a tube heated by a heat exchange fluid to a self-cleaning mixer reactor LIST TCP4 CONTI sold by LIST TECHNOLOGY AG with a free volume of 7.4 liters. The transfer of the product between the discharge of the extruder and the input of the mixer reactor was carried out under gravity.

[0172] The mixer reactor was equipped with two co-rotating agitators forming 11 chambers, the walls of the mixer reactor and the two agitator shafts were heated to the same temperature by a heat exchange fluid. The product was fed from the first compartment to the reactor mixer. The product from the reactor mixer was ensured by two vertical discharge screws through the discharge ports located on the vertical end walls of the mixer reactor. Gear pumps located downstream of these discharge screws allowed the regulation of the discharge flow and the conveyance of the product through a heated die. The resulting rods were cooled in a water bath and granulated.

[0173] A stream of nitrogen gas was fed countercurrently to the gas phase of the ninth section of the reactor. The gas phase of the reactor was vented in the fourth section. The gas phase first passed through a partial condenser heated by a heat exchange fluid, the condensate was directed towards the reactor in the fourth section, after which the gas phase entered an electrically heated downstream devolatilization line. A total condenser heated by a heat exchange fluid was placed at the end of this devolatilization line.

[0174] The melting of the monomers and the charging of the various additives were carried out in an extruder. The monomers corresponded to the compositions PA11 (polymer A), PA11 / 10T (polymer B), PA11 / B10 (polymer C) and PA BACT / 10T (polymer D).

[0175] The diacid was added to the feed hopper in solid form and its mass flow was metered by a gravimetric feeder.

[0176] The diamine was heated in a vessel to 80° C. and then pumped into barrel 6 by a positive displacement pump servo-controlled by a mass flow meter to control the mass flow rate. For polymer D, the two diamines 1,3-1

[0177] The BAC and DA10 were premixed in a vessel before being injected into barrel 6 at a single injection point.

[0178] The additives in liquid form were fed by injection into barrel 4 of the extruder and / or into the first section of the mixer reactor. The additives in solid form were added in the form of a dry blend with one monomer. The feeding conditions are listed in Table 1. In Example 5, the mixture of the two additives was injected into the extruder through a single injection point in barrel 4.

[0179] [Table 1]

[0180] [Table 2]

[0181] [Table 3] TIFF2024546929000005.tif225170

[0182] The terms used in Tables 1 to 3 above have the following meanings:

[0183] "wt%" indicates percent by weight.

[0184] "Level" refers to the percentage of the free volume of the mixer reactor occupied by the mixture obtained after step a) and fed to the mixer reactor.

[0185] "Residence time" refers to the residence time in the mixer reactor.

[0186] "Dilution ratio": The flow rate of the inert gas, in particular nitrogen gas, fed to the reactor is defined such that the steam dilution ratio F is less than 1.40, preferably less than 1.20, more preferably less than 1.10.

[0187] (Formula 1) TIFF2024546929000006.tif16153

[0188] "Diamine loss" is the total weight of diamine monomer recovered at the discharge of the total condenser equipped with a devolatilizer line compared to the total weight of diamine monomer fed to the extruder.

Claims

1. 1. A process for the continuous production of polyamides by condensation, comprising successive steps a) and b), Step a) melting a mixture comprising polyamide monomers in an extruder or co-kneader, wherein the polyamide monomers are fed to the extruder or co-kneader without adding water; Step b) carrying out a polycondensation reaction of the mixture obtained after step a) in a horizontal mixer reactor, A method wherein steps a) and b) are carried out at near atmospheric pressure.

2. 10. The method of claim 1, wherein the polyamide produced according to the method is an aliphatic, cycloaliphatic, arylaliphatic, aromatic or semi-aromatic polyamide.

3. 2. The method of claim 1, wherein the polyamide is selected from polyamide 11, 11 / B10, 11 / BI / BT, B10, B12, MXD10, MXD.6, 11 / 10T, 11 / BACT / 10T, BACT / 10T.

4. 10. The method of claim 1, wherein the mixture in step a) comprises an additive.

5. 5. The method of claim 4, wherein the additives include at least one catalyst, at least one stabilizer, at least one antioxidant, at least one chain limiter, and at least one antifoaming agent.

6. The method of claim 1, wherein step a) is carried out in an extruder.

7. 2. The method according to claim 1, wherein the monomer mixture is heated in the extruder or co-kneader to melt the monomer mixture so that the discharge temperature in step a) is 160°C to 300°C.

8. 2. The process according to claim 1, wherein the mixture obtained after step a) is fed to the horizontal mixer reactor in step b) without prior devolatilization.

9. 10. The method of claim 1, wherein the horizontal mixer reactor comprises at least two shafts containing stirring elements.

10. 2. The method of claim 1, wherein the agitator shaft of the horizontal mixer reactor is heated.

11. 2. The method according to claim 1, wherein the polycondensation reaction in step b) is carried out at a temperature of at most 50° C. above the solidification temperature of the polyamide and / or at least 5° C. above this solidification temperature.

12. 2. The method according to claim 1, wherein step b) is carried out under flushing with inert gas.

13. 10. A system for carrying out the method according to claim 1, comprising the extruder or co-kneader directly connected to the input of a horizontal mixer reactor.

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