Continuous process for the polymerization or oligomerization of diphenylamine

Abstract

The present invention relates to an at least partially continuous process for the preparation of at least one oligomer and / or polymer comprising at least one diphenylamine repeat unit and optionally at least one phenyl alpha-naphthylamine repeat unit.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of polymeric antioxidants for lubricants. It particularly relates to the solvent-free manufacturing of antioxidants which are oligomers or polymers of at least one diphenylamine and optionally at least one phenyl alpha-naphthylamine. TECHNICAL BACKGROUND

[0002] Diphenylamine and / or naphthylamine based antioxidants are well known and widely used in the field of lubricants. They can in particular be used in monomeric form for standard performance lubricants, but diphenylamine and / or naphthylamine based antioxidants in oligomeric or polymeric form have been developed for use in high performance lubricants.

[0003] In the above-mentioned field, different processes for synthesizing oligomers or polymers of at least one diphenylamine and optionally at least one phenyl alpha-naphthylamine have been described in the prior art.

[0004] Thus, patent applications US 2019 / 0127526, EP 0 734 432, EP 0 799 289, FR 2 832 417, EP 2 217 687, WO 2008 / 022028, US 3,494,233 and WO 95 / 17488 describe processes for preparing oligomers or polymers comprising at least one diphenylamine and / or phenyl alpha-naphthylamine repeat unit.

[0005] For example, document EP 0 734 432 describes a process for the discontinuous preparation of an antioxidant stabilizer composition which is the reaction product between an N-aryl naphthylamine, a diphenylamine, an organic peroxide and a solvent. The reaction is carried out in a distillation column. The resulting composition has a brown color (Example 2).

[0006] All these processes are discontinuous processes, also denoted by the term "batch", i.e. the process is carried out in a closed reactor, the reactants are introduced therein, the polymerization reaction is completed and then at the end of the reaction, the product is isolated from the reaction medium.

[0007] For technical and practical reasons, batch reactors and continuous reactors are intrinsically different. At the technical level, for example for exothermic reactions, the size of the discontinuous reactor can be limited by the heat transfer. In large capacity reactors, it is often necessary to dilute the reactants by adding solvents in order to be able to control the exothermicity of the reaction or to limit the size of the reactor. At the practical level, the discontinuous process requires the reactor to be depressurized, cooled, opened and emptied at the end of the reaction in order to recover the reaction mixture under good safety conditions; these discontinuous operations are complex and labor intensive.

[0008] Some methods of the prior art also involve the use of at least one solvent to dilute the reactants. Whether the method is discontinuous or continuous, the use of solvents has drawbacks from an energy point of view, in particular in terms of cost of separation or heating of larger masses, from an environmental point of view, in particular in terms of emissions, and from an economic point of view, in particular in terms of investment costs for the separation step, the cost of the solvent and / or the reduction of the reaction rate.

[0009] Finally, the implementation of discontinuous oligomerization and / or polymerization processes often faces the difficulty of reproducing the properties of the polymer or oligomer from one batch to another, in particular in terms of viscosity, color, flash point and residual monomer content, which can be related to more or less significant variations in the molecular weight distribution.

[0010] In the lubricant industry, in particular for the aviation and / or automotive industry, the color of the lubricant and of the additives is an important parameter, since a visually dark lubricant is generally associated with a waste lubricant. In contrast, a visually clear lubricant is generally associated with a new lubricant. The reproducibility from one synthesis to another of the parameters of the oligomers and / or polymers that influence their color is therefore an important point that should be optimized.

[0011] SUMMARY

[0012] In this respect, the Applicant has demonstrated that it is possible to prepare oligomers or polymers comprising at least one diphenylamine repeat unit and optionally at least one phenyl alpha-naphthylamine repeat unit using at least partially continuous processes, which have many advantages compared to the discontinuous processes described above. DETAILED DESCRIPTION

[0014] The present invention thus relates to a process for the preparation of at least one oligomer and / or polymer comprising at least one diphenylamine repeat unit and optionally at least one phenyl alpha-naphthylamine repeat unit, comprising the following steps:

[0015] (a) introducing into a suitable reactor:

[0016] - at least one diphenylamine,

[0017] - optionally at least one phenyl alpha-naphthylamine,

[0018] - at least one organic peroxide, and

[0019] - at least one ester lubricant;

[0020] (b) polymerization or oligomerization of the diphenylamine and optionally the phenyl alpha-naphthylamine to obtain a mixture comprising at least one oligomer or polymer comprising at least one diphenylamine unit and optionally at least one phenyl alpha-naphthylamine unit, and

[0021] (c) subjecting the mixture obtained in step (b) to conditions suitable for reducing and / or removing at least a part of the residual reactants and / or reaction by-products other than the oligomers or polymers comprising at least one diphenylamine unit and optionally at least one phenyl a-naphthylamine unit,

[0022] wherein steps (a) and (b) are performed consecutively and wherein step (b) is performed at a temperature equal to or higher than 170°C.

[0023] According to the present application, a temperature equal to or higher than 170°C comprises the following values or any interval between these values: 170; 175; 180; 185; 190; 195; 200; 205; 210; 215; 220; 225; 230; 235; 240; 245; 250; etc.

[0024] Generally, step (b) is performed at a temperature ranging from 180°C to 250°C, preferably from 180°C to 230°C.

[0025] According to one feature of the present application, the mixture obtained in step (b) comprises an unreacted peroxide content lower than or equal to 60%, preferably lower than or equal to 45%, generally lower than or equal to 40%, the peroxide content being determined by gas chromatography.

[0026] According to another feature of the present application, the mixture obtained in step (b) comprises a residual monomer content lower than or equal to 25%, preferably lower than or equal to 10%, generally lower than or equal to 5%, the residual monomer content being the weight percentage determined by gas (GC) and supercritical (SFC) chromatography.

[0027] Compared to the methods of the prior art, this method is particularly characterized by a reduced cycle time, an improvement in the quality of the resulting oligomers or polymers, in particular in terms of color, a great reduction in the variability of the properties of the product such as its viscosity, its molecular weight distribution, its flash point, its color and / or its residual monomer content, an improved safety, environmental advantages, simplified maintenance, space savings and ease of use.

[0028] Of course, the different features, variants and embodiments of the present application can be associated with each other in various combinations, provided they are not incompatible or mutually exclusive.

[0029] For the rest of the description, unless otherwise indicated, the indication of a numerical interval "from X to Y" or "between X and Y" is to be understood in the present application as including the numerical values X and Y.

[0030] Comparative Example 1 according to the prior art discontinuous process

[0031] "Continuous" in the present invention refers to the usual meaning in the art. In particular, it relates to an implementation of a process in which the supply of at least one reactant and / or the withdrawal of all or part of the content of the reactor is carried out continuously, preferably with the same flow rate at the inlet and outlet of the reactor. Preferably, the process carried out according to the present invention is continuous so that the control of the supply, withdrawal and other polymerization conditions ensures constant operating conditions in the reactor.

[0032] In one embodiment, all steps of the process according to the present invention are carried out continuously.

[0033] "Polymer" of at least one diphenylamine and optionally at least one phenyl a-naphthylamine in the present invention refers to a compound comprising at least two repeating units of at least one diphenylamine and / or phenyl a-naphthylamine.

[0034] "Oligomer" of at least one diphenylamine and optionally at least one phenyl a-naphthylamine in the present invention refers to a polymer of at least one diphenylamine and optionally at least one phenyl a-naphthylamine comprising from 2 to 10 repeating units, or a mixture of these compounds. In particular, it can consist of dimer, trimer, tetramer, pentamer, hexamer, heptamer, octamer, nonamer, decamer and / or any mixture of these compounds. Preferably, the oligomer contains at least 90 wt% of dimer, trimer, tetramer, pentamer or a mixture of these compounds.

[0035] Preferably, the residual monomer ratio in the oligomer or polymer obtained at the end of step (b) is lower than or equal to 10 wt%, in particular lower than or equal to 5 wt%.

[0036] "Diphenylamine" refers to a compound of formula (I):

[0037]

[0038] wherein R1to R10are each independently selected from a hydrogen atom, an alkyl group and an aralkyl group.

[0039] In one embodiment, the at least one diphenylamine of formula (I) is an alkylated diphenylamine, i.e. at least one of R1to R10is an alkyl group or an aralkyl group. In another embodiment, at least one of R1to R5is an alkyl group or an aralkyl group and at least one of R6to R10is an alkyl group or an aralkyl group.

[0040] "Alkyl" in the present invention refers to a linear, branched or cyclic saturated hydrocarbon group comprising 1 to 24 carbon atoms. Preferably, the alkyl group comprises 1 to 12 carbon atoms. In alkyl groups, one can particularly mention methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, i-butyl, n-pentyl, i-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, t-octyl, i-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl and i-dodecyl. In a particular embodiment, the alkyl group is selected from t-butyl and t-octyl.

[0041] "Aryl" in the present invention refers to a monocyclic or polycyclic aromatic hydrocarbon group. Each aromatic or polyaromatic ring comprises 5 to 14 atoms. In examples of aryl groups, one can particularly mention phenyl.

[0042] "Aryl" in the present invention refers to a monocyclic or polycyclic aromatic hydrocarbon group. Each aromatic or polyaromatic ring comprises 5 to 14 atoms. In examples of aryl groups, one can particularly mention phenyl.

[0043] In one embodiment, the diphenylamines of formula (I) are selected from the group consisting of N,N-diphenylamine, N,N-di-(p-tert-butylphenyl)amine, N,N-di-(p-tert- octylphenyl)amine, N-(p-tert-butylphenyl)-N-phenylamine, N-(p-tert-octylphenyl)-N- phenylamine, N-(p-tert-butylphenyl)-N-(p-tert-octylphenyl)amine and any mixture thereof.

[0044] The diphenylamines can be supplied separately according to the present invention, or as a mixture with each other. For example, they can be in the form of a mixture of N,N-diphenylamine, N,N-di-(p-tert-butylphenyl)amine, N,N-di-(p-tert-octylphenyl)amine, N-(p-tert-butylphenyl)-N-phenylamine, N-(p-tert-octylphenyl)-N-phenylamine and N-(p-tert-butylphenyl)-N-(p-tert-octylphenyl)amine, in particular under the name L57 and CAS number 68411-46-1.

[0045] Phenyl alpha-naphthylamine according to the present invention refers to a compound of formula (II):

[0046]

[0047] wherein R11to R22are each independently selected from a hydrogen atom and an alkyl group.

[0048] In one embodiment, at least one of R11to R22is an alkyl group. In one embodiment, only one of R11to R22is an alkyl group, in particular t-octyl.

[0049] In a particular embodiment, the phenyl alpha-naphthylamine is N-phenyl 1,1,3,3- tetramethylbutyl naphthalen-1 -amine, having the CAS number 68259-36-9.

[0050] In a particularly preferred embodiment, the at least one diphenylamine is in the form of a mixture of N,N-diphenylamine, N,N-di-(p-tert-butylphenyl)amine, N,N-di-(p-tert- octylphenyl)amine, N-(p-tert-butylphenyl)-N-phenylamine, N-(p-tert-octylphenyl)-N- phenylamine and N-(p-tert-butylphenyl)-N-(p-tert-octylphenyl)amine, and the at least one phenyl alpha-naphthylamine is N-phenyl 1,1,3,3-tetramethylbutyl naphthalen-1 -amine.

[0051] The relative weight proportions of these two types of diphenylamine and phenyl alpha- naphthylamine units within the polymer or oligomer can vary greatly from 0 / 100 to 100 / 0. Preferably, the relative weight proportions of diphenylamine / phenyl alpha-naphthylamine are between 100 / 0 and 50 / 50, in particular between 100 / 0 and 90 / 10, in particular between 100 / 0 and 95 / 5. In a particular embodiment, the polymer or oligomer obtained by the process according to the application comprises only diphenylamine units. The person skilled in the art is able to adjust the amounts of diphenylamine and phenyl alpha-naphthylamine to be introduced into the reactor, in particular according to the desired structure of the oligomer or polymer to be synthesized and the desired thermal properties.

[0052] In one embodiment, step (a) is the step of introducing into a suitable reactor:

[0053] - at least one diphenylamine,

[0054] - at least one phenyl alpha-naphthylamine,

[0055] - at least one organic peroxide, and

[0056] - at least one ester lubricant.

[0057] In this embodiment, the polymer and / or oligomer obtained at the end of the process according to the application comprises diphenylamine repeat units and phenyl alpha-naphthylamine repeat units.

[0058] Of course, since steps (a) and (b) of the process according to the application are carried out consecutively and lead to the successive consumption of all or part of the reactants introduced into the reactor, all the proportions and amounts of the various reactants mentioned in the present application correspond to their proportions and amounts at the time of introduction into the reactor.

[0059] The at least one diphenylamine and / or the at least one phenyl alpha-naphthylamine can be introduced into the reactor in pure form or diluted in at least one diluent.

[0060] "Diluent" in the present invention refers to a compound which is not intended to be removed or isolated from the polymer or oligomer obtained at the end of the reaction, in particular in step (c). For example, it can be a diluent which is intended to be present in a lubricating composition comprising the polymer or oligomer obtained by the process according to the present invention. Preferably, the diluent is an ester lubricant, in particular an ester lubricant which is introduced into the reactor in step (a).

[0061] In one embodiment, the at least one diphenylamine and / or the at least one phenyl a-naphthylamine is introduced into the reactor in the form of a solution in an ester lubricant. In one embodiment, the solution comprising the at least one diphenylamine and / or the at least one phenyl a-naphthylamine does not comprise any diluent other than the ester lubricant. Preferably, the at least one diphenylamine and / or the at least one phenyl a-naphthylamine is in the form of a solution in an ester lubricant in an amount of 40 to 80 wt.%. In particular, the at least one diphenylamine and / or the at least one phenyl a-naphthylamine is in the form of a solution in an ester lubricant of about 60 wt.%. In one particular embodiment, the at least one diphenylamine and the at least one phenyl a-naphthylamine are introduced into the reactor in the form of a solution in an ester lubricant comprising the at least one diphenylamine and the at least one phenyl a-naphthylamine.

[0062] The reactants are introduced into the reactor in step (a) of the process according to the present invention in the absence of a solvent. "Solvent" according to the present invention refers to a compound in which at least one of the reactants can be at least partially dissolved and / or dispersed, which is not reactive under the reaction conditions and which is intended to be removed or isolated from the polymer or oligomer obtained at the end of the reaction. The solvent differs from the diluent at least in that its boiling point is generally lower than 250°C, which enables its separation from the resulting polymer or oligomer by evaporation at the end of the reaction.

[0063] "Absence of a solvent" in the present invention refers to the condition that the solution under consideration comprises less than 20 wt.% of a solvent, preferably less than 10 wt.% of a solvent, in particular less than 5 wt.% of a solvent, in particular less than 1 wt.% of a solvent.

[0064] By "repeating unit" of a diphenylamine or a phenyl a-naphthylamine, the following fact is to be understood, that in the final structure of the oligomer or polymer obtained according to the present invention at least one, preferably at least two units of a diphenylamine or a phenyl a-naphthylamine, respectively, are present.

[0065] The diphenylamine and phenyl a-naphthylamine repeat units can be positioned in any manner relative to each other in the structure of the polymer or oligomer obtained according to the present application. Thus, the polymer or oligomer can comprise a regular alternation of diphenylamine and phenyl a-naphthylamine repeat units at least over a portion of its structure. It can comprise a random distribution of diphenylamine and phenyl a-naphthylamine repeat units at least over a portion of its structure. Finally, it can comprise segments containing only a single type of diphenylamine or phenyl a-naphthylamine repeat units over at least a portion of its structure.

[0066] In one embodiment, the polymer and / or oligomer obtained by the process according to the present application comprises only diphenylamine and phenyl a-naphthylamine repeat units in its structure. In another embodiment, the polymer and / or oligomer obtained by the process according to the present application comprises only diphenylamine repeat units in its structure.

[0067] "Organic peroxide" means in the present application any organic compound comprising two oxygen atoms which are bonded together by a single covalent bond. Preferably, it is a compound of formula (III):

[0068] R 23 -O-O-R 24 (III)

[0069] wherein R 23 and R 24 are independently of each other an alkyl group.

[0070] In some embodiments, R 23 and R 24 are identical. For example, it can consist of di-tert-butyl peroxide. The organic peroxide is the initiator of the polymerization and / or oligomerization of the different repeat units. The organic peroxide can be present in the reactor in any suitable proportion relative to the other reactants, in particular relative to the at least one diphenylamine, relative to the at least one phenyl a-naphthylamine and relative to the ester lubricant. For example, the organic peroxide can be present in a proportion of 10 to 50% by weight relative to the total mass of organic peroxide, this amount being adjusted according to the desired average molecular mass and viscosity of the polymer, of the at least one diphenylamine, of the at least one phenyl a-naphthylamine and of the ester lubricant and according to the amount of peroxide lost during the reaction. Preferably, the organic peroxide is liquid under the reaction conditions. Preferably, the peroxide is volatile so as to be able to remove the residual peroxide at the end of the reaction if necessary.

[0071] The organic peroxide can be introduced into the reactor in pure form or in diluted form in a diluent. Preferably, the diluent is an ester lubricant, in particular the ester lubricant introduced into the reactor in step (a). In one embodiment, the organic peroxide solution does not comprise a solvent. Preferably, the organic peroxide is in the form of a solution in an ester lubricant in an amount of 30 to 70 wt.-%. In particular, the organic peroxide is in the form of a solution in an ester lubricant in an amount of about 50 wt.-%.

[0072] The organic peroxide can be introduced in an amount of 1.0 to 2.0 molar equivalents, preferably 1.3 to 1.6 molar equivalents, relative to the total amount of diphenylamine and phenyl a-naphthylamine.

[0073] An "ester lubricant" in the present invention refers to any ester or mixture of esters having lubricating properties. Preferably, the polymer or oligomer obtained at the end of the process according to the present invention is intended to be used as an antioxidant in a lubricating composition comprising at least said ester lubricant. Preferably, the ester lubricant used according to the present invention is saturated, i.e. it does not comprise any double or triple chemical bonds other than the C=0 bond of each ester function. Among the ester lubricants which can be used in the process according to the present invention, mention can be made of the monoesters of octyl acetate, decyl acetate, octadecyl acetate, methyl myristate, butyl stearate, and the polyesters of dibutyl phthalate, dioctyl adipate, bis-2-ethylhexyl azelate and bis-2-ethylhexyl sebacate. The polyol ester type lubricants can be prepared from technical pentaerythritol or trimethylolpropane and a mixture of linear and / or branched carboxylic acids having 4 to 18 carbon atoms, for example having 9 carbon atoms. Technical pentaerythritol is a mixture comprising about 85 to 92 wt.-% of monopentaerythritol and 8 to 15 wt.-% of dipentaerythritol. A common commercially available technical pentaerythritol contains about 88 wt.-% of monopentaerythritol and about 12 wt.-% of dipentaerythritol relative to the total weight of the ester lubricant. Technical pentaerythritol can also contain an amount of tripentaerythritol and tetrapentaerythritol which are usually formed as by-products during the production of technical pentaerythritol. In particular, the ester lubricant can be selected from the group consisting of trimethylolpropane trisazylate and esters made from pentaerythritol and at least one branched carboxylic acid comprising 9 carbon atoms.

[0074] In one embodiment, the ester lubricant is linear. In another embodiment, the ester lubricant is branched. The person skilled in the art is able to select the ester lubricant to be used in the process according to the present invention, in particular depending on the properties of the at least one diphenylamine, the properties of the at least one phenyl a-naphthylamine, the properties of the peroxide, the properties required for the solution of the oligomer and / or polymer and the ester lubricant to be prepared and / or the intended field of application of the resulting solution of the oligomer and / or polymer and the ester lubricant.

[0075] The ester lubricant is introduced into the reactor in an amount suitable to obtain the desired mixture of oligomers or polymers in the ester lubricant. For example, depending on the nature of the ester, the solution withdrawn from the reactor can comprise from 20 to 60% by weight, in particular about 30 to 50% by weight, of oligomers or polymers in the ester lubricant.

[0076] Steps (a) and (b) can be carried out in any reactor suitable for being implemented continuously. In particular, it can consist of a static mixer, a dispersion mixer, a roll mill mixer, an extruder or a reactor of the horizontal shaft mixer type. In particular, it can consist of a continuous reactor of the G1 to G4 type marketed by Corning. In particular, the useful volume of the reactor can be between 50 milliliters and 5 liters, preferably between 50 milliliters and 1 liter (for example, the Corning type reactors used in the examples below are suitable). The person skilled in the art is able to select the appropriate reactor as a function of the nature of the reactants, the reaction conditions (in particular the residence time) and in particular the volume to be produced.

[0077] In one particular embodiment, the reactor is a G1 static mixer type reactor with 10 fluid modules. The system can further comprise two metering lines connected to the reactor, as well as at least one sensor and at least one temperature display. A back pressure regulator and a device capable of controlling the temperature can also be included in the system.

[0078] The pressure at the inlet of the reactor can be between 1 and 20 bars. In particular, the pressure at the inlet of the reactor can be between 5 and 20 bars, preferably between 15 and 19 bars, in particular for reactors in which all the reactants are in the liquid phase. For example, these pressure ranges are suitable for the Corning type reactors used in the examples below. Indeed, the pressure at the inlet (and the back pressure at the outlet) is a parameter that depends on the type of reactor used and can therefore be modified as a function of the latter. In addition, the pressure is also inherent to the reaction temperature used during step (b) (parameter imposed and not adjustable).

[0079] In the reactor, the reactants can in particular be in the liquid phase or in the gaseous phase. In some reactor types, all the reactants are in the liquid phase, in which case the pressure at the inlet of the reactor can be between 5 and 20 bars, preferably between 15 and 19 bars. In other reactor types, part of the reactants is in the liquid phase and part of the reactants is in the gaseous phase. In this case, the pressure at the inlet of the reactor can be lower and can be between 1 and 20 bars.

[0080] Of course, step (a) can further comprise introducing into the reactor any other reactant, solvent or diluent necessary for carrying out step (b) or the subsequent steps of the process.

[0081] Step (a) is carried out continuously, that is to say at least one of the reactants is introduced continuously into the reactor. The rate at which each reactant is introduced into the reactor in step (a) can vary over time, preferably ensuring a constant inlet flow rate of all reactants.

[0082] A "reactant" in the present invention refers to all compounds introduced into the reactor in step (a), in particular the at least one diphenylamine, the at least one phenyl a-naphthylamine, the at least one organic peroxide and the at least one ester lubricant. In case a small proportion of a solvent is introduced into the reactor in step (a), the solvent is not one of the compounds referred to as "reactive".

[0083] In one embodiment, the process according to the present invention comprises, prior to step (a), a step (a1 ) of premixing at least two of the at least one diphenylamine, the at least one phenyl a-naphthylamine, the ester lubricant and the organic peroxide to form a solution comprising them. The mixing of the reactants prior to their introduction into the reactor is particularly helpful to minimize their residence time in the reactor, in particular when the solution comprising at least two of the at least one diphenylamine, the at least one phenyl a-naphthylamine, the ester lubricant and the organic peroxide is subsequently subjected to a preheating step (a2) as described below.

[0084] In one embodiment, step (a1 ) is a premixing of the at least one diphenylamine and the at least one phenyl a-naphthylamine, optionally in the presence of the ester lubricant. In one embodiment, step (a1 ) is a premixing of the at least one diphenylamine and the organic peroxide, optionally in the presence of the ester lubricant. In one embodiment, step (a1 ) is a premixing of the at least one phenyl a-naphthylamine and the organic peroxide, optionally in the presence of the ester lubricant. In one preferred embodiment, step (a1 ) is a premixing of the at least one diphenylamine, the at least one phenyl a-naphthylamine and the organic peroxide, optionally in the presence of the ester lubricant.

[0085] In one embodiment, the process according to the present invention comprises, prior to step (a), and if necessary after step (a1 ), a step (a2) of preheating the at least one diphenylamine, the at least one phenyl a-naphthylamine, the ester lubricant, the organic peroxide and / or the solution comprising at least two of them obtained in step (a1 ) at a temperature referred to as "preheating temperature". The preheating temperature is higher than room temperature and lower than or equal to the temperature at which step (b) is carried out. In particular, the preheating temperature can be between 40 and 100°C. In particular, such a preheating step is helpful to minimize the residence time of the reactants in the reactor.

[0086] Steps (al) and / or (a2) can be carried out independently of each other, either continuously or discontinuously. They can each independently be carried out in a discontinuous reactor, or in a part of a continuous reactor, which part is connected to the part of the continuous reactor used to carry out step (b). Preferably, steps (al) and (a2) are carried out continuously.

[0087] In the case where the process comprises a step (al) of premixing all or part of the reactants and / or a step (a2) of preheating all or part of the reactants, the introduction of the reactants of step (a) is carried out by introducing into the reactor, in particular, the premixed and / or preheated reactants obtained at the end of steps (al) and / or (a2).

[0088] Step (b) can be carried out under any conditions suitable for carrying out the radical polymerization or oligomerization of said at least one diphenylamine, optionally said at least one phenyl a-naphthylamine and any other possible reactant to be polymerized or oligomerized.

[0089] The temperature of step (b) is higher than or equal to 170°C. Preferably, this temperature is actually at least sufficient to promote the reaction triggered by the organic peroxide. Preferably, this temperature is between 180°C and 250°C, in particular between 180°C and 230°C.

[0090] According to the invention, "a temperature between 180°C and 250°C" comprises the following values and any interval between these values: 180; 185; 190; 195; 200; 205; 210; 215; 220; 225; 230; 235; 240; 245; 250.

[0091] According to the indications of the continuous reactor manufacturers and in a common way, to convert a chemical synthesis from a discontinuous (batch) mode to a continuous mode, it is recommended to reduce the reaction temperature (here also the temperature is reduced to a value lower than 160°C) compared to the temperature commonly used to carry out the reaction. Indeed, in particular due to its specific geometry and due to the pressure applied inside the reactor (the reaction is pushed by the pressure), the continuous reactor is able to obtain a better mixing and contact quality between the reactants of the starting components and significantly improves their contact, thus making it unnecessary to use high reaction temperatures or the same reaction temperatures as those commonly used in the process of the discontinuous method.

[0092] However, the Applicant has found, contrary to this and surprisingly and unexpectedly, that the temperature used in the batch mode, i.e. 150-160°C, does not induce any reaction in the continuous mode, unless the reaction temperature is increased above the usual reaction temperature (i.e.: 160°C), to allow the synthesis (triggering of the polymerization and polymerization with good yield) of oligomers and / or polymers comprising at least one diphenylamine repeating unit and optionally at least one phenyl a-naphthylamine unit to be continuous and complete (see below comparative and according to the present application embodiments).

[0093] Without being bound to any theory, but this unexpected phenomenon (increase of the temperature instead of decrease) seems to be related to the fact that the limiting reaction of this chemical synthesis is not the polymerization itself, but the dissociation of the peroxide into radicals. The latter reaction is a reversible monomolecular reaction, and therefore to shift the reaction equilibrium towards the synthesis of oligomers and / or polymers (i.e.: shift the equilibrium to the right), the reaction temperature should be increased above the usual temperature (the pressure in the reactor is likely to induce the recombination of the radicals into the starting peroxide, i.e. the pressure will promote the reverse reaction).

[0094] Step (b) can be performed in the presence of a back pressure (at the outlet), in particular to keep all the compounds present in the reactor, in particular the alcohol produced upon degradation of the organic peroxide, in liquid form. In particular, the back pressure can be between 3 and 20 bars, in particular between 10 and 16 bars. According to the present application, "a pressure between 3 and 20 bars" includes the following values and any interval between these values: 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20.

[0095] In general, step (b) is performed at a temperature between 180°C and 230°C, in particular between 190°C and 220°C, and at a pressure (inlet pressure and outlet back pressure) between 10 and 16 bars, or between 15 and 20 bars.

[0096] The residence time of the reactants in the reactor can be adjusted by the person skilled in the art in particular according to the temperature / pressure pair, the inlet flow rate of each reactant and the nature of the reactants. In general, the residence time of the reactants in the reactor is less than 10 minutes, preferably less than 5 minutes. In particular, the residence time of the reactants in the reactor can be between 1 minute and 5 minutes, optionally between 0 and 1 minute. Too long residence time of the reactants can lead to significant pressure drop problems, in particular related to the length of the channel and the number of baffles and obstacles, but also to a Gardner color of the sample which is too high compared to the requirements in certain application fields, in particular oils for the automotive or aerospace industry.

[0097] The Gardner colour scale is a visual comparative scale of the colour of a clear and transparent liquid. It comprises 18 levels numbered from 1 to 18, ranging from light yellow (Gardner colour 1) to dark brown (Gardner colour 18). The colour intensity goes from level 1 to level 18. However, the light shades go from level 1 to level 11, while the darker shades go from level 12 to 18. In particular, the levels of this Gardner colour scale can correspond to the following colours:

[0098] - scales 1 to 4: very light yellow to light yellow;

[0099] - scales 5 to 10: light yellow to yellow;

[0100] - scales 11 to 12: more intense yellow to orange yellow;

[0101] - scales 13-14: more intense orange yellow to orange;

[0102] - scales 15-16: more intense orange to orange / red;

[0103] - scale 17: reddish brown;

[0104] - scale 18: brown.

[0105] The continuous process according to the application makes it possible to obtain oligomers and / or polymers having a relatively moderate Gardner colour, in particular when they are dissolved in an ester lubricant. The Gardner colour of the oligomers and / or polymers obtained according to the application, dissolved at 1.5% by weight in an ester lubricant, is in particular lower than or equal to 12, preferably between 9 and 11. The continuous process according to the application achieves a good reproducibility of these Gardner colour values, in particular better than that obtained when this process is carried out in a discontinuous mode. As mentioned above, a Gardner colour grade of 9 to 11 after dilution of the lubricant in a base oil still corresponds to a light colour suitable for the lubricant field, in particular for the lubricant field used in the aeronautical or automotive industry.

[0106] Preferably, a step (bl) of withdrawing from the reactor at least one oligomer or polymer of diphenylamine and optionally of at least one phenyl a-naphthylamine, preferably dissolved in an ester lubricant, is carried out after step (b). Preferably, the withdrawal flow rate is equal to the inlet flow rate of the reactants of step (a).

[0107] Step (c) comprises subjecting the reaction mixture obtained in step (b), optionally withdrawn in step (bl) and optionally cooled in step (d) as described below, to conditions suitable for removing at least a part of the residual reactants and / or reaction by-products other than the oligomers or polymers comprising at least one diphenylamine unit and optionally at least one phenyl alpha-naphthylamine unit. The conditions for carrying out step (c) can vary to a large extent and can be adapted by the person skilled in the art in particular depending on the compounds to be removed, the reactor used and / or the conditions for carrying out step (b). In the context of the present step (c), the term "removing" a compound and variants thereof means separating said compound from the oligomers or polymers comprising at least one diphenylamine unit and optionally at least one phenyl alpha-naphthylamine unit. In particular, the removal can be carried out by evaporation or by distillation.

[0108] Among the residual reactants and / or reaction by-products that can be removed during step (c), one can in particular mention residual organic peroxide, said at least one residual diphenylamine, said at least one residual phenyl alpha-naphthylamine and said at least one alcohol resulting from the decomposition of the organic peroxide. In particular, when the organic peroxide is di-tert-butyl peroxide, said at least one alcohol resulting from the decomposition of the organic peroxide can be tert-butyl alcohol. In this case, step (c) comprises a step of removing the tert-butyl alcohol, preferably by evaporation.

[0109] In particular, step (c) can be carried out by evaporation of at least a part of the residual reactants and / or reaction by-products other than the oligomers or polymers comprising at least one diphenylamine unit and optionally at least one phenyl alpha-naphthylamine unit. The evaporation can be carried out in different ways. In some embodiments, the evaporation is carried out by a reduction of the pressure in at least one part of the reactor that has been used for carrying out step (b), the reduction of the pressure leading to the evaporation of all or a part of the compound(s) to be removed. Alternatively or additionally, the evaporation can be carried out by vacuum evaporation of the mixture obtained at the end of step (b) or (d), preferably after cooling as detailed below in step (d).

[0110] Step (c) can be carried out continuously at the outlet of the reactor or of the part of the reactor that has been used for carrying out step (b), or discontinuously in a different reactor. For example, the reactor used for carrying out step (c) can be a column evaporator.

[0111] Step (d) of cooling the at least one oligomer or polymer obtained at the end of step (b), for example withdrawn in step (bl), at a temperature referred to as "cooling temperature", can also be carried out after or before step (c). The cooling temperature is lower than the temperature at which step (b) is carried out and higher than or equal to room temperature. In particular, the cooling temperature can be between 50°C and 90°C, in particular can be about 70°C.

[0112] In particular, the continuous process according to the application is characterized by a reduced cycle time, the quality of the obtained oligomers or polymers, in particular the improvement of its color quality, the low variability of the technical features of the polymers or oligomers such as color and / or molecular weight distribution, the improved safety, the environmental advantages, the simplified maintenance, the space saving and the ease of use compared to the discontinuous processes known in the art.

[0113] In terms of cycle time, the reaction time is generally a few minutes, while for discontinuous processes, similar oligomerization or polymerization reaction times are generally 8 to 15 hours per cycle at industrial scale. In particular, this enables significant gains in terms of production capacity.

[0114] In terms of product quality, the oligomers or polymers of at least one diphenylamine and at least one phenyl a-naphthylamine obtained at the end of the process according to the application have a satisfactory coloration, which can be weaker than that obtained by discontinuous processes. In batch systems, the color variation is greatly enhanced compared to continuous systems. From one batch to another, it is possible to count up to 4 Gardner points of variation under the same operating conditions. In continuous systems, as is the case in the present application, the variation is less than 1 Gardner, preferably less than 0.5 G. In the field of high-performance lubricants such as automotive lubricants, the coloration of lubricants and additives such as antioxidants is a real concern, since a lubricant with a lower coloration is associated with a cleaner and newer lubricant and is therefore considered a sign of quality.

[0115] In addition, the process according to the application makes it possible to obtain constant performance and good reproducibility, and thus control of the parameters, such as the molar mass of the obtained oligomers and polymers, their molecular weight distribution and / or the content of oligomers or polymers in ester lubricants.

[0116] In terms of safety, the danger of the reaction is greatly reduced due to the relatively small volume of the reactor compared to the implementation in a discontinuous manner, in particular if one considers the specific risks associated with the use of exothermic oxidation / radical polymerization reactions. This element is an undeniable advantage of the process according to the application, since oxidation and polymerization reactions are the primary source of industrial accidents in the chemical field.

[0117] In terms of the environment, the loss of reactants such as peroxides is significantly reduced compared to discontinuous processes, which leads to a reduction of waste and effluents. By way of comparison, in conventional batch processes, which are run at between 140 and 170°C, the loss of unreacted alkyl peroxides, for example di-tert-butyl peroxide, is at least 50%. The continuous process according to the application enables a significant reduction of these organic peroxide waste compared to discontinuous processes, since values of less than 10% of unreacted peroxide can be achieved. In one embodiment according to the application, at least 90% of the organic peroxide, preferably at least 95%, in particular at least 99%, is reacted during the course of the reaction in step (b). Industrially, the reduction of the residual peroxide amount at the end of step (b) enables in particular a reduction of the chemical risks associated with the management of hazardous effluents, since peroxides are explosive under certain conditions, in particular during long-term storage in the presence of other reactants or volatile impurities. Low and even zero organic peroxide concentrations within the reactor and at the reactor outlet guarantee improved safety at the plant level and easy cleanability of the effluents.

[0118] Finally, the continuous process according to the application also offers advantages in terms of energy consumption, simplified maintenance, space saving and ease of use compared to discontinuous processes.

[0119] The present application also relates to an oligomer and / or polymer comprising at least one diphenylamine repeat unit and optionally at least one phenyl alpha-naphthylamine repeat unit, obtainable, in particular obtained, by the process according to the application. Advantageously, the oligomer and / or polymer comprising at least one diphenylamine repeat unit and optionally at least one phenyl alpha-naphthylamine repeat unit, obtainable, in particular obtained, by the process according to the application, is in solution in an ester lubricant.

[0120] In the present application, any range or any interval defined by a limit is to be understood as including the limits, unless otherwise stated.

[0121] Unless otherwise stated, the percentages indicated in the present application are percentages by weight.

[0122] "Room temperature" is to be understood in the present application as a temperature of about 25°C.

[0123] In the present application, the term "about" a numerical value V means an interval between 0.9 x V and 1.1 x V. In some embodiments, it means an interval between 0.95 x V and 1.05 x V, in particular an interval between 0.99 x V and 1.01 x V. Examples

[0124] Different tests were performed with the following raw materials:

[0125] A mixture of N,N-diphenylamines: N,N-diphenylamine, N,N-di-(p-tert-butylphenyl)amine, N,N-di-(p-tert-octylphenyl)amine, N-(p-tert-butylphenyl)-N-phenylamine, N-(p-tert-octylphenyl)-N-phenylamine and N-(p-tert-butylphenyl)-N-(p-tert-octylphenyl)amine, named as L57 and CAS number 68411-46-1 are known to be

[0126] 1-Phenylanthylamine: N-Phenyl 1,1,3,3-Tetramethylbutylnaphthalene-1-amine

[0127] -Organic peroxide: di-tert-butyl peroxide

[0128] - The amine was introduced as a mixture in the form of a 60% by weight solution of tris(hydroxymethyl)propane trinonyl ester.

[0129] - Introduced as an organic peroxide in the form of a 50% by mass solution of trimethylolpropane trinonyl ester.

[0130] Examples and comparative examples according to the continuous process of the present application (continuous process, temperature T° < 170°C)

[0131] For this comparative test, the applicant reproduced Example 2 of Patent EP 0 734 432 using the above-mentioned raw materials.

[0132] In particular, the experimental conditions and characteristics of the final product of this discontinuous method are summarized in Table I below:

[0133] [Table 1]

[0134]

[0135] Table I

[0136] Measure the amount of unreacted peroxides in the distillate. Measure the Gardner color (ASTM D6166-12 method) on a sample of 0.75 wt% active ingredient (amine polymer) in tri-monoate using a spectrometer.

[0137] This comparative test 1 was repeated three times. As shown in Table I above, the method according to the prior art has an unreacted peroxide content of about 65%. Such a high unreacted peroxide content represents a clear disadvantage - on the one hand from an economic point of view (loss of raw materials) and on the other hand from a safety point of view, since the storage and destruction of effluents containing peroxides is complex. Moreover, the method according to the prior art does not make it possible to obtain a final product having constant characteristics, in particular in terms of colour. The samples obtained from the discontinuous method according to the prior art do not have a constant colour, which can vary from 9.8 to 13.8 on the Gardner scale. However, a colour of 13.8 corresponds to a dark brown colour which is not suitable for the automotive and / or aeronautical field.

[0138] ​

[0139] By carrying out the reaction in a continuous manner in a reactor with Therminol fluid (supplied by Total) as heat transfer fluid Advanced-Flow TM The method according to the application was carried out in a G1 type glass reactor, producing several samples 1-8.

[0140] The raw materials used were the same as those mentioned above. The conditions used to carry out the reaction are summarised in Table 1 below. In particular, the cooling temperature was 70°C.

[0141] Comparative examples 2 to 7 were also carried out from the same raw materials and according to a substantially identical procedure (except for the temperature during the polymerisation step) according to a continuous method.

[0142] [Table 2]

[0143]

[0144] The results obtained in terms of percentage of residual monomer, unreacted peroxide and Gardner colour are reported in Table 3 below for each of the four samples.

[0145] The Gardner colour was measured on a 1.5% by weight sample of trimethylolpropane trisnonylate using a spectrophotometer, in particular according to the method described in the standards ASTM D6166-12 or ASTM D 1544. The colour was determined taking into account the absence of loss of peroxide or alcohol during the continuous reaction.

[0146] The percentage of residual monomer was determined by gas phase (GC) and supercritical (SFC) chromatography.

[0147] The percentage of unreacted peroxide was determined by gas chromatography.

[0148] [Table 3]

[0149]

[0150] Thus, the continuous process according to the present application is able to obtain oligomers of diphenylamine and phenyl α-naphthylamine in a few minutes, which contain less than 45.5% of residual monomers and have a light Gardner color, very suitable for lubricants, in particular to be used in the aeronautical and / or automotive industry. In particular, a reaction temperature of 180°C is able to obtain results at least similar to those of Comparative Example 1 of the discontinuous process according to the prior art, in terms of % of unreacted peroxide and % of residual monomers. However, the Gardner color of the final product is much lighter (Gardner color of 5.1 / 5.9 for Examples 1 and 2 at 180°C, while the Gardner color of Comparative Example 1 is 13.8). Moreover, when the reaction temperature is increased to at least 190°C, the continuous process according to the present application is able to obtain oligomers of diphenylamine and phenyl α-naphthylamine in a few minutes, which contain less than 5% of residual monomers, while having a light Gardner color (about 10). The characteristics of the product formed are also constant (constant Gardner color). Moreover, the minimum reaction temperature (170°C) during step (b) can also be obtained with other continuous type reactors able to use mixed mixtures composed of gas and liquid substances at lower pressures.

[0151] The process is carried out directly in the ester lubricant (in which diphenylamine, phenyl α-naphthylamine and organic peroxide are dissolved) in the absence of solvents,

[0152] Of course, various other modifications can be made to the present application within the scope of the appended claims.

Claims

1. A method for preparing at least one oligomer and / or polymer comprising at least one diphenylamine repeating unit and optionally at least one phenylα-naphthylamine repeating unit, comprising the following steps: (a) Introducing into a suitable reactor: -At least one diphenylamine, -Optionally at least one phenylα-naphthylamine, - at least one organic peroxide, and - At least one ester lubricant; (b) Polymerization or oligomerization of diphenylamine and optionally phenyl-α-naphthylamine to obtain a mixture comprising at least one oligomer or polymer, said oligomer or polymer comprising at least one diphenylamine unit and optionally at least one phenyl-α-naphthylamine unit, and (c) Applying conditions to the mixture obtained in step (b) suitable for reducing and / or removing at least a portion of residual reactants and / or reaction byproducts other than oligomers or polymers containing at least one diphenylamine unit and optionally at least one phenyl-α-naphthylamine unit. Steps (a) and (b) are performed consecutively, and step (b) is performed at a temperature of 180°C to 250°C.

2. The method of claim 1, wherein step (b) is performed at a temperature of 180°C to 230°C.

3. The method of claim 1, wherein the at least one diphenylamine is selected from N,N-di-(p-tert-butylphenyl)amine, N,N-di-(p-tert-octylphenyl)amine, N-(p-tert-butylphenyl)-N-phenylamine, N-(p-tert-octylphenyl)-N-phenylamine, N-(p-tert-butylphenyl)-N-(p-tert-octylphenyl)amine and any mixture thereof.

4. The method of claim 1, wherein the phenyl α-naphthylamine is N-phenyl 1,1,3,3-tetramethylbutylnaphthyl-1-amine.

5. The method of claim 1, wherein the polymer and / or oligomer obtained by the method according to the invention contains only diphenylamine and phenyl-α-naphthylamine repeating units in its structure.

6. The method of claim 1, wherein the at least one diphenylamine and / or the at least one phenyl-α-naphthylamine is introduced into the reactor in the form of a solution in an ester lubricant.

7. The method of claim 1, wherein the organic peroxide is di-tert-butyl peroxide.

8. The method of claim 1, wherein the ester lubricant is selected from trimethylolpropane trinonanoate and esters made from pentaerythritol and at least one branched carboxylic acid containing nine carbon atoms.

9. The method of claim 1, wherein the method comprises, prior to step (a1): premixing at least two of the at least one diphenylamine, the at least one phenyl-α-naphthylamine, the ester lubricant, and the organic peroxide to form a solution comprising them.

10. The method of claim 1, wherein the method comprises, prior to step (a), step (a2): preheating the at least one diphenylamine, the at least one phenyl-α-naphthylamine, the ester lubricant, the organic peroxide, and / or a solution comprising at least two of them at a temperature above room temperature and below or equal to the temperature at which step (b) is performed.

11. The method of claim 1, wherein step (d) is performed after or before step (c): cooling the at least one oligomer or polymer of diphenylamine and optionally at least one phenyl-α-naphthylamine obtained at the end of step (b) at a temperature lower than that at which step (b) is performed and higher than or equal to room temperature.

12. The method of claim 1, wherein the mixture obtained in step (b) contains less than or equal to 60% unreacted peroxide content, the peroxide content being determined by gas chromatography.

13. The method of claim 12, wherein the mixture obtained in step (b) contains less than or equal to 45% unreacted peroxide content, the peroxide content being determined by gas chromatography.

14. The method of claim 13, wherein the mixture obtained in step (b) contains less than or equal to 40% unreacted peroxide content, the peroxide content being determined by gas chromatography.

15. The method of claim 1, wherein the mixture obtained in step (b) contains less than or equal to 25% residual monomer content, the residual monomer content being a mass percentage determined by gas chromatography (GC) and supercritical fluid chromatography (SFC).

16. The method of claim 15, wherein the mixture obtained in step (b) contains less than or equal to 10% residual monomer content, the residual monomer content being a mass percentage determined by gas chromatography (GC) and supercritical fluid chromatography (SFC).

17. The method of claim 16, wherein the mixture obtained in step (b) contains less than or equal to 5% residual monomer content, the residual monomer content being a mass percentage determined by gas chromatography (GC) and supercritical fluid chromatography (SFC).

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