PURIFICATION OF ALKYL HYDROPEROXIDE BY EXTRACTIVE DISTILLATION

Abstract

The invention relates to a method for purifying an alkyl hydroperoxide from dialkyl peroxide thereof, comprising a step of distillation in the presence of alcohol and water followed by extraction of the condensates using a hydrocarbon or a hydrocarbon blend.

Claims

1-16. (canceled)

17. A process for separating an alkyl hydroperoxide from a dialkyl peroxide, comprising the steps of: a) distilling a composition comprising the alkyl hydroperoxide and said dialkyl peroxide in the presence of alcohol and water, and b) extracting the dialkyl peroxide with the aid of a hydrocarbon.

18. The process as claimed in claim 17, wherein the alkyl hydroperoxide is selected from the group consisting of tert-butyl hydroperoxide, tert-amyl hydroperoxide, hexylene glycol hydroperoxide, tert-octyl hydroperoxide, tert-hexyl hydroperoxide, 1-methylcyclopentyl hydroperoxide and 1-methylcyclohexyl hydroperoxide.

19. The process as claimed in claim 17, wherein the dialkyl peroxide is selected from the group consisting of di-tert-butyl, di-tert-amyl peroxide, di(3-hydroxy-1,1-dimethylbutyl) peroxide, di-tert-octyl peroxide, di-tert-hexyl peroxide, di(1-methylcyclopentyl) peroxide and di(1-methylcyclohexyl) peroxide.

20. The process as claimed in claim 17, wherein the content by weight of alcohol present in step a) is greater than 5 times that of said dialkyl peroxide.

21. The process as claimed in claim 17, wherein the extraction step b) is performed by contacting said hydrocarbon with the condensate obtained in step a) so as to obtain an organic phase containing said hydrocarbon and also all or some of the dialkyl peroxide and an aqueous phase containing the hydroperoxide, the water and the alcohol.

22. The process as claimed in claim 17, wherein the hydrocarbon is selected from the group consisting of C.sub.6 to C.sub.12 hydrocarbons.

23. The process as claimed in claim 17, wherein the aqueous phase obtained in step a) is recycled to the reboiler of the distillation.

24. The process as claimed in claim 17, wherein the organic phase from the condenser is distilled in order to separate the hydrocarbon(s) from the dialkyl peroxide.

25. The process as claimed in claim 17, wherein the distillation step a) is carried out at a temperature of between 25° C. and 60° C.

26. The process as claimed in claim 17, wherein the distillation step a) is carried out at a pressure of between 30 and 200 mbar (millibars).

27. The process as claimed in claim 17, wherein it comprises a step a′), prior to step a), of synthesizing said alkyl hydroperoxide in an acidic medium.

28. A composition of alkyl hydroperoxide obtainable by the process as claimed in claim 17.

29. The composition as claimed in claim 28, comprising less than 1% by weight of alcohol, relative to the total weight of the composition.

30. The composition as claimed in claim 28, comprising less than 1000 ppm of hydrocarbon relative to the total weight of said composition.

31. The composition as claimed in claim 28, wherein the alkyl hydroperoxide comprises from 5 to 8 carbon atoms.

32. The composition as claimed in claim 28, comprising less than 1000 ppm of dialkyl peroxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0051] Distillation, evaporation and extraction are methods well known per se to the person skilled in the art.

[0052] The condensation of the distillation top product comprising the dialkyl peroxide to be removed, that is to say the condensation step, preferentially takes place between −30° C. and 0° C., preferentially between −20° C. and −10° C. The distillation top product is recovered by any means well known to the person skilled in the art, such as for example a condenser.

[0053] During the passage of the composition comprising the dialkyl peroxide to be removed into a hydrocarbon, the hydrocarbon is maintained in liquid form by adjustment of the temperature, this preferentially being between −30° C. and 0° C., very preferentially between −20° C. and −10° C., in order to limit the risk of boiling of the alcohol phase and to maintain good separation of the phases during the selective capturing of the dialkyl peroxide by the hydrocarbon.

[0054] The hydrocarbon is preferably chosen from hydrocarbons comprising from 6 to 12 carbon atoms. Said hydrocarbons comprising from 6 to 12 carbon atoms remain liquid at the condensation temperature of the distillation top product. C.sub.7 hydrocarbons are preferred for their ease of removal in the event of entrainment with the alcoholic solution into the reboiler during its recycling.

[0055] On contact of the top composition with the hydrocarbon, two phases form, an upper organic phase consisting of the dialkyl peroxide and the hydrocarbon and a lower aqueous phase comprising the mixture of water and alcohol.

[0056] Advantageously, the choice of hydrocarbon allows for selective retention of the dialkyl peroxide such as DTA or DI.

[0057] The aqueous phase can thus be recycled into the mixture to be purified so as to enable the depletion of dialkyl peroxide by means of distillation. The recycling can be done continuously or batchwise.

[0058] The purification process according to the invention, that is to say including the evaporation of the alcoholic composition, its condensation, its extraction by the hydrocarbon and the recycling of the aqueous phase generated, can be performed batchwise, semi-continuously or continuously, depending on the manner in which the peroxide to be purified, the alcohol, the water and the hydrocarbon are supplied.

[0059] During the distillation, the hydrocarbon becomes concentrated in dialkyl peroxide. This hydrocarbon solution can be withdrawn and renewed continuously. This hydrocarbon solution comprising the dialkyl peroxide can be distilled so as to recycle the hydrocarbon to the purification process according to the invention, and to profitably exploit the dialkyl peroxide thus isolated.

[0060] At the end of the batch distillation according to the invention, the purified mixture generally comprises the alkyl hydroperoxide, water and alcohol. A major amount of water and alcohol can be removed by any means well known to the person skilled in the art, for example by evaporation, for example by heating the mixture to a temperature of between 30 and 50° C., under reduced pressure of between 60 and 200 mbar.

[0061] During the distillation process, the degradation of the alkyl hydroperoxide is between 0% and 1% by weight relative to the organic peroxide initially present in the solution to be purified.

[0062] The separation process according to the invention can comprise a step a′), prior to step a), of synthesizing said alkyl hydroperoxide.

[0063] Step a′) of synthesizing the alkyl hydroperoxide can be effected by any method known to the person skilled in the art which leads to the formation of dialkyl peroxide as an impurity. In particular, step a′) can be performed via the reaction of at least one alcohol or at least one alkene with hydrogen peroxide in the presence of an acid, preferably sulfuric acid. Such a process results in particular in the synthesis of dialkyl peroxide as impurities.

[0064] Preferably, the alkyl hydroperoxide can be prepared in an acidic medium.

[0065] In this case, synthesis step a′) consists in particular in reacting oxygenated water (hydrogen peroxide) in the presence of at least one alcohol or at least one alkene in an acidic medium.

[0066] Preferably, synthesis step a′) consists in particular in reacting oxygenated water (hydrogen peroxide) in the presence of at least one alcohol or an unsaturated compound in an acidic medium.

[0067] Synthesis step a′) may be effected at a temperature which can range from 10° C. to 80° C., preferably from 20° C. to 40° C.

[0068] Preferably, synthesis step a′) is effected in the presence of one or more inorganic or organic acids, in particular one or more inorganic acids.

[0069] More preferentially, the inorganic acid is sulfuric acid.

[0070] The composition comprising at least one alkyl hydroperoxide and at least one dialkyl peroxide (before step a)) can comprise at least 50% by weight of alkyl hydroperoxide, preferably at least 60% by weight of alkyl hydroperoxide, more preferentially at least 68% by weight of alkyl hydroperoxide, even more preferentially at least 70% by weight of alkyl hydroperoxide, relative to the total weight of organic peroxides.

[0071] According to some embodiments, the composition comprising an alkyl hydroperoxide and a dialkyl peroxide (before step a)) comprises from 0.1% to 40% by weight of dialkyl peroxide, preferably from 1% to 30% by weight of dialkyl peroxide, more preferentially from 2% to 22% by weight of dialkyl peroxide, even more preferentially from 3% to 20% by weight of dialkyl peroxide, relative to the total weight of alkyl hydroperoxide and dialkyl peroxide.

[0072] The present invention also relates to a composition of alkyl hydroperoxide obtainable by the process according to the invention.

[0073] Preferably, the composition thus obtained comprises less than 1% by weight of alcohol, preferably less than 1000 ppm, and even more preferably less than 100 ppm, relative to the total weight of the composition.

[0074] Advantageously, the composition thus obtained comprises less than 1000 ppm of hydrocarbon relative to the total weight of said composition, preferably less than 100 ppm.

[0075] Another subject of the present invention relates to a purified composition of alkyl hydroperoxide comprising less than 1000 ppm of dialkyl peroxide, preferentially less than 500 ppm, preferentially less than 250 ppm, and more preferentially less than 100 ppm of dialkyl peroxide.

[0076] Preferably, said composition is an aqueous composition containing at least 60% by weight of alkyl hydroperoxide, as defined above, and less than 1000 ppm by weight of dialkyl peroxide as defined above, the proportions being calculated by weight relative to the total weight of the composition.

[0077] Preferably, the aqueous composition contains at least 70% by weight of alkyl hydroperoxide, as defined above, more preferentially at least 80% by weight.

[0078] Preferably, the group R of the alkyl hydroperoxide as defined hereinabove represents a branched, optionally substituted C.sub.4-C.sub.8, preferably C.sub.5-C.sub.8, more preferentially C.sub.5-C.sub.6, even more preferentially C.sub.5, alkyl group.

[0079] The alkyl hydroperoxide is preferably chosen from the group consisting of tert-amyl hydroperoxide, hexylene glycol hydroperoxide, tert-octyl hydroperoxide and tert-hexyl hydroperoxide.

[0080] More preferentially, the alkyl hydroperoxide is tert-amyl hydroperoxide (TAHP).

[0081] Advantageously, the aqueous composition contains less than 800 ppm by weight, preferably less than 700 ppm by weight of dialkyl peroxide, preferably less than 500 ppm by weight of dialkyl peroxide, preferably less than 250 ppm by weight of dialkyl peroxide, more preferentially less than 100 ppm by weight of dialkyl peroxide, relative to the total weight of the composition.

[0082] Preferably, the dialkyl peroxide chosen from the group consisting of di-tert-amyl peroxide, di(3-hydroxy-1,1-dimethylbutyl) peroxide, di-tert-octyl peroxide and di-tert-hexyl peroxide.

[0083] More preferentially, the dialkyl peroxide is di-tert-amyl peroxide.

[0084] Advantageously, the composition is a composition of tert-amyl hydroperoxide and comprises less than 1000 ppm of dialkyl peroxide, preferentially less than 1000 ppm of tert-amyl peroxide (DTA).

[0085] Advantageously, the aqueous composition contains at least 60% by weight of tert-amyl hydroperoxide (TAHP) and less than 1000 ppm by weight of di-tert-amyl peroxide (DTA), the proportions being calculated by weight relative to the total weight of the composition.

[0086] The present invention also relates to the use of the composition as defined above for the preparation of crosslinking agent(s) or polymerization initiator(s).

[0087] Preferably, the initiator(s) is or are initiators of free-radical polymerization, in particular of ethylene under high pressure.

[0088] For the purposes of the present invention, “high pressure” means a pressure greater than 50 MPa. Preferably, the pressure varies from 500 bar (50 MPa) to 3000 bar (300 MPa), preferentially from 1200 bar (120 MPa) to 3000 bar (300 MPa), better still from 1200 bar (120 MPa) to 2600 bar (260 MPa).

[0089] Preferably, the crosslinking agents or the polymerization initiators are chosen from the group consisting of organic peroxides, in particular peroxyesters, hemiperoxyacetals and peroxyacetals.

[0090] The term “hemiperoxyacetal” means a compound of the general formula (R.sub.3)(R.sub.4)C(—OR.sub.1)(—OOR.sub.2), in which:

[0091] R.sub.1 represents a linear or branched, preferably C.sub.1-C.sub.12, preferably C.sub.1-C.sub.4, more preferably C.sub.1, alkyl group, or a cycloalkyl group with R.sub.2,

[0092] R.sub.2 represents a linear or branched, preferably C.sub.1-C.sub.12, preferably C.sub.4-C.sub.12, more preferably C.sub.5, alkyl group, or a cycloalkyl group with R.sub.1,

[0093] R.sub.3 represents a hydrogen atom or a linear or branched, preferably C.sub.1-C.sub.12, more preferably C.sub.4-C.sub.12, alkyl group, or a cycloalkyl group with R.sub.4,

[0094] R.sub.4 represents a hydrogen atom or a linear or branched, preferably C.sub.1-C.sub.12, more preferably C.sub.4-C.sub.12, alkyl group, or a cycloalkyl group with R.sub.3.

[0095] Preferably, R.sub.3 forms a cycloalkyl group with R.sub.4.

[0096] Preferably, when R.sub.3 is a hydrogen atom, R.sub.4 is a linear or branched, preferably C.sub.1-C.sub.12, more preferably C.sub.4-C.sub.12, alkyl group.

[0097] In the description of the present invention, the percentages are indicated by weight;

[0098] “ppm” signifies parts per million by weight.

[0099] The examples that follow illustrate the invention without limiting it.

EXAMPLES

Example 1: Purification by Extractive Distillation of a Solution of TAHP

Set-up:

[0100] The set-up consists of a flask surmounted by a distillation column equipped with temperature measurement means at the bottom and at the top. A condenser is attached at the top of the column to condense the vapors.

[0101] The system for recovering/separating the overhead vapors (Dean-Stark type) is connected to the condenser and has a cooled jacket. This system contains the hydrocarbon which makes it possible to recover the DTA and the methanolic aqueous phase.

[0102] This system is equipped with a bottom valve which makes it possible to recycle the lower methanolic aqueous phase to the reboiler of the column.

[0103] The reboiler is stirred and heated. The distillation is carried out under a vacuum of approximately 110 mbar. At equilibrium, the temperature of the reboiler is approximately 31° C. and at the top of the column is approximately 28° C.

[0104] The vapors condense in the condenser and the condensate falls into the hydrocarbon. On contact with the hydrocarbon, two phases form. The DTA is selectively retained in the upper organic phase and the methanol forms with the water the lower methanolic aqueous phase which is recycled to the reboiler.

[0105] The distillation is continued by proceeding in the manner described until virtually all of the DTA is removed from the reboiler.

Starting Mixture:

[0106] The mixture to be distilled is produced by mixing commercial TAHP, comprising DTA, with methanol and water so as to obtain the following composition of: 58.7 g of TAHP, 3.1 g of DTA, 74.5 g of methanol and 79.8 g of water.

[0107] Into the (Dean-Stark) recovery/separation system are introduced 2.1 g of water, 3.9 g of methanol and 15.7 g of isododecane hydrocarbon.

[0108] At the end of extractive distillation, 200.8 g of solution containing 0.02 g of DTA, 57.5 g of TAHP and 65.6 g of methanol are recovered in the reboiler.

[0109] 18.5 g of hydrocarbon phase containing 3 g of DTA and 15.5 g of hydrocarbon are recovered in the distillation top product.

[0110] After the removal of the DTA, the contents of the reboiler are distilled to remove the methanol in the same experimental system. The procedure is similar to the preceding one, except that nothing is recycled to the reboiler during this second distillation. Thus, 102.0 g of the previous mixture (composed of 28.3 g of TAHP, 33.8 g of MeOH and 39.9 g of water) are introduced into the reboiler. The distillation is then performed with a bath temperature of 32 to 35° C. and a partial vacuum of from 120 to 80 mbar. After distillation, the solution in the reboiler separates into 2 phases, the upper organic phase (27.6 g) is composed of 23.3 g of TAHP, 0.25 g of methanol and 4 g of water. DTA is no longer detected by gas-phase chromatography within the detection limit of <100 ppm. The lower aqueous phase (27.2 g) is composed of 1.5 g of TAHP, 0.4 g of methanol and 25.3 g of water. At the top of the column, 3.2 g of TAHP are recovered with the condensed methanol.

[0111] This example shows the possibility of reducing the amount of DTA present in the commercial TAHP to a content of around one hundred ppm (0.01%), by virtue of the extractive distillation according to the invention, and in total safety.

Example 2

Example 2a: Extractive Distillation of TAHP using Alcohols other than Methanol

[0112] Extractive distillation as described in example 1 was performed with alcohols other than methanol, such as tert-amyl alcohol and ethanol. The distillation of these mixtures was performed under total reflux for around one hundred minutes at 40° C. The DTA/alcohol/water mixtures subjected to distillation were mixed in a 1:1:1 weight ratio.

[0113] The products obtained in the distillation top product are presented below.

TABLE-US-00001 TABLE 1 P (mbar) at Alcohol TAHP % DTA % Alcohol % 40° C. Methanol 1.1 8.3 75.1 150 Tert-amyl 3.1 4.6 57.9 74 alcohol Ethanol 3.1 6.8 60.1 93

[0114] These experiments show that the process according to the invention, comprising a step of distillation in the presence of water and of the alcohols mentioned above, makes it possible to obtain a high entrainment rate of DTA to be removed.

[0115] These experiments also show that methanol is particularly advantageous for leading to a high entrainment rate of DTA to be removed, while at the same time minimizing the entrainment rate of TAHP in the distillation top product.

Example 3: Removal of di-tert-butyl Peroxide (DI) in Tert-butyl Hydroperoxide (TBH)

[0116] The set-up created corresponds to the set-up of example 1. The starting mixture is composed of 34.7 g of tert-butyl hydroperoxide (TBH), 2.7 g of di-tert-butyl peroxide (DI), 49.4 g of methanol and 62.4 g of water. This mixture is placed in the flask at the distillation bottom.

[0117] The Dean-Stark apparatus is initially charged with a methanolic aqueous phase composed of 2.4 g of water, 1.7 g of methanol, and an upper phase of 6.9 g of isododecane. The amount of DI present in the distillation bottom in the initial TBH thus diluted is 1.8% by weight of the methanolic composition.

[0118] The flask is heated with the aid of a water bath, set to 35° C., and is stirred with a magnetic bar at 500 rpm. The distillation is performed under a vacuum of between 112 mbar (millibar) and 106 mbar, in order to maintain a top temperature of between 28° C. and 30° C. The condensates are recovered in the Dean-Stark apparatus containing the isododecane. Thus, 2 phases appear, the upper hydrocarbon phase containing the DI and a lower water-methanol phase. The latter is recycled to the bottom. The method makes it possible to reduce the amount of DI to 0.17% by weight of the bottom composition by the selective removal permitted by the capture of the DI in the hydrocarbon, according to the invention. If the distillation is continued further, the amount of DI is lowered further to 0.07% in the bottom composition.

Example 4: Simple Distillation of the Mixture as in Example 3 Without Hydrocarbon in the Dean-Stark Apparatus

[0119] A mixture comprising TBH, DI, MeOH and water, of the following weight composition: DI/methanol/water/TBH 3.5%/32.6%/64.0%/27.9% respectively, was distilled but without hydrocarbon in the Dean-Stark apparatus. The condensed vapors were not recycled to the reboiler. GC analysis of the distillation top product at equilibrium indicates a DI/MeOH/water/TBH composition of 48.2%/36.5%/10.7%/4.6% (top temperature of between 30.4° C. and 31° C. and a pressure of between 115 mbar and 119 mbar). After 180 minutes, the analysis of the distillation bottom indicates a depletion of DI, but not as significantly as in example 3 since it still represents 2.1% for 28.9% of TBHP and 31.6% of methanol. This experiment shows that in the absence of recovery of the DI by extraction with hydrocarbon, the recycling of methanol to the bottom is not possible and the distillation is no longer as efficient.