WO2001066506A1

WO2001066506A1 - Method for oxidising hydrocarbons into acids

Info

Publication number: WO2001066506A1
Application number: PCT/FR2001/000685
Authority: WO
Inventors: Eric Fache
Original assignee: Rhodia Polyamide Intermediates
Priority date: 2000-03-08
Filing date: 2001-03-07
Publication date: 2001-09-13
Also published as: KR20020079994A; FR2806078B1; FR2806078A1; EP1265836A1; TW574202B; CN1430593A

Abstract

The invention concerns a method for oxidising hydrocarbons, in particular saturated aliphatic hydrocarbons, whether or not branched, cycloaliphatic or alkylaromatic hydrocarbons into acid or polyacid compounds. More particularly, the invention concerns oxidation of cyclohexane into adipic acid with an oxidising agent containing molecular oxygen, in the presence of a fluorinated compound, enabling easier separation and recycling of unreacted cyclohexane from the oxidation intermediates.

Description

PROCESS FOR THE OXIDATION OF HYDROCARBONS TO ACIDS

The present invention relates to a process for the oxidation of hydrocarbons, in particular of branched or unbranched saturated aliphatic hydrocarbons, of cycloaliphatic or alkylaromatic hydrocarbons to acid or polyacid compounds

It relates more particularly to oxidation by an oxidizing agent containing molecular oxygen of cyclohexane to adipic acid

The oxidation of cyclohexane to adipic acid is a process which has been studied for many years. Indeed, adipic acid is an important chemical compound used as raw material in many manufacturing such as the production of polymers such as polyamides, polyesters or polyurethanes

Several methods of manufacturing adipic acid from hydrocarbons such as benzene, phenol, cyclohexene cyclohexane have been proposed

Oxidation of cyclohexane either directly or in two stages are the most advantageous ways to produce adipic acid

Thus, American patent 2,223,493 published in December 1940, describes the oxidation of cyclic hydrocarbons to corresponding diacids, in the liquid phase generally comprising acetic acid, at a temperature of at least 60 ° C, using '' a gas containing oxygen and in the presence of an oxidation catalyst such as a cobalt compound

Many other patents and articles describe this reaction for the direct oxidation of cyclohexane to adipic acid. However, to obtain acceptable yields for the production of adipic acid, these documents describe the use of acetic acid as solvent, in the presence of either homogeneous catalyst or heterogeneous catalyst Mention may be made, by way of illustration, of the article which appeared in the journal "Chemtech", 555-559 (September 1974), the author of which is K Tanaka, which summarizes and comments on the oxidation process Direct mention of cyclohexane One can also cite the American patents 3,231, 608, 4,032,569, 4,158,73, 4,263,453 and 5,321, 157, the European patent 870751 which describe different homogeneous catalytic systems li has also been proposed direct oxidation processes of cyclohexane presence of heterogeneous catalyst such as aluminophosphates substituted by cobalt, as in European patent n ° 519569

The choice of solvent, namely acetic acid, is an important characteristic for obtaining an acceptable cyclohexane conversion rate and production of adipic acid. The use of such a solvent has many drawbacks caused by, for example, its corrosive nature at the temperature and pressure conditions used In addition, the use of this solvent poses many problems for the stages for separation and extraction of the adipic acid produced and the recycling of various compounds

Indeed, in the presence of acetic acid, it is difficult to separate and extract from the reaction medium the compounds by-products of oxidation such as cyclohexanone and cyclohexanol formed

In addition, the extraction of adipic acid by crystallization and its purification are made difficult because the cold solubility of this acid is higher at 25 ° C in acetic acid and lower at 80 ° C in acid acetic only in water

The separation and recycling of the homogeneous catalyst is also difficult in the presence of acetic acid. In fact, on the one hand recycling the catalyst without extracting it does not make it possible to retain sufficient catalytic activity, and on the other hand operations for separating the catalyst before recycling, as described in particular in French patents no. 2722783, 2746671, are complex and costly In addition, this solvent makes it difficult and costly to dehydrate the reaction medium

A few single-step oxidation processes of cyclohexane to adipic acid have also been proposed without the use of acetic acid. Some propose to carry out this reaction in the absence of solvents, others with solvents such as organic esters such as acetates (US 4,098,817), acetone (US 2,589,648) or alcohols such as butanol, methanol , cyclohexanol or acetonitrile (Ep 784045)

These processes generally lead to very low adipic acid selectivities. In addition, the solvents used often have low stability under the conditions of oxidation of the hydrocarbon such as cyclohexane. This low stability causes significant consumption of the solvent, which makes it unusable to such processes

One of the aims of the present invention is to propose a process for the oxidation of hydrocarbons in a single step to produce acids or polyacids, in a liquid medium under the conditions of the oxidation reaction and allowing separation of the acid produced and recycling of the catalyst by simple operations with acceptable yields

To this end, the invention provides a process for the oxidation of substituted or unsubstituted saturated aliphatic or cycloahphatic hydrocarbons or of alkylaromatic hydrocarbons to acids or polyacids in a liquid medium by an oxidizing agent comprising molecular oxygen, characterized in that one of the constituents of the liquid medium is a fluorinated organic compound According to the invention, the fluorinated organic compound is a compound which must form, at the temperature and pressure conditions of the oxidation reaction, at least one homogeneous liquid phase with the hydrocarbon (s) to be oxidized. Thus, the fluorinated compound may be, advantageously at least partially miscible with the hydrocarbon (s) to be oxidized, under the temperature and pressure conditions used to carry out the oxidation reaction.

By at least partially miscible is meant that, under the conditions of the oxidation reaction, the solubility of one compound in the other is at least greater than 2% by weight, and that a homogeneous liquid phase comprising at least one part of the hydrocarbons to be oxidized and of the fluorinated organic compound is formed.

In a preferred embodiment of the invention, the miscibility between the hydrocarbon and the fluorinated compound is such that, under the conditions of implementation of the invention, these two compounds form a single homogeneous liquid phase.

By fluorinated compound, it is necessary to understand either a single compound, or a mixture of fluorinated compounds. These compounds may be liquid or solid, in the latter case they will be dissolved in the hydrocarbon to be oxidized, in particular under the conditions of implementation of the invention.

In addition, and obviously, these fluorinated compounds are stable at least, under the conditions for carrying out the oxidation reaction described later. Advantageously, these suitable fluorinated compounds can be chosen from the group comprising

- fluorinated aliphatic hydrocarbons or perfluorinated cyclic or acyclic, aromatic fluorinated hydrocarbons, such as perfluorotoluene, perfluoromethylcyclohexane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluorononane, perfluorodecalin, perfluoromethyldecalin, α, α, α-trifluorotoluene, 1, 3-bis (methyl trifluoropropyl) benzene.

- Perfluorinated or fluorinated esters such as alkyl perfluorooctanoates, alkyl perfluoronanoates

- Fluorinated or perfluorinated ketones or ethers such as perfluorinated acetone - Fluorinated or perfluorinated alcohols such as hexanol, octanoi, nonanol, perfluorinated decanol, perfluorinated t-butanol, perfluorinated isopropanol, hexafluoro-1, 1, 1, 3,3,3-propanol -2

- Fluorinated or perfluorinated nitrite such as perfluorinated acetonitrile

- Fluorinated or perfluorinated acids such as frifluoromethyl benzoic acids, pentafluorobenzoic acid, hexanoic, heptanoic, octanoic, nonanoic acid, perfluorinated adipic acid, perfluorinated

- Fluorinated or perfluorinated halides such as perfluorinated iodo octane, perfluorinated bromooctane - Fluorinated or perfluorinated amines such as perfluorinated tpropylamine, perfluorinated tributylamine, perfluorinated tripentylamine

The concentration of fluorinated compounds in the liquid oxidation medium can vary within wide limits. Thus, it can be between 1 and 99% by weight relative to the total weight of the liquid medium, more advantageously it can be between 10 and 80. % by weight of the liquid medium

It is also possible without departing from the scope of the invention, to use the fluorinated component in combination with another compound which may in particular have the effect of improving the selectivity and / or the productivity of the oxidation reaction in adipic acid

As an example of such compounds, mention may be made, in particular, of organic acids, nitriles. As more particularly suitable compounds, mention may be made of acetic acid, propionic acid, butyric acid, valéπque acid, acids. lipophiies comprising at least 6 carbon atoms, nitrates such as acetonitrile, benzonitrile, halogenated derivatives such as dichloromethane

The oxidation is carried out, in general, in the presence of a catalyst. This catalyst advantageously comprises a metallic element chosen from the group comprising Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Al, Ga , In, Tl, Se, Y, Ti, Zr, Hf, Ge, Sn, Pb, V, Nb, Ta, Cr, Mo, W, Mn, Te, Re, Fe, Ru, Os, Co, Rh, Ir , Ni, Pd, Pt, lanthanides like Ce and combinations thereof

These catalytic elements are used either in the form of compounds advantageously at least partially soluble in the liquid oxidation medium under the conditions for carrying out the oxidation reaction, or supported, absorbed or linked to an inert support such as silica , alumina The catalyst is preferably, in particular under the conditions for carrying out the oxidation reaction

- Either soluble in the hydrocarbon to be oxidized,

- Either soluble in the fluorinated compound,

- Either soluble in the hydrocarbon / fluorinated compound mixture forming a homogeneous liquid phase under the conditions for carrying out the reaction

According to a preferred embodiment of the invention, the catalyst used is soluble in the hydrocarbon to be oxidized and / or in the fluorinated compound to allow recycling of this catalyst

By the term soluble, it is meant that the catalyst is at least partially soluble in the medium considered

In the case of heterogeneous catalysis, the catalytically active metallic elements are supported or incorporated in a micro or mesoporous mineral matrix or in a polymeπque matrix or are in the form of organometallic complexes grafted onto an organic or mineral support By incorporated, it is meant that the metal is an element of the support or that one works with complexes sterically trapped in porous structures under the conditions of oxidation

In a preferred embodiment of the invention, the homogeneous or heterogeneous catalyst consists of salts or metal complexes of groups IVb (group of Ti), Vb (group of V), Vllb (group of Cr), Vllb ( Mn group), VIII (Fe or Co or Ni group), Ib (Cu group), and cerium, alone or as a mixture The preferred elements are, in particular, Co and / or Mn and / or Cr and / or Zr, Hf, Ce and or Zr, Hf The metal concentration in the liquid oxidation medium varies between 0.00001 and 5% (% by weight), preferably between 0.001% and 2%

The invention applies more particularly to the oxidation of cycloaliphatic compounds such as cyclohexane, cyclododecane leading respectively to adipic acid and dodecanoic acid

According to a preferred embodiment of the invention, it relates to the direct oxidation of cyclohexane to adipic acid, by an oxygen-containing gas, in liquid medium and in the presence of a catalyst. The catalyst preferably comprises cobalt

The oxidation reaction is carried out at a temperature between 50 ° C and 200 ° C, preferably between 70 ° C and 180 ° C. It can be carried out under atmospheric pressure However, it is generally carried out under pressure for maintain the components of the reaction medium in liquid form The pressure can be between 10 KPa (0.1 bar) and 20,000 KPa (200 bar), preferably between 100Kpa (1 bar) and 10,000 Kpa (100 bar)

The oxygen used can be in pure form or in admixture with an inert gas such as nitrogen or helium. It is also possible to use air more or less enriched with oxygen. The quantity of oxygen supplied to the medium is advantageously between 1 and 1000 moles per mole of compounds to be oxidized

The oxidation process can be carried out continuously or according to a discontinuous process Advantageously, the liquid reaction medium leaving the reactor is treated according to known methods allowing on the one hand to separate and recover the acid produced and on the other hand to recycle non-oxidized or partially oxidized organic compounds such as cyclohexane, cyclohexanol and / or cyclohexanone, the catalyst and the fluorinated compound.

The amount of catalyst, expressed as a percentage by weight of cobalt relative to the reaction mixture, is generally between 0.00001% and 5% and preferably between 0.001% and 2%, without these values being critical. '' have sufficient activity while not using too large quantities of a catalyst which must then be separated from the final reaction mixture and recycled The catalyst, in addition to cobalt, can also comprise other compounds based on metals chosen from the group comprising manganese, copper, cerium, vanadium, chromium, zirconium, hafnium or a combination of some of these elements It is advantageous to also use a compound which initiates the oxidation reaction, such as for example a ketone or an aldehyde Cyclohexanone which is a reaction intermediate in the case of the oxidation of cyclohexane, is very particularly indicated Generally, the initiator represents from 0.01% to 20% by weight of the weight of the reaction mixture used, without these proportions having a critical value. The initiator is especially useful when starting the oxidation and when performs oxidation at a temperature below 120 ° C II can be introduced at the start of the reaction

The oxidation can also be carried out in the presence of water introduced from the initial stage of the process. As indicated above, the reaction mixture resulting from the oxidation is subjected to different operations of separation of some of its constituents for, by example, allowing the recycling of certain constituents such as the non-oxidized hydrocarbon, the oxidation intermediates, the catalyst, at the level of the oxidation and the recovery of the acids produced. According to a first variant of the process, it is possible to submit first of all the crude reaction mixture at cooling to a temperature of 16 ° C to 30 ° C for example, which causes the crystallization of at least part of the acid formed. A medium is thus obtained comprising a solid phase consisting essentially of acid, at least one organic liquid phase containing essentially the unreacted compound to be oxidized, optionally the dissolved fluorinated compound and / or the oxidation intermediates, (or more organic phases if the fluorinated compound and the hydrocarbon are not completely miscible at low temperature) and an aqueous liquid phase essentially containing acid by-products of oxidation and the water formed. The catalyst can be in one of the organic phases if it is soluble in said phase, or in the aqueous phase

After filtration or centπfugation of the solid, the organic and aqueous liquid phases constituting the filtrate or the centπfugat are separated, if necessary, by decantation, the organic phase or phases can be recycled in a new oxidation reaction II can be advantageous to carry out, prior to the acid crystallization operation, a concentration of the reaction mixture

According to a second variant of the process, the final raw reaction mixture can be drawn off hot, for example at a temperature which can reach 75 ° C. The reaction mixture then settles in at least two liquid phases one or more organic phases containing essentially the unreacted hydrocarbon, the fluorinated compound and possibly the oxidation intermediates and an aqueous liquid phase containing essentially the acids formed and the water formed Depending on the solubility and the nature of the catalyst, this can be present in the organic phase or phases and recycled with the recycling of these or recovers by solid / liquid separation before precipitation or crystallization of the acid formed in the case of '' heterogeneous catalysis or by liquid / liquid extraction, electrodyahse, treatment on resins if it is soluble in the aqueous phase As in the first variant, the liquid phases are separated by decantation the organic phase or phases can be recycled in a new oxidation reaction

In these embodiments, the fluorinated compound used in accordance with the invention is generally contained or forms an essential element of the organic phase or phases Consequently, after separation of the acid formed and optionally from the liquid phase containing the water formed , the oxidation intermediates, the catalyst and the fluorinated compound are recycled in the oxidation step with the hydrocarbon not having been oxidized

Furthermore, if the fluorinated compound is solid in a phase of treatment of the reaction medium, it will advantageously be separated and recovered by implementing solid / liquid separation processes either before treatment of the reaction medium to recover the acid produced, or with the acid produced In the latter case, the acid can be recovered by extraction with water

In these exemplary embodiments of the invention, water can be added to the reaction medium to obtain better dissolution of the acid byproducts of oxidation and better recovery of the acid formed.

The acid is generally recovered by precipitation during the cooling of the reaction medium. The acid thus recovered can be purified according to usual techniques and described in numerous patents. Mention may be made, for example, of French patents no. 2749299 and 2749300

If the non-organic or aqueous liquid phase contains the catalyst, it is extracted either before the crystallization of the acid formed by precipitation or extraction according to known methods such as liquid-liquid extraction, electrodialysis, treatment on exchange resins d for example, either after crystallization of the acid formed by extraction techniques described above or the like

Other advantages and details of the invention will appear more clearly in the light of the examples given below solely for information and illustration. EXAMPLE 1

In a 125 ml titanium autoclave, provided with heating means using a heating collar, a turbine and means for introducing gas and regulating pressure,

- 16.5 g (196.4 mmol) of cyclohexane

- 23.5 g (161 mmol) of trifluoromethylbenzene

- 0.44 g (4.49 mmol) of cyclohexanone

- 0.3344 g (0.94 mmol of Co) of Cobalt (III) acetylacetonate

After closing the reactor, it is stirred at 1000 revolutions per minute, an air pressure is created (100 bar at 20 ° C.) and it is heated The temperature reaches 105 ° C. in the mass in 10 min and this temperature is maintained for a further 3 hours

After cooling and depressurization, the reaction mixture is homogenized by adding acetic acid. The constituents of the mixture obtained are determined by gas chromatography

The following results are obtained

- conversion rate (TT) of cyclohexane 3.3%

- selectivity (ST) for cyclohexanol with respect to transformed cyclohexane 43.8%

- selectivity (ST) in cyclohexanone compared to cyclohexane transformed 12.7%

- ST in adipic acid relative to cyclohexane transformed 29.6%

- ST in adipic acid + cyclohexanone + cyclohexanol compared to cyclohexane transformed 86.1%

- adipic acid / total molar ratio of the diacids formed (adipic, glutanic and succinic acids) 73%

COMPARATIVE TEST 1

Example 1 is repeated in the same apparatus and under the same operating conditions, but not loading a fluorinated compound and using an amount of cyclohexane of 40.2 g (479 mmol) The following results are obtained - conversion rate (TT) cyclohexane 0.80%

- ST in adipic acid compared to transformed cyclohexane - <10% EXAMPLE 2

In a 125 ml titanium autoclave, provided with heating means using a heating collar, a turbine and means for introducing gas and regulating pressure, the following are charged:

- 16.5 g (196.4 mmol) of cyclohexane

- 23.5 g (64.6 mmol) of CF ₃ (CF ₂ ) ₅ C0 ₂ H (solid compound at room temperature)

- 0.44 g (4.49 mmol) of cyclohexanone

- 0.3344 g (0.94 mmol of Co) of Cobalt (III) acetylacetonate

After closing the reactor, it is stirred at 1000 revolutions per minute, an air pressure is created (100 bar at 20 ° C.) and it is heated. The temperature reaches 105 ° C. in the mass in 10 min and this temperature is maintained for a further 3 hours.

After cooling and depressurization, the reaction mixture is homogenized by adding acetic acid. The constituents of the mixture obtained are determined by gas chromatography.

The following results are obtained:

- conversion rate (TT) of cyclohexane: 8.5%

- selectivity (ST) in cyclohexanol with respect to the transformed cyclohexane: 15.8%

- selectivity (ST) in cyclohexanone compared to the transformed cyclohexane: 7.1%

- ST in adipic acid relative to the transformed cyclohexane: 52.8%

- ST in adipic acid + cyclohexanone + cyclohexanol relative to the transformed cyclohexane: 75.6%

- adipic acid / total molar ratio of the diacids formed (adipic, glutaric and succinic acids): 74.4%

EXAMPLE 3 AND COMPARATIVE TEST 4C

In a shaken reactor, cobalt is added in the form of Cobalt acetylacetonate to obtain a content of 300 ppm of Co in the reaction medium and of cyclohexanone to have a concentration of 1% by mole relative to cyclohexane. The reaction is carried out at a temperature of 105 ° C under an air pressure of 100 bar for 3 hours.

The concentrations of cyclohexane and components of the solvent are indicated in the table below and are expressed as% by weight of each component. The yields and selectivities obtained are also listed in the table.

Claims

Process for the oxidation of substituted or unsubstituted saturated aliphatic or cycloaliphatic hydrocarbons or alkyl aromatic hydrocarbons in liquid medium by an oxidizing agent comprising molecular oxygen to acids or acids, characterized in that one of the constituents of the medium liquid is a fluorinated organic compound

Process according to Claim 1, characterized in that the hydrocarbon to be oxidized is at least partially miscible with the fluorinated organic compound, under the conditions for carrying out the oxidation reaction

Method according to one of claims 1 to 2, characterized in that the fluorinated compound is chosen from the group comprising fluorinated or perfluorinated aliphatic or cycloaliphatic hydrocarbons, fluorinated or perfluorinated aromatic hydrocarbons, fluorinated or perfluorinated esters, fluorinated ketones or perfluorinated, fluorinated or perfluorinated alcohols, fluorinated or perfluorinated nitriles, fluorinated or perfluorinated acids, fluorinated or perfluorinated amines, fluorinated or perfluorinated ethers

Method according to one of the preceding claims, characterized in that the weight percentage of fluorinated compounds in the liquid medium is between 1 and 99% by weight relative to the total weight of the liquid medium

5 Method according to claim 4, characterized in that the aforementioned weight percentage is between 10 and 80% by weight

6 Method according to one of the preceding claims, characterized in that the oxidation is carried out in the presence of a catalyst

7 Method according to claim 6, characterized in that the catalyst is soluble in the liquid medium under the conditions of implementation of the oxidation reaction

8. Method according to claim 6, characterized in that the catalyst is insoluble in the liquid medium under the conditions for carrying out the oxidation reaction

9. Method according to claim 8, characterized in that the catalyst is a supported catalyst comprising an inorganic or polyméπque support

10. Method according to one of the preceding claims, characterized in that the hydrocarbon to be oxidized is chosen from the group comprising cyclohexane, cyclododecane.

1 1. Method according to claim 10, characterized in that the acid produced is adipic acid or dodecanedioi acid ^' that

12. Method according to one of the preceding claims, characterized in that the liquid medium after oxidation is decanted, in at least one organic phase formed by the non-oxidized hydrocarbon and the fluorinated compound, said organic phases being recycled into a new oxidation, the acid produced being extracted from the aqueous liquid phase.

13. Method according to claim 12, characterized in that the acid is extracted from the aqueous liquid phase by crystallization.

14. Method according to one of claims 8 and 12 or 13, characterized in that the catalyst is recycled with the organic phase or phases.

15. Method according to one of claims 9 and 12 or 13, characterized in that the catalyst is separated from the liquid medium by decantation or solid / liquid separation.

16, Method according to one of claims 12 or 13. characterized in that the catalyst soluble in the aqueous liquid phase is extracted by liquid / liquid extraction, separation on resins, electrodialysis

17 Method according to one of the preceding claims, characterized in that the catalyst comprises cobalt as a catalytically active element.