KR20020079994A - Method for oxidising hydrocarbons into acids - Google Patents

Abstract

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

More preferably, the present invention relates to a method of oxidizing cyclohexane to adipic acid in the presence of a fluorinated compound by an oxidizing agent containing molecular oxygen, which method comprises: unreacted cyclohexane, an oxidizing intermediate and a catalyst The separation and recycling of can be made easier.

Description

HOW TO oxidize hydrocarbons to acids {METHOD FOR OXIDISING HYDROCARBONS INTO ACIDS}

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

More preferably, the present invention relates to the oxidation of cyclohexane to adipic acid by an oxidizing agent containing molecular oxygen.

Oxidation of cyclohexane to adipic acid is a method that has been studied for many years. This is because adipic acid is an important chemical compound used as a starting material in many production methods such as the production of polymers such as polyamides, polyesters or polyurethanes.

Several methods of preparing adipic acid from hydrocarbons such as benzene, phenol, cyclohexene or cyclohexane have been provided.

Thus, U.S. Patent 2,223,493, published in December 1940, generally describes the use of an oxygen-containing gas in the presence of an oxidation catalyst, such as a cobalt compound, in a liquid phase containing acetic acid, at temperatures above 60 ° C. The oxidation of hydrocarbons to the corresponding diacids is described.

Many other patents and articles describe this reaction for the direct oxidation of cyclohexane to adipic acid. However, in order to obtain acceptable yields in the production of adipic acid, these documents describe the use of acetic acid as a solvent in the presence of a homogeneous catalyst or a heterogeneous catalyst. As an explanation, mention may be made of the paper ["Chemtech", 555-559 (September 1974), the author of K. Tanaka, which summarizes and explains how to oxidize cyclohexane directly. have. Mention may also be made of US patents 3231608, 4032569, 415873, 4263453 and 5321157 and European patent 870 751, which describe various homogeneous catalyst systems.

A method of directly oxidizing cyclohexane in the presence of a heterogeneous catalyst such as cobalt substituted aluminophosphate has also been proposed as in European Patent 519 569.

The choice of solvent, i.e. acetic acid, is an important property in obtaining acceptable conversion of cyclohexane and acceptable production of adipic acid. The use of such solvents results in a number of disadvantages caused by, for example, its corrosiveness, under the temperature and pressure conditions used. In addition, the use of this solvent presents a number of problems in the separation and extraction of the adipic acid produced and in the recycling of various compounds.

This is because in the presence of acetic acid, it is difficult to separate and extract byproduct compounds from oxidation such as cyclohexanone and cyclohexanol formed from the reaction mixture.

In addition, extraction of adipic acid by crystallization and its purification are difficult because the solubility of these acids under cold conditions is higher at 25 ° C. in acetic acid and lower at 80 ° C. than in water.

Separation and recycle of the homogeneous catalyst is also difficult in the presence of acetic acid. In fact, on the one hand, recycling the catalyst without extracting the latter does not sufficiently retain the catalytic activity, and on the other hand, before recycling, as described in French patents 2 722 783 and 2 746 671, on the other hand, The operation of separating the catalyst is complicated and expensive.

This solvent also requires that the dehydration of the reaction mixture to be carried out is difficult and expensive.

Several methods have also been provided for oxidizing cyclohexane to adipic acid in a single step without the use of acetic acid. Some are in the absence of solvent, others are solvents such as organic esters such as acetate (US 4 098 817), acetone (US 2 589 648) or alcohols such as butanol, methanol, cyclohexanol or acetonitrile (EP 784 045).

These methods generally have very low selectivity for adipic acid. In addition, the solvents used often exhibit low stability under conditions for oxidizing hydrocarbons such as cyclohexane. This low stability increases the consumption of solvent, which renders this method unusable.

One of the objects of the present invention is to provide a process for oxidizing a hydrocarbon in a single step in a liquid medium under the conditions of an oxidation reaction to produce an acid or a polyacid, which method is characterized by the separation of the acid produced by simple operation and It is possible to recycle the catalyst in an acceptable yield.

To this end, the present invention is a method of oxidizing a substituted or unsubstituted saturated aliphatic or cycloaliphatic hydrocarbon, or alkylaromatic hydrocarbon, to an acid or polyacid in a liquid medium by an oxidant containing molecular oxygen, wherein one of the components of the liquid medium is Is a fluorinated organic compound.

According to the invention, fluorinated organic compounds are compounds which, together with the hydrocarbon or hydrocarbons to be oxidized, form one or more homogeneous liquid phases under the conditions of temperature and pressure of the oxidation reaction. Thus, the fluorinated compound may advantageously be at least partially miscible with the hydrocarbon or hydrocarbons to be oxidized, under the temperature and pressure conditions applied for carrying out the oxidation reaction.

The term “at least partially miscible” refers to a homogeneous liquid phase containing, under the conditions of an oxidation reaction, the solubility of one compound in another compound of at least 2% by weight and containing at least some of the hydrocarbons and fluorinated organic compounds to be oxidized. It should be understood as meaning formed.

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

The term "fluorinated compound" is to be understood as meaning a single compound or mixture of fluorinated compounds. Such compounds may be liquid or solid; In the latter case they will be dissolved in the hydrocarbon to be oxidized, especially under the conditions of the invention.

In addition and obviously, such fluorinated compounds are stable under the conditions of carrying out the oxidation reaction described at least subsequently.

Such suitable fluorinated compounds can advantageously be selected from the group containing:

Cyclic or bicyclic fluorinated or perfluorinated aliphatic hydrocarbons or fluorinated aromatic hydrocarbons such as perfluorotoluene, perfluoromethylcyclohexane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluor Rononane, perfluorodecalin, perfluoromethyldecalin, α, α, α-trifluorotoluene or 1,3-bis (trifluoromethyl) benzene

Perfluorinated or fluorinated esters such as perfluoro (alkyl octanoate) or perfluoro (alkyl nonanoate)

Fluorinated or perfluorinated ketones or ethers such as perfluoroacetone

Fluorinated or perfluorinated alcohols such as perfluorohexanol, perfluorooctanol, perfluorononanol, perfluorodecanol, perfluoro-t-butanol, perfluoroisopropanol or 1, 1,1,3,3,3-hexafluoro-2-propanol

Fluorinated or perfluorinated nitriles, such as perfluoroacetonitrile

Fluorinated or perfluorinated acids such as trifluoromethylbenzoic acid, pentafluorobenzoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorooctanoic acid, perfluorononanoic acid or perfluoroadipic acid

Fluorinated or perfluorinated halides such as perfluoroiodooctane or perfluorobromooctane

Fluorinated or perfluorinated amines such as perfluorotripropylamine, perfluorotributylamine or perfluorotripentylamine.

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

However, it is also possible to use other compounds in combination with the fluorinated component, which may in particular have the effect of improving the selectivity and / or productivity of the reaction oxidized to adipic acid without departing from the scope of the present invention.

In particular, mention may be made of organic acids or nitriles as examples of such compounds. More particularly suitable compounds may include acetic acid, propionic acid, butyric acid, valeric acid, lipophilic acids containing at least 6 carbon atoms, nitriles such as acetonitrile or benzonitrile, or halogenated derivatives such as dichloromethane.

Oxidation is generally carried out in the presence of a catalyst. This catalyst is advantageously Cu, Ag, Au, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Al, Ga, In, Tl, Sc, Y, Ti, Zr, Hf, Ge, Sn, Pb, Consisting of V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, lanthanides such as Ce, and combinations thereof It contains a metal atom selected from the group.

Such catalyst atoms are advantageously applied in a form supported, absorbed or bound on a compound which is at least partially soluble in the liquid oxidation medium under the conditions of the oxidation reaction, or on an inert support such as silica or alumina.

Especially under the conditions of carrying out the oxidation reaction, the catalyst is preferably as follows:

-Soluble in hydrocarbons to be oxidized,

Or soluble in fluorinated compounds,

Or soluble in a mixture of hydrocarbon / fluorinated compounds which form a homogeneous liquid phase under the conditions of the present reaction.

According to a preferred embodiment of the invention, the catalyst used is soluble in the hydrocarbons and / or fluorinated compounds to be oxidized, so that the catalyst is recycled.

The term "soluble" is understood to mean that the catalyst is at least partially soluble in the medium under consideration.

In the case of heterogeneous catalysts, catalytically active metal atoms are in the form of organometallic complexes supported or incorporated in fine or mesoporous inorganic matrices or polymeric matrices, or grafted to organic or inorganic supports. The term "incorporation" is understood to mean that the metal is an element of the support, or that the manipulation is carried out with a complex stericly bound to the porous structure under oxidizing conditions.

In a preferred embodiment of the invention, the homogeneous or heterogeneous catalyst is a Group IVb (Ti group), Vb (V group), VIb (Cr group), VIIb (Mn group), VII (Fe or Co or Ni group), or Ib (Cu group) and salts or metal complexes of metals from cerium alone or as mixtures. Preferred elements are in particular Co and / or Mn and / or Cr and / or Zr, Hf, Ce and / or Zr, Hf. The concentration of metal in the liquid oxidation medium varies between 0.00001 and 5% (% by weight), preferably between 0.001% and 2%.

The invention is more particularly applied to the oxidation of cycloaliphatic compounds such as cyclohexane or cyclododecane to produce adipic acid and dodecanedioic acid, respectively.

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

The oxidation reaction is carried out at a temperature of 50 ° C to 200 ° C, preferably 70 ° C to 180 ° C. This can be done at atmospheric pressure. In general, however, it is carried out under a pressure capable of maintaining the components of the reaction medium in liquid form. The pressure may be between 10 kPa (0.1 bar) and 20000 kPa (200 bar), preferably between 100 kPa (1 bar) and 10000 kPa (100 bar).

The oxygen used may be in pure form or as a mixture with an inert gas such as nitrogen or helium. It is also possible to use air in which oxygen is somewhat concentrated. The amount of oxygen supplied to the medium is advantageously from 1 to 1000 moles per mole of compound to be oxidized.

The oxidation process can be carried out continuously or batchwise. The liquid reaction medium exiting the reactor is advantageously treated according to known methods, which on the one hand separate and recover the produced acid and on the other hand non-oxidized or partially oxidized organic compounds such as cyclohexane It is possible to recycle cyclohexanol and / or cyclohexanone, catalysts and fluorinated compounds.

The amount of catalyst expressed in weight percent of cobalt relative to the reaction mixture is generally from 0.00001% to 5%, preferably from 0.001% to 2%, provided that this value is not critical. However, this is a substance with sufficient activity, without using an excess of catalyst which must then be separated from the final reaction mixture and recycled.

In addition to cobalt, the catalyst may also contain other compounds based on metals selected from the group consisting of manganese, copper, cerium, vanadium, chromium, zirconium, hafnium and combinations of some of these elements.

It is also advantageous to apply compounds which initiate the oxidation reaction, such as ketones or aldehydes. Particularly preferred is cyclohexanone, the reaction intermediate, when oxidizing cyclohexane. Initiators generally represent from 0.01% to 20% by weight of the weight of the reaction mixture applied, provided that this ratio is not critical. Initiators are particularly useful at the start of oxidation and when the oxidation is carried out at temperatures below 120 ° C. This can be introduced from the beginning of the reaction.

Oxidation can also be carried out in the presence of water introduced from the beginning of the process.

As indicated above, various operations are carried out to separate some of its components from the reaction mixture produced from oxidation, for example by recycling some components such as non-oxidizing hydrocarbons, oxidation intermediates or catalysts, and Recover the acid produced.

According to a first alternative form of the process, the crude reaction mixture may first be cooled to a temperature of, for example, 16 ° C. to 30 ° C., which crystallizes at least part of the acid formed. Thus, essentially an acid-containing solid phase, essentially an unreacted compound to be oxidized, an optionally dissolved fluorinated compound and / or one or more liquid organic phases (or fluorinated compounds and hydrocarbons) containing an oxidation intermediate are fully miscible at low temperatures. If not, a medium is obtained which contains several aqueous phases) and essentially a liquid aqueous phase containing acid by-products from oxidation and water formed. If soluble in this phase or in the aqueous phase, the catalyst may be in one of the organic phases.

The solid is filtered or centrifuged, and if necessary, separation is carried out by sedimentation of the organic and aqueous liquid phases that make up the filtrate or centrifuge; The organic phase or phases can be recycled in further oxidation reactions.

Prior to the operation of crystallizing the acid, it may be advantageous to concentrate the reaction mixture.

According to a second alternative form of the process, it is possible to take the final crude reaction mixture at high temperatures, for example at temperatures which can reach 75 ° C. The reaction mixture is then separated by sedimentation of two or more liquid phases: one or more organic phases essentially containing unreacted hydrocarbons, fluorinated compounds and optionally oxidizing intermediates, and liquid water essentially containing the formed acid and water formed. Appearance.

Depending on the solubility and nature of the catalyst, the latter may be present in the organic phase or in the phases, and may be recycled while recycling the organic phase, or in the case of a homogeneous catalyst, either by solid / liquid separation or prior to precipitation or crystallization of the acid formed, or the aqueous phase. If soluble in, it can be recovered by liquid / liquid extraction, electrodialysis or treatment on resin.

As in the first alternative form, the liquid phases are separated by sedimentation; The organic phase or phases can be recycled in further oxidation reactions.

In such embodiments, the fluorinated compounds used according to the invention are generally present in or form the essential phase of the organic phase or phases. As a result, after separating the formed acid and any liquid phase containing the formed water, the oxidation intermediate, catalyst and fluorinated compound are recycled in the oxidation step together with the non-oxidized hydrocarbon.

In addition, when the fluorinated compound is a solid in the phase treating the reaction medium, it is advantageously separated and applied by applying the solid / liquid separation method before or with the acid produced by treating the reaction medium. It will be recovered. In the latter case, the acid can be recovered by extraction with water.

In this exemplary embodiment of the invention, water can be added to the reaction medium to obtain better decomposition of acid by-products from oxidation and better recovery of the acid formed.

Acids are generally recovered by precipitation while cooling the reaction medium. The acid thus recovered can be purified according to the familiar techniques described in many patents. By way of example, mention may be made of French patents 2 749 299 and 2 749 300.

If the organic or aqueous liquid phase contains a catalyst, the latter is formed by crystallization or extraction following known methods, such as liquid-liquid extraction, electrodialysis or treatment on an ion exchange resin, or before the acid formed is crystallized. After the acid is crystallized, it is extracted by the extraction technique described above or a similar technique.

Other advantages and details of the present invention will become more apparent as the examples set forth below by purely indication and explanation.

Example 1

A 125 ml titanium autoclave equipped with a heating device, a turbine, and a gas introduction and pressure control device by a ring heater was charged with the following materials:

16.5 g (196.4 mmol) of cyclohexane,

23.5 g (161 mmol) trifluoromethylbenzene,

0.44 g (4.49 mmol) of cyclohexanone,

0.3344 g (Co 0.94 mmol) of cobalt (III) acetylacetonate.

After the reaction was complete, the mixture was stirred at 1000 revolutions per minute, air pressure (100 bar at 20 ° C.) was produced and the mixture was heated. The bulk temperature reached 105 ° C. in 10 minutes, and this temperature was maintained for an additional 3 hours.

After cooling and reduced pressure, the reaction mixture was homogenized by addition of acetic acid. The components of the obtained mixture were quantitatively determined by gas chromatography.

The following results were obtained:

Degree of conversion (DC) of cyclohexane: 3.3%

Selectivity of cyclohexanol (ST) to converted cyclohexane: 43.8%

Selectivity of cyclohexanone to converted cyclohexane (ST): 12.7%

ST of adipic acid to converted cyclohexane: 29.6%

-ST of adipic acid + cyclohexanone + cyclohexanol on converted cyclohexane: 86.1%

-Molar ratio of adipic acid to the total amount of diacids formed (adipic acid, glutaric acid and succinic acid): 73%

Comparative test example 1

Example 1 was repeated in the same apparatus and under the same operating conditions, using cyclohexane in an amount of 40.2 g (479 mmol) without charging the fluorinated compound.

The following results were obtained:

Degree of conversion (DC) of cyclohexane: 0.80%

ST of adipic acid to converted cyclohexane: <10%

Example 2

A 125 ml titanium autoclave equipped with a heating device, a turbine, and a gas introduction and pressure control device by a ring heater was charged with the following materials:

16.5 g (196.4 mmol) of cyclohexane,

23.5 g (64.6 mmol) of CF ₃ (CF ₂ ) ₅ CO ₂ H (solid compound at ambient temperature),

0.44 g (4.49 mmol) of cyclohexanone,

0.3344 g (Co 0.94 mmol) of cobalt (III) acetylacetonate.

After the reaction was complete, the mixture was stirred at 1000 revolutions per minute, air pressure (100 bar at 20 ° C.) was produced and the mixture was heated. The bulk temperature reached 105 ° C. in 10 minutes, and this temperature was maintained for an additional 3 hours.

After cooling and reduced pressure, the reaction mixture was homogenized by addition of acetic acid. The components of the obtained mixture were quantitatively determined by gas chromatography.

The following results were obtained:

Degree of conversion of cyclohexane (DC): 8.5%

Selectivity of cyclohexanol (ST) to converted cyclohexane: 15.8%

Selectivity of cyclohexanone to converted cyclohexane (ST): 7.1%

ST of adipic acid to converted cyclohexane: 52.8%

-ST of adipic acid + cyclohexanone + cyclohexanol on converted cyclohexane: 75.6%

-Molar ratio of adipic acid to the total amount of diacids formed (adipic acid, glutaric acid and succinic acid): 74.4%

Example 3 and Comparative Test Example 4C

Cobalt, in the form of cobalt acetylacetonate, and cyclohexanone are added to the stirred reactor by vibration, to obtain cyclohexanone at a concentration of 1 mol% relative to 300 ppm of Co and cyclohexane in the reaction medium, respectively. It was. The reaction was carried out for 3 hours under an air pressure of 100 bar at a temperature of 105 ℃.

The concentrations of the components of cyclohexane and the solvent are shown in the table below and each component is expressed as weight percent. The yields and selectivities obtained are also listed in the table.

Yes ingredient weight% DC of cyclohexane Adipic acid ST 3 Cyclohexanetrifluoromethylbenzeneoctanoic acid 502525 4.6 61.4 4C Cyclohexaneoctanoic acid 7525 One 22.5

Claims (17)

A method of oxidizing a substituted or unsubstituted saturated aliphatic or cycloaliphatic hydrocarbon, or alkylaromatic hydrocarbon, to an acid or a polyacid in a liquid medium by an oxidant containing molecular oxygen, wherein one of the components of the liquid medium is a fluorinated organic compound. Characterized in that the method. The method of claim 1 wherein the hydrocarbon to be oxidized is at least partially miscible with the fluorinated organic compound under the conditions of the oxidation reaction. The fluorinated compound of claim 1 or 2, wherein the fluorinated compound is a fluorinated or perfluorinated aliphatic or cycloaliphatic hydrocarbon, a fluorinated or perfluorinated aromatic hydrocarbon, a fluorinated or perfluorinated ester, a fluorinated or perfluorinated ketone , Fluorinated or perfluorinated alcohols, fluorinated or perfluorinated nitriles, fluorinated or perfluorinated acids, fluorinated or perfluorinated amines and fluorinated or perfluorinated ethers. How to. The process according to claim 1, wherein the weight percent of the fluorinated compound in the liquid medium is 1 to 99% by weight relative to the total weight of the liquid medium. 5. A process according to claim 4, wherein said weight percent is from 10 to 80 weight percent. The process according to any one of claims 1 to 5, characterized in that the oxidation is carried out in the presence of a catalyst. 7. A process according to claim 6, wherein the catalyst is soluble in the liquid medium under the conditions of carrying out the oxidation reaction. 7. A process according to claim 6, wherein the catalyst is insoluble in the liquid medium under the conditions of carrying out the oxidation reaction. 10. The process of claim 8, wherein the catalyst is a supported catalyst containing an inorganic or polymeric support. 10. The process according to any one of claims 1 to 9, wherein the hydrocarbon to be oxidized is selected from the group consisting of cyclohexane and cyclododecane. The method of claim 10 wherein the acid produced is adipic acid or dodecanedioic acid. 12. The method according to any one of the preceding claims, characterized in that after oxidation, the liquid medium is separated by sedimentation by at least one organic phase formed by non-oxidized hydrocarbons and fluorinated compounds, wherein the organic phase is subjected to further oxidation. Recycled and the produced acid is extracted from the liquid aqueous phase. 13. The process according to claim 12, wherein the acid is extracted by crystallization from the liquid aqueous phase. 14. A process according to any one of claims 8, 12 or 13, characterized in that the catalyst is recycled with the organic phase or phases. 14. Process according to any one of claims 9 and 12 or 13, characterized in that the catalyst is separated from the liquid medium by sedimentation or solid / liquid separation. The process according to claim 12 or 13, characterized in that the catalyst soluble in the liquid aqueous phase is extracted by liquid / liquid extraction, separation on resin or electrodialysis. 17. The process according to any one of claims 1 to 16, wherein the catalyst contains cobalt as catalytically active element.