The isolation and purification of adipic acid

 

The invention relates to an improved method of isolation and purification of adipic acid, used for the production of polyamide-6,6 or polyurethanes, which consists in treating the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid by molecular oxygen in an organic solvent and in the presence of a catalyst, removing by-products from the reaction mixture and the adipic acid by crystallization, and before adipic acid from the reaction environment carry out consistently the following operations: the decantation of the two phases of the reaction medium with the formation of the upper organic the cyclohexane phase, containing mainly cyclohexane, and the lower phase, containing mainly the solvent, the resulting dicarboxylic acid, the catalyst and other reaction products and unreacted cyclohexane; distillation bottom phase to separate, on the one hand, distillate containing at least a part of the most volatile compounds, such as organic solvent, water and unreacted cyclohexane, cyclohexanone, cyclohexanol, complex cyclohexylamine esters and possibly the highlight adipic acid from residue from distillation by means of crystallization and thus obtained crude adipic acid is subjected in aqueous solution purification by hydrogenation and/or oxidation with subsequent crystallization and recrystallization of the purified adipic acid in water. The method allows to obtain adipic acid of high purity confirmed by the decrease in light absorption at a wavelength of 454 nm in 12 and 8 times, compared with adipic acid, selected classical way. 16 C.p. f-crystals, 1 table.

The present invention relates to the treatment of the reaction mixtures resulting from the oxidation of cyclohexane to adipic acid, and in particular to the separation of the various components of the above mixtures and purification of adipic acid.

Direct oxidation of cyclohexane to adipic acid is a method that is developed for a long time, in particular, because of its inherent competitive advantages, which consists in the conversion of cyclohexane to adipic acid in a single stage without the use of an oxidant such as nitric acid, since this compound gives the oxides of nitrogen, which then need to process in order to avoid contamination.

In International patent A-94/07834 describes the oxidation of cyclic hydrocarbons to the corresponding decislon in the solvent liquid phase by including the oxygen gas in the presence of an oxidation catalyst such as a compound of cobalt, and vysokoltnymi carbon atoms. In this patent, in particular, attention is paid to the stages of processing of the final reaction mixture. This processing consists in the allocation of the formed decollate by cooling the mixture to cause precipitation of the above decollate, separation by filtration of decollate of the two liquid phases: non-polar, which recycle, and polar, which also recycle after a possible hydrolysis and allocation of an additional amount of decollate.

This patent proposes a solution in terms of one-stage oxidation of cyclohexane to adipic acid with industrial acceptable selectivity, but is not acceptable from the industrial point of view, decisions regarding treatment produced during the oxidation reaction mixture, taking into account the separation of the various products and by-products of the reaction, neprivrednih products and catalyst.

Moreover, in practice, it turns out that the total processing method does not lead to adipic acid with purity required for many uses this is a very important raw material.

In fact, in regard to the production of polyamide-6,6 or in the case of other applications, such as obtaining some polio the organic by-products, which can lead to undesirable stains, and the content of residual metals, in particular traces of the used catalyst.

The present invention relates, therefore, to an improved method of processing the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid by molecular oxygen in an organic solvent and in the presence of a catalyst, including the removal of by-products from the reaction mixture and adipic acid by crystallization, characterized in that before the adipic acid from the reaction environment carry out consistently the following operations: - the decantation of the two phases of the reaction medium with the formation of the upper organic the cyclohexane phase, containing mainly cyclohexane, and the lower phase, containing mainly solvent, the resulting dicarboxylic acid, the catalyst and other reaction products and unreacted cyclohexane; - distillation bottom phase to separate, on the one hand, distillate containing at least a part of the most volatile compounds, such as organic solvent, water and unreacted cyclohexane,and distillation, including the formed decollate and the catalyst; then allocate adipic acid from residue from distillation by means of crystallization and thus obtained crude adipic acid is subjected in aqueous solution purification by hydrogenation and/or oxidation with subsequent crystallization and recrystallization of the purified adipic acid in water.

Obtained in stage decanting cyclohexane phase often again enter into the process of oxidation of cyclohexane.

Used in the oxidation of cyclohexane organic solvent mainly selected from aliphatic carboxylic acids. This is frequently acetic acid.

The catalyst preferably contains cobalt, manganese, a mixture of cobalt with one or more other metals such as manganese, chromium, iron, zirconium, hafnium, copper. Mixtures of cobalt-based particularly suitable catalysts containing either cobalt and chromium, or cobalt, chromium and zirconium, or cobalt and iron, or cobalt and manganese, or cobalt and zirconium and/or hafnium. This catalyst for the oxidation of cyclohexane is introduced in the form of compounds of these metals, soluble in the reaction medium.

Stage distillation bottom phase osushestvliayut neprevyshenie cyclohexane, which may still be present in this lower phase, and the solvent is particularly preferably used carboxylic acid. This stage allows you to separate the lighter (more volatile than decollate) organic compounds, which are beneficial recycling in phase oxidation of cyclohexane, if necessary, after intended for dehydration processing. As examples of such light organic compounds can be called adipogenesis (which can be converted into adipic acid) compounds, such as cyclohexanol, cyclohexanone, cyclohexylacetate, and other compounds such as lactones (mainly butyrolactone, valerolactone).

Stage distillation is usually carried out at a temperature of 25-250oC and at an absolute pressure of from 10 PA to atmospheric pressure. The temperature of the mixture during the distillation is preferably maintained within the range of from 70oWith up to 150oC.

If necessary, the distillation can be carried out in several successive stages, in particular, in the case of the preferred option, under which removes the largest portion, for example more than 90% and even more than 99%, of the solvent, such as aliphatic carboxylic acid.

To increase the floor of the tel, which can be either water in the form of steam, or inert gas, such as nitrogen.

Stage distillation, if necessary, can also be added to the extraction residue after distillation using a water-immiscible organic solvent. This extraction may serve to separate the esters, in particular cyclohexylamin esters, which may be found in the distillation residue. As not limiting the scope of protection of the invention examples of such organic solvents can be used aliphatic, cycloaliphatic or aromatic hydrocarbons, esters of aliphatic, cycloaliphatic or aromatic carboxylic acids, ketones. Because it is preferable, whenever possible, to avoid the introduction of new compounds in the method according to the invention, as the extracting solvent is preferably used cyclohexane. The extract can be recycled into a new oxidation reaction, either directly or after hydrolysis of esters.

Obtained by the above process of distillation, the distillate contains various volatile compounds and water. These volatile compounds valorized and therefore recycle into a new reaction is by azeotropic distillation.

Obtained after distillation and subjected, if necessary, operation of the extraction residue is treated to separate the contained catalyst.

This separation can be accomplished, according to the first variant, by crystallization, which consists essentially in dissolving the above distillation residue in a minimal amount of water, usually by heating, and then crystallization is mainly adipic acid. Containing the catalyst aqueous solution can be processed, in addition, with the aim of identifying the above-mentioned catalyst can be recycled in a new process of oxidation.

Separation can also be accomplished using other known methods, for example, after dissolving the above distillation residue in water, through the implementation of electrodialysis resulting solution or by passing the above solution through ion-exchange resin. Electrodialysis can be carried out as described in the International patent application A-97/36673. Ion exchange resins are resins capable of cations of metals of the catalyst. They usually contain a functional group with an acid or complexing ha is cselenyi group. Functional groups of complexing character are often the group iminodiacetonitrile or aminophosphonate type.

The Department also possible according to another variant, by one or more washes with water distillation residue. By this washing, in particular, dissolve the catalyst, as well as part of decislon, in particular glutaric acid and to a lesser extent succinic acid. To avoid or greatly limit the dissolution of adipic acid, use of water or saturated adipic acid water, which is 1-100 wt.% and preferably 10-50% relative to the weight of the distillation residue.

After phase separation of the catalyst should be cleaning stage of adipic acid, which is used in aqueous solution.

This cleaning can be accomplished by hydrogenation and/or treatment with nitric acid, and/or by oxidation with molecular oxygen or any other oxidizing agent such as ozone and hydroperoxides (including hydrogen peroxide).

The hydrogenation is preferably carried out using hydrogen in the presence of a catalyst. As the catalyst can be called as not ograniciti of the periodic system of elements, such as palladium, platinum, ruthenium, osmium, rhodium, iridium, Nickel, cobalt. These metals are preferably in the metallic form and is preferably deposited on a solid carrier. As a solid carrier can be used, among others, coal, clay, zeolites, oxides, such as silica, aluminum oxide, aluminosilicates, magnesium oxide. The catalyst may be used in the form of a stationary layer or in the form of a fluidized bed or a transportable layer. The hydrogenation can be performed continuously or periodically, however, in the installation of industrial-type continuous process is particularly suitable.

The nitric acid treatment can be conducted by using an aqueous solution containing typically 20-80 wt.% pure nitric acid relative to the weight of the solution. This treatment is usually carried out by heating the mixture at a temperature of 25oWith up to 120oC and preferably at a temperature of from 40oWith up to 100oWith in a period of time of several minutes to several hours. The heating is preferably possible to carry out successive steps at temperatures in the above ranges. The amount of nitrogen millenia and on the other hand, should not be too great at the same time for technical and economic reasons. Usually use from 0.8 to 4 mol, and preferably 1 to 2 mol of nitric acid per 100 g of the treated solution of adipic acid. This treatment is usually carried out in the absence of catalyst. It can also be carried out in the presence of a catalyst containing one or more compounds of cobalt, copper and/or vanadium. Processing, which may yield nitrogen pairs, preferably complementary to remove when heated above the formed nitrous vapors by circulating a liquid mixture of inert gas, such as nitrogen.

Oxidation by molecular oxygen in particular is carried out using air, enriched or depleted in oxygen and in the presence of a catalyst. For this treatment by molecular oxygen suitable catalysts mentioned above for processing by hydrogenation. Preferably, you can use a metal selected from the group consisting of palladium, platinum, ruthenium, osmium, rhodium, iridium.

Oxidation using hydroperoxides, preferably carried out using hydrogen peroxide, can be performed without catalysis is sustained fashion heterogeneous catalysts of the type molecular sieves. You can, for example, make reference to the catalysts described in the International patent application 96/31455 or in the application for French patent A-2744719. Particularly preferably can be used containing titanium catalysts.

Purification by hydrogenation and/or treatment with nitric acid, and/or by oxidation with molecular oxygen, ozone or hydroperoxide can be done before or after treatment by adsorption of impurities with fine solids, such as, for example, carbon black or alumina. This processing is schematically includes adding carbon black or alumina in a hot aqueous solution containing adipic acid, and filtered in the hot state, the above solution for the separation of soot and adsorbed impurities. This processing can also be carried out continuously using a fixed layer.

For processing by hydrogenation and/or by treatment with nitric acid, and/or treatment by oxidation with molecular oxygen, ozone or hydroperoxide is usually followed by the operation of the crystallization of adipic acid from the water, which allows, in particular, to separate the present glutaric and succinic acid, and then recrystallization in what omashu crystallization, usually sufficient recrystallization.

These crystallization and/or recrystallization can be performed in the above-mentioned conditions. They consist essentially in the extension of adipic acid in a minimum amount of water, usually by heating, and then crystallization or recrystallization of the above adipic acid by cooling the solution under normal conditions of crystallization (for example, gradual programmed reduction temperature, if necessary, the seed crystals of adipic acid).

The following examples illustrate the invention.

Examples 1 and 2 In an autoclave with a capacity of 1.5 l, covered by a shell of titanium and equipped with a turbine with six blades and different holes for the introduction of reagents and fluids or removal of the reaction products and fluids, which is purged with nitrogen at room temperature upload acetate tetrahydrate cobalt - 4.0 g (16 mmol); acetic acid - 357 g (5,95 mol), cyclohexane - 292,5 g (3,48 mol); cyclohexanone - 3.2 g (to 32.7 mmol).

After closing the autoclave, the nitrogen pressure was adjusted to 20 bar, begin stirring at a speed of 1000 revolutions per minute and the temperature was adjusted to 105oWith in 20 minutes. Then the nitrogen replaces otrov per hour.

After an induction period of about 10 minutes, during which there is no consumption of oxygen, the temperature is increased to 2-3oWith starts and oxygen consumption. The percentage of oxygen in the inlet air in the autoclave was gradually brought up to 21% depending on the flow rate due to oxidation.

The percentage of oxygen at the outlet of the reactor remains below 5% throughout the entire experience. The temperature in the autoclave varies from 104,9oTo 105,1oC.

After absorption of 50 l of oxygen (degree of conversion of cyclohexane is about 20%) start continuous injection of the liquid phase: the injection of a solution of acetic acid containing 1.1 wt.% acetate tetrahydrate cobalt, with a flow rate of 3.7 ml/min and the injection of cyclohexane with a flow rate of 4.1 ml/min Liquid product is continuously introduced into the decanter capacity 7 l with a temperature of 70oC.

After 400 minutes after start of the reaction, the air gradually replaced by nitrogen, the contents of the autoclave are transferred into the decanter. The contents of the decanter is a two-phase mixture. The upper, essentially cyclohexane phase, which contains a few products and cobalt are separated. Bottom, acetic acid phase (2340 g) contains mostly products of oxidation and cobalt. Exasperator 135oC.

The results presented in the table.

The distillate is 1830, and the distillation residue is about 510,

b) distillation stage 2: From originating from stage 1) of the residue after distillation to remove the contained volatile organic compounds by entering a water vapor with a temperature of 150oC at a pressure of 10 kPa (743 g of steam for 7 hours).

The results presented in the table.

To the residue after the distillation stage 2 add 1000 grams of water. The entire mixture is heated to a temperature of 70oWith, then gradually cooled down to room temperature according to the following temperature profile: 12oC/hour from the 70oWith up to 60oC; 5oWith/h 60oWith up to 55oS; 11oWith/hour 55oWith up to 44oS; 24oC/hour from 44oWith up to 20oC. After filtration and washing with water to obtain 200 g of crude adipic acid with an average grading of 300 μm, containing (mass/mass): - succinic acid: 0,2000%; - glutaric acid: 0,0030%; cobalt: 0,0100%.

Recrystallization from water 65 g of this crude adipic acid causes acid (A) with an average grading of 300 μm, containing (mass/mass): - succinic acid: is 0.0002%;
- glutaric acid: < 0,0001%;
- cobalt is an ever got adipic acid is subjected to the next process by hydrogenation.

In the autoclave with a capacity of 500 ml, Tacloban shake and heated with an electric furnace, enter 65 g viseporodicnog crude adipic acid from the residue after the distillation stage 2, 152 g of water and 2.8 g of Pd/C catalyst with 10 wt. % palladium. After purging at room temperature using nitrogen can create an increased pressure of 20 bar with hydrogen.

Heated at a temperature of 135oC for two hours. Cooled to a temperature of 70oWith carefully relieve the pressure and the catalyst is filtered off at this temperature. Then adipic acid is recrystallized as above to acid (And). So get purified adipic acid (In), which is very close to adipic acid (A) characteristics in regard to the content of succinic and glutaric acids and cobalt.

65 g of crude adipic acid is subjected to the next process with nitric acid.

158 g 52 wt. % nitric acid heated to a temperature of 65oC. for 10 minutes add 32 g viseporodicnog crude adipic acid from the residue after the distillation stage 2. Then add 70 mg of sodium nitrite. The temperature was raised to 75oC. Maintaining this temperature for 10 minutes d is for 1 hour, then remove the formed nitrous vapours by ozonation of nitrogen for 30 minutes.

Then adipic acid is recrystallized as described above for the acid (a), then washed with water until neutral reaction of the wash water. So get purified adipic acid(C) very close to adipic acid (A) characteristics in regard to the content of succinic and glutaric acids and cobalt.

Party (A), (b) and (C) adipic acid test by heating. This test consists in heating 50 g (acid) each party at a temperature of 215oWith over 205 minutes, then introduce each of them in 415 ml of an aqueous 5% ammonium hydroxide solution.

Then measure the absorbance at 454 nm (yellow part of the spectrum of the received adipate ammonium.

Get the following results, expressed as the absorption attributed to taken as a standard acid (A) having the value 1:
- adipic acid (A): 1
- adipic acid (In): 0,08
- adipic acid (C): 0,12
Adipic acid (b) and (C), treated according to the present invention, significantly less colored than adipic acid (A) not in accordance with the invention. The absorbance at 454 nodnol purity in regard to the content of the lower digisat or catalyst (Co), but which contains more significant trace amounts of other colored impurities.


Claims

1. The method of processing the reaction mixture obtained by direct oxidation of cyclohexane to adipic acid by molecular oxygen in an organic solvent and in the presence of a catalyst, including the removal of by-products from the reaction mixture and adipic acid by crystallization, characterized in that before the adipic acid from the reaction environment carry out consistently the following operations: the decantation of the two phases of the reaction medium with the formation of the upper organic the cyclohexane phase, containing mainly cyclohexane, and the lower phase, containing mainly solvent, the resulting dicarboxylic acid, the catalyst and other reaction products and unreacted cyclohexane; the distillation bottom phase to separate, on the one hand, distillate containing at least a part of the most volatile compounds, such as organic solvent, water and unreacted cyclohexane, cyclohexanone, cyclohexanol, complex cyclohexylamine esters and possibly lactones, and, with depinova acid from residue from distillation by means of crystallization and thus obtained crude adipic acid is subjected in aqueous solution purification by hydrogenation and/or oxidation with subsequent crystallization and recrystallization of the purified adipic acid in water.

2. The method according to p. 1, characterized in that the upper cyclohexane phase obtained in stage decanting, re-enter the stage of oxidation of cyclohexane.

3. The method according to p. 1 or 2, characterized in that the organic solvent used in the oxidation of cyclohexane, which are selected from aliphatic carboxylic acids, preferably acetic acid.

4. The method according to one of paragraphs.1-3, characterized in that the catalytic oxidation of cyclohexane contains cobalt, manganese, a mixture of cobalt with one or more other metals selected from manganese, chromium, iron, zirconium, hafnium, copper.

5. The method according to one of paragraphs.1-4, characterized in that stage distillation bottom phase is conducted in such a way that separate the major part, preferably almost all, of unreacted cyclohexane present in this lower phase, and a solvent.

6. The method according to one of paragraphs.1-5, characterized in that stage distillation is carried out at 25 - 250oC and an absolute pressure of from 10 PA to atmospheric, preferably 70 to 150oC.

7. The method according to one of paragraphs.1-6, characterized in that the stage of distillation of complement extraction residue from distillation with an organic solvent that is not miscible with water. the aliphatic, cycloaliphatic or aromatic hydrocarbons, ethers, aliphatic, cycloaliphatic or aromatic acids and ketones, preferably cyclohexane.

9. The method according to one of paragraphs.1-8, characterized in that the purification is carried out by hydrogenation, and/or by treatment with nitric acid, and/or by oxidation by molecular oxygen, ozone or a hydroperoxide.

10. The method according to p. 9, characterized in that the hydrogenation is carried out using hydrogen in the presence of a catalyst.

11. The method according to one of paragraphs.9 and 10, characterized in that the catalyst contains at least one metal of group VIII of the Periodic system of elements, such as palladium, platinum, ruthenium, osmium, rhodium, iridium, Nickel and cobalt, preferably deposited on a solid support.

12. The method according to p. 9, characterized in that the nitric acid treatment is carried out using an aqueous solution containing 20 to 80% pure nitric acid by weight of solution.

13. The method according to p. 12, characterized in that the nitric acid treatment is carried out by heating the mixture at 25 - 120oWith, preferably 40 - 100oWith in a period of time from several minutes to several hours.

14. The method according to p. 12 or 13, characterized in that the processing Isotko compounds of cobalt, copper and/or vanadium.

15. The method according to p. 9, characterized in that the purification by oxidation is carried out with the help of air, air enriched with oxygen, or air depleted in oxygen and in the presence of a catalyst.

16. The method according to p. 15, characterized in that the catalyst is a metal of group VIII of the Periodic system of elements selected from palladium, platinum, ruthenium, osmium, rhodium, iridium.

17. The method according to p. 9, characterized in that the oxidation is carried out with hydrogen peroxide.

 

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