IE48737B1 - Process for the manufacture of carboxylic peracids - Google Patents

Description

The present invention relates to a continuous process for the manufacture of carboxylic peracids by reaction of the corresponding carboxylic acids with hydrogen peroxide in the presence of a catalyst, From French Patent No. 2 300 085, filed on 2nd February 1976 in the name of Interox Chemicals Ltd., a process for the manufacture of percarboxylic acids is known, which comprises making an aqueous solution containing sulphuric acid and hydrogen peroxide^nT^ reactor-extractor in countercurrent fashion with an organic solution of a carboxylic acid. At the reactor outlets one collects an organic solution of percarboxylic acid and a dilute aqueous solution of sulphuric acid, which latter must be concentrated before recycling in the reactor.

It is known to manufacture carboxylic peracids by reacting the corresponding carboxylic acid with hydrogen peroxide, generally employed in the form of an aqueous solution, in the presence of small amounts of a catalyst such as sulphuric acid. This reaction gives rise to the formation of water. In order to obtain the carboxylic peracid directly in the anhydrous form, it has been proposed, in U.S. Patent 2 814 641, filed on 31st July 1956, and granted to Union Carbide Corporation, to carry out the reaction in the presence of a solvent which is capable of forming a minimum boiling-point azeotrope with water, and to remove the water formed by the reaction, and also the water for dilution of the reactants, by distillation of this azeotrope.

This known process exhibits certain serious disadvantages. In fact, the proportion of peroxide compounds (hydrogen peroxide and carboxylic peracid) present in the reaction mixture is very large and increases as the reaction and the azeotropic distillation proceed. This involves risks of explosion which make the reaction particularly difficult to carry out. Furthermore, in this known process, the catalyst is present in the organic solution of peracid at the end of the process and it is therefore necessary to provide for the removal of this catalyst. This removal is extremely difficult to carry out. Furthermore, the presence of spent catalyst in the organic solution of peracid proves very inconvenient for all the subsequent uses of this solution, such as its use as an epoxidising agent. Moreover, this process involves a high consumption of catalyst which cannot be recovered. 4-87 37 Thus, in order to limit the disadvantages associated with the presence of the catalyst in the organic solution of peracid, it is necessary to use small relative amounts of catalyst, which generally do not exceed 5% of the weight of carboxylic acid employed, and this has the adverse consequence of substantially reducing the reaction rates. Finally, since the. reaction for the formation of the peracid takes place mainly in the aqueous phase and, furthermore, since this aqueous phase is removed by azeotropic distillation, the rate of production of the peracid decreases very substantially with time aa the aqueous phase disappears. In order to achieve high degrees of conversion, it is therefore appropriate to use very long reaction times. Thus, it is only with great difficulty that this known process can be carried out in installations which operate continuously.

A process has now been found which can very easily be carried out continuously and which does not exhibit the abovementioned disadvantages.

The present invention therefore relates to a continuous process for the manufacture of carboxylic peracids by reaction of the corresponding carboxylic acid with hydrogen peroxide in the presence of a catalyst and of an inert organic liquid which is a solvent for the peracid and is capable of forming a heterogeneous azeotrope with water, in which water present in the reaction mixture is removed by distillation of the water/organic liquid azeotrope, wherein water is kept in the reaction mixture in a sufficient amount for the formation of an aqueous phase which is distinct from an organic phase containing the carboxylic acid, the carboxylic peracid and the organic liquid and wherein part of the reaction mixture is removed and the aqueous phase is separated from the organic phase.

In general, the amount of water kept in the reaction mixture is sufficient for the weight ratio of the aqueous phase to the organic phase, in the reaction mixture, to be more than 0.05. Preferably, this ratio is more than 0.1. The best results are obtained when the ratio is more than 0.2.

Furthermore, in most cases, it is of no value to keep amounts of water in the reaction mixture which are such that the weight ratio of the aqueous phase to the organic phase is more than 20. Preferably, this ratio is less than 10. The best results are .obtained when it is less than 5.

The aqueous phase generally comprises from 5 to 95%, and most frequently from 10 to 70%, of its weight of water, the remainder substantially consisting of the constituents of the reaction mixture and mainly of the hydrogen peroxide and the catalyst when the latter is soluble and is not in the form of a solid suspension. It also generally comprises part of the carboxylic acid and part of the carboxylic peracid.

The water present in the aqueous phase can originate, in particular, from the reaction or from the introduction of certain constituents of the reaction mixture, in general the hydrogen peroxide and, if appropriate/the catalyst, in the form of aqueous solutions. It may also have been added intentionally.

The organic phase generally comprises from 30 to 98%, and most frequently from 40 to 95%, of its weight of organic liquid, the remainder substantially consisting of constituents of the reaction mixture and mainly of the carboxylic acid and the carboxylic peracid.

It can also contain small amounts of hydrogen peroxide and, if appropriate, small amounts of catalyst.

In general, the proportion of hydrogen peroxide in the organic phase does not exceed 5% of its weight and the proportion of catalyst therein does not exceed 1% of its weight. Most frequently, the respective proportions of hydrogen peroxide and catalyst in the organic phase do not exceed 2 and 0.4% of its weight.

The organic liquid employed in the reaction mixture must be inert with respect to the various constituents . of the reaction mixture under the reaction conditions.

Moreover, it must be able to form, with water, a minimum boiling-point heterogeneous azeotrope of which the boiling point, under the same pressure conditions, must be lower than the boiling point of the other constituents and of the other possible azeotropes which could be formed in the reaction mixture.

Finally, it must dissolve the carboxylic peracid formed during the reaction and preferably to such an extent that, under the reaction conditions, the concentration of the peracid in the organic phase, expressed in mols per litre, is equal to at least 0.05 and preferably at least 0.2 times the concentration of the peracid in the aqueous phase.

According to a preferred embodiment of the process according to the invention, part of the reaction mixture is withdrawn continuously and the aqueous phase is separated from the organic phase, by decantation, in the part which has been withdrawn. Preferably, the aqueous phase separated in this way is re-introduced into the reaction mixture. The organic phase separated in this way constitutes the production.

This embodiment is particularly advantageous when employing an organic liquid which is very sparingly soluble in water and in which water is sparingly soluble. Preferably, the organic liquid chosen is such that the proportion of water in the organic phase is less than the proportion of water in the water/organic liquid azeotrope, under the same temperature and pressure conditions; most frequently, it is chosen so that the amount of water in the organic phase is less than 5% and preferably less than 1%. On the other hand, the amount of organic liquid dissolved in the aqueous phase is less critical; in general, the organic liquid is chosen so as to ensure that this amount does not exceed 10% and most frequently 5%. Moreover, the organic liquid chosen is such that the densities of the aqueous and organic phases are sufficiently different to permit their separation by decantation. - 48737 The invention also relates to the use of the organic phase obtained on decantation of the abovementioned embodiment, without prior separation into its main constituents, for the manufacture of epoxides from olefins, in accordance with processes which are in them5 selves well known.

This organic phase contains variable amounts of carboxylic peracid, which are generally between 5 and 40% by weight. Before being employed for epoxidation, it . can be subjected to various treatments, for example in order to remove the final traces of·moisture and catalyst.

However, these treatments are not essential. During the epoxidation reaction, the molar ratio of the carboxylic peracid to the olefin which is to be epoxidised, is generally between 0.01 and 20. It is preferably between 0.1 and.

. It is also possible to add to the reaction mixture small amounts of various additives such as polymerisation inhibitors, stabilisers for the peracid, or sequestering agents .

The epoxidation reaction is generally carried out at temperatures between 0 and 15O°C. These temperatures are preferably between 15 and 120°C. The reaction pressure is generally sufficient to maintain at least one liquid phase. It is generally between 0.05 and 80 kg/cm . Of course, the reaction temperature and pressure depend on the particular nature of the olefin which is to be epoxidised. Thus, in order to epoxidise propylene, a temperature of 20 to 100°C and a pressure of 0.8 to 30 Π kg/cm are most frequently used. In order to epoxidise allyl chloride and allyl alcohol, a temperature of 20 to 150°C and a pressure of 0.1 to 10 kg/cm2 are most frequently used. The reactors used for carrying out the epoxidation reaction are generally reactors which assist heat exchange so as to permit a better control of the reaction temperatures. Tubular reactors or autoclaves, a single reactor or reactors in cascades can thus be used.

The reaction mixture obtained on epoxidation 4-8 73 7 consists essentially of the organic liquid, olefin oxide, carboxylic acid and. unconverted reactants; it may contain small amounts of by-products and small amounts of various additives. It is usually subjected to a first separa5 tion so as to recover, on the one hand, the unconverted, olefin, and, on the other hand, a first organic solution consisting essentially of organic liquid, the olefin oxide, carboxylic acid and, possibly, unconverted carboxylic peracid.

In the case of volatile olefins, for example propylene, this separation is advantageously carried out by a simple rapid reduction in pressure to atmospheric pressure. In the case of less volatile olefins, for. example allyl chloride or allyl alcohol, this first separation can be I5 carried out by distillation. The olefin collected is advantageously recycled to the epoxidation reaction. In order to do this, the olefin can be absorbed in the gaseous form in the organic phase containing the peracid, before . sending it to the epoxidation reaction. It is also pos20 sible to condense the olefin and then simply to send it to the epoxidation reaction.

The first organic solution collected from the first separation is usually subjected to a second separation, advantageously by distillation, so as to recover, on the one hand, the desired olefin oxide, and, on the other hand, a second organic solution of carboxylic acid in the organic liquid. The olefin oxide can be used as obtained or can be subjected to certain subsequent purification steps in order to remove therefrom the possible traces of by-products such as aldehydes.

According to the variant which is now being described, the solution of carboxylic acid in the organic liquid, which may additionally contain the unconverted carboxylic peracid and also certain by-products and additives such as those mentioned above, is returned directly to the manufacture of the peracid. This solution is .. 48 7 37 advantageously pre-heated before being introduced into the reaction zone, so as to provide at least part of the heat required for the azeotropic distillation.

When using this preferred variant, the organic 5 liquid is chosen from amongst those of which the boiling point is higher than the boiling point of the olefin and the olefin oxide. Furthermore, the organic liquid should not form an azeotrope with the olefin and the olefin oxide. Finally, in the case where the organic liquid is capable of forming an azeotrope with the carboxylic acid or the carboxylic peracid, the boiling points of these azeotropes should be higher than those of the olefin and the olefin oxide.

Any organic compound which is liquid under the reac15 tion conditions corresponding to the conditions defined above can be suitable for carrying out the process according to the invention. These liquids are generally chosen from amongst carboxylic acid esters, ethers, halogenohydrocarbons, unsubstituted hydrocarbons, hydrocarbons substituted by nitro groups, non-acidic esters of nitric acid, carbonic acid and phosphoric acid^ and mixtures thereof.

As carboxylic acid esters which are generally very suitable, there may be mentioned aliphatic, alicyclic or aromatic esters of mono- or poly-carboxylic acids with mono- or poly-hydric alcohols containing from 4 to 20, and preferably from 4 to 10, carbon atoms in the molecule. Amongst these carboxylic acid esters, those which are- particularly suitable are isopropyl, propyl, butyl, isobutyl, sec.-butyl, tert.-butyl, amyl, isoamyl and sec.-amyl formates and acetates, methyl, ethyl, propyl, isopropyl, butyl, isobutyl and isoamyl mono- and di-chloroacetates, propionates, butyrates and isobutyrates, methyl, ethyl and propyl valerates, isovalerates and caproates, methoxyethyl, ethoxy35 ethyl and cyclohexyl acetates, methyl pivalate and the diethyl esters of phthalic acid and adipic acid.

As ethers which are generally very suitable, there may be mentioned symmetric or asymmetric aliphatic ethers containing from 4 to 12 carbon atoms, such as 2,2'-dichlorodiethyl ether, butyl ethyl ether, tert.-butyl ethyl ether, tert.-amyl methyl ether, diisopropyl ether, dipropyl ether, dibutyl ether, ethyl hexyl ether and diisobutyl ether.

As halogenohydrocarbons which are generally very suitable, there may be mentioned aromatic, aliphatic and alicyclic halogenohydrocarbons which contain from 1 to 8 carbon atoms in their molecule and are substituted by at least one halogen which is preferably chosen from amongst chlorine, fluorine and bromine. Particularly suitable halogenohydrocarbons are carbon tetrachloride, chloroform, methylene chloride, di-, tri-, tetra- and penta-chloroethanes, trichlorotrifluoroethanes, tri- and tetra-chloroethylene, mono-, di- and tri-chloropropanes, monochloro- or polychloro-butanes, -methylpropanes, -pentanes and -hexanes, mono- and di-chlorobenzenes and chlorotoluenes.

As hydrocarbons substituted by nitro groups which are generally very suitable, there may be mentioned aromatic, aliphatic or alicyclic hydrocarbons containing from 3 to 8 carbon atoms, such as nitropropanes, nitrobenzene and nitrocyclohexane.

As unsubstituted hydrocarbons which are generally very suitable, there may be mentioned aliphatic, aromatic or alicyclic hydrocarbons containing from 5 to 14 carbon atoms, such as benzene, toluene, xylene, pentane, hexane, heptane, octane, diisobutyl, cyclohexane, methylcyclohexane and tetralin.

As carbonic acid esters which are generally very suitable, there may be mentioned aliphatic esters containing from 3 to 9 carbon atoms in the molecule, such as dimethyl, diethyl, diisobutyl, dibutyl, di-tert.-butyl, dipropyl and diisopropyl carbonates. Nitric acid esters which are generally very suitable are those chosen from amongst aliphatic esters containing from 1 to 5 carbon atoms in the molecule, such as methyl, propyl, butyl and isoamyl nitrates. Phosphoric acid esters which are very suitable are those which correspond to the formula OR1 = P -ORg in which Rg, Rg and R^ are identical or different and represent alkyl, aryl, arylalkyl or alkylaryl groups which are such that the molecule contains from 3 to 30 carbon atoms. Trimethyl, tributyl, trioctyl and dioctyl phenyl phosphates may be mentioned as examples of particular phosphates.

Organic liquids which are particularly suitable for use in the manufacture of peracetic acid and perpropionic acid are benzene, toluene, 1,2-dichloropropane, 1,1,2,2-tetrachloroethane, pentachloroethane, tetrachloroethylene, 1-nitropropane, chlorobenzene, para-chlorotoluene, methyl chloroacetate, diethyl carbonate, dichloroethane, butyl acetate, cyclohexane and tributyl phosphate. Particularly good results are obtained with 1,2-dichloropropane, 1,2-dichloroethane, 1,1,2,2-tetrachloroethane and mixtures thereof.

The azeotrope collected by distillation is generally condensed and separated by decantation, so as to separate the water from the organic liquid. The organic liquid thus collected can advantageously be used, at least in paid:, for ensuring reflux in the distillation zone. It can also be re-introduced, in general after vaporisation, into the reaction zone in order to serve the purpose of forming the organic phase. This introduction in the form of a vapour makes it possible to provide at least part of the heat required for the vaporisation of the water/organic liquid azeotrope.

The process of the invention can be applied to the manufacture of a large number of carboxylic peracids.

Thus, it can be used for forming peracids starting from mono- or poly-carboxylic acids. In the latter case, the polycarboxylic acid can also he employed in the form of the corresponding anhydride in the process according to the invention. The process according to the invention is particularly suitable for the production of peracids from carboxylic acids containing from 1 to 10 carbon atoms, such as aliphatic, alicyclic or aromatic carboxylic acids, for example formic acid, acetic acid, chloroacetic acids, propionic acid, butanoic acid, maleic acid or maleic anhydride, benzoic acid, cyclohexanecarboxylic acid and phthalic acids and phthalic anhydride. Particularly advantageous results are obtained when manufacturing peracetic acid and perpropionic acid starting from acetic acid and propionic acid respectively.

The catalyst employed is generally an aoid catalyst which is suitable for esterification reactions, such as, for example, sulphuric acid, alkyl-, aryl-, arylalkyl- and alkylaryl-sulphonic acids, phosphoric acid, alkyl, aryl, alkylaryl and arylalkyl acid phosphates, trifluoroacetic acid, acetylsulphoacetic acid and also ion exchange resins of the sulphonated polymer or copolymer type. Preferred, catalysts which may be mentioned more particularly are sulphuric aoid and methane-, ethane-, benzene-, toluene-, xylene-, butane-, propane- and naphthalene-sulphonic acids. Amongst these catalysts, it is preferred to use those which are soluble in water and are insoluble or sparingly soluble in the organic liquid. The best results are obtained with the water-soluble catalysts of which the concentration in the organic phase is less than 3%, and preferably less than 1%, by weight, under the reaction conditions. Particularly advantageous results have been obtained with sulphuric aoid.

The concentration of catalyst in the reaction mixture can vary within wide proportions. In order to obtain fast reaction rates, high concentrations of catalsysts are generally used. The amount of catalyst used is generally more than 5% of the total weight of carboxylic acid and carboxylic peracid present in the reaction mixture. The proportion by weight of catalyst is preferably between 0.1 and 30 times the total weight of carboxylic acid and carboxylic peracid present in the reaction mixture. The best results are obtained when this proportion is between 0.2 and 10 times the total weight of carboxylic acid and carboxylic peracid.

The catalyst can be employed in the pure state. However, it is advantageously employed in the form of an aqueous solution if it is soluble in water. In this case, the catalyst can advantageously be employed by reintroducing, into the reaction mixture, the aqueous phase originating from the separation of the latter by decantation, after having added an additional amount of catalyst if necessary. In general, the concentration of watersoluble catalyst in the aqueous phase is between 10 and 605$ by weight.

The carboxylic acid can be employed in the pure state in the process according to the invention. How- . ever, it is generally employed in the form of a solution in the organic liquid. Such solutions containing from 2 to 705$, and preferably from 5 to 605$, by weight of carboxylic acid are advantageously introduced into the reaction mixture. In order to prepare these solutions, it is possible to use organic liquid originating from the separation of the distilled azeotrope by decantation, fresh organic liquid or also organic liquid which has been recovered after using the organic solution of peracid.

The hydrogen peroxide used for the reaction can be employed either in the pure state or in the form of aqueous solutions.

The hydrogen peroxide can be employed in the form of an aqueous solution. Concentrated solutions of hydrogen peroxide, containing from 20 to 905$ by weight of hydrogen peroxide, are advantageously used. Other concentrations can also be suitable but are less favourable.

In fact, at lower concentrations of hydrogen peroxide, the amounts of water to be removed by azeotropic distillation are very large, whereas solutions which are more highly concentrated in hydrogen peroxide are difficult to produce industrially.

The proportions of reactants in the reaction mixture can vary within wide limits, in absolute terms and relative to one another, depending especially on the chosen rates of introduction of the reactants. Thus, the amount of hydrogen peroxide is generally between 0.1 and 10, and preferably between 0.2 and 5, mols per mol of carboxylic acid function. The most advantageous results are usually obtained when the amounts of hydrogen peroxide and carboxylio acid introduced into the reaction mixture are in a ratio which is close to, or slightly less than, the stoichiometric ratio. The hydrogen peroxide and the carboxylic acid are therefore preferably introduced in amounts such that between 0.2 and 2, and preferably between 0.4 and 1.2, mols of hydrogen peroxide are introduced per mol of carboxylic acid function.

The hydrogen peroxide can be introduced directly into the reactor or into the aqueous solution of catalyst sent to the reactor, when this catalyst is soluble in water.

The hydrogen peroxide is advantageously introduced into the aqueous solution of catalyst sent to the reactor. The hydrogen peroxide is most frequently introduced into the aqueous phase which is collected by separation of the reaction mixture by decantation and is recycled continuously to the reactor. This introduction is advantageously carried out in stages so as to prevent the local concentrations of hydrogen peroxide from becoming too high. The flow rate of the continuously recycled aqueous phase must be sufficient for the composition of the resulting aqueous phase enriched in hydrogen peroxide to always be such that the reaction mixture remains outside the explosion limits.

The temperature of the reaction mixture is generally chosen to be below 100°C and it is most frequently between 20 and 70°C. Higher temperatures are less valuable because they involve a risk of sudden decomposition of the peroxide compounds. The pressure is regulated as a function of the temperature, so as to maintain boiling.

Thus, it can vary within wide proportions. It is most frequently between 0.01 and 1.2 kg/cm .

The heat required to maintain boiling can be provided in accordance with conventional techniques which are m themselves known. Thus, it is possible to heat the reaction mixture (aqueous phase and organic phase) by bringing it into contact with an exchange surface heated by means of a heat-transfer fluid such as steam. It is also possible and advantageous to introduce the organic liquid, 10 the carboxylic acid or also mixtures thereof into the reaction mixture in the form of vapour.

In order to carry out the process according to the invention, any apparatus which is suitable for liquid reaction mixtures can be used, in particular vat - reactors equipped with a stirring system. More particularly, it is advantageous to use reactors, in themselves known, which make it possible to distil one of the constituents of a liquid reaction mixture during the reaction. In general, the reactors used make it possible to. ensure intimate mixing of the aqueous and organic phases and a good exchange between the liquid phases and the gaseous phase, so as to assist the vaporisation of the water/ organic liquid azeotrope.

These reactors are advantageously coupled to dis25 filiation columns which are in themselves known, such as plate columns or packed columns.

The various parts of the reactors and of the columns in contact with the reaction mixture are advantageously made of corrosion-resistant materials such as stainless steels, the alloys known by the Trade Marks, INCONEL, HASTELLOY, INCOLOY, NIMONIC, NI-RESIST and CHLORIMET, and enamelled steels.

The separation, by decantation, of the reaction mixture withdrawn from the reactor, and that of the water/ organic liquid azeotrope collected at the top of the column, can be carried out in accordance wi'th various techniques which are in themselves known, such as separation by gravity or by the action of a centrifugal force, or passage through porous membranes which are selectively wetted by one or other of the phases. Various types of apparatuses which are in themselves known can be used for this purpose. Thus, it is possible to use florentine separators, centrifugal separators, separating filters with membranes, or electrical separators. The separation by decantation can be facilitated by a prior operation for coalescing the droplets in apparatuses which are in themselves known, such as pads or shells made of fibrous materials which can preferably be wetted by the disperse phase.

The process according to the invention can be carried out continuously in an apparatus such as that shown schematically in the single figure of the attached drawing, which relates to a particular practical embodiment.

A concentrated solution of hydrogen peroxide and catalyst, obtained by mixing, in the mixer 22, aqueous hydrogen peroxide introduced via 3 with catalyst introduced via 8, is introduced via 23 into a reactor 1 surmounted by a distillation column 2, and a solution of carboxylic acid in an organic liquid, obtained by mixing, in the mixer 6, the carboxylic acid introduced via 4 with the organic liquid introduced via 7, is introduced via 5 into the said reactor 1.

In the course of the reaction, the water/organic liquid azeotrope leaves the distillation column 2 via 9, is condensed in the condenser 10 and is sent via 11 to the separator 12. If the organic liquid has a higher density than that of water, the water is collected via 13 at the top of the separator and the organic liquid is collected via 14 at the bottom of the separator; in the opposite case, the withdrawals are reversed. The organic liquid is recycled via 15 to the distillation column, where it constitutes the reflux. In certain cases, part of this organic liquid can be sent via 16 into the mixer 6, where it acts as a solvent for carboxylic acid.

Part of the reaction mixture is withdrawn continuously from the mixer reactor via 17 and is sent to the separator 18. If the density of the organic phase is lower than that of the aqueous phase, the organic phase, which contains the carboxylic peracid produced, is withdrawn at the top of the separator 18 (via 20) and the aqueous phase, vzhich is recycled to the reactor via 19, is withdrawn at the bottom of the separator 18. A bleed 21 makes it,possible to remove some of the by-products which build up in the aqueous phase. The organic phase collected via 20 can be directly used as obtained, especi10 ally for carrying out epoxidation reactions, or it can also be subjected to purification treatments for removing therefrom the final traces of moisture or catalyst.

The process according to the invention proves particularly valuable because it makes it possible to obtain continuously organic solutions which are essentially anhydrous and have a high concentration of carboxylic peracid. Moreover, the explosion risks due to the decomposition of the peroxide compounds in the reaction medium are greatly reduced because the total concentration of peroxide com20 pounds is kept at a constant level and because points of concentration of peroxide compounds are never observed.

The total proportion of peroxide compounds in the reaction mixture remains permanently at a relatively low level. Furthermore, the degree of conversion of the reactants is excellent. Similarly, the process does not cause the destruction of the catalyst and does not require any complicated process for the recovery of the catalyst and, in particular, it does not require any distillation. Finally, the process makes it possible to choose reaction conditions which enable remarkably fast reaction rates to be achieved.

The carboxylic peracids obtained in accordance with the process of the present invention can be used as a source of active oxygen in numerous chemical reactions and more particularly for the manufacture of epoxides from olefins. For this purpose, any optionally substituted organic compound can be employed vzhich contains at least one unsaturated carbon-carbon bond and which more particularly contains from 2 to 20 carbon atoms in its molecule. Examples of such olefins which may be mentioned are propylene, allyl chloride, allyl alcohol and styrene.

In order to illustrate the invention, without thereby limiting its scope, an example of the manufacture of a carboxylic peracid is given below.

Example The apparatus used is similar to that represented schematically in Figure 1.

The reactor, which has a capacity of 1 litre, initially contains 0.2 kg of 45% strength sulphuric acid.

The temperature of the reactor is maintained at about 39°C and the pressure therein is about 100 mm of mercury. 0.12 kg.per hour of a 70% strength by weight aqueous solution of hydrogen peroxide and 1.07 kg per hour of a 27% strength by weight solution of propionic acid in 1,2-dichloropropane are introduced continuously into the reactor.

The weight ratio of the aqueous phase to the organic phase present in the reactor is 1.04. A stirring system keeps the aqueous phase and the organic phase as an emulsion.

Part of the reaction mixture is withdrawn continuously. After separation of the withdrawn fraction by decantation 1.11 kg per hour of an organic solution having the following composition: g/kg perpropionic acid 200 propionic acid 92.2 hydrogen peroxide 2.89 water traces sulphuric acid 1.27 1,2-dichloropropane 703-64 are obtained.

An examination of the results obtained in the example shows that it is possible, by using the process of the invention, to obtain organic solutions having high concentrations (20%) of perpropionic acid, which is virtually free from water and catalyst.

The concentrated organic solution obtained in this way can be used directly, for example in order to epoxidise propylene. A solution of propylene oxide in 1,2-dichloropropane, additionally containing propionic acid and unreacted propylene, is thus collected. A first distillation of this solution makes it possible to collect the unreacted propylene at the top of the column. A second distillation yields propylene oxide at the top of the column and a solution of propionic acid in 1,2-dichloropropane at the bottom. This solution can be used directly for carrying out the reaction for the manufacture of perpropionic acid.

Claims (14)

1. Continuous process for the manufacture of percarboxylic acids by reacting the corresponding carboxylic acid with hydrogen peroxide in the presence of a catalyst and of an inert organic liquid which is a solvent for the peracid and is capable of forming a heterogeneous azeotrope with water, in which water present in the reaction mixture is removed by distillation of the water/organic liquid azeotrope, wherein water is kept in the reaction mixture in a sufficient amount for the formation of an aqueous phase which is distinct from an organic phase containing the carboxylic acid, the carboxylic peracid and the organic liquid, and wherein part of the reaction mixture is removed and the aqueous phase is separated from the organic phase.

2. Process according to Claim 1, wherein the weight ratio of the aqueous phase to the organic phase in the reaction mixture is greater than 0.1 and less than 10.

3. Process according to Claim 1 or 2, wherein the aqueous phase is separated from the organic phase by decantation.

4. Process according to Claim 3, wherein the aqueous phase separated off is reintroduced into the reaction mixture.

5. Process according to any one of Claims 1 to 4, wherein the organic liquid is chosen such that the solubility of water in the organic phase is less than the water content of the water/organic liquid azeotrope.

6. Process according to any one of Claims 1 to 5, wherein the amount of catalyst present in the reaction mixture is betweeen 0.1 and 30 times the total weight of carboxylic acid and percarboxylic acid.

7. Process according to any one of Claims 1 to 6, wherein the organic liquid is chosen from amongst unsubstituted hydrocarbons, hydrocarbons substituted by nitro groups, and non-acid esters of nitric, phosphoric and carbonic acids.

8. Process according to any one of Claims 1 to 7, wherein the carboxylic acid is propionic acid or acetic acid. 4,8737

9. Process according to any one of Claims 1 to 8, wherein the catalyst is chosen from amongst sulphuric acid, alkyl-, aryl-, arylalkyl- and alkyl aryl-sulphonic acids, phosphoric acid, alkyl, aryl, alkylaryl and arylalkyl acid phosphates, trifluoroacetic acid, acetylsulphoacetic acid and sulphonated ion exchange resins.

10. Process according to any one of Claims 1 to 9, ^herein the organic liquid is chosen from amongst 1,2-dichloropropane and 1,2-dichloroethane, the carboxylic acid is propionic acid and the catalyst is sulphuric acid.

11. Use of the organic phase containing percarboxylic acid, obtained in the process according to any one of Claims 1 to 10, for the manufacture of epoxides from olefines, wherein the unreacted olefine and the olefine oxide produced are successively separated from the reaction mixture originating from the manufacture of epoxides, and the carboxylic acid, in the form of the solution which is collected, is returned directly to the manufacture of the peracid.

12. Use according to Claim 11, wherein an organic liquid is chosen, the boiling point of which is higher than that of the olefine and that the olefine oxide, which does not form an azeotrope with the olefine and the olefine oxide, and of which the possible azeotropes with the carboxylic acid and the percarboxylic acid have a boiling point which is higher than that of the olefine and that of the olefine oxide.

13. A process for the manufacture of percarboxylic acids substantially as described herein with reference to the Example.

14. A percarboxylic acid whenever prepared by a process as claimed in any one of claims 1 to 10.