JPS5946230B2 - Separation method of propylene glycol diester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for separating propylene glycol diester in the production of propylene oxide by reaction of propylene with an organic solution of percarboxylic acid.

Propylene glycol diesters are used as solvents for polymers or as nontoxic inhibitors of bacterial growth (US Pat. No. 2,446,505). The method of obtaining propylene oxide by epoxidizing propylene by the action of percarboxylic acid has been known for a long time (P
rileshayev9Ber. dtsch. chem
．． Ges. 42, p. 4811, 1909).

D●Swern is “0rganicPer0xides
He has written a comprehensive and more recent review in Wiley Interscience 11971, Vol. 2, pp. 355-533, especially pp. 375-378. Percarboxylic acids are generally used in the form of organic solutions for the epoxidation of propylene. (D. Swern, cited above, 37
7, lines 28-29). By-products such as propylene glycol, propylene glycol monoester and propylene glycol diester are readily produced in significant amounts in this reaction for the production of propylene oxide from propylene. This is especially the case when water, a carboxylic acid (commonly corresponding to a percarboxylic acid) or a mineral acid is present in the organic percarboxylic acid solution (e.g. U.S. Pat. No. 3,350,422). , column 2, lines 5-11 and West German Patent Application No. 1,923,392, page 2, lines 19-25). Contaminants of this type, which promote the formation of the above-mentioned by-products, are generally unavoidable in organic percarboxylic acid solutions commonly used for epoxidations.

For example, water is always present from the production of percarboxylic acids. Thus, for example, peracetic acid or perpropionic acid resulting from the respective oxidation reaction of acetaldehyde or propionaldehyde with the formation of various by-products, including water, as a solution in an inert organic solvent, for example ethyl acetate or acetone There is a possibility of separation. (West German Patent Specification No. 1,201,324) (NA.SOk
OlOva et al., Zh. Fiz. Khim. , Volume 35, 85
Page 0 (1961) and RussianJourna
lOfPhysical Chemistry Volume 35 (
(1961) pp. 415-419, especially p. 415, last section of the right column). When percarboxylic acids are prepared from hydrogen peroxide and the corresponding carboxylic acids, percarboxylic acid solutions are obtained which generally also contain water and often also mineral acids. for example,
According to the method of German Patent Application No. 1,043,316, a percarboxylic acid solution is obtained which contains all the catalysts required for the reaction of carboxylic acid with hydrogen peroxide.

In detail, the method involves reacting acetic acid or propionic acid with a hydrogen peroxide solution in the presence of sulfuric acid in a water-immiscible solvent and combining the solvent water and a portion of the water formed during the reaction as an azeotrope. This is a method of removing it by distillation. In this process, the organic solution of percarboxylic acid obtained contains the acid catalyst used in the reaction, for example sulfuric acid (Example 1 of German Patent Application No. 1,043,316).
.

A further method for preparing an organic solution of percarboxylic acid from a carboxylic acid and hydrogen peroxide is the corresponding method.・This is a method in which a carboxylic acid is reacted with hydrogen peroxide in an aqueous solution in the presence of an acid catalyst, and then the resulting reaction mixture is extracted using an organic solvent.

A process of this type is described, for example, in German Patent Application No. 2,141,156, in which according to process J organic solutions of percarboxylic acids having 2 to 4 carbon atoms or the corresponding It can be obtained by reacting a carboxylic acid with an aqueous hydrogen peroxide solution and then extracting it with a hydrocarbon or chlorinated hydrocarbon. The resulting percarboxylic acid solution contains from 0.8 to 4.1% by weight of water (West German Patent Application No. 2,141,156, Example 2).
. It is clear that when using an extraction method of this type, an organic solution of percarboxylic acid is obtained which also contains the acid catalyst, provided that water and a soluble acid catalyst are present in the starting solution to be extracted.

Of course, there will always be some amount of unreacted carboxylic acid. When this type of organic solution of percarboxylic acid is used to epoxidize propylene to obtain propylene oxide, the formation of by-products propylene glycol diester, propylene glycol monoester and propylene glycol due to the presence of water, carbon In order to suppress acids and mineral acids as much as possible, attempts are made, on the one hand, to remove as completely as possible the contaminant water and mineral acids which promote the formation of this type of by-products, and on the other hand, to remove them during the reaction and of the reaction mixture. The process design conditions during the treatment were chosen to minimize these side reactions.

In order to obtain percarboxylic acid solutions dehydrated to the desired degree, an azeotropic dehydration process has been proposed (German Patent Application No. 2,141,156).

It should be pointed out, however, that the desired degree of dehydration of percarboxylic acid solutions cannot be achieved without significant outlay. For example, West German Patent Application Publication No. 1 and 6
No. 18,625, p. 3, last section to p. 4, line 1, it is stated that ``It is desirable to use an anhydrous reaction mixture, but it is not easy or economical to prepare performic acid solutions containing less than 0.3% water.''"It is preferable to use a reaction mixture containing only a small amount of water." The formation of the above-mentioned by-products can also be suppressed to some extent by excluding as much water and mineral acids as possible in the propylene epoxidation reaction (West German Patent Application No. 1,618,625, (page 5, lines 10-14), however, the side reactions giving rise to propylene glycol, propylene glycol monoester and propylene glycol diester cannot be completely stopped.

For example, West German Patent Application No. 1,618,
According to Example 3 of No. 625, the yield of propylene oxide based on the consumed percarboxylic acid is only 8.5%. The reasons for this are, on the one hand, that organic percarboxylic acid solutions generally cannot be used in an absolutely anhydrous state in epoxidations, and on the other hand, even with complete exclusion of water and mineral acids during epoxidation, percarboxylic acid solutions As shown in formula (1), the carboxylic acid corresponding to
This is because the oxirane ring may be opened. ' In the formula, R means a hydrocarbon group.

The glycol monoester produced by opening this propylene oxide ring can itself be further reacted to produce propylene glycol and propylene glycol diester as shown in formula (2).

As is known, an equilibrium between glycol monoesters and glycols on the one hand and glycol diesters on the other hand is established in this reaction (see also German Published Application No. 2,425,844, pages 8 and 9). section).

From equations (1) and (2), even if the reaction is carried out with a very pure percarboxylic acid solution, if propylene oxide is prepared from percarboxylic acid and propylene,
It can be seen that mixtures of propylene glycol, propylene glycol monoesters and propylene glycol diesters must always be expected as by-products. The process design conditions in the reaction also influence the formation of the above-mentioned by-products, and efforts are being made to select the conditions under which this process is carried out industrially so as to prevent the formation of by-products as much as possible. There is.

In this context, in British Patent Specification No. 1,105,261, a non-aqueous solution of peracetic acid and propylene are combined using a series of closed reaction loops that largely prevent mixing of the reaction products with the starting materials. It has been proposed to carry out the following reaction.

However, even under these conditions, 2.5 mol % of propylene glycol monoacetate and a further 2.5 mol % of other high boiling by-products are produced (UK Patent Specification No. 1).
, No. 105, 261, p. 3, lines 63-68). In the method of West German Patent Application No. 1,923,392, propylene is added in the form of bubbles to a reaction system (peracetic acid solution) using a reaction system consisting of a number of reaction zones (actually multi-stage bubble towers). It is said that a reduction in the formation of products from side reactions is achieved when the reaction mixture is introduced at

However, even in this case, it is not possible to completely suppress the production of the above-mentioned by-products. (West German Patent Application No. 1,923,392, page 14, lines 19-20).
However, the glycol and glycol ester by-products mentioned above are not only formed during the reaction between propylene and percarboxylic acids, but can also be formed during the processing of reaction mixtures containing propylene oxide (e.g. in West Germany). Patent Publication No. 2,013,877, page 3, lines 9-16)
.

In order to reduce as much as possible the increase in by-product formation during the process, the epoxidation mixture containing propylene oxide, propylene, acetic acid, solvent and by-products is prepared, for example, according to German Patent Specification No. 1,802,241. It is continuously fed to a first distillation column in which propylene and propylene oxide are distilled off from the top, and then fed to a second distillation column to separate propylene oxide and propylene.

The solvent and acetic acid can be separated from the sump of the first distillation column by redistillation, and the propylene glycol, propylene glycol monoacetate, which may arise partly from epoxidation and partly by side reactions during distillation. and high-boiling by-products or residues such as polypropylene glycol acetate. According to Examples 1 and 3 of West German Patent Specification No. 1,802,241, from 4.4 to 6.2% by weight of such high-boiling ester by-products, based on the propylene oxide introduced into the distillation. (West German Patent Specification No. 1,802,2)
No. 41, column 3, lines 2-3, column 4, lines 24-26 and column 2, lines 28-41). To summarize the problem of producing propylene glycol, propylene glycol monoester and propylene glycol diester during the production of propylene oxide from propylene using percarboxylic acid, the percarboxylic acid is as completely anhydrous as possible and free of mineral acids. The formation of this by-product can be suppressed by using an organic solution of It can be said that it is not possible to completely prevent it. However, since industrial propylene oxide plants are generally very large production units, only a few percent of propylene glycol, a mixture of propylene glycol monoester and propylene glycol diester,
For example, the production of amounts of 1 to 3 mol % of propylene oxide in absolute terms represents a significant amount and its processing and application may give rise to various difficulties.
A particular disadvantage is that the product obtained is always a mixture of the three by-products mentioned above, rather than a product derived from propylene glycol and which is at least substantially homogeneous. In the present invention, a solution of percarboxylic acid in an organic solvent having a boiling point lower than the boiling point of the carboxylic acid corresponding to the percarboxylic acid used as an epoxidizing agent and higher than the boiling point of propylene oxide and propylene are used. essentially propylene oxide, the carboxylic acid corresponding to the percarboxylic acid used as the epoxidizing agent and one or more of the by-products propylene glycol, propylene glycol monocarboxylate and propylene glycol dicarboxylate and propylene and the organic solvent are separated by distillation into a portion containing propylene oxide and propylene and a portion containing carboxylic acid, the above-mentioned by-products and the organic solvent, and these portions are further separated into individual components by distillation. In the production of propylene oxide, a moiety containing a carboxylic acid, one or more of the by-products propylene glycol, propylene glycol monocarboxylate and propylene glycol dicarboxylate and an organic solvent is
．． The organic solvent is removed as overhead product and the carboxylic acid and the corresponding propylene glycol dicarboxylate are distilled in a column with a pressure of 5 to 6 bar and a typical residence time of 10 to 90 minutes at the bottom. A process has now been found for the separation of propylene glycol dicarboxylate, which is obtained as a product and is characterized in that the propylene glycol dicarboxylate is separated off by methods known per se.

The process according to the invention provides a method for preparing propylene oxide by reacting propylene with solutions of a wide variety of percarboxylic acids, i.e. for separating the dicarboxylate of propylene glycol corresponding to a particular variety of percarboxylic acids. It can be used.

For example, D. Swern″0rganicPer0xi
It is possible to use the percarboxylic acids described in "Des", Volume 1, Chapter, pages 313 et seq. Percarboxylic acids having from 1 to 411!L of carbon atoms are particularly suitable.

Acids which may be mentioned individually are performic acid, peracetic acid, perpropionic acid and perbutyric acid. Peracetic acid, perpropionic acid and perisobutyric acid are very particularly suitable. However, percarboxylic acids substituted, for example by chlorine, fluorine or nitro or alkoxy groups, are also suitable. Examples that may be mentioned individually are monofluoroperacetic acid, trifluoroperacetic acid, 1-fluoroethane percarboxylate, 2-
Chloroethane-1 monocarboxylic acid, 2-fluoropropane-1 monocarboxylic acid, 1-fluoropropane-1 monocarboxylic acid, 3-fluoropropane percarboxylic acid, and 2-chloropropane-1 monocarboxylic acid It is an acid. Aromatic peracids such as perbenzoic acid, p-nitrobenzoic acid and monoperphthalic acid may also be used. Very particular preference is given to using perpropionic acid. In principle, all compounds which are essentially inert under the reaction conditions and have a boiling point higher than propylene oxide and lower than the corresponding carboxylic acid of the percarboxylic acid used are suitable as solvents for the peracids.

Generally, the boiling point of the solvent is 37°C or higher. The upper limit for the boiling point of a suitable solvent is generally about 220°C. However, in individual cases it is also possible to use solvents with even higher boiling points. The boiling point of the solvent usually used for percarboxylic acids is about 40-15"C1, e.g. 60
and 120°C. Suitable solvents which may be mentioned are hydrocarbons such as alkanes having 5 to 10 carbon atoms, cycloalkanes such as cyclohexane, methylcyclohexane or ethylcyclohexane, benzene, toluene, xylene, ethylbenzene,
Aromatic hydrocarbons such as chlorobenzene or dichlorobenzene, chlorinated hydrocarbons such as methylene chloride, chloroform, 1,2-dichloroethane, 1,2-dichloropropane or chlorobenzene, containing 1 to 4 carbon atoms Esters of carboxylic acids with alcohols containing 1 to 5 carbon atoms, such as ethyl formate, propyl formate,
Methyl acetate, ethyl acetate, isopropyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate or ethyl isobutyrate.

Particularly suitable solvents are chloroform, methylene chloride, methyl acetate, ethyl acetate and benzene. It is preferable to use benzene. To carry out the epoxidation reaction within the scope of the method embodiment according to the invention, it is also possible to use percarboxylic acid solutions in solvent mixtures.

Poorly compatible solvent for propylene epoxidation. For example, solutions of percarboxylic acids in triisooctyl phosphate can be made compatible with the method by adding more compatible solvents. The concentration of percarboxylic acid in the organic solution can vary within a wide range.
The upper limit is determined by the volatility of such solutions, which increases with increasing concentration of percarboxylic acid. The normal concentration is, for example, 5~
50 weight percent percarboxylic acid. It is appropriate to add stabilizers to the percarboxylic acid solution. Examples of suitable stabilizers are partially esterified vicinal acids or salts thereof, such as Na5(2-ethylhexyl, (P3Ol
O) 2). Stabilizers are often 50-500mg/
Present in an amount of 1 kg of percarboxylic acid solution, typical amounts are 8
0-160 instant/Kg. The reaction between propylene and organic percarboxylic acid can be carried out according to a conventional method.

The reaction can be carried out in a homogeneous liquid phase. Heterogeneous reaction mixtures (eg gas phase/liquid phase) can also be used. The reaction is carried out at normal pressure or at elevated pressure, for example up to 50 bar. A suitable pressure range is 2 to 30 bar. The reaction temperature is generally 0 to 120°C, preferably 20 to 100°C. The molar ratio of propylene to percarboxylic acid can vary within a wide range.

It is appropriate to use an excess of propylene. for example,
The reaction is carried out using a 0.01 to 8.00 molar excess of propylene relative to the percarboxylic acid. All conventional equipment can be used as reaction system for the reaction of propylene with percarboxylic acid, such as tubular reactors or stirred kettle vessels of various sizes as appropriate in terms of diameter and length.

It is also possible to use a cascade of a very large variety of reactor units, for example kettle vessels, loop reactors or reaction loops, for example from 2 to 10 units. Generally, the reaction is carried out in such a way that the percarboxylic acid is completely reacted.

The composition of the mixture resulting from the reaction can also vary widely.

The propion oxide content is, for example, 1 to 50% by weight, preferably 3 to 25% by weight. The concentration of carboxylic acid corresponding to the percarboxylic acid used is therefore also 1 to 50% by weight,
Preferably it can be 3 to 30% by weight. As is clear from the published method description, the content of the by-products propylene glycol, propylene glycol monoester and/or propylene glycol diester depends on the purity (water, mineral acid and carboxylic acid content) and reaction conditions. up to about 25 mole percent of the amount of propylene oxide produced. However, it is also possible without difficulty to obtain even larger quantities of by-products by optionally adding water or mineral acids. However, reaction conditions are generally chosen such that only small unavoidable amounts of these by-products are produced. This is often 1 to 101 usually about 2 to 5 mole percent of the amount of propylene oxide produced. The amount of solvent is generally from 20 to 90% by weight, although amounts above or below this limit may be used in specific cases. The reaction mixture still contains unconverted propylene depending on its solubility. Generally, the reaction mixture is treated by distillation so that the propylene and propylene oxide are co-distilled out of the head in the first distillation, and by-products derived from the solvent, carboxylic acid and propylene glycol are obtained as a pool phase.

A further possible operating method is to take part of the solvent from the head together with propylene and propylene oxide. By separating the head product consisting essentially of propylene, propylene oxide and if appropriate solvent,
Propylene oxide is obtained by known methods and other components are separated off. The bottom product from the first distillation, including by-products derived from carboxylic acid, solvent and propylene glycol, is now again in accordance with the invention with a concentration of 1.5 to
Distilled at a pressure of 6 bar and with an average residence time of 10 to 90 minutes in the reservoir, the organic solvent is removed as head product and the carboxylic acid and the corresponding propylene glycol dicarboxylate are removed in this second distillation. Obtained as a bottom product from the column.

The pressure within the distillation column is preferably between 2.5 and 4 bar, more preferably between 2.8 and 3.2 bar. Generally, the reservoir temperature is about 130-250°C, preferably 150-220°C
, more preferably 160 to 190°C. The temperature at the head is likewise determined by the pressure and also by the temperature of the solvent. The temperature at the head of the column is usually up to 160'C, preferably between 100 and 140C. Fractionation columns are generally designed in such a way that substantially pure solvent is obtained at the top of the distillation column.

It is possible to use small amounts of carboxylic acid, for example less than 1% by weight. The conditions are suitably selected such that the head product contains less than 0.3% by weight of carboxylic acid, preferably less than 0.1% by weight. When the distillation is carried out according to the invention, virtually only propylene glycol dicarboxylate is produced instead of the propylene glycol/propylene glycol monoester/propylene glycol diester by-product.

The water of esterification produced in these reactions is removed from the head together with the solvent and condensed. A portion of the condensate is sent to the column as reflux, suitably after separation of the water. The reflux ratio is generally between 0.2 and 10, preferably 0.
3 to 5, more preferably 0.5 to 2.0. In addition to the propylene glycol diester, carboxylic acids are also present in the reservoir.

Additionally, small amounts of solvent and high boiling components may be present. The amount of solvent is, for example, 1% by weight or less, usually 0.3% by weight or less. Generally, an average residence time of at least 10 minutes is required to direct the formation of by-products as completely as possible in the direction of propylene glycol dicarboxylate. A residence time of 90 minutes is usually sufficient. An average residence time of 20 to 40 minutes is often adequate. All commonly used industrial equipment is suitable as the evaporator of the distillation column. It is appropriate to use a reboiler or a circulating reboiler.
Known fractionating apparatus such as a plated column or a packed column can be used as the column. Because of the corrosive properties of carboxylic acids, special attention must be paid to the material of the reservoir. Solutions to this problem are known. A suitable material is high quality stainless steel which, besides iron, also essentially contains chromium and nickel. Examples of high quality stainless steels that can be mentioned include, in addition to iron, 17.5% by weight of chromium, 11.5% by weight of nickel, 2.25% by weight of molybdenum and also up to 2% by weight of manganese. , materials with DIN designation 1,4571 containing up to 1% by weight silicon, up to 0.1% by weight carbon and small amounts of titanium, or in addition to iron 25% by weight chromium, 25% by weight nickel, 2.
25% by weight of molybdenum and up to 2% by weight (Ff) of manganese, up to 1% by weight of silicon, up to 0.06% by weight of carbon and also small amounts of titanium and according to DIN 1.
This material is designated by the number 4577.

It is designated by the number 2,4812 according to DIN and contains, in addition to nickel, 16% by weight of molybdenum and 16% by weight of molybdenum.
Materials containing % chromium by weight or DIN l, 4439
and in addition to iron, 16.5-18.5% by weight of chromium, 12.5-14.5% by weight of nickel,
4-5 wt.% molybdenum and 0.12-0.22 wt.% nitrogen and up to 0.04 wt. (Ft) carbon, 0
．． Up to 1% by weight silicon, up to 2% by weight manganese, 0.
Materials containing up to 0.03% by weight phosphorus and up to 0.02% by weight sulfur are also suitable. Surprisingly, it is not necessary to add an esterification catalyst in the distillation.

However, it is also possible to add small amounts of esterification catalysts. Catalysts that can be mixed are, for example, sulfuric acid, phosphoric acid, polyphosphoric acid or sulfonic acid. When carrying out the process according to the invention, the mixture of carboxylic acid and propylene glycol diester obtained as bottom product from the distillation column can be easily separated into the individual components.

Generally, the carboxylic acid is distilled off from the dicarboxylate in one further distillation. The propylene glycol dicarboxylate can then be subjected to final purification in known manner, for example by vacuum distillation, until the desired purity is obtained. In a particular embodiment of the process according to the invention, a benzene solution containing, for example, about 15-25% by weight perpropionic acid is used for the epoxidation of propylene.

The water content of this solution is 0.1-2% by weight. A solution of perpropionic acid in benzene is reacted with propylene at a temperature of 60-80° C. and a pressure of 6-12 bar using a molar ratio of perpropionic acid to propylene of 1.2-3. For example, 3 stirred kelt vessels arranged in a cascade are used as reaction vessels and the reaction is carried out in the reaction vessels at 1.5-3.
Perform at residence time of hours. The conversion of percarboxylic acid is from 98 to
It is 100%. The selectivity of the reaction for propylene oxide is 90-98%. Propylene glycol, propylene glycol monopropionate and propylene glycol dipropionate are mainly present in an amount of about 1 to 6 mol % based on the amount of propylene oxide. The composition of the reaction mixture is about 8-12% by weight propylene oxide;
5% by weight propylene, 20-35% by weight propionic acid and 0.15-0.8% by weight propylene glycol, propylene glycol monopropionate and propylene glycol dipropionate, the balance being benzene. The process by distillation begins with the separation of propylene oxide and propylene head products containing about 30 to 5001) benzene, and a bottom product containing residual benzene, propionic acid, and by-products derived from propylene glycol. .

The product withdrawn from the sump of this distillation column is transferred to a second fractionation column equipped with a circulation reboiler and a cooler with a phase separator. At a pressure of 2-3 bar, the benzene is distilled off from the head and the water of esterification is separated from the condensate.

A portion of the upper phase of the reflux is returned to the column as reflux. The reflux ratio is 0.5-2. A solution of about 1-10% by weight propylene glycol dipropionate in propionic acid is obtained as a pool product. In a further distillation column, propionic acid is distilled off from the top at a pressure of 100 to 400 mmH9.

The resulting propylene glycol dipropionate as distillate product is separated with a purity of more than 99% in a final fractionation column equipped with a thin-layer evaporator. It may be possible to directly use it for other purposes. The advantage of the process according to the invention is that in the production of propylene oxide from propylene and percarboxylic acid, the propylene glycol dicarboxylate corresponding to the percarboxylic acid is It is to be separated without any specific other effort.

The problem of separation and/or suitable further application of by-product mixtures of propylene glycol and propylene glycol carboxylic acid esters obtained using methods known to date is also eliminated as a result. Example In one reaction system, 12.67% by weight of propionic acid,
A benzene solution of perpropionic acid containing 0.16% by weight of hydrogen peroxide, up to 0.1% by weight of water and also 250 W/Kg of partially esterified polyphosphate Na salt as stabilizer was prepared at 68.27k9/kg. (20.48 weight - 155.2 mol/hour) to produce 7.4 kg/hour of high purity propylene.
Epoxidation was carried out at a rate of 175.8 mol/hour.

The excess propylene relative to the amount of perpropionic acid supplied is 13
．． It was 3 mol%.

The reaction system consisted of two loop reactors arranged in series and one downward flow delay tube. The reaction was carried out at a pressure of 4 bar. All propylene was fed to the first loop reactor. The reaction temperature in the two loop reactors was 65° C. and the average residence time of the reaction mixture was in each case about 45 minutes. In the delay tube, the reaction temperature was 70°C and the average residence time of the reaction mixture was about 70 minutes. Upon exiting the second loop reactor, the perpropionic acid was approximately 90% converted and after the delay tube the conversion reached 99.8%. As a result, the reaction mixture contained, in addition to the solvent benzene, an average of 1.16% by weight of propylene, 11.8% by weight of propylene oxide, and 2% by weight of propylene.
It contained 6.5% by weight propionic acid and about 0.2% by weight propylene glycol monopropionate. This reaction mixture is sent directly to the distillation column (1) where it contains all of the propylene, propylene oxide and about 1% of the benzene.
0% was isolated as distillate.

In the distillation column (), this distillate is separated from its components, propylene, propylene oxide (8.911<g/h, 99.
90/) Purity - 98 relative to the perpropionic acid used
．． 7%) and benzene as a pool product. The bottom product from column (1) is combined with the bottom product from column (l) and the combined product is transferred to distillation column (1).
was supplied to.

The combined product stream averages 30.5% by weight propionic acid, 69.1% by weight benzene, about 0.2% by weight propylene glycol monopropionate, and small amounts of propylene glycol and propylene glycol dipropionate. Contained. The distillation column () is a packed column (length = 6
m, diameter = 150 mm) and was equipped with a circulation reboiler, a condenser and a separator for phase separation of the distillate at the top of the column.

Feeding took place in the center of the tower. A pressure of 2.6 bar, a residence time of 80 minutes in the column sump, a sump temperature of 180°C,
Benzene (0.11 wt.% propionic acid and 0.09 wt.% propionic acid and 0.09 wt.%
% water) was obtained at 45.5 kg/h.

Over the course of 24 hours, an aqueous phase of 0.51<9 containing about 5% by weight of propionic acid was obtained in the separator.

The bottom product containing about 1% by weight of propylene glycol dipropionate was fed into a distillation column (packed column, length - 4 ml diameter - 150 m 77!). 1007n7tH
propionic acid (approximately 99° C.) at a pressure of 9° C., a sump temperature of 170° C., a column head temperature of 89° C., and a reflux ratio of approximately 0.2.
8% purity) or 19.8 kg/hour.

Claims (1)

[Claims] 1. A solution of percarboxylic acid in an organic solvent having a boiling point lower than the boiling point of the carboxylic acid corresponding to the percarboxylic acid used as an epoxidizing agent and higher than the boiling point of propylene oxide is reacted with propylene, Essentially propylene oxide, a carboxylic acid corresponding to the percarboxylic acid used as an epoxidizing agent and one or more of the by-products propylene glycol, propylene glycol monocarboxylate and propylene glycol dicarboxylate, as well as propylene and an organic solvent. Propylene by separating a reaction mixture containing propylene oxide and propylene by distillation into a portion containing propylene oxide and propylene and a portion containing carboxylic acid, the above-mentioned by-products and an organic solvent, and further separating these portions into individual components by distillation. In the production of the oxide, a portion comprising the carboxylic acid, one or more of the by-products propylene glycol, propylene glycol monocarboxylate and propylene glycol dicarboxylate and an organic solvent is heated at a pressure of 1.5 to 6 bar and at a reservoir. 10
Distillation in a column with an average distillation time of ˜90 minutes removes the organic solvent as an overhead product and yields the carboxylic acid and the corresponding propylene glycol dicarboxylate as a bottom product, from which the propylene glycol dicarboxylate 1. A method for separating propylene glycol dicarboxylate, characterized in that the dicarboxylate is separated by a method known per se. 2. A process according to claim 1 for separating propylene glycol diesters of carboxylic acids containing 1 to 4 carbon atoms. 3. Process according to claim 1 or 2, characterized in that the distillation is carried out at a pressure of 2.5 to 4 bar and a reservoir temperature of 160 to 190°C. 4. The method according to claim 1 or 2, for separating propylene glycol dipropionate. 5. A solution of perpropylene acid in an organic solvent with a boiling point below that of propionic acid and above that of propylene oxide is reacted with propylene to produce essentially propylene oxide, propionic acid and the by-products propylene glycol, propylene glycol mono The reaction mixture containing one or more of propionate and propylene glycol dipropionate and propylene and an organic solvent is distilled into a portion containing propylene oxide and propylene and a portion containing propionic acid, the above by-products and the organic solvent. In the production of propylene oxide by separating and further separating these parts into individual components by distillation, one of the propionic acid, the by-products propylene glycol, propylene glycol monopropionate and propylene glycol dipropionate is separated. the portions containing one or more organic solvents at a pressure of 1.5 to 6 bar and a reservoir of 10
Distillation in a column with an average residence time of ~90 minutes removes the organic solvent as a head product and yields propionic acid and propylene glycol dipropionate as bottom products, then propylene glycol dipropionate. A method for separating propylene glycol dipropionethane according to any one of claims 1 to 4, characterized in that the separation is carried out by a method known per se. 6. The method according to any one of claims 1 to 5, wherein benzene is used as the organic solvent.