CS265079B1 - Method of concentrating 1-methoxy-2-propanone in its mixtures with 1-methoxy-2-propanol - Google Patents

Abstract

The method of concentrating 1-ethoxy-2-propanone in its mixtures with 1-methoxy-2-propanol by rectification consists in that the rectification of the mixture is carried out under reduced pressure of 80 to 1 kPa, preferably 50 to 5 kPa. 1-Methoxy-2-propanone is an important intermediate in the production of oesticides.

Description

l-L'ethoxy-2-propanone /1/ is a special intermediate in the production of pesticides, etc. When it is produced from l-methoxy-2-propanol /11/ by dehydrogenation, after the removal of by-products, usually only dilute solutions of ketone I are obtained, most often about 25 to 55 wt. %, in the initial unreacted proportion of alcohol II. In some cases, these solutions can be used directly, but it is often necessary to increase the concentration of l-methoxy-2-propanone in them. Both considered components I and II are liquid, relatively thermally stable, and their distillation separation and thus enrichment should seemingly be easy. In reality, this is a very difficult problem given the similarity of the boiling points of both components, 116 °C and 118 °C at atmospheric pressure, and in addition, the fact that these components behave non-ideally and pass together during normal rectifications. Therefore, it is not possible to obtain solutions more concentrated than about 62% from diluted mixtures of ketone I, the remainder being alcohol II. The problem of separating or concentrating l-methoxy-2-propanone in its mixtures with l-methoxy-2-propanol has already been addressed in several patents.

According to the data of US-pat. 2 170 855, alcohol II is separated from mixtures of substances I and II by first adding acid anhydrides, e.g. butyric, to the corresponding ester, from which ketone I is then more easily separated by distillation. However, the remaining ester must then be hydrolyzed, and the liberated alcohol II and acid isolated and concentrated. The method is therefore complicated by the consumption of chemicals and the number of operations. Another US-pat. 2 805 983 recommends adding a suitable aliphatic alcohol to the mixture of substances I and II, which forms an azeotropic mixture with ketone I, which is more easily separated from component II. For example, propanol forms the corresponding mixture with a content of 40% by weight of ketone I, which then needs to be further modified by changing the conditions to an azeotrope of about 15%, while the rest of the ketone in question is obtained

2.

265 079 by atmospheric rectification as high-percentage. The method thus again requires auxiliary chemicals as well as equipment and operations. US-pat.<5 625 856 recommends water as a cheaper azeotropic additive, forming with l-methoxy-2-propanone a mixture boiling at 95 °C and containing approximately 70 wt. % of the ketone in question. However, this does not greatly simplify the separation from l-methoxy-2-propanol, because it also forms an azeotropic mixture with water, only with a slightly higher boiling point, approximately 96 °C. In addition, water can only be removed from the azeotrope with ketone I by further azeotropic distillation with benzene, in a separate column. Another, allegedly more effective separation of ketone I from alcohol II is reported in NSR-pat.c2 526 748 and independently also US-pat.I4 155 156, namely by extractive distillation with glycols, or with triols to polyols. These additives are introduced at the top of the distillation column against the vapors of components I and II, while component II is extracted and ketone I is distilled. Its achievable concentration in the condensates depends on the amount of extraction agent /up to 20 times greater than the injection of the separated mixture/, on the efficiency of the columns /up to 50 theoretical plates/ and on the reflux ratio /up to 20:1/.

The descriptions of the aforementioned patents state that the achieved concentrations of ketone I are mostly about 91 to 96%, the remainder being alcohol II. It is clear that despite the high technical complexity of the process, achieving concentrated l-methoxy-2-propanone is also very difficult.

A substantially simpler method of efficient concentration of 1-methoxy-2-propanone in its mixtures with 1-methoxy-2-propanol, which is the subject of this invention, consists in separating the starting mixtures of the considered components I and II by rectification under reduced pressures in the range of 80 to 1 kPa, preferably 50 to 5 kPa. We have found that under reduced pressures azeotropic mixtures are formed which have a higher concentration of ketone lj than under atmospheric pressure. This makes it possible to relatively easily obtain distillates enriched with ketone I, approximately 70 to 90% by weight, depending on the composition of the starting mixtures, on the reduced pressure and on the rectification device. The decisive factor in concentrating ketone I in its mixtures with alcohol II according to this invention is the real need for a particular use of the ketone, so it is not always expedient to strive to achieve the highest concentration. This makes it possible to choose a specific embodiment relatively widely according to need and with regard to the lowest possible investment and operating costs. In the rectifications considered, azeotropes with a minimum boiling point are always formed. In practice, this means that all ketone I present in its initial dilute solutions of l-methoxy-2-propanol can pass in the form of an azeotrope at a lower boiling point than methoxypropanol itself. The differences in boiling points are understandably small here even at reduced pressures, and therefore the sharpness of the separation of azeotropes from the alcohol II considered depends on the efficiency of the rectification. The advantage of the method according to the present invention, however, is that satisfactory separation is achieved even on relatively simpler columns, with a lower number of theoretical plates than would correspond to the general assumptions based on the difference in boiling points. This is manifested only by a certain reduction in the content of l-methoxy-2-propanone in the distillates, which, however, is not a defect for various uses, as already mentioned.

As typical examples, the dependencies that were found between the concentrations of methoxypropanone in azeotropic solutions are given.

mixtures and pressure with propanol /4 for equilibrium pressure during rectification kPa with rectifications of its 9% I and 51% 11/ on medium starting mixture with methoxy-effective column /8 TP/ azeotropes ÍAaO t . /ΰ II of states: boiling point of azeotropes °C composition I 101.3 115 62.1 37.9 80.0 107 72.2 27.8 53.3 94 75.2 24.8 26.6 76 77.7 22.3 13.3 58 80.6 19.4 6.6 43 82.4 '· 17.6 5.6 31 . 84.2 15.8 1.8 19 87.4 12.6 /Note: Term the azeotrope is here considered from a practical point of view/

Example 1

The proportion of the reaction mixture after partial dehydrogenation of l-methoxy-2-propanol and after separation of by-products by atmospheric precipitation4

265,079 lacs, contained 49 wt. % l-methoxy-2-propanone /1/ and 51 % starting alcohol /11/. The mixture was rectified at a pressure of 6.6 kPa on a column packed with mesh /22 TP with a length of 90 cm and a diameter of 3 cm/ at a reflux ratio of 8 to 12:1, when the average throughput was 70 g of the starting mixture per hour. The distillates were condensed with water and the remaining vapor in a freezer at -55 °C. The composition of the fractions was checked by chromatographic analysis. From 1000 g of the starting mixture, the following was obtained:

Faction I 571 g, with a weight of 42 until 45 °C, with content 82.1 % I and 17.9% II, 2nd faction 78 g, with b.v. 45 until 45 °C, with content 22.7 % I and 77.5% II, dist. residue 340 g........ = with content 1.1 % I and 98.9% II.

Losses during distillation were 11 g.

1. Fraction was directly used for the reaction of ketone I in the downstream production. Fraction 2 was added to the further rectification of diluted mixtures I and II. The distillation residue was used for dehydrogenation.

Example 2

200 g of the initial liquid mixture contained 29.8 wt. % ketone I, 64.2 % alcohol II and 6 % by-products. From this mixture, 7.5 g of lower boiling by-products with boiling points up to approximately 70 °C were first distilled off at atmospheric pressure on a column /13 TP, length 60 cm, diameter 1.5 cm/. Then the pressure in the column was reduced to 30 kPa and at a reflux ratio of 6 to 12:1 and a throughput of 35 to 45 g/hour ^- }· /depending on the rectification phase/ the following was obtained:

1st fraction 71.0 g, with b.p. 77 to 80 °C, with a content of 74.5% I and

25.7% II,

2nd fraction 55.8 g, with b.p. 80.5 to 84 °C, with a content of 18.5% I and

81.7% II,

3rd fraction 81.3 g, with b.p. 84 to 86 °C, with a content of 0.05% I and % II, dist. residue 4.8 g /mainly higher boiling by-products/.

Losses during distillation were 1.8 g.

Claims (1)

Process for concentrating 1-methoxy-2-propanone in its mixtures with 1-methoxy-2-propanol by rectification, characterized in that the rectification of the mixture is carried out under reduced pressures of 80 to 1 kPa, preferably 50 to 5 kPa.