JPS6364433B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention discloses that α, ω in the presence of aluminum oxide
-Relating to a method for producing cyclic ethers by dehydrating diols. A number of methods of this type are known in the art, for example, a method of dehydrating butanediol-1,4 to obtain tetrahydrofuran (THF). The state of the art up to 1955 is summarized in Liebitz Hiss Annalen der Chemie, vol. 596, p. 81, 1955. Examples of the water removing agent include phosphoric acid, sulfuric acid, oxalic acid, copper sulfate, magnesium chloride, zinc chloride, and other various agents. With these acid-reactive compounds, the desorption of water is usually carried out in the liquid phase at temperatures below 250°C. When operating at temperatures above 250° C., some other catalysts, such as oxides of aluminum, titanium, zircon or tungsten, as well as acid clays and phosphates, also become effective. Especially butanediol is 245
Since it boils at .degree. C., the reaction of this substance is carried out in the gas phase or operated under pressure (see German Patent No. 711 709). However, at extremely high reaction temperatures,
Butadiene formation occurs to a significant extent. However, the known methods suffer from a number of drawbacks.
That is, with soluble catalysts, significant catalyst losses occur and yields generally do not exceed 90%. Improvements that subsequently became known, such as the German patent
According to the method of 850750, the reaction is carried out on a synthetic resin substrate with a cation exchanger. However, no substantial improvement was obtained, and moreover, commonly available exchange resins have low stability at temperatures above 150°C. When using small amounts of concentrated sulfuric acid, for example as described in German Patent No. 1043342,
It is necessary to use synthesis equipment with a corrosion-resistant lining and is therefore relatively expensive. Moreover, experience has shown that even with this method, it is difficult to react more than 10,000 parts of butanediol per 1 part by weight of sulfuric acid, after which the catalyst must be discarded due to poisoning by impurities. Considering, for example, that tetrahydrofuran is a mass product, it will be appreciated that the amount of catalyst that is wasted is a significant drawback. German Patent No. 700036 discloses the use of aluminum oxide as a catalyst in the production of tetrahydrofuran from butylene glycol. According to the operating instructions in Example 5 therein, when operating at temperatures between 185 and 200°C with 10% by weight of activated aluminum oxide as a catalyst, tetrahydrofuran is converted from 1,4-butylene glycol.
Obtained with a yield of 92.5%. Further testing revealed that the use of aluminum oxide (described simply as "active" aluminum oxide without a detailed definition) did not immediately yield good results. It is therefore an object of the present invention to provide a process in which the reaction of α,ω-diols to cyclic ethers is achieved without any problems, with high yields and with little consumption of the catalyst, and also to provide a method for this process. The aim was to find a catalyst based on aluminum oxide that makes it possible. In this case, it is necessary that the purpose can be achieved without any problem even if a diol of a grade that is common in industry and is not particularly pure is used. We carried out the desorption of water in the liquid phase and suspended in the reaction mixture as aluminum oxide, and the precipitation of an alkaline aluminate solution with an acid and subsequent
It has been found that this problem can be advantageously solved when using aluminum oxide obtained by heating at 400-800°C. This solution was unexpected since it is known that γ-aluminum oxide is always formed, regardless of whether ortho or meta-aluminum hydroxide is the starting transformation. The production of aluminum oxides of this type, usually leading to so-called γ-aluminum oxides, is known and is not included in the present invention. Their preparation is described, for example, in the book by Gumelin, 8th edition Aluminum, Part B, and in Ullmans Entiklopedei der Technicien Chemie, 4th edition, volume 7, page 294. Experience has shown that particularly active catalysts are obtained if care is taken to ensure that the PH number does not fall below 6 even in localized portions of the reaction mixture during the precipitation process. Therefore, when using mineral acids for precipitation, special care must be taken to stir vigorously. This is not critical if carbonic acid is used for precipitation. Furthermore, the activity of the catalyst is influenced by the washing process that follows the precipitation, requiring that the aluminum hydroxide be as alkali-free as possible. Particularly active and therefore superior aluminum oxides exhibit a PH number, measured by a glass electrode, of 5 to 8, preferably 5.5 to 7.5, in a stirred aqueous slurry. In addition, this PH value can be determined by adding small amounts of slightly volatile organic or inorganic acids, such as oxalic acid, glutaric acid, succinic acid, maleic acid, fumaric acid, propionic acid, benzoic acid, phthalic acid, phosphoric acid or sulfuric acid, if necessary. or by the addition of bases such as alkali metal or alkaline earth metal oxides, hydroxides or carbonates, optionally by addition of slightly volatile amines such as tributylamine or tridecylamine. be done. According to this method, for example, the following formula A cyclic ether of the formula (A in the formula means an alkylene group having 4 to 8 carbon atoms) is obtained. Furthermore, the process is also applicable to the preparation of cyclic ethers of this type whose alkylene group contains other heteroatoms, such as nitrogen atoms or especially oxygen atoms, for example 1,4-dioxane is It is a cyclic ether which can be prepared particularly advantageously from diethylene glycol by the process. The preparation of olefinically unsaturated cyclic ethers, for example the preparation of 2,5-dihydrofuran obtained by dehydration of (cis)butene-2-diol-1,4, is of particular value. It is known to produce dihydrofuran in the gas phase with aluminum oxide catalysts, in which case some by-products which are difficult to separate, such as crotonaldehyde, hydroxyisobutyraldehyde, 2,3-dihydrofuran, furan, tetrahydrofuran, are produced. etc., reaches 30% (see German Patent No. 695219). On the other hand, German patent 1211219 for obtaining dihydrofuran in the liquid phase using an aluminum oxide catalyst.
When the method described in the specification is carried out, the yield is higher than 95%, which appears to be advantageous at first glance. However, follow-up tests revealed that the catalyst described there loses selectivity in a short period of time. Also, as the catalyst is used for a long time,
Large amounts of by-products are formed, especially the formation of furan is increased. Moreover, the product becomes increasingly yellow in color. When reacting 100 parts of butenediol per part of catalyst, for example, an initially 95% yield quickly drops to about 80%. The color value of the distillate is 200-300 APHA units. We recognized the reasons for the unreliability or impossibility of implementing this conventional method on an industrial scale, and also found that the special surface structure of special aluminum oxide is a decisive factor for its ability as a dehydration catalyst. Therefore, the present invention was devised. It is also worth noting that the method can be universally used for all practically relevant cyclization reactions. This new process gives virtually quantitative yields, has an almost arbitrarily high catalyst productivity, and is also environmentally friendly. Since the reaction mixture is free of corrosive substances, production equipment made of inexpensive construction materials, such as common equipment steel, can be used. The process is particularly advantageous when using undistilled crude butanediol which is optionally contaminated with sodium or calcium sulfate (see, for example, German Patent Application No. 2303619). According to the method of the present invention, the salt salt can be separated from the catalyst by washing with water or dilute acid. High reaction rates are possible with this method and depend on the selected reaction temperature and amount of catalyst. 210
℃, 1 to 3 parts of tetrahydrofuran can be produced from butanediol in 1 hour per part by weight of catalyst. Dehydration by the new method is preferably 160-230℃
It is carried out at 175 DEG -215 DEG C., without the need for solvents or diluents. Normally, it is operated at normal or slightly above or below atmospheric pressure. Under reduced pressure, the boiling point of butanediol is simply
At that time, care should be taken not to lower the temperature below the reaction temperature. The amount of catalyst used obviously depends on the technical rather than chemical conditions and is regulated, for example, by the achievable distillation rate, the geometrical factors of the reactor, etc. Generally, the catalyst has a particle size of 0.001 to 5 mm.
Used as a ~30% suspension (parts by volume). Dehydration can also be carried out in the presence of chemically inert diluents to stabilize the reaction temperature. Preferred diluents are, for example, hydrocarbons such as benzene fractions, high-boiling ketones or ethers such as dodecane and decanone or dihexyl ether, and optionally water. Normally no diluent can be used. Although the process can also be operated batchwise, continuous operation is particularly advantageous. In that case, the diol to be subjected to the reaction is particularly preferably added to the reaction mixture with stirring, and the operation is carried out in such a way that the low-boiling cyclic ether is usually removed from the top of the reaction vessel via the corresponding fractionation column. do. Owing to the absence of corresponding side reactions, a pure product is usually obtained at the top of the column, together with the water produced or optionally added to the crude product. Example 1 A spherical flask equipped with a stirrer and a fractionator was used as a container, and sodium aluminate was precipitated with nitric acid as a catalyst, dried at 120-200°C,
Use aluminum oxide obtained by heating at 400 °C for 12 hours. It has a particle size of 40-250μ and exhibits a pH of 7 in a slurry with 2 parts water. Using this catalyst, 940 parts of butanediol-1,4 can be reacted in one hour to obtain tetrahydrofuran in quantitative yield. If the catalyst is simply dried without heating to 400°C, only 450 parts of butanediol will react within one hour. COMPARATIVE EXAMPLE 1 The same procedure was followed according to the instructions given in Example 1, except that the catalyst was obtained by precipitating aluminum sulfate with a caustic soda solution, and
Use the same amount of aluminum hydroxide (boehmite) dried at 120-200 °C. The particle size of this catalyst is 40
~250μ. The catalyst is heated to 400°C for 12 hours before use. In this case, 480 parts of butanediol can be reacted within one hour. Drying the catalyst at 120-200°C instead of heating to 400°C and then adjusting the pH value to 6.8 in the aqueous slurry by treatment with phosphoric acid converts 200 parts of butanediol-1,4 into tetrahydrofuran within 1 hour. change. Examples 2-5 The catalyst is used to dehydrate various α,ω-diols listed below under the same conditions as described in Example 1. The results are shown in the table below. 【table】

Claims (1)

[Claims] 1 The elimination of water is carried out in the liquid phase and the oxidation is suspended in the reaction mixture as aluminum oxide and obtained by acid precipitation of an alkaline aluminate solution and subsequent heating at 300-1000 °C. Characterized by the use of aluminum,
Process for the preparation of cyclic ethers by dehydration of α,ω-diols in the presence of aluminum oxide.