HU191468B - Process for preparing 2,5-dimethyl-2,4-hexadiene - Google Patents

Abstract

In the process of the present invention, 2,5-dimethyl-2,4-hexadiene in a 2,5-dimethyl-2,5-hexanediol phosphorus reactor at atmospheric pressure is prepared by 2,5-dimethyl-2-one, 5-Hexanediol in the form of an aqueous melt is fed into the reactor 3 at a temperature of 300-400 ° C and a catalytically inactive gamma-aluminum (HI) containing 0.1 to 20% chromium (III) oxide (hereinafter Cr2O3). ) -Doxid (hereinafter γ-γ12Ο3) is dehydrated on a catalyst containing a mixture of catalytically active substances. The essence of the shell catalyst used for dehydration is that it has a core core, e.g. without a binder for spherical a-Al2O3, the active layer containing Cr2O3 and γ-Α1203-οί is applied in a thin layer of 0.1-0.5 mm. -1-

Description

The present invention relates to a novel process for the preparation of 2,5-dimethyl-2,4-hexadiene from 2,5-dimethyl-2,5-hexanediol in a vapor phase at atmospheric pressure in a packed tube reactor such that hexanediol is fed to the reactor 3 in the form of an aqueous melt at a temperature of 300-400 ° C and a gamma-aluminum (III) containing 0.1 to 20% by weight of chromium (III) oxide (hereinafter referred to as Cr ₂ O ₃ ) on a catalytically inactive pellet. shell (deli idon on an allizer) containing a catalytically active mixture of oxide (γ-Α1 ₂ Ο ₃ ).

The process is preferably carried out by adding 2,5-dinictyl-2,5-hexanediol as a melt containing 10-25% by weight of water. The Catholics! the active layer preferably has a thickness of 0.05-0.5 mm and has a composition of 3 to 10% by weight of Cr ₂ 0 ₃ containing γ-Λ! ₂ Ο ₃ powder mix. The catalytically active Cr ₂ O ₃ and γ-Α! ₂ x ₃ powder mixtures are applied to catalytically inactive alpha-aluminum (III) oxide particles.

One of the starting materials for the preparation of 2,5-dimethyl-2,4-hexadiene pyrethroid insecticides.

All the processes used to dehydrate 2,5-methyl-2,5-hexanediol to date have been such as to hinder the industrial realization of the production of large quantities of product. No. 2,715,649. According to US patent, 2,5-dimethyl-2,5-hexanediol is dehydrated on Al ₂ O ₃ catalyst containing 10% phosphoric acid at a temperature of about 250 ° C.

Λ A yield of 83% of 2,5-inclil-2,4-hxxadiene was achieved in a 36 hour experiment. The disadvantage of using H ₃ PO ₄ as a catalyst is that its activity at this temperature decreases rapidly due to the evaporation loss of H ₃ PO ₄ and its partial decomposition. Λ 2,5-Dinethyl-2,5-beexanediol was introduced into the reactor in the form of steam, which is a difficult process to control given the material's melting point at 92 ° C and its boiling point around 200 ° C. At this temperature, 2,5-dimethyl-2,5-hexanediol may undergo decomposition before entering the reactor. This explains the low yield of 83% 2,5-dimethyl-2,4-hexadiene.

No. 2,957,929. U.S. Patent A1 ₂ O ₃ catalyst at 350 ° C 26% 2,5-dimethylethyl-2,4-hcxadién 64% 2,5-dimethyl-1,5-hexadiene and 6% 2,5-dimethyl-1 , 4-hexadiene is obtained. The 2,5-dimethyl-2,5-hexanediol was introduced into the reactor by dissolving it in a lower aliphatic alcohol. However, these alcohols are largely reactive at the reaction temperature to form olefins and ethers.

This means both loss of material and the removal of olefins and ethers for environmental and safety reasons.

Ju. K. Jurev and G. Ja. Kondratyeva [Zs. Obs. Male. 26, 275 (1956)] also dehydrated with Al ₂ 0 ₃ at 350 ° C and 2,5-dimethyl-2,5-hcxándiolt, but 60% of 2,5-dimethyl-2,4-hexadiene only 9% isomerizable 2,5-dimethyl-1,5-hexadiene was obtained. The 2,5-dimethyl-2,5-lexanediol was introduced into the reactor in the melted state.

IN Nazarov and Μ. V. Mavrev [Zs. Obs. Male. 28, 3066 (1958)] on Cr ₂ O ₃ -AI ₂ O ₃ catalyst

Dehydration of 2,5-dimethyl-2,5,5-hexanediol in 95% yield, including 55% 2,5-dimethyl-2,4-hexadiene and 45%

2.5-Dimethyl-1,5-hexadiene was obtained. For feed, 146 g (1 mol) of 2,5-dimethyl-2,5-hexanediol are dissolved in 100 ml (1.7 mol) of ethanol. These data, expressed in moles, illustrate the high amount of ethanol needed, which requires a significant amount of heat to be dehydrated endothermically. This results in a significant temperature gradient across the reactor cross-section. As a result, the catalyst is rapidly deactivated along the reactor wall due to the deposition of tar, while the temperature inside the reactor is not sufficient to dehydrate 2,5-dimethyl-2,5-hexanediol.

During dehydration, 2,5-dimethyl-1,5-hexadiene and a.

A mixture of 2,5-dimethyl-2,4-hexadiene is formed, the proportion of which depends on the selectivity of the catalyst. With the use of the catalyst, the amount of 2,5-dimethyl-2,4-hexadiene formed is always reduced and that of 2,5-dimethyl-1,5-hexadiene increases. The 2,5-dimethyl-1,5-hexadiene may be formed by isomerization in the presence of an inorganic (e.g. HCl, H ₂ SO ₄ H ₃ PO ₄ ) or organic (e.g. acetic, benzenesulfonic, p-toluenesulfonic) acid catalyst. to 2,5-dimethyl-2,4-hexadiene. None of the above-mentioned publications is concerned with the isomerization of 2,5-dimethyl-1,5-hexadiene to 2,5-dimethyl-2,4-hexadiene.

The disadvantages of the prior art procedures can be summarized as follows. Due to the difficulties described, it is not possible to uniformly add 2,5-dimethyl-2,5-hexanediol to the catalyst bed and to avoid side reactions that interfere with the target reaction by competitive reaction, and the four essential requirements (activity, selectivity, lifetime, regenerability) are only partially satisfactory. The activity of the A1 ₂ O ₃ catalyst containing H ₃ PO ₄ is already low, as shown by the 83% yield. Although selectivity is good, its life is very short due to the evaporation of H ₃ PO ₄ . Only Al ₂ 0 ₃ or. For catalysts containing Al ₂ O ₃ and Cr ₂ O ₃ , the life of the catalysts is not given. These catalysts, which are homogeneous in particle size, have a rapidly declining activity due to the oxidation reactions occurring inside the catalyst beads leading to the frequent interruption of continuous operation. It takes longer to regenerate these distant parts.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an economical, industrially readily feasible process for the preparation of 2,5-dimethyl-2,4-hexanediol which has a high purity of -dimethyl-2,4-hexadiene, and the development of a catalyst capable of dehydrating 2,5-dimethyl-2,5-hexanediol is highly active, long-lived, mechanically stable and easy to regenerate.

The present invention is based on the surprising discovery not found in the prior art that 2,5-dimethyl-2,550-hexanediol in the form of a melt containing 10-25 wt. The melt containing 10 wt% water, e.g. It freezes at 65 ° C, at 44 ° C containing 20 wt%.

The addition of water also increases the life of the catalyst because, in the presence of it, the oxidation side reactions leading to the tar are suppressed. After the reaction, the added water is completely separated from the reaction and can be used for further reactions or directly channeled.

Because the specific heat capacity of the water (~ 4.2 J / g-° C) is significantly higher than that of the C 1-3 alcohols (-2.5 J / g-° C), it is heated to the reaction temperature in the reactor preheater and remains constant in the reactor. The water passing through the form of the reactor wall acts as a saline heat transfer medium between the wall and the interior of the reactor and thus significantly

191,468 contributes to providing radial isotherm in the reactor. Surprisingly, the properties of the water-dehydration catalyst can be improved by the addition of water.

Another important discovery of the process according to the invention is that the dehydration of a known catalyst of Cr ₂ O ₃ - γ-Α _{1 2} Ο _{3 in} the form of a shell catalyst significantly increases its lifetime since the thin catalyst layer slows down more slowly without the need for deeper diffusion. However, the thin catalyst layer can be regenerated in a short time. The selectivity of the catalyst used to dehydrate 2,5-dimethyl-2,5-hexanediol with respect to 2,5-dimethyl-2,4-lexadiene may decrease during the use of the catalyst if, at the same time, The conditions for the isomerization of dimethyl-1,5-hexadiene may be selected to provide isomerization of a variable amount of 2,5-dimethyl-1,5-hexadiene to 2,5-dimethyl-2,4-hexadiene without damage.

The catalyst used is the same, the core of the shell of the catalyst to a suitable size (usually 1-6 mm) and shape (preferably spherical) and material quality catalytically inactive particles (central core) in a conventional coating method gamma-Al ₂ O ₃ - and a relatively thin layer (typically 0.1-0.5 mm) of Cr ₂ O ₃ and without a binder, thereby providing a geometric depth as long as the catalyst particles are catalytically active. The advantageous properties of the shell catalyst are enhanced by the fact that the compact, heat-conducting inert core and the thin-shell catalyst practically provide full radial isometry in the reactor. Alkalmas Suitable for core core of oil catalyst · Any material that has an inertia coefficient of expansion under reaction conditions close to that of the shell containing the active substances is mechanically stable. Suitable material e.g. that aA! ₂ O ₃ , MgO, etc., preferably spherical a-Al ₂ 0 ₃ .

The so-called catalyst used in the preparation of the catalyst The coating powder, i.e. the material of the active layer, is prepared by suspending γ-Α1 ₂ 0 ₃ -οί in a solution of a water-soluble Cr salt and then evaporating this suspension to dryness at 105 ° C. The solid thus obtained is cured for a sufficient period of time and at a temperature such that the conversion to Cr ₂ O _{3 is} effected without any change in the 7-Al ₂ O ₃ . Thus, the material is e.g. It is heated to 520 ° C at a heating rate of 50 ° C / h and maintained at this temperature for 3 hours. After the heat treatment, the solid consisting of γ-Α1 ₂ O ₃ and Cr ₂ O _{3 is} ground to a level below 100 μιπ in a metal debris exclusion mill. The coating powder containing the catalytically active substances is applied to the inert central core by rolling the inert cores placed in a pelleting apparatus, then alternately spraying with distilled water or spraying the coating powder to a given film thickness. The wet catalyst particles thus obtained are then heat-treated at 120 ° C in an airtight container and then air-dried to constant weight.

The content of Cr ₂ O _{3 in} the active layer may vary from 0.1 to 20% by weight, preferably from 3 to 10% by weight. Such a catalyst has a temperature of 300-400 ° C, preferably 350 ° C, with 100% conversion of 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-1,5-hexadiene and 2,5-dimethyl- The combined yield of 2,4-hexadiene was 96%. Composition of product on fresh catalyst 40-50% 2,5-dimethyl-1,5-hexadiene and 50-60%

5-dimethyl-2,4-hexadiene. After 2-3 hours of use, the composition changes from 65-70% to 2,5-dimethyl-1,5-hexadiene and 30-35% to 2,5-dimethyl-2,4-hexadiene. Regeneration of the catalyst at 400 ° C for 4 hours in an air stream restores the original ratio of 2,5-dimethyl-1,5-hexadiene and 2,5-dimethyl-2,5-hexadiene. During regeneration, the catalyst does not suffer mechanical damage.

After dehydration, 2,5-dimethyl-1,5-hexadiene and a

The mixture of 2,5-dimethyl-2,4-hexadiene is completely separated from the water and can be separated continuously. After separation it can be directly flavored and the water reused. The isomerisation can also be carried out in a continuous apparatus. Continuous isomerization is conveniently carried out in the presence of organic acids, both inorganic and organic acids suitable for flavoring, and in suitable solvents, e.g. When dissolved in a C 1-3 aliphatic alcohol, they can be added to the mixture to be isomerized in a concentrated solution to form a homogeneous phase so that both acid and solvent can be removed by washing with aqueous NaCl ₃ . The organic acid is preferably used in an amount of 0.1 to 2.0% by weight based on the total weight of 2,5-dimethyl-2,4-hexadiene and 2,5-dimethyl-1,5-hexadiene. Equipment suitable for carrying out isomerization e.g. the reactor cascade, which undergoes isomerization at an average residence time of 110-125 ° C and 5C-8O min. The yield of the isomerization was 95% and the purity of the 2,5-dimethyl-2,4-hexadiene was above 98%, thus, based on the starting 2,5-dimethyl-2,5-hexanediol, 2,5-dimethyl-2,4 - the total yield of hexadiene production exceeded 90% of the theoretical value.

The preparation of 2,5-dimethyl-2,4-hexadiene from 2,5-dimethyl-2,5-hxanediol by the process of the invention can be carried out, for example, as shown in the figure. From the heated dosing tank 1, the aqueous melt of 2,5-dimethyl-2,5-hexanediol was acl injected into the heated reactor 3, where N ₂ was also injected as inert gas. The aqueous melt evaporates on the inlet layer 4 to the catalyst layer 5. The vapors leaving the reactor are condensed in the cooler 6. In the 7 continuous separator flasks is 2,5 dimethyl-1,5-hexadiene and

The mixture of 2.5-dinethyl-2,4-hexadiene separates from the water and enters the first member of a three-member, side-flow countercurrently heated cascade. The 8 ', 8, 8' cascade members, 9 ', 9, 9' mixing! and 10 ', IC, 10', the vapors are condensed and provided with a refrigeration isa. A solution of p-toluenesulfonic acid is introduced into the first member 8 'from the container 11 by means of the pump 12. The material runs through 8 ', 8'. 8 '' cascade members and enters the downstream neutralization reactor 14 provided with stirrer 13. The reactor 14 of the pump 16 with aqueous NaHC0 ₃ solution szá'iít the reservoir 15. After neutralization, the final product, 2,5-dimethyl-2,4-hexadiene, is separated from the wash solution in the continuous separation vessel 18.

An exemplary embodiment of the process of the invention is described below:

Example 1

Production of the shell catalyst

131.6 g of Cr (NO ₃ ) ₃ -9 H ₂ O are dissolved in 500 ml of distilled water and 475 g of y-Al ₂ O ₃ are suspended and the suspension is evaporated to dryness at 105 ° C. The resulting solid is heated to 520 C for 5 hours at 50 ° C heating rate for conversion to Cr ₂ O ₃ and maintained at this temperature for 3 hours. After the curing, the solid consisting of 7-Al ₂ O ₃ and Cr ₂ O _{3 is} ground to below 100 µm in a metal contamination mill.

The coating powder, prepared as described above, is applied to the inoculated core by rolling 1000 g of a-Al ₂ O ₃ carrier with a particle fraction of 2.0-2.5 mm in a rotating drum and spraying distilled water alternately on its surface or vibrated silage. Coating powder is sprayed to a thickness of 0.3 mm. The wet catalyst particles are then placed in an airtight aluminum container, held at 120 ° C for 6 hours, and air-dried to constant weight.

95% by weight in the active layer obtained as above

780 ml (1320 g) of a shell catalyst containing 7-Al ₂ 0 ₃ and 5% by weight of Cr ₂ O ₃ (35% of the total weight of the catalyst) was charged to a 800 mm long tube reactor having an inside diameter of 46 mm Above 150 ml of an inhaled a-Al ₂ O ₃ ball are placed and the reactor is heated at 350 ° C by external heating. A 60 ° C melt of 2,5-dimethyl-2,5-hexanediol containing 20% by weight of water is fed to the reactor at 390 g / h (420 ml / h), which corresponds to a catalyst load of 400 g / l a. N ₂ is passed through the reactor at 40 l / h. After dehydration, the condensed vapors in the condenser 6 are separated by a continuous separator 7, the mixture of 2,5-dimethyl-1,5-hexadiene and 2,5-dimethyl-2,4-hexadiene being passed at 225 g / h (300 ml / h). 8 'of the first member of a three-membered reactor cascade of 100 ml each. At the same time, the pump 12 delivers a solution of p-toluenesulfonic acid in 130 g / l methanol at a rate of 4.4 ml / h. In reactors 8 ', 8, 8', the reaction mixture is heated to 120 ° C with external heating, and the average residence time per member is 20 minutes. The isomerized mixture exiting the 8 is fed to a reactor volume 14 (180 ml), which is pumped with pump 16 at a rate of 200 ml / h in 10% aqueous NaHCO ₃ . After neutralization, 2,5-dimethyl-2,4-hexadiene is separated from the wash solution in the continuous separator 18. The outlet mass flow rate of 2,5-dimethyl-2,4-hexadiene is 216 g / h and 98.8%

Contains, in addition to 2,5-dimethyl-2,4-hexadiene, 1.2% of 2,5-dimethyl-1,5-hexadiene. The yield of 2,5-dimethyl-2,4-hexadiene is thus 90.8% of theory.

Example 2

The shell catalyst prepared in Example 1 was used for 720 hours under the conditions described in Example 1. After 184 hours and 385 hours respectively, the catalyst was regenerated for 4 hours at 40 ° C with an air passage of 40 L / h. The performance of the catalyst was monitored by gas chromatography analysis of the material leaving the selector 7. The conversion of 2,5-dimethyl-2,5-hexanediol was 100% in each case. and the sum of the masses of 2,5-dimethyl-1,5-hexadiene and 2,5-dimethyl-2,4-hexadiene did not fall below 96% of theory. The percentages of 2,5-dimethyl-1,5-hexadiene and 2,5-dimethyl-2,4-bexadiene in the mixture are shown in Table 1.

Table 7

"2,5-Dimethyl-1,5- 2,5-dimethyl-2,4- -hexadién crowd% 2,5-dimethyl-2,5- -hexándiol crowd% 1ÜO b -hexadién by weight 5 46.1 53.9 73 55.1 44.5 - 136 67.3 32.7 - 184 72.4 reclamation 27.6 198 34.3 65.7 - 251 54.7 45.3 - 325 60.0 40.0 385 67.7 reclamation 32.3 396 44.2 55.8 511 58.8 41.2 - 611 64.3 35.7 - 720 65.8 34.2 -

Example 3

Preparation of the solid catalyst [1. N. Nazarov, Μ. V. Mavrev: Zs. Obs. Him.2 ?, 3066 (1958)]. 1500 g of a γ-Α1 ₂ Ο ₃ sphere with a particle fraction of 2.0-2.5 mm was held under a vacuum of 2 kPa for 30 minutes and then impregnated with 500 g of Cr (NO ₃ ) ₃ '9 H ₂ O in 1000 ml of distilled water for 1 hour. The spheres are then washed with distilled water, dried at 105 ° C for 4 hours and then heated to 520 ° C in a heating furnace at 50 ° C / h for ₃ hours to convert to Cr ₂ O ₃ . The catalyst thus obtained

Contains 5.3% by weight of Cr ₂ 0 ₃ and 94.7% by weight of γ-Α1 ₂ Ο ₃ -οί,

780 ml (1270 g) of the catalyst prepared above were placed in the reactor described in Example 1 and dehydrated under the conditions described in Example 1. The composition of the reaction mixture is monitored by gas chromatography analysis of the exit material from the selector 7. The measurement results are shown in Table 2.

Table 2

2,5-dimethyl-1,5-hexadiene ''% by weight 2,5-dimethyl-2,4- -hexadién crowd% 2,5-dimethyl-2,5- -hexándiol crowd% 5 42.8 57.2 __ 70 70.6 29.4 124 81.2 18.8 - 162 86.0 8.6 5.4

191,468

Example 4

780 mL (1270 g) of the catalyst prepared in Example 3 was charged to the reactor described in Example 1 and dehydrated under the conditions described in Example 1 except that 2,5-dimethyl-2,5-hexanediol was an aqueous melt. Instead, feed into the reactor dissolved in ethanol (1460 g of 2,5-dimethyl-2,5-hexanediol dissolved in 1000 mL of ethanol). The composition of the reaction mixture is monitored by gas chromatographic analysis of the exit material from selector 7. The measurement results are shown in Table 3.

Table 3 15

2,5-dimethyl-1,5- 2,5-dimethyl-2,4- -hexadicn crowd% 2,5-dimethyl- -2,5-hcxándiol crowd% 1OO ii -hexadien crowd% 5 43.0 57.0 70 75.2 24.8 - 124 83.8 13.8 2.4 162 88.4 4.5 7.1

Claims

Claims (5)

Claims A process for the preparation of 2,5-dimethyl-2,4-hexadiene from 2,5-dimethyl-2,5-hexanediol in a vapor phase at atmospheric pressure. in a packed tube reactor, characterized in that: 2,5-Dimethyl-2,5-hexanediol is fed to the reactor in the form of a water-melt at 300-400 ° C and in a catalytically inactive pellet containing from 0.1 to 20% by weight of gamma-aluminum containing chromium (III) oxide. III) oxide is dehydrated on a shell catalyst containing a catalytic active mother mixture. The process according to claim 1, wherein the 2,5-dimethyl-2,5-hexanediol is added to the reactor in the form of a melt containing 10-25% by weight of water. The process according to claim 1, wherein the thickness of the catalytically active layer of the shell catalyst is 0.05-0.5 mm. 4. A process according to any one of claims 1 to 3, characterized in that the catalytically active layer consists of a gamma-aluminosilim (III) oxide powder mixture containing from 3 to 10% by weight of chromium (III) oxide. 5. The process of claim 1, wherein the catalytically inactive particulate is spherical alpha-aluminum oxide.