RU2190468C2 - Catalyst for dehydrogenation of cyclohexanol into cyclohexanone and method of its production - Google Patents

Abstract

FIELD: catalysts. SUBSTANCE: catalyst contains copper as active component and α-oxide of aluminum with surface acc. To BET measured by DIN 66131 no less than 30 sq.m/g; method of production includes application of copper on carrier - aluminum α--oxide with characteristics given above by impregnation, settling, dry mixing or currentless copper plating and calcinations. EFFECT: enhanced activity and selectivity of catalyst. 3 cl, 1 tbl, 2 ex

Description

 The invention relates to a technology for the production of cycloalkanones, and more particularly to a catalyst for the dehydrogenation of cyclohexanol to cyclohexanone, as well as to a method for its production.

Cyclohexanone, being an important preliminary step in the preparation of polyamide 6 and - 6.6, is manufactured on a large-scale scale using catalytic dehydrogenation of cyclohexanol. Two technological options are distinguished in the catalytic dehydrogenation of cyclohexanol. In the high-temperature variant, cyclohexanol is dehydrogenated at 320 - 420 ^o С, while the low-temperature variant passes in the range of 220 - 260 ^o С.

 The disadvantage of dehydrogenation at high temperatures is the low selectivity of valuable products relative to the possibility of their conversion to cyclohexanol, since at high temperatures there are a significant number of side reactions, such as dehydration of cyclohexanol to cyclohexene, or dimerization reactions similar to the formation of cyclohexenylcyclohexanone. The formation of by-products requires a high-cost refinement and reduces the efficiency of the method.

For dehydrogenation of cyclohexanol at low temperatures, copper-based catalysts are primarily used. These catalysts make it possible to lower the reaction temperature to about 240-280 ^{° C.} , thereby providing increased selectivity for cyclohexanone. True, the degree of conversion at relatively low temperatures, due to equilibrium, is usually not very high.

 One of the classes of these low-temperature catalysts contains compositions consisting of copper and a ceramic support, which can be either silicon oxide or aluminum oxide, or a mixture of both of these oxides. The copper content in these catalysts can be up to 50 wt.%. Additionally, these catalysts may contain minor amounts of alkali metals as promoters.

 For example, the following compositions are known to be used for dehydrogenation of cyclohexanol without oxidation: copper / alumina (British Patent Application 1081491), copper / lithium / silica (USSR Patent Application 465217) and copper / potassium / alumina (USSR Patent Application 522853). The mentioned copper-based catalysts are made in most cases in such a way that the active component (copper) is either deposited on a prefabricated carrier by precipitation of a copper salt, or by impregnation with an appropriate solution of copper salts, or the components that make up this catalyst are deposited together. Another possibility for the manufacture of copper-based catalysts is the dry mixing of constituent components, followed by calcination.

From the publication of Chang et al., Appl. Catal. A 103 (1994), pp. 233-42, is known about currentless copper plating, or deposition of copper on a carrier using a reducing agent in the presence of a complexing agent, in the manufacture of copper-based catalysts for dehydrogenation of cyclohexanol without oxidation. As a carrier, α-alumina with a surface of 22.6 m ² / g is used. According to Chang, selectivity depends on the acidity of the support: acidic supports, such as alumina or silica, have a catalytic effect on side reactions like dehydration to cyclohexanol or dimerization. And although acidity can be reduced by the addition of alkali or alkaline earth metals (see, for example, Appl. Cat. A: Volume 83, 2 (1992), pp. 201-11), this measure simultaneously leads to a decrease in activity. The advantage of increased activity of copper-based catalysts over high-temperature catalysts is thus again partially lost due to the use of alkali or alkaline earth metal additives.

 Described in Appl. Cat. A 103 (1994), pp. 233-42, the catalysts are not suitable for use on a large industrial scale because they are presented in powder form. Their manufacture by pressing in the form of molded products, like tablets, is complicated by the poor tabletability of this powder. In addition, the low hardness of the molded products manufactured in this way leads to low wear resistance in the reactor, associated with an increase in pressure loss with an increasing reaction time. Thus, in general, their use on a large technical scale is not possible.

 Another disadvantage of using α-alumina as a carrier material is a weak relationship with the active component (copper), as a result of which the agglomeration of the active component begins too quickly, associated with the loss of catalytically active surface and thus with a decrease in activity. But in order to maintain a high degree of conversion despite this, it would be necessary to increase the operating temperature of the dehydrogenation reaction in the reactor, as a result of which, of course, the agglomeration process and the related catalyst deactivation would continue to progress.

 The fundamental objective of the present invention was to create a catalyst that does not have the above disadvantages. In particular, the catalyst should have a high service life, as well as ensure dehydrogenation of cyclohexanol to cyclohexanone with a high yield of the target product and high selectivity at relatively low reaction temperatures, and would also prevent the need for constant control of the reaction temperature. In addition, the catalyst should provide the possibility of its processing without high costs into molded products in the form of tablets, piles, rings, cylinders, as well as the possibility of its further use on the basis of high hardness and wear resistance.

The objective of the invention is solved by the proposed catalyst for dehydrogenation of cyclohexanol to cyclohexanone containing copper as an active component and α-alumina with a BET surface, measured according to DIN 66131, not less than 30 m ² / g

Further, the objective of the invention is also solved by the method of obtaining the proposed catalyst, which consists in the fact that copper is deposited on a carrier - α-alumina with a BET surface, measured according to DIN 66131, at least 30 m ² / g by impregnation, precipitation, dry mixing or currentless copper plating and calcify.

Preferably, α-alumina with a BET surface of 50 to 300 m ² / g is used, particularly preferably 100 to 250 m ² / g. Such high surface α-alumina is commercially available (e.g., Alcoa).

 When the active component is applied by impregnation, the carrier is impregnated with an aqueous solution of copper salts (mainly nitric, sulfuric, acetic or hydrochloric acids), dried and then calcined in an impregnated form.

 During precipitation, an aqueous solution of a copper salt (see above) is usually mixed in the presence of a carrier with a precipitant, which provides the formation of sparingly soluble copper compounds. Soda is predominantly used to precipitate copper. Then, drying and calcination are carried out in the usual manner.

 With dry mixing, as a rule, the carrier is mixed with the desired copper salt and then calcined.

 The next form of preparation consists of the manufacture of a catalyst using currentless copper recovery (copper plating) in the presence of the claimed high surface α-alumina (see also APPL. Catal. A 103 (1994), pp. 233-242). To do this, first some rare-earth metal (platinum, rhodium, iridium, gold or palladium) is deposited on the support, mainly palladium, that is, crystallization centers are created, and then copper is separated from the complex form on the support surface using a reducing agent.

 To prevent premature precipitation of copper at the usually required high pH values, usually some strong complexing agent such as ethylenediaminetetraacetate, its alkali metal salts such as sodium tetraacetate, as well as ethylenediamine or phenatrolin are added. Recovery (or copper plating itself) occurs, as a rule, using a reducing agent such as formaldehyde or sodium formate, which is able to separate copper (0) from a solution of copper salts.

 According to the observations made to date, especially small particles of copper are obtained with its current-free isolation. Their value, recorded by X-ray diffraction, is generally less than 50 nm, and mainly less than 20 nm.

Regardless of the method of applying copper to the carrier, the resulting powder or the corresponding molded product is calcined at 250-450 ^° C for 1-24 hours in air or in an inert gas atmosphere, most preferably nitrogen. The manufacture of molded products can be carried out before or after calcination.

 The catalyst obtained by currentless isolation or by other methods described is pressed in powder form, as a rule, by mixing tabletting additives into molded articles (tablets, pallets, rings, wheels, sprockets, pieces, balls, crumbs or syringes), preferably tablets. As tabletting additives, commonly used excipients can be used, for example graphite, magnesium stearate, methyl cellulose (Valocel® type), copper powder or mixtures thereof.

 The copper content in the catalyst is usually selected in the range of 0.01 to 50.0%, preferably 2 to 30%, most preferably 5 to 20% of the total weight of the catalyst.

The BET catalyst surface (measured according to DIN 66131) is usually not less than 30 m ² / g, preferably 50 to 300 m ² / g, most preferably 100 to 250 m ² / g.

The dehydrogenation of cyclohexanol to cyclohexanone is usually carried out in the gas phase at 180 - 400 ^o C, preferably 200 - 350 ^o C and most preferably 220 - 260 ^o C. Typically, the pressure is selected in the range of 50 kPa - 5 MPa, the optimal mode of operation achieved at atmospheric pressure.

 As a raw material for the reaction, as a rule, a mixture of cyclohexanol and cyclohexanone is used. Of course, pure cyclohexanol can also be used. A commonly used mixture consists of cyclohexanol (50 - 100%, preferably 60 - 99%, optimally 96 wt.%) And cyclohexanone (50 - 0%, preferably 40 - 1%, optimally 4 wt.%). Cyclohexanone and cyclohexanol are usually obtained by oxidation of cyclohexane followed by an increase in the concentration of cyclohexanol due to the distillative distillation of cyclohexanone and other low boiling components.

As a rule, the reduction of the catalyst with hydrogen is carried out before the reaction itself. This procedure is carried out generally in such a way that a stream of hydrogen diluted with an inert gas (preferably nitrogen) is conducted through the catalyst at a certain temperature, preferably 120 - 300 ^° C. The proportion of hydrogen in the reducing gas is then usually increased until the characteristic temperature changes disappear.

Further, in accordance with a preferred embodiment of the method, the gaseous feed is passed through the catalyst, it is desirable that the volumetric flow rate be 0.1 to 100.0 h ^-1 , preferably 0.1 to 20.0 h ^-1 . The feed can be mixed with an inert gas (nitrogen) or with steam. The dehydrogenation product in the usual way (see, for example, the German patent application 1,296,625 and the German patent application 1,443,462) is processed and passed on for further processing.

 Further, in accordance with another preferred embodiment of the method, hydrogen is extracted from the mixture leaving the reaction zone and added to the gas mixture entering the reaction zone. Subsequently, it is advisable to keep the reaction mixture in the circulation loop until the desired degree of conversion is achieved.

 The claimed catalyst can operate due to its high activity at significantly lower temperatures than the catalysts used in large industrial production. It has short molding phases, high selectivity and a degree of conversion close to equilibrium. In addition, a significant decontamination occurs only after much longer periods of use than the currently accepted for known catalysts.

 The claimed catalyst is distinguished by good tableting ability, sufficient hardness, a high degree of conversion at low temperatures, high selectivity to cyclohexanol and a good service life.

Examples
Example 1 - Fabrication of the catalyst
To a mixture of 27.27 g of an 11% (w / w) solution of palladium nitrate (calculated by palladium), 495 ml of bidistillate water and 495 ml of ethanol, 5 g of polyvinylpyrrolidone (PVP, Merck, order number 7443 , average molar mass of 25,000 g / mol); the resulting solution was heated for 4 hours under reflux. Thus obtained sol ("palladium sol") contains 0.34 wt.% Palladium (in terms of the total weight of the palladium sol).

To 20.6 ml of the palladium sol prepared by the above method, 23 ml of water and 125 g of α-alumina are mixed (Alcoa company, BET surface 156 m ² / g, water absorption 0.35 ml / g of aluminum oxide). Then the impregnated carrier is dried in air. The pre-treated and dried carrier is suspended in 3894 ml of a freshly prepared solution consisting of 0.1 molar concentration of Cu (OAc) ₂ ; 0.2 molar concentration of sodium ethylenediaminetetraacetate; 0.2 molar concentration of formaldehyde and 0.0125 molar concentration of pyridine. With strong stirring, a pH value of 12.5 is established using a 35% (by weight) sodium hydroxide solution. In this case, a color change is observed from gray-black to red-brown. This suspension is heated to 70 ^o C, and the pH value is maintained in the range from 12 to 12.5 due to the subsequent addition of caustic soda (caustic soda consumption is about 400 ml). Then, after reaching a temperature of 70 ^o With stirring the suspension continues for another 30 minutes, after which it is cooled to room temperature. The suspension is filtered and washed with water until a normal pH value is established in the water (the filtrate has a weak blue color). Then the washed solid is dried for 16 hours at a temperature of 110 ^o C under a nitrogen pad and then calcined for 2 hours at a temperature of 300 ^o C.

 The catalyst thus prepared contains 16.5 wt.% Copper and 0.046 wt.% Sodium, calculated on the total weight of the gray-black catalyst.

 X-ray analysis of crystalline components gives the following results: aluminum oxide (19 nm), copper oxide (13.0 nm), copper oxide (traces).

Pill making
(thickness 5 mm, diameter 3 mm)
100 g of the catalyst powder prepared in the aforementioned manner are pre-compacted with 1% (by weight) FFL copper powder (North German Precious Metal Extraction Company, 10914) and 1% (by weight) magnesium stearate (Riedel de Haën, 4162757), respectively, based on the weight of the catalyst, into cylinders (20 mm long, 1 mm in diameter), which are then pressed through a die with a mesh size of 1.6 mm and pressed when 2% of graphite is fed into tablets with a thickness of 5 mm and a diameter of 3 mm

 The lateral pressure of the tablets is 53 N, the standard deviation is 16 N (measured by a Frank device, type 81557).

Example 2 - Catalyst Test
The test of the catalyst is carried out in a tubular reactor with a diameter of 5 cm and a length of 60 cm. Accordingly, 200 ml of catalyst are loaded, which is activated before the start of the reaction with hydrogen. Before loading raw materials, the catalyst is activated at 120 ^o With a flow of 150 l of nitrogen per hour and 1.5 l of hydrogen per hour. When the temperature rises by more than 10 ^o With the flow of hydrogen stops. Then the temperature is increased stepwise (in increments of 20 ^{° C.} ) to reach 240 ^{° C.} , the flow rate of hydrogen is kept constant. Then, at a temperature of 240 ^{° C.} , the catalyst is activated by supplying 150 liters of nitrogen per hour and 7.5 liters of hydrogen per hour. After activation, the catalyst is loaded with an anol / anolone mixture (96% cyclohexanol, 4% cyclohexanone), and the hourly space velocity is about 0.7 hour ^-1 . The products of the exit from the reactor are subjected to gas chromatographic analysis. The results are presented in the table.

Comparative example
During the test, the operations described in Example 1 are performed, with the only difference being that a commercial copper catalyst (CU 940 catalyst from Prokatalyse) is used for dehydrogenation.

The claimed catalyst shows already at a temperature> 230 ^o With the conversion close to equilibrium, while at the same time a very high selectivity> 99%.

At this temperature, no noticeable deactivation of this catalyst occurs. With a slight increase in temperature to about 240 ^o With the conversion can be increased without loss of selectivity up to about 60%. But even at this temperature there is only a very slow loss of activity.

As can be seen from the results, for a comparative experiment, the temperature adjustment must be done after 168 hours to maintain the degree of conversion, while for the claimed catalyst, such adjustment is necessary only after about 600 hours. In addition, the temperatures used in the comparative example are about 40 ^{° C.} higher than in the example with the claimed catalyst. Finally, it should be pointed out that the selectivity indices in the example with the claimed catalyst are optimal, which is unexpected when using aluminum oxide with a BET surface of at least 30 m ² / g.

Claims (3)

1. The catalyst for dehydrogenation of cyclohexanol to cyclohexanone containing copper as an active component and α-alumina as a carrier, characterized in that it contains α-alumina with a BET surface, measured according to DIN 66131, not less than 30 m ² / g. 2. A method of producing a catalyst for dehydrogenation of cyclohexanol to cyclohexanone according to claim 1, characterized in that copper is deposited on a support - α-alumina with a BET surface, measured according to DIN 66131, not less than 30 m ² / g by impregnation, deposition, dry mixing or currentless copper plating and calcinate.  3. The method according to claim 2, characterized in that the catalyst is subjected to molding, in particular, in tablets, racks, rings, cylinders.

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