PROCESS FOR PRODUCING CYCLOHEXANONE OXIME

Abstract: The invention relates to a process of producing ketoximes, characterized in that a secondary alcohol, cor­ responding to the desired ketoxime, is partially oxidated in the liquid phase with 0₂, an oxidated mixture being the­ reby formed, which contains an excess of unreacted alco­ hol, the ketone corresponding to said alcohol, and H₂O₂, and that said oxidated mixture is directly reacted with NH₃ in the liquid phase (without isolating the alcohol, the ketone and H₂O₂) in the presence of an ammoximation catalyst.

Description: DE-A-12 45 371 discloses the preparation of cyclohexanone-oxime by means of the catalytic reaction, in the liquid phase, of cyclohexanone with NH₃ and H₂O₂ (ammoximation reaction), at 5-40°C and in the presence of a catalyst constituted by phosphotungstic acid, or by similar compounds. This type of catalyst, however, is difficult to handle, above all during the step of separation of the product from the catalyst; EP-A-208 311 teaches an efficacious alternative route, constituted by the catalysis with a titanium-silicalite, of the type disclosed, e.g., in US-A-4,410,501 and 4,480,135 and in EP-A-132 550, 190 609 and 200 260. A particular type of post-treatment with H₂O₂ of the titanium-silicalites (or of zirconium-silicalites) can endow them with exceptional and quite surprising catalytic properties in the ammoximation reaction of various carbonylic compounds (see EP-A-267 362). A disadvantage of the heretofore used technique is however the need of providing, upstream of an ammoximation facility, at least two further synthesis facilities, i.e.: a facility for cyclohexanone synthesis, generally by cyclohexanol dehydrogenation in the gas phase, also comprising an efficacious distillation section, in order to separate cyclohexanone from unreacted cyclohexanol; a facility for the synthesis of hydrogen peroxide, which usually requires the presence of a (more or less hydrogenated) anthraquinonic vehicle, a high hydrogen consumption and a complex series of operations. It has now surprisingly been found that the need of a facility for the ketone production from its corresponding alcohol, as well as of a separate facility for the H₂O₂ production from H₂ and O₂ can be overcome at all, the complexity of the operations being drastically reduced. In its broadest aspect, the present invention provides a process for the preparation of cyclohexanone oxime, wherein a mixture formed by partial oxidation, in the liquid phase and at a temperature of from 50 to 150°C, of cyclohexanol with oxygen or an oxygen-containing gas and containing unreacted cyclohexanol, cyclohexanone, hydrogen peroxide and organic peroxides and/or hydroperoxides is directly reacted with ammonia, in the liquid phase and in the presence of a titanium-silicalite ammoximation catalyst. Information on the catalyst and on the operating conditions for the ammoximation can be found in the patents hereinabove. Information as to the partial oxidation in the liquid phase of cyclohexanol (also called: "self-oxidation") and on the resulting oxidized mixture, also containing, besides alcohol, ketone and H₂O₂,a few organic hydroperoxides and peroxides, as well as carboxylic acids (very undesired) can also be found in the relevant literature; see, e.g., US-A-2,869,989; 2,871,104; and 3,592,776; GB-A-1,318,525; DE-A-1,002,295; CA-A-1,003,189 and a paper by R.V. Neginskaya et al., published on Zhurnal Prikladnoi Khimii, November 1985 (volume 58, No 11, pages 2512-2516). These documents teach that the partial oxidation of a secondary alcohol with O₂ (in the liquid phase, and, possibly, in the presence of a free-radical initiator) not only causes the formation of the corresponding ketone and of H₂O₂, but also of substances having hydroperoxidic and/or peroxidic character, e.g., according to the schematic equation: wherein (x+y)=1. However, the literature in this field (see, e.g., GB-A-1,113,687) suggests the most efficacious methods involve isolating the unreacted alcohol, the ketone, H₂O₂ and, above all, the carboxylic acids, in order to prevent H₂O₂ decomposition and a negative impact on the reactions downstream this step. It has now surprisingly been found that the titanium-silicalites cause the above impurities not to hinder the specific realization of the ammoximation, and hence enable said oxidized mixture to be "directly" used, without the alcohol, ketone, H₂O₂ being isolated in the pure state. The alcohol conversion is generally from 5 to 50% and the amount of said carboxylic acids is generally from 0.001 to 15%, and preferably of from 0.001 to 5%, by weight, on the ketone. The alcohol conversion can be increased to even higher levels (above said 50% level) if a suitable diluent solvent, e.g., tert.-butyl alcohol, is present. The consequence of this discovery, unexpected from all viewpoints, are of a tremendous importance, both in terms of reduction in plant complexity, and in terms of raw material saving. The advantage of the process according to the invention consists in fact precisely in that when the starting compound is cyclohexanol, i.e., the precursor of the desired cyclohexanone, the use of separately synthesized H₂O₂ is no longer necessary, the basic oxidant raw material being constituted by such a much easier available oxidant as oxygen. The "self-oxidation" can be carried out on cyclohexanol in pure form, or on a mixture obtained by dilution with an inert solvent, e.g., water, tert.-butyl alcohol, benzene, and so forth, and is advantageously carried out inside a stirred reactor, whose walls are made of materials compatible with the presence of hydrogen peroxide. The self-oxidation reaction is in fact carried out under stirring, in order to cause a good contact to occur between the liquid phase and the gas phase (which contains oxygen). The oxidation temperature is from 50 to 150°C, preferably from 80 to 120°C, and the pressure shall be such that the reactants and the oxidation products remain in the liquid phase; the pressure values can be generally from 0.1 to 10 MPa (1 to 100 bar), and preferably of from 0.1 to 5 MPa (1 to 50 bar). The cyclohexanol self-oxidation process can be carried out continuously or batchwise; in this latter case, it is suitable to operate in the presence of a suitable reaction initiator, selected from the compounds commonly used for oxidations of the radicalic type. For merely exemplifying purposes, azo-bis-isobutyronitrile, or the same hydrogen peroxide may be cited; the relevant literature (see, e.g., US-A-2,871,104; DE-A-10 02 295 and GB-A-1,421,449) also teaches to operate in the presence of agents capable of stabilizing H₂O₂ (e.g., potassium metaphosphate or pyrophosphate, ammonium nitrate and their mixtures; see also US-A-4,320,102). Sometimes, the self-oxidation can be advantageously carried out in a plurality of steps in series, with the reactants feed being optionally subdivided; in this case, a gradual temperature decrease form step to step is recommended. The ammoximation reaction can be carried out, either batchwise or as a continuous process, in a reactor, to which the catalyst is charged, said catalyst being constituted by a titanium-silicalite, i.e., a crystalline and porous synthetic material, having a zeolitic structure, containing Si, Ti and oxygen in combined form and having, unlike simple silicalite, a characteristic band in its I.R. spectrum, situated at about 950 cm⁻¹ (see, in this regard, US-A-4,410,510). To the reactor, from two different feed lines, the mixture obtained from the self-oxidation of the cyclohexanol and ammonia (either as a gas, or dissolved in aqueous solution) arrive simultaneously. The ammoximation reaction occurs only inside the reactor, where the catalyst is present, and where the temperature is controlled at an optimum level (25-150°C, preferably 40-120°C, and still better from 60 to 120°C); tests run at 15°C did not result in very satisfactory results. The reaction can be carried out under atmospheric or slightly superatmospheric pressure , in order to keep dissolved in the reaction medium an amount of ammonia at least equal to the amount required by the synthesis. The catalyst can be arranged on a fixed bed, or it can be finely dispersed in the reaction medium (suspended bed), provided reactors having surfaces compatible with the presence of hydrogen peroxide are used. If the process is carried out batchwise: from 0.5 to 100 parts by weight (preferably from 1 to 100 parts) of pure catalyst, excluding the binder, per 100 parts by weight of ketone should be used; when the process is run in a continuous way, a space velocity from 0.1 to 100 kg/hour of ketone (as defined above) per kg of pure catalyst (excluding the binder) is suggested. The active oxygen:ketone molar ratio should generally be from 0.8:1 to 1:1, and preferably from 0.9:1 to 1:1, wherein by the term "active oxygen" the (molar) sum of H₂O₂ and the above-mentioned peroxidic and hydroperoxidic organic compounds is meant. The NH₃: H₂O₂ molar ratio should be equal to, or higher than, 1:1 (preferably, 1.5:1), otherwise disturbing parallel reactions may occur. The reaction medium can be constituted by water, or by a water-miscible/organic solvent; really outstanding results were obtained when as the solvent tert.-butyl alcohol, or the same cyclohexanol, were used. Very good results were obtained when in the ammoximation a titanium-silicalite was used, which previously had undergone a particular type of H₂O₂-based post-treatment, of such a type as disclosed in EP-A-267 362 and in IT-A-21,266 A/87. The oxime can be recovered from the ammoximation reaction product by several ways, e.g., by extraction with suitable solvents (e.g., benzene, toluene, and cyclohexanol), with a hydrophobic organic phase and an aqueous phase being thereby obtained. The oxime and the unreacted cyclohexanol are contained in the organic layer: the cyclohexanol can be recovered and recycled to the oxidation reaction and NH₃ can be recovered from the aqueous phase and recycled to the ammoximation reaction. As an alternative, the extraction may take place simultaneously to the oxime formation, by operating in a biphasic system; this system can be advantageously realized by using a couple of solvents having different characteristics, e.g., blends of tert.-butanol (and/or cyclohexanol, i.e., hydrophilic compounds) with toluene (a hydrophobic compound). The invention is now also illustrated by referring to figures, which however in no way limit the scope of the invention. Referring to figure 1, cyclohexanol (1), optionally diluted with water or another solvent, and an oxygen stream (2) enter the reactor R₁, equipped with a rotary-blade stirrer. The resulting oxidized mixture (3) contains the unreacted alcohol, cyclohexanone and H₂O₂, as well as the optional solvent charged together with the alcohol. Said oxidized mixture is transferred to the ammoximation reactor R₂ (which contains the catalyst), equipped with a temperature-control jacket and with a rotary-blade stirrer, fed, through a dipleg, with a stream of tert.-butanol (4) wherein the catalyst is suspended. NH₃ is fed, in the gas form or as an aqueous solution, through the line (5), by means of a dipleg. A porous wall (6) keeps the catalyst suspended, and a valve (7) controls the level of the liquid inside the reactor and the flowrate of the crude ammoximation effluent (8), which flows to a separation area (A), wherein an extractor (not shown in figure) enables the aqueous phase (9), containing possible by-products, which are removed from the cycle, to be discharged. A second separation area (B) makes it possible to recover excess ammonia (10); the recovered ammonia is recycled to the ammoximation reactor, and waste water (11) is removed. The organic phase is subdivided, according to usual techniques, into a tert.-butanol stream (12), which is recycled to the ammoximation reactor, a stream of unreacted cyclohexanol (13), which is recycled to the reactor R₁, where the oxidized mixture (3) is formed, and a stream of cyclohexanone oxime (14), which is the desired product. Figure 2 shows an experimental chart, which shows how the efficiency ratio of the self-oxidation reactions (defined in the following) is strongly reduced when the concentration of the carboxylic acids is too high. The following examples illustrate the present invention, without however limiting in any way the scope thereof. Example 1 (Preparation of the Ammoximation Catalyst) 544 g of tetraethyl orthosilicate were charged to a pyrex-glass, flame-resistant flask equipped with stirrer, and maintained under an inert atmosphere of nitrogen. Then, 24 g of tetraisopropyl titanate was added, and then 1,200 g of an aqueous solution of tetrapropylammonium hydroxide at 20% by weight was slowly added dropwise. The mixture was kept stirred for 1 hour at room temperature, and was then allowed to stand, still at room temperature, for a further hour. The temperature was slowly increased to 78°C, in order to eliminate ethyl alcohol, and was subsequently increased to 98°C, in order to remove isopropyl alcohol. The removal of the alcohols formed during the reaction was carried out under stirring within 5 hours. After cooling, the volume of the liquid was increased to 2 litres by adding deionized water, and the (homogeneous and opalescent) solution was transferred to an autoclave equipped with a stirrer, inside which the hydrothermal synthesis was realized at 175°C within 10 days, under the autogenous pressure. At the end, after cooling, the synthesis mixture was filtered and the solid product was thoroughly washed, to neutral pH, and was dried at 120°C for 15 hours. The dried product was finally calcined at 420°C for 10 hours. The calcined product was placed in a glass beaker, and was mixed with an aqueous solution, prepared by pouring 100 ml of hydrogen peroxide (at 30% by weight) into 1,000 of diluted sulphuric acid (at 5% by weight); the mixing operation ("activating washing") was continued for 2 hours at 70°C, and the supernatant was then decanted. The operation was repeated twice, with fresh solutions, and after the last washing a filtration was carried out, which was followed by a long-time washing with deionized water (to neutral pH); then the product was dried at 120°C for 15 hours and finally calcined at 550°C for 2 hours. Example 2 40 g of cyclohexanol and 0.4 g of free-radical initiator (azo-bis-isobutyronitrile), to which 100 ppm of potassium pyrophosphate and 20 ppm of ammonium nitrate had been added, were charged to a temperature-controlled glass autoclave (of 200 ml of capacity) equipped with a stirrer. After pressurization with oxygen, the temperature of the liquid was increased to 90°C and sufficient amounts of oxygen were then fed (every 10 minutes) in order to maintain a constant pressure level (of approximately 0.2 MPa (2 bar)). After 135 minutes of oxidation, always at 90°C, the reaction mixture was quickly cooled down to room temperature, the residual gases were vented off, and the resulting mixture was discharged. The gas-chromatographic analysis made it possible to ascertain that the conversion to cyclohexanol was 4.9%, with a 96% selectivity to cyclohexanone, the selectivity to active oxygen (H₂O₂ + hydroperoxidic and peroxidic organic compounds) being of 96%, and that the acidity, as carboxylic acids, was 1.5 milliequivalents per 100 millimol of ketone. The efficiency ratio (R): was 0.965 (by mols); these data are reported in Table 1. The thus obtained oxidized mixture was used for the ammoximation reaction. For that purpose a glass reactor, equipped with stirrer and cooling jacket, was pressurized with an inert gas (nitrogen). Then 1 g of fine titanium-silicalite powder, prepared according to example 1, 25 g of tert.-butyl alcohol, 10.5 g of H₂O and 2 g of NH₃ were charged. The stirring was started, and the temperature was increased to 80°C, by circulating a diathermal fluid through the reactor jacket; then the feed of the oxidized mixture to the reactor, by means of a metering pump, was started. The addition was continued for 5 hours, and an overall amount of 25.9 g of solution was fed; during the addition, a decrease in pressure took place. The reaction suspension was cooled to room temperature, ethyl ether was added to it, and the suspension was stirred for a few minutes; the aqueous phase and the ether phase were then separated from the catalyst by filtration, and the liquid phases were finally separated from each other (by a dripping funnel). The analysis supplied the results listed in Table 2. Example 3 The self-oxidation of Example 2 was repeated, cyclohexanol being replaced by 40 g of a solution containing cyclohexanol and water (according to a ratio of 95/5 by weight) and the reaction temperature being increased to 100°C; after 3 hours, the cyclohexanol conversion was 8.8% and the corresponding selectivity to cyclohexanone was 98%, the selectivity to active oxygen (H₂O₂ + hydroperoxidic and peroxidic organic compounds) being 95%. The other results of the cyclohexanol self-oxidation are shown in Table 1. The thus obtained oxidized mixture was used for the ammoximation reaction, according to the same modalities as shown in Example 2; the results are reported in Table 2. Example 4 A mixture containing 300 g of cyclohexanol, 1.5 g of free-radical initiator (azo bis-isobutyronitrile) and 15 g of H₂O, to which 100 ppm of potassium pyrophosphate and 20 ppm of ammonium nitrate had been added, was charged to a temperature-controlled glass autoclave (500 ml) equipped with a gaseous-effect stirrer. After pressurizing with oxygen to 0.5 MPa (5 bar), the temperature was increased to 110°C. The oxygen pressure was then increased to 0.8 MPa (8 bar), and was maintained at this level, with replenishments every 5 minutes. After a reaction time of 90 minutes, always at 110°C, the mixture was rapidly cooled down to room temperature, and was analyzed. The conversion of cyclohexanol was 11.2% and the corresponding selectivity to cyclohexanone was 98.5%. The selectivity to active oxygen (H₂O₂ + organic hydroperoxidic or peroxidic compounds) was 96%; the other results of the self-oxidation are reported in Table 1. The thus obtained oxidized mixture was used for the ammoximation reaction according to the same conditions as shown in Example 2; the results are reported in Table 2. Example 5 The self-oxidation of Example 2 was repeated, the following reactants being used: 25 g of cyclohexanol; 25 g of a solution of water in tert.butyl-alcohol, wherein the water:alcohol ratio was of 1:10 by weight; 0.25 g of initiator (azo-bis-isobutyronitrile), the temperature being maintained at 100°C. After 4 hours, 13% of cyclohexanol had been converted, and the corresponding selectivity to cyclohexanone was higher than 97%, the selectivity to hydrogen peroxide (and other peroxidic forms) being approximately 95%; the other results of the self-oxidation are reported in Table 1. The thus obtained oxidized mixture was used in the ammoximation reaction according to the conditions shown in Example 2; the results are reported in Table 2. Example 6 The self-oxidation of Example 2 was repeated, the temperature being increased to 110°C; the results are reported in Table 1. The thus obtained oxidized mixture was used in the ammoximation reaction, according to the same conditions as shown in Example 2; the results are reported in Table 2.

Claims: Process for the preparation of cyclohexanone oxime, wherein a mixture formed by partial oxidation ,in the liquid phase and at a temperature of from 50 to 150°C, of cyclohexanol with oxygen or an oxygen-containing gas and containing unreacted cyclohexanol, cyclohexanone, hydrogen peroxide and organic peroxides and/or hydroperoxides is directly reacted with ammonia, in the liquid phase and in the presence of a titanium-silicalite ammoximation catalyst. Process according to claim 1, wherein the conversion of cyclohexanol in the oxidation step is from 5 to 50%. Process according to any one of the preceding claims, wherein the partial oxidation of cyclohexanol is carried out in a way such that the corresponding reaction mixture contains carboxylic acids in amounts of from 0.001 to 15, and preferably 0.001 to 5% by weight, based on cyclohexanone. Process according to any one of the preceding claims, wherein the partial oxidation of cyclohexanol is carried out in the presence of an inert solvent, preferably selected from water, tert-butanol, benzene and mixtures thereof, under a pressure of from 0.1 to 10 MPa, preferably 0.1 to 5 MPa. Process according to any one of the preceding claims, wherein the partial oxidation of cyclohexanol is carried out in the presence of a free-radical generator, preferably selected from H₂O₂, azo-bis-isobutyronitrile and mixtures thereof. Process according to any one of the preceding claims, wherein the partial oxidation of cyclohexanol is carried out in the presence of a stabilizing agent for the hydrogen peroxide, preferably selected from potassium metaphosphate, potassium pyrophosphate, ammonium nitrate and mixtures thereof. Process according to any one of the preceding claims, wherein the partial oxidation of cyclohexanol is carried out in a plurality of steps in series, preferably with a decreasing temperature profile from one step to the next. Process according to any one of the preceding claims, wherein said titanium-silicalite, optionally diluted with inert material, is employed in the form of extruded granules, preferably polylobated and optionally showing helical grooves. Process according to any one of the preceding claims, wherein said titanium-silicalite, optionally diluted with inert material, is washed, before being used, with an activating liquid based on hydrogen peroxide, whereafter the thus treated catalyst is dried and calcined.

Inventors: CESANA, ALBERTO, PAPARATTO, GIUSEPPE, ROFFIA, PAOLO, TAUSZIK, GIORGIO
Applicants: ENICHEM ANIC S.R.L.
Application year: 1988
Main classification: C07C249
IPC codes: C07C67, C07B31, C07B43, B01J29, B01J21, C07C239, C07B61, C07C251, C07C249