Process for producing epsilon-caprolactam by Beckmann-rearrangement in the gas phase in the presence of a zeolite catalyst and water

Abstract: ε -Caprolactam is prepared by subjecting cyclohexanone oxime in a gas phase to a catalytic reaction using zeolite catalysts in the presence of water and at least one compound selected from alcohols and ether compounds.

Description: The present invention relates to a process for producing ε-caprolactam from cyclohexanone oxime using solid catalysts under gas phase reaction conditions. ε-Caprolactam is an important raw material for nylon. The inventors have proposed processes for producing ε-caprolactam by rearrangment of cyclohexanone oxime (Beckmann rearrangement) using solid catalysts under gas phase reaction conditions (Japanese Patent Kokai Nos. Hei 2-275850 and 2-250866). EP-A-0380364 discloses reaction of cyclohexanone oxime in a mixture with methanol, ethanol, n-propanol, isopropanol, n-hexanol, or 2,2,2-trifluoroethanol and mentions the possibility of replacing the alcohols by an ether though no examples are given. This disclosure does not make any reference to the presence of water in the reaction mixture. The reaction is carried out in the gas phase over a zeolite catalyst. The inventors have further conducted intensive research on a rearrangement reaction of cyclohexanone oxime and have found that, when the rearrangement reaction is carried out in the presence of alcohols using zeolite catalysts and additionally in the presence of water in the reaction system, life of the catalysts is prolonged and yield of ε-caprolactam is also improved. As a result, the present invention has been accomplished. That is, the present invention provides an industrially superior process for producing ε-caprolactam which comprises subjecting cyclohexanone oxime in a gas phase to a catalytic reaction using zeolite catalysts of the pentasil type in the presence of water and an alcohol under the conditions according to Claim 1. The present invention will be explained in detail below. The zeolite catalysts used in the present invention are of the pentasil type and include, for example, crystalline silica and crystalline metallosilicate. The crystalline silica comprises substantially silicon and oxygen. The crystalline metallosilicate contains a metal in addition to silicon and oxygen, such as those which have a ratio of the number of silicon atom to that of a metal atom (Si/metal atomic ratio) of 5 or higher, preferably at least 500. As examples of the metal, mention may be made of at least one metal selected from Al, Ga, Fe, B, Zn, Cr, Be, Co, La, Ge, Ti, Zr, Hf, V, Ni, Sb, Bi, Cu and Nb. The Si/metal atomic ratio is obtained by usual analytical methods such as atomic absorption spectrometry and X-ray fluorescence analysis. These catalysts are prepared by known processes. The crystalline silica and crystalline metallosilicate have various crystalline forms and those which belong to a pentasil type structure are used. The process of the present invention is characterised in that water is allowed to exist in the reaction system in defined proportions. According to the present invention a process for producing ε-caprolactam comprises subjecting mixtures of cyclohexanone oxime, water, and alcohols in a gas phase to catalytic reaction using zeolite catalysts, characterised in that the alcohols are those having the formula (1): R 1 -O-H (wherein R 1 represents a C 1 -C 6 alkyl group which may be substituted with at least one fluorine atom), in that the mixture contains water in an amount of 0.06-2.5 moles per mole of the cyclohexanone oxime, and in that the space velocity of the cyclohexanone oxime is 0.1-40hr -1 , and in that the zeolite has a pentasil type structure. The amount of water is 0.06-2.5 moles, preferably 0.18-1.9 mole, more preferably 0.18-0.65 mole per mole of cyclohexanone oxime used. When the amount of water is less than 0.06 mole or more than 2.5 moles per mole of cyclohexanone oxime, activity of the catalyst greatly reduces. In the present invention, alcohols are allowed to exit together with water in the reaction system. Examples of the lower alcohols are methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, n-amyl alcohol and n-hexanol. Methanol and ethanol are preferred. In the reaction system, vapours of compounds inert to the reaction, such as benzene, cyclohexane and toluene or inert gases such as nitrogen and carbon dioxide may also be allowed to coexist as a diluent gas. The reaction in carrying out the present invention will be explained. The starting material cyclohexanone oxime is subjected to a catalytic reaction in the gas form. The reaction is carried out in either a fixed-bed or fluidised bed. Cyclohexanone oxime may be fed to a reactor after it is mixed with water and alcohols. Alternatively, these reactants may be fed separately. In the alternative case, water and alcohols may be fed in two or more portions. In the case of the fixed-bed reaction, it is preferred to pass a thorough mixture of these reactants through the catalyst bed. Space velocity of the starting material cyclohexanone oxime is WHSV=0.1-40 hr -1 (namely, feeding rate of cyclohexanone oxime per kg of the catalyst is 0.1-40 kg/hr), preferably 0.2-20 hr -1 , more preferably 0.5-10 hr -1 . Reaction temperature is usually 250-500°C, preferably 300-450°C, more preferably 300-400°C. When the temperature is lower than 250°C, reaction rate is not sufficient and selectivity of ε-caprolactam tends to decrease and when it is higher than 500°C, selectivity of ε-caprolactam tends to decrease. The present process is carried out under pressure, atmospheric pressure or reduced pressure and is usually carried out under pressure of 0.05-10 kg/cm 2 . Isolation of ε-caprolactam from the reaction mixture and purification thereof are carried out, for example, by cooling and condensing the reaction product gas, followed by extraction, distillation or crystallisation. The catalyst having small activity which is caused by use for long time is easily reactivated to the initial activity by being calcined in a molecular oxygen-containing gas, for example, air stream or a molecular oxygen-containing gas to which alcohols such as methanol are added. The reactivated catalyst is repeatedly used. According to the present invention, life of the catalysts is greatly prolonged and yield of ε-caprolactam increases. The following examples explain the present invention. Reference Example 1 (Preparation of catalyst) In a stainless steel autoclave (1.5 ℓ) were charged tetraethylorthosilicate (Si(OC 2 H 5 ) 4 , 100 g, Al content: less than 10 ppm), 10% aqueous tetra-n-propyl-ammonium hydroxide solution (224.0 g) and ethanol (214 g) and were vigorously stirred for 30 minutes. The mixed solution had a pH of 13. The autoclave was sealed and then was dipped in an oil bath in order to keep the internal temperature at 105°C. Hydrothermal synthesis was effected for 120 hours under stirring at a revolution rate of at least 400 rpm. Pressure in the autoclave reached 2-3 kg/cm 2 . pH at the completion of the hydrothermal synthesis was 11.8. A white solid product was filtered off and washed continuously with distilled water until pH of filtrate reached about 7. The white solid was dried and calcined in an air stream at 530°C for 4 hours to obtain powdery white crystals (27 g) which were identified to be pentasil type zeolite by powder X-ray diffractometry. Al content was 3 ppm according to atomic absorption spectroscopy assay. To the crystals (10 g) was added 5% aqueous ammonium chloride solution (100 g) to carry out an ion exchange treatment at 50-60°C for 1 hour. The crystals were filtered off. The ion exchange treatment was carried out four times and then the crystals were washed with distilled water until no Cl - ion was detected in filtrate. Subsequently, the crystals were dried at 120°C for 16 hours. The resulting crystals of ammonium salt form were shaped under pressure and sifted to obtain particles of 24-48 meshes (US Sieve Series which have openings 710 micrometres to 297 micrometres across), which were calcined at 500°C for 1 hour in a nitrogen gas stream to obtain a catalyst. Example 1 In a quartz glass reaction tube (1 cm inner diameter) was packed the catalyst (0.375 g, 0.6 ml) prepared in Reference Example 1 and was preheated in a nitrogen gas stream (4.2 l/hr) at 350°C for 1 hour. Then, to the reaction tube was fed a mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.31 in molar ratio) at a rate of 8.58 g/hr to carry out a reaction. At this time, ammonia gas and nitrogen gas were fed as carrier gases at rates of 0.21 l/hr and 3.99 l/hr, respectively. The space velocity WHSV of cyclohexanone oxime was 8 hr -1 and temperature of the catalyst bed (react ion temperature) was 380°C. The reaction product was trapped and collected using water cooling and was analyzed by gas chromatography. The results are shown in Table 1. The space velocity WHSV of cyclohexanone oxime, the conversion of cyclohexanone oxime and the selectivity of ε-caprolactam were calculated by the following formulas. WHSV (hr -1 )=O/C Conversion of cyclohexanone oxime (%)=[(X-Y)/X]× 100 Selectivity of ε-caprolactam (%)=[Z/(X-Y)] × 100 wherein O=Feeding rate (kg/hr) of cyclohexanone oxime, C=Weight of catalyst (kg), X=Mole number of the fed cyclohexanone oxime, Y=Mole number of unaltered cyclohexanone oxime and Z=Mole number of ε-caprolactam in the product. Elapsed time (hr) Conversion (%) Selectivity (%) 1.25 99.9 95.4 45.25 96.7 95.4 Example 2 Reaction was carried out under the same conditions as in Example 1 except that a mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.1 in molar ratio) was fed to the reaction tube at a rate of 8.48 g/hr (WHSV=8 hr -1 ) in place of the mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.31 in molar ratio) at a rate of 8.58 g/hr. Results of the reaction are shown in Table 2. Elapsed time (hr) Conversion (%) Selectivity (%) 1.25 92.9 94.2 45.25 79.8 95.2 Example 3 Reaction was carried out under the same conditions as in Example 1 except that a mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.63 in molar ratio) was fed to the reaction tube at a rate of 8.73 g/hr (WHSV=8 hr -1 ) in place of the mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.31 in molar ratio) at a rate of 8.58 g/hr. Results of the reaction are shown in Table 3. Elapsed time (hr) Conversion (%) Selectivity (%) 1.25 99.8 93.3 45.25 95.6 93.9 Example 4 Reaction was carried out under the same conditions as in Example 1 except that a mixed solution of cyclohexanone oxime/methanol/water (1/6.4/1.89 in molar ratio) was fed to the reaction tube at a rate of 9.33 g/hr (WHSV=8 hr -1 ) in place of the mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.31 in molar ratio) at a rate of 8.58 g/hr. Results of the reaction are shown in Table 4. Elapsed time (hr) Conversion (%) Selectivity (%) 1.25 99.1 94.3 45.25 93.2 94.9 Comparative Example 1 Reaction was carried out under the same conditions as in Example 1 except that a mixed solution of cyclohexanone oxime/methanol (1/1.8 in weight ratio) was fed to the reaction tube at a rate of 8.44 g/hr (WHSV=8 hr -1 ) in place of the mixed solution of cyclohexanone oxime/methanol/water (1/6.4/0.31 in molar ratio) at a rate of 8.58 g/hr. Results of the reaction are shown in Table 5. Water content in the starting material cyclohexanone oxime was analyzed to obtain 0.3% by weight. This corresponded to 0.019 mole per mole of the cyclohexanone oxime. Elapsed time (hr) Conversion (%) Selectivity (%) 1.25 96.8 93.5 45.25 58.7 95.2 Comparative Example 2 (Application to boric acid catalyst) Reaction was carried out under the same conditions as in Example 1 except that 0.375 g of boric acid was used in place of the catalyst prepared in Reference Example 1. Immediately after a reaction started, boric acid was dissolved out and substantially no reaction occured.

Claims: A process for producing ε-caprolactam which comprises subjecting mixtures of cyclohexanone oxime, water, and alcohols in a gas phase to catalytic reaction using zeolite catalysts, characterised in that the alcohols are those having the formula (1): R 1 -O-H (wherein R 1 represents a C 1 -C 6 alkyl group which may be substituted with at least one fluorine atom), in that the mixture contains water in an amount of 0.06-2.5 moles per mole of the cyclohexanone oxime, in that the space velocity of the cyclohexanone oxime is 0.1-40 hr -1 , and in that the zeolite has a pentasil type structure. A process as claimed in claim 1, characterised in that the alcohol is at least one alcohol selected from methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, n-amyl alcohol and n-hexanol. A process as claimed in claim 2, characterised in that the alcohol is methanol or ethanol. A process as claimed in any one of claims 1 to 3, characterised in that the reaction temperature is 250-500°C. A process as claimed in any one of claims 1 to 4, characterised in that the reaction pressure is 0.05-10 kg/cm 2 . A process as claimed in any one of claims 1 to 5, characterised in that the zeolite catalyst having a low activity which is caused by use for a long time is activated by being calcined in a molecular oxygen-containing gas. A process as claimed in claim 6, characterised in that the molecular oxygen-containing gas is air. A process as claimed in claim 6 or claim 7, characterised in that the molecular oxygen containing gas contains alcohols. A process as claimed in claim 8, characterised in that the alcohol is methanol.

Inventors: HIGASHIO YASUHIKO, KAJIKURI HIROSHI, KITAMURA MASARU, HIGASHIO, YASUHIKO, KAJIKURI, HIROSHI, KITAMURA, MASARU
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1992
Main classification: C07D201
IPC codes: C07D201, B01J29