PROCESS FOR THE PRODUCTION OF PSEUDOCUMENE OR DURENE

Abstract: A process for producing pseudocumene or durene is described, comprising methylating xylene by the use as a catalyst of a crystalline borosilicate. The specific crystalline silicate catalyst increases the conversion of xylene and the selectivity of pseudo-cumene or durene. The process of the invention can be performed either in one step or in two steps. The two-step reaction provides various industrial advantages, such as a high degree of utilization of the methylating agent and a great increase in the selectivity of the product.

Description: The present invention relates to a process for the production of pseudocumene or durene, and more particularly, to a process for efficiently producing pseudoCumene or durene from xylene by the use of specific crystalline silicates as a catalyst. This application is a divisional application from EP-A-0 104 607 describing also a process for efficiently producing pseudocumene or durene from xylen by the use of specific crystalline silicates as a catalyst. As is well known, pseudocumene or durene is produced by a method using a Lewis acid catalyst such as AlCl₃ or a method using a liquid acid type catalyst, such as sulfuric acid. In the both methods, however, it is necessary to use anti-corrosion equipment and moreover the selectivity of the desired product is undesirably low. Moreover, the latter method has a disadvantage that the conversion of the starting material is very low. In order to improve such a low conversion, Japanese Patent Application Laid-Open No. 43930/74 has proposed a method in which trimethoxy borate is added. In this method, however, either of the conversion and selectivity are not yet sufficiently satisfactory. In US-A-4 292 457 a crystalline borosilicate is disclosed which comprises a molecular sieve material and is used to catalyze processes such as isomerization, disproportionation, alkylation, transalkylation and conversion of alcohols into gasoline-boiling-range products, olefins, and/or aromatics. As a result of extensive investigations to overcome the problems as described above, it has been found that pseudocumene or durene can be efficiently produced by using crystalline borosilicate as a catalyst. The present invention relates to a process for producing pseudocumene or durene by methylating xylene in the presence of a catalyst, characterized in that the catalyst is a crystalline borosilicate and the methylating agent is methyl alcohol or dimethyl ether, and the reaction is carried out at a temperature of 250 to 400°C. Further the invention relates to a process for producing durene by methylating pseudocumene in the presence of the above-mentioned catalyst. Figure 1 shows X-ray the diffraction pattern of crystalline silicate obtained in the Preparation Example as described hereinafter. In the figure, 2Θ means the Bragg angle (degree). The crystalline silicate used as a catalyst in the process of the invention is crystalline borosilicate. Various types of crystalline borosilicate are available . In particular, those silicates in which the molar ratio of SiO₂ to B₂O₃ ( SiO₂/B₂O₃ ) is at least 12, especially from 20 to 500 are usually preferred. Suitable examples are the crystalline-borosilicates as described in Japanese Patent Application Laid-Open Nos. 55500/78, 7598/80, 84313/81, 123817/82 and 129820/82. The crystalline borosilicates as described above can be prepared by various procedures, and there is no special limitation to the method of preparation thereof. A method of preparation as generally used comprises adding a silica source and a boron oxide source and, if desired, a crystallization agent, e.g., alkylammonium salts, to water to prepare an aqueous mixture, and then subjecting the aqueous mixture thus prepared to a hydrothermal reaction. Various compounds can be used as the silica source, including silica powder, silicic acid, colloidal silica, and dissolved silica. This dissolved silica includes water glass silicate and alkali metal silicates, all containing from 1 to 5 moles of silicon dioxide per mole of sodium oxide or potassium oxide. As the boron oxide source, metaboric acid, tetraboric acid, anhydrous boric acid, and borates, such as borax, as well as boric acid can be used. In performing the hydrothermal reaction of the aqueous mixture containing the silica and boron oxide source, there is no special limitation to the reaction conditions; i.e.,it is sufficient for the reaction to be performed under such conditions (temperature, pressure, and heating time) that permit the preparation of crystalline borosilicate. In general, the reaction is performed at a temperature of 120 to 250°C, preferably 150 to 200°C for a period of 10 hours to 7 days, preferably 24 hours to 2 days under autogenous pressure. The pH of the reaction system in performing the hydrothermal reaction can be determined appropriately; it is usually adjusted to a range of from 8 to 11 and preferably to a range of from 9 to 10. It is preferred that a suitable amount of crystallization agent be added to the reaction system. Examples of such crystallization agents include tetraalkylammonium bromide, and tetraethylammonium bromide. The crystalline borosilicate as prepared by the above-described preparation method takes various crystal structures depending on the type and amount of each of the silica and boron oxide source, the hydrothermal reaction conditions, the type of the crystallization agent, and so forth. In the process of the invention, any of such crystalline borosilicates can be used. Of these borosilicates, crystalline borosilicates in which the molar ratio of SiO₂ to B₂O₃ is at least 12 are preferred. Particularly preferred are those crystalline borosilicates in which the molar ratio of SiO₂ to B₂O₃ is from 20 to 500. In preparing the crystalline borosilicates as described above, it is sufficient for the silica and boron oxide sources to be added to the reaction system in such a manner that the ratio of the silica source to be boron oxide source is from 20:1 to 500:1 (calculated as the molar ratio of SiO₂ to B₂O₃ ). The crystalline borosilicate prepared as described above is usually in the form of powder. If desired, it can be molded after adding a binder, e.g., alumina sol. In the process of the invention, xylene (including p-xylene, o-xylene, m-xylene, and mixtures thereof) is used as a starting material, and is methylated using a methylating agent in the presence of the catalyst as described above to produce pseudocumene or durene. As the methylating agent methanol and dimethyl ether can be used. The amount of the methylating agent used herein can be determined appropriately depending on the reaction conditions, the type of the desired product, and so forth. The molar ratio of the xylene to the methylating agent is usually from 20:1 to 1:20, preferably from 5:1 to 1:5, and more preferably from 2:1 to 1:4. Other reaction conditions in carrying out the process of the invention are not critical. The reaction temperature is from 250 to 400°C, preferably from 280 to 350°C; in general the reaction pressure is from atmospheric pressure to 98 bars (100 kilograms per square centimeter) by gauge and preferably from atmospheric pressure to 9.8 bars (10 kilograms per square centimeter) by gauge; and the liquid hourly space velocity (LHSV) is from 0.05 to 100 per hour and preferably from 0.1 to 10 per hour. In the process of the invention, xylene is usually used as the starting material, but pseudocumene can be used in place of xylene as the starting material. when pseudocumene is used as the starting material, the main product obtained by the process of the invention is durene. The methylation reaction in the process of the invention is usually carried out in one step. If it is carried out in two steps, the degree of utilization of the methylating agent increases and moreover it is possible to increase the selectivity of pseudocumene or durene. The two-step reaction as described above usually comprises the first reaction step where xylene is methylated and the second reaction step where at least a part of the reaction mixture from the first reaction step is further methylated. This two-step reaction will hereinafter be explained in detail. At the first reaction step, the production of pseudocumene from xylene is mainly conducted. Various methylating agents can be used for the first reaction step, including methanol and dimethyl ether. If only pseudocumene is desired to produce at the first reaction step, it is preferred to use a' methylating agent composed mainly of dimethyl ether having a relatively low methylating ability. After completion of the first reaction step, the reaction mixture from the first reaction step is sent to the second reaction step where it is further methylated. In this case, the entire reaction mixture may be introduced in the second reaction step, or after separation or removal of a part of light gases from the reaction mixture, the remainder may be introduced in the second reaction step. At the second reaction step, the reaction mixture as introduced above is further methylated. As in the first reaction step, various methylating agents, such as methanol and dimethyl ether, can be used at the second reaction step. At the second reaction step, the methylation reaction of pseudocumene produced at the first reaction step and unreacted xylene mainly proceeds. If durene, in particular, is desired to produce, it is preferred to use a methylating agent composed mainly of methanol having a relatively high methylating ability. When the methylating agent composed mainly of methanol as described above is used at the second reaction step, the methylating agent recovered contains a relatively large amount of dimethyl ether. Thus, by using the recovered methylating agent as a methylating agent for the first reaction step, the methylating agent can be effectively utilized. Although only the methylating agent recovered from the second reaction step can be used for the first reaction step, it is also possible to supply the recovered methylating agent in combination with a fresh methylating agent. In the process of the invention using the specific crystalline silicate as described above, the transmethylation reaction of the starting material and the product, and the decomposition of the methylating agent are inhibited; i.e., side-reactions are reduced. This will increase the conversion of xylene and the selectivity of pseudocumene or durene. The crystalline silicate catalyst as used herein possesses a very long service life. Hence the process of the invention can be performed continuously for long periods of time while maintaining high catalytic activity. In the process of the invention, any one of pseudocumene and durene can be produced or both the pseudocumene and durene can be produced in a desired ratio by appropriately selecting the reaction conditions and the reaction time. For example, if the reaction is performed under relatively moderate conditions or for a short period of time, the methylation does not proceed so much, resulting in the production of a large amount of pseudocumene, whereas if the reaction is performed under severe conditions or for a long period of time, the proportion of durene being produced increases. If the process of the invention is performed in two steps and the methylating agent is recovered for re-use, the degree of utilization of the methylating agent (the ratio of the methylating agent used only in the methylation reaction to the methylating agent reacted in overall reaction) is high and the selectivity of pseudocumene or durene is greatly high compared with the one-step reaction. Hence the process of the invention is very advantageous for the industrial production of pseudocumene or durene and is of high practical value. The present invention is described in greater detail with reference to the following Examples and Comparative Examples. PREPARATION EXAMPLE Preparation of Crystalline Borosilicate Solution A was prepared by adding 0.67 gram of boric acid, 17.68 grams of concentrated sulfuric acid, and 26.32 grams of tetrapropylammonium bromide to 250 milliliters of water, and Solution B was prepared by adding 211.1, grams of water glass (consisting of 28.95% by weight of silicon oxide, 9.40% by weight of sodium oxide, and 61.65% by weight of water) to 250 milliliters of water. Solutions A and B were added dropwise simultaneously to a solution of 79.0, grams of sodium chloride dissolved in 122 milliliters of water at room temperature over 60 minutes. The mixture thus obtained was adjusted to pH 9.5 using sulfuric acid and placed in an autoclave where it was heated at 170°C for 20 hours. The contents of the autoclave was filtered while cooling and the solids thus obtained were washed with water. Then 300 milliliters of a 1 normal (NJ aqueous solution of ammonium nitrate was added thereto and an ion exchange procedure was performed three times at 90°C for 8 hours to obtain ammonium type crystalline borosilicate. The contents were then filtered and washed with water, dried at 120°C for 24 hours, and calcined at 550°C for 6 hours to obtain 58 grams of H type crystalline borosilicate ( SiO₂/B₂O₃=100/1 (by mole)). Thus obtained crystalline borosilicate gave an X-ray diffraction pattern as shown in the figure 1. To the H type crystalline borosilicate powder prepared above was added alumina sol as a binder so that the binder content was 20% by weight. The resulting mass was molded, dried at 120°C for 3 hours, and then calcined in air at 550°C for 6 hours to produce H type crystalline borosilicate pellets. PREPARATION EXAMPLE 2 Preparation of Crystalline Aluminosilicate Solution A was prepared by adding 6.2 grams of aluminum sulfate (18 hydrate), 17.68 grams of concentrated sulfuric acid, and 26.32 grams of tetrapropylammonium bromide to 250 milliliters of water, and Solution B was prepared by adding 211.1, grams of water, glass (consisting of 28.95% by weight of silicon oxide, 9.40% by weight of sodium oxide, and 61.65% by weight of water) to 250 milliliters of water. Solutions A and B were added dropwise simultaneously to a solution of 79.0 grams of sodium chloride in 122 milliliters of water at room temperature over 60 minutes. The mixture thus prepared was adjusted to pH 9.5 using sulfuric acid and placed in an autoclave where it was heated at a temperature of 170°C for 20 hours. The contents of the autoclave was filtered while cooling and the solids thus obtained were washed with water. Then 300 milliliters of a 1 normal aqueous solution of ammonium nitrate was added thereto and an ion exchange procedure was performed three times at 90°C for 8 hours to obtain ammonium type crystalline aluminosilicate. The contents were then filtered, washed with water, dried at 120°C for 24 hours, and calcined at 550°C for 6 hours to obtain H type crystalline aluminosilicate ( SiO₂/Al₂O₃=100/1 (by mole)). To the H type crystalline aluminosilicate prepared above was added alumina sol as a binder so that the binder content was 20% by weight, and the resulting mass was molded, dried at 120°C for 3 hours, and calcined in air at 550°C for 6 hours to produce molded crystalline aluminosilicate zeolite (ZSM-5). EXAMPLE 1 A flow type reactor was packed with H type crystalline borosilicate pellets prepared in preparation Example 1, and a 1:4 (by mole) mixture of p-xylene and methyl alcohol was passed therethrough and reacted at a temperature of 330°C under atmospheric pressure at a liquid hourly space velocity (LHSV) of 1 per hour. The conversion of xylene, the selectivity of the product, and so forth were measured after four hours from the start of the reacton. The results are shown in Table 1. EXAMPLE 2 A reaction tube was packed with the crystalline aluminosilicate zeolite (ZSM-5) prepared in Preparation Example 2, and methyl alcohol was passed therethrought at 250° under atmospheric pressure at a liquid hourly space velocity (LHSV) of 1 per hour to produce dimethyl ether. Then a 1:1 (by mole) mixture of dimethyl ether as prepared above and p-xylene was reacted by passing through a reaction tube packed with H type crystalline borosilicate pellets prepared in Preparation Example 1 at 330°C under atmospheric pressure at a liquid hourly space velocity (LHSV) of 1 per hour. The conversion of p-xylene, the selectivity of the product, and so forth were measured after four hours from the start of the reaction. The results are shown in Table 1. COMPARATIVE EXAMPLE 1 The reaction was performed in the same manner as in Example 1 except that H type aluminosilicate zeolite prepared in Preparation Example 2 was used in place of H type crystalline borosilicate. The results are shown in Table 1. PREPARATION EXAMPLE 3 Preparation of Crystalline Boroaluminosilicate Solution A was prepared by adding 3.35 grams of boric acid, 6.2 grams of aluminum sulfate (18 hydrate), 17.68 grams of concentrated sulfuric acid, and 26.32 grams of tetrapropylammonium bromide to 250 milliliters of water, and Solution B was prepared by adding 211.1 grams of water glass (consisting of 28.95% by weight of silicon oxide, 9.40% by weight of sodium oxide, and 61.65% by weight of water) to 250 milliliters of water. Solutions A and B were added dropwise simultaneously to a solution of 79.0 grams of sodium chloride dissolved in 122 milliliters of water at room temperature over 60 minutes. The mixture thus prepared was adjusted to pH 9.5 using sulfuric acid and placed in an autoclave where it was heated at 170°C for 20 hours. The contents of the autoclave was filtered while cooling and the solids thus obtained were washed with water. Then, 300 milliliters of a 1 normal aqueous solution of ammonium nitrate was added thereto and an ion exchange procedure was performed three times at 90°C for 8 hours to obtain ammonium type crystalline boroaluminosilicate. The contents were then filtered, washed with water, dried at 120°C for 24 hours, and then calcined at 550°C for 6 hours to obtain 58 grams of H type crystalline boroaluminosilicate ( SiO₂/Al₂O₃/B₂O₃=100/1/5 (by mole)). Thus obtained crystalline boroaluminosilicate gave an X-ray diffraction pattern as shown in the figure 2. To the H type crystalline boroaluminosilicate powder prepared above was added alumina sol as a binder so that the binder content was 20 by weight. The resulting mass was molded, dried at 110°C for 3 hours, and calcined in air at 550°C for 6 hours to produce molded crystalline boroaluminosilicate. COMPARATIVE EXAMPLE 2 The procedure of Example 1 was repeated except that the crystalline boroaluminosilicate as prepared in Preparation Example 3 was used as such in place of the crystalline borosilicate and that a temperature of 300°C was used. The results as measured after four hours from the start of the reaction are shown in Table 1.

Claims: A process for producing pseudocumene or durene by methylating xylene in the presence of a catalyst, characterized in that the catalyst is a borosilicate and the methylating agent is methyl alcohol or dimethyl ether, and the reaction is carried out at a temperature of 250 to 400°C. A process as claimed in the claim 1 which comprises a first reaction step where the xylene is methylated and a second reaction step where at least a part of the reaction mixture from the first reaction step is further methylated. The process as claimed in claim 2, wherein a methylating agent containing dimethyl ether is used at the first reaction step and a methylating agent containing methanol is used at the second reaction step. The process as claimed in claim 2, wherein the methylating agent recovered at the second reaction step is used as at least a part of the methylating agent to be used at the first reaction step. A process for producing durene by methylating pseudocumene in the presence of a catalyst, characterized in that the catalyst is as defined in claim 1.

Inventors: HARUHITO, SATO
Applicants: IDEMITSU KOSAN COMPANY LIMITED
Application year: 1983
Main classification: C07C15
IPC codes: C07C67, C07B61, B01J21, C07C15, C07C2, B01J29, C07C1