Dimethylnaphthalene isomerization

Abstract: A dimethylnaphthalene is isomerised by contact in liquid form with a solid isomerization catalyst comprising either beta zeolite or an acidic ultrastable Y-type crystalline zeolite having a silica-to-alumina molar ratio of 4:1 to 10:1 and pore windows provided by twelve-membered rings containing oxygen and a unit cell size of from 24.2 to 24.7 angstroms (10⁻¹⁰m). The isomerization is performed at elevated temperature and a pressure sufficiently high to maintain the feedstock in the liquid phase.

Description: This invention relates to a method of isomerizing dimethylnaphthalene. Naphthalene dicarboxylic acids are monomers that are known to be useful for the preparation of a variety of polymers. For example, poly(ethylene 2,6-naphthalate) prepared from 2,6-naphthalene dicarboxylic acid and ethylene glycol has better heat resistance and mechanical properties than polyethylene terephthalate and is useful in the manufacture of films and fibres. Dimethylnaphthalenes are desirable feedstocks for oxidation to the corresponding naphthalene dicarboxylic acids. A known conventional process for producing a naphthalene dicarboxylic acid comprises the oxidation of a dimethylnaphthalene with oxygen in the liquid phase in an acetic acid solvent at an elevated temperature and pressure and in the presence of a catalyst comprising cobalt, manganese and bromine components. Typically dimethylnaphthalenes are found in refinery or coal-derived streams as mixtures of all of the ten possible dimethylnaphthalene isomers. However, separation of these isomers is very difficult and expensive. Consequently, methods for producing specific dimethylnaphthalenes or mixtures of two or three specific dimethylnaphthalenes in high purity and quality are highly desirable. One type of such method is a multistep synthesis involving (1) the formation of an alkenylbenzene by the reaction of o-, m- or p-xylene or ethylbenzene with butadiene, (2) the cyclization of the resulting alkenyl-benzene to form one or more dimethyltetralins belonging to one or two of three groups of three isomeric dimethyltetralins - that is, either group A containing the 1,5-, 1,6-, 2,5- and 2,6-dimethyltetralins, group B containing the 1,7-, 1,8-, 2,7- and 2,8-dimethyltetralins, or group C containing the 1,3-, 1,4-, 2,3-, 5,7-, 5,8- and 6,7-dimethyltetralins, (3) the dehydrogenation of the dimethyltetralin(s) to form the corresponding dimethyl naphthalene(s), and (4) the isomerization of the resulting dimethylnaphthalene(s) to the desired specific dimethylnaphthalene. For example, Thompson, U.S. Patents Nos. 3,775,496; 3,775,497; 3,775,498; 3,775,500 disclose processes for the cyclization of specific alkenylbenzenes to one or more specific dimethyltetralins at 200-450°C in the presence of any suitable solid acidic cyclization catalyst such as acidic crystalline zeolites as well as silica-alumina, silica-magnesia and silica-alumina-zirconia and phosphoric acid, followed by the dehydrogenation of the resulting dimethyltetralin(s) in the vapour state to the corresponding dimethylnaphthalene(s) in a hydrogen atmosphere at 300-500°C and in the presence of a solid dehydrogenation catalyst such as noble metals on carriers and chromia-alumina, and thereafter isomerization of each of the aforesaid dimethylnaphthalene(s) to the desired isomer within the triad of dimethylnaphthalenes to which the isomer being isomerized belongs, at 275-500°C in the presence of a solid acidic isomerization catalyst of the same type as described in respect of the cyclization disclosed therein. In the alternative, both the cyclization and isomerization reactions can be performed in the liquid phase, in which case the cyclization is performed at 200-275°C with a solid phosphoric acid catalyst, at 70-140°C with an acidic ion exchange resin, an acidic crystalline zeolite, hydro-fluoric or sulphuric acid as the catalyst or a siliceous cracking catalyst. More specifically, Thompson, U.S. Patent No. 3,775,496 discloses the cyclization of 5-(m-tolyl)-pent-2-ene to 1,6- and 1,8-dimethyltetralins, which are then dehydrogenated to 1,6- and 1,8-dimethylnaphthalenes, which in turn are isomerized to 2,6- and 2,7-dimethylnaphthalenes, respectively. Thompson, U.S. Patent No. 3,775,497 discloses the cyclization of 5-phenyl-hex-2-ene to 1,4-dimethyltetralin which is then dehydrogenated to 1,4-dimethylnaphthalene, which is in turn isomerized to 2,3-dimethylnaphthalene. Thompson, U.S. Patent No. 3,775,498 discloses the cyclization of 5-(o-tolyl)-pent-2-ene to 1,5-dimethyltetralin, which is then dehydrogenated to 1,5-dimethylnaphthalene, which is in turn isomerized to 2,6-dimethylnaphthalene. Thompson, U.S. Patent No. 3,775,500 discloses the cyclization of 5-(p-tolyl)-pent-2-ene to 1,7-dimethyltetralin, which is then dehydrogenated to 1,7-dimethylnaphthalene, which in turn is isomerized to 2,7-dimethylnaphthalene. Shimada et al., U.S. Patent No. 3,780,119 disclose a method for the isomerization of dimethylnaphthalene by the use at a temperature above 260°C of a mordenite catalyst in which a metal form of mordenite is in excess of 20 weight percent of the mordenite, with the metal being selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, strontium, barium, zinc and aluminium. Suld et al., U.S. Patent No. 3,803,253 disclose a method for the hydroisomerization of a dimethylnaphthalene by the use of a combination of a hydrogenation catalyst and a calcium-containing zeolite catalyst, such as a calcium-exchanged synthetic faujasite, for example, a Y-type molecular sieve. Shima et al., U.S. Patent No. 3,806,552 disclose a method for the isomerization of dimethylnaphthalenes in the gas phase by the use of a mixed catalyst consisting of (a) 65-95 weight percent of a hydrogen form of mordenite in which above 80 weight percent of the metal cations are replaced with hydrogen ions, and (b) 5-35 weight percent of catalyst selected from the group consisting of bentonite and fuller's earth. Hedge, U.S. Patent No. 3,855,328 discloses a method for the isomerization of dimethylnaphthalenes by the use of a Type Y alumino silicate zeolite at 120-300°C in the liquid phase. The catalysts have aluminum-to-silicon atomic ratios of 0.1-1.0. Ogasawara et al., U.S. Patent No.3,888,938 disclose a method for the isomerization of dimethylnaphthalenes in the liquid phase by the use of a mixed catalyst consisting of (a) 70-95 weight percent of a hydrogen form of mordenite in which above 80 weight percent of the metal cations are replaced with hydrogen ions, and (b) 5-30 weight per cent of a promoter selected from the group consisting of bentonite and fuller's earth. Hedge et al., U.S. Patent No. 3,928,482 disclose the isomerization of either dimethyldecalins, dimethyltetralins or dimethylnaphthalenes in the presence of an alumino silicate zeolite containing polyvalent metal cations in exchange positions, such as a rare earth-exchanged Type Y zeolite. Yokayama et al., U.S. Patent No. 3,957,896 disclose the selective isomerization of dimethylnaphthalenes in the presence of any kind of natural or synthetic, solid acid catalyst, such as Y-type zeolite as well as silica-alumina, silica-magnesia, silica-zirconia, silica-alumina-zirconia, fuller's earth, natural or synthetic mordenite, X-type zeolite, A-type zeolite and L-type zeolite. These catalysts may be substituted partly or wholly by hydrogen or metal. Furthermore, these catalysts can be unsupported or supported on carriers. Onodera et al., U.S. Patent No. 4,524,055 disclose a crystalline aluminosilicate zeolite that is useful in the isomerization of dimethylnaphthalenes and has a silica-to-alumina mole ratio of 10 to 100, specific x-ray lattice distances, and a specific cyclohexane-to-n-hexane adsorption ratio of at least 0.7. Maki et al., U.S. Patent No. 4,556,751 disclose the isomerization of dimethylnaphthalenes in the presence of a crystalline aluminosilicate having a pentasil structure and a silica-to-alumina molar structure of 12 or higher. In addition, the aluminosilicate may contain some other metals as non-exchangeable metals. A problem in all such prior art methods is the presence of other dimethylnaphthalene isomers and unconverted dimethyltetralin and alkenylbenzene as impurities and by-products in the finally obtained, desired specific dimethylnaphthalene isomer. The presence of such impurities and by-products markedly reduces the utility and commercial value of the desired dimethylnaphthalene isomer, especially as a precursor for the formation of a naphthalene dicarboxylic acid for use as a monomer in the manufacture of a polymer. In addition, catalysts tend to deactivate relatively rapidly at the high temperatures employed in vapour phase processes. Therefore, it is highly desirable to employ relatively lower temperature liquid phase processes and to improve the completeness of each step in the aforesaid multistep synthesis and the selectivity of each step therein for the production of the desired product therefrom. In this regard, it is known that in the presence of an acid catalyst, the dimethylnaphthalene isomers are isomerizable within each triad of dimethylnaphthalene isomers - that is, within the 1,5-, 1,6- and 2,6-dimethylnaphthalenes of triad A, within the 1,7-, 1,8-, and 2,7-dimethylnaphthalenes of triad B, and within the 1,3-, 1,4- and 2,3-dimethylnaphthalenes of triad C. It is also known that the interconversion of a dimethylnaphthalene isomer within one of the aforesaid triads to a dimethylnaphthalene isomer within another of the aforesaid triads occurs to a relatively lesser extent. Consequently, it is highly desired to improve the selectivity of the cyclization step in the aforesaid multistep synthesis for the formation of dimethyltetralin isomers that belong to the same triad to which also belongs the specific desired dimethyltetralin isomer, which upon dehydrogenation is converted to the desired specific corresponding dimethylnaphthalene isomer. It is also highly desired to improve the selectivity and completeness of the isomerization step in the aforesaid multistep synthesis for the formation of the specific dimethylnaphthalene isomer desired. Accordingly, the invention provides a method for isomerizing at least 20 weight percent of the total of at least one dimethylnaphthalene isomer to form at least one desired other dimethylnaphthalene isomer in the same triad of dimethylnaphthalene isomers to which the isomer being isomerized belongs comprising: contacting each aforesaid dimethylnaphthalene isomer to be isomerized in liquid form with a solid isomerization catalyst comprising either beta zeolite or an acidic ultrastable Y-type crystalline zeolite having a silica-to-alumina molar ratio of from 4:1 to 10:1, and having pore windows provided by twelve-membered rings containing oxygen and a unit cell size of from 24.2 to 24.7 angstroms and at an elevated temperature and at a pressure that is sufficiently high to maintain the isomerization feedstock substantially in the liquid phase. The dimethylnaphthalene isomers being isomerized comprise, in an embodiment of the invention, (a) 1,5- and 1,6-dimethylnaphthalene, (b) 1,5-, 1,6-, 1,7- and 1,8-dimethylnaphthalenes, (c) 1,7- and 1,8-dimethylnaphthalenes or (d) 1,3- and 1,4-dimethylnaphthalenes. A convenient isomerisation temperature is 200°C - 300°C. Further details of the invention are described below and in the Examples. The isomerization of the invention is suitable for use in a three stage process comprising cyclization, dehydrogenation and isomerisation for the formation of dimethylnaphthalenes. References to cyclisation and dehydrogenation are retained below when describing the present isomerisation invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Suitable feedstocks for use in the cyclization are 5-(o-, m-, or p-tolyl)-pent-1- or -2-ene or 5-phenyl-hex-1- or -2-ene. When 5-(o-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization step, 1,5-, 1,6-, 2,5-, or 2,6-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight per cent of the dimethyltetralins produced therefrom, which resulting dimethytetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding 1,5-, 1,6- and 2,6- dimethylnaphthalenes, which are then the feedstock in the isomerization step of the present invention and are converted therein to 2,6-dimethylnaphthalene. When 5-(m-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization step, 1,5- 1,6- 1,7-, 1,8- 2,5- 2,6-, 2,7- or 2,8-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding 1,5-, 1,6-, 1,7-, 1,8- 2,6- and 2,7-dimethylnaphthalenes, which are then the feedstock in the isomerization step and are converted to 2,6- and 2,7-dimethylnaphthalenes. When 5-(p-tolyl)-pent-1- or -2-ene is the feedstock to the cyclization step, 1,7-, 1,8-, 2,7- or 2,8-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding 1,7-, 1,8- and 2,7-dimethylnaphthalenes which are then the feedstock and are converted in the isomerization step to 2,7-dimethylnaphthalene. When 5-phenyl-1- or -2-hexene is the feedstock to the cyclization step, 1,3-, 1,4-, 2,3-, 5,7, 5,8-, or 6,7-dimethyltetralin or a mixture thereof comprises at least 80, preferably at least 85 weight percent of the dimethyltetralins produced therefrom, which dimethyltetralins are in turn the feedstock and are converted in the dehydrogenation step to the corresponding, 1,3-, 1,4- and 2,3-dimethylnaphthalenes, which are then the feedstock in the isomerization step and are converted to 2,3-dimethyl- naphthalene. Each of the aforesaid cyclization, dehydrogenation and isomerization reactions is performed in the liquid phase at an elevated temperature and at a sufficiently high pressure to ensure that the feedstock for the particular step is maintained substantially in the liquid phase. The cyclization reaction is performed at a temperature in the range of 120°C, preferably from 150°C, to 250°C, and generally at a pressure in the range of from 0.1, preferably from 0.3, to 5, preferably to 1.3, atmospheres absolute (30.4 to 506, preferably 132kPa). The dehydrogenation reaction is performed at a temperature in the range of from 200°C, preferably from 220°C, to 300°C, preferably to 270°C, and generally at a pressure in the range of from 0.5, preferably from 0.8 to 5 preferably to 1.3 atmospheres absolute (51, preferably 80 to 506, preferably to 132 kPa). The isomerization reaction is performed at a temperature in the range of from 200°C, preferably from 240°C, to 300°C preferably to 280°C, and generally at a pressure in the range of from 0.5, preferably from about 0.8, to 5, preferably to 1.3 atmospheres absolute (51, preferably 80 to 506, preferably to 132 kPa). Each of the cyclization, dehydrogenation and isomerization reactions can be performed with or without a solvent for the respective feedstock. Preferably a solvent is not employed in the aforesaid steps. If employed, a solvent in any of the aforesaid steps must be inert under the conditions employed and suitably comprise a paraffin such as a tetradecane, or an aromatic hydrocarbon such as anthracene, or mixtures thereof, which preferably boils above 270°C. In the cyclization step, if water is present, its concentration is less than 0.5 weight percent, preferably less than 0.1 weight percent, based on the weight of the alkenylbenzene feedstock. More preferably water is not present in the cyclization reaction medium. Each of the cyclization, dehydrogenation and isomerization steps can be performed either batchwise or continuously. The reaction apparatus to be used in each aforesaid step can be of any known type such as a fixed bed, moving bed, fluidized bed, liquid phase suspended bed or a solid-liquid mixture in a stirred tank. Generally, however, the use of a fixed bed is commercially preferred for continuous operation. The improved conversion of the feedstock and selectivity for the production of the desired product or set of products for each of the cyclization,dehydrogenation and isomerization steps of the method of this invention are the result of the temperature and pressure conditions employed and the high activity and selectivity of the catalysts employed in each aforesaid step, which in turn permits the use of less severe conditions -- that is, lower temperatures and pressures --such that greater selectivity and reduced catalyst deactivation can be achieved. The catalyst employed in the isomerization step of the method of this invention comprises either beta zeolite or an acidic ultrastable -- that is, a thermally stabilized or delaminated -- Y-type crystalline aluminosilicate zeolite having a silica-to-alumina molar ratio of from 4:1 preferably from 5:1, to 10:1, preferably to 6:1, and having pore windows provided by twelve-membered rings containing oxygen, and a unit cell size of from 24.2, preferably from 24.3 to 24.7, preferably to 24.6 angstroms. A suitable such zeolite is marketed by Union Carbide under the name LZ-Y72 or LZ-Y20. Water is not detrimental to catalytic activity or selectivity in the isomerization process. The isomerization catalyst preferably comprises beta zeolite. The composition, structure and preparation of beta zeolite are described in Wadlinger et al., U.S. patent No. 3,308,069 which in its entirety is specifically incorporated herein by reference. The structure of beta zeolite is also reported in J. Haggin, "Structure of Zeolite Beta Determined," in Chemical & Engineering News, p. 23 (June 20, 1988). Beta zeolite is also commercially available from PQ Corporation. The aforesaid ultrastable Y-type zeolite which can be employed in the catalyst for the isomerization method of this invention is in the hydrogen form and contains from 0.01, preferably from l, up to 5, preferably up to 3, weight percent of sodium, calculated as elemental sodium and based on the weight of the zeolite. Preferably the isomerization catalyst comprises a hydrogenation component comprising a Group VIII metal, which more preferably is palladium, platinum or nickel. The aforesaid zeolite of the isomerization catalyst can be employed either unsupported or supported on a porous refractory, inorganic oxide that is inert under the conditions employed, such as silica, alumina, silica-alumina, magnesia, bentonite or other such clays. If a support is employed, preferably the support comprises silica, alumina or silica-alumina. When a support is employed, the zeolite comprises from 10, preferably from 20 to 90, preferably to 80 weight percent based on the weight of the catalyst. If the isomerization is performed on a batch basis, the catalyst is employed at a level in the range of from 0.1, preferably from 1.0, to 5, preferably to 3 weight percent of the zeolite component of the catalyst, based on the weight of the dimethylnaphthalene feedstock, and the reaction time is from 0.5 preferably from 2, to 10, preferably to 6 hours. If the isomerization is performed on a continuous basis, the space velocity is in the range of from 0.1, preferably from 0.5 to 10, preferably to 5 parts of dimethylnaphthalene feedstock per part of zeolite component of the catalyst by weight per hour. The present invention will be more clearly understood from the following specific examples. EXAMPLES 1-29 These Examples relate to cyclization and dehydrogenation and appear in the parent application no. 89306236.4, published as EP-A-0351074. These Examples and Tables I, II and III have been deleted from the specification. EXAMPLES 30-47 In these Examples, no.s 30-36 are comparative Examples and no.s 37-47 illustrate the invention. In each of Examples 30-47, the particular isomer of dimethylnaphthalene employed as the feed was mixed in liquid form with unsupported catalyst in a stirred reaction vessel with a continuous nitrogen purge to preclude oxygen from the system. The temperature of the reaction vessel was raised to the reaction temperature and samples were withdrawn at various times after commencement of the reaction and analyzed. The conditions employed, the compositions of the feedstock employed and of the resulting products containing up to 13 carbon atoms, the percent conversion of the feedstock, and the percent selectivity of the formation of desired product from the total amount of feedstock converted in each of Examples 30-47 are presented in Table 4. The catalyst employed in Example 30 was a crystalline borosilicate molecular sieve (HAMS-1B from Amoco Chemical). The catalyst employed in Example 31 was Union Carbide's LZ-Y20 ultra-stable Y-type sieve, containing 2 weight percent of copper, calculated as elemental copper. The catalyst employed in Example 32 was Union Carbide's LZ-Y62, a non-ultra-stable, Y-type sieve in the ammonia-exchanged form and having a unit cell size of 24.73A. The catalyst employed in Examples 33 and 34 was commercially available Union Carbide's LZ-Y82, an ultra-stable molecular sieve having a unit cell size of 24.56A and a sodium content of less than 0.2 weight percent. In Example 33, the sieve was in the ammonia form and had not been calcined. In Example 34, the sieve had been calcined to form the hydrogen form. The catalyst employed in Example 35 was a commercially available amorphous silica-alumina containing 13 weight percent of alumina. The catalyst employed in Example 36 was commercially available mordenite in the acid form. The catalyst employed in Examples 37, 38, 40-45 was commercially available Union Carbide's LZ-Y72 in the hydrogen form as received from the manufacturer. The catalyst employed in Example 39 was commercially available Grace USY sieve containing 2.6 weight percent of sodium and has chemical and physical properties that are very similar to those of Union Carbide's LZ-Y72, and is also suitable for use as a catalyst in either the cyclization or isomerization step in the method of this invention. 1,5-dimethylnaphthalene was the feed in Examples 30-44. The feed was 1,7-dimethylnaphthalene in Example 45 and 1,4 dimethylnaphthalene in Examples 46 and 47. For the purposes of Table 4, the concentration of 2,7-DMN in the product is taken to be approximately equal to the concentration of 1,7-DMN and is subtracted from the sum of 2,6-DMN and 2,7-DMN (which are determined together) for the purpose of determining the concentration of 2,6-DMN alone. The effective maximum concentrations of a particular desired DMN in its triad is its equilibrium concentration in the triad, which generally is 40-45 weight percent. EXAMPLE 48 7.5 kilograms of distilled water, 7.5 kilograms of an aqueous solution containing 40 weight percent of tetraethylamine hydroxide, 50 grams of sodium hydroxide and 300 grams of sodium aluminate were stirred and dissolved in a 5-gallon stainless steel tank. The resulting solution and 12.2 kilograms of a silica sol containing 40 weight percent of silica were mixed and stirred in a 10-gallon autoclave at 150°C for 72 hours. The resulting mixture was filtered, and the separated solids were washed three times with distilled water, dried at 120°C and then calcined at 538°C for 4 hours. The resulting dried powder contained 0.37 weight percent of sodium, calculated as elemental sodium, and x-ray diffraction analysis indicated that the powder had the x-ray diffraction pattern of beta zeolite. The following is the x-ray diffraction pattern of the powder product, showing only the lines that are common to all 4 sources of beta zeolite in U.S. Patent No. 3,308,069. Line d(A) Relative Intensity 4.18 16.2 3.99 100.0 3.54 6.1 3.35 12.6 3.11 3.0 3.05 14.6 2.94 5.3 2.69 4.1 2.54 1.5 2.08 11.5 The powder was employed as the catalyst without being ion-exchanged. Some powder was ion-exchanged using the procedure of Example 50 to reduce the sodium content, and after being ion-exchanged, the powder's alumina content, silica-to-alumina mole ratio and silicon-to-aluminum atom ratio were measured as 1.14 weight percent, 68:1 and 34:1, respectively. EXAMPLE 49 8 kilograms of distilled water, 8 kilograms of an aqueous solution containing 40 weight percent of tetraethylamine hydroxide, 3.81 kilograms of an aqueous solution containing 20 weight percent of tetraethylamine hydroxide, 0.6 kilogram of sodium aluminate, and 12.2 kilograms of a silica gel containing 40 weight percent of silica were mixed and stirred in a 10-gallon autoclave at 150°C for 72 hours. The resulting mixture was filtered, and the separated solids were washed three times with distilled water, dried at 120°C for about 16 hours and then calcined at 38°C for 6 hours. The resulting dried powder contained 0.17 weight percent of sodium, calculated as elemental sodium. X-ray diffraction analysis indicated that the powder had the x-ray diffraction pattern of beta zeolite. The following is the x-ray diffraction pattern of the powder product, showing only the lines that are common to all 4 sources of beta zeolite in U.S. Patent No. 3,308,069. Line d(A) Relative Intensity 4.19 17.7 4.01 100.0 3.54 Weak 3.35 13.8 3.11 Weak 3.05 13.4 2.95 2.8 2.67 Weak 2.49 0.6 2.09 7.6 The powder was employed as the catalyst without being ion-exchanged. After being ion-exchanged using the procedure of Example 50 in order to reduce the sodium content, the powder's silica-to-alumina mole ratio and silicon-to-aluminum atom ratio were measured as 30:1 and 14.8:1, respectively. EXAMPLE 50 2.3 kilograms of the un-ion-exchanged catalyst powder produced in Example 49, 4 kilograms of distilled water, and 12 kilograms of an aqueous solution containing 19 weight percent of ammonium nitrate were stirred in a 22-litre flask at 72°C for 4 hours. The mixture was then cooled; the liquid was removed by decantation, and the resulting ion-exchanged catalyst was then washed with water. The catalyst was then dried at 120°C and calcined at 538°C for 3 hours. The ion-exchanged catalyst contained 0.01 weight percent of sodium (calculated as elemental sodium), 2.43 weight percent of aluminum (calculated as elemental aluminum), and a silica-to-alumina mole ratio and a silicon-to-aluminum atomic ratio of 30:1 and 14.8:1, respectively. 163 grams of this dry, ion-exchanged beta zeolite powder, 454 grams of an alumina sol containing 8.8 weight percent of solids, and 123 grams of distilled water were blended to obtain a smooth, uniform slurry. The slurry as maintained at 23°C for 5 hours to permit liquid to evaporate from the slurry. The slurry was then dried at 20°C for about 16 hours and calcined at 538°C for 2 hours, to afford solids containing 80 weight percent of beta zeolite and 20 weight percent of alumina, which were then ground and sieved to form particles having a 20-40 mesh size. EXAMPLES 51-69 In each of Examples 51-69, the particular feedstock employed was mixed in liquid form with unsupported catalyst in a stirred reaction vessel with a continuous nitrogen purge to preclude oxygen from the system. The weight ratio of the feedstock-to-zeolite component of the catalyst was 49:1 in each case. The pressure of the contents of the reaction vessel was maintained at about 1 pound per square inch gauge. The temperature of the reaction vessel was raised to the reaction temperature and samples were withdrawn at various times after commencement of the reaction and analyzed. The conditions employed, the compositions of the feedstock employed and of the resulting products, the percent of the 1,5-, 1,6- and 2,6-DMN triad in each thereof, the percent of 2,6-DMN in each such 1,5-, 1,6- and 2,6-DMN triad, the percent decreases in each 1,5-, 1,6- and 2,6-DMN triad, the percent gains in each 1,7-, 1,8- and 2,7-DMN triad and the percent gain in total methylnaphthalene and trimethylnaphthalene content in each of Examples 51-69 are presented in Tables 5-9. The catalyst employed in examples 51-53 was commercially available Union Carbide's unsupported LZ-Y72 in the hydrogen form as received from the manufacturer. The catalyst employed in Examples 54-57 was an unsupported beta zeolite having a relatively high silicon-to-aluminum ratio and prepared by the procedure of Example 48. The catalyst employed in Examples 58-66 was an unsupported beta zeolite having a relatively low silicon-to-aluminum ratio and prepared by the procedure of Example 49. A single sample of his catalyst was used for four cycles in Examples 61-66. The catalyst employed in Examples 67-70 was also the beta zeolite having the relatively low silicon-to-aluminum ratio and prepared by the procedure of Example 49, but in this instance ion-exchanged to reduce the sodium content and supported on an alumina matrix by the procedure of example 50. Comparison of the results in Tables 5-9 illustrates clearly that (1) the use of a beta zeolite catalyst affords reduced losses of the 1,5-, 1,6- and 2,6-dimethylnaphthalene triad, reduced formation of methylnaphthalenes, trimethylnaphthalenes and the 1,7-, 1,8- and 2,7-dimethylnaphthalene triad relative to the use of the LZ-Y72 zeolite catalyst; and (2) the use of a beta zeolite catalyst either unsupported or supported on a base material and having a relatively lower silicon-to-aluminum ratio affords greater formation of 2,6-dimethylnaphthalene and reduced losses of the 1,5-, 1,6- and 2,6-dimethylnaphthalene triad relative to the use of a beta zeolite catalyst having a relatively higher silicon- to-aluminum ratio and permits the use of lower reaction temperatures or the use at a higher temperature of even a partially deactivated catalyst relative to the use of a LZ-Y72 zeolite catalyst. Conditions Feed Ex. 51 Ex. 52 Ex. 53 Catalyst LZ-Y72 LZ-Y72 LZ-Y72 Temperature (°C) 250 250 250 Hours on Stream 1 3 4.75 Product Composition (wt.%) 1,5-DMN 91.03 38.70 18.30 12.84 1,6-DMN 3.73 36.92 40.67 40.35 2,6-DMN 0 18.42 32.40 36.18 1,7-DMN 0.74 0.81 0.93 1.08 2,7-DMN 0 0.73 1.37 1.81 Methylnaphthalenes 0.06 0.62 1.43 2.03 Trimethylnaphthalenes 0.44 0.53 1.33 2.02 Other 4.00 3.27 3.57 3.69 Total 100.00 100.00 100.00 100.00 1,5-, 1,6- and 2,6-DMN triad content 94.76 94.04 91.37 89.37 2,6-DMN percent in 1,5-, 1,6- and 2,6-DMN triad 0 19.59 35.46 40.49 1,5-, 1,6- and 2,6-DMN triad percent loss 0 0.72 3.39 5.39 1,7-, 1,8- and 2,7-DMN triad percent gain 0 0.80 1.56 2.15 Methylnaphthalene and trimethylnaphthalene percent gain 0 0.71 2.32 3.61 Conditions Feed Ex. 54 Ex. 55 Ex. 56 Ex. 57 Catalyst from Example 48 48 48 48 Temperature (°C) 250 250 250 250 Hours on Stream 1 3 5 7 Product Composition (wt.%) 1,5-DMN 91.03 54.00 28.93 18.94 14.09 1,6-DMN 3.73 28.76 37.62 39.70 40.41 2,6-DMN 0 0 12.91 28.63 35.96 1,7-DMN 0.74 0.61 0.58 0.60 0.67 2,7-DMN 0 0.67 1.09 1.13 1.28 Methylnaphthalenes 0 0.12 0.29 0.41 0.57 Trimethylnaphthalenes 0.44 0.10 0.19 0.34 0.46 Other 4.06 2.83 2.67 2.92 2.97 Total 100.00 100.00 100.00 100.00 100.00 1,5-, 1,6- and 2,6-DMN triad content 94.76 95.67 95.18 94.60 94.05 2,6-DMN percent in 1,5-, 1,6- and 2,6-DMN triad 0 13.49 30.08 38.01 42.05 1,5-, 1,6- and 2,6-DMN triad percent loss 0 -0.91 -0.42 0.16 0.71 1,7-, 1,8- and 2,7-DMN triad percent gain 0 0.54 0.93 0.99 1.21 Methylnaphthalene and trimethylnaphthalene percent gain 0 -0.23 0.04 0.31 0.59 Conditions Feed Ex. 58 Ex. 59 Ex. 60 Catalyst from Example 49 49 49 Temperature (°C) 250 250 250 Hours on Stream 1.25 3 5 Product Composition (wt.%) 1,5-DMN 91.03 21.94 10.79 8.20 1,6-DMN 3.73 38.62 40.89 41.20 2,6-DMN 0 35.59 43.28 44.94 1,7-DMN 0.74 0.52 0.60 0.64 2,7-DMN 0 0.30 0.53 0.47 Methylnaphthalenes 0 0.33 0.59 0.84 Trimethylnaphthalenes 0.44 0.16 0.46 0.78 Other 4.06 2.54 2.86 2.93 Total 100.00 100.00 100.00 100.00 1,5-, 1,6- and 2,6-DMN triad content 94.76 96.15 94.96 94.34 2,6-DMN percent in 1,5-, 1,6- and 2,6-DMN triad 0 37.02 45.58 47.63 1,5-, 1,6- and 2,6-DMN triad percent loss 0 -1.39 -0.20 0.42 1,7-, 1,8- and 2,7-DMN triad percent gain 0 0.08 0.39 0.37 Methylnaphthalene and trimethylnaphthalene percent gain 0 0.05 0.61 1.18 Conditions Feed Ex. 67 Ex. 68 Ex. 69 Catalyst from Example 50 50 50 Temperature (°C) 250 250 250 Hours on Stream 1 2 3 Product Composition (wt.%) 1,5-DMN 88.14 16.50 11.20 9.23 1,6-DMN 3.66 38.10 39.30 39.70 2,6-DMN 0 37.42 41.07 42.15 1,7-DMN 0.74 0.53 0.55 0.58 2,7-DMN 0 0.97 0.84 1.00 Methylnaphthalenes 0.13 0.52 0.69 0.83 Trimethylnaphthalenes 0.54 0.32 0.62 0.75 Other 6.79 5.64 5.73 5.76 Total 100.00 100.00 100.00 100.00 1,5-, 1,6- and 2,6-DMN triad content 91.80 92.02 91.57 91.08 2,6-DMN percent in 1,5-, 1,6- and 2,6-DMN triad 0 40.67 44.85 46.28 1,5-, 1,6- and 2,6-DMN triad percent, loss 0 -0.22 0.23 0.72 1,7-, 1,8- and 2,7-DMN triad percent gain 0 0.76 0.65 0.84 Methylnaphthalene and trimethylnaphthalene percent gain 0 0.17 0.64 0.91

Claims: A method for isomerizing at least 20 weight percent of the total of at least one dimethylnaphthalene isomer to form at least one desired other dimethylnaphthalene isomer in the same triad of dimethylnaphthalene isomers to which the isomer being isomerized belongs comprising: contacting each aforesaid dimethylnaphthalene isomer to be isomerized in liquid form with a solid isomerization catalyst comprising either beta zeolite or an acidic ultrastable Y-type crystalline zeolite having a silica-to-alumina molar ratio of from 4:1 to 10:1, and having pore windows provided by twelve-membered rings containing oxygen and a unit cell size of from 24.2 to 24.7 angstroms and at an elevated temperature and at a pressure that is sufficiently high to maintain the isomerization feedstock substantially in the liquid phase. A method according to Claim 1 wherein the dimethylnaphthalene isomers being isomerized comprise (a) 1,5- and 1,6-dimethylnaphthalene, (b) 1,5-, 1,6-, 1,7- and 1,8-dimethylnaphthalenes, (c) 1,7- and 1,8-dimethylnaphthalenes or (d) 1,3- and 1,4-dimethylnaphthalenes. A method according to Claims 1 or 2 wherein the isomerization catalyst employed comprises beta zeolite. A method according to any of Claims 1-3 wherein the isomerization catalyst comprises a hydrogenation component comprising a Group VIII metal. A method according to any of Claims 1-4 wherein the isomerization catalyst employed is free of a support material. A method according to any of Claims 1-4 wherein the isomerization catalyst is supported on an inorganic support material. A method according to any of Claims 1-6 wherein the isomerization is performed at a temperature of from 200°C to 300°C.

Inventors: LAMB JOYCE DALE, SIKKENGA DAVID LEE, WILLIAMS GREGORY SCOTT, ZAENGER IAN CLAYTON, LAMB, JOYCE DALE, SIKKENGA, DAVID LEE, WILLIAMS, GREGORY SCOTT, ZAENGER, IAN CLAYTON
Applicants: AMOCO CORP, AMOCO CORPORATION
Application year: 1989
Main classification: C07C15
IPC codes: C07C5