A process for the dealumination of zeolite beta

Abstract: A process for the dealumination of a zeolite having the structure of zeolite Beta by contacting the zeolite with a dicarboxylic acid, such as oxalic acid.

Description: This application is directed to a process for the dealumination of zeolite Beta by contacting with dicarboxylic acid. Zeolitic materials, both natural and synthetic, have been demonstrated to have catalytic properties for various types of hydrocarbon conversion. It is often advantageous to dealuminate these materials in order to improve their process performance. Performance measures which are typically improved include product selectivity, product quality and catalyst stability. Conventional techniques for zeolite dealumination include hydrothermal treatment, mineral acid treatment with HCl, HNO 3 , and H 2 SO 4 , and chemical treatment with SiCl 4 or ethylenediaminetetraacetic acid (EDTA). The treatments are limited, in many cases, in the extent of dealumination by the onset of crystal degradation and loss of sorption capacity. U.S. Patent 4,419,220 to LaPierre et al discloses that dealumination of zeolite Beta via treatment with HCl solutions is limited to SiO 2 /Al 2 O 3 ratios of 200 to 300 beyond which significant losses to zeolite crystallinity are observed. U.S. Patent 3,442,795 to Kerr et al. describes a process for preparing highly siliceous zeolite-type materials from crystalline aluminosilicates by means of a solvolysis, e.g. hydrolysis, followed by a chelation. In this process, the acid form of a zeolite is subjected to hydrolysis, to remove aluminum from the aluminosilicate. The aluminum can then be physically separated from the aluminosilicate by the use of complexing or chelating agents such as EDTA or carboxylic acid, to form aluminum complexes that are readily removable from the aluminosilicate. The examples are directed to the use of EDTA to remove alumina. EP 0 259 526 B1 discloses the use of dealumination in producing ECR-17. The preferred dealumination method involves a combination of steam treatment and acid leaching, or chemical treatments with silicon halides. The acid used is preferably a mineral acid, such as HCl, HNO 3 or H 2 SO 4 , but may also be weaker acids such as formic, acetic, citric, oxalic, tartaric acids and the like. Dealumination of zeolite Beta is not disclosed. The present invention provides a process for the dealumination of a zeolite having the structure of zeolite Beta by contacting the zeolite with dicarboxylic acid. The treatment with dicarboxylic acid is believed to remove aluminum from the crystalline framework of the zeolite via a chelating mechanism. The invention provides a process for the dealumination of a zeolite having the structure of zeolite Beta, which comprises contacting the zeolite having the structure of zeolite Beta with dicarboxylic acid for a sufficient time to effect greater than about 50% dealumination, the contacting resulting in less than 10% loss in crystalline of the zeolite. The process of this invention is useful for the dealumination of a zeolite having the structure of zeolite Beta. Zeolite Beta is described in U.S. Patent Nos. 3,308,069 and Re 28,341. It is well known that the crystalline zeolites, including zeolite Beta, have a structure consisting of a porous, robust framework. The framework consists principally of silicon tetrahedrally coordinated and interconnected with oxygen bridges. Other framework components may include Group IIIB elements of the Periodic Table, e.g. aluminum, baron and gallium, and iron. EP A 0 095 304 discloses aluminium extraction of zeolite beta with inorganic or organic acids. It may be desirable to incorporate the zeolite with another material resistant to the temperature and other conditions employed in the process, prior to dealumination. Such matrix materials include synthetic or natural substances as well as inorganic materials such as clay, silica and/or metal oxides, such as titania or zirconia. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Naturally occurring clays which can be composited with the zeolite include those of the montmorillonite and kaolin families. These clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification. These materials, i.e. clays, oxides, etc., function, in part, as binders for the catalyst. Prior to or following dealumination the zeolite may be composited with a porous matrix material, such as alumina, silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania as well as ternary compositions, such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia, and silica-magnesia-zirconia. The matrix may be in the form of a cogel. The relative proportions of zeolite component and inorganic oxide gel matrix may vary widely with the zeolite content ranging from between 1 to 99, more usually 5 to 80, percent by weight of the composite. Suitable dicarboxylic acids for use in the process of this invention include oxalic, malonic, succinic, glutaric, adipic, maleic, phthalic, isophthalic, terephthalic, fumaric or mixtures thereof. Oxalic acid is preferred. The dicarboxylic acid may be used in solution, such as an aqueous dicarboxylic acid solution. Generally, the acid solution has a concentration in the range from 0.01 to 4 M. Preferably, the acid solution concentration is in the range from 1 to 3 M. The dicarboxylic acid is generally in a volume solution to volume catalyst ratio of at least 1:1, preferably at least 4:1. Treatment time with the dicarboxylic acid solution is as long as required to provide the desired dealumination. Generally the treatment time is at least 10 minutes. Preferably, the treatment time is at least 1 hour. More than one dicarboxylic acid treatment step may be employed in the process of the present invention for enhanced dealumination. The treatment temperature is generally in the range from 0°C (32°F) to reflux. Preferably, the treatment temperature is from 15°C to 93°C (60°F to 200°F), and more preferably from 48°C to 82°C (120°F to 180°F). The dicarboxylic acid treatment of this invention results in greater than 50% dealumination, preferably greater than 75% dealumination and more preferably greater than about 85% dealumination, with no significant loss in crystallinity (that is less than 10%). Crystallinity, as described herein, is a measure of the difference in cyclohexane sorption between the untreated material and the material treated with dicarboxylic acid. The dealuminated products obtained have a broad silica to alumina ratio. Generally, the silica to alumina ratio is in the range of from 100:1 to 800:1, preferably from 400:1 to 800:1, and more preferably from 600:1 to 800:1. Ammonium exchange, a conventional sodium removal method, is not required in the process of this invention. The dicarboxylic acid treatment removes sodium along with the aluminum. The dicarboxylic acid treatment of this invention may also be combined with other conventional dealumination techniques, such as steaming and chemical treatment. The following examples illustrate the process of the present invention. Example 1 Zeolite Beta, prepared in accordance with U.S. Patent Nos. 3,308,069 and Re 28,341, is exchanged with a solution of NH 4 NO 3 to remove sodium and dried at 121°C (250°F) for 8 hours. Organics are removed by first treating in N 2 at 510°C (950°F) for 3 hours followed by air calcination at 537°C (1000°F) for 6 hours. The calcined zeolite referred to henceforth as material A has the following properties: Sodium, ppmw 510 Cyclohexane Sorption, wt% 21 Al 2 O 3 , wt% 4.6 Example 2 A sample of material A as set forth in Example 1 is treated with a 2 M solution of oxalic acid at a volume ratio of solution to catalyst of 8 to 1. Treatment is conducted at 65°C (150°F) for 1 hour. The treated catalyst is dried at 121°C (250°F) overnight. The dried material is air calcined at 537°C (1000°F) for 3 hours. The treatment results in 91% dealumination with no significant loss in cyclohexane sorption capacity. The treated material has the following properties: Sodium, ppmw 41 Cyclohexane Sorption, wt% 20 Al 2 O 3 , wt% 0.40 Example 3 A sample of material A as set forth in Example 1 is treated with a 2 M solution of oxalic acid at a volume ratio of solution to catalyst of 8 to 1. Treatment is conducted at 71°C (160°F) for 3 hours. The treated catalyst is dried at 121°C (250°F) overnight. The dried material is air calcined at 537°C (1000°F) for 3 hours. The treatment results in 94% dealumination with essentially no loss in cyclohexane sorption capacity. The treated material has the following properties: Sodium, ppmw 21 Cyclohexane Sorption, wt% 21 Al 2 O 3 , wt% 0.26 Example 4 Zeolite Beta, prepared in accordance with U.S. Patent Nos. 3,308,069 and Re 28,341, is mull/mixed with SiO 2 at a composition of 65 wt% zeolite and 35 wt% SiO 2 on an ash basis. The material is extruded into pellets. Organics are removed by first treating in N 2 at 510°C (950°F) for 3 hours followed by air calcination at 537°C (1000°F) for 8 hours. The calcined extrudate referred to henceforth as material B has the following properties: Sodium, ppmw 15000 Cyclohexane Sorption, wt% 12 Al 2 O 3 , wt% 3.0 Example 5 A sample of material B as set forth in Example 4 is treated with a 2 M solution of oxalic acid at a volume ratio of solution to catalyst of 8 to 1. Treatment is conducted at 71°C (160°F) for 2 hours. The treated catalyst is dried at 121°C (250°F) overnight. The dried material is air calcined at 537°C (1000°F) for 3 hours. The treatment results in 87% dealumination with no significant loss in cyclohexane sorption capacity. The treated material has the following properties: Sodium, ppmw 795 Cyclohexane Sorption, wt% 11 Al 2 O 3 , wt% 0.40 Example 6 A sample of material B as set forth in Example 4 is treated with a 2 M solution of oxalic acid at a solution to catalyst ratio of 16 to 1. Treatment is conducted at 71°C (160°F) for 3 hours. The treated catalyst is dried at 121°C (250°F) overnight. The dried material is air calcined at 537°C (1000°F) for 3 hours. The treatment results in 88% dealumination with no significant loss in cyclohexane sorption capacity. The treated material has the following properties: Sodium, ppmw 525 Cyclohexane Sorption, wt% 11 Al 2 O 3 , wt% 0.37 Example 7 A sample of material B as set forth in Example 4 is treated with a 3 M solution of oxalic acid at a volume ratio of solution to acid of 8 to 1. Treatment is conducted at 71°C (160°F) for 3 hours. The material is washed with water and exposed to a second treatment with a fresh 3 M oxalic acid solution at the same conditions. The treated catalyst is dried at 121°C (250°F) overnight. The dried material is air calcined at 537°C (1000°F) for 3 hours. The treatment results in 93% dealumination with essentially no loss in cyclohexane sorption capacity. The treated material has the following properties: Sodium, ppmw 93 Cyclohexane Sorption, wt% 12 Al 2 O 3 , wt% 0.22 Example 8 Zeolite Beta, prepared in accordance with U.S. Patents 3,308,069 and Re 28,341, incorporated herein by reference, is treated by contacting 126 parts by weight oxalic acid and 63 parts by weight zeolite in 1000 parts by weight water at 71°C (160°F) for 1 hour. The treated zeolite is dried at 121°C (250°F) and then is air calcined at 537°C (1000°F) for 3 hours. The treatment results in 88% dealumination. There is no significant loss in cyclohexane sorption capacity. Example 9 This is a comparative example which demonstrates increased % dealumination with oxalic acid over EDTA. Zeolite Beta, prepared in accordance with U.S Patents 3,308,069 and Re 28,341, incorporated herein by reference, is treated by contacting 10 parts by weight of EDTA and 10 parts by weight zeolite in 300 parts by weight water at 71°C (160°F) for 1 hour. The treated zeolite is washed twice with 10 cc water/cc zeolite, dried at 121°C (250°F) and then is air calcined at 537°C (1000°F) for 3 hours. The treatment results in only 15% dealumination. There is no significant loss in cyclohexane sorption capacity. Treatment with oxalic acid as shown in Example 8 produces a much higher % dealumination. Example 10 Zeolite Beta, prepared in accordance with U.S. Patent Nos. 3,308,069 and Re 28,341, having an SiO 2 /Al 2 O 3 ratio of 36:1, is ammonium exchanged twice at room temperature, with 1M NH 4 NO 3 , dried at 121°C (250°F) overnight, mixed with SiO 2 at a composition of 65 wt.% zeolite and 35 wt.% SiO 2 and extruded. The extrudate catalyst is calcined by heating in N 2 at 482°C (900°F) for 3 hours, then in air at 537°C (1000°F) for 3 hours. The Al 2 O 3 content of the bound catalyst is 3.0 wt.%. The catalyst is treated with 8 ml oxalic acid/ml catalyst of 2.0 M oxalic acid at 71°C (160°F) for 1 hour. The catalyst is water washed, dried at 121°C (250°F) overnight and calcined by heating in air at 537°C (1000°F) for 3 hours. The resultant catalyst has an Al 2 O 3 content of 0.28 wt.%. The treatment results in 91% dealumination. Example 11 This is a comparative example which demonstrates increased % dealumination with oxalic acid over HCl. The same zeolite Beta used in Example 10 (SiO 2 /Al 2 O 3 = 36:1) is ammonium exchanged twice at room temperature with 1 M NH 4 NO 3 , washed, dried at 121°C (250°F) overnight, mixed with SiO 2 and extruded to provide an analogous catalyst to Example 10 having a zeolite:SiO 2 weight ratio of 65:35. The extrudate catalyst is calcined by heating in N 2 at 482°C (900°F) for 3 hours, then in air for 3 hours. The Al 2 O 3 content of the bound catalyst is 3.0 wt.%. The catalyst is treated with 8 cc hydrochloric acid/cc catalyst of 2.0 M hydrochloric acid at 71°C (160°F). The catalyst is water washed, dried at 121°C (250°F) overnight and calcined by heating in air at 537°C (1000°F) for 3 hours. The resultant catalyst has an Al 2 O 3 content of 2.35 wt.%. The treatment results in only 22% dealumination. Treatment with oxalic acid as shown in Example 10 produces a much higher % dealumination.

Claims: A process for the dealumination of a zeolite having the structure of zeolite Beta, which comprises contacting the zeolite Beta with a dicarboxylic acid for a sufficient time to effect greater than about 50% dealumination, said contacting resulting in less than 10% loss in crystallinity of the zeolite. The process of claim 1 wherein the dealuminated zeolite Beta has a silica to alumina ratio of greater than 400 to 1. The process of claim 1 or claim 2 wherein the dicarboxylic acid is in solution. The process of claim 3 wherein the solution of dicarboxylic acid is at a volume ratio of solution to catalyst of at least 1:1. The process of any preceding claim wherein the dicarboxylic acid is an aqueous dicarboxylic acid solution. The process of any preceding claim wherein the dicarboxylic acid is in a concentration in the range of from 0.01 to 4 M. The process of any preceding claim wherein the dicarboxylic acid is selected from oxalic, malonic, succinic, glutaric, adipic, maleic, phthalic, isophthalic, terephthalic, fumaric and mixtures thereof. The process of any preceding claim wherein the contacting is for a time of at least about 10 minutes. The process of any preceding claim wherein the contacting is at a temperature in the range of from 16°C to 93°C. The process of any preceding claim wherein zeolite Beta is incorporated with a binder prior to the dealumination. The process of claim 10 wherein the binder is silica.

Inventors: APELIAN MINAS ROBERT, DEGNAN THOMAS FRANCIS JR, FUNG SHIU LUN ANTHONY, KENNEDY GORDON JOHN, APELIAN, MINAS ROBERT, DEGNAN, THOMAS FRANCIS, JR., FUNG, SHIU LUN ANTHONY, KENNEDY, GORDON JOHN
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1992
Main classification: B01J20
IPC codes: B01J29, B01J20, C01B39