CATALYTIC CONVERSION OF METHANOL INTO LIGHT OLEFINS

Abstract: A methanol-containing feed is converted over a ZSM-12 zeolite-containing catalyst containing magnesium and/or manganese into an olefin-containing hydrocarbon product rich in C₂ to C₄ olefins and especially rich in propylene.

Description: CATALYTIC CONVERSION OF METHANOL INTO LIGHT OLEFINS This invention relates to a process for converting methanol into light olefins over a modified ZSM-12 zeolite. A remarkable growth in the production of synthetic fibers, plastics and rubber has taken place in recent decades. Such growth, has, to a large extent, been supported and encouraged by an expanding supply of inexpensive petroleum-derived raw materials such as ethylene and propylene. However, increasing demand for tnese light olefins has, from time to time, led to periods of snortage, either due to a diminisned supply of suitable feedstocks or to limited processing capacity. In any event, it is now considered highly desirable to provide efficient means for converting raw materials other than petroleum into light olefins. One such non-petroleum source of light olefins is coal-derived methanol. In tnis respect, it is known that methanol can be catalytically converted into olefin-containing nydrocarbon mixtures by contact under certain conditions with particular types of crystalline zeolites. U.S. Patents 4,025,575 and 4,083,889, for example, botn describe processes whereby methanol and/or dimethyl ether can be converted into an olefin-containing product over a ZSM-5 type (Constraint Index 1-12) zeolite catalyst. ZSM-5, in fact, converts methanol and/or methyl ether into hydrocarbons containing a relatively hign concentration of light (C2 and C3) olefins. Modification of zeolite methanol-conversion catalysts with, for example, silica, phosphorus, metal ions and metal oxides, can ennance selectivity of the methanol-conversion reaction for production of light olefins. For example, U.S. Patents 4,247,731 and 4,296,266 describe modification of zeolites such as Zeolite X with manganese and optionally with additional materials such as magnesium in order to enhance the ethylene selectively of such zeolites when tney are used to catalyze methanol/dimethyl ether conversion. It is also known that the production of light olefins, especially ethylene, by catalytic conversion of methanol can be optimized by varying one or more reaction parameters. Variations in reaction temperature, pressure and reactant space velocity can, for example, alter the selectivity of tne methanol conversion reaction to produce different kinds of hydrocarbon products, for example to maximize light olefin production. Similarly, utilization of dilute methanol feeds or inert diluents tends to increase selectivity towards ethylene and light olefin production. Notwithstanding tne existence of processes suitable for converting methanol into high yields of light olefins, 'there is a cqntinuing need to develop additional catalytic procedures suitable for converting an organic charge comprising methanol into light olefin products with improved light olefin selectivity and especially with improved selectivity to propylene, which, like ethylene, is a valuaole material. The present invention.seeks to provide a process for converting a methanol feed into olefin-containing products with high selectivity to propylene. According to the invention, there is provided a process for converting a methanol-containing feed into an olefin-containing hydrocarbon product rich in propylene, which comprises contacting the methanol-containing feed under conversion conditions with a ZSM-12 zeolite-containing catalyst characterized in that the catalyst contains a minor amount of magnesium and/or manganese. In accordance with the invention, a methanol-containing feed is catalytically converted into an olefin-containing nydrocarbon product The methanol-containing feed will, of course, contain methanol but may also contain dimethyl ether and/or additional components such as water or other diluents. Since methanol is miscible with water, tne methanol may contain relatively large amounts of water. The methanol-containing feed should, however, contain at least 60 wt. % methanol. Substantially pure methanol, such as industrial grade anhydrous methanol, is eminently suitaole, althougn crude methanol, which usually contains from 12 to 20 wt. S water, or more dilute solutions, also may be used. Small amounts of impurities sucn as higher alcohols, aldehydes, or other oxygenated compounds in the methanol-containing feed have little effect on the process of the invention. The methanol-containing feed may include dimethyl etner. In fact, the feed to the process may be up to 100E dimethyl ether but it is preferred that dimethyl ether constitutes not more than 20 wt. % of the total feed. Such amounts of dimethyl ether as may be formed in tne process may, however, be recovered and recycled with fresn methanol feed, and tne dimethyl ether content calculated on the total of recycle and fresh feed preferably will not exceed 20 wt. S. According to one aspect of the invention, the feed to the process comprises only the methanol and associated organic oxygenates. According to another, preferreo, aspect, the selectivity of methanol conversion for the production of light (C2-C3) olefins is increased by contacting the metnanol feed with the catalyst descrioed in detail below, in the presence of up to 20 mols, and preferaoly from 1 to 10 mols, of steam per mol of methanol feed. The steam may be provided directly by injecting the required amount of water or steam into the reaction zone; alternatively, steam may be provided totally or in part by water present in the methanol-containing feed in a molar ratio of water to methanol of up to 20:1, preferably from 1:1 to 10:1. That water in the feed forms steam in tne reaction zone under the process conditions. According to the invention, the methanol-containing feed is catalytically converted into a light olefin-containing hydrocarbon product rich in propylene by contact with a modified catalyst comprising zeolite ZSM-12. ZSM-12 is described in detail in U.S. Patent 3,832,449 and is characterized by its X-ray diffraction pattern as set out in that U.S. Patent. The ZSM-12 zeolite used in the process of the invention preferably has a crystal size from 0.02 to 0.5 micron. The ZSM-12 zeolite-containing catalyst used in the process of the invention is preferably characterized by an activity, in terms of alpha value, from 25 to 250, and preferably from 50 to 150. The alpha value reflects the relative activity of the catalyst with respect to a high activity silica-alumina cracking catalyst. The method of determining alpha values is described in Journal of Catalysis, Vol. VI, Pages 278-287, 1966. In the process of the invention, the ZSM-12 zeolite is preferably incorporated in a matrix comprising a material resistant to the temperature and other conditions employed in the process. Such matrix materials are useful as binders and impart greater resistance to the catalyst for the temperature, pressure and reactant feed stream velocity cqnditions which may be encountered in the process. Useful matrix materials include both synthetic and naturally occurring substances, as well as inorganic materials such as clay, silica and/or metal oxides, and are well known in the art. The relative proportions of zeolite component and matrix material, on an anhydrous basis, may be from 1 to 99 percent Dy weight and more usually from 5 to 80 percent by weight of zeolite, based on the dry composite. The present invention is based on the observation that modification of ZSM-12 zeolite catalysts with magnesium and/or manganese can enhance the selectivity of such catalysts even further to the production of C2-C4 light olefins, and especially to the production of propylene, during conversion of methanol and/or methyl either into hydrocarbons. The ZSM-12 zeolite-containing catalysts are modified by incorporation of a minor proportion of magnesium and a minor proportion of manganese. The modified zeolite composites can be prepared by contacting the ZSM-12 zeolite-containing composition with one or more compounds or complexes of magnesium and/or manganese and then preferably heating the composite to convert the modifying element(s) into oxide form. Incorporation can occur by the mechanisms of ion exchange or "stuffing" i.e. adsorption and/or impregnation. It should be emphasized that, while ion exchange can be used to incorporate the modifying metals into the zeolite, ion exchange alone will generally not provide the necessary amount or form preferred (i.e. the oxide form) of incorporated magnesium and manganese onto the zeolite catalyst. Generally, the zeolite composite can be modified by contacting the composite with solutions of appropriate compounds of magnesium and/or manganese. Such solutions may be formulated from any suitable solvent which is inert to the metal-containing compound and the zeolite, including for example water, aromatic and aliphatic hydrocarbons, alcohols, and organic acids (such as acetic acid, formic acid and propionic acid) halogenated hydrocarbons, ketones and ethers. Generally, the most useful solvent will be water. Suitable magnesium-containing compounds include the acetate, nitrate, benzoate, propionate, 2-ethylhexanoate, carbonate, formate, oxalate, amide, bromide, hydride, lactate, laurate, oleate, palmitate, salicylate, stearate and sulfide. Suitable manganese-containing compounds include the acetate, nitrate, lactate, oxalate, carbonate, citrate, tartrate, bromide, chloride, sulfate and sulfide. The amount of modifying metal incorporated onto the zeolite composition will, of course, depend upon several factors, for example reaction time, reaction temperature, concentration of the treating compound in tne reaction mixture, the degree to wnicn tne zeolite composition nas been dried prior to reaction with the metal-containing compounds, the conditions of drying of the zeolite composition after reaction with the treating compounds, and the amount and type of binder incorporated with the zeolite composition. After the modifying magnesium and manganese compounds have been incorporated into the zeolite composite to the extent desired, the metal-containing composite is heated in tne presence of oxygen, for example, in air. Although heating may be carried out at a temperature of about 1500C, higher temperatures, for example up to about 500 C, are preferred. Heating is generally carried out for 1-5 hours but may De extended to 24 hours or longer. While heating temperatures above aoout 500at may be employed, they are generally not necessary. After the metal-containing composite is heated in air at elevated temperatures, the modifying metals are actually present at least in part in the zeolite composite in an oxidized state, such as MgO and MnO. Generally, the modifying metal oxides are incorporated in amounts from 0.1% to 10% by weight of. the zeolite composite, preferably from 1% to 10% Dy weight of the zeolite composite, calculated on tne elemental metals. Magnesium oxide is advantageously incorporated in an amount from 0.1% to 10%, more preferably from 0.1S to 5S; by weight, calculated as magnesium. Manganese oxide is advantageously incorporated in an amount from 0.1% to 10%, more preferaoly from 1% to 10%, by weight, calculated as manganese. In accordance with the invention, a feed comprising methanol, dimethyl ether, methanol/dimethyl ether mixtures or mixtures of sucn organic materials with water is contacted in the vapor phase with the magnesium and/or manganese modified ZSM-12 catalyst materials under reaction conditions suitable for effecting conversion of methanol and/or dimethyl ether into olefins. Such conditions include an operating temperature from 2600C to 5400C, preferably 4000C to 4500C; a pressure from 10 kPa to 3000 kPa, 500 to 1000 kPa; and a weight hourly space velocity (WHSV) of the organic reactants from 0.1 to ;JO, preferably 1 to 10. Carrier gases or diluents may be injected into the reaction zone, for example hydrogen, nitrogen, helium, water, carbon monoxide, carbon dioxide, or mixtures of these gases. When water is employed along with the organic feed, the amount of water is generally at least 0.25 moles of water per mole of organic reactant. Preferably, the amount of water added is greater than 0.5 moles of water per mole of organic reactant. The amount of water initially added to the organic reactant will not usually exceed 40 moles per mole of organic reactant. water in these amounts can generally be passed to the reaction zone at a WHSV from 1 to 20, more preferably from 2 to M. The reaction conditions, including the presence or absence of diluents, can affect the selectivity of the process to light olefin and propylene production as well as percent conversion of organic reactants to hydrocarbon product. However, it has been discovered that for a given set of reaction conditions, the magnesium and/or manganese-modified ZSM-12 catalysts provide improved methanol conversion and/or propylene selectivity in comparison with similar processes employing other zeolites. The process may be carried out as a batch-type, semi-continuous or continuous operation utilizing a fixed, fluidized or moving bed catalyst system. A preferred process entails use of a catalyst zone in which tne alcohol or ether charge optionally together with added water is passed concurrently or countercurrently through a fluidized or moving Ded of particle-form catalyst. The latter, after use may be conducted to a regeneration zone where coke is burned from the catalyst in an oxygen-containing atmosphere, for example air, at an elevated temperature, after which the regenerated catalyst is recycled to the conversion zone for further contact witn the methanol- and/or ether-containing feed. The product stream of the process contains steam and a hydrocarbon mixture of paraffins and olefins, substantially devoid of aromatics. The mixture is particularly rich in light olefins, and especially ricn in propylene. Thus, the predominant hydrocarbon products constitute valuable petrochemicals. The steam and hydrocarbon products may be separated from one another by methods well known in the art. Preferably, the unconverted methanol and/or dimethyl ether, as well as at least part of the water in the product, are recycled to the reaction zone. The following Examples illustrate the invention. EXAMPLE I Zeolite ZSM-12 is prepared in the following manner: five grams of soduim aluminate (41.8% A1203) are dissolved in a solution of 96.2 grams of tetraethylammoniumbromide and 17.5 grams of NaOH in 300 grams ¸0. Five hundred grams of colloidal silica, e.g., Ludox, are added to the solution and mixed for 15 minutes. The resulting mixture is crystallized in a polypropylene jar without agitation for 84 days at 1000C. Analysis by X-ray diffraction identifies the product as ZSM-12 with a SiO2/A1203 ratio of 82. The product is washed and dried at 110 C. The dried powder is pre-calcined for 3 hours at 3700C in air and then cooled to room temperature in a dessicator. This is followed by four contacts each with 10 ml. of 5 percent NH4Cl/gram of calcined powder at 900C for 1 hour. Eacn contact is made with stirring. The product is washed free of Cl ions at room temperature and then dried at 1100C. The sodium content of the zeolite at this stage is less than 0.01 percent. The dried powder is then calcined by heating it in air at 5380C for 10 hours, and then cooled in a dessicator. Zeolite ZSM-12 made in this general manner can be synthesized with various silica to alumina ratios and can be pretreated, e.g. by steaming, to produce zeolites of various alpha values. Example II ZSM-12 samples, prepared in the general manner described in Example I, are modified in their ammonium exchanged form to incorporate both magnesium and manganese. Composites of NH4-ZSM-12 in 35 % alumina binder are wasned twice with an aqueous solution of 1M Mh(OAc)2 and 0.2M Mg (OAc)2, for two hours at reflux, followed by water washes, drying and calcination in air at 5000C. Samples prepared in this manner contain 4.2 S Mn and 0.5 S Mg by weight. Catalyst samples containing only magnesium and catalyst samples containing only manganese are also made in similar manner using either a 1 M solution of magnesium acetate or a 1 M solution of manganese acetate. Mg-modified zeolites prepared in this manner contain 3.0S Mg by weight and Mn-modified zeolites prepared in tnis manner contain about 3.9S Mn by weight. EXAMPLE III Using catalyst samples prepared in the general manner of Examples I and II, methanol/water mixtures are catalytically converted into hydrocarbons and the resulting hydrocarbon products are analyzed In such a procedure, a fixed bed, down-flow quartz reactor with a central thermowell is used for atmospheric pressure runs. Liquids are fed with a syringe pump. Gas is metered with a manual low flow controller. A 12.7mm stainless steel reactor with central thermowell is used in the down-flow mode for pressure runs. 1.5 grams of catalyst are used in the reactors and products are collected for one hour periods. Gases are measured in a dry gas tower with a mercury-sealed float, and analyzed on a silica gel column with a thermoconductivity detector. Liquids are condensed with ice-water cooling. Methanol/dimethyl ether conversions are calculated on a carbon molar basis (approximately equivalent to a CH2 basis). Methanol conversion runs are made using several types of ZSM-12 zeolite catalysts. Catalyst description, reaction conditions and methanol conversion results are set forth in Table I. Table I Methanol Conversion Over ZSM-12 Effect of Cation and Short Term Aging Effects Run No. 1 2 3 4 5 Catalyst HZSM-12 HZSM-12 MgZSM-12 Mn-ZSM-12 Mg/Mn-ZSM-12 SiO2:Al2O3/ (180/103) (180/103) (180/20) (180/-) (180/13) WHSV MeOH 2.1 2.1 2.1 2.1 2.1 H2O 3.5 3.5 3.5 3.5 3.5 Temperature ( C) 390 450 450 450 450 Time on Stream (hrs.) - - - - 2 Conversion to 97.3 99.5 80.5 93 91.9 Hydrocarbons (C Mol. %) Selectivity to Hydrocarbons (Wt. %) COX 0.1 0.1 0.1 0 0 C1 0.4 0.5 0.4 0.4 0.5 C2 0.1 0.1 0.1 0.1 0.1 C2= 3.2 6.4 3.1 3.5 3.8 C3 5.2 5.4 1.5 2.4 2.5 C3= 20.0 35.1 48.3 42.0 59.5 C4 18.6 13.5 4.6 7.9 6.1 C4= 16.2 20.9 17.6 17.8 16.9 C5 2.0 3.4 10.4 13.6 1.2 C6 0 0.2 0.9 1.6 0 liquid 34.3 14.4 12.9 10.6 9.6 C2-C4= 39.4 62.4 69.0 63.3 80.2 The Table I data demonstrate that methanol conversion over a ZSM-12 zeolite catalyst modified by incorporation of both magnesium and manganese is especially selective to light olefin production with the major light olefin product being propylene. EXAMPLE IV Using the general testing procedures described in Example III, additional conversion runs are made at various reaction temperatures using the Mg/Mn-ZSM-12 zeolite sample employed in Example III. Reaction conditions and conversion results are set forth in Table II. TABLE II Methanol Conversion Over Mg/Mn-2SM-12 Effect of Temperature Run No. 1 2 3 4 5 6 WHSV MeOH 2.1 2.1 2.1 2.1 2.1 2.1 H20 3.5 3.5 3.5 3.5 3.5 3.5 Temperature ( C) 350 370 390 420 450 475 Conversion to 32.9 43.3 65.5 90.0 99.2 100 Hydrocarbons (C mol. X) Selectivity to Hydrocarbons (Wt.%) COX 0 0 0 0 0 0 C1 O.5 0.5 0.4 0.3 0.4 0.5 C20 0 0 0 0 0.1 0.1 C2= 0.7 0.7 1.1 2.1 3.7 5.3 C3 1.1 1.0 1.4 1.8 2.1 2.1 C3= 39.3 34.5 40.2 45.4 49.6 52.1 C4 10.4 9,0 9.5 7.9 5.8 4.7 c4= 18.7 20.5 19.0 19.0 18.3 18.6 C5 16.4 13.7 13.9 12.8 11.8 11.4 C6 1.4 1.5 1.8 1.7 1.5 1.4 liquid 11.4 18.4 12.8 8.7 6.6 3.6 C2-C4= 58.8 55.8 60.3 66.5 71.6 76.0 The Table II data demonstrate that, at higher temperatures, Mg/Mn-ZSM-l2 promotes -greater conversion of methanol into hydrocarbons with generally higher selectivity to production of C2-C4 olefins. Propylene is the major light olefin product at all temperatures. EXAMPLE V Using the general testing procedures described in Example III, additional methanol conversion runs are made over MglMn-ZSM-l2 using different temperatures, different space velocities for methanol and water and, in one instance, using a nitrogen diluent. Reaction conditions and conversion results are set forth in Table III. Table III Methanol Conversion Over Mg/Mn - ZSM-12 Effect of Dilution Run No. 1 2 3 4 5 WHSV MeOH 2.2 2.1 2.1 2.2 2.2 H20 - 3.5 3.5 6.2 - N2 - - - - 2.8 Temperature ( C) 362 362 450 460 450 Conversion to 64.6 19.9 99.2 99.2 98.6 Hydrocarbons (C mol. %) Selectivity to Hydrocarbons (Wt S) COX - - 0 0 0 C1 0.6 0 0.4 0.4 0.7 C2 0 0 0.1 0 0 C2= 1.6 1.0 3.7 3.6 1.5 C3 1.3 0.9 2.1 1.3 1.4 C3: : 17.4 28.7 49.6 55.1 44.4 C4 14.5 7.8 5.8 3.8 7.3 C4= 15.2 26.0 18.3 18.9 22.0 C5 28.9 25.8 11.8 11.3 18.6 C6 28.9 25.8 1.5 1.8 2.0 liquid 20.5 9 6.6 3.6 0 C2-C4= 34.2 55.7 71.6 77.6 67.9 The Table III data demonstrate the selectivity to light olefins in general and to propylene in particular for methanol conversion over Mg/Mn-ZSM-12.

Claims: CLAIMS: 1. A process for converting a methanol-containing feed into an olefin-containing hydrocarbon product rich in propylene, which comprises contacting the methanol-containing feed under conversion conditions with a ZSM-12 zeolite-pontaining catalyst characterized in that the catalyst contains a minor amount of magnesium and/or manganese. 2. A process according to Claim 1, wherein the magnesium and/or manganese are present in the catalyst at least in part in the form of tneir oxides. 3. A process according to Claim 1 or Claim 2, wherein the catalyst contains from 0.1% to 10% by weight magnesium. 4. A process according to any one of Claims 1 to 3, wherein the catalyst contains from 0.1S to 10% by weight manganese. 5. A process according to any one of Claims 1 to 4, wherein the conversion conditions include a reaction temperature from 4000C to 4500C and a pressure from 500 to 1000 kPa. 6. A process according to any one of Claims 1 to 5, wherein the conversion conditions include a weight hourly space velocity for the organic reactants of the methanol-containing feed from 0.1 to 30. 7. A process according to any one of Claims 1 to 6, wnerein the methanol-containing feed contains water in an amount from 1 to 20 moles of water per mole of organic reactants. 8. A process according to Claim 7, wherein the weignt hourly space velocity of the water is from 1 to 20.

Inventors: LEE, CAROL SANA, STEAD, GEORGE EDWARD
Applicants: MOBIL OIL CORPORATION
Application year: 1983
Main classification: C07C1
IPC codes: B01J29, C07C67, C07B61, C07C1, C07C11