Hybrid Extruded Mixed Zeolite Catalysts for Synthesis of Light Olefins

Abstract

A catalyst for converting dimethyl ether into light olefins, including ethylene and propylene. The catalyst comprises a mixture of two zeolites, ZSM-5 and ZSM-35, intimately mixed and kept in close proximity in a porous extruded binder system. The resulting combination of zeolites demonstrates a synergistic effect with respect to the conversion of the dimethyl ether and has improved resistance to deactivation due to carbon and coke formation than the individual zeolites alone when operating in this reaction. The catalyst is used to produce ethylene and propylene from a feed mixture containing methanol, dimethyl ether and water.

Claims

1. A composition comprising a ZSM-5 zeolite catalyst and a ZSM-35 zeolite catalyst.

2. The composition of claim 1 wherein said ZSM-5 zeolite is present in an amount of from about 10 wt. % to about 95 wt. % of the total amount of zeolite in said composition.

3. The composition of claim 2 wherein said ZSM-5 zeolite is present in an amount of from about 10 wt. % to about 90 wt. % of the total amount of zeolite in said composition.

4. The composition of claim 3 wherein said ZSM-5 zeolite is present in an amount of from about 40 wt % to about 90 wt. % of the total amount of zeolite in said composition.

5. The composition of claim 4 wherein said ZSM-5 zeolite is present in an amount of from about 55 wt. % to about 85 wt. % of the total amount of zeolite in said composition.

6. The composition of claim 1 wherein said ZSM-35 zeolite is present in an amount of from about 5 wt. % to about 90 wt. % of the total amount of zeolite in said composition.

7. The composition of claim 6 wherein said ZSM=35 zeolite is present in an amount of from about 10 wt. % to about 90 wt. % of the total amount of zeolite in said composition.

8. The composition of claim 7 wherein said ZSM-35 zeolite is present in an amount of from about 10 wt. % to about 60 wt. % of the total amount of zeolite in said composition.

9. The composition of claim 8 wherein said ZSM-35 zeolite is present in an amount of from about 15 wt. % to about 45 wt. % of the total amount of zeolite in said composition.

10. The composition of claim 1 and further comprising a binder.

11. The composition of claim 10 wherein said binder is selected from the group consisting of silicas, clays, aluminas, and mixtures thereof.

12. The composition of claim 11 wherein said binder is a silica.

13. The composition of claim 12 wherein said silica is derived from colloidal silica.

14. The composition of claim 12 wherein said silica is an amorphous silica.

15. The composition of claim 11 wherein said binder is a clay.

16. The composition of claim 11 wherein said binder is an alumina.

17. The composition of claim 16 wherein said alumina is an amorphous alumina.

18. A composition comprising an MFI zeolite catalyst and a ZSM-35 zeolite catalyst.

19. A composition comprising a ZSM-5 zeolite catalyst and an FER zeolite catalyst.

20. A composition comprising an MFI zeolite catalyst and an FER zeolite catalyst.

21. A method of producing at least one olefin from dimethyl ether, comprising: reacting a feed comprising dimethyl ether under catalytic conversion conditions in the presence of a composition comprising a ZSM-5 zeolite catalyst and a ZSM-35 zeolite catalyst to produce a product comprising at least one olefin.

22. The method of claim 21 wherein said feed further comprises methanol.

23. The method of claim 22 wherein said feed further comprises water.

24. The method of claim 21 wherein said at least one olefin is ethylene.

25. The method of claim 21 wherein said at least one olefin is propylene.

26. The method of claim 21 wherein said at least one olefin comprises ethylene and propylene.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0111] The following terms are defined below:

DME—Dimethyl ether.

IMPCA—International Methanol Producers and Consumers Association.

[0112] FER—a group of zeolite materials comprising forms of ZSM-35 zeolite.
Mordenite Framework Inverted, or MFI—a group of zeolite materials comprising forms of ZSM-5 zeolite.
WHSV—Weight Hourly Space Velocity as the weight of feed per hour per unit weight of catalyst loaded in the reactor.
medium pore size zeolites—a group of zeolites classified on the size of the pore structure, which includes ZSM-5 and ZSM-35.

[0113] Renewable material used for producing methanol and dimethyl ether is gasified by any known means such as the methods and processes described in U.S. Pat. No. 8,137,655 and U.S. Pat. No. 8,192,647. Synthesis gas produced in the gasification process is used for the methanol synthesis. The production of methanol from syngas is carried out at a temperature in the range of about 200 to 300° C. and a pressure range of about 20 to 100 bar over a catalyst including mixed oxides of copper, zinc and chromium, and copper zinc aluminum oxide catalyst as described in U.S. Pat. No. 3,326,956.

[0114] Catalysts used for methanol synthesis are available commercially with details of manufacture given in U.S. Pat. No. 3,840,478 wherein the manufacture of copper oxide-zinc oxide and chromium oxide catalysts for methanol synthesis are described.

[0115] The synthesis gas used for manufacturing the methanol can also be obtained from any other known method for producing syngas, such as steam, partial oxidation, or autothermal reforming of hydrocarbons or other carbon sources including natural gas.

[0116] Reactant dimethyl ether, (DME), is produced by dehydrating methanol over commercially available acid catalyst. It is not necessary for the methanol used for dimethyl ether synthesis to be pure. Methanol with a purity of 99.85% as defined by the IMPCA reference specification for methanol, can be used or a less pure methanol such as 70-80% w/w of methanol with a 20-30% w/w water content can be used as the methanol source for the dehydration reaction.

[0117] Synthesis gas produced from renewable materials through gasification technology, can be used to synthesize dimethyl ether directly. This process is referred to as the “one step dimethyl ether production process”. Methods for direct synthesis of dimethyl ether from synthesis gas are described in EP2028173 and US2015/0018582.

[0118] EP2028173 describes a catalytic process for the conversion of syngas consisting of carbon monoxide, carbon dioxide and hydrogen to dimethyl ether in a catalytic process comprising contacting a stream of synthesis gas comprising carbon dioxide in a first dimethyl ether synthesis step with one or more catalysts active in the formation of methanol and the dehydration of methanol to dimethyl ether to produce a product comprising dimethyl ether, methanol, carbon dioxide and unconverted synthesis gas, and washing the product mixture comprising carbon dioxide and unconverted synthesis gas in a scrubbing zone with a liquid solvent.

[0119] The solid catalyst extrudate is used for the production of a product comprising light olefins from a feed mixture that contains one or more of methanol and dimethyl ether and optionally water at reaction conditions that produce light olefins. The solid catalyst extruded form comprises a mixture of two different zeolites and an inert binder such that the combination of zeolites results in an improved and positive synergistic effect on catalytic performance and a reduced rate of coke formation that otherwise would not be realized if the individual zeolite simply were mixed or layered in a reactor and not in intimate contact within a single catalyst form and bound by a porous inert binder.

[0120] In a non-limiting aspect of this invention, light olefins are synthesized from a mixture of dimethyl ether, water, and methanol. The reaction is carried out at a temperature of from about 200 to 500° C. and at atmospheric or higher pressures.

[0121] The reaction is carried out in a reactor that is a catalytic fixed bed, a fluidized bed, a tubular reactor, or other type of reactor into which the catalyst can be placed.

[0122] In a non-limiting embodiment, the catalyst used for the synthesis of light olefins from dimethyl ether and methanol and water mixture, comprises ZSM-5 and ZSM-35 and a binder.

[0123] In a non-limiting embodiment, the catalyst used for the synthesis of light olefins is in an extruded form.

[0124] A another non-limiting embodiment, is that the catalyst used for the synthesis of light olefins is pelletized.

[0125] In yet another non-limiting embodiment, the extruded catalyst herein described that is used for the synthesis of light olefins is in the form of small solid cylinders or spheres.

[0126] In another non-limiting embodiment, one form of the ZSM-5 zeolite dispersed in the binder for light olefins synthesis is an MFI type zeolite as described in the “Atlas of Zeolite Framework types”, D H Olson, Ch. Baerlocher et al., 6th edition, 2007, wherein such atlas states that ZSM-5 zeolites are tridimensional zeolites with pore aperture dimensions of 5.1×5.7 Å and 5.3×5.6 Å.

[0127] In another non-limiting embodiment, one form of the ZSM-35 zeolite dispersed in the binder has specific properties and characteristics for olefin synthesis, and is an MFI type zeolite described in the “Atlas of Zeolite Framework types”, D H Olson, Ch. Baerlocher et al., 6th edition, 2007. ZSM-35 is a tridimensional zeolite with pore aperture dimension of 5.5×4.3 Å and 4.8×3.4 Å.

[0128] Both ZSM-5 and ZSM-35 are in a class of zeolites that is referred to as medium pore size zeolites.

[0129] The zeolite powder materials are mixed in suitable proportions as herein described and mixed with a binder. The resulting mixture is then formed into an extrudate which is then shaped before being dried and calcined to give the calcined catalyst. The calcined catalyst is then cross linked by adding ammonium nitrate, drying and then calcined a second time. The resulting extruded form is the cross-linked catalyst and also is the activated catalyst. The ammonium nitrate and calcination steps activate the catalyst.

[0130] Mixing the zeolites in this way and forming them into a single catalyst extrudate results in a hybrid catalyst which also can be referred to as a hybrid zeolite catalyst.

[0131] The hybrid catalyst is produced, in a non-limiting embodiment, by mixing powder forms of the zeolites as herein described, followed by dispersing the mixture of zeolite powders in water and then adding colloidal silica to form a first dispersion, and adding hydroxyethylcellulose to the mixture to form a first plastic paste. The paste then is passed through an extrusion die and cut to give uniformly sized cylindrical catalyst forms. The cylindrical catalyst forms are allowed to dry at room temperature before being calcined in an oven to about 550° C. to provide a calcined catalyst.

[0132] The calcined catalyst is used in a reactor for the conversion of dimethyl ether to olefins as described herein.

[0133] The catalyst produced in this manner was found to have improved performance with respect to carbon formation. The catalyst showed an improved capacity for reduced coke formation with one combination of ZSM-5 and ZSM-35 presenting surprising results that would not have been expected.

[0134] In a non-limiting embodiment of the invention, the performance of the catalyst and its selectivity towards producing olefins was measured in a fixed catalytic bed. Oxygenated hydrocarbons such as methanol and dimethyl ether were used in the experiments for testing the catalysts. Methanol, dimethyl ether and water were mixed in a fixed-bed reactor at temperatures from about 400 to about 515° C. with Weight Hourly Space Velocities in the range of from about 15 to about 50 h.sup.−1. The catalyst was found to have exhibited high conversion and selectivity toward light olefins while demonstrating a reduced susceptibility to the loss of activity because of coke and carbon formation.

[0135] In a non-limiting embodiment, the water content in the feed to the reactor is from about 25 wt. % to about 60 wt. %.

[0136] In another non-limiting embodiment, the water content in the feed to the reactor is from about 30 wt. % to about 40 wt. %.

[0137] In a further non-limiting embodiment, the temperature of the reaction in the reactor is from about 250° C. to about 500° C.

[0138] In another non-limiting embodiment, the temperature of the reaction in the reactor is from about 400° C. to about 500° C.

[0139] In a non-limiting embodiment, the gas hourly space velocity is from about 15 to about 50 h.sup.−1.

EXAMPLES

[0140] Embodiments of the present invention are further illustrated by the non-limiting examples which follow. It is to be understood, however, that the scope of the present invention is not intended to be limited thereby.

Example 1

[0141] Two commercial zeolites, NH.sub.4 ZSM-5 and NH.sub.4 FER, were supplied by Zeolyst International in powder form. These were used to manufacture a number of extruded catalysts with varying loadings of zeolite.

[0142] The hybrid catalyst extrusions used for testing and demonstrating the performance of the catalyst were prepared as described below.

[0143] An aliquot of each catalyst was weighed in an appropriate proportion so as to give the desired weight ratio for each zeolite in the final extrusion.

[0144] The NH.sub.4 ZSM-5 and NH.sub.4 FER zeolites powder aliquots then were mixed together for 10 minutes.

[0145] A colloidal silica (W.R. Grace, Ludox™ HS-40) solution then was added to the zeolite mixture with agitation and the resulting solution was mixed for a further 10 minutes. The colloidal silica was used as a binder for the zeolites and adds strength to the resulting extrudate.

[0146] Sufficient colloidal silica was added to the mixture so that the dry form of the extrudate would contain 75% (w/w) zeolite and 25% (w/w) silica on a dry basis. For example when using a colloidal silica solution supplied as a 40% weight solution of silica, 100 g of colloidal silica solution is added to every 120 g of dry zeolite mixture to give a suspension of zeolite and colloidal silica.

[0147] An about 8.5% (w/w) solution hydroxyethylcellulose solution was prepared by dissolving the polymer in deionized water with mixing for 10 minutes or until the solid had dissolved.

[0148] The hydroxyethylcellulose adds a degree of plasticity to the unformed extrudate of the catalyst mixture. An optimal liquid/solid relationship of 0.6 was used and found to be effective.

[0149] 98 g of the hydroxyethylcellulose solution then was mixed with the zeolite-colloidal silica mixture and mixing continued for at least 20 minutes after which time it gave a smooth paste blend.

[0150] The hydroxyethylcellulose is added as a temporary binder to bind the solid particles of the dispersion and form a paste with plastic properties that allow the paste to be formed and extruded into a stable shape.

[0151] The smooth paste blend then was passed through an extrusion die to give cylindrical sticks with a diameter of about 3 to 4 mm and lengths of about 10 to 30 cm. The extruded forms then were cut into about 3 to 5 mm long pellets that were then allowed to dry at room temperature for 24 h.

[0152] The dried catalyst pellets then were placed in a calcination oven at room temperature. The calcination process heated the oven from room temperature up to about 550° C. with a heating ramp of 2° C./minute. The catalyst then was left to stand in the oven at 550° C. for 3 hours or more. After this time the calcined catalyst was allowed to cool slowly with the oven to give the calcined extrudate.

[0153] After cooling, a nitrate impregnation and crosslinking process was used to activate the catalyst. The calcined extrudate so produced was mixed with a 2M aqueous ammonium nitrate (NH.sub.4NO.sub.3) solution. The solution was maintained at 55° C. with 100 ml of nitrate solution added per 10 g of calcined extrudate used. The resulting nitrate impregnated calcined extrudate solid material was then left to dry in air for 4 h.

[0154] The resulting nitrate impregnated dry calcined extrudate was then calcined a second time using a similar process to the first. The dry nitrated impregnated calcined extrudate was placed in an oven at room temperature and heated to a temperature of 550° C. at a rate of 2° C./minute and then allowed to soak at 550° C. for 3 hours. The extrudates were allowed to cool with the oven and then placed in a desiccator.

[0155] This catalyst preparation process herein described produced an activated solid, compression resistant catalyst that could be used directly in a reactor.

[0156] The resulting solid calcined catalyst particles were removed from the oven and allowed to cool in a desiccator in a nitrogen purged atmosphere. The catalyst particles were uniform in shape and size with sufficient strength to resist compression.

[0157] The calcined cross-linked catalyst form was then allowed to cool slowly with the oven, before being removed and stored in a desiccator until used

[0158] Table 1 shows the composition and combinations of each component and zeolite in the catalyst particles manufactured using this process. Table 2 shows the sample identifiers and composition of each of the catalyst prepared and the amount of each zeolite used for each on a dry basis of calcined catalyst.

TABLE-US-00001 TABLE 1 Extrusion sample preparation - material compositions before drying. Material Weight g Total Zeolite 187.5 40% Colloidal silica 156.25 (Ludox-HS40) Hydroxyethylcellulose 12.75 Water 43.5

TABLE-US-00002 TABLE 2 Mixed Zeolite Catalyst Sample Composition - excluding Binder. Weight Percentage Catalyst Zeolite % Weight Zeolite g Name FER ZSM-5 FER ZSM-5 100-H-ZSM-5 0 100 0 187.5 Hybrid I 10 90 18.75 168.75 Hybrid II 20 80 37.5 150 Hybrid III 40 60 75 112.5 Hybrid IV 60 40 112.5 75 100-H-FER 100 0 187.5 0

Example 2

[0159] The catalysts produced in Example 1 were analyzed using a number of techniques to quantify the structure, surface area, and pore sizes within the catalyst. This was done to confirm that the pore structure had not changed significantly during the preparation of the mixed catalyst extrudate.

[0160] Table 3 shows the results obtained in these measurements and a number of conclusions and observations can be drawn from these data. The percentage crystallinity between the pure catalyst and the extruded form of the pure catalyst appears to change in line with the ratio of binding material and zeolite loading. The binding material, present as silica, would be expected to be present as an amorphous material after classification.

TABLE-US-00003 TABLE 3 Catalyst Properties and Characterization Results. BET Weigh % N.sub.2 Adsorption Surface Zeolite % (cm.sup.3/g zeolite) Area PORE SIZE FER ZSM-5 Crystallinity V.sub.micro V.sub.meso m.sup.2/g (nm) H-ZSM5 (P) — 10 100 0.12 0.06 409.84 5.5 H-ZSM5 (E) — 10 75 0.13 0.14 329.48 9.2 H-FER (P) 10 — 100 0.12 0.02 361.8 9.2 H-FER (E) 10 — 75 0.13 0.13 324.33 9.2 Hybrid I (E) 1 9 0.13 0.13 324.57 9.24 Hybrid II (E) 2 8 0.13 0.14 329.5 9.22 Hybrid III (E) 4 6 0.13 0.14 332 9.27 Hybrid IV (E) 6 4 0.13 0.14 329.5 9.23 (E): Extruded, (P): Powder

[0161] It is surprising to note that after mixing and calcination, the catalysts all have a pore size that is about 9.2 nm. This remains the case when 90% of the catalyst is made up of ZSM-5, which has an average pore size of 5.5 nm before being incorporated in the catalyst extrudate.

[0162] The catalyst produced using the method of Example 1 with the compositions given in Table 4 each were tested in a reactor with various feed mixtures containing dimethyl ether, water, and methanol. The methanol and dimethyl ether to olefin reaction conditions at which each catalyst was tested are given in Table 5. The methanol, water, and dimethyl ether feed composition was kept constant in these reactions while the reactions were done at atmospheric pressure.

TABLE-US-00004 TABLE 4 Mixed Zeolite Catalyst Sample Composition with binder. Catalyst Weight Percentage % Weight of component g Name FER ZSM-5 Silica FER ZSM-5 Silica 100-H-ZSM-5 0 75 25 0 187.5 62.5 Hybrid I 7.5 67.5 25 18.75 168.75 62.5 Hybrid II 15 60 25 37.5 150 62.5 Hybrid III 30 45 25 75 112.5 62.5 Hybrid IV 45 30 25 112.5 75 62.5 100-H-FER 75 0 25 187.5 0 62.5

TABLE-US-00005 TABLE 5 Methanol to olefin reaction operating conditions. Feed composition (wt. %) Temperature (° C.) WHSV (h.sup.−1) MeOH DME Water 400 15 5 60 35 All reactions were done at atmospheric pressure.

[0163] The results for each case were tabulated in Table 6. The sample containing 20% HFER and 80% HZSM shows a capability that is surprising and unexpected relative to the other catalyst compositions. This formulation of catalyst demonstrates ability for increased dimethyl ether conversion, with up to about 90.2% conversion which is a significant improvement compared to the other catalyst mixtures and the catalysts containing only a single zeolite. This performance was surprising and would not and could not have been predicted from the data obtained for the other mixtures. It is clear the having both zeolites present at this ratio has a significant and measurable synergic effect on catalyst performance.

TABLE-US-00006 TABLE 6 Product distribution by molar percentage after 350 minutes reaction time on hybrid catalyst mixtures of H-ZSM-5 (HZSM) and H-ZSM-35 (HFER). HZSM HFER 10HFER- 20HFER- 40HFER- 60HFER- (280) (20) 90HZSM 80HZSM 60HZSM 40HZSM Mol % Mol % Mol % Mol % Mol % Mol % C.sub.1-C.sub.4 0.0 0.0 0.0 0.0 0.0 0.0 C.sub.2═ 13.04 92.98 30.17 16.24 32.49 23.48 C.sub.3═ 56.61 2.05 40.60 53.29 30.69 38.85 C.sub.4═ 6.75 0.66 4.29 6.98 6.24 9.06 C.sub.5.sup.+═ 3.63 1.26 4.33 5.06 5.96 6.52 Paraffin's (C.sub.5.sup.+) 14.34 1.63 14.56 13.24 17.30 14.93 Naphtha's (C.sub.5.sup.+) 1.50 0.40 1.04 1.63 1.43 2.07 Aromatics 4.13 1.01 5.00 3.56 5.89 5.09 Conversion DME 82.6 34.6 70.7 90.2 71.1 87.3 after 5 hours Coke (wt. %) 1.48 5.7 1.49 1.14 0.8 1.25

[0164] It also is seen that the 20% HFER-80% HZSM catalyst mixture also produces a product mixture that contains about 53.3% propylene, which is significantly more than any of the other mixtures. The single zeolite version of the catalyst is the only catalyst that produces more than 53.3% propylene. The 20% HFER-80% HZSM catalyst mixture also produced less aromatic compounds in the product mixture while also not producing the lowest carbon formation rate of the catalyst tested. This mixture did have a slower rate of carbon formation than either of the catalysts produced using only one zeolite. The carbon produced after 5 hours of operation was about 1.14 wt. % on the catalyst.

Example 3

[0165] The catalysts were tested in a fixed bed stainless steel reactor (2.03 cm i.d, length=100 cm). The catalyst samples were conditioned in situ by heating them to 515° C. at a rate of 5° C./minute under nitrogen with a flow of 200 actual milliliters minute measured at laboratory conditions. The catalysts then were kept at to 515° C. for 5 h or more.

[0166] The catalyst temperature then was set to the required experiment temperature, Table 5, and allowed to equilibrate. All the catalyst formulations were exposed to a given feed composition for a continuous 5 hour periods. Liquid methanol and water was mixed with a metered amount of dimethyl ether. The resulting mixture was then fed into the top of the reactor and passed down through the catalyst bed before leaving the reactor.

[0167] The hot vapor reaction product vapor mixture leaving the reactor then was cooled to 30° C. before liquid and vapor fractions were separated into a vapor stream and a liquid stream. Analysis of these streams showed that the liquid stream was a mixture of water, and organic compounds while the vapor stream was a mixture of non-condensable hydrocarbon vapors.

[0168] All process runs resulted in 100% conversion of the feed methanol and up to about 90.2% conversion of dimethyl ether, with conversion being calculated as the ratio of {the number of moles of feed component less the number of feed component in the reaction product} to the number of feed component in the feed.

[0169] The conversion of dimethyl ether was between 34.6 and 90.2 wt. %. Hybrid catalyst containing 80 wt. % ZSM and 20 wt. % FER resulted in a dimethyl ether conversion of about 90.2 wt. %. A hybrid catalyst consisting of 40 wt % ZSM and 60 wt. % FER that gave a dimethyl ether conversion of about 87.3 wt. %.

[0170] The preceding example(s) can be repeated with similar success by substituting the various components and configurations for each zeolite as described herein.

[0171] Although the invention has been described in detail with particular reference to a number of embodiments, embodiments can be derived at that give the same or similar results. Upon studying this application it will be possible that those skilled in the art will realize other equivalent variations and/or modifications. It is intended that the claims contained in any patent issued on this application cover all such equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated herein by reference to the same extent as if each patent, patent application, and reference were incorporated individually by reference.

[0172] It is to be understood, however, that the scope of the present invention is not to be limited to the specific embodiments described above. The invention may be practiced other than as particularly described, and still be within the scope of the accompanying claims.