WO2012005864A1

WO2012005864A1 - Production of olefins from a mixed alcohols feed

Info

Publication number: WO2012005864A1
Application number: PCT/US2011/039891
Authority: WO
Inventors: Yu Liu; Andrzej Malek; Brien Stears
Original assignee: Dow Global Technologies Llc
Priority date: 2010-07-09
Filing date: 2011-06-10
Publication date: 2012-01-12

Abstract

A process for producing olefins comprises contacting a feed including at least two alcohols, selected from C₁-C₆ alcohols, and, as a synergistic co-feed, at least one aromatic compound, and a porous crystalline aluminosilicate catalyst having a pore size greater than the critical diameter of the aromatic compound, under reaction conditions such that an olefin is formed. Selectivity to one or more target olefins may be conveniently enhanced via choice of, and proportions of, the mixed alcohols feed. Reaction conditions may include a temperature as low as 250°C.

Description

PRODUCTION OF OLEFINS FROM A MIXED ALCOHOLS FEED

This application is a non-provisional application claiming priority from the U.S. Provisional Patent Application No. 61/363,063, filed on July 9, 2010, entitled "PRODUCTION OF OLEFINS FROM A MIXED ALCOHOLS FEED" the teachings of which are incorporated by reference herein, as if reproduced in full hereinbelow. BACKGROUND

Field of the Invention

[0001] The invention relates to conversion of alcohols to olefins. More particularly, the invention relates to a process for producing olefins from a feed of mixed alcohols and an aromatic hydrocarbon or mixture of aromatic hydrocarbons, using an aluminosilicate catalyst.

Background of the Art

[0002] Light olefins, defined herein as ethylene and propylene, are important commodity petrochemicals useful in a variety of processes for making plastics and other chemical compounds. Ethylene is used to make, for example, polyethylene plastics, vinyl chloride, ethylene oxide, ethyl benzene and alcohol. Propylene is used to make polypropylene plastics, acrylonitrile and propylene oxide.

[0003] The petrochemical industry has known for some time that oxygenates, especially alcohols, are convertible to light olefins. The preferred conversion process is generally referred to as an "oxygenate to olefin" ("OTO") reaction process. In an OTO reaction process an oxygenate contacts a molecular sieve catalyst composition under conditions effective to convert at least a portion of the oxygenate to light olefins. When an alcohol is the oxygenate, the process may be referred to as an "alcohol to olefin" ("ATO") reaction process. Methanol is a particularly preferred oxygenate for the synthesis of ethylene and/or propylene because of its relatively low cost and convenient availability via syngas, which may be produced by the steam reformation of methane, a primary constituent of natural gas. Processes for olefin production that employ primarily methanol are often termed "methanol to olefin" ("MTO") or "methanol to propylene" ("MTP") processes.

[0004] Examples of known OTO reactions include the process described in WO 99/51548 (Brown, et al.), wherein methanol and/or dimethyl ether are converted to C₂ to C₄ olefins, with ethylene being more than 40 weight percent (wt ) of the product. The catalyst is a porous crystalline material and the reaction is carried out in the presence of a co-fed aromatic compound at a temperature of from 350 degrees Celsius (°C) to 500°C, preferably 400°C to 480°C, at a methanol partial pressure in excess of 10 pounds per square inch absolute (psia) (70 kilopascals, kPa). The porous crystalline material has a pore size greater than the critical diameter of the aromatic compound, and ZSM-5 zeolite is preferred. Related US 6,506,954 (Brown, et al.) describes a process wherein the co-fed aromatic is a C9 or higher aromatic compound. That patent also describes separating the C₂ to C₄ olefin product stream from a C9 or higher aromatic compound stream and recycling at least a portion of the C9 or higher aromatic compound stream. Another related patent is US 6,538,167 (Brown, et al.), which describes a similar process wherein the temperature ranges from 350°C to 550°C while the methanol and/or DME partial pressure is less than or equal to 345 kPa.

[0005] US 4,499,314 (Seddon, et al.) discloses a process for producing hydrocarbons by contacting aqueous methanol with a crystalline aluminosilicate zeolite catalyst (e.g., ZSM-5) that is hydrothermally stable in a temperature ranging from 250°C to 500°C, using a promoter such as an aromatic hydrocarbon (e.g., benzene and alkyl-substituted benzene hydrocarbons), precursors to aromatic hydrocarbons, and olefins (e.g., alkenes such as ethylene, propylene and butene). The process yields a mixture comprising light olefins, lower alkanes, and monocyclic aromatic hydrocarbons, and includes recovering the hydrocarbons. Use of an aromatic promoter reduces the temperature required to achieve total conversion of the methanol and enhances yield of ethylene and, in some instances, propylene.

[0006] /. Catalysis 82 (1983) 261 (Mole, et al.) describes co-feeding 1 percent ( ) benzene, toluene, or xylene with methanol. The product is ethylene, propylene and C₄ and higher hydrocarbons and the catalyst is ZSM-5, which has been calcined and acid-washed. The authors suggest that, while conversion appears to be highly dependent upon reaction temperature, such can be attributed to autocatalysis because both olefins and aromatic hydrocarbons are products of methanol conversion. They therefore conclude that these low levels of co-fed aromatic hydrocarbons serve as promoters or co-catalysts to increase catalytic activity.

[0007] US 2006/0106270 (Glover, et al.) uses a dual-function oxygenate conversion catalyst to enhance average propylene cycle selectivity in an oxygenate to propylene (OTP) process. The process employs a combination of moving bed technology, a hydrothermally stabilized and dual functional molecular sieve catalyst, and a catalyst on-stream cycle time of less than 400 hours. The catalyst may be a zeolitic molecular sieve having a structure corresponding to ZSM-5, ZSM-11, or SAPO-34. A diluent is used to control partial pressure of the oxygenate reactant, and may be helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, a Ci to C₄ paraffin, an aromatic hydrocarbon, or a combination thereof, with water being preferred. Temperature may range from 350°C to 500°C, preferably from 400°C to 500°C.

[0008] US 2005/0107481 (Janssen, et al.) describes use of a raw methanol stream of the type commonly produced in methanol plants. Such streams commonly comprise ethanol and C3 and C₄ alcohols. The process forms ethylene and propylene, and optionally butenes or pentenes, using SAPO catalysts. The ethylene to propylene ratio can be varied by varying the ratio of the methanol to the fuel alcohol in the stream.

[0009] Unfortunately, many of the prior art methods are inherently expensive due to high capital costs, and offer limited opportunities to alter the selectivity to target olefins. Alteration of selectivity is often desirable particularly for ethylene and/or propylene, because production must often be tailored according to cyclic swings of the commercial markets for these commodity products. While the prior art methods may allow increases in total conversion of starting feed by changing reaction conditions, e.g., temperature, the proportions of ethylene and propylene products resulting from these OTO reactions tend to remain constant.

[0010] In view of the above-described challenges, there is a continuing need for processes that enable modification of selectivity without substantially increasing costs or process steps.

SUMMARY OF THE INVENTION

[0011] In one embodiment the invention provides a process for producing olefins comprising contacting a feed including at least two alcohols, selected from Ci-C₆ alcohols, and, as a synergistic co-feed, at least one aromatic compound, and a porous crystalline aluminosilicate catalyst having a pore size greater than the critical diameter of the at least one aromatic compound, under reaction conditions such that at least two olefins are formed.

[0012] In another embodiment the invention provides a process for producing olefins comprising contacting a feed including methanol and at least one other alcohol selected from C₂-C₆ alcohols, and, as a synergistic co-feed, at least one aromatic compound selected from benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, styrene, and combinations thereof, and a catalyst selected from ZSM-5, MCM-22, US-Y, and combinations thereof, under reaction conditions such that at least two olefins are formed.

[0013] In still another embodiment the invention provides a process for producing olefins comprising contacting a process feed including methanol and at least one other alcohol, selected from C₂-C6 alcohols, and, as a synergistic co-feed, at least one aromatic compound selected from benzene, toluene, xylene, an alkylated benzene, and combinations thereof, and an aluminosilicate catalyst selected from ZSM-5, MCM-22, US-Y, and combinations thereof, under reaction conditions such that an olefin- containing product, including at least ethylene and one other olefin, and an unreacted portion of at least one compound selected from the at least one aromatic compound, the methanol or the at least one other alcohol, or a combination thereof, is formed; separating the ethylene and the at least one other olefin from the unreacted portion; and recycling the at least one unreacted portion back into the process feed.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The invention provides for improved feed efficiency, reduced capital outlay requirements, greater flexibility in ethylene (C₂H₄)/propylene (¾¾) product ratios, and a reduction in overall aromatics production relative to many prior art methods. Such is accomplished by beginning with a mixed feed of at least two Ci-C₆ alcohols and, as a synergistic co-feed, an aromatic compound. Selection of an appropriate porous crystalline catalyst is also important.

[0015] The starting feed includes a mixture of at least two alcohols. Such are selected from Ci-C₆ alcohols and may therefore include methanol (CH₃OH, MeOH); ethanol (C₂H₅OH, EtOH); propanol (C₃H₇OH); butanol (C₄H₉OH); pentanol (C₅H₁₁OH); or hexanol (C₆l½OH). In particular embodiments a combination of Cr C₃ alcohols is preferred, and in other particular embodiments, a combination of Ci-C₂ alcohols is preferred. The alcohols may be combined beginning with discrete alcohols, and/or may be already combined, for example, in the effluent from a process other than the inventive process. In some embodiments a source of the alcohols is the inventive process itself, where one or more alcohols is included in unreacted form in the final olefin-containing product and can then be appropriately separated therefrom for recycle purposes.

[0016] The starting feed also includes, as a synergistic co-feed, an aromatic compound. Such is desirably selected from a wide range of aromatic compounds, including both monocyclic and polycyclic arenes and heteroarenes, which may in some embodiments contain an oxygen atom in place of at least one carbon atom. Such compounds may be formed from an unsaturated or partially unsaturated cyclic precursor via an aromatization reaction. Among these are reactions including cycloaddition, alkyne trimerization, and other aromatization reactions. Aromatic compounds may be prepared or purchased specifically for this process or may be separated from the product stream and recycled to the feed. In another embodiment, a combination of recycled and fresh aromatic co-feed can be used.

[0017] Non-limiting examples of particularly suitable aromatic compounds to use as the synergistic co-feed in the invention may include benzene; toluene; xylene; alkylated benzenes, such as ethylbenzene and diethylbenzene; dehydrogenated products of alkylated benzenes, such as vinyl benzene (styrene); and combinations thereof. Of these, benzene, toluene, xylene, and combinations thereof are, in many embodiments, preferred for reasons of convenience and cost. However, heavier alkylated aromatic compounds, such as tri-, tetra-, and pentamethylbenzene, may be selected. Combinations of any or all of the above may also be selected.

[0018] As used herein, the adjective "synergistic" and the noun "synergism" further define the co-fed aromatic compound as one that, due to its character, amount, or both, affects the inventive process in a measurable way, for example, by enabling the process to proceed at a reduced temperature but in an otherwise substantially identical manner; and/or by changing its selectivity to one or more of the products. Thus, the use and selection of the aromatic compound co-feed, in conjunction with the selected mixed alcohols, in the present invention enables alteration of the proportions of the constituents of the final product, and reduction of temperature at which the process is carried out in comparison to an otherwise identical process without an aromatic compound co-feed. It is this synergism that distinguishes the present invention from processes that include an aromatic compound as a diluent only or in insignificant amount. In preferred embodiments the aromatic compound co-feed is used in an amount of at least 2 percent by weight (wt ), more preferably from 2 wt to 15 wt , still more preferably from 4 wt to 12 wt , and most preferably 10 wt , based on the weight of the mixed alcohols.

[0019] The third required material is a suitable porous crystalline catalyst. In particular embodiments the catalyst is an aluminosilicate material, and may be a crystalline microporous zeolite. Defined as an aluminosilicate, its structure cannot be phosphate-based, but it may contain phosphorus in minor amount as a modifying element. Selection of the appropriate catalyst desirably corresponds to selection of the aromatic compound to be used as the synergistic co-feed. This is because it is desirable, in certain particular embodiments, that the diameter of the pores of the catalyst be sufficiently large to admit, and hold, i.e., to adsorb, the aromatic compound molecule, but not significantly larger than that. Thus, this is called the critical diameter of the pores, which means by definition that the internal adsorption surface of the zeolite is accessible to adsorbate molecules having a diameter that is smaller than, or comparable to, the effective pore diameter of the porous catalyst. For catalysts that have access pores of essentially circular cross-section it is sufficient to characterize molecules with one value of critical diameter. Where a selected aromatic compound has a critical diameter larger than the pore size of the selected catalyst, it may be desirable to transalkylate the aromatic to produce therefrom a smaller- diameter alkyl benzene, such as toluene and/or xylene, in order to facilitate the inventive process.

[0020] It has been found that non-limiting examples of suitable and conveniently- obtained catalysts may include the materials having a framework of the type designated by the International Zeolite Association (IZA) as an "MFI type." A particular example of this is the zeolite known as ZSM-5, which has a pore diameter ranging from approximately 5.3 to 5.6 Angstroms (A). Another useful framework structure is exhibited by zeolites having a faujasite structure, categorized as "FAU type." An example of this type is denoted US-Y. Yet another suitable type is denoted "MWW type." An example of this type is MCM-22, which has a pore diameter ranging from 4 to 7.1 A. Combinations of any of these zeolites or zeolite types may also be selected. In particular embodiments the ZSM-5 zeolite is employed. "AFI type" zeolites, such as SAPO-5 and other silicoaluminophosphate materials, are not suitable for use in the present invention.

[0021] Starting proportions of the three categories of materials employed in the inventive process may be altered according to the desire and understanding of the skilled practitioner, but in general the ratio of the mixed alcohols feed to the synergistic aromatic compound co-feed preferably ranges from 75:25 to 99: 1, more preferably from 80:20 to 98:2, and most preferably from 85: 15 to 96:4. The relative amount of the selected catalyst will vary according to the type of processing equipment selected, but in some embodiments it is desirable to use a weight hourly space velocity (WHSV) for the feed ranging from 0.1 to 20 per hour (h ¹), preferably from 0.5 to 10 h^"1, and more prefer from 0.7 to 5 h^"1.

[0022] In the inventive process it is necessary to contact the mixed alcohols feed, the synergistic aromatic compound co-feed, and the catalyst, using any suitable means and method. Particularly convenient methods may include use of a fixed bed, a fluidized bed, or a moving bed, with the mixed alcohols combined, in some embodiments, with a suitable inert diluent, such as nitrogen, argon, methane, and other alkanes, such as, for example, ethane, propane, butane, pentane, hexane and/or heptane. A suitable means of final product collection is desirably provided. The reaction may be carried out at any suitable temperature and pressure. One advantage of the inventive process, and evidence of the synergism afforded by the aromatic compound co-feed, is that the process may be initiated and progressed at a lower temperature than in an otherwise identical process without the aromatic compound co- feed. For example, in some embodiments a temperature as low as 250°C may be effective, and in general a temperature ranging from 250°C to 500°C is desirable. Pressure may be any that is suitable for use according to the equipment selected and production goals, but injection of the mixed alcohols feed and aromatic compound co- feed may desirably be accomplished at a pressure ranging from atmospheric (1 atm, 101.3 kPa) to 2,000 kPa, preferably from 1 atm to 300 kPa, and more preferably from 100 kPa to 250 kPa.

[0023] The final product of the reaction will, in many embodiments, include at least three olefins. In preferred embodiments these include at least ethylene and propylene, but may also include higher olefins depending upon the mixed alcohols feed selected. Appropriate separation and/or purification means, such as, for example, distillation, oil-water separations, absorption, cryogenic separations, and combinations thereof, may be employed as desired.

[0024] The particular advantage of the inventive process, further supporting the finding of synergism of the aromatic compound co-feed, is that the proportions of the constituents of the final product may be altered by the selection of the mixed alcohols feed and the synergistic aromatic compound co-feed. Furthermore, production of undesired alkanes in general may also be measurably reduced compared to the product of a process that lacks a synergistic aromatic compound co-feed but is otherwise identical. This means of increasing selectivity toward a particular target olefin, for example, ethylene and/or propylene, is convenient and may also provide cost benefits when compared with other methods of altering selectivity. Thus, for example, where it is desirable to increase selectivity toward propylene, this may be effectively accomplished by selecting, as a mixed alcohols feed, a combination of methanol and ethanol, preferably at a methanol to ethanol ratio ranging from 0.01: 1 to 200: 1, more preferably from 0.01 to 10: 1, still more preferably from 1: 1 to 3: 1, and most preferably from 2: 1 to 3: 1.

[0025] Yet another advantage of the inventive process is that a portion of the final product may, in some embodiments, be recycled following separation of target olefin(s). In such embodiments the final product may also contain unreacted compounds, such as, for example, a portion of unreacted alcohol feed or aromatic compound co-feed. Recycle of such back into the process, as part of the mixed alcohols feed and/or synergistic aromatic compound co-feed, may effectively reduce costs and reduce or eliminate disposal issues relating to such product constituents. EXAMPLES

Example 1 and Comparative Example A

[0026] Both Example 1 and Comparative Example A are carried out in a continuous flow micro reactor system at ambient pressure. Flow of the liquid mixture, with or without the aromatic compound, is controlled by an ISCO pump (ISCO 100DM). The mixed alcohols feed, or mixed alcohols feed with aromatic compound co-feed, is introduced into the reactor with 20 milliliters per minute (mL/min) of mixed gases comprising helium (He) and nitrogen (N₂), wherein the alcohol mixture is approximately 14 volume percent (vol ), based on the combined volume of the alchohol mixture and the mixed gases, or of the alcohol mixture, mixed gases and aromatic compound co-feed, at standard temperature and pressure (STP). The reactor is a stainless steel tube (internal diameter ¼ inch by length 6 inches) with 200 milligrams (mg) of ZSM-5 catalyst in a fixed bed. The catalyst has a S1O2/AI2O₃ ratio of 280, the catalyst being in comminuted form, average U.S. mesh size of 20-50, as received from a commercial supplier. The comminuted catalyst is positioned among and between quartz chips, 20-50 U.S. mesh size, in the reactor. Prior to the reaction process, the catalyst is heated at 500°C for 2 hours (h) in He to remove adsorbed water and organic volatiles.

[0027] In Example 1, a methanol/ethanol mixture (26 wt ethanol, 64 wt methanol) is combined with a synergistic aromatic compound co-feed, which is toluene in an amount of 10 wt based on the weight of the mixed alcohols feed. Flow rate is 0.0053 g/min (STP). Reaction temperatures are varied at 250°C, 300°C, 350°C, 400°C, and 450°C, respectively. Selectivity to various products is shown in Table 1.

[0028] In Comparative Example A, a mixture of methanol and ethanol (29 wt ethanol, 71 wt methanol) is employed and the flow rate is 0.0048 g/min (STP). This approximates the flow rate in Example 1 while taking into account the absence of toluene in Comparative Example A. The selectivity to various products at the various temperatures is shown in Table 1.

Examples 2-4 and Comparative Examples B-F

[0029] The same reactor and fixed bed are used as in Example 1 and Comparative Example A, except that the catalysts are varied. Tested catalysts include zeolite US- Y, MCM-22, and ZSM-5, which are defined as crystalline aluminosilicate catalysts, as well as SAPO-5, which is not an example of the invention. The inventive process is carried out at 350°C in each instance, but two different feeds are used for each catalyst. One feed is a combination of methanol and ethanol (71.0 mole percent (mol ) methanol, 29.0 mol ethanol), and the other feed is a combination of methanol and ethanol (63.7 mol methanol, 26.0 mol ethanol) plus toluene in an amount of 10.3 wt . Table 2 shows the overall feed composition. Feed rates are those given in the previous example, i.e., 0.0048 g/min (STP) for the methanol/ethanol feed alone, and 0.0053 g/min (STP) for the combination methanol/ethanol/toluene feed. Other parameters are the same as in the previous example. Products and selectivities are shown in Table 3.

Examples 5-8 and Comparative Examples G-H

[0030] Experiments are conducted to compare the performance of various synergistic aromatic compound co-feeds; of one aromatic compound at two different concentrations (toluene at 4 wt and 10 wt ); and use of water as diluent, as well as a neat alcohols feed. For these, the catalyst is ZSM-5 and varying temperatures ranging from 250°C to 450°C are employed. The general procedure is the same as in previous Examples and Comparative Examples. Data showing the total percent of C₂H₄, C₃H6, and C₄H₈ in the final product with each of the feeds and at each temperature is reported in Table 4.

[0031] The results of Examples 5-8 shown in Table 4 illustrate the significantly- increased selectivity of the inventive process to the three products at lower temperatures, e.g., 250-350°C in particular, in comparison with use of a neat alcohols mixture (Comparative Example G) or an alcohols mixture using a water diluent (Comparative Example H).

Example 9 and Comparative Examples I-K [0032] Experiments are conducted to compare performance of ZSM-5 (Example 9) and SAPO-5 (Comparative Examples I-K) as catalysts, using a range of temperatures. The procedure is carried out similarly to those of previous examples and comparative examples. The same mixed alcohols as shown in Table 2 are employed, and toluene is present in an amount of 10 wt in Example 9 and Comparative Example K, but absent in Comparative Examples I and J. Combined selectivity to C₂H₄, C3¾, and C₄H₈ is shown as mole percent (mol ) in Table 5.

Claims

What is claimed is:

1. A process for producing olefins comprising contacting a feed including at least two alcohols, selected from Ci-C₆ alcohols, and, as a synergistic co-feed, at least one aromatic compound, and a porous crystalline aluminosilicate catalyst having a pore size greater than the critical diameter of the at least one aromatic compound, under reaction conditions such that at least two olefins are formed.

2. The process of claim 1 wherein one of the at least two alcohols is methanol.

3. The process of claim 2 wherein the at least two alcohols are methanol and ethanol in a ratio of from 0.01 : 1 to 200: 1.

4. The process of claim 3 wherein the at least two olefins include ethylene and propylene.

5. The process of claim 1 wherein the at least one aromatic compound is selected from the group consisting of benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, styrene, and combinations thereof.

6. The process of claim 1 wherein the ratio of the alcohols to the at least one aromatic compound ranges from 80:20 to 98:2.

7. The process of claim 1 wherein the reaction conditions include a temperature ranging from 250°C to 500°C and pressure ranging from 101.3 kPa to 2,000 kPa.

8. The process of claim 1 wherein the catalyst is selected from microporous zeolites having framework types as defined by the International Zeolite Association as

MFI, FAU, and MWW types.

9. The process of Claim 8 wherein the catalyst is selected from ZSM-5, MCM-22, US-Y, and combinations thereof.

10. The process of claim 9 wherein the catalyst is ZSM-5.

11. A process for producing olefins comprising contacting a feed including methanol and at least one other alcohol selected from C₂-C₆ alcohols, and, as a synergistic co-feed, at least one aromatic compound selected from benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, styrene, and combinations thereof, and a catalyst selected from ZSM-5, MCM-22, US-Y, and combinations thereof, under reaction conditions such that at least two olefins are formed.

12. The process of claim 11 wherein the at least one alcohol selected from C₂-

C₆ alcohols is ethanol, and the ratio of methanol to ethanol ranges from 0.01 : 1 to 200: 1, and the at least two olefins are ethylene and propylene.

13. The process of claim 11 wherein the ratio of the alcohols to the at least one aromatic compound ranges from 80:20 to 98:2.

14. The process of claim 11 wherein the reaction conditions include a temperature ranging from 250°C to 500°C and a pressure ranging from 101.3 kPa to 2,000 kPa.

15. A process for producing olefins comprising contacting a process feed including methanol and at least one other alcohol, selected from C₂-C₆ alcohols, and, as a synergistic co-feed, at least one aromatic compound selected from benzene, toluene, xylene, an alkylated benzene, and combinations thereof, and an aluminosilicate catalyst selected from ZSM-5, MCM-22, US-Y, and combinations thereof, under reaction conditions such that an olefin-containing product, including at least ethylene and one other olefin, and an unreacted portion of at least one compound selected from the at least one aromatic compound, the methanol or the at least one other alcohol, or a combination thereof, is formed; separating the ethylene and the at least one other olefin from the unreacted portion; and recycling the at least one unreacted portion back into the process feed.