(19)
(11)EP 0 323 138 A1

(12)EUROPEAN PATENT APPLICATION

(43)Date of publication:
05.07.1989 Bulletin 1989/27

(21)Application number: 88312181.6

(22)Date of filing:  22.12.1988
(51)International Patent Classification (IPC)4C07C 41/06, C07C 41/09, C07C 43/04
(84)Designated Contracting States:
BE DE FR GB IT NL SE

(30)Priority: 30.12.1987 US 139566

(71)Applicant: MOBIL OIL CORPORATION
New York New York 10017 (US)

(72)Inventors:
  • Huang, Tracy Jau-Hua
    Lawrenceville New Jersey 08648 (US)
  • Sorenson, Charles Mitchell, Jr.
    Wilmington Delaware 19810 (US)
  • Varghese, Philip
    Voorhees New Jersey 08043 (US)

(74)Representative: Colmer, Stephen Gary 
Mobil Services Company Limited, Office of Legal Counsel, European IP Group, Mobil Court, 3 Clements Inn
London WC2A 2EB
London WC2A 2EB (GB)


(56)References cited: : 
  
      


    (54)Process for the production of ethers


    (57) In a process for producing an ether, at least one light olefin is contacted with water and an alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst to provide an aqueous mixture of the alcohol and an ether, the olefin conversion unit being operated under conditions effective to provide the alcohol by the reaction of olefin and water and the ether by the dehydration of the alcohol and/or by the reaction of the olefin and the alcohol. The aqueous mixture of the alcohol and the ether is then introduced into a distillation unit which is operated under conditions effective to provide an azeotropic overheads fraction comprising the ether and minor amounts of the alcohol and water, and a bottoms fraction comprising aqueous alcohol. At least a portion of the bottoms fraction is recycled into the olefin conversion unit and, the azeotropic overheads fraction is introduced into an alcohol separation unit which is operated under conditions effective to provide an ether product containing at most negligible amounts of alcohol and water and an aqueous alcohol product.


    Description


    [0001] This invention relates to a process for the production of ether(s). More particularly, the invention relates to a process for the conversion of a light olefin such as ethylene, propylene, butenes, pentenes, hexenes, heptenes, etc., and their mixtures, in a conversion unit employing an acidic zeolite as olefin conversion catalyst to produce a mixture of alcohol(s) and ether(s) and thereafter recovering the ether(s) containing at most only small amounts of co-produced alcohol(s) and water.

    [0002] There is a need for an efficient catalytic process for manufacturing ethers from light olefins thereby augmenting the supply of high octane blending stocks for gasoline. Lower molecular weight ethers such as diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have a high blending octane number. In addition, by-product propylene from which DIPE can be made is usually available in a fuels refinery. The petrochemicals industry also produces mixtures of light olefin streams in the C₂ to C₇ molecular weight range and the conversion of such streams or fractions thereof to ethers can also provide products which are useful as solvents and as blending stocks for gasoline.

    [0003] The catalytic hydration of olefins to provide alcohols and ethers is a well-established art and is of significant commercial importance. Representative olefin hydration processes are disclosed in U.S. Patent Nos. 2,162,913; 2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,849 and 3,989,762.

    [0004] Olefin hydration employing zeolite catalysts is also known. As disclosed in U.S. Patent No. 4,214,107, lower olefins, in particular,propylene, can be catalytically hydrated over a crystalline aluminosilicate zeolite catalyst having a silica to alumina ratio of at least 12 and a Constraint Index of 1 to 12, e.g., HZSM-5, to provide the corresponding alcohol, essentially free of ether and hydrocarbon by-product.

    [0005] According to U.S. Patent No. 4,499,313, an olefin is hydrated to the corresponding alcohol in the presence of hydrogen-type mordenite or hydrogen-type zeolite Y, each having a silica-alumina molar ratio of 20 to 500. The use of such a catalyst is said to result in higher yields of alcohol than olefin hydration processes which employ conventional solid acid catalysts. Use of the zeolite catalyst is also said to offer the advantage over ion-exchange type olefin hydration catalysts of not being restricted by the hydration temperature.

    [0006] Reaction conditions employed in the process include a temperature of from 50-300°C, preferably 100-250°C, a pressure of 5 to 200 kg/cm² to maintain liquid phase or gas-liquid multi-phase conditions and a mole ratio of water to olefin of from 1 to 20. The reaction time can be 20 minutes to 20 hours when operating batchwise and the liquid hourly space velocity (LHSV) is usually 0.1 to 10 in the case of continuous operation.

    [0007] The reaction of light olefins with alcohols to provide ethers is also well known. According to U.S. Patent No. 4,042,633, DIPE is prepared from isopropyl alcohol (IPA) employing montmorillonite clay catalysts, optionally in the presence of added propylene. U.S. Patent No. 4,175,210 discloses the use of silicatungstic acid as catalyst for the reaction of olefin(s) with alcohol to provide ether(s). As disclosed in U.S. Patent No. 4,182,914, DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cation exchange resin as catalyst. In the process for producing a gasoline blending stock described in U.S. Patent No. 4,334,890, a mixed C₄ stream containing isobutylene is reacted with aqueous ethanol to form a mixture of ethyl tertiary butyl ether and tertiary butanol. U.S. Patent No. 4,418,219 describes the preparation of methyl tertiary-butyl ether (MTBE), a high octane blending agent for motor fuels, by reacting isobutylene and methanol in the presence of, as catalyst, boron phosphate, blue tungsten oxide or a crystalline aluminosilicate zeolite having a silica to alumina mole ratio of at least 12:1 and a Constraint Index of 1 to 12 as catalyst. U.S. Patent No. 4,605,787 discloses the preparation of alkyl tert-alkyl ethers such as MTBE and methyl tert-amyl ether (MTAE) by the reaction of a primary alcohol with an olefin having a double bond on a tertiary carbon atom employing as catalyst an acidic zeolite having a Constraint Index of 1 to 12, e.g., zeolite ZSM-5, 11, 12 and 23, dealuminized zeolite Y and rare earth-­exchanged zeolite Y. European Published Patent Application No. 55,045 describes a process for reacting an olefin and an alcohol to provide an ether, e.g., isobutene and methanol to provide MTBE, in the presence of an acidic zeolite catalyst such as zeolite Beta and zeolites ZSM-5, 8, 11, 12, 23, 35, 43 and 48.

    [0008] It is an object of the present invention to provide a process for converting low cost, readily available sources of light olefins to ether(s) which can be used as high octane blending stocks for gasoline.

    [0009] Accordingly, the invention resides in a process for producing an ether comprising:

    a) contacting at least one light olefin with water and an alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst to provide an aqueous mixture of an alcohol and an ether, the olefin conversion unit being operated under conditions effective to provide the alcohol by the reaction of the olefin and water and the ether by the dehydration of the alcohol and/or by the reaction of the olefin and the alcohol;

    b) introducing the aqueous mixture of the alcohol and the ether into a distillation unit which is operated under conditions effective to provide an azeotropic overheads fraction comprising the ether and minor amounts of the alcohol and water, and a bottoms fraction comprising the aqueous alcohol;

    c) recycling at least a portion of the bottoms fraction into the olefin conversion unit; and,

    d) introducing the azeotropic overheads fraction into an alcohol separation unit which is operated under conditions effective to provide an ether product containing at most negligible amounts of alcohol and water and an aqueous alcohol product.



    [0010] By recycling alcohol to the olefin conversion unit, it is possible to increase the overall conversion of olefin to predominantly ether. This capability for directing the hydration of feed olefin to a product which is predominantly ether can be of particular benefit where the product is employed as an octane boost for gasoline as it eliminates or minimizes the possibility of phase separation which can occur in the case of etheric mixtures containing substantial quantities of alcohol.

    [0011] The accompanying drawing is a schematic representation of a process according to one embodiment of the invention as applied to the production of DIPE.

    [0012] Referring to the drawing, the present invention is applicable to the conversion of individual light olefins and mixtures of olefins of various structure, preferably within the C₂₋₇ range, to ethers. Accordingly, the invention is applicable to the conversion of ethylene, propylene, butenes, pentenes, hexenes and heptenes, mixtures of these and other olefins such as gas plant off-gas containing ethylene and propylene, naphtha cracker off-gas containing light olefins, fluidized catalytic cracked (FCC) light gasoline containing pentenes, hexenes and heptenes, refinery FCC propane/propylene streams. For example, a typical FCC light olefin stream possesses the following composition:
    Typical Refinery FCC Light Olefin Composition
     Wt.%Mole%
    Ethane 3.3 5.1
    Ethylene 0.7 1.2
    Propane 14.5 15.3
    Propylene 42.5 46.8
    Isobutane 12.9 10.3
    n-Butane 3.3 2.6
    Butenes 22.1 18.3
    Pentanes 0.7 0.4
    The process of the invention is especially applicable to the conversion of propylene and propylene-containing streams to DIPE containing at most a minor amount of IPA.

    [0013] The conversion of the light olefin takes place in an olefin conversion unit 11 wherein several reactions occur simultaneously to provide a mixture of alcohol and ether. Thus, olefin will react with water fed to the unit 11 to produce alcohol, alcohol will react with olefin to produce ether and/or alcohol will undergo dehydration to produce ether.

    [0014] The foregoing olefin conversion reactions can be carried out under liquid phase, vapor phase or mixed vapor-liquid phase conditions in batch or in a continuous manner under stirred tank reactor or fixed bed flow reactor conditions, e.g., trickle-bed, liquid-up-flow, liquid-down-flow, counter- current flow and co-current flow.

    [0015] In general, the useful olefin conversion catalysts embrace two categories of zeolite, namely, the intermediate pore size variety as represented, for example, by ZSM-5, which possess a Constraint Index (see U.S. Patent No. 4016218) of greater than about 2 and the large pore variety as represented, for example, by zeolites Y and Beta, which possess a Constraint Index no greater than about 2. Both varieties of zeolites will possess a framework silica-to- alumina ratio of greater than 7, usually greater than 20. The zeolite will be in the acid form and as such, will possess an alpha value of at least 1, preferably at least 10 and more preferably at least 100. It will often be advantageous to provide the zeolite as a composite bound with a catalytically active or inactive material such as alumina or silica which is stable under the olefin conversion conditions employed.

    [0016] Of particular interest for use herein are the large pore acidic zeolites, e.g., zeolite Beta, X, L, Y, USY, REY, Deal Y, ZSM-3, ZSM-4, ZSM-l2, ZSM-20 and ZSM-50.

    [0017] The olefin hydration step can be effected under essentially any practical set of hydration conditions which provides alcohol(s) and ether(s) in appreciable amounts. However, good results can generally be obtained employing a temperature ranging from ambient (20°C) up to 300°C, preferably from 50 to 220°C and more preferably from 90 to 200°C, a total system pressure of at least about 500 kPa (5 atm), preferably at least 2000 kPa (20 atm) and more preferably at least 4000 kPa (40 atm), a water to total olefin mole ratio of 0.1 to 30, preferably 0.2 to 15 and most preferably 0.3 to 5, and an LHSV of 0.1 to 10. It is to be noted that low water:olefin mole ratios, namely 0.1 - 1 and preferably 0.2 - 0.8, employing zeolite Beta as the catalyst shifts olefin hydration products towards ether(s) and away from alcohol(s).

    [0018] The aqueous mixture of alcohol and ether produced in the olefin conversion unit 11, together with unconverted olefin, any inert gaseous material such as saturated hydrocarbon which may have been part of the olefin feed stream and the small quantities of oligomer which are typically present in the reaction effluent are then passed to a high pressure separator unit 12 which is operated below the temperature of the olefin conversion unit 11. Two liquid phases form in the high pressure separator unit 12, an aqueous phase which is recycled to the olefin conversion unit 11 and a hydrocarbon-rich phase which is flashed at lower pressure to effect separation of unconverted olefin together with any other gaseous material from the aqueous mixture of alcohol, ether and oligomer. The gaseous material is recycled to the olefin conversion unit 11 with part of it being vented off if necessary to avoid build-up of inert gaseous components in the system. The aqueous mixture of alcohol, ether and oligomer is then introduced into a distillation tower 13 which is preferably operated at or below atmospheric pressure to provide an azeotropic overheads fraction containing ether and minor amounts of alcohol, water and oligomer and a bottoms fraction containing water and a major part of the alcohol. Part or all of the bottoms fraction is recycled to the olefin conversion unit 11 and the azeotropic overheads fraction, following condensation, is introduced into an alcohol separation unit 14 which is operated under conditions effective to provide an ether-rich fraction containing oligomer, generally in an amount of less than about 10 weight percent, and little if any alcohol and water, e.g., less than about 3 weight percent, and preferably less than 2 weight percent, of these materials individually or in combination.

    [0019] In one embodiment of this process, as shown in the drawing, the alcohol separation unit 14 is provided as an extraction column with process feed water serving as the extraction medium. Due to the extraction of alcohol from the ether-rich phase, the solubility of water in said phase is reduced thus leading to further loss of water from the ether product. Following extraction of the condensed azeotropic overheads from the distillation tower, the aqueous alcohol-containing extractant is introduced into the olefin conversion unit.

    [0020] In another embodiment, the alcohol separation unit is provided as a decanter with the condensed azeotropic overheads from the distillation tower 13 separating into an ether-rich upper phase as previously described and an aqueous alcohol phase which is recycled to the olefin conversion unit 11.

    [0021] The following examples are illustrative of the process of the invention.

    EXAMPLES 1-4



    [0022] The zeolite olefin conversion catalyst employed in these examples is zeolite Beta (82.5 wt.%) extrudate bound with colloidal silica (17.5 wt.%). The extrudate was prepared by thoroughly mixing the zeolite and colloidal silica together with a sufficient amount of water to provide an extrudable mass in the absence of any added alkali metal base and/or basic salt. Extrusion of the mass into 1/16˝ (1.6mm) average diameter extrudate was followed by drying, calcining, ammonium-exchange and calcining in the conventional manner to provide an activated catalyst.

    [0023] The foregoing silica-bound zeolite Beta catalyst was employed in the conversion of propylene to a mixture of IPA and DIPE under the following fixed conditions: 166°C (330°F), 7000 kPa (1000 psig) total system pressure and 0.5 weight hourly velocity (WHSV) based on propylene. The amount of IPA recycle was varied from 0.0 to 0.8, the effect of recycle on DIPE production being shown in Table 1 below as follows:
    Table 1
    Effect of IPA Recycle on DIPE Production
    ExampleIPA WHSVPropylene Conversion, %DIPE Wt% Yield
    1 0.0 44 26
    2 0.04 35 21
    3 0.3 28 38
    4 0.8 23 36


    [0024] While propylene conversion decreases with additional alcohol recycle, as these data show, overall ether yield increases. Accordingly, it is generally advantageous to maintain a high rate of aqueous alcohol recycle from the various operations downstream from the olefin conversion unit.

    EXAMPLES 5-6



    [0025] These examples illustrate a vacuum distillation operation carried out under two different sets of conditions, and with the results, shown in Table 2 as follows:
    Table 2
    Vacuum Distillation Results
    ExamplePressure, torr (kPa)Boiling Pt, °F (°C)Condensed DIPEOverhead IPAComposition, WaterWt.% Oligomer
    - charge - 39.48 46.71 13.29 0.51
    5 760 (101) 140 (60) 88.71 8.54 1.22 1.53
    6 200 (27) 131 (55) 91.20 6.06 0.97 1.77


    [0026] These data show that both water and IPA content in the upper layer of the condensed overhead is reduced at lower distillation pressure, and a small amount of oligomer present in the charge is concentrated in the overhead.

    EXAMPLE 7



    [0027] A condensed azeotropic overheads composition containing 11 wt.% water, 38.4 wt.% IPA, 47.3 wt.% DIPE and 3.4% oligomer was subjected to 4 successive extractions with water, and with the results, shown in Table 3 below:
    Table 3
    Multi-stage Extraction With Water
    Weight Percent Composition
    StageWaterIPADIPEOligomerYield*
    Charge 11.0 38.4 47.3 3.4 100.0
    1 3.5 18.9 71.7 5.2 60.6
    2 1.1 5.1 87.3 6.5 49.4
    3 0.8 0.9 91.6 6.8 51.5
    4 0.7 0.2 92.1 6.9 52.5
    *Extraction yields are cumulative, volume recovered/volume charged.


    [0028] When process water is employed in the extraction of alcohol from the IPA/DIPE azeotrope, it is generally desirable to avoid the use of large volumes of water as this would lead to the creation of a dilute IPA recycle stream.

    [0029] It is within the scope of this invention to combine the foregoing aqueous extraction operation with co-extraction with other media, e.g., gasoline, which would provide a recycle stream rich in alcohol.

    EXAMPLE 8



    [0030] The conversion of propylene contained in a propylene/ propane refinery stream is illustrated in the process scheme shown in Fig. 1. The conditions of the propylene conversion are similar to those used in Examples 1-4. The results in moles/hr of feeds/products are set forth in Table 4 below as follows:
    Table 4
    DIPE Production
    Feed/Product StreamMoles/Hr
     1234567891011Wt%
    Propane 155.0 - 1503.0 - 305.3 155.0 - - - - - -
    Propylene 361.6 - 90.9 - 184.5 93.7 - - - - - -
    DIPE - - - 0.1 - - 122.4 122.4 - 0.1 122.3 90.1
    IPA - - - 101.0 - - 114.4 14.5 99.9 1.1 13.4 5.8
    Oligomer - - - - - - 4.9 4.9 - 4.9 4.9 3.0
    Water - 144.5 - 31.6 - - 40.3 40.3 - 31.6 8.7 1.1
                            100.0



    Claims

    1. A process for producing an ether comprising the steps of:

    a) contacting at least one light olefin with water and an alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst to provide an aqueous mixture of the alcohol and an ether, the olefin conversion unit being operated under conditions effective to provide the alcohol by the reaction of olefin and water and the ether by the dehydration of the alcohol and/or by the reaction of the olefin and the alcohol;

    b) introducing the aqueous mixture of the alcohol and the ether into a distillation unit which is operated under conditions effective to provide an azeotropic overheads fraction comprising the ether and minor amounts of the alcohol and water, and a bottoms fraction comprising aqueous alcohol;

    c) recycling at least a portion of the bottoms fraction into the olefin conversion unit; and,

    d) introducing the azeotropic overheads fraction into an alcohol separation unit which is operated under conditions effective to provide an ether product containing at most negligible amounts of alcohol and water and an aqueous alcohol product.


     
    2. The process of Claim 1 wherein the zeolite has a Constraint Index no greater than 2.
     
    3. The process of Claim 1 or Claim 2 wherein the zeolite is selected from zeolite Beta, X, L, Y, REY, Deal Y, ZSM-3, ZSM-4, ZSM-l2, ZSM-20 and ZSM-50.
     
    4. The process of any preceding Claim wherein the light olefin is at least one member of the group consisting of ethylene, propylene, butenes, pentenes, hexenes and heptenes.
     
    5. The process of any preceding Claim wherein the olefin conversion unit is maintained under conditions comprising a temperature of from ambient to 300°C, an overall system pressure of at least 500 kPa, a water to total olefin mole ratio of 0.1 to 30 and an LHSV of 0.1 to 10.
     
    6. The process of any preceding Claim wherein the zeolite is zeolite Beta and the water to total olefin mole ratio is less than about 1.
     
    7. The process of any preceding Claim wherein the effluent from the olefin conversion unit containing unconverted olefin is introduced into a separator unit operated under conditions which are effective to provide a hydrocarbon-containing fraction containing ether, a small amount of alcohol, water and unconverted olefin and an aqueous alcohol fraction, the hydrocarbon-containing fraction being flashed at reduced pressure to release unconverted olefin prior to introduction of the remaining components of said fraction into the distillation unit.
     
    8. The process of any preceding Claim wherein the alcohol separation unit is provided as an extraction apparatus employing water as the extraction agent.
     
    9. The process of Claim 8 wherein following extraction of the azeotropic overheads fraction, all or part of the recovered water containing alcohol is introduced to the olefin conversion unit.
     
    10. The process of any one of Claims 1 to 7 wherein the alcohol separation unit is provided as a decantation apparatus providing an upper ether-rich phase and a lower aqueous alcohol phase, and wherein all or part of said lower aqueous alcohol phase is recycled to the olefin conversion unit.
     




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