WO2008069982A2

WO2008069982A2 - Process for making dibutyl ethers from aqueous ethanol

Info

Publication number: WO2008069982A2
Application number: PCT/US2007/024666
Authority: WO
Inventors: Leo Ernest Manzer; Michael B. D'amore; Edward S. Miller
Original assignee: E. I. Du Pont De Nemours And Company
Priority date: 2006-12-01
Filing date: 2007-11-30
Publication date: 2008-06-12
Also published as: WO2008069982A3; EP2097364A2; CN101541722A; CA2668878A1; BRPI0717692A2; JP2010511619A

Abstract

The present invention relates to a process for making dibutyl ethers using aqueous ethanol optionally obtained from a fermentation broth. The dibutyl ethers made by this process find use as additives for fuels, including transportation fuels such as gasoline and diesel fuels.

Description

TITLE Process for Making Dibutyl Ethers from Aqueous Ethanol

FIELD OF THE INVENTION The present invention relates to a process for making dibutyl ethers from aqueous ethanol, optionally provided by fermentation.

BACKGROUND Dibutyl ethers are useful as diesel fuel cetane enhancers (R. Kotrba, "Ahead of the Curve", in Ethanol Producer Magazine, November 2005); an example of a diesel fuel formulation comprising dibutyl ether is disclosed in WO 2001018154. The production of dibutyl ethers from butanol is known (see Karas, L. and Piel, W. J. Ethers, in Kirk-Othmer Encyclopedia of Chemical Technology, Fifth Ed., Vol. 10, Section 5.3, p. 576) and is generally carried out via the dehydration of n-butyl alcohol by sulfuric acid, or by catalytic dehydration over ferric chloride, copper sulfate, silica, or silica-alumina at high temperatures. The dehydration of butanol to dibutyl ethers results in the formation of water, and thus these reactions have historically been carried out in the absence of water. Efforts directed at improving air quality and increasing energy production from renewable resources have resulted in renewed interest in alternative fuels, such as ethanol and butanol, that might replace gasoline and diesel fuel, or be additives in these fuels as well as others.

It is known that ethanol can be recovered from a number of sources, including synthetic and fermentation feedstocks. Synthetically, ethanol can be obtained by direct catalytic hydration of ethylene, indirect hydration of ethylene, conversion of synthesis gas, homologation of methanol, carbonylation of methanol and methyl acetate, and synthesis by both homogeneous and heterogeneous catalysis. Fermentation feedstocks can be fermentable carbohydrates (e.g., sugar cane, sugar beets, and fruit crops) and starch materials (e.g., grains including corn, cassava, and sorghum). When fermentation is used, yeasts from the species including Saccharomyces can be employed, as can bacteria from the species Zymomonas, particularly Zymomonas mobilis. Ethanol is generally recovered as an azeotrope with water, so that it is present at about 95 weight percent with respect to the weight of water and ethanol combined. See Kosaric, et. al, Ullmann's Encyclopedia of Industrial Chemistry, Sixth Edition, Volume 12, pages 398-473, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, and P. L. Rogers, et al., Adv. Biochem. Eng. 23 (1982) 27-84. The ethanol can be further dried by methods known in the art (see Kosaric, supra), including passing the ethanol-water azeotropic mixture over molecular sieves and azeotropic distillation of the ethanol-water mixture with an entraining agent, usually benzene.

Methods for producing 1-butanol from ethanol are known. It is known that 1-butanol can be prepared by condensation from ethanol over basic catalysts at high temperature using the so-called "Guerbet Reaction." See for example, J. Logsdon in Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley and Sons, Inc., New York, 2001.

Some references further describing the production of 1-butanol from ethanol include: Chinese Pat. No. CN 12168383C; C. Yang and Z. Meng, J. of Catalysis (1993), 142(1 ), 37-44; A. S. Ndou, N. Plint, and N. J. Coville, Applied Catalysis, A: General (2003), 251(2), 337-345; T. Takahashi, Kogyo Kagaku Zasshi (1946), 49 113-114; T. Takahashi, Kogyo Kagaku Zasshi (1946), 49 114-115; V. Nagarajan, N. R. Kuloor, Indian Journal of Technology (1966), 4(2), 46-54; V. Nagarajan, Chemical Processing & Engineering (Bombay) (1970), 4(11 ), 29-31 , 38; V. Nagarajan, Indian Journal of Technology (1971 ), 9(10), 380-386; V.

Nagarajan, Chemical Processing & Engineering (Bombay) (1971 ), 5(10), 23-27; K. W. Yang, X. Z. Jiang and W. C. Zhang, Chinese Chemical Letters (2004), 15(112), 1497-1500; K. Yang, W. Zhang, and X. Jiang, Chinese Patent No. 1528727 (assigned to Zhejiang Univ.); C. A. Radlowski and G. P. Hagen, U. S. Pat. No. 5,095,156 (assigned to Amoco Corp.); C. Y. Tsu and K. L. Yang, Huaxue (1958), (No. 1 ), 39-47; B. N. Dolgov and Yu. N. Volnov, Zhurnal Obshchei Khimii (1993), 3 313-318; M. J. L. Gines and E. Iglesia, J. of Catalysis (1998), 176(1 ), 155-172; T. Tsuchida, AK. Atsumi, S. Sakuma, and T. Inui, US Pat. No. 6,323,383 (assigned to Kabushiki Kaisha Sangi); and GB Pat. No. 381 ,185, assigned to British Industrial Solvents, Ltd.

SUMMARY OF THE INVENTION

The present invention relates to a process for making dibutyl ethers, comprising: a) contacting a reactant comprising wet ethanol with a base catalyst to make a first reaction product comprising 1-butanol and water; b) recovering from the first reaction product a partially-purified first reaction product consisting essentially of 1-butanol and at least 5 weight percent water based on the weight of the 1-butanol and water combined; and c) contacting the partially-purified first reaction product, optionally in the presence of a solvent, with at least one acid catalyst at a temperature of about 50 degrees C to about 450 degrees C and a pressure from about 0.1 MPa to about 20.7 MPa to produce a second reaction product comprising at least one butyl ether, and recovering said at least one butyl ether from said second reaction product to obtain at least one recovered butyl ether.

In a preferred embodiment, the reactant of step (a) above is obtained from an ethanol-containing fermentation broth by a process comprising distilling the fermentation broth to obtain a distillate that comprises ethanol and water, and optionally reducing the water in the distillate to achieve an ethanol concentration in the distillate of between about 50 and about 95 weight percent relative to the weight of the remaining water and ethanol combined.

In another preferred embodiment, the partially-purified first reaction product is obtained from the first reaction product by distillation. The dibutyl ethers thus formed by the processes of the present invention find use as additives for fuels, including transportation fuels such as gasoline, diesel and jet fuel. DETAILS

The present invention relates to a process for making dibutyl ethers from aqueous ethanol via aqueous butanol. As used herein, "aqueous butanol" refers to a product consisting essentially of 1 -butanol and at least about 5 weight percent water based on the weight of the 1 -butanol and water combined. The expression "consisting essentially of means herein that the 1 -butanol may include small amounts of other components as long as they do not affect substantially the performance of combined 1- butanol and water in subsequent process steps. The aqueous ethanol can be obtained from any convenient source, including fermentation using microbiological processes known to those skilled in the art. The fermentative microorganism and the source of the substrate are not critical for the purposes of this invention. The result of the fermentation is a fermentation broth, which is then refined to produce a stream of aqueous ethanol. The refining process may comprise at least one distillation column to produce a first overhead stream that comprises ethanol and water. If the first distillation column is insufficient to produce a first overhead stream with a desired ethanol content, then the first overhead stream can be introduced into a second distillation column to produce a second overhead stream, and so on, ultimately leading to the aqueous ethanol (having at least 5% water) required as the reactant in the present invention. These streams, which are vaporous, can be used directly in the current process, or can be condensed and revaporized for use at a later time. The stream of aqueous ethanol (which may be diluted with an inert gas such as nitrogen and carbon dioxide) is contacted with at least one base (or basic) catalyst in the vapor or liquid phase at a temperature of about 150 degrees C to about 500 degrees C and a pressure from about 0.1 MPa to about 20.7 MPa to produce a first reaction product comprising water and butanol. Typically, the first reaction product will also comprise unreacted ethanol, a variety of organic products, and water. The organic products include butanols, predominantly 1 -butanol. The at least one base catalyst can be a homogeneous or heterogeneous catalyst. Homogeneous catalysis is catalysis in which all reactants and the catalyst are molecularly dispersed in one phase. Homogeneous base catalysts include, but are not limited to, alkali metal hydroxides.

Heterogeneous catalysis refers to catalysis in which the catalyst constitutes a separate phase from the reactants and products. See, for example, Hattori, H. (Chem. Rev. (1995) 95:537-550) and Solid Acid and Base Catalysts (Tanabe, K., in Catalysis: Science and Technology, Anderson, J. and Boudart, M (eds.) 1981 Springer-Verlag, New York) for a description of solid catalysts and how to determine whether a particular catalyst is basic.

A suitable base catalyst useful in the current process is either a substance which has the ability to accept protons as defined by Brόnsted, or as a substance which has an unshared electron pair with which it can form a covalent bond with an atom, molecule or ion as defined by Lewis.

Examples of suitable base catalysts may include, but are not limited to, metal oxides, hydroxides, carbonates, silicates, phosphates, aluminates and combinations thereof. Preferred base catalysts may be metal oxides, carbonates, silicates, and phosphates. Preferred metals of the aforementioned compounds may be selected from Group 1 , Group 2, and rare earth elements of the Periodic Table. Particularly preferred metals may be cesium, rubidium, calcium, magnesium, lithium, barium, potassium and lanthanum. The base catalyst may be supported on a catalyst support, as is common in the art of catalysis. Suitable catalyst supports may include, but may not be limited to, alumina, titania, silica, zirconia, zeolites, carbon, clays, double-layered hydroxides, hydrotalcites and combinations thereof. Any method known in the art to prepare the supported catalyst can be used. One method for preparing supported catalysts is to dissolve a metal carboxylate salt in water. A support such as silica is wet with the solution, then calcined. This process converts the supported metal carboxylate to the metal oxide, carbonate, hydroxide or combination thereof. The support can be neutral, acidic or basic, as long as the surface of the catalyst/support combination is basic. Commonly used techniques for treatment of supports with metal catalysts can be found in B. C. Gates, Heterogeneous Catalysis, Vol. 2, pp. 1-29, Ed. B. L. Shapiro, Texas A & M University Press, College Station, TX, 1984.

The base catalysts of the present invention may further comprise catalyst additives and promoters that will enhance the efficiency of the catalyst. The relative percentage of the catalyst promoter may vary as desired. Promoters may be selected from the Group 8 metals of the Periodic Table, as well as copper and chromium.

The base catalysts of the invention can be obtained commercially, or can be prepared from suitable starting materials using methods known in the art. The catalysts employed for the current invention may be used in the form of powders, granules, or other particulate forms. Selection of an optimal average particle size for the catalyst will depend upon such process parameters as reactor residence time and desired reactor flow rates.

Examples of methods of using base catalysts to convert ethanol to butanol are discussed in the following references. M. N. Dvornikoff and M. W. Farrar, J. of Organic Chemistry (1957),

11 , 540-542, disclose the use of MgO-K₂CO₃-CuCrO₂ catalyst system to promote ethanol condensation to higher alcohols, including 1 -butanol. The disclosed liquid phase reaction using this catalyst showed a 13% conversion of ethanol and 47% selectivity to 1 -butanol. U.S. Pat. No. 5,300,695, assigned to Amoco Corp., discloses processes in which an alcohol having X carbon atoms is reacted over an L-type zeolite catalyst to produce a higher molecular weight alcohol. In some embodiments, a first alcohol having X carbon atoms is condensed with a second alcohol having Y carbon atoms to produce an alcohol having X+Y carbons. In one specific embodiment, ethanol is used to produce butanol using a potassium L-type zeolite.

J. I. DiCosimo, et al., in Journal of Catalysis (2000), 190(2), 261- 275, describe the effect of composition and surface properties on alcohol- coupling reactions using Mg_xAIO_x catalysts for alcohol reactions, including ethanol. Also condensation reactions on Mg_yAIO_x samples involved the formation of a carbanion intermediate on Lewis acid-strong Brόnsted base pair sites and yielded products containing a new C-C bond, such as n- C₄H₈O (or n-C₄H₉OH) and iso-C₄H₈O (or iso-C₄H₉OH). They also describe, in Journal of Catalysis (1998), 178(2), 499-510, that the oxidation to acetaldehyde and the aldol condensation to n-butanol both involve initial surface ethoxide formation on a Lewis acid-strong base pair. PCT Publ. No. WO 2006059729 (assigned to Kabushiki Kaisha Sangi) describes a clean process for efficiently producing, from ethanol as a raw material, higher molecular weight alcohols having an even number of carbon atoms, such as 1-butanol, hexanol and the like. The higher molecular weight alcohols are yielded from ethanol as a starting material with the aid of a calcium phosphate compound, e.g., hydroxyapatite Caio(PO₄)₆(OH)₂, tricalcium phosphate Ca₃(PO₄)₂, calcium monohydrogen phosphate CaHPO₄*(0-2)H₂O, calcium diphosphate Ca₂P₂O₇, octacalcium phosphate Ca₈H₂(PO₄)₆ ^χ5H₂O, tetracalcium phosphate Ca₄(PO₄)₂O, or amorphous calcium phosphate Ca₃(PO-O₂XnH₂O, preferably hydroxyapatite, as a catalyst, the contact time being 0.4 second or longer. The catalytic conversion of the wet ethanol to the first reaction product comprising 1-butanol and water can be run in either batch or continuous mode as described, for example, in H. Scott Fogler, (Elements of Chemical Reaction Engineering. 2^nd Edition, (1992) Prentice-Hall Inc, CA). Suitable reactors include fixed-bed, adiabatic, fluid-bed, transport bed, and moving bed. During the course of the reaction, the catalyst may become fouled, and therefore it may be necessary to regenerate the catalyst. Preferred methods of catalyst regeneration include, contacting the catalyst with a gas such as, but not limited to, air, steam, hydrogen, nitrogen or combinations thereof, at an elevated temperature. One skilled in the art will know that conditions, such as temperature, catalytic metal, support, reactor configuration and time can affect the reaction kinetics, product yield and product selectivity. Standard experimentation can be used to optimize the yield of 1-butanol from the reaction.

The first reaction product is then subjected to a suitable refining process to produce a partially-purified first reaction product consisting essentially of 1-butanol and at least 5 weight percent water based on the weight of the 1-butanol and water combined. An example of a suitable refining process may include phase separation (depending on the product mix) followed by distillation of the organic phase to recover the partially- purified first reaction product. In its first aspect, the present invention relates to a process for making at least one dibutyl ether comprising contacting the partially- purified first reaction product consisting essentially of 1-butanol and at least 5 weight percent water based on the weight of the 1-butanol and water combined with at least one acid catalyst to produce a second reaction product comprising at least one dibutyl ether, and recovering said at least one dibutyl ether from said second reaction product to obtain at least one recovered dibutyl ether. The "at least one dibutyl ether" comprises primarily di-n-butyl ether, however the dibutyl ether reaction product may comprise additional dibutyl ethers, wherein one or both butyl substituents of the ether are selected from the group consisting of 1 -butyl, 2-butyl, t-butyl and isobutyl.

The reaction to form at least one dibutyl ether is performed at a temperature of from about 50 degrees Celsius to about 450 degrees Celsius. In a more specific embodiment, the temperature is from about 100 degrees Celsius to about 250 degrees Celsius.

The reaction can be carried out under an inert atmosphere at a pressure of from about atmospheric pressure (about 0.1 MPa) to about 20.7 MPa. In a more specific embodiment, the pressure is from about 0.1 MPa to about 3.45 MPa. Suitable inert gases include nitrogen, argon and helium.

The reaction can be carried out in liquid or vapor phase and can be run in either batch or continuous mode as described, for example, in H. Scott Fogler, (Elements of Chemical Reaction Engineering, 2^nd Edition, (1992) Prentice-Hall Inc, CA).

The at least one acid catalyst can be a homogeneous or heterogeneous catalyst. Homogeneous catalysis is catalysis in which all reactants and the catalyst are molecularly dispersed in one phase. Homogeneous acid catalysts include, but are not limited to inorganic acids, organic sulfonic acids, heteropolyacids, fluoroalkyl sulfonic acids, metal sulfonates, metal trifluoroacetates, compounds thereof and combinations thereof. Examples of homogeneous acid catalysts include sulfuric acid, fluorosulfonic acid, phosphoric acid, p-toluenesulfonic acid, benzenesulfonic acid, hydrogen fluoride, phosphotungstic acid, phosphomolybdic acid, and trifluoromethanesulfonic acid.

Heterogeneous catalysis refers to catalysis in which the catalyst constitutes a separate phase from the reactants and products. Heterogeneous acid catalysts include, but are not limited to 1 ) heterogeneous heteropolyacids (HPAs), 2) natural clay minerals, such as those containing alumina or silica, 3) cation exchange resins, 4) metal oxides, 5) mixed metal oxides, 6) metal salts such as metal sulfides, metal sulfates, metal sulfonates, metal nitrates, metal phosphates, metal phosphonates, metal molybdates, metal tungstates, metal borates, and 7) zeolites, 8) combinations of groups 1 - 7. See, for example, Solid Acid and Base Catalysts, pages 231-273 (Tanabe, K., in Catalysis: Science and Technology, Anderson, J. and Boudart, M (eds.) 1981 Springer- Verlag, New York) for a description of solid catalysts. The heterogeneous acid catalyst may also be supported on a catalyst support. A support is a material on which the acid catalyst is dispersed. Catalyst supports are well known in the art and are described, for example, in Satterfield, C. N. (Heterogeneous Catalysis in Industrial Practice, 2^nd Edition, Chapter 4 (1991 ) McGraw-Hill, New York). One skilled in the art will know that conditions, such as temperature, catalytic metal, support, reactor configuration and time can affect the reaction kinetics, product yield and product selectivity. Depending on the reaction conditions, such as the particular catalyst used, products other than dibutyl ethers may be produced when 1-butanol is contacted with an acid catalyst. Additional products comprise butenes and isooctenes. Standard experimentation, performed as described in the Examples herein, can be used to optimize the yield of dibutyl ether from the reaction.

The present invention also includes a process whereby the first reaction product comprising 1-butanol and water is subjected to distillation, so that a partially-purified first reaction product consisting essentially of 1- butanol and at least 5 weight percent water based on the weight of the 1- butanol and water combined forms a distillate, which can be in vapor form. When this vapor is condensed, it produces a butanol-rich liquid phase having a water concentration of at least about about 18% by weight relative to the weight of the water plus 1-butanol, and a water-rich liquid phase. These phases can then be separated so that the butanol-rich phase can be subjected to the process described herein, namely being contacted, optionally in the presence of a solvent, with at least one acid catalyst at a temperature of about 50 degrees C to about 450 degrees C and a pressure from about 0.1 MPa to about 20.7 MPa to produce a second reaction product comprising at least one butyl ether, and recovering said at least one butyl ether from said second reaction product to obtain at least one recovered butyl ether.

Following the reaction, if necessary, the catalyst can be separated from the reaction product by any suitable technique known to those skilled in the art, such as decantation, filtration, extraction or membrane separation (see Perry, R. H. and Green, D.W. (eds), Perry's Chemical Engineer's Handbook, 7^th Edition, Section 13, 1997, McGraw-Hill, New York, Sections 18 and 22).

The at least one dibutyl ether can be recovered from the reaction product by distillation as described in Seader, J. D., et al (Distillation, in Perry, R. H. and Green, D.W. (eds), Perry's Chemical Engineer's Handbook, 7^th Edition, Section 13, 1997, McGraw-Hill, New York). Alternatively, the at least one dibutyl ether can be recovered by phase separation, or extraction with a suitable solvent, such as trimethylpentane or octane, as is well known in the art. Unreacted 1-butanol can be recovered following separation of the at least one dibutyl ether and used in subsequent reactions. The at least one recovered dibutyl ether can be added to a transportation fuel as a fuel additive. EXAMPLES

GENERAL METHODS AND MATERIALS

In the following examples, "C" is degrees Celsius, "mg" is milligram;

"ml" is milliliter; "temp" is temperature; "MPa" is mega Pascal; "GC/MS" is gas chromatography/mass spectrometry, Amberlyst® (manufactured by Rohm and Haas, Philadelphia, PA), tungstic acid, 1-butanol and H₂SO₄ were obtained from Alfa Aesar (Ward

Hill, MA); CBV-3020E was obtained from PQ Corporation (Berwyn, PA);

Sulfated Zirconia was obtained from Engelhard Corporation (Iselin, NJ);

13% Nafion®/Siθ₂ can be obtained from Engelhard; and H-Mordenite can be obtained from Zeolyst Intl. (Valley Forge, PA).

General Procedure for the Conversion of 1-Butanol to Dibutyl Ethers

A mixture of 1-butanol, water, and catalyst was contained in a 2 ml vial equipped with a magnetic stir bar. The vial was sealed with a serum cap perforated with a needle to facilitate gas exchange. The vial was placed in a block heater enclosed in a pressure vessel. The vessel was purged with nitrogen and the pressure was set at 6.9 MPa. The block was brought to the indicated temperature and controlled at that temperature for the time indicated. After cooling and venting, the contents of the vial were analyzed by GC/MS using a capillary column (either (a) CP-Wax 58 [Varian; Palo Alto, CA], 25 m X 0.25 mm, 45 C/6 min, 10 C/min up to 200 C, 200 C/10 min, or (b) DB-1701 [J&W (available through Agilent; Palo Alto, CA)], 3O m X 0.2 5 mm, 50 C /10 min, 10 C/min up to 250 C, 250 C/2 min). The examples below were performed according to this procedure under the conditions indicated for each example. EXAMPLES 1-10

Reaction of 1-butanol (1 -BuOH) with an acid catalyst to produce dibutyl ethers

The reactions were carried out for 2 hours at 6.9 MPa of N₂. The feedstock was 80% 1 -butanol/20% water (by weight).

As those skilled in the art of catalysis know, when working with any catalyst, the reaction conditions need to be optimized. Examples 1 to 10 show that the indicated catalysts were capable under the indicated conditions of producing the product dibutyl ethers. Some of the catalysts shown in Examples 1 to 10 were ineffective when utilized at suboptimal conditions (data not shown).

Claims

CLAIMS What is claimed is:

1. A process for making butyl ethers, comprising: a) contacting a reactant comprising wet ethanol with a base catalyst to make a first reaction product comprising 1-butanol and water; b) recovering from the first reaction product a partially-purified first reaction product consisting essentially of 1-butanol and at least 5 weight percent water based on the weight of the 1-butanol and water combined; c) contacting the partially-purified first reaction product, optionally in the presence of a solvent, with at least one acid catalyst at a temperature of about 50 degrees C to about 450 degrees C and a pressure from about 0.1 MPa to about 20.7 MPa to produce a second reaction product comprising at least one butyl ether, and recovering said at least one butyl ether from said second reaction product to obtain at least one recovered butyl ether.

2. The process of Claim 1 , wherein the reactant of step a) is obtained from an ethanol-containing fermentation broth by a process comprising distilling the fermentation broth to obtain a distillate that comprises ethanol and water, and optionally reducing the water in the distillate to achieve an ethanol concentration in the distillate of between about 50 and about 95 weight percent relative to the weight of the remaining water and ethanol combined.

3. The process of Claim 2, wherein said partially-purified first reaction product is recovered from the first reaction product by distillation.

4. The process of Claim 3, wherein said distillate is a vapor.