Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
io 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.
3o 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.
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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.
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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.
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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,
io 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 Bronsted,
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
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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
lo 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
is 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.
20 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.
25 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
3o 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-
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coupling reactions using MgYAIOX catalysts for alcohol reactions, including
ethanol. Also condensation reactions on MgyAIO,, samples involved the
formation of a carbanion intermediate on Lewis acid-strong Bronsted base
pair sites and yielded products containing a new C-C bond, such as n-
C4H8O (or n-C4H9OH) and iso-C4Ha0 (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
lo 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
i5 Ca1o(PO4)6(OH)2, tricalcium phosphate Ca3(PO4)2, calcium monohydrogen
phosphate CaHPO4X(0-2)H20, calcium diphosphate Ca2P2O7, octacalcium
phosphate Ca$H2(PO4)6x5H2O, tetracalcium phosphate Ca4(PO4)20, or
amorphous calcium phosphate Ca3(PO4)2XnH2O, preferably
hydroxyapatite, as a catalyst, the contact time being 0.4 second or longer.
20 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"d Edition, (1992) Prentice-Hall Inc,
CA). Suitable reactors include fixed-bed, adiabatic, fluid-bed, transport
25 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.
30 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
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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.
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Scott Fogier, (Elements of Chemical Reaction Engineering, 2"d 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
io 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"d 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,
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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, 7th 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, 7th 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
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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 /Si02 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)], 30 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.
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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).
Example Catalyst (50 mg) Temp 1-BuOH Dibutyl Ethers
Number (C) % Conversion % Selectivity
1 HZSO4 200 69.6 45.0
2 Amberlyst 15 200 26.0 68.4
3 13% Nafion /Si02 200 8.2 67.0
4 CBV-3020E 200 41.8 51.5
5 H-Mordenite 200 28.0 44.7
6 Tungstic Acid 200 3.1 22.9
7 Sulfated Zirconia 200 2.5 7.7
8 H2SO4 120 4.3 12.9
9 CBV-3020E 120 0.3 27.1
H-Mordenite 120 0.5 6.0
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
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).
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