Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR MAKING ETHANOL FROM ACETIC ACID
USING ACIDIC CATALYSTS
PRIORITY CLAIM
[00011 This application claims priority to the following applications: (1)
U.S. App. No.
12/588,727, filed October 26, 2009; (2) U.S. App. No. 12/698,947, filed
February 2, 2010; (3)
U.S. App. No. 12/699,024, filed February 2, 2010; (4) U.S. Provisional App.
No. 61/300,815,
filed February 2, 2010; (5) U.S. Provisional App. No. 61/332,696, filed May 7,
2010; (6) U.S.
Provisional App. No. 61/332,699, filed May 7, 2010; (7) U.S. App. No.
12/852,269, filed August
6, 2010; and (8) U.S. App. No. 12/852,227, filed August 6, 2010. U.S. App. No.
12/588,727,
filed October 26, 2009 is a continuation-in-part of U.S. App. No. 12/221,141,
filed July 31, 2008.
The entireties of these applications are incorporated herein by reference.
FIELD OF THE INVENTION
[00021 The present invention relates generally to processes for producing
ethanol and, in
particular, to processes for producing ethanol from the hydrogenation of
acetic acid using acidic
catalysts.
BACKGROUND OF THE INVENTION
[00031 Ethanol for industrial use is conventionally produced from
petrochemical feed stocks,
such as oil, natural gas, or coal, from feed stock intermediates, such as
syngas, or from starchy
materials or cellulose materials, such as corn or sugar cane. Conventional
methods for producing
ethanol from petrochemical feed stocks, as well as from cellulose materials,
include the acid-
catalyzed hydration of ethylene, methanol homologation, direct alcohol
synthesis, and Fischer-
Tropsch synthesis. Instability in petrochemical feed stock prices contributes
to fluctuations in
the cost of conventionally produced ethanol, making the need for alternative
sources of ethanol
production all the greater when feed stock prices rise. Starchy materials, as
well as cellulose
material, are converted to ethanol by fermentation. However, fermentation is
typically used for
consumer production of ethanol for fuels or consumption. In addition,
fermentation of starchy or
cellulose materials competes with food sources and places restraints on the
amount of ethanol
that can be produced for industrial use.
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[0004] Ethanol production via the reduction of alkanoic acids and/or other
carbonyl group-
containing compounds has been widely studied, and a variety of combinations of
catalysts,
supports, and operating conditions have been mentioned in the literature.
During the reduction
of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol
or are formed in side
reactions. These impurities and byproducts limit the production and recovery
of ethanol from
such reaction mixtures. For example, during hydrogenation, esters are produced
that together
with ethanol and/or water, form azeotropes, which are difficult to separate.
In addition, when
conversion is incomplete, unreacted acid remains in the crude ethanol product,
which must be
removed to recover ethanol.
[0005] Thus, the need remains for improved processes for producing ethanol via
alkanoic acid
reduction, which yield crude ethanol products containing fewer impurities and
byproducts.
SUMMARY OF THE INVENTION
[0006] In a first embodiment, the present invention is directed to a process
for producing
ethanol, comprising hydrogenating acetic acid in the presence of a catalyst to
form ethanol,
wherein the hydrogenation has a selectivity to ethanol of at least 65% wherein
the catalyst
comprises a first metal on an acidic support selected from the group
consisting of (i) an acidic
support material selected from the group consisting of iron oxide, alumina,
silica/aluminas,
titania, zirconia, and mixtures thereof, and (ii) a support material modified
with an acidic
modifier.
[0007] In a second embodiment, the present invention is directed to a process
for producing
ethanol, comprising hydrogenating acetic acid in the presence of a first
catalyst to form an
intermediate product comprising ethanol and unreacted acetic acid; and
hydrogenating the
unreacted acetic acid in the present of a second catalyst to form ethanol. The
first catalyst
comprising a catalyst comprising one or more metals, a silicaceous support,
and at least one
basic support modifier. The second catalyst comprises a first metal on an
acidic support selected
from the group consisting of (i) an acidic support material selected from the
group consisting of
iron oxide, alumina, silica/aluminas, titania, zirconia, and mixtures thereof,
and (ii) a support
material modified with an acidic modifier.
[0008] In a third embodiment, the present invention is directed to a process
for producing
ethanol, comprising hydrogenating acetic acid in the presence of a first
catalyst and a second
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catalyst in a reactor to form ethanol. The first catalyst may be in a first
reactor region and the
second catalyst may be in a second reactor region, that is separated from the
first reactor region.
The first catalyst comprising a catalyst comprising one or more metals, a
silicaceous support, and
at least one basic support modifier. The second catalyst comprises a first
metal on an acidic
support selected from the group consisting of. (i) an acidic support material
selected from the
group consisting of iron oxide, alumina, silica/aluminas, titania, zirconia,
and mixtures thereof,
and (ii) a support material modified with an acidic modifier.
[0009] In a fourth embodiment, the present invention is directed to a process
for recovering
ethanol, comprising hydrogenating an acetic acid feed stream in a reactor
comprising a catalyst
to form a crude ethanol product. The catalyst comprises a first metal on an
acidic support
selected from the group consisting of (i) an acidic support material selected
from the group
consisting of iron oxide, alumina, silica/aluminas, titania, zirconia, and
mixtures thereof, and (ii)
a support material modified with an acidic modifier. The process further
comprises separating at
least a portion of the crude ethanol product in a first column into a first
distillate comprising
ethanol, water and ethyl acetate, and a first residue comprising acetic acid;
separating at least a
portion of the first distillate in a second column into a second distillate
comprising ethyl acetate
and a second residue comprising ethanol and water; returning at least a
portion of the second
distillate to the reactor; and separating at least a portion of the second
residue in a third column
into a third distillate comprising ethanol and a third residue comprising
water.
[0010] The acidic modifier used in embodiments of the present invention
preferably is selected
from the group consisting of oxides of Group IVB metals, oxides of Group VB
metals, oxides of
Group VIB metals, oxides of Group VIIB metals, oxides of Group VIIIB metals,
aluminum
oxides, and mixtures thereof.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The invention is described in detail below with reference to the
appended drawings,
wherein like numerals designate similar parts.
[0012] FIG. 1 is a schematic diagram of a hydrogenation system in accordance
with one
embodiment of the present invention.
[0013] FIG. 2A is a schematic diagram of a reaction zone having dual reactors
in accordance
with one embodiment of the present invention.
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[0014] FIG. 2B is a schematic diagram of a reaction zone having a reactor with
two reactor
regions in accordance with another embodiment of the present invention.
[0015] FIG. 3 is a graph of acetic acid conversion in accordance with an
example of the present
invention.
[0016] FIG. 4 is a graph of acetic acid conversion of different catalysts in
accordance with an
example of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention relates to processes for producing ethanol and to
processes for
recovering ethanol from a crude ethanol product. The crude acetic acid
product, in one
embodiment, is produced by a hydrogenation process comprising hydrogenating
acetic acid in
the presence of an acidic catalyst. In one embodiment, the acidic catalyst
comprises a first metal
on an acidic support. In one embodiment, the acidic catalyst comprises a first
metal on an
support and an acidic support modifier.
[0018] During hydrogenation of acetic acid, there are other side reactions
that produce
impurities and byproducts. One principal side reaction is an equilibrium
reaction between acetic
acid/ethanol and ethyl acetate/water also occurs. The two main reactions are:
HOAc + 2 H2 EtOH + H2O Reaction 1
HOAc + EtOH - EtOAc + H2O Reaction 2
[0019] Reaction 2 is reversible and the equilibrium constant, Keq is given by
Equation 1:
k2 [EtOAcIH2O]
Kea k-2 [HOAcIEtOH] Equation 1
[0020] Generally, to produce ethanol the reaction conditions favor the first
reaction over the
second reaction, which consumes ethanol and increases the ethyl acetate
byproducts in the crude
ethanol product. In U.S. Pub. No. 2010/0197985, the entirety of which is
incorporated herein by
reference, the first reaction is favored and is promoted by the use of a
catalyst comprising a basic
modifier.
[0021] In some embodiments, the present invention uses an acidic catalyst,
which preferably
comprises a first metal on an acidic support. Without being bound by theory,
it is believed that
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the second reaction is promoted in the presence of acid. Also in the vapor
phase, Keq is believed
to decrease at higher temperatures. In embodiments of the present invention,
Keq may be less
than 20, e.g., less than 15 or less than 12. Preferably, Keq may be less than
6, e.g., less than 4 or
less than 3. As such, the acidic catalyst increases forward and reverse
reaction rates for the
equilibrium reaction. In embodiments where Keq > 1, and under reaction
conditions that favor
high conversions of acetic acid, the selectivity to ethanol is surprisingly
and unexpectedly high.
The productivity of ethanol also increases at high conversions. Increasing
conversion and
selectivity to ethanol advantageously reduce the amount of byproducts in the
crude ethanol
product and, as a result, may improve the efficiency of recovering ethanol.
[0022] For purposes of the present invention, the term "conversion" refers to
the amount of
acetic acid in the feed that is converted to a compound other than acetic
acid. Conversion is
expressed as a mole percentage based on acetic acid in the feed. Selectivity
is expressed as a
mole percent based on converted acetic acid. It should be understood that each
compound
converted from acetic acid has an independent selectivity and that selectivity
is independent from
conversion. For example, if 50 mole % of the converted acetic acid is
converted to ethanol, the
ethanol selectivity is 50%.
[0023] At low conversion of acetic acid, e.g. less than about 50%, an acidic
catalyst tends to
show increased selectivity to ethyl acetate over ethanol. Thus, in some
embodiments of the
present invention, to produce ethanol, the conversion of acetic acid is
preferably greater than
70%, e.g., greater than 80%, greater than 90% or greater than 95%.
[0024] In the inventive processes, the selectivity to ethanol is preferably at
least 65%, e.g., at
least 70%, at least 80%, at least 85%, or at least 90%. At lower conversions
of acetic acid,
around 70%, the selectivity to ethanol may be approximately 30% to 40%.
Preferably, as the
acetic acid conversion increases the selectivity to the ethanol also
increases. In addition, the
selectivity to ethyl acetate may be low, e.g., less than 35%, less than 30%,
less than 10%, or less
than 5%. Preferably, the hydrogenation process also have low selectivity to
undesirable
products, such as methane, ethane, and carbon dioxide. The selectivity to
these undesirable
products preferably is less than 4%, e.g., less than 2% or less than 1%. More
preferably, these
undesirable products are not readily detectable in the crude ethanol product.
Formation of
alkanes may be low. Ideally less than 2% of the acetic acid passed over the
catalyst is converted
to alkanes, e.g., less than 1%, or less than 0.5%.
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[0025] Embodiments of the present invention provide for increased productivity
of ethanol at
high conversions of acetic acid. When acetic acid conversion is preferably
greater than 90%, the
selectivity to ethanol preferably is at least 70%. Selectivity may continue to
increase as
conversion of acetic acid increases.
[0026] The term "productivity," as used herein, refers to the grams of a
specified product, e.g.,
ethanol, formed during the hydrogenation per kilogram of catalyst used per
hour. A productivity
of at least 200 grams of ethanol per kilogram catalyst per hour is preferred,
e.g., at least 400 or at
least 600. In terms of ranges, the productivity preferably is from 200 to
3,000 grams of ethanol
per kilogram catalyst per hour, e.g., from 400 to 2,500 or from 600 to 2,000.
[0027] Embodiments of the present invention provide for increase productivity
at high
conversion of acetic acid. At 70% or greater acetic acid conversion the
productivity of ethanol is
at least 350 grams of ethanol per kilogram catalyst per hour. Productivity may
continue to
increase as conversion of acetic acid increases.
[0028] The hydrogenation of acetic acid to form ethanol and water is conducted
in the present
of an acidic catalyst. In one embodiment, hydrogenation catalysts comprises a
first metal on an
acidic support and optionally one or more of a second metal, a third metal or
additional metals.
The first and optional second and third metals may be selected from Group IB,
IIB, II1B, IVB,
VB, VIB, VIIB, VIII transitional metals, a lanthanide metal, an actinide metal
or a metal selected
from any of Groups IIIA, IVA, VA, and VIA. Preferred metal combinations for
some exemplary
catalyst compositions include platinum/tin, platinum/ruthenium,
platinum/rhenium,
palladium/ruthenium, palladium/rhenium, cobalt/palladium, cobalt/platinum,
cobalt/chromium,
cobalt/ruthenium, silver/palladium, copper/palladium, nickel/palladium,
gold/palladium,
ruthenium/rhenium, and ruthenium/iron. Exemplary catalysts are further
described in U.S.
Patent No. 7,608,744 and U.S. Pub. Nos. 2010/0029995 and 2010/0197985, the
entireties of
which are incorporated herein by reference.
[00291 In one exemplary embodiment, the catalyst comprises a first metal
selected from the
group consisting of copper, iron, cobalt, nickel, ruthenium, rhodium,
palladium, osmium,
iridium, platinum, titanium, zinc, chromium, rhenium, molybdenum, and
tungsten. Preferably,
the first metal is selected from the group consisting of platinum, palladium,
cobalt, nickel, and
ruthenium. More preferably, the first metal is selected from platinum and
palladium. When the
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first metal comprises platinum, it is preferred that the catalyst comprises
platinum in an amount
less than 5 wt.%, e.g., less than 3 wt.% or less than 1 wt.%, due to the high
demand for platinum.
[0030] As indicated above, the catalyst optionally further comprises a second
metal, which
typically would function as a promoter. If present, the second metal
preferably is selected from
the group consisting of copper, molybdenum, tin, chromium, iron, cobalt,
vanadium, tungsten,
palladium, platinum, lanthanum, cerium, manganese, ruthenium, rhenium, gold,
and nickel.
More preferably, the second metal is selected from the group consisting of
copper, tin, cobalt,
rhenium, and nickel. More preferably, the second metal is selected from tin
and rhenium.
[0031] If the catalyst includes two or more metals, e.g., a first metal and a
second metal, the
first metal optionally is present in the catalyst in an amount from 0.1 to 10
wt.%, e.g., from 0.1 to
wt.%, or from 0.1 to 3 wt.%. The second metal preferably is present in an
amount from 0.1
and 20 wt.%, e.g., from 0.1 to 10 wt.%, or from 0.1 to 5 wt.%. In one
embodiment, the metal
loading of the acidic catalyst may be reduced. This may advantageously
decrease the costs
associated with catalyst having higher metal loadings. Thus, in embodiments
having reduced
metal loadings, the first metal may be present in amounts from 0.1 to 1.7 wt.%
and the second
metal may be present in amounts from 0.1 to 1.3 wt.%. For catalysts comprising
two or more
metals, the two or more metals may be alloyed with one another or may comprise
a non-alloyed
metal solution or mixture.
[0032] The preferred metal ratios may vary depending on the metals used in the
catalyst. In
some exemplary embodiments, the mole ratio of the first metal to the second
metal is from 10:1
to 1:10, e.g., from 4:1 to 1:4, from 2:1 to 1:2, from 1.5:1 to 1: 1.5 or from
1.1:1 to 1:1.1. In one
embodiment, to favor selectivity to ethanol where the catalyst comprises
platinum and tin, the
Pt/Sn molar ratio preferably is from 0.4:0.6 to 0.6:0.4, e.g., from 0.45:0.55
to 0.55:0.45 or about
1:1. In another embodiment, to favor selectivity to ethanol in embodiments
where the catalyst
comprises rhenium and palladium, the Re/Pd molar ratio preferably is from
0.6:0.4 to 0.85:0.15,
e.g., from 0.7:0.3 to 0.85:0.15, or a molar ratio of about 0.75:0.25.
[0033] The catalyst may also comprise a third metal selected from any of the
metals listed
above in connection with the first or second metal, so long as the third metal
is different from the
first and second metals. In preferred aspects, the third metal is selected
from the group
consisting of cobalt, palladium, ruthenium, copper, zinc, platinum, tin, and
rhenium. More
preferably, the third metal is selected from cobalt, palladium, and ruthenium.
When present, the
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total weight of the third metal preferably is from 0.05 and 4 wt.%, e.g., from
0.1 to 3 wt.%, or
from 0.1 to 2 wt.%.
[0034] In addition to the one or more metals, the inventive acidic catalysts,
in some
embodiments, further comprise an acidic support material or modified support
material. A
modified support material comprises a support material and an acidic support
modifier. An
acidic support modified adjusts the acidity of the support material. The total
weight of the
support material or modified support material, based on the total weight of
the catalyst,
preferably is from 75 wt.% to 99.9 wt.%, e.g., from 78 wt.% to 97 wt.%, or
from 80 wt.% to 95
wt.%. In embodiments that use a modified support material, the catalyst may
comprise the
support modifier in an amount from 0.1 wt.% to 50 wt.%, e.g., from 0.2 wt.% to
25 wt.%, from
0.5 wt.% to 15 wt.%, or from 1 wt.% to 8 wt.%, based on the total weight of
the catalyst.
[0035] Suitable support materials may include, for example, stable metal oxide-
based supports
or ceramic-based supports. Preferred support materials include are selected
from the group
consisting of silica, silica/alumina, calcium metasilicate, pyrogenic silica,
high purity silica,
carbon, iron oxide, alumina, silica/aluminas, titania, zirconia, and mixtures
thereof. In one
preferred embodiment, an acidic support material may be used for the catalyst.
Acidic support
materials are selected from the group consisting of iron oxide, alumina,
silica/aluminas, titania,
zirconia, and mixtures thereof.
[0036] In the production of ethanol, the catalyst support material may be
modified with a
support modifier. Preferably, the catalyst support material that are basic or
neutral, such as
silica, metasilicate, pyrogenic silica, high purity silica, carbon, or
mixtures thereof are modified
with an acidic support modifier. Acidic support materials may also be modified
with an acidic
support modifier. In some embodiments, the acidic support modifier adjusts the
support material
by increasing the number or availability of acid sites. The acidic sites
promote the kinetic rate of
the esterification equilibrium. Preferably, the support modifier is an acidic
modifier that has a
low volatility or no volatility. Suitable acidic support modifiers may be
selected from the group
consisting of: oxides of Group IVB metals, oxides of Group VB metals, oxides
of Group VIB
metals, oxides of Group VIIB metals, oxides of Group VIIIB metals, aluminum
oxides, and
mixtures thereof. Acidic support modifiers include those selected from the
group consisting of
Ti02, Zr02, Nb205, Ta2O5, A1203, B203, P205, and Sb203. Preferred acidic
support modifiers
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include those selected from the group consisting of Ti02, Zr02, Nb205, Ta2O5,
and A1203. The
acidic modifier may also include W03, MoO3, Fe203, Cr203, V205, Mn02, CuO,
Co203, Bi203.
[0037] In one preferred aspect of the present invention, the acidic catalyst
comprises:
(i) a first metal comprising a Group VIII metal,
(ii) a second metal comprising copper, molybdenum, tin, chromium, iron,
cobalt,
vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese,
ruthenium, rhenium,
gold, and nickel, and
(iii) an acidic support that comprises an acidic support material selected
from the group
consisting of iron oxide, alumina, silica/aluminas, titania, zirconia, and
mixtures thereof.
[0038] The acidic support may further comprise an acidic support modifier.
[0039] In another preferred aspect of the present invention, the acidic
catalyst comprises:
(i) a first metal comprising a Group VIII metal,
(ii) a second metal comprising copper, molybdenum, tin, chromium, iron,
cobalt,
vanadium, tungsten, palladium, platinum, lanthanum, cerium, manganese,
ruthenium, rhenium,
gold, and nickel, and
(iii) an acidic support that comprises a support material and an acidic
support modifier.
[0040] A preferred silica support material is SS61138 High Surface Area (HSA)
Silica Catalyst
Carrier from Saint-Gobain NorPro. The Saint-Gobain NorPro SS61138 silica
contains
approximately 95 wt.% high surface area silica; a surface area of about 250
m2/g; a median pore
diameter of about 12 nm; an average pore volume of about 1.0 cm3/g as measured
by mercury
intrusion porosimetry and a packing density of about 0.352 g/cm3 (22 lb/ft).
[0041] A preferred silica/alumina support material is KA-160 (Sud Chemie)
silica spheres
having a nominal diameter of about 5 mm, a density of about 0.562 g/ml, in
absorptivity of about
0.583 g H20/g support, a surface area of about 160 to 175 m2/g, and a pore
volume of about 0.68
ml/g.
[0042] As will be appreciated by those of ordinary skill in the art, support
materials are
selected such that the catalyst system is suitably active, selective and
robust under the process
conditions employed for the formation of ethanol.
[0043] The metals of the catalysts may be dispersed throughout the support,
coated on the
outer surface of the support (egg shell) or decorated on the surface of the
support.
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[0044] The catalyst compositions suitable for use with the present invention
preferably are
formed through metal impregnation of the modified support, although other
processes such as
chemical vapor deposition may also be employed. Such impregnation techniques
are described
in U.S. Patent No. 7,608,744, U.S. Pub. Nos. 2010/0029995, and 2010/0197985,
the entireties of
which are incorporated herein by reference.
[0045] Embodiments of the invention may include a variety of reactor
configurations using a
fixed bed reactor or a fluidized bed reactor, as one of skill in the art will
readily appreciate. In
many embodiments of the present invention, an "adiabatic" reactor can be used;
that is, there is
little or no need for internal plumbing through the reaction zone to add or
remove heat. In other
embodiments, radial flow reactor or reactors may be employed, or a series of
reactors may be
employed with or with out heat exchange, quenching, or introduction of
additional feed material.
Alternatively, a shell and tube reactor provided with a heat transfer medium
may be used. In
many cases, the reaction zone may be housed in a single vessel or in a series
of vessels with heat
exchangers therebetween.
[0046] In preferred embodiments, the catalyst is employed in a fixed bed
reactor, e.g., in the
shape of a pipe or tube, where the reactants, typically in the vapor form, are
passed over or
through the catalyst. Other reactors, such as fluid or ebullient bed reactors,
can be employed. In
some instances, the hydrogenation catalysts may be used in conjunction with an
inert material to
regulate the pressure drop of the reactant stream through the catalyst bed and
the contact time of
the reactant compounds with the catalyst particles.
[0047] The hydrogenation reaction may be carried out in either the liquid
phase or vapor phase.
Preferably, the reaction is carried out in the vapor phase under the following
conditions. The
reaction temperature may range from 125 C to 350 C, e.g., from 200 C to 325 C,
from 225 C to
300 C, or from 250 C to 300 C. The pressure may range from 10 KPa to 3000 KPa
(about 1.5 to
435 psi), e.g., from 50 KPa to 2300 KPa, or from 100 KPa to 1500 KPa. The
reactants may be
fed to the reactor at a gas hourly space velocity (GHSV) of greater than 500
hr"1, e.g., greater
than 1000 hr"1, greater than 2500 hr-1 or even greater than 5000 hr-1. In
terms of ranges the
GHSV may range from 50 hr-1 to 50,000 hr-1, e.g., from 500 hr-1 to 30,000
hr"1, from 1000 hr-' to
10,000 hr-1, or from 1000 hr-1 to 6500 hr-1.
[0048] The hydrogenation optionally is carried out at a pressure just
sufficient to overcome the
pressure drop across the catalytic bed at the GHSV selected, although there is
no bar to the use of
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higher pressures, it being understood that considerable pressure drop through
the reactor bed may
be experienced at high space velocities, e.g., 5000 hr-1 or 6,500 hr-'.
[0049] Although the reaction consumes two moles of hydrogen per mole of acetic
acid to
produce one mole of ethanol, the actual molar ratio of hydrogen to acetic acid
in the feed stream
may vary from about 100:1 to 1:100, e.g., from 50:1 to 1:50, from 20:1 to 1:2,
or from 12:1 to
1:1. Most preferably, the molar ratio of hydrogen to acetic acid is greater
than 2:1, e.g., greater
than 4:1 or greater than 8:1.
[0050] Contact or residence time can also vary widely, depending upon such
variables as
amount of acetic acid, catalyst, reactor, temperature and pressure. Typical
contact times range
from a fraction of a second to more than several hours when a catalyst system
other than a fixed
bed is used, with preferred contact times, at least for vapor phase reactions,
of from 0.1 to 100
seconds, e.g., from 0.3 to 80 seconds or from 0.4 to 30 seconds.
[0051] The raw materials, acetic acid and hydrogen, used in connection with
the process of this
invention may be derived from any suitable source including natural gas,
petroleum, coal,
biomass, and so forth. As examples, acetic acid may be produced via methanol
carbonylation,
acetaldehyde oxidation, ethylene oxidation, oxidative fermentation, and
anaerobic fermentation.
As petroleum and natural gas prices fluctuate, becoming either more or less
expensive, methods
for producing acetic acid and intermediates such as methanol and carbon
monoxide from
alternate carbon sources have drawn increasing interest. In particular, when
petroleum is
relatively expensive compared to natural gas, it may become advantageous to
produce acetic acid
from synthesis gas ("syn gas") that is derived from any available carbon
source. U.S. Pat. No.
6,232,352, the disclosure of which is incorporated herein by reference, for
example, teaches a
method of retrofitting a methanol plant for the manufacture of acetic acid. By
retrofitting a
methanol plant, the large capital costs associated with CO generation for a
new acetic acid plant
are significantly reduced or largely eliminated. All or part of the syn gas is
diverted from the
methanol synthesis loop and supplied to a separator unit to recover CO and
hydrogen, which are
then used to produce acetic acid. In addition to acetic acid, such a process
can also be used to
make hydrogen which may be utilized in connection with this invention.
[0052] Methanol carbonylation processes suitable for production of acetic acid
are described in
U.S. Patent Nos. 7,208,624, 7,115,772, 7,005,541, 6,657,078, 6,627,770,
6,143,930, 5,599,976,
5,144,068, 5,026,908, 5,001,259, and 4,994,608, the disclosure of which is
incorporated herein
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by reference. Optionally, the production of ethanol may be integrated with
such methanol
carbonylation processes.
[0053] U.S. Pat. No. RE 35,377, also incorporated herein by reference,
provides a method for
the production of methanol by conversion of carbonaceous materials such as
oil, coal, natural gas
and biomass materials. The process includes hydrogasification of solid and/or
liquid
carbonaceous materials to obtain a process gas which is steam pyrolized with
additional natural
gas to form synthesis gas. The syn gas is converted to methanol which may be
carbonylated to
acetic acid. The method likewise produces hydrogen which may be used in
connection with this
invention as noted above. U.S. Pat. No. 5,821,111, which discloses a process
for converting
waste biomass through gasification into synthesis gas as well as U.S. Pat. No.
6,685,754, the
disclosures of which are incorporated herein by reference.
[0054] In one optional embodiment, the acetic acid fed to the hydrogenation
reaction may also
comprise other carboxylic acids and anhydrides, as well as acetaldehyde and
acetone.
Preferably, a suitable acetic acid feed stream comprises one or more of the
compounds selected
from the group consisting of acetic acid, acetic anhydride, acetaldehyde,
ethyl acetate, and
mixtures thereof. These other compounds may also be hydrogenated in the
processes of the
present invention. In some embodiments, the present of carboxylic acids, such
as propanoic acid
or its anhydride, may be beneficial in producing propanol.
[0055] Alternatively, acetic acid in vapor form may be taken directly as crude
product from the
flash vessel of a methanol carbonylation unit of the class described in U.S.
Pat. No. 6,657,078,
the entirety of which is incorporated herein by reference. The crude vapor
product, for example,
may be fed directly to the ethanol synthesis reaction zones of the present
invention without the
need for condensing the acetic acid and light ends or removing water, saving
overall processing
costs.
[0056] The acetic acid may be vaporized at the reaction temperature, following
which the
vaporized acetic acid can be fed along with hydrogen in an undiluted state or
diluted with a
relatively inert carrier gas, such as nitrogen, argon, helium, carbon dioxide
and the like. For
reactions run in the vapor phase, the temperature should be controlled in the
system such that it
does not fall below the dew point of acetic acid. In one embodiment the acetic
acid may be
vaporized at the boiling point of acetic acid at the particular pressure, and
then the vaporized
acetic acid may be further heated to the reactor inlet temperature. In another
embodiment, the
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acetic acid is transferred to the vapor state by passing hydrogen, recycle
gas, another suitable
gas, or mixtures thereof through the acetic acid at a temperature below the
boiling point of acetic
acid, thereby humidifying the carrier gas with acetic acid vapors, followed by
heating the mixed
vapors up to the reactor inlet temperature. Preferably, the acetic acid is
transferred to the vapor
by passing hydrogen and/or recycle gas through the acetic acid at a
temperature at or below
125 C, followed by heating of the combined gaseous stream to the reactor inlet
temperature.
[0057] In various embodiments, the crude ethanol product produced by the
hydrogenation
process, before any subsequent processing, such as purification and
separation, will typically
comprise unreacted acetic acid, ethanol and water. As used herein, the term
"crude ethanol
product" refers to any composition comprising from 5 to 70 wt.% ethanol and
from 5 to 35 wt.%
water. In some exemplary embodiments, the crude ethanol product comprises
ethanol in an
amount from 5 wt.% to 70 wt.%, e.g., from 10 wt.% to 60 wt.%, or from 15 wt.%
to 50 wt.%,
based on the total weight of the crude ethanol product. Preferably, the crude
ethanol product
contains at least 10 wt.% ethanol, at least 15 wt.% ethanol or at least 20
wt.% ethanol. The crude
ethanol product typically will further comprise unreacted acetic acid,
depending on conversion,
for example, in an amount of less than 90 wt.%, e.g., less than 80 wt.% or
less than 70 wt.%. In
terms of ranges, the unreacted acetic acid is preferably from 0 to 90 wt.%,
e.g., from 5 to 80
wt.%, from 15 to 70 wt.%, from 20 to 70 wt.% or from 25 to 65 wt.%. As water
is formed in the
reaction process, water will generally be present in the crude ethanol
product, for example, in
amounts ranging from 5 to 35 wt.%, e.g., from 10 to 30 wt.% or from 10 to 26
wt.%. Ethyl
acetate may also be produced during the hydrogenation of acetic acid or
through side reactions
and may be present, for example, in amounts ranging from 0 to 20 wt.%, e.g.,
from 0 to 15 wt.%,
from 1 to 12 wt.% or from 3 to 10 wt.%. Acetaldehyde may also be produced
through side
reactions and may be present, for example, in amounts ranging from 0 to 10
wt.%, e.g., from 0 to
3 wt.%, from 0.1 to 3 wt.% or from 0.2 to 2 wt.%. Other components, such as,
for example,
esters, ethers, aldehydes, ketones, alkanes, and carbon dioxide, if
detectable, collectively may be
present in amounts less than 10 wt.%, e.g., less than 6 wt.% or less than 4
wt.%. In terms of
ranges, other components may be present in an amount from 0.1 to 10 wt.%,
e.g., from 0.1 to 6
wt.%, or from 0.1 to 4 wt.%. Exemplary embodiments of crude ethanol
compositional ranges are
provided in Table 1.
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TABLE 1
CRUDE ETHANOL PRODUCT COMPOSITIONS
Conc. Conc. Conc. Conc.
Component (wt.%) (wt.%) (wt.%) (wt.%)
Ethanol 5 to 70 10 to 70 15 to 70 25 to 70
Acetic Acid 0 to 80 0 to 50 0 to 25 0 to 10
Water 5 to 35 5 to 30 10 to 30 10 to 26
Ethyl Acetate 0 to 30 0 to 20 0 to 15 0 to 10
Acetaldehyde 0 to 10 0 to 3 0.1 to 3 0.2 to 2
Others 0.1 to 10 0.1 to 6 0.1 to 4 --
[0058] FIG. 1 shows a hydrogenation system 100 suitable for the hydrogenation
of acetic acid
and separating ethanol from the crude reaction mixture according to one
embodiment of the
invention. System 100 comprises reaction zone 101 and distillation zone 102.
Reaction zone
101 comprises reactor 103, hydrogen feed line 104 and acetic acid feed line
105. Distillation
zone 102 comprises flasher 106, first column 107, second column 108, and third
column 109.
Hydrogen and acetic acid are fed to a vaporizer 110 via lines 104 and 105,
respectively, to create
a vapor feed stream in line 111 that is directed to reactor 103. In one
embodiment, lines 104 and
105 may be combined and jointly fed to the vaporizer 110, e.g., in one stream
containing both
hydrogen and acetic acid. The temperature of the vapor feed stream in line 111
is preferably
from 100 C to 350 C, e.g., from 120 C to 310 C or from 150 C to 300 C. Any
feed that is not
vaporized is removed from vaporizer 110, as shown in FIG. 1, and may be
recycled thereto. In
addition, although FIG. 1 shows line 111 being directed to the top of reactor
103, line 111 may
be directed to the side, upper portion, or bottom of reactor 103. Further
modifications and
additional components to reaction zone 101 are described below in FIGS. 2A and
2B.
[0059] Reactor 103 contains the catalyst that is used in the hydrogenation of
the carboxylic
acid, preferably acetic acid. In one embodiment, one or more guard beds (not
shown) may be
used to protect the catalyst from poisons or undesirable impurities contained
in the feed or
return/recycle streams. Such guard beds may be employed in the vapor or liquid
streams.
Suitable guard bed materials are known in the art and include, for example,
carbon, silica,
alumina, ceramic, or resins. In one aspect, the guard bed media is
functionalized to trap
particular species such as sulfur or halogens. During the hydrogenation
process, a crude ethanol
product stream is withdrawn, preferably continuously, from reactor 103 via
line 112. The crude
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ethanol product stream may be condensed and fed to flasher 106, which, in
turn, provides a
vapor stream and a liquid stream. The flasher 106 in one embodiment preferably
operates at a
temperature of from 50 C to 500 C, e.g., from 70 C to 400 C or from 100 C to
350 C. In one
embodiment, the pressure of flasher 106 preferably is from 50 KPa to 2000 KPa,
e.g., from 75
KPa to 1500 KPa or from 100 to 1000 KPa. In one preferred embodiment the
temperature and
pressure of the flasher is similar to the temperature and pressure of the
reactor 103.
[0060] The vapor stream exiting the flasher 106 may comprise hydrogen and
hydrocarbons,
which may be purged and/or returned to reaction zone 101 via line 113. As
shown in FIG. 1, the
returned portion of the vapor stream passes through compressor 114 and is
combined with the
hydrogen feed and co-fed to vaporizer 110.
[0061] The liquid from flasher 106 is withdrawn and pumped as a feed
composition via line
115 to the side of first column 107, also referred to as the acid separation
column. The contents
of line 115 typically will be substantially similar to the product obtained
directly from the
reactor, and may, in fact, also be characterized as a crude ethanol product.
However, the feed
composition in line 115 preferably has substantially no hydrogen, carbon
dioxide, methane or
ethane, which are removed by flasher 106. Exemplary components of liquid in
line 115 are
provided in Table 2. It should be understood that liquid line 115 may contain
other components,
not listed, such as components in the feed.
TABLE 2
FEED COMPOSITION
Conc. (wt.%) Conc. (wt.%) Conc. (wt.%)
Ethanol 5 to 70 10 to 70 25 to 70
Acetic Acid < 80 0 to 50 0 to 10
Water 5 to 35 5 to 30 10 to 26
Ethyl Acetate <30 0.001 to 20 1 to 10
Acetaldehyde <10 0.001 to 3 0.1 to 3
Acetal < 5 0.001 to 2 0.005 to 1
Acetone < 5 0.0005 to 0.05 0.001 to 0.03
Other Esters < 5 < 0.005 < 0.001
Other Ethers < 5 < 0.005 < 0.001
Other Alcohols < 5 < 0.005 < 0.001
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[0062] The amounts indicated as less than (<) in the tables throughout present
application are
preferably not present and if present may be present in trace amounts or in
amounts greater than
0.0001 wt.%.
[0063] The "other esters" in Table 2 may include, but are not limited to,
ethyl propionate,
methyl acetate, isopropyl acetate, n-propyl acetate, n-butyl acetate or
mixtures thereof. The
"other ethers" in Table 2 may include, but are not limited to, diethyl ether,
methyl ethyl ether,
isobutyl ethyl ether or mixtures thereof. The "other alcohols" in Table 2 may
include, but are not
limited to, methanol, isopropanol, n-propanol, n-butanol or mixtures thereof.
In one
embodiment, the feed composition, e.g., line 115, may comprise propanol, e.g.,
isopropanol
and/or n-propanol, in an amount from 0.001 to 0.1 wt.%, from 0.001 to 0.05
wt.% or from 0.001
to 0.03 wt.%. It should be understood that these other components may be
carried through in any
of the distillate or residue streams described herein and will not be further
described herein,
unless indicated otherwise.
[0064] In one embodiment, the conversion of acetic acid may be greater than
95%, and the
crude ethanol product in line 115 may contain less than 5 wt.% acetic acid. In
such
embodiments, the acid separation column 107 may be skipped and line 115 may be
introduced
directly to second column 108, also referred to herein as a light ends column.
[0065] In the embodiment shown in FIG. 1 A, line 115 is introduced in the
lower part of first
column 107, e.g., lower half or lower third. In first column 107, unreacted
acetic acid, a portion
of the water, and other heavy components, if present, are removed from the
composition in line
115 and are withdrawn, preferably continuously, as residue. Some or all of the
residue may be
returned and/or recycled back to reaction zone 101 via line 116. First column
107 also forms an
overhead distillate, which is withdrawn in line 117, and which may be
condensed and refluxed,
for example, at a ratio of from 10:1 to 1:10, e.g., from 3:1 to 1:3 or from
1:2 to 2:1.
[0066] Any of columns 107, 108 or 109 may comprise any distillation column
capable of
separation and/or purification. The columns preferably comprise tray columns
having from 1 to
150 trays, e.g., from 10 to 100 trays, from 20 to 95 trays or from 30 to 75
trays. The trays may
be sieve trays, fixed valve trays, movable valve trays, or any other suitable
design known in the
art. In other embodiments, a packed column may be used. For packed columns,
structured
packing or random packing may be employed. The trays or packing may be
arranged in one
continuous column or they may be arranged in two or more columns such that the
vapor from the
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first section enters the second section while the liquid from the second
section enters the first
section, etc.
[0067] The associated condensers and liquid separation vessels that may be
employed with
each of the distillation columns may be of any conventional design and are
simplified in FIG. 1.
As shown in FIG. 1, heat may be supplied to the base of each column or to a
circulating bottom
stream through a heat exchanger or reboiler. Other types of reboilers, such as
internal reboilers,
may also be used in some embodiments. The heat that is provided to reboilers
may be derived
from any heat generated during the process that is integrated with the
reboilers or from an
external source such as another heat generating chemical process or a boiler.
Although one
reactor and one flasher are shown in FIG. 1, additional reactors, flashers,
condensers, heating
elements, and other components may be used in embodiments of the present
invention. As will
be recognized by those skilled in the art, various condensers, pumps,
compressors, reboilers,
drums, valves, connectors, separation vessels, etc., normally employed in
carrying out chemical
processes may also be combined and employed in the processes of the present
invention.
[0068] The temperatures and pressures employed in any of the columns may vary.
As a
practical matter, pressures from 10 KPa to 3000 KPa will generally be employed
in these zones
although in some embodiments subatmospheric pressures may be employed as well
as
superatmospheric pressures. Temperatures within the various zones will
normally range between
the boiling points of the composition removed as the distillate and the
composition removed as
the residue. It will be recognized by those skilled in the art that the
temperature at a given
location in an operating distillation column is dependent on the composition
of the material at
that location and the pressure of column. In addition, feed rates may vary
depending on the size
of the production process and, if described, may be generically referred to in
terms of feed
weight ratios.
[0069] When column 107 is operated under standard atmospheric pressure, the
temperature of
the residue exiting in line 116 from column 107 preferably is from 95 C to 120
C, e.g., from
105 C to 117 C or from 110 C to 115 C. The temperature of the distillate
exiting in line 117
from column 107 preferably is from 70 C to 110 C, e.g., from 75 C to 95 C or
from 80 C to
90 C. In other embodiments, the pressure of first column 107 may range from
0.1 KPa to 510
KPa, e.g., from 1 KPa to 475 KPa or from 1 KPa to 375 KPa. Exemplary
components of the
distillate and residue compositions for first column 107 are provided in Table
3 below. It should
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also be understood that the distillate and residue may also contain other
components, not listed,
such as components in the feed. For convenience, the distillate and residue of
the first column
may also be referred to as the "first distillate" or "first residue." The
distillates or residues of the
other columns may also be referred to with similar numeric modifiers (second,
third, etc.) in
order to distinguish them from one another, but such modifiers should not be
construed as
requiring any particular separation order.
TABLE 3
FIRST COLUMN
Conc. (wt.%) Conc. (wt.%) Conc. (wt.%)
Distillate
Ethanol 5 to 75 10 to 70 25 to 70
Water 10 to 40 15 to 35 20 to 35
Acetic Acid < 2 0.001 to 0.5 0.01 to 0.2
Ethyl Acetate < 60 0 to 20 0 to 10
Acetaldehyde <10 0.001 to 5 0.01 to 4
Acetal < 0.1 < 0.1 < 0.05
Acetone < 0.05 0.001 to 0.03 0.01 to 0.025
Residue
Acetic Acid 60 to 100 70 to 95 85 to 92
Water <30 1 to 20 1 to 15
Ethanol < 1 < 0.9 < 0.07
[0070] As shown in Table 3, without being bound by theory, it has surprisingly
and
unexpectedly been discovered that when any amount of acetal is detected in the
feed that is
introduced to the acid separation column (first column 107), the acetal
appears to decompose in
the column such that less or even no detectable amounts are present in the
distillate and/or
residue.
[0071] Depending on the reaction conditions, the crude ethanol product exiting
reactor 103 in
line 112 may comprise ethanol, acetic acid (unconverted), ethyl acetate, and
water. After exiting
reactor 103, a non-catalyzed equilibrium reaction may occur between the
components contained
in the crude ethanol product until it is added to flasher 106 and/or first
column 107. This
equilibrium reaction tends to drive the crude ethanol product to an
equilibrium between
ethanol/acetic acid and ethyl acetate/water, as shown below (Reaction 2).
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EtOH + HOAc 'EtOAc + H2O Reaction 2
[0072] In the event the crude ethanol product is temporarily stored, e.g., in
a holding tank,
prior to being directed to distillation zone 102, extended residence times may
be encountered.
Generally, the longer the residence time between reaction zone 101 and
distillation zone 102, the
greater the formation of ethyl acetate. For example, when the residence time
between reaction
zone 101 and distillation zone 102 is greater than 5 days, significantly more
ethyl acetate may
form at the expense of ethanol. Thus, shorter residence times between reaction
zone 101 and
distillation zone 102 are generally preferred in order to maximize the amount
of ethanol formed.
In one embodiment, a holding tank (not shown), is included between the
reaction zone 101 and
distillation zone 102 for temporarily storing the liquid component from line
115 for up to 5 days,
e.g., up to 1 day, or up to 1 hour. In a preferred embodiment no tank is
included and the
condensed liquids are fed directly to the first distillation column 107. In
addition, the rate at
which the non-catalyzed reaction occurs may increase as the temperature of the
crude ethanol
product, e.g., in line 115, increases. These reaction rates may be
particularly problematic at
temperatures exceeding 30 C, e.g., exceeding 40 C or exceeding 50 C. Thus, in
one
embodiment, the temperature of liquid components in line 115 or in the
optional holding tank is
maintained at a temperature less than 40 C, e.g., less than 30 C or less than
20 C. One or more
cooling devices may be used to reduce the temperature of the liquid in line
115.
[0073] As discussed above, a holding tank (not shown) may be included between
the reaction
zone 101 and distillation zone 102 for temporarily storing the liquid
component from line 115,
for example from 1 to 24 hours, optionally at a temperature of about 21 C,
and corresponding to
an ethyl acetate formation of from 0.01 wt.% to 1.0 wt.% respectively. In
addition, the rate at
which the non-catalyzed reaction occurs may increase as the temperature of the
crude ethanol
product is increased. For example, as the temperature of the crude ethanol
product in line 115
increase from 4 C to 21 C, the rate of ethyl acetate formation may increase
from about 0.01
wt.% per hour to about 0.005 wt.% per hour. Thus, in one embodiment, the
temperature of
liquid components in line 115 or in the optional holding tank is maintained at
a temperature less
than 21 C, e.g., less than 4 C or less than -10 C.
[0074] In addition, it has now been discovered that the above-described
equilibrium reaction
may also favor ethanol formation in the top region of first column 107.
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[0075] The distillate, e.g., overhead stream, of column 107 optionally is
condensed and
refluxed as shown in FIG. 1, preferably, at a reflux ratio of 1:5 to 10:1. The
distillate in line 1.17
preferably comprises ethanol, ethyl acetate, and water, along with other
impurities, which may
be difficult to separate due to the formation of binary and tertiary
azeotropes.
[0076] The first distillate in line 117 is introduced to the second column
108, also referred to as
the "light ends column," preferably in the middle part of column 108, e.g.,
middle half or middle
third. As one example, when a 25 tray column is utilized in a column without
water extraction,
line 117 is introduced at tray 17. In one embodiment, the second column 108
may be an
extractive distillation column. In such embodiments, an extraction agent, such
as water, may be
added to second column 108. If the extraction agent comprises water, it may be
obtained from
an external source or from an internal return/recycle line from one or more of
the other columns,
such as via optional line 121'.
[0077] Second column 108 may be a tray column or packed column. In one
embodiment,
second column 108 is a tray column having from 5 to 70 trays, e.g., from 15 to
50 trays or from
20 to 45 trays.
[0078] Although the temperature and pressure of second column 108 may vary,
when at
atmospheric pressure the temperature of the second residue exiting in line 118
from second
column 108 preferably is from 60 C to 90 C, e.g., from 70 C to 90 C or from 80
C to 90 C.
The temperature of the second distillate exiting in line 120 from second
column 108 preferably is
from 50 C to 90 C, e.g., from 60 C to 80 C or from 60 C to 70 C. Column 108
may operate at
atmospheric pressure. In other embodiments, the pressure of second column 108
may range
from 0.1 KPa to 510 KPa, e.g., from 1 KPa to 475 KPa or from 1 KPa to 375 KPa.
Exemplary
components for the distillate and residue compositions for second column 108
are provided in
Table 4 below. It should be understood that the distillate and residue may
also contain other
components, not listed, such as components in the feed.
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TABLE 4
SECOND COLUMN
Conc. (wt.%) Conc. (wt.%) Cone. (wt.%)
Distillate
Ethyl Acetate 10 to 90 25 to 90 50 to 90
Acetaldehyde 1 to 25 1 to 15 1 to 8
Water 1 to 25 1 to 20 4 to 16
Ethanol <30 0.001 to 15 0.01 to 5
Acetal < 5 0.001 to 2 0.01 to 1
Residue
Water 30 to 70 30 to 60 30 to 50
Ethanol 20 to 75 30 to 70 40 to 70
Ethyl Acetate < 3 0.001 to 2 0.001 to 0.5
Acetic Acid < 0.5 0.001 to 0.3 0.001 to 0.2
[0079] The weight ratio of ethanol in the second residue to ethanol in the
second distillate
preferably is at least 3:1, e.g., at least 6:1, at least 8:1, at least 10:1 or
at least 15:1. The weight
ratio of ethyl acetate in the second residue to ethyl acetate in the second
distillate preferably is
less than 0.4:1, e.g., less than 0.2:1 or less than 0.1:1. In embodiments that
use an extractive
column with water as an extraction agent as the second column 108, the weight
ratio of ethyl
acetate in the second residue to ethyl acetate in the second distillate
approaches zero.
[0080] As shown, the second residue from the bottom of second column 108,
which comprises
ethanol and water, is fed via line 118 to third column 109, also referred to
as the "product
column." More preferably, the second residue in line 118 is introduced in the
lower part of third
column 109, e.g., lower half or lower third. Third column 109 recovers
ethanol, which
preferably is substantially pure other than the azeotropic water content, as
the distillate in line
119. The distillate of third column 109 preferably is refluxed as shown in
FIG. 1 A, for example,
at a reflux ratio of from 1:10 to 10:1, e.g., from 1:3 to 3:1 or from 1:2 to
2:1. The third residue in
line 121, which preferably comprises primarily water, preferably is removed
from the system
100 or may be partially returned to any portion of the system 100. Third
column 109 is
preferably a tray column as described above and preferably operates at
atmospheric pressure.
The temperature of the third distillate exiting in line 119 from third column
109 preferably is
from 60 C to 110 C, e.g., from 70 C to 100 C or from 75 C to 95 C. The
temperature of the
third residue exiting from third column 109 preferably is from 70 C to 115 C,
e.g., from 80 C to
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110 C or from 85 C to 105 C, when the column is operated at atmospheric
pressure. Exemplary
components of the distillate and residue compositions for third column 109 are
provided in Table
below. It should be understood that the distillate and residue may also
contain other
components, not listed, such as components in the feed.
TABLE 5
THIRD COLUMN
Conc. (wt.%) Conc. (wt.%) Conc. (wt.%)
Distillate
Ethanol 75 to 96 80 to 96 85 to 96
Water <12 1 to 9 3 to 8
Acetic Acid < 1 0.001 to 0.1 0.005 to 0.01
Ethyl Acetate < 5 0.001 to 4 0.01 to 3
Residue
Water 75 to 100 80 to 100 90 to 100
Ethanol < 0.8 0.001 to 0.5 0.005 to 0.05
Ethyl Acetate < 1 0.001 to 0.5 0.005 to 0.2
Acetic Acid < 2 0.001 to 0.5 0.005 to 0.2
[0081] Any of the compounds that are carried through the distillation process
from the feed or
crude reaction product generally remain in the third distillate in amounts of
less 0.1 wt.%, based
on the total weight of the third distillate composition, e.g., less than 0.05
wt.% or less than 0.02
wt.%. In one embodiment, one or more side streams may remove impurities from
any of the
columns 107, 108 and/or 109 in the system 100. Preferably at least one side
stream is used to
remove impurities from the third column 109. The impurities may be purged
and/or retained
within the system 100.
[0082] The third distillate in line 119 maybe further purified to form an
anhydrous ethanol
product stream, i.e., "finished anhydrous ethanol," using one or more
additional separation
systems, such as, for example, distillation columns (e.g., a finishing column)
or molecular sieves.
[0083] Returning to second column 108, the distillate in line 120 preferably
is refluxed as
shown in FIG. 1, for example, at a reflux ratio of from 1:10 to 10:1, e.g.,
from 1:5 to 5:1 or from
1:3 to 3:1. In one embodiment, all or a portion of the distillate from second
column 108 may be
recycled to reaction zone 101 via line 120. As shown in FIG. 1, all or a
portion the distillate may
be recycled to reactor 103, as shown by line 120, and may be co-fed with the
acetic acid feed line
105. In one embodiment, ethyl acetate in line 120 does not build up in the
reaction zone 101
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and/or distillation zone 102 due to the presence of the catalyst comprising an
acidic support.
Due to the increase in kinetics of the equilibrium reaction, embodiments of
the present invention
are able to process ethyl acetate in the feed and/or recycle stream as well.
Thus, because of the
increased kinetics, the recycled ethyl acetate in line 120 may be converted to
ethanol, or the
generated ethyl acetate may be equal to the converted ethyl acetate so there
will be certain steady
state achieved relatively fast and recycled ethyl acetate concentration will
remain constant;
without building up in the recycle loop. A portion of the distillate from
second column 108 may
be purged via line 122. Optionally, the second distillate in line 120 may be
further purified to
remove impurities, such as acetaldehyde, using one or more additional columns
(not shown)
before being returned to the reaction zone, as described in co-pending U.S.
App. No. 12/852,269,
the entirety of which is hereby incorporated by reference.
[0084] FIGS. 2A and 2B show modified reaction zones 130 and 140, respectively.
As
discussed above, some embodiments of the present invention may use multiple
reactors. In
reaction zone 130 of FIG. 2A, vapor feed stream 111 is fed to first reactor
131. Reactor effluent
133 is fed to second reactor 132. Preferably, reactor effluent 133 comprises
ethanol and
unreacted acetic acid and may have a composition as described above in Table
1. Optionally,
fresh reactants (not shown) may be fed to the second reactor 132. Crude
ethanol product 134 of
second reactor is fed to flasher 106. For purposes of illustration FIG. 2A
shows two reactors. In
further embodiments, however, there may be more than two reactors, e.g., more
than three or
more than four. Each of reactors, 131 and 132 of FIG. 2A operate within the
reaction conditions
stated above.
[0085] In the reaction zone 140 of FIG. 2B, vapor feed stream 111 is fed to
reactor 141 that
comprises multiple reaction regions. Reactor 141 comprises at least a first
reaction region 142
and a second reaction region 143. Each region may have a different catalyst.
First reaction
region 142 and second reaction region 143 may be separated in reactor 141 as
shown in FIG. 2B.
In other embodiments, first reaction region 142 and second reaction region 143
overlap and the
respective catalysts may be dispersed between the regions. Crude ethanol
product 144 of reactor
141, e.g., second reactor region 143, may be fed to flasher 106. Regions 142
and regions 143
operate within the reaction conditions as stated above.
[0086] In preferred embodiments, different catalysts may be used in each of
the reactors of
reactions zones 130 in FIG. 2B or in each of the reaction regions in reaction
zones 140 shown in
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FIG. 2B. Different catalysts may have different metals and/or different
supports. In preferred
embodiments, the catalyst in first reactor 131 or first reactor region 142 may
be cobalt catalyst as
described in U.S. Pat. No. 7,608,744, a platinum/tin catalyst as described in
U.S. Pub. No.
2010/0029995, or a metal catalyst comprising a basic modifier as described in
U.S. Pub. No.
2010/0197959, the entireties of which are hereby incorporated by reference.
[0087] In some embodiments, the catalyst in first reactor 131 or first reactor
region 142 is a
basic catalyst. Suitable metal catalysts that comprise a basic modifier
include those having a first
metal and an optional second metal. These metals may be the same as those
described above
with respect to the acidic supported catalysts of the present invention.
Preferably, the first metal
is Group VIII metal, selected from the group consisting of iron, cobalt,
nickel, ruthenium,
rhodium, palladium, osmium, iridium, and platinum. The optional second metal
preferably may
be selected from the group consisting of copper, tin, cobalt, rhenium, and
nickel. The catalyst
may comprise from 0.1 to 10 wt.% first metal and from 0.1 to 10 wt.% second
metal.
[0088] Suitable support materials may include, for example, stable metal oxide-
based supports
or ceramic-based supports. Preferred supports include silicaceous supports,
such as silica,
silica/alumina, a Group IIA silicate such as calcium metasilicate, pyrogenic
silica, high purity
silica, and mixtures thereof. Other supports may include, but are not limited
to, iron oxide,
alumina, titania, zirconia, magnesium oxide, carbon, graphite, high surface
area graphitized
carbon, activated carbons, and mixtures thereof.
[0089] The catalyst support may be modified with a support modifier.
Preferably, the support
modifier is a basic modifier that has a low volatility or no volatility. Such
basic modifiers, for
example, may be selected from the group consisting of. (i) alkaline earth
oxides, (ii) alkali metal
oxides, (iii) alkaline earth metal metasilicates, (iv) alkali metal
metasilicates, (v) Group IIB metal
oxides, (vi) Group IIB metal metasilicates, (vii) Group IIIB metal oxides,
(viii) Group IIIB metal
metasilicates, and mixtures thereof. In addition to oxides and metasilicates,
other types of
modifiers including nitrates, nitrites, acetates, and lactates may be used.
Preferably, the support
modifier is selected from the group consisting of oxides and metasilicates of
any of sodium,
potassium, magnesium, calcium, scandium, yttrium, and zinc, as well as
mixtures of any of the
foregoing. Preferably, the support modifier is a calcium silicate, and more
preferably calcium
metasilicate (CaSiO3). If the support modifier comprises calcium metasilicate,
it is preferred that
at least a portion of the calcium metasilicate is in crystalline form. In
preferred embodiments
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WO 2011/056597 PCT/US2010/054136
that use a basic support modifier, the basic support modifier is present in an
amount from 0.1
wt.% to 50 wt.%, e.g., from 0.2 wt.% to 25 wt.%, from 0.5 wt.% to 15 wt.%, or
from 1 wt.% to 8
wt.%, based on the total weight of the catalyst.
[0090] The acidic catalyst of the present invention is preferably used in
second reactor 132 or
second reactor region 143. In one exemplary embodiment, first reactor 131 or
first reactor
region 142 may comprise a Si02-CaSiO3-Pt-Sn catalyst, and the second reactor
133 or second
reactor 143 may comprise Si02-TiO2-Pt-Sn catalyst. In alternative embodiments,
the acidic
catalyst may be used in first reactor 131 or first reactor region 142.
[0091] The acetic acid conversion in first reactor 131 or first reactor region
142 may be
relatively lower than that of second reactor 132 or second reactor region 143,
respectively. The
acetic acid conversion of the first reactor 131 or first reaction region 142
may be at least 10%,
e.g., at least 20%, at least 40%, at least 50%, at least 60%, at least 70% or
at least 80%. In one
embodiment, the acetic acid conversion in first reactor 131 or first reactor
region 142 is from
10% to 80% and is lower than the conversion of the unreacted acetic acid in
second reactor 132
or second reactor region 143. In second reactor 132 or second reactor region
143, the conversion
of the unreacted acetic acid may be increased to at least 70%, e.g., at least
80% or at least 90%.
Advantageously, a lower conversion of acetic acid in first reactor 131 or
first reactor region 142
allows the unreacted acid of first reactor 131 or first reactor region 142 to
be hydrogenated in
second reactor 132 or second reactor region 143 without the addition of fresh
acetic acid.
[0092] The overall ethanol selectivity of the dual reactors shown in FIG. 2A
and/or dual
reactor regions shown in FIG. 2B may be at least 65%, e.g., at least 70%, at
least 80%, at least
85%, or at least 90%. Ethyl acetate, which may be produced by the first
reactor 131 or first
reactor region 142, may be consumed in the second reactor 132 or second
reactor region 143.
Finished Ethanol
[0093] The finished ethanol composition obtained by the processes of the
present invention
preferably comprises from 75 to 96 wt.% ethanol, e.g., from 80 to 96 wt.% or
from 85 to 96
wt.% ethanol, based on the total weight of the finished ethanol composition.
Exemplary finished
ethanol compositional ranges are provided below in Table 6.
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TABLE 6
FINISHED ETHANOL COMPOSITIONS
Component Conc. (wt.%) Conc. (wt.%) Conc. (wt.%)
Ethanol 75 to 96 80 to 96 85 to 96
Water <12 1 to 9 3 to 8
Acetic Acid < 1 0.001 to 0.1 0.005 to 0.01
Ethyl Acetate < 5 0.001 to 4 0.01 to 3
Acetal < 0.05 < 0.01 < 0.005
Acetone < 0.05 < 0.01 < 0.005
Isopropanol < 0.5 < 0.1 < 0.05
n-propanol < 0.5 < 0.1 < 0.05
[0094] The finished ethanol composition of the present invention preferably
contains very low
amounts, e.g., less than 0.5 wt.%, of other alcohols, such as methanol,
butanol, isobutanol,
isoamyl alcohol and other C4-C20 alcohols. In one embodiment, the amount of
isopropanol in the
finished ethanol is from 80 to 1,000 wppm, e.g., from 95 to 1,000 wppm, from
100 to 700 wppm,
or from 150 to 500 wppm. In one embodiment, the finished ethanol composition
preferably is
substantially free of acetaldehyde and may comprise less than 8 wppm of
acetaldehyde, e.g., less
than 5 wppm or less than 1 wppm.
[0095] The finished ethanol composition produced by the embodiments of the
present
invention may be used in a variety of applications including fuels, solvents,
chemical feedstocks,
pharmaceutical products, cleansers, sanitizers, hydrogenation transport or
consumption. In fuel
applications, the finished ethanol composition may be blended with gasoline
for motor vehicles
such as automobiles, boats and small piston engine aircrafts. In non-fuel
applications, the
finished ethanol composition may be used as a solvent for toiletry and
cosmetic preparations,
detergents, disinfectants, coatings, inks, and pharmaceuticals. The finished
ethanol composition
may also be used as a processing solvent in manufacturing processes for
medicinal products,
food preparations, dyes, photochemicals and latex processing.
[0096] The finished ethanol composition may also be used a chemical feedstock
to make other
chemicals such as vinegar, ethyl acrylate, ethyl acetate, ethylene, glycol
ethers, ethylamines,
aldehydes, and higher alcohols, especially butanol. In the production of ethyl
acetate, the
finished ethanol composition may be esterified with acetic acid or reacted
with polyvinyl acetate.
The finished ethanol composition may be dehydrated to produce ethylene. Any of
known
dehydration catalysts can be employed in to dehydrate ethanol, such as those
described in
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copending U.S. Application No. 12/221,137 and U.S. Application No. 12/221,138,
the entire
contents and disclosures of which are hereby incorporated by reference. A
zeolite catalyst, for
example, may be employed as the dehydration catalyst. Preferably, the zeolite
has a pore
diameter of at least about 0.6 nm, and preferred zeolites include dehydration
catalysts selected
from the group consisting of mordenites, ZSM-5, a zeolite X and a zeolite Y.
Zeolite X is
described, for example, in U.S. Pat. No. 2,882,244 and zeolite Y in U.S. Pat.
No. 3,130,007, the
entireties of which are hereby incorporated by reference.
[0097] In order that the invention disclosed herein may be more efficiently
understood, the
following examples are provided below.
Examples
Example 1
[0098] Acetic acid was hydrogenated in the present of an acidic catalyst
comprising Si02-
Ti02(10 wt.%)-Pt(1.6 wt.%)-Sn(1.0 wt.%). There were 2 runs with this catalyst
in a reactor at
200 psig, 250 C. First run was at 4500 hr"1 GHSV, and the second run was at
2200 hf1 GHSV.
In FIG. 3, the theoretical calculations for a Keg of 4 and for a Keq of 12. As
indicated in FIG. 3,
the amount of ethyl acetate at lower acetic acid conversion is greater than
that of ethanol.
However, at higher acetic acid conversions, the kinetics of the equilibrium
reaction surprisingly
drive the ethyl acetate content lower and increase the ethanol content. Table
7 summarizes the
results.
Table 7
HOAc Selectivity (mol %)
Run GHSV Conversion EtOH EtOAc
1 4500 hr" 71.9% 58.8% 40.6%
2 2200 hr-' 92.9% 79.2% 20.4%
Example 2
[0099] Acetic acid was hydrogenated in the present of an acidic catalyst
comprising Si02-
Ti02(10 wt.%)-Pt(1.6 wt.%)-Sn(1.0 wt.%) and an acidic catalyst comprising Si02-
A1203(7
wt.%)-Pt(1.6 wt.%)-Sn(1.0 wt.%). Each hydrogenation was performed several
times under
different acetic acid conversion levels. The results are compared in FIG. 4.
At lower
conversions, the Si02-Al203(7 wt.%)-Pt(1.6 wt.%)-Sn(1.0 wt.%) catalyst showed
increased
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selectivity to ethanol. However, at higher conversions, the Si02-TiO2(10 wt.%)-
Pt(1.6 wt.%)-
Sn(1.0 wt.%) catalyst showed similar selectivity to ethanol. In addition,
surprisingly and
unexpectedly, the productivity of the acidic catalyst at high acetic acid
conversion showed a
significant improvement.
Example 3
[0100] The acidic catalyst comprising Si02-A1203(7 wt.%)-Pt(1.6 wt.%)-Sn(l.0
wt.%) from
Example 2 was also used to hydrogenate acetic acid in several runs under the
following different
reaction conditions set forth in Table 8.
Table 8
HOAc Selectivity (mol %)
Run Pressure Temperature GHSV Conversion EtOH EtOAc
1 200 psig 250 C 4500 hr" 87.5 65.8 33.4
2 200 psig 250 C 2200 hr-1 93.4 81.4 18.0
3 250 psig 300 C 4500 hr4 94.3 75.4 20.8
4 250 psig 300 C 1300 hr-1 97.3 89.2 7.2
[0101] While the invention has been described in detail, modifications within
the spirit and
scope of the invention will be readily apparent to those of skill in the art.
In view of the
foregoing discussion, relevant knowledge in the art and references discussed
above in connection
with the Background and Detailed Description, the disclosures of which are all
incorporated
herein by reference. In addition, it should be understood that aspects of the
invention and
portions of various embodiments and various features recited below and/or in
the appended
claims may be combined or interchanged either in whole or in part. In the
foregoing descriptions
of the various embodiments, those embodiments which refer to another
embodiment may be
appropriately combined with other embodiments as will be appreciated by one of
skill in the art.
Furthermore, those of ordinary skill in the art will appreciate that the
foregoing description is by
way of example only, and is not intended to limit the invention.
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