U.S. patent application number 13/681858 was filed with the patent office on 2014-05-22 for process for producing ethanol from methyl acetate.
This patent application is currently assigned to CELANESE INTERNATIONAL CORPORATION. The applicant listed for this patent is CELANESE INTERNATIONAL CORPORATION. Invention is credited to Brian Hokkanen, Tianshu Pan, Mark O. Scates, Ronald D. Shaver, Andrew Shuff, G. Paull Torrence.
Application Number | 20140142349 13/681858 |
Document ID | / |
Family ID | 50692210 |
Filed Date | 2014-05-22 |
United States Patent
Application |
20140142349 |
Kind Code |
A1 |
Shuff; Andrew ; et
al. |
May 22, 2014 |
PROCESS FOR PRODUCING ETHANOL FROM METHYL ACETATE
Abstract
The present invention relates to a process for producing ethanol
by methyl acetate hydrogenolysis. The process comprises the step of
reacting carbon monoxide and methanol in a reaction medium to form
a reaction solution that comprises acetic acid and from 0.5 to 25
wt. % methyl acetate. The process further comprises the step of
esterifying the acetic acid and feeding the methyl acetate to a
distillation column to remove alkyl halides. The process further
comprises the steps of reacting the methyl acetate stream that does
not contain alkyl halides and hydrogen in the presence of a second
catalyst to form an alcohol product that comprises ethanol and/or
methanol.
Inventors: |
Shuff; Andrew; (League City,
TX) ; Torrence; G. Paull; (League City, TX) ;
Hokkanen; Brian; (Houston, TX) ; Pan; Tianshu;
(Houston, TX) ; Scates; Mark O.; (Houston, TX)
; Shaver; Ronald D.; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CELANESE INTERNATIONAL CORPORATION |
Irving |
TX |
US |
|
|
Assignee: |
CELANESE INTERNATIONAL
CORPORATION
Irving
TX
|
Family ID: |
50692210 |
Appl. No.: |
13/681858 |
Filed: |
November 20, 2012 |
Current U.S.
Class: |
568/876 |
Current CPC
Class: |
Y02P 20/582 20151101;
Y02P 20/127 20151101; C07C 51/12 20130101; Y02P 20/10 20151101;
C07C 67/08 20130101; C07C 29/00 20130101; C07C 67/54 20130101; C07C
67/36 20130101; C07C 29/149 20130101; C07C 51/12 20130101; C07C
53/08 20130101; C07C 67/36 20130101; C07C 69/14 20130101; C07C
67/08 20130101; C07C 69/14 20130101; C07C 67/54 20130101; C07C
69/14 20130101; C07C 29/149 20130101; C07C 31/08 20130101 |
Class at
Publication: |
568/876 |
International
Class: |
C07C 29/00 20060101
C07C029/00 |
Claims
1. A process for producing ethanol by hydrogenolysis of methyl
acetate comprising: reacting carbon monoxide and methanol in a
reaction medium to form a reaction solution that comprises acetic
acid and from 0.5 to 25 wt. % methyl acetate, wherein the reaction
medium comprises water, acetic acid, methyl acetate, a first
catalyst, and an alkyl halide; flashing the reaction solution to
yield a carbonylation product and a liquid catalyst recycle stream;
separating the carbonylation product into a first methyl acetate
stream and acetic acid stream; esterifying the acetic acid stream
to form a second methyl acetate stream; feeding the first methyl
acetate stream and the second methyl acetate stream to a
distillation column to remove alkyl halides and obtain a third
methyl acetate stream; reacting the third methyl acetate stream and
hydrogen in the presence of a second catalyst to form an alcohol
product that comprises ethanol and methanol; and recovering ethanol
from the alcohol product.
2. The process of claim 1, wherein the third methyl acetate stream
comprises at least 60 wt. % methyl acetate.
3. The process of claim 1, wherein the third methyl acetate stream
comprises less than 5 wt. % acetic acid.
4. The process of claim 1, wherein the third methyl acetate stream
is substantially free of methyl iodide.
5. The process of claim 1, further comprising withdrawing the
acetic acid as a sidedraw.
6. The process of claim 5, wherein the sidedraw comprises at least
30 wt. % acetic acid.
7. The process of claim 5, wherein the sidedraw comprises less than
10 wt. % methyl acetate.
8. The process of claim 5, wherein the sidedraw comprises less than
0.1 wt. % alkyl halide.
9. The process of claim 1, wherein the first methyl acetate stream
comprises at least 20 wt. % methyl acetate.
10. The process of claim 1, wherein the second methyl acetate
stream comprises at least 50 wt. % methyl acetate.
11. The process of claim 1, wherein the second methyl acetate
stream comprises less than 5 wt. % acetic acid.
12. The process of claim 1, wherein the second methyl acetate
stream comprises less than 2 wt. % water.
13. The process of claim 1, further comprising esterifying the
acetic acid stream with methanol in a reactive distillation
column.
14. The process of claim 13, further comprising separating a water
stream from the reactive distillation column.
15. A process for producing ethanol by hydrogenolysis of methyl
acetate comprising: reacting carbon monoxide and methanol in a
reaction medium to form a reaction solution that comprises acetic
acid and from 0.5 to 25 wt. % methyl acetate, wherein the reaction
medium comprises water, acetic acid, methyl acetate, a first
catalyst, and an alkyl halide; flashing the reaction solution to
yield a carbonylation product and a liquid catalyst recycle stream,
wherein the carbonylation product comprises acetic acid and methyl
acetate; esterifying the carbonylation product to form a methyl
acetate enriched stream; feeding the methyl acetate enriched stream
to a distillation column to form an alkyl halides stream and a
methyl acetate stream; reacting the methyl acetate stream and
hydrogen in the presence of a second catalyst to form an alcohol
product that comprises ethanol and methanol; and recovering ethanol
from the alcohol product.
16. A process for producing ethanol by hydrogenolysis of methyl
acetate comprising: reacting carbon monoxide and methanol in a
reaction medium to form a reaction solution that comprises acetic
acid, acetaldehyde, and methyl acetate, wherein the reaction medium
comprises water, acetic acid, a first catalyst, and an alkyl
halide; flashing the reaction solution to yield a carbonylation
product and a liquid catalyst recycle stream; separating the
carbonylation product into an acetic acid stream and a first
overhead stream comprising methyl acetate, acetaldehyde, and alkyl
halide; separating the first overhead stream into a methyl acetate
residue and a second overhead stream comprising acetaldehyde and
alkyl halide; extracting the second overhead stream with an aqueous
stream to obtain a raffinate comprising alkyl halide and an
extractant comprising acetaldehyde; combining the methyl acetate
residue and extractant to form a feed stream; reacting the feed
stream and hydrogen in the presence of a second catalyst to form an
alcohol product that comprises ethanol and methanol; and recovering
ethanol from the alcohol product.
17. The process of claim 16, further comprising esterifying the
acetic acid stream to form a methyl acetate stream and introducing
the methyl acetate stream with the first overhead stream prior to
separation.
18. A process for producing ethanol by hydrogenolysis of methyl
acetate comprising: reacting carbon monoxide and methanol in a
reaction medium to form a reaction solution that comprises acetic
acid, acetaldehyde, and methyl acetate, wherein the reaction medium
comprises water, acetic acid, a first catalyst, and an alkyl
halide; flashing the reaction solution to yield a carbonylation
product and a liquid catalyst recycle stream; separating the
carbonylation product into an acetic acid stream and a first
overhead stream comprising methyl acetate, acetaldehyde, and alkyl
halide; separating the first overhead stream into a methyl acetate
residue and a second overhead stream comprising acetaldehyde and
alkyl halide; extracting the second overhead stream with an alkane
to obtain a raffinate comprising acetaldehyde and an extractant
comprising the alkyl halide and alkane; combining the methyl
acetate residue and the raffinate to form a feed stream; reacting
the feed stream and hydrogen in the presence of a second catalyst
to form an alcohol product that comprises ethanol and methanol; and
recovering ethanol from the alcohol product.
19. The process of claim 18, further comprising esterifying the
acetic acid stream to form a methyl acetate stream and introducing
the methyl acetate stream with the first overhead stream prior to
separation.
20. The process of claim 18, wherein the alcohol product is free of
water.
21. The process of claim 18, wherein the ethanol comprises less
than 1 wt. % water.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to alcohol
production processes and, in particular, to ethanol production
processes that use carbonylation processes to produce methyl
acetate as an intermediate to form ethanol.
BACKGROUND OF THE INVENTION
[0002] 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 cellulosic materials, such as corn or sugar cane. Conventional
methods for producing ethanol from petrochemical feed stocks, as
well as from cellulosic 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 cellulosic
material, are converted to ethanol by fermentation. However,
fermentation is typically used for consumer production of ethanol,
which is suitable for fuels or human consumption. In addition,
fermentation of starchy or cellulosic materials competes with food
sources and places restraints on the amount of ethanol that can be
produced for industrial use.
[0003] 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 often formed with ethanol or are formed in side reactions.
These impurities may limit the production of ethanol and may
require expensive and complex purification trains to separate the
impurities from the ethanol.
[0004] For example, U.S. Pat. No. 7,884,253 discloses methods and
apparatuses for selectively producing ethanol from syngas. The
syngas is derived from cellulosic biomass (or other sources) and
can be catalytically converted into methanol, which in turn can be
catalytically converted into acetic acid or acetates. The ethanoic
acid product may be removed from the reactor by withdrawing liquid
reaction composition and separating the ethanoic acid product by
one or more flash and/or fractional distillation stages from the
other components of the liquid reaction composition such as iridium
catalyst, ruthenium and/or osmium and/or indium promoter, methyl
iodide, water and unconsumed reactants which may be recycled to the
reactor to maintain their concentrations in the liquid reaction
composition. As another example, EP2060553 discloses a process for
the conversion of a carbonaceous feedstock to ethanol wherein the
carbonaceous feedstock is first converted to ethanoic acid, which
is then hydrogenated and converted into ethanol. Also, U.S. Pat.
No. 4,497,967 discloses an integrated process for the preparation
of ethanol from methanol, carbon monoxide and hydrogen feedstock.
The process esterifies an acetic anhydride intermediate to form
ethyl acetate and/or ethanol. In addition, U.S. Pat. No. 7,351,559
discloses a process for producing ethanol including a combination
of biochemical and synthetic conversions results in high yield
ethanol production with concurrent production of high value
co-products. An acetic acid intermediate is produced from
carbohydrates, such as corn, using enzymatic milling and
fermentation steps, followed by conversion of the acetic acid into
ethanol using esterification and hydrogenation reactions. Also,
U.S. Pub. No. 2010/0261800 discloses a process for the production
of ethanol of ethanol from synthesis gas through methanol
carbonylation to form ethanoic acid and esterifing ethanoic acid to
methyl ethanoate and/or ethyl ethanoate.
[0005] In additional to alkanoic acids, methyl acetate can also be
used to make ethanol. For example, U.S. Pat. No. 8,088,832
discloses a method and apparatus for synthesizing ethanol using
stepwise catalytic reaction to convert carbon monoxide and hydrogen
into ethanol through intermediates, such as methanol and methanol
acetate, using catalysts including iridium acetate. U.S. Pat. No.
8,080,693 discloses a process for converting methanol to ethanol
which comprises reacting methanol and carbon monoxide in the
presence of a catalyst to produce a product comprising at least 25
mole % methyl acetate and, in some instances, acetic acid. U.S.
Pat. No. 4,454,358 discloses a process for continuously producing
ethanol via the carbonylation of methanol and hydrogenating a
mixture of methanol and methyl acetate to form ethanol. Another
route to ethanol is proposed by U.S. Pub. No. 2011/0124927 for
converting syngas to dimethyl ether, carbonylating the dimethyl
ether to methyl acetate, hydrogenating the methyl acetate to
methanol and ethanol, and recovering the ethanol product.
[0006] In view of the conventional processes and literature, the
need remains for improved ethanol production processes that are
capable of effectively using methyl acetate, which may be formed
from methanol and/or carbon monoxide feed sources.
SUMMARY OF THE INVENTION
[0007] In one embodiment, the present invention relates to a
process for producing ethanol by hydrogenolysis of methyl acetate.
The process comprises the step of reacting carbon monoxide and
methanol in a reaction medium to form a reaction solution that
comprises acetic acid and from 0.5 to 25 wt. % methyl acetate. In
one embodiment, the reaction medium comprises water, acetic acid,
methyl acetate, a first catalyst, and an alkyl halide. The process
further comprises the steps of flashing the reaction solution to
yield a carbonylation product and a liquid catalyst recycle stream,
separating the carbonylation product into a first methyl acetate
stream and acetic acid stream, and esterifying the acetic acid
stream to form a second methyl acetate stream. The process further
comprises the steps of feeding the first methyl acetate stream and
the second methyl acetate stream to a distillation column to remove
alkyl halides and obtain a third methyl acetate stream and reacting
the third methyl acetate stream and hydrogen in the presence of a
second catalyst to form an alcohol product that comprises ethanol
and methanol. The process further comprises the steps of recovering
ethanol from the alcohol product. Preferably, the third methyl
acetate stream comprises at least 60 wt. % methyl acetate, less
than 5 wt. % acetic acid, and is substantially free of methyl
iodide. Preferably, the first methyl acetate stream comprises at
least 20 wt. % methyl acetate and the second methyl acetate stream
comprises at least 50 wt. % methyl acetate, less than 5 wt. %
acetic acid and less than 2 wt. % water.
[0008] The process further comprises the step of withdrawing the
acetic acid as a sidedraw. Preferably, the sidedraw comprises at
least 30 wt. % acetic acid, less than 10 wt. % methyl acetate, and
less than 0.1 wt. % alkyl halide.
[0009] The process further comprises the steps of esterifying the
acetic acid stream with methanol in a reactive distillation column
and separating a water stream from the reactive distillation
column.
[0010] In another embodiment, the process comprises the step of
esterifying the carbonylation product to form a methyl acetate
enriched stream.
[0011] In another embodiment, the process further comprises the
step of separating the carbonylation product into an acetic acid
stream and a first overhead stream comprising methyl acetate,
acetaldehyde, and alkyl halide. The process further comprises the
step of separating the first overhead stream into a methyl acetate
residue and a second overhead stream comprising acetaldehyde and
alkyl halide. The process further comprises the step of extracting
the second overhead stream with an aqueous stream to obtain a
raffinate comprising alkyl halide and an extractant comprising
acetaldehyde. The process further comprises the step of combining
the methyl acetate residue and extractant to form a feed stream.
The process further comprises the step of esterifying the acetic
acid stream to form a methyl acetate stream and introducing the
methyl acetate stream with the first overhead stream prior to
separation. The process further comprises the step of reacting the
feed stream and hydrogen in the presence of a second catalyst to
form an alcohol product that comprises ethanol and methanol.
Preferably, the ratio between ethanol and methanol is greater than
50%.
[0012] In another embodiment, the process comprises the step of
extracting the second overhead stream with an alkane to obtain a
raffinate comprising acetaldehyde and an extractant comprising the
alkyl halide and alkane. The process further comprises the step of
combining the methyl acetate residue and raffinate to form a feed
stream. The process further comprises the steps of reacting the
feed stream and hydrogen in the presence of a second catalyst to
form an alcohol product that comprises ethanol and methanol and
recovering ethanol from the alcohol product.
BRIEF DESCRIPTION OF DRAWINGS
[0013] The invention is described in detail below with reference to
the appended drawings, wherein like numerals designate similar
parts.
[0014] FIG. 1 is a schematic diagram of an ethanol production
process in accordance with one embodiment of the present
invention.
[0015] FIG. 2 is a schematic diagram of an ethanol production
process that directly feds the carbonylation product to the
esterification unit in accordance with one embodiment of the
present invention.
[0016] FIG. 3 is a schematic diagram of an ethanol production
process with the recovery and recycle of acetaldehyde using an
aqueous solvent in accordance with one embodiment of the present
invention.
[0017] FIG. 4 is a schematic diagram of an ethanol production
process with the recovery and recycle of acetaldehyde using an
organic solvent in accordance with one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
Introduction
[0018] In general, the present invention relates to processes for
making ethanol through an intermediate methyl acetate. In one
embodiment, the invention is a process for producing ethanol
comprising the steps of reacting methyl acetate, under
hydrogenolysis conditions, with hydrogen to form methanol and
ethanol. The methyl acetate is formed by carbonylation of methanol
using alkyl halides, such as halogen promoters, e.g., methyl iodide
(MeI). During the carbonylation reaction acetic acid is also
formed. In order to increase the amount of methyl acetate to
maximize the amount of ethanol being made, the acetic acid may be
separated from the reaction mixture and esterified to form
additional methyl acetate. As a result of using alkyl halides in
the carbonylation reaction, the methyl acetate streams may comprise
a small amount of alkyl halides. Embodiments of the present
invention provide a method to remove the alkyl halides, such that
an alkyl halide-free methyl acetate stream may be used for the
hydrogenolysis reaction to form ethanol.
[0019] In one embodiment, due to the reaction conditions and
reaction medium of the carbonylation reaction, permanganate
reducing compounds (PRC's) are also formed as side products. PRC's
may be recovered and combined with the methyl acetate stream to
undergo reduction to form ethanol. However, when recovering PRC's
from the carbonylation reaction mixture, the alkyl halides may pass
through into the stream and as such, the resulting PRC's stream may
comprise the alkyl halides. Embodiments of the present invention
advantageously increase the amounts of alkyl halides that can be
removed from the PRC's stream to yield an alkyl halide-free PRC's
stream, which may be combined with the alkyl halide-free methyl
acetate.
[0020] In one embodiment, alkyl halides may be removed from the
PRC's stream by using an aqueous solvent or an organic solvent. The
use of an aqueous solvent may increase the amount of water in the
resulting ethanol product and a drying column may be used to remove
water from the ethanol. In one embodiment, an alkane may be used as
the organic solvent to remove alkyl halides from the PRC's
stream.
[0021] Accordingly, the present invention, in one embodiment,
relates to a process for producing ethanol by methyl acetate
hydrogenolysis. The process comprises the step of reacting carbon
monoxide and methanol in a reaction medium to form a reaction
solution. The reaction medium comprises water, acetic acid, methyl
acetate, a first catalyst and an alkyl halide. The reaction
solution comprises acetic acid, methyl acetate, water, and alkyl
halide. The reaction solution comprises acetic acid in an amount
from 1 to 40 wt. %, e.g., from 2 to 35 wt. %, or from 3 to 30 wt.
%. In one embodiment, the reaction solution comprises methyl
acetate in an amount from 0.5 to 25 wt. %, e.g., from 5 to 25 wt. %
or from 10 to 24.9 wt. %.
[0022] The process further comprises the step of flashing the
reaction solution to yield a carbonylation product and a liquid
catalyst recycle stream. In one embodiment, a portion of the acetic
acid may be removed in the liquid catalyst recycle stream. The
liquid catalyst recycle stream may also comprise methyl acetate.
The carbonylation product comprises acetic acid, methyl acetate,
water and alkyl halides. The carbonylation product comprises acetic
acid in an amount greater than 15 wt. %, e.g., greater than 20 wt.
%. In terms of ranges the acetic acid concentration in the
carbonylation product may range from 15 to 50 wt. %, e.g., from 20
to 50 wt. %. In addition, the carbonylation product comprises
methyl acetate in an amount from 10 wt. % to 45 wt. %, e.g., from
15 wt. % to 40 wt. % and from 20 wt. % to 35 wt. %.
[0023] The process further comprises the step of separating the
carbonylation product into a first methyl acetate stream and an
acetic acid stream. In one embodiment, the acetic acid stream is a
sidedraw from a distillation column. The sidedraw comprises at
least 30 wt. % acetic acid, e.g., at least 40 wt. %, or at least 50
wt. %. The sidedraw comprises less than 10 wt. % methyl acetate,
less than 8 wt. %, or less than 6 wt. %. The sidedraw comprises
less than 0.1 wt. % alkyl halide, e.g., less than 0.05 wt. %, or
less than 0.01 wt. %. In one embodiment, the first methyl acetate
stream comprises methyl acetate and alkyl halide. The first methyl
acetate stream comprises at least 20 wt. % methyl acetate, e.g., at
least 35 wt. %, or at least 40 wt. %. The first methyl acetate
stream comprises at least 10 wt. % alky halide, e.g., at least 15
wt. %, or at least 25 wt. %.
[0024] The process further comprises the step of esterifying the
acetic acid stream to form a second methyl acetate stream. In one
embodiment, the esterification of acetic acid stream is conducted
in an esterification unit, e.g., a reactive distillation column,
with methanol to form an esterified product. In one embodiment, an
excess amount of methanol is used in the esterification unit to
convert most of the acetic acid to methyl acetate. The excess
methanol may be recovered and directed to the carbonylation reactor
or back to the esterification reactor. The esterified product
comprises less than 5 wt. % acetic acid, e.g., less than 1 wt. %,
or less than 0.1 wt. %. The esterified product may be separated
into a second methyl acetate stream and an aqueous stream. The
second methyl acetate stream comprises at least 50 wt. % methyl
acetate, e.g., at least 60 wt. %, or at least 75 wt. %. The second
methyl acetate stream comprises less than 1 wt. % water, e.g., less
than 0.1 wt. %, or less than 0.01 wt. %. The second methyl acetate
stream comprises less than 50 wt. % methanol, e.g., less than 30
wt. %, or less than 25 wt. %. The second methyl acetate stream is
substantially free of acetic acid, e.g., less than 1 wt. %, e.g.,
less than 0.1 wt. %, or less than 0.01 wt. %. In one embodiment,
most of the acetic acid is reacted to form methyl acetate. Any
unreacted acetic acid is removed in the aqueous stream. The aqueous
stream comprises less than 10 wt. % acetic acid, e.g., less than 5
wt. %, or less than 3 wt. %. The aqueous stream comprises at least
80 wt. % water, e.g., at least 90 wt. %, or at least 95 wt. %.
[0025] The process further comprises the step of feeding the first
methyl acetate and the second methyl acetate stream to a
distillation column to remove alkyl halides and to obtain a third
methyl acetate stream. The removal of alkyl halide from the methyl
acetate stream is beneficial because (1) the alkyl halide may be
recycled to the carbonylation reaction, and (2) alkyl halides may
be detrimental to the hydrogenolysis reaction. Therefore, the
removal of alkyl halides may yield a purified third methyl acetate
stream that is a more suitable feed to a hydrogenolysis process for
the production of methanol and/or ethanol. In one embodiment, the
first methyl acetate stream and the second methyl acetate stream
may be fed separately to the distillation column. In another
embodiment, the first methyl acetate stream may be combined with
the second methyl acetate stream and fed to the distillation column
to yield a third methyl acetate stream. The third methyl acetate
stream comprises at least 60 wt. % methyl acetate, e.g., at least
70 wt. %, or at least 80 wt. %. The third methyl acetate stream may
also comprise unreacted methanol from the esterification reaction.
The third methyl acetate stream comprises less than 30 wt. %
methanol, e.g., less than 20 wt. %, or less than 10 wt. %. The
third methyl acetate stream is substantially free of alkyl halides,
e.g., less than 0.01 wt. %, or less than 0.001 wt. %.
[0026] The process further comprises the step of reacting the third
methyl acetate stream and hydrogen in the presence of a second
catalyst to form an alcohol product that comprises ethanol and
methanol. The hydrogenolysis reaction may take place in the
presence of a suitable hydrogenolysis catalyst. Examples of
hydrogenolysis catalysts include copper containing catalysts,
especially those with copper in a reduced or partially reduced
state. Examples of such copper containing catalysts are described
in U.S. Pat. Nos. 5,198,592; 5,414,161; and 7,947,746; U.S. Pub.
No. 2009/0326080, and WO83/03409, the entireties of which are
incorporated herein by reference.
[0027] After methanol and ethanol are produced by hydrogenolysis,
the methanol and ethanol may be separated by a suitable separation
technique, such as distillation, to form an ethanol stream and a
methanol stream. The ethanol stream comprises at least 88 wt. %
ethanol, e.g., at least 90 wt. %, or at least 93 wt. %. The
methanol stream comprises at least 60 wt. % methanol, e.g., at
least 70 wt. %, or at least 80 wt. %. In one embodiment, the
methanol stream, when enriched in methanol, may be fed in whole or
part to the carbonylation reactor and/or esterification reactor. In
one embodiment, the methanol stream comprises methanol and methyl
acetate. The methanol stream may be recycled to the esterification
step to generate additional methyl acetate. The amount of methyl
acetate, when present, may be less than 30 wt. %, e.g., less than
20 wt. % or less than 15 wt. %.
[0028] In another embodiment, the carbonylation product is fed
directly to the esterification unit with methanol to form methyl
acetate prior to separating the carbonylation product. By
eliminating the separation, the acetic acid may be sent to the
esterification unit in the vapor phase.
[0029] As stated above, the methyl acetate streams are fed to a
distillation column to remove alkyl halides. In addition to alkyl
halides, methyl acetate and PRC's are present in the alkyl halides
stream and the methyl acetate and PRC's may be recovered and fed to
the hydrogenolysis reactor to form ethanol. In another embodiment,
the PRC's may be recovered with a PRC recovery system (PRS) that
comprises one or more distillation column. PRC's, may include
acetaldehyde, acetone, methyl ethyl ketone, butyraldehyde,
crotonaldehyde, 2-ethyl crotonaldehyde, 2-ethyl butyraldehyde, the
aldol condensation products thereof, or mixtures thereof. Exemplary
PRS include those described in U.S. Pat. Nos. 7,855,306; 7,223,886;
7,855,306; 6,143,930 and 6,339,171, and U.S. Pub. No. 2012/0090981,
the entire contents and disclosures of which is hereby incorporated
by reference. A stream enriched with PRC's may be separated from
the carbonylation production process and introduced to the PRS.
This stream may also comprise alkyl halides.
[0030] Although it is preferred to recover methyl iodide for
returning to the carbonylation reactor, other alkyl halides such as
ethyl iodide, propyl iodide, butyl iodide, pentyl iodide, hexyl
iodide, and isomers thereof, may also be removed from the treated
streams of the PRS. The alkyl halides, including halogen promoters,
may cause corrosion in the system by forming hydroiodic (HI) acid
in distillation portions of the PRS as described in several
reactions that involve the halogen promoter, methyl iodide.
[0031] In one embodiment, one or more distillation columns are used
to recover PRC's. The alkyl halides stream is fed to a distillation
column to form a vapor phase stream overhead, a higher boiling
liquid phase residuum, and a sidestream. The vapor phase stream
overhead is enriched with PRC's with respect to the alkyl halides
stream. The sidestream is enriched with methyl acetate with respect
to the alkyl halides stream. The sidestream may be in vapor phase
and may be fed directly to the hydrogenolysis reactor. The vapor
phase stream may be condensed and extracted with an aqueous
solvent, i.e., water, to obtain an aqueous stream comprising an
aqueous PRC's stream and a raffinate comprising methyl iodide.
[0032] In another embodiment, the vapor phase stream may be
condensed an extracted with an organic solvent, e.g., alkane, to
obtain an organic stream comprising methyl iodide and a raffinate
comprising the PRC's. The PRC's may be combined with the methyl
acetate stream and fed to the hydrogenolysis reactor.
[0033] In one embodiment, methyl acetate may be in liquid form and
required to be vaporized prior to being fed to the hydrogenolysis
reactor. In another embodiment, the methyl acetate stream may be in
vapor phase and the purified liquid PRC's may be vaporized by
combining with the vapor methyl acetate streams. As such a
vaporizer may not be needed.
Carbonylation
[0034] The raw materials, methanol 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. For purposes of the present invention, acetic acid and
methyl acetate may be produced using a methanol feed via methanol
carbonylation as described in U.S. Pat. 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 entire disclosures of
which are incorporated herein by reference. In one embodiment, the
production of ethanol is integrated with such methanol
carbonylation processes that form mixtures of acetic acid and
methyl acetate.
[0035] As petroleum and natural gas prices fluctuate becoming
either more or less expensive, methods for producing acetic acid,
and methyl acetate and intermediates such as methanol and carbon
monoxide from alternate carbon sources have drawn increasing
interest. In particular, when petroleum is relatively expensive, it
may become advantageous to produce acetic acid from synthesis gas
("syngas") that is derived from more available carbon sources. U.S.
Pat. No. 6,232,352, the entirety 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 syngas is diverted from the
methanol synthesis loop and supplied to a separator unit to recover
CO, which is then used to produce acetic acid and/or methyl
acetate. In a similar manner, hydrogen for the hydrogenolysis step
may be supplied from syngas.
[0036] In some embodiments, some or all of the raw materials for
the above-described carbonylation process may be derived partially
or entirely from syngas. For example, the acetic acid and/or methyl
acetate may be formed from methanol and carbon monoxide, both of
which may be derived from syngas. The syngas may be formed by
partial oxidation reforming or steam reforming, and the carbon
monoxide may be separated from syngas. Similarly, hydrogen that is
used in the step of methyl acetate hydrogenolysis to form the crude
ethanol product may be separated from syngas. The syngas, in turn,
may be derived from variety of carbon sources. The carbon source,
for example, may be selected from the group consisting of natural
gas, oil, petroleum, coal, biomass, and combinations thereof.
Syngas or hydrogen may also be obtained from bio-derived methane
gas, such as bio-derived methane gas produced by landfills or
agricultural waste.
[0037] Examples of biomass include, but are not limited to,
agricultural wastes, forest products, grasses, and other cellulosic
material, timber harvesting residues, softwood chips, hardwood
chips, tree branches, tree stumps, leaves, bark, sawdust, off-spec
paper pulp, corn, corn stover, wheat straw, rice straw, sugarcane
bagasse, switchgrass, miscanthus, animal manure, municipal garbage,
municipal sewage, commercial waste, grape pumice, almond shells,
pecan shells, coconut shells, coffee grounds, grass pellets, hay
pellets, wood pellets, cardboard, paper, plastic, and cloth. Black
liquor, which is an aqueous solution of lignin residues,
hemicellulose, and inorganic chemicals, may also be used as a
biomass source. Biomass-derived syngas has a detectable .sup.14C
isotope content as compared to fossil fuels such as coal or natural
gas.
[0038] Although carbonylation may be a preferred acetic acid and
methyl acetate production method, other suitable methods may be
employed. In a preferred embodiment that employs carbonylation, the
carbonylation system preferably comprises a reaction zone, which
includes a reactor, a flasher and optionally a reactor recovery
unit. In one embodiment, carbon monoxide is reacted with methanol
in a suitable reactor, e.g., a continuous stirred tank reactor
("CSTR") or a bubble column reactor. Preferably, the carbonylation
process is a low water, catalyzed, e.g., rhodium-catalyzed,
carbonylation of methanol to acetic acid, as exemplified in U.S.
Pat. No. 5,001,259, which is hereby incorporated by reference.
[0039] The carbonylation reaction may be conducted in a homogeneous
catalytic reaction system comprising a reaction solvent, methanol
and/or reactive derivatives thereof, a Group VIII catalyst, at
least a finite concentration of water, and optionally an iodide
salt.
[0040] Suitable catalysts include Group VIII catalysts, e.g.,
rhodium and/or iridium catalysts. The rhodium catalyst may be added
in any suitable form such that the active rhodium catalyst is a
carbonyl iodide complex. Exemplary rhodium catalysts are described
in Michael Gau.beta., et al., Applied Homogeneous Catalysis with
Organometallic Compounds: A Comprehensive Handbook in Two Volume,
Chapter 2.1, p. 27-200, (1.sup.st ed., 1996). Iodide salts
optionally maintained in the reaction mixtures of the processes
described herein may be in the form of a soluble salt of an alkali
metal or alkaline earth metal or a quaternary ammonium or
phosphonium salt. In certain embodiments, a catalyst co-promoter
comprising lithium iodide, lithium acetate, or mixtures thereof may
be employed. The salt co-promoter may be added as a non-iodide salt
that will generate an iodide salt. The iodide catalyst stabilizer
may be introduced directly into the reaction system. Alternatively,
the iodide salt may be generated in-situ since under the operating
conditions of the reaction system, a wide range of non-iodide salt
precursors will react with methyl iodide or hydroiodic acid in the
reaction medium to generate the corresponding co-promoter iodide
salt stabilizer. For additional detail regarding rhodium catalysis
and iodide salt generation, see U.S. Pat. Nos. 5,001,259;
5,026,908; and 5,144,068, which are hereby incorporated by
reference.
[0041] When an iridium catalyst is utilized, the iridium catalyst
may comprise any iridium-containing compound which is soluble in
the liquid reaction composition. The iridium catalyst may be added
to the liquid reaction composition for the carbonylation reaction
in any suitable form which dissolves in the liquid reaction
composition or is convertible to a soluble form. Examples of
suitable iridium-containing compounds which may be added to the
liquid reaction composition include: IrCl.sub.3, IrI.sub.3,
IrBr.sub.3, [Ir(CO).sub.2I].sub.2, [Ir(CO).sub.2Cl].sub.2,
[Ir(CO).sub.2Br].sub.2, [Ir(CO).sub.2I.sub.2].sup.-H.sup.+,
[Ir(CO).sub.2Br.sub.2].sup.-H.sup.+,
[Ir(CO).sub.2I.sub.4].sup.-H.sup.+,
[Ir(CH.sub.3)I.sub.3(CO.sub.2].sup.-H.sup.+, Ir.sub.4(CO).sub.12,
IrCl.sub.3.3H.sub.2O, IrBr.sub.3.3H.sub.2O, iridium metal,
Ir.sub.2O.sub.3, Ir(acac)(CO).sub.2, Ir(acac).sub.3, iridium
acetate, [Ir.sub.3O(OAc).sub.6(H.sub.2O).sub.3][OAc], and
hexachloroiridic acid [H.sub.2IrCl.sub.6]. Chloride-free complexes
of iridium such as acetates, oxalates and acetoacetates are usually
employed as starting materials. The iridium catalyst concentration
in the liquid reaction composition may be in the range of 100 to
6,000 ppm. The carbonylation of methanol utilizing iridium catalyst
is well known and is generally described in U.S. Pat. Nos.
5,942,460; 5,932,764; 5,883,295; 5,877,348; 5,877,347; and
5,696,284, which are hereby incorporated by reference.
[0042] A halogen co-catalyst/promoter is generally used in
combination with the Group VIII metal catalyst component. Methyl
iodide is a preferred halogen promoter. Preferably, the
concentration of halogen promoter in the reaction medium ranges
from 1 wt. % to 50 wt. %, and preferably from 2 wt. % to 30 wt.
%.
[0043] The halogen promoter may be combined with the salt
stabilizer/co-promoter compound. Particularly preferred are iodide
or acetate salts, e.g., lithium iodide or lithium acetate.
[0044] Other promoters and co-promoters may be used as part of the
catalytic system of the present invention as described in U.S. Pat.
No. 5,877,348, which is hereby incorporated by reference. Suitable
promoters are selected from ruthenium, osmium, tungsten, rhenium,
zinc, cadmium, indium, gallium, mercury, nickel, platinum,
vanadium, titanium, copper, aluminum, tin, antimony, and are more
preferably selected from ruthenium and osmium. Specific
co-promoters are described in U.S. Pat. No. 6,627,770, which is
incorporated herein by reference.
[0045] A promoter may be present in an effective amount up to the
limit of its solubility in the liquid reaction composition and/or
any liquid process streams recycled to the carbonylation reactor
from the acetic acid recovery stage. When used, the promoter is
suitably present in the liquid reaction composition at a molar
ratio of promoter to metal catalyst of 0.5:1 to 15:1, preferably
2:1 to 10:1, more preferably 2:1 to 7.5:1. A suitable promoter
concentration is 400 to 5000 wppm.
[0046] In one embodiment, the temperature of the carbonylation
reaction in the reactor is preferably from 150.degree. C. to
250.degree. C., e.g., from 150.degree. C. to 225.degree. C., or
from 150.degree. C. to 200.degree. C. The pressure of the
carbonylation reaction is preferably from 1 to 20 MPa, preferably 1
to 10 MPa, most preferably 1.5 to 5 MPa. Acetic acid and methyl
acetate are typically manufactured in a liquid phase reaction at a
temperature from 150.degree. C. to 200.degree. C. and a total
pressure from 2 to 5 MPa.
[0047] In one embodiment, reaction mixture comprises a reaction
solvent or mixture of solvents. The solvent is preferably
compatible with the catalyst system and may include pure alcohols,
mixtures of an alcohol feedstock, and/or the desired carboxylic
acid and/or esters of these two compounds. In one embodiment, the
solvent and liquid reaction medium for the (low water)
carbonylation process is preferably acetic acid and methyl
acetate.
[0048] Water may be formed in situ in the reaction medium, for
example, by the esterification reaction between methanol reactant
and acetic acid product. In some embodiments, water is introduced
to reactor together with or separately from other components of the
reaction medium. Water may be separated from the other components
of reaction product withdrawn from reactor and may be recycled in
controlled amounts to maintain the required concentration of water
in the reaction medium. Preferably, the concentration of water
maintained in the reaction medium ranges from 0.1 wt. % to 16 wt.
%, e.g., from 1 wt. % to 14 wt. %, or from 1 wt. % to 3 wt. % of
the total weight of the reaction product.
[0049] The desired reaction rates are obtained even at low water
concentrations by maintaining in the reaction medium an ester of
the desired carboxylic acid and an alcohol, desirably the alcohol
used in the carbonylation, and an additional iodide ion that is
over and above the iodide ion that is present as hydrogen iodide.
An example of a preferred ester is methyl acetate. The additional
iodide ion is desirably an iodide salt, with lithium iodide (LiI)
being preferred. It has been found, as described in U.S. Pat. No.
5,001,259, that under low water concentrations, methyl acetate and
lithium iodide act as rate promoters only when relatively high
concentrations of each of these components are present and that the
promotion is higher when both of these components are present
simultaneously. The absolute concentration of iodide ion content is
not a limitation on the usefulness of the present invention.
[0050] In low water carbonylation, the additional iodide over and
above the organic iodide promoter may be present in the catalyst
solution in amounts ranging from 2 wt. % to 20 wt. %, e.g., from 2
wt. % to 15 wt. %, or from 3 wt. % to 10 wt. %; the methyl acetate
may be present in amounts ranging from 0.5 wt % to 30 wt. %, e.g.,
from 1 wt. % to 25 wt. %, or from 2 wt. % to 20 wt. %; and the
lithium iodide may be present in amounts ranging from 5 wt. % to 20
wt %, e.g., from 5 wt. % to 15 wt. %, or from 5 wt. % to 10 wt. %.
The catalyst may be present in the catalyst solution in amounts
ranging from 200 wppm to 2000 wppm, e.g., from 200 wppm to
1500.
Esterification
[0051] According to embodiments of the present invention, the
acetic acid present in the acetic acid stream is reacted with an
alcohol stream, e.g., comprising methanol, in an esterification
unit to produce methyl acetate and water. The methyl acetate is
reacted with hydrogen in a hydrogenolysis reactor to form ethanol
and methanol.
[0052] An esterification unit of the present invention comprises a
reaction zone and a separation zone. In some embodiments, an
esterification unit comprises a reactor coupled to one or more
distillation columns. In other embodiments, the esterification unit
comprises a reactive distillation column (also referred to herein
as the second column) comprising a reaction section and a
distillation section, to produce a distillate stream comprising
methyl acetate and a residue stream comprising water.
[0053] As indicated above, acetic acid from the acetic acid stream
is reacted with methanol to form methyl acetate. The methanol is
preferably fed to the esterification unit in a counter-current flow
to the acetic acid stream to facilitate the production of methyl
acetate. The process parameters for the esterification step may
vary widely depending, for example, on the catalyst employed and
the ester being formed.
Hydrogenolysis
[0054] As discussed above, the processes of the invention involve a
step of subjecting methyl acetate to hydrogenolysis in a
hydrogenolysis reactor to form methanol and ethanol. In this
context, the term "hydrogenolysis" of methyl acetate refers to the
reaction of methyl acetate with hydrogen to form methanol and
ethanol, but it should be understood that this reaction is not
limited to any particular mechanism and may occur via one or more
intermediates, e.g., acetic acid, which may undergo further
reaction, e.g., hydrogenation, to form one or more alcohol species,
e.g., ethanol.
[0055] The invention may be described in relation to the production
of ethanol, but, as indicated above, methanol is coproduced. At
least a portion of the methanol produced preferably is recycled to
the process for producing acetic acid in the carbonylation reaction
or to the process of producing methyl acetate in the esterifying
unit. Additionally or alternatively, at least a portion of the
methanol may be recovered as a saleable end product.
[0056] In embodiments where at least a portion of the methanol is
recycled to carbonylation reaction or esterification reaction, at
least a portion of any methanol stream may be treated in one or
more purification steps, prior to being introduced into the
reaction zone for synthesis of acetic acid or methyl acetate.
[0057] The hydrogenolysis step may include a variety of
configurations using a fixed bed reactor or a fluidized bed
reactor. 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, a radial flow reactor or
reactors may be employed, or a series of reactors may be employed
with or without 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.
[0058] The catalyst may be 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, may be employed.
In some instances, the hydrogenolysis 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.
[0059] Contact or residence time may also vary widely, depending
upon such variables as amount of methyl acetate, 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. Contact times, at least for
vapor phase reactions, may be from 0.1 to 100 seconds.
[0060] The hydrogenolysis of methyl acetate to form methanol and
ethanol is preferably conducted in the presence of a hydrogenolysis
catalyst. Suitable hydrogenolysis catalysts include catalysts
comprising a first metal and optionally one or more of a second
metal, a third metal or any number of additional metals, optionally
on a catalyst support. The first and optional second and third
metals may be selected from Group IB, IIB, IIIB, IVB, VB, VIIB,
VIIB, VIII transition metals, a lanthanide metal, an actinide metal
or a metal selected from any of Groups IIIA, IVA, VA, and VIA.
[0061] Particularly useful hydrogenolysis catalysts include copper
containing catalysts. These copper containing catalysts may further
comprise one or more additional metals, optionally, on a catalyst
support. The optional additional metal or metals may be selected
from Group IB, IIB, IIIB, IVB, VB, VIIB, VIIB, VIII transition
metals, a lanthanide metal, an actinide metal or a metal selected
from any of Groups IIIA, IVA, VA, and VIA. Particular metal
combinations for some exemplary catalyst compositions include
copper/cobalt/zinc, copper/zinc/iron, copper/cobalt/zinc/iron,
copper/cobalt/zinc/iron/calcium, and
copper/cobalt/zinc/molybdenum/sodium. Particular copper containing
catalysts may comprise copper chromite, copper and zinc, and/or
copper-zinc-oxide. Exemplary catalysts are further described in
U.S. Pat. Nos. 5,198,592; 5,414,161; and 7,947,746; U.S. Pub. No.
2009/0326080, and WO83/03409, the entireties of which are
incorporated herein by reference. Hydrogenolysis catalysts may
comprise CuO or ZnO. However, CuO and ZnO may be reduced or
partially reduced by hydrogen during the course of the
hydrogenolysis reaction. It is also possible to pre-reduce CuO
and/or ZnO by passing hydrogen over the catalyst before the
introduction of the methyl acetate feed.
[0062] As indicated above, in some embodiments, the catalyst
further comprises at least one additional metal, which may function
as a promoter.
[0063] In addition to one or more metals, in some embodiments of
the present invention the catalysts further comprise a support or a
modified support. As used herein, the term "modified support"
refers to a support that includes a support material and a support
modifier, which adjusts the acidity of the support material.
[0064] In particular, the hydrogenolysis of methyl acetate may
achieve favorable conversion of methyl acetate and favorable
selectivity and productivity to methanol and ethanol. For purposes
of the present invention, the term "conversion" refers to the
amount of methyl acetate in the feed that is converted to a
compound other than methyl acetate. Conversion is expressed as a
mole percentage based on methyl acetate in the feed. The conversion
may be at least 75%, e.g., at least 85%, or at least 90%. Although
catalysts that have high conversions are desirable, such as at
least 95% or at least 97%, in some embodiments a low conversion may
be acceptable at high selectivity for methanol/ethanol. It is, of
course, well understood that in many cases, it is possible to
compensate for conversion by appropriate recycle streams or use of
larger reactors, but it is more difficult to compensate for poor
selectivity.
[0065] Selectivity is expressed as a percentage of moles of product
per moles of converted methyl acetate. It should be understood that
each compound converted from methyl acetate has an independent
selectivity and that selectivity is independent from conversion.
Generally, methanol and ethanol will be produced in equal molar
ratios. The catalyst selectivity to each product, i.e., methanol
and ethanol, may be at least 70%, e.g., at least 80%, or at least
90%. Preferred embodiments of the hydrogenolysis 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 present in
undetectable amounts. Formation of alkanes may be low, and ideally
less than 2%, less than 1%, or less than 0.5% of the methyl acetate
passed over the catalyst is converted to alkanes, which have little
value other than as fuel.
[0066] The term "productivity," as used herein, refers to the grams
of a specified product, e.g., ethanol, formed during the
hydrogenolysis based on the kilograms of catalyst used per hour. A
productivity of at least 100 grams of ethanol per kilogram of
catalyst per hour, e.g., at least 400 grams of ethanol per kilogram
of catalyst per hour or at least 600 grams of ethanol per kilogram
of catalyst per hour, is possible. In terms of ranges, the
productivity may be from 100 to 3,000 grams of ethanol per kilogram
of catalyst per hour, e.g., from 400 to 2,500 grams of ethanol per
kilogram of catalyst per hour or from 600 to 2,000 grams of ethanol
per kilogram of catalyst per hour.
[0067] In various embodiments of the present invention, the crude
alcohol product produced by the hydrogenolysis process, before any
subsequent processing, such as purification and separation, will
typically comprise methanol, ethanol and, possibly, water. The
product stream from the hydrogenolysis reaction zone may also
comprise unconverted methyl acetate. This unconverted methyl
acetate may be separated from methanol and ethanol and saponified,
for example, at room temperature with caustic on a stoichiometric
basis. When aqueous sodium hydroxide is used as the caustic, the
saponification product will comprise sodium acetate in aqueous
solution. Caustic may be recovered, for example, by using a bipolar
membrane. Sodium acetate may be converted to acetic acid by
adjustment of pH. Caustic may be recycled to the saponification
reaction zone. Acetic acid may be recycled to a reaction zone for
converting acetic acid into vinyl acetate, which may be in turn
polymerized.
[0068] The ethanol product produced by the process of the present
invention may be an industrial grade ethanol comprising 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 ethanol product.
[0069] 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 C.sub.4-C.sub.20 alcohols.
Producing Ethanol from Methanol Via Methyl Acetate
[0070] FIG. 1 shows a schematic diagram of an ethanol production
process in accordance with one embodiment of the present invention.
Process 100 comprises carbonylation system 102, esterification unit
104, alkyl halide removal system 106, and hydrogenolysis system
108. Carbonylation system 102 comprises reaction zone 110 and
separation zone 112. Reaction zone 110 comprises carbonylation
reactor 114 and flasher 116, and separation zone 112 comprises at
least one distillation column 118. Esterification unit 104
comprises at least one column, e.g., a reactive distillation column
120. Alkyl halide removal system 106 comprises at least one column
122. Hydrogenolysis system 108 comprises vaporizer (not shown),
hydrogenolysis reactor 124, one or more flashers 126 and column
128. FIGS. 2-4 show exemplary embodiments of the present invention.
FIG. 2 shows a schematic diagram without the use of distillation
column 118. FIGS. 3 and 4 show the recovery of permanganate
reducing compounds (PRC's) using additional columns and
extractors.
[0071] Returning to FIG. 1, in carbonylation system 102, a methanol
feed stream 130 and carbon monoxide feed stream 132 are fed to a
lower portion of carbonylation reactor 114. At least some of the
methanol may be converted to, and hence present as, methyl acetate
in the liquid reaction composition by reacting with acetic acid
product or solvent. The concentration in the liquid reaction
composition of methyl acetate is suitably in the range from 0.5 wt.
% to 25 wt. %, e.g., from 5 wt. % to 25 wt. %, or from 10 wt. % to
24.9 wt. %.
[0072] Reactor 114 is preferably either a stirred vessel, e.g.,
CSTR, or bubble-column type vessel, with agitator or without an
agitator, within which the reaction medium is maintained,
preferably automatically, at a predetermined level. This
predetermined level may remain substantially constant during normal
operation. Into reactor 114, methanol, carbon monoxide, and
sufficient water (not shown) may be continuously introduced as
needed to maintain at least a finite concentration of water in the
reaction medium. In one embodiment, carbon monoxide, e.g., in the
gaseous state, is continuously introduced into reactor 114. The
temperature of reactor 114 may be controlled, as indicated above.
Carbon monoxide feed 132 is introduced at a rate sufficient to
maintain the desired total reactor pressure.
[0073] The gaseous carbon monoxide feed is preferably thoroughly
dispersed through the reaction medium by an agitator. A gaseous
purge is desirably vented via an off-gas line (not shown) from
reactor 114 to prevent buildup of gaseous by-products, such as
methane, carbon dioxide, and hydrogen, and to maintain a carbon
monoxide partial pressure at a given total reactor pressure.
[0074] The crude methyl acetate product is drawn off from reactor
114 at a rate sufficient to maintain a constant level therein and
is provided to flasher 116 via stream 134. The crude methyl acetate
product has the compositions as shown in Table 1.
TABLE-US-00001 TABLE 1 CRUDE METHYL ACETATE PRODUCT Component Conc.
(wt. %) Conc. (wt. %) Conc. (wt. %) Methyl Acetate 0.5 to 25 5 to
25 .sup. 10 to 24.9 Acetic Acid 10 to 90 20 to 70 30 to 50 Water
.sup. 5 to 40 5 to 30 10 to 30 Methyl Iodide 0.05 to 30 0.1 to
25.sup. 1 to 15
[0075] In flasher 116, the crude methyl acetate product is
separated in a flash separation step to obtain a volatile ("vapor")
overhead stream 136 comprising methyl acetate and acetic acid and a
less volatile stream 138 comprising a catalyst-containing solution.
Less volatile stream 138 may be also be referred to as a "liquid
catalyst recycle stream." In one embodiment, overhead stream 136
may be considered as the carbonylation product, as discussed above.
The catalyst-containing solution in line 138 comprises acetic acid
containing the rhodium and the iodide salt along with lesser
quantities of methyl acetate, methyl iodide, and water. Less
volatile stream 138 preferably is recycled to reactor 114. Vapor
overhead stream 136 also comprises methyl iodide, methyl acetate,
acetic acid, water, and permanganate reducing compounds
("PRCs").
[0076] Overhead stream 136 from flasher 116 is directed to
separation zone 112 having a first column 118. Separation zone 112
may also comprise additional units, e.g., a drying column, one or
more columns for removing PRCs, heavy ends columns, extractors,
etc.
[0077] In first column 118, overhead stream 136 is separated to
yield a low-boiling overhead vapor stream 140, an acetic acid
stream, and a high boiling residue stream 144. In one embodiment,
the acetic acid product that is removed via sidestream 142
preferably is conveyed, e.g., directly, without removing
substantially any water therefrom, to esterification unit 104,
e.g., reactive distillation column 120 of esterification unit
104.
[0078] In one embodiment, low-boiling overhead vapor stream 140
comprises methyl acetate and methyl iodide. Low-boiling overhead
vapor stream 140 may be referred to as a "first methyl acetate
stream." Methyl iodide may be removed from overhead vapor stream
140 using one or more distillation columns, e.g., distillation
column 122, to yield a substantially alkyl halide free methyl
acetate stream 152. Low-boiling overhead vapor stream 140 may
comprise other by-products, such as methanol, acetaldehyde, carbon
monoxide, and hydrogen.
[0079] In one embodiment, column 118 may comprise trays having
different concentrations of water. In these cases, the composition
of a withdrawn sidedraw may vary throughout the column. As such,
the withdrawal tray may be selected based on the amount of water
that is desired, e.g., more than 0.5 wt %. In another embodiment,
the configuration of the column may be varied to achieve a desired
amount or concentration of water in a sidedraw. Thus, an acetic
acid feed may be produced, e.g., withdrawn from a column, based on
a desired water content. Accordingly, in one embodiment, the
invention is to a process for producing ethanol comprising the step
of withdrawing a purified acetic acid sidedraw from a distillation
column in a carbonylation process, wherein a location from which
the sidedraw is withdrawn is based on a water content of the
sidedraw. The water content of the sidedraw may be from 20 to 70
wt. % water. The process further comprises the steps of esterifying
acetic acid in the presence of methanol under conditions effective
to form a methyl acetate product comprising methyl acetate and
methanol, reacting methyl acetate in a hydrogenolysis reactor to
form ethanol, and recovering ethanol.
[0080] The acetic acid stream in line 142, in some embodiments,
comprises methyl acetate, e.g., in an amount ranging from 0.01 wt.
% to 10 wt. %, e.g., from 0.1 wt. % to 8 wt. %, or from 1 wt. % to
6 wt. %. In addition to acetic acid, water, and methyl acetate, the
acetic acid stream may comprise halogens, e.g., methyl iodide,
which may be removed from the purified acetic acid stream.
[0081] Acetic acid stream 142 is fed to esterification system 104,
e.g., reactive distillation column 122, for esterification. In some
embodiments, acetic acid stream 142 may comprise at least 30 wt. %
acetic acid, at least 40 wt. %, or at least 50 wt. %. In terms of
ranges, the acetic acid stream optionally comprises from 30% to 95%
or from 50% to 90% of the acetic acid from the crude methyl acetate
product stream. The acetic acid stream may comprise from 30 to 80
wt. % acetic acid and from 20 to 70 wt. % water.
[0082] As shown in FIG. 1, acetic acid stream 142 is co-fed with
methanol stream in line 146 to esterification unit 104 to form
methyl acetate, thus yielding an ester enriched stream 148
comprising methyl acetate and methanol. Ester enriched stream 148
comprises methyl acetate and may be referred to as a "second methyl
acetate stream." Methanol stream 146 and acetic acid stream 142 may
be fed to the distillation column in a counter-current manner to
facilitate the production of a reaction product. In another
embodiment, not shown, methanol stream 146 may be added directly to
acetic acid stream 142 prior to being introduced into
esterification unit 104.
[0083] Although expressed as column 120 in FIG. 1, in some
embodiments, esterification unit 104 comprises a reaction zone
comprising a reactor, coupled to a separation zone comprising one
or more distillation columns and/or stripping columns. Suitable
reactors for use in the esterification include batch reactors,
continuously-fed stirred-tank reactors, plug-flow reactors,
reactive distillation towers, or a combination thereof. An acid
catalyst may be fed to the reactor to facilitate the esterification
of the acetic acid. Suitable acid catalysts for use in the present
invention include, but are not limited to sulfuric acid, phosphoric
acid, sulfonic acids, heteropolyacids, other mineral acids and a
combination thereof.
[0084] In one embodiment, second column 120 comprises an ion
exchange resin bed, an acidic catalyst, or combinations thereof.
Non-limiting examples of ion exchange resins suitable for use in
the present invention include macroporous strong-acid cation
exchange resins such as those from the Amberlyst.RTM. series
distributed by Rohm and Haas. Additional ion exchange resins
suitable for use in the present invention are disclosed in U.S.
Pat. Nos. 4,615,806, 5,139,981, and 7,588,690, the disclosures of
which are incorporated by reference in their entireties. Second
column 120 may comprise an acid selected from the group consisting
of sulfuric acid, phosphoric acid, sulfonic acids, heteropolyacids,
other mineral acids and a combination thereof. In other
embodiments, acid catalysts include zeolites and supports treated
with mineral acids and heteropolyacids.
[0085] The operating parameters of esterification unit 104 may be
varied to achieve a desired composition in ester enriched stream
148. For example, temperature, pressure, feed rates, and residence
times can be varied to increase conversion of acetic acid to an
ester, decrease the formation of impurities, achieve more efficient
separation, reduce energy consumption, or combinations thereof.
[0086] In one embodiment, esterification unit 104 operates at a
base temperature from 100.degree. C. to 150.degree. C., e.g., from
100.degree. C. to 130.degree. C. In terms of pressure,
esterification unit 104 may be operated at atmospheric pressure,
subatmospheric pressure, or superatmospheric pressure. For example,
esterification unit 104 operates at a pressure from 50 kPa to 500
kPa, e.g., from 50 kPa to 400 kPa.
[0087] In some embodiments, the feed rates of acetic acid and
methanol to the esterification unit 104 may be adjusted to control
the mole ratio of acetic acid to methanol being fed to
esterification unit 104. For example, the mole ratio of acetic acid
to methanol fed to esterification unit 118 is from 1:1 to 1:15,
e.g., from 1:1 to 1:5, or from 1:1 to 1:2.
[0088] The processes of the present invention preferably provide
for a high conversion of acetic acid to ester(s). In some
embodiments, for example, at least 80%, at least 90% or at least
95% of the acetic acid in acetic acid stream 142 is converted to an
ester.
[0089] Ester enriched stream 148 exiting esterification unit 104
preferably comprises at least 60 wt. % methyl acetate, e.g., at
least 70 wt. % or more preferably at least 75 wt. %. In terms of
ranges, ester enriched stream 148 may comprise at least methyl
acetate in an amount from 40 to 99 wt. %, e.g., from 50 to 90 wt. %
or from 65 to 90 wt. %.
[0090] When excess methanol is reacted with the acetic acid from
acetic acid stream 142, some methanol may be present in ester
enriched stream 148. Thus, ester enriched stream 148 may comprise
methanol in an amount from 0.1 to 80 wt. %, e.g., from 1 to 60 wt.
%, or from 10 to 30 wt. %. In other embodiments, where the acetic
acid is present in an excess relative to methanol or where the
acetic acid is present in about the same molar amount as methanol,
ester enriched stream 148 may be substantially free of methanol,
e.g., containing less than 10 wt. %, less than 5 wt. % or less than
1 wt. %.
[0091] Methyl acetate in stream 148 may be removed from
esterification unit 104 and fed directly, or combined with
low-boiling overhead vapor stream 140, to distillation column 122.
As a result of esterification, the total conversion of acetic acid,
may be greater than 90%, e.g., greater than 95% or greater than
99%. As a result of esterification, a water stream in line 150 may
be recovered with high purity. In some embodiments, water stream
150 may be separated from ester enriched stream 148 in the residue.
Preferably, water stream 150 comprises little, if any, unreacted
acetic acid, which may be further neutralized, and/or separated
from water stream 150. In some embodiments, water stream 150 may
comprise little, if any acetic acid, e.g., containing less than 5
wt. % acetic acid, and more preferably less than 1.5 wt. % acetic
acid.
[0092] As stated above, acetic acid stream in line 142 may comprise
hydrogen iodide. For example, acetic acid stream in line 142 may
comprise less than 5 wt. % HI, e.g., less than 1 wt. % or less than
0.5 wt. %. HI may be fed to reactive distillation column 120 along
with acetic acid, water and methyl acetate. In some embodiments, a
minor amount of methyl iodide may also be fed to reactive
distillation column 120. Any HI in reactive distillation column 120
may be converted to MeI and removed in distillate 148. In addition,
HI may beneficially act as a catalyst to promote the esterification
of acetic acid to methyl acetate. Therefore, the need to add
corrosive metals, such as sulfuric acid, may be reduced or
eliminated depending the concentration of HI.
[0093] Embodiments of the present invention beneficially generate
additional methyl acetate from acetic acid to increase the yield of
the final product ethanol. The esterification of acetic acid with
methanol increases the overall raw material efficiency by at least
5% relative to the same system but without an esterification
unit.
[0094] As shown, ester enriched stream 114 is combined with
low-boiling overhead vapor stream 140 and co-fed to distillation
column 122 to recover a substantially alkyl halide-free methyl
acetate stream 152 in the residue. The substantially alkyl
halide-free methyl acetate stream 152 may also be referred to as a
"third methyl acetate stream." In one embodiment, ester enriched
stream 114 and low-boiling overhead vapor stream 140 may be fed
separately to distillation column 122.
[0095] Returning to first column 118, low-boiling overhead vapor
stream 140 and ester enriched stream 148 is directed to
distillation column 122, which serves to form an alkyl halide
enriched distillate 154, which is also enriched in PRC's, notably
acetaldehyde, due to the similar boiling points of alkyl halide,
e.g., methyl iodide, and PRC's, acetaldehyde. Preferably, alkyl
halide enriched distillate 154 comprises most of the alkyl halide
in low-boiling overhead vapor stream 140 and ester enriched stream
148. In one embodiment, streams 140 and 142 are introduced in the
lower part of distillation column 122, e.g., lower half or lower
third. Distillation column 122 removes alkyl halides and PRC's, as
the distillate in line 154. Alkyl halide enriched distillate 154
preferably is refluxed, for example, at a reflux ratio from 1:10 to
10:1. Distillation column 122 is preferably a tray column as
described above and preferably operates at atmospheric pressure.
The temperature of the alkyl halide enriched distillate exiting in
line 154 from distillation column 122 preferably is from 0.degree.
C. to 70.degree. C., e.g., from 10.degree. C. to 50.degree. C. The
temperature of the residue exiting from column 122 preferably is
from 60.degree. C. to 115.degree. C., e.g., from 70.degree. C. to
110.degree. C.
[0096] In one embodiment, alkyl halide enriched distillate 154
comprises at least 95% of the alkyl halide in streams 140 and 142,
e.g., at least 98 wt. %, or at least 99.5 wt. %. In some
embodiments, alkyl halide enriched distillate 154 comprises methyl
acetate. Methyl acetate and PRC's in alkyl halide enriched
distillate 154 may be recovered and react with hydrogen to generate
additional ethanol product.
[0097] The substantially alkyl halide-free methyl acetate stream
152 is withdrawn from distillation column 122 and fed to
hydrogenolysis system 108. Preferably, methyl acetate stream 152
comprises methyl acetate and methanol from low-boiling overhead
vapor stream 140 and ester enriched stream 148. In one embodiment,
methyl acetate stream 152 comprises greater than 50 wt. % methyl
acetate, greater than 60 wt. %, or greater than 70 wt. %.
[0098] Methyl acetate stream comprises methyl acetate and methanol
in line 152 is directed to the hydrogenolysis zone 108. Methyl
acetate stream 152 may be vaporized via a vaporizer (not shown) and
co-fed with hydrogen in line 156 to hydrogenolysis reactor 124.
Optionally, methyl acetate stream 152 may be withdrawn from column
122 as a vapor stream and be fed directly to hydrogenolysis reactor
124 without the use of a vaporizer. In addition, methyl acetate
stream in line 152 may also be pre-heated before being fed to
hydrogenolysis reactor 124. Methyl acetate stream 152 and hydrogen
in line 156 may be preheated to a temperature of at least
150.degree. C., e.g., at least 200.degree. C., before being fed to
hydrogenolysis reactor 124, provided that the feed remains in the
vapor phase and above the dew point.
[0099] Hydrogenolysis reactor 124 preferably comprises a
hydrogenolysis catalyst. The reactants, namely the methyl acetate
in the methyl acetate of column 122, react in the presence of
hydrogen and the catalyst to form methanol. Suitable hydrogenolysis
catalysts include copper support on silica or copper oxide
supported on magnesia-silica, Raney copper catalysts, and Group
VIII supported catalysts. Further catalysts are described in U.S.
Pat. No. 5,198,592, and Claus, et al., "Selective Hydrogenolysis of
methyl and ethyl acetate in the gas phase on copper and supported
Group VIII metal catalysts," Applied Catalysts A: General, Vol. 79
(1991) pages 1-18, which are incorporated herein by reference. The
reduction of methyl acetate to produce ethanol, e.g., in the
hydrogenolysis reactor, is typically conducted at elevated
temperatures from 125.degree. C. to 350.degree. C., e.g., from
180.degree. C. to 345.degree. C., from 225.degree. C. to
310.degree. C. The pressure in the hydrogenolysis reactor may
operate under high pressure of greater than 1000 kPa, e.g., greater
than 3,000 kPa or greater than 5,000 kPa. In terms of ranges the
pressure in the hydrogenolysis reaction may be from 700 to 8,500
kPa, e.g., from 1,500 to 7,000 kPa, or from 2,000 to 6,500 kPa.
Pressure greater than 2,500 kPa may be more favorable for improving
ethanol productivity and/or selectivity. The reactants may be fed
to hydrogenolysis reactor at a gas hourly space velocity (GHSV) of
greater than 500 hr.sup.-1, e.g., greater than 1000 hr.sup.-1,
greater than 2500 hr.sup.-1 or even greater than 5000 hr.sup.-1.
The hydrogenolysis reaction may be conducted with excess molar
amounts of hydrogen and preferably the molar ratio of hydrogen to
methyl acetate is greater than 10:1, e.g., greater than 15:1, or
greater than 20:1. In one preferred embodiment, the molar ratio is
about 25:1.
[0100] The crude reaction product of hydrogenolysis reactor 124 is
continuously withdrawn via line 158. In one embodiment, the crude
reaction product comprises at least 5% less methyl acetate than the
methyl acetate stream in line 152, e.g., at least 75% less methyl
acetate or at least 90% less methyl acetate. The crude reaction
product of hydrogenolysis reactor 124 may comprise at least 5% more
methanol than the methanol in line 152, e.g., at least 10% more
methanol, or at least 25% more methanol. Methanol and ethanol are
the primary products of the hydrogenolysis reaction, and the crude
reaction product comprises at least 15 wt. % methanol and at least
15 wt. % ethanol, e.g., at least 20 wt. %, or at least 25 wt. %. In
addition, depending on conversion, the crude reaction product
comprises less than 20 wt. % methyl acetate, e.g. less than 15 wt.
%, or less than 10 wt. %. Other components, such as water,
hydrogen, acetaldehyde, and other impurities may be present in the
crude product of hydrogenolysis reactor 124 in minor amounts.
[0101] The crude reaction product in line 158, which may be
referred to as a crude ethanol product, may be condensed and fed to
separator 126, which, in turn, provides a vapor stream and a liquid
stream. Separator 126, e.g., a flasher or knock-out pot, in one
embodiment operates at a temperature from 50.degree. C. to
500.degree. C. and a pressure from 50 kPa to 2,000 kPa. In an
embodiment, one or more separators may be used to condense the
crude reaction product.
[0102] The vapor stream exiting separator 126 may comprise hydrogen
and hydrocarbons, which may be purged and/or returned to
hydrogenolysis reactor 124 via line 160. As shown in FIG. 1, the
returned portion of the vapor stream in line 160 is combined with
the fresh hydrogen in line 156. In another embodiment, the fresh
hydrogen in line 156 may passes through compressor 126 along with
hydrogen vapor stream 160. In another embodiment, fresh hydrogen in
line 156 and vapor stream in line 160 may be fed separately into
hydrogenolysis reactor 124.
[0103] The liquid stream exiting separator 126 comprises ethanol
and methanol, and may have some unreacted methyl acetate. As shown
in FIG. 1, the liquid stream in line 162 is fed to column 128 to
recover ethanol. Liquid stream 162 from separator 126 is fed to
column 128, also referred to as the "product column." More
preferably, the liquid stream in line 162 is introduced in the
middle part of product column 128. Product column 128 recovers
ethanol, which preferably is substantially pure other than the
azeotropic water content, as the residue in line 166. Distillate in
line 164, which preferably comprises methanol and methyl acetate,
is preferably removed and may be recycled to esterification column
120 to generate additional methyl acetate to be converted into
ethanol. The distillate of product column 128 preferably is
refluxed, for example, at a reflux ratio from 1:10 to 10:1. Product
column 128 is preferably a tray column as described above and
preferably operates at atmospheric pressure. The temperature of the
distillate exiting in line 164 from product column 128 preferably
is from 30.degree. C. to 100.degree. C., e.g., from 40.degree. C.
to 90.degree. C. The temperature of the third residue exiting from
product column 128 preferably is from 60.degree. C. to 110.degree.
C., e.g., from 70.degree. C. to 100.degree. C. Exemplary components
of the distillate and residue compositions for product column 128
are provided in Table 2 below. It should be understood that the
distillate and residue may also contain other components, not
listed, such as components in the feed.
TABLE-US-00002 TABLE 2 PRODUCT COLUMN Conc. (wt. %) Conc. (wt. %)
Conc. (wt. %) Distillate Ethanol <2 <1 0.01 to 1 Methanol
<60 70 to 95 80 to 90 Methyl Acetate 1 to 40 1 to 30 10 to 20
Residue Ethanol >70 .sup. 80 to 99.9 90 to 99 Water <12 1 to
9 3 to 8 Methanol <1 0.001 to 1 0.05 to 0.5
[0104] In another embodiment, overhead stream 136 from flasher 116
may be fed directly to esterification unit 104. As shown in FIG. 2,
overhead stream 236, which comprises methyl acetate and acetic
acid, bypasses the first column and is fed directly to
esterification unit 204 along with excess methanol via line 246 to
form a methyl acetate enriched stream. The methyl acetate enriched
stream is recovered from esterification unit 204, e.g., reactive
distillation column 220, in line 248. Methyl acetate enriched
stream 248 comprises methyl acetate generated in carbonylation
reactor 214 and methyl acetate generated in esterification unit
204. In one embodiment, the methyl acetate enriched stream
comprises greater than 50 wt. % methyl acetate, e.g., greater than
60 wt. %, or greater than 70 wt. %. In one embodiment, the methyl
acetate enriched stream comprises at most 86 wt. % methyl acetate,
e.g., at most 82 wt. %, or at most 80 wt. %. In addition, methyl
acetate enriched stream 248 also comprises methanol, alkyl halide,
i.e., methyl iodide, PRC's, and other side products.
[0105] The light end column in FIG. 1 is used to remove a large
portion of water from the reaction. As such, some of the acetic
acid is also removed in the residue and therefore reducing the
amount of acetic acid that is fed to the esterification unit from
the sidestream. In accordance with the embodiment as illustrated in
FIG. 2, all of the acetic acid generated in the carbonylation unit
is fed to esterification unit 204. Therefore, more methyl acetate
may be generated, which in turn beneficially increases the overall
production of ethanol.
[0106] Any unreacted acetic acid, along with water, may be removed
in residue stream 250, In one embodiment, portions of residue
stream 250 may be returned to carbonylation system 202 to regulate
the water level for the carbonylation system.
[0107] As stated above, byproducts such as PRC's, i.e.,
acetaldehyde, may be formed during the carbonylation reaction. In
an embodiment of the present invention, PRC's is recovered from the
alkyl halide enriched stream and may be fed to the hydrogenolysis
reactor to form ethanol. As shown in FIG. 3, alkyl halide enriched
distillate 154 is fed to permanganate recovery system (PRS) 306 to
recover the PRC's.
[0108] As shown in FIG. 3, alkyl halide enriched stream 354 is
directed to distillation column 368, which serves to form a vapor
phase 370 enriched in PRC's, i.e., acetaldehyde, but also
containing alkyl halide, i.e., methyl iodide, due to the similar
boiling points of methyl iodide and acetaldehyde. Vapor phase 370
is condensed and then extracted with water to recover PRC's. In a
preferred embodiment, a portion of vapor stream 370 is provided as
reflux to distillation column 368. This can be accomplished, as
shown in FIG. 3, by providing vapor stream 370 to an overhead
receiver 372, from which a portion of vapor stream 370 can be
provided to extraction unit 374 by light phase stream 376 and
another portion of vapor stream 370 can be provided as reflux to
distillation column 368 by stream 378.
[0109] Acetaldehyde may be extracted by water to obtain aqueous
acetaldehyde stream 380, which may be fed to the hydrogenolysis
reactor to make ethanol. In one embodiment, aqueous acetaldehyde
stream 380 may be fed directly to hydrogenolysis reactor 324, or
may be co-fed to hydrogenolysis reactor 324 with methyl acetate
stream 352. In one embodiment, each or both of streams 380 and 352
may be vaporized in a vaporizer prior to being fed to
hydrogenolysis reactor 324.
[0110] In another embodiment, a drying column may be used to remove
water from the acetaldehyde stream to yield a substantially water
free acetaldehyde stream. This acetaldehyde stream may be vaporized
by a vaporized methyl acetate stream in line 352'. The combined
vaporized stream may be fed directly to hydrogenolysis reactor 324
without the need of a vaporizer.
[0111] The raffinate in line 382 from extraction unit 374, notably
containing methyl iodide is desirably returned to the carbonylation
process.
[0112] In another embodiment of the present invention, distillation
column 368 separates alkyl halide enriched stream 354 into vapor
stream 370, a higher boiling liquid phase residuum stream 386, and
sidestream 384, which comprises methyl acetate.
[0113] Sidestream 384 allows distillation column 368 to be operated
under conditions desirable for obtaining a higher concentration of
acetaldehyde in vapor stream 370 while providing a mechanism for
removing methyl acetate that might otherwise build up in the center
of distillation column 368 or be pushed into vapor phase stream
370. Sidestream 384 comprises at least 80 wt. % methyl acetate,
e.g., at least 90 wt. % or at least 95 wt. %. In one embodiment,
sidestream 384 is in vapor phase. Therefore, aqueous acetaldehyde
stream 380, or a substantially water-free acetaldehyde stream, may
be vaporized by methyl acetate sidestream 384 and be co-fed to
hydrogenolysis reactor 324.
[0114] In this embodiment, vapor stream 370 is enriched with PRC,
notably acetaldehyde, with respect to alkyl halide enriched stream
354. Vapor stream 370 is deficient with methyl acetate, methanol,
and/or acetic acid (desirably all three) with respect to alkyl
halide enriched stream 354. Vapor stream 370 is deficient with
methyl acetate, methanol, and/or acetic acid (desirably all three)
with respect to sidestream 384 and, desirably, also with respect to
higher boiling liquid phase residuum stream 386. Desirably, vapor
stream 370 is enriched with PRC, notably acetaldehyde, with respect
to both sidestream 384 and higher boiling liquid phase residuum
stream 386.
[0115] In another embodiment, the alkyl halide is extracted from
light phase stream 476 with an organic extractant. Preferably, the
organic extractant is selected is selected from the group
consisting of C.sub.6 to C.sub.16 alkanes and combinations thereof.
As a result of this extraction, light phase 476 is separated into
an extractant stream 480 comprising the extractant and alkyl
halide, and a raffinate 482 comprising methyl acetate and
PRC's.
[0116] Accordingly, it is desirable that the extraction be
conducted at a combination of temperature and pressure such that
the extractor contents can be maintained in the liquid state. In
some embodiments, extraction is conducted at a temperature from
10.degree. C. to 40.degree. C.
[0117] Although the specific compositions of extract stream 480 may
vary widely, it is preferred that a majority of the alkyl halides
in light phase 476 pass through to extract stream 480. In one
embodiment, at least 70% of the alkyl halides in light phase 476
pass through to extract stream 480, e.g., more preferably at least
85% or at least 95%. In a preferred embodiment, about 99% or more
of the alkyl halides in light phase 476 pass through to the extract
stream 480. When methyl iodide is present in light phase 476, at
least 70% of the methyl iodide passes through to extract stream
480, e.g., more preferably at least 85% or at least 95%. In
addition, extract stream 480 preferably comprises a low weight
percent of PRC's, e.g., less than 10 wt. % of the total weight of
extract stream 480 comprises PRC's, or more preferably less than 5
wt. %. In one embodiment, extract stream 480 preferably comprises
substantially no PRC's and the PRC's in light phase 476 pass
through to raffinate stream 482.
[0118] Raffinate stream 482 comprises PRC's, i.e., acetaldehyde,
and is fed directly or indirectly to hydrogenolysis reactor 424 to
make ethanol. In addition, raffinate stream 482 from extractor 474
may comprise methyl acetate and water. Although the specific
compositions may vary widely, raffinate stream 482 preferably
comprises less than 2 wt. % of the halogen promoter and/or C.sub.2+
alkyl halides, e.g., less than 1 wt. % or less than 0.5 wt. %, or
less than 0.1 wt. %.
[0119] Extract stream 480 is directed to removal column 490 to
produce a distillate stream 492 comprising halogen promoter and/or
C.sub.2+ alkyl halides, and a residue stream 488 comprising the
extractant. Residue stream 488 may be cooled and recycled directly
to extractor 474, or preferably is combined with extractant feed
stream 488' and fed to extractor 474.
[0120] Distillate stream is condensed and returned to the process
via stream 492. At least a portion of the condensed distillate
stream is refluxed back to the removal column. Distillate stream
492 primarily comprises halogen promoter.
[0121] In some embodiments, an alkyl halide purge stream 494 can be
taken from removal column 490. Alkyl halide purge stream 494
comprises one or more C.sub.2+ alkyl halides selected from the
group consisting of ethyl iodide, propyl iodide, butyl iodide,
pentyl iodide, hexyl iodide, and isomers and mixtures thereof. In
some embodiments, C.sub.2+ alkyl halides purge stream 494 is
directed to a holding tank and stored (not shown). Optionally,
C.sub.2+ alkyl halides purge stream 494 can be further processed to
recover any halogen promoters or iodine value, such as HI,
contained in the purge stream, wherein the halogen promoter or
iodine value is returned to the process.
[0122] As a result of recovering additional methyl acetate and
PRC's from the alkyl halide enriched streams as illustrated in
FIGS. 3 and 4, the overall all production of ethanol is
increased.
Ethanol Composition
[0123] The ethanol product made using the embodiments of the
present invention may be an industrial grade ethanol comprising
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 ethanol
product. Exemplary finished ethanol compositional ranges are
provided below in Table 3.
TABLE-US-00003 TABLE 3 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 <0.1
<0.01 Ethyl Acetate <2 <0.5 <0.05 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
[0124] 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 C.sub.4-C.sub.20 alcohols. In one embodiment, the
amount of isopropanol in the finished ethanol composition is from
80 to 1,000 wppm, e.g., from 95 to 850 wppm, or from 100 to 700
wppm. In one embodiment, the finished ethanol composition is
substantially free of acetaldehyde, optionally comprising less than
8 wppm acetaldehyde.
[0125] In some embodiments, when further water separation is used,
the ethanol product may be withdrawn as a stream from the water
separation unit such as an adsorption unit, membrane, molecular
sieve, or extractive distillation column. Ethanol concentration of
the ethanol product may be higher than indicated in Table 7, and
preferably is greater than 97 wt. % ethanol, e.g., greater than 98
wt. % or greater than 99.5 wt. %. The ethanol product in this
aspect preferably comprises less than 3 wt. % water, e.g., less
than 2 wt. % or less than 0.5 wt. %.
[0126] The finished ethanol composition produced by the embodiments
of the present invention may be used in a variety of applications
including applications as fuels, solvents, chemical feedstock,
pharmaceutical products, cleansers, sanitizers, hydrogen 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 aircraft. 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.
[0127] The finished ethanol composition may also be used as 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. In another application, the
finished ethanol composition may be dehydrated to produce ethylene.
Any known dehydration catalyst, such as zeolite catalysts or
phosphotungstic acid catalysts, can be employed to dehydrate
ethanol, as described in U.S. Pub. Nos. 2010/0030002 and
2010/0030001 and WO2010146332, the entire contents and disclosures
of which are hereby incorporated by reference.
[0128] 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.
EXAMPLE
Example 1
[0129] Multiple simulations of processes under different catalyst
performances in accordance with FIG. 1 were completed using
ASPEN.TM. software. In each stream, the flow rate and composition
vary with the catalyst performance and design specifications. In
general, an illustrative composition for the various process
streams is demonstrated in Table 4 based upon the simulation
results. For simplicity, the composition of a component in Table 4
is displayed as 0% if its level is so low that it becomes hardly
detectable. For simplicity, the composition of a component in Table
4 is displayed as 100% if other components are so low and hardly
detectable.
TABLE-US-00004 TABLE 4 SIMULATED COMPOSITIONAL DATA FOR PROCESS
STREAMS Composition (wt. %) MeOAc HOAc MeOH EtOH H.sub.2O MeI
Heavies AcH Other Carbonylation Reaction Zone Crude Methyl Acetate
24.9 42.4 3 -- 11.1 10.6 7 -- 1 Stream 134 Overhead stream 136 40.9
19 4.1 -- 10.4 24.1 0 -- 1.5 First Column Vapor Stream 140 44.6 0
3.1 -- 1.8 39.7 -- -- -- Sidestream 142 5.4 59.6 5.2 -- 29.3 0 --
-- -- Esterification Zone Ester Enriched Stream 148 76.5 0 23.4 --
0.1 -- -- -- -- Reside Stream 150 0 1.4 0 -- 97.8 -- -- -- -- Alkyl
Halide Removal System Distillate 154 2.5 0 5.6 -- 0 86.8 -- 0.4 --
Methyl Acetate Stream 152 86.2 0 11.4 -- 2.4 0 -- 0 --
Hydrogenolysis System Distillate 164 15 -- 83.4 0 0 -- -- -- --
Residue 166 0 -- 0 93.6 4.4 -- -- -- --
[0130] As shown by the table above, methyl acetate may be used to
make ethanol through hydrogenolysis, where the methyl acetate is
obtained through carbonylation of methanol and carbon monoxide and
esterification of acetic acid and methanol. The process produces a
final ethanol product with less than 5 wt. % water.
* * * * *