Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
10970~7
BACKGROUND OF THE INVENTION
_
Field of the Invention:
This is a partial-oxidation process in which syn-
thesis gas having a controlled H2/CO mole ratio and either a
C0-rich gas or substantially pure C0 are simultaneously
produced. Methanol may be made from the synthesis gas and
then may be reacted with the C0-rich gas or with substan-
tially pure CO to produce acetic acid.
Description of the Prior Art:
10Synthefiis gas may be prepared by partial oxidation
of a fossil fuel with a free-oxygen-containing gas, option-
ally in the presence of a temperature moderator. The efflu-
ent gas stream from the gas generator is cooled (below the
temperature at which the gas composition approaches equilib-
rium) by, for example, direct immersion in water in a ~uench
. ~
drum such as described in coassigned U.S. Patent No.
2,896,927. By this method of gas cooling the sensible heat
in the effluent gas stream is used to produce steam in the
pxoduct gas.
Alternatively, the effluent gas stream from the
gas~ generator may be cooled in a syngas cooler, such as
shown in coassigned U.S. Patent No. 3,920,717. By this
,
method of gas cooling, the efluent gas stream does not
become saturated with the water. In coassigned U.S.
1~ :
Patent No. 3,929,429, in order to prepare an oil-carbon
dispersion and a separate water-carbon dispersion which
. ~
are simultaneously fed to a gas generator for producing
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fuel gas, a portion of the effluent gas stream is cooled in a
syngas cooler and then scrubbed with oil; and another stream
is quenched in water. Noncatalytic thermal shift is used to
adjust the H2/CO mole ratio of a single stream of synthesis
gas in coassigned U.S. Patent No. 3,920,717.
SUMM~RY
The present invention provides a process for
simultaneous production of a product stream of purified
synthesis gas and a product stream of CO-rich gas, comprising:
(1~ reacting a hydrocarbonaceous feedstock with a free-
oxygen-containing gas, optionally in the presence of a temper-
ature moderator, in the reaction zone of a free-flow
noncatalytic partial-oxidation gas generator at a temperature
in the range of about 130a to 3Q00F and at a pressure in the
range of about 1 to 250 atmospheres to produce an effluent gas
stream comprising H2, C0, H2O, CO2, and optionally at least one
mater~al from the group H2S, COS, CH4, N2, Ar~ and solid
particles;
~2~ rem~ving a portion o~ said solid particles if present,
2a coolin~ the effluent g~s stream hy indirect heat exchange in a
s.epa.rate heat-exchange zone, removing any remaining entrained
: s~lid particles, and dehumidifying the cooled gas stream;
(~3~ intxoducing at le.ast a portion of the clean dehumidi-
fied gas stream from (2~ into a first gas-purification zone
and by-passing said first gas-purification zone with the
remainder if any; removing from the gas stream in said first
gas-purification zone any H2S, COS, and at least a portion
of the CO2;
(.4) introducing partially purified gas from the first gas
3~ purification zone in (3~ into a second gas-purification zone
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` 10~70'~7
and by-passing said second gas-purification zone with at least
a portion of the remainder, if any, and removing from said
second gas-purification zone said product stream of C0-rich
gas and a separate stream of H2-rich gas; and
(5) mixing together at least a portion of the H2-rich gas
from (.4) with at least a portion of at least one of the
following:
(a~ gas processed in the first gas purification zone
that ~y-passes the second gas purification zone in (4);
lQ (.b~ soot-free dehumidified gas that by-passes the
first gas-purification zone in (~31; producing said product
stream of purifi,ed $ynthesis gas having a controlled H2/C0 mole
rati
In the subject process, the effluent gas stream
directly from a ~ree-flow unpacked noncatalytic partial-oxidation
synthesis gas generator may have an H2/C0 mole ratio in the
: range of about 0.5 to 1.~ and may contain entrained particulate
solids, i.e. ash and carbon soot. A portion of the ash if
present, may first be removed as slag. The gas stream is then
, 2~ cooled by indirect heat exchange in a gas cooler, and boiler-
feed w.ater is. thexe~y converted into steam. Any remaining
entrained soli.ds, i,.e. pa~ticulate carbon are then removed.
The soot-free gas stream is dehumidified and then at least a
.~ poxtion of the s~ot-free and dehumidi.fied gas stream is
int~oduced ~nto a ~.Xst gas-purifi.cation zone. The remainder of
the soot-~ree and dehumidified gas stream if any, by-passes
the ~iræt gas-puXi~ication zone. In the first gas-puri~ication
æone, depending on the composi.t~on of the soot-free and
: ~ h.umidified ~afi stream any H2S, COS, ~nd at leaæt a portion of
3~ the'C02 is xem~ed ~x con~entional procedures. This may be
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109'7(9';~7
done in one or t~o stages. Gas which has been processed in the
first gas-purification zone is introduced into a second gas-
purification or separation zone where, by conventional
procedures a product
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109~0~77
stream of CO-rich gas and a separate stream of H2-rich
gas, and optionally CH4-rich gas are separated. For
example, at least a portion of the gas from the first
gas purification zone containing no H S and COS and
with at least a portion of the CO2 removed is passed into
the second gas purification zone. The remainder of the
gas which has been processed in the first gas puri~ication
zone if any, by-passes the second gas purification zone.
The product stream of purified synthesis gas having a
controlled H2/CO mole ratio i.e. in the range of about
2 to 12 is produced by mixing together at least a portion
of the H2-rich gas from the second gas purification zon~
with at least one i.e. either one or both of the following:
(a) gas processed in the first gas purification zone that
by-passes the second gas purification zone if any; and
(b) soot-free dehumidified gas stream that by-passes the
first gas-purification zone if any. For example: In one
embodiment where the soot-free and dehumidified synthesis
gas stream is substantially free-from H2S and COS, then
:` ~
H2-rich gas may be mixed with at least a portion of at
least one of the following: (a) soot-free and
dehumidified gas that by-passes the first gas-purificltlo~
zone; (b) soot-free and dehumidified gas having at least
1: :
a portion of the CO removed from the first gas purification
zone that by-passes the second gas-purificalion zone.
Ir. another embodiment where the soot-free and
dehumidified gas stream contains H2S and COS tnen the H2-rich
:
gas may be mixed with at least a portion of at least one i.e.
either one or both of the following: (a) desulfurized gas
from the firs~t stage of the first gas purification zone;
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1097077
(b) desulfurized gas with at least a portion of the CO2
removed from the second stage of the first gas purification
zone that by passes the second gas purification zone.
The step of catalytic water-gas shift reaction is
not a required step in the subject process. Optionally,
thermal noncatalytic shift may be employed to increase the
H2/CO mole ratio of the raw effluent gas stream from the gas
generator.
In another aspect, the subject invention pertains
to a process for the production of methanol, comprising:
(1) reacting a substantially sulfur-free hydrocar-
bonaceous feedstock with substantially pure oxygen, op-
tionally in the presence of a temperature moderator, in the
reaction zone of a free-flow noncatalytic partial-oxidation
gas generator at a temperature in the range of about 1300
to 3000~F and at a pressure in the range of about 1 to 250
atmospheres to produce an effluent gas stream comprising H2,
~` CO, H2O, CO2, and at least one material from the group
consisting of CH4, N2, Ar, particulate carbon, and ash;
(2) cooling the effluent gas stream by indirect heat
~ exchange in a separate heat-exchange zone, removing any en-
.~ trained particulate carbon and ash, and dehumidifying the
~ cooled gas stream;
~ (3) splitting the soot-free dehumidified gas stream
-: ~ from (2) into first and second gas streams with said first `-
split gas stream comprising about 10 to 90 volume percent of
the effluent gas stream from (2~, and said second split
stream comprising the remainder;
(4) purifying said first split gas stream from (3) in
; 30 a first gas-purification æone and separating therefrom at
least a portion of the CO2;
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~0970~7
(S) splitting the gas stream from (4) into third and
fourth gas stream with said third gas stream comprising
about 10 to loO volum~ percent of said synthesis-gas stream
from (4) and said fourth gas stream containing the remainder
if any and introducing all of said third gas stream into a
second gas-purification zone;
(6) removing a stream of CO-rich gas and a stream of
H2-rich gas from said second gas-purification zone;
(7) mixing together at least a portion of said second
gas stream from (3), at least a portion of said H2-rich gas
stream from (6), and at least a portion of said fourth gas
stream if any from (5), to produce a stream of methanol-
synthesis gas; and
(8) reacting at least a portion of said methanol
synthesis gas in the presence of a methanol catalyst in a
methanol-synthesis zone at a temperature in the range of
about 400 to 750F and at a pressure in the range of about
40 to 350 atm. to produce crude methanol, and purifying
said crude methanol to produce substantially pure methanol
and by-product oxygen-containing organic materials.
: In still another aspect, the subject invention
pertains to a pxocess for producing acetic acid comprising
steps (1) to (8) of the previously described process for
producing substantially pure methanol and in which the
~: CO-rich gas in step (6) is substantially pure CO, and
provided with the additional steps of reacting at least a
portion of said substantially pure methanol with at least a
portion of said substantially pure carbon monoxide in the
presence of a carbonylation catalyst in an acetic acid-syn-
thesis zone, at a temperature in the range of about 302 to
608 F and at a pressure in the range of about 1 to 700
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109~ 7~
a~mospheres, to produce impure acetic acid, and purifying
said impure acetic acid to produce substantially pure
acetic acid and by-product oxygen-containing organic
materials.
BRIEF DESCRIPTION OF_THE DRAWING
The invention will be further understood by
reference to the accompanying drawing. Fig. lA is a sche-
matic representation of a preferred embodiment of the
process for simultaneously making a product stream of
clean and purified synthesis gas having a mole ratio H2/CO
in the range of about 2 to 12, and a separate product stream
of CO-rich gas and preferably substantially pure CO. Fig.
lB as shown to the right of the line A-A is a schematic
representation of another embodiment of the process, in
which pure methanol is produced from a product stream of
methanol synthesis gas made by the subject process. Op-
tionally, at least a portion of said pure methanol may be
- then reacted with at least a portion of the substantially
pure carbon monoxlde stream to produce acetic acid.
DESCRIPTION OF THE INVENTION
In the first step of the subject process, raw
synthesis gas, substantially comprising hydrogen and carbon
monoxide and having a mole ratio (H2/CO) in the range of
about 0.5 to 1.9, is produced by partial oxidation of a
hydrocarbonaceous fuel with substantially pure oxygen, op-
tionally in the presence of a temperature moderator in the
reaction zone of an unpacked
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A
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~097(~77
free-flow noncatalytic partial-o~idation gas generator.
The steam-to-fuel weight ratio in the reactio~ ~one is in
the range of about 0.1 to 5, and preferably about 0.2 to
O.7. The atomic ratio of fre~~oxygen to carbon in the fuel
(O/C ratio), is in the range of about 0.6 ~o 1.6, and pref-
erably about 0.~ to 1.4. The reaction time is in the range
of about l to lO seconds, and preferably about 2 to 6
seconds.
The raw synthesis gas stream exits from the
r~ac'ior. zor.e at a temperature in the range of about 1300
to 3000F., such as 1600 to 3000F, say 2000 to 2800F and
at a pressure in the range of about 1 to 250 atmospheres
(atm.), such as lO to 200 atm. say 40 to 150 atm.
The composition of the raw synthesis gas leaving
the gas generator is about as follows, in mole percent:
H2 60 to 29, CO 30 to 60, CO2 2 to 25, H 0 2 to 20,
CH4 nil to 25, H2S nil to 2, COS nil to 0.1,
N2 nil to l, and ~.rnil to 0.5. There may also be present
particulate carbon in the range of nil to 20 weight %
(basis carbon content in the original feed), and ash in
the amount of nil to 60 weight % of the original hydrocar-
bonaceous feed.
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1097(~77
The synthesis gas generator comprises a vertical
cylindrically shaped steel pressure vessel lined with re-
fractory, such as shown in coassigned U.S. Patent No.
2,809,1~4. A typical quench drum is also shown in said
patent. A burner, such as shown in coassigned U.S. Patent
No. 2,928,460, may be used to introduce the feed streams
into the reaction æone.
A wide range of combustible carbon-containing
organic materials may be reacted in the gas generator with
a free-oxygen containing gas, optionally in the presence of
a temperature-moderating gas, to produce the synthesis gas.
The term hydrocarbonaceous as used herein to
describe various suitable feedstocks is intended to include -
gaseous, liquid, and solid hydrocarbons, carbonaceous
materials, and mixtures thereof. In fact, substantially
any combustible carbon-containing organic material, or
slurries thereof, may be included within the definition of
the term "hydrocarbonaceous". For example, there are (l)
pumpable slurries of solid carbonaceous fuels, such as coal,
particulate carbon, petroleum coke, concentrated sewer
sludge, and mixtures thereof, in a vaporizable liquid
carrier, such as water, liquid hydrocarbon fuel, and
mixtures thereof; (2) gas-solid suspensions such as finely
; ground solid carbonaceous fuels dispersed in either a
temperature-moderating gas or in a gaseous hydrocarbon;
and (3) gas-liquid-solid dispersions, such as atomized
liguid hydrocarbon fuel or water and particulate carbon
dispersed in a temperature moderating gas. The hydro-
carbonaceous fuel may have a sulfur content in the range
of about 0 to lO wt. percent and an ash content in the
range of about 0 to 60 wt. percent. By definition, the term
1 097(~ ~7!7
"substan,ially sulfur-free hydxocarbonaceous fuel" as used
herein shall be a hydrocarbonaceous fuel as previously des-
cribed which when subjected to the noncatalytic partial oxida-
tion process will produce raw synthesis gas, in the manner
previously described, containing less than 5 parts per
million (PPM) of M2S and COS.
The term liquid hydrocarbon, as used herein to de-
scribe suitable liquid feedstocks, is intended to include var-
ious materials, such as liquefied petroleum, liquefied nat-
ural gas, petroleum distillates and residua, gasoline, naph-
tha, kerosine,crude petroleum, asphalt, gas oil, residual oil,
tar-sand oil and shale oil, coal derived oil, aromatic hydro- -
carbons (such as benzene, toluene, xylene fractions), coal
tar, cycle gas oil from fluid-catalytic-cracking operations,
furfural extract of coker gas oil, and mixtures thereof.
Gaseous hydrocarbon fuels, as used herein to describe
suitable gaseous feedstocks, include methane, ethane, propane,
butane and other unsaturated light hydrocarbon gases, pentane,
natural gas, water-gas, coke-oven gas, refinery gas, acetylene
tail gas, ethylene off-gas, synthesis gas, and mixtures there-
: of. Solid, gaseous, and liquid feeds may be mixed and used
simultaneously; and these may include paraffinic, olefinic,
~; acetylenic, naphthenic, and aromatic compounds in any proportion.
,
. Also included within the definition of the term
hydrocarbonaceous are oxygenated hydrocarbonaceous organ.ic
~:;: materials including carbohydrates, cellulosic materials,
: aldehydes, organic acids, alcohols, ketones, oxygenated
fuel oil, waste llquids and by-products from chemical process-
es containing oxygenated hydrocarbonaceous organic materials,
and mixtures thereof.
The hydrocarbonaceous feed may be at room tem-
perature, or it may be preheated to a temperature up to as
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1~9'7(1 7~
high as about 600 to 1200F. ~ut preferably below its
crackirg temperature. The h~drocarhonaceous feed may be
introduced into the gas~genera-tor burner in llquid phase
or in a vaporized mixture with the temperature moderator.
The need for a temperature moderator to control
the t~mperature in the reaction zone depends in general on
the carbon-to-hydrogen ration of the feedstock and the
oxygen content of the oxidant stream. A temperature mod-
erator may not be required with some gaseous hydrocarbon
fuels; however, generally one is used with liquid hydro-
carbon fuels and with substantially pure oxygen. Steam may
lo be introduced as the preferred temperature moderator in
admixture with either or both reactant streams. Alternative-
ly, the temperature moderator may be introduced into the
reaction zone of the gas generator by way of a separate
conduit in the burner. Other suitable temperature
moderators may include CO2 and a portion of cooled and
; recycled synthesis gas separated downstream in the process.
The term free-oxygen-containing sas as used here-
in means substantially pure oxygen, i.e. g~eater than about
- 95 mole % oxygen (the remainder usually comprising ~l2 ard
rare ga9es). Free-oxygen-containing gas may be introduced
by way of the partial-oxidation burner at a temperatu;~e
in the range of about ambient to 1800F.
; A continuous stream of hot effluent gas, at
substantially the same temperature and pressure as in the
reaction zone leaves from the axial exit port of the
gas generator and is cooled in a gas cooler. Howe~er,
for hydrocarbonaceous fuels containing a high ash con,ent
such as coal, a solids separation zone is pref2rably inserted
between the exit port of the gas generator and said gas
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1097(~77
.
cooler in order to remove the larger entrained solid
particles. This solids separation zone may comprise a
catch-pot, slag chamber, cyclone separator, electrostatic
precipitator, or combinations of such schemes for removing
at least a portion of any solid matter i.e. particulate
carbon, ash, metal constituents, scale, slag, refractory,
and mixtures thereof that may be entrained in the hot
effluent gas stream, or which may flow from the gas
generator i.e. slag, ash, bits of refractory. T~us, a
portion of the larger solid particles, if present may be
separated from the effluent gas stream and recovered with
very little, if any temperature or pressure drop in the
process gas stream. A typical slag chamber that may be
employed is shown in the drawing, or in Fig. 1 of the drawing
for coassigned U.S. Patent No. 3,528,930. Any coarse
solid particles above the size of about 12 microns are
;~ preferably removed at this time by means of gravity or
cyclone sepaxation or other physical cleaning process. If
particulate carbon soot is entrained in the ~~fluent gas
~ stream, a small amount may be removed with the coarser
-~ ; ;20 particles. However, most of the soot and finer entrained
solids are remo~ed subsequently by scrub~ing the process
gas stream with water. In the preferred embodiment, the
step of water-gas shift reaction to increase the H /CO mole
ratio is not required. This wlll eliminate costly water-gas
shlft catalysts. Optionally, in a separate embodiment,
noncatalytic thermal shifting, as described in coassigned
U.S. Patent No. 3,723,345 may be employed.
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In such case, the stream of hot effluent gas leaving
the gas generator is passed into a separate refractory lined
free-flow reactior. -h~r where some of the entrained solids are
removed and adjustment of the mole ratio (E2/CO) is effected.
Preferably the process gas stream is at a temperature in the
range of about 1600 to 3500F as produced in the gas generator
and at the same pressure as in the gas generator e.g. 15 to
200 atmospheres such as 60 to 150 atmospheres. A chamber
as'shown in coassigned U.S. Pat. No. 3,565,588 may be used.
For example, spherical chamber 37 as shown in the drawing is
unpacked and free from catalyst or obstruction to the flow
of gas therethrough. A portion of the solid matter that
may be entrained in the process gas stream may drop out
and may be removed through an outlet located at the bottom
of the spherical chamber which leads to a lock hopper.
A stream of supplemental H20 i.e. cteam as prcduced
subsequently in the process is simultaneously introduced
into the spherical chamber at a temperature in the range of
about 500 to 1500F and at a pressure slightly above
that in the gas generator. On a dry basis, about 0.1 to
2.5 moles of supplemental H 0 are preferably introduced
into the spherical chamber per mole of effluent synthesis
gas from the gas generator,where the gases mix.
Alternatively, the supplemental H20 may be introduced into
~ the separate noncatalytic unobstructed thermal shift
- ~ conversion zone in admixtura with the effluent synthesis
~ gas from the gas generator. By noncatalytic thermal direct
~ :~
water-gas shift reaction at a temperature of at least
1500F and preferably in the range of about 1700F to 2800F,
the supplemental H20 reacts with a portion of the carbon
1C~97077
monoxide in the effluent synthesis gas stream from the
generator so as to produce additional H2 and CO2. The
mole ratio (H2/CO) of the effluent stream of gases from
the gas generator may be increased by this step to a value
in the range of about 0.8 to 6, such as 2.0 to 4Ø The
aforesaid high temperature adiabatic nonc~talytic ther~al
direct water-gas shift reaction may begin for example in
the insulated spherical chamber. The shift reaction
may continue in an insulated line connecting the side outlet
of the spherical chamber with the bottom flanged inlet
to a gas cooler. Thus, the effluent stream of synthesis
gas is thermally shifted without a catalyst in transit
between stages in the process. Residence time in the
water gas shift conversion zone is in the range of about
0.1 to 5 seconds. Preferably, the condition of temperature
and presure at which the noncatalytic thermal direct water-
gas shift reaction takes place are substantially the same
as those in the synthesis gas generator, less ordinary line
drop and less any cooling due to the sensible heat of the
supplemental H20 and any heating due to the heat of reaction.
Next, the process gas stream is passed through
; an inline separate gas cooler in noncontact heat exchange
with water. The stream of-synthesis gas is cooled to a
temperature in the range of about ~50 to 750F. By-product
saturated steam may be produced thereby at a pressure
above the pressure of the synthesis gas for use elsewhere
in the process. Substantially all of the steam requirement
in the system may be therefore met. For example, the
aforesaid steam may be used as a working fluid in an
- expansion turbine for the production of power, The steam
turbine may be used to drive the air and oxygen compressors
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lO9~V~7~ .
in a conventional air separation unit, the recycle gas
compressor in the methanol synthesis loop to be further
described, or the feed gas compressor if any. Preferably,
a portion of the steam may be introduced into the gas
generator as at least a portion of the temperature
moderator and into the thermal shift reactor as a reactant.
It may also be used to provide heat in a reboiler in a
methanol or DME distillation column.
The stream of synthesis gas leaving the waste
heat boiler may be passed through a gas cleaning zone
where any remaining entrained solid particles if present,
are removed.
When there is substantially no entrained particulate
matter in the process gas stream, such as with some gaseous
fee~stocks, both gas cleaning zones may be by-passed
or eliminated. The amount of solid particles i.e.,
selected from the group: particulate carbon, ash, and
mixtures thereof, that may be entrained in the synthesis
gas is dependent on the type of hydrocarbonaceous
fuel and the atomic ratio tO/C) in the reaction zone.
When the generator fuel contains metals i.e. nickel and
vanadium compounds, a small amount o~ entrained
particulate carbon i.e., about 1-2 wt. ~ ~basis weight of C
in the hydrocarbonaceous feed), will increase the life
~ of the refractory lining the gas generator.
; Any suitable means may be used for cleaning
entrained solid particles from the process gas streams.
For example the gas stream leaving the gas cooler may
be contacted with a scrubbing fluid, such as water or
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1097077
liquid hydrocarbon in one or more steps in a gas-
scrubbing zone, such as shown in coassigned U.S. Patent
No. 3,544,291. The solids dispersed in scrubbing fluid
from the gas cleaning zone, may be returned to the gas
generator as at least a portion of the feed. Thus, if the
gas stream is scrubbed with water, the dispersion of
particulate carbon and water which is formed may be concen-
trated or separated by conventional means to yield clarified
water. This water may be recycled to an orifice, nozzle, or
venturi scrubber in the gas cleaning zone. Carbon concen-
tration may be effected by any suitable means; e.g.,
filtration, centrifuge, gravity settling, or by well-known
lir~uid hydrocarbon extraction, such as the process described
in coassigned U.S. Patent No. 2,992,906.
The gas stream leaving the cleaning zone is
cooled below the dew point by indirect i.e. noncontact
heat exchange and then introduced into a knockout or
separation vessel in which substantially all of the water
is removed to produce a clean i.e. soot-free dehumidified
gas stream.
When the H2S and COS content of the soot-free
dehumidified gas stream is less than about 5 PPM (parts
per million), then the gas stream does not have to be
desulfurized. In such case, the ~irst gas purification
zone is used only to remove at least a portion i.e. about
10 to 100 vol. % of the C02 present~ Thus, about 10 to
100 vol. %, such as 10 to 90 vol. ~ of the clean
dehùmidified gas from the partial oxidation gas generator
may be introduced into the first gas prufication zone.
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1097(~77
The remainder of the soot-free dehumidified gas stream
if any by-passes the first purification zone. The CO2-rich
gas stream removed in the first gas purification zone may
comprise the following in mole %: CO2 40 to 100, H2 5 to 25,
Co 10 to 40, and C~ nil to 5.
When a portion i.e. (about 10-90 vol %) of the
soot-free dehumidified synthesis gas by-passes the first
gas purification zone then, at least a portion i.e. about
10 to 100 vol. % of the gas stream leaving the first gas
purification zone with at least a portion of the CO2
removed is passed into a second gas purification zone.
The remainder of the gas stream from the first gas
purification zone if any, by-passes the second gas
purification zone. When no soot-free dehumidified synthesis
gas by-passes the first gas purification zone then a portion
i.e, about 10 to 90 vol. % of the gas stream leaving the
first gas purification zone is passed into the second gas
purification zone, and the remainder i.e. about 90 to 10
; ~ vol. % by-passes the second gas purification zone. Thus,
in this embodiment there is always at least one gas stream
that by-passes the first, second, or both gas purification
zones, and which may be mixed with H2-rich gas stream
produced in the second gas purification zone to produce
the product synthesis gas.
A CO-riah product gas stream and a H2-rich gas
stream are separated in said second gas purification or
separation zone. The composition of the CO~rich gas
stream produced in the second gas purification zone is about
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as follows in mole % : CO 61 to 99; N nil to l; CO nil
to 15; H2 2 to 8; CH4 nil to 1; and Ar nil to 0.5.
Preferablv by further purification, substantially pure
carbon monoxide ~go~gg,5mole % CO) may be produced, The
H2-rich gas stream produced in the second purification
zone may comprise in mole ~ : H2 98 to 60; CO nil to 5;
C2 nil to 5; CH4 nil to 5; Ar nil to 4; and N2 nil to 20.
From about 20 to 100 vol. %, and preferably all of the
H2-rich gas stream may be included as one of the ingredients
in the product gas. The remainder of the H2-rich gas stream
may be exported.
When the soot-free dehumidified process gas
stream contains substantially no H2S and CoS, the product
gas stream of purified synthesis gas is made by mixing at
least a portion i.e. about 10 to 100 vol. % of said H~-rich
gas stream with at least-a portion i.e. about 10 to 100 vol.
% of at least one of the following by-pass gas streams:
(a) soot-free dehumidified gas that by-passes the first
gas purification zone; (b) soot-free dehumidified gas with
at least a portion of the CO2 removed that leaves the
first gas purification zone and which by-passes the second ~ -
gas purification zone. Mixtures o (a) and (b~ may include
about 10 to 90 vol. % of ~a) and the remainder (b).
In another embodiment, more than 5 PPM of acid
gases i.e. H2S, COS, and CO are found in the soot-ree
dehumidiied gas stream. In such case, all of this gas
stream is introduced into a first gas purification zone
which comprises a first-stage for desulfurizing the
process gas streams and a second-stage for removing at
;
1097077
least a portion of the Co2. At least a portion i.e. about
10 to 100 volume % of the desulfurized gas stream from
the first stage is introduced into the second stage
where at least a portion of the CO2 contained therein
is removed. The remainder of the desulfurized gas stream
by-passes said second stage and the second gas purification
zone. One or more liquid solvent absorbents may be used
in the two-stages to absorb the acid-gas impurities. The
rich liquid solvent absorbent is then removed from the
absorption tower and regenerated by heating, stripping, or
flashing, or a combination thereof to produce a lean liquid
solvent absorbent which is then recycled to the conventional
gas a~sorption tower. The acid-gases are recovered during
the regeneration of the solvent absorbent and may be sent
to a Claus unit for the production of sulfur. When a
; portion of the desulfurized gas stream from the first stageby-passes the second i.e. CO2-absorption stage of the first
gas purification zone and the second gas purification zone
then at least a portion i.e. about 10 to 100 vol. % of the
desulfurized gas stream leaving the second stage of the
first gas puri~ication zone is introduced into a second
gaa purification zone where a H2-rich gas stream and a
CO-rich product gas stream are separated. The remainder of
~; the gas stream leaving the second stage of the first gas
purification zone if any, ~y-passes said second gas
purification zone. Alternately, when all of the
desulfurized gas stream from the first stage is introduced
into ~he second stage of the first gas purification zone,
-17-
1097077
then a portion i.e. about 10 to 90 vol. % of the
desulfurized gas stream with at least a portion of the
Co removed from the first gas purification zone is
introduced into the second gas purification ~one. The
remainder i.e. about 90 to 10 vol. ~ of the gas stream
leaving the second stage of the first gas purification
zone by-passes the second gas purification zone. Thus,
in this embodiment there is always at least one gas
stream that by-passes the second gas purification zone
which may be mixed with the H2-rich gas stream to produce
the purified synthesis gas product. As previously
mentioned, the H2-rich gas is produced in the second gas
purification zone along with a CO-rich product stream.
The product stream of purified synthesis gas
having a controlled mole ratio H2/CO is produced in this
embodiment by the following manner. At least a portion
i.e, about 10 to 100 vol. % of the H2-rich gas from the
second purification zone i5 mixed with at least a portion
- i.e. about 10 to 100 vol. % of at least one i.e, either
one or both of the following gas streams: (a) desulfurized
~as stream from the first stage that by-passes the CO2-
removal stage of the first gas purification zone; (b)
desulfurized gas stream with at laast a portion i.e. about
10 to 100 vol. % of the CO2 removed that leaves the second
stage of said first gas purification zone and by-passes
said second gas purification zone. Mixtures of (a) and
; (b) may comprise about 10-90 vol. ~ of (a) and the
remainder ~b).
-18-
1097077
Alternately, a liquid solvent absorbent may be
employed which absorbs all of the H2S and COS and at
least a portion of the C0 in a single stage absorption tower
which constitutes the first gas purification zone. In
such case all of the clean soot-free dehumidified gas stream
is passed into the first gas purification zone and a
portion i.e. about 10 to 90 vol. % of the desulfurized
gas with at least a portion i.e. 10 to 100 vol. % of the CO2
removed from the first gas purification zone is introduced
into the second gas purification zone, while the remainder
of this gas stream by-passes the second gas purification
zone. A CO-rich product gas stream and a H2-rich gas
stream are separated in the second gas purification zone.
The purified synthesis gas product stream is produced
; by mixing together at least a portion i.e. 10 to 100 vol.
% of ~aid H2-rich gas stream and at least a portion i.e.
about 10-100 vol. % of the desulfurized gas with at least
a portion i.e. 10 to 100 vol. ~ of the CO2 removed that
by-passes the second gas purification zone.
Any suitable conventional proaess may be used for
purifying the gas stream in the first gas purification zone~
` Typical gas purification processes may involve refrigeration
:
and physical or chemical absorption with a solvent, such as
methanol, N-methyl-p-~rrolidone, triethanolamine, prop~-lene
carbonate, or alternatively with hot potassium carbonate.
` Advantageously, when methanol is used as the
; solvent, a portion of the product methanol may be used as
make-up to the gas-purification zone. By scrubbing the
--19-- -
10~7(~77
synthesis gas with methanol at 0C and 10 atmospheres
100 volumes of CO2 are absorbed per volume of methanol.
This concentration is increased to 270 vol/vol at - 30C.
At a high partial pressure of CO2 e.g. 25~ psi. methanol
offers a very high absorption power. Similarly, cold
methanol is an excellent selective solvent for separating
H2S and COS from CO2. For example, the gas stream may be
washed with cold methanol and the total sulfur, H2S + COS,
may be reduced to less than 0.1 ppm. By selective absorp-
tion of H2S and COS a concentration of high sulfur in the
off-gas is obtained that contributes toward economic sulfur
recovery.
In physical absorption processes, most of the CO2
absorbed in the solvent may be released by simple flashing.
The rest may be removed by stripping. This may be done most
- economically with nitrogen. Nitrogen may be available as
a low cost by-product when a conventional air separation
unit is used for producing substantially pure oxygen (95
mole % 0 or moxe) for use as the free-oxygen contalning
gas in the synthesis gas generator. ~ptionally, a portion
of the CO2 separated in the first gas purification ~one may
be recycled to the gas generator. ~he regenerated solvent
is then recycled to the absorption column for reuse. When
necessary, final cleanup may be accomplished by passing the
gas stream thxough iron oxide, zinc oxide, or activated
carbon to remove residual traces of H2S or organic sulfur,
Similarly, the H2S and COS-containing solvent may be
regenerated by flashing or by stripping with nitrogen or,
-20-
1097077
alternatively, by heating and refluxing at reduced pressure
without using an inert gas. The H2S and CoS may be then
converted into sulfur by a suitable process. For example,
the Claus process may be used for producing elemental
sulfur from H2S, as described in Kirk-Othmer Encyclopedia
of Chemical Technolo~y, Second Edition Volume 19, John Wiley,
1969, Page 352. Excess S02 may be removed and discarded
in chemical combination with limestone, or by means of a
suitable commercial extraction process.
In an alt~rnate gas purification scheme employing
autorefrigeration, from about 30 to 95% of the carbon
dioxlde may be removed from the synthesis gas stream,
along with substantially all of the H2S, in the first
gas purification zone. For example, reference is made
to coassigned U.S. Patent No. 3,614,872 in which a stream
`~ of shifted synthesis gas is separated into an enriched
~; hydrogen stream and an enriched carbon-dioxide stream by
;~ counter-current cooling with a departing stream of liquid
C2 which is expanded and vaporized to produce low
temperature.
The partially purified synthesis gas stream leaves
~ ~ the first gas puxification zone at a temperature in the
;~ range of about -80 to 250F and at a pressure in the range of
about 10 to 450 atmospheres (pxeferably substantially equal
~ ,~
to the pressure in the reaction zone of the synthesis gas
generator, less ordinary line drop). The composition of
this partially purified stream of synthesis gas is about as
follows in mole %: H 70 to 30, CO 30 to 60, CO2 nil to 15,
H20 nil to 2, CH4 nil to 2, Ar nil to 2, N2 nil to 15,
H S nil, and COS nil.
, ..,.._ _
-21-
1097~77
The aforesaid stream of partially purified
synthesis gas may be split into two streams, depending
upon the amount and composition of the carbon monoxide-ri h
gas required and the desired composition of the product
stream of synthesis gas. The split may be pre-determined
by material balances. Thus from about 10 to 100 vol. %,
such as 10 to 90 vol. % of the stream of cleaned and
partially purified synthesis gas leaving the first gas
purification zone may be introduced into a second gas
purification zone.
The second gas purification or separation zone may
comprise any suitable conventional process for separating
out a CO-rich gas, a H2-rich gas stream, and optionally a
CH4-rich gas stream. Cryogenic cooling or physical
absorption with a liquid solvent e.g. copper ammonium
acetate or cuprous aluminum chloride, liquid nitrogen, and
liquid methane may be employed.
One system for remo~ing CO from the gas stream
by physical absorption in cold copper liquor in a CO-
absorption column will be described below. Upon applying
heat and releasing the pressure on the cop~er liquor in a
. ~
copper-liquor regeneration column, a relatively pure carbon
;~ monoxide i9 obtained. The reaction is shown in Equation I.
~ ~ .
Cu2 (NH3)~+4 + 2CO + 2NH3-~-Cu2(NH4)6 (CO)2 (I)
Thus, in the second gas purification zone at least
a portion of the effluent gas stream from the first gas
purification zone may be contacted in a conventional packed
or tray-type column with a countercurrent flowing stream
. ~ .
-22-
~09~()77
of, for example, cuprous acetate dissolved in aqua-ammonia
solution. The temperature is preferably in the range of
about 32 to 100F and the pressure is preferably in the
range of about 50 to 600 atm. Preferably, the pressure
in the CO separation zone is substantially the same as
that in the gas generator, less ordinary pressure drop in
the lines and equipment. By keeping the pressure in the
gas generator high enough, a gas compressor may be
avoided between the acid-gas-absorption column in the first
gas purification zone and the CO-absorption column in
the second gas purification zone. Advantageously, the
product stream of purified synthesis gas may be delivered at
a pressure which is about that in the partial oxidation gas
; generator less ordinary drop in the intervening lines and
equipment.
;~ A typical analysis (by weight %) of the copper-
liquor solution may include the following: C`u 10; Cu++ 2.2;
+
CO3 (carbonate) 13.9; HCO3 (bicarbonate) 1.3; and NH4 16.5.
The acid radical in the aqueous solution may be either car-
bonate, formate, or acetate.
20~ Regeneration of the copper liquor and release of
the CO-rich gas stxeam takes place in a copper-liquor
regenerator. The pressure difference between the scrubber
-: '
and the regenerator is about 68 to 204 atm. e.g, 109 atm.
By the reduction of pressure and the addition of heat and a
free-oxygen conta ming gas, e.g. air, pure 0 , and mixtures
thereof, the direction of Equation I may be reversed and
the carbonate and bicarbonate ions may be regenerated. The
-23-
~0~70~7
normal temperature range in the regenerator may be about
170 to 180F. Fresh make-up ammonia and, for example,
acetic acid may be added to the copper liquor in the
regenerator in order to maintain the proper solution
chemistry. Optionally, the acetic acid may be produced
subsequently in one embodiment of the subject process.
In one separation process, the partially purified synthesis
gas stream from the first gas purification zone is contacted
with liquid methane or a sulfur-free liquefied C~4-rich
gas comprising at least 85 vol. % CH4, such as liquid natural
- 10 gas in a separation column. The bottoms stream from the
column may be then passed into the partial oxidation gas
generation operation as at least a portion of the feed.
In one embodiment of the subject invention,
clean purified methanol synthesis gas is produced having
a mole ratio H2/CO in the range of about 2 to 4 by the
previously described process steps. ~y conventional
catalytic steps the synthesis gas may be converted into
~; methanol.
The equilibrium exothermic reaction of carbon
; 20 oxldes and hydrogen to produce methanol, as shown in
Equations II and III below, is favored by low temperature
a~d high pressure. However, elevated tempera~ures may be
~; ~ necessary with some catalysts to obtain commercially
adequate reaction rates.
CO + 2H2 _ CH30H II
CO2~ 3H2~ CH30~ III
Conventional high-pressure methanol processes
opexate at temperatures in the range of about 650 to 750F,
at pressures in the range of about 250 to 350 atm. and
with zinc-oxide/chromium-oxide catalysts.
~a_
1~97(~77
Conventional low- and intermediate-pressure
methanol processes operate at temperatures in the range
of about 400 to 660F., such as 440-520F.; at pressures
in the range of about 40 to 250 atm., such as 40 to 150,
and with catalysts composed largely of copper oxide with a
lesser amount of zinc oxide and either chrome or aluminum
oxides. The proportions of these three oxides are 30 to
60%, 20 to 40%, and 5 to 20%, respectively, Durability
and thermal stability of the catalyst may be improved by
the addition of manganese or vanadium. Methanol catalysts
may be prepared by alkaline precipitation from nitric-acid
solution, followed by drying, calcining, and pelletizing.
Space velocities may range from about 10,000 to 40,000
hr 1. Contact times are below 1.0 second. This rate of
methanol formation is from about 0.3 to 2.0 kg/liter of
catalyst/hr.
Optionally, the gaseous feed to the methanol
converter may contain about 2 to 12 mole % of CO2. Also,
the mole ratio, H2/(~CO+3CO2), in the feed gas stream
to the methanol converter may be in the range o~ about
1.01 to 1.05. The presence of sQme CO2 reduces the cost
of the prior g~s purification step. Further, the greater
mo}ar specific heat of the CO2 relative to CO and the lower
heat of reaction of the CO2 provide a more uniform tempera-
. ~
ture control in the methanol reactor. The presence of
C2 appears to be beneficial in repressing the formation
of dimethyl ether. Optionally, CO2 obtained from said
first gas puriication zone may be mixed with the methanol
synthesis gas to adjust the mole % of CO2 present.
. .
i
-25-
1097(;~77
Each mole of fresh methanol synthesis gas may
be mixed with 0 to 10 moles of unconverted recycle gas
from the methanol converter, i.e. 3 to 8 moles of
recycle gas per mole of fresh methanol synthesis gas. A
steam-turbine-driven circulating compressor may be used to
compress and to circulate a mixture comprising the fresh
methanol synthesis gas and the recycle gas. The working
fluid for the turbine, i.e. steam, may be obtained from
the main syngas cooler following the gas generator.
The feed-gas mixture to the methanol con-
verter is prefera~ly preheated by indirect heat exchange
with the gaseous effluent stream departing from the
methanol converter at a temperature in the range of
about 500 to 800F and at a pressure in the range of
.
about ~ to 4S0 atm., preferably at the pressure in
.
the synthesis gas generator less ordinary drop in the
tervening lines and equipment.
::
`
-26-
~ ,
;
1097()77
The effluent stream from the methanol reactor may have the
following pri~ ~pal ingredients, in mole %: CH30H 5 to 15
C0 8 to 25; H2 40 to 80; Co2 3 to 12; H20 0.5 to 15; and
(CH3)20 0.5 to 0.6. Minor amounts of other alcohols,
aldehydes, and ketones may be present.
Further cooling of the effluent gas stream in
air and water coolers may be effected to condense crude
methanol and water. This condensate flows to a separation
zone in which uncondensed unreacted gases, i.e H2, C02,
CH4, N2, Ar are separated, for example by flashing, and re-
cycyled to the gas compressor, with the exception of any
purge stream. The crude methanol is purified by fractional
distillation. Impurities including low-boiling compounds,
principally dimethyl ether and higher alcohols, may be
withdrawn from the distillaticn zone and optionally may be
disposed as a waste stream or be used by recycling to the
gas generator as a portion of the feed. Advantageously,
these waste streams contain combined oxygen and therefore
reduce the free-oxygen gas required for a given level of
soot production. A portion of the product methanol may ~e
introduced into one or both gas-purification zones in the
first and second trains, as make-up solvent absorbent.
In the following embodiment of the subject invention,
first methanol synthesis gas having a mole ratio H2/C0 in
the range of about 2 to 4 is made by the previously des-
cribed process steps, concurrently with the C0-rich gas
stream (or preferably substantially pure carbon monoxide.)
Crude methanol is then prepared in the manner previously
; described and purified. Although unpurified methanol and
~ 30 the C0-rich gas stream may be reacted to produce crude
~09~77
acetic acid, it is preferable to react purified methanol
with substantially pure carbon monoxide in order to in-
crease the reaction rate and to improve the selectivity.
Theoretically, one mole of carbon monoxide per
mole of methanol is necessary to produce one mole of acetic
acid, as shown in Equation IV below. The reaction is mildly
exothermic; and, in practice, excess carbon monoxide is
re~uired, i.e. about 22%.
CH30H + CO -~ CH3COOH IV
Catalysts are commercially available for car-
bonylation reactions to produce acetic acid at high or
low pressure, by either li~uid-or vapor-phase reaction.
High-pressure carbonylation reactions for the
preparation of crude acetic acid may take place at a
temperature in the range of about 338 to 608F., such as
392-482F and at a pressure in the range of about 15 to
700 atmospheres, such as 150 to 315 atmospheres.
Suitable commercially-available high-temperature
carbonylation catalysts for the preparation of acetic acid
often comprise two main compounds. One component is a
carbonyl-forming metal of the iron group, i.e. Fe, CO, or
Ni in the form of a salt i.e. acetate. The other component
is a halogen i.e. I, Br, or Cl as a free halogen ar a
halogen compound. For example, CoI or a mixture of cobalt
; acetate with an iodine compound are suitable catalysts. A
contact time of about 2-3 minutes may be required to obtain
50-65% conversion of methanol by vapor-phase reaction at
high pressure. Liquid phase reaction at about 356F at 25~
atm. may take about 3 hrs., for about 51% conversion. Water
is used as a solvent or diluent, and it increases the
-28-
.. . .
-:, , . : .. ., . - . ~ ,
1097()77
methanol conversion while suppressing the production of
methyl acetate. For example, about 30-40 wt. % of water
may be present in th~ reaction zone.
Carbonylation reactions, ~or the preparation of
crude acetic acid by reacting together methanol and carbon
monoxide-rich gas or preferably substantially pure C0, may
take place at a temperature in the range of about 302 to
392F. and at a pressure in the range of about 34 to 680
atm., for liquid phase. ~or 50% conversion of the methanol,
the reaction time is about 40-200 minutes. A temperature
in the range of about 392 to 572F. and a pressure in the
range of about 1 to 10 atm. may be used for vapor-phase
reaction.
Suitable commercially available low-temperature
carbonylation catalysts for the preparation of acetic acid
comprise the following combination of ingredients: (1)
noble metal catalyst, (2) catalyst promoter, and (3~ dis-
persant or carrier. The noble metal active catalyst may be
, ~
selected from the group consisting of rhodium, palladium,
platinum, iridium, osmium, or ruthenium~ in the ~orm of an
oxide, organometallic compound, salt, or a coordination
compound, consisting of one of said noble metals, C0, a
halide, such as chloride, bromide, or iodide, and a suitable
amine, organo pho~phine, organoarsine, or organostibine
ligand. The catalyst promoter may consist of a halogen or
~; halogen compound. The dispersant in liquid-phase processes
is a solvent for the metal catalytic component i.e. mixture
o~ acetic acid and water. In vapor-phase processes the
same noble-metal compound and promoter as previously
described are dispersed on a carrier, i.e. pumice, alumina,
activated carbon, or silica.
--2g--
10970'77
For example, a typical low-pressure catalyst for
the li~uid-phase process may comprise 10 2 to 10 4 mol/liter
of chlorocarbonyl-bis-triphenolphosphine rhodium, and 10 4
to 2 mol/liter of methyl iodide dissolved in a mixture of
acetic acid and water. The ratio of atoms of halogen in the
promoter to atoms of noble metal in the catalyst is prefer-
ably in the range of about 3 to 300.
In the low-pressure process for the production of
glacial acetic acid by li~uid-phase carbonylation, at least
a portion of the pure methanol as produced previously is
mixed in a reactor surge tank with recovered recycled unre-
acted methanol, catalyst, catalyst promoter, acetic acid
solvent for the catalyst, methyl acetate, and water. The
mixture is then pumped into a carbonylation reactor, along
with substantially pure carbon monoxide, in which the carbony-
lation reaction takes place at a temperature, for example,
of 392F. and at a pressure of about 35 atmospheres. The
gaseous product is cooled and sent to a separation zone in
which uncondensed gases and condensate are separated. The
uncondensed gas may be scrubbed with fresh methanol to
,
recover the entrained methanol, methyl acetate, and methyl
iodide for recycle to the reactor surge tank. Optionally,
the residual o~f-gas may be recycled to the gas generator,
~ -
or to the water-gas shift converter, or vented. The liquid
product rom the reactor and the condensate are sent to a
separation zone, i.e. distillation zone, in which at a pres-
sure o~ about 1-3 atm. the low-boiling constituents, such as
methanol, methyl acetate and methyl iodide, are separated
~and recycled to the reactor surge tank, along with recovered
rhodium compound catalyst dissolved in acetic acid, and with
-30-
109'7U77
water which may be recovered by azeotropically dehydrating
acetic acid. Glacial acetic acid product is also separated
along with a bottoms stream comprising propionic acid and
heavy ends.
Advantageously, the waste bottoms stream of prop-
ionic acid and heavy ends, as well as any off-gas stream
that is not purged may be recycled to the gas generator as
a portion of the feed. By this means the environment is
not polluted. Preferably, the pressure in the acetic-acid
synthesis zone is the same as that in the partial oxidation
gas generator less ordinary pressure drop in the intervening
lines and e~uipment.
, ~
.~ .
-31-
1()9'7077
DESCRIPTION OF THE DRAWING
A more complete understanding of the invention
- may be had by reference to the accompanying schematic --
drawing, A preferred embodiment of the process of this
invention is illustrated by that portion of the drawing,
Fig, IA, to the left of line A-A. Other embodiments are
shown ~n Fig. IB to the right of line A-A. It is not
intended to limit the continuous process illustrated to the
particular apparatus and materials described.
With reference to the Fig. I~, unpacked, free-flow
noncatalytic partial oxidation-synthesis gas generator 1,
as previously described has a refractory lining 2 and
an annulus-type burner 3 mounted in its upper inlet
port 4 along the vertical axis. The feed streams are
introduced into the reaction zone 5 of the gas generator
by way of burner 3. They include an oxygen stream which
passes through line 6, and the central conduit 7 o the
burner, a stream of steam which passes through lines 8 and 9,
and a stream of hydrocarbonaceous fuel which passes through
lines 10 and 9. The latter two streams are mixed together
.
~ in line 9 and the mixture is then passed through the annulus
passage 4 in burner 3.
The effluent stream of raw synthesis gas lea~es
the reaction zone and passes through exit passage 15 and
directly into a spherically shaped insulated chamber 16.
A portion of any entrained solids may drop out of the
~ ~ ,
~ gas stream and pass through bottom outlet 17 and into slag
, ~ ,
pot 18 by way of upper inlet 19. The solid material
; which collects in slag pot I8 is periodically removed
:
~ _32-
,~ . . -
105~7(~'7
through bottom outlet 20, line 21, valve 22, and line
23, or by a lock-hopper system hot shown. When the process
gas stream contains little or no entrained solids such as
the csse with gaseous and some liquid fuels, slag pot 18
may be deleted. Optionally, steam in line 24 may be
passed through inlet 25 and injected into the stream of
synthesis gas in chamber 16. By this means, the H2/CO
mole ratio of the process gas stream may be increased by
the thermal noncatalytic wate.r~ga~ ift reaction.
The stream of synthesis gas is passed through
outlet 26 of chamber 16, insulated line 27 and then through
inlet 29 of gas ~ooler 30 where it is cooled by indirect.
heat exchange with a stream of boiler feed water from line
31. The boiler feed water.passes through inlet 32 and leaves
as steam through outlet 33 and line 34. The cooled
synthesis gas leaves through outlet 35, lines 36, 37, valve
38, line 39 and is contacted with water from line 40 in
orifice or venturi scrubber 41. Any remaining entrained
solids i.e. particulate carbon and ash are thereby scrubbed
from the raw synthesis gas and pass with the water through line
~20 42 into separation vessel 43. A mixture of solid particles
and water is removed through line 44 near the bottom of
vessel 43 and is sent to a separator tnot shown) where
clarified water is separated and recycled to lines 40 and 45.
~ .
Additional gas scrubbing may be achieved t for example, by
passing the stream of synthesis gas through water spray 46 prior
to leaving vessel 43 through line 47. ~hen ~n gas
,
-33-
10~'7()~7
scrubbing is required then all or a portion of the process
gas stream in line 36 may be by-passed through line 48,
valve 49 and line 50.
The synthesis gas in line 51 is cooled below
the dew point in heat exchanger 52 by indirect heat
exchange with cold water entering through line 53 and
leaving by line 54. The cooled stream passes through line
- 55 into separation vessel 56 where the condensed water is
removed at the bottom by way of line 57 and the gas stream
leaves through line 58 at the top.
In the embodiment is the process in which the
soot-free dehumidified synthesis gas stream in line 58
contains less than SPPM of H2S and COS, valve 59 lS closed,
valves 60 and 61 are opened, and valve 62 may be opened
or closed to permit at least a portion of the gas in line
58 to pass into the CO2-absorption section 63 of first
; gas purification zone 64 by way of line 65, valve 60,
lines 66, 67, valve 51, and line 68. Optionally, a
portion of the soot-free dehumidified gas in line 58 by-
passes first gas purification zone 64 and second gas
purification zone 85, by way of line 69, valve 62,
lines 70, 71, valve 72, and lines 73, 74~ and 91.
Optionally, a portion of the soot-free dehumidified gas
stream in line 70 may be removed from the system through
-~ }ine 75, valve 76, and line 77. Lean liquid solvent
absorbent enters CO2-absorption zone 63 through line 78
and passes down the column over trays or packing thereby
co~ing in direct contact with the gas stream passing
up the column. Rich solvent absorbent leaves section 63
saturated with CO through line 79 and goes to a regeneration
zone (not shown). The synthesis gas stream containing
' ' ' - ' ' ' ' ~
-34-
~097(~77
substantially no CO2 or a controlled amount leaves section
63 through line 80.
The partially purified synthesis gas stream
leaving the first gas purification zone by way of line 80
may be then split into two streams 81 and 82. At least
a portion of the stream of synthesis gas in line 80 is
passed through line 81, valve 83, line 84, and is then
subjected to further treatment in a second gas purification
zone 85. The remainder of the gas stream if any
comprising about 0 to 90vol. %, such as about 10 to 90
vol. % of the gas stream from line 80 is pasced through
line 82, valve 86, lines 87-88, valve 89, line 90 and
may be mixed in line 91 with the soot-free dehumidified
stream of synthesis gas which by-passes the first gas
purification zone,if any, from line 74. Optionally, a
portion i.e. 0 to 50 vol. % of the partially purified
: synthesis gas 3n line 87 may be removed from the system
through line 92, valve 93, and line 94.
At least a portion and preferably all of the
CO-rich gas or substantially pure carbon monoxide product
gas which exlts the second gas purification zone 85
through line 95 and 96 may be used in organic synthesis.
The remainder may be exported through line 97, valve 98,
and line 99. A stxeam of H2-rich gas leaves CO-separation
.
: zone 85 by way of lines 100, 101, valve 102, and line 103.
~ In line 104 at least a portion of the H2-rich gas stream
: ~ from line 103 is mixed with all of the stream of synthesis
gas from line 91. ~ Thus the purifie~ synthesis gas
,: .
-35-
1~97(~77
product stream having an increased and controlled H2/C0
mole ratio in line 104 is made by mixing together at least
a portion of the H2-rich gas stream from line 103 with
at least a portion of one or both of the following streams:
(a) soot-free dehumidified synthesis gas which by-passes
first and second gas purification zones 64 and 85 in line
91 by way of lines 69, 70, 71, 73, 74, and 91. (b) soot-
free dehumidified synthesis gas with at least a portion of
the C02 removed from line 80 that by-passes the second gas
purification zone 85 by way of lines 82, 87, 88, 90, and 91.
Any remaining H2-rich gas from line 100 may be
exported through line 105 valve 106 and line 107. The
synthesis gas product stream in line 104 has a H2/C0 mole
ratio in the range of about 2 to 12. At least a portion and
preferably all of this gas stream may be passed through
line 108 for use in organic synthesis. Any remaining
portion of the synthesis gas product stream from line 104
may be passed through line 109, valve 110, and line 111 to
export, or recycle to the gas generator either alone or in
admixture with other recycle streams.
In another embodiment in which the soot-~ree
dehumidified gas stream in line 58 comprises more than
5 PPM, a desulfurization section 120 is added to the
bottom of the first gas purification zone 64. In such
case with valves 61 and 62 closed and valves 59 and 60
. . .
. open, all of the soot-free dehumidified synthesis gas in
line 58 is passed into first gas purification zane 64,
and none of this gas stream i~ by-passed around the first
. gas purification zone by way of line 69, valve 62, line 70
10~7~)77
etc. Thus the soot-free dehumidified gas in line 58 is
passed through line 65, valve 60, lines 66, 121, valve 59,
line 122, into the first stage i.e. lower desulfurization
section 120 containing trays or packing where it passes
up through the absorption column in direct contact with
a stream of liquid solvent absorbent flowing down the
column. Lean solvent absorbent in line 123 enters
section 120, absorbs H2S and COS from the synthesis gas,
and leaves as rich liquid solvent absorbent by way of
line 124. The rich solvent absorbent passes into a
regenerator tnot shown) to produce lean liquid solvent
absorbent which is recycled to section 120 by way of line
123. Desulfurized synthesis gas leaves through line 125 and
optionally may be split into two streams. At least a portion
of the desulfurized synthesis gas may be passed through
line 126, valve 127, and line 128 into upper section 63 of
the first gas purification zone where at least a portion
of the CO2 in the gas stream is removed in the manner
previously described. The remainder of the desulfurized
gas stream if any, in line 125 is passed through line 129,
valve 130, and lines 131, 132, 74 and 91. Optionally,
a portion of this desulfurized gas stream is removed from
::
the system through line 133j valve 134, and line 135.
. ~ :
~ A desulfurized synthesis gas stream with at
::,
leaæt~a portion of the CO2 removed leaves the first gas
purification zone through line 80, At least a portion of
this stream passes into the second gas purification zone
by way of line 81, valve 83, and line 84. The remainder
of gas stream 80 if any, by-passes the second gas purification
zone by way of line 82, valve 86, lines 87, 88, valve 89,
~ .,
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., -
1097077
and lines 90 and 91. Optionally, a portion of this
by-pass stream may be exported through line 92. A CO-rich
or substantially pure CO product stream is removed through
line 95 of the second gas purification zone, and a H2-rich
gas stream is removed through lines 100, 101, valve 102,
and line 103. A product stream of purified synthesis gas
having a controlled and increased H2/CO mole ratio in the
range of about 2 to 12 is produced by mixing in line 104
at least a portion of the H2-rich gas stream produced in
the second gas puxification zone in line 103 with at least
a portion of one or both of the following: (a) desulfurized
synthesis gas produced in the first stage 120 of first gas
purification zone 64 and which by-passes the second stage
63 and the second purification zone 85 by way of lines
125/ 129, valve 130, lines 131/ 132/ 74/ and 91; (b)
desulfurized synthesis gas with at least a portion of the
C2 removed produced in the second stage 63 of first gas
purification zone 64 and which by-passes the second gas
purification zone 85 by way of lines 80/ 82/ valve 86,
lines 87, 88, valve 89/ and lines 90 and 91.
:~ .
`:
.
-3a-
!
1~)9~()77
In another embodiment shown in Fig. lB, pure
methanol is made by the catalytic reaction of at least a
portion of cleaned and purified product stream of methanol
synthesis gas from line 108. The process steps are shown
to the right of section line A-A in the drawing. The
process gas stream from line 108 is passed through valve 200,
and line 201 into steam turbocompressor-circulator 202 along
with unconverted recycle gases from line 203. The compressed
gases in line 204 are then preheated in heat exchanger 205
- by indirect heat exchange with the hot impure methanol vapor
leaving catalytic methanol reactor 206 by way of line 207.
The preheated methanol synthesis gas stream in line 208 is
passed through methanol reactor 206 where reactionS be~e9n .
and carbonic oxides take place to produce crude methanol.
Ater being partially cooled in heat exchanger 205, the
methanol reaction products pass through line 209 into separ-
ation zone 210 where the unreacted gases are separated from
the crude methanol. The unreacted gases are passed through
; lines 215 and 203 into recycle compressor 202, except for the
purge gas which is passed through line 216, valve 217, and
line 218. The crude methanol in line 219 i9 introduced into
the purification zone 220 where impurities are removed, ~or
example, by distillation. Dimethyl ether may be removed through
~ , .
Iine 221, mixed alcohols through line 222, and water through
line 223. Pure methanol may be drawn off through lines 224,
225, ~alve 226, and line 227. Optionally, by-product oxygen-
containing organic compounds from lines 221, 222, and 218 may
be recycled to the gas generator as a portion of the fuel and
to reduce the free-oxygen requiremer.ts for a gi~en level of
soot production.
In 9till another embodiment of the invention a raw
stream of acetic acid is prepared by the low pressure liquid-
~ ., ,, , . .. ... ~, ,. ... ... . . , ~ , ....... . .
- '
10970~;'7
phase catalytic carbonylation reaction between the pure
methanol and the substantially pure carbon monoxide made
previously in the subject process. In such case, at least
a portion of the pure methanol in line 224 is passed through
line 240, valve 241, and line 242 into reactor surge tank 243
and mixed with a mixture of recycle materials from line 244.
Recycle stream 244 comprises a mixture of methanol, methyl
acetate, and methyl iodide from lines 245 and 246 and a
rhodium catalyst compound i.e. Rh(CO)~P(C6H5)3)2 Cl dissolved
in a mixture of acetic acid and water from line 247.
By ~eans of pump 248, the reactant mixture in tank
243 is pumped through lines 249 and 250 into vertical carbony-
lation reactor 251. Simultaneously, at least a portion of
the substantially Fure CO gas stream in line 96 is passed
into c-arbonylation reactor 251 by way of valve 255, line 256,
optionally steam turbocompressor 257, and line 258. In
reactor 251, methanol and CO react to produce acetic acid.
: An overhead gaseous stream is passed through line 259,
cooled in heat exchanger ~60, and passed through line 261
into æeparator 262. The uncondensed gases in line 263 are
scrubbed with fresh methanol in a tower ~not shown) to re-
cover ~ntrained methanol, methyl acetate and methyl iodide
:: for recycle to the reactor surge tank 243. Residual off-gas
rom the scrubber may be recycled to the gas generator or
: vented.
The liquid product from the reactor in line 264
:~ and the condensate from line 265 are passed through line 270
into separation zone 271. For example, by distillation,
~ ~ .
-40
10~'70~7
the low boiling constituents comprising a mixture of
methanol, methyl acetate, and methyl iodide may be
separated and leave by way of line 245; water is removed
through line 272; recovered rhodium compeund catalyst
dissolved in acetic acid is removed through line 247;
and impure acetic acid is removed through line 273 and
fed into separation zone 274. Glacial acetic acid is recov-
ered as a distillate from line 275. Propionic acid and heav-
ier components leave through line 276 and may be recycled
to the gas generator as a portion of the fuel.
EXAMPLE
The following example illustrates an embodiment
of the process of this invention for simultaneously and
continuously producing a stream of methanol synthesis gas
and a stream of substantially pure carbon monoxide. The
example should not be construed as limiting the scope of
,~ the invention. Reference is made to the drawing.
The feed to a noncatalytic free-flow partial-
oxidation gas generator comprises 20.99 million standard
cubic feet per day of natural gas and 13.94 million
standard cubic feet per day of substantially pure oxygen
(99 mole ~ 2) The compo~ition of the natural gas
follows: CH4 87.62, C2H6 7.96, C3H8 , 2 2
2.56. No H20 is introduced into the ga~ generator.
65.01 miliion standard cubic feet per day of raw
synthesis gas leave the reaction zone of the gas generator
at a temperature of 2600F and a pressure of 896,0 psig.
-41-
109'7V77
The amount in million standard cubic feet per day
(MMSCF/day) and composition in mole ~ of the raw synthesis
gas stream leaving the reaction zone at reference number 15
in the drawing is shown in column 1 of Table I, which follows,
Because no solids are entrained in the gas stream leaving
the gas generator, slag pot 18 and the carbon-scrub~ing
zone comprising 41 and 43 in Fig. lA may be deleted.
Further, no water-gas shifting is required in the subject
process to increase the H2/CO mole ratio.
The amount and composition of the dehumidified
gas stream leaving gas-liquid separator 56 by way of line
58 is shown in column 2 o Table I. The gas stream in line
58 is then divided into two streams, One stream in line
69 by-passes tha first gas purification zone 64. The other
stream in line 65 is introduced into the first gas
purification zone. The amounts and compositions of gas
streams 69 and 65 are shown respectively in columns 3 and 4
of Table I, Substantially all of the CO is separated in
the first gas-purification zone. The amount and composition
of the CO2 tail gas recovered in a solvent regenerator
(not shown) is shown in column 5 of Table I,
The purified synthesis gas stream leaving the first
gas-purification zone through line 80 is shown in column
6 of Table Io Ali of this gas stream is introduced into
~ the second gas-purification zone, in which it is separated
,~ into the CO-rich product ga~ stream in line 96 and the
H2-rich gas stream in line 100~ The amounts and
compoæitions of these gas streams are shownr respectively,
.,
in columns 7 and 8 of Table I.
-42-
~",". -
109~(~77
The product gas of methanol-synthesis ~as is
then produced by mixing together in line 104 all of the
soot-free dehumidified gas stream that by-passes the
first gas purification zone by way of line 69, valve 62,
lines 70, 71, valve 72, and lines 73, 74, and 91 with
all of the H2-rich gas stream from lines 100, 101, valve
102 and line 103. The amount and composition of this
methanol-synthesis product gas stream in line 108 is
shown in column 9 of Table I. This is the proper gas
composition for mixing with unconverted recycle gas from a
catalytic methanol converter to produce a feed gas for
converting into crude methanol. Pure methanol may be
produced by distillation and reacted in a catalytic
carbonylation reactor with at least a portion of the stream
of substantially pure carbon monoxide from stream 96 to
produce crude acetic acid in the manner described previously
~ in connection with Fig. 1 B of the drawing. Glacial acetic
- acid may be then produced by purification.
`: : :
The process of the invention has been described
generally and by examples, with reference to a hydrocarbon-
aceous fuel, synthesis gas, and H2-rich gas of partlculax
compositions, for purposes of clarity and illustration only.
It wil} be apparent to those skilled in the art from the
,. ~
foregoing that various modifications of the process and
materials disclosed herein can be made without departure
from the spirit of the invention.
'''; ~ ' '
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