Note: Descriptions are shown in the official language in which they were submitted.
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ALKYNE HYDROGENATION PROCESS
BACKGROUND OF THE INVENTION
This invention relates to an improved process for catalytically
hydrogenating hydrocarbon-containing fluid comprising at least one alkyne in a
single-
stage reaction zone.
The selective hydrogenation of alkynes, which generally are present in
small amounts in alkene-containing streams (e.g., acetylene contained in
ethylene
streams from thermal ethane crackers), is commercially carried out in the
presence of
alumina-supported palladium hydrogenation catalysts. In the case of the
selective
hydrogenation of acetylene to ethylene, previous commercial operation includes
the use
of, for example, an alumina-supported palladium/silver hydrogenation catalyst
such as in
accordance with the disclosure in U.S. Patent 4,404,124 and its division, U.S.
Patent
4,484,015. However, use of these conventional acetylene removal hydrogenation
catalysts release substantial heat during operation because of the undesired
hydrogenation of ethylene to ethane which can result in loss of ethylene as
has been
pointed out in the above-identified patents. Since ethylene and hydrogen are
present in
the reacting stream to substantial excess, there is significant danger that
this unselective
reaction will occur to such a great extent that a "runaway" reaction, i.e.,
uncontrollable
hydrogenation of ethylene to ethane, will occur.
Conventional reactor designs avoid the problem of a possible "runaway"
reaction by controlling the extent of the reaction by removing heat part way
through the
hydrogenation catalyst mass. The removal of heat requires a multi-stage
reactor system,
such as, for example, at least two catalyst beds, with expensive heat removal
apparatus,
such as, for example, inter-stage cooling apparatus such as a heat exchanger,
between
stages, e.g., between catalyst beds. Thus, the development of a process to
avoid a
"runaway" reaction, and the resulting loss of ethylene, in a single-stage
reaction system
without expensive heat removal apparatus would be of significant contribution
to the art.
It is generally known by those skilled in the art that fluctuations in carbon
monoxide concentration, especially increases in carbon monoxide concentration,
can
occur during the catalytic hydrogenation of alkyne-containing feeds such as,
for
example, when furnaces are brought into operation during the hydrogenation
reaction.
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Sharp increases in carbon monoxide concentration can significantly hinder the
hydrogenation of alkynes to corresponding alkenes requiring the temperature of
the
reaction to be increased to maintain such hydrogenation at the same rate that
was
occurring before the increase in carbon monoxide concentration. However, when
the
reaction temperature is increased to counteract the increase in carbon
monoxide
concentration, there is an increased chance that a "runaway" reaction as
described above
will occur. The catalytic hydrogenation of alkyne-containing feeds is
especially
vulnerable to a runaway reaction at this point because of a rapid return of
the carbon
monoxide concentration to initial levels which is a frequently observed event.
The rapid
return of the carbon monoxide concentration to initial levels frequently
occurs faster
than the rate at which heat can be removed. Thus, the reaction system is in an
overheated condition.
Conventional reactor designs avoid the problem of the reaction system
being in an overheated condition by controlling the extent of the reaction by
removing
heat part way through the hydrogenation catalyst mass as described above.
Thus, the
development of a method to handle such fluctuations in carbon monoxide
concentration,
especially increases in carbon monoxide concentration, and the subsequent
increase in
feed temperature in a single-stage reaction system without expensive heat
removal
apparatus would also be of significant contribution to the art.
SUMMARY OF THE INVENTION
It is desirable to carry out the selective hydrogenation, i.e., conversion, of
an alkyne(s) containing about 2 carbon atoms to about 6 carbon atoms per
molecule to
the corresponding alkene(s) utilizing an improved hydrogenation process in the
presence
of a catalyst (also referred to as "catalyst B") comprising palladium, silver,
and an alkali
metal compound where such process prevents the uncontrollable hydrogenation of
an
alkene(s) (e.g., ethylene) to an alkane(s) (e.g., ethane) in a single-stage
reaction zone,
preferably in a single-stage adiabatic reaction zone, without expensive heat
removal
apparatus.
It is also desirable to carry out the selective hydrogenation, i.e.,
conversion, of an alkyne(s) containing about 2 carbon atoms to about 6 carbon
atoms per
molecule to the corresponding alkene(s) utilizing an improved hydrogenation
process in
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the presence of catalyst B and in the presence of fluctuations in carbon
monoxide
concentration, especially increases in carbon monoxide concentration, and
subsequent
increases in feed temperature while preventing the uncontrollable
hydrogenation of an
alkene(s) (e.g., ethylene) to an alkane(s) (e.g., ethane) in a single-stage
reaction zone,
preferably in a single-stage adiabatic reaction zone, without expensive heat
removal
apparatus.
The present invention is directed to a process of improving the operation
of a process system used for selectively hydrogenating, i.e., for the
conversion of, a
hydrocarbon-containing fluid comprising at least one alkyne, preferably
acetylene
(ethyne), containing about 2 carbon atoms to about 6 carbon atoms per molecule
with
hydrogen, preferably hydrogen gas, to at least one corresponding alkene,
preferably
ethylene (ethene), containing about 2 carbon atoms to about 6 carbon atoms per
molecule. The process system utilizes a volumetric amount of a hydrogenation
catalyst
(also referred to as "hydrogenation catalyst A") which can comprise, for
example, an
alumina-supported palladium hydrogenation catalyst or alumina-supported
palladium/silver hydrogenation catalyst required for providing the conversion
of the at
least one alkyne so as to provide a conversion product containing less alkyne
than the
hydrocarbon-containing fluid.
The process of improving the operation of such process system utilizing a
volumetric amount of a hydrogenation catalyst A comprises substituting such
hydrogenation catalyst A with a conversion-improving volumetric amount of a
catalyst
B comprising palladium, silver, and an alkali metal compound contained in a
single-
stage adiabatic reaction zone. The conversion-improving volumetric amount of a
catalyst B comprising palladium, silver, and an alkali metal compound is less
than the
volumetric amount of such hydrogenation catalyst A present in the process
system
before utilizing the process of improving. The process also includes
contacting under
reaction conditions such hydrocarbon-containing fluid with such catalyst B
comprising
palladium, silver, and an alkali metal compound and charging the hydrocarbon-
containing fluid to the single-stage reaction zone at a temperature sufficient
to provide
for the desired selective hydrogenation. Preferably, the improved process
system does
not contain any heat removal apparatus such as a heat exchanger, i.e., the
improved
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process system is an adiabatic system. The conversion-improving volumetric
amount of
a catalyst B comprising palladium, silver, and an alkali metal compound is
generally at
least 20 percent of the volumetric amount of hydrogenation catalyst A present
in the
process system before utilizing the process of improving.
The present invention is also directed to a process of charging, at reaction
conditions, a hydrocarbon-containing fluid comprising at least one alkyne
containing
about 2 carbon atoms to about 6 carbon atoms per molecule with hydrogen to a
single-
stage adiabatic reaction zone containing a catalyst B comprising palladium,
silver, and
an alkali metal compound. The process then includes converting the at least
one alkyne
containing about 2 carbon atoms to about 6 carbon atoms per molecule to at
least one
corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms
per
molecule. The process then includes yielding a conversion product containing
less
alkyne than the hydrocarbon-containing fluid and further, the conversion of
the at least
one alkyne is at least as high as the conversion of the at least one alkyne
would
otherwise be for a mufti-stage reaction zone having intercooling between
stages of such
mufti-stage reaction zone.
The present invention is also directed to a process of modifying a multi-
stage reaction zone, e.g., two or more reactor vessels in series, having
intercooling
between stages of such mufti-stage reaction zone, used for the selective
hydrogenation,
i.e., conversion, of a hydrocarbon-containing fluid comprising at least one
alkyne
containing about 2 carbon atoms to about 6 carbon atoms per molecule with
hydrogen to
at least one corresponding alkene containing about 2 carbon atoms to about 6
carbon
atoms per molecule. Such mufti-stage reaction zone utilizes a volumetric
amount of a
hydrogenation catalyst A required for providing the conversion of the at least
one alkyne
so as to provide a conversion product containing less alkyne than the
hydrocarbon-
containing fluid.
The process comprises modifying such mufti-stage reaction zone by
providing for a single-stage adiabatic reaction zone having a conversion-
improving
volumetric amount of a catalyst B comprising palladium, silver, and an alkali
metal
compound that is less than the volumetric amount of hydrogenation catalyst A
present in
the mufti-stage reaction zone before modifying such mufti-stage reaction zone.
The
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modifying of such mufti-stage reaction zone can comprise converting e.g., one
or more
stages (e.g., one or more reactor vessels) of such mufti-stage reaction zone
into a single-
stage adiabatic reaction zone (comprising, for example, an adiabatic reactor
vessel or
one or more adiabatic reactor vessels) or into a set of single-stage adiabatic
reaction
zones (comprising, for example, a set of adiabatic reactor vessels).
The inventive process offers several benefits such as: (1) a smaller and
less expensive reaction zone, (2) the ability to convert an existing mufti-
stage reaction
zone to several single-stage adiabatic reaction zones with at least one single-
stage
adiabatic reaction zone in service with at least one single-stage adiabatic
reaction zone
in stand-by allowing an essentially unlimited time to pass between shut-down
of the
entire reaction system, and (3) expansion of existing reactor capacity with
minimal
economic investment.
Other objects and advantages will become apparent from the detailed
description and the appended claims.
1 S DETAILED DESCRIPTION OF THE INVENTION
Catalyst B which is employed in the selective hydrogenation process, i.e.,
conversion process, of this invention can be any supported palladium catalyst
composition which also comprises silver and an alkali metal compound.
Generally, the
alkali metal compound is selected from the group consisting of alkali metal
halides,
alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates,
alkali metal
nitrates, alkali metal carboxylates, and the like and mixtures thereof.
Preferably, the
alkali metal compound is an alkali metal fluoride. Generally, the alkali metal
of such
alkali metal compound is selected from the group consisting of potassium,
rubidium,
cesium, and the like and mixtures thereof. Preferably, the alkali metal of
such alkali
metal compound is potassium. Most preferably, the alkali metal compound is
potassium
fluoride.
Catalyst B can be fresh or it can be a used and thereafter oxidatively
regenerated catalyst composition. Catalyst B can contain any suitable
inorganic solid
support material. Preferably, the inorganic support material is selected from
the group
consisting of alumina, titanic, zirconia, and the like and mixtures thereof.
The presently
more preferred support material is alumina, most preferably alpha-alumina.
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Generally, catalyst B contains in the range of from about 0.001 weight
percent palladium (on a total catalyst composition weight basis) to about 1
weight
percent palladium. More preferably, catalyst B contains in the range of from
about 0.01
weight percent palladium to about 0.5 weight percent palladium and, most
preferably, in
the range from 0.01 weight percent palladium to 0.2 weight percent palladium.
Generally, catalyst B contains in the range of from about 0.05 weight
percent alkali metal (on a total catalyst composition weight basis) to about 5
weight
percent alkali metal. More preferably, catalyst B contains in the range of
from about
0.05 weight percent alkali metal to about 3 weight percent alkali metal and,
most
preferably, in the range from 0.1 weight percent alkali metal to 1 weight
percent alkali
metal. Generally, the weight ratio of alkali metal to palladium is in the
range of from
about 0.05:1 to about 500:1. Preferably, the weight ratio of alkali metal to
palladium is
in the range of from about 0.2:1 to about 100:1.
When catalyst B comprises an alkali metal fluoride, the catalyst contains
in the range of from about 0.03 weight percent fluorine (chemically bound as
fluoride)
(on a total catalyst composition weight basis) to about 10 weight percent
fluorine. More
preferably, catalyst B contains in the range of from about 0.1 weight percent
fluorine to
about 5 weight percent fluorine and, most preferably, in the range from 0.2
weight
percent fluorine to 1 weight percent fluorine. Generally, the atomic ratio of
fluorine to
alkali metal is in the range of from about 0.5:1 to about 4:1. Preferably, the
atomic ratio
of fluorine to alkali metal is in the range of from about 1:1 to about 3:1.
Generally, catalyst B contains in the range of from about 0.01 weight
percent silver (on a total catalyst composition weight basis) to about 10
weight percent
silver. More preferably, catalyst B contains in the range of from about 0.01
weight
percent silver to about 5 weight percent silver and, most preferably, in the
range from
0.02 weight percent silver to 2 weight percent silver. Preferably, the
silver:palladium
(Ag:Pd) weight ratio in the catalyst is in the range of from about 2:1 to
about 10:1.
Generally, the particles of catalyst B have a size in the range of about 1
mm to about 10 mm, preferably in the range of from about 2 mm to about 6 mm.
The
particles of catalyst B can have any suitable shape, preferably spherical or
cylindrical.
Generally, the surface area of the catalyst (determined by the BET method
employing
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NZ) is in the range of from about 1 m2/g to about 100 m2/g.
The presently preferred catalysts for use as catalyst B are those described
in U.S. Pat. Nos. 5,585,318 and 5,587,348, the disclosures of which are
incorporated
herein by reference.
The selective hydrogenation process, i.e., conversion process, of this
invention is generally carried out by contacting a hydrocarbon-containing
fluid which
comprises at least one alkyne containing about 2 carbon atoms to about 6
carbon atoms
per molecule and hydrogen with a catalyst B comprising palladium, silver, an
alkali
metal compound, and an inorganic support material in a single-stage reaction
zone,
preferably in a single-stage adiabatic reaction zone, wherein such single-
stage adiabatic
reaction zone does not utilize heat removal apparatus. Thus, the phrase
"adiabatic"
generally means without a significant loss or significant gain of heat.
The selective hydrogenation process of this invention can be used to
improve the method of operation of a process system used for selectively
hydrogenating,
i.e., for the conversion of, a hydrocarbon-containing fluid comprising at
least one
alkyne, preferably acetylene (ethyne), containing about 2 carbon atoms to
about 6 carbon
atoms per molecule with hydrogen to at least one corresponding alkene,
preferably
ethylene (ethene), containing about 2 carbon atoms to about 6 carbon atoms per
molecule wherein such process system utilizes a volumetric amount of a
hydrogenation
catalyst A required for providing the conversion of the at least one alkyne so
as to
provide a conversion product containing less alkyne than the hydrocarbon-
containing
fluid. Hydrogenation catalyst A can comprise, for example, an alumina-
supported
palladium hydrogenation catalyst or alumina-supported palladium/silver
hydrogenation
catalyst such as in accordance with the disclosure in U.S. Patent 4,404,124
and its
division, U.S. Patent 4,484,015.
The process of improving the operation of such process system utilizing a
volumetric amount of a hydrogenation catalyst A comprises substituting such
hydrogenation catalyst A with a conversion-improving volumetric amount of a
catalyst
B comprising palladium, silver, and an alkali metal compound (preferably such
alkali
metal compound is an alkali metal fluoride) contained in a single-stage
reaction zone,
preferably in a single-stage adiabatic reaction zone. The conversion-improving
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volumetric amount of a catalyst B comprising palladium, silver, and an alkali
metal
compound is less than the volumetric amount of hydrogenation catalyst A
present in the
process system before utilizing the method of improvement. The process of
improving
includes contacting under reaction conditions such hydrocarbon-containing
fluid with
such catalyst B comprising palladium, silver, and an alkali metal compound.
The phrase
"substituting" generally refers to substituting in whole or substituting in
part
hydrogenation catalyst A with a conversion-improving volumetric amount of a
catalyst
B comprising palladium, silver, and an alkali metal compound. Thus, the phrase
"substituting" can refer to the conversion-improving volumetric amount of a
catalyst B
taking the place of in whole or in part, or being put in the place of in whole
or in part, or
being exchanged for in whole or in part, the hydrogenation catalyst A present
in the
process system before utilizing the method of improvement.
The conversion-improving volumetric amount of a catalyst B comprising
palladium, silver, and an alkali metal compound (preferably such alkali metal
compound
is an alkali metal fluoride) is generally in the range of from about 20 volume
percent to
about 80 volume percent of the volumetric amount of hydrogenation catalyst A
(hydrogenation catalyst A can comprise, for example, an alumina-supported
palladium
hydrogenation catalyst or alumina-supported palladium/silver hydrogenation
catalyst),
present in the process system before utilizing the method of improvement.
Preferably,
the conversion-improving volumetric amount of a catalyst B comprising
palladium,
silver, and an alkali metal compound is in the range of from about 25 volume
percent to
about 75 volume percent of the volumetric amount of hydrogenation catalyst A
present
in the process system before utilizing the method of improvement. More
preferably, the
conversion-improving volumetric amount of a catalyst B comprising palladium,
silver,
and an alkali metal compound is in the range of from about 30 volume percent
to about
70 volume percent of the volumetric amount of hydrogenation catalyst A present
in the
process system before utilizing the method of improvement. Most preferably,
the
conversion-improving volumetric amount of a catalyst B comprising palladium,
silver,
and an alkali metal compound is in the range of from 35 volume percent to 65
volume
percent of the volumetric amount of hydrogenation catalyst A present in the
process
system before utilizing the method of improvement. The phrase "conversion-
improving
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volumetric amount" refers to the volumetric amount of catalyst B comprising
palladium,
silver, and an alkali metal compound which can be used to improve the
conversion of a
hydrocarbon-containing fluid in accordance with the inventive processes
disclosed
herein.
The selective hydrogenation process of this invention can also comprise
charging, at reaction conditions, a hydrocarbon-containing fluid comprising at
least one
alkyne containing about 2 carbon atoms to about 6 carbon atoms per molecule
with
hydrogen to a single-stage adiabatic reaction zone containing a catalyst B
comprising
palladium, silver, and an alkali metal compound (preferably such alkali metal
compound
is an alkali metal fluoride). The process then includes converting the at
least one alkyne
containing about 2 carbon atoms to about 6 carbon atoms per molecule to at
least one
corresponding alkene containing about 2 carbon atoms to about 6 carbon atoms
per
molecule. The process then includes yielding a conversion product containing
less
alkyne than the hydrocarbon-containing fluid and further, the conversion of
the at least
one alkyne is at least as high as the conversion of the at least one alkyne
would
otherwise be for a mufti-stage reaction zone having intercooling between
stages of such
mufti-stage reaction zone.
The selective hydrogenation process of this invention can also be used to
modify a mufti-stage reaction zone, e.g., two or more reactor vessels in
series, having
intercooling between stages (e.g., having heat exchangers) between reactor
vessels) of
such mufti-stage reaction zone, used for conversion of a hydrocarbon-
containing fluid
comprising at least one alkyne containing about 2 carbon atoms to about 6
carbon atoms
per molecule with hydrogen to at least one corresponding alkene containing
about 2
carbon atoms to about 6 carbon atoms per molecule. Such mufti-stage reaction
zone
utilizes a volumetric amount of a hydrogenation catalyst A (such hydrogenation
catalyst
A can comprise, for example, an alumina-supported palladium hydrogenation
catalyst or
alumina-supported palladium/silver hydrogenation catalyst) required for
providing the
conversion of the at least one alkyne so as to provide a conversion product
containing
less alkyne than the hydrocarbon-containing fluid.
The process comprises modifying such mufti-stage reaction zone by
providing for a single-stage adiabatic reaction zone having a conversion-
improving
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volumetric amount of a catalyst B comprising palladium, silver, and an alkali
metal
compound (preferably such alkali metal compound is an alkali metal fluoride)
that is
less than the volumetric amount of hydrogenation catalyst A present in such
mufti-stage
reaction zone before utilizing such process of modifying.
The modifying of such mufti-stage reaction zone can comprise converting
one or more stages (e.g., one or more reactor vessels) of such mufti-stage
reaction zone
into a single-stage adiabatic reaction zone (comprising, for example, an
adiabatic reactor
vessel or one or more adiabatic reactor vessels) or into a set of single-stage
adiabatic
reaction zones (comprising, for example, a set of adiabatic reactor vessels)
with each
single-stage adiabatic reaction zone having a conversion-improving volumetric
amount
of a catalyst B comprising palladium, silver, and an alkali metal compound
(preferably
such alkali metal compound is an alkali metal fluoride) that is less than the
volumetric
amount of hydrogenation catalyst A present in such mufti-stage reaction zone
before
utilizing such process of modifying.
For example, depending upon the desired levels of selective
hydrogenation needed, the modifying of such mufti-stage reaction zone may
comprise
modifying such mufti-stage reaction zone to several single-stage adiabatic
reaction zones
with one single-stage adiabatic reaction zone to be in service while bypassing
the other
single-stage adiabatic reaction zones (e.g., the other single-stage adiabatic
reaction zones
can be in stand-by, to be used when the single-stage adiabatic reaction in
service needs
to be shut down, or to be used for further acetylene removal if necessary)
allowing an
essentially unlimited time to pass between shut-down of the entire reaction
system.
Also for example, the modifying of such mufti-stage reaction zone may comprise
modifying such mufti-stage reaction zone to several single-stage adiabatic
reaction
zones, which can be operated, for example, in parallel or in series, allowing
an
expansion of existing reactor capacity. The actual physical modifications of
such multi-
stage reaction zone into a single-stage adiabatic reaction zone or into a set
of single-
stage adiabatic reaction zones in accordance with the inventive process, i.e.,
for
example, the piping and equipment changes necessary to modify such mufti-stage
reaction zone in accordance with the inventive process described herein, are
within the
capabilities of persons of ordinary skills in the field of selective
hydrogenation
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technology.
The conversion-improving volumetric amount of a catalyst B comprising
palladium, silver, and an,alkali metal compound (preferably such alkali metal
compound
is an alkali metal fluoride) used in the modifying of such multi-stage
reaction zone is
generally in the same ranges of volume percents of the volumetric amount of a
hydrogenation catalyst A as disclosed above. The conversion-improving
volumetric
amount of a catalyst B comprising palladium, silver, and an alkali metal
compound is
generally in the range of from about 20 volume percent to about 80 volume
percent of
the volumetric amount of hydrogenation catalyst A present in the process
system before
utilizing the process of modifying. Hydrogenation catalyst A can comprise, for
example, an alumina-supported palladium hydrogenation catalyst or alumina-
supported
palladium/silver hydrogenation catalyst as described above. Preferably, the
conversion-
improving volumetric amount of a catalyst B comprising palladium, silver, and
an alkali
metal compound is in the range of from about 25 volume percent to about 75
volume
percent, more preferably, in the range of from about 30 volume percent to
about 70
volume percent, and most preferably, in the range of from 35 volume percent to
65
volume percent of the volumetric amount of hydrogenation catalyst A present in
the
process system before utilizing the process of modifying.
Any suitable hydrocarbon-containing fluid which comprises at least one
Cz-C6 alkyne can be used as the fluid to the single-stage reaction zone,
preferably single-
stage adiabatic reaction zone, of this invention. The term "fluid" is used
herein to
denote gas, liquid, vapor, or combinations thereof. Generally, such
hydrocarbon-
containing fluid contains at least one alkyne as an impurity at a level of
about 1 part by
weight alkyne per million parts by weight hydrocarbon-containing fluid to
about 50,000
parts by weight alkyne per million parts by weight hydrocarbon-containing
fluid (i.e.,
about 1 ppm alkyne to about 50,000 ppm alkyne). Preferably, such hydrocarbon-
containing fluid contains at least one alkyne as an impurity at a level of
about 1 ppm
alkyne to about 30,000 ppm alkyne, more preferably such hydrocarbon-containing
fluid
contains at least one alkyne as an impurity at a level of about 1 ppm alkyne
to about
20,000 ppm alkyne and, most preferably, such hydrocarbon-containing fluid
contains at
least one alkyne as an impurity at a level of about 1 ppm alkyne to about
10,000 ppm
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alkyne. Generally, such hydrocarbon-containing fluid is a CZ-C6 alkene stream.
Non-limiting examples of suitable, available hydrocarbon-containing
fluid include ethylene, propylene, and butylene streams, such as those from
thermal
hydrocarbon-(e.g., ethane, propane, butane, and naphtha) cracking processes,
and
mixtures thereof. A particularly preferred hydrocarbon-containing fluid is an
ethylene
stream from a thermal ethane-cracking process.
Preferred alkynes include acetylene, propyne, butyne-l, butyne-2 and the
like and mixtures thereof. A particularly preferred alkyne is acetylene. These
alkynes
are primarily hydrogenated to the corresponding alkenes, i.e., acetylene is
primarily
hydrogenated to ethylene, propyne is primarily hydrogenated to propylene, and
the
butynes are primarily hydrogenated to the corresponding butenes (butene-1,
butene-2).
A particularly preferred corresponding alkene is ethylene.
It is within the scope of this invention to have additional compounds such
as carbon monoxide, sulfur compounds, methane, ethane, propane, butane, water,
alcohols, ethers, ketones, carboxylic acids, esters, other oxygenated
compounds, and the
like and mixtures thereof present in the hydrocarbon-containing fluid, as long
as such
additional compounds do not significantly interfere with the selective
hydrogenation of
alkyne(s) to alkene(s). An important benefit of the improved process system is
the
ability to handle fluctuations in carbon monoxide concentration, especially
increases in
carbon monoxide concentration, without significantly affecting the
hydrogenation
reaction. Generally, the sulfur compounds are present in the hydrocarbon-
containing
fluid in trace amounts, preferably at a level of less than about 1 weight
percent sulfur,
and preferably at a level of about 0.01 ppm by weight sulfur to about 1,000
ppm by
weight sulfur (i.e., about 0.01 to about 1,000 parts by weight sulfur per
million parts by
weight hydrocarbon-containing fluid).
The molar ratio of hydrogen to hydrocarbon of the hydrocarbon-
containing fluid in the single-stage adiabatic reaction zone should be in the
range of
from about 0.01:1 to about 25:1. Preferably, the molar ratio of hydrogen to
hydrocarbon
should be in the range of from about 0.01:1 to about 10:1. More preferably,
the molar
ratio of hydrogen to hydrocarbon should be in the range of from about 0.05:1
to about
5:1, and, most preferably, the molar ratio of hydrogen to hydrocarbon should
be in the
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range from 0.10:1 to 1:1. In order to best attain substantially complete
removal of CZ-C~
alkyne, preferably acetylene, there should be at least one mole of hydrogen
for each
mole of CZ-C6 alkyne present. Generally, the molar ratio of hydrogen to CZ-C6
alkyne is
in the range of from about 0.5:1 to about 200:1, preferably about 1:1 to about
100:1.
The hydrogen and the hydrocarbon-containing fluid can be charged to the
single-stage adiabatic reaction zone by any manner or methods) which maintains
the
molar ratio of hydrogen to hydrocarbon. Generally, the hydrocarbon-containing
fluid
and the hydrogen are premixed before their contact with a catalyst in the
single-stage
adiabatic reaction zone.
The single-stage reaction zone, preferably single-stage adiabatic reaction
zone, comprises a structure having an inlet, an outlet, and a length-to-
diameter ratio
(L:D ratio) in the range of from about 0.25:1 to about 40:1, preferably in the
range of
from about 0.5:1 to about 30:1, more preferably in the range of from about
0.5:1 to
about 20:1, and, most preferably, in the range from 0.5:1 to 5:1. Such
structure can
comprise, for example, a reactor vessel, preferably an adiabatic reactor
vessel.
The contacting step (i.e., the contacting of hydrocarbon-containing fluid
with a catalyst in the single-stage adiabatic reaction zone) can be operated
as a batch
process step or, preferably, as a continuous process step. In the latter
operation, a solid
catalyst bed is generally used although conceptually a moving catalyst bed or
a fluidized
catalyst bed can be employed. Any of these operational modes have advantages
and
disadvantages, and those skilled in the art can select the one most suitable
for a
particular fluid and catalyst. Further discussion is provided in Perry's
Chemical
Engineers' Handbook, Sixth Edition, published by McGraw-Hill, Inc., copyright
1984, in
sections entitled "Reactors for Solid-Catalyzed Reactions" at pages 4-36
through 4-48,
and "Uses of Fluidized Beds" at pages 20-70 through 20-75, which pages are
incorporated herein by reference.
Reaction conditions of the single-stage reaction zone, preferably single-
stage adiabatic reaction zone, of the contacting step of the inventive process
include a
reaction temperature in the range of from about 24°C to about
260°C (about 75°F to
about 500°F). Preferably, the reaction temperature can be in the range
of from about
27°C to about 204°C (about 80°F to about 400°F)
and, most preferably, the reaction
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temperature can be in the range from about 32°C to about 149°C (
90°F to 300°F).
The reaction pressure of the single-stage adiabatic reaction zone can be in
the range of
from below atmospheric pressure upwardly to 6.89MPa (about 1000 pounds per
square
inch absolute (psia)), preferably, from 689kPa to about 6201kPa (about 100
psia to
about 900 psia) and, most preferably, 1378kPa to 4832kPa from (200 psia to 700
psia).
The flow rate at which the hydrocarbon-containing fluid is charged (i.e.,
the charge rate of hydrocarbon-containing fluid) to the single-stage reaction
zone,
preferably single-stage adiabatic reaction zone, is such as to provide a gas
hourly space
velocity ("GHSV") in the range of from exceeding 0 hour' upwardly to about
100,000
hour'. The term "gas hourly space velocity", as used herein, shall mean the
numerical
ratio of the rate at which a hydrocarbon-containing fluid is charged to the
single-stage
adiabatic reaction zone in standard cubic feet ("SCF") per hour divided by the
SCF of
catalyst contained in the single-stage adiabatic reaction zone to which the
hydrocarbon-
containing fluid is charged. The preferred GHSV of the hydrocarbon-containing
fluid to
the single-stage adiabatic reaction zone can be in the range of from about 500
hour' to
about 50,000 hour' and, most preferably, in the range from 1000 hour' to
20,000 hour''.
The GHSV of the hydrogen gas stream is chosen so as to provide the molar
ratios of
hydrogen to hydrocarbon of the hydrocarbon-containing fluid as disclosed
above.
After catalyst B has been deactivated by, for example, coke deposition or
feed poisons, to an extent that the selective hydrogenation has become
unsatisfactory,
the catalyst can be reactivated by any means or methods) known to one skilled
in the art
such as, for example, calcining in air to burn off deposited coke and other
carbonaceous
materials, such as oligomers or polymers, preferably at a temperature in the
range of
from about 399°C to about 982°C (about 750°F to about
1800°F). Optionally, the
oxidatively regenerated catalyst is reduced with HZ or a suitable hydrocarbon
before its
redeployment in the selective alkyne hydrogenation of this invention. The
optimal time
periods of the calcining depend generally on the types and amounts of
deactivating
deposits on the catalyst composition and on the calcination temperatures.
These optimal
time periods can easily be determined by those possessing ordinary skills) in
the art and
are omitted herein in the interest of brevity.
The following example is presented to further illustrate this invention and
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is not to be construed as unduly limiting the scope of this invention.
EXAMPLE
The data presented in Table I below was developed by testing the novel
process in a Phillips Petroleum Company ethylene plant at Sweeny, Texas. The
ethylene
plant utilized a mufti-stage reactor system, i.e., two reactor vessels in
series, with
intercooling between stages, i.e., with heat removal apparatus comprising a
heat
exchanger between the two reactor vessels. Each reactor vessel contained a
catalyst bed,
approximately 3 metres length by 3 metres width ( 10 feet in length and 10
feet in width),
comprising approximately 22.4m3 (800 cubic feet) (approximately 60,000 pounds)
of a
commercially available catalyst, available from Phillips Petroleum Company,
comprising palladium, silver, and alkali metal fluoride. The hydrocarbon-
containing
feed was passed through the first reactor vessel and then through the second
reactor
vessel with the product exiting the second reactor vessel. Heat was removed
between
the first and second reactor vessel via the heat exchanger.
A hydrocarbon-containing feed consisting of an ethylene stream, from a
thermal ethane cracker, containing about 25 volume percent hydrogen, about 10
volume
percent methane, about 25 volume percent ethane, about 40 volume percent
ethylene,
about 0.35 volume percent acetylene, and about 0.025 volume percent carbon
monoxide
was introduced into the first reactor vessel at a pressure of 3803 kPa (about
552 pounds
per square inch absolute (psia)) and at a gas hourly space velocity of about
9400 hour'.
The hydrogen to hydrocarbon molar ratio was about 0.33:1. The hydrogen to
acetylene
molar ratio was greater than 50:1.
Over a time period of approximately 60 hours, the inlet temperature to
the first reactor vessel was slowly raised and the heat removal between the
first and
second reactor vessels was slowly increased. At maximum available heat
removal, the
inlet of the second reactor vessel had been reduced from a normal operating
condition of
93.3°C (about 200°F) to less than about 65.5°C (about
150°F) while still maintaining
the required product specifications of the product exiting the second reactor
vessel.
The concentration of acetylene in the product exiting from the outlet of
the second reactor vessel controlled the inlet temperature of the first
reactor vessel.
Product specifications required a concentration of acetylene in the product
exiting the
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second reactor vessel of less than 0.3 ppm (i.e., 0.3 parts by weight
acetylene per million
parts by weight product) throughout the approximately 60-hour run. An increase
in
concentration of acetylene in the product resulted in an increase in the inlet
temperature
of the first reactor vessel thus increasing the hydrogenation of acetylene to
ethylene, i.e.,
increasing the severity of the reaction. Increasing the severity of the
reaction resulted in
more acetylene being hydrogenated to ethylene in the first reactor vessel and
thus
reducing the concentration of acetylene in the product exiting the second
reactor vessel.
Thus, the inlet temperature of the first reactor vessel was monitored with any
increase in
inlet temperature of the first reactor vessel being an indication of
hydrogenation of
acetylene to ethylene.
The inlet temperature of the first reactor vessel was obtained from a
thermocouple 3 metres (about 10 feet) from the actual inlet of the first
reactor vessel.
The outlet temperature of the first reactor vessel was obtained from a
thermocouple at
the immediate exit, i.e. bottom, of the first reactor vessel. The change in
temperature
across the first reactor vessel was the difference between the inlet and
outlet
temperatures.
The inlet temperature of the second reactor vessel was obtained by
averaging the temperatures from three thermocouples axially located (i.e., one
near the
wall of the vessel, one about half way to the center of the vessel, and one
near the
center of the vessel) about 0.76m (about 2.5 feet) into the second reactor
vessel. The
outlet temperature of the second reactor vessel was obtained from a
thermocouple at the
immediate exit, i.e. bottom, of the second reactor vessel. The change in
temperature
across the second reactor vessel was the difference between the inlet and
outlet
temperature.
Trend data were obtained throughout the approximately 60-hour run
testing the above-described novel process. In addition, data were also
obtained from
specific points in time during the testing of the novel process and are
presented in Table
I below. The data presented in Table I below were verified against the trend
data to
ensure that the data presented in Table I are a true reflection of what was
indicated in the
trend data.
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TABLEI
TIME INLET OUTLET 0T INLET OUTLET 0T
(HRS) TEMP. TEMP. ACROSS TEMP. TEMP. ACROSS
OF 1 OF 1 ST OF 2ND OF 2ND
ST 1 ST REACTOR REACTO 2ND REACTOR
REACTO REACTOR VESSEL R REACTOR VESSEL
R VESSEL (F) VESSEL VESSEL (F)
VESSEL (F) (F) (F)
(F)
* 181.4 206.0 24.6 191.8 193.6 1.8
0** 171.8 195.8 23.6 176.6 176.4 -0.2
0.5 175.1 199.3 24.2 166.0 167.1 1.1
1 175.5 199.5 24.0 159.7 159.5 -0.2
1.5 175.9 201.7 25.8 157.6 157.0 -0.6
2 177.4 202.6 25.2 157.1 157.2 0.1
6.5 180.0 205.6 25.6 145.5 144.7 -0.8
17 175.6 201.8 26.2 142.7 142.0 -0.7
19.3 177.3 205.7 28.4 146.6 146.2 -0.4
19.6 177.4 203.7 26.3 145.5 144.9 -0.6
23.5 176.6 203.0 26.4 144.7 144.0 -0.7
* Conditions
of
two
reactor
vessel
operation
prior
to
beginning
test
of
inventive
process.
** Beginning
of
test
of
inventive
process.
As the data in Table I, which was verified against the trend data, clearly
demonstrate, there was basically no change in temperature across the second
reactor
vessel indicating that virtually no hydrogenation of acetylene to ethylene was
occurring
in the second reactor vessel. The data in Table I demonstrate that the inlet
temperature
of the first reactor vessel, an indication of the severity of the
hydrogenation reaction of
acetylene to ethylene, had increased only slightly from about 172°F to
about 177°F.
The data in Table I also demonstrate that due to fluctuations of the carbon
monoxide
content of the feed, the first reactor vessel temperature varied, but never
exceeded about
180°F. Further, the trend data indicated that when the carbon monoxide
content of the
feed fluctuated as a result of bringing a cold furnace into operation, the
inventive
process was able to handle the fluctuations in carbon monoxide and subsequent
increases in inlet temperature without a "runaway" reaction occurnng, i.e.,
without
uncontrollable hydrogenation of ethylene to ethane occurring. The data in
Table I also
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indicate that the change in temperature across the first reactor vessel
increased only
slightly from about 22 °F to about 26 °F.
The data demonstrate that a single-stage adiabatic reaction zone
(comprising, for example, one or more adiabatic reactor vessels), utilizing a
catalyst
comprising palladium, silver, and an alkali metal compound such as alkali
metal
fluoride, can be used in place of a traditional mufti-stage reaction zone,
with heat
removal apparatus between one or more stages, while still maintaining the
product
specifications required for products exiting the final stage of such mufti-
stage reaction
zone.
Further, since the data demonstrate that the single-stage adiabatic
reaction zone of the inventive process can be used in place of an existing
mufti-stage
reaction zone, the data therefore demonstrate that the volumetric amount of a
catalyst
comprising palladium, silver, and an alkali metal compound such as alkali
metal
fluoride, used in the inventive process is significantly less than the
volumetric amounts
of catalyst present in such mufti-stage reaction zone before utilizing the
inventive
process. As demonstrated in the Example, the volumetric amount of catalyst
comprising
palladium, silver, and an alkali metal compound such as alkali metal fluoride,
used in
the single-stage adiabatic reaction zone of the inventive process was about
half, i.e.,
about 50 percent of, that used in a two-stage reaction zone with heat removal
apparatus
between stages.
The data further demonstrate that the selective hydrogenation process of
the invention can be used to modify at least one stage (e.g., at least one
reactor vessel),
and conceptually all stages (e.g., all reactor vessels), of a mufti-stage
reaction zone into a
single-stage adiabatic reaction zone (comprising, for example, an adiabatic
reactor
vessel or one or more adiabatic reactor vessels), or, e.g., into a set of
single-stage
adiabatic reaction zones (e.g., a set of adiabatic reactor vessels), wherein
each single-
stage adiabatic reaction zone contains a catalyst comprising palladium,
silver, and an
alkali metal compound such as alkali metal fluoride. Modifying such mufti-
stage
reaction zone eliminates the need to have intercooling between one or more
stages of
such mufti-stage reaction zone. The above-described modification of a mufti-
stage
reaction zone to several single-stage adiabatic reaction zones allows at least
one single-
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stage adiabatic reaction zone to be in service with at least one single-stage
adiabatic
reaction zone to be in stand-by or to be used for additional acetylene removal
allowing
an essentially unlimited time to pass between shut-down of the entire reaction
system.
The data also demonstrate that increases in feed temperature to offset
operational parameter upsets such as fluctuations in carbon monoxide can be
handled in
the single-stage adiabatic reaction zone of the inventive process.
The results shown in the above example clearly demonstrate that the
present invention is well adapted to carry out the obj ects and attain the
ends and
advantages mentioned as well as those inherent therein.
Reasonable variations, modifications and adaptations for various
operations and conditions can be made within the scope of the disclosure and
the
appended claims without departing from the scope of this invention.
