U.S. patent application number 11/357533 was filed with the patent office on 2009-11-05 for dehydrogenation process with water control.
Invention is credited to Andrea G. Bozzano, Hiroiku Kawai, Dean E. Rende, Christopher J. Vogel, Paul G. Wing.
Application Number | 20090275792 11/357533 |
Document ID | / |
Family ID | 41257530 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090275792 |
Kind Code |
A1 |
Vogel; Christopher J. ; et
al. |
November 5, 2009 |
Dehydrogenation process with water control
Abstract
The activity of a dehydrogenation catalyst is improved by
increasing the water concentration maintained in the reactants
toward the start of the catalyst's life, but after the catalyst has
deactivated to the extent that the temperature required to maintain
the conversion per pass of paraffinic hydrocarbon through the
reaction zone increases by at least 2.degree. C.
Inventors: |
Vogel; Christopher J.;
(Chicago, IL) ; Rende; Dean E.; (Arlington
Heights, IL) ; Bozzano; Andrea G.; (Des Plaines,
IL) ; Wing; Paul G.; (Wheaton, IL) ; Kawai;
Hiroiku; (Yokohama, JP) |
Correspondence
Address: |
HONEYWELL/UOP;PATENT SERVICES
101 COLUMBIA DRIVE, P O BOX 2245 MAIL STOP AB/2B
MORRISTOWN
NJ
07962
US
|
Family ID: |
41257530 |
Appl. No.: |
11/357533 |
Filed: |
February 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60654243 |
Feb 18, 2005 |
|
|
|
Current U.S.
Class: |
585/660 |
Current CPC
Class: |
C07C 2523/14 20130101;
B01J 23/626 20130101; C07C 2523/04 20130101; C07C 5/3337 20130101;
B01J 35/008 20130101; B01J 37/0221 20130101; C07C 2523/42 20130101;
C07C 5/3337 20130101; C07C 2521/04 20130101; B01J 23/56 20130101;
C07C 11/02 20130101 |
Class at
Publication: |
585/660 |
International
Class: |
C07C 5/333 20060101
C07C005/333 |
Claims
1. A process for the catalytic dehydrogenation of a paraffinic
hydrocarbon having from 5 to 20 carbon atoms per molecule in a
reaction zone at a temperature required to effect a conversion per
pass of the paraffinic hydrocarbon through the reaction zone, the
process comprising: a) passing a combined feed comprising the
paraffinic hydrocarbon to the reaction zone, the combined feed
having a first water concentration comprising the sum of a water
concentration and an equivalent concentration of water precursors,
the first water concentration being less than 50 wt-ppm based on
the weight of the combined feed passed to the reaction zone, the
reaction zone containing a dehydrogenation catalyst comprising a
platinum group component and a promoter component supported on a
carrier material, the temperature being a first temperature and the
conversion per pass being a first conversion per pass; and b)
increasing at least one of the water or the water precursors in the
combined feed such that the combined feed has a second water
concentration and a second equivalent concentration of water
precursors, the sum of the second water concentration and the
second equivalent concentration being at least 200 wt-ppm based on
the weight of the combined feed passed to the reaction zone, after
the temperature required to maintain the first conversion per pass
exceeds the first temperature by at least 2.degree. C.
2. The process of claim 1 wherein said increasing of at least one
of the water or the water precursors in the combined feed occurs
when the temperature required to maintain the first conversion per
pass exceeds the first temperature by from 2 to 8.degree. C.
3. The process of claim 1 wherein said increasing of at least one
of the water or the water precursors in the combined feed occurs
when the temperature required to maintain the first conversion per
pass exceeds the first temperature by at least 15.degree. C.
4. The process of claim 1 further characterized in that after said
increasing of at least one of the water or the water precursors in
the combined feed the temperature required to maintain the first
conversion per pass decreases by at least 2.degree. C.
5. The process of claim 1 further characterized in that after said
increasing of at least one of the water or the water precursors in
the combined feed the temperature required to maintain the first
conversion per pass decreases by at least 15.degree. C.
6. The process of claim 1 further characterized in that, after said
increasing of at least one of the water or the water precursors in
the combined feed, the combined feed has a third water
concentration and a third equivalent concentration of water
precursors, the sum of the third water concentration and the third
equivalent concentration being not more than the sum of the second
water concentration and the second equivalent concentration.
7. The process of claim 1 wherein the sum of the second water
concentration and the second equivalent concentration is from 200
to about 10000 wt-ppm based on the weight of the combined feed
passed to the reaction zone.
8. The process of claim 1 further characterized in that said
increasing of at least one of the water or the water precursors in
the combined feed occurs when the reaction zone is at a second
temperature that is at least 2.degree. C. higher than the first
temperature.
9. The process of claim 1 further characterized in that after said
increasing of at least one of the water or the water precursors in
the combined feed the reaction zone is at a temperature that is at
least 2.degree. C. less than the first temperature.
10. The process of claim 1 wherein the platinum group component
comprises a component selected from the group consisting of
platinum, palladium, iridium, rhodium, osmium, ruthenium, and
mixtures thereof and the promoter component comprises a component
selected from the group consisting of tin, germanium, rhenium,
gallium, bismuth, lead, indium, cerium, zinc, and mixtures
thereof.
11. The process of claim 1 wherein the dehydrogenation catalyst
comprises a modifier component comprising a component selected from
the group consisting of an alkali metal, an alkaline earth metal,
and mixtures thereof.
12. The process of claim 1 wherein the dehydrogenation catalyst
comprises a layered composition comprising an inner core, an outer
layer bonded to the inner core, the outer layer comprising the
carrier material, the carrier material comprising a refractory
inorganic oxide, the outer layer having a thickness of from about
40 to about 150 microns and having uniformly dispersed thereon the
platinum group component and the promoter component.
13. The process of claim 1 wherein the dehydrogenation catalyst
comprises catalyst particles, the platinum group component is
surface-impregnated upon the catalyst particles such that the
average concentration of the surface-impregnated platinum group
component on the outside 200 micron layer of the catalyst particle
is at least 2 times the concentration of the platinum group
component in the 200 micron diameter center core of the catalyst
particles.
14. The process of claim 1 wherein the dehydrogenation catalyst has
an atomic ratio of platinum group component to promoter component
of from about 0.05 to about 5.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from Provisional
Application No. 60/654,243 filed Feb. 18, 2005, the contents of
which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a process for the catalytic
dehydrogenation of hydrocarbons.
BACKGROUND OF THE INVENTION
[0003] Processes for the catalytic dehydrogenation of hydrocarbons
are well known. Paraffins having from 5 to 20 carbon atoms per
molecule undergo such treatment to form the corresponding olefin.
Olefins having from 9 to 16 carbon atoms per molecule are used to
alkylate benzene to produce alkylbenzenes, which is an intermediate
in the manufacture of detergents. Shorter chain olefins having 5
carbon atoms per molecule are used to alkylate isoparaffins or to
etherify alcohols to make motor fuel blending components. A great
many other uses for such olefins are known.
[0004] Many catalytic dehydrogenation processes use a reactor
containing a bed of catalyst. The activity of the catalyst
decreases in a gradual manner and the reactor inlet temperature is
gradually increased to compensate for this. As this temperature
rises, the rate of undesired side reactions will increase, and the
selectivity of the process to the desired olefin will suffer. When
the temperature rises to an upper limit (e.g., the design
temperature of process equipment) or the selectivity of the process
drops below a useful level (e.g., the minimum profitable
selectivity), the effective life of the catalyst is reached, the
"run" of the catalyst is completed, and the catalyst must be
replaced.
[0005] The effective life of the catalyst typically is
approximately inversely proportional to the conversion per pass at
which the dehydrogenation process is operated. Operators of these
processes select a value of conversion per pass of the feed
hydrocarbon through the reactor to optimize operation of the
process. This desired conversion per pass will vary with the
objectives of the operator. The value may be preselected prior to
the start of a run of dehydrogenation catalyst and then maintained
throughout the run as the catalyst ages. Alternatively, the value
may be varied during the run as the catalyst ages. A process can be
operated at a number of different conversions per pass as the
catalyst ages and the temperature required to maintain the initial
preselected conversion per pass increases. The most important
factors in determining the desired conversion per pass are the
temperature required to maintain a given conversion per pass as the
catalyst ages and the selectivity of the process at a given
conversion per pass. The temperature required in a dehydrogenation
process to maintain a given conversion per pass depends on the
conversion per pass, the composition and condition of the catalyst,
the reactants, and other dehydrogenation conditions.
[0006] Dehydrogenation processes and catalysts have previously been
found to be affected by the presence of water, as described in U.S.
Pat. Nos. 3,448,165 (Bloch); 3,907,921 (Winter, III); 5,321,192
(Cottrell et al.); 6,177,381 (Jensen et al.); 6,486,370 B1 (Rende
et al.); and 6,756,515 B2 (Rende et al.). U.S. Pat. No. 3,907,921,
for example, describes injecting water at an initially optimum
value and then increasing the water concentration in the reactant
stream as the catalyst becomes less active. U.S. Pat. No. 6,756,515
B2 describes a dehydrogenation process wherein water at less than
1000 wt-ppm based on the hydrocarbon weight is passed to a layered
composition in order to decrease the catalyst deactivation
rate.
[0007] Processes for dehydrogenating hydrocarbons with improved
effective catalyst lives and decreased temperatures at a given
conversion per pass are sought.
SUMMARY OF THE INVENTION
[0008] The process disclosed herein is for catalytically
dehydrogenating hydrocarbons using a very low concentration of or
essentially no water or water precursors in the combined feed to a
reactor when the dehydrogenation catalyst is fresh, and then
increasing the concentration of water, water precursor, or both as
the catalyst becomes less active or the conversion per pass
declines. The benefits of this process can include increased
catalyst life, reduced reactor inlet temperature for a given
conversion per pass of the dehydrogenatable hydrocarbons, or
improved selectivity. The catalysts used in the process contain a
platinum group component and a promoter component supported on a
carrier material. The process is particularly useful for layered
catalyst compositions and surface-impregnated catalysts.
[0009] The water, water precursors, or both is increased after the
conversion per pass has decreased by at least 0.1 molar percentage
points. In one embodiment, the water, water precursors, or both is
increased after the temperature required to maintain a preselected
conversion per pass of paraffinic hydrocarbon through the reactor
exceeds the initial temperature required to achieve the preselected
conversion per pass by at least 2.degree. C. (4.degree. F.). In
another embodiment, the water, water precursors, or both is
increased while maintaining the temperature substantially
constant.
INFORMATION DISCLOSURE
[0010] U.S. Pat. No. 3,907,921 (Winter III) describes a
dehydrogenation process characterized by initially injecting 5 to
25 wt-ppm water into the feed stream, and then increasing the rate
of water injection to 25 to 125 wt-ppm after at least 40% of the
normal paraffins which may be processed before the catalyst
requires replacement have passed through the reaction zone.
[0011] U.S. Pat. No. 5,321,192 (Cottrell et al.) describes a
dehydrogenation process characterized by introducing a relatively
small amount of water or water precursor at the inlet of two or
more catalytic dehydrogenation zones.
[0012] U.S. Pat. No. 6,177,381 (Jensen et al.) describes a
dehydrogenation process using a layered catalyst composition and
includes test results of several catalysts for dehydrogenation
activity using a hydrocarbon feed and injecting a water
concentration of 2000 wt-ppm based on the hydrocarbon weight.
[0013] U.S. Pat. Nos. 6,486,370 B1 (Rende et al.) and 6,756,515 B2
(Rende et al.) describe a dehydrogenation process characterized by
using a layered catalyst composition and dehydrogenation conditions
comprising adding water to the dehydrogenation zone to provide less
than 2000 wt-ppm and less than 1000 wt-ppm, respectively, of the
hydrocarbon feed stream. Both patents describe providing water at
possibly even less than 1 wt-ppm of the hydrocarbon feed
stream.
DETAILED DESCRIPTION
[0014] Hydrocarbons having from 5 to 20, and preferably 8 to 16,
carbon atoms can be dehydrogenated in the process disclosed herein.
These hydrocarbons include normal paraffins, isoparaffins including
monomethyl paraffins and dimethyl paraffins, alkylaromatics,
naphthenes, and olefins, either alone or in a mixture thereof.
[0015] A suitable arrangement for the dehydrogenation process
disclosed herein is described, for instance, in U.S. Pat. No.
6,670,516 B1, herein incorporated in its entirety by reference.
Fresh hydrocarbon feed combines with hydrogen, which may be
provided in a hydrogen-containing gaseous recycle stream. This
forms a reactant stream which is called a combined feed. Recycled
unconverted hydrocarbons may also be a component of the combined
feed. The combined feed is passed through a bed of suitable
catalyst maintained at the proper dehydrogenation conditions such
as temperature, pressure and space velocity. The effluent from the
catalytic reaction zone is passed to a separation zone wherein the
effluent is cooled and partially condensed.
[0016] At least a portion of the uncondensed material is recycled
as the gaseous recycle stream comprising hydrogen and light
hydrocarbon gases. The net hydrogen which is produced in the
process is vented for use in other applications such as
desulfurization. The separation zone produces a liquid stream
containing the dehydrogenated and undehydrogenated hydrocarbons.
The liquid stream is then separated to recover the dehydrogenated
hydrocarbons from the unconverted hydrocarbons which may then be
recycled. This separation is done by passing the liquid stream into
a stripping column to remove dissolved gases and cracked light
ends. The liquid stream which has been treated in the stripping
column is then separated to recover the dehydrogenated
hydrocarbons.
[0017] When paraffins are being processed, the olefins may be
alkylated with benzene to produce detergent intermediates such as
alkylbenzenes. The practice in this situation is to pass the liquid
stream from the stripping column into the detergent alkylation
process. However, the liquid stream may contain diolefinic and
aromatic byproducts formed during dehydrogenation which can
adversely affect the quality of the detergent. Therefore, the
liquid stream may be optionally further treated before entering the
detergent alkylation process to selectively hydrogenate diolefins
to the corresponding monoolefin and to selectively remove
aromatics.
[0018] The paraffins used to make the olefins for detergent
intermediates may vary widely and may be branched, linear or
slightly branched acyclic paraffins of from about 9 to about 19,
often 9 to 14, carbon atoms per molecule, and are often present as
a mixture of paraffins. Due to environmental concerns, where the
alkylbenzenes are intended to be sulfonated to make detergents, the
paraffins are linear (making linear alkylbenzenes (LAB's) or
slightly branched (making modified alkylbenzenes (MAB's)). During
dehydrogenation, skeletal isomerization of the paraffin is minimal,
and the resulting olefin has usually the same hydrocarbon backbone
and extent of branching as the paraffin. The resulting olefin is
usually monoolefinic, and the positioning of the olefinic bond in
the molecule is not critical. However, the branching of the
hydrocarbon backbone is often more of a concern as the structural
configuration of the alkyl group on the alkylbenzene product can
affect performance. For instance, where alkylbenzenes are
sulfonated to produce detergents, undue branching can adversely
affect the biodegradability of the detergent. On the other hand,
some branching may be desired such as the lightly branched modified
alkylbenzenes such as described in U.S. Pat. No. 6,187,981 B1,
herein incorporated in its entirety by reference. The paraffin may
be unbranched or lightly branched, which as used herein, refers to
a paraffin having three or four primary carbon atoms and for which
none of the remaining carbon atoms are quaternary carbon atoms. A
primary carbon atom is a carbon atom which, although perhaps bonded
also to other atoms besides carbon, is bonded to only one carbon
atom. A quaternary carbon atom is a carbon atom that is bonded to
four other carbon atoms.
[0019] The process disclosed herein uses a catalyst that comprises
a platinum group component and a promoter component on a carrier
material. Preferably, the catalyst also comprises a modifier
component, a halogen component, or both.
[0020] The carrier material used in the process disclosed herein
may be formed in any desired shape such as spheres, pills, cakes,
extrudates, powders, granules, etc. and it may be used in any
particle size. A preferred form of carrier material is the sphere.
A preferred range of particle diameters is about 0.50 to about 2.00
mm (0.020 to 0.079 in). Preferred particle diameters are about 1.59
mm ( 1/16 in) and about 0.79 mm ( 1/32 in). Other preferred forms
include cylinders, polylobular shapes having 2, 3 or up to about 8
lobes, and shapes having one or more open channels such as a
tubular or cartwheel particle. See U.S. Pat. Nos. 4,652,687 and
4,717,781. The carrier material can be prepared in any suitable
manner from synthetically prepared or naturally occurring
materials.
[0021] The catalyst used in the process disclosed herein can
comprise a layered composition. The layered composition comprises
an inner core composed of a material which has substantially lower
adsorptive capacity for catalytic metal precursors, relative to the
outer layer. Some of the inner core materials are also not
substantially penetrated by liquids, e.g., metals including but not
limited to aluminum, titanium and zirconium. Examples of the inner
core material include, but are not limited to, refractory inorganic
oxides, silicon carbide and metals. Examples of refractory
inorganic oxides include without limitation alpha alumina, theta
alumina, cordierite, zirconia, titania and mixtures thereof. A
preferred inorganic oxide is alpha alumina.
[0022] These materials which form the inner core can be formed into
a variety of shapes such as pellets, extrudates, spheres or
irregularly shaped particles although not all materials can be
formed into each shape. Preparation of the inner core can be done
by means known in the art such as oil dropping, pressure molding,
metal forming, pelletizing, granulation, extrusion, rolling methods
and marumerizing. A spherical inner core is preferred. The inner
core whether spherical or not has an effective diameter of about
0.05 mm to about 5 mm (0.002 to 0.2 in) and preferably from about
0.8 mm to about 3 mm (0.03 to 0.12 in). For a non-spherical inner
core, effective diameter is defined as the diameter the shaped
article would have if it were molded into a sphere. Once the inner
core is prepared, it is calcined at a temperature of about 400 to
about 1500.degree. C. (752 to 2732.degree. F.).
[0023] The inner core is now coated with a layer of a refractory
inorganic oxide which is different from the inorganic oxide which
may be used as the inner core and is referred to herein as the
outer refractory inorganic oxide. This outer refractory inorganic
oxide is one which has porosity, has a surface area of at least 50
m.sup.2/g, and preferably at least 150 m.sup.2/g, an apparent bulk
density of about 0.2 g/ml, and is chosen from the group consisting
of (1) gamma alumina, delta alumina, eta alumina, theta alumina,
titania, zirconia, and silica-alumina; (2) zeolites such as
naturally occurring or synthetically prepared zeolite Y, zeolite X,
zeolite L, zeolite beta, ferrierite, MFI, mordenite, erionite,
faujasite, silicalite, or other zeolites, either in the hydrogen
form or in a form that has been exchanged with metal cations; (3)
non-zeolitic molecular sieves (NZMS) such as the SAPOs, ELAPOs, and
MeAPOs. Preferred outer refractory inorganic oxides are gamma and
eta alumina.
[0024] A preferred way of preparing a gamma alumina is by the
well-known oil drop method which is described in U.S. Pat. No.
2,620,314, herein incorporated in its entirety by reference. The
oil drop method comprises forming an aluminum hydrosol by any of
the techniques taught in the art and preferably by reacting
aluminum metal with hydrochloric acid; combining the hydrosol with
a suitable gelling agent, e.g., hexamethylenetetraamine; and
dropping the resultant mixture into an oil bath maintained at
elevated temperatures (about 93.degree. C. (199.degree. F.)). The
droplets of the mixture remain in the oil bath until they set and
form hydrogel spheres. The spheres are then continuously withdrawn
from the oil bath and typically subjected to specific aging and
drying treatments in oil and ammoniacal solutions to further
improve their physical characteristics. The resulting aged and
gelled spheres are then washed and dried at a relatively low
temperature of about 80 to 260.degree. C. (176 to 500.degree. F.)
and then calcined at a temperature of about 455 to 705.degree. C.
(851 to 1301.degree. F.) for a period of about 1 to about 20 hours.
This treatment effects conversion of the hydrogel to the
corresponding crystalline gamma alumina.
[0025] The layer is applied by forming a slurry of the outer
refractory inorganic oxide and then coating the inner core with the
slurry by means well known in the art. Slurries of inorganic oxides
can be prepared by means well known in the art which usually
involve the use of a peptizing agent. For example, any of the
transitional aluminas can be mixed with water and an acid such as
nitric, hydrochloric, or sulfuric to give a slurry. Alternatively,
an aluminum sol can be made by for example, dissolving aluminum
metal in hydrochloric acid and then mixing the aluminum sol with
the alumina powder.
[0026] The slurry may contain an organic bonding agent which aids
in the adhesion of the outer refractory inorganic oxide layer to
the inner core. Examples of this organic bonding agent include but
are not limited to polyvinyl alcohol (PVA), hydroxy propyl
cellulose, methyl cellulose and carboxy methyl cellulose. The
amount of organic bonding agent which is added to the slurry will
vary considerably from about 0.1 wt-% to about 3 wt-% of the
slurry. How strongly the outer layer is bonded to the inner core
can be measured by the amount of layer material lost during an
attrition test, i.e., attrition loss. Loss of the outer layer by
attrition is measured by agitating the catalyst, collecting the
fines and calculating an attrition loss. It has been found that by
using an organic bonding agent as described above, the attrition
loss is less than about 10 wt-% of the outer layer. Finally, the
thickness of the outer layer varies from about 40 to about 150
microns. One micron equals 10.sup.-6 meter.
[0027] Depending on the particle size of the outer refractory
inorganic oxide, it may be necessary to mill the slurry in order to
reduce the particle size and simultaneously give a narrower
particle size distribution. This can be done by means known in the
art such as ball milling for times of about 30 minutes to about 5
hours and preferably from about 1.5 to about 3 hours. It has been
found that using a slurry with a narrow particle size distribution
improves the bonding of the outer layer to the inner core.
[0028] The slurry may also contain an inorganic bonding agent
selected from an alumina bonding agent, a silica bonding agent or
mixtures thereof. Examples of silica bonding agents include silica
sol and silica gel, while examples of alumina bonding agents
include alumina sol, boehmite and aluminum nitrate. The inorganic
bonding agents are converted to alumina or silica in the finished
composition. The amount of inorganic bonding agent varies from
about 2 to about 15 wt-% as the oxide, and based on the weight of
the slurry.
[0029] Coating of the inner core with the slurry can be
accomplished by means such as rolling, dipping, spraying, etc. One
preferred technique involves using a fixed fluidized bed of inner
core particles and spraying the slurry into the bed to coat the
particles evenly. The thickness of the layer can vary considerably,
but usually is from about 40 to about 150 microns. The optimum
layer thickness depends on the choice of the outer refractory
inorganic oxide. Once the inner core is coated with the layer of
outer refractory inorganic oxide, the resultant layered support is
dried at a temperature of about 100 to about 320.degree. C. (212 to
608.degree. F.) for a time of about 1 to about 24 hours and then
calcined at a temperature of about 400 to about 900.degree. C. (752
to 1652.degree. F.) for a time of about 0.5 to about 10 hours to
effectively bond the outer layer to the inner core and provide a
layered catalyst support. Of course, the drying and calcining steps
can be combined into one step.
[0030] When the inner core is composed of a refractory inorganic
oxide (inner refractory inorganic oxide), preferably the outer
refractory inorganic oxide be different from the inner refractory
inorganic oxide. Additionally, it is preferably that the inner
refractory inorganic oxide have a substantially lower adsorptive
capacity for catalytic metal precursors relative to the porous
carrier material.
[0031] Having obtained the layered carrier material, the platinum
group component, promoter component, and optional modifier
component can be dispersed on the layered carrier material by means
known in the art. Thus, these three components can be dispersed on
the outer layer. The platinum group component may be selected from
the group consisting of platinum, palladium, iridium, rhodium,
osmium, ruthenium, and mixtures thereof. Platinum, however, is the
preferred platinum group component. The promoter component may be
selected from the group consisting of tin, germanium, rhenium,
gallium, bismuth, lead, indium, cerium, zinc, and mixtures thereof.
The preferred promoter component is tin. The modifier component may
be selected from the group consisting of alkali metals (IUPAC Group
1), alkaline earth metals (IUPAC Group 2), and mixtures thereof.
All references herein to groups of elements are to the Periodic
Table of the Elements, "CRC Handbook of Chemistry and Physics," CRC
Press, Boca Raton, Fla., 80.sup.th Edition, 1999-2000. The alkali
and alkaline earth metals which can be used as modifier components
on the catalyst used in the process disclosed herein include
lithium, sodium, potassium, cesium, rubidium, beryllium, magnesium,
calcium, strontium and barium. Most commonly used modifier metals
are lithium, potassium, sodium and cesium.
[0032] The platinum group component, promoter component, and
optional modifier component can be deposited on the layered carrier
material in any suitable manner known in the art. One method
involves impregnating the layered carrier material with a solution
(preferably aqueous) of a decomposable compound of the metal or
metals. By decomposable it is meant that upon heating the metal
compound is converted to the metal or metal oxide with the release
of byproducts. Illustrative of the decomposable compounds of the
platinum group component are chloroplatinic acid, ammonium
chloroplatinate, bromoplatinic acid, dinitrodiamino platinum,
sodium tetranitroplatinate, rhodium trichloride, hexa-aminerhodium
chloride, rhodium carbonylchloride, sodium hexanitrorhodate,
chloropalladic acid, palladium chloride, palladium nitrate,
diaminepalladium hydroxide, tetraaminepalladium chloride,
hexachloroiridate (IV) acid, hexachloroiridate (III) acid, ammonium
hexachloroiridate (III), ammonium aquohexachloroiridate (IV),
ruthenium tetrachloride, hexachlororuthenate, hexa-amineruthenium
chloride, osmium trichloride and ammonium osmium chloride.
Illustrative of the decomposable promoter component compounds are
the halide salts of the promoter components. A preferred promoter
component is tin and preferred decomposable compounds are stannous
chloride or stannic chloride. Illustrative of the decomposable
compounds of the optional modifier component are the halide,
nitrate, carbonate or hydroxide compounds of the alkali and
alkaline earth metals, e.g., potassium hydroxide, lithium
nitrate.
[0033] The platinum group component, promoter component, and
optional modifier component can be impregnated using one common
solution or they can be sequentially impregnated in any order, but
not necessarily with equivalent results. A preferred impregnation
procedure involves the use of a steam-jacketed rotary dryer. The
support is immersed in the impregnating solution containing the
desired metal compound contained in the dryer and the support is
tumbled therein by the rotating motion of the dryer. Evaporation of
the solution in contact with the tumbling support is expedited by
applying steam to the dryer jacket. The resultant composite is
allowed to dry under ambient temperature conditions, or dried at a
temperature of about 80 to about 350.degree. C. (176 to 662.degree.
F.), followed by calcination at a temperature of about 200 to about
700.degree. C. (392 to 1292.degree. F.) for a time of about 1 to
about 4 hours, thereby converting the component to the metal or
metal oxide. For the platinum group component, the preferred
calcination temperature is about 400 to about 700.degree. C. (752
to 1292.degree. F.).
[0034] In one method of preparation, the promoter component is
first deposited onto the layered carrier material and calcined as
described above and then the modifier component and platinum group
component are simultaneously dispersed onto the layered support by
using an aqueous solution which contains a compound of the modifier
component and a compound of the platinum group component. The
support is impregnated with the solution as described above and
then calcined at a temperature of about 400 to about 700.degree. C.
(752 to 1292.degree. F.) for a time of about 1 to about 4
hours.
[0035] An alternative method of preparation involves adding one or
more of the components to the outer refractory inorganic oxide
prior to applying it as a layer onto the inner core. For example, a
decomposable salt of the promoter component, e.g., tin (IV)
chloride, can be added to a slurry composed of gamma alumina and
aluminum sol. Further, either the modifier component or the
platinum group component or both can also be added to the slurry
before the slurry is applied to the inner core. Thus, in one
method, all three catalytic components are deposited onto the outer
refractory inorganic oxide prior to depositing the outer refractory
inorganic oxide onto the inner core. Again, the three catalytic
components can be deposited onto the outer refractory inorganic
oxide powder in any order although not necessarily with equivalent
results.
[0036] Another method of preparation involves first impregnating
the promoter component onto the outer refractory inorganic oxide
and calcining as described above. Next, a slurry is prepared (as
described above) using the outer refractory inorganic oxide
containing the promoter component and applied to the inner core by
means described above. Finally, the platinum group component and
the modifier component are simultaneously impregnated onto the
layered composition and calcined as described above to give the
desired layered catalyst.
[0037] As a final step in the preparation of the layered catalyst
composition, the catalyst composition is reduced under hydrogen or
other reducing atmosphere. Reduction is carried out at a
temperature of about 100 to about 650.degree. C. (212 to
1202.degree. F.) for a time of about 0.5 to about 10 hours in a
reducing environment, preferably dry hydrogen. The reduction
conditions ensure that at least 90% and more preferably at least
95% of the platinum group component exists within the final
catalytic composite in the metallic state (zero valent). The
platinum group component may be combined with other catalyst
components. For example, the platinum group component may be
present in the form of an alloy with the promoter component, such
as a platinum-tin alloy. However, the reduction conditions are such
that more than 50% and preferably more than 75% of the promoter
component is present in an oxidation state above that of the
elemental metal, that is, in the +2 or +4 oxidation state in the
case of tin, as a chemical compound such as the oxide, for example,
and combined with the carrier material or with the platinum group
component. The modifier component is mainly present in an oxidation
state above that of the elemental metal. The modifier component may
be present as a compound such as the oxide, for example, or
combined with the carrier material or with the other components.
The state of the promoter component and modifier component can be
metallic (zero valent), metal oxide or metal oxychloride.
[0038] The layered catalyst composition can also contain a halogen
component which can be fluorine, chlorine, bromine, iodine or
mixtures thereof with chlorine and bromine preferred. This halogen
component is present in an amount of 0.03 to about 1.5 wt-% with
respect to the weight of the entire catalyst composition. The
halogen component can be applied by means well known in the art and
can be done at any point during the preparation of the catalyst
composition although not necessarily with equivalent results. It is
preferred to add the halogen component after all the catalytic
components have been added either before or after treatment with
hydrogen. The halogen component is generally present in a combined
state with the carrier material.
[0039] Although all three metals are uniformly distributed
throughout the outer layer of outer refractory oxide and
substantially present only in the outer layer, it is also within
the bounds of the process disclosed herein that the modifier
component can be present both in the outer layer and the inner
core. This is owing to the fact that the modifier component can
migrate to the inner core, when the core is other than a metallic
core.
[0040] Although the concentration of each component can vary
substantially, it is desirable that the platinum group component be
present in a concentration of about 0.01 to about 5 weight percent
on an elemental basis of the entire weight of the catalyst and
preferably from about 0.05 to about 2.0 wt-%. The promoter
component is present in an amount from about 0.05 to about 10 wt-%
of the entire catalyst while the modifier component is present in
an amount from about 0.1 to about 5 wt-% of the entire catalyst.
Finally, the atomic ratio of the platinum group component to
promoter component varies from about 0.05 to about 5. In particular
when the promoter component is tin, the atomic ratio is from about
0.1:1 to about 5:1 and preferably from about 0.5:1 to about 3:1.
When the promoter component is germanium the ratio is from about
0.25:1 to about 5:1 and when the promoter component is rhenium, the
ratio is from about 0.05:1 to about 2.75:1.
[0041] The preferred layered catalyst disclosed herein has a
preferred concentration of the platinum group component in the
outer layer. This concentration is generally from about 0.026 to
about 0.26 gram-mole of the platinum group component, on an
elemental basis per kilogram of the outer layer. When the platinum
group component is platinum, this concentration is from about 0.5
to about 5 wt-% of platinum on an elemental basis and based on the
weight of the outer layer. For a given concentration of the
platinum group component in the outer layer, there is a preferred
atomic ratio of the platinum group component to the promoter
component. For example, when the platinum concentration is between
about 0.5 and about 3 wt-% of platinum on an elemental basis and
based on the weight of the outer layer, the preferred atomic ratio
of platinum to tin is from between about 0.6:1 to about 1.3:1,
increasing as the platinum concentration increases.
[0042] Suitable catalysts generally have a loading of the platinum
group component of from about 5 to about 30 gram-mole of the
platinum group component on an elemental basis per cubic meter of
the layered catalyst. When the platinum group component is
platinum, this loading is from about 0.0010 to about 0.0060 gram of
platinum on an elemental basis per cubic centimeter of
catalyst.
[0043] The concentration of the platinum group component in the
outer layer can be readily determined in at least three ways.
First, the concentration can be computed based on the weight of the
ingredients used in preparing the layered catalyst. Second, in the
case where the layered catalyst has previously been prepared and
the inner refractory inorganic oxide is different from the outer
refractory inorganic oxide, then the inner layer refractory
inorganic oxide can be separated from the outer refractory
inorganic oxide, and the platinum group metal can be separately
recovered, by known chemical and/or mechanical methods. Then, the
concentration of the weight of the platinum group component can be
determined from the weight of recovered platinum group component
and the weight of recovered inner refractory inorganic oxide.
Finally, energy dispersive x-ray spectroscopy or wavelength
dispersive spectroscopy (EPMA) using a scanning electron microscope
of a sample of the layered catalyst may also be used.
[0044] Another embodiment of the process disclosed herein uses a
catalytic composite comprising a platinum group component and a
promoter component, and the platinum group component, and
optionally the promoter component, are surface-impregnated upon the
catalytic composite. The platinum group component is selected from
the components disclosed and taught hereinabove as suitable for the
platinum group component in another embodiment of the process
disclosed herein. The promoter component is selected from the
components disclosed and taught hereinabove as suitable for the
promoter component in another embodiment of the process disclosed
herein.
[0045] A component can be surface-impregnated upon the catalytic
composite by any means suitable or any known technique which
achieves the necessary distribution of components as described
herein. One method for the surface impregnation of the components
on a dehydrogenation catalyst is to adjust the pH of the
impregnation solution to control the location of the components.
Another method for the surface impregnation is to restrict the
total volume of the impregnation solution in order to restrict the
penetration of solution and thereby components into the support
particle. Further information on surface impregnation is in U.S.
Pat. Nos. 4,716,143; 4,880,764; 4,973,779; and 5,012,027.
[0046] Both the platinum group and promoter components are located
on a carrier material having a nominal diameter (d) of from 50 to
10000 microns, where d is the nominal diameter of the catalyst
particle in microns. In one aspect of this embodiment, a component
is considered to be surface-impregnated upon the catalytic
composite when the average concentration of the component within
the 0.2 d micron exterior layer of the catalytic composite is at
least two times the average concentration of the component in the
0.4 d micron diameter center core of the catalyst particle. It is
to be understood that the term "exterior" is defined as the
outermost layer of the catalytic composite. By "layer" it is meant
a stratum of substantially uniform thickness. By "0.2 d" and "0.4
d", it is meant that the nominal diameter (d) is multiplied by 0.2
or 0.4. In another aspect of this embodiment, a component is
considered to be surface-impregnated upon the catalytic composite
when the average concentration of the component within the exterior
5 to 200 micron layer of the catalytic composite is at least two
times the average concentration of the component in the 200 micron
diameter center core of the catalyst particle. In this aspect, the
exterior layer of the catalytic composite is preferably from 25 to
150 microns in thickness. In a third aspect of this embodiment, a
component is considered to be surface-impregnated on the catalytic
composite when substantially all of the component is located within
at most a 400 micron exterior layer of the catalytic composite. By
"substantially all" it is meant that at least about 75% of the
surface-impregnated component in question.
[0047] Alternatively, where the catalytic composite has a nominal
diameter of at least 850 micron, the surface-impregnated component
may be described as being on average at least twice as concentrated
in the outer 100 micron layer exterior layer of the catalytic
composite in comparison to the average concentration of the
surface-impregnated component in the 200 micron center core of the
catalyst particle. The exterior layer wherein 75% of the
surface-impregnated component is located will approach 100 microns.
The exterior layer wherein 75% of the surface-impregnated component
is located will approach a maximum value of 400 microns as the
diameter of the catalyst support increases beyond 2000 microns.
[0048] This characterization of the catalytic composite is intended
to describe a platinum group component concentration and an
optionally surface-impregnated promoter component concentration
gradient upon and within the catalytic composite. The platinum
group component concentration, and optionally the promoter
component concentration, tapers off from the exterior layer as the
center of the catalytic composite is approached. The actual
gradient of the platinum group component and optionally the
promoter component within the catalytic composite varies depending
upon the exact manufacturing method employed to fabricate the
catalytic composite.
[0049] Although it is not understood completely, it is believed
that by concentrating the surface-impregnated components to an
exterior layer of the catalyst support, more facile and selective
access to these catalytic sites is achieved, allowing the
hydrocarbon reactions and products much shorter diffusion paths. By
decreasing the length of the diffusion paths the reactants and
products have a shorter residence time in the catalyst particle
thereby lessening the likelihood of undesirable side reaction due
to secondary reactions. This results in an increase in selectivity
to the desired product. For example, in the dehydrogenation of the
paraffin to a monoolefin, reducing the length of the diffusion path
decreases the chances of dehydrogenating the desired monoolefin
consecutively to undesirable skeletal isomers, cracked products,
and aromatics by their readsorption onto a catalytic site before
they can exit the catalyst particle.
[0050] The carrier material for the surface-impregnated catalytic
composite may be selected from the inorganic oxides disclosed and
taught hereinabove as suitable for the outer refractory inorganic
oxide in another embodiment of the process disclosed herein. In
addition, the carrier material may be (1) activated carbon, coke,
or charcoal; (2) silica or silica gel, silicon carbide, clays, and
silicates including those synthetically prepared and naturally
occurring, which may or may not be acid treated, for example,
attapulgus clay, china clay, diatomaceous earth, fuller's earth,
kaolin, kieselguhr, etc.; (3) ceramics, porcelain, crushed
firebrick, bauxite; (4) other refractory inorganic oxides such as
chromium oxide, beryllium oxide, vanadium oxide, cesium oxide,
hafnium oxide, zinc oxide, magnesia, boria, thoria,
silica-magnesia, chromia-alumina, alumina-boria, silica-zirconia,
etc.; (5) spinels such as MgAl.sub.2O.sub.4, FeAl.sub.2O.sub.4,
ZnAl.sub.2O.sub.4, CaAl.sub.2O.sub.4, and other like compounds
having the formula MO--Al.sub.2O.sub.3 where M is a metal having a
valence of 2; and (6) combinations of materials from one or more of
these groups and the inorganic oxides disclosed and taught
hereinabove as suitable for the outer refractory inorganic oxide.
Preferred inorganic oxides for this embodiment of the process
disclosed herein are gamma and eta alumina. In this embodiment, a
modifier component, a halogen component, or both, may be
incorporated into the catalytic composite by any known technique.
Optionally, the catalytic composite used in this embodiment of the
process disclosed herein can also contain a sulfur component.
Generally, the sulfur component will comprise about 0.01 to about
1.0 wt-%, calculated on an elemental basis, of the final catalytic
composite. The sulfur component may be incorporated into the
catalytic composite in any suitable manner. Preferably sulfur or a
compound containing sulfur such as hydrogen sulfide or a lower
molecular weight mercaptan, for example, is contacted with the
catalytic composite in the presence of hydrogen at a hydrogen to
sulfur ratio of about 10 and a temperature of from about 10 to
about 540.degree. C. (50 to 1004.degree. F.), preferably under
water-free conditions, to incorporate the sulfur component.
[0051] After the components have been surface-impregnated or
otherwise incorporated, the resultant composite is allowed to dry
under ambient temperature conditions, or dried at a temperature of
from about 80 to about 350.degree. C. (176 to 662.degree. F.),
followed by calcination at a temperature of about 200 to about
700.degree. C. (392 to 1292.degree. F.) for a time of about 1 to
about 4 hours, thereby converting the component to the metal or
metal oxide. For the platinum group component, the preferred
calcination temperature is about 400 to about 700.degree. C. (752
to 1292.degree. F.). As a final step in the preparation of the
surface-impregnated catalytic composite used in this embodiment of
the process disclosed herein, the catalytic composite is reduced
under hydrogen or other reducing atmosphere, in the manner
described for another embodiment of the process disclosed
herein.
[0052] A third embodiment of the process disclosed herein uses a
catalytic composite comprising a platinum group component and a
promoter component, and the platinum group component and the
promoter component are uniformly distributed upon the catalytic
composite. The platinum group and promoter components are selected
from those disclosed and taught hereinabove as suitable for these
respective components in another embodiment of the process
disclosed herein. A component can be uniformly distributed upon the
catalytic composite by any means suitable or any known technique
which achieves the a uniform distribution of components. Further
information on preparing such a catalytic composite, including the
optional incorporation of a modifier component, halogen component,
a sulfur component, or any combination thereof, is in U.S. Pat. No.
4,486,547.
[0053] This detailed discussion of preferred dehydrogenation
catalysts is not intended to limit the scope of the process
disclosed herein. The great difficulty of accurately predicting
which catalytic materials are beneficially affected by increased
water addition precludes a complete listing of those compositions
to which the process disclosed herein applies. It is envisioned
that the process disclosed herein could be applied to other
catalysts such as those containing osmium, iridium, or indium in
addition to or in place of the promoter component of the preferred
catalyst.
[0054] Although it is not understood completely, it is believed
that the catalyst used in the process disclosed herein can
deactivate according to two different mechanisms depending in part
on the presence of water during the dehydrogenation reactions. One
mechanism, which is believed to be based on coke formation,
predominates at the beginning of a run when there is little or no
water present. A second mechanism, which is believed to be based on
interaction between the platinum group component (e.g., platinum)
and the promoter component (e.g., tin), predominates once water is
present. The introduction of a sufficient amount of water gives the
catalyst an opportunity to deactivate by the second mechanism,
despite having already deactivated somewhat by the first mechanism,
and this extends the effective life of the catalyst. Neither the
claims nor the process disclosed herein, however, is limited to any
particular theory.
[0055] The effective life of the preferred dehydrogenation catalyst
is approximately inversely proportional to the conversion per pass
at which the process is operated. For example, at 2% conversion per
pass the catalyst shows only a minimal rate of deactivation. At 10%
conversion per pass the deactivation rate is higher and the useful
life of a typical commercial catalyst is less, and at about 13%
conversion per pass the commercially useful life is even shorter.
The term "conversion per pass" as used herein is computed by
subtracting the moles of undehydrogenated hydrocarbons in the
reaction zone effluent from the moles of dehydrogenatable
hydrocarbons in the reaction zone feed, then dividing by the moles
of dehydrogenatable hydrocarbons in the reaction zone feed, and
finally multiplying by 100. For example, if the dehydrogenatable
hydrocarbons are C.sub.9-C.sub.13 paraffins, conversion per pass is
computed by subtracting the moles of C.sub.9-C.sub.13 paraffins in
the reaction zone effluent from the moles of C.sub.9-C.sub.13
paraffins in the reaction zone feed, then dividing by the moles of
C.sub.9-C.sub.13 paraffins in the reaction zone feed, and finally
multiplying by 100. The process disclosed herein is typically
practiced at a conversion per pass in the range of from about 8 to
about 20%, although the conversion per pass may be below or above
this range.
[0056] The term "preselected conversion per pass" as used herein is
intended to refer to a value of conversion per pass selected by the
operator of a dehydrogenation process to optimize operation of the
process. This desired conversion per pass will vary with the
objectives of the operator. The value may be preselected prior to
the start of a "run" of dehydrogenation catalyst and then
maintained substantially constant throughout the run as the
catalyst ages. Alternatively, the value may be varied during the
"run" as the catalyst ages. For example, the conversion per pass of
the reactants through the catalyst bed may be preselected at 12 or
15% at the start of the run and 9 or 11% at the end of the run. It
may be desirable to operate the process to obtain a number of
different preselected conversions per pass as the catalyst ages and
the temperature required to maintain the initial preselected
conversion per pass increases. For the dehydrogenation catalysts
described above, operating at a conversion per pass of from about 8
to about 20 weight percent of the paraffinic hydrocarbon passed to
the reaction zone, the initial required temperature for fresh
catalyst at start-of-run is in the range of from about 450 to about
485.degree. C. (842-905.degree. F.), and the final required
temperature at which the catalyst requires replacement at
end-of-run is from about 480 to about 520.degree. C.
(896-968.degree. F.).
[0057] The process disclosed herein is based on the discovery that
increasing the water environment surrounding the dehydrogenation
catalyst after the catalyst has deactivated somewhat can
significantly increase the length of the run or the effective life
of the catalyst. Initially, the process described herein is
operated with a sum of a concentration of water and an equivalent
concentration of water precursors in the combined feed of less than
50 wt-ppm and preferably less than 10 wt-ppm based on the weight of
the combined feed passed to the reaction zone. This relatively low
concentration of water and water precursors can usually be achieved
simply by not injecting or introducing water or water precursors
into the combined feed or any of the streams that combine to form
the combined feed. Even without injection or introduction of water
or water precursors into these, one or more of these streams may
contain water or water precursors. For example, the hydrocarbon
feed or a stream of unconverted dehydrogenatable hydrocarbons may
contain a low or trace concentration of water or water precursors.
Preferably the hydrocarbon feed stream is as dry as possible and
there is no introduction of water or water precursor into the
hydrocarbon feed. The gaseous recycle stream may also contain water
and may in fact contribute more water to the combined feed than the
hydrocarbon feed. Water is present in the recycle gas results when
the reactor effluent contains water since phase separating the
reaction effluent concentrates a majority of the water in the
gaseous stream. The separation conditions and the ratio of the
gaseous recycle stream to the gaseous net stream from the separator
have a large influence on the amount of water carried in the
gaseous recycle stream. If any of these streams contains an
excessive amount of water or water precursors such that the initial
maximum sum of 50 wt-ppm or preferably 10 wt-ppm is exceeded, a
person of ordinary skill in the art can use known methods such as
drying, adsorption, or stripping, for removing water or water
precursors from each stream as needed.
[0058] In order to increase the concentration of water, water
precursors, or both in the combined feed, water or water precursors
may be injected or introduced into the combined feed itself, the
hydrocarbon feed, the gaseous recycle stream, a stream of
unconverted hydrocarbons, or any other stream that combines to form
the combined feed. A person of ordinary skill in the art knows
analytical techniques for measuring the content of water or water
precursors in these streams.
[0059] When a combined feed containing water precursor is
introduced into a dehydrogenation zone containing dehydrogenation
catalyst at dehydrogenation conditions, the water precursor is
rapidly converted to water. A water precursor is preferably any
convenient oxygen-containing compound that performs according to
the teachings contained herein. A water precursor in the
hydrocarbon feed or the unconverted hydrocarbons may, for example,
be any alcohol, aldehyde, epoxide, ketone, phenol or ether that has
a molecular weight or boiling point within the range of molecular
weights or boiling points of the hydrocarbons in the hydrocarbon
feed. A water precursor in the gaseous recycle stream may be any
low molecular weight alcohol or ether such as, for example,
methanol, ethanol, propanol ethyl ether, methyl tert-butyl ether
and isopropyl ether.
[0060] The combined feed has a concentration of water that is
expressed herein in units of wt-ppm of water based on the weight of
the combined feed. The combined feed has a concentration of water
precursors that is referred to herein as an equivalent
concentration of water precursors. The equivalent concentration of
a water precursor is the concentration of water that would result
from the water precursor converting to water in the combined feed.
A person of ordinary skill in the art can compute the equivalent
concentration of a water precursor by multiplying the concentration
of water precursor in a feed or stream by a factor equal to the
amount of water that would be produced per water precursor
converted. The concentration of water precursor in the combined
feed is expressed herein in units of wt-ppm based on the weight of
the combined feed. Therefore, the equivalent concentration of water
precursor is computed by multiplying the concentration of water
precursor in wt-ppm by a factor equal to the weight of water that
would be produced per unit weight of water precursor converted.
(The factor is 0.56 for methanol (CH.sub.3OH) and 0.58 for ethylene
glycol (C.sub.2H.sub.4(OH).sub.2).)
[0061] In one embodiment of the process disclosed herein, the
water, water precursors, or both in the combined feed is increased
when the temperature required to maintain an preselected initial
conversion per pass of the dehydrogenatable hydrocarbon to the
reactor increases by at least 2.degree. C. (4.degree. F.), by from
2 to 8.degree. C. (4 to 14.degree. F.), or by at least 15.degree.
C. (27.degree. F.). The actual reaction temperature may be higher
than the initial temperature required to maintain the preselected
conversion by the same amounts when the increase occurs. The
increase results in the sum of the concentration of water and the
equivalent concentration of a water precursor being at least 200
wt-ppm, or from 200 to about 10000 wt-ppm, based on the weight of
the combined feed passed to the reaction zone. As an example of the
increase in the length of the run in terms of days on stream, an
optimized unit may run about ninety days per catalyst loading. If
the increase in water or water precursors is started on the second
day, the run may be extended about nine days. If the increase is
started on the ninetieth day, the run may be extended about sixty
days.
[0062] The reaction temperature or the required temperature is
generally measured at the inlet of the combined feed to the
reaction zone. The dehydrogenation reactions tend to be
endothermic, which typically causes a temperature drop across the
reaction zone. If heat is supplied to the reaction zone, as
described for instance in U.S. Pat. No. 6,118,038, the temperature
drop may be reduced significantly compared to that in an adiabatic
reaction zone. In any event, a suitable location in or at the
reaction zone can be selected for measuring the reaction or
required temperature that is indicative of the change in
temperature that is made as a result of catalyst deactivation.
[0063] The difference between the initial temperature required to
maintain a preselected conversion per pass and the temperature at
which the catalyst must be replaced is typically from 15 to
30.degree. C. (27-54.degree. F.). This temperature difference is
often the difference between the start-of-run temperature (SORT)
and end-of-run temperature (EORT). In this embodiment, the increase
in the water, water precursors, or both to the reaction zone may be
made after the temperature required to maintain the preselected
conversion per pass increases by at least 2.degree. C. (4.degree.
F.) but by less than 40%, less than 30%, or less than 20% of the
difference between the initial temperature required to maintain a
preselected conversion per pass and the temperature at which the
catalyst must be replaced. That is, the increase is made after the
temperature required to maintain the preselected conversion per
pass increases by at least 2.degree. C. (4.degree. F.) but before
the temperature increase is 6 to 12.degree. C. (11 to 22.degree.
F.), or when the temperature increase is less than 5 to 9.degree.
C. (9 to 16.degree. F.).
[0064] After the increase in water, water precursors, or both in
the combined feed to the reaction zone, the sum of the
concentration of water and the equivalent concentration of water
precursors in the combined feed is preferably maintained not less
than the sum prior to the increase. In this embodiment, the sum can
be further increased after an initial increase. However, once the
sum of the concentration of water and the equivalent concentration
of water precursors in the combined feed is relatively high, such
as above 2000 wt-ppm or above 4000 wt-ppm based on the weight of
the combined feed passed to the reaction zone, further increases in
the sum may effect relatively little further improvement in the
duration of the run or the effective life of the catalyst. Thus, in
some cases it may be preferable to not raise the sum of the water
concentration and the equivalent concentration of water precursors
above the sum that is obtained as a result of an initial increase
in the sum.
[0065] In practicing the process disclosed herein, the conversion
per pass of feed paraffins to monoolefinic product increases, often
dramatically by several molar percentage points, after the increase
in water or water precursors. Although high conversions per pass
appear to be beneficial, they often lead to undesired consequences,
such as increases in side reactions and undesirable byproducts.
High conversions per pass can create a sudden need for storage for
the product olefins when the production of olefins in the
dehydrogenation unit exceeds the capacity of downstream units to
process the olefins. Therefore, it is often desirable in commercial
practice to maintain the paraffin feed rate, the conversion per
pass, and the olefin production rate substantially constant.
Accordingly, in practicing this embodiment of the process disclosed
herein, the inlet temperature of the dehydrogenation reaction zone
may be decreased after the increase in water or water precursors.
The required decrease in inlet temperature to maintain the
preselected conversion per pass can be at least 2.degree. C.
(4.degree. F.), from 2 to 8.degree. C. (4 to 14.degree. F.), at
least 10.degree. C. (18.degree. F.), at least 15.degree. C.
(27.degree. F.) or from 15 to 30.degree. C. (27 to 54.degree. F.).
However, the extent that the temperature is decreased depends on
several factors, including the catalyst, the reactor inlet
temperature when the water or water precursors is increased, and
the rate at which the water or water precursors are introduced.
[0066] The optimum conversion per pass of the process may be less
than the maximum possible conversion per pass at any given catalyst
life. Thus, it is possible to operate the process to obtain a
number of different conversions per pass as the catalyst ages and
as the temperature required to maintain the initial conversion per
pass increases. However, it is preferable to operate the process at
the maximum possible conversion per pass for a given catalyst
life.
[0067] In another embodiment of the process disclosed herein, after
the conversion per pass of the dehydrogenatable hydrocarbon through
the reaction zone has decreased by at least 0.1, at least 0.5, or
at least 1.0 molar percentage points, the sum of the concentration
of water and the equivalent concentration of water precursors in
the combined feed is increased to at least 100 wt-ppm based on the
combined feed passed to the reaction zone. As the catalyst ages in
this embodiment, the temperature of the reaction zone is preferably
either not increased or maintained substantially constant. As used
herein, maintaining the temperature of the reaction zone
substantially constant means that the reaction temperature is
changed by less than 2.degree. C. (4.degree. F.). This can improve
the average selectivity over the duration of the run compared to a
run in which higher reaction temperatures are used or a run in
which the reaction temperature is increased throughout the run to
maintain the initial preselected conversion. Preferably in this
embodiment, the initial preselected conversion per pass is
maintained during the run by increasing the sum of the
concentration of water and the equivalent concentration of water
precursors.
[0068] Accordingly, in this embodiment the sum of the concentration
of water and the equivalent concentration of water precursors is
increased from less than 50 wt-ppm and preferably less than 10
wt-ppm based on a decline in the conversion per pass of the
process. For example, when the sum of the concentration of water
and equivalent concentration of water precursors is less than 50
wt-ppm and preferably less than 10 wt-ppm, the dehydrogenation
conditions result in an initial conversion per pass of, say, 10.0
mol-%. Then, after the conversion per pass of the process drops by
at least 0.1 or at least 0.5 molar percentage points below the
initial conversion per pass, the sum of the concentration of water
and the equivalent concentration of water precursors is raised from
less than 50 wt-ppm and preferably less than 10 wt-ppm to a higher
sum of up to about 10000 wt-ppm, from 100 to about 10000 wt-ppm,
from about 100 to about 300 wt-ppm, based on the weight of the
combined feed passed to the reaction zone. This higher sum is
referred to herein as the second sum and can result in an
improvement to a higher conversion per pass, referred to herein as
the second conversion per pass. Ideally, this second conversion per
pass is as high as the initial conversion per pass, however it may
be from 0.1 to about 5.0 molar percentage points, more commonly
from about 0.1 to about 1.0 molar percentage points, below the
initial conversion per pass. As the catalyst ages and the
conversion per pass declines by a minimum of 0.1 or 0.5 molar
percentage points below the second conversion per pass, the sum of
the concentration of water and the equivalent concentration of
water precursors is then raised from the second sum to what is
referred to herein as the third sum of up to about 10000 wt-ppm,
from 100 to about 10000 wt-ppm, or from about 300 to about 1000
wt-ppm, based on the weight of the combined feed passed to the
reaction zone. Again, this increase may result in an improvement to
a higher conversion per pass, referred to herein as the third
conversion per pass. Preferably, the difference between the initial
and third conversions per pass is small, but it may be between 0
and about 5.0 molar percentage points, more commonly from about 0.1
to about 1.0 molar percentage points. As the catalyst ages yet
further and the conversion per pass drops again by at least 0.1 or
at least 0.5 molar percentage points below the third conversion per
pass, the sum of the concentration of water and the equivalent
concentration of water precursors is raised from the third sum to a
higher sum of up to about 10000 wt-ppm, from 100 to about 10000
wt-ppm, or from about 1000 to about 4000 wt-ppm, based on the
weight of the combined feed passed to the reaction zone. This
sequence of increasing the sum of the concentrations of water and
water precursors in response to decreases in conversion per pass
can be continued until the conversion per pass drops to such a low
level that the process is no longer profitable or useful or until
an upper limit is reached on the concentration of water or water
precursors. Also, once the sum of the concentration of water and
the equivalent concentration of water precursors in the combined
feed is relatively high, further increases in the sum may have a
diminishing effect on maintaining the conversion. The upper limit
on the concentration of water or water precursors may be about
4000, about 10000, or from about 4000 to about 10000 wt-ppm, based
on the weight of the combined feed to the reaction zone, or higher.
After this upper limit is reached, if the reaction temperature is
less than the EORT, the reaction temperature can be increased to
the EORT in order to extend the duration of the run.
[0069] In this embodiment, the frequency, size, and/or the number
of the changes in the sum of the concentration of water and
equivalent concentration of water precursors can be chosen as
needed to achieve a desired processing objective. In a preferred
embodiment to maintain the conversion per pass close to the initial
conversion per pass, each increase in the sum of the concentration
of water and equivalent concentration of water precursors is
relatively small and the increases are relatively frequent. For
example, each increase may be in the range of from about 1 to about
1000 wt-ppm or from about 100 to about 300 wt-ppm based on the
weight of the combined feed passed to the reaction zone. Such
increases could be made as soon as the conversion per pass drops by
at least 0.1, at least 0.5, or at least 1.0 molar percentage
points. The increases are continued until the end of the run or
until the previously-mentioned upper limit on the concentration of
water or water precursors is reached.
[0070] The cause of the decrease in the conversion per pass of the
dehydrogenatable hydrocarbon through the reaction zone can be any
cause that results in a decrease in the conversion per pass,
including but not limited to catalyst deactivation, catalyst aging,
or a decrease in the temperature of the reaction zone. For example,
the cause can be an intentional decrease in the temperature of the
reaction zone by at least 2.degree. C. (4.degree. F.), from 2 to
8.degree. C. (4 to 14.degree. F.), at least 10.degree. C.
(18.degree. F.), at least 15.degree. C. (27.degree. F.) or from 15
to 30.degree. C. (27 to 54.degree. F.).
[0071] The increase in water, water precursors, or both in the
combined feed may occur simultaneously with other changes in the
process. For example, the increase may occur after the selectivity
at the preselected conversion per pass of the paraffinic
hydrocarbon to the reactor decreases by a specified amount of, for
instance, at least 1 molar percentage point. Selectivity is defined
as the moles of monoolefins produced divided by the moles of feed
paraffins that are converted, and as the catalyst ages the
selectivity tends to decrease. The increase may also be made before
a certain percentage, say 40%, 30%, or 20%, of the paraffins that
may be processed before the catalyst requires replacement have
passed through the reaction zone.
[0072] The period of time over which the increase in water or water
precursors to the reaction zone occurs is believed to be not
critical to the success of the process disclosed herein. Typically,
the time for a change in the sum of the concentration of water and
the equivalent concentration of water precursors is relatively
short and may occur, for instance, as a step change over 10 or less
seconds or less. Alternatively, the water or water precursors can
be ramped up over a period of minutes or hours.
[0073] Other ways of practicing the process disclosed herein
include maintaining the concentration of water at less than 5
wt-ppm and preferably less than 2 wt-ppm in the fresh hydrocarbon
feed, or at less than 70 wt-ppm and preferably less than 40 wt-ppm
in the combined feed, during an initial period of preferably at
least one-half (50%) and more preferably at least 60% of the
catalyst life has elapsed. During this initial period, water is not
injected into the fresh hydrocarbon feed and water is prevented
from mixing with the fresh hydrocarbon feed. After the initial
period of preferably at least one-half (50%) and more preferably at
least 60% of the catalyst life has elapsed, these other ways of
practicing the process disclosed herein further include injecting
water into the fresh hydrocarbon feed and maintaining the
concentration of water at 30 to 1900 wt-ppm and preferably at 30 or
60 to 1500 wt-ppm in the fresh hydrocarbon feed, or at 200 to 6200
wt-ppm and preferably at 200 or 500 to 6200 wt-ppm in the combined
feed. Once water injection is started, the concentration of water
can be maintained constant or be increased gradually.
[0074] The dehydrogenatable hydrocarbons may be admixed with a
diluent material before or while flowing through the reaction zone.
The diluent material may be hydrogen, steam, methane, ethane,
propane, butane, pentane, hexane, carbon dioxide, nitrogen, argon
and the like or a mixture thereof. When hydrogen is the diluent,
the hydrogen to hydrocarbon mole ratio is from about 0.1:1 to about
40:1, preferably from about 1:1 to about 10:1. The diluent will
typically be separated from the reaction zone effluent and recycled
to the reaction zone. Hydrogen or hydrocarbons having from 2 to 6
carbon atoms formed as byproducts in the reaction zone can be
diluent.
[0075] Dehydrogenation conditions include a temperature of from
about 400.degree. C. to about 900.degree. C., a pressure of from
about 1 to about 1013 kPa and a liquid hourly space velocity (LHSV)
of from about 0.1 to about 100 hr.sup.-1. As used herein, the
abbreviation "LHSV" means liquid hourly space velocity, which is
defined as the volumetric flow rate of liquid per hour divided by
the catalyst volume, where the liquid volume and the catalyst
volume are in the same volumetric units. In general for paraffins,
the lower the molecular weight, the higher is the temperature
required for comparable conversion per pass. The pressure in the
dehydrogenation zone is maintained as low as practicable,
consistent with equipment limitations, to maximize the chemical
equilibrium advantages.
[0076] In practicing the process disclosed herein, dehydrogenatable
hydrocarbons are contacted with a dehydrogenation catalyst in a
dehydrogenation zone maintained at dehydrogenation conditions. This
contacting can be accomplished in a fixed catalyst bed system, a
moving catalyst bed system, a fluidized bed system, etc., or in a
batch-type operation. A fixed bed system is preferred. In this
fixed bed system the hydrocarbon feed stream is preheated to the
desired reaction temperature and then flowed into the
dehydrogenation zone containing a fixed bed of the catalyst. The
dehydrogenation zone may itself comprise one or more separate
reaction zones with heating means there between to ensure that the
desired reaction temperature can be maintained at the entrance to
each reaction zone, but preferably the reaction zone is a single
reactor. The hydrocarbon may be contacted with the catalyst bed in
either upward, downward or radial flow fashion. The reaction zone
may be an arrangement that provides indirect heat exchange, as
described, for instance, in U.S. Pat. No. 6,118,038. Radial flow of
the hydrocarbon through the catalyst bed is preferred. The
hydrocarbon may be in the liquid phase, a mixed vapor-liquid phase
or the vapor phase when it contacts the catalyst. Preferably, it is
in the vapor phase.
[0077] The effluent stream from the dehydrogenation zone generally
will contain unconverted dehydrogenatable hydrocarbons, hydrogen
and the products of dehydrogenation reactions. This effluent stream
is typically cooled and passed to a hydrogen separation zone to
separate a hydrogen-rich vapor phase from a hydrocarbon-rich liquid
phase. Generally, the hydrocarbon-rich liquid phase is further
separated by means of either a suitable selective adsorbent, a
selective solvent, a selective reaction or reactions or by means of
a suitable fractionation scheme. Unconverted dehydrogenatable
hydrocarbons are recovered and may be recycled to the
dehydrogenation zone. Products of the dehydrogenation reactions are
recovered as final products or as intermediate products in the
preparation of other compounds.
[0078] The following examples are presented in illustration of the
process disclosed herein and are not intended as limitations on the
generally broad scope of the invention as set out in the appended
claims.
Example 1
[0079] Catalysts A, B, and C were dehydrogenation catalysts, each
comprised a layered composition having an inner core and an outer
layer bonded to the inner core. The properties of catalysts A, B,
and C are in Table 1. Catalysts A, B, and C contained platinum and
tin distributed uniformly on the outer layer. Catalyst D was a
dehydrogenation catalyst containing platinum, tin, and lithium
distributed uniformly on a gamma alumina support, and not a layered
composition. Based on the weight of the catalyst, catalyst D
contained 0.4 wt-% platinum, 0.5 wt-% tin, 0.6 wt-% lithium, and
0.4 wt-% indium. The atomic ratio of platinum to tin in catalyst D
was 0.49.
TABLE-US-00001 TABLE 1 Catalyst A B C Core Cordierite Cordierite
Cordierite Core Diameter, mm 1.80 1.76 1.68 Layer Gamma Gamma Gamma
alumina alumina alumina Layer Thickness, micron 100 100 60
Platinum, wt-% of catalyst 0.16 0.16 0.43 Tin, wt-% of catalyst
0.13 0.13 0.32 Lithium, wt-% of catalyst 0.20 0.21 0.14
Platinum/Tin Ratio, atomic 0.74 0.74 0.83
[0080] The catalysts were tested for dehydrogenation activity in a
laboratory scale plant. Catalyst was placed in a reactor and a
hydrocarbon feed composed of 8.8-9.3 wt-% n-C.sub.10, 40.0-41.8
wt-% n-C.sub.11, 38.6 wt-% n-C.sub.12, 8.6-10.8 wt-% n-C.sub.13,
0.3-0.8 wt-% n-C.sub.14 and 1-1.4 wt-% non-normals was flowed over
the catalyst under a pressure of 138 kPa(g) (20 psi(g)), a
H.sub.2:hydrocarbon molar ratio of 4:1, and a liquid hourly space
velocity (LHSV) of 28 hr.sup.-1. The total normal olefin
concentration in the product (% TNO) was maintained at 15 wt-% by
adjusting the reactor inlet temperature. The conversion was stable
and in the range of from 16 to 19%. Hydrogen and hydrocarbon feed
were combined upstream of the reactor to form a combined feed, and
the combined feed was vaporized prior to entering the reactor.
Without any water injection, the concentration of water in the
combined feed was less than 1 wt-ppm based on the weight of the
combined feed. Catalysts were tested with and without water
injection into the combined feed.
[0081] Tables 2-5 present the starting times for water injection,
the concentrations of water based on the weight of the combined
feed after injection began, and the improvements in run duration
resulting from the injection.
Example 2
[0082] Catalyst A was tested following the procedure in Example 1
in eight runs (Runs 2A to 2H), and water was injected into the
combined feed during seven of the eight runs. Table 2 presents the
test conditions and results for the runs. The start-of-run
temperatures (SORTs) for the eight runs were within a range of
2.degree. C. (4.degree. F.), and the differences between the SORTs
and the end-of-run temperatures (EORTs) were within a range of
2.degree. C. (3.degree. F.) for all eight runs except one. However,
the variations in SORTs and in the differences between SORT and
EORT did not have a significant effect on the improvements reported
in Table 2, except as described below. Once water injection was
started in runs 2B, 2D, and 2G, approximately 6000 wt-ppm water
based on the weight of the combined feed was injected for varying
periods of time, but these increases also did not have a
significant effect on the improvements reported in Table 2. Shortly
after water injection began after the start of a run, the reactor
inlet temperature was lowered by from 2 to 17.degree. C. (4 to
30.degree. F.) depending on the run to maintain the % TNO at 15
wt-%. Thereafter, as the catalyst continued to age, the reactor
inlet temperature was increased to maintain the % TNO at 15
wt-%.
TABLE-US-00002 TABLE 2 Increase in Run Start of Water Injection
Duration Time on over Run Temperature - SORT Stream, Water, 2A, %
of (EORT - % of Run wt- % of Run Run .degree. C. (.degree. F.)
SORT) Duration ppm 2A Duration 2A 0 (0) 0 0 2000 NA 2B 2 (4) 12 16
200 18 2C 2 (3) 9 17 2000 11 2D 11 (19) 86 75 200 23 2E 11 (20) 67
63 2000 47 2F 10 (18) 58 53 4000 72 2G 18 (32) 100 66 4000 82 2H NA
NA NA NA 25
[0083] Run 2A was a comparative run which had continuous 2000
wt-ppm water injection during the entire run. Slightly postponing
the start of injection until only 2.degree. C. (3-4.degree. F.) of
catalyst deactivation had occurred after the start of the run
improved the run duration by 18% (Run 2B) and 11% (Run 2C). Further
postponement until the reactor inlet temperature was about
10-11.degree. C. (18-20.degree. F.) above SORT increased the
improvement to from 23% to 72% (Runs 2D, 2E, and 2F). The
improvement in Run 2D's duration would have been significantly
greater but for the fact that Run 2D ended earlier than the other
seven runs and the difference between SORT and EORT for Run 2D was
about one-fourth to one-third less than those of the other seven
runs. Nevertheless, in Runs 2D, 2E, and 2F, the higher the water
injection, the greater is the improvement in run duration. Run 2G,
in which the start of water injection was postponed until EORT had
been reached, had the greatest improvement (82%) of all eight runs
and more than triple the improvement of Run 2H, which had no water
injection. The approximately 6000 wt-ppm water injection in Run 2G
occurred throughout the final 8.degree. C. (15.degree. F.) of
catalyst deactivation at end of the run. Neither this relatively
long increase to approximately 6000 wt-ppm nor the much shorter
approximately 6000 wt-ppm surges in Runs 2B and 2D improved the
durations of the run in which each occurred.
Example 3
[0084] Catalyst B was tested twice according to the procedure in
Example 1, and water was injected into the combined feed during
both runs (Runs 3A and 3B). Table 3 presents the testing conditions
and the resulting improvements. The SORTs for the runs were within
2.degree. C. (3.degree. F.), as were the differences between the
SORTs and EORTs.
TABLE-US-00003 TABLE 3 Increase in Run Start of Water Injection
Duration Time on over Run Temperature - SORT Stream, Water, 3A, %
of (EORT - % of Run wt- % of Run Run .degree. C. (.degree. F.)
SORT) Duration ppm 3A Duration 3A 0 (0) 0 0 2000 NA 3B* 17 (31) 100
79 4000 69 3B** NA NA NA NA 34 *Entire run. **Until water injection
started.
[0085] Run 3A was a comparative run which had continuous 2000
wt-ppm water injection during the entire run. In Run 3B, the start
of injection was postponed until EORT had been reached. Without
water injection the run duration improved by only 34%. Shortly
after water injection began, the reactor inlet temperature was
lowered by from 16.degree. C. (29.degree. F.) to maintain the % TNO
at 15 wt-%. Subsequently the reactor inlet temperature was
increased to maintain the % TNO at 15 wt-% as the catalyst aged.
When the reactor inlet temperature had been raised to EORT a second
time, the duration of Run 3B had improved by 69%, which was more
than double the improvement that had been attained without water
injection.
Example 4
[0086] Catalyst C was tested according to the procedure in Example
1. Table 4 presents the test conditions and results of the run (Run
4). After water injection began, the reactor inlet temperature was
first lowered by 9.degree. C. (16.degree. F.) and then subsequently
increased, to maintain the % TNO at 15 wt-%. Starting water
injection when EORT was reached improved the duration of Run 4 by
51%.
TABLE-US-00004 TABLE 4 Start of Water Injection Increase in Time on
Run Temperature - SORT Stream, Water, Duration % of (EORT - % of
Run wt- over BASE, Run .degree. C. (.degree. F.) SORT) Duration ppm
% of BASE 4* 13 (23) 100 79 4000 51 4** NA NA NA NA BASE *Entire
run. **Until water injection started.
Example 5
[0087] Catalyst D was tested twice according to the procedure in
Example 1. Table 5 presents the test conditions and results. A
temperature was chosen for the runs (Runs 5A and 5B) to be the
basis (BASE temperature) from which point catalyst deactivation,
time on stream, and run duration were measured. The BASE
temperature for the runs was within 0.5.degree. C. (1.degree. F.)
of the SORTs, as were the differences between the BASE temperature
and EORTs. After water injection began in Run 5B, the reactor inlet
temperature was lowered by from 11.degree. C. (20.degree. F.) to
maintain the % TNO at 15 wt-%.
TABLE-US-00005 TABLE 5 Increase in Run Start of Water Injection
Duration Time on over Temperature - BASE Stream, Water, Run 5A, %
of (EORT - % of Run wt- % of Run 5A Run .degree. C. (.degree. F.)
BASE) Duration*** ppm Duration*** 5A 0 (0) 0 0 2000 NA 5B* 14 (27)
100 77 4000 53 5B** NA NA NA NA 18 *Entire run. **Until water
injection started. ***Time on stream and run duration were measured
from the point when the temperature was the BASE temperature.
[0088] Run 5A was a comparative run which had 2000 wt-ppm water
injection continuously throughout the entire run. By postponing the
start of injection until EORT had been reached in Run 5B, the
duration of Run 5B improved by 53%, which was nearly than triple
the improvement (18%) achieved in Run 5B before water was
injected.
Example 6
[0089] Catalyst D was tested according to the procedure in Example
1. A temperature was chosen for the run (Run 6) to be the basis
(BASE temperature) from which point catalyst deactivation, time on
stream, and run duration were measured. The BASE temperature for
Run 6 was the same as the BASE temperature for Runs 5A and 5B. The
SORT was within 3.degree. C. (5.degree. F.) of those in Example 5,
as was the difference between the SORT and EORT. However, the
variations in SORTs and in the differences between SORT and EORT
did not have a significant effect on the improvements reported in
Table 6. Water was injected continuously throughout the entire run.
Initially the water injection was 100 wt-ppm based on the weight of
the combined feed. The reactor inlet temperature was adjusted to
maintain the % TNO at 15 wt-% until the reactor inlet temperature
was 12.degree. C. (22.degree. F.) above the BASE temperature, the
difference between the reactor inlet temperature and the BASE
temperature was 82% of the difference between EORT and the BASE
temperature, and the time on stream was 81% of what would be the
duration of Run 6. Water injection was then increased to 4000
wt-ppm based on the weight of the combined feed, and the reactor
inlet temperature was lowered by from 6.degree. C. (11.degree. F.)
to maintain the % TNO at 15 wt-%. Subsequently, the reactor inlet
temperature was increased to maintain the % TNO at 15 wt-% until
EORT was reached again, at which time the duration of Run 6 was 47%
longer than that of Run 5A.
TABLE-US-00006 TABLE 6 Increase in Start/Increase Run of Water
Injection Duration Time on over Run Temperature - BASE Stream,
Water, 5A, % of % of (EORT - % of Run wt- Run 5A Run .degree. C.
(.degree. F.) BASE) Duration*** ppm Duration*** 6* 12 (22) 82 81
4000 47 6** 0 (0) 0 0 100 18 *Entire run. **Until water injection
increased. ***Time on stream and run duration were measured from
the point when the temperature was the BASE temperature.
[0090] Therefore, the duration of the run using Catalyst D with a
delay in the start of water injection (Run 5B) was improved by 6
percentage points over that obtained when water was injected
continuously first at 100 wt-ppm and then at 4000 wt-ppm (Run 6).
Postponing the start of water injection to both layered and
non-layered compositions resulted in a much greater benefit over
continuously injecting water at a constant 2000 wt-ppm.
Example 7
[0091] This is a prophetic example. Catalyst A is tested following
the procedure in Runs 2A, 2G, and 2H (Runs 7A to 7C), and water is
injected into the combined feed during two of the runs. The
conversion is 8%. Table 7 presents the test conditions and results
for the runs.
TABLE-US-00007 TABLE 7 Start of Water Injection Increase in Time on
Run Duration Temperature - BASE Stream, Water, over Run 7A, % of
(EORT - % of Run wt- % of Run 7A Run .degree. C. (.degree. F.)
BASE) Duration ppm Duration 7A 0 (0) 0 0 2000 NA 7B 18 (32) 100 57
4000 75 7C NA NA NA NA 25
[0092] Run 7A is a comparative run which has continuous 2000 wt-ppm
water injection. Postponing the start of water injection until EORT
is reached improves the run duration by 75% (Run 7B) and triples
the improvement of Run 7C, which has no water injection.
Example 8
[0093] This is a prophetic example. Catalyst A is tested following
the procedure in Example 1, except that the total normal olefin
concentration in the product (% TNO) is maintained at 15 wt-% by
increasing the water injection and without adjusting the reactor
inlet temperature. The conversion is stable and in the range of 16
to 17%. Initially there is no water injection. Without any water
injection, the concentration of water in the combined feed is less
than 1 wt-ppm based on the weight of the combined feed. The
concentration of water based on the weight of the combined feed is
increased first to 100 wt-ppm and then in increments to 4000 wt-ppm
to maintain the % TNO at 15 wt-%. Then the reactor inlet
temperature is increased from the SORT to the EORT, which
temperatures are the same as in Run 2A. The postponement in raising
the reactor inlet temperature keeps the average reactor inlet
temperature over the duration of the run less than that in Run 2A.
The duration of the run is not less than that of Run 2A, and the
average selectivity over the duration of the run is greater than
that in Run 2A
* * * * *