U.S. patent number RE29,314 [Application Number 05/721,418] was granted by the patent office on 1977-07-19 for asphaltene hydrodesulfurization with small catalyst particles in a parallel reactor system.
This patent grant is currently assigned to Gulf Research & Development Company. Invention is credited to BY Gulf Research & Development Company, Edgar Carlson, deceased, Alfred M. Henke, William R. Lehrian, Joel D. McKinney, Kirk J. Metzger.
United States Patent |
RE29,314 |
Carlson, deceased , et
al. |
July 19, 1977 |
Asphaltene hydrodesulfurization with small catalyst particles in a
parallel reactor system
Abstract
The hydrodesulfurization of a crude oil or a reduced crude
containing the asphaltene fraction proceeds at unexpectedly low
temperatures by utilizing a Group VI and Group VIII metal
containing catalyst on alumina when the catalyst particles are very
small and have a diameter between about 1/20 and 1/40 inch and are
disposed in a parallel catalyst bed system.
Inventors: |
Carlson, deceased; Edgar (LATE
OF Allison Park, PA), BY Gulf Research & Development
Company (Pittsburgh, PA), Henke; Alfred M. (Springdale,
PA), Lehrian; William R. (Verona, PA), McKinney; Joel
D. (Pittsburgh, PA), Metzger; Kirk J. (Verona, PA) |
Assignee: |
Gulf Research & Development
Company (Pittsburgh, PA)
|
Family
ID: |
27110425 |
Appl.
No.: |
05/721,418 |
Filed: |
September 8, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
770725 |
Oct 25, 1968 |
03563886 |
Feb 16, 1971 |
|
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Current U.S.
Class: |
208/216R;
208/216PP |
Current CPC
Class: |
C10G
65/12 (20130101); C10G 2300/107 (20130101) |
Current International
Class: |
C10G
65/00 (20060101); C10G 65/00 (20060101); C10G
65/12 (20060101); C10G 65/12 (20060101); C10G
023/02 () |
Field of
Search: |
;208/210,216,213,89 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Hydrodesulfurization of Khafii Crude Oil", Ohtsuka et al. Bulletin
of the Japan Petroleum Institute, vol. 10, May 1968..
|
Primary Examiner: Crasanakis; George
Claims
We claim:
1. A process for the hydrodesulfurization of a crude oil or a
reduced crude oil containing the asphaltene fraction of the crude
comprising passing said oil together with hydrogen through a
plurality of reactors arranged in parallel, each of said reactors
containing a series of compact beds of catalyst particles
comprising a Group VI metal and Group VIII metal on alumina, the
particles in said compact catalyst beds being between about 1/20
and 1/40 inch in diameter, .[.and.]. the hydrogen partial pressure
in said plurality of compact parallel beds being .[.about.]. 1,000
to 5,000 pounds per square inch .Iadd.and a throughput of at least
127 volumes of oil per volume of catalyst is continued for at least
10 days. .Iaddend.
2. The process of claim 1 wherein the particles in said beds are
between about 1/25 and 1/36 inch in diameter.
3. The process of claim 1 wherein the particles in said beds are
between about 1/29 and 1/34 inch in diameter.
4. The process of claim 1 wherein the catalyst comprises
nickel-cobalt-molybdenum on alumina.
5. The process of claim 1 wherein the charge oil contains between
about 0.002 and 0.03 weight percent of nickel and vanadium.
6. The process of claim 1 including the step of applying a hydrogen
quench to said reactors to control the temperature thereof.
7. A process for the hydrodesulfurization of a crude oil or a
reduced crude oil containing the asphaltene fraction of the crude
comprising passing said oil together with hydrogen through a
plurality of reactors arranged in parallel, each of said reactors
containing a series of compact beds of catalyst particles
comprising a Group VI metal and Group VIII metal on alumina, the
particles in said compact catalyst beds being between about 1/20
and 1/40 inch in diameter, the hydrogen partial pressure in said
plurality of compact parallel beds being .[.about.]. 1,000 to 5,000
pounds per square inch, .[.and.]. injecting a portion of the
hydrogen .Iadd.as a .Iaddend.quench between the catalyst beds in
each of said series .Iadd.and a throughput of at least 127 volumes
of oil per volume of catalyst is continued for at least 10
days..Iaddend.
8. The process of claim 7 wherein the particles in said beds are
between about 1/25 and 1/36 inch in diameter.
9. The process of claim 7 wherein the particles in said beds are
between about 1/29 and 1/34 inch in diameter.
10. The process of claim 7 wherein the catalyst comprises
nickel-cobalt-molybdenum on alumina.
11. The process of claim 7 wherein the charge oil contains between
about 0.002 and 0.03 weight percent of nickel and vanadium.
12. The process of claim 1 wherein the hydrogen partial pressure is
1,000 to 3,000 pounds per square inch.
13. The process of claim 1 wherein the hydrogen partial pressure is
1,500 to 2,500 pounds per square inch. .[.14. The process of claim
1 wherein throughput is continued for at least 10 days and 127
volumes of oil per
volume of catalyst..]. 15. The process of claim 7 wherein the
hydrogen
partial pressure is 1,000 to 3,000 pounds per square inch. 16. The
process of claim 7 wherein the hydrogen partial pressure is 1,500
to 2,500 pounds per square inch. .[.17. The process of claim 7
wherein throughput is continued for at least 10 days and 127
volumes of oil per volume of
catalyst..]. .Iadd.18. Claim 1 wherein a throughput of at least
1,293 volumes of oil per volume of catalyst is continued for at
least 97.6 days. .Iaddend. .Iadd.19. Claim 7 wherein a throughput
of at least 1,293 volumes of oil per volume of catalyst is
continued for at least 97.6 days. .Iaddend.
Description
The present invention relates to a process for the
hydrodesulfurization of a crude oil or a reduced crude oil in the
presence of a supported Group VI and Group VIII metal
hydrodesulfurization catalyst having an exceptionally small
particle size. Substantially all or a large proportion of the
catalyst particles of the present invention have a diameter of
between about 1/20 and 1/40 inch.
Although nickel-cobalt-molybdenum is the preferred active metals
combination for the catalyst of this invention, other combinations
can be utilized such as cobalt-molybdenum, nickel-tungsten and
nickel-molybdenum. Alumina is the preferred supporting material but
other non-cracking supports can also be used such as silica alumina
and silica magnesia.
Hydrodesulfurization catalysts comprising supported Group VI and
Group VIII metals, such as nickel-cobalt-molybdenum on alumina,
having a particle size as small as the catalyst particles of the
present invention were not heretofore considered advantageous for
use in a large or commercial scale because a bed comprising
particles of the small size of the present invention induces an
extremely high pressure drop, which is highly deleterious to a
hydrodesulfurization process which has a limited inlet pressure
because the temperature required by a catalyst to accomplish a
given degree of desulfurization increases with loss of hydrogen
pressure.
The present invention relates to a hydrodesulfurization process in
which the small particle size catalyst is utilized in a manner
which manifests an unexpectedly high activity so that
hydrodesulfurization of crude oil charge to any desired sulfur
level, such as a 1 percent sulfur level, proceeds at an
unexpectedly low temperature. Although extrapolation of the initial
temperature required to produce a liquid product having a 1 percent
sulfur content with 1/8 inch diameter and 1/16 inch diameter NiCoMo
catalyst particles, which are above the size of the present
invention, indicates that the temperature requirement would be
lower with the small catalyst particles of this invention we have
found that the small size NiCoMo catalyst particles of the present
invention permit the use of a hydrodesulfurization temperature
which is considerably lower than the temperature which would be
expected by extrapolation of the temperature data obtained with
larger size catalyst particles. Moreover, the very discovery that
hydrodesulfurization with the catalyst of the present invention
could be carried out at an unexpectedly low temperature has
heretofore been obscured by the extremely high pressure drop
through a bed of the small size catalyst particles of the present
invention. The reason is that in a hydrodesulfurization process
pressure drop itself increases the temperature requirement to
achieve a given degree of desulfurization usually by an extent
which equals or exceeds the temperature advantage due to the small
particle size of this invention.
It is seen that there are two unexpected features surrounding the
present invention. The first is that there is an unexpectedly great
temperature advantage achievable in a hydrodesulfurization process
by employing a bed of catalyst having a particle size of the
present invention. FIG. 1 (all figures are discussed in detail
herein below) shows that the hydrodesulfurization temperature
required to produce a residual product having 1 percent sulfur with
a 1/32 inch catalyst of the present invention is much lower than
what would be expected by extrapolation of the line connecting the
data obtained with 1/8 and 1/16 inch catalyst particles even though
the surface area defined by the pores of all three catalysts is
about the same. The second feature is that the unexpected
temperature advantage is completely disguised by the ordinary
approach to its determination, i.e. by making a test in a reactor
with relatively large size catalyst particles as a blank and then
making a test in the same reactor under the same conditions except
that the catalyst particle size is within the range of the present
invention (particle size being the only variable changed in the two
tests). In this regard, the vertical dashed line in FIG. 2 shows
that if a 1/16 inch catalyst, which is larger than a catalyst of
this invention, is tested in a 9.5 foot diameter reactor and then a
1/32 inch catalyst of this invention is tested in the same reactor
under unchanged conditions, including an unchanged space velocity,
the pressure drop in the 1/32 inch catalyst bed in the same reactor
is so much greater than that for the 1/16 inch catalyst that the
pressure drop increase itself would easily nullify the temperature
advantage achievable because of particle size and therefore the
advantage of the present invention would be completely masked. The
horizontal dashed line of FIG. 2 shows that if the 1/16 inch
catalyst is tested in a 9.5 foot diameter reactor a comparable
pressure drop can only be achieved if the 1/32 inch catalyst is
tested in an 11 foot diameter reactor, when both tests are
performed at a liquid hourly space velocity of one. Therefore, it
is only by making the tests in two different reactors, to equalize
pressure drop, that the temperature advantage of the 1/32 inch
catalyst becomes apparent. It is clear that not merely one but
rather two variables must be changed to reveal the advantage of the
present invention.
The great effect of pressure drop upon temperature requirements to
produce a hydrocarbon product having a 1 percent sulfur content is
demonstrated by reference to FIG. 3. In FIG. 3 the solid line
represents a hydrodesulfurization process having a constant
hydrogen partial pressure of 1830-1850 p.s.i.a. The dashed line
represents a decreasing hydrogen partial pressure starting with the
1830-1850 p.s.i.a. range to a range of 1720-1740 p.s.i.a. which
reduction is caused by the recycle hydrogen stream becoming
progressively diluted with other gases. FIG. 3 shows that as the
hydrogen partial pressure progressively decreases the temperature
required to produce a 1 percent sulfur product progressively
increases, so that it is considerably above the temperature
required with constant hydrogen partial pressure. Since pressure
drop due to flow across a catalyst bed similarly reduces partial
hydrogen pressure, FIG. 3 illustrates the detrimental effect upon
reaction temperature of pressure drop through a catalyst bed of
this invention.
The charge to the process of this invention can be a full crude or
a reduced crude containing substantially all of the residual
asphaltenes of the full crude. The residual asphaltenes are
deficient in hydrogen and comprise only about 10 percent of the
charge oil but contain substantially all of the metallic components
present in the crude, such as nickel and vanadium. Since the
desulfurization catalyst has a greater activity for demetalization
than for desulfurization, it removes nickel and vanadium from a
charge stock more rapidly than it removes sulfur. These metals
deposit most heavily on the outermost regions of the catalyst cross
section and tend to reduce the desulfurization activity of the
catalyst. Nickel and vanadium removal constitutes substantially the
entire deactivation of the catalyst while sulfur and nitrogen
removal contributes very little to catalyst deactivation.
Furthermore, the asphaltenes comprise the highest boiling fraction
of the full crude and contain the largest molecules in the crude.
These large molecules are the ones least able to penetrate catalyst
pores and most likely to plug these pores. The present invention is
directed towards the hydrodesulfurization of a full crude or a
residual oil containing substantially the entire asphaltene
fraction of the crude from which it is derived and which therefore
contains 95 to 99 weight percent or more of the nickel and vanadium
content of the full crude. The nickel, vanadium and sulfur content
of the liquid charge can vary over a wide range. For example,
nickel and vanadium can comprise 0.002 to 0.03 weight percent (20
to 300 parts per million) or more of the charge oil while sulfur
can comprise about 2 to 6 weight percent or more of the charge oil.
If an oil containing smaller quantities of nickel, vanadium and
sulfur is processed, such as a furnace oil, considerably lower
temperature conditions, pressures as low as 1000 pounds per square
inch, lower gas circulation rates and hydrogen of lower purity than
required by this invention, will suffice to produce a liquid
product containing 1 percent sulfur, and therefore the process of
the present invention wll not be essential.
As the hydrodesulfurization reaction proceeds, nickel and vanadium
removal from the charge tends to occur preferentially over sulfur
removal. However, deposition of nickel and vanadium upon the
catalyst results in a greater degree of catalyst deactivation than
does sulfur removal because the removed metals deposit upon the
catalyst whereas sulfur removed from the charge escapes as hydrogen
sulfide gas. Low hydrodesulfurization temperatures tend to inhibit
metal removal from the charge and thereby reduce catalyst
deactivation. Since the hydrodesulfurization reaction is
exothermic, it is important to quench the reactor to maintain a
reaction temperature as low as the small catalyst size of this
invention permits to obtain the desired degree of desulfurization
in order to inhibit catalyst deactivation. Unnecessarily high
temperatures by encouraging catalyst deactivation will result in
loss of the initial temperature advantage of the catalyst of this
invention. Quenching is advantageously accomplished by dividing the
total catalyst bed into a plurality of relatively small beds in
series and injecting relatively cool hydrogen between the beds, as
demonstrated below. It is seen that there is a high degree of
interdependence between the use of a high metals content asphaltene
charge, the small size catalyst particles of this invention, and
the use of a quench to insure that the reactor remains at a
temperature as low as the catalyst size permits.
The hydrodesulfurization process of this invention employs
.[.conventional reaction conditions such as, for example,.]. a
hydrogen partial pressure of 1,000 to 5,000 pounds per square inch,
generally, 1,000 to 3,000 pounds per square inch, preferably, and
1,500 to 2,500 pounds per square inch most preferably. Reactor
design limitations usually restrict inlet pressures under the
conditions of the present invention to not more than 2,000, 2,500,
or 3,000 p.s.i.g. It is the partial pressure of hydrogen rather
than total reactor which determines hydrodesulfurization activity.
Therefore, the hydrogen stream should be as free of other gases as
possible. Furthermore, since reactor design limitations restrict
hydrogen inlet pressures, hydrogen pressure drop in the reactor
should be held as low as possible.
The gas circulation rate can be between about 2,000 and 20,000
standard cubic feet per barrel, generally, or preferably about
3,000 to 10,000 standard cubic feet per barrel of gas preferably
containing 85 percent or more of hydrogen. The mol ratio of
hydrogen to oil can be between about 8:1 and 80:1. Reactor
temperatures can range between about 650 and 900.degree. F.,
generally, and between about 680 and 800.degree. F., preferably.
The temperature should be low enough so that not more than about
10, 15 or 20 percent of the charge will be cracked to furnace oil
or lighter. At temperatures approaching 800.degree. F. the steel of
the reactor walls rapidly loses strength and unless reactor wall
thicknesses of 7 to 10 inches or more are utilized a temperature of
about 800.degree. F. constitutes a metallurgical limitation. The
liquid hourly space velocity in each reactor of this invention can
be between about 0.2 and 10, generally, between about 0.3 and 1 or
1.25, preferably or between about 0.5 and 0.6 most preferably.
The catalyst employed in the process is conventional and comprises
sulfided Group VI and Group VIII metals on a support such as
nickel-cobalt-molydbnum or cobalt-molybdenum on alumina.
Hydrodesulfurization catalyst compositions suitable for use in the
present invention are described in U.S. 2,880,171 and also in U.S.
3,383,301. However, an essential feature of the catalyst particles
of the present invention is that the smallest diameter of these
particles is considerably smaller than the diameter of
hydrodesulfurization catalyst particles of the prior art. The
smallest diameter of the catalyst particles of the present
invention is broadly between about 1/20 and 1/40 inch,
preferentially between 1/25 and 1/36 inch, and most preferably
between about 1/29 and 1/34 inch. Particle sizes below the range of
this invention would induce a pressure drop which is too great to
make them practical. The catalyst can be prepared so that nearly
all or at least about 92 or 96 percent of the particles are within
the range of this invention. The catalyst can be in any suitable
configuration in which the smallest particle diameter is within the
range of the present invention such as roughly cubical,
needle-shaped or round granules, spheres, cylindrically-shaped
extrudates, etc. By smallest particle diameter we mean the smallest
surface to surface dimension through the center or axis of the
catalyst particle, regardless of the shape of the particle. The
cylindrical extrudate form having a length between about 1/10 and
1/4 inch is highly suitable.
Since the asphaltene molecules which are hydrodesulfurized in
accordance with the present invention are large molecules and must
enter and leave the pores of the catalyst without plugging the
pores, in order to obtain good aging properties most of the pore
volume of the catalyst of this invention should be in pores above
50 A. in size. Advantageously 60 to 75 percent or more of the pore
volume should be in pores of 50 A, or more. Most preferably, 80 to
85 percent or more of the pore volume should be in pores above 50
A. in size. Catalysts having smaller size pores have good initial
activity but poor aging characteristics due to gradual plugging of
the pores by the asphaltene molecules. For example, catalyst A
below exhibited good activity in the process of this invention for
about one month while catalyst B below exhibited good activity for
about three months.
______________________________________ Catalyst Catalyst A percent
B percent of pore of pore volume volume
______________________________________ Pore size, A: 200-300 1.2
2.3 100-200 4.3 21.7 41.7 87.3 50-100 16.2 43.3 40-50 16.4 6.4
30-40 22.6 6.6 20-30 26.6 1.0 7-20 12.5 0.0
______________________________________
As indicated above, as the diameter of conventional
hydrodesulfurization catalyst particles progressively decreases
within a range which is above the range of the present invention,
hydrodesulfurization of a crude oil to a one percent sulfur level
proceeds at progressively lower temperatures. However, the
following tests show that the diminishing of catalyst diameter size
to a level within the range of the present invention results in an
unexpectedly great reduction in hydrodesulfurization temperature
which is much greater than indicated by the particle
diameter-temperature relationship exhibited by larger size
particles. However, counteracting this temperature advantage is the
fact that the small catalyst particle diameters of the present
invention result in a large pressure drop through a catalyst bed
comprising them, and this pressure drop tends to nullify the
temperature advantage achievable with the catalyst of the present
invention because hydrodesulfurization temperature requirements
increase as hydrogen partial pressures decrease.
Although it is expected that reduction in catalyst particle size
will increase pressure drop, we have found that under
desulfurization conditions the increase in pressure drop occasioned
by using a bed of catalyst particles of the size of this invention
as compared to a bed of catalyst particles only slightly larger
than those of this invention is great within reactors having
moderate diameters. As shown in FIG. 2 the increase in pressure
drop occasioned by utilizing the catalyst size of the present
invention as compared to slightly higher catalyst sizes can be
greatly moderated by utilizing a reactor having a very high
diameter such as 10 or 11 feet or more. However, high pressure
reactors having large diameters require extremely thick walls,
especially under the elevated temperature conditions of the present
process.
As indicated above, in the temperature vicinity of 800.degree. F.
which is required for hydrodesulfurization of crude oil or reduced
crude oil a considerable metallurgical weakening occurs in the
steel reactor walls. In order to guard against reactor failures at
the 2,000 or 2,500+ pounds per square inch operating pressures of
the process extremely thick steel walls are required, for example,
a thickness of 8, 10 or 12 inches. At the reaction temperatures of
this invention the required reactor wall thickness increases
appreciably with relatively small increases in reactor inlet
pressure. Furthermore, at any temperature or pressure of this
invention the wall thickness required also increases with reactor
diameter. Therefore the excessive increase in reactor wall
thickness which is required upon any increase in reactor diameter
or reactor temperature exerts a practical design limitation upon
maximum allowable pressure in a reactor of the present
invention.
The existence of a maximum pressure limitation tends to be
prohibitive to the use of a hydrodesulfurization catalyst having a
small diameter because a bed comprising such a small catalyst
induces a very high pressure drop, diminishing still further the
average pressure within the reactor, and the magnitude of this
pressure drop is closely related to reactor diameter. For example,
FIG. 2 shows that the pressure drop curves for 1/12 inch, 1/16 inch
and 1/32 inch catalyst beds are roughly parallel at reactor
diameters of 11 feet or greater. However, the pressure drop curve
for the 1/32 inch catalyst of this invention is much steeper at
reactor diameters less than 11 feet than the pressure drop curves
for the 1/12 inch and 1/16 inch catalyst. Therefore, for a catalyst
of the present invention the diameter of the reactor within the
range of conventional reactor sizes has an important effect upon
pressure drop.
Since there is a practical limit on reactor inlet pressure, as
explained above, due to reactor wall thickness requirements, it is
important to hold pressure drop in the reactor as low as possible.
In effect there is a pressure squeeze in the system in that inlet
hydrogen pressure should be held down while reactor outlet pressure
should be as high as possible. Therefore, in reactors having an
inlet pressure limitation of about 2,000, 2,500 or 3,000 p.s.i.g.,
the diameter to depth ratio of the catalyst bed should be high
enough to reduce pressure drop so that the reactor outlet pressure
is not more than about 150, 250 or 350 p.s.i.g. lower than the
inlet pressure. Control of reactor pressure differential with a
high diameter to depth ratio catalyst bed is especially important
in single reactor systems capable of accepting only relatively low
inlet pressures. The diameter to depth ratio becomes less important
in reactors which can accept relatively high inlet pressures or in
parallel reactor systems wherein pressure drop can be reduced by
diverting a portion of reactant flow to another reactor.
There is an additional problem relating to pressure drop arising
when utilizing the very small catalyst particles of this invention
that is alleviated considerably by utilizing a large diameter
reactor or parallel reactors. When catalyst particles have the very
small size within the range of this invention, reactant flow
through them causes them to shift and scrape against each other in
a process of compaction. Scraping of particles against one another
results in production of fines which further increases pressure
drop. Since a catalyst bed may be in continuous operation for long
periods of time, production of fines can be considerable. The use
of a large diameter reactor or a parallel reactor system, by
permitting a greater catalyst cross-section per volume of reactor
flow, inhibits fines formation and thereby inhibits an increasing
pressure drop across the catalyst field due to this cause.
In accordance with the present invention a hydrodesulfurization
catalyst whose diameter is between 1/20 and 1/40 inch which
provides an unexpected and substantial temperature advantage due to
its size but whose size also induces a large pressure drop in
reactors of common or standard size which pressure drop tends to
nullify said temperature advantage is distributed between a
plurality of reactor beds arranged in parallel. The catalyst in
each parallel reactor is advantageously divided into separate beds
arranged in series to form a reactor train in each parallel reactor
with each succeeding bed in series containing a greater quantity of
catalyst than its preceding bed. The total liquid charge stream
comprising crude oil or reduced crude oil together with a portion
of total hydrogen requirements is apportioned between said parallel
reactors. An effluent stream comprising desulfurized liquid
together with gases is withdrawn from the reactors and cooled.
Liquid and gases are separated from each other in the cooled
effluent stream. Impurities are removed from said effluent gases to
provide a recycle hydrogen stream having an increased proportion of
hydrogen. The recycle hydrogen is recycled to a plurality of
positions in series in each of the parallel reactor trains between
the separate catalyst beds therein.
In the described process the use of parallel reactor trains serves
to minimize overall liquid pressure drop in the system by dividing
the total liquid charge between a plurality of reactors. The number
of parallel reactors should be adequate to reduce the pressure drop
across each catalyst bed sufficiently to permit the reaction to
occur near the low temperature level permitted by the small
catalyst size. The apportioning of the recycle hydrogen to separate
positions in each reactor train rather than total recycle of the
hydrogen to the beginning of each parallel reactor train serves to
minimize overall hydrogen pressure drop in the system. Finally, the
apportioning of the recycle hydrogen so that it is injected between
the separate catalyst beds permits it to serve as a quench to cool
the flowing stream as it passes between catalyst beds thereby
permitting reaction temperature to remain near the low temperature
level permitted by the small catalyst size. In the absence of a
hydrogen quench as described the temperature increase of reactants
across each bed would become cumulative so that neither deep beds
nor a number of beds in series could be used, necessitating a
greater number of parallel and shallow reactors. Furthermore,
temperatures even slightly higher than necessary are detrimental
because, as shown in FIG. 4, moderate temperature elevations
considerably enhance thermal cracking of liquid producing among
other products light hydrocarbon gases which dilute the hydrogen
stream and reduce the partial pressure of hydrogen therein.
The hydrogen quench by reducing the actual temperature also reduces
the required temperature and therefore cooperates interdependently
with the small catalyst particles of this invention. By lowering
the temperature, the hydrogen quench reduces cracking, which would
consume hydrogen and produce light hydrocarbon gases leading to a
lower hydrogen concentration, which in turn would reduce the
hydrogen partial pressure and increase the required reaction
temperature.
It is seen that the feature of parallel reactors, each of which has
a plurality of separate catalyst beds and the feature of recycle
hydrogen injection between the separate catalyst beds function
highly interdependently with respect to each other and with respect
to the use of the small catalyst particle size of this invention.
The small catalyst particle size permits hydrodesulfurization to
occur at an unexpectedly low temperature level but imposes a high
pressure drop which tends to nullify the temperature advantage. The
use of parallel reactors reduces the pressure drop in the liquid
flow stream while the use of separated catalyst beds in series in
each of the parallel reactors with injection of recycle hydrogen
between the beds serves not only to reduce the pressure drop of the
hydrogen flowing through the system but also serves to minimize the
number of parallel reactors required by quenching reactant
temperature along the length of the reactor. As stated above, the
quenching effect inhibits thermal cracking of liquid and thereby
avoids hydrogen consumption for cracking and excessive dilution of
the hydrogen stream with light hydrocarbon gases which would reduce
the partial pressure of the hydrogen stream, thereby also tending
to nullify the advantageous temperature effect of the small
particle size catalyst.
As shown in FIG. 2, at reactor diameters below about 11 feet, the
pressure drop through the 1/32 inch catalyst bed of the present
invention increases extremely rapidly with reduction in reaction
diameter at the indicated space velocity. However, in the diameter
range shown the pressure drops through a 1/16 inch catalyst bed and
a 1/12 inch catalyst bed, which are both above the range of this
invention, are not nearly as sensitive to reduction in reactor
diameter below 11 feet. FIG. 2 also shows that at reactor diameters
above 11 feet the pressure drop through a 1/32 inch catalyst bed is
not significantly more sensitive to changes in reactor diameter
than are the pressure drops through the 1/12 inch and 1/16 inch
catalyst beds. Therefore, there is a much more sensitive pressure
drop relationship between a 1/32 inch catalyst bed of this
invention at the reactor diameters shown in FIG. 2 than there is
with beds of larger size catalyst particles. However, at the high
temperature and pressure conditions of the hydrodesulfurization
process of this invention metallurgical requirements require
reactor walls of great thickness at reactor diameters of 11 feet or
more, reactor wall thickness requirements increasing with
increasing reactor diameter, so that economic considerations
prohibit reactor diameters much larger than 11 feet in the process
of this invention. Therefore, with a 1/32 inch catalyst bed in
order to accommodate charge rates which would require a reactor
diameter much greater than 11 feet, it is necessary to utilize a
parallel reactor system. FIG. 2 clearly indicates that at the
indicated space velocity below and with the reactor diameters shown
a criticality regarding pressure drop sensitivity arises when
employing a 1/32 inch catalyst bed which is far greater than in the
case of the 1/12 inch and a 1/16 inch catalyst bed.
All of the tests indicated in FIG. 2 for the various catalyst sizes
were made at the same liquid hourly space velocity, as indicated
below. Therefore, in the tests within a reactor of relatively large
diameter, the catalyst bed depth was relatively shallow. In the
tests within a reactor of relatively small diameter, the catalyst
bed was deeper. FIG. 2 shows that in utilizing a 1/32 inch catalyst
rather than a larger size catalyst, if parallel reactors are not
employed the catalyst bed configuration must provide a diameter
which is sufficiently great that the pressure drop is held at a
level low enough to retain the advantage of the lower
hydrodesulfurization temperature possible with said catalyst.
Therefore, when utilizing a bed of small size catalyst particles of
the present invention the configuration of the bed becomes critical
if a parallel reactor system is not employed and the ratio of
diameter to depth of the bed must be sufficiently high to retain
the temperature advantage of the catalyst bed.
EXAMPLE 1
A series of tests were conducted to illustrate the temperature
advantage of a small particle size catalyst of the present
invention. These tests were conducted by employing NiCoMo on
alumina catalysts of various sizes for hydrodesulfurizing a 36
percent Kuwait reduced crude from which furnace oil having an
800.degree. F. TBP had been removed at a 2000 p.s.i.a. partial
pressure of hydrogen and a space velocity of 3.0 liquid volumes per
hour per volume of catalyst. The charge was 78 percent desulfurized
to a 1.0 percent product sulfur content. The arrangement of the
reactor was such that there was no significant or readily
detectable pressure drop in any of the tests. FIG. 1 shows the
effect of catalyst size upon the initial temperature required to
produce a product containing 1 percent sulfur. The solid line is
based upon initial temperatures determined in tests with 1/8 inch
and 1/16 inch diameter extrudate catalyst whose particle size is
above the range of this invention. The dashed extrapolation of the
solid line indicates that a 1/32 inch diameter extrudate catalyst
would be expected to require an initial temperature of about
775.degree. F. However, FIG. 1 surprisingly shows that the 1/32
inch diameter extrudate catalyst requires an initial temperature of
only 750.degree. F. It is noted that the surface area defined by
the pores of all three catalysts tested is about the same. The
position of the data point for the 1/32 inch catalyst is highly
surprising because if the dashed line in FIG. 1 were curved
downwardly towards the 1/32 inch catalyst data point the resulting
curve would tend to indicate that as catalyst particle size becomes
very small the activity of the catalyst becomes unlimited, which is
obviously unreasonable. Therefore, the straight configuration of
the dashed extension of the curve in FIG. 1 is a reasonable
extrapolation of the solid line and the position of the 1/32 inch
data point is highly unexpected.
EXAMPLE 2
When catalysts similar to the 1/32 inch catalyst of Example 1
except that the particle size is smaller within the range of this
invention, such as 1/34 or 1/40 inch, or except that the particle
size is larger within the range of this invention, such as 1/29 or
1/20 inch, are utilized under the conditions of Example 1, the
initial temperature in each instance to achieve
hydrodesulfurization to one percent sulfur is at about the same
level as that shown in FIG. 1 for the 1/32 inch catalyst.
EXAMPLE 3
When catalyst compositions other than NiCoMo on alumina, such as
NiCoMo on silica alumina, CoMo on alumina, NiW on alumina, NiW on
silica alumina, NiW on silica magnesia or NiMo on alumina having a
particle size within the range of this invention are utilized under
the conditions of Example 1 to achieve hydrodesulfurization to one
percent sulfur, a similar unexpected temperature advantage is
realized as compared to the extrapolated temperature based on
larger size particles of the same composition.
EXAMPLE 4
Tests were made which demonstrate that a 1/32 inch
nickel-cobalt-molybdenum on alumina extrudate is not only capable
of hydrodesulfurizing a reduced crude oil to a one percent sulfur
level at a considerably lower initial temperature than a similar
catalyst in the form of a 1/16 inch extrudate but also is capable
of maintaining a lower hydrodesulfurization temperature with age.
The tests with the 1/32 inch catalyst were based on a 0.55 liquid
hourly space velocity and a hydrogen partial pressure of 1830
pounds per square inch. The reactor pressure drop was about 50
pounds per square inch. The charge was a 50 percent Kuwait reduced
crude. The reaction was performed in a single reactor having three
separate beds and recycle hydrogen gas was used as a quench after
each bed. There was no separate guard chamber before the reactor.
The first, second and third beds contained 13.3 percent, 41.6
percent and 45.1 percent of the total catalyst, respectively.
Typical data for the test utilizing the 1/32 inch catalyst are
shown below and the general data is illustrated in FIGS. 5 and 6.
FIG. 5 shows the aging characteristics for the entire 1/32 inch
catalyst reactor as compared with a comparable aging run with a
1/16 inch catalyst reactor. FIG. 6 shows the aging characteristics
for the individual beds within the 1/32 inch reactor and shows that
when the first bed becomes deactivated the second bed assumes a
greater desulfurization load.
The test utilizing the 1/16 inch nickel-cobalt-molybdenum on
alumina catalyst was performed at a 1.1 liquid hourly space
velocity, but is illustrated in FIG. 5 on a basis comparable to the
0.55 space velocity of the test made with the 1/32 inch catalyst.
The total pressure for the 1/16 inch catalyst test was 2500 pounds
per square inch gauge. 5000 s.c.f./bbl. of gas was charged to the
reactor. The reactor contained four catalyst beds and recycle gas
was used as a quench after each bed. The average reactor
temperature was increased throughout the test to maintain a 1.0
percent by weight sulfur level in the 660.degree. F.+ residual
product. Typical data for both the 1/32 and the 1/16 inch catalyst
tests are shown below.
______________________________________ 1/32 inch 1/16 inch catalyst
catalyst ______________________________________ Oil charge .sup.(1)
.sup.(1) Catalyst .sup.(2) .sup.(3) Volume, cc 2,294 2,254 Weight,
gram 1,543.0 1,764,0 Age, days this measurement 97.6 87.6 Total
throughput, volume oil per volume catalyst 1,293 2,323 Operating
conditions: Reactor bed temp., .degree. F. (Inlet, Outlet) 694,716
-- Reactor pressure 2,050 2,519 Avg. reactor temp., .degree. F. 703
784 Space velocity: Vol/hr./vol 0.54 1.11 wt/hr./wt. 0.78 1.26
Reactor Gas Charge: S.c.f./bbl 4,385 4,969 Percent H.sub.2 91 81
Makeup Gas: S.c.f./bbl 890 735 Percent H.sub.2 93 96 Recycle Gas:
S.c.f./bbl 3,495 4,233 Percent H.sub.2 89 80 Product yields, wt.
percent: Bottoms (680 .degree. F. +) 91.1 84.7 Furnace oil
(380-680.degree. F.) 4.9 9.4 Naphtha (B.P. 380.degree. F.) 0.8 2.2
Gas 5.4 5.4 Chemical hydrogen consumption, s.c.f./bbl 476 617
Hydrogen sulfide, s.c.f./bbl 139 127
______________________________________ .sup.1 Kuwait 50 percent
reduced crude. .sup.2 1/32 inch diameter NiCoM on alumina
extrudates having 0.5 wt. percent nickel, 1.0 wt. percent cobalt
and 8.0 wt. percent molybdenum, a surface area of 200 m..sup.1 /g.
and a pore volume of 0.5 cc./g. .sup.3 1/16 inch diameter NiCoMo on
alumina extrudates.
The charge and product inspections for the test employing the 1/32
inch catalyst are as follows:
______________________________________ Product Charge bottoms
______________________________________ Gravity, .degree. API 14.6
20.1 Sulfur, percent by wt 4.07 1.03 Nitrogen, percent by wt 0.23
0.17 Carbon residue, percent by wt 8.59 4.97 Nickel, p.p.m. 16 5.1
Vanadium, p.p.m. 55 9.3 Heat of comb. B.t.u./lb 18,360 19,094
Distillation, vacuum, .degree. F.: At 10% 715 716 At 30% 809 807 At
50% 918 At 60% 982 ______________________________________ Note-
Charge, cracked at 995.
The 660.degree. F.+ residual oil product inspections for the 1/16
inch catalyst test are as follows:
______________________________________ Gravity, .degree. API 21.4
Sulfur, percent 1.08 Nitrogen, percent 0.17 Pour point, D97,
.degree. F. 65 Viscosity kin. D445, cs.: 122.degree. F. 104.9
210.degree. F. 16.36 Carbon residue, rams. D524, percent by wt.
4.86 Vanadium, p.p.m. 14 Nickel, p.p.m. 6.8 Flash point, D93,
.degree. F. 390 Distillation vacuum, D1160 10% at 719.degree. F.
30% at 788.degree. F. 50% at 874.degree. F. 70% at 1010.degree. F.
90% at -- ______________________________________
EXAMPLE 5
Tests were made to show the effect of temperature upon liquid yield
in a hydrodesulfurization process. The tests were made in a pilot
plant equipped with a four-bed 2254 cc. adiabatic reactor. Reactor
charge gas was used as quench between the catalyst beds for
temperature control. The charge stock passed through a cotton fiber
cartridge filter before it was preheated and charged to the
reactor. The filter which was at steam tracing temperature takes
out most of any solid contaminants in the feed, but does very
little in removing any small or organically combined metals present
in the charge stock.
The reactor effluent flowed into a high pressure separator where
hydrogen-rich gas was separated from the hydrocarbon liquid. The
hydrogen-rich gas was scrubbed with 3 percent to 5 percent
diethanolamine and water and recycled to the reactor. After high
pressure separation of high pressure hydrogen-containing gas, the
liquid product flowed to distillation towers where gases, naphtha,
furnace oil, and residual were removed from the unit.
The charge to the unit was a 50 percent Kuwait reduced crude. The
operation was designed to produce a 660.degree. F.+ product having
a 1.0 percent sulfur level. The catalyst was 1/16 inch extruded
NiCoMo on alumina. The operating conditions were 2500 pounds per
square inch gauge total pressure, 1.1 liquid hourly space velocity
and 5000 s.c.f./bbl. of 80 percent hydrogen with recycle gas quench
as required for temperature control. The results of the tests are
illustrated in FIG. 4 and in the following data.
______________________________________ CATALYST-NiCoMo ON ALUMINA
HAVING 0.97 WEIGHT PERCENT COBALT, 8.6 WEIGHT PERCENT MOLYB- DENUM
AND 0.59 WEIGHT PERCENT NICKEL
______________________________________ Age: Days at this
measurement 45.9 Bbl./lb. 4.43 Space velocity, LHSV 1.1 Average
reactor temp., .degree. F. 760 Reactor gas: Inlet: S.c.f./bbl.
5,008 Percent H.sub.2 82 Quench: S.c.f./bbl. 2,920 Percent H.sub.2
82 Reactor pressure, p.s.i.g. 2,500 Hydrogen consumption,
s.c.f./bbl. 623 Product yields: Percent by weight
______________________________________ H.sub.2 S 3.4 C.sub.1 0.2
C.sub.2 0.1 C.sub.3 0.2 C.sub.4 0.2 C.sub.5 -380.degree. F. 1.5
380-460.degree. F. 1.4 460-600.degree. F. 2.8 600-660.degree. F.
2.5 660.degree. F. + 88.6
______________________________________
EXAMPLE 6
Tests were conducted to illustrate the effect of a change in
hydrogen partial pressure upon the temperature required to
hydrodesulfurize a reduced crude to 1 percent sulfur in the
residual product. The comparative tests were performed by, in one
case, not recycling hydrogen containing light hydrocarbons which
build up in the hydrogen stream and reduce the partial pressure of
the hydrogen in the stream but instead charging to the
hydrodesulfurizer only fresh hydrogen charge having a uniform
hydrogen purity. In the other case, a recycle hydrogen stream which
was not subjected to naphtha scrubbing to remove light hydrocarbons
so that the hydrogen partial pressure therein continually decreased
throughout the test was recycled to the hydrodesulfurizer. The
reactor system catalyst and operating conditions for both tests are
generally the same as that described in the tests of Example 4. The
results are illustrated in FIG. 3. The solid line in FIG. 3
represents the test utilizing only fresh hydrogen at 1830-1850
pounds per square inch of hydrogen pressure. The broken line in
FIG. 3 represents the test wherein non-naphtha scrubbed recycle gas
is recycled causing hydrogen partial pressure to continually
decrease so that at the last data point shown the hydrogen partial
pressure was 1720-1740 pounds per square inch. The following data
are representative of the test represented by the broken line.
______________________________________ Oil charge, percent Kuwait
reduced crude 50 Catalyst, inch NiCoMo on alumina 1/32 Volume, cc.
2,296 Weight, grams 1,771 Age, days at time of this measurement 7.2
Throughput, vol. oil per vol. cat. 96 Reactor bed temp., .degree.
F. (inlet, outlet) 668,690 Operating conditons: Reactor pressure,
p.s.i.g. 2,058 Avg. reactor temp., .degree. F. 676 Space velocity:
Vol./hr./vol. 0.53 Wt./hr./wt. 0.66 Reactor gas charge: S.c.f./bbl.
4,462 Percent H.sub.2 88 Makeup gas: S.c.f./bbl. 587 Percent
H.sub.2 94 Recycle gas: S.c.f./bbl. 3,874 Percent H.sub.2 85
Product yields, wt. percent: Stripper bottoms 92.5 Furnace oil 4.7
Naphtha 0.6 Gas 3.7 Net hydrogen sulfide, s.c.f./bbl. 108
______________________________________
______________________________________ Product Charge stripper oil
bottoms ______________________________________ Gravity, .degree.
API 15.7 20.6 Viscosity, SUS D2161: 100.degree. F. 4,906 2,181
210.degree. F. 171.8 114.8 Carbon, wt. percent 84.52 85.52
Hydrogen, wt. percent 11.43 11.68 Nitrogen, wt. percent 0.20 0.17
Sulfur, wt. percent 4.06 1.11 Carbon residue, wt. percent 8.16 5.12
Nickel, p.p.m. 16 4.7 Vanadium, p.p.m. 54 6.1 Heat of Combustion,
B.t.u./lb 18,423 19,908 Distillation, vacuum, .degree. F.: At 5%
608 654 At 10% 674 682 At 20% 762 750 At 30% 829 807 At 40% 866 At
50% 925 At 60% 992 ______________________________________ NOTE.
Charged oil, cracked at 888. Product stripper bottoms, cracked at
1,011.
The above data state that the space velocity is 0.53 vol./hr./vol.
so that after 10 days (240 hours) the throughput is 0.53.times.240
or 127 vol./vol. FIG. 3 shows that at the 10 day data point the bed
outlet temperature is higher for the decreasing hydrogen pressure
test as compared to the constant hydrogen pressure test.
EXAMPLE 7
Simulation experiments were conducted to show the effect of
catalyst particle size on pressure drop in hydrodesulfurization
process in reactors of various diameters. All tests were made with
the same liquid hourly space velocity in a single bed reactor,
charging a 75 percent reduced Kuwait crude, using recycle hydrogen
and maintaining a hydrogen purity of 77 percent, using reactor
inlet and outlet temperatures of 780 and 815.degree. F.,
respectively, a reactor inlet pressure of 2500 p.s.i.g., and a 1.0
liquid hourly space velocity. Three series of tests were made
utilizing reactors of various diameters with 1/12 inch, 1/16 inch
and 1/32 inch NiCoMo on alumina catalyst particles. The results are
illustrated in FIG. 2.
The following description of the process of this invention is made
in reference to FIGS. 7a and 7b. FIGS. 7a and 7b themselves
indicate suitable temperature and pressure conditions at various
points in the process, and these indicated conditions are not
reiterated in the following description.
Referring to FIGS. 7a and 7b, a full crude or a reduced crude, such
as a 50 percent reduced Kuwait crude which contains the entire
asphaltene content of the full crude and therefore also contains
substantially all of the nickel, vanadium and sulfur content of the
full crude, is charged to the process through line 10 and is pumped
by pump 12 through line 14, preheater 16, line 18, solids filter 20
and line 22 to drum 24. From drum 24 the liquid oil charge is
passed through line 26 to two substantially identical reactor
systems in parallel through lines 28 and 208, respectively.
Although two parallel reactor systems are shown, three, four, five
or more parallel reactor systems could be employed.
In the parallel reactor systems, equal portions of the liquid
charge entering through line 10 are pumped by pumps 30 and 300, are
admixed with hydrogen from lines 52 and 502, and passed through
lines 32 and 302, valves 34 and 304, preheaters 36 and 306, lines
38 and 308 and furnaces 40 and 400. Liquid flow valves 34 and 304
are both disposed in a nonfully preheated liquid hydrocarbon line
but no valves are utilized in any fully preheated liquid
hydrocarbon lines because at the reaction temperatures of this
invention if any hydrocarbon should descend into any indentation or
crevice of a valve and become stagnant therein for even a brief
period without full exposure to hydrogen, coking would occur and
render the valve inoperative. Therefore, there is no other valve in
any liquid line in the vicinity of the reactor until the hot
reactor liquid has been cooled downstream from the reactor, as will
be shown subsequently.
A mixture of fresh and recycle hydrogen is introduced into the
liquid charge to each reactor prior to preheating thereof. Recycle
hydrogen is admitted to the liquid charge through lines 42 and 402
and valves 44 and 404. Makeup hydrogen is charged through lines 46
and 406, compressors 48 and 408 and valves 50 and 500. A mixture of
fresh and recycle hydrogen is introduced to the relatively cool
liquid charge through lines 52 and 502.
The preheated mixture of liquid charge and hydrogen is charged
through lines 54 and 504, to guard reactors 56 and 506, each
containing a bed of catalyst 58 and 508. Effluent streams from the
guard reactor are charged to maintain reactors 60 and 600
containing catalyst beds 62, 64, 66 and 602, 604, and 606,
respectively. The catalyst beds each contain NiCoMo on alumina
catalyst as 1/32 inch extrudates which have the following typical
specifications:
Surface area--150 meters .sup.2 /gram
Pore volume in 50-300 A. radius--60% to 90% of total pore
volume
Pore volume--0.5 to 0.8 cc./gram
Compacted density--0.45 to 0.65 gram/cc.
Specific volume of pores--30-40 cc./100 cc.
In each reactor train, each succeeding catalyst bed has a larger
volume than the bed just prior to it. If desired there can be four,
five, six or more catalyst beds in each reactor. Also, if desired,
each reactor bed can have 25 percent, 50 percent, 100 percent, or
more, catalyst than the bed just prior to it.
If desired, guard chambers 56 and 506 can be omitted in which case
line 54 will lead directly into reactor 60 and line 504 will lead
directly into reactor 600.
The effluent from the guard reactors is charged through lines 68
and 608 to which temperature quenching hydrogen stream are charged
through lines 70 and 700 and valves 72 and 702 so that a quenched
hydrocarbon and hydrogen stream is charged to the top of each
reactor through lines 74 and 704. The reaction stream is passed
through catalyst beds 62 and 602 and due to the exothermic nature
of the hydrodesulfurization reaction it is heated in passage
therethrough and is quenched by recycle hydrogen entering through
lines 76 and 706, valves 78 and 708, and spargers 80 and 800. The
cooled reaction stream is then passed through catalyst beds 64 and
604 wherein they increase in temperature so that they are then
cooled by a quenching hydrogen stream entering through lines 82 and
802, valves 84 and 804, and spargers 86 and 806. Temperatures
between the various catalyst beds are controlled by regulating the
valves in the various hydrogen quench lines to apportion hydrogen
recycle flow. Finally, the reaction mixture passes through catalyst
beds 66 and 606 and then leaves each reactor in a desulfurized
condition through lines 88 and 808. The separate reactor effluent
streams then give up some heat at charge preheaters 36 and 306 and
pass through lines 90 and 900 to air coolers 92 and 902 where the
effluent is sufficiently cooled so that the valves 94 and 904 can
be utilized. Because they are disposed after the air coolers,
valves 94 and 904 are the first valves in a liquid-containing line
downstream from the reactors which can be employed without the
danger of coking therein rendering the valves inoperative. The
final stage in the separate parallel reactor trains is flash
chambers 96 and 906 whence desulfurized liquid is discharged
through lines 98 and 908 to a common header 100 which enters
distillation column 102. Gaseous streams comprising primarily
hydrogen together with ammonia and hydrogen sulfide formed by
nitrogen and sulfur removal from the charge and light hydrocarbons
formed by thermal hydrocracking of some of the charge is discharged
from flash chambers 96 and 906 through lines 99 and 909 which merge
into common header 104.
The gaseous effluent stream passes through unit 106 to which water
is added through line 108 and from which aqueous ammonia is removed
through line 110. The gaseous effluent from unit 106 is passed
through line 112 to light hydrocarbon wash unit 114 to which
naphtha from distillation column 102 is pumped in order to wash
light hydrocarbons from the hydrogen stream. The wash naphtha is
removed through line 116 and passed to flash chamber 118 where some
of the dissolved hydrocarbons are flashed off through line 120.
Then the naphtha is passed through line 122, heater 124 and hot
naphtha flash chamber 126 from which additional light hydrocarbons
are flashed through line 128. The regenerated naphtha is recycled
through line 130 with makeup naphtha entering through line 132.
The hydrogen stream is then passed through line 134 to hydrogen
sulfide removed unit 136 to which an amine such as monoethanolamine
is added through line 138. Hydrogen sulfide-rich amine is removed
through line 140 and passed to amine regenerator 142 from which
hydrogen sulfide is discharged through line 144 and recycle amine
exits through line 146. Makeup amine is charged through line 148. A
recycle hydrogen stream is then returned to the reactors through
line 150.
It is important to remove a substantial amount of the ammonia,
hydrogen sulfide and light hydrocarbons from the hydrogen stream
prior to recycle because these gases reduce the partial pressure of
hydrogen in the reactor. It is the partial pressure of hydrogen
rather than the total pressure in the reactor which affects
hydrodesulfurization activity. It is not possible to arbitrarily
increase total hydrogen pressure in the reactors to compensate for
a low hydrogen partial pressure because of severe design pressure
limitations in the reactor, as explained above. The recycle
hydrogen is about equally apportioned to the two parallel reactors
through lines 152 and 1052 which lead to compressors 154 and 1054
for increasing the pressure of the hydrogen stream to the
reactor.
Hydrodesulfurized residual oil is removed from distillation column
102 through line 156 and is used to supply heat to inlet crude oil
heat exchanger 16 prior to its discharge from the system through
line 158. Hydrodesulfurized furnace oil is removed from the
distillation column through line 160 while naphtha product is
removed from the system through line 162.
FIG. 8 is a cutaway segment of a multibed reactor in which the
lower two catalyst beds are shown. FIG. 8 shows that a bed of the
small size catalyst of the present invention is prepared in a
manner to secure the particles from excessive relative movement and
to prevent the particles from producing fines and plugging screens,
both of which conditions would greatly increase the pressure drop
in the reactor and tend to further nullify the temperature
advantage of the small size catalyst particles.
FIG. 8 shows a steel reactor wall 1000 which may be 7 to 10 inches
thick. One bed of catalyst lies above hydrogen quench line 1002 and
another catalyst bed lies below this line, each bed filling the
entire cross-section of the reactor. The greatest volume of the
upper bed comprises 1/32 inch catalyst bed 1004 which rests upon a
smaller bed of 1/12 inch catalyst 1005 and 1/4 inch aluminum balls
1006 which in turn rests upon a bed of 1/2 inch aluminum balls
1008. Beds 1005, 1006, and 1008 prevent the 1/32 inch catalyst
particles from surrounding and plugging the sparger openings of
hydrogen quench line 1002. Above catalyst bed 1004 is a bed 1010 of
1/4 inch aluminum balls and a bed 1012 of 1/2 inch aluminum balls.
These latter two beds contribute stabilizing weight to the 1/32
inch catalyst bed to prevent shifting of particles therein during
flow of reactants, which shifting would tend to cause catalyst
disintegration and fines formation and thereby greatly enhance
pressure drop through the 1/32 inch bed.
The lower bed of catalyst rests upon screen 1014. Screen 1014 is
protected from plugging by 1/32 inch catalyst bed 1016 by a gradual
increase in particle size between it and the 1/32 inch catalyst bed
as indicated by 1/12 inch catalyst bed 1018, 1/4 inch aluminum
balls bed 1020 and 1/2 inch aluminum balls bed 1022. Proper
distribution of hydrogen and liquid reactant as they approach lower
catalyst bed 1016 is insured by bed 1024 of 1/4 inch aluminum balls
and bed 1026 of 1/2 inch aluminum balls.
FIG. 8 shows that an elaborate arrangement is required in preparing
a catalyst bed of the present invention in order that nearly all
the pressure drop through the bed can be confined to the 1/32 inch
catalyst beds themselves with very little pressure drop at
retaining screens and with a minimum of pressure increase occurring
due to fines formation during the reaction.
* * * * *