U.S. patent number 3,658,681 [Application Number 05/013,401] was granted by the patent office on 1972-04-25 for production of low sulfur fuel oil.
This patent grant is currently assigned to Texaco, Inc.. Invention is credited to Frank E. Guptill, Jr., Reese A. Peck, Raymond F. Wilson.
United States Patent |
3,658,681 |
Wilson , et al. |
April 25, 1972 |
PRODUCTION OF LOW SULFUR FUEL OIL
Abstract
Low sulfur fuel oil is prepared by distilling an
asphalt-containing petroleum fraction to obtain a vacuum gas oil
and vacuum residuum. The vacuum gas oil is passed downwardly with
hydrogen through an upper bed of desulfurization catalyst; the
residuum fraction is passed upwardly through one or more lower beds
of desulfurization catalyst, and the desulfurized effluents are
combined. It is found advantageous to pass the distilled fraction
down through the desulfurization zone with less residence time and
the residual fraction up through the zone to subject it to more
back-mixing and turbulence and thereby effecting a longer residence
time.
Inventors: |
Wilson; Raymond F. (Fishkill,
NY), Peck; Reese A. (Fishkill, NY), Guptill, Jr.; Frank
E. (Fishkill, NY) |
Assignee: |
Texaco, Inc. (New York,
NY)
|
Family
ID: |
21759777 |
Appl.
No.: |
05/013,401 |
Filed: |
February 24, 1970 |
Current U.S.
Class: |
208/211;
208/216PP; 208/216R; 208/218 |
Current CPC
Class: |
C10G
45/02 (20130101); C10G 65/16 (20130101) |
Current International
Class: |
C10G
45/02 (20060101); C10G 65/00 (20060101); C10G
65/16 (20060101); C10g 023/02 () |
Field of
Search: |
;208/211,218,209,213,216,217,210,89,59 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: Crasanakis; G. J.
Claims
We claim:
1. A process for the production of fuel oil of reduced sulfur
content which comprises subjecting an asphalt-containing petroleum
fraction to distillation to produce a vacuum gas oil and a vacuum
residuum, introducing said vacuum gas oil into a desulfurization
zone containing a series of catalyst beds comprising an upper bed
and at least one lower bed, each of said beds in said series
comprising a Group VI-B metal or compound thereof and a Group VIII
metal or compound thereof supported on an inert refractory
inorganic oxide, said vacuum gas oil passing downwardly with
hydrogen through said upper bed at a temperature between
400.degree. and 900.degree.F. a pressure between 200 and 5,000
psig, a space velocity between 0.2 and 5.0 v/v/hr. and a hydrogen
rate between 1,000 and 20,000 SCFB, introducing said vacuum
residuum into said desulfurization zone to flow upwardly with
hydrogen through said at least one lower catalyst bed at a
temperature between 400.degree. and 900.degree.F., a pressure
between 200 and 5,000 psig, a space velocity between 0.2 and 5.0
v/v/hr. and a hydrogen rate between 1,000 and 20,000 SCFB.
combining the effluents from said catalyst beds and recovering a
fuel oil of reduced sulfur content from said combined stream.
2. The process of claim 1 in which the asphalt containing petroleum
fraction is an atmospheric reduced crude.
3. The process of claim 1 in which the space velocity for the
desulfurization of the gas 0:1 fraction is about three times that
for the desulfurization of the residual fraction.
4. The process of claim 1 in which additional hydrogen at a
temperature below the desulfurization temperature is introduced
between catalyst beds when said vacuum residuum passes upwardly
with hydrogen through more than one catalyst bed.
5. The process of claim 1 in which the catalysts are in the form of
fixed beds of pellets.
6. The process of claim 1 in which the catalyst in said at least
one lower catalyst bed has an alumina-silica support with a surface
area of at least 250 m.sup.2 /g, a pore volume of at least 0.5 cc/g
and an average pore diameter between 50 and 100 A.
7. The process of claim 1 in which the space velocity of the
residual fraction through said at least one lower catalyst bed is
lower than the space velocity of the distillate fraction through
said upper bed.
8. The process of claim 1 in which the catalysts in both the upper
and said at lease one lower catalyst bed have the same composition
and physical characteristics.
Description
This invention relates to the production of fuel oils of low sulfur
content. More particularly, it is concerned with a method for the
conversion of heavy petroleum hydrocarbon fractions such as
atmospheric reduced crude into a fuel oil having a sulfur content
of less than 1 percent. In one of its more specific embodiments it
is concerned with a flexible process for the production of large
volumes of low sulfur fuel oil when the demand is greater and
reduced amounts of fuel oil when the demand is lesser.
In the refining of petroleum, the hydrodesulfurization of various
fractions to reduce the sulfur content thereof is well known and
many refineries have units designed particularly for this purpose.
However, the demand for different petroleum products varies with
the season. For example, in the summer months when pleasure travel
is at its peak, there is a great demand for gasoline whereas in the
winter months when the weather is not conducive to travel there is
considerably less need for gasoline but there is a far greater
demand for fuel oil, particularly for domestic heating purposes.
The fluctuation in demand for industrial fuel oil is much less.
When a particular unit is installed in a refinery, it is most
advisable for economical purposes to operate the unit at capacity.
However, it is impractical to produce a product in excess of the
demand therefor. It would be advantageous to produce various
products in amounts corresponding to the demands changing with the
seasons of the year. Accordingly, it is an object of this invention
to provide a process whereby large volumes of low sulfur fuel oil
can be produced when the demand is greater and smaller volumes are
produced when the demand is lower. Similarly, the process is
adapted to supply larger volumes of feedstock for catalytic
cracking units when the demand for gasoline is greater.
According to our invention, there is provided a process for the
production of fuel oil of reduced sulfur content which comprises
subjecting an asphalt-containing petroleum fraction to distillation
to produce a distillate fraction and a residual fraction, passing
said distillate fraction in admixture with hydrogen downwardly
through a first bed of desulfurization catalyst under
desulfurization conditions, passing said residual fraction in
admixture with hydrogen upwardly through a second bed of
desulfurization catalyst under desulfurization conditions including
a space velocity lower than that for the desulfurization of said
distillate fraction and combining the desulfurized distillate and
residual fractions.
Our process may be more readily understood by reference to the
accompanying drawing which shows diagrammatically a flow scheme for
the practice of one embodiment of the invention. For simplicity,
various pieces of equipment such as pumps, heaters, compressors,
coolers and the like have been omitted from the drawing.
The charge, preferably an atmospheric reduced crude, is introduced
into the system through line 11 and charged to vacuum still 12
wherein it is separated into a vacuum gas oil removed through line
13 and a residual fraction removed through line 14. With valve 51
closed, the vacuum gas oil passes through open valve 50 in line 15
into desulfurization unit 16 where with hydrogen from line 17 it
passes downwardly through a fixed bed of desulfurization catalyst
in the upper section of desulfurization unit 16. The residual
fraction from line 14 with hydrogen from line 18 is introduced into
the bottom of desulfurization unit 16 where it passes upwardly
through catalyst in the lower section of the reactor and the
reactant streams merge and pass through open valve 53 in line 20
through which the mixed reactant stream passes to high pressure
separator 22.
A hydrogen rich stream is removed from high pressure separator 22
through line 24 and is introduced into scrubber 26 where H.sub.2 S
and NH.sub.3 are removed by contact with solvents such as water and
diethanolamine. The purified hydrogen is recycled to the system
through line 17 with make-up hydrogen being introduced into the
system through line 30. The combined desulfurized stream is
withdrawn from high pressure separator 22 through line 32 and sent
to low pressure separator 33 from which a normally gaseous stream
is removed through line 34, the liquid effluent being transferred
through line 35 to still 36 from which a low molecular weight
hydrocarbon stream is removed through line 37, a naphtha stream
through line 38, a light gas oil stream through line 39 and a
product fuel oil stream through line 40.
In a specific embodiment the lower catalyst bed in desulfurization
unit 16 is separated into sections. To assist in temperature
control, hydrogen for cooling purposes is introduced into the lower
bed from line 18 through lines 21 and 23.
The above description presents the method for maximum fuel oil
production. When it is desired to reduce the volume of residual
fuel oil and increase the gasoline production, valve 50 in line 15
is closed and valve 51 in line 13 is opened and the vacuum gas oil
recovered from vacuum still 12 is sent to catalytic cracking for
conversion to gasoline. In the meantime valve 53 in line 20
connecting desulfurization unit 16 with high pressure separator 22
is closed and valve 54 in line 55 is opened thereby permitting
residual fraction from vacuum still 12 to pass upwardly through the
entire catalytic bed system of desulfurization unit 16 and then
pass on through lines 55 and 20 to high pressure seperator 22. In
this way only the residual fraction is processed into low sulfur
fuel oil and the vacuum gas oil is converted to gasoline in a
catalytic cracking unit, not shown. Valve 59 in line 19 may be
opened to permit the introduction of additional cooling
hydrogen.
The charge to our process may be any petroleum fraction containing
asphaltic materials. However preferably the charge is an
atmospheric reduced crude, that is, a fraction from which all
materials volatile at atmospheric pressure and a temperature up to
about 650.degree. F. have been removed.
Hydrogen used in the process of our invention need not be pure.
Hydrogen of at least 60 percent purity is satisfactory with
hydrogen having a purity of between about 70 and 95 percent being
preferred. Hydrogen obtained as a by-product from the catalytic
reforming of naphtha, by the partial oxidation of carbonaceous
material followed by shift conversion and CO.sub.2 removal or
electrolytic hydrogen are satisfactory for the purposes of this
invention.
The desulfurization unit contains two catalyst beds, an upper and a
lower bed. In the drawing the lower bed is depicted as having three
sections but the invention is not limited thereto. In this
specification and the appended claims, the lower bed through which
the residual fraction passes is considered to be a single bed
although as shown it may contain several sections.
The catalysts used in the upper and lower beds may be the same or
different. In a preferred embodiment, catalysts having the same
composition and physical characteristics are used in both beds.
They are composed of a hydrogenating component supported on an
inert base. Suitable hydrogenating components comprise Group VIII
metals and compounds thereof such as oxides and sulfides used alone
or in conjunction with a Group VI metal or compound thereof such as
the oxide or sulfide. Particularly suitable catalysts are those
containing nickel and molybdenum, nickel and tungsten, cobalt and
molybdenum or nickel, cobalt and molybdenum. The Group VIII metal
should be present in an amount between about 2 and 20 percent,
preferably 3-10 percent and the group VI metal in an amount between
about 5 and 40 percent, preferably 7-30 percent. The hydrogenating
component preferably is supported on an inert refractory oxide such
as silica, alumina, chromia, magnesia and mixtures thereof. The
catalyst used in the lower bed should have a surface area of at
least 250 m.sup.2 /g, a pore volume of 0.4-1.0 cc/g, an average
pore diameter between 50 and 100 A. and at least 2 percent silica.
Catalysts having these characteristics have been found to be
superior both in activity and in life for the desulfurization of
asphalt containing hydrocarbon fractions.
Broadly, the reaction conditions for the desulfurization of the
different fractions are the same. Temperatures may range between
about 400.degree. and 900.degree. F., pressures between 200 and
5,000 psig, space velocity in volumes of oil per volume of catalyst
per hour between 0.2 and 5 with hydrogen rates of 1,000-20,000 SCFB
(standard cubic feet per barrel of feed). For the desulfurization
of the vacuum gas oil preferred conditions are temperatures of
600.degree.-800.degree. F., pressures of 500-2,000 psig, space
velocities of 0.5-3.0 v/v/hr. and hydrogen rates of 3,000 to 10,000
SCFB. For the desulfurization of the residual fraction preferred
conditions are temperatures of 650.degree.-850.degree.F., pressures
of 500-2,500 psig, space velocities of 0.50 to 2.0 and hydrogen
rates of 3,000 to 15,000 SCFB.
By operating the desulfurization unit in the manner of our
invention, advantage is taken of the fact that it is better to
desulfurize the vacuum gas oil downflow while it is in the vapor
phase and the residual fraction upflow in the liquid phase. Since
the gas oil has a lower sulfur content than the residual fraction,
by contacting it in vapor phase with the catalyst there is less
turbulence and less residence time and therefore not too much
cracking takes place while effecting adequate desulfurization. On
the other hand, by flowing the residual fraction upwardly through
the catalyst bed, it is subjected to more back-mixing and
turbulence thereby in effect having a longer residence time which
is desirable as it has a higher sulfur content.
EXAMPLE
In this example, the charge, an atmospheric reduced Arabian crude,
is distilled to yield a vacuum gas oil and a vacuum residuum.
Characteristics of the charge and distillation products are
tabulated below:
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TABLE 1
Charge Gas Oil Residuum
__________________________________________________________________________
Yield, vol. % -- 55.0 45.0 Yield, wt. % -- 53.4 46.6 Gravity,
.degree.API 15.4 19.8 10.4 Sulfur, wt. % 3.1 2.4 3.7 CCR*, wt. %
10.9 -- 23.4 Pour Point, .degree.F. 40 85 110 Distillation, vol. %.
IBP-650.degree. F. 0.8 1.4 -- 650-1,000.degree. F. 54.5 98.6 9.7
1000.degree. F.+ 44.7 -- 90.3
__________________________________________________________________________
With 2,000 SCFB hydrogen (85 percent purity), the gas oil is passed
downwardly through a bed of pelletized catalyst composed of 3.2
percent nickel and 18 percent molybdenum in the oxide form
supported on alumina. The catalyst has a surface area of 178
m.sup.2 /g, a pore volume of 0.46 cc/g and an average pore diameter
of 103.2 A. Reaction conditions are 700.degree.F., 1,500 psig exit
hydrogen partial pressure and a space velocity of 1.5 v/v/hr.
The vacuum residuum with 5,000 SCFB hydrogen (85 percent purity) is
passed upwardly through a bed of pelletized catalyst composed of
3.3 percent cobalt and 14.0 percent molybdenum in oxide form, 3.3
percent silica and the balance alumina. The one-sixteenth inch
extruded catalyst has a surface area of 257 m.sup.2 /g, a pore
volume of 0.56 cc/g, and an average pore diameter of 87.2 A.
Reaction conditions are a temperature of 725.degree.F., an exit
hydrogen partial pressure of 1,500 psig and a space velocity of 0.5
v/v/hr. A 97 wt. percent yield based on the original charge is
obtained by combining the desulfurized gas oil with the
desulfurized residuum. The product has the following composition.
---------------------------------------------------------------------------
TABLE 2
Yield Wt. %
__________________________________________________________________________
NH.sub.3 0.1 H.sub.2 S 2.3 C.sub.1 -C.sub.3 0.3 C.sub.4 -C.sub.5
0.6 C.sub.6 -400.degree. F. 0.1 400.degree. F. + 97.0 Sulfur 0.68
__________________________________________________________________________
In this way the entire charge of atmospheric reduced crude is
converted to low sulfur fuel oil.
EXAMPLE II
In this example the gas oil obtained from the vacuum distillation
of the same atmospheric reduced Arabian crude as Example I is sent
to catalytic cracking for conversion to gasoline and the residual
fraction is passed upwardly through all of the catalyst in the
desulfurization unit. The reaction conditions are maintained the
same as in Example I except that in this case the space velocity is
now 0.33 v/v/hr. because of the larger volume of catalyst, and the
temperature is 750.degree.F. The reduced space velocity compensates
for the fact that no low sulfur gas oil is present to blend into
the residual fuel oil product. The more severe conditions of higher
temperature and lower space velocity result in a slightly greater
conversion to products boiling below 400.degree.F. but the fuel oil
product again has a sulfur content of less than 0.7 wt.
percent.
Composition of the product appears in Table 3.
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TABLE 3
Yield Wt. % NH.sub.3 0.1 H.sub.2 S 3.3 C.sub.1 -C.sub.3 1.7 C.sub.4
-C.sub.5 0.7 C.sub.6 -400.degree. F. 3.0 400.degree. F. + 93.7
Sulfur 0.62
__________________________________________________________________________
Obviously, various other modifications of the invention as
hereinbefore set forth may be made without departing from the
spirit and scope thereof, and therefore only such limitations
should be imposed as are indicated in the appended claims.
* * * * *