Note: Descriptions are shown in the official language in which they were submitted.
01 --1--
TWO-STAGE PETROLEUM RESIDUUM HYDROCONVERSION
USING A COUNTERCURRENT GAS-LIQ~ID YIRST STAGE
05
BACKGROUND OF THE INVENTION
The present invention relates to processes for
the hydroconversion of heavy hydrocarbonaceous fractions
or residua. In particular, it relates to two-stage pro-
cesses for the hydrothermal and hydrocatalytic conversionof petroleum residua.
The production of liquid products by the high
temperature and pressure hydrogenation of heavy hydro-
carbonaceous fractions or residua derived from petroleum,
; 15 oil shale, tar sands or coal is well known. The resulting
liquids, however, are often inefficiently obtained with
high consumption of hydrogen and catalyst and excess
production of lighter, normally gaseous products.
In a preferred embodiment of a two-stage process
~0 for the hydroconversion of heavy hydrocarbons, the heavy
material is first heated and subjected to a high severity
hydrothermal treatment, preferably without added catalyst
or contact materials, in the presence of hydrogen at about
400C to 480C, i.e., 750F to 900F, then the entire
effluent ~rom the first stage ~gases, liquids and solids)
may be passed directly to a catalytic,hydrocracking zone,
preferably at a temperature below 800F and lower than the
temperature in the hydrothermal zone. In a preferred
embodiment of that process, the hydrothermal zone and the
catalytic reactor are close-coupled. Residuum conversion
and distillate yield are maximized. A consequence of
higher severity hydrothermal stage operation is that more
cracked products and light gases are produced jn the
hydrothermal stage. Furthermore, the distillate species
formed in the hydrothermal stage are further hydrogenated
in the catalytic reactor, and although this improves
product quality, hydrogen consumption is higher. The hiyh
temperature hydrothermal stage produces saturated light
products which can form an unstable mixture with the
remaining heavy uncracked materials, which are thought to
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be aromatic, and other unsaturates. The heavy portion of
residuum is mostly asphaltenes which require an aromatic
n5 medium for solubilization. There may be insufficient
solvency in the bulk of the material to retain the
uncracked heavier asphaltenes in solution. The result is
phase separation and precipitation of asphaltenes which
tends to occur as the temperature is dropped between the
hydrothermal stage and the lower temperature hydrocracking
stage.
In the case of coal liquefaction with added
petroleum residuum, U.S. Patent No. 4,330,393 teaches that
the small quantities of water and Cl to C4 gases produced
in the hydrothermal stage are preferably removed before
the effluent enters the hydrocracking zone for the purpose
of increasing the hydrogen partial pressure in the hydro-
cracking stage. The physical structuring of the
hydrothermal zone in U.S. Patent No. 4,330,393 is such
2~ that the coal/residuum slurry may flow upwardly or
downwardly in said zone. In the multistage coal lique-
faction process of U.S. Patent No. 4,110,192, it has been
found advantageous to vent most of the gases from the
dissolver zone while co-currently passing hydrogen and
liquids into the dissolver zone and out of the dissolver
zone to the catalytic treatment zone.¦
In general, two-stage (hydrothermal-
hydrocracking) treatments require more hydrogen, which can
be supplied by known processes from natural gas or coal at
a price. The cost could be reduced without loss of
benefit if (i) light products which consume hydrogen in
the catalytic reactors could be separated before the
catalytic hydrocracking stage; (ii) some heavy material
rejection occurred before the catalytic stage; and
(iii) milder operating conditions were selected.
It would be advantageous i f hydrogen utilization
efficiency could be improved in two-stage residuum hydro-
conversion processes by reducing the hydrogenation of the
mid-distillate fraction of the product of the two-stage
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process. This could be accomplished if the lighter frac-
tions, optionally including mid-distillates, could be
05 continuously removed from the dissolver stage product. It
would also be advantageous if the light products, includ-
ing light saturated hydrocarbons found in the hydrothermal
staye of a two-stage residuum hydroconversion process,
could be continuously stripped away from the remaining
liquid together with water, carbon monoxide, and other
materials which cause instability and are deleterious to
the processes of the catalytic hydrocracking stage. By
this means the second stage would operate more efficiently
and the instability of the product towards asphaltene pre-
cipitation would be overcome. This, and other advantages,
are achieved by the process of the present invention.
SUMMAR~ OF THE INVENTION
A process for hydroprocessing a petroleum
residuum fraction. In a hydrothermal treating-stripping
~0 zone, ~orming a mixture comprising said petroleum residuum
fraction and hydrothermal reaction products, and simul-
taneously stripping substantial amounts of light products
from said mixture by contacting said mixture counter-
currently with a first hydrogen gas stream at elevated
temperatures. A gaseous stream comprising the light prod-
ucts is withdrawn from the hydrothermal treating-stripping
zone and a heavier effluent stream is left behind. At
least a substantial portion of the heavier effluent stream
is contacted in a reaction zone with a second hydrogen gas
stream and an externally supplied hydrocracking catalyst
under hydrocracking conditions which include a temperature
lower than the temperature of the hydrothermal treating-
stripping zone. A second effluent stream is withdrawn
from the hydrocracking zone.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a block flow diagram of suitable
flow paths for use in practicing an embodiment of the
invention.
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DETAILED DESCRIPTION OF PREFERRED
EMBODIMENTS OF THE INVENTION
05 Referring to the drawing, in a preferred
embodiment of the present invention, a heated (pumpable)
petrolaum residuum fraction enters via line 1 into the
hydrothermal treating-stripping zone 10 which it traverses
in a generally downflow manner in countercurrent contact
with added hydrogen gas entering the hydrother~al
treating-stripping zone 10 through line 5. The residuum
is heated and hydrotreated in the presence of the added
hydrogen gas, thereby forming a mixture of petroleum,
residuum and hydrothermal reaction products. The hydrogen
gas traverses zone 10 in a generally upflow manner,
thereby stripping substantial amounts of the lighter
products Erom the mixture and conveying same out of the
treating~stripping zone via line 15. The mixture from
zone 10 passes via line 20 to zone 25 where it is cooled,
if necessary, to a temperature lower than the temperature
of the hydrothermal stage and preferably up to about 85C
lower than the temperature of the hydrothermal stage.
The cooled mixture is then conveyed by line 30 to hydro-
cracking zone 35 where it is catalytically hydrocracked in
the presence of hydrogen supplied via line 40 to produce a
relatively low-viscosity liquid produ~t which may be
readily separated from any solid residue.
Referring to the drawing in detail, a petroleum
residuum fraction may be mixed with a solvent to form a
pumpable slurry or the residuum fraction may be heated by
conventional means to form a pumpable liquid. The basic
feedstock of the invention is a petroleum residuum frac-
tion, heavy oil, or hydrocarbonaceous material derived
from petroleum, coal, oil shale, tar sands, bitumen, lig-
nite, or mixtures thereof. The petroleum residua derivedfrom heavy crudes such as Maya (Mexico), Beta (Offshore
California~, Hondo (Offshore California), and Pt. Arguello
(Offshore California), are particularly preferred. ~ sol-
vent used in preparation of the feedstock may be selected
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from the various solvents known to the art, and it may be
process-derived.
o5 The process of the present invention, however,
is capable of tolerating a higher metals content in the
hydrocracking zone without prior demetalation or pretreat-
ment precautions if a small amount, up to about 5 weight
percent, of comminuted coal is slurried with the
feedstock. A substantial portion of the metals of the
crude are bound to or deposited upon the coal residue
suspended in the liquid feedstock and thus do not deposit
on the cracking catalyst.
The feedstock oil is fed or pumped through
line l to a hydrothermal treating-stripping zone lO com-
prising one or more treater-strippers wherein the oil is
heated, with added hydrogen, to a temperature i'n the range
of about 400C to 480C (750E' to 900F), preferably about
425C to 455C (800F to 850F) for a lenyth of time to
react a portion of the feedstock, thereby forming a
mixture of feedstock and hydrothermal reaction products,
including light products. Such lighter products include
acid gases, such as carbon monoxide; light saturated
hydrocarbons, such as methane, ethane and butane; and the
lighter fractions of hydrocarbonaceous oils, optionally
including those which are generally kn'ow~ as mid-
distillates, i.e., having normal boiling points up to
about 370C (700F~.
'It is preferred that the feedstock be heated to
at least 490C (750F) to obtain sufficient conversion in
the hydrothermal zone. Furthermore, it is usually
preferred that the feedstock not be heated to temperatures
above about 480C (900F) in order to prevent excessive
thermal cracking which could substantially reduce the
overall yield of normally liquid product.
The hydrothermal treating-stripping zone lO
basically comprises one or more elongated vessels,
preferably free of added external catalysts or contact
materials, which are designed so that in at least one
vessel of said zone, the feedstock flows downwardly while
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hydrogen gas flows upwardly in countercurrent contact ~ith
the heated feed, and the mixture resulting from the
~5 hydrothermal reaction. More generally, the vessel used
for continuous contacting of hydrogen gas and the feed can
be a tower filled with solid packing material, or an empty
tower into which the feed may be sprayed and through which
the gas flows, or a tower which contains a number of
bubble-cap sieve or valve-type plates, but the gas and the
feed flow in substantially countercurrent contact with
each other to obtain the greatest concentration driving
force and therefore the greatest rate of desorption, i.e.,
stripping. Design factors in this unit operation are
lS dealt with in "Chemical Engineers Handbook", Perry and
Chilton, 5th Edition, McGraw-Hill, Sections 4, 14, and 18.
The hydrothermal treating-stripping zone 10 may
comprise one or more treating vessels in which feed and
added hydrogen move countercurrently or co-currently, but
it is essential that it comprises at least one treating-
stripping vessel in which the hydrothermal product mixture
of feedstock and reaction product flows countercurrently
; to a hydrogen gas stream. The treating-stripping vessel
may be operated as a liquid-full vessel with level control
to ensure that the vessel operates with a liquid mixture
to a certain level, thereby regulating the residence time
of the mixture in the hydrothermal zone. Level control is
exemplified by Perry and Chilton, supra, Section 22. ~me
latter operating configuration is ~referred under'~conditions where
substantial backmixing is not detrimental to the process
and its products. Preferably, the treating-stripping
vessel is operated as a continuous staged reactor of the
vertical type (Perry and Chilton, supra, Section 4,
page 21) by the use of the aforementioned reactor inter-
nals. The latter operating configuration is preferred
under conditions requiring minimum backmixing.
The yield structure of prQducts obtained from
the hydrothermal treating-stripping zone 10 is improved
J
... .. .
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(i.e., less light, normally gaseous products are produced~
i~ the vessels comprising zone 10 are temperature staged
oS in series, i.e., going from a higher temperature vessel
near the inward of zone 10 at line 1 to a lower tempera-
ture vessel near the outlet of zone 10 at line 20, with
all the temperatures in zone 10 still within the afore-
mentioned range. By dropping the temperature toward the
outlet of zone 10, the mixture is not only prepared for
the lower temperature next stage in zone 25 and zone 35,
but the cracking reactions are turned down. Temperature
control along a series of vessels is easily achieved by
intermediate cooling between vessels by means of heat
exchange or guench gas injection. Similar benefits are
obtainable in a single vessel treating-stripping zone 10
by the use of the aforementioned continuous staged
reactor. With backmixing eliminated or reduced in a
staged reactor, a descending temperature profile is
2~ obtained in the treating-stripping vessel by the use oE,
for example, a downflowing preheated feedstock 1 and an
upflowing hydrogen quench gas stream 5. In an alternative
embodiment, hydrogen gas is injected into the vertically
elongated treating-stripping vessel at several positions
along the vertical length o the vessel. In yet another
embodiment, cooling stage 25 may not ~e necessary to
achieve the lower temperature necessary for hydrocracking
stage 35 within the ranges of temperatures specified when
such a temperature staged dissolving stripping zone is
used.
Depending on operating conditions, and the
aforementioned design factors which are within the
kno~ledge of those skilled in the art, the counterflowing
hydrogen gas entering through line 5 and comprising fresh
and recycle hydrogen, will strip the mixture more or less
deeply as to the amount of the light products stripped and
the normal boiling points of the light products stripped
from the mixture. It is optionally preferred that
substantial amounts of mid-distillates having normal
boiling points below about 260C (50~F) be stripped from
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the hydrothermal treating-stripping zone 10 and removed
via line 15. It is preferred that substantial amounts of
o5 all light hydrocarbons having normal boiliny points below
about 20C (70F) be stripped from the hydrothermal
treating-stripping zone 10 and removed via line 15. It is
most preferred that substantially all gases having boiling
points below about 0C (32F) be stripped from the
hydrother~al treating-stripping zone 10 and removed via
line 15. Hydrogen should be separated from the effluent
stream 15 for recycle to the process. The light
hydrocarbon products in the effluent stream should be
fractionated and used directly or, if necessary, for
particular usages, subjected to further treatment.
Operating conditions in the hydrothermal
treating-stripping zone can vary widely, except for tem-
perature Other reaction conditions in the hydrothermal
treating-stripping zone include a residence time of 0.01
2~ to 3.0 hours, preferably 0.1 to 1.0 hours; a pressure of 0
to 10,000 psig, preferably 1,500 to 5,000 psig, and more
preferably 1,500 to 2,500 psig; a hydrogen gas rate of 0
to 20,000 standard cubic feet per barrel of feed, prefera-
bly 3,000 to 10,000 standard cubic feet per barrel of
feed; and a feed hourly space velocity of about 0.3 to
100 hr~l, preferably about 1 to 10 hr~l.
A remarkable advantage of the process of the
present invention is the decoupling of the hydrogen supply
to the treating and hydrocracking stages 10 and 35 while
the treating and hydrocracking stages may remain closely
coupled, if desired. Consequently, optimal hydrogen pres-
sure and gas rate may be provided to the hydrothermal
treating-stripping zone lC while, simultaneously, a dif-
ferent optimal hydrogen pressure and gas rate is provided
in the catalytic hydrocracking zone 35. In the co-current
hydrogen gas flow and liquid process, this ~lexibility is
not practical In general, hydrogen gas flow rate should
be higher in the hydrocracking zone because of greater
hydrogen consumption. By placing a pump (not shown) in
01 _9_
line 30, one may operate at a lower hydrogen pressure in
zone l0 and a higher pressure in zone 35.
The treating zone will, in general, contain no
catalyst from any external source, although the mineral
matter contained in added coal, if any, may have some
catalytic effect. The mixture of heavier products and
unconverted feed, as well as any remaining lighter
products, is passed via line 20 to a cooling æone 25.
Cooling zone 25 will typically contain a heat exchanger or
similar means whereby the effluent from treater l0 is
cooled to a temperature below the temperature of the
treating stage and at least below 425C (800F). Some
cooling in zone 25 may also be effected by the addition of
fresh cold hydrogen, if desired. Cooling zone 25 is an
optional feature of this embodiment and may not be
necessary to effect the temperature gradient between
zone l0 and zone 35. Optionally, zone 25 comprises a
2~ flash unit to remove light solvent fractions from the
remaining light products in the heavier effluent stream.
The light solvent fractions may be burned to provide
process heat.
The mixture of heavier reaction products and
feed and remaining light products is fed through line 30
into reaction zone 35 containing a hy'drocracking catalyst.
Hydrogen comprising fresh and/or recycle hydrogen is fed
via line 40 into the hydrocracking zone 35. In the hydro-
; cracking reaction æone, hydrogenation and cracking occur
simultaneously and the higher molecular weight compoundsare converted to lower molecular weight compounds, the
sulfur in the sulfur-containing compounds are converted to
hydrogen sulfide, the nitrogen in the nitrogen-contcining
compounds are converted to ammonia, and the oxygen in the
oxygen-containing compounds are converted to water.
Preferably, the catalytic reaction zone is a fixed bed
type, but an ebullating or moving bed may also be used.
The mixture of heavier reaction products and unconverted
feed preferably passes upwardly through the catalytic
3L24~3
~1 -10-
reaction zone, but may also pass downwardly. Counter-
current or co-current movement of the added hydrogen gas
oS with respect to the liquid flow is also optional. The
primary advantage of passing such a mixture upwardly
through the fixed bed of particulate catalysts is that the
probability of plugging is reduced.
A particularly desirable method of operating the
process is for the fixed catalyst bed to be operated in an
upflow mode, with the lower portion of the catalyst in the
bed being removed as the catalyst becomes fouled. Fresh
catalyst can be added to the top of the fixed bed to
replace the catalyst which is removed from the bottom.
This addition and removal of catalyst can take place
periodically or in a continuous or semi-continuous manner.
Continuous catalyst replacement according to this inven-
tion is carried out at such a low rate that the catalyst
bed is properly described as a fixed bed.
~0 The catalyst used in the hydrocracking zone may
be any of the well known, commercially available hydro-
cracking catalysts. A suitable catalyst for use in the
hydrocracking reaction stage comprises a hydrogenation
component and a cracking component. Preferably the hydro-
genation component is supported on a refractory cracking
base. Suitable bases include, for ex'~mple, silica,
alumina, or composites of two or more refractory oxides
such as silica-alumina, silica-magnesia, silica-zirconia,
alumina-boria, silica-titania, silica-zirconia-titania,
acid-treated clays, and the like. Acidic metal phosphates
such as alumina phosphate may also be used. Preferred
cracking bases comprise alumina and composites of silica
and alumina. Suitable hydrogenation components are
selected from Group VI-B metals, Group VIII metals, and
their oxides, or mixtures thereof. Particularly useful
are cobalt-molybdenum, nickel-molybdenum, or nickel-
tungsten on silica-alumina or alumina supports.
Hydrocracking zone 35 comprises one or more hydrocrac~ing
reactor vessels containing one or more of the afore-
mentioned catalysts in any combination.
?~
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It is preferred to maintain the temperature in
the hydrocracking zone below 425C (300F), preferably in
05 the range of 340C to 425C ~645F to 800F), and more
preferably 340C to 400C (645F to 750F), to prevent
catalyst fouling. The temperature in the hydrocracking
zone should be preferably maintained below the temperature
in the hydrothermal zone by about 55C to about 85C.
Other hydrocracking conditions include a pressure from 500
; to 5,000 psig, preferably 1,000 to 3,000 psig, and more
preferably 1,500 to 2,500 psig; a hydrogen gas rate of
2,000 to 20,000 standard cubic feet per barrel of slurry,
preferably 3,000 to 10,000 standard cubic feet per barrel
of slurry; and a slurry hourly space velocity in the range
of from 0.1 to 2.0, preferably 0.2 to 0.5.
The product effluent 50 from reaction zone 35 is
separated in separation æone 55 into a gaseous fraction 60
comprising light oils boiling below about 150C to 260C
(300F to 500F), preferably below 200C (400F), and
normally gaseous components such as hydrogen, carbon
monoxide, carbon dioxide, hydrogen sulfide, and the C1 to
C4 hydrocarbons. Preferably, the hydrogen is separated
from the other gaseous components and recycled. Liquid
fraction 65 is available for fractionation or further
processing. ,
The process of the present invention produces
; extremely clean, normally liquid products. The normally
liquid products, that is, all of the product fractions
boiling above C4, ha~e an unusually low specific gravity;
a low sulfur content of less than 0.2 weight percent; and
a low nitrogen content of less than 0.5 weight percent.
