U.S. patent application number 09/223574 was filed with the patent office on 2001-05-24 for low-pressure hydrocracking process.
Invention is credited to HATZIKOS, GEORGE H., KILIANY, THOMAS R., KIRKER, GARRY W., MO, W. THOMAS.
Application Number | 20010001449 09/223574 |
Document ID | / |
Family ID | 22837093 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001449 |
Kind Code |
A1 |
KILIANY, THOMAS R. ; et
al. |
May 24, 2001 |
LOW-PRESSURE HYDROCRACKING PROCESS
Abstract
A catalytic process is provided for converting a high boiling
point range petroleum stream to distillate range product which
includes contacting a petroleum feedstock having a boiling range
from about 600.degree. F. to about 1100.degree. F. with a
hydrocracking catalyst having a zeolite component with a framework
silica to alumina ratio of at least 200:1, preferably 2000:1, and a
hydrogenation component. The process is conducted under
superatmospheric hydrogen partial pressure to effect at least 20%
conversion, with at least 50% of the converted product remaining in
the boiling range of about 330 to about 730.degree. F.
Inventors: |
KILIANY, THOMAS R.; (WEST
CHESTER, PA) ; MO, W. THOMAS; (FAIRFAX, VA) ;
KIRKER, GARRY W.; (SINGAPORE, SG) ; HATZIKOS, GEORGE
H.; (HADDONFIELD, NJ) |
Correspondence
Address: |
PAUL E. PURWIN
ASSISTANT CHIEF ATTORNEY
RESEARCH AND ENGINEERING
180 PARK AVENUE
FLORHAM PARK
NJ
07932-0390
US
|
Family ID: |
22837093 |
Appl. No.: |
09/223574 |
Filed: |
December 30, 1998 |
Current U.S.
Class: |
208/111.01 ;
208/108; 208/111.15; 208/111.35 |
Current CPC
Class: |
C10G 45/64 20130101;
C10G 47/20 20130101; C10G 47/18 20130101; C10G 65/12 20130101 |
Class at
Publication: |
208/111.01 ;
208/108; 208/111.15; 208/111.35 |
International
Class: |
C10G 047/16 |
Claims
We claim:
1. A catalytic hydrocracking process for converting a high boiling
point range petroleum stream to a distillate range product
comprising contacting a petroleum feedstock having a boiling range
of from about 600.degree. F. to about 1100.degree. F. with a
hydrocracking catalyst comprising a zeolite component with a
framework silica to alumina molar ratio of at least 200:1 and a
hydrogenation component under superatmospheric hydrogen partial
pressure for a residence time sufficient to effect at least 20%
conversion, with at least 50% of the converted product remaining in
the boiling range of about 330 to about 730.degree. F.
2. A process according to claim 1 wherein said feedstock has a 10%
boiling point above 650.degree. F. and a nitrogen level of about
200 ppm or less.
3. A process according to claim 1 wherein said zeolite component is
selected from the group consisting of faujasite, zeolite X, zeolite
Y, zeolite USY, ZSM-3, ZSM-20, ENT, ECR-30, CSZ-1.
4. A process according to claim 1 wherein said silica to alumina
molar ratio is greater than 2000:1 and said superatmospheric
hydrogen partial pressure is 1000 psi or less.
5. A process according to claim 1 wherein said hydrogenation
component is selected from the group consisting of platinum,
palladium, gold, silver, iridium, rhodium, ruthenium, osmium, or a
combination thereof.
6. A process according to claim 1 which further comprises
contacting said feedstock with a dewaxing catalyst before,
simultaneous with, or after said contact with said hydrocracking
catalyst, wherein the pour point and/or cloud point of the
unconverted bottoms fraction is reduced.
7. A process according to claim 6 wherein said dewaxing catalyst
contains a zeolite selected from the group consisting of zeolite
beta, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, SAPO-11.
8. A process according to claim 6 wherein said hydrocracking
catalyst contains zeolite USY and said dewaxing catalyst contains
zeolite beta.
9. A process according to claim 6 wherein said hydrocracking
process and said dewaxing process are performed simultaneously
having said hydrocracking catalyst and said dewaxing catalyst
co-formulated in one extrudate.
10. A process according to claim 1 which further comprises
contacting the unconverted bottoms fraction produced by said
hydrocracking process having a boiling point above approximately
730.degree. F. with a dewaxing catalyst, wherein the pour point
and/or cloud point of said unconverted bottoms fraction is reduced.
Description
BACKGROUND OF INVENTION
[0001] The present invention relates to petroleum hydrocracking
and, in particular, to converting a high boiling point range
petroleum stream to a predominantly distillate product utilizing
improved zeolite catalysts. In addition, the hydrocracking process
can be coupled with a dewaxing process to produce high distillate
yields and dewaxed bottoms.
[0002] Zeolites have been described structurally as "framework"
aluminosilicates which are based on an infinitely extending
three-dimensional network of AlO.sub.4 and SiO.sub.4 tetrahedra
linked to each other by sharing all of the oxygen atoms. Such
zeolites have pores of uniform size which are uniquely determined
by the structure of the crystal. The zeolites are referred to as
"molecular sieves" because the uniform pore size of the zeolite
material allows it to selectively sorb molecules of certain
dimensions and shapes.
[0003] The particular faujasitic or Y-type zeolite preferred in
this invention has come to be known as ultrastable Y (USY) and is
sometimes referred to as dealuminated Y (DAY). USY is not a single
entity but a family of materials related to zeolite Y. USY is
similar to zeolite Y in that its characteristic x-ray diffraction
lines are substantially those of zeolite Y. USY differs from
as-synthesized zeolite Y in that by the nature of the various
processing schemes and the degree to which zeolite Y is
dealuminated, the effective framework silica-to-alumina ratio is
increased.
[0004] Hydrocracking utilizing a zeolite catalyst is a process
which has achieved widespread use in petroleum refining for
converting various petroleum fractions to lighter and more valuable
products, especially gasoline and distillates such as jet fuels,
diesel oils and heating oils.
[0005] Large pore zeolites such as zeolites X and Y possessing
relatively low silica to alumina ratios, e.g., less than about
40:1, have been conventionally used in hydrocracking reactions
because the principal components of the feedstock are high
molecular weight hydrocarbons which will not enter the internal
pore structure of the smaller pore zeolites and will therefore not
undergo conversion. Large pore zeolites also possess a high degree
of intrinsic cracking activity.
[0006] U.S. Pat. No. 5,171,422 claims a process for producing a
lubricating oil base stock by hydrocracking a feedstock utilizing a
zeolite of the faujasite structure possessing a silica to alumina
ratio of at least 50:1, preferably 100:1, more preferably 150:1.
U.S. Pat. No. 4,820,402 describes a process for increasing the
selectivity of production of higher boiling distillate range
product and hydrocracking reactions by utilizing a large pore
zeolite with a silica to alumina ratio of at least about 50:1,
preferably up to 200:1.
[0007] Even with these higher silica to alumina ratio catalysts, a
significant amount of unwanted secondary cracking of paraffins
occurs along with the desired cracking of aromatic and naphthenic
components because of the acidic alumina sites within the catalyst.
This secondary cracking results in distillate yield loss. Thus,
there is a need for a distillate selective hydrocracking catalyst
with a very high silica to alumina ratio.
[0008] Processes for dewaxing petroleum distillates are well known.
High pour points are caused by higher molecular weight, straight
chain, normal and slightly branched paraffins which must be removed
to obtain adequately low pour points.
[0009] In order to obtain the desired selectivity, the dewaxing
catalyst used has usually been a zeolite having a pore size which
admits the straight chain n-paraffins, but which excludes more
highly branched materials such as cycloparaffins and aromatics.
Since dewaxing processes of this kind function by means of cracking
reactions, a number of useful products become degraded to lower
molecular weight materials.
[0010] Another unit process frequently encountered in petroleum
dewaxing is isomerization. In this process, n-paraffins are
converted to iso-paraffins in the presence of an acidic catalyst
such as an acidic zeolite. These processes operate at relatively
high temperatures and pressures, which causes extensive cracking
thereby degrading useful distillate products into less valuable
lighter products. Thus, there is a need for a dewaxing process
which does not result in significant distillate yield loss.
SUMMARY OF THE INVENTION
[0011] In accordance with the present invention, a catalytic
hydrocracking process is provided for converting a high boiling
point range petroleum stream to distillate product. A petroleum
feedstock having a boiling range from about 600 to about
1100.degree. F. is contacted with a hydrocracking catalyst
containing a zeolite component with a framework silica to alumina
molar ratio of at least 200:1 and a hydrogenation component. The
catalyst and feedstock are contacted at superatmospheric hydrogen
partial pressure for a residence time sufficient to effect at least
20% conversion, with at least 50% of the converted product
remaining in the boiling range of 330 to 730.degree. F.
[0012] The preferred feedstock has a 10% boiling point above
650.degree. F. and a nitrogen level of less than about 200 ppm.
[0013] The zeolite component can be selected from the group
consisting of faujasite, zeolite X, zeolite Y, zeolite USY, ZSM-3,
ZSM-20, ENT, ECR-30, CSZ-1, preferably zeolite USY. In the
preferred embodiment, the silica to alumina molar ratio is greater
than 2000:1 and said superatmospheric hydrogen partial pressure is
1000 psi or less.
[0014] The hydrogenation component can be platinum, palladium,
gold, silver, iridium, rhodium, ruthenium, osmium, or a combination
thereof.
[0015] The process of the invention can also include pour point
and/or cloud point reduction of the unconverted bottoms fraction by
contacting the feedstock with a dewaxing catalyst before,
simultaneous with, or after contact with the hydrocracking
catalyst. Any conventional dewaxing catalyst may be used including
zeolite beta, ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-35, ZSM-48, and
SAPO-11. Zeolite beta is preferred.
[0016] The hydrocracking process and the dewaxing process can be
performed simultaneously by having the hydrocracking zeolite and
the dewaxing zeolite catalyst co-formulated in one extrudate.
[0017] The process of the invention also includes contacting the
unconverted bottoms fraction produced by the hydrocraking process
having a boiling point above approximately 730.degree. F. with a
dewaxing catalyst so as to reduce the pour point and/or cloud point
of the unconverted bottoms fraction.
[0018] The process of the invention is primarily a hydrocracking
process selective for distillate product, with dewaxed bottoms as a
byproduct if the dewaxing catalyst is incorporated. While known
methods have been fairly effective in reducing high boiling point
hydrocarbon feeds, the distillate yields begin to decrease due to
paraffin selective secondary crackings at high 650.degree.
F..sup.+conversions (i.e. conversion above 50%). With the use of a
hydrocracking catalyst with an exceptionally high silica to alumina
ratio, the process of the present invention permits conversions
above 50% e.g., 70% to 80%, with little or no loss in distillate
yield. When combined with a dewaxing catalyst, reduced pour point
bottoms can be produced.
BRIEF DESCRIPTION OF THE FIGURES
[0019] FIG. 1 is a graph showing the overall yield structure for a
process of the invention.
[0020] FIG. 2 is a graph showing a comparison between a catalyst
used in the process of the invention and a conventional catalyst in
converting the bottoms feed to distillate range product.
[0021] FIG. 3 is a graph showing the gas yield for a process of the
invention.
[0022] FIG. 4 is a graph showing the naphtha yield for a process of
the invention.
[0023] FIG. 5 is a graph showing the yield structure for a process
of the invention at higher hydrogen partial pressure.
[0024] FIG. 6 is a graph showing the aging of a catalyst used in
the process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] It has now been found that enhanced hydrocracking can be
achieved by utilizing a catalyst comprising a zeolite component
with an exceptionally high silica to alumina ratio, i.e., greater
than 200:1. Such catalysts provide superior distillate selectivity,
are capable of running at high conversion levels, i.e., at or about
70 percent, provide low LPG yield, operate with lower hydrogen
consumption, operate at a lower psi, i.e., 400 psi, and have a low
aging rate.
[0026] When waxy feedstocks are hydrocracked with a large pore
catalyst, such as zeolite Y, in combination with a hydrogenation
component, the viscosity of the oil is reduced by cracking most of
the 650.degree. F..sup.+material into material that boils at
330.degree. F..sup.+to 650.degree. F. Although the viscosity is
reduced, the unconverted 650.degree. F..sup.+material retains a
relatively high pour point, i.e., the lowest temperature at which a
liquid will flow when a test container is inverted. The unconverted
fraction also retains a relatively high cloud point, i.e. the
temperature at which solids start to separate from solution when
the oil is cooled. The pour point and/or cloud point can be reduced
through catalytic dewaxing.
Feedstocks
[0027] The hydrocarbon feed materials suitable for use in the
hydrocracking step of the present invention include crude
petroleum, reduced crudes, vacuum tower residua, vacuum gas oils,
deasphalted residua and other heavy oils. These feedstocks contain
a substantial amount of components boiling above about 260.degree.
C. (about 500.degree. F.) and normally have an initial boiling
point of about 290.degree. C. (about 554.degree. F.) and more
usually about 343.degree. C. (about 650.degree. F.). Typical
boiling ranges are from about 316.degree. C. to about 593.degree.
C. (from about 600.degree. F. to about 1100.degree. F.) or from
about 343.degree. C. to about 510.degree. C. (from about
650.degree. F. to about 950.degree. F.). Generally, the feedstock
will have a 10% boiling point above 650.degree. F., meaning that
approximately 10% of the feedstock will initially boil below
650.degree. F., with a very small portion boiling below 600.degree.
F.
[0028] The hydrocarbon feedstock can be treated prior to
hydrocracking in order to reduce or substantially eliminate its
heteroatom content. As necessary or desired, the feedstock can be
hydrotreated under mild or moderate hydroprocessing conditions to
reduce its sulfur, nitrogen, oxygen and metal content. The
preferred feedstock for the process of the invention contains less
than about 200 ppm nitrogen. Conventional hydrotreating process
conditions and catalysts can be employed, e.g., those described in
U.S. Pat. No. 4,283,272, the contents of which are incorporated by
reference herein.
Catalyst for the Hydrocracking Step
[0029] The catalyst used in the hydrocracking step of the present
process contains a large pore zeolite of the faujasite family as
the acidic component. The zeolite has a silica to alumina ratio of
at least about 200:1, preferably at least 2000:1, and a hydrocarbon
sorption capacity for n-hexane of at least about 6 percent.
[0030] The catalyst also contains at least one hydrogenation
component which may be at least one noble metal and/or at least one
non-noble metal or a combination thereof. Suitable noble metals
include platinum, palladium, gold, silver, iridium, rhodium,
ruthenium, osmium, or a combination thereof. Platinum, palladium or
a combination thereof are preferred.
[0031] The metal can be incorporated into the zeolite by any
suitable method such as impregnation or exchange. The metal can be
incorporated in the form of a cationic, anionic or neutral complex;
Pt(NH.sub.3).sub.4.sup.2+and other cationic complexes of this type
are convenient for exchanging metals onto the zeolite.
[0032] The amount of hydrogenation component can range from about
0.01 to about 30 percent by weight and is normally from about 0.1
to about 15 percent by weight. The precise amount will, of course,
vary with the nature of the component; less of the highly active
noble metals, particularly platinum, being required than of the
less active metals.
[0033] The hydrocarbon sorption capacity of a zeolite is determined
by measuring its sorption at 25.degree. C. and at 40 mm Hg (5333
Pa) hydrocarbon pressure in an inert carrier such as helium. The
sorption test is conveniently carried out in a thermogravimetric
analysis (TGA) with helium as a carrier gas flowing over the
zeolite at 25.degree. C. The hydrocarbon of interest, e.g.,
n-hexane, is introduced into the gas stream adjusted to 40 mm Hg
hydrocarbon pressure and the hydrocarbon uptake, measured as an
increase in zeolite weight, is recorded. Sorption capacity is then
calculated as a percentage in accordance with the relationship: 1
Hydrocarbon Sorption Capacity ( % ) = Wt . of Hydrocarbon Sorbed Wt
. of Zeolite
[0034] It should be understood that the silica:alumina ratio
referred to in this specification is the structural or framework
ratio, that is, the ratio of the SiO.sub.4 to the AlO.sub.4
tetrahedra which, together, constitute the structure of the
zeolite. This ratio can vary according to the analytical procedure
used for its determination. For example, a gross chemical analysis
may include aluminum which is present in the form of cations
associated with the acidic sites on the zeolite thereby giving a
low silica:alumina ratio. Similarly, if the ratio is determined by
TGA of ammonia desorption, a low ammonia titration may be obtained
if cationic aluminum prevents exchange of the ammonium ions onto
the acidic sites. These disparities are particularly troublesome
when certain treatments such as the dealuminization methods
described below, which result in the presence of ionic aluminum
free of the zeolite structure, are employed. Due care should
therefore be taken to ensure that the framework silica:alumina
ratio is correctly determined. The preferred method of determining
silica:alumina ratio is NMR (nuclear magnetic resonance)
analysis.
[0035] Included among the zeolites which can be used in the
hydrocracking operation of this invention are faujasite, zeolite X,
zeolite Y, ultrastable zeolite Y (USY), ZSM-3, ZSM-20, ENT
(hexagonal faujasite), ECR-30, and CSZ-1. USY is preferred.
[0036] A number of different methods are known for increasing the
structural silica:alumina ratio of various zeolites. Many of these
methods rely upon the removal of aluminum from the structural
framework of the zeolite employing suitable chemical agents.
Specific methods for preparing dealuminized zeolites are described
in the following to which reference may be made for specific
details: "Catalysis by Zeolites" (International Symposium on
Zeolites, Lyon, Sep. 9-11, 1980), Elsevier Scientific Publishing
Co., Amsterdam, 1980 (dealuminization of zeolite Y with silicon
tetrachloride); U.S. Pat. No. 3,442,795 and U.K. Pat. No. 1,058,188
(hydrolysis and removal of aluminum by chelation); U.K. Pat. No.
1,061,847 (acid extraction of aluminum); U.S. Pat. No 3,493,519
(aluminum removal by steaming and chelation); U.S. Pat. No.
3,591,488 (aluminum removal by steaming); U.S. Pat. No. 4,273,753
(dealuminization by silicon halide and oxyhalides); U.S. Pat. No.
3,691,099 (aluminum extraction with acid); U.S. Pat. No. 4,093,560
(dealuminization by treatment with salts); U.S. Pat. No. 3,937,791
(aluminum removal with Cr(III) solutions); U.S. Pat. No. 3,506,400
(steaming followed by chelation); U.S. Pat. No. 3,640,681
(extraction of aluminum with acetylacetonate followed by
dehydroxylation); U.S. Pat. No. 3,836,561 (removal of aluminum with
acid); German Offenleg. No. 2,510,740 (treatment of zeolite with
chlorine or chlorine-containing gases at high temperatures), Dutch
Pat. No. 7,604,264 (acid extraction), Japanese Pat. No. 53/101,003
(treatment with EDTA--ethylene diamine tetra-acetic acid--or other
materials to remove aluminum) and J. Catalysis, 54, 295 (1978)
(hydrothermal treatment followed by acid extraction).
[0037] Highly siliceous forms of zeolite Y can be prepared either
by steaming or by acid extraction of structural aluminum or by
both. Due to its convenience, steaming is the preferred method.
Since zeolite Y in its normal, as-synthesized condition is unstable
to acid, the zeolite must ordinarily be converted to an acid-stable
form prior to dealumination by acid treatment. Methods for doing
this are known and one of the most common forms of acid-resistant
zeolite Y is known as "Ultrastable Y" (USY). Zeolite USY is
described in U.S. Pat. Nos. 3,293,192 and 3,402,996. In general,
"ultrastable" refers to a Y-type zeolite which is highly resistant
to degradation of crystallinity by high temperature and steam
treatment and is characterized by a R.sub.2O content (wherein R is
Na, K or any other alkali metal ion) of less than 4 weight percent
and preferably less than 1 weight percent, a unit cell size of less
than about 24.5 .ANG. and a silica:alumina mole ratio in the range
of 3.5:1 to 7:1 or higher. The ultrastable form of Y-type zeolite
is obtained primarily by a substantial reduction of the alkali
metal ions and the unit cell size.
[0038] The ultrastable form of the Y-type zeolite can be prepared
by successively base exchanging a Y-type zeolite with an aqueous
solution of an ammonium salt such as ammonium nitrate until the
alkali metal content of the zeolite is reduced to less than about 4
weight percent. The base exchanged zeolite is then calcined at a
temperature of from about 540.degree. C. to about 800.degree. C.
for up to several hours, cooled and successively base exchanged
with an aqueous solution of an ammonium salt until the alkali metal
content is reduced to less than about 1 weight percent, followed by
washing and calcination again at a temperature of from about
540.degree. C. to about 800.degree. C. to produce an ultrastable
zeolite Y. The sequence of ion exchange and heat treatment results
in the substantial reduction of the alkali metal content of the
original zeolite and results in a unit cell shrinkage which is
believed to lead to the ultra high stability of the resulting
Y-type zeolite.
[0039] The ultrastable zeolite Y can then be extracted with acid to
produce a highly siliceous form of the zeolite which is then
suitable for use in the hydrocracking operation of the present
process. Other methods for increasing the silica:alumina ratio of
zeolite Y by acid extraction are described in U.S. Pat. Nos.
4,218,307; 3,591,488 and 3,691,099 which are incorporated herein by
reference.
[0040] It may be desirable to incorporate the zeolite in another
material which is resistant to the temperature and other conditions
employed in the process. Such matrix, or binder materials include
synthetic or natural substances as well as inorganic materials such
as clay, silica and/or metal oxides. The latter can be either
naturally occurring or in the form of gelatinous precipitates or
gels including mixtures of silica and metal oxides. Naturally
occurring clays which can be composited with the catalyst include
those of the montmorillonite and kaolin families. These clays can
be used in the raw state as originally mined or they can be
initially subjected to calcination, acid treatment or chemical
modification.
[0041] The zeolite can be composited with a porous matrix material,
e.g., an inorganic oxide binder such as alumina, silica, titania,
zirconia, silica-alumina, silica-magnesia, silica-zirconia,
silica-thoria, silica-berylia, silica-alumina-thoria,
silica-alumina-zirconia, silica-alumina-magnesia and
silica-magnesia zirconia, and the like. The matrix can be in the
form of a cogel with the zeolite. The relative proportions of
zeolite component and inorganic oxide binder material can vary
widely with the zeolite content ranging from about 1 to about 99,
and more usually from about 5 to about 80, percent by weight of the
composite.
Hydrocracking Conditions
[0042] In the hydrocracking step of the present process, the
feedstock is contacted with the hydrocracking catalyst in the
presence of hydrogen under hydrocracking conditions of elevated
temperature and pressure. Conditions of temperature, pressure,
space velocity, hydrogen:feedstock ratio and hydrogen partial
pressure which are similar to those used in conventional
hydrocracking operations can conveniently be employed herein.
Process temperatures of from about 230.degree. C. to about
500.degree. C. (from about 446.degree. F. to about 932.degree. F.)
can conveniently be used although temperatures above about
425.degree. C. (about 797.degree. F.) will normally not be employed
because of standard reactor metallurgy limits. Generally,
temperatures of from about 260.degree. C. to about 425 .degree. C.
(from about 500.degree. F. to about 800.degree. F.) will be
employed. The process is operated in the presence of hydrogen with
superatmospheric hydrogen partial pressures normally being from
about 496 to about 19,300 kPa (from about 72 to about 2,800 psi),
preferably from about 2,069 to about 13,790 kPa (from about 300 to
about 2000 psi). Relatively low superatmospheric hydrogen partial
pressures are required to increase distillate yield and prevent
desired paraffins from being further hydrocracked to gaseous
by-products. The hydrogen:feedstock ratio (hydrogen circulation
rate) is normally from about 10 to about 3,500 n.l.1.sup.-1 (from
about 56 to about 19,660 SCF/bbl.), preferably from about 18 to
about 713 n.1.1.sup.-1 (from about 100 to abut 4000 SCF/bbl). The
space velocity of the feedstock will normally be from about 0.1 to
about 20 LHSV and preferably from about 0.3 to about 5.0 LHSV. In
all circumstances, the process of the invention requires a
feedstock residence time sufficient to effect at least 20%
conversion, with at least 50% of the converted product remaining in
the distillate product boiling range of 330 to 730.degree. F.
[0043] Employing the foregoing hydrocracking conditions, conversion
of feedstock to distillate range product having a boiling point
range of between about 330 to about 730.degree. F. can be made to
come within the range of from about 20 to about 80 weight percent.
The hydrocracking conditions are advantageously selected so as to
provide a conversion of from about 30 to about 80, and preferably
from about 40 to about 50, weight percent.
[0044] The conversion can be conducted by contacting the feedstock
with a fixed stationary bed of catalyst, a fixed fluidized bed or
with a transport bed. A simple configuration is a trickle-bed
operation in which the feed is allowed to trickle through a
stationary fixed bed. With such a configuration, it is desirable to
initiate the hydrocracking reaction with fresh catalyst at a
moderate temperature which is raised as the catalyst ages in order
to maintain catalytic activity.
Dewaxing Process
[0045] As defined herein, dewaxing refers to a removal of at least
some of the normal paraffin content of the feed so as to reduce its
pour point and/or cloud point. Any conventional petroleum dewaxing
catalysts now used or hereinafter developed may be used for the
dewaxing process. Although isomerization dewaxing catalysts are
preferred to maximize distillate yields, a significant amount of
hydrocracking is acceptable, and may be preferred when maximum
conversion of feed to lighter materials is desired. Preferred
catalysts include zeolite beta, ZSM-5, ZSM-11, ZSM-22, ZSM-23,
ZSM-35, ZSM-48, SAPO-11. Zeolite beta is most preferred.
[0046] Zeolite beta is disclosed in U.S. Pat. No. 4,419,220, the
entire contents of which are incorporated herein by reference. This
patent discloses that hydrocarbons such as distillate fuel oils and
gas oils may be dewaxed primarily by isomerization of the waxy
components over a zeolite beta catalyst. The process may be carried
out in the presence or absence of added hydrogen, although
operation with hydrogen is preferred. The patent demonstrates that
the process may also be carried out on a wide range of
feedstocks.
[0047] The feedstock for the dewaxing process is the feedstock
previously discussed for the hydrocracking process. The dewaxing
process can occur before, simultaneously with, or after the
hydrocracking process described above. The feedstock can be
contacted with the dewaxing catalyst in a separate reactor or the
same reactor. Within the same reactor, the hydrocracking catalyst
and dewaxing catalyst can be located in separate layers or comprise
a mixed layer. The dewaxing catalyst and hydrocracking catalyst can
also be co-formulated into one extrudate.
[0048] The optimal catalyst configuration and ratio of the
hydrocracking catalyst to the dewaxing catalyst will vary for a
given feedstock and desired product yield end properties. The
preferred range of hydrocracking catalyst to dewaxing catalyst is
between about 9:1 and 1:9, respectively; more preferably between
about 2:1 and 1:2, respectively.
[0049] Instead of contacting the initial feedstock to the dewaxing
catalyst, it is also possible, and preferred in some circumstances,
to recycle the heavy fraction of the product from the hydrocracking
process for use as the feed for the dewaxing process.
[0050] In general, the process conditions for the dewaxing process
are within the same ranges as those specified for the hydrocracking
process, as must be the case when both types of catalysts are in
the same reactor. However, it is known in the art that certain
adjustments in the preferred process conditions, within the ranges
specified above, may be desired when incorporating the dewaxing
process into the process of the invention. For example, when the
dewaxing process is introduced, a lower superatmospheric partial
hydrogen pressure is preferred, usually in the range of about 1,379
to about 6,895 kPa (about 200 to about 1000 psi), more preferably
from about 2,758 to about 5,516 kPa (about 400 to about 800 psi).
If the dewaxing process is conducted in a separate reactor, high
end hydrocracking pressures can be utilized, e.g. about 2800 psi.
Adjustments may also be made based upon the ratio of hydrocracking
to dewaxing catalyst. For example, if the hydrocracking to dewaxing
catalyst ratio within the reactor is high, a lower range LHSV may
be preferred, within the range specified above, so as to achieve
the desired level of pour point and/or cloud point reduction. The
temperature and hydrogen circulation ranges can be the same as
those specified for the hydrocracking process alone.
[0051] Along with reducing the pour point and/or cloud point, the
dewaxing process also creates a high hydrogen content in the
bottoms fraction. The low pour point, together with the high
hydrogen content of the bottoms fraction, makes it suitable as a
high performance turbine fuel.
[0052] The following examples serve to provide further appreciation
of the invention but are not meant in any way to restrict the
effective scope of the invention.
EXAMPLE 1
[0053] This example illustrates the properties of two distillate
selective catalysts. Pt/USY/Al.sub.2O.sub.3 possess the properties
required by the method of the invention. Pt/zeolite
beta/Al.sub.2O.sub.3 is a distillate selective hydroprocessing
catalyst presently used in the art. The properties of Pt/USY and
Pt/zeolite beta are set forth in Table 1 below.
1TABLE 1 Distillate Selective Catalyst Properties Identification
Pt/USY Pt/zeolite beta Catalyst Alpha 6 2 SiO.sub.2/Al.sub.2O.sub.3
Molar Ratio 3,300 800 (Determined by NMR) Unit Cell Size, A 24.22
N/A X-Ray Crystallinity, % -- 20 Particle Density, g/cc 0.833 0.977
Real Density, g/cc 2.581 2.255 Surface Area, m.sup.2/g 557 344 Pore
Volume, cc/g 0.813 0.580 Platinum, wt % 0.56 0.57 Zeolite, wt % 65
65 Alumina Binder, wt % 35 35
[0054] The catalyst utilized in the method of the invention,
Pt/USY/Al.sub.2O.sub.3 was prepared by steaming a commercially
available low acidic USY catalyst for 16 hours at 1,025.degree. F.
The finished extrudate consisted of 65 wt % zeolite supported on
gamma alumina. The extrudate was exchanged with
Pt(NH.sub.3).sub.4Cl.sub.2 in 0.2 N ammonium nitrate solution; and
calcined in air at 660.degree. F. for 3 hours. The resulting Pt/USY
has an extremely high silica to alumina ratio of about 3300.
EXAMPLE 2
[0055] This example illustrates the method for increasing the
selectivity for distillate range product from hydrocracked bottoms
feedstock, the properties of which are set forth in Table 2 below.
Two different, but very similar, bottoms feedstocks were contacted
with Pt/USY and Pt/zeolite beta, respectively.
2TABLE 2 Hydrocracked Bottoms Feedstock Properties (650.degree. F.+
fraction) Catalyst Contacted Pt/USY Pt/zeolite beta Hydrogen, wt %
14.04 13.91 Nitrogen, ppm 27 10 Basic Nitrogen, ppm 5 5 Sulfur, wt
% <0.002 0.016 API Gravity 31.8 31.9 Pour Point, .degree. F. 110
100 Paraffin, wt % 43.9 48.5 Naphthenes, wt % 36.0 30.2 Aromatics,
wt % 20.1 21.3
[0056] The reduction of the hydrocracked bottoms feedstock was
carried out in a packed-bed, trickle-flow reactor to compare the
performance of Pt/USY and Pt/zeolite beta described in Example 1.
The operations were conducted in a cascade mode with a
hydrotreating catalyst loaded upstream in a 1:1 volume ratio. In
each case, the distillate selective catalyst was pre-sulfided with
2% H.sub.2S in hydrogen at 500 psi for 12 hours. The sulfiding
temperature starting from 550.degree. F., was raised step-wise to
700.degree. F., at an increment of 50.degree. F. each period. The
reaction was carried out under various reactor temperatures and
hydrogen pressure, with an LHSV of about 1.0.
[0057] The overall yield structure for Pt/USY, a catalyst utilized
in the process of the invention, is shown in FIG. 1 where the
330-730.degree. F. fraction is designated as distillate, the
C.sub.5 to 330.degree. F. fraction as naphtha, and total
C.sub.1-C.sub.4 as LPG. Even after 150 days on stream, catalyst
Pt/USY demonstrated excellent distillate selectivity. Unlike
conventional catalysts, the distillate yield does not show a
maximum with temperature range tested, up to about 58% at 75% of
650.degree. F.+ conversion, and with only 4% LPG. This indicates
the ability of running the catalyst at very high conversion levels,
resulting in high distillate yields and low unconverted bottom
fractions, while still keeping hydrogen consumptions very low. Most
importantly, the distillate yield increased with conversions, even
for conversion levels approaching 80%, and remained very close to
the 100% distillate selective limit. This demonstrates that
secondary cracking reactions were reduced by the ultra high silica
Pt/USY catalyst.
EXAMPLE 3
[0058] The 330.degree.-730.degree. F. distillate yield was compared
between Pt/USY and Pt/zeolite beta. FIG. 2 shows the superiority of
Pt/USY over Pt/zeolite beta in converting the bottoms feed to a
high quality distillate range product. At 650.degree. F. plus
conversions above 50%, the distillate yields from Pt/zeolite beta
begin to decrease due to paraffin selective secondary cracking. On
the other hand, the larger pores in Pt/USY together with its low
acidity allow the catalyst to continue processing heavier molecules
in the feed non-preferentially with minimum excess cracking. This
is further demonstrated by the lower gas yields of Pt/USY as shown
in FIG. 3. The lower level of naphtha yield by Pt/USY as compared
Pt/zeolite beta is demonstrated in FIG. 4.
EXAMPLE 4
[0059] The performance of high silica to alumina ratio Pt/USY was
also examined at a higher hydrogen partial pressure (i.e. 800 psi
H.sub.2). The results are shown in FIG. 5. In general, the lower
hydrogen partial pressure achieved a higher distillate yield. For
example, at 35% conversion, the change from 400 to 800 psi H.sub.2
caused the distillate yield to decrease from 42% to 37%,
respectively.
EXAMPLE 5
[0060] The normalized temperatures at 50% conversion and 1.0 LHSV
under 400 psi H.sub.2 are plotted in FIG. 6. FIG. 6 demonstrates
that Pt/USY undergoes very little aging as the catalyst remains on
stream. This is consistent with its low acidity and strong metal
hydrogenation function, both of which reduce the coking
tendency.
EXAMPLE 6
[0061] Table 3 lists selected product properties from the process
of the invention at 38% and 74% conversion.
3TABLE 3 650.degree. F. Product IBP-330.degree. F. 330-650.degree.
F. 650.degree. F.+ Conv. Properties Cut Cut Cut 38% H.sub.2
Content, wt % 14.9 13.7 14.0 Cetane Index 51 Freeze Pt., .degree.
F. -32 Pour Pt., .degree. F. -65 85 Cloud Pt., .degree. F. -40 92
Viscosity Index 100 74% H.sub.2 Content, wt % 14.8 13.4 12.9 Cetane
Index 52 Freeze Pt., .degree. F. -23 Pour Pt., .degree. F. -65 25
Cloud Pt., .degree. F. -26 Viscosity Index 89
[0062] The results demonstrate that the distillate range cut
(330-650.degree. F.) has good cetane levels and flow properties
even at a high level of conversion, i.e. 74%.
[0063] The bottoms fraction contains a relatively high pour point
(25.degree. F.). The pour point of the bottoms fraction can be
reduced by combining the method for increasing the selectivity for
distillate range product with a dewaxing process. After separation
of the distillate yield product, the bottom fraction can either be
recycled or fed to a catalytic dewaxing unit to further reduce the
pour point to produce fuel oil and lubricating oil products.
[0064] Alternatively, the dewaxing catalyst can be installed in the
hydrocracking reactor to improve the bottom quality, without first
separating the bottom fraction.
EXAMPLE 7
[0065] This example illustrates one use of the invention for
distillate selective conversion as well as dewaxing of the high
pour point unconverted bottoms.
[0066] The first of two reactors was loaded with Pt/USY catalyst.
The Pt was exchanged onto the extrudate at a 0.6 weight percent
level. The Pt/USY catalyst was followed by a second reactor loaded
with Pt/zeolite beta containing 0.6 wt % platinum. Table 4 contains
the catalyst properties.
4TABLE 4 Catalyst Properties Catalyst Pt/USY Pt/zeolite beta
Zeolite, wt % 65 65 Alumina, wt % 35 35 Platinum, wt % 0.58 0.66
Particle Density, g/cc 0.836 0.821 Real Density, g/cc 2.629 2.582
Surface Area, m.sup.2/g 532 392 Pore Volume, cc/g 0.816 0.831
Silica: Alumina ratio 200:1 35:1
[0067] Both of the catalysts were loaded with 80-120 mesh sand.
[0068] The catalysts were reduced for 1 hour in flowing hydrogen at
300.degree. F. before sulfiding. The catalysts were sulfided using
400 ppmv hydrogen sulfide in hydrogen gas at 100 psi while holding
catalyst temperature at 300.degree. F. The properties of the
feedstock are shown in Table 5. The bottoms feedstock was started
at a temperature of 300.degree. F. After sulfiding was completed,
process conditions were 400 psi H.sub.2, 1.0 LHSV, 2,000 SCF/B
hydrogen circulation, and an initial reaction temperature of
550.degree. F.
5 TABLE 5 Hydrogen in Petroleum Product, wt % 14.22 Nitrogen in
Petroleum Product, ppm 14 Sulfur in Petroleum Product, ppm <20
API Gravity of Petroleum Product 32.5 Pour Point of Petroleum
.degree. F. 95 IBP .degree. F. 628 30 Vol. Percent Distilled 772 50
Vol. Percent Distilled 806 70 Vol. Percent Distilled 845 90 Vol.
Percent Distilled 907 End Point 960
[0069] When the temperature of the Pt/zeolite beta catalyst was
increased to reaction temperature, it contributed to the
conversion, and more importantly, to the dewaxing of the feed.
Table 6 lists the product properties from Pt/USY alone at 60 wt %
conversion.
6TABLE 6 Product Properties from Pt/USY at 60 wt % Conversion
330.degree. F.-730.degree. F. 43 wt % 730.degree. F.+ properties
Hydrogen, wt % 14.59 Nitrogen, ppmw 8 Sulfur, wt % <0.002 Pour
Point, .degree. F. 95 n-paraffin, wt % 6.98
[0070] Table 7 demonstrates the product properties from
Pt/USY/Al.sub.2O.sub.3 and Pt/zeolite beta/Al.sub.2O.sub.3 at a
67:33 ratio at 61 wt % conversion.
7 TABLE 7 330.degree. F.-730.degree. F. 36 wt % 730.degree. F+
properties Hydrogen, wt % 14.16 Nitrogen, ppmw 4 Sulfur, wt %
<0.002 Pour Point, .degree. F. (D97) -35 n-paraffin, wt %
0.44
[0071] The results demonstrate that the pour point of the
730.degree. F..sup.+cut was dramatically reduced when the dewaxing
catalyst, Pt/zeolite beta, is coupled with the Pt/USY catalyst.
This corresponds to the much lower n-paraffins content of the cut.
Further, the dramatic reduction in pour point, 95.degree. F. down
to -35.degree. F., is achieved by the tandem use of the two
catalysts with an only moderate decrease in the distillate
selectivity of the system, i.e. a decrease from 43 wt % to 36 wt %
distillate yield.
[0072] The example demonstrates that the Pt/USY catalyst has high
330-730.degree. F. distillate selectivity at high conversion, and
converts only a small portion of the n-paraffins in the feed as
evidenced by the high pour point of the 730.degree. F..sup.+cut.
The pour point of the 730.degree. F..sup.+cut can be reduced by
coupling the high silica to alumina ratio hydrocracking Pt/USY
catalyst with a dewaxing catalyst such as Pt/zeolite beta.
[0073] Thus, while there have been described what are presently
believed to be the preferred embodiments of the invention, those
skilled in the art will realize that changes and modifications may
be made thereto without departing from the spirit of the invention,
and it is intended to claim all such changes and modifications as
fall within the scope of the invention.
* * * * *