Molecular sieve abstract
The present invention relates to a hydrocracking and isomerization
process for preparing low pour point middle distillate hydrocarbons
and lube oil from a hydrocarbonaceous feedstock boiling above about
600.degree. F. by contacting the feedstock with a catalyst containing
an intermediate pore size silicoaluminophosphate molecular sieve
and a hydrogenation component.
Molecular sieve claims
What is claimed is:
1. A process for preparing low pour middle distillate hydrocarbons
and lube oil comprising:
(a) contacting under hydrocracking conditions a hydrocarbonaceous
feed wherein at least about 90% of said feed has a boiling point
greater than about 600.degree. F., with a catalyst comprising an
intermediate pore size silicoaluminophosphate molecular sieve and
at least one hydrogenation component,
(b) recovering a hydrocarbonaceous effluent wherein greater than
40% by volume of said effluent (i) boils above about 300.degree.
F. and below about 725.degree. F. and (ii) has a pour point below
about 0.degree. F.; and
(c) distilling the hydrocarbonaceous effluent to produce a first
fraction containing middle distillate products having a boiling
point below about 725.degree. F., and a second fraction containing
a lube oil having a boiling above about 700.degree. F. and having
a pour point of less than about 30.degree. F.
2. The process of claim 1 wherein said hydrocarbonaceous feed has
a paraffin content of at least about 20% by weight.
3. The process of claim 1 wherein said intermediate pore size silicoaluminophosphate
molecular sieve is selected from the group consisting of SAPO-11
SAPO-31 and SAPO-41.
4. The process of claim 1 wherein said hydrogenation component
is selected from the group consisting of at least one of platinum,
palladium, molybdenum, nickel, vanadium, cobalt, tungsten and zinc.
5. The process of claim 4 wherein said hydrogenation component
is selected from the group consisting of platinum and palladium.
6. The process of claim 1 wherein said hydrogenation component
is present in an amount of from about 0.01% to 10% based on the
weight of molecular sieve.
7. The process of claim 1 wherein said catalyst further comprises
an inorganic oxide matrix.
8. The process of claim 7 wherein said matrix is alumina.
9. The process of claim 1 wherein said feed is a gas oil.
10. The process of claim 1 wherein said feed has a content of nitrogen-containing
impurities, calculated as nitrogen, which is below about 50 ppmw.
11. The process of claim 1 wherein said feed has a content of nitrogen-containing
impurities, calculated as nitrogen, which is below about 10 ppmw.
12. The process of claim 1 wherein said hydrocarbon feed is selected
from the group consisting of petroleum distillates, solvent deasphalted
residua, and shale oils.
13. The process of claim 1 wherein greater than 50% by weight of
converted product boils above about 300.degree.0 F. and below about
725.degree. F.
14. The process of claim 1 wherein said catalyst is disposed downstream
of a reaction zone in which a hydrocarbon feed is contacted under
hydroprocessing conditions with an active hydrodenitrogenation catalyst.
15. The process of claim 14 wherein said hydrodenitrogenation catalyst
is disposed in a single reactor with said catalyst.
16. The process of claim 1 wherein said process is carried out
at a temperature of from about 260.degree. to about 482.degree.
C., a pressure of from about 200 psig to about 3000 psig, a liquid
hourly space velocity of from about 0.05 hr.sup.-1 to about 20 hr.sup.-1
and a hydrogen circulation rate of from about 500 to about 30000
SCF/bbl.
17. The process of claim 1 further comprising hydrofinishing said
lube oil.
18. The process of claim 17 wherein hydrofinishing is carried out
at a temperature of from about 190.degree. C. to about 340.degree.
C. and pressure of from about 400 psig to about 3000 psig.
19. The process of claim 17 wherein hydrofinishing is carried out
in the presence of a metallic hydrogenation catalyst.
20. A process for preparing low pour middle distillate hydrocarbons
and lube oil comprising:
(a) contacting under hydrocracking conditions a hydrocarbonaceous
feed wherein at least about 90% of said feed has a boiling point
greater than about 600.degree. F., with a catalyst comprising an
intermediate pore size nonzeolitic molecular sieve containing AlO.sub.2
and PO.sub.2 tetrahedral oxide units, and at least one Group VIII
metal.
(b) recovering a hydrocarbonaceous effluent wherein greater than
about 40% by volume of said effluent (i) boils above about 300.degree.
F. and below about 725.degree. F. and (ii) has a pour point of below
about 0.degree. F.; and
(c) distilling the hydrocarbonaceous effluent to produce a first
fraction containing middle distillate products having a boiling
point below about 725.degree. F., and a second fraction containing
a lube oil having a boiling point above about 700.degree. F. and
having a pour point of less than about 30.degree. F.
21. The process of claim 20 wherein said feed has a content of
nitrogen-containing impurities, calculated as nitrogen, which is
below about 50 ppmw.
22. The process of claim 20 wherein said feed has a content of
nitrogen-containing impurities, calculated as nitrogen, which is
below about 10 ppmw.
23. The process of claim 20 wherein said hydrocarbon feed is selected
from the group consisting of petroleum distillates, solvent deasphalted
residua, and shale oils.
24. The process of claim 20 wherein greater than 50% by weight
of converted product boils above about 300.degree. F. and below
about 725.degree. F.
25. The process of claim 20 wherein said catalyst is disposed downstream
of a reaction zone in which a hydrocarbon feed is contacted under
hydroprocessing conditions with an active hydrodenitrogenation catalyst.
26. The process of claim 25 wherein said hydrodenitrogenation catalyst
is disposed in a single reactor with said catalyst.
27. The process of claim 20 wherein said process is carried out
at a temperature of from about 26020 to about 482.degree. C., a
pressure of from about 200 psig to about 3000 psig, a liquid hourly
space velocity of from about 0.05 hr.sup.-1 to about 20 hr.sup.-1
and a hydrogen circulation rate of from about 500 to about 30000
SCF/bbl.
28. The process of claim 20 further comprising hydrofinishing said
lube oil.
Molecular sieve description
BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing low pour
point middle distillate hydrocarbons and lube oil. More specifically,
the invention relates to a hydrocracking and isomerization process
for selectively preparing low pour point middle distillate hydrocarbons
and lube oil from a hydrocarbonaceous feedstock boiling above about
600.F by contacting the feedstock with a catalyst comprising an
intermediate pore size silicoaluminophosphate molecular sieve and
a hydrogenation component.
DESCRIPTION OF THE PRIOR ART
Hydrocracking, used either in a one-step process or in a multi-step
process coupled with hydrodenitrogenation and/or hydrodesulfurization
steps, has been used extensively to upgrade poor-quality feeds and
produce middle distillate materials. Over the years, much work has
been done to develop improved cracking conditions and catalysts.
Tests have been carried out using catalysts containing only amorphous
materials and catalysts containing zeolites composited with amorphous
materials.
Large pore size zeolites such as zeolites X and Y are presently
considered the most active hydrocracking catalysts. However, high
activity is not the only essential characteristic of midbarrel cracking
in catalysts. Midbarrel selectivity, namely, the percentage of total
conversion accounted for by products boiling within the midbarrel
range of from about 300.degree. F. to about 725.degree. F. is also
important. As noted in U.S. Pat. No. 3853742 many commercial
midbarrel hydrocracking processes do not use zeolitic catalysts
due to their relatively low midbarrel selectivity.
Also, middle distillates conventionally serve as fuels such as
diesel oils, jet fuels, furnace oils, and the like. For convenience
in the handling and use of these middle distillates, it is desirable
for the pour point to be as low as practical consistent with the
temperatures to which they may be exposed. Specifications for these
products often include a requirement that the pour point or freeze
point not exceed a certain maximum value. In some instances, it
is necessary to subject these distillate fuels to additional processing,
the principle purpose of which is to reduce the pour point of the
feed stream. Pour point can also be lowered by lowering the distillate
end point, however this reduces yield.
As noted in U.S. Pat. No. 4486296 although zeolite catalysts
have been employed in hydrocracking processes and may be effective
in providing distillate yields having one or more properties consistent
with the intended use of the distillate, these catalysts suffer
the disadvantage of providing product yields that do not have good
low temperature fluidity characteristics, particularly reduced pour
point and viscosity.
The prior art has utilized a separate dewaxing process to reduce
the pour point of middle distillates wherein selective intermediate
pore size zeolites such as ZSM-5 (U.S. Pat. No. RE. 28398), and
ZSM-23 (European Patent Application No. 0092376) are employed.
Other methods in the art for producing middle distillates possessing
acceptable viscosity and pour point properties include processes
wherein the hydrocarbon feeds are concurrently or sequentially subjected
to hydrocracking and dewaxing in a continuous process using a large
pore size zeolite hydrocarbon cracking catalyst such as zeolite
X or zeolite Y and an intermediate pore size zeolite dewaxing catalyst
such as ZSM-5 (U.S. Pat. No. 3758402).
These processes have two drawbacks. The first is that while the
pour point is reduced, the viscosity is increased, possibly above
acceptable limits. The second drawback is that the process operates
by cracking wax primarily to light products (e.g., C.sub.3 -C.sub.4)
thereby significantly reducing distillate yield. PCT International
Application WO86/03694 discloses a hydrocracking process to produce
high octane gasoline using a catalyst comprising silicoaluminophosphates,
either alone or in combination with traditional hydrocracking catalysts
such as zeolite aluminosilicates.
As set forth in co-pending application Ser. No. 07/002087 now
U.S. Pat. No. 4859312 applicant has discovered that middle distillate
products can be selectively produced in a simplified process over
a single catalyst in high yields which exhibit reduced pour points
and viscosities as compared to prior art processes. Applicant has
found that heavy hydrocarbon oils may be simultaneously hydrocracked
and hydrodewaxed to produce a midbarrel liquid product of improved
yield and satisfactory pour point and viscosity by using a catalyst
containing an intermediate pore size silicoaluminophosphate molecular
sieve component and a hydrogenation component to promote isomerization.
High-quality lubricating oils are critical for the machinery of
modern society. Unfortunately, the supply of natural crude oils
having good lubricating properties, e.g., Pennsylvania and Arabian
Light feedstocks, is not enough to meet present demands. Additionally,
because of uncertainties in world crude oil supplies, it is necessary
to be able to produce lubricating oils efficiently from ordinary
crude feedstocks.
Numerous processes have been proposed to produce lubricating oils
by upgrading the ordinary and low-quality stocks which ordinarily
would be converted into other products.
The desirability of upgrading a crude fraction normally considered
unsuitable for lubricant manufacture into one from which good yields
of lube oils can be obtained has long been recognized. Hydrocracking
processes have been proposed to accomplish such upgrading. U.S.
Pat. Nos. 3506565 3637483 and 3790472 teach hydrocracking
processes for producing lubricating oils.
Hydrocracked lubricating oils generally have an unacceptably high
pour point and require dewaxing. The bottoms from distilling the
hydrocracked product are generally recycled back to the hydrocracker
for further conversion to lower boiling products. It would be of
utility if the hydrocracking process produced a distillation bottoms
fraction of low pour point and high viscosity index which could
therefore be used as a lube oil.
Solvent dewaxing is a well-known and effective process but is expensive.
More recently, catalytic methods for dewaxing have been proposed.
U.S. Pat. No. Re. 28398 discloses dewaxing petroleum charge stocks
using ZSM-5 type zeolites. U.S. Pat. No. 3755145 discloses a process
for preparing low pour point lube oils by hydrocracking a lube oil
stock using a catalyst mixture comprising a conventional cracking
catalyst and ZSM-5.
It has also been suggested that in order to improve the oxidation
resistance of lubricants it is often necessary to hydrogenate or
hydrofinish the oil after hydrocracking, with and without catalytic
dewaxing as illustrated in U.S. Pat. Nos. 4325805; 4347121;
4162962; 3530061; and 3852207. U.S. Pat. Nos. 4283272 and
4441097 teach continuous processes for producing dewaxed lubricating
oil base stocks including hydrocracking a hydrocarbon feedstock,
catalytically dewaxing the hydrocrackate and hydrofinishing the
dewaxed hydrocrackate. These patents teach the use of catalysts
comprising zeolite ZSM-5 and ZSM-23 respectively, for the dewaxing
phase.
European Patent Application No. 225053 discloses a process for
producing lubricant oils of low pour point and high viscosity index
by partially dewaxing a lubricant base stock by isomerization using
a large pore, high silica zeolite dewaxing catalyst followed by
a selective dewaxing step.
The prior art does not provide a process whereby both low pour
mid-distillate hydrocarbons and lube oil can be prepared in the
same reactor.
Generally, the high boiling bottoms from distilling the hydrocracked
product are high in pour point and therefore are of limited value
without further processing. These bottoms therefore are generally
recycled back to the hydrocracker for further conversion to lower
boiling products. It would be of utility if the hydrocracking process
were to produce a distillation bottoms fraction of low pour point
and high viscosity index which could therefore be used as a lube
oil.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior
art by providing a process for simultaneously preparing low pour
and freeze point mid-distillate hydrocarbons and low pour point
lube oil base stock in the same reactor.
It is an object of the invention to provide a process for preparing
both low pour mid-distillates and lube oil base stock wherein the
amount of bottoms recycled is reduced or eliminated thereby providing
increased throughput.
It is a further object of the invention to provide a process for
producing low pour middle distillate hydrocarbons and low pour,
high viscosity index lube oil in the same reactor.
Additional objects and advantages of the invention will be set
forth in part in the description which follows, and in part will
be obvious from the description or may be learned by practice of
the invention. The objects and advantages of the invention will
be realized and attained by means of the instrumentalities and combinations,
particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the
invention, as embodied and broadly described herein, the invention
provides a process for selectively preparing low pour middle distillate
hydrocarbons and low pour, high viscosity index, low viscosity lube
oil comprising (a) contacting under hydrocracking conditions a hydrocarbonaceous
feed wherein at least about 90% of said feed has a boiling point
greater than about 600.degree. F., with a catalyst comprising an
intermediate pore size silicoaluminophosphate molecular sieve and
at least one hydrogenation component; (b) recovering a hydrocarbonaceous
effluent wherein greater than about 40% by volume of said effluent
(1) boils above 300.degree. F. and below from about 675.degree.
F. to about 725.degree. F. (2) and has a pour point below about
0.degree. F.; and (c) distilling the hydrocarbonaceous effluent
to produce a first fraction containing middle distillate products
having a boiling point below from about 675.degree. F. to about
725.degree. F., and a second fraction containing a lube oil having
a boiling point above about 700.degree. F.
In the process of the invention, the hydrocarbon feedstock is contacted
with the intermediate pore size silicoaluminophosphate molecular
sieve catalyst under conversion conditions appropriate for hydrocracking.
During conversion, the aromatics and naphthenes present in the feedstock
undergo hydrocracking reactions such as dealkylation, ring opening,
and cracking, followed by hydrogenation. The long-chain paraffins
present in the feedstock undergo mild cracking reactions to yield
non-waxy products of higher molecular weight than products obtained
using prior art dewaxing zeolitic catalysts such as ZSM-5. At the
same time, a measure of isomerization occurs so that not only is
the pour point reduced by the cracking reactions described above,
but in addition, the n-paraffins become isomerized to isoparaffins
to form liquid-range materials which contribute to low viscosity,
low pour point products. In the bottoms portion of the effluent,
a measure of hydrocracking and isomerization takes place which contributes
not only to the low pour point and viscosity of the lube oil base
stock but also to its high viscosity index, since isoparaffins are
known to have high viscosity indices.
The process of the invention enables heavy feedstock, such as gas
oils, boiling above about 600.degree. F. to be more selectively
converted to middle distillate range products having improved pour
points than prior art processes using large pore catalysts, such
as zeolite Y. Further, in the process of the invention, the consumption
of hydrogen will be reduced even though the product will conform
to the desired specifications for pour point and viscosity. Further,
the process of the invention provides bottoms having a low pour
point, low viscosity and high viscosity index which are suitable
for use as lube oil.
In comparison with prior art dewaxing processes using shape selective
catalysts such as zeolite ZSM-5 the yields of the process of the
invention will be improved and the viscosity kept acceptably low.
The latter is ensured because the bulk conversion involves not only
the cracking of low viscosity paraffins but high viscosity components
(e.g., multi-ring naphthenes) as well. In addition, unlike the prior
art ZSM-5 catalyst, the process of the invention provides low pour
point middle distillates and high viscosity index lube oil base
stock due to a measure of isomerization which produces isoparaffins
which contribute not only to the low pour point and viscosity, but
also to the high viscosity index in the bottoms. Thus, the present
process is capable of effecting bulk conversion together with simultaneous
dewaxing. It is also possible to operate at partial conversion,
thus effecting economies in hydrogen consumption while still meeting
pour point and viscosity requirements. Overall, the present process
reduces or eliminates the amount of bottoms recycled, thereby increasing
throughput.
The accompanying drawings, which are incorporated in and constitute
a part of this specification illustrate several exemplary embodiments
of this invention and together with the description, serve to explain
the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a ternary diagram showing the compositional parameters
of the silicoaluminophosphates of U.S. Pat. No. 4440871 in terms
of mole fractions of silicon, aluminum, and phosphorus.
FIG. 2 is a ternary diagram showing the preferred compositional
parameters of the silicoaluminophosphates in terms of mole fractions
of silicon, aluminum, and phosphorus.
FIG. 3 is a graph showing a comparison for a crystalline silicoaluminophosphate
catalyst used in the process of this invention and a sulfided cogelled
nickel-tungsten-silica-alumina catalyst with respect to yields.
FIG. 4 is a graph showing a comparison for a crystalline silicoaluminophosphate
catalyst used in the process of this invention and a ZSM-5 catalyst
with respect to yields.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments
of applicant's invention.
Feedstocks
The feedstock for the process of the invention comprises a heavy
hydrocarbon oil such as a gas oil, coker tower bottoms fraction,
reduced crude, vacuum tower bottoms, deasphalted vacuum resids,
FCC tower bottoms, or cycle oils. Oils of this kind generally boil
above about 600.degree. F. (316.degree. C.) although the process
is also useful with oils which have initial boiling points as low
as 436.degree. F. (260.degree. C.). Preferably, at least 90% of
the feed will boil above 600.degree. F. (316.degree. C.). Most preferably,
at least about 90% of the feed will boil between 700.degree. F.
(371.degree. C.) and about 1200.degree. F. (649.degree. C.). These
heavy oils comprise high molecular weight long-chain paraffins and
high molecular weight ring compounds with a large proportion of
fused ring compounds. During processing, both the fused ring aromatics
and naphthenes and paraffinic compounds are cracked by an intermediate
pore size silicoaluminophosphate molecular sieve catalyst to middle
distillate range products. A substantial fraction of the paraffinic
components of the initial feedstock also undergo conversion to isoparaffins.
The process is of particular utility with highly paraffinic feeds
because with such feeds, the greatest improvement in pour point
may be obtained. The degree of paraffinicity will depend to some
degree on the viscosity index desired in the product. For example,
when the paraffinic content is greater than about 50% by weight,
a viscosity index of at least about 130 can be obtained. The higher
the paraffinic content, the higher the viscosity index. Preferably,
the paraffinic content of the feed employed is greater than about
20% by weight, more preferably greater than about 40% by weight.
The most preferable paraffinic content of the feed will be determined
by the viscosity index requirements of the product.
The feedstocks employed in the process of the present invention
may be subjected to a hydrofining and/or hydrogenation treatment,
which may be accompanied by some hydrocracking, prior to use in
the present process.
Silicoaluminophosphate Molecular Sieve Catalysts
As set forth above, the process of the invention combines elements
of hydrocracking and isomerization. The catalyst employed in the
process has an acidic component and a hydrogenation component. The
acidic component comprises an intermediate pore size silicoaluminophosphate
molecular sieve which is described in U.S. Pat. No. 4440871 the
pertinent disclosure of which is incorporated herein by reference.
Among other factors, the present invention is based on my discovery
that the use of a catalyst containing a silicoaluminophosphate intermediate
pore size molecular sieve and a Group VIII metal in a hydrocracking
and isomerization reaction of hydrocarbonaceous feeds boiling above
about 600.degree. F. results in unexpectedly high yields of middle
distillates and lube oil base stock having excellent pour point
characteristics.
The most preferred intermediate pore size silicoaluminophosphate
molecular sieve for use in the process of the invention is SAPO-11.
When combined with a hydrogenation component, the SAPO-11 produces
a midbarrel liquid product and a lube oil base stock of improved
yields and satisfactory pour point and viscosity.
SAPO-11 comprises a silicoaluminophosphate material having a three-dimensional
microporous crystal framework structure of [PO.sub.2 ], [AlO.sub.2
]and [SiO.sub.2 ] tetrahedral units whose unit empirical formula
on an anhydrous basis is:
wherein "R" represents at least one organic templating
agent present in the intracrystalline pore system; "m"
represents the moles of "R" present per mole of (Si.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of from zero to about 0.3
"x", "y" and "z" represent respectively,
the mole fractions of silicon, aluminum and phosphorus, said mole
fractions being within the compositional area bounded by points
A, B, C, D and E on the ternary diagram of FIG. 1 or preferably
within the area bounded by points a, b, c, d and e on the ternary
diagram of FIG. 2. The silicoaluminophosphate molecular sieve has
a characteristic X-ray powder diffraction pattern which contains
at least the d-spacings (as-synthesized and calcined) set forth
below in Table I. When SAPO-11 is in the as-synthesized form, "m"
preferably has a value of from 0.02 to 0.3.
Another intermediate pore size silicoaluminophosphate molecular
siever preferably employed in the process of this invention is SAPO-31.
SAPO-31 comprises a silicoaluminophosphate material having a three-dimensional
microporous crystal framework of [PO.sub.2 ], [AlO.sub.2 ] and [SiO.sub.2
] tetrahedral units whose unit empirical formula on an anhydrous
basis is:
wherein R represents at least one organic templating agent present
in the intracrystalline pore system; "m" represents the
moles of "R" present per mole of (Si.sub.x Al.sub.y P.sub.z)O.sub.2
and has a value of from zero to 0.3; "x", "y"
and "z" represent respectively, the mole fractions of
silicon, aluminum and phosphorus, said mole fractions being within
the compositional area bounded by points A, B, C, D and E on the
ternary diagram of FIG. 1 or preferably within the area bounded
by points a, b, c, d and e on the ternary diagram of FIG. 2. The
silicoaluminophosphate has a characteristic X-ray powder diffraction
pattern (as-synthesized and calcined) which contains at least the
d-spacings set forth below in Table III. When SAPO-31 is in the
as-synthesized form, "m" preferably has a value of from
0.02 to 0.3.
mR:(Si.sub.x Al.sub.y P.sub.z)O.sub.2
wherein "R" represents at least one inorganic templating
agent present in the intracrystalline pore system; "m"
represents the moles of "R" present per mole of (Si.sub.x
Al.sub.y P.sub.z)O.sub.2 and has a value of from zero to 0.3; "x",
"y", and "z" represent respectively, the mole
fractions of silicon, aluminum and phosphorus, said mole fractions
being within the compositional area bounded by points A, B, C, D
and E on the ternary diagram of FIG. 1 or preferably within the
area bounded by points a, b, c, d and e on the ternary diagram of
FIG. 2 said silicoaluminophosphate having a characteristic X-ray
powder diffraction pattern (as-synthesized and calcined) which contains
at least the d-spacings set forth below in Table V. When SAPO-41
is in the as-synthesized form, "m" preferably has a value
of from 0.02 to 0.3.
The above silicoaluminophosphates are generally synthesized by
hydrothermal crystallization from a reaction mixture comprising
reactive sources of silicon, aluminum and phosphorus, and one or
more organic templating agents. Optionally, alkali metal(s) may
be present in the reaction mixture. The reaction mixture is placed
in a sealed pressure vessel, preferably lined with an inert plastic
material, such as polytetrafluoroethylene, and heated, preferably
under autogenous pressure at a temperature of at least about 100.degree.
C., and preferably between 100.degree. C. and 250.degree. C., until
crystals of the silicoaluminophosphate product are obtained, usually
for a period of from two hours to two weeks. While not essential
to the synthesis of SAPO compositions, it has been found that in
general, stirring or other moderate agitation of the reaction mixture
and/or seeding of the reaction mixture with seed crystals of either
the SAPO to be produced or a topologically similar composition,
facilitates the crystallization procedure. The product is recovered
by any convenient method such as centrifugation or filtration.
After crystallization the SAPO may be isolated and washed with
water and dried in air. As a result of the hydrothermal crystallization,
the as-synthesized SAPO contains within its intracrystalline pore
system at least one form of the template employed in its formation.
Generally, the template is a molecular species, but it is possible,
steric considerations permitting, that at least some of the template
is present as a charge-balancing cation. Generally, the template
is too large to move freely through the intracrystalline pore system
of the formed SAPO and may be removed by a post-treatment process,
such as by calcining the SAPO at temperatures of between about 200.degree.
C. and about 700.degree. C. so as to thermally degrade the template,
or by employing some other post-treatment process for removal of
at least part of the template from the SAPO. In some instances the
pores of the SAPO are sufficiently large to permit transport of
the template, and, accordingly, complete or partial removal thereof
can be accomplished by conventional desorption procedures such as
are carried out in the case of zeolites.
The SAPOs are preferably formed from a reaction mixture having
a mole fraction of alkali metal cation that is sufficiently low
to not interfere with the formation of the SAPO composition. Although
the SAPO compositions will form if alkali metal cations are present,
reaction mixtures, having the following bulk composition are preferred:
wherein "R" is a template; "a" has a value
great enough to constitute an effective concentration of "R"
and is within the range of from greater than zero to about 3; "b"
has a value of from zero to 500; "x", "y" and
"z" represent the mole fractions, respectively, of silicon,
aluminum and phosphorus wherein x, y and z each have a value of
at least 0.01. The reaction mixture is preferably formed by combining
at least a portion of the reactive aluminum and phosphorus sources
in the substantial absence of the silicon source and thereafter
combining the resulting reaction mixture comprising the aluminum
and phosphorus sources with the silicon source. When the SAPOs are
synthesized by this method the value of "m" is generally
above about 0.02.
Though the presence of alkali metal cations are not preferred,
when they are present in the reaction mixture, it is preferred to
first admix at least a portion of each of the aluminum and phosphorus
sources in the substantial absence of the silicon source. This procedure
avoids adding the phosphorus source to a highly basic reaction mixture
containing the silicon and aluminum source.
The reaction mixture from which these SAPOs are formed contain
one or more organic templating agents (templates) which can be most
any of those heretofore proposed for use in the synthesis of aluminosilicates.
The template preferably contains at least one element of Group VA
of the Periodic Table, more preferably nitrogen or phosphorus and
most preferably nitrogen. The template contains at least one alkyl,
aryl, araalkyl, or alkylaryl group. The template preferably contains
from 1 to 8 carbon atoms, although more than eight carbon atoms
may be present in the template. Nitrogen-containing templates are
preferred, including amines and quaternary ammonium compounds, the
latter being represented generally by the formula R'.sub.4 N+ wherein
each R' is an alkyl, aryl, alkylaryl, or araalkyl group; wherein
R' preferably contains from 1 to 8 carbon atoms or higher when R'
is alkyl and greater than 6 carbon atoms when R' is otherwise. Polymeric
quaternary ammonium salts such as [(C.sub.14 H.sub.32 N.sub.2)(OH).sub.2
].sub.x wherein "x" has a value of at least 2 may also
be employed. The mono-, di- and tri-amines, including mixed amines,
may also be employed as templates either alone or in combination
with a quaternary ammonium compound or another template.
Representative templates, phosphorus, aluminum and silicon sources
as well as detailed process conditions are more fully described
in U.S. Pat. No. 4440871 which is incorporated herein by reference.
The process of the invention may also be carried out by using a
catalyst comprising an intermediate pore size nonzeolitic molecular
sieve containing AlO.sub.2 and PO.sub.2 tetrahedral oxide units,
and at least one Group VIII metal. Exemplary suitable intermediate
pore size nonzeolitic molecular sieves are set forth in European
Patent Application No. 158977 which is incorporated herein by reference.
The intermediate pore size molecular sieve is used in admixture
with at least one Group VIII metal. Preferably, the Group VIII metal
is selected from the group consisting of at least one of platinum
and palladium, and optionally, other catalytically active metals
such as molybdenum, nickel, vanadium, cobalt, tungsten, zinc, and
mixtures thereof. More preferably, the Group VIII metal is selected
from the group consisting of at least one of platinum and palladium.
The amount of metal ranges from about 0.01% to about 10% by weight
of the molecular sieve, preferably from about 0.2% to about 5% by
weight of the molecular sieve. The techniques of introducing catalytically
active metals into a molecular sieve are disclosed in the literature,
and pre-existing metal incorporation techniques and treatment of
the molecular sieve to form an active catalyst such as ion exchange,
impregnation or occlusion during sieve preparation are suitable
for use in the present process. Such techniques are disclosed in
U.S. Pat. Nos. 3236761; 3226339; 3236762; 3620960; 3373109;
4202996; 4440781 and 4710485 which are incorporated herein
by reference.
The term "metal" or "active metal" as used
herein means one or more metals in the elemental state or in some
form such as sulfide, oxide and mixtures thereof. Regardless of
the state in which the metallic component actually exists, the concentrations
are computed as if they existed in the elemental state.
The physical form of the catalyst depends on the type of catalytic
reactor being employed and may be in the form of a granule or powder,
and is desirably compacted into a more readily usable form (e.g.,
larger agglomerates), usually with a silica or alumina binder for
fluidized bed reaction, or pills, prills, spheres, extrudates, or
other shapes of controlled size to accord adequate catalyst-reactant
contact. The catalyst may be employed either as a fluidized catalyst,
or in a fixed or moving bed, and in one or more reaction stages.
The intermediate pore size molecular sieve can be manufactured
into a wide variety of physical forms. The molecular sieves can
be in the form of a powder, a granule, or a molded product, such
as an extrudate having a particle size sufficient to pass through
a 2-mesh (Tyler) screen and be retained on a 40-mesh (Tyler) screen.
In cases wherein the catalyst is molded, such as by extrusion with
a binder, the silicoaluminophosphate can be extruded before drying,
or dried or partially dried and then extruded.
In a preferred embodiment, the final catalyst will be a composite
and includes an intermediate pore size silicoaluminophosphate molecular
sieve, a platinum or palladium hydrogenation metal component and
an inorganic oxide matrix. The most preferred silicoaluminophosphate
is SAPO-11 the most preferred metal component is palladium, and
the most preferred support is alumina. A wide variety of procedures
can be used to combine the molecular sieve and refractory oxide.
For example, the molecular sieve can be mulled with a hydrogel of
the oxide followed by partial drying if required and extruding or
pelletizing to form particles of a desired shape. Alternatively,
the refractory oxide can be precipitated in the presence of the
molecular sieve. This is accomplished by increasing the pH of the
solution of a refractory oxide precursor such as sodium aluminate
or sodium silicate. The combination can then be partially dried
as desired, tableted, pelleted, extruded, or formed by other means
and then calcined, e.g., at a temperature above 600.degree. F. (316.degree.
C.), usually above 800.degree. F. (427.degree. C.). Processes which
produce larger pore size supports are preferred to those producing
smaller pore size supports when cogelling.
The molecular sieves may be composited with other materials resistant
to temperatures and other conditions employed in the process. Such
matrix materials include active and inactive materials and synthetic
or naturally occurring zeolites as well as inorganic materials such
as clays, silica and metal oxides. The latter may be either naturally
occurring or in the form of gelatinous precipitates, sols or gels
including mixtures of silica and metal oxides. Inactive materials
suitably serve as diluents to control the amount of conversion in
the hydrocracking process so that products can be obtained economically
without employing other means for controlling the rate of reaction.
The silicoaluminophosphate molecular sieve may be incorporated into
naturally occurring clays, e.g., bentonite and kaolin. These materials,
i.e., clays, oxides, etc., function, in part, as binders for the
catalyst. It is desirable to provide a catalyst having good crush
strength, because in petroleum refining, the catalyst is often subjected
to rough handling. This tends to break the catalyst down into powder-like
materials which cause problems in processing.
Naturally occurring clays which can be composited with the catalyst
include the montmorillonite and kaolin families, which families
include the sub-bentonites, and the kaolins commonly known as Dixie,
McNamee, Georgia and Florida clays or others in which the main mineral
constituent is halloysite, kaolinite, dickite, nacrite or anauxite.
Fibrous clays such as halloysite, sepiolite and attapulgite can
also be used as supports. Such clays can be used in the raw state
as originally mined or initially subjected to calcination, acid
treatment or chemical modification.
In addition to the foregoing materials, the molecular sieve can
be composited with porous inorganic oxide matrix materials and mixtures
of matrix materials such as silica, alumina, titania, magnesia,
silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,
silica-beryllia, silica-titania, titania-zirconia, as well as ternary
compositions such as silica-alumina-thoria, silica-alumina-titania,
silica-alumina-magnesia and silica-magnesia-zirconia. The matrix
can be in the form of a cogel.
The hydrocracking step of the invention may be conducted by contacting
the feed with a fixed stationary bed of catalyst, with a fixed fluidized
bed, or with a transport bed. A simple and therefore preferred configuration
is a trickle-bed operation in which the feed is allowed to trickle
through a stationary fixed bed, preferably in the presence of hydrogen.
The hydrocracking conditions employed depend on the feed used and
the desired pour point. Generally, the temperature is from about
260.degree. C. to about 482.degree. C., preferably from about 316.degree.
C. to about 482.degree. C. The pressure is typically from about
200 psig to about 3000 psig, preferably from about 500 psig to about
3000 psig. The liquid hourly space velocity (LHSV) is preferably
from about 0.05 to about 20 more preferably from about 0.2 to about
10 most preferably from about 0.2 to about 5.
Hydrogen is preferably present in the reaction zone during the
hydrocracking process. The hydrogen to feed ratio is typically from
about 500 to about 30000 SCF/bbl (standard cubic feet per barrel),
preferably from about 1000 to about 20000 SCF/bbl. Generally,
hydrogen will be separated from the product and recycled to the
reaction zone.
The crystalline catalyst used in the hydrocracking step provides
selective conversion of the waxy components to non-waxy components
as well as conversion of 700.degree. F. + boiling feed components
to middle distillate hydrocarbons. During processing, isomerization
of the oil occurs to reduce the pour point of the unconverted 700.degree.
F.+ components below that of the feed and form a lube oil which
has a low pour point and excellent viscosity index.
Because of the selectivity of the intermediate pore size molecular
sieve used in this invention, the yield of product boiling below
middle distillate made by cracking is reduced, thereby preserving
the economic value of the feedstock.
Process Conditions
Although the catalyst used in this method exhibits excellent stability,
activity and midbarrel selectivity, reaction conditions must nevertheless
be correlated to provide the desired conversion rates while minimizing
conversion to less desired lower-boiling products. The conditions
required to meet these objectives will depend on catalyst activity
and selectivity and feedstock characteristics such as boiling range,
as well as organonitrogen and aromatic content and structure. The
conditions will also depend on the most judicious compromise of
overall activity, i.e., conversion and selectivity. For example,
these systems can be operated at relatively high conversion rates
on the order of 70 80 or even 90% conversion. However, higher conversion
rates generally result in lower selectivity. Thus, a compromise
must be drawn between conversion and selectivity. The balancing
of reaction conditions to achieve the desired objectives is part
of the ordinary skill of the art.
The overall conversion rate is primarily controlled by reaction
temperature and liquid hourly space velocity. However, selectivity
is generally inversely proportional to reaction temperature. It
is not as severely affected by reduced space velocities at otherwise
constant conversion. Conversely, selectivity for pour point reduction
of lube oil is usually improved at lower pressures. Thus, the most
desirable conditions for the conversion of a specific feed to a
predetermined product can be best obtained by converting the feed
at several different temperatures, pressures, space velocities and
hydrogen addition rates, correlating the effect of each of these
variables and selecting the best compromise of overall conversion
and selectivity.
The conditions should be chosen so that the overall conversion
rate will correspond to the production of at least about 40%, preferably
at least about 50%, of the products boiling below from about 675.degree.
F. (343.degree. C.) to about 725.degree. F. (385.degree. C.) in
the middle distillate range. Midbarrel selectivity should be such
that at least about 40%, preferably at least about 50% of the product
is in the middle distillate range, preferably below from about 675.degree.
F. to about 725.degree. F. and above about 300.degree. F. The process
can maintain conversion levels in excess of about 50% at selectivities
in excess of 60% to middle distillate products boiling between 300.degree.
F. (149.degree. C.) and about 675.degree. F. (343.degree. C.) to
about 725.degree. F. (385.degree. C.). Preferably, the hydrocarbonaceous
effluent contains greater than about 40% by volume boiling above
about 300.degree. F. and below from about 675.degree. F. to about
725.degree. F. and has a pour point below about 0.degree. F., more
preferably below about -20.degree. F. The lube oil produced by the
process of the invention has a low pour point, for example, below
about 30.degree. F., and a high viscosity index, for example, from
about 95 to about 150. In another embodiment, the pour point of
the lube oil is from about 30.degree. F. to about -70.degree. F.
The process can be operated as a single-stage hydroprocessing zone.
It can also be the second stage of a two-stage hydrocracking scheme
in which the first stage removes nitrogen and sulfur from the feedstock
before contact with the middle distillate-producing catalyst.
Nitrogen Content of Feedstocks
While the process herein can be practiced with utility when the
feed contains organic nitrogen (nitrogen-containing impurities),
for example as much as several thousand parts per million by weight
of organic nitrogen, it is preferred that the organic nitrogen content
of the feed be less than 50 ppmw, more preferably less than 10 ppmw.
Particularly good results, in terms of activity and length of catalyst
cycle (period between successive regenerations or start-up and first
regeneration), are I0 obtained when the feed contains less than
-0 ppmw of organic nitrogen. This is surprising in view of the art
(see, for example, U.S. Pat. No. 3894938).
Sulfur Content Feedstocks
The presence of organic sulfur (sulfur-containing impurities) in
the feedstock does not appear to deleteriously affect the desired
hydrocracking of the feed, for example, in terms of activity and
catalyst life. In fact, hydrodesulfurization of the feed of organic
sulfur is in large part a significant concurrent reaction. However,
the resulting product will usually contain at least some thiols
and/or thioethers as a result of inter-reaction of hydrogen sulfide
and olefinic hydrocarbons in the effluent product stream. Thus,
it may be desirable in some instances that the feed prior to use
in the process herein by hydrofined or hydrotreated for at least
substantial removal of both organic sulfur- and nitrogen-containing
compounds.
Upstream hydrodenitrogenation can be performed in the reactor with
the molecular sieve-containing catalyst or preferably in a separate
reactor. When a separate hydrodenitrogenation reactor is used, it
may be desirable to remove, e.g., flash, light gaseous products
such as NH3 upstream of the reactor containing the molecular sieve-containing
catalyst. If the hydrotreating is performed in the same reactor,
the molecular sieve-containing catalyst is disposed in one or more
layers downstream of an active hydrodenitrogenation catalyst. The
single reactor should preferably be operated under hydrotreating
conditions sufficient to reduce the organic nitrogen of the feed
to 10 ppmw or less before the feed encounters the molecular sieve-containing
layer. The volume of hydrodenitrogenation catalyst relative to molecular
sieve-containing catalyst can vary over a wide range, such as from
about 0.1 to 1 to 20 to 1 preferably at least 0.2 to 1 and more
preferably at least 0.5 to 1. The ratio depends upon such parameters
as: (a) the organic nitrogen content of the feedstock; (b) the hydrodenitrogenation
and hydrocracking activities of the upstream hydrotreating catalyst;
and (c) the degree of overall hydrocracking desired.
The upstream hydrotreating catalysts can be any of the conventional
catalysts having hydrodenitrogenation and hydrocracking activity.
See, for example, U.S. Pat. No. 3401125 incorporated herein by
reference. In general, such hydrotreating catalysts are porous composites
or inorganic matrix oxides such as alumina, silica, and magnesia,
which contain one or more hydrogenation components such as transition
elements, particularly elements of Group VIB or Group VIII of the
Periodic Table of the Elements. Handbook of Chemistry and Physics,
45th Ed., Chemical Rubber Company. The Group VIB and/or Group VIII
or other transition elements can be present as metals, oxides, or
sulfides. The hydrotreating catalyst can also contain promoters
such as phosphorus, titanium and other materials known in the art,
present as metals, oxides or sulfides. The upstream hydrotreating
catalyst need not contain a silicoaluminophosphate component. Typical
upstream hydrogenation catalysts suitable for use herein contain
10 to 30 wt.% amorphous silica, 20 to 40 wt.% amorphous alumina,
15 to 30 wt.% Group VIB metal oxide, such as WO.sub.3 5 to 15 wt.%
Group VIII metal oxide, such as NiO and 2 to 15 wt.% of a promoter
oxide, such as TiO.sub.2. The hydrotreating catalyst should have
an average pore size in the range of about 30 to 200 Angstroms and
a surface area of at least about 150 square meters per gram.
Following the hydrocracking step over the silicoaluminophosphate
catalyst, the middle distillate and lighter boiling products are
separated from the lube oil base stock by distillation. It is often
desirable to then treat this base stock by mild hydrogenation referred
to as hydrofinishing to improve color and produce a more stable
oil. Hydrofinishing is typically conducted at temperatures ranging
from about 190.degree. C. to about 340.degree. C., at pressures
from about 400 psig to about 3000 psig, at space velocities (LHSV)
from about 0.1 to about 20 and hydrogen recycle rates of from about
400 to about 15000 SCF/bbl. The hydrogenation catalyst employed
must be active enough not only to hydrogenate the olefins, diolefins
and color bodies within the lube oil fractions, but also to reduce
the aromatic content. The hydrofinishing step is beneficial in preparing
an acceptably stable lubricating oil.
Suitable hydrogenation catalysts include conventional metallic
hydrogenation catalysts, particularly the Group VIII metals such
as cobalt, nickel, palladium and platinum. The metals are typically
associated with carriers such as bauxite, alumina, silica gel, silica-alumina
composites, and crystalline aluminosilicate zeolites. Palladium
is a particularly preferred hydrogenation metal. If desired, non-noble
Group VIII metals can be used with molybdates. Metal oxides or sulfides
can be used. Suitable catalysts are disclosed in U.S. Pat. Nos.
3852207; 4157294; 3904513 and 4673487 which are incorporated
herein by reference.
The high viscosity index lube oil produced by the process of the
present invention can be used as a blending component to raise the
viscosity index of lube oils to a higher value. The lube oil is
particularly suitable for use as a blending component when the lube
oil has a high viscosity index, for example, greater than 130. Since
yield decreases with increasing viscosity index in either hydrocracking
or solvent refining, the use of an ultra-high viscosity oil to increase
the viscosity index improves yield. |