U.S. patent application number 10/266341 was filed with the patent office on 2004-04-08 for enhanced lube oil yield by low hydrogen pressure catalytic dewaxing of paraffin wax.
Invention is credited to Ansell, Loren Leon, Bishop, Adeana Richelle, Genetti, William Berlin, Jiang, Zhaozhong, Johnson, Jack Wayne, Page, Nancy Marie, Ryan, Daniel Francis.
Application Number | 20040065582 10/266341 |
Document ID | / |
Family ID | 32042652 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040065582 |
Kind Code |
A1 |
Genetti, William Berlin ; et
al. |
April 8, 2004 |
Enhanced lube oil yield by low hydrogen pressure catalytic dewaxing
of paraffin wax
Abstract
Catalytic dewaxing of paraffin containing feeds, preferably
feeds produced from a non-shifting Fischer-Tropsch catalyst, is
accomplished at relatively low hydrogen partial pressures without
substantial affect on the life of a catalyst having a certain pore
structure.
Inventors: |
Genetti, William Berlin;
(Baton Rouge, LA) ; Jiang, Zhaozhong; (Somerville,
NJ) ; Ryan, Daniel Francis; (Baton Rouge, LA)
; Bishop, Adeana Richelle; (Baton Rouge, LA) ;
Ansell, Loren Leon; (Baton Rouge, LA) ; Johnson, Jack
Wayne; (Clinton, NJ) ; Page, Nancy Marie;
(Baton Rouge, LA) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
32042652 |
Appl. No.: |
10/266341 |
Filed: |
October 8, 2002 |
Current U.S.
Class: |
208/27 ; 208/108;
208/950 |
Current CPC
Class: |
C10G 45/64 20130101;
B01J 29/7461 20130101; B01J 29/7492 20130101; C10G 45/62 20130101;
C10G 2400/10 20130101; B01J 29/7484 20130101; B01J 29/7415
20130101; C10G 65/043 20130101; B01J 29/67 20130101; B01J 29/068
20130101 |
Class at
Publication: |
208/027 ;
208/108; 208/950 |
International
Class: |
C10G 073/38 |
Claims
What is claimed is:
1. A catalytic dewaxing process comprising contacting an 80+%
paraffin containing feed at dewaxing conditions including a
hydrogen partial pressure of less than about 500 psig with a
catalyst comprised of a molecular sieve with a one dimensional pore
structure having an average diameter of 0.50 to 0.65 nm and a metal
dehydrogenation component, the catalyst having a deactivation rate,
measured by temperature increase required (TIR) for meeting a
pre-determined pour point or cloud point, of less than 30.degree.
F./year.
2. The process of claim 1 wherein the hydrogen partial pressure is
less than 400 psig.
3. The process of claim 2 wherein TIR is less than 25.degree.
F./year.
4. The process of claim 3 wherein the paraffin containing feed
contains greater than 80 wt % paraffins and boils in the range
above 430.degree. F.
5. The process of claim 4 wherein the feed is derived from a
Fischer-Tropsch process and contains less than 50 wppm each of
nitrogen and sulfur.
6. The process of claim 5 wherein the dehydrogenation component is
platinum or palladium.
7. The process of claim 6 wherein the hydrogen partial pressure
ranges from about 100 to about 350 psig.
8. The process of claim 7 wherein reaction temperatures ranges from
about 550.degree. F. to about 800.degree. F.
9. The process of claim 7 wherein total reaction pressure ranges
from about 100 to about 2000 psi.
10. The process of claim 7 wherein the pour point is -21.degree. C.
or lower.
11. The process of claim 7 wherein the product of the catalytic
dewaxing process is a lube base stock or a diesel range material,
and is subjected to a hydrofinishing step.
12. The process of claim 11 wherein the product of the catalytic
dewaxing process is a lube base stock.
13. The process of claim 12 wherein the molecular sieve is selected
from the group consisting of ZSM-23, ZSM-35, ZSM-48, ZSM-22,
SSZ-32, zeolite beta, mordenite, rare earth ion exchanged
ferrierite and mixtures thereof.
14. The process of claim 13 wherein the molecular sieve is
ZSM-48.
15. The process of claim 14 wherein the metal dehydrogenation
component comprises a Group VIII metal.
16. The process of claim 15 wherein the Group VIII metal is a noble
metal.
17. The process of claim 15 wherein the metal dehydrogenation
component is a noble metal and the molecular sieve is ZSM-48.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a process for catalytically
dewaxing paraffin containing hydrocarbons. More particularly, this
invention relates to the production of lube base oils having a
pre-determined or pre-selected pour point by catalytically dewaxing
a paraffin containing feed at low hydrogen partial pressures.
BACKGROUND OF THE INVENTION
[0002] The production of lube base oils by hydroprocessing paraffin
containing feeds is well known, e.g., hydroisomerization or
hydrocracking of the feed to produce lube base oils. These
processes are catalytic and are usually carried out at relatively
high hydrogen pressures, e.g., >500 psig hydrogen partial
pressures. Catalytic dewaxing is a form of hydroprocessing and
involves paraffin isomerization and some hydrocracking in the
production of lube base oils.
[0003] Hydrogen has always been used in the hydroprocessing, i.e.,
isomerization, cracking, dewaxing, of paraffins to produce lube
base oils. Hydrogen is believed to be important for promoting
extended catalyst life by e.g., reductive coke removal; see, for
example U.S. Pat. No. 4,872,968. The hydrogen partial pressures
usually employed in catalytic dewaxing processes range from about
200 psig to about 1000 psig or more, e.g., see U.S. Pat. No.
5,614,079 with hydrogen pressures in the higher end of this range
being preferred--for reasons of catalyst life.
[0004] U.S. Pat. No. 5,362,378 discloses hydrogen partial pressures
of 72-2305 psig for use with large pore zeolite beta. This patent
does not mention catalyst life or TIR, i.e., temperature increase
required, necessary for maintaining product specifications, such as
pour point or cloud point.
[0005] We have now found, however, that a particular combination of
features allows for conducting catalytic dewaxing at low hydrogen
pressures and conditions that are selective to hydroisomerization
with little or no hydrocracking, without sacrificing catalyst
life.
SUMMARY OF THE INVENTION
[0006] In an embodiment of this invention, a paraffin containing
feed, preferably a feed containing at least 80 wt % paraffins, can
be catalytically dewaxed in the presence of a molecular sieve
catalyst with one dimensional pore structures having an average
diameter of 0.50 nm to 0.65 nm, wherein the difference between the
maximum diameter and the minimum diameter is preferably
.ltoreq.0.05 nm. The molecular sieve catalyst is exemplified by,
for example, ZSM-23, ZSM-35, ZSM-48, ZSM-22, SSZ-32, zeolite beta,
mordenite and rare earth ion exchanged ferrierite in conjunction
with a dehydrogenation component. Preferably, the molecular sieve
catalyst is ZSM-48 (ZSM-48 zeolites herein include EU-2, EU-11 and
ZBM-30 which are structurally equivalent to ZSM-48) with a
dehydrogenation component. The dewaxing process is carried out at
hydrogen partial pressures of less than about 500 psig while
maintaining a catalyst deactivation rate of less than 30.degree.
F./year.
[0007] The invention includes a catalytic dewaxing process
comprising contacting an 80+% paraffin containing feed at dewaxing
conditions including a hydrogen partial pressure of less than about
500 psig with a catalyst comprised of a molecular sieve with a one
dimensional pore structure having an average diameter of 0.50 to
0.65 nm and a metal dehydrogenation component, the catalyst having
a deactivation rate, measured by temperature increase required
(TIR) for meeting a pre-determined pour point or cloud point, of
less than 30.degree. F./year.
[0008] Catalyst deactivation rate is reported herein as TIR; that
is "temperature increase required" for maintaining a pre-determined
pour point, the predetermined pour point preferably being less than
about -12.degree. C., more preferably less than about -21.degree.
C. Catalytic dewaxing is, essentially, the conversion of
n-paraffins to branched paraffins. That is, the conversion of waxy
molecules to molecules exhibiting better flow properties,
particularly at lower temperatures.
DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a plot of pour point, .degree. C. (ordinate)
against temperature, .degree. F. (abscissa) showing that catalytic
activity increases with decreasing hydrogen pressure.
[0010] FIG. 2 is a plot of % conversion (ordinate) against pour
point, .degree. C. (abscissa) showing that selectivity to
isomerization increases with decreasing hydrogen pressure.
[0011] FIG. 3 is a plot of average reactor temperature, .degree. F.
(ordinate) against days on stream (abscissa) and shows a
deactivation rate by regression when producing a lube base oil of
-21.degree. C. pour point at a hydrogen partial pressure of 150
psig.
[0012] FIG. 4 is a plot of Temperature, .degree. C. (ordinate)
against days on stream (abscissa) at 250 psig hydrogen pressure to
meet a diesel cloud point of -15.degree. C.
[0013] FIG. 5 is a plot similar to FIG. 4 to meet a -21.degree. C.
wide cut lube base oil pour point.
[0014] FIG. 6 is a plot of reactor temperature, .degree. F.
(ordinate) against days on stream (abscissa) to meet a -21.degree.
C. pour point for a 700-950.degree. F. isomerate.
[0015] FIG. 7 is a plot of reactor temperature, .degree. F.
(ordinate) against days on stream (abscissa) to meet a +8.degree.
C. cloud point for a 950.degree. F.+ isomerate.
[0016] For the particular set of features described herein,
reducing hydrogen partial pressure results in increased catalyst
activity, and increased yield. That is, the increase in activity is
almost entirely an increase isomerization activity, and little
hydrocracking occurs. Nevertheless, while decreasing hydrogen
partial pressure should result in decreased catalyst life, the
features of this invention show that catalyst life is not
sacrificed.
[0017] For purposes of this invention, pour point is determined by
ASTM D-5950, cloud point is determined by ASTM D-5773.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The feed that can be employed in various embodiments of this
invention is a paraffin containing feed, preferably a feed that
contains greater than 80 wt % n-paraffins, more preferably greater
than 90 wt % n-paraffins, still more preferably greater than 95 wt
% n-paraffins and still more preferably 98 wt % n-paraffins. The
feed generally boils in the range 430.degree. F.+, preferably
450.degree. F.+, more preferably 450-1200.degree. F. (minor
amounts, e.g., less than about 10% of 1200.degree. F.+ material may
be present).
[0019] The feed is preferably low in unsaturates, that is, low in
both aromatics and olefins. Preferably, the unsaturates level is
less than 10 wt %, preferably less than 5 wt %, more preferably
less than 2 wt %. Also, the feed is relatively low in nitrogen and
sulfur, e.g., less than 50 wppm of each. Where a Fischer-Tropsch
derived feed is employed, there is no need to pre-sulfide the
catalyst, and indeed, pre-sulfiding should be avoided.
[0020] Most preferably, the feed is the product of a
Fischer-Tropsch reaction that produces essentially n-paraffins, and
still more preferably the Fischer-Tropsch process is conducted with
a non-shifting catalyst, e.g., cobalt or ruthenium, preferably a
cobalt containing catalyst.
[0021] The catalyst employed in the catalytic dewaxing step
comprises a molecular sieve with one dimensional pore structure and
a metal dehydrogenation component. The molecular sieves include
ZSM-23, ZSM-35, ZSM-22, SSZ-32, zeolite beta, mordenite and rare
earth ion exchanged ferrierite. Preferably, a ZSM-48 catalyst
containing a metal dehydrogenation functionality, preferably
supplied by the presence of platinum or palladium or both platinum
and palladium, preferably platinum.
[0022] The molecular sieve catalyst support is described in J.
Schlenker, et al., Zeolites 1985, vol. 5, November, 355-358, hereby
incorporated by reference. ZSM-48 is characterized by the X-ray
diffraction pattern shown in Table 1 below. The material is further
characterized by the fact that it exhibits a single line within the
range of 11.8.+-.0.2 Angstrom units. The presence of a single line
at the indicated spacing structurally distinguishes ZSM-48 from
closely related materials such as ZSM-12 (described in U.S. Pat.
No. 3,832,449) which has two lines, i.e., a doublet, at 11.8.+-.0.2
Angstrom units, and high silica ZSM-12 (described in U.S. Pat. No.
4,104,294) which also has a doublet at the indicated spacing.
1TABLE 1 Characteristic lines of ZSM-48 (calcined, Na Exchanged
Form) d(A) Relative Intensity (I/I.sub.O) 11.8 .+-. 0.2 S 10.2 .+-.
0.2 W-M 7.2 .+-. 0.15 W 4.2 .+-. 0.08 VS 3.9 .+-. 0.08 VS 3.6 .+-.
0.06 W 3.1 .+-. 0.05 W 2.85 .+-. 0.05 W
[0023] The values were determined by standard technique, i.e.,
radiation was K-alpha doublet of copper, and diffractometer
equipped with a scintillation counter. The peak heights, I, and the
positions as a function of two times theta, where theta is the
Bragg angle, were determined by a compactor. From these the
relative intensities, 100 I/I.sub.O, where I.sub.O is the intensity
of the strongest line or peak, and d(obs.), the interplanar spacing
in A corresponding to the recorded lines, were calculated. Table 1
gives the intensities in terms of the symbols W=weak, VS=very
strong, M=medium, and W-S=weak to strong (depending on the cationic
form). Ion exchange of the sodium ion with other cations reveals
substantially the same pattern with some minor shifts in
interplanar spacing and variation in relative intensity. Other
minor variations can occur depending on the silicon to aluminum
ratio of the particular sample, as well as any subsequent thermal
treatment.
[0024] ZSM-48 and methods for its preparation are described in U.S.
Pat. Nos. 4,375,573; 4,397,827; 4,448,675; 4,423,021; and
5,075,269. The method of preparation described in U.S. Pat. No.
5,075,269 is particularly preferred, and is incorporated herein by
reference. This method is for preparing a catalyst particularly
suitable for the catalytic dewaxing process.
[0025] The zeolite, ZSM-48, and other utilizable zeolites such as
ZSM-23, ZSM-35, ZSM-22, SSZ-32, zeolite beta, mordenite and rare
earth ion exchanged ferrierite are usually employed with a
dehydrogenation component in an amount of about 0.01 to 5.0 wt/o,
the component being manganese, tungsten, vanadium, zinc, chromium,
molybdenum, rhenium, Group VIII metals such as nickel, cobalt, or
the noble metals platinum and palladium. The noble metals are
preferred components. Such component can be exchanged into the
composition, impregnated thereon, or physically intimately admixed
therewith. Such component can be impregnated in or onto the zeolite
such as, for example, in the case of platinum, by treating the
zeolite with a platinum metal-containing ion. Thus, suitable
platinum compounds include chloroplatinic acid, platinous chloride
and various compounds containing the platinum tetra-ammonia
complex. Platinum and palladium are preferred hydrogenation
components.
[0026] The compounds of the useful platinum or other metals can be
divided into compounds in which the metal is present in the cation
of the compound and compounds in which it is present in the anion
of the compound. Both types of compounds which contain the metal in
the ionic state can be used. A solution in which platinum metals
are in the form of a cation or cationic complex, e.g.,
Pt(NH.sub.3).sub.4Cl.sub.2, is particularly useful.
[0027] Prior to its use, the ZSM-48 catalyst should be dehydrated
at least partially. This can be done by heating to a temperature in
the range of from about 100.degree. C. to about 600.degree. C. in
an inert atmosphere, such as air, nitrogen, etc., and at
atmospheric or subatmospheric pressures for between 1 and 48 hours.
Dehydration can also be performed at lower temperature merely by
placing the catalyst in a vacuum, but a longer time is required to
obtain sufficient amount of dehydration. ZSM-48 is formed in a wide
variety of particle sizes. Generally speaking, the particles can be
in the form of a powder, a granule, or a molded product, such as
extrudate having a particle size sufficient to pass through a 2
mesh (Tyler) screen and be retained on a 400 mesh (Tyler) screen.
In cases where the catalyst is molded, such as by extrusion, the
crystalline silicate can be extruded before drying or dried or
partially dried and then extruded.
[0028] As in the case of many other zeolite catalysts, it may be
desired to incorporate the ZSM-48 with a matrix material which is
resistant to the temperatures and other conditions employed in the
dewaxing process herein. Such matrix materials include active and
inactive materials and synthetic or naturally occurring zeolites as
well as inorganic materials such as clays, silica and/or metal
oxides e.g., alumina. The latter may be either naturally occurring
or in the form of gelatinous precipitates, sols or gels including
mixtures of silica and metal oxides. Use of a material in
conjunction with the ZSM-48, i.e., combined therewith, which is
active, may enhance the conversion and/or selectivity of the
catalyst herein. Inactive materials suitably serve as diluents to
control the amount of conversion in a given process so that
products can be obtained economically and orderly without employing
other means for controlling the rate or reaction. Frequently,
crystalline silicate materials have been 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 since in a petroleum refinery the catalyst is often
subject to rough handling which tends to break the catalyst down
into powder-like materials which cause problems in processing.
[0029] Naturally occurring clays which can be composited with
ZSM-48 include the montmorillonite and kaolin families which
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. Such clays can be used in the raw state as originally
mined or initially subjected to calcination, acid treatment or
chemical modification.
[0030] In addition to the foregoing materials, ZSM-48 can be
composited with a porous matrix material such as silica-alumina,
silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia,
silica-titania, as well as ternary compositions such as
silica-alumina-thoria, silica-alumina-zirconia,
silica-alumina-magnesia and silica-magnesia-zirconia. The matrix
can be in the form of a cogel. Mixtures of these components can
also be used. The relative proportions of finely divided
crystalline silicate ZSM-48 and inorganic oxide gel matrix vary
widely with the crystalline silicate content ranging from about 1
to about 90 percent by weight, and more usually in the range of
about 2 to about 80 percent by weight, of the composite.
[0031] In general, reaction conditions for dewaxing may vary widely
even when the hydrogen partial pressures are maintained at low
levels. Thus, start of run temperatures may vary between about
550-650.degree. F. (288-343.degree. C.). End of run conditions can
be defined by the nature of the product being produced, for
example, when predetermined color specifications can no longer be
met (an indication of catalyst deactivation), or when the
predetermined pour point or cloud point can no longer be obtained,
or the selectivity to isomerization is reduced as evidenced by an
increase in methane yield due to hydrocracking. In general,
however, end of run temperatures should be less than about
800.degree. F. (427.degree. C.), preferably less than about
750.degree. F. (399.degree. C.), more preferably less than about
725.degree. F. (385.degree. C.).
[0032] In one embodiment of this invention, hydrogen partial
pressure is maintained as low as reasonably possible without
sacrificing desired catalyst life. Catalyst life may be longer or
shorter depending on desired results and severity of the dewaxing
process, i.e., higher severity obtained by increasing temperature
or decreasing feed velocity, or both. However, at end of run
conditions the catalyst must be either rejuvenated or replaced, if
rejuvenation is no longer possible. In either case the unit must be
shut down and valuable operating time is lost. Reasonable catalyst
life will be a function of operator choice but, measured by TIR, is
preferably not more than 30.degree. F./year, more preferably less
than 25.degree. F./year, still more preferably less than 20.degree.
F./year, and still more preferably less than 10.degree. F./year. In
another aspect of this invention, the catalyst deactivation rate at
dewaxing conditions allows the process to be carried out, while
still meeting a predetermined pour point or cloud point, for a
period of at least six months, preferably at least about twelve
months, more preferably at least about 18 months, and still more
preferably for at least about 24 months, or longer, for example,
greater than 30 months or greater than 36 months.
[0033] Catalyst deactivation is believed to be a result of coke
formation on the surface of the catalyst, the coke covering or
blocking access to the catalytic metal, as well as blocking the
pores of the zeolite.
[0034] The catalyst may be regenerated by known methods including
hot hydrogen stripping, coke removal by oxygen treatment or a
combination of hydrogen stripping and oxygen treatment.
[0035] Briefly, hydrogen stripping can be carried out with hydrogen
or a mixture of hydrogen and an inert gas such as nitrogen, at
isomerization reaction temperatures for a period of time sufficient
to allow the catalyst to regain at least about 80%, preferably at
least about 90% of its original lined out activity. Oxygen
treatment can be carried out at calcining conditions, e.g., using
air at temperatures from about 500.degree. C. to 650.degree. C.,
again for a period of time sufficient to allow the catalyst to
regain at least about 80%, preferably at least about 90% of initial
lined out activity after subsequent reduction.
[0036] The catalyst life requirements can be satisfied with
positive hydrogen partial pressures greater than 0 psig and less
than 400 psig, preferably at hydrogen partial pressures ranging
from about 100-400 psig, more preferably about 100-350 psig, and
still more preferably at about 150-350 psig.
[0037] The catalyst may be sulfided or unsulfided. Where low sulfur
feeds are used, e.g., derived from the Fischer-Tropsch process, the
catalyst is preferably unsulfided. In general, other gases may be
present and will not interfere with the reaction. Such other gases
may be nitrogen, methane, or other light hydrocarbons (that may be
produced during the reaction). Total pressure may range up to 2000
psi, preferably 100-2000 psi, more preferably 150-1000 psi, still
more preferably 150-500 psi. Hydrogen can make up 50-100% of total
gas, preferably 70-100%, more preferably 70-90%. At the low
hydrogen partial pressures recited herein small amounts of olefins
and aromatics may be produced, and hydrofinishing, at well known
conditions, may be necessary to remove these components.
[0038] The liquid hourly space velocity is generally between about
0.1 and about 10, and preferably is generally between about 0.5 and
4. The hydrogen to feed ratio is generally between about 100 and
about 10,000, and preferably between about 800 and about 4,000
standard cubic feet (scf) of hydrogen per barrel of fuel.
[0039] Alpha Value is an approximate indication of the catalytic
cracking activity of the catalyst compared to a standard catalyst
and provides a relative rate constant (rate of normal hexane
conversion per volume of catalyst per unit time). The value is
based on the activity of a silica-alumina cracking catalyst taken
as an Alpha of 1 (rate constant=0.016 sec.sup.-1). The test for
Alpha Value is described in U.S. Pat. No. 3,354,078 in the Journal
of Catalysis. vol. 4, p. 527 (1965); vol. 6, p. 278 (1966); and
vol. 61. 395 (1980), each incorporated herein by reference. The
Alpha Value of the catalyst prior to metal loading is preferably in
the range of about 10 to about 50.
[0040] The following examples will serve to illustrate this
invention:
EXAMPLE 1
[0041] This example explores the benefits in lube base oil yield
obtained as hydrogen partial pressure is reduced from 500 to 150
psig. The following unit conditions and process variables were
studied with ZSM-48 using a wide cut Fischer-Tropsch feed, i.e.,
430.degree. F.+ feed.
[0042] Catalytic dewaxing was carried out in a downflow reactor
simulating a trickle bed reactor immersed in a sand bath to
maintain isothermal reactor conditions. The reactor contained 80 cc
of an unsulfided ZSM-48 catalyst with 0.6 wt % Pt diluted with
glass beads. Conversion of a 430.degree. F.+ wax obtained from a
cobalt slurry catalyzed Fischer-Tropsch process was controlled by
temperature.
[0043] The process was operated at temperatures ranging from
580-640.degree. F. with reactor hydrogen pressures, at the reactor
exit of 150-500 psig. The hydrogen treat gas rate was 1800-2500
scf/bbl, and the liquid hourly space velocity was 1.25 v/v/hr.
[0044] The liquid product was fractionated by 15/5 distillation
unit and the following fractions were recovered: IBP/320.degree.
F., 320/700.degree. F., and 700.degree. F.+. The 700.degree. F.+
fraction was analyzed for pour and cloud points, and kinematic
viscosity and viscosity index; the 320/700.degree. F. fraction was
analyzed for cloud point.
[0045] In FIG. 1, lines A, B, and C refer to hydrogen pressures of
150, 250, and 500 psig. At a pour point of -21.degree. C.,
catalytic activity increases with decreasing operating pressure, as
shown in Table 2 below.
2TABLE 2 Operating H.sub.2 Pressure, psig Temperature required for
-21.degree. C. P.P. 500 627.4 250 612.8 150 602.8
[0046] Because the kinetics of the dewaxing process are negative
second order in hydrogen the activity increase with reduced
pressure may be anticipated.
[0047] Selectivity to lubes increased with decreasing hydrogen
pressure. In FIG. 2, where lines A, B, and C again refer to
hydrogen pressures of 150, 250, and 500 psig. The lubes yield,
(i.e., 1-conversion), at a -21.degree. C. pour point is shown for
each pressure in Table 3, below.
3 TABLE 3 Operating H.sub.2 Pressure, psig Lubes Yield, at
-21.degree. C. P.P., % 500 66.7 250 73.9 150 77.7
[0048] The data show that catalyst activity and lube selectivity
increased at lower pressure. Consequently, overall lube yield
increased.
[0049] Nevertheless, the prevailing wisdom is that catalyst life
decreases substantially as hydrogen pressure decreases, thereby
leading to shortened on stream periods and longer down times. To
determine the effect of reduced hydrogen pressure on catalyst life
(and the rate of catalyst deactivation) another experiment was
conducted over a period of 70 days at 150 psig hydrogen pressure
and producing lube base oil of -21.degree. C. pour point. By
regression, the deactivation rate was 21.degree. F./year, by two
point activity check the deactivation rate was 26.degree. F./year.
Consequently, operating at a very low hydrogen pressure results in
a quite acceptable deactivation rate, and clearly suggests that
hydrogen pressures of less than 150 psig, e.g., 125 psig, or less
than 100 psig, e.g., about 75 psig, will benefit both selectivity
to isomerization and increased lube base oil yield while
maintaining deactivation rates of less than about 30.degree.
F./year, or preferably less than about 25.degree. F./year, and more
preferably less than about 15.degree. F./year.
EXAMPLE 2
[0050] The reactor described in Example 1 was operated with a
430.degree. F.+ wide cut Fischer-Tropsch wax feed to study the
operation of a dewaxing unit at 250 psig. The catalyst of Example 1
was used, as well. The hydrogen treat gas rate was 2500 SCF/bbl.
The liquid hourly space velocity was 1.0. Temperature was adjusted
to meet lube pour point or diesel cloud point. When operated to
meet a diesel cloud point of -15.degree. C., the deactivation rate
was less than 1.8.degree. F./year (1.degree. C./year). The results
are shown in FIG. 4.
[0051] Operation of this unit to meet a -21.degree. C. wide-cut
lube pour point resulted in a deactivation rate of about 3.degree.
C./year (5.4.degree. F./year). The results are shown in FIG. 5.
EXAMPLE 3
[0052] The same feed as used in Example 1 was hydroisomerized and
the isomerate was distilled into two fractions: (i) 700-950.degree.
F. light cut, and (ii) a 950.degree. F.+ heavy cut. Each fraction
was processed in the reactor described in Example 1 and conditions
described in Example 2 to meet a -21.degree. C. pour point and a
cloud point of +8.degree. C., respectively. Each fraction was run
for four (4) months. The results are shown in FIGS. 6 and 7; FIG. 6
showing a deactivation rate (by regression) for fraction (i) of
about 2.degree. F./year, FIG. 7 showing a deactivation rate (by
regression) for fraction (ii) of about 2.degree. F./year.
* * * * *