U.S. patent application number 11/298728 was filed with the patent office on 2006-04-27 for dual catalyst system for hydroisomerization of fischer-tropsch wax and waxy raffinate.
Invention is credited to Terry Eugene Helton, Larry E. Hoglen, Zhaozhong Jiang, Randall David Partridge.
Application Number | 20060086643 11/298728 |
Document ID | / |
Family ID | 32042662 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060086643 |
Kind Code |
A1 |
Jiang; Zhaozhong ; et
al. |
April 27, 2006 |
Dual catalyst system for hydroisomerization of Fischer-Tropsch wax
and waxy raffinate
Abstract
The present invention relates to a process for converting
Fischer-Tropsch wax to high quality lube basestocks using a
molecular sieve Beta catalyst followed by a unidimensional
intermediate pore molecular sieve with near circular pore
structures having an average diameter of 0.50 nm to 0.65 nm wherein
the difference between the maximum diameter and the minimum is
.ltoreq.0.05 nm. Both catalysts comprise one or more Group VIII
metals. For example, a cascaded two-bed catalyst system consisting
of a first bed Pt/Beta catalyst followed by a second bed Pt/ZSM-48
catalyst is highly selective for wax isomerization and lube
hydrodewaxing with minimal gas formation.
Inventors: |
Jiang; Zhaozhong;
(Somerville, NJ) ; Helton; Terry Eugene;
(Bethlehem, PA) ; Partridge; Randall David;
(Califon, NJ) ; Hoglen; Larry E.; (Mickleton,
NJ) |
Correspondence
Address: |
EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
P.O. BOX 900
1545 ROUTE 22 EAST
ANNANDALE
NJ
08801-0900
US
|
Family ID: |
32042662 |
Appl. No.: |
11/298728 |
Filed: |
December 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10266369 |
Oct 8, 2002 |
|
|
|
11298728 |
Dec 9, 2005 |
|
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Current U.S.
Class: |
208/18 ; 208/19;
208/950 |
Current CPC
Class: |
Y10S 208/95 20130101;
C10G 45/62 20130101; C10G 2400/10 20130101 |
Class at
Publication: |
208/018 ;
208/019; 208/950 |
International
Class: |
C10M 101/02 20060101
C10M101/02 |
Claims
1. An isoparaffinic basestock made by a process for converting a
Fischer-Tropsch wax to an isoparaffinic lube basestock, comprising:
first, passing the Fischer-Tropsch wax and a hydrogen co-feed over
a Beta catalyst comprising a Zeolite Beta and one or more Group
VIII metals, to form an intermediate product; and second, passing
the intermediate product over a unidimensional molecular sieve
catalyst comprising a unidimensional intermediate pore molecular
sieve with near circular pore structures having an average diameter
of 0.50 nm to 0.65 nm wherein the difference between a maximum
diameter and a minimum diameter is .ltoreq.0.05 nm and one or more
Group VIII metals; wherein the isoparaffinic lube basestock has a
viscosity index of at least 160 at a -20.degree. C. lube pour point
and a viscosity index of at least 135 at a pour point of no more
than -50.degree. C.
2. The isoparaffinic lube basestock of claim 1, wherein the
isoparaffinic lube basestock has less than 1 wt % aromatic
content.
3. A lubricant made by a process for converting a Fischer-Tropsch
wax to an isoparaffinic lube basestock, comprising: first, passing
the Fischer-Tropsch wax and a hydrogen co-feed over a Beta catalyst
comprising a Zeolite Beta and one or more Group VIII metals, to
form an intermediate product; and second, passing the intermediate
product over a unidimensional molecular sieve catalyst comprising a
unidimensional intermediate pore molecular sieve with near circular
pore structures having an average diameter of 0.50 nm to 0.65 nm
wherein the difference between a maximum diameter and a minimum
diameter is .ltoreq.0.05 nm and one or more Group VIII metals;
wherein the lubricant has a viscosity index of at least 160 at a
-20.degree. C. lube pour point and a viscosity index of at least
135 at a pour point of no more than -50.degree. C.
4. A lubricant made by a process for converting a Fischer-Tropsch
wax to an isoparaffinic lube basestock, comprising: first, passing
the Fischer-Tropsch wax and a hydrogen co-feed over the first bed
of a cascaded two-bed catalyst system comprised of a Pt/Beta
catalyst at a temperature of 500-600.degree. F. (260 to 316.degree.
C.) and at a feed liquid hourly space velocity of 0.5 to 2 h.sup.-1
to form an intermediate product; and second, passing the
intermediate product over the second bed of a cascaded two-bed
catalyst system comprised of a Pt/ZSM-48 catalyst at a temperature
of 600-700.degree. F. (316 to 371.degree. C.) and at a feed liquid
hourly space velocity of 0.5 to 2 h.sup.-1 to form a lubricant; and
wherein the process further comprises less than about 1,500 psig
(102 atm) hydrogen, wherein the hydrogen is circulated at 1,000 to
6,000 scf/bbl (178 to 1068 n.L.L.sup.-1); and wherein the Pt/Beta
catalyst is comprised of a Zeolite Beta loaded with about 0.5 wt %
to about 1 wt % of Pt based on the total weight of the Zeolite
Beta, and the Zeolite Beta has an Alpha value less than about 15
prior to loading of the Pt; and the ZSM-48 catalyst is loaded with
about 0.5 wt % to about 1 wt % of Pt based on the total weight of
the ZSM-48; and wherein the lubricant has a viscosity index of at
least 160 at a -20.degree. C. lube pour point and a viscosity index
of at least 135 at a pour point of no more than -50.degree. C.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a divisional of U.S. patent
application Ser. No. 10/266,369 filed Oct. 8, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for converting
Fischer-Tropsch wax to lube basestocks. More particularly, the
present invention relates to converting Fischer-Tropsch waxes to
lubes using a dual molecular sieve catalysts system.
BACKGROUND OF THE INVENTION
[0003] There is significant economic incentive to convert
Fischer-Tropsch (F-T) wax to high quality lube basestocks,
especially base oils with properties and performance comparable to,
or better than, those of polyalphaolefins (PAO). The upgrading of
Fischer-Tropsch wax greatly relies on advanced wax isomerization
technology that transforms linear paraffins to multi-branched
isoparaffins with minimal cracking.
[0004] Processes for converting Fischer-Tropsch wax to paraffinic
lube base-stocks are known. A typical process is a two-stage
process that hydroisomerizes Fischer-Tropsch wax to a waxy
isoparaffins mixture in the first step, followed by either solvent
dewaxing or catalytic dewaxing the waxy isoparaffins mixture in the
second step to remove residual wax and achieve a target lube pour
point.
[0005] The hydroisomerization catalysts disclosed previously, such
as Pt supported on amorphous aluminosilicate or Zeolite Beta
(Beta), normally possess large pores that allow the formation of
branch structures during paraffin isomerization. Examples of other
large pore molecular sieves include ZSM-3, ZSM-12, ZSM-20, MCM-37,
MCM-68, ECR-5, SAPO-5, SAPO-37 and USY. However, these large pore
catalysts are not selective enough to preferentially convert normal
and lightly branched paraffin waxes in the presence of
multi-branched isoparaffin molecules. As a result, the isoparaffin
products derived from Fischer-Tropsch wax often contain residual
wax that needs to be dewaxed in order to meet target lube cloud
points or pour points. The cloud point of a lube is the temperature
at which the first trace of wax starts to separate, causing the
lube to become turbid or cloudy (e.g., ASTM D2500). The pour point
of a lube is the temperature at which lube and wax crystallize
together as a whole and will not flow when poured (e.g., ASTM D97).
Dewaxing can be achieved by additionally using either a solvent
dewaxing process or a catalytic dewaxing process.
[0006] Most selective dewaxing catalysts used in a catalytic
dewaxing process have relatively small pore structures and catalyze
lube pour point reduction by selectively cracking normal and
lightly branched paraffin waxes. Such dewaxing catalysts usually
have low paraffin isomerization selectivity.
[0007] Few catalysts have been reported to be efficient in
catalyzing both hydroisomerization and dewaxing of paraffin wax to
low pour point lubes. One example of such catalysts is a noble
metal, such as Pt, supported on SAPO-11. It was previously assumed
that oval-shaped pore structures are common feature of
isomerization and dewaxing catalysts. See, for example U.S. Pat.
No. 5,246,566.
[0008] There remains a need therefore and a higher isomerization
selectivity to achieve a low enough pour point with minimal
molecular weight changes.
SUMMARY OF THE INVENTION
[0009] The present invention relates to a process for converting
Fischer-Tropsch wax to high quality lube basestocks by contacting
the wax with a molecular sieve catalyst (e.g., Zeolite Beta)
followed by a unidimensional molecular sieve catalyst with a near
circular pore structure having an average diameter of 0.50 nm to
0.65 nm wherein the difference between the maximum diameter and the
minimum is .ltoreq.0.05 nm (e.g., ZSM-48). Both catalysts comprise
one or more Group VIII metals (i.e., Fe, Ru, Os, Co, Rh, Ir, Pd,
Pt, Ni).
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIG. 1 is a plot of hydroisomerization yields versus lube
pour point for lubes derived from SASOL.TM. C80 Fischer-Tropsch wax
(C80) treated over Pt/Beta followed by Pt/ZSM-48.
[0011] FIG. 2 is a plot of lube yield versus lube pour point for
isomerization of C80 wax over Pt/Beta followed by Pt/ZSM-48,
Pt/ZSM-48 followed by Pt/Beta, and stand-alone Pt/ZSM-48 catalyst
systems.
[0012] FIG. 3 is a plot of lube viscosity versus lube pour point
for isomerization of C80 wax over Pt/Beta followed by Pt/ZSM-48,
Pt/ZSM-48 followed by Pt/Beta, and stand-alone Pt/ZSM-48 catalyst
systems.
[0013] FIG. 4 is a plot of viscosity index (VI) versus lube pour
point for isomerization of C80 wax over Pt/Beta followed by
Pt/ZSM-48, Pt/ZSM-48 followed by Pt/Beta, and stand-alone Pt/ZSM-48
catalyst systems.
[0014] FIG. 5 is a plot of light gas yields versus lube pour point
for isomerization of C80 wax over Pt/Beta followed by Pt/ZSM-48,
Pt/ZSM-48 followed by Pt/Beta, and stand-alone Pt/ZSM-48 catalyst
systems.
[0015] FIG. 6 is a plot of naphtha yields versus lube pour point
for isomerization of C80 wax over Pt/Beta followed by Pt/ZSM-48,
Pt/ZSM-48 followed by Pt/Beta, and stand-alone Pt/ZSM-48 catalyst
systems.
[0016] FIG. 7 is a plot of diesel yields versus lube pour point for
isomerization of C80 wax over Pt/Beta followed by Pt/ZSM-48,
Pt/ZSM-48 followed by Pt/Beta, and stand-alone Pt/ZSM-48 catalyst
systems.
DETAILED DESCRIPTION
[0017] The invention provides high isomerization and dewaxing
selectivity of a F-T wax with a molecular sieve catalyst followed
by a unidimensional catalyst molecular sieve with near circular
pore structure having an average diameter of 0.50-0.65 nm (5.0-6.5
angstroms) wherein the maximum diameter-minimum diameter
.ltoreq.0.05 nm (0.5 angstroms), to form a lubricant. Group VIII
metals on the two catalysts are preferred and platinum is the most
preferred. The invention improves lube basestock products and their
properties (e.g., pour point, cloud point).
[0018] There is a synergy between the two catalysts. It is believed
that the first catalyst (e.g., Zeolite Beta) improves yield and
pour point by creating the first few branches while the second
catalyst (i.e., a unidimensional molecular sieve catalyst) does
most of the dewaxing with minimal cracking. This method can easily
improve yield of high viscosity index (VI) lubes at a target pour
point by 10% over prior methods.
[0019] Preferably, F-T wax feed is first passed over a single
Zeolite Beta catalyst. The resulting intermediate product is then
passed over a unidimensional molecular sieve catalyst to form the
final lube. These first and second stages can be separated or
preferably are integrated process steps (e.g., cascaded).
[0020] Zeolite Beta catalysts are 12 ring acidic silica/alumina
zeolites with or without boron (replacing some of the aluminum
atoms). Zeolite Y (USY), though less preferred than Beta, is also
contemplated in the scope of the invention. Pre-sulfided Zeolite
Beta is preferred when some residual sulfur in the product is
acceptable.
[0021] Zeolite Betas used in the invention preferably have an Alpha
value below 15, more preferably below 10, at least prior to metal
loading. Alpha is an acidity metric that is an approximate
indication of the catalytic cracking activity of the catalyst
compared to a standard catalyst. Alpha is a relative rate constant
(rate of normal hexane conversion per volume of catalyst per unit
time). Alpha is based on the activity of the highly active
silica-alumina cracking catalyst taken as an Alpha of 1 in U.S.
Pat. No. 3,354,078 (incorporated by reference) and measured at
538.degree. C. as described in the Journal of Catalysis, vol. 4, p.
527 (1965); vol. 6, p. 278 (1966); and vol. 61, p. 395 (1980). The
use of Fischer Tropsch waxes and waxy raffinates requires a low
Alpha value of the Zeolite Beta catalyst due to minimal nitrogen
content in the feeds. In comparison, catalysts with high Alpha
values are used for cracking. Alpha values may be reduced by
steaming.
[0022] The Beta catalyst (e.g., Pt/Beta), when contacting the feed,
is most preferably kept at temperatures of 400-700.degree. F.
(204-371.degree. C.), more preferably at 500-650.degree. F.
(260-343.degree. C.), and most preferably at 520-580.degree. F.
(271-304.degree. C.).
[0023] The unidimensional molecular sieve catalyst with
near-circular pore structures does most of the dewaxing. The pores
are smaller than in large pore molecular sieves thereby excluding
bulkier (e.g., highly branched) molecules. Unidimentional means
that the pores are essentially parallel to each other.
[0024] The pores of the second catalyst have an average diameter of
0.50 nm to 0.65 nm wherein the difference between a minimum
diameter and a maximum diameter is .ltoreq.0.05 nm. The pores may
not always have a perfect geometric circular or elliptical
cross-section. The minimum diameter and maximum diameter are
generally only measurements of an ellipse of an cross-sectional
area equal to the cross-sectional area of an average pore. The
average pore diameter can be defined by finding the center of the
pore cross-section, and measuring the minimum diameter and the
maximum diameter across the center, and calculating the average of
the two diameters.
[0025] The preferred unidimensional molecular sieve catalyst is an
intermediate pore molecular sieve catalyst of which the preferred
version is ZSM-48. U.S. Pat. No. 5,075,269 describes the procedures
for making ZSM-48 and is incorporated by reference herein. ZSM-48
is roughly 65% zeolite crystal and 35% alumina. Of the crystals, at
least 90%, preferably at least 95%, and most preferably 98-99% are
ideal crystals. The ZSM-48 is preferably in the protonated form
though some sodium is acceptable. ZSM-48 is more robust than other
catalysts with similar functions. However, ZSM-48 is preferably
used with ultraclean feeds such as F-T wax to avoid
deactivation.
[0026] In the second stage of the process, the unidimensional
intermediate pore molecular sieve catalyst (e.g., Pt/ZSM-48) is
preferably kept at 500-800.degree. F. (260-427.degree. C.), more
preferably at 600-700.degree. F. (316-371.degree. C.), and most
preferably at 630-660.degree. F. (332-349.degree. C.). ZSM-48
catalysts used in the invention preferably have an Alpha value of
about 10 to about 50 prior to metal loading.
[0027] The temperature of each catalyst is preferably controlled
independently. Temperature choice partly depends on the feed liquid
hourly space velocity of which 0.1-20 h.sup.-1 is preferred, 0.5-5
h.sup.-1 is more preferred, and 0.5-2 h.sup.-1 is most
preferred.
[0028] The contact time for both catalysts is preferably similar to
each other. It is understood that the space velocity can be
different. The pressure for both catalysts is preferably similar to
each other. Hydrogen cofeed flow rate is 100-10,000 scf/bbl
(17.8-1,780 n.L.L.sup.-1), more preferably 1,000-6,000 scf/bbl
(178-1,068 n.L.L.sup.-1), and more preferably 1,500-3,000 scf/bbl
(267-534 n.L.L.sup.-1).
[0029] Each catalyst comprises 0.01-5 wt % of at least one Group
VIII metal (i.e., Fe, Ru, Os, Co, Rh, Ir, Pd, Pt, Ni). Platinum and
palladium are most preferred. Platinum or palladium blended with
each other or other group VIII metals follow in preference. Nickel
may also be blended with group VIII precious metals and is included
in the scope of the invention whenever group VIII blends, alloys,
or mixtures are mentioned. Preferred metal loading on both
catalysts are 0.1-1 wt % with approximately 0.6 wt % most
preferred.
[0030] The feed is preferably F-T wax with a melting point over
50.degree. C., less than 7,000 ppm sulfur, and less than 50 ppm
nitrogen. The nitrogen is preferably significantyl less than 50 ppm
if hydrogen pressure is greater than 500 psig (34 atm).
[0031] The feed is converted by the Zeolite Beta catalyst to form
an inter-mediate product which is then preferably passed directly
from the Beta catalyst to the unidimensional intermediate pore
molecular sieve catalyst. In a preferred embodiment of the
invention, a cascaded two-bed catalyst system consisting of a first
bed Pt/Beta (i.e., platinum on Zeolite Beta) catalyst followed by a
second bed Pt/ZSM-48 catalyst allows a highly selective process for
wax isomerization and lube hydrodewaxing with minimal gas
formation. In cascading, the intermediate product preferably
directly passes from the first bed to the second bed without
inter-stage separation. Optionally, light byproducts (e.g.,
methane, ethane) can be removed between the Beta and unidimensional
intermediate pore molecular sieve catalysts.
[0032] Feeds usually have at least about 95% n-paraffins and a
boiling point distribution of at least 500-1300.degree. F.
(260-704.degree. C.). Preferred feed contains C.sub.24-C.sub.60
with tail having a T.sub.5 of about 700.degree. F. (371.degree. C.)
and a T.sub.95 of about 1100.degree. F. (593.degree. C.) with less
than 1,000 ppm and preferably less than 200 ppm sulfur or nitrogen.
More branching in feed structures facilitates the present invention
and improves its yield. U.S. Pat. No. 6,090,989 describes typical
branching indices and is incorporated by reference. The feed is
preferably mixed with hydrogen and preheated before contacting it
with the Beta catalyst. Preferably, at least 95% of the wax is in
liquid form before contacting it with the Beta catalyst.
[0033] The preferred measurements, as taught by the specification,
are described in this paragraph. Where there are two values, the
value in parenthesis are approximate metric conversions of the
first value. The weight percent of paraffins may be measured by
high-resolution .sup.1H-NMR, for example, by the method described
in ASTM standard D5292, in combination with GC-MS. This approach
may also be used to determine the weight percentage of unsaturates,
alcohols, oxygenates, and other organic components. The iso- to
normal-paraffin ratio may be measured by performing gas
chromatography (GC) or GC-MS in combination with .sup.13C-NMR.
Sulfur may be measured by XRF (X-Ray Fluorescence), as described,
for example, in ASTM standard D2622. Nitrogen may be measured by
syringe/inlet oxidative combustion with chemiluminescence
detection, for example, by the method described in ASTM standard
D4629. Aromatics may be measured as described below. As taught by
the specification, olefins may be measured by using a Bromine index
determined by coulimetric analysis, for example, by using ASTM
standard D2710. The weight percent of total oxygen may be measured
by neutron activation in combination with high-resolution
.sup.1H-NMR. If necessary, the total oxygen content may be placed
on a water-free basis by measuring water content. For samples
having a water content known to be less than about 200 ppm by
weight, one may use known derivitization methods (e.g., by using
calcium carbide to form acetylene) followed by GC-MS. For samples
having a water content known to be greater than about 200 ppm by
weight, one may use the Karl-Fischer method, for example, by the
method described in ASTM standard D4928. The total alcohol content
may be determined by high-resolution .sup.1H-NMR, and the
percentage present primarily as C.sub.12-C.sub.24 primary alcohols
may be determined by GC-MS. Cetane number may be determined by
using, for example, ASTM standard D613. The level of aromatics may
be determined by using high-resolution .sup.1H-NMR, for example, by
using ASTM standard D5292. Dioxygenates are measured by using
infrared (IR) absorbance spectroscopy. Branching characteristics of
iso-paraffins may be measured by a combination of high-resolution
.sup.13C-NMR and GC with high-resolution MS.
EXPERIMENTAL
[0034] A cascaded two-bed catalyst system consisting of a first
stage Pt/Beta catalyst immediately followed by a second stage of
Pt/ZSM-48 catalyst is shown to be highly active and selective for
F-T wax hydroisomerization and dewaxing. A combination of Pt/ZSM-48
followed by Pt/Beta and stand-alone Pt/ZSM-48 were less effective.
The use of the Beta catalyst in front of Pt/ZSM-48 has minimal
effects on lube viscosity-pour point or viscosity index-pour point
correlation. The isomerization of SASOL.TM. C80 F-T wax resulted in
high lube yield and only small amount of gas over a wide range of
processing severity. Detailed preferred operating conditions,
material balance data, lube yields and properties are summarized in
Table 1. TBP x % indicates temperature below which x wt % of
hydrocarbon samples boils. The total product distribution at
various processing severity is shown in FIG. 1. Time on stream
(TOS) is the time during which the feed contacts the catalyst. IBP
is initial boiling point. TBP is terminal boiling point. The best
S.I. equivalent of standard cubic feet of hydrogen per barrel of
feed (SCF/bbl) is normal liters of hydrogen gas per liter of feed
(n.l.l.sup.-1. or n.L.L.sup.-1 or n.L (gas)/L (feed)). LHSV is
defined as liquid hourly space velocity. WHSV is defined as weight
hourly space velocity. TABLE-US-00001 TABLE 1 Hydroisomerization of
SASOL .TM. C80 Fischer-Tropsch Wax Catalyzed by a Cascaded Pt/Beta
Followed by Pt/ZSM-48 (1.0 h.sup.-1 LHSV for Each Catalyst) Run
Number 401- 3-34 3-37 3-38 3-41 3-50 3-53 3-55 Time on Stream, Days
47.7 50.7 51.7 56.1 70.1 73.7 77.2 Beta Temperature, .degree. F.
580 560 540 560 540 520 520 Beta Temperature, .degree. C.
approximate 304 293 282 293 282 271 271 ZSM-48 Temperature,
.degree. F. 630 660 660 640 640 660 650 ZSM-48 Temperature,
.degree. C. approximate 332 349 349 338 338 349 343 Pressure, psig
1000 1000 1000 1000 1000 1000 1000 (Pressure, atm) approximate 68
68 68 68 68 68 68 H.sub.2 Cofeeding Rate, scf/bbl 5477 5188 5228
4965 5610 5790 5332 (H.sub.2 Cofeeding Rate, n L L.sup.-1)
approximate 975 923 931 884 999 1031 949 700.degree. F.+
(371.degree. C.+) Conversion, wt % 22.0 60.9 65.3 28.6 38.2 75.2
48.8 H.sub.2 Consumption, scf/bbl 110 392 435 150 211 511 286
(H.sub.2 Consumption, n L L.sup.-1) approximate 18 70 77 27 38 91
51 Product Yield, wt % on Feed C.sub.1-C.sub.4 Gas 1.4 5.5 6.0 2.1
2.4 7.7 4.0 C.sub.5-330.degree. F.(166.degree. C.) Naphtha 5.5 21.3
24.6 7.3 11.3 27.8 14.0 330-700.degree. F. Diesel (166-371.degree.
C.) 15.2 34.8 35.5 19.5 24.9 40.6 31.4 700.degree. F.+ Lube
(371.degree. C.+) 78.0 39.1 34.7 71.4 61.8 24.8 51.2 Total
Hydrocarbon 100.2 100.7 100.8 100.3 100.4 100.9 100.5 700.degree.
F.+ (371.degree. C.+) Lube Properties Feed KV @ 40.degree. C., cSt
35.0 33.6 35.9 29.7 30.2 25.6 23.5 KV @ 100.degree. C., cSt 9.4
7.20 6.49 6.71 6.32 6.35 5.20 5.16 Viscosity Index 175.5 149.8
145.9 171.2 168.9 138.1 157.1 Pour Point, .degree. C. 82 3 -45 -51
-12 -21 -65 -33 Cloud Point, .degree. C. 25 -16 -51 12 9 -65 -- TBP
5%, .degree. F. 780 754 781 697 717 681 639 TBP 5%, .degree. C.
approximate 416 401 416 366 380 360 337 TBP 50%, .degree. F. 926
896 903 915 907 852 855 TBP 50%, .degree. C. approximate 497 480
484 491 486 455 457 TBP 95%, .degree. F. 1056 1030 1030 1056 1051
1024 1014 TBP 95%, .degree. C. approximate 569 554 554 569 566 551
546 MB Closure, wt % 99.1 97.1 98.5 97.5 98.2 99.8 99.4
[0035] To obtain desirable wax isomerization results, a mild (e.g.,
500-630.degree. F. (260-332.degree. C.)) first bed Pt/Beta
temperature should be employed during lube hydroprocessing. The
mild Pt/Beta temperature should be employed with varying Pt/ZSM-48
temperature to achieve a target lube pour point. At a constant
Pt/ZSM-48 (second bed) temperature, a high Pt/Beta temperature was
found to have negative effects on (i.e., increase) lube pour point.
To achieve maximal lube yield, low operating pressure (<2,000
psi (136 atm) hydrogen pressure) should be used.
[0036] A cascaded Pt/ZSM-48 followed by Pt/Beta and stand-alone
Pt/ZSM-48 were also evaluated and it was found that both catalyst
systems were less selective in isomerizing and dewaxing C80 F-T wax
to 700.degree. F.+ (371.degree. C.+) lube basestocks (Tables 2 and
3). Comparison of lube yields for the three catalyst systems tested
is illustrated in FIG. 2. Pt/Beta followed by Pt/ZSM-48 gave
approximately 10 wt % higher lube yield at a given pour point than
Pt/ZSM-48 followed by Pt/Beta or Pt/ZSM-48 alone. TABLE-US-00002
TABLE 2 Hydroisomerization of SASOL .TM. C80 Fischer-Tropsch Wax
Catalyzed by Pt/ZSM-48 Run Number, 401- 3-27 3-28 3-29 3-30 3-31
Time on Stream, Days 35.6 37.0 38.0 39.0 40.9 Temperature, .degree.
F. 665 660 655 650 645 Temperature, .degree. C. approximate 352 349
352 343 341 Pressure, psig 1000 1000 1000 1000 1000 (Pressure, atm)
approximate 68 68 68 68 68 LHSV, hr.sup.-1 1.0 1.0 1.0 1.0 1.0
WHSV, hr.sup.-1 1.4 1.5 1.5 1.4 1.4 H.sub.2 Cofeeding Rate, scf/bbl
5656 5643 5603 5674 5657 (H.sub.2 Cofeeding Rate, n L L.sup.-1)
approximate 1007 1004 997 1010 1007 700.degree. F.+ (371.degree.
C.+) Conversion, wt % 78.0 70.6 60.0 49.9 44.2 H.sub.2 Consumption,
scf/bbl 544 473 377 306 261 (H.sub.2 Consumption, n L L.sup.-1)
approximate 97 84 67 54 46 Product Yield, wt % on Feed
C.sub.1-C.sub.4 Gas 8.3 6.8 5.4 4.4 3.5 C.sub.5-330.degree. F.
(C.sub.5-166.degree. C.) Naphtha 30.0 26.1 19.6 15.6 13.7
330-700.degree. F. (166-371.degree. C.) Diesel 40.8 38.6 35.7 30.4
27.5 700.degree. F.+ (371.degree. C.+) Lube 22.0 29.4 40.0 50.1
55.8 Total Hydrocarbon 101.0 100.9 100.7 100.6 100.5 700.degree.
F.+ (371.degree. C.+) Lube Properties Feed KV @ 40.degree. C., cSt
14.8 34.8 31.2 32.9 34.0 KV @ 100.degree. C., cSt 9.4 3.65 6.59
6.29 6.66 6.90 Viscosity Index 135.5 147.4 156.9 163.8 168.6 Pour
Point, .degree. C. 82 -54 -48 -33 -24 -12 TBP 5%, .degree. F. 570
778 753 766 770 (TBP 5%, .degree. C.) approximate 299 414 400 407
410 TBP 50%, .degree. F. 783 899 906 918 918 (TBP 50%, .degree. C.)
approximate 417 482 485 492 492 TBP 95%, .degree. F. 998 997 1007
1014 1057 (TBP 95%, .degree. C.) approximate 537 536 542 546 569 MB
Closure, wt % 99.6 98.8 98.8 97.9 97.1
[0037] TABLE-US-00003 TABLE 3 Hydroisomerization of SASOL .TM. C80
Fischer-Tropsch Wax Catalyzed by a Cascaded Pt/ZSM-48 Followed by
Pt/Beta (1.0 h.sup.-1 HSV for Each Catalyst) Run Number, 401- 3-3
3-11 3-16 3-20 3-22 3-24 Time on Stream, Days 3.6 15.1 21.6 26.5
28.6 31.1 ZSM-48 Temperature, .degree. F. 660 660 640 655 645 640
(ZSM-48 Temperature, .degree. C.) approximate 349 349 338 346 341
338 Beta Temperature, .degree. F. 560 560 540 560 560 560 (Beta
Temperature, .degree. C.) approximate 293 293 282 293 293 293
Pressure, psig 1000 1000 1000 1000 1000 1000 (Pressure, atm)
approximate 68 68 68 68 68 68 H.sub.2 Cofeeding Rate, scf/bbl 5786
6150 5575 5528 5607 5619 (H.sub.2 Cofeeding Rate, n L L.sup.-1)
approximate 1030 1095 992 984 5607 1000 700.degree. F.+
(371.degree. C.) Conversion, wt % 83.5 79.4 34.6 60.7 47.7 40.4
H.sub.2 Consumption, scf/bbl 499 516 205 377 270 225 (H.sub.2
Consumption, n L L.sup.-1) approximate 89 92 36 67 48 40 Product
Yield, wt % on Feed C.sub.1-C.sub.4 Gas 4.0 6.2 3.2 5.7 3.4 2.8
C.sub.5-330.degree. F. (C.sub.5-166.degree. C.) Naphtha 33.4 31.2
9.6 18.2 13.2 11.4 330-700.degree. F. (166-371.degree. C.) Diesel
47.0 42.9 22.1 37.5 31.6 26.6 700.degree. F.+ (371.degree. C.+)
Lube 16.5 20.6 65.4 39.3 52.3 59.6 Total Hydrocarbon 100.9 101.0
100.4 100.7 100.5 100.4 700.degree. F.+ (371.degree. C.+) Lube
Properties Feed KV @ 40.degree. C., cSt 34.7 24.8 34.0 28.1 28.8
28.3 KV @ 100.degree. C., cSt 9.4 6.31 5.06 6.91 5.77 5.98 6.00
Viscosity Index 133.5 136.0 168.7 153.4 159.8 165.2 Pour Point,
.degree. C. 82 -60 -54 0 -33 -21 -9 Cloud Point, .degree. C. -60
-54 13 0 -10 4 TBP 5%, .degree. F. 754 702 783 723 719 716 (TBP 5%,
.degree. C.) approximate 401 372 417 384 382 380 TBP 50%, .degree.
F. 875 840 922 877 879 895 (TBP 50%, .degree. C.) approximate 468
449 494 469 471 479 TBP 95%, .degree. F. 1004 1006 1062 1030 1019
1028 (TBP 95%, .degree. C.) approximate 540 541 572 554 548 553 MB
Closure, wt % 97.6 95.6 98.2 98.5 98.0 98.1
[0038] Approximately 5.degree. F. (2.8.degree. C.) less Pt/ZSM-48
temperature is required to achieve a target pour point when a
cascaded Pt/Beta and Pt/ZSM-48 was used instead of stand-alone
Pt/ZSM-48 (Tables 1 and 2). This resultant reduction of Pt/ZSM-48
severity should reduce the cracking activity of the catalyst and is
assumed to be a primary contributor to the yield benefit for the
dual catalyst system. The addition of Pt/Beta had minimal effects
on the range of Pt/ZSM-48 operating temperature, which was also
observed for the catalyst system Pt/ZSM-48 followed by Pt/Beta
(Tables 2 and 3).
[0039] The viscosity and viscosity index of the nominal 700.degree.
F.+ (371.degree. C.+) C80 wax isomerates vs. hydroprocessing
severity are plotted in FIGS. 3 and 4, respectively. The three sets
of data compared in the two diagrams correspond to the F-T wax
isomerates prepared using Pt/Beta followed by Pt/ZSM-48, Pt/ZSM-48
followed by Pt/Beta, and Pt/ZSM-48 alone. For products of the
invention, a viscosity index of at least 160 at a -20.degree. C.
lube pour point and a viscosity index of at least 135 at a pour
point of no more than -50.degree. C. is preferred.
[0040] As shown in FIG. 3, the viscosity of the Pt/Beta-Pt/ZSM-48
F-T lubes changes only slightly vs. pour point and is very close to
that of the Pt/ZSM-48 lubes. The small viscosity differences are
also partially attributable to variation in the initial boiling
point of the actual 700.degree. F.+ (371.degree. C.+) distillation
cuts. However, the Pt/ZSM-48-Pt/Beta F-T isomerates had lower
viscosities presumably due to the relatively high cracking activity
of Pt/Beta catalyst towards multi-branched isoparaffins. The
cracking activity of Pt/Beta with pure wax or lightly branched
paraffins should be low as in the case of C80 wax isomerization
catalyzed by Pt/Beta followed by Pt/ZSM-48 system.
[0041] The viscosity index of the Pt/Beta-Pt/ZSM-48 F-T lubes is
similar to that of the Pt/ZSM-48 isomerates except at an extremely
low pour point (FIG. 4). For comparison, Pt/ZSM-48 followed by
Pt/Beta yields a lower lube VI at a given pour point (e.g., 4-9
viscosity index numbers). The VI differences observed for the three
catalyst systems could be attributable to the higher shape
selectivity of ZSM-48 vs. Zeolite Beta towards multi-branched
isoparaffins. During the wax hydroisomerization process, the
smaller pore structure of ZSM-48 (0.53.times.0.56 nm,
unidimensional) could effectively exclude highly branched, low
pour, paraffins and selectively convert waxy normal paraffins or
lightly branched paraffins, thus prohibiting the formation of
excessively branched (or low VI) isomers. However, the large pore
structure of Zeolite Beta (0.64.times.0.76 nm) is expected to be
less shape-selective and possibly continue to transform highly
branched paraffins to even more branched molecules, which would, of
course, lower VI of the lube product and cause the catalyst being
less effective in reducing lube pour point. The easy accessibility
of Beta Zeolite's larger pore structure to highly branched
isoparaffins also promotes cracking of these hydrocarbon molecules,
resulting in a lower lube viscosity and yield. More details
regarding the shape selectivity of ZSM-48 in lube isomerization and
dewaxing will be discussed in the following sections.
[0042] The spread between the lube cloud and pour points for
Pt/Beta-Pt/ZSM-48 and Pt/ZSM-48-Pt/Beta is typically less than
30.degree. C. (Tables 1 and 3). In general, the spread between the
lube cloud and pour points narrows with decreasing pour point.
[0043] A combination of Pt/Beta followed by Pt/ZSM-48 exhibited an
unusual relationship between reaction temperature and lube product
pour point during the wax hydroisomerization (Table 4). At constant
Pt/Beta temperature, the lube pour point decreases with increasing
Pt/ZSM-48 temperature. However, at constant Pt/ZSM-48 temperature,
the lube pour point increases with increasing Pt/Beta temperature.
TABLE-US-00004 TABLE 4 Hydroisomerization of SASOL .TM. C80 F-T Wax
to Lubes Catalyzed by Pt/Beta Followed by Pt/ZSM-48 (Conditions:
1000 psig (68 atm), 1.0 h.sup.-1 LHSV for Each Catalyst) Beta Temp.
(.degree. F.) 560 560 560 520 540 560 580 Beta Temp. 293 293 293
271 282 293 304 (approx. .degree. C.) ZSM-48 Temp. 630 645 660 660
645 645 645 (.degree. F.) ZSM-48 Temp. 332 341 349 349 341 341 341
(approx. .degree. C.) Lube Properties Pour Point, .degree. C. 15
-15 -45 -65 -18 -15 -9 KV @ 100.degree. C., cSt 7.60 7.16 6.49 5.20
6.62 7.16 6.01 Viscosity Index 179.2 167.8 149.8 138.1 165.2 167.8
173.4
[0044] Since degree of branching of the Pt/Beta isomerates is
anticipated to increase at high Beta temperature, this experimental
result indicates that Pt/ZSM-48 is more effective in isomerizing
and dewaxing less branched isoparaffins, and thus is shape
selective. In case that a feed contains both lightly branched and
highly branched isoparaffins, it is likely that the ZSM-48 catalyst
would preferentially convert/isomerize the lightly branched
molecules. This explains why Pt/ZSM-48 is an efficient catalyst for
reducing lube pour point.
[0045] The shape selectivity of the catalyst is presumably due to
its relatively small pore structure (0.53.times.0.56 nm,
unidimensional) capable of differentiating different isoparaffins.
The ability of ZSM-48 to preferentially convert normal paraffins or
lightly branched paraffins and exclude highly branched isoparaffins
reduces undesirable reactions such as cracking (leading to low lube
yield) and excessive further isomerization (leading to low VI) of
low pour, highly branched isomers. This is consistent with the low
cracking activity, high lube yield, minimal viscosity loss, and
high lube VI observed for Pt/ZSM-48 in isomerizing and dewaxing
various waxy feeds including F-T waxes.
[0046] The correlation between reaction temperature and lube pour
point was found to be normal for Pt/ZSM-48 followed by Pt/Beta
(Table 5). The lube pour point decreases either with increasing
Pt/ZSM-48 temperature and constant Pt/Beta temperature or with
constant Pt/ZSM-48 temperature and increasing Pt/Beta temperature.
This is not unexpected since the large pore Beta should be less
selective than ZSM-48 in reacting with various branched
isoparaffins, and would convert even highly branched paraffin
isomers via cracking and additional isomerization. TABLE-US-00005
TABLE 5 Hydroisomerization of SASOL .TM. C80 F-T Wax to Lubes
Catalyzed by Pt/ZSM-48 Followed by Pt/Beta (Conditions: 1000 psig
(68 atm), 1.0 h.sup.-1 LHSV for Each Catalyst) ZSM-48 Temp. 640 640
640 640 655 660 (.degree. F.) ZSM-48 Temp. 338 338 338 338 346 349
(approx. .degree. C.) Beta Temp. 530 560 590 560 560 560 (.degree.
F.) Beta Temp. 277 293 310 293 293 293 (approx. .degree. C.) Lube
Properties Pour Point, 0 -18 -45 -18 -33 -54 .degree. C. KV @ 6.92
5.97 5.16 5.97 5.77 5.06 100.degree. C., cSt Viscosity Index 169.4
158.0 138.4 158.0 153.4 136.0
[0047] Pt/Beta-Pt/ZSM-48 system has superior isomerization
selectivity and low cracking activity, and gives lower yields of
light gases, naphtha, and diesel than Pt/ZSM-48-Pt/Beta and
Pt/ZSM-48 alone (FIGS. 5-7). The overall light byproduct
selectivity for the latter two catalysts is comparable. As
expected, the yields of gases, naphtha, and diesel increase for all
catalysts with increasing process severity (decreasing lube pour
point) that promotes hydrocracking.
[0048] The following examples will serve to illustrate the
invention.
Example 1
[0049] Feedstock. The hydrotreated SASOL.TM. PARAFLINT.TM. C80
Fischer-Tropsch wax feed was obtained from Moore and Munger, Inc.,
(Shelton, Conn.) and used as received without additional
pretreatment. The C80 wax was a mixture of predominantly linear
paraffins with very low content of olefins and oxygenates.
SASOL.TM. has been marketing three commercial grades of F-T waxes:
PARAFLINT.TM. H1, a 700.degree. F.+ (371.degree. C.+) full range
Fischer-Tropsch wax; PARAFLINT.TM. C80 and C105, 700-1100.degree.
F. (371-593.degree. C.) and 1100.degree. F.+(593.degree. C.+)
distillate fractions, respectively. The molecular weight
distribution (in terms of boiling point) of the waxes is
illustrated briefly in Table 6. TABLE-US-00006 TABLE 6 Molecular
Weight Distribution of SASOL .TM. Fischer-Tropsch Waxes F-T Wax
Feed H1 C80 C105 Pour Point, .degree. C. 99 82 106 IBP-700.degree.
F. (<C.sub.24), wt % 0 3 0 700-1100.degree. F.
(C.sub.24-C.sub.60), wt % 44 89 20 1100.degree. F.+ (>C.sub.60),
wt % 56 8 80
Example 2
[0050] Preparation of Pt/Beta Catalyst. Pt/Beta catalyst was
prepared by extruding a water-containing mull mix or paste
containing 65 parts of Zeolite Beta with 35 parts of alumina (dry
basis). After drying, the Zeolite Beta containing catalyst was
calcined under nitrogen at 900.degree. F. (482.degree. C.) and
exchanged at ambient temperature with a sufficient quantity of
ammonium nitrate to remove residual sodium in the zeolite channels.
The extrudate was then washed with deionized water and calcined in
air at 1000.degree. F. (538.degree. C.). After air calcination, the
65% Zeolite Beta/35% Alumina extrudate was steamed at 1020.degree.
F. (549.degree. C.) to reduce the Alpha value of the calcined
catalyst to less than 10. The steamed, 65% low acidity Beta/35%
Alumina catalyst was ion exchanged with a tetraammine platinum
chloride solution under ion exchange conditions to uniformly
produce a catalyst containing 0.6% Pt. After washing with
de-ionized water to remove residual chlorides, the catalyst was
dried at 250.degree. F. (121.degree. C.) followed by a final air
calcination at 680.degree. F. (360.degree. C.).
Example 3
[0051] Preparation of Pt/ZSM-48 Catalyst. Pt/ZSM-48 catalyst was
prepared by extruding a water-containing mull mix or paste
containing 65 parts of ZSM-48 with 35 parts of alumina (dry basis).
After drying, the ZSM-48 containing catalyst was calcined under
nitrogen at 900.degree. F. (482.degree. C.) and exchanged at
ambient temperature with a sufficient quantity of ammonium nitrate
to remove residual sodium in the zeolite channels. The extrudate
was then washed with deionized water and calcined in air at
1000.degree. F. (538.degree. C.). After air calcination, the 65%
ZSM-48/35% Alumina catalyst was impregnated with a tetraammine
platinum nitrate solution under incipient wetness conditions to
unifommly produce a catalyst containing 0.6% Pt. Finally, the
catalyst was dried at 250.degree. F. (121.degree. C.) followed by
air calcination at 680.degree. F. (360.degree. C.).
Example 4
[0052] Wax Hydroprocessing. The wax hydroisomerization experiments
were performed using a micro-unit equipped with two three-zone
furnaces and two down-flow trickle-bed tubular reactors (1/2'' ID)
in cascade (with option to bypass the second reactor). The unit was
carefully heat-traced to avoid freezing of the high melting point
C80 wax. To reduce feed bypassing and lower zeolite pore diffusion
resistance, the catalysts extrudates were crushed and sized to
60-80 mesh. The reactors 1 and 2 were then loaded with 15 cc of the
60-80 mesh Pt/ZSM-48 catalyst and the 60-80 mesh Pt/Beta catalyst,
respectively. 5 cc of 80-120 mesh sand was also added to both
catalyst beds during catalyst loading to fill the void spaces.
After pressure testing of the unit, the catalysts were dried and
reduced at 400.degree. F. (204.degree. C.) for one hour under 1
atmosphere (atm.), 255 cc/min hydrogen flow. At the end of this
period, the flow of pure hydrogen was stopped and flow of H.sub.2S
(2% in hydrogen) was initiated at 100 cc/min. After H.sub.2S
breakthrough, the reactors 1 and 2 were gradually heated to
700.degree. F. (371.degree. C.) and maintained at 700.degree. F.
(371.degree. C.) for 1 h (hour). After the completion of catalyst
pre-sulfiding, the gas flow was switched back to pure hydrogen at
255 cc/minute rate, and the two reactors were cooled down.
[0053] Hydroisomerization of the C80 Fischer-Tropsch wax over a
cascaded Pt/ZSM-48 followed by Pt/Beta was conducted at 1.0
h.sup.-1 LHSV for each catalyst and 1000 psig (68 atm) with 5500
scf (979 n.L.L.sup.-1) hydrogen/bbl circulation rate. The wax
isomerization experiments were started first by saturating the
catalyst beds with the feed at 400.degree. F. (204.degree. C.) then
heating the reactors to the initial operating temperatures.
Material balances were carried out overnight for 16-24 h. Reactor
temperatures were then gradually changed to vary pour point.
[0054] Performance of stand-alone Pt/ZSM-48 was evaluated by
cooling and bypassing the Pt/Beta catalyst in the second reactor.
The experiments were conducted under identical process conditions
(1.0 LHSV, 1000 psig (68 atm), 5500 scf/bbl (979 n.L.L.sup.-1)
H.sub.2) and according to similar procedures used for testing the
cascade Pt/ZSM-48 and Pt/Beta combination.
[0055] Performance of Pt/Beta followed by Pt/ZSM-48 was evaluated
after switching the two reactors, i.e. order of Pt/ZSM-48 and
Pt/Beta catalysts. Process conditions and experimental procedures
similar to those for testing the cascaded Pt/ZSM-48 and Pt/Beta
combination were employed.
Example 5
[0056] Product Separation and Analysis. Off-gas samples were
analyzed by GC using a 60 m DB-1 (0.25 mm ID) capillary column with
FID detection. Total liquid products (TLP's) were weighed and
analyzed by simulated distillation (Simdis, such as D2887) using
high temperature GC. TLP's were distilled into IBP-330.degree. F.
(IBP-166.degree. C.) naphtha, 330-700.degree. F. (166-371.degree.
C.) distillate, and 700.degree. F.+(371.degree. C.+) lube
fractions. The 700.degree. F.+ (371.degree. C.+) lube fractions
were again analyzed by Simdis to ensure accuracy of the actual
distillation operations. The pour point and cloud point of
700.degree. F.+ (371.degree. C.+) lubes were measured by D97 and
D2500 methods, and their viscosities were determined at both
40.degree. C. and 100.degree. C. according to D445-3 and D445-5
methods, respectively.
* * * * *