U.S. patent application number 10/682244 was filed with the patent office on 2005-07-28 for synthetic transportation fuel and method for its production.
This patent application is currently assigned to Syntroleum Corporation. Invention is credited to Abazajian, Armen N., Freerks, Robert, Tomlinson, H. Lynn.
Application Number | 20050165261 10/682244 |
Document ID | / |
Family ID | 32776315 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050165261 |
Kind Code |
A1 |
Abazajian, Armen N. ; et
al. |
July 28, 2005 |
Synthetic transportation fuel and method for its production
Abstract
A transportation fuel or blending stock for a transportation
fuel which contains substantially no FT oxygenates and no sulfur is
provided. An economical method of producing a transportation fuel
or blending stock which eliminates oxygenates and which does not
cause any significant yield loss is also provided.
Inventors: |
Abazajian, Armen N.;
(Houston, TX) ; Tomlinson, H. Lynn; (Tulsa,
OK) ; Freerks, Robert; (Jenks, OK) |
Correspondence
Address: |
BAKER & MCKENZIE LLP
711 LOUISIANA
SUITE 3400
HOUSTON
TX
77002-2716
US
|
Assignee: |
Syntroleum Corporation
Tulsa
OK
|
Family ID: |
32776315 |
Appl. No.: |
10/682244 |
Filed: |
October 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60455224 |
Mar 14, 2003 |
|
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|
Current U.S.
Class: |
585/1 ; 208/15;
208/950 |
Current CPC
Class: |
C10L 1/08 20130101 |
Class at
Publication: |
585/001 ;
208/015; 208/950 |
International
Class: |
C10L 001/04 |
Claims
What is claimed is:
1. A hydrocarbon mixture comprising: an olefin/paraffin mixture
having a carbon number range from about C.sub.8 to about C.sub.20+
wherein the olefin/paraffin mixture comprises: substantially no
oxygenates; between about 1 wt % and 20 wt % olefin wherein at
least about 1 wt % of the olefin is mono-olefin; at least about 5
wt % n-paraffins; between about 2 and 94 wt % branched paraffins
wherein at least about 30% of all branch groups are monomethyl and
wherein the ratio of terminal monomethyl branching to internal
monomethyl branching is at least about 1:1.5.
2. The hydrocarbon mixture of claim 1 wherein the ratio of terminal
monomethyl branching to internal monomethyl branching is at least
about 1:1.
3. The hydrocarbon mixture of claim 1 wherein the n-paraffins are
present in an amount of at least about 10 wt % and wherein the
ratio of terminal monomethyl branching to internal monomethyl
branching is at least about 1.5:1.
4. The hydrocarbon mixture of claim 1 wherein the n-paraffins are
present in an amount of at least about 10 wt % and wherein the
ratio of terminal monomethyl branching to internal monomethyl is at
least about 2:1.
5. The hydrocarbon mixture of claim 1 wherein the olefin/paraffin
mixture is a product of a Fischer-Tropsch reaction.
6. The synthetic fuel of claim 5 wherein the Fischer-Tropsch
reaction feed syngas comprises 10-65% N.sub.2.
7. A process for producing a synthetic fuel comprising the steps
of: (a) producing a light Fischer-Tropsch liquid; (b) dehydrating
all or a part of the FT oxygenates in the LFTL while retaining the
olefin content in the LFTL; (c) recovering an organic phase from
the product of step (b); (d) blending the organic phase into a
transportation fuel.
8. The process of claim 7 further comprising the step of (a.sub.1)
vaporizing the LFTL before step (b) and after step (a).
9. The process of claim 8 wherein the dehydrated product from step
(b) is in the gaseous state and step (c) further includes
condensing the dehydrated product.
10. The process of claim 9 wherein the heat from condensing the
dehydrated product is recycled to at least partially vaporize the
LFTL in step (a.sub.1).
11. The process of claim 7 wherein the light Fischer-Tropsch liquid
is produced from a feed syngas having 10-65% N.sub.2.
12. The process of claim 11 wherein the feed syngas is produced by
autothermal reformation in the presence of air.
13. A hydrocarbon mixture comprising: a paraffin mixture having a
carbon number range from about C.sub.8 to about C.sub.20+ wherein
the paraffin mixture comprises: substantially no FT oxygenates; at
least about 5 wt % n-paraffins; between about 2 and about 95 w/o
branched paraffins wherein at least about 20% of all branch groups
are monomethyl and wherein the ratio of terminal monomethyl
branching to internal monomethyl branching is at least about
1:1.5.
14. The synthetic fuel of claim 13 wherein the ratio of terminal
monomethyl branching to internal monomethyl branching is at least
about 1:1.
15. The synthetic fuel of claim 13 wherein the n-paraffins are
present in an amount of at least about 10 wt % and wherein the
ratio of terminal monomethyl branching to internal monomethyl
branching is at least about 1.5:1.
16. The synthetic fuel of claim 13 wherein the n-paraffins are
present in an amount of at least about 10 wt % and wherein the
ratio of terminal monomethyl branching to internal monomethyl is at
least about 2:1.
17. The synthetic fuel of claim 13 wherein the base fluid is a
product of a Fischer-Tropsch reaction.
18. The synthetic fuel of claim 17 wherein the Fischer-Tropsch
reaction feed syngas comprises 10-65% N.sub.2.
19. A process for producing a synthetic fuel comprising the steps
of: (a) producing a light Fischer-Tropsch liquid; (b) distilling
the light Fischer-Tropsch liquid to obtain a
C.sub.8-C.sub.20+product having C.sub.8-C.sub.20+ hydrocarbons and
FT oxygenates. (c) dehydrating all or a part of the FT oxygenates
in the C.sub.8-C.sub.20+ product while retaining the olefin content
of the C.sub.8-C.sub.20+ product; (d) recovering the dehydrated
product; (e) separating the aqueous and organic phases of the
dehydrated product; and (f) blending the organic phase of the
dehydrated product into a transportation fuel.
20. The process of claim 19 wherein a C.sub.10-C.sub.20 product is
obtained in step (b) and dehydrated in step (c).
21. The process of claim 19 further comprising the step of
(b.sub.1) vaporizing the C.sub.8-C.sub.20+ product before step (c)
and after step (b).
22. The process of claim 19 wherein the dehydrated product from
step (c) is in the gaseous state and step (d) further includes
condensing the dehydrated product.
23. The process of claim 23 wherein the heat from condensing the
dehydrated product is recycled to at least partially vaporize the
C.sub.8-C.sub.20+ product in step (b.sub.1).
24. The process of claim 19 wherein the light Fischer-Tropsch
liquid is produced from a feed syngas having 10-65% N.sub.2.
25. The process of claim 24 wherein the feed syngas is produced by
autothermal reformation in the presence of air.
26. A synthetic transportation fuel comprising a non-hydroprocessed
middle distillate fraction of a crude Fischer-Tropsch synthesis
product comprising substantially no FT oxygenates.
27. The synthetic transportation fuel of claim 26 wherein the fuel
has a cloud point of less than or equal to 5.degree. C.
28. The synthetic transportation fuel of claim 27 wherein the fuel
contains less than 1 wt % aromatics.
29. The synthetic transportation fuel of claim 27 wherein the fuel
contain less than or equal to 1 ppm of nitrogen.
30. A transportation fuel produced by the process of claim 7.
31. A transportation fuel produced by the process of claim 19.
32. A blending stock for a transportation fuel produced by the
process of claim 7.
33. A blending stock for a transportation fuel produced by the
process of claim 19.
34. A synthetic transportation fuel consisting essentially of
olefins and paraffins without presence of hetero-atoms or additives
wherein the transportation fuel has a lubricity measured in
accordance with ASTM D-6079 of less than or equal to 0.45 mm at
60.degree. C.
35. A synthetic transportation fuel comprising paraffins and
olefins derived from the product of a Fischer-Tropsch synthesis and
comprising no hetero-atoms or additives and having total insolubles
of less than or equal to 1.5 mg/100 ml measured in accordance with
ASTM D-2274.
36. A synthetic transportation fuel comprising paraffins and
olefins derived from the product of a Fischer-Tropsch synthesis and
containing no hetero-atoms having a lubricity measured in
accordance with ASTM D-6079 of less than or equal to 0.45 mm at
60.degree. C. and a stability of total insolubles of less than or
equal to 1.5 mg/100 ml measured in accordance with ASTM D-2274.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application Ser.
No. 60/455,224 filed on Mar. 114, 2003, the contents of which is
hereby incorporated by reference in its entirety.
FEDERALLY SPONSORED RESEARCH
[0002] Not applicable.
REFERENCE TO MICROFICHE APPENDIX
[0003] Not applicable.
FIELD OF THE INVENTION
[0004] The invention relates to a method of producing a
transportation fuel or blending stock therefor derived from the
products of a Fischer-Tropsch synthesis. More specifically, the
invention relates to a process in which the oxygenates are
converted in a selective low-cost process. The invention further
relates to a transportation fuel or blending stock therefor, having
a high cetane number, high lubricity, high stability, and having
substantially no oxygenates, sulfur or other hetero-atom
components.
BACKGROUND OF THE INVENTION
[0005] Synthetic transportation fuels are increasingly in demand
because they contain no sulfur or aromatics and typically have high
cetane numbers. The Fischer-Tropsch process used to make synthetic
transportation fuels, however, results in a syncrude product
containing oxygenates ("FT oxygenates"). The FT oxygenates
typically include primary and internal alcohols, which constitute
the major portion of the total FT oxygenate, as well as aldehydes,
ketones and acids. The presence of FT oxygenates presents certain
problems with processing the syncrude, including a negative impact
on hydroprocessing catalysts which necessitates an increase in the
severity of hydroprocessing conditions. With increasing severity of
hydroprocessing, yield loss increases. The term "hydroprocessing"
as used herein means hydrocracking, hydroisomerization,
hydrodewaxing, or a combination of two or more of these
processes.
[0006] Alternatively, the FT oxygenates may be removed through
hydrotreatment. However, hydrotreatment requires significant
additional capital equipment expenditures. The FT oxygenate content
is generally higher in the lower boiling range distillation cuts of
the Fischer-Tropsch product and declines precipitously above a
600.degree. F. cut point. One method of avoiding the negative
impact of the FT oxygenates on the hydrocracking catalysts is to
bypass the lower boiling range distillation cuts around the
hydrocracking unit. The lower boiling range distillation cuts,
including any FT oxygenate content therein, are then re-blended
with the hydrocracked higher boiling range distillation cut to form
the product fuel. While a bypassed 250-400.degree. F. distillation
cut has no appreciable negative impact when re-blended into the
product fuel, reincorporation of a bypassed 400.degree. F.+
distillation cut impairs the low temperature properties of the
product fuel due to the presence of FT oxygenates. Therefore, it is
common to hydroprocess the entire 400.degree. F.+ fractions,
including hydrogenation of FT oxygenates, which has significant
negative impact on hydroprocessing catalyst life and further causes
yield loss. Catalytic hydroprocessing catalysts of noble metals are
well known, some of which are described in U.S. Pat. Nos.
3,852,207; 4,157,294; 3,904,513 the disclosures of which are
incorporated herein by reference. Hydroprocessing utilizing
non-noble metals, such as cobalt catalysts, promoted with rhenium,
zirconium, hafnium, cerium or uranium, to form a mixture of
paraffins and olefins has also been used. As mentioned above,
however, hydroprocessing at severe conditions raises the costs of
processing and the resulting product and further results in yield
loss.
[0007] There remains a need, therefore, for an improved integrated
Fischer-Tropsch process in which the FT oxygenates may be wholly or
partially removed at a lower cost than known hydroprocessing means
and without a substantial yield loss. There remains a further need
for a transportation fuel or blending stock therefor which contains
substantially no sulfur, FT oxygenates or other hetero-atom
components, but which has a high lubricity and high stability, and
which can be produced economically.
SUMMARY OF THE INVENTION
[0008] The invention meets these and other needs by providing a
transportation fuel or blending stock for a transportation fuel
which contains substantially no FT oxygenates, sulfur or other
hetero-atom components. The invention further provides a method of
producing a transportation fuel or blending stock which eliminates
oxygenates, improves lubricity and lower temperature properties,
but which is economical and does not cause any significant yield
loss or which results in significantly less yield loss than known
hydroprocessing and hydrotreatment methods.
[0009] In one embodiment of the invention, a synthetic fuel is
provided wherein the synthetic fuel comprises a hydrocarbon mixture
having a carbon number range from about C.sub.7 to about C.sub.24
wherein the hydrocarbon mixture comprises substantially no FT
oxygenates, at least about 5 wt % n-paraffins and between about 11%
and about 20% olefins by weight, and between about 2 wt % and about
90 wt % branched paraffins wherein less than 50% of all branch
groups are monomethyl and wherein the ratio of terminal monomethyl
branching to internal monomethyl branching is at least about
1:1.5.
[0010] In another embodiment of the invention, a process for
producing a synthetic fuel is provided wherein the process
comprises the steps of: (a) producing a light Fischer-Tropsch
liquid; (b) dehydrating all or a part of the FT oxygenates in the
LFTL while retaining the olefin content in the LFTL; (c) recovering
a dehydrated product; (d) separating the aqueous and organic phases
of the dehydrated product; and (e) blending the organic phase of
the dehydrated product into a transportation fuel.
[0011] Additional embodiments and advantages of the invention will
be apparent by reference to the figures, description of the
embodiments and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic of an embodiment of the integrated
Fischer-Tropsch process of the invention.
[0013] FIG. 2 is a schematic of an alternative embodiment of the
Fischer-Tropsch process of the invention.
[0014] FIG. 3 is a schematic of a possible hydroprocessing
arrangement of the Fischer-Tropsch process of the invention.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0015] The term "C.sub.x", where x is a number greater than zero,
refers to a hydrocarbon compound having predominantly a carbon
number of x. As used herein, the term C.sub.x may be modified by
reference to a particular species of hydrocarbons, such as, for
example, C.sub.5 olefins. In such instance, the term means an
olefin stream comprised predominantly of pentenes but which may
have impurity amounts, i.e. less than about 10%, of olefins having
other carbon numbers such as hexene, heptene, propene, or butene.
Similarly, the term "C.sub.x+" refers to a stream wherein the
hydrocarbons are predominantly those having a hydrocarbon number of
x or greater but which may also contain impurity levels of
hydrocarbons having a carbon number of less than x. For example,
the term C.sub.15+ means hydrocarbons having a carbon number of 15
or greater but which may contain impurity levels of hydrocarbons
having carbon numbers of less than 15. The term "C.sub.x-C.sub.y",
where x and y are numbers greater than zero, refers to a mixture of
hydrocarbon compounds wherein the predominant component
hydrocarbons, collectively about 90% or greater by weight, have
carbon numbers between x and y inclusive. For example, the term
C.sub.5-C.sub.9 hydrocarbons means a mixture of hydrocarbon
compounds which is predominantly comprised of hydrocarbons having
carbon numbers between 5 and 9 inclusive, but may also include
impurity level quantities of hydrocarbons having other carbon
numbers.
[0016] As used herein the term "high lubricity" means having a wear
scar of average diameter of about .ltoreq.0.46 mm at 60.degree. C.
tested in accordance with ASTM Standard D-6079-02 entitled
"Standard Test Method for Evaluating Lubricity of Diesel Fuels by
the High-Frequency Reciprocating Rig." The terms "high stability"
and "high oxidative stability" mean having a total solids
.ltoreq.1.5 mg/100 ml tested in accordance with ASTM Standard
D-22-74-01a entitled "Standard Test Method for Oxidation Stability
of Distillate Fuel Oil (Accelerated Method)." Note that these
methods are being applied herein to the analysis and
characterization of synthetic products although the standards refer
expressly to petroleum derived products.
[0017] Unless otherwise specified, all quantities, percentages and
ratios herein are by weight.
[0018] The Fischer-Tropsch process includes processing of synthesis
gas to produce a hydrocarbon stream via the Fischer-Tropsch
reaction, recovery of the Fischer-Tropsch product, catalytic
dehydration of all or part of the Fischer-Tropsch product, and
recovery of the hydrocarbons by phase separation. For the purposes
of the inventive process, the Fischer-Tropsch synthesis are useful
in the invention described in inter alia, in U.S. Pat. Nos.
4,973,453; 6,172,124; 6,169,120; and 6,130,259; the disclosures of
which are all incorporated herein by reference.
[0019] The Fischer-Tropsch conversion system for converting
hydrocarbon gases to liquid or solid hydrocarbon products using
autothermal reforming includes a synthesis gas unit, which includes
a synthesis gas reactor in the form of an autothermal reforming
reactor (ATR) containing a reforming catalyst, such as a
nickel-containing catalyst. A stream of light hydrocarbons to be
converted, which may include natural gas, is introduced into the
reactor along with oxygen (O.sub.2). The oxygen may be provided
from compressed air or other compressed oxygen-containing gas, or
may be a pure oxygen stream. The ATR reaction may be adiabatic,
with no heat being added or removed from the reactor other than
from the feeds and the heat of reaction. The reaction is carried
out under sub-stoichiometric conditions whereby the
oxygen/steam/gas mixture is converted to syngas.
[0020] The Fischer-Tropsch reaction for converting syngas, which is
composed primarily of carbon monoxide (CO) and hydrogen gas
(H.sub.2), may be characterized by the following general
reaction:
2nH.sub.2+nCO.fwdarw.(--CH.sub.2--).sub.n+nH.sub.2O (1)
[0021] Non-reactive components, such as nitrogen, may also be
included or mixed with the syngas. This may occur in those
instances where air, enriched air, or some other non-pure oxygen
source is used during the syngas formation.
[0022] The syngas is delivered to a synthesis unit, which includes
a Fischer-Tropsch reactor (FTR) containing a Fischer-Tropsch
catalyst. Numerous Fischer-Tropsch catalysts may be used in
carrying out the reaction. These include cobalt, iron, ruthenium as
well as other Group VIIIB transition metals or combinations of such
metals, to prepare both saturated and unsaturated hydrocarbons. The
Fischer-Tropsch catalyst may include a support, such as a
metal-oxide support, including silica, alumina, silica-alumina or
titanium oxides. For example, a Co catalyst on transition alumina
with a surface area of approximately 100 to about 200 m.sup.2/g may
be used in the form of spheres of about 50 to about 150 .mu.m in
diameter. The Co concentration on the support may be between about
15% and about 30% by weight. Certain catalyst promoters and
stabilizers may be used. The stabilizers include Group IIA or Group
IIIB metals, while the promoters may include elements from Group
VIII or Group VIIB. The Fischer-Tropsch catalyst and reaction
conditions may be selected to be optimal for desired reaction
products, such as for hydrocarbons of certain chain lengths or
number of carbon atoms. Any of the following reactor configurations
may be employed for Fischer-Tropsch synthesis: fixed bed, slurry
bed reactor, ebullating bed, fluidizing bed, or continuously
stirred tank reactor (CSTR). The FTR may be operated at a pressure
of about 100 psia to about 500 psia and a temperature of about
375.degree. F. to about 500.degree. F. The reactor gas hourly space
velocity ("GHSV") may be from about 1000 to about 8000 hr.sup.-1.
Syngas useful in producing a Fischer-Tropsch product useful in the
invention may contain gaseous hydrocarbons, hydrogen, carbon
monoxide and nitrogen with H.sub.2/CO ratios from about 1.8:1 to
about 2.4:1. The hydrocarbon products derived from the
Fischer-Tropsch reaction may range from methane (CH.sub.4) to high
molecular weight paraffinic waxes containing more than 100 carbon
atoms.
[0023] Referring to FIG. 1, an overview of the Fischer-Tropsch
process is illustrated. Synthesis gas produced in ATR 11 is fed
through line 1 to a Fischer-Tropsch reactor (FTR) 2. The tail gas
of the Fischer-Tropsch product is recovered overhead in line 3 and
the Fischer-Tropsch oil and wax are fractionated and recovered
through lines 4 and 5, respectively. The product recovered in line
4 is a Light Fischer-Tropsch Liquid (LFTL), and the product
recovered in line is a Heavy Fischer-Tropsch Liquid (HFTL).
[0024] The LFTL fraction will contain between about 2% and about
15% of isoparaffins. Substantially all of the isoparaffins are
terminal monomethyl species. For the purposes of this invention,
the terminal species are 2- and 3-methyl branched. The ratio of
terminal monomethyl to internal monomethyl branching in the LFTL
paraffins may range from about 1:1.5, 1:1, 1.5:1, 2:1, or greater.
Unless otherwise noted, all percentages herein are by weight.
[0025] All or part of the LFTL, which is comprised primarily of
C.sub.2 to C.sub.24 hydrocarbons, is fed into dehydration unit 6.
In dehydration unit 6, primary and internal alcohols, i.e., FT
oxygenates, present in the LFTL are dehydrated to yield
corresponding olefins. A detailed discussion of the dehydration
process is contained in co-pending, commonly-owned application
entitled "Integrated Fischer-Tropsch Process with Improved
Oxygenate Processing Capability", Provisional Application Ser. No.
60/455,224, naming Armen Abazajian et al. as inventors, now utility
application Ser. No. 10/426,154, the disclosures of which are
incorporated herein by reference. Alternatively, the LFTL may be
distilled prior to dehydration to separate out a C.sub.8-C.sub.20+
cut which is then passed into dehydration unit 6.
[0026] The dehydrated product produced in dehydration unit 6 is
recovered and condensed. The condensed product will contain aqueous
and organic phases which may be separated using any appropriate
method, such as phase separation. Both the organic and aqueous
phases are essentially free of alcohols, the alcohols having been
substantially completely dehydrated. The organic phase primarily
contains paraffins with some olefins, the olefins arising from
dehydration of the alcohols as well as from the Fischer-Tropsch
product.
[0027] The organic phase may be passed to a fractionator 8. HFTL
from FTR 2 may also be passed into fractionator 8 through conduit
5. A naphtha product may be removed overhead from fractionator 8
through conduit 13 and a C.sub.8+ fraction passed into
hydrocracker/hydrotreatment unit 10 in which the C.sub.8+ fraction
is cracked to lower molecular weight hydrocarbons.
[0028] The hydrocracked product produced in
hydrocracker/hydrotreatment unit 10 is passed to a second
fractionating unit 12 where a middle distillate having a nominal
boiling range of between about 250.degree. F. and about 700.degree.
F. is recovered through conduit 14. All or part of the middle
distillate may be used as a transportation fuel or blending stock
therefor.
[0029] FIG. 2 illustrates an alternative embodiment of the
integrated Fischer-Tropsch process.
[0030] The LFTL and HFTL are combined and fractionated in a
distillation column 30. Nominal 30.degree.-600.degree. F. product
is removed as one or more side-streams, including a nominal
30.degree.-250.degree. F. fraction through line 32, a nominal
250.degree.-500.degree. F. fraction though line 34, and a nominal
500.degree. F.+ fraction through line 35. Only the
250.degree.-500.degree. F. fraction is routed to the dehydration
unit 6. Following dehydration may then be recovered, fractionated
The dehydrated 250.degree.-500.degree. F. fraction is sent through
conduit 33 to a product receptacle and/or blending unit 37.
[0031] FIG. 1 depicts the dehydrated product mixture of paraffins
and olefins as also being routed to hydrocracking/hydrotreating
unit 10, which is appropriate where a fully hydrotreated product is
desired. However, the dehydrated product mixture may alternatively
be separately hydroisomerized. In yet another embodiment, the
dehydrated product mixture may receive no post-dehydration
hydroprocessing. FIG. 3 depicts several acceptable
hydrocracker/hydroisomerizer arrangement. However, any of a number
of alternative post-dehydration and higher boiling range fraction
treatment schemes may be employed within the integrated
Fischer-Tropsch process depending upon the desired slate of
products. For example, referring to FIG. 3, alternative treatment
schemes include:
[0032] a) Hydroisomerization of the dehydrated product;
hydrocracking of the 500.degree. F.+ fraction followed by
hydrotreatment.
[0033] b) No post-dehydration treatment of the dehydrated product;
hydrocracking of the 500.degree. F.+ fraction.
[0034] c) No post-dehydration treatment of the dehydrated product;
hydrocracking of the 500.degree. F.+ fraction followed by
hydrotreatment.
[0035] d) Hydroisomerization of the dehydrated product; no
hydroprocessing of the 500.degree. F.+ fraction; reblending of the
dehydrated--hydroisomerized product with the 500.degree. F.+
fraction followed by fractionation; hydrocracking of the bottoms
stream of the fractionation.
[0036] e) Hydroisomerization of the dehydrated product;
hydrocracking of the 500.degree. F.+ fraction.
[0037] f) No post-dehydration treatment of the dehydrated product;
hydrotreatment followed by hydrocracking of the 500.degree. F.+
fraction.
[0038] g) No post-dehydration treatment of the dehydrated product;
hydrotreatment of the 500.degree. F.+ fraction.
[0039] h) No post-dehydration treatment of the dehydrated product;
hydrotreatment, hydrocracking and hydrofinishing of the 500.degree.
F.+ fraction.
[0040] i) No post-dehydration treatment of the dehydrated product;
hydrotreatment and hydrocracking of the 500.degree. F.+ fraction;
hydrodewaxing of the unconverted hydrocracker bottoms and
hydrofinishing of a lubricant basestock.
[0041] j) No post-dehydration treatment of the dehydrated product;
hydrocracking of the 500.degree. F.+ fraction; hydrotreatment of
the unconverted wax.
[0042] These alternative treatment schemes are only some of the
variations encompassed by and useful in the inventive
Fischer-Tropsch process. Thus, the list above and FIG. 3 are
intended to merely illustrate, and not limit, a portion of the
inventive Fischer-Tropsch process. Possible process conditions and
parameters for hydroisomerizing, hydrotreating and hydrocracking
the relevant hydrocarbon streams are well known in the art. One
example of hydroprocessing conditions and parameters is described
in U.S. Pat. Nos. 5,286,455, 6,296,757, and 6,180,842, the
disclosure of which are incorporated herein by reference. A large
number of alternative hydroprocessing conditions and parameters are
also well known in the art and may be useful in connection with the
integrated Fischer-Tropsch process described herein. Therefore,
incorporation of the above-referenced U.S. Patents are not intended
to limit the inventive process.
[0043] Processing schemes (a), (b), (c), (d), (e), (f), and (O) are
most useful for producing ultra-clean synthetic middle distillate
fuels. The product of the integrated Fischer-Tropsch process may be
used directly as a transportation fuel or as a blending stock for
formulating a transportation fuel. In addition, schemes (b), (c),
(f), (g), (h), (i), and (O) are most useful for making
olefin/paraffin mixtures as dehydrated product which can be used as
feedstocks for single product middle distillate fuel feedstocks.
Note that where the dehydration product is not subjected to
hydroprocessing or hydrotreatment, olefins produced in the
Fischer-Tropsch reaction remain in the middle distillate fraction
and are incorporated into the synthetic transportation fuel.
[0044] Because the middle distillate portion of the dehydrated LFTL
contains only a relatively low level, i.e., about 2 wt % to about
10 wt %, of branched paraffins essentially all of which are
monomethyl branched, the middle distillate by itself is generally
not used as a transportation fuel. That is, the high ratio of
normal paraffins results in cloud and freeze points which prohibit
the incorporation of higher molecular weight paraffins. Most diesel
and essentially all jet fuels may require blending with the
hydrocracked HFTL portion. Because the hydrocracking process yields
more highly branched paraffins, the hydrocracked HFTL portion
generally lowers the cloud and freeze points of the final blended
fuel. In fact, the hydrocracked HFTL contains a large proportion of
multimethyl-branched isoparaffins. Moreover, those molecules in the
hydrocracked HFTL that are monomethyl-branched are more likely to
be terminally branched. As a consequence, between about 20 and
about 75% of the branched paraffins in the resulting blended fuel
are monomethyl-branched, depending on the final properties of the
fuel. Furthermore, among the monomethyl-branched paraffins, the
terminal monomethyl species predominate.
[0045] In another embodiment of the invention, a hydrocarbon
mixture produced by the integrated Fischer-Tropsch process is
provided.
[0046] In yet another aspect of the invention, a synthetic
transportation fuel or blending stock therefor having no sulfur,
essentially no FT oxygenates, a cetane number of at least 50, and a
cloud point or freezing point of less than about 5.degree. C. The
synthetic transportation fuel may contain between about 1 wt % and
about 20 wt % olefins, of which at least about 1 wt % is
mono-olefin in the 200.degree. to 700.degree. F. boiling point
range.
EXAMPLE 1
[0047] A pilot installation consisting of two distillation columns
was used to produce C.sub.10-13 light kerosene and C.sub.13-20+
drilling fluid feedstock streams. The columns were fed
approximately 3400 g/hr of liquid Fischer-Tropsch oil. The
Fischer-Tropsch oil had approximately the following
composition:
1 Carbon # % by wt. 4 <0.1 5 0.01 6 0.3 7 1.0 8 2.9 9 5.9 10 8.1
11 9.2 12 9.5 13 9.2 14 8.4 15 7.9 16 7.1 17 6.2 18 5.4 19 4.6 20
3.7 21 3.0 22 2.3 23 1.7 24 1.2 25+ 2.6 Total 100.00
[0048] The Fischer-Tropsch oil was fed into the first column and
C.sub.13 and lighter materials were distilled overhead. The column
conditions were: 10 psig pressure, 480.degree. F. feed preheat
temperature, 407.degree. F., overhead temperature, 582.degree. F.
bottoms temperature. The first column had approximately 98 inches
of Sulzer Mellapack 750Y packing. The overheads of the first column
was fed into the second column operating at 12 psig pressure,
370.degree. F. overhead temperature and 437.degree. F. bottoms
temperature. The second column was packed with 28 inches of Sulzer
EX packing. The bottoms of the second column constituted the
product C.sub.10-13 light kerosene stream. The bottoms of the first
column constituted C.sub.13-20+ heavy diesel and drilling fluid
feedstock. The compositions of C.sub.10-13 light kerosene stream
(Feed A) and C.sub.13-20+ (Feed B) are shown in Tables 1 and 2,
respectively.
2 TABLE 1 Total n-paraffins, isoparaffins, olefins and alcohols
Mass % C7- 0.02 C8 0.25 C9 1.29 C10 9.83 C11 33.51 C12 43.04 C13
11.47 C14 0.49 TOTAL C15+ 0.10 100.00
[0049]
3 TABLE 2 Total n-paraffins, isoparaffins, olefins and alcohols
Mass % C11-: 0.97 C12: 1.77 C13: 11.43 C14: 13.68 C15: 12.35 C16:
10.96 C17: 9.06 C18: 7.84 C19: 6.79 C20: 7.04 C21: 5.66 C22: 4.63
C23+: 7.83 100.0
EXAMPLE 2
[0050] 30 cc/hr of a Feed A from Example 1 was fed via a syringe
pump and mixed with 20 cc/min of nitrogen. The gas/liquid mixture
was introduced upflow into a vessel packed with stainless steel
mesh saddles, where the liquid was vaporized and superheated to
reaction temperature of 560.degree. F. The vaporized feed was fed
upflow into a reactor packed with 1/8 Alcoa S-400 alumina catalyst
and suspended in a heated sandbath. The sandbath was maintained at
the reaction temperature and ebulated by air. Reactor LHSV was
maintained at about 0.26 hr.sup.-1. The reactor outlet was
condensed and Product A and water by-product was collected in a
product accumulator. System pressure was maintained by controlling
the product accumulator overhead pressure at 50 psig. A water layer
was drained and the organic layer product analyzed in a HP 5890
Series II GC with a 60 m RTXI capillary column with a 0.32 mm bore
and 3-micron film thickness. The compositions of Feed A and Product
A are reported in Table 3. The product was also analyzed on a
.sup.1H NMR 300 MHz JOEL analyzer, confirming complete absence of
alcohols.
EXAMPLE 3
[0051] 15 cc/hr of Feed A from Example 1 was processed in a
benchscale process described in Example 2. The feed was vaporized
and superheated to 650.degree. F. Reactor LHSV was approximately
0.26 hr.sup.-1 to make Product A and, 0.13 hr.sup.-1 to make
Product B. Composition of Product B from this example is reported
in Table 3. .sup.1H NMR analysis confirmed absence of alcohols in
the product.
4 TABLE 3 Sample Reference Number Feed A Product A Product B Mass %
Mass % Mass % N-PARAFFIN 80.64 80.23 79.90 ALPHA OLEFIN 4.43 8.20
7.96 INTERNAL OLEFIN 3.04 3.37 3.91 BRANCHED PARAFFIN 8.21 8.19
8.22 ALCOHOL 3.68 0.00 0.00 100.00 100.00 100.00
EXAMPLE 4
[0052] Feed A from Example 1 was spiked with approximately 5% of
hexanol, composing Feed A' and fed at 15 cc/min into a benchscale
process described in Example 3. Nitrogen feed was maintained at 10
cc/min. Composition of Product C from this example is reported in
Table 4. .sup.1H NMR analysis confirmed absence of alcohols in the
product.
5 TABLE 4 Feed A' Product C Mass % Mass % N-PARAFFIN 75.12 75.14
ALPHA OLEFIN 4.15 10.75 INTERNAL OLEFIN 3.03 4.47 BRANCHED PARAFFIN
9.67 9.64 ALCOHOL 8.03 0.00 TOTAL 100.00 100.00
EXAMPLE 5
[0053] Feed B from Example 1 was fed into the process described in
Example 4. The reaction temperature was maintained at 675.degree.
F. and the outlet pressure was maintained at about 5 psig. The
reaction Product D is shown in Table 5.
6 TABLE 5 Sample Reference Number Feed B Product D Mass % Mass %
N-PARAFFIN 82.46 82.87 ALPHA OLEFIN 2.26 3.48 INTERNAL OLEFIN 2.75
3.68 BRANCHED PARAFFIN 10.10 9.97 ALCOHOL 2.45 0.00 Total 100.00
100.00
EXAMPLE 6
[0054] Products A and D from Examples 3 and 5, respectively, were
blended in a ratio of about 1:2.5. The blended product was flashed
to remove approximately 7% of the total volume of the blended
product was collected overhead as a light end fraction and the 15%
of the total volume of the blended product was retained as a heavy
end fraction. The remaining middle cut, about 78% of the total
volume of the blended product, contained about 8% olefins. This
middle cut was then blended 1:1 with a fully hydroprocessed
Fischer-Tropsch diesel having no unsaturation or significant
hetero-atom content (Fuel Y). The resulting fuel sample (Fuel X)
had a flashpoint of 146.degree. F., and a cloud point -6.degree. C.
Fuel X was submitted for a blind HFRR (ASTM D-6079) lubricity test
with two comparative samples: Fuel Y, having a flashpoint of
136.degree. F. and cloud point of -21.degree. C. and an ASTM
supplied mineral-based ULSD diesel (Fuel Z), having a flashpoint of
130.degree. F. and a cloud point of -11.degree. C. The lubricity
test results are summarized in Table 6.
7 TABLE 6 (D-6079) mm @ Samples 60.degree. C. Y 0.574 X 0.391 Z
0.501
[0055] HFRR test results report an average wear scar diameter. A
smaller number indicates a smaller wear scar and, consequently, a
more lubricious fuel.
EXAMPLE 7
[0056] Fuel X' was produced by mixing Fuel X (from Example 6) with
a mixture of Fuel Y and 1-dodecene in a ratio of 1 part of Fuel X
to 2.2 parts of the Fuel Y plus 1-dodecene mixture. The ratio of
Fuel Y to 1-dodecene was determined so that Fuel X' contained about
4% olefins. Fuel X', Fuel Y, and Fuel Z were submitted for
oxidative stability testing in accordance with ASTM D-2274.
8 TABLE 7 Samples Y X' Z Filterable Insolubles (mg./100 ml) 1.1 0.1
0.1 Adherent Insolubles (mg/100 ml) 0.2 0.4 0.3 Total Insolubles
(mg/100 ml) 1.3 0.5 0.4
EXAMPLE 8
[0057] Fischer-Tropsch oil and Fischer-Tropsch wax were fed into a
pilot hydrotreater and hydrocracker arrangement in series. The
hydrotreater was operated at 500.degree. F. and the hydrocracker
was operated at 716.degree. F. and total LHSV of about 1 hr.sup.-1.
The gas/oil ratio was 3568 scf/bbl. The resulting diesel fuel E had
the following properties:
9 TABLE 8 Analysis Testing Method Fuel E Density @ 15.degree. C.,
D4052 0.7679 g/ml Cetane Number D613 >74.8 Cetane Index D4737 78
Flash Point, .degree. C. D93 62 CFPP, .degree. C. D6317 -21 Cloud
Point, .degree. C. D5773 -11.9 Flash Point, .degree. C. D56 --
[0058] Fuel E was analyzed on a capillary GC to identify the type
of branching in the sample. The results, in vol %, are summarized
in Table 9.
10 TABLE 9 2/3-Me 4-Me + Mono Methyl Multi-Methyl 10.6978 13.3841
24.0820 18.3575
[0059] The balance of the sample is normal paraffins. The ratio of
2/3 methyl-branched isoparaffins or terminal-branched isoparaffins
to internal-branched isoparaffins (4-Me+) in Fuel E is about
1:1.25. Further, the ratio of the monomethyl content of Fuel E to
the multi-methyl content is about 1.3:1 (57% of the branching is
monomethyl and 43% is multi-methyl).
[0060] As can be seen from the discussion above, the process and
synthetic fuel of the invention provide one or more of several
advantages and benefits, which are discussed below.
[0061] Lower capital cost is incurred by elimination of a
hydrotreatment unit. At a minimum, lower operating costs are
achieved by reduction in hydrotreatment and milder hydroprocessing
conditions.
[0062] One advantage of the inventive Fischer-Tropsch process is
improvement of yield of useful products. It is known by those
skilled in the art that oxygenates in the hydrocracking feed reduce
hydrocracking catalyst life and therefore, necessitate higher
hydrocracking temperatures to achieve the required low temperature
properties of a specific boiling range and to maintain conversion
per pass. Higher hydrocracking temperatures lead to lower product
yields. Moreover, bypassing the Fischer-Tropsch product in the
middle distillate range directly to product blending introduces
alcohols into the final product. Alcohols are known to have poor
low temperature properties, such as freeze point and cloud point.
Poor low temperature properties are especially detrimental in
formulating military and jet fuels. Hydrocracking conditions must
be intensified to compensate for the impact of the alcohols thereby
resulting in yield loss. Similarly, if the product being bypassed
is hydrotreated, it is well known that paraffins generated in
hydrotreatment have higher freeze point and yet again cause
deterioration in the low temperature properties of the blended
product. The inventive Fisher-Tropsch process disposes of the
alcohols by converting them into olefins which have beneficial low
temperature properties.
[0063] In processing mineral, petroleum-based transportation fuels,
much effort is spent to hydrogenate any olefins present to improve
the stability of the fuel. This is necessary because in mineral
transportation fuel processing the unsaturation comes from a number
of thermal and catalytic refining cracking processes, which are not
selective, and, in addition to mono-olefins also produce dienes,
trienes, and alkynes. These species are known to oligomerize and
polymerize readily in storage or in fuel tanks, thus producing gums
deleterious for fuel systems. Because of the selectivity of the
inventive Fischer-Tropsch process the inventive transportation fuel
has virtually none of the higher unsaturates, but only internal and
alpha-mono-olefins, which do not oligomerize easily and do not form
gum. Furthermore, elimination of oxgenates from the transportation
fuel as it is done in the inventive process, assures that the fuel
is not hygroscopic. Water retention of the fuels is not an
attractive characteristic as it may lead to freezing of the
retained water in the fuel lines during ambient temperatures below
32.degree. F.
[0064] It is known in the art that linear and internal olefins
exhibit higher lubricity and higher metal adherence than either
paraffins or isoparaffins. This is explained by the higher electron
density of the double bond being attracted to positive sites on the
partially oxidized metal surface. Thus, a fuel with a sufficiently
high content of both alpha-and internal olefins will have somewhat
better lubricity than the entirely paraffinic component of the same
fuel.
[0065] It is known that compounds containing hetero-atoms, such as
sulfur and oxygen, are beneficial to lubricity and stability, and,
in fact, are used as additives for those purposes.
[0066] However, use of hetero-atoms is disadvantageous as described
above. The invention provides hydrocarbon fuel which does not
contain hetero-atoms and which has the lubricity and stability
characteristics of a hetero-atom containing fuel.
[0067] A distinguishing characteristic of Fischer-Tropsch derived
fuels is their high cetane number credited to very high normal and
slightly-branched paraffin content. It is well known in the art
that the cetane number of linear alpha-and internal-olefins is also
very high. Typically, the cetane number of alpha- and internal
olefins is only 5-10 units lower than for a corresponding linear
paraffin and about equivalent to the mono-branched isomers of the
same carbon number.
* * * * *