U.S. patent application number 11/054833 was filed with the patent office on 2005-07-07 for methods for treating organic compounds and treated organic compounds.
This patent application is currently assigned to ConocoPhillips Company. Invention is credited to Barker, Craig T., Espinoza, Rafael L., Gopalakrishnan, Sridhar, Jack, Douglas S., Lawson, Keith H..
Application Number | 20050145544 11/054833 |
Document ID | / |
Family ID | 32926880 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145544 |
Kind Code |
A1 |
Lawson, Keith H. ; et
al. |
July 7, 2005 |
Methods for treating organic compounds and treated organic
compounds
Abstract
Embodiments include processes for producing streams containing
organic molecules (for example, diesel fuels and diesel fuel
blending agents) including ultra-low severity hydrotreatment of at
least a portion of a hydrocarbon synthesis product stream. Also,
streams containing organic molecules (for example, diesel fuels and
diesel fuel blending agents) produced by the processes are
described.
Inventors: |
Lawson, Keith H.; (Ponca
City, OK) ; Jack, Douglas S.; (Ponca City, OK)
; Barker, Craig T.; (Ponca City, OK) ;
Gopalakrishnan, Sridhar; (Ponca City, OK) ; Espinoza,
Rafael L.; (Ponca City, OK) |
Correspondence
Address: |
DAVID W. WESTPHAL
CONOCOPHILLIPS COMPANY - I.P. Legal
P.O. BOX 1267
PONONCA CITY
OK
74602-1267
US
|
Assignee: |
ConocoPhillips Company
Houston
TX
|
Family ID: |
32926880 |
Appl. No.: |
11/054833 |
Filed: |
February 10, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11054833 |
Feb 10, 2005 |
|
|
|
10382339 |
Mar 5, 2003 |
|
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|
Current U.S.
Class: |
208/115 |
Current CPC
Class: |
C10G 2400/04 20130101;
C10G 49/06 20130101; C10G 47/00 20130101; C10G 49/04 20130101; C10G
69/02 20130101; B01J 23/755 20130101; C10G 65/12 20130101; B01J
23/74 20130101 |
Class at
Publication: |
208/115 |
International
Class: |
C10G 011/08 |
Claims
What is claimed is:
1. A hydroprocessed product stream wherein the hydroprocessed
product stream is produced by the method comprising: hydrotreating
at least a portion of a hydrocarbon synthesis product stream to
produce a hydroprocessed product stream; wherein at least a portion
of a hydrocarbon synthesis product stream comprises paraffins,
olefins, and at least one heteroatomic compound: wherein the
hydroprocessed product stream comprises no more than an
insubstantial amount of olefins; and wherein a substantial amount
of the heteroatoms remain attached to their parent molecules during
hydrotreating.
2. The hydroprocessed product stream of claim 1 wherein the
hydrocarbon synthesis product stream comprises a Fischer-Tropsch
product stream.
3. The product stream of claim 1 wherein at least one heteroatomic
compound is an .oxygenate.
4. The product stream of claim 3 wherein the hydrotreating step
retains at least 50% of the oxygen content of the at least a
portion of a hydrocarbon synthesis product stream in the
hydroprocessed product stream.
5. The product stream of claim 3 wherein the hydrotreating step
retains at least 75% of the oxygen content of the at least a
portion of a hydrocarbon synthesis product stream in the
hydroprocessed product stream.
6. The product stream of claim 1 wherein the at least a portion of
a hydrocarbon synthesis product stream is fractionated upstream of
the hydrotreater.
7. The product stream of claim 6 wherein the at least a portion of
the hydrocarbon synthesis product stream comprises primarily
diesel.
8. The method of claim 1 wherein the hydrotreater comprises a
catalyst, wherein the catalyst comprises at least one metal
selected from the group consisting of Ni, Pd, Pt, Ru, Mo, W, Fe,
and Co.
9. The method of claim 8 wherein the catalyst comprises Co, Fe, or
combination thereof.
10. The method of claim 9 wherein the hydrotreater is operated at a
temperature of between about 350.degree. F. and about 570.degree.
F.
11. The method of claim 8 wherein the hydrotreater comprises a
catalyst, and said catalyst comprises at least one metal selected
from the group consisting of Ni, Pd, Pt, Ru, Mo, and W.
12. The product stream of claim 11 wherein the hydrotreater
comprises a nickel catalyst.
13. The product stream of claim 12 wherein the hydrotreater is
operated at a temperature of between about 180.degree. F. and about
350.degree. F.
14. The product stream of claim 12 wherein the hydrotreater is
operated at a temperature of between about 180.degree. F. and about
320.degree. F.
15. The product stream of claim 12 wherein the hydrotreater is
operated at a temperature of between about 180.degree. F. and about
300.degree. F.
16. The product stream of claim 1 wherein the hydroprocessed
product stream comprises a diesel fraction and wherein the diesel
fraction has an oxygen content of about 0.1 wt % or greater and an
oxidation stability of about 25 g/m.sup.3 or less.
17. The product stream of claim 1 wherein the at least a portion of
a hydrocarbon synthesis product stream is fractionated downstream
of the hydrotreater.
18. The product stream of claim 1 wherein wherein the
hydroprocessed product stream comprises a diesel fraction and has a
Bromine number of less than about 0.1 g Br/i 00 g.
19. A hydrotreated diesel product derived from synthesis gas having
the following properties: Oxidation stability.ltoreq.25 g/m.sup.3;
oxygen content.gtoreq.0.1 wt %; and lubricity HFRR.ltoreq.400
.mu.m; wherein the hydrotreated diesel product consists essentially
of molecules which have been hydrotreated.
20. The diesel product of claim 19 having an oxygen content of
about 0.7 wt %.
21. The diesel product of claim 19 having a lubricity of less than
or equal to about 340 .mu.m.
22. The diesel product of claim 19 having a pour point of less than
about 2.degree. C.
23. The diesel product of claim 19 having a Bromine number of less
than about 0.1 g Br/100 g.
24. The diesel product of claim 19 having an oxidation stability of
between about 0.5 g/m.sup.3 and about 25 g/m.sup.3.
25. The diesel product of claim 19 having an oxidation stability of
less than about 0.5 g/m.sup.3.
26. The diesel product of claim 19 having an oxidation stability of
less than about 10 g/m.sup.3.
27. The diesel product of claim 19 having an oxidation stability of
less than about 5 g/m.sup.3.
28. The diesel product of claim 19 having an oxidation stability of
less than about 2 g/m.sup.3.
29. The diesel product of claim 19 having an oxygen content of
greater than about 0.35 wt %.
30. The diesel product of claim 19 having an oxygen content of
greater than about 0.525 wt %.
31. The diesel product of claim 19 having an oxygen content of
greater than about 0.63 wt %.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/382,339 filed on Mar. 5, 2003, the
disclosure of which is incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
FIELD OF THE INVENTION
[0003] The present invention relates to methods and processes
comprising a ultra-low severity hydrotreatment of a hydrocarbon
stream for producing middle distillates. Particularly the present
invention relates to processes comprising a ultra-low severity
hydrotreatment of a hydrocarbon stream derived from synthesis
gas.
BACKGROUND OF THE INVENTION
[0004] Natural gas is a naturally-occurring abundant energy
resource. Wells that provide natural gas are often remote from
locations with a demand for its consumption. The costs associated
with transporting natural gas from these remote wells are generally
very high and may not be economical.
[0005] As opposed to natural gas, fuels that are liquid under
standard atmospheric conditions have the advantage that they can be
transported more economically. Thus, there has been interest in
developing technologies for converting natural gas to more readily
transportable liquid fuels.
[0006] One method for converting natural gas to liquid fuels
involves two sequential chemical transformations. In the first
transformation natural gas (which contains primarily methane) is
reacted to form a mixture of CO and H.sub.2 ("synthesis gas" or
"syngas"). This syngas generation usually occurs by dry reforming,
steam reforming, or partial oxidation, respective examples of which
are set forth below for methane:
CH.sub.4+CO.sub.2.fwdarw.2CO+2H.sub.2 (1)
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2 (2)
CH.sub.4+1/2O.sub.2.fwdarw.CO+2H.sub.2 (3)
[0007] Examples of syngas generation processes are disclosed in
U.S. Pat. No. 6,402,989 to Gaffney and Gunardson, Harold,
"Industrial Gases in Petrochemical Processing" 41-80 (1998), both
incorporated herein by reference.
[0008] In the second transformation, hydrocarbon synthesis, (by way
of example only, the Fischer-Tropsch process), carbon monoxide
reacts with hydrogen to form organic molecules. An example of a
Fischer-Tropsch process is disclosed in U.S. Pat. No. 6,333,294 to
Chao et al., incorporated herein by reference. The product stream
produced by conversion of natural gas commonly contains a range of
hydrocarbons including light gases, gases, light naphtha, naphtha,
kerosene, diesel, heavy diesel, heavy oils, waxes, and heavy waxes.
These cuts are approximate and there is some degree of overlapping
of components in each range. The product stream also often contains
many byproducts such as olefins (i.e., hydrocarbons containing at
least one carbon-carbon double bond) and heteroatomic compounds
(e.g., aldehydes, alcohols).
[0009] Usually, the most valuable fractions of a hydrocarbon
synthesis product stream are the middle distillate fractions. The
middle distillates or "middle cuts" generally comprise kerosene,
diesel, heating oil, heavy diesel, and heavy oils. Thus, it is
desirable to maximize the production of the middle distillates. One
method for increasing the production of middle distillates is to
crack the heavy waxy products to middle distillate range molecules.
For example, a method of processing syncrude to produce diesel fuel
may include distillation to separate diesel and wax fractions from
the lighter fraction, cracking of the wax fraction, and further
distillation of the cracked product to separate its diesel
fraction. The diesel fraction is then often blended with other
compounds to produce commercial diesel products. It is within the
skill of one of ordinary skill in the art to determine which
products are desirable based on the intended uses of the products.
Likewise, separation of the components of a hydrocarbon stream is
well known in the art, and it will be within the ability of one of
ordinary skill in the art to determine the conditions which will
effect the desired separation. In the instance of a distillation
column, it will be within the ability of one of ordinary skill in
the art to determine various parameters such as height and internal
design of the column, the distillation temperature, the feed
location, and the product withdrawal/sidedraw locations.
[0010] Another traditional step in the preparation of products
derived from a hydrocarbon synthesis product stream (such as from a
Fischer-Tropsch synthesis) is hydrotreatment. Traditionally,
hydrotreatment takes place at temperatures of at least 350.degree.
F. and usually from about 380.degree. F. to about 450.degree. F.
over a nickel catalyst. Under these conditions, traditional
hydrotreatment removes olefins that are known to cause chemical
instability. This instability frequently manifests itself in the
formation of gums which may form solid deposits in the fuel system
and engine. This instability is typically measured by the oxidation
stability ASTM D2274 test. Traditional hydrotreatment also removes
heteroatomic compounds such as sulfur-containing compounds,
oxygenates and amines.
[0011] Specific examples of methods of processing a Fischer-Tropsch
product stream are disclosed in various patents: U.S. Pat. Nos.
6,296,757; 5,766,274; 5,378,348 and patent applications WO
00/20535; WO 01/59034. While some methods describe the use of a
hydrotreatment step above 350.degree. F., more typically around
400.degree. F.-450.degree. F. with a nickel catalyst, others do not
hydrotreat certain cuts of the Fischer-Tropsch product stream in
order to retain some oxygenates into the final product. Oxygenates
indeed have been shown to be beneficial in the Fischer-Tropsch
products as disclosed in U.S. Pat. No. 5,645,613.
[0012] Although it is desirable to hydrotreat at least a portion of
the hydrocarbon synthesis products to remove olefins (which render
the product (e.g., diesel) unstable), the disclosed hydrotreating
schemes have the additional effect of also converting the
heteroatomic compounds (e.g., oxygenates). When present, the
oxygenates (particularly alcohols) may advantageously increase the
lubricity of the product. Others have reported methods to maintain
the oxygenates in the diesel fraction of a hydrocarbon synthesis
product stream by causing the diesel fraction to avoid
hydrotreatment.
SUMMARY
[0013] Surprisingly it has been found that ultra-low severity
hydrotreating, for example, with a conventional nickel catalyst at
350 psia of hydrogen partial pressure in the hydrotreater outlet,
at 250.degree. F. and a liquid hourly space velocity of about 3
hr.sup.-1, is likely to cause only partial conversion (i.e.,
converts substantially all of the olefins while leaving a
substantial amount of the heteroatoms comprised in the heteroatomic
compounds (e.g., oxygenates) attached to their parent molecules),
and that this partial conversion can enhance the lubricity of the
diesel fuel.
[0014] In accordance with the present invention, there are herein
disclosed methods and processes for producing a distillate. Some
embodiments disclosed herein comprise a hydrotreater for ultra-low
severity hydrotreatment of a hydrocarbon synthesis product stream
and removing much of the undesirable byproducts and impurities
while leaving at least some of the oxygenates, and a fractionation
unit for separating the hydrotreater effluent. Additional process
embodiments disclosed herein comprise ultra-low severity
hydrotreating of a hydrocarbon synthesis product stream,
hydrocracking of a heavy fraction of the hydrocarbon synthesis
product stream, and fractionating in order to produce middle
distillate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a more detailed description, reference will now be made
to the accompanying figures.
[0016] FIG. 1 is a schematic drawing of a first reactor scheme in
accordance with an embodiment of the present invention.
[0017] FIG. 2 is a schematic drawing of a second reactor scheme in
accordance with an embodiment of the present invention.
[0018] FIG. 3 is a schematic drawing of a third reactor scheme in
accordance with an embodiment of the present invention.
[0019] FIG. 4 is a schematic drawing of a fourth reactor scheme in
accordance with an embodiment of the present invention.
[0020] FIG. 5 is a schematic drawing of a fifth reactor scheme in
accordance with an embodiment of the present invention.
[0021] FIG. 6 is a schematic drawing of a sixth reactor scheme in
accordance with an embodiment of the present invention.
[0022] FIG. 7 is a schematic drawing of a seventh reactor scheme in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
[0023] In the reactor scheme of FIG. 1, there is shown a
hydrocarbon synthesis reactor 101, an ultra-low severity
hydrotreater 111, a fractionation unit 120, and a hydrocracker 131.
Feedstream 140 comprising CO and H.sub.2 in preferably about a
2:1H.sub.2:CO molar ratio is fed into hydrocarbon synthesis reactor
101. Reactor 101 includes a hydrocarbon synthesis catalyst in
reaction zone 100. Feedstream 140 reacts in reaction zone 100 to
produce a product stream 180. Product stream 180 comprises
primarily hydrocarbons with 3 carbon atoms or more (C.sub.3+),
preferably hydrocarbons with 5 carbon atoms or more (C.sub.5+). The
product stream 180 is introduced to hydrotreating catalyst 110 in
ultra-low severity hydrotreater 111 where stream 180 is
hydrotreated. This ultra-low severity hydrotreating saturates the
olefinic compounds present in product stream 180 while allowing a
substantial amount of the oxygenates to remain unconverted.
Advantageously, the ultra-low severity hydrotreater can also remove
or reduce solid material that can be present in the product stream
180, particularly when the hydrocarbon synthesis reactor 101
comprises free-flowing or suspended catalyst particles. The
hydrotreater product stream 190 exits hydrotreater 111 and is
combined with cracked hydrocarbon stream 210 recycled from
hydrocracker 131 to form stream 200. Combined stream 200 is then
introduced to fractionator 120 where it is separated into light cut
230, middle cuts 240 and 250, and heavy cut 220. Middle cuts 240
and 250 are preferably a diesel cut and a naphtha cut respectively.
It is possible that only one middle distillate cut or more than two
middle distillate cuts are desirable as determined by one of
ordinary skill in the art based on the desired product composition.
Heavy cut 220 is sent to hydrocracker 131 where it is cracked in
hydrocracking catalyst zone 130 to cracked hydrocarbon stream 210
which comprises on average lighter hydrocarbons than heavy cut 220.
Preferably, but not necessarily, cracked hydrocarbon stream 210
comprises primarily middle distillates and most preferably
comprises the most desired middle distillate or middle distillate
mix. The cracked hydrocarbon stream 210 is recycled into
fractionator 120 for separation. In a preferred embodiment stream
220 (which may comprise primarily C.sub.20+ hydrocarbons) is
recycled to extinction.
[0024] Referring now to FIG. 2, a reactor scheme similar to FIG. 1
is shown except that stream 210 leaving hydrocracker 131 is not
recycled to fractionator 120, but is instead sent to a second
fractionator 260.
[0025] Referring now to FIG. 3, there is shown a reactor scheme
similar to that of FIGS. 1 and 2, except that cracked hydrocarbon
stream 210 is split into streams 270 and 280. Stream 280 is
recycled to fractionator 120 and stream 270 is sent to second
fractionator 260. Stream 280 can be combined with stream 190 from
the hydrotreater 111 to form stream 200 which is then sent to
fractionator 120.
[0026] Referring now to FIG. 4, there is shown an embodiment of the
present invention including a hydrocarbon synthesis reactor 101
having a hydrocarbon synthesis reaction zone 100, fractionator 120,
ultra-low severity hydrotreaters 300 and 310 (which can optionally
be one ultra-low severity hydrotreater 320 which alternately
hydrotreats individual streams 240 and 250), hydrocracker 131
having hydrocracking reaction zone 130 and second fractionator 260.
Feed stream 140 comprising CO and H.sub.2 enter hydrocarbon
synthesis reactor 101 where it reacts in reaction zone 100 to form
product stream 190. The product stream 190 is combined with recycle
stream 280 from hydrocracker 131 to form combined stream 200 being
fed into fractionator 120 and separated into streams 230, 240, 250,
and 220. Streams 240 and 250 are each fed to ultra-low severity
hydrotreaters 310 and 300 respectively where they are hydrotreated
and exit ultra-low severity hydrotreaters 310 and 300 as product
streams 340 and 330 respectively. Alternatively, individual streams
240 and 250 are fed to a single ultra-low severity hydrotreater 320
alternately. Under this alternate feed configuration, stream 250 is
hydrotreated in single ultra-low severity hydrotreater 320 to
become product stream 330; then, stream 240 is hydrotreated in
single ultra-low severity hydrotreater 320 to become product stream
340. Heavy cut 220 exits fractionator 120 to hydrocracker 131 where
it is hydrocracked in hydrocracking zone 130. The hydrocracked
stream 210 leaves hydrocracker 131 where it is split into streams
270 and 280. Stream 280 is recycled back to fractionator 120 and
stream 270 is sent to second fractionator 260.
[0027] Referring now to FIG. 5, there is shown a configuration
similar to FIG. 4 in which the hydrotreaters are downstream of the
fractionation. In FIG. 5, one of the downstream hydrotreaters 350
is a traditional or "deep" hydrotreater while the second
hydrotreater 310 is a ultra-low severity hydrotreater.
[0028] Referring now to FIG. 6, there is shown a configuration
comprising a hydrocarbon synthesis reactor 101 having a hydrocarbon
synthesis reaction zone 100, a fractionator 120, two ultra-low
severity hydrotreaters 310 and 360, hydrocracker 370, and optional
second fractionator 380. Feed stream 140 comprising CO and H.sub.2
enter hydrocarbon synthesis reactor 101 where it reacts in reaction
zone 100 to form product stream 190. The product stream 190 is
combined with recycle stream 390 before being fed into fractionator
120 and separated into streams 230, 240, 250, and 220. Streams 220
and 240 are then hydrotreated in ultra-low severity hydrotreaters
310 and 360 respectively. The stream hydrotreated in ultra-low
severity hydrotreater 360 is then sent to hydrocracker 370 where it
is cracked into stream 400. Stream 400 can be totally combined with
stream 190 to be recycled to fractionator 120, or sent in its
entirety to second fractionator 380, or split into streams 390 and
410. If stream 400 is optionally split, at least a portion (i.e.,
stream 390) is recycled to fractionator 120 and another portion
(i.e., stream 410) is sent to second fractionator 380. In alternate
embodiments of FIGS. 4-6, stream 220 (which may comprise primarily
C.sub.20+ hydrocarbons) is recycled to extinction.
[0029] Referring now to FIG. 7, there is shown a configuration
comprising a hydrocarbon synthesis reactor 101 having a hydrocarbon
synthesis reaction zone 100, a fractionator 120, a ultra-low
severity hydrotreater 310, and a hydrocracker 370. Feed stream 140
comprising CO and H.sub.2 enter hydrocarbon synthesis reactor 101
where it reacts in reaction zone 100 to form 2 product streams 175
and 185. Even though FIG. 7 shows that product streams 175 and 185
are represented as two separate streams exiting the hydrocarbon
synthesis reactor 101, it is conceivable that one outlet stream is
exiting hydrocarbon synthesis reactor 101 for example in a fixed
bed reactor embodiment, and this single outlet stream is then
divided ex situ (for example by a disengagement step) into the 2
separate product streams 175 and 185. Product stream 175 preferably
comprises lighter hydrocarbons than product stream 185. The product
stream 175 is hydrotreated in the ultra-low severity hydrotreater
310 to produce hydrotreated stream 195. Product stream 185 is
combined with heavy cut stream 220 from fractionator 120 before
being fed into hydrocracker 370, where the combined stream is
cracked into hydrocracked stream 205. Hydrotreated stream 195 and
hydrocracked stream 205 are combined to form stream 200. Stream 200
is then introduced to fractionator 120 where it is separated into
light cut 230, middle cut 240, and heavy cut 220. It is to be noted
that the combination of streams 195 and 205 is not necessary as
long as both streams 195 and 205 are both fed to the fractinator
310. In one embodiment, stream 220 (which may comprise primarily
C.sub.20+hydrocarbons) is recycled to extinction.
[0030] The hydrocarbon synthesis reactor 101 preferably comprises a
Fischer-Tropsch synthesis and generates primarily hydrocarbons
comprising one carbon to 100 carbons or more from a mixture of
carbon monoxide (CO) and hydrogen (H.sub.2), also called synthesis
gas or syngas. H.sub.2/CO mixtures suitable as a feedstock for
conversion to hydrocarbons can be obtained by one or more of the
following processes: conversion of biomass, conversion of coal by
gasification conversion of light hydrocarbons (such as methane or
natural gas) by partial oxidation, reforming or combination
thereof. Preferably the hydrogen is provided by free hydrogen,
although some Fischer-Tropsch catalysts have sufficient water gas
shift activity to convert some water and carbon monoxide to
hydrogen and carbon dioxide, for use in the hydrocarbon synthesis
process. It is preferred that the molar ratio of hydrogen to carbon
monoxide in the feed be greater than 0.5:1 (e.g., from about 0.67
to about 2.5). Preferably, when the hydrocarbon synthesis catalysts
comprise cobalt, nickel, and/or ruthenium, the feed gas stream
contains hydrogen and carbon monoxide in a molar ratio preferably
of about 1.6:1 to about 2.3:1. When the hydrocarbon synthesis
catalysts comprise iron, the feed gas stream contains hydrogen and
carbon monoxide in a molar ratio preferably between about 1.4:1 and
about 2.3:1. The feed gas may also contain carbon dioxide. The feed
gas stream should contain only a low concentration of compounds or
elements that have a deleterious effect on the catalyst, such as
poisons. For example, the feed gas may need to be pretreated to
ensure that it contains a low concentration of sulfur or nitrogen
compounds such as hydrogen sulfide, hydrogen cyanide, ammonia and
carbonyl sulfide. The feed gas is contacted with the catalyst in
the reaction zone 100 as shown in FIGS. 1-7. Mechanical
arrangements of conventional design may be employed as the reaction
zone including, for example, fixed bed, fluidized bed, slurry
bubble column or ebullating bed reactors, among others.
Accordingly, the preferred size and physical form of the catalyst
particles may vary depending on the reactor in which they are to be
used. The hydrocarbon synthesis process is typically run in a
continuous mode. In this mode, the gas hourly space velocity
through the reaction zone typically may range from about 50 to
about 10,000 hr.sup.-1, preferably from about 300 hr.sup.-1 to
about 2,000 hr.sup.-1. The gas hourly space velocity is defined as
the volume of reactants per time per reaction zone volume. The
volume of reactant gases is at standard conditions of pressure (101
kPa) and temperature (32.degree. F. or 0.degree. C.). The reaction
zone volume is defined by the portion of the reaction vessel volume
where reaction takes place and which is occupied by a gaseous phase
comprising reactants, products and/or inerts; a liquid phase
comprising liquid/waxy products and/or other liquids; and a solid
phase comprising catalyst. The reaction zone temperature is
typically in the range from about 320.degree. F. to about
570.degree. F. (about 160.degree. C. to about 300.degree. C.).
Preferably, the reaction zone is operated at conversion promoting
conditions at temperatures from about 375.degree. F. to about
500.degree. F. (about 190.degree. C. to about 260.degree. C.). The
reaction zone pressure is typically in the range of about 80 psia
(552 kPa) to about 1000 psia (6895 kPa), more preferably from 80
psia (552 kPa) to about 600 psia (4137 kPa), and still more
preferably, from about 140 psia (965 kPa) to about 500 psia (3447
kPa).
[0031] In accordance with embodiments of the present invention,
there is herein a process for producing a predominantly paraffinic
stream comprising heteroatomic compounds, said process comprising
the following steps: feeding a feedstream comprising synthesis gas
to a hydrocarbon synthesis reactor; reacting at least a portion of
the feedstream comprising synthesis gas on a hydrocarbon synthesis
catalyst to produce a hydrocarbon synthesis product stream; and
hydrotreating at least a portion of the hydrocarbon synthesis
product stream to produce a hydrotreated stream; wherein the
hydrotreated stream comprises no more than an insubstantial amount
of olefins; and wherein a substantial amount of the heteroatoms
remain attached to their parent molecules during hydrotreating.
EXAMPLE
[0032] A Fischer-Tropsch product was prepared by contacting a
synthesis gas mixture (2:1 molar ratio of H.sub.2:CO) with a cobalt
catalyst in a continuously stirred tank reactor (CSTR) reactor
under typical reaction conditions (430.degree. F. or 221.degree.
C.; 350 psia or 2410 kPa). A full range Fischer-Tropsch product was
collected and this hydrocarbon stream was fed to a hydrotreater
where it was hydrotreated under various conditions. The
hydrotreated stream was then distilled to yield a 350-650.degree.
F. distillation cut. The hydrotreating catalyst was a commercial
nickel based material (NI-3298 E1/16 3F from Engelhard). The
hydrotreater comprised a catalytic bed containing about 87 g (100
ml) of said hydrotreating catalyst, and was operated at 350 psia of
hydrogen partial pressure in the hydrotreater outlet with a
hydrogen flow of 2500 standard cubic feet per barrel of
hydrotreater liquid feed (scf/bbl) at a liquid hourly space
velocity of 3 hr.sup.-1 in trickle flow mode.
[0033] In the first experiment the hydrotreater bed temperature was
held at 400.degree. F. (204.degree. C.) and in the second
experiment at 250.degree. F. (121.degree. C.). The results for
Bromine number (ASTM D1149), oxidation stability (ASTM D2274),
viscosity (ASTM D445), pour point (ASTM D97), and lubricity HFRR
(ASTM D6079) are shown in Table 1. Oxygen content, also included in
Table 1, is measured using a Bruker Instruments Avance 400 nuclear
magnetic resonance (NMR) spectrometer. The .sup.1H NMR spectra of
the `untreated` sample (i.e., feed of the hydrotreater) and
hydrotreated samples were obtained at 400.13 MHz and were run as
solutions in deuteriated chloroform (CDCl.sub.3). The signal
intensities for olefins, esters and alcohols were compared to those
for the total --CH, --CH.sub.2, and --CH.sub.3 groups. The oxygen
content in percentage is calculated as --OCH.sub.2 and the
percentage approximates weight percentage of O.
1 TABLE 1 Feed Hydrotreating Hydrotreating (350-650.degree. F. cut)
at 250.degree. F. at 400.degree. F. Bromine number 5.8 <0.1
<0.1 (ASTM D1159) (g Br/100 g) Oxidation Stability 80 <0.5
<0.5 (ASTM D2274) (g/m.sup.3) Viscosity @ 40.degree. C. -- 1.886
1.909 (ASTM D445) (cSt) Pour Point -- 2 3 (ASTM D97) (.degree. C.)
Oxygenate content 0.7 0.7 0.03 (wt % oxygen) Lubricity -- 340 415
HFRR(ASTM D6079) (.mu.m)
[0034] From the results in Table 1 the diesel range stream which
has been hydrotreated in an ultra-low severity hydrotreater has an
improved lubricity and no decline in oxidation stability (i.e.,
potential gum formation) as compared to the diesel range stream
which has been hydrotreated at 400.degree. F. The Bromine (Br)
number method measures the amount of unsaturated hydrocarbons; the
example above before hydrotreatment shows a significant presence of
unsaturated compounds with a Br number of 5.8 g Br per 100 g of
sample; after both hydrotreatments, the Br number was less than 0.1
g Br per 100 g of sample pointing out that both hydrotreating
conditions were successful in removing substantially most of the
unsaturated compounds so that the hydrotreated samples comprises a
significantly reduced amount of olefins. Similarly both
hydrotreatment conditions resulted in a much improved oxidation
stability (ASTM D2274) of lower than 0.5 g/m.sup.3 from a value of
80 g/m.sup.3 in the untreated sample. It is conceivable that a
lower hydrotreatment temperature (i.e., less than 250.degree. F.)
would result in less effective oxidation stability; therefore an
oxidation stability value greater than 0.5 g/m.sup.3 but smaller
than 25 g/m.sup.3 is expected at these less severe conditions.
Therefore it is highly desirable to have the oxidation stability to
be lower than 25 g/m.sup.3 in the hydrotreated sample, preferably
less than 10 g/m.sup.3, more preferably lower than 5 g/m.sup.3 and
yet more preferably lower than 2 g/m.sup.3.
[0035] The ultra-low severity hydrotreatment with the nickel based
catalyst at 250.degree. F. was successful in retaining most of the
oxygenates, as the oxygen content after ultra-low severity
treatment resulted in an unchanged value of 0.7 wt %, whereas the
hydrotreatment with the nickel based catalyst at 400.degree. F.
resulted in almost complete removal of the oxygenates with a
resulting oxygen content of 0.03 wt %. Typically the
350-650.degree. F. cut of the untreated hydrocarbon synthesis
product stream which would feed the hydrotreater would have an
oxygen content from about 0.1 wt % to about 15 wt % when the
hydrocarbon synthesis reactor uses an iron-based catalyst, and from
about 0.1 wt % to about 8 wt % when the hydrocarbon synthesis
reactor uses a cobalt-based catalyst. It is conceivable that a
higher hydrotreatment temperature (i.e., greater than about
250.degree. F. and less than about 350.degree. F.) would result in
a more effective removal of oxygen atoms; therefore the oxygen
content of a stream comprising primarily a 350-650.degree. F.
boiling range after an ultra-low severity hydrotreating could be
lower than the untreated stream comprising primarily a
350-650.degree. F. boiling range. It is preferable therefore to
retain as much as of the oxygen content as possible, retaining at
least 50% of the oxygen content, preferably at least 75%, and more
preferably at least 90%, to obtain the desirable oxygen content
equal to or greater than 0.1 wt %, for improving diesel or middle
distillate properties after the ultra-low severity
hydrotreating.
[0036] Therefore a hydrotreated middle distillate cut derived from
synthesis gas, obtained after an ultra-low severity hydrotreating
step has preferably an oxidation stability (gum) less than 25
g/m.sup.3; and an oxygen content equal to or greater than 0.1 wt %.
Similarly, a hydrotreated diesel product derived from synthesis gas
and obtained after an ultra-low severity hydrotreating without the
addition of property enhancing agents has preferably the following
properties:
[0037] Bromine number<0.1 gBr/100 g;
[0038] Oxidation stability (gum).ltoreq.25 g/m.sup.3;
[0039] oxygen content.gtoreq.0.1 wt %; and
[0040] lubricity HFRR-.ltoreq.400 .mu.m.
[0041] As used herein, to "hydroprocess" means to treat a
hydrocarbon stream with hydrogen.
[0042] "Hydrocarbon synthesis" can be any method now known or later
discovered for synthesizing liquid hydrocarbons. An example is the
Fischer-Tropsch process.
[0043] To "hydrotreat" means to treat a hydrocarbon stream with
hydrogen without making any substantial change to the carbon
backbone of the molecules in the hydrocarbon stream. For example,
hydrotreating a hydrocarbon stream comprising predominantly
H.sub.2C.dbd.CH--CH.sub.2--CH- .sub.2--CH.sub.3 would yield a
hydrocarbon stream comprising predominantly
CH.sub.3--CH.sub.2--CH.sub.2--CH.sub.2--CH.sub.3. As used herein,
to "hydrocrack" means to split an organic molecule and add hydrogen
to the resulting molecular fragments to form two smaller
hydrocarbons (e.g., C.sub.10H.sub.22+H.sub.2.fwdarw.C.sub.4H.sub.10
and skeletal isomers +C.sub.6H.sub.14 and skeletal isomers).
Because a hydrocracking catalyst can be active in
hydroisomerization, there can be some skeletal isomerization during
the hydrocracking step, therefore isomers of the smaller
hydrocarbons can be formed. Methods for hydrocracking are legion
and well known in the art. Preferably, the hydrocracking takes
place over a platinum catalyst at a temperature of about
550.degree. F. to about 750.degree. F. (260-400.degree. C.) and at
a pressure of about 500 psig to about 1500 psig (3,550-10,440
kPa).
[0044] "Heteroatomic compounds" are organic compounds which
comprise not only carbon and hydrogen, but also other atoms, such
as nitrogen, sulfur, oxygen. The non-carbon and non-hydrogen atoms
(e.g., oxygen, sulfur and nitrogen, respectively) are
"heteroatoms". Examples of heteroatomic compounds comprising oxygen
are alcohols, aldehydes or ketones. Examples of heteroatomic
compounds comprising nitrogen are amines. For example, acetone
(CH.sub.3COCH.sub.3) and dipropyl amine ((C.sub.3H.sub.7).sub.2NH-
) are heteroatomic compounds. With respect to, for example,
acetone, a related heteroatomic compound is isopropyl alcohol
((CH.sub.3).sub.2CHOH). In a situation in which acetone is
converted to isopropyl alcohol, the heteroatom (oxygen), although
differently bonded, remains attached to its parent molecule (e.g.,
is not removed from its carbon backbone). Likewise, when, for
example, acetone has gone through a process unconverted, the
heteroatom (oxygen) has also remained attached to its parent
molecule.
[0045] As used herein, "ultra-low severity hydrotreatment" means
hydrotreatment at conditions such that a substantial portion of the
olefins in a stream becomes saturated, but a substantial amount of
the heteroatoms in the stream remain attached to their parent
molecule. The two most important factors in determining whether a
hydrotreating process does not convert a substantial amount of
oxygenates to paraffins are catalyst composition and temperature.
Ultra-low severity hydrotreating can take place with hydrotreating
catalysts comprising at least one of the following metals: a group
VIB metal (from the previous IUPAC notation), such as molybdenum
(Mo) and tungsten (W), or a group VIII metal, such as nickel (Ni),
palladium (Pd), platinum (Pt), ruthenium (Ru), iron (Fe), cobalt
(Co). Highly active catalysts, such as those comprising Ni, Pd, Pt,
W, Mo, Ru or combinations thereof, must be operated at relatively
low temperatures between about 180.degree. F. and about 350.degree.
F. (about 80-180.degree. C.), more preferably between about
180.degree. F. and about 320.degree. F. (about 80-160.degree. C.),
still more preferably between about 180.degree. F. to about
300.degree. F. (about 80-150.degree. C.). By way of example only, a
highly active catalyst such as a nickel-based catalyst begins to
convert a substantial amount of oxygenates at about 220.degree. F.
In contrast, a less active catalysts such as those comprising Fe or
Co do not begin to convert a substantial amount of the oxygenates
until it reaches a temperature of about 350.degree. F. For these
catalysts with lower hydrotreating activity (e.g., Co or Fe), a
preferred temperature range for ultra-low severity hydrotreating is
between about 350.degree. F. and about 570.degree. F. (about
180-300.degree. C.). Additionally, there are other parameters such
as for example, pressure and liquid hourly space velocity which may
be varied by one of ordinary skill in the art to effect the desired
ultra-low severity hydrotreating. Preferably the hydrogen partial
pressure is between about 100 psia and about 1,000 psia (690-6900
kPa), more preferably between about 300 psia and about 500 psia
(2060-3450 kPa). The liquid hourly space velocity is preferably
between 1 and 10 hr.sup.-1, more preferably between 0.5 and 6
hr.sup.-1, still more preferably between about 1 and about 5
hr.sup.-1. It should be understood that the hydrotreating catalyst
for ultra-low severity hydrotreatment can be with or without
support, and can comprise promoters to improve catalyst performance
and/or support structural integrity.
[0046] As used herein, a "diesel" is any hydrocarbon cut having at
least a portion which falls within the diesel range. The diesel
range in this application includes hydrocarbons which boil in the
range of about 300.degree. F. to about 750.degree. F. (about
150-400.degree. C.), preferably in the range of about 350.degree.
F. to about 650.degree. F. (about 170-350.degree. C.).
[0047] As used herein, a "middle distillate" means a hydrocarbon
stream which includes kerosene, home heating oil, range oil, stove
oil, and diesel that has a 50 percent boiling point in the ASTM D86
standard distillation test falling between 371.degree. F. and
700.degree. F.
[0048] As used herein, "deep hydrotreatment" means hydrotreatment
over a hydrotreating catalyst comprising at least one metal from
the group consisting of Ni, Pd, Pt, Mo, W, and Ru, preferably
comprising Ni, over at temperatures above 350.degree. F.
(170.degree. C.), preferably from 350.degree. F. to about
600.degree. F. (315.degree. C.), more preferably from 360.degree.
F. to about 600.degree. F. (180-315.degree. C.), with a hydrogen
partial pressure in the hydrotreater outlet between about 100 psia
and about 2,000 psia (690-13,800 kPa).
[0049] Should the disclosure of any of the patents and publications
that are incorporated herein by reference conflict with the present
specification to the extent that it might render a term unclear,
the present specification shall take precedence.
[0050] While the preferred embodiments of the invention have be
disclosed herein, it will be understood that various modifications
can be made to the system described herein without departing from
the scope of the invention. Without further elaboration, it is
believed that one skilled in the art can, using the description
herein, utilize the present invention to its fullest extent.
* * * * *