U.S. patent application number 12/944922 was filed with the patent office on 2012-03-01 for selective desulfurization of fcc gasoline.
This patent application is currently assigned to CATALYTIC DISTILLATION TECHNOLOGIES. Invention is credited to Purvis K. Ho, Arvids Judzis, Gary G. Podrebarac, Luis Simoes, Mahesh Subramanyam.
Application Number | 20120048778 12/944922 |
Document ID | / |
Family ID | 46051482 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120048778 |
Kind Code |
A1 |
Podrebarac; Gary G. ; et
al. |
March 1, 2012 |
SELECTIVE DESULFURIZATION OF FCC GASOLINE
Abstract
Processes for the desulfurization of high end point naphtha,
such as naphtha fractions having an ASTM D-86 end point of greater
than 450.degree. F., greater than 500.degree. F., or greater than
550.degree. F., and containing hindered sulfur compounds, are
disclosed.
Inventors: |
Podrebarac; Gary G.;
(Houston, TX) ; Judzis; Arvids; (Pasadena, TX)
; Ho; Purvis K.; (Houston, TX) ; Subramanyam;
Mahesh; (Houston, TX) ; Simoes; Luis;
(Houston, TX) |
Assignee: |
CATALYTIC DISTILLATION
TECHNOLOGIES
Pasadena
TX
|
Family ID: |
46051482 |
Appl. No.: |
12/944922 |
Filed: |
November 12, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12862845 |
Aug 25, 2010 |
|
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12944922 |
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Current U.S.
Class: |
208/210 |
Current CPC
Class: |
C10G 35/06 20130101;
C10G 2300/301 20130101; C10G 2400/02 20130101; C10G 2300/1044
20130101; C10G 2300/202 20130101; C10G 2300/4087 20130101; C10G
2300/1055 20130101; C10G 2400/04 20130101; C10G 2300/207
20130101 |
Class at
Publication: |
208/210 |
International
Class: |
C10G 35/06 20060101
C10G035/06 |
Claims
1. A process for the desulfurization of a full boiling range
catalytically cracked naphtha comprising the steps of: (a) feeding
(1) a full boiling range naphtha containing olefins, diolefins,
mercaptans and other organic sulfur compounds and having an ASTM
D86 end boiling point of at least 350.degree. F., and (2) hydrogen
to a first distillation column reactor; (b) concurrently in the
first distillation column reactor, (i) contacting the diolefins and
the mercaptans in the full boiling range naphtha in the presence of
a Group VIII metal catalyst in the rectification section of the
first distillation column reactor thereby reacting: (A) a portion
of the mercaptans with a portion of the diolefins to form
thioethers, and/or (B) a portion of the dienes with a portion of
the hydrogen to form olefins; and (ii) fractionating the full
boiling range cracked naphtha into a distillate product containing
C5 hydrocarbons and a first heavy naphtha containing sulfur
compounds; (c) recovering the first heavy naphtha from the first
distillation column reactor as a first bottoms; (d) feeding the
first bottoms and hydrogen to a second distillation column reactor;
(e) concurrently in the second distillation column reactor, (i)
reacting at least a portion of the organic sulfur compounds in the
first bottoms with hydrogen in the presence of a
hydrodesulfurization catalyst in the rectification section of the
second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; (f) recovering the
first intermediate naphtha, unreacted hydrogen, and hydrogen
sulfide from the second distillation column reactor as a second
overheads; (g) recovering the second heavy naphtha containing
hindered organic sulfur compounds from the second distillation
column reactor as a second bottoms; (h) feeding the second bottoms
and hydrogen to a first fixed bed reactor containing a
hydrodesulfurization catalyst; (i) contacting the hindered organic
sulfur compounds and hydrogen with the hydrodrodesulfurization
catalyst in the first fixed bed reactor to convert at least a
portion of the hindered organic sulfur compounds to hydrogen
sulfide; (j) recovering an effluent from the first fixed bed
reactor.
2. The process of claim 1, further comprising at least one of: (k)
separating unreacted hydrogen and hydrogen sulfide from the
effluent from the first fixed bed reactor; (l) separating unreacted
hydrogen and hydrogen sulfide from the second overheads; (m)
separating at least a portion of the hydrogen sulfide from the
effluent from the second fixed bed reactor to form a naphtha
fraction having a reduced sulfur content.
3. The process of claim 1, further comprising admixing a diesel
hydrocarbon fraction with the second bottoms prior to the
contacting step (i).
4. A process for the desulfurization of a full boiling range
catalytically cracked naphtha comprising the steps of: (a) feeding
(1) a full boiling range naphtha containing olefins, diolefins,
mercaptans and other organic sulfur compounds and having an ASTM
D86 end boiling point of at least 350.degree. F., and (2) hydrogen
to a first distillation column reactor; (b) concurrently in the
first distillation column reactor, (i) contacting the diolefins and
the mercaptans in the full boiling range naphtha in the presence of
a Group VIII metal catalyst in the rectification section of the
first distillation column reactor thereby reacting: (A) a portion
of the mercaptans with a portion of the diolefins to form
thioethers, and/or (B) a portion of the dienes with a portion of
the hydrogen to form olefins; and (ii) fractionating the full
boiling range cracked naphtha into a distillate product containing
C5 hydrocarbons and a first heavy naphtha containing sulfur
compounds; (c) recovering the first heavy naphtha from the first
distillation column reactor as a first bottoms; (d) feeding the
first bottoms and hydrogen to a second distillation column reactor;
(e) concurrently in the second distillation column reactor, (i)
reacting at least a portion of the organic sulfur compounds in the
first bottoms with hydrogen in the presence of a
hydrodesulfurization catalyst in the rectification section of the
second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; (f) recovering the
first intermediate naphtha, unreacted hydrogen, and hydrogen
sulfide from the second distillation column reactor as a second
overheads; (g) recovering the second heavy naphtha containing
hindered organic sulfur compounds from the second distillation
column reactor as a second bottoms; (h) feeding the second bottoms
and hydrogen to a first fixed bed reactor containing a
hydrodesulfurization catalyst; (i) contacting the hindered organic
sulfur compounds and hydrogen with the hydrodrodesulfurization
catalyst in the first fixed bed reactor to convert at least a
portion of the hindered organic sulfur compounds to hydrogen
sulfide; (j) recovering an effluent from the first fixed bed
reactor; (k) separating unreacted hydrogen and hydrogen sulfide
from the effluent from the first fixed bed reactor; (l) separating
unreacted hydrogen and hydrogen sulfide from the second overheads;
(m) feeding at least a portion of the second overheads and hydrogen
to a second fixed bed reactor containing a hydrodesulfurization
catalyst to convert at least a portion of the sulfur compounds in
the second overheads to hydrogen sulfide; (n) recovering an
effluent from the second fixed bed reactor; (o) separating at least
a portion of the hydrogen sulfide from the effluent from the second
fixed bed reactor to form a naphtha fraction having a reduced
sulfur content.
5. The process of claim 4, wherein the full boiling range naphtha
has an ASTM D86 end boiling point of at least 450.degree. F.
6. The process of claim 4, wherein the full boiling range naphtha
has an ASTM D86 end boiling point of at least 500.degree. F.
7. The process of claim 4, further comprising at least one of: (p)
feeding at least a portion of the separated effluent in (k) to the
second fixed bed reactor; and (q) fractionating the naphtha
fraction having a reduced sulfur content to form a heavy naphtha
fraction and a mid-range gasoline fraction, and recycling at least
a portion of the heavy naphtha fraction to the second fixed bed
reactor.
8. The process of claim 7, wherein (p) comprises at least one of:
conveying at least a portion of the effluent recovered in (j) to
the separating (l); and conveying at least a portion of the
effluent recovered in (j) to the feeding (m).
9. The process of claim 4, wherein a total sulfur content in the
second overhead product is less than about 100 ppm S, by
weight.
10. The process of claim 9, further comprising forming a gasoline
fraction from at least a portion of one or more of the distillate
product, the naphtha fraction, and the effluent from the first
fixed bed reactor, wherein the gasoline fraction has a total sulfur
content of less than about 20 ppm S, by weight.
11. The process of claim 10, wherein the gasoline fraction has a
total sulfur content of less than about 10 ppm S, by weight.
12. The process of claim 9, further comprising: reacting at least a
portion of C5 and C6 olefins in the distillate product with an
alcohol to form an ether.
13. The process of claim 12, further comprising forming a gasoline
fraction from at least a portion of one or more of the reacted
distillate product, the naphtha fraction, and the effluent from the
first fixed bed reactor, wherein the gasoline fraction has a total
sulfur content of less than about 20 ppm S, by weight.
14. The process of claim 13, wherein the gasoline fraction has a
total sulfur content of less than about 10 ppm S, by weight.
15. The process of claim 4, wherein the second distillation column
reactor contains hydrodesulfurization catalyst only in the
rectification section.
16. The process of claim 4, wherein the second distillation column
reactor contains hydrodesulfurization catalyst in both the
rectification section and in the stripping section.
17. The process of claim 4, further comprising forming a diesel
fraction from at least a portion of the effluent from the first
fixed bed reactor.
18. The process of claim 7, further comprising forming a diesel
fraction from at least one of at least a portion of the effluent
from the first fixed bed reactor and at least a portion of the
heavy naphtha fraction.
19. The process of claim 4, wherein hydrodesulfurization catalyst
in the first fixed bed reactor comprises a supported
cobalt-molybdenum catalyst.
20. The process of claim 19, wherein the supported
cobalt-molybdenum catalyst comprises from 2 to 5 wt % cobalt and
from 5 to 20 wt % molybdenum.
21. The process of claim 19, wherein the hydrodesulfurization
catalyst in the first fixed bed reactor further comprises a
supported nickel-molybdenum catalyst.
22. A process for the desulfurization of a full boiling range
catalytically cracked naphtha comprising the steps of: (a) feeding
(1) a full boiling range naphtha containing olefins, diolefins,
mercaptans and other organic sulfur compounds and having an ASTM
D86 end boiling point of at least 350.degree. F., and (2) hydrogen
to a first distillation column reactor; (b) concurrently in the
first distillation column reactor, (i) contacting the diolefins and
the mercaptans in the full boiling range naphtha in the presence of
a Group VIII metal catalyst in the rectification section of the
first distillation column reactor thereby reacting: (A) a portion
of the mercaptans with a portion of the diolefins to form
thioethers, and/or (B) a portion of the dienes with a portion of
the hydrogen to form olefins; and (ii) fractionating the full
boiling range cracked naphtha into a distillate product containing
C5 hydrocarbons and a first heavy naphtha containing sulfur
compounds; (c) recovering the first heavy naphtha from the first
distillation column reactor as a first bottoms; (d) feeding the
first bottoms and hydrogen to a second distillation column reactor;
(e) concurrently in the second distillation column reactor, (i)
reacting at least a portion of the organic sulfur compounds in the
first bottoms with hydrogen in the presence of a
hydrodesulfurization catalyst in the rectification section of the
second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; (f) recovering the
first intermediate naphtha, unreacted hydrogen, and hydrogen
sulfide from the second distillation column reactor as a second
overheads; (g) recovering the second heavy naphtha containing
hindered organic sulfur compounds from the second distillation
column reactor as a second bottoms; (h) feeding the second bottoms
and hydrogen to a first fixed bed reactor containing a
hydrodesulfurization catalyst; (i) contacting the hindered organic
sulfur compounds and hydrogen with the hydrodrodesulfurization
catalyst in the first fixed bed reactor to convert at least a
portion of the hindered organic sulfur compounds to hydrogen
sulfide; (j) recovering an effluent from the first fixed bed
reactor; (k) separating unreacted hydrogen and hydrogen sulfide
from the effluent from the first fixed bed reactor; (l) partially
condensing the second overheads and separating the uncondensed
portion of the second overheads including unreacted hydrogen and
hydrogen sulfide from the condensed portion of the second
overheads; (m) feeding at least a portion of the condensed portion
of the second overheads to the second distillation column reactor
as reflux; (n) feeding the separated effluent (k), the uncondensed
portion of the second overheads, and at least a portion of the
condensed second overheads to a fractionation column for separating
unreacted hydrogen and hydrogen sulfide and to recover a bottoms
hydrocarbon fraction; (o) feeding the bottoms hydrocarbon fraction
and hydrogen to a second fixed bed reactor containing a
hydrodesulfurization catalyst to convert at least a portion of the
sulfur compounds in the bottoms hydrocarbon fraction to hydrogen
sulfide; (p) recovering an effluent from the second fixed bed
reactor; (q) separating at least a portion of the hydrogen sulfide
from the effluent from the second fixed bed reactor to form a
naphtha fraction having a reduced sulfur content; and (r) forming a
gasoline from one or more of (i) at least a portion of the naphtha
fraction and (ii) at least a portion of the distillate fraction,
wherein the gasoline has a total sulfur content of less than about
20 ppm S, by weight.
23. A process for the desulfurization of a full boiling range
naphtha comprising the steps of: (a) feeding (1) a full boiling
range naphtha containing olefins, diolefins, mercaptans and other
organic sulfur compounds and having an ASTM D86 end boiling point
of at least 350.degree. F., and (2) hydrogen to a first
distillation column reactor; (b) concurrently in the first
distillation column reactor, (i) contacting the diolefins and the
mercaptans in the full boiling range naphtha in the presence of a
Group VIII metal catalyst in the rectification section of the first
distillation column reactor thereby reacting: (A) a portion of the
mercaptans with a portion of the diolefins to form thioethers,
and/or (B) a portion of the dienes with a portion of the hydrogen
to form olefins; and (ii) fractionating the full boiling range
cracked naphtha into a distillate product containing C5
hydrocarbons and a first heavy naphtha containing sulfur compounds;
(c) recovering the first heavy naphtha from the first distillation
column reactor as a first bottoms; (d) feeding the first bottoms
and hydrogen to a second distillation column reactor; (e)
concurrently in the second distillation column reactor, (i)
reacting at least a portion of the organic sulfur compounds in the
first bottoms with hydrogen in the presence of a
hydrodesulfurization catalyst in the rectification section of the
second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; (f) recovering the
first intermediate naphtha, unreacted hydrogen, and hydrogen
sulfide from the second distillation column reactor as a second
overheads; (g) recovering the second heavy naphtha containing
hindered organic sulfur compounds from the second distillation
column reactor as a second bottoms; (h) feeding the second bottoms
and hydrogen to a first fixed bed reactor containing a
hydrodesulfurization catalyst; (i) contacting the hindered organic
sulfur compounds and hydrogen with the hydrodrodesulfurization
catalyst in the first fixed bed reactor to convert at least a
portion of the hindered organic sulfur compounds to hydrogen
sulfide; (j) recovering an effluent from the first fixed bed
reactor; (k) separating unreacted hydrogen and hydrogen sulfide
from the effluent from the first fixed bed reactor; (l) separating
unreacted hydrogen and hydrogen sulfide from the second overheads;
(m) feeding at least a portion of the second overheads and hydrogen
to a second fixed bed reactor containing a hydrodesulfurization
catalyst to convert at least a portion of the sulfur compounds in
the second overheads to hydrogen sulfide; (n) recovering an
effluent from the second fixed bed reactor; (o) separating at least
a portion of the hydrogen sulfide from the effluent from the second
fixed bed reactor to form a H.sub.2S separated naphtha fraction;
(p) fractionating the H.sub.2S separated naphtha fraction to form a
heavy naphtha fraction and a mid-range gasoline fraction; and (q)
recycling at least a portion of the heavy naphtha fraction to the
second fixed bed reactor; and (r) forming a gasoline from one or
more of (i) at least a portion of the distillate product, (ii) at
least a portion of the naphtha fraction, and (iii) at least a
portion of the effluent from the first fixed bed reactor, wherein
the gasoline has a total sulfur content of less than about 20 ppm
S, by weight.
24. The process of claim 23, further comprising feeding at least a
portion of the separated effluent in (k) to the second fixed bed
reactor.
25. The process of claim 23, further comprising reacting at least a
portion of C5 and C6 olefins in the distillate product with an
alcohol to form an ether prior to the forming a gasoline (r).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a Continuation-In-Part
application of U.S. patent application Ser. No. 12/862,845, filed
Aug. 25, 2010, the contents of which are hereby incorporated by
reference in their entirety herein.
FIELD OF THE DISCLOSURE
[0002] Embodiments disclosed herein generally relate to processes
for the desulfurization of gasoline fractions, such as FCC naphtha,
having a high ASTM D86 end point. More particularly, embodiments
disclosed herein relate to processes for the desulfurization of
high end point naphthas to produce gasoline fractions having a
total sulfur content of less than 20 ppm, by weight. In some
embodiments, the total sulfur content of the gasoline fraction may
be less than 10 ppm, by weight. Other embodiments disclosed herein
may additionally provide for control of the end point of the
gasoline product.
BACKGROUND
[0003] Petroleum distillate streams contain a variety of organic
chemical components. Generally the streams are defined by their
boiling ranges, which determines the composition. The processing of
the streams also affects the composition. For instance, products
from either catalytic cracking or thermal cracking processes
contain high concentrations of olefinic hydrocarbons (alkenes,
alkynes, and polyunsaturated compounds such as diolefins) as well
as saturated hydrocarbons (alkanes). Additionally, these components
may be any of the various isomers of the compounds.
[0004] The composition of untreated naphtha as it comes from the
crude still, or straight run naphtha, is primarily influenced by
the crude source. Naphthas from paraffinic crude sources have more
saturated straight chain or cyclic compounds. As a general rule
most of the "sweet" (low sulfur) crudes and naphthas are
paraffinic. The naphthenic crudes contain more unsaturated and
cyclic and polycylic compounds. The higher sulfur content crudes
tend to be naphthenic. Treatment of the different straight run
naphthas may be slightly different depending upon their composition
due to crude source. FCC gasoline is the product of catalytic
cracking and is also referred to as catalytically cracked naphtha,
which may be further processed. Cracked gasolines, especially
catalytically cracked gasolines, ordinarily have a sufficiently
high octane, and one of the most important objectives in refining
these involves the removal of sulfur compounds.
[0005] Reformed naphtha or reformate generally requires no further
treatment except perhaps distillation or solvent extraction for
valuable aromatic product removal. Reformed naphthas have
essentially no sulfur contaminants due to the severity of their
pretreatment for the process and the process itself.
[0006] Cracked naphtha as it comes from the catalytic cracker has a
relatively high octane number as a result of the olefinic and
aromatic compounds contained therein. In some cases this fraction
may contribute as much as half of the gasoline in the refinery pool
together with a significant portion of the octane. Although olefin
concentration in gasoline increases the octane number, olefins are
often limited in their concentration in gasoline as they are a
known contributor to smog formation. An attractive alternative to
increased olefin content is the addition of alcohols to the
gasoline product to raise the octane number. Alcohols such as
methanol and ethanol can be used as additives.
[0007] Catalytically cracked naphtha (gasoline boiling range
material) currently forms a significant part (>1/3) of the
gasoline product pool in the United States and it provides the
largest portion of the sulfur. The sulfur impurities may require
removal, usually by hydrotreating, in order to comply with product
specifications or to ensure compliance with environmental
regulations. Some users require the sulfur of the final product to
be below 50 ppm or at or below 10 ppm.
[0008] Various processes for the desulfurization of gasoline
boiling range hydrocarbon fractions may include U.S. Pat. Nos.
5,510,568, 5,595,634, 5,779,883, 5,597,476, 5,837,130, 6,083,378,
6,946,068, 6,592,750, 6,303,020, 6,413,413, 6,338,793, 6,503,864,
6,495,030, 6,444,118, 6,824,676, 7,351,327, 7,291,258, 7,153,415,
6,984,312, and 7,431,827, among others.
[0009] High end point FCC gasoline typically has a higher sulfur
concentration than normal boiling range catalytically cracked
gasoline, requiring a higher conversion of the sulfur compounds to
meet the sulfur requirements. However, due to a higher
concentration of multi-substituted benzothiophenes (versus
methylbenzothiophenes in normal boiling range catalytically cracked
gasoline), hydrotreating high end point naphthas becomes more
challenging. This is due to the fact that sulfur atoms in
multi-substituted benzothiophenes are more hindered and slower to
react with hydrogen than the sulfur atoms in
methylbenzothiophenes.
[0010] In addition to supplying high octane blending components,
the cracked naphthas are often used as sources of olefins in other
processes such as etherifications, oligomerizations and
alkylations. The conditions of hydrotreating of the naphtha
fraction to remove sulfur will also saturate some of the olefinic
compounds in the fraction, reducing the octane and causing a loss
of source olefins. Severe operating conditions typically used to
remove sulfur from high end point fractions may cause an excessive
loss of olefins.
[0011] Accordingly, there exists a need for processes for the
hydrodesulfurization of high end point FCC gasoline, including
processes which preserve, to an extent, the olefinic content of the
naphtha, minimizing olefins lost to hydrogenation and recombinant
mercaptan formation during the processing of the naphtha.
SUMMARY OF CLAIMED EMBODIMENTS
[0012] In one aspect, embodiments disclosed herein relate to a
process for the desulfurization of a full boiling range
catalytically cracked naphtha including the steps of: (a) feeding
(1) a full boiling range naphtha containing olefins, diolefins,
mercaptans and other organic sulfur compounds and having an ASTM
D86 end boiling point of at least 350.degree. F., and (2) hydrogen
to a first distillation column reactor; (b) concurrently in the
first distillation column reactor, (i) contacting the diolefins and
the mercaptans in the full boiling range naphtha in the presence of
a Group VIII metal catalyst in the rectification section of the
first distillation column reactor thereby reacting: (A) a portion
of the mercaptans with a portion of the diolefins to form
thioethers, and/or (B) a portion of the dienes with a portion of
the hydrogen to form olefins; and (ii) fractionating the full
boiling range cracked naphtha into a distillate product containing
C.sub.5 hydrocarbons and a first heavy naphtha containing sulfur
compounds; (c) recovering the first heavy naphtha from the first
distillation column reactor as a first bottoms; (d) feeding the
first bottoms and hydrogen to a second distillation column reactor;
(e) concurrently in the second distillation column reactor, (i)
reacting at least a portion of the organic sulfur compounds in the
first bottoms with hydrogen in the presence of a
hydrodesulfurization catalyst in the rectification section of the
second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; (f) recovering the
first intermediate naphtha, unreacted hydrogen, and hydrogen
sulfide from the second distillation column reactor as a second
overheads; (g) recovering the second heavy naphtha containing
hindered organic sulfur compounds from the second distillation
column reactor as a second bottoms; (h) feeding the second bottoms
and hydrogen to a first fixed bed reactor containing a
hydrodesulfurization catalyst; (i) contacting the hindered organic
sulfur compounds and hydrogen with the hydrodrodesulfurization
catalyst in the first fixed bed reactor to convert at least a
portion of the hindered organic sulfur compounds to hydrogen
sulfide; and (j) recovering an effluent from the first fixed bed
reactor. In some embodiments, the second bottoms may be combined
with a diesel hydrocarbon fraction for processing in the first
fixed bed reactor.
[0013] In another aspect, embodiments disclosed herein relate to a
process for the desulfurization of a full boiling range
catalytically cracked naphtha including the steps of: [0014] (a)
feeding (1) a full boiling range naphtha containing olefins,
diolefins, mercaptans and other organic sulfur compounds and having
an ASTM D86 end boiling point of at least 350.degree. F., and (2)
hydrogen to a first distillation column reactor; [0015] (b)
concurrently in the first distillation column reactor, [0016] (i)
contacting the diolefins and the mercaptans in the full boiling
range naphtha in the presence of a Group VIII metal catalyst in the
rectification section of the first distillation column reactor
thereby reacting: [0017] (A) a portion of the mercaptans with a
portion of the diolefins to form thioethers, and/or [0018] (B) a
portion of the dienes with a portion of the hydrogen to form
olefins; and [0019] (ii) fractionating the full boiling range
cracked naphtha into a distillate product containing C5
hydrocarbons and a first heavy naphtha containing sulfur compounds;
[0020] (c) recovering the first heavy naphtha from the first
distillation column reactor as a first bottoms; [0021] (d) feeding
the first bottoms and hydrogen to a second distillation column
reactor; [0022] (e) concurrently in the second distillation column
reactor, [0023] (i) reacting at least a portion of the organic
sulfur compounds in the first bottoms with hydrogen in the presence
of a hydrodesulfurization catalyst in the rectification section of
the second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and [0024] (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; [0025] (f)
recovering the first intermediate naphtha, unreacted hydrogen, and
hydrogen sulfide from the second distillation column reactor as a
second overheads; [0026] (g) recovering the second heavy naphtha
containing hindered organic sulfur compounds from the second
distillation column reactor as a second bottoms; [0027] (h) feeding
the second bottoms and hydrogen to a first fixed bed reactor
containing a hydrodesulfurization catalyst; [0028] (i) contacting
the hindered organic sulfur compounds and hydrogen with the
hydrodrodesulfurization catalyst in the first fixed bed reactor to
convert at least a portion of the hindered organic sulfur compounds
to hydrogen sulfide; [0029] (j) recovering an effluent from the
first fixed bed reactor; [0030] (k) separating unreacted hydrogen
and hydrogen sulfide from the effluent from the first fixed bed
reactor; [0031] (l) separating unreacted hydrogen and hydrogen
sulfide from the second overheads; [0032] (m) feeding at least a
portion of the second overheads and hydrogen to a second fixed bed
reactor containing a hydrodesulfurization catalyst to convert at
least a portion of the sulfur compounds in the second overheads to
hydrogen sulfide; [0033] (n) recovering an effluent from the second
fixed bed reactor; [0034] (o) separating at least a portion of the
hydrogen sulfide from the effluent from the second fixed bed
reactor to form a naphtha fraction having a reduced sulfur
content.
[0035] In another aspect, embodiments disclosed herein relate to a
process for the desulfurization of a full boiling range
catalytically cracked naphtha including the steps of: [0036] (a)
feeding (1) a full boiling range naphtha containing olefins,
diolefins, mercaptans and other organic sulfur compounds and having
an ASTM D86 end boiling point of at least 350.degree. F., and (2)
hydrogen to a first distillation column reactor; [0037] (b)
concurrently in the first distillation column reactor, [0038] (i)
contacting the diolefins and the mercaptans in the full boiling
range naphtha in the presence of a Group VIII metal catalyst in the
rectification section of the first distillation column reactor
thereby reacting: [0039] (A) a portion of the mercaptans with a
portion of the diolefins to form thioethers, and/or [0040] (B) a
portion of the dienes with a portion of the hydrogen to form
olefins; and [0041] (ii) fractionating the full boiling range
cracked naphtha into a distillate product containing C5
hydrocarbons and a first heavy naphtha containing sulfur compounds;
[0042] (c) recovering the first heavy naphtha from the first
distillation column reactor as a first bottoms; [0043] (d) feeding
the first bottoms and hydrogen to a second distillation column
reactor; [0044] (e) concurrently in the second distillation column
reactor, [0045] (i) reacting at least a portion of the organic
sulfur compounds in the first bottoms with hydrogen in the presence
of a hydrodesulfurization catalyst in the rectification section of
the second distillation column reactor to convert a portion of the
other organic sulfur compounds to hydrogen sulfide, and [0046] (ii)
separating the first heavy naphtha into a first intermediate
naphtha having an ASTM D86 end point in the range from 270.degree.
F. to 400.degree. F. and a second heavy naphtha; [0047] (f)
recovering the first intermediate naphtha, unreacted hydrogen, and
hydrogen sulfide from the second distillation column reactor as a
second overheads; [0048] (g) recovering the second heavy naphtha
containing hindered organic sulfur compounds from the second
distillation column reactor as a second bottoms; [0049] (h) feeding
the second bottoms and hydrogen to a first fixed bed reactor
containing a hydrodesulfurization catalyst; [0050] (i) contacting
the hindered organic sulfur compounds and hydrogen with the
hydrodrodesulfurization catalyst in the first fixed bed reactor to
convert at least a portion of the hindered organic sulfur compounds
to hydrogen sulfide; [0051] (j) recovering an effluent from the
first fixed bed reactor; [0052] (k) separating unreacted hydrogen
and hydrogen sulfide from the effluent from the first fixed bed
reactor; [0053] (l) partially condensing the second overheads and
separating the uncondensed portion of the second overheads
including unreacted hydrogen and hydrogen sulfide from the
condensed portion of the second overheads; [0054] (m) feeding at
least a portion of the condensed portion of the second overheads to
the second distillation column reactor as reflux; [0055] (n)
feeding the separated effluent (k), the uncondensed portion of the
second overheads, and at least a portion of the condensed second
overheads to a fractionation column for separating unreacted
hydrogen and hydrogen sulfide and to recover a bottoms hydrocarbon
fraction; [0056] (o) feeding the bottoms hydrocarbon fraction and
hydrogen to a second fixed bed reactor containing a
hydrodesulfurization catalyst to convert at least a portion of the
sulfur compounds in the bottoms hydrocarbon fraction to hydrogen
sulfide; [0057] (p) recovering an effluent from the second fixed
bed reactor; [0058] (q) separating at least a portion of the
hydrogen sulfide from the effluent from the second fixed bed
reactor to form a naphtha fraction having a reduced sulfur content;
and [0059] (r) forming a gasoline from one or more of (i) at least
a portion of the naphtha fraction and (ii) at least a portion of
the distillate fraction, wherein the gasoline has a total sulfur
content of less than about 20 ppm S, by weight.
[0060] In another aspect, embodiments disclosed herein relate to a
process for the desulfurization of a full boiling range naphtha
including the steps of: [0061] (a) feeding (1) a full boiling range
naphtha containing olefins, diolefins, mercaptans and other organic
sulfur compounds and having an ASTM D86 end boiling point of at
least 350.degree. F., and (2) hydrogen to a first distillation
column reactor; [0062] (b) concurrently in the first distillation
column reactor, [0063] (i) contacting the diolefins and the
mercaptans in the full boiling range naphtha in the presence of a
Group VIII metal catalyst in the rectification section of the first
distillation column reactor thereby reacting: [0064] (A) a portion
of the mercaptans with a portion of the diolefins to form
thioethers, and/or [0065] (C) a portion of the dienes with a
portion of the hydrogen to form olefins; and [0066] (ii)
fractionating the full boiling range cracked naphtha into a
distillate product containing C5 hydrocarbons and a first heavy
naphtha containing sulfur compounds; [0067] (c) recovering the
first heavy naphtha from the first distillation column reactor as a
first bottoms; [0068] (d) feeding the first bottoms and hydrogen to
a second distillation column reactor; [0069] (e) concurrently in
the second distillation column reactor, [0070] (i) reacting at
least a portion of the organic sulfur compounds in the first
bottoms with hydrogen in the presence of a hydrodesulfurization
catalyst in the rectification section of the second distillation
column reactor to convert a portion of the other organic sulfur
compounds to hydrogen sulfide, and [0071] (ii) separating the first
heavy naphtha into a first intermediate naphtha having an ASTM D86
end point in the range from 270.degree. F. to 400.degree. F. and a
second heavy naphtha; [0072] (f) recovering the first intermediate
naphtha, unreacted hydrogen, and hydrogen sulfide from the second
distillation column reactor as a second overheads; [0073] (g)
recovering the second heavy naphtha containing hindered organic
sulfur compounds from the second distillation column reactor as a
second bottoms; [0074] (h) feeding the second bottoms and hydrogen
to a first fixed bed reactor containing a hydrodesulfurization
catalyst; [0075] (i) contacting the hindered organic sulfur
compounds and hydrogen with the hydrodrodesulfurization catalyst in
the first fixed bed reactor to convert at least a portion of the
hindered organic sulfur compounds to hydrogen sulfide; [0076] (j)
recovering an effluent from the first fixed bed reactor; [0077] (k)
separating unreacted hydrogen and hydrogen sulfide from the
effluent from the first fixed bed reactor; [0078] (l) separating
unreacted hydrogen and hydrogen sulfide from the second overheads;
[0079] (m) feeding at least a portion of the second overheads and
hydrogen to a second fixed bed reactor containing a
hydrodesulfurization catalyst to convert at least a portion of the
sulfur compounds in the second overheads to hydrogen sulfide;
[0080] (n) recovering an effluent from the second fixed bed
reactor; [0081] (o) separating at least a portion of the hydrogen
sulfide from the effluent from the second fixed bed reactor to form
a H.sub.2S separated naphtha fraction; [0082] (p) fractionating the
H.sub.2S separated naphtha fraction to form a heavy naphtha
fraction and a mid-range gasoline fraction; and [0083] (q)
recycling at least a portion of the heavy naphtha fraction to the
second fixed bed reactor; and [0084] (r) forming a gasoline from
one or more of (i) at least a portion of the distillate product,
(ii) at least a portion of the naphtha fraction, and (iii) at least
a portion of the effluent from the first fixed bed reactor, wherein
the gasoline has a total sulfur content of less than about 20 ppm
S, by weight.
[0085] In some embodiments, the high end point naphtha being
treated may have an ASTM endpoint of greater than about 470.degree.
F.; greater than about 470.degree. F. in other embodiments; greater
than about 500.degree. F. in other embodiments; greater than about
525.degree. F. in other embodiments; and greater than about
550.degree. F. in yet other embodiments.
[0086] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0087] FIG. 1 is a simplified flow diagram in schematic form of one
embodiment of processes for hydrodesulfurization of naphtha
fractions according to embodiments disclosed herein.
[0088] FIG. 2 is a simplified flow diagram in schematic form of one
embodiment of processes for hydrodesulfurization of naphtha
fractions according to embodiments disclosed herein.
[0089] FIG. 3 is a simplified flow diagram in schematic form of one
embodiment of processes for hydrodesulfurization of naphtha
fractions according to embodiments disclosed herein.
DETAILED DESCRIPTION
[0090] In one aspect, embodiments disclosed herein relate to a
process for the desulfurization of a high end point FCC gasoline.
Embodiments disclosed herein generally relate to processes for the
desulfurization of FCC naphtha having a high ASTM D86 end point,
such as greater than about 350.degree. F., greater than 400.degree.
F., greater than 450.degree. F., greater than 470.degree. F.,
greater than 500.degree. F., greater than 525.degree. F., or
greater than 550.degree. F. More particularly, embodiments
disclosed herein relate to processes for the desulfurization of
high end point naphthas to produce gasoline fractions having a
total sulfur content of less than 20 ppm, by weight. In some
embodiments, the total sulfur content of the resulting gasoline
fraction may be less than 10 ppm, by weight. Other embodiments
disclosed herein may additionally provide for control of the end
point of the gasoline product.
[0091] "Recombinant mercaptans," as used herein, refers to
mercaptans that are not in the feed to the present process but are
the reaction products of the H.sub.2S generated by the
hydrogenation of sulfur-containing compounds in the present process
and alkenes in the feed. Thus, the recombinant mercaptans are not
necessarily the same as those destroyed by the hydrodesulfurization
of a first portion of the present process, although they may
be.
[0092] Within the scope of this application, the expression
"catalytic distillation reactor system" denotes an apparatus in
which the catalytic reaction and the separation of the products
take place at least partially simultaneously. The apparatus may
comprise a conventional catalytic distillation column reactor,
where the reaction and distillation are concurrently taking place
at boiling point conditions, or a distillation column combined with
at least one side reactor, where the side reactor may be operated
as a liquid phase reactor or a boiling point reactor. While both
catalytic distillation reactor systems described may be preferred
over conventional liquid phase reaction followed by separations, a
catalytic distillation column reactor may have the advantages of
decreased piece count, reduced capital cost, increased catalyst
productivity per pound of catalyst, efficient heat removal (heat of
reaction may be absorbed into the heat of vaporization of the
mixture), and a potential for shifting equilibrium. Divided wall
distillation columns, where at least one section of the divided
wall column contains a catalytic distillation structure, may also
be used, and are considered "catalytic distillation reactor
systems" herein.
[0093] The hydrocarbon feed to the processes disclosed herein may
be a sulfur-containing petroleum fraction which boils in the
gasoline boiling range, including FCC gasoline, coker
pentane/hexane, coker naphtha, FCC naphtha, straight run gasoline,
pyrolysis gasoline, and mixtures containing two or more of these
streams. Such gasoline blending streams typically have a normal
boiling point within the range of 0.degree. F. and 470.degree. F.,
as determined by an ASTM D86 distillation. Feeds of this type
include light naphthas typically having a boiling range of about
C.sub.6 to 330.degree. F.; full range naphthas, typically having a
boiling range of about C.sub.5 to 420.degree. F., heavier naphtha
fractions boiling in the range of about 260.degree. F. to
412.degree. F., or heavy gasoline fractions with high end points
boiling in the range of about 330.degree. F. to 470.degree. F. or
higher.
[0094] Processes disclosed herein are additionally suitable for the
desulfurization of "high end point" petroleum fractions, which is
herein defined as a naphtha fraction having an ASTM D86 end point
of at least 450.degree. F. Increasing the end point of the naphtha
changes the behavior of the gasoline toward hydrodesulfurization,
as the sulfur content of the gasoline increases dramatically with
an increase in end point, rendering a significant number of prior
processes unsuitable. Further, higher end point fractions typically
include multi-substituted sulfur compounds, as described above,
including multi-substituted benzothiophenes. These high end point
sulfur-containing compounds are referred to herein as "hindered
sulfur compounds" as these compounds are much less reactive during
hydrodesulfurization processes. In some embodiments, high end point
gasoline fractions that may be processed according to processes
disclosed herein may have an ASTM D86 end point of at least
450.degree. F., at least 470.degree. F. in other embodiments; at
least 500.degree. F. in other embodiments; at least 510.degree. F.
in other embodiments; at least 520.degree. F. in other embodiments;
at least 525.degree. F. in other embodiments; and at least
550.degree. F. in yet other embodiments. In other embodiments, high
end point gasoline fractions that may be processed according to
embodiments disclosed herein may have an ASTM D86 end point in the
range from about 450.degree. F. to about 550.degree. F.; from about
470.degree. F. to about 550.degree. F. in other embodiments; and
from about 500.degree. F. to about 520.degree. F. in yet other
embodiments.
[0095] Organic sulfur compounds present in these gasoline fractions
occur principally as mercaptans, aromatic heterocyclic compounds,
and disulfides. Relative amounts of each depend on a number of
factors, many of which are refinery, process and feed specific. In
general, heavier fractions contain a larger amount of sulfur
compounds, and a larger fraction of these sulfur compounds are in
the form of aromatic heterocyclic compounds. In addition, certain
streams commonly blended for gasoline, such as FCC naphthas,
contain high amounts of the heterocyclic compounds. Gasoline
streams containing significant amounts of these heterocyclic
compounds are often difficult to process using many of the prior
art processes. Very severe operating conditions have been
conventionally specified for hydrotreating processes to desulfurize
gasoline streams, resulting in loss of olefinic content and a large
octane penalty. Prior methods of catalytic distillation for
high-end point gasolines have not been successful in removing the
required amount of sulfur due to the difficulty of breaking the
hindered sulfur bonds in high-end point naphtha. Adsorption
processes, used as an alternative to hydrogen processing, have very
low removal efficiencies, as the aromatic heterocyclic sulfur
compounds have adsorptive properties similar to the aromatic
compounds in the hydrocarbon matrix.
[0096] Aromatic heterocyclic compounds that may be removed by the
processes disclosed herein include alkyl substituted thiophene,
thiophenol, alkylthiophene, benzothiophene, and multi-substituted
benzothiophenes. Among the aromatic heterocyclic compounds of
particular interest are thiophene, 2-methylthiophene,
3-methylthiophene, 2-ethylthiophene, benzothiophene and
dimethylbenzothiophene. Mercaptans that may be removed by the
processes described herein often contain from 2-10 carbon atoms,
and are illustrated by materials such as 1-ethanthiol,
2-propanethiol, 2-butanethiol, 2-methyl-2-propanethiol,
pentanethiol, hexanethiol, heptanethiol, octanethiol, nonanethiol,
and thiophenol.
[0097] Sulfur in these gasoline streams may be in one of several
molecular forms, including thiophenes, mercaptans and disulfides.
For a given gasoline stream, the sulfur compounds tend to be
concentrated in the higher boiling portions of the stream (i.e.,
the heavier fractions of the stream), with hindered sulfur
compounds being present in higher concentrations at elevated
boiling points, such as above about 350.degree. F., and especially
above about 450.degree. F., and even more especially above about
500.degree. F. The sulfur within the higher boiling portions of the
stream may be more difficult to remove due to increased
concentration of multi-substituted benzothiophenes. High end point
naphtha streams that are particularly rich in hindered sulfur
compounds may be suitably treated according to embodiments
disclosed herein to produce a gasoline range product meeting
desired sulfur specifications.
[0098] The total sulfur content of gasoline streams to be treated
using the processes disclosed herein will generally exceed 50 ppm
by weight, and typically range from about 150 ppm to as much as
several thousand ppm sulfur. For fractions containing at least 5
volume percent boiling over about 520.degree. F., the sulfur
content may exceed about 1000 ppm by weight, and may be as high as
5000 to 10000 ppm by weight or even higher.
[0099] In addition to the sulfur compounds, naphtha feeds,
including FCC naphtha, may include paraffins, naphthenes, and
aromatics, as well as open-chain and cyclic olefins, dienes, and
cyclic hydrocarbons with olefinic side chains. A cracked naphtha
feed useful in the processes described herein may have an overall
olefins concentration ranging from about 5 to 60 weight percent in
some embodiments; from about 25 to 50 weight percent in other
embodiments.
[0100] In general, processes described herein may treat a naphtha
or gasoline fraction in one or more catalytic distillation reactor
systems. Each catalytic distillation reactor system may have one or
more reaction zones containing one or more of a hydrogenation
catalyst, a thioetherification catalyst, and/or a
hydrodesulfurization catalyst. For example, reactive distillation
zones may be contained within the stripping section,
hydrodesulfurizing the heavier compounds in the feed, or within the
rectification section, hydrodesulfurizing the lighter compounds in
the feed, or both. Hydrogen may also be fed to the catalytic
distillation reactor system, and in some embodiments, a portion of
the hydrogen may be fed below each respective reaction zone.
[0101] In each catalytic distillation reactor system, the steps to
catalytically react the naphtha feed with hydrogen may be carried
out at a temperature in the range of 100.degree. F. to 1000.degree.
F., at pressures in the range from about 0.1 to 500 psig, with
hydrogen partial pressures in the range from 0.01 to 100 psi at 2
to 2000 scf/bbl at weight hourly space velocities (WHSV) in the
range of 0.1 to 10 hf.sup.-1 based on feed rate and a particulate
catalyst packaged in structures. If advanced specialty catalytic
structures are used (where catalyst is one with the structure
rather than a form of packaged pellets to be held in place by
structure), the liquid hourly space velocity (LHSV) for such
systems should be about in the same range as those of particulate
or granular-based catalytic distillation catalyst systems as just
referenced. In other embodiments, conditions in a reaction
distillation zone of a naphtha hydrodesulfurization distillation
column reactor system are: temperatures in the range from
450.degree. F. to 700.degree. F., total pressure in the range from
75 to 300 psig, hydrogen partial pressure in the range from 6 to 75
psia, WHSV of naphtha in the range from about 1 to 5, and hydrogen
feed rates in the range from 10-1000 scf/bbl.
[0102] The operation of a distillation column reactor results in
both a liquid and a vapor phase within the distillation reaction
zone. A considerable portion of the vapor is hydrogen, while a
portion of the vapor is hydrocarbons from the hydrocarbon feed. In
catalytic distillation it has been proposed that the mechanism that
produces the effectiveness of the process is the condensation of a
portion of the vapors in the reaction system, which occludes
sufficient hydrogen in the condensed liquid to obtain the requisite
intimate contact between the hydrogen and the sulfur compounds in
the presence of the catalyst to result in their hydrogenation. In
particular, sulfur species concentrate in the liquid while the
olefins and H.sub.2S concentrate in the vapor, allowing for high
conversion of the sulfur compounds with low conversion of the
olefin species.
[0103] As in any distillation, there is a temperature gradient
within the catalytic distillation reactor system. The lower end of
the column contains higher boiling material and thus is at a higher
temperature than the upper end of the column. The lower boiling
fraction, which contains more easily removable sulfur compounds, is
subjected to lower temperatures at the top of the column, which may
provide for greater selectivity, that is, no hydrocracking or less
saturation of desirable olefinic compounds. The higher boiling
portion is subjected to higher temperatures in the lower end of the
distillation column reactor to crack open the sulfur containing
ring compounds and hydrogenate the sulfur. The heat of reaction
simply creates more boil up, but no increase in temperature at a
given pressure. As a result, a great deal of control over the rate
of reaction and distribution of products can be achieved by
regulating the system pressure.
[0104] Processes disclosed herein may additionally treat a naphtha
or gasoline fraction, or a select portion thereof, in one or more
fixed bed reactor systems. Each fixed bed reactor system may
include one or more reactors in series or parallel, each reactor
having one or more reaction zones containing one or more
hydrodesulfurization catalysts. Such fixed bed reactors may be
operated as a vapor phase reactor, a liquid phase reactor, or a
mixed phase (V/L) reactor and may include traditional fixed bed
reactors, trickle bed reactors, pulse flow reactors, and other
reactor types known to those skilled in the art. The operating
conditions used in the fixed bed reactor systems may depend upon
the reaction phase(s), the boiling range of the naphtha fraction
being treated, catalyst activity, selectivity, and age, and the
desired sulfur removal per reaction stage, among other factors.
[0105] The flow of components through processes disclosed herein
provides for efficient processing of high end point naphtha streams
to reduce the total sulfur content of the streams to meet
specifications and regulations. Further, the process flow schemes
provide for the processing of high olefin-content portions of the
naphtha at less severe conditions, maintaining a significant
portion of the olefin content, and thus preserving high octane
value components.
[0106] Referring now to FIG. 1, a simplified process flow diagram
of an embodiment of the hydrodesulfurization processes disclosed
herein is illustrated. Hydrogen and a naphtha or other organic
sulfur-containing hydrocarbon feed, which may include hindered
sulfur compounds, may be fed via flow lines 6 and 8, respectively,
to a first catalytic distillation reactor system 10 having one or
more reactive distillation zones 12 for hydrotreating the
hydrocarbon feed. As illustrated, catalytic distillation reactor
system 10 includes at least one reactive distillation zone 12,
located in an upper portion of the column, above the feed inlet,
for treating the light hydrocarbon components in the feed.
[0107] Reaction zone 12 may include one or more catalysts for the
hydrogenation of dienes, reaction of mercaptans and dienes
(thioetherification), and/or hydrodesulfurization. For example,
conditions in the first catalytic distillation reactor system 10
may provide for thioetherification and/or hydrogenation of dienes
and removal of mercaptan sulfur from the C.sub.5/C.sub.6 portion of
the hydrocarbon feed. The C5/C6 portion of the naphtha, having a
reduced sulfur content as compared to the C5/C6 portion of the
feed, may be recovered from catalytic distillation reactor system
10 as a side draw product 16.
[0108] An overheads fraction may be recovered from catalytic
distillation reactor system 10 via flow line 18, and may contain
light hydrocarbons, unreacted hydrogen and hydrogen sulfide. The
first overheads 18 may be cooled, such as using a heat exchanger
14, and fed to a stripper 20. In stripper 20, hydrogen sulfide and
unreacted hydrogen may be separated from the hydrocarbons contained
in the overhead fraction, with unreacted hydrogen and hydrogen
sulfide withdrawn from stripper 20 via flow line 22. Condensed
hydrocarbons may be withdrawn from stripper 20 and fed to first
catalytic distillation reactor system 10 as a total or partial
reflux via flow line 24 and pump 26.
[0109] The C5/C6 side draw product withdrawn from catalytic
distillation reactor system 10 via flow line 16 may contain many of
the olefins present in the hydrocarbon feed. Additionally, dienes
in the C5/C6 cut may be hydrogenated during treatment in catalytic
distillation reactor system 10. This hydrogenated, desulfurized
C5/C6 side draw product may thus be recovered for use in various
processes. In various embodiments, the C5/C6 side draw product may
be used as a gasoline blending fraction, hydrogenated and used as a
gasoline blending feedstock, and as a feedstock for ethers
production, among other possible uses. The particular processing or
end use of the C5/C6 fraction may depend upon various factors,
including availability of alcohols as a raw material, and the
allowable olefin concentration in gasoline for a particular
jurisdiction, among others
[0110] The heavy naphtha, e.g. C7+ boiling range components,
including any thioethers formed in reaction zone 12 and various
other sulfur and hindered sulfur compounds in the hydrocarbon feed,
may be recovered as a bottoms fraction from catalytic distillation
reactor system 10 via flow line 20. Where catalytic distillation
reactor system 10 includes a reaction zone in the stripping section
of the column, or where boil-up of C7+ components into reaction
zone 12 occurs, the recovered bottoms fraction may be at least
partially desulfurized.
[0111] The bottoms fraction recovered via flow line 20 is then fed
to a second catalytic distillation reactor system 30 containing one
or more reactions zones containing one or more hydrodesulfurization
catalysts. Hydrogen may be fed to catalytic distillation reactor
system 30 via flow line 28.
[0112] In some embodiments, catalytic distillation reactor system
30 may contain a reaction zone 32 in the rectification section
reacting at least a portion of the organic sulfur compounds in the
hydrocarbon feed with hydrogen, converting at least a portion of
the organic sulfur compounds to hydrogen sulfide. Catalytic
distillation reactor system 30 may be operated at conditions to
facilitate the aforementioned reaction and to concurrently separate
the hydrocarbon feed into a first intermediate naphtha fraction
having an ASTM D86 end point in the range from about 270.degree. F.
to about 400.degree. F., recovered as an overheads via flow line
36, and a heavy naphtha fraction, recovered as a bottoms fraction
via flow line 54.
[0113] If desired, catalytic distillation reactor system 30 may
include distillation reaction zones 32, 34, in each of the
rectification and stripping sections of the column, such that the
heavy fraction may be at least partially hydrodesulfurized as it
traverses downward through catalytic distillation reactor system
30. In such a case, hydrogen may be fed below the lowermost
reaction zone via flow line 28b, or alternatively may be fed below
each reactive distillation zone 32 and 34, such as via flow lines
28a and 28b, respectively.
[0114] The overheads product recovered from catalytic distillation
reactor system 30 via flow line 36 may contain the intermediate
fraction hydrocarbons as well as hydrogen sulfide and unreacted
hydrogen. The overheads fraction may then be processed to separate
the hydrogen and hydrogen sulfide. For example, the overheads
fraction may be partially condensed via indirect heat exchange
using a heat exchanger 40 and fed to a "hot drum" 42 for separation
of the condensate from the uncondensed vapors, which include
hydrocarbons, hydrogen sulfide, and hydrogen. The condensate may be
recovered from drum 42 via flow line 48, a portion of which may be
fed as reflux to catalytic distillation reactor 30 via pump 46 and
flow line 38. The remainder of the condensate may be fed via flow
line 51, and the uncondensed vapors may be fed via flow line 44, to
"cold drum" 50. Cold drum 50 may then separate hydrogen and
hydrogen sulfide, recovered via flow line 52, from the intermediate
and heavy hydrocarbon components, recovered via flow line 68.
[0115] The bottoms product recovered via flow line 54 may have a
fairly high concentration of sulfur. However, it is actually
beneficial to the process to have a minimal amount of catalyst in
reaction zone 34, leaving a high concentration of sulfur in the
bottoms product, as this minimizes the concentration of hydrogen
sulfide available for recombinant mercaptan formation in the upper
portion of catalytic distillation column reactor 30 and the
associated overheads recovery system.
[0116] The bottoms fraction recovered via flow line 54 from
catalytic distillation reactor system 30 is hot (at reboil
temperature) and does not contain a significant amount of hydrogen
sulfide due to the counter-current flow pattern of the reactive
distillation process. The bottoms fraction recovered via flow line
54 is then fed to a fixed bed reactor 60 for additional
hydrotreating. Additional hydrogen, over that dissolved in the
bottoms, may be fed to fixed bed reactor 60 via flow line 58, if
necessary or desired. The partial pressure of hydrogen in the fixed
be unit is typically greater than about 20 psi, such as between
about 25 psi and about 350 psi, providing additional driving force
for the removal of sulfur from any hindered sulfur compounds in the
heavy end of the hydrocarbon feed 8. High hydrogen concentrations
may be used in the fixed bed reactor 60 as most olefins have been
separated and recovered via flow lines 16 and 36. Additionally, use
of select hydrodesulfurization catalysts, such as Co/Mo catalysts,
in fixed bed reactor 60 may prevent saturation of aromatic
compounds, thus avoiding the accompanying octane loss. Fixed bed
reactor 60 and the resulting hydrodesulfurization of hindered
sulfur compounds allows for the processing of very high endpoint
feedstocks, even those having an endpoint in excess of 550.degree.
F. in some embodiments.
[0117] The heavy gasoline effluent from fixed bed reactor 60 may be
recovered via flow line 62. The effluent may then be fed via flow
line 62 to drum 64, separating hydrogen sulfide and unreacted
hydrogen from the liquid hydrocarbon effluent. The hydrogen and
hydrogen sulfide may be withdrawn from drum 64 via flow line 66.
The hydrocarbon effluent, having a reduced sulfur concentration,
may be recovered via flow line 82.
[0118] In some embodiments, the hydrocarbon effluent recovered via
flow line 82 may be combined with one or more of the lighter
fractions, recovered via flow lines 16 and 68, for use as a
gasoline blend stock or for further processing, as will be
described below. In other embodiments, the heavy hydrocarbon
fraction may be processed along with a heavy hydrocarbon fraction,
such as a diesel hydrocarbon fraction, fed via flow line 70, for
further reducing the sulfur content of the heavy fraction and the
diesel fraction.
[0119] Referring now to FIGS. 2 and 3, simplified process flow
diagrams of embodiments of the hydrodesulfurization processes
disclosed herein is illustrated, where like numerals represent like
parts. Hydrogen and a naphtha or other organic sulfur-containing
hydrocarbon feed, which may include hindered sulfur compounds, may
be fed via flow lines 6 and 8, respectively, to a first catalytic
distillation reactor system 10 having one or more reactive
distillation zones 12 for hydrotreating the hydrocarbon feed. As
illustrated, catalytic distillation reactor system 10 includes at
least one reactive distillation zone 12, located in an upper
portion of the column, above the feed inlet, for treating the light
hydrocarbon components in the feed.
[0120] Reaction zone 12 may include one or more catalysts for the
hydrogenation of dienes, reaction of mercaptans and dienes
(thioetherification), and/or hydrodesulfurization. For example,
conditions in the first catalytic distillation reactor system 10
may provide for thioetherification and/or hydrogenation of dienes
and removal of mercaptan sulfur from the C.sub.5/C.sub.6 portion of
the hydrocarbon feed. The C5/C6 portion of the naphtha, having a
reduced sulfur content as compared to the C5/C6 portion of the
feed, may be recovered from catalytic distillation reactor system
10 as a side draw product 16.
[0121] An overheads fraction may be recovered from catalytic
distillation reactor system 10 via flow line 18, and may contain
light hydrocarbons, unreacted hydrogen and hydrogen sulfide. The
first overheads 18 may be cooled, such as using a heat exchanger
14, and fed to a stripper 20. In stripper 20, hydrogen sulfide and
unreacted hydrogen may be separated from the hydrocarbons contained
in the overhead fraction, with unreacted hydrogen and hydrogen
sulfide withdrawn from stripper 20 via flow line 22. Condensed
hydrocarbons may be withdrawn from stripper 20 and fed to first
catalytic distillation reactor system 10 as a total or partial
reflux via flow line 24 and pump 26.
[0122] The C5/C6 side draw product withdrawn from catalytic
distillation reactor system 10 via flow line 16 may contain many of
the olefins present in the hydrocarbon feed. Additionally, dienes
in the C5/C6 cut may be hydrogenated during treatment in catalytic
distillation reactor system 10. This hydrogenated, desulfurized
C5/C6 side draw product may thus be recovered for use in various
processes. In various embodiments, the C5/C6 side draw product may
be used as a gasoline blending fraction, hydrogenated and used as a
gasoline blending feedstock, and as a feedstock for ethers
production, among other possible uses. The particular processing or
end use of the C5/C6 fraction may depend upon various factors,
including availability of alcohols as a raw material, and the
allowable olefin concentration in gasoline for a particular
jurisdiction, among others
[0123] The heavy naphtha, e.g. C7+ boiling range components,
including any thioethers formed in reaction zone 12 and various
other sulfur and hindered sulfur compounds in the hydrocarbon feed,
may be recovered as a bottoms fraction from catalytic distillation
reactor system 10 via flow line 20. Where catalytic distillation
reactor system 10 includes a reaction zone in the stripping section
of the column, or where boil-up of C7+ components into reaction
zone 12 occurs, the recovered bottoms fraction may be at least
partially desulfurized.
[0124] The bottoms fraction recovered via flow line 20 is then fed
to a second catalytic distillation reactor system 30 containing one
or more reactions zones containing one or more hydrodesulfurization
catalysts. Hydrogen may be fed to catalytic distillation reactor
system 30 via flow line 28.
[0125] In some embodiments, catalytic distillation reactor system
30 may contain a reaction zone 32 in the rectification section
reacting at least a portion of the organic sulfur compounds in the
hydrocarbon feed with hydrogen, converting at least a portion of
the organic sulfur compounds to hydrogen sulfide. Catalytic
distillation reactor system 30 may be operated at conditions to
facilitate the aforementioned reaction and to concurrently separate
the hydrocarbon feed into a first intermediate naphtha fraction
having an ASTM D86 end point in the range from about 270.degree. F.
to about 400.degree. F., recovered as an overheads via flow line
36, and a heavy naphtha fraction, recovered as a bottoms fraction
via flow line 54.
[0126] If desired, catalytic distillation reactor system 30 may
include distillation reaction zones 32, 34, in each of the
rectification and stripping sections of the column, such that the
heavy fraction may be at least partially hydrodesulfurized as it
traverses downward through catalytic distillation reactor system
30. In such a case, hydrogen may be fed below the lowermost
reaction zone via flow line 28b, or alternatively may be fed below
each reactive distillation zone 32 and 34, such as via flow lines
28a and 28b, respectively.
[0127] The bottoms product recovered via flow line 54 may have a
fairly high concentration of sulfur. However, it is actually
beneficial to the process to have a minimal amount of catalyst in
reaction zone 34, leaving a high concentration of sulfur in the
bottoms product, as this minimizes the concentration of hydrogen
sulfide available for recombinant mercaptan formation in the upper
portion of catalytic distillation column reactor 30 and the
associated overheads recovery system.
[0128] The bottoms fraction recovered via flow line 54 from
catalytic distillation reactor system 30 is hot (at reboil
temperature) and does not contain a significant amount of hydrogen
sulfide due to the counter-current flow pattern of the reactive
distillation process. The bottoms fraction recovered via flow line
54 is then fed to a fixed bed reactor 60 for additional
hydrotreating. Additional hydrogen, over that dissolved in the
bottoms, may be fed to fixed bed reactor 60 via flow line 58. The
partial pressure of hydrogen in the fixed be unit is greater than
about 20 psi, such as between about 25 psi and about 350 psi,
providing additional driving force for the removal of sulfur from
any hindered sulfur compounds in the heavy end of the hydrocarbon
feed 8. High hydrogen concentrations may be used in the fixed bed
reactor 60 as most olefins have been separated and recovered via
flow lines 16 and 36. Additionally, use of select
hydrodesulfurization catalysts, such as Co/Mo catalysts, in fixed
bed reactor 60 may prevent saturation of aromatic compounds, thus
avoiding the accompanying octane loss. Fixed bed reactor 60 and the
resulting hydrodesulfurization of hindered sulfur compounds allows
for the processing of very high endpoint feedstocks, even those
having an endpoint in excess of 550.degree. F. in some
embodiments.
[0129] The heavy gasoline effluent from fixed bed reactor 60 may be
recovered via flow line 62. In some embodiments, a portion of the
effluent in flow line 62 may be recycled to the inlet of reactor
60, such as via flow line 61. The effluent may then be fed via flow
line 62 to drum 64, separating hydrogen sulfide and unreacted
hydrogen from the liquid hydrocarbon effluent. The hydrogen and
hydrogen sulfide may be withdrawn from drum 64 via flow line 66.
The hydrocarbon effluent, having a reduced sulfur concentration,
may be recovered via flow line 82.
[0130] The overheads product recovered from catalytic distillation
reactor system 30 via flow line 36 may contain the intermediate
fraction hydrocarbons as well as hydrogen sulfide and unreacted
hydrogen. The overheads fraction may then be processed to separate
the hydrogen and hydrogen sulfide. For example, the overheads
fraction may be partially condensed via indirect heat exchange
using a heat exchanger 40 and fed to a "hot drum" 42 for separation
of the condensate from the uncondensed vapors, which include
hydrocarbons, hydrogen sulfide, and hydrogen. The condensate may be
recovered from drum 42 via flow line 48, a portion of which may be
fed as reflux to catalytic distillation reactor 30 via pump 46 and
flow line 38. The remainder of the condensate may be fed via flow
line 51, and the uncondensed vapors may be fed via flow line 44, to
"cold drum" 50. Cold drum 50 may then separate hydrogen and
hydrogen sulfide, recovered via flow line 52, from the intermediate
and heavy hydrocarbon components, recovered via flow line 68.
[0131] In some embodiments of the hydrodesulfurization processes
disclosed herein, it may be desired to recover a desulfurized
hydrocarbon stream inclusive of both the intermediate fraction and
the heavy fraction. Referring now to FIG. 1, the separated heavy
gasoline effluent recovered from drum 64 via flow line 82 may be
fed to cold drum 50 for additional removal of hydrogen and hydrogen
sulfide, if necessary, and recovered for further processing along
with the intermediate fraction via flow line 68. The heavy gasoline
effluent may alternatively be combined with the intermediate
fraction downstream of drum 50.
[0132] The combined heavy and intermediate fractions may then be
fed via flow line 68 and hydrogen via flow line 72 to a second
fixed be reactor 74 containing a hydrodesulfurization catalyst. The
desulfurized heavy gasoline fraction may thus act as a heavy, inert
diluent for the hydrodesulfurization of the intermediate fraction
in second fixed bed reactor 74. Second fixed bed reactor 74 may be
especially useful for removing mercaptan and recombinant mercaptan
sulfur formed in the overhead system and present in the
intermediate fraction. The effluent from second fixed bed reactor
74 may then be fed via flow line 76 to stripper 80 for the
separation of hydrogen and hydrogen sulfide, recovered via flow
line 78, from the hydrodesulfurized intermediate and heavy gasoline
fractions, recovered via flow line 84.
[0133] In some embodiments, processes disclosed herein may provide
control over the end point of the intermediate gasoline fractions
recovered as a product. Referring now to FIG. 2, the intermediate
fraction may be fed via flow line 68 and hydrogen via flow line 72
to a second fixed be reactor 74 containing a hydrodesulfurization
catalyst. The effluent from second fixed bed reactor 74 may then be
fed via flow line 76 to stripper 80 for the separation of hydrogen
and hydrogen sulfide, recovered via flow line 78, from the
hydrodesulfurized intermediate gasoline fraction, recovered via
flow line 84.
[0134] The intermediate gasoline fraction may then be fed to
separator 92 for fractionation of the hydrodesulfurized
intermediate gasoline fraction to recover a light intermediate
naphtha fraction via flow line 94 and a heavy naphtha fraction via
flow line 86. Control of the end point of the intermediate naphtha
fraction may be controlled by the operating conditions used in
separator 92. An intermediate naphtha fraction having a higher end
point may be achieved using higher temperatures and/or lower
pressures in separator 92.
[0135] In some embodiments, the heavy naphtha fraction recovered
via flow line 86 may be recycled to fixed bed reactor 74 to act as
a heavy, inert diluent, as described above. A portion of the heavy
gasoline recovered from drum 64 via flow line 82 may also be fed
via flow line 90 to second fixed bed reactor 74 to act as a
diluent, to provide heavy hydrocarbons for additional control of
the end point of the intermediate naphtha recovered via flow line
94, and to provide heavy material for control of reboil temperature
in separator 92. As necessary, heavy hydrocarbons recirculating
from separator 92 to fixed bed reactor 74 may be withdrawn via flow
line 98 and recovered with the heavy gasoline fraction in flow line
82.
[0136] In the configuration as illustrated in FIG. 2, the heavy
fraction recovered via flow line 82 may be useful as a diesel
gasoline fraction. In such instances, it may be desired to saturate
aromatics in the heavy gasoline fraction. Thus, a refiner may opt
to load a Ni/Mo catalyst, a Co/Mo catalyst, a Ni/W catalyst, or a
mixture thereof in fixed bed reactor 60 to meet the local diesel
specifications.
[0137] To result in high end point gasoline products having a low
sulfur content, such as less than 50 ppm sulfur, by weight, in some
embodiments, and less than 20 ppm or 10 ppm sulfur in other
embodiments, the hydrocarbons recovered from drum 50 via flow line
68 may have a target sulfur concentration of less than about 150
ppm sulfur, by weight. In some embodiments, the target sulfur
concentration of the hydrocarbons recovered via flow line 68 may be
less than 125 ppm sulfur, by weight; less than 100 ppm sulfur, by
weight in other embodiments; and from 50 ppm to 100 ppm sulfur, by
weight, in yet other embodiments.
[0138] Operating conditions useful in each of catalytic
distillation reactor systems 10, 30 and fixed bed reactor systems
60, 74 are provided in Table 1 below. Such conditions are useful in
attaining the target product sulfur concentrations as detailed
above.
TABLE-US-00001 TABLE 1 Reaction Zone Reactor 10 30 60 74
Temperature (.degree. F.) 260-400 300-700 500-700 400-600 Pressure
(psig) 75-300 75-300 50-500 50-350 WHSV 1-5 1-5 0.5-10.sup. 5-10
Hydrogen partial 5-75 5-75 20-400 pressure (psi) Hydrogen feed
rates 10-1000 10-1000 (scf/bbl)
[0139] Catalysts useful in the first catalytic distillation reactor
column may be characterized as thioetherification catalysts or
alternatively hydrogenation catalysts. In the first catalytic
distillation reactor column, reaction of the diolefins with the
sulfur compounds is selective over the reaction of hydrogen with
olefinic bonds. The preferred catalysts are palladium and/or nickel
or a Ni/Pd dual bed as shown in U.S. Pat. No. 5,595,643, which is
incorporated herein by reference, since in the first catalytic
distillation reactor column the sulfur removal is carried out with
the intention to preserve the olefins. Although the metals are
normally deposited as oxides, other forms may be used. The nickel
is believed to be in the sulfide form during the hydrogenation.
[0140] Another suitable catalyst for the thioetherification
reaction may be 0.34 wt % Pd on 7 to 14 mesh alumina spheres,
supplied by Sud-Chemie, designated as G-68C. The catalyst also may
be in the form of spheres having similar diameters. They may be
directly loaded into standard single pass fixed bed reactors which
include supports and reactant distribution structures. However, in
their regular form they form too compact a mass for operation in a
catalytic distillation reactor system column and must then be
prepared in the form of a catalytic distillation structure. The
catalytic distillation structure must be able to function as
catalyst and as mass transfer medium. The catalyst must be suitably
supported and spaced within the column to act as a catalytic
distillation structure.
[0141] Without being bound to any specific theory, the catalyst is
believed to be the hydride of palladium which is produced during
operation. The hydrogen rate to the catalytic reactor must be
sufficient to maintain the catalyst in the active form because
hydrogen is lost from the catalyst by hydrogenation, but kept below
that which would cause flooding of the column which is understood
to be the "effectuating amount of hydrogen" as that term is used
herein. Generally the mole ratio of hydrogen to diolefins and
acetylenes in the feed is at least 1.0 to 1.0 and preferably 2.0 to
1.0.
[0142] In second and subsequent catalytic distillation reactor
columns and catalytic fixed bed reaction zones used in embodiments
disclosed herein, it may be the purpose of the catalyst to destroy
the sulfur compounds to produce a hydrocarbon stream containing
hydrogen sulfide, which is easily separated from the heavier
components therein. Hydrogen and hydrogen sulfide may be separated
from heavy hydrocarbon components in a stripping column, as
described above. The focus of these catalytic reactions that occur
after the first catalytic distillation reactor column is to carry
out destructive hydrogenation of the sulfides and other organic
sulfur compounds.
[0143] Catalysts useful as the hydrodesulfurization catalyst in the
reaction zones of the catalytic distillation reactor systems may
include Group VIII metals, such as cobalt, nickel, palladium, alone
or in combination with other metals, such as molybdenum or
tungsten, on a suitable support, which may be alumina,
silica-alumina, titania-zirconia or the like. Normally the metals
are provided as the oxides of the metals supported on extrudates or
spheres and as such are not generally useful as distillation
structures. Alternatively, catalyst may be packaged in a suitable
catalytic distillation structure, which characteristically can
accommodate a wide range of typically manufactured fixed-bed
catalyst sizes.
[0144] The catalysts may contain components from Group V, VIB, VIII
metals of the Periodic Table or mixtures thereof. The incorporation
of the distillation column reactor systems may reduce the
deactivation of catalysts and may provide for longer runs than the
fixed bed hydrogenation reactors of the prior art. The Group VIII
metal may also provide increased overall average activity.
Catalysts containing a Group VIB metal, such as molybdenum, and a
Group VIII metal, such as cobalt or nickel, are preferred.
Catalysts suitable for the hydrodesulfurization reaction include
cobalt-molybdenum, nickel-molybdenum and nickel-tungsten. The
metals are generally present as oxides supported on a neutral base
such as alumina, silica-alumina or the like. The metals are
converted to the sulfide either in use or prior to use by exposure
to sulfur compound containing streams and hydrogen.
[0145] The catalyst may also catalyze the hydrogenation of the
olefins and dienes contained within the light cracked naphtha and
to a lesser degree the isomerization of some of the mono-olefins.
The hydrogenation, especially of the mono-olefins in the lighter
fraction, may not be desirable.
[0146] The catalyst typically is in the form of extrudates having a
diameter of 1/8, 1/16 or 1/32 inches and an L/D of 1.5 to 10. The
catalyst also may be in the form of spheres having similar
diameters. They may be directly loaded into standard single pass
fixed bed reactors which include supports and reactant distribution
structures. However, in their regular form they form too compact a
mass for operation in the catalytic distillation reactor system
column and must then be prepared in the form of a catalytic
distillation structure. As described above, the catalytic
distillation structure must be able to function as catalyst and as
mass transfer medium. The catalyst must be suitably supported and
spaced within the column to act as a catalytic distillation
structure.
[0147] In some embodiments, the catalyst is contained in a
structure as disclosed in U.S. Pat. No. 5,730,843, which is hereby
incorporated by reference. In other embodiments, catalyst is
contained in a plurality of wire mesh tubes closed at either end
and laid across a sheet of wire mesh fabric such as demister wire.
The sheet and tubes are then rolled into a bale for loading into
the distillation column reactor. This embodiment is described, for
example, in U.S. Pat. No. 5,431,890, which is hereby incorporated
by reference. Other useful catalytic distillation structures are
disclosed in U.S. Pat. Nos. 4,731,229, 5,073,236, 5,431,890 and
5,266,546, which are each incorporated by reference.
[0148] Hydrodesulfurization catalysts described above with relation
to the operation of the catalytic distillation reactor systems may
also be used in the fixed bed reactors. In selected embodiments,
catalysts used in the fixed bed reactors may include
hydrodesulfurization catalysts that only promote the
desulfurization of mercaptan species, which are among the easiest
to convert to hydrogen sulfide. Conditions in the fixed bed
reactors, including high temperature and high hydrogen mole
fractions, are conducive to olefin saturation. For preservation of
olefin content and conversion of mercaptans to hydrogen sulfide at
these conditions, suitable catalysts may include nickel catalysts
with very low molybdenum promotion, or no promoters at all, and
molybdenum catalysts with very low copper promotion, or no
promoters at all. Such catalysts may have lower hydrogenation
activity, promoting the desulfurization of the mercaptan species
without significant loss of olefins.
[0149] The effluent streams from the catalytic distillation reactor
systems may be condensed in one or more stages, separating the
hydrocarbons from the hydrogen sulfide and the hydrogen. As
described above, it may be advantageous to use a hot drum-cold drum
system to limit the formation of recombinant mercaptans. The
recovered hydrogen may be compressed and recycled to various
portions of the hydrodesulfurization systems described herein.
[0150] As mentioned above, heavy hydrocarbons may act as a diluent
in fixed bed reactor 74 in embodiments disclosed herein. Dilution
may result in a decreased driving force for the reverse reaction
(recombinant mercaptan formation) as well as aid in olefin
preservation. The heavy gasoline fraction recycle may dilute the
olefins and hydrogen sulfide in the overhead fraction fed to the
fixed bed reactor. This may reduce the amount of hydrogen required
to provide dilution in the fixed bed reactors, and may also reduce
the pressure drop across the associated control valve. This
non-hydrogen dilution of the fixed bed reactor feed may in turn
reduce the power required to run compressors, due to decreased
hydrogen traffic.
[0151] As described above, embodiments disclosed herein may provide
for the production of a high end point gasoline, such as may be
recovered by one or more of flow lines 94, 84, and 82, having a
total sulfur content of less than 50, 20, or even 10 ppm by
weight.
[0152] After treatment according to the processes described herein,
the sulfur content of the C5/C6 side draw product recovered via
flow line 16 may be less than about 50 ppm in some embodiments;
less than 40 ppm in other embodiments; less than 30 ppm in other
embodiments; less than 20 ppm in other embodiments; less than 10
ppm in other embodiments; less than 5 ppm in other embodiments; and
less than 1 ppm in yet other embodiments, where each of the above
are based on weight.
[0153] After treatment according to the processes described herein,
the sulfur content of the hydrocarbon fraction recovered via flow
line 82 may be less than about 50 ppm in some embodiments; less
than 40 ppm in other embodiments; less than 30 ppm in other
embodiments; less than 20 ppm in other embodiments; less than 10
ppm in other embodiments; less than 5 ppm in other embodiments; and
less than 1 ppm in yet other embodiments, where each of the above
are based on weight.
[0154] After treatment according to the processes described herein,
the sulfur content of the intermediate hydrocarbon fraction
recovered via flow line 94 may be less than about 50 ppm in some
embodiments; less than 40 ppm in other embodiments; less than 30
ppm in other embodiments; less than 20 ppm in other embodiments;
less than 10 ppm in other embodiments; less than 5 ppm in other
embodiments; and less than 1 ppm in yet other embodiments, where
each of the above are based on weight.
[0155] After treatment according to the processes described herein,
the sulfur content of the heavy hydrocarbon fraction recovered via
flow line 82 may be less than about 50 ppm in some embodiments;
less than 40 ppm in other embodiments; less than 30 ppm in other
embodiments; less than 20 ppm in other embodiments; less than 10
ppm in other embodiments; less than 5 ppm in other embodiments; and
less than 1 ppm in yet other embodiments, where each of the above
are based on weight.
[0156] In contrast to typical hydrodesulfurization processes, which
often use harsh operating conditions resulting in significant loss
of olefins, desulfurized products resulting from the processes
disclosed herein may retain a significant portion of the olefins,
resulting in a higher value end product. In some embodiments,
products resulting from the processes described herein may have an
overall olefins concentration ranging from 5 to 55 weight percent;
from about 10 to about 50 weight percent in other embodiments; and
from about 20 to about 45 weight percent in other embodiments. As
compared to the initial hydrocarbon feed (flow line 8) the overall
product streams recovered from embodiments disclosed herein
(including flow lines 16, 94, 82, and 84 as appropriate for the
respective embodiments) may retain at least 25% of the olefins in
the initial hydrocarbon feed; at least 30% of the olefins in the
initial hydrocarbon feed in other embodiments; at least 35% of the
olefins in the initial hydrocarbon feed in other embodiments; at
least 40% of the olefins in the initial hydrocarbon feed in other
embodiments; at least 45% of the olefins in the initial hydrocarbon
feed in other embodiments; at least 50% of the olefins in the
initial hydrocarbon feed in other embodiments; and at least 60% of
the olefins in the initial hydrocarbon feed in other
embodiments.
[0157] Advantageously, embodiments disclosed herein may provide for
the production of a low sulfur content gasoline fraction (having
<10 ppm S, by weight in some embodiments) from a hydrocarbon
feedstock having an ASTM D-86 end point of at least 350.degree. F.,
and even from a high end point hydrocarbon feedstock (e.g., having
an end point of greater than 450.degree. F., 470.degree. F.,
500.degree. F., 525.degree. F., or 550.degree. F. and containing
hindered sulfur compounds). Additionally, due to the treatment at
varying severities and selected operating conditions, including
dilution with heavy hydrocarbons or use of appropriate catalysts,
embodiments disclosed herein may provide for one or more a high
retention of olefins, select saturation of olefins and/or
aromatics, and reduced recombinant mercaptan formation. A further
benefit of processes according to embodiments disclosed herein is
the ability to control the end point of the intermediate gasoline
fraction produced.
[0158] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
* * * * *