U.S. patent application number 10/015863 was filed with the patent office on 2004-09-30 for process for sulfur reduction in naphtha streams.
This patent application is currently assigned to CATALYTIC DISTILLATION TECHNOLOGIES. Invention is credited to Groten, Willibrord A..
Application Number | 20040188327 10/015863 |
Document ID | / |
Family ID | 21774060 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040188327 |
Kind Code |
A1 |
Groten, Willibrord A. |
September 30, 2004 |
Process for sulfur reduction in naphtha streams
Abstract
A process for fractionating and treating of a full range naphtha
stream. The full boiling range naphtha stream is first split into a
light boiling range naphtha, an intermediate boiling range naphtha
and a heavy boiling range naphtha. The bottoms are subjected to
hydrodesulfurization and the effluent combined with the
intermediate boiling range naphtha containing thiophene and
thiophene boiling range mercaptans and subjected to a second
hydrodesulfurization. The effluent from the polishing reactor may
be combined with the light boiling range naphtha to produce a new
full boiling range naphtha containing substantially less total
sulfur than the original feed. The mercaptans in the light naphtha
may be removed by thioetherification prior to splitting or by wet
caustic wash afterwards. The object being to meet higher standards
for sulfur removal, by treating the components of the naphtha feed
with the process that preserves the olefinic while most expediently
removing the sulfur compounds.
Inventors: |
Groten, Willibrord A.;
(Houston, TX) |
Correspondence
Address: |
KENNETH H. JOHNSON
P.O. BOX 630708
HOUSTON
TX
772630000
|
Assignee: |
CATALYTIC DISTILLATION
TECHNOLOGIES
|
Family ID: |
21774060 |
Appl. No.: |
10/015863 |
Filed: |
December 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60299508 |
Jun 20, 2001 |
|
|
|
60315161 |
Aug 27, 2001 |
|
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Current U.S.
Class: |
208/210 ;
208/211; 208/212 |
Current CPC
Class: |
C10G 2400/02 20130101;
C10G 67/16 20130101; C10G 65/04 20130101; C10G 45/02 20130101; C10G
19/02 20130101 |
Class at
Publication: |
208/210 ;
208/211; 208/212 |
International
Class: |
C10G 045/02; C10G
065/04 |
Claims
The invention claimed is:
1. A process for reducing the organic sulfur content of a full
boiling range cracked naphtha stream containing olefins, diolefins,
mercaptans, thiophenes, and other organic sulfur compounds,
comprising the steps of: (a) separating the full boiling range
cracked naphtha stream into three fractions comprising a light
cracked naphtha fraction, an intermediate cracked naphtha fraction
and a heavy cracked naphtha; (b) subjecting the heavy cracked
naphtha to hydrodesulfurization in a first hydrodesulfurization
reactor containing a hydrodesulfurization catalyst; and (c)
combining the effluent from the first hydrodesulfurization reactor
with the intermediate cracked naphtha and subjecting the combined
stream to hydrodesulfurization in a second hydrodesulfurization
reactor.
2. The process according to claim 1 wherein said light cracked
naphtha contains substantially all of the mercaptans and is
subjected to a wet caustic wash process wherein the mercaptans
contained therein are converted to sulfides and said sulfides are
removed.
3. The process according to claim 1 wherein said intermediate
cracked naphtha contains mercaptans and substantially all of the
thiophenes and substantially all of said mercaptans and thiophenes
are converted to hydrogen sulfide in said second
hydrodesulfurization reactor.
4. The process according to claim 1 wherein said heavy cracked
naphtha contains thiophenes and substantially all of said other
organic sulfur compounds and a portion of said thiophenes and other
organic sulfur compounds are converted to hydrogen sulfide in said
first hydrodesulfurization reactor.
5. The process according to claim 4 wherein substantially all of
the remaining thiophenes and other organic sulfur compounds are
converted to hydrogen sulfide in said second hydrodesulfurization
reactor.
6. The process according to claim 1 wherein said full boiling range
cracked naphtha stream is first subjected to thioetherification in
a thioetherification reactor prior to separating the full boiling
range cracked naphtha stream into said three fractions, wherein
substantially all of said mercaptans are reacted with a portion of
said diolefins to form sulfides.
7. The process according to claim 6 wherein said sulfides are
removed in said heavy cracked naphtha and substantially all of said
sulfides are converted to hydrogen sulfide in said first
hydrodesulfurization reactor.
8. The process according to claim 7 wherein the remaining sulfides
are converted to hydrogen sulfide in said second
hydrodesulfurization reactor.
9. The process according to claim 1 wherein said light cracked
naphtha fraction boils in the range of C.sub.5 to about 150.degree.
F., said intermediate cracked naphtha fraction boils in the range
of about 150 to about 250.degree. F. and said heavy cracked naphtha
boils in the range of about 250 to 450.degree. F.
10. A process for reducing the organic sulfur content of a full
boiling range cracked naphtha stream containing olefins, diolefins,
mercaptans, thiophenes, and other organic sulfur compounds,
comprising the steps of: (a) subjecting the full boiling range
naphtha to thioetherification in a thioetherification reactor
wherein substantially all of said mercaptans are reacted with a
portion of said diolefins to form sulfides; (b) separating the
effluent from the thioetherification reactor into three fractions
comprising a light cracked naphtha fraction boiling in the range of
C.sub.5 to about 150.degree. F, an intermediate cracked naphtha
fraction boiling in the range of about 150 to about 250.degree. F.
and a heavy cracked naphtha boiling in the range of about 250 to
450.degree. F.; (b) subjecting the heaving cracked naphtha to
hydrodesulfurization in a first hydrodesulfurization reactor
containing a hydrodesulfurization catalyst; and (c) combining the
effluent from the first hydrodesulfurization reactor with the
intermediate cracked naphtha and subjecting the combined stream to
hydrodesulfurization in a second hydrodesulfurization reactor.
11. A process for reducing the organic sulfur content of a full
boiling range cracked naphtha stream containing olefins, diolefins,
mercaptans, thiophenes, and other organic sulfur compounds,
comprising the steps of: (a) separating the full boiling range
cracked naphtha stream into three fractions comprising a light
cracked naphtha fraction boiling in the range of C.sub.5 to about
150.degree. F., an intermediate cracked naphtha fraction boiling in
the range of about 150 to about 250.degree. F. and a heavy cracked
naphtha boiling in the range of about 250 to 450.degree. F.; (b)
subjecting the heaving cracked naphtha to hydrodesulfurization in a
first hydrodesulfurization reactor containing a
hydrodesulfurization catalyst; (c) combining the effluent from the
first hydrodesulfurization reactor with the intermediate cracked
naphtha and subjecting the combined stream to hydrodesulfurization
in a second hydrodesulfurization reactor and (d) subjecting said
light cracked naphtha to a wet caustic wash wherein substantially
all of the mercaptans contained therein are converted to sulfides.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for concurrently
fractionating and hydrotreating a full range naphtha stream. More
particularly the full boiling range naphtha stream is split into a
light boiling range naphtha, a medium boiling range naphtha and a
heavy boiling range naphtha. Each boiling range naphtha is treated
separately to achieve a combined desired total sulfur content.
[0003] 2. Related Information
[0004] Petroleum distillate streams contain a variety of organic
chemical components. Generally the streams are defined by their
boiling ranges which determine the compositions. 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 materials as well as
saturated (alkanes) materials and polyunsaturated materials
(diolefins). Additionally, these components may be any of the
various isomers of these compounds.
[0005] 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 unsaturates 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.
[0006] 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.
[0007] 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.
[0008] Catalytically cracked naphtha gasoline boiling range
material currently forms a significant part (.apprxeq.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.
[0009] The most common method of removal of the sulfur compounds is
by hydrodesulfurization (HDS) in which the petroleum distillate is
passed over a solid particulate catalyst comprising a hydrogenation
metal supported on an alumina base. Additionally copious quantities
of hydrogen are included in the feed. The following equations
illustrate the reactions in a typical HDS unit:
RSH+H.sub.2.fwdarw.RH+H.sub.2S (1)
RCI+H.sub.2.fwdarw.RH+HCl (2)
RN+2H.sub.2.fwdarw.RH+NH.sub.3 (3)
ROOH+2H.sub.2.fwdarw.RH+2H.sub.2O (4)
[0010] Typical operating conditions for the HDS reactions are:
1 Temperature, .degree. F. 600-780 Pressure, psig 600-3000 H.sub.2
recycle rate, SCF/bbl 1500-3000 Fresh H.sub.2 makeup, SCF/bbl
700-1000
[0011] The reaction of organic sulfur compounds in a refinery
stream with hydrogen over a catalyst to form H.sub.2S is typically
called hydrodesulfurization. Hydrotreating is a broader term which
includes saturation of olefins and aromatics and the reaction of
organic nitrogen compounds to form ammonia. However
hydrodesulfurization is included and is sometimes simply referred
to as hydrotreating.
[0012] After the hydrotreating is complete, the product may be
fractionated or simply flashed to release the hydrogen sulfide and
collect the now desulfurized naphtha.
[0013] In addition to supplying high octane blending components the
cracked naphthas are often used as sources of olefins in other
processes such as etherifications. 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.
[0014] Various proposals have been made for removing sulfur while
retaining the more desirable olefins. Since the olefins in the
cracked naphtha are mainly in the low boiling fraction of these
naphthas and the sulfur containing impurities tend to be
concentrated in the high boiling fraction the most common solution
has been prefractionation prior to hydrotreating. The
prefractionation produces a light boiling range naphtha which boils
in the range of C.sub.5 to about 250.degree. F. and a heavy boiling
range naphtha which boils in the range of from about
250-475.degree. F.
[0015] The predominant light or lower boiling sulfur compounds are
mercaptans while the heavier or higher boiling compounds are
thiophenes and other heterocyclic compounds. The separation by
fractionation alone will not remove the mercaptans. However, in the
past the mercaptans were frequently removed by oxidative processes
involving caustic washing. A combination oxidative removal of the
mercaptans followed by fractionation and hydrotreating of the
heavier fraction is disclosed in U.S. Pat. No. 5,320,742. In the
oxidative removal of the mercaptans the mercaptans are converted to
the corresponding disulfides.
[0016] In addition to treating the lighter portion of the naphtha
to remove the mercaptans the lighter fraction traditionally has
been used as feed to a catalytic reforming unit to increase the
octane number if necessary. Also the lighter fraction may be
subjected to further separation to remove the valuable C.sub.5
olefins (amylenes) which are useful in preparing ethers.
[0017] Simultaneous treatment and fractionation of petroleum
products, including naphtha, especially fluid catalytically cracked
naphtha (FCC naphtha)is disclosed in U.S. Pat. Nos. 5,510,568;
5,597,476; 5,779,883; 5,807,477 and 6,083,378.
[0018] U.S. Pat. No. 5,510,568 for example discloses full boiling
range FCC naphtha hydrotreated in a splitter which contains a
thioetherification catalyst in the upper portion. Mercaptans in the
light fraction react with the diolefins contained therein
(thioetherification) to produce higher boiling sulfides which are
removed as bottoms along with the heavy (higher boiling) FCC
naphtha.
[0019] It has now been found that the light FCC naphtha cut in the
splitter just below the light fraction also contains mercaptans and
a significant amount of thiophenes. The mercaptans in this cut may
be removed by the thioetherification. The total sulfur content of
the thiophene cut is relatively low and more significantly does not
require as severe treatment as the sulfur compounds in the heavy
fraction to convert the thiophene to H.sub.2S, thus the olefins in
the thiophene cut are less likely to be hydrogenated.
[0020] It is an advantage of the present invention that the sulfur
may be removed from the light olefin portion of the stream to a
heavier portion of the stream without any substantial loss of
olefins. Substantially all of the sulfur in the heavier portion is
converted to H.sub.2S by hydrodesulfurization and easily distilled
away from the hydrocarbons. Also, the sulfur in the middle cut will
also be lowered.
SUMMARY OF THE INVENTION
[0021] Briefly the present invention is a process for removal of
sulfur from a full boiling range fluid cracked naphtha stream to
meet higher standards for sulfur removal, by splitting the light
portion of the stream and treating the components of the naphtha
feed with the process that preserves the olefinic while most
expediently removing the sulfur compounds.
[0022] Preferably the process comprises the steps of:
[0023] (a) separating the full boiling range cracked naphtha stream
into three fractions comprising a light cracked naphtha fraction,
preferably boiling in the range of C.sub.5 to about 150.degree. F.,
an intermediate cracked naphtha fraction preferably boiling in the
range of about 150 to about 250.degree. F. and a heavy cracked
naphtha preferably boiling in the range of about 250 to 450.degree.
F.;
[0024] (b) subjecting the heavy cracked naphtha to
hydrodesulfurization in a first hydrodesulfurization reactor
containing a hydrodesulfurization catalyst; and
[0025] (c) combining the effluent from the first
hydrodesulfurization reactor with the intermediate cracked naphtha
and subjecting the combined stream to hydrodesulfurization in a
second hydrodesulfurization reactor.
[0026] The advantage of this system is that the size and capital
investment of the hydrodesulfurization distillation column reactor
are reduced. The level of recombinant mercaptans coming for the
hydrodesulfurization distillation column is reduced. Finally there
is a potential savings in octane due to the milder treatment of the
olefin rich thiophene cut.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a simplified flow diagram of one embodiment of the
invention.
[0028] FIG. 2 is a simplified flow diagram of an alternative
embodiment having a having a thioetherification pretreatment.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The feed to the process comprises a sulfur-containing
petroleum fraction which boils in the gasoline boiling range. Feeds
of this type include light naphthas having a boiling range of about
C.sub.5 to 330.degree. F. and full range naphthas having a boiling
range of C.sub.5 to 420.degree. F. Generally the process is useful
on the naphtha boiling range material from catalytic cracker
products because they contain the desired olefins and unwanted
sulfur compounds. Straight run naphthas have very little olefinic
material, and unless the crude source is "sour", very little
sulfur.
[0030] The sulfur content of the catalytically cracked fractions
will depend upon the sulfur content of the feed to the cracker as
well as the boiling range of the selected fraction used as feed to
the process. Lighter fractions will have lower sulfur contents than
higher boiling fractions. The front end of the naphtha contains
most of the high octane olefins but relatively little of the
sulfur. The sulfur components in the front end are mainly
mercaptans and typical of those compounds are: methyl mercaptan
(b.p. 43.degree. F.), ethyl mercaptan (b.p. 99.degree. F.),
n-propyl mercaptan (b.p. 154.degree. F.), iso-propyl mercaptan
(b.p. 135-140.degree. F.), iso-butyl mercaptan (b.p. 190.degree.
F.), tert-butyl mercaptan (b.p. 147.degree. F.), n-butyl mercaptan
(b.p. 208.degree. F.), sec-butyl mercaptan (b.p. 203.degree. F.)
and 3-mercapto hexane (b.p. 135.degree. F.). Typical sulfur
compounds found in the heavier boiling fraction include the heavier
mercaptans, thiophenes sulfides and disulfides.
[0031] The reaction of these mercaptans with diolefins contained
within the naphtha is called thioetherification and the products
are higher boiling sulfides. A suitable catalyst for the reaction
of the diolefins with the mercaptans is 0.4 wt. % Pd on 7 to 14
mesh Al.sub.2O.sub.3 (alumina) spheres, supplied by Sud-Chemie,
designated as G-68C-1. Typical physical and chemical properties of
the catalyst as provided by the manufacturer are as follows:
2 TABLE I Designation G-68C-1 Form Spheres Nominal size 7 .times.
12 mesh Pd. wt. % 0.4 .+-. 0.03 Support High purity alumina
(99.0-99.5)
[0032] Another catalyst useful for the mercaptan-diolefin reaction
is Ni silica/alumina extrudates, supplied by Sud-Chemie, designated
as C46-7-03RS. Typical physical and chemical properties of the
catalyst as provided by the manufacturer are as follows:
3 TABLE II Designation 046-7-03 RS Form Extrudate Nominal size
{fraction (1/16)}" Ni wt. % 52 .+-. 4 Support Silica/Alumina
[0033] The hydrogen rate to the reactor must be sufficient to
maintain the reaction, but which is understood to be the
"effectuating amount of hydrogen" as that term is used herein. 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.
[0034] Another method suitable for removing mercaptans from a light
naphtha is the wet caustic washing process. In such a process the
light naphtha is contacted with caustic. The mercaptans are
solublized into the aqueous caustic phase. The mercaptans are then
reacted to form disulfides. The amount of mercaptan extracted is
limited by the solubility of the mercaptan in the caustic
solution.
[0035] Catalyst which are useful for the hydrodesulfurization
reaction 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.
[0036] The catalysts contain components from Group V, VIB, VIII
metals of the Periodic Table or mixtures thereof. The use of the
distillation system reduces the deactivation and provides for
longer runs than the fixed bed hydrogenation units of the prior
art. The Group VIII metal provides increased overall average
activity. Catalysts containing a Group VIB metal such as molybdenum
and a Group VIII 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 base such as
alumina, silica-alumina or the like. The metals are reduced to the
sulfide either in use or prior to use by exposure to sulfur
compound containing streams. The catalyst may also catalyze the
hydrogenation of the olefins and polyolefins 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.
[0037] Typical preferred conditions for the thiothetherification
reaction in a standard down flow fixed bed reactor include
temperatures in the range of 170 to 400.degree. F., pressures of
145 to 290 psia and liquid hourly space velocities of 1 to 10 vol.
of naphtha/volume of catalyst/hr.
[0038] The properties of a typical hydrodesulfurization catalyst
are shown in Table I below.
4 TABLE III Manufacture Criterion Catalyst Co. Designation C-448
Form Tri-lobe Extrudate Nominal size 1.2 mm diameter Metal, Wt. %
Cobalt 2-5% Molybdenum 5-20% Support Alumina
[0039] The catalyst typically is in the form of extrudates having a
diameter of 1/8, {fraction (1/16)} or {fraction (1/32)} inches and
an L/D of 1.5 to 10. The catalyst also may be in the form of
spheres having the same diameters. They may be directly loaded into
standard straight pass fixed bed reactors which include supports
and reactant distribution structures.
[0040] Reaction conditions for sulfur removal only in a standard
straight pass fixed bed reactor are in the range of 500-700.degree.
F. at pressures of between 400-1000 psig. Residence times expressed
as liquid hourly space velocity are generally typically between 1.0
and 10. The naphtha in the straight pass fixed bed reaction may be
in the liquid phase or gaseous phase depending on the temperature
and pressure, with total pressure and hydrogen gas rate adjusted to
attain hydrogen partial pressures in the 100-700 psia range. The
operation of the straight pass fixed bed hydrodesulfurization is
otherwise well known in the art.
[0041] Referring now to the FIG. 1 a simplified flow diagram in
schematic form of one embodiment is shown. The naphtha feed enters
a naphtha splitter 10 via flow line 101. A light naphtha containing
mostly C.sub.5's is taken as overheads via flow line 102. The light
naphtha also contains most of the mercaptans and little other
organic sulfur compounds. An intermediate naphtha boiling in the
range of C.sub.6 to about 300.degree. F. is taken via flow line 104
as a side draw. The intermediate naphtha containing predominantly
thiophenes along with some mercaptans. A heavy naphtha boiling in
the range of 300-450.degree. F. is taken as bottoms via flow line
106. The heavy naphtha may contain some thiophene but basically
contains the heavier boiling organic sulfur compounds which for a
better term are called other organic sulfur compounds.
[0042] The light naphtha in flow line 102 is treated by a wet
caustic wash to in reactor 20 remove the mercaptans and taken as
product via flow line 103 to be used primarily as feed to a
tertiary amyl methyl ether process. The bottoms in flow line 106 is
subjected to hydrodesulfurization in reactor 40 with hydrogen for
the process being added via flow line 107. In reactor 40
substantially all of the thiophene and most of the other organic
sulfur compounds are converted to hydrogen sulfide which can easily
be removed by flashing or distillation. The effluent from the
reactor 40 is combined with the intermediate naphtha in flow line
104 and fed to a second hydrodesulfurization reactor 30 where
hydrogen is added via flow line 105 for polishing. Basically the
thiophene in the intermediate naphtha and the remaining organic
sulfur compounds in the heavy naphtha are converted to hydrogen
sulfide. A combined naphtha product is taken from reactor 30 via
flow line 109
[0043] Referring now to FIG. 2 a second embodiment is shown. The
entire naphtha feed is fed via flow line 101 to a
thioetherification reactor 20 where the diolefins in the naphtha
react with the mercaptans to sulfides. The effluent from the
reactor 20 is fed via flow line 102 to the naphtha splitter 10
where the naphtha is split into three fractions. A light naphtha
containing mostly C.sub.5's is taken as overheads via flow line
103. Because the mercaptans have been removed in the
thioetherification reactor the light naphtha contains very little
organic sulfur. An intermediate naphtha boiling in the range of
C.sub.6 to about 300.degree. is taken via flow line 104 as a side
draw. The intermediate naphtha containing predominantly thiophenes
along with some mercaptans. A heavy naphtha boiling in the range of
300-450.degree. is taken as bottoms via flow line 106. The heavy
naphtha may contain some thiophene but basically contains the
heavier boiling organic sulfur compounds which for a better term
are called other organic sulfur compounds.
[0044] The bottoms in flow line 106 is subjected to
hydrodesulfurization in reactor 40 with hydrogen for the process
being added via flow line 107. In reactor 40 substantially all of
the thiophene and most of the other organic sulfur compounds are
converted to hydrogen sulfide which can easily be removed by
flashing or distillation. The effluent from the reactor 40 is
combined with the intermediate naphtha in flow line 104 and fed to
a second hydrodesulfurization reactor 30 where hydrogen is added
via flow line 105 for polishing. Basically the thiophene in the
intermediate naphtha and the remaining organic sulfur compounds in
the heavy naphtha are converted to hydrogen sulfide. A combined
naphtha product is taken from reactor 30 via flow line 109.
* * * * *