U.S. patent application number 16/545001 was filed with the patent office on 2020-04-09 for process and apparatus for treating mercaptans in a naphtha boiling range feed.
The applicant listed for this patent is CHEVRON U.S.A. INC.. Invention is credited to Zunqing Alice HE, Stephen Edward LEICHTY, Cameron Adams McCORD.
Application Number | 20200109337 16/545001 |
Document ID | / |
Family ID | 70051987 |
Filed Date | 2020-04-09 |
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United States Patent
Application |
20200109337 |
Kind Code |
A1 |
HE; Zunqing Alice ; et
al. |
April 9, 2020 |
PROCESS AND APPARATUS FOR TREATING MERCAPTANS IN A NAPHTHA BOILING
RANGE FEED
Abstract
Processes and apparatuses are disclosed for treating a naphtha
boiling range stream containing mercaptan compounds. The process
includes oxidizing mercaptan compounds in the naphtha boiling range
stream to provide a mercaptan-depleted naphtha stream rich in
disulfide compounds; passing the mercaptan-depleted naphtha stream
rich in disulfide compounds to a naphtha splitter column; and
fractionating at least a portion of the mercaptan-depleted naphtha
stream rich in disulfide compounds into at least two streams, a
light naphtha stream lean in disulfide compounds and a heavy
naphtha stream rich in disulfide compounds. The heavy naphtha
stream rich in disulfide compounds may be passed to a
hydroprocessing unit to convert organic disulfides in the stream to
hydrocarbons and hydrogen sulfide. A heavy naphtha stream lean in
disulfide compounds can be recovered and routed as desired by the
refiner.
Inventors: |
HE; Zunqing Alice; (San
Rafael, CA) ; LEICHTY; Stephen Edward; (Boulder,
CO) ; McCORD; Cameron Adams; (Martinez, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CHEVRON U.S.A. INC. |
San Ramon |
CA |
US |
|
|
Family ID: |
70051987 |
Appl. No.: |
16/545001 |
Filed: |
August 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62742603 |
Oct 8, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 7/00 20130101; C10G
2300/1025 20130101; C10G 2300/202 20130101; C10G 2300/1044
20130101; C10G 27/04 20130101; C10G 53/14 20130101; C10G 2300/4018
20130101; C10G 2300/104 20130101 |
International
Class: |
C10G 53/14 20060101
C10G053/14; C10G 27/04 20060101 C10G027/04; C10G 7/00 20060101
C10G007/00 |
Claims
1. A process for treating a naphtha boiling range stream containing
mercaptan compounds, the process comprising: (a) oxidizing
mercaptan compounds in the naphtha boiling range stream to provide
a mercaptan-depleted naphtha stream rich in disulfide compounds;
(b) passing the mercaptan-depleted naphtha stream rich in disulfide
compounds to a naphtha splitter column; and (c) fractionating at
least a portion of the mercaptan-depleted naphtha stream rich in
disulfide compounds into at least two streams, a light naphtha
stream lean in disulfide compounds and a heavy naphtha stream rich
in disulfide compounds.
2. The process of claim 1, wherein the naphtha boiling range stream
comprises straight-run naphtha.
3. The process of claim 1, wherein oxidizing mercaptan compounds
comprises contacting the mercaptan compounds in the naphtha boiling
range stream with an oxidizing catalyst and oxygen.
4. The process of claim 3, wherein the oxidizing catalyst comprises
a metal component retained on an inorganic oxide support, wherein
the metal component is selected from one or more of vanadium,
chromium, manganese, cobalt, nickel, copper, and zinc.
5. The process of claim 4, wherein the metal component comprises
copper.
6. The process of claim 5, wherein the copper is present as copper
metal, copper oxide, copper sulfide, or a combination thereof.
7. The process of claim 4, wherein the metal component is present
in an amount of from 10 to 40 wt. %, based on a total weight of the
catalyst.
8. The process of claim 4, wherein the inorganic oxide support is
selected from alumina, silica, zirconia, titania, thoria, boria,
magnesia, chromia, stannic oxide, and combinations thereof.
9. The process claim 1, wherein conditions for oxidizing mercaptan
compounds include a pressure of from 101 to 2068 kPa; a temperature
of from 35.degree. C. to 200.degree. C.; and a liquid hourly space
velocity of from 1 to 10 h.sup.-1 (e.g., 1 to 5 h.sup.-1).
10. The process of claim 1, wherein mercaptan compounds in the
naphtha boiling range stream are depleted in the substantial
absence of any caustic solvent.
11. The process of claim 1, wherein the straight-run naphtha is
derived from crude oil or natural gas condensate resources.
12. An apparatus for treating a naphtha boiling range stream
containing mercaptan compounds, the apparatus comprising: (a) an
oxidation unit to provide a mercaptan-depleted naphtha stream rich
in disulfide compounds; and (b) a naphtha splitter column in
downstream communication with the oxidation unit to provide a light
naphtha stream lean in disulfide compounds in a naphtha splitter
overhead line and a heavy naphtha stream rich in disulfide
compounds in a naphtha splitter bottoms line.
13. The apparatus of claim 12, further comprising a hydroprocessing
unit in downstream communication with the naphtha splitter bottoms
line to provide a heavy naphtha stream lean in disulfide
compounds.
14. The apparatus of claim 12, further comprising a distillation
unit in upstream communication with the oxidation unit to provide a
naphtha boiling range stream.
15. The apparatus of claim 14, wherein the distillation unit is a
crude oil atmospheric distillation unit or a natural gas condensate
splitter column.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Application Ser. No. 62/742,603, filed Oct. 8,
2018.
FIELD
[0002] The present disclosure generally relates to processes and
apparatuses for treating petroleum fractions. More particularly,
the field relates to an improved process and apparatus for removing
mercaptan compounds from petroleum fractions such as naphtha.
BACKGROUND
[0003] Most distillate hydrocarbon streams produced from crude oil
contain some amount of sulfur in one form or another unless these
streams have been subjected to extensive sulfur removal procedures
such as hydrotreating. Often a major amount of this sulfur is
present in the form of mercaptans. Mercaptan sulfur content must be
reduced in the hydrocarbon distillate stream in order to meet
certain product specifications such as a limitation on the total
sulfur content of a product. It may also be desirable to remove
mercaptan compounds from a hydrocarbon stream for the purpose of
eliminating the rather malodorous mercaptan compounds and thereby
improve or reduce the odor associated with the hydrocarbon stream.
Another reason for removing mercaptan compounds from a hydrocarbon
stream would be to eliminate the passage of sulfur-containing
compounds into a catalyst bed which is sensitive to the presence of
sulfur. It may therefore be necessary to remove mercaptans from a
hydrocarbon distillate stream for the purpose of preserving the
activity of a catalyst employed in a downstream conversion
unit.
[0004] In many regions, naphtha is useful for motor fuel and
petrochemical feedstock and its further recovery is desirable. Due
to environmental concerns and newly enacted rules and regulations,
saleable fuels must meet lower and lower limits on contaminates,
such as sulfur and nitrogen. For example, the U.S. Environmental
Protection Agency (EPA) is implementing its Tier 3 Gasoline Sulfur
Program, a goal of which is to decrease the average gasoline sulfur
content from 30 parts per million (ppm) to 10 ppm across each
refining company's total annual output.
[0005] Hydroprocessing, such as hydrotreating, can be effective for
reducing the sulfur content of a naphtha boiling range fraction to
a desired sulfur level. In many cases, however, the existing
hydrotreating assets do not have sufficient available hydraulic
capacity to process the petrochemical naphtha stream and building a
grass roots hydrotreater for this purpose is a very expensive
option.
[0006] Sweetening of petroleum fractions, such as naphtha boiling
range hydrocarbons or other liquid hydrocarbons, that contain
mercaptans (or sour petroleum fractions) are well-developed
commercial processes commonly used in many petroleum refineries. In
the sweetening process, mercaptans contained in the feed
hydrocarbon stream (e.g., sour hydrocarbon stream) are converted to
disulfide compounds that remain in the hydrocarbon stream (e.g.,
sweetened hydrocarbon stream). Sweetening processes, therefore, do
not remove sulfur from the hydrocarbon stream but rather convert
the sulfur to an acceptable form. The sweetening process involves
an admixture of an oxygen-containing stream to the sour hydrocarbon
stream to supply the required oxygen. Typically, the admixture of
hydrocarbons and oxygen contacts an oxidation catalyst in an
aqueous alkaline environment to oxidize the mercaptans. Typically,
a caustic (e.g., an aqueous caustic solution) is combined with the
sour hydrocarbon stream to create the aqueous alkaline environment.
After contacting the oxidation catalysts, at least a portion of the
caustic is carried with the sweetened hydrocarbon stream and can be
problematic for further downstream processing. Current approaches
for removing caustic from sweetened hydrocarbon streams often
require additional downstream equipment and can be costly and/or
are relatively inefficient.
[0007] Accordingly, it is desirable to provide improved processes
and apparatuses for treating naphtha streams containing mercaptan
compounds. Additionally, it is desirable to provide such processes
and apparatuses that can sweeten naphtha streams without the need
for caustic and separate washing apparatus/procedures.
SUMMARY
[0008] In one aspect, there is provided a process for treating a
naphtha boiling range stream containing mercaptan compounds, the
process comprising: (a) oxidizing mercaptan compounds in the
naphtha boiling range stream to provide a mercaptan-depleted
naphtha stream rich in disulfide compounds; (b) passing the
mercaptan-depleted naphtha stream rich in disulfide compounds to a
naphtha splitter column; and (c) fractionating at least a portion
of the mercaptan-depleted naphtha stream rich in disulfide
compounds into at least two streams, a light naphtha stream lean in
disulfide compounds and a heavy naphtha stream rich in disulfide
compounds.
[0009] In another aspect, there is provided an apparatus for
treating a naphtha boiling range stream containing mercaptan
compounds, wherein the apparatus comprises: (a) an oxidation unit
to provide a mercaptan-depleted naphtha stream rich in disulfide
compounds; and (b) a naphtha splitter column in downstream
communication with the oxidation unit to provide a light naphtha
stream lean in disulfide compounds in a naphtha splitter overhead
line and a heavy naphtha stream rich in disulfide compounds in a
naphtha splitter bottoms line.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The FIG. 1s a process flow diagram illustrating an exemplary
process and apparatus of the present disclosure.
DETAILED DESCRIPTION
[0011] In this specification, the following words and expressions,
if and when used, have the meanings ascribed below.
[0012] The term "naphtha" or "naphtha boiling range" refers to
hydrocarbons boiling in a range of about 25.degree. C. to
190.degree. C. atmospheric equivalent boiling point (AEBP), as
determined by any standard gas chromatographic simulated
distillation method such as ASTM D2887, and can include one or more
C.sub.5-C.sub.10 hydrocarbons.
[0013] The term "light naphtha" refers to hydrocarbons boiling in a
range of about 25.degree. C. to 85.degree. C., and can include one
or more C.sub.5-C.sub.6 hydrocarbons.
[0014] The term "heavy naphtha" refers to hydrocarbons boiling in
the range of about 85.degree. C. to 190.degree. C. (e.g.,
110.degree. C. to 170.degree. C.), and can include one or more
C.sub.6-C.sub.10 hydrocarbons.
[0015] The modifying term "straight-run" is used herein having its
well-known meaning, that is, describing fractions derived directly
from the atmospheric distillation unit, optionally subjected to
steam stripping, without other refinery treatment such as
hydroprocessing, fluid catalytic cracking or steam cracking. An
example of this is "straight-run naphtha" and its acronym "SRN"
which accordingly refers to "naphtha" defined above that is derived
directly from the atmospheric distillation unit, optionally
subjected to steam stripping, as is well known. Straight-run
naphtha may also be derived from natural gas condensates.
[0016] The term "rich" refers to a stream exiting a vessel that has
a concentration of one or more compounds exceeding a stream
entering the vessel.
[0017] The term "lean" refers to a stream exiting a vessel that has
a concentration of one or more compounds less than a stream
entering the vessel.
[0018] The term "depleted" is synonymous with reduced from
originally present. For example, removing a substantial portion of
a material from a stream would produce a material-depleted stream
that is substantially depleted of that material.
[0019] The term "mercaptan" means thiol compounds of the formula
R--SH where R is a hydrocarbon group, such as an alkyl or aryl
group, that is saturated or unsaturated and optionally
substituted,
[0020] The term "disulfide" means compounds having the molecular
formula R--S--S--R' where R and R' are each, independently, a
hydrocarbon group, such as an alkyl or aryl group, that is
saturated or unsaturated and optionally substituted. Generally, the
term "disulfide" as used herein excludes carbon disulfide
(CS.sub.2).
[0021] The notation "C.sub.x" means hydrocarbon molecules that have
"x" number of carbon atoms, "C.sub.x" means hydrocarbon molecules
that have "x" and/or more than "x" number of carbon atoms, and
"C.sub.x-" means hydrocarbon molecules that have "x" and/or less
than "x" number of carbon atoms.
[0022] The term "communication" means that material flow is
operatively permitted between enumerated components.
[0023] The term "downstream communication" means that at least a
portion of material flowing to the subject in downstream
communication may operatively flow from the object with which it
communicates.
[0024] The term "upstream communication" means that at least a
portion of the material flowing from the subject in upstream
communication may operatively flow to the object with which it
communicates.
[0025] Numbers expressing quantities, percentages or proportions,
and other numerical values used in the specification and claims are
to be understood as being modified in all instances by the term
"about." The term "about" can be understood as within 10%, 5%,
2.5%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the reported numerical
value.
[0026] As depicted, process flow lines in the FIGURE can be
referred to interchangeably as, for example, lines, pipes, feeds,
gases, products, discharges, parts, portions, conduits or
streams.
[0027] The following description is merely exemplary in nature and
is not intended to limit the various embodiments or the application
and uses thereof. The FIGURE has been simplified by the deletion of
a large number of apparatuses customarily employed in a process of
this nature, such as vessel internals, temperature and pressure
control systems, flow control valves, recycle pumps, etcetera which
are not specifically required to illustrate the performance of the
invention.
[0028] With reference to the FIGURE, a feed 2 that is a crude oil
or a natural gas condensate stream containing a range of
hydrocarbons is passed to a distillation unit 10 where the feed is
separated into a light stream 3, a naphtha boiling range stream 5,
and/or one or more heavier or bottoms fractions. In embodiments
where the feed 2 is a crude oil, the distillation unit 10 may be an
atmospheric distillation unit. In embodiments where the feed 2 is a
natural gas condensate stream, the distillation unit 10 may be a
natural gas condensate splitter.
[0029] The feed in line 2 may be dried and/or pre-treated to reduce
and/or remove one or more of undesired components such as carbon
dioxide, mercury, and water prior to fractionation.
[0030] Naphtha boiling range streams typically contain one or more
mercaptan compounds. The mercaptans occurring in naphtha boiling
range streams are generally C.sub.1-C.sub.10 mercaptans (e.g.,
C.sub.1-C.sub.6 mercaptans). The mercaptans are generally
concentrated in the light fractions of the naphtha and more
precisely in the fraction with a boiling point of less than
120.degree. C. The mercaptan sulfur may be present in the naphtha
boiling range stream in an amount ranging from about 2 ppm to 300
wppm or more, depending on the particular stream to be treated.
[0031] Upon exiting the distillation unit 10, the
mercaptan-containing naphtha boiling range stream 5 is passed to an
oxidation unit 20 where mercaptan compounds in the naphtha stream
are converted to disulfide compounds. The flow direction in
oxidation unit 20 can be down flow or up flow. The naphtha stream 5
is mixed with an air or other oxygen-containing gas stream 7
supplied at a rate that supplies at least the stoichiometric amount
of oxygen necessary to oxidize the mercaptan compounds in the
naphtha boiling range stream 5 to disulfide compounds. The mole
ratio of oxygen to mercaptan sulfur may range from about 1:4 to
10:1 (e.g., about 1:1 to 10:1, or about 1:1 to 3:1). The oxidation
of the mercaptan compounds is promoted through the presence of a
catalytically effective amount of an oxidation catalyst capable of
functioning at the conditions found in the oxidation unit 20. The
oxidation unit 20 may be configured in a packed bed configuration
to ensure adequate mixing between the naphtha boiling range feed,
the catalyst, and the oxygen. The oxidation unit 20 may comprise a
cylindrical fixed bed of catalyst through which the reactants move
in a vertical direction.
[0032] The oxidation conditions utilized in oxidation unit 20 may
include a pressure of from about 101 to 2068 kPa (gauge) (15 to 300
psig), such as from 172 to 689 kPa (gauge) (25 to 100 psig); a
temperature of from 35.degree. C. to 200.degree. C. (e.g.
50.degree. C. to 150.degree. C.); and a liquid hourly space
velocity of from 1 to 10 h.sup.-1 (e.g., 1 to 5 h.sup.-1).
[0033] In an aspect, mercaptan compounds are depleted in the
naphtha boiling range stream in the substantial absence of any
caustic solvent, such as an aqueous solution of alkali metal
hydroxide (e.g., sodium hydroxide, potassium hydroxide).
[0034] Suitable oxidation catalysts are any known conventional
catalysts for oxidizing mercaptans to disulfides and can include
those which are comprised of a Group 5-12 metal component (e.g.,
one or more of vanadium, chromium, manganese, cobalt, nickel,
copper, zinc) retained on a refractory inorganic oxide support.
[0035] The inorganic oxide binder of the catalyst may comprise
materials such as alumina, silica, zirconia, titania, thoria,
boria, magnesia, chromia, stannic oxide, and the like as well as
combinations and composites thereof, for example silica-alumina,
alumina-zirconia, alumina-titania, aluminum phosphate, and the
like. Alumina is a preferred refractory inorganic oxide binder. As
is well known in the art, a precursor of the desired refractory
inorganic oxide may be used to form, bind, and/or otherwise prepare
the catalyst. Such binder precursors or sources may be converted
into a refractory inorganic oxide binder, for example, by
calcination. The alumina may be any of the various aluminum oxides,
hydroxides, and gels, including boehmite, pseudo-boehmite,
gibbsite, bayerite, and the like, especially transition and gamma
aluminas. Suitable aluminas are commercially available, for
example, under the trade names CATAPAL.COPYRGT. B and VERSAL.TM.
250.
[0036] The metal component of the catalyst may comprise a metal
selected from the group consisting of vanadium, chromium,
manganese, cobalt, nickel, copper, zinc, and combinations thereof.
In one embodiment, the metal component comprises copper. The metal
content of the catalyst can range from 10 to 40 wt. % (e.g., 15 to
30 wt. %) as the metal based upon the total weight of the
catalyst.
[0037] The metal component may be incorporated into the catalyst in
any suitable manner such as co-mulling, co-precipitation or
co-gellation with the carrier material, ion exchange, or
impregnation. The metal component may exist within the final
catalyst as a compound such as an oxide, sulfide, halide, or
oxyhalide, in chemical combination with one or more of the other
ingredients of the composite, or as an elemental metal. In an
embodiment where the metal component is copper, the metal component
may be present as copper metal, copper, oxide, copper sulfide, or a
combination thereof.
[0038] For practical applications, the catalyst is most preferably
used in particulate form, for example as pellets, extrudate,
spheres or granules, although other solid forms also are suitable.
Particle size of the catalyst is selected such that a bed of
catalyst particles is easily maintained in a suitable reactor for
the oxidation process but permits flow of the naphtha boiling range
through the bed without undesirable pressure drop. Preferred
average particle sizes are such that catalyst particles pass
through a 2-mesh screen but are retained on a 24-mesh screen (U.S.
Sieve Series) and more preferably pass through a 4-mesh screen but
are retained on a 12-mesh screen.
[0039] The oxidation catalyst may have a BET surface area in a
range of 30 to 300 m.sup.2/g (e.g., 50 to 200 m.sup.2/g).
[0040] In one embodiment, the oxidation catalyst may be a fresh or
spent sulfur sorbent having application in eliminating residual
sulfur from conventionally desulfurized reformer or isomerization
feed streams, such as described in U.S. Pat. No. 4,259,213.
[0041] The effluent from oxidation unit 20 comprises a
mercaptan-depleted naphtha stream rich in disulfide compounds.
Organic disulfides have higher boiling points than those of their
mercaptan precursors. Thus, mercaptans that typically boil in a
light naphtha fraction are converted in the oxidation unit 20 into
disulfides that typically boil in a heavy naphtha fraction.
[0042] The mercaptan-depleted naphtha stream rich in disulfide
compounds in line 11 is passed to a naphtha splitter column 30 in
which it is fractionated to provide a light naphtha stream lean in
disulfide compounds in a naphtha splitter overhead line 13 and a
heavy naphtha stream rich in disulfide compounds in a naphtha
splitter bottoms line 23. The light naphtha stream, typically a
C.sub.5-C.sub.6 or a C.sub.5-C.sub.7 stream, with reduced sulfur
content may be condensed and separated in a receiver with a portion
of the condensed liquid being sent in line 19 for blending to the
gasoline pool. Any light ends may be vented to an appropriate
combustion destination such as a furnace burner of a flare equipped
for streams with high levels of oxygen via line 17. The heavy
naphtha stream, typically comprising C.sub.7+ naphtha, is rich in
disulfide compounds, and may be taken from a bottoms outlet in the
naphtha splitter bottoms line 23 for further processing.
[0043] The naphtha splitter column 30 may be operated with a top
pressure of 69 to 448 kPa (gauge) (10 to 65 psig) and a bottom
temperature of 121.degree. C. to 232.degree. C. (250.degree. F. to
450.degree. F.). Alternatively, the naphtha splitter column 30 may
be operated at a vacuum. The naphtha splitter column 30 may include
a reboiler at a bottom of the column to vaporize and send a portion
of the heavy naphtha stream back to the bottom of the column.
[0044] The heavy naphtha stream rich in disulfide compounds in line
23 may be passed to a hydroprocessing unit to convert organic
disulfides in the stream to hydrocarbons and hydrogen sulfide. A
heavy naphtha stream lean in disulfide compounds can be recovered
and routed as desired by the refiner.
EXAMPLES
[0045] The following illustrative examples are intended to be
non-limiting.
Example 1
[0046] A mercaptan-containing whole straight-run naphtha (boiling
range of 30.degree. F.-330.degree. F.; API gravity of 62.5) mixed
with a selected air rate was flowed continuously through a 10 mL
reactor bed loaded with a spent copper-containing oxidation
catalyst that was previously used as an adsorbent in a sulfur guard
bed for a refinery process. The catalyst contained about 30 wt. %
copper and was prepared by co-mulling and impregnating an alumina
support with copper, as described in U.S. Pat. No. 4,259,213. The
unit was operated at various temperatures and liquid hourly space
velocities (LHSV) at a pressure of 65 psig. The results are
summarized in Table 1.
TABLE-US-00001 TABLE 1 SRN Treated Naphtha Feed Run 1 Run 2 Run 3
Run 4 Run 5 Sulfur as RSH, 20.66 Not De- 0.07 0.58 0.68 0.25 wppm
(ASTM tectable D3227) Process Conditions T, .degree. F. 210 210 230
230 230 LHSV, h.sup.-1 2.0 1.2 2.0 2.0 3.0 O.sub.2/RSH mole 1.5 1.5
1.5 0.75 0.75 ratio
[0047] As shown in Table 1, the treated naphtha products in Runs
1-5 contained less than 1 ppm mercaptans.
Example 2
[0048] A treated naphtha product prepared as described in Example 1
was then distilled into light (200.degree. F.-) and heavy
(200.degree. F.+) naphtha cuts. The physical properties and
composition of the light and heavy naphtha cuts are summarized in
Tables 2.
TABLE-US-00002 TABLE 2 Light Naphtha Heavy Naphtha Fraction
Fraction Cu Strip Corrosion.sup.(a) 1a 1a (ASTM D130) Ag Strip
Corrosion.sup.(b) 1 1 (ASTM D7667) Unwashed Gum, mg/100 mL 3.4
(ASTM D381) Washed Gum.sup.(c), mg/100 mL 0 (ASTM D381) Hydrocarbon
Class Distibution.sup.(d), vol % (Modified ASTM D6729) Aromatics
2.72 13.03 i-Paraffins 37.48 28.43 n-Paraffins 37.10 22.75
Naphthenes 22.56 32.08 Olefins 0.07 0.02 Oxygen 0.00 0.00
Unclassified 0.07 3.69 .sup.(a)A copper strip rating of 1a
indicates slight tarnish, almost the same as a freshly polished
strip. ASTM D4814 requires that fuels for automotive spark engines
have a copper strip corrosion maximum of 1. .sup.(b)A silver strip
rating of 1 indicates slight tarnish. ASTM D4814 requires that
fuels for automotive spark engines have a silver strip corrosion
maximum of 1. .sup.(c)ASTM D4814 requires that fuels for automotive
spark engines have a maximum solvent-washed gum content of 5 mg/100
mL. .sup.(d)Hydrocarbon class distribution was analyzed via
detailed hydrocarbon analysis using gas chromatography (GC-DHA) by
a method derived from the ASTM D6729 method. To improve
identifications of GC species, 60 meter high resolution dual
columns (one polar column and one non-polar column) were used.
Those peaks that were not identified were grouped in the
"Unclassified" category.
[0049] The GC-DHA analysis showed that very small amounts of
olefins were found in either the light or heavy treated naphtha.
This indicates the mercaptan oxidation process did not
dehydrogenate hydrocarbons to any substantial extent. Furthermore,
the heavy naphtha has a higher relative concentration of aromatics
as compared to the light naphtha. Most aromatics are higher boiling
than paraffins with the same carbon number. These results indicate
that the mercaptan oxidation process does not reveal any product
quality concerns nor require a need for additives in order meet US
EPA Tier 3 requirements for gasoline.
[0050] The thermal stability of disulfides in the light and heavy
naphtha cuts was determined at the naphtha splitter bottom
temperature. Disulfides are products from mercaptan oxidation and
can convert reversibly back to mercaptans at higher temperature.
Each cut was heated to 350.degree. F. in a Parr bomb type reactor
for one and four hours. Sulfur speciation studies using gas
chromatography sulfur chemiluminescence detection (GC-SCD)
indicated no detectable reappearance of any mercaptans in the light
and heavy naphtha cuts.
Example 3
[0051] Example 1 was repeated except that the whole straight-run
naphtha feed was a 300.degree. F.- cut from a blend of Canadian
condensates CFT and CRW. The feed contained 90.4 wppm of
C.sub.1-C.sub.9 mercaptans including cyclic and aromatic
mercaptans. The mercaptan conversion results for this "tough feed"
are summarized in Table 3.
TABLE-US-00003 TABLE 3 Treated Naphtha SRN Feed Run 6 Run 7 Run 8
Sulfur as RSH, wppm 90.4 Not Not Not (ASTM D3227) Detectable
Detectable Detectable Process Conditions T, .degree. F. 210 210 210
LHSV, h.sup.-1 1.2 2.0 3.0 O.sub.2/RSH mole ratio 0.75 0.75
0.75
[0052] The results show complete mercaptan conversion of the high
mercaptan content feed.
[0053] A treated naphtha product was then distilled into light
(200.degree. F.-) and heavy (200.degree. F.+) naphtha cuts. Both
cuts were tested for their thermal stability at 302.degree. F.
GC-SCD indicated no detectable reappearance of any mercaptans in
the light and heavy naphtha cuts.
Example 4
[0054] Example 1 was repeated except that a fresh copper-containing
oxidation catalyst was used. The test was conducted on a
conventional whole straight-run naphtha under the following
conditions:
[0055] Pressure=70 psig
[0056] Temperature=210.degree. F.
[0057] LHSV=1.2 h-1
[0058] O.sub.2/RSH mole ratio=3
[0059] Time=2 months
Complete mercaptan conversion was achieved during the run.
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