Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR REDUCING THE LEVEL OF
ELEMENTAL SULFUR IN HYDROCARBON STREAMS
FIELD OF THE INVENTION
[0001] This invention relates to a process for reducing the level of
elemental sulfur
and organic sulfur pick-up by refined hydrocarbon streams such as gasoline,
diesel, jet
fuel, kerosene or fuel additives such as ethers or iso-octane that are
transported
through a pipeline used to transport various sulfur-containing petroleum
streams. The
oxygen level of the hydrocarbon stream of interest to be pipelined as well as
the
oxygen level in at least the first hydrocarbon stream sequenced immediately
ahead of
the hydrocarbon stream of interest is reduced.
BACKGROUND OF THE INVENTION
100021 It is well known that elemental sulfur in hydrocarbon streams, such
as
petroleum streams, is corrosive and damaging to metal equipment, particularly
to
copper and copper alloys. Sulfur and sulfur compounds may be present in
varying
concentrations in refined petroleum streams, such as in gasoline and
distillate boiling
range streams. Additional contamination will typically take place as a
consequence of
transporting the refined stream through pipelines that contain sulfur
contaminants
remaining in the pipeline from the transportation of sour hydrocarbon streams,
such as
petroleum crudes. The sulfur has a particularly corrosive effect on equipment
such as
brass valves, gauges and in-tank fuel pump copper commutators.
[00031 The total sulfur in gasoline after 2005 will be limited to less than
30 wppm
while the total sulfur in diesel after 2006 will be limited to a maximum of 15
wppm.
Elemental and organic sulfur contaminants that are picked-up in the pipeline
by
gasoline and diesel products will adversely affect their ability to meet the
ultra low
sulfur specifications. Organic sulfur pick-up is any non-elemental sulfur
component
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in the hydrocarbon stream that was not present in the hydrocarbon product
stream
prior to injecting it into the pipeline.
[0004] Various techniques have been reported for removing elemental sulfur
from
petroleum products. For example, U.S. Patent No. 4,149,966 discloses a method
for
removing elemental sulfur from refined hydrocarbon fuels by adding an organo-
mercaptan compound plus a copper compound capable of forming a soluble complex
with the mercaptan and sulfur and contacting the fuel with an adsorbent
material to
remove the resulting copper complex and substantially all the elemental
sulfur.
[0005] U.S. Patent No. 4,011,882 discloses a method for reducing sulfur
contamination of refined hydrocarbon fluids transported in a pipeline for the
transportation of sweet and sour hydrocarbon fluids by washing the pipeline
with a
wash solution containing a mixture of light and heavy amines, a corrosion
inhibitor, a
surfactant and an alkanol containing from 1 to 6 carbon atoms.
[0006] U.S. Patent No. 5,618,408 teaches a method for reducing the amount
of
sulfur and other sulfur contaminants picked-up by refined hydrocarbon
products, such
as gasoline and distillate fuels, which are pipelined in a pipeline used to
transport
heavier sour hydrocarbon streams. The method involves controlling the level of
dissolved oxygen in the refined hydrocarbon stream that is to be pipelined.
[0007] The removal of elemental sulfur from pipelined fuels is also
addressed in
U.S. Patent No. 5,250,181 which teaches the use of an aqueous solution
containing a
caustic, an aliphatic mercaptan, and optionally a sulfide to produce an
aqueous layer
containing metal polysulfides and a clear fluid layer having a reduced
elemental sulfur
level. U.S. Patent No. 5,199,978 teaches the use of an inorganic caustic
material, an
alkyl alcohol, and an organo mercaptan, or sulfide compound, capable of
reacting
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with sulfur to folin a fluid-insoluble polysulfide salt reaction product at
ambient
temperatures.
[0008] While such methods have varying degrees of success, there still
exists a
need in the art for reducing elemental and organic sulfur pick-up by
hydrocarbon
products when transported in pipelines. Reducing the elemental and organic
sulfur
pick-up in products transported in the pipelines reduces the treating
requirements as
taught in U.S. Patent No. 5,250,181. It may even alleviate these requirements
if the
elemental and organic sulfur pick-up is sufficiently low.
SUMMARY OF THE INVENTION
[0009] In accordance with the present invention, there is provided a
process for
reducing the level of sulfur picked-up in a hydrocarbon stream of interest
being
transported in a pipeline that is used to transport various sulfur-containing
petroleum
streams, which process comprises: (i) reducing the level of oxygen to less
than 30
wppm in the hydrocarbon stream of interest to be transported through a
pipeline; and
(ii) reducing the level of oxygen to less than 30 wppm in at least the first
hydrocarbon
stream transported in the pipeline immediately ahead of the transport of said
hydrocarbon stream of interest.
[0010] In a preferred embodiment of the present invention the oxygen level
in both
the hydrocarbon stream of interest and at least the first hydrocarbon stream
transported immediately ahead of the said hydrocarbon stream of interest is
reduced to
less than 10 wppm and a most preferably to less than 1 wppm.
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DETAILED DESCRIPTION OF THE INVENTION
[0011] Hydrocarbon streams that are treated in accordance with the present
invention are any petroleum or chemical streams that can be transported via a
pipeline used to transport various sulfur-containing petroleum streams. Such
streams will generally contain from 10 wppm to 50 wppm sulfur and they will
typically pick-up additional quantities of elemental sulfur as high as 1000 mg
sulfur
per liter, typically from 10 to 100 mg per liter, more typically from 10 to 60
mg per
liter, and most typically from 10 to 30 mg per liter. In addition to elemental
sulfur
such streams will also typically pick-up organic sulfur as high as 100 mg
sulfur per
liter, typically from 1 to 50 mg per liter and more typically from 1 to 20 mg
per
liter. These streams can be effectively treated by any conventional sulfur-
reduction
techniques to reduce the elemental and organic sulfur contamination to less
than 10
mg per liter, preferably to less than 1 mg sulfur per liter, or lower.
Hydrocarbon
streams transported through pipelines are those streams that have become
contaminated with elemental sulfur and/or organic sulfur contaminants as a
result
of being transported in a pipeline that was previously used to transport sour
hydrocarbon streams, such as sour petroleum crudes, sour condensates or
products
containing high sulfur levels. Residual H2S and organic sulfur from the sour
crudes
will contaminate the pipeline. Non-limiting examples of such hydrocarbon
streams
that can be treated in accordance with the present invention include gasoline,
jet
fuel, diesel fuel, kerosene and dialkyl ethers. Alkyl ethers and iso-octane
are
typically used to improve the octane rating of gasoline. These ethers are
typically
dialkyl ethers having 1 to 7 carbon atoms in each alkyl group. Illustrative
ethers
are methyl tertiary-butyl ether, methyl tertiary-amyl ether, methyl tertiary-
hexyl
ether, ethyl tertiary-butyl ether, n-propyl tertiary-butyl ether, and
isopropyl tertiary-
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amyl ether. Mixtures of these ethers and hydrocarbon streams may also be
treated
in accordance with this invention.
[0012]
Preferred are refined hydrocarbon streams, particularly those wherein the
elemental and organic sulfur picked-up is detrimental to the performance of
the
intended use of the hydrocarbon stream. The preferred streams to be treated in
accordance with the present invention are naphtha boiling range streams that
are
also referred to as gasoline boiling range streams and distillate boiling
range
streams that are also referred to as diesel boiling range streams. Naphtha
boiling
range streams can comprise any one or more refinery streams boiling in the
range
from 10 C to 230 C, at atmospheric pressure. The naphtha stream generally
contains cracked naphtha that typically comprises fluid catalytic cracking
unit
naphtha (FCC catalytic naphtha, or cat cracked naphtha), coker naphtha,
hydrocracker naphtha, resid hydrotreater naphtha, debutanized natural gasoline
(DNG), and gasoline blending components from other sources from which a
naphtha boiling range stream can be produced. FCC catalytic naphtha and coker
naphtha are generally more olefinic naphthas since they are products of
catalytic
and/or thermal cracking reactions. Hydrocarbon streams boiling in the
distillate
range include diesel fuels, jet fuels, heating oils, and lubes. Such streams
typically
have a boiling range from 150 C to 600 C, preferably from 175 C to 400 C.
[0013] As previously mentioned, such hydrocarbon streams are often
transported great distances via a network of pipelines. These pipelines can
often
transport several hundred thousand barrels of different types of petroleum
fluids
each day. Each type of petroleum fluid is generally transported simultaneously
with one or more other types of petroleum fluids, either upstream, downstream,
or
both through the pipeline. Because a variety of petroleum fluids (hydrocarbon
streams) having various ranges of sulfur are transported through a given
pipeline
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each day, an undesirable amount of elemental and organic sulfur is picked-up
by a
less sulfur tolerant petroleum fluid, such as gasoline or diesel, from an
earlier
transported dirtier fluid, such as a crude oil, condensate or high sulfur
product.
[0014] It has been found that reducing the oxygen level in the hydrocarbon
stream of interest will result in a lower level of sulfur pick-up when that
fluid of
interest is transported in a pipeline. There still remains a problem because
merely
reducing the oxygen level in the hydrocarbon stream of interest may not result
in a
desired reduction of sulfur pick-up. In accordance with the present invention
it has
been found by the inventor hereof that not only must the oxygen level be
reduced in
the hydrocarbon stream of interest before being transported via pipeline, but
that is
preferred that at least the first and up to the first to third hydrocarbon
stream
immediately ahead of the hydrocarbon stream of interest should also have the
oxygen content reduced as well. It is most preferred that the three, more
preferably the two, and most preferably the one hydrocarbon stream immediately
transported ahead of the hydrocarbon stream of interest have its oxygen level
reduced. By reduced oxygen level we mean that the oxygen level in both the
hydrocarbon stream of interest and the hydrocarbon streams ahead of the said
hydrocarbon stream of interest, will be reduced to less than 30 wppm oxygen,
preferably less than 10 wppm oxygen, and more preferably to less than 1 wppm
oxygen. By oxygen we mean dissolved molecular oxygen and not atomic oxygen
that are part of chemical compounds.
[0015] Any suitable method can be used to reduce the oxygen level of the
hydrocarbon streams. Non-limiting examples of such methods include the use of
mercaptans, nitrogen purging, pulling a vacuum on the petroleum fluid, and
limiting the exposure of the petroleum fluid of interest to air.
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100161 It is preferred that a mercaptan be used and that it be mixed with
the
hydrocarbon stream of interest. It is also preferred that the mercaptan bean
organ
mercaptan that includes a relatively wide variety of compounds having the
general
formula RSH, where R represents an organic radical that may be alkyl, alkenyl,
cycloalkyl, cycloalkenyl, aryl or arylalkyl having from 1 to 16 carbon atoms.
Thus,
the radical may be, for example methyl, ethyl, n-propyl, I-propyl, n-butyl, 1-
butyl, sec-
butyl, t-butyl, amy, n-octyl, decyl, dodecyl, octadecyl, phenyl, benzyl, and
the like.
Most preferably, RSH is an alkyl mercaptan containing 2 to 5 carbon atoms. The
concentration of mercaptan that is added to the stream to be treated will be
an
effective amount. That is, an amount that will be capable of reducing the
level of
elemental sulfur by a predetermined amount, preferably by at least 80 wt.%,
more
preferably by at least 90 wt.%, and most preferably by at least 95 wt.%, of
the
elemental contaminants. This amount of mercaptan compound will typically range
from 1 wppm to 1000 wppm, preferably from 10 wppm to 100 wppm. In terms of
mole ratios, the amount of mercaptan compound will range from 0.2 to 20 moles
of
mercaptan per mole of elemental sulfur in the refined hydrocarbon stream, or
the
estimated moles of elemental sulfur that will be picked-up by the stream
during its
transport through a pipeline.
[0017] In general, the process of the present invention preferably involves
the
addition of an effective amount of mercaptan to the hydrocarbon stream to be
treated.
The mercaptan can be added at any time, such as prior to, during, or after the
hydrocarbon stream has been transported through a pipeline. It is preferred to
mix the
mercaptan with the stream prior to its being transported through a pipeline.
Conditions at which the stream is treated with the mercaptan will be
relatively mild
conventional conditions. That is, the mercaptan is added when either or both
the
product stream and mercaptan are at a temperature from ambient temperature (22
C)
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to 100 C, or higher. Substantially atmospheric pressures are suitable,
although
pressures may, for example, range up to 1000 psig. The contact time will be an
effective contact time. Contact times may vary widely depending on the
particular
hydrocarbon product stream to be treated, the amount of elemental sulfur
present, and
the particularly mercaptan used. The contact time will be chosen to affect the
desired
degree of mixing and subsequent elemental sulfur reduction. In most cases,
contact
times ranging from a few hours to a few days will be adequate. The reaction
proceeds
faster with aliphatic mercaptans than with aromatic mercaptans. Lower carbon
number mercaptans will react faster than the higher carbon number mercaptans.
[0018] It is preferred that the mercaptan be adequately mixed with the
hydrocarbon product stream to be treated. For example, if the mercaptan is
added
prior to the product stream being pipelined, the transportation of the product
stream
through the pipeline will provide adequate mixing of the mercaptan with the
hydrocarbon product stream. If the mercaptan is added to the product stream
after it
is pipelined, then it is preferred to use a suitable mixing devise, such as a
static mixer
wherein the mercaptan is injected into a moving flow of hydrocarbon product
stream
prior to entry into the static mixer.
EXAMPLES
[0019] The following examples are illustrative of the invention and are not
to be
taken as limiting in any way.
EXAMPLE 1
[0020] A 5% H2S in N2 mixture was bubbled through four litres of crude at 4
ft3/hr
for approximately one hour in order to replace any H2S that may have evolved
from
the original crude sample. The H2S/crude mixture was then recycled overnight
at 10
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cc/min through a 0.75-inch OD x 18-inch long column of iron filings (-40 mesh)
to
simulate the crude cycle in a pipeline. The packed bed of iron filings was
used to
simulate the pipeline wall effects. The column was then subjected to a series
of
refined products to simulate the product cycle in a pipeline. The following
product
cycle was tested: (1) 300 cc of ultra low sulfur diesel (ULSD) initially
containing 0.5
mg/1 total sulfur and 0 mg/I of elemental sulfur (S ); (2) 1 litre of MTBE
initially
containing 9.3 mg/1 total sulfur and 0 mg/1 of elemental sulfur (S ); (3) four
litres of
ULSD initially containing 0.5 mg/1 total sulfur and 0 mg/1 of Sc); and (4)
four litres of
regular unleaded gasoline (RUL) initially containing 1.7 mg/1 total sulfur and
0 mg/1
of S . All products were first N2-purged to displace oxygen and then pumped
through
the column of iron filings on a once-through basis at 50 cc/min. Following the
product cycle the column of iron filings was then flushed with air-purged
toluene to
remove residual sulfur compounds from the iron filings. The total sulfur
content in
the total sample of RUL exiting the column was determined by ASTM D5453. The
S content in the total sample of RUL exiting the column was determined by
HPLC.
The total sulfur pick-up in the RUL was determined by the subtracting the
total sulfur
content in the RUL exiting the column minus the total sulfur content in the
original
RUL. The S pick-up was determined in a similar fashion. The organic sulfur
pick-
up in RUL was determined by subtracting the total sulfur pick-up minus the S
pick-
up. The sulfur pick-up in ULSD was determined by the same methodology
described
above for RUL.
EXAMPLE 2
100211 A 5% H2S in N2 mixture was bubbled through four litres of crude at 4
ft3/hr
for approximately one hour in order to replace any H2S that may have evolved
from
the original crude sample. The H2S/crude mixture was then recycled overnight
at 10
cc/min through a 0.75-inch OD x 18-inch long column of iron filings (-40 mesh)
to
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simulate the crude cycle in a pipeline. The packed bed of iron filings was
used to
simulate the pipeline wall effects. The column was then subjected to a series
of
refined products to simulate the product cycle in a pipeline. The following
product
cycle was tested: (1) 300 cc of ultra low sulfur diesel (ULSD) initially
containing 0.5
mg/1 total sulfur and 0 mg/1 of elemental sulfur (S ); (2) 1 litre of MTBE
initially
containing 9.3 mg/1 total sulfur and 0 mg/1 of Sc); (3) four litres of ULSD
initially
containing 0.5 mg/1 total sulfur and 0 mg/1 of S'; and (4) four litres of
regular
unleaded gasoline (RUL) initially containing 1.7 mg/1 total sulfur and 0 mg/1
of S .
The ULSD and RUL products were first N2-purged to displace oxygen and then
pumped through the column of iron filings on a once-through basis at 50
cc/min. The
MTBE was first air-purged to saturate the product with oxygen and then pumped
through the column of iron filings on a once-through basis at 50 cc/min.
Following
the product cycle the column of iron filings was then flushed with air-purged
toluene
to remove residual sulfur compounds from the iron filings. The total sulfur
content in
the total sample of RUL exiting the column was determined by ASTM D5453. The
S content in the total sample of RUL exiting the column was determined by
HPLC.
The total sulfur pick-up in the RUL was determined by the subtracting the
total sulfur
content in the RUL exiting the column minus the total sulfur content in the
original
RUL. The S pick-up in RUL was determined in a similar fashion. The organic
sulfur pick-up in RUL was determined by subtracting the total sulfur pick-up
minus
the S pick-up. The sulfur pick-up in ULSD was determined by the same
methodology described above for RUL.
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TABLE 1
Effect of Nitrogen-Purging Products on Sulfur Pick-up
Example 1 Example 2
MTBE Purge N2 Air
ULSD Sulfur Pick-up
- Total Sulfur Pick-up, wppm 4
7
- S Pick-up, worn . 1 2
- Organic Sulfur Pick-up, wppm
3 5
RUL Sulfur Pick-up
- Total Sulfur Pick-up, wppm 5
9
- S Pick-up, wppm 1 2
- Organic Sulfur Pick-up, wppm
4 7
100221 Table 1 shows that very low sulfur pick-up values were found in ULSD
and RUL when both the products and the MTBE transported ahead of the products
were purged with nitrogen. However, a significant increase in the total sulfur
pick-
up (-, 80%) was observed in both the ULSD as well as the RUL when the MTBE
ahead of these products contained oxygen (i.e., air-purged). As shown in Table
1,
both the elemental and organic sulfur pick-up increased when the MTBE ahead of
these products contained oxygen.
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