Note: Descriptions are shown in the official language in which they were submitted.
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(iACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a process for removing elemental
sulfur from fluids, particularly fuels such as gasoline transported in
a pipeline for the transportation of sour hydrocarbon streams.
Description of Related Art
It is well known that elemental sulfur and other sulfur
compounds contained in hydrocarbon streams is corrosive and damaging
to metal equipment, particularly copper and copper alloys. Sulfur and
sulfur compounds may be present in varying concentrations in the
refined fuels and additional contamination may take place as a conse-
quence of transporting the refined fuel through pipelines containing
sulfur contaminants resulting from the transportation of sour hydro-
carbon streams such as petroleum crudes. The sulfur has a particu-
larly corrosive effect on equipment such as brass valves, gauges and
in-tank fuel pump copper commutators.
Various techniques have been reported for removing elemental
sulfur from petroleum products. For example U.S. Patent 4,149,966
discloses a method for removing elemental sulfur from refined hydro-
carbon fuels by adding an organo-mercaptan compound and a copper
compound capable of forming a soluble complex with said mercaptan and
said sulfur and contacting said fuel with an adsorbent material to
remove the resulting copper complex and substantially ail the a
elemental sulfur.
U.S. Patent 4,908,122 discloses a process far sweetening a
sour hydrocarbon fraction containing mercaptans by contacting the
hydrocarbon fraction in the presence of an oxidizing agent with a
catalytic composite, ammonium hydroxide and a quaternary ammonium salt
other than hydroxide.
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U.S. Patent 3,185,641 describes a method for removing
elemental sulfur from a liquid hydrocarbon which comprises contacting
with solid sodium hydroxide a hydrocarbon stream having dissolved
therein at least 7.6 parts by weight of water per part of sulfur
contained therein to yield both a hydrocarbon phase and an aqueous
phase. The method is claimed to be effective and convenient for
treating gasoline containing from trace to more than 25 ppm sulfur
employing temperatures as high as about 140°F (60°C).
U.S. Patent 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.
U.S. Patent 2,460,227 discloses a method for removing
elemental sulfur from petroleum fractions, such as gasoline, by
contacting the petroleum fraction with an aqueous solution containing
an alkali metal hydroxide, an aromatic mercaptan and a reducing
compound such as sodium monosulfide to limit the oxidation and conse-
quent loss of the aromatic mercaptan.
SUMMARY OF THE INDENTION
The present invention provides a process for removing
elemental sulfur from fluids such as hydrocarbon fuels, fuel blending
components such as octane improvers, liquified petroleum gas (LPG),
solvents and other petroleum streams transported in a pipeline for the
transportation of sour hydrocarbon streams, comprising contacting the
sulfur-containing fluid with an inorganic caustic material, water, an
aliphatic mercaptan and optionally a sulfide to form an aqueous layer
containing polysulfides and a fluid layer having a reduced elemental
sulfur level. The fluid layer is decanted from the aqueous layer
leaving a treated product having a low residual elemental sulfur
content.
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DETAILED DESCRIPTION OF THE INVENTION
The inorganic caustic material which is employed in this
invention includes alkali metal or ammonium hydroxides having the
formula MOH wherein M is selected from the group consisting of
lithium, sodium, potassium, NH4 or mixtures thereof. M is preferably
sodium or potassium.
The sulfide which is employed in this invention includes
mono sulfides and polysulfides of metals from Groups I and II of the
Periodic Table. Examples of sulfides include Na2S, K2S, LizS, NaHS,
(NH4)2S, and the like. Na2S is preferred. The sulfide in caustic
reacts with the elemental sulfur in the fluid to be treated to form
polysulfides in caustic. The sulfide may be present in a convenient
source of caustic such as white liquor from paper pulp mills.
Aliphatic mercaptans are employed in the process of the
invention. These mercaptans in the presence of caustic form a sulfur
complex which transfers easily into the Fuel to react with the
elemental sulfur, thereby accelerating its removal. Aliphatic
mercaptans have been found to be more effective than aromatic
mercaptans for elemental sulfur removal from fluids such as gasoline.
The aliphatic mercaptans which may be used include a wide variety of
compounds having the general formula RSH, where R represents an a
organic radical which may be alkyl, alkenyl, cycioalkyl or cyclo-
alkenyl having from 1 to about 10 carbon atoms. Thus, the radical may
be, for example methyl, ethyl, n-propyl, i-propyi, n-butyl, i-butyl,
sec-butyl, t-butyl, amyl, n-octyl, cyclohexyl, n-hexyl, n-heptyl,
n-octyl, cycloheptyl, cyclo-octyl, n-nonyl, n-decyl and the like.
Preferably, RSH is an alkyl mercaptan containing 2 to 5 carbon atoms.
Most preferably RSH is n-propyl mercaptan.
Alcohols such as methanol, ethanol, propanol, ethylene
glycol, propylene glycol and the like may also be added to the mixture
which is contacted with the fluid to be treated. The amount of
alcohol used may vary within wide limits. In the case of methanol,
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for example, from 0 to about 90 volume percent of the water may be
replaced with alcohol.
The fluids which are treated in accordance with the inven-
tion include fluids containing elemental sulfur where the elemental
sulfur is detrimental to the performance of the fluid. The invention
is particularly applicable to those liquid products, such as gasoline,
which have become contaminated with elemental sulfur as a result of
being transported in a pipeline previously used to transport sour
hydrocarbon streams such as petroleum crudes.
The fluids treated in accordance with the invention include
a wide variety of petroleum fuels and particularly refined hydrocarbon
fuels such as gasoline, jet fuel, diesel fuel and kerosene.
Other fluids include ethers used to improve the octane
- ratings 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, isopropyl tertiary-amyl ether. Mixtures of these ethers
and hydrocarbons may be treated in accordance with the invention.
Fluids containing quantities of elemental sulfur as high as
100 mg, or higher, sulfur per liter, more usually from about 10 to
about 60 mg per liter, can be effectively treated in accordance with
this invention to reduce the sulfur contamination to about 5 mg sulfur
per liter, preferably 3 mg sulfur per liter or lower.
In general, the process of the invention involves the
addition to the fluid to be treated of effective amounts of caustic,
water, sulfide, aliphatic mercaptan and optionally alcohol. The
mixture is allowed to settle so as to form an aqueous layer containing
metal polysulfides and a clear fluid layer having a reduced elemental
sulfur level. Contact with the aliphatic mercaptan results in a clear
fluid layer having a reduced elemental sulfur level and containing
soluble polysulfide reaction products which are relatively non-
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corrosive. The treated fluid may be recovered by decantation. The
recovered aqueous layer may be recycled back to the mixing zone for
contact with the fluid to be treated or it may be discarded or used,
for example, as a feedstock to pulping paper mills, such as those
employing the Kraft pulp mill process.
The treating conditions which may be used to carry out the
present invention are conventional. Contacting of the fluid to be
treated is effected at ambient temperature conditions, although higher
temperatures up to 100°C or higher may be employed. Substantially
atmospheric pressures are suitable, although pressures may, for
example, range up to 1000 psig. Contact times may vary widely
depending on the fluid to be treated, the amount of elemental sulfur
therein and the treating materials used. The contact time will be
chosen to effect the desired degree of elemental sulfur conversion.
The reaction proceeds relatively fast, usually within several minutes,
depending on solution strengths and compositions. Contact times from
30 seconds to a few hours may be employed.
The reactants may be dispersed within the fluid to be
treated using any suitable mixing device which will provide adequate
mixing with the fluid. Thereafter the mixture is allowed to settle to
produce the aqueous and fluid layers.
The proportion of water, caustic, sulfide and aliphatic
mercaptan to be mixed may vary within wide limits. Typically, the
aqueous treating solution contains caustic in the range of 0.01 to
20M, the sulfide concentration is from 0 to 20M. The amount of
aliphatic mercaptan which is added may range from 0.1 to about 2 moles
of aliphatic mercaptan per mole of elemental sulfur present in the
fluid to be treated. The relative amount of aqueous treating solution
containing caustic, metal sulfide and aliphatic mercaptan and the
fluid to be treated may also vary within wide limits. Usually about
0.05 to 10, more usually, 0.1 to 0.3 volumes of aqueous treating
solution will be used per volume of fluid to be treated.
i
The following examples are illustrative of the invention.
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Example 1
In this Example the following solutions were prepared.
Solution A: 20g rsodium hydroxide -E 24g sodium sulfide (9H20) + 0.53
g elemental sulfur in 100 ml water (5M NaOH, lOM Na2S, ,
0.53 wt% S)
Solution B: 20g sodium hydroxide + 24g sodium sulfide (9H20) in 100
ml water (5M NaOH, lOM Na2S).
Solution C: 20g sodium hydroxide in 100 ml water (5M NaOH)
Solution D: 50 mi of saturated sodium hydroxide in water + 12g of
sodium sulfide (9H20).
Example 2
Into a beaker were added 100 ml of pipelined gasoline having
an elemental sulfur level of 30 mg/L elemental sulfur (Mercury Number
Method; UOP Method 286-59). The gasoline was stirred for 1 hour with
50 ml of Solution A, allowed to settle and thereafter decanted to
produce a treated gasoline having an elemental sulfur level of 7 mg/L.
Exam~l a 3
Into a beaker were added 100 ml of pipelined gasoline having
an elemental sulfur level of 44 mg/L elemental sulfur. The gasoline
was stirred for 1 hour with 25 ml of Solution A and 25 ml of Solution
B, allowed to settle and thereafter decanted to produce a treated
gasoline having an elemental sulfur level of 4 mg/L. The treated
gasoline was treated again as above in 'this example to produce a
gasoline having an elemental sulfur level of 3 mg/L.
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Example 4
100 ml of the pipelined gasoline of Example 3, 25 ml of
Solution A and 25 ml of Solution C were mixed for 1 hour. The mixture
was then allowed to settle and the gasoline removed by decantation.
The treated gasoline had an elemental sulfur level of 3 mg/L, showing
that dilution with caustic still achieved significant sulfur removal.
Example 5
100 ml of the gasoline of Example 3 and 50 ml of Solution C
were mixed for 1 hour. The mixture was then allowed to settle and the
treated gasoline removed by decantation. The treated gasoline had an
elemental sulfur level of 41 mg/L, showing that caustic alone does not
remove significant amounts of elemental sulfur.
Example 6
100 ml of the gasoline of Example 3 and 50 ml of aqueous
solution containing 12g of sodium sulfide (9H20) (10M) were mixed for
1 hour. The mixture was then allowed to settle and then the treated
gasoline removed by decantation. The 'treated gasoline had an elemen-
tal sulfur level of 30 mg/L, showing that sulfide alone is not very
effective for removing elemental sulfur.
Example 7
100 ml of the gasoline of Example 3 and 50 ml of solution D
were mixed for 24 hours. The mixture was then allowed to settle and
then the treated gasoline removed by decantation. The treated
gasoline had an elemental sulphur of 3 mg/L, showing that addition of
elemental sulphur in the aqueous phase is not essential to remove 'the
elemental sulphur from the gasoline.
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Example ~
This Example compares the effectiveness of aliphatic
mercaptan and aromatic mercaptan for the removal of elemental sulfur
from gasoline.
A number of 100 ml samples of gasoline containing 33 mg per
liter elemental sulfur (Polarograph Method) were each stirred for two
minutes in a Eberbach Shaker with 30 ml of a treating solution
containing either a mixture of 30 ml of pulp mill white liquor and 2.0
wtf° of n-propyl mercaptan (Solution 1) or a mixture of 30 m~l of pulp
mill white liquor and 2.0 wt% of thiophenol (Solution 2). The pulp
mill white liquor contained 30g/L sodium sulfide and 100 g/L sodium
hydroxide and was made by heating 146 g of caustic and 24 g of
elemental sulfur in one liter of water at 190°F. The two treating
solutions were repeatedly used to treat fresh samples of gasoline.
The results shown in the following Table demonstrate that aliphatic
mercaptan is more effective for a longer period of time in removing
elemental sulfur from gasoline.
Elemental Sulfur Level of Gasoline After Contact
with Treating Solution, mg/L
Gasoline Sample Solution 1 Solution
2
1 1 19
2 0.5 -
3 0.5 24
4 0.5 -
1 20
3
26
g 5 -
6 26
7 24
11 11 28
12 11 -
13 12 27
14 13 -
16 24
Avera a 6 24
