CA2456491C - Improved process for removing elemental sulfur from pipeline-transported refined hydrocarbon fuels - Google Patents

Abstract

A method for removing sulfur from a hydrocarbon stream, the method comprising: mixing said hydrocarbon stream with an aqueous-alkali or alcohol-alkali solution containing an alkali metal sulfide under effective conditions; separating the majority of the aqueous-alkali or alcohol-alkali solution from the hydrocarbon phase; and treating the recovered hydrocarbon phase containing a residual amount of entrained aqueous-alkali or alcohol-alkali solution in a packed bed of solids to produce a hydrocarbon product which is substantial free of elemental sulfur.

Description

IMPROVED PROCESS FOR REMOVING ELEMENTAL SULFUR
FROM PIPELINE-TRANSPORTED REFINED HYDROCARBON FUELS
FIELD OF THE INVENTION
[0001] The invention generally relates to methods and systems for reducing the sulfur level in elemental sulfur-containing hydrocarbon streams, especially hydrocarbon streams such as gasoline, diesel and jet fuel transported through crude pipelines. More specifically, one embodiment of the invention is directed to a method comprising mixing an elemental sulfur-containing hydrocarbon stream with an alkali solution containing an alkali metal sulfide. After adequately mixing the two phases, the majority of the alkali solution is separated from the hydrocarbon phase. The hydrocarbon phase, which contains a residual amount of entrained alkali solution, is then passed through a packed-bed of solids to extract the elemental sulfur from the fuel phase into the alkali phase containing the alkali metal sulfide. The alkali solution may be an aqueous-, an alcohol-alkali solution, or a mixture thereof.
BACKGROUND OF THE INVENTION

[0002] Elemental sulfur in hydrocarbon streams is corrosive and damaging to metal equipment, particularly copper and copper alloys found in motor vehicle gauges and in-tank fuel pumps. Elemental sulfur and sulfur compounds may be present in varying concentrations in refined petroleum streams such as gasoline, diesel and jet fuel. Additional contamination may typically occur as a consequence of transporting the refined fuel streams through crude pipelines that contain sulfur contaminants from sour hydrocarbon streams such as petroleum crudes. Often as much as 200 wppm elemental sulfur can be picked-up by refined products transported in crude pipelines.

[0003] Environmental regulations require lower future limits for sulfur in gasoline and other hydrocarbon fuels. For example, regulations in Canada require a sulfur reduction in gasoline to 1 SO wppm year pool average (YPA) by July 1, 2002 and 30 wppm YPA in January 2005. U.5. regulations require a sulfur reduction in gasoline to 30 wppm YPA in January 2005. Both Canada and the U. S. require additional sulfur reduction in diesel to 1 S wppm in 2007. In order to meet the legislated sulfur levels in fuel products the elemental sulfur picked-up in pipeline-transported products must be removed.
]0004] Various techniques have been reported for removing elemental sulfur from petroleum products. For example U.S. 4,149,966 discloses a method for removing elemental sulfur from refined hydrocarbon 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 all the elemental sulfur.
[0005] U.S. 4,908,122 discloses a process for 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.
[0006] U.S. 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).
[0007] U.S. 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.
[0008] U.S. 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 Iimit the oxidation and consequent loss of the aromatic mercaptan.
(0009] U.S. 5,160,045 to Falkiner et al, assigned to the same entity as the present invention, describes a method for reducing the elemental sulfur content of a hydrocarbon fuel that has been contaminated with elemental sulfur as a result of being transported in a pipeline used to transport sour hydrocarbon streams such as petroleum crudes. The disclosed method includes mixing the hydrocarbon fuel with water, inorganic caustic and a sulfide in amounts effective to form after completion of mixing an aqueous layer containing polysulfides and a hydrocarbon fuel layer having a reduced elemental sulfur level. The method further includes recovering the hydrocarbon fuel layer. Falkiner describes that the inorganic caustic can be NaOH, and the sulfide can be Na2S.
[0010] U.S. 5,674,378 to Kraemer et al, assigned to the same entity as the present invention, describes a method for removing elemental sulfur from hydrocarbon fuels. The Kraemer method includes contacting the hydrocarbon fuel with an immiscible treating solution comprising water or immiscible alcohol solution, caustic and sulfide or hydrosulf de to form a mixture in a mixer wherein the immiscible treating solution constitutes the continuous phase of the mixture and the elemental sulfur containing fuel constitutes the dispersed phase of the mixture. An organic mercaptan is added to the fuel prior to being mixed with the immiscible treating solution. The elemental sulfur is converted to polysulfides which are insoluble in the fuel but are soluble in the immiscible treating solution. The mixture is then passed to a liquid/liquid separation vessel wherein the mixture separates into two phases, a hydrocarbon fuel phase and an immiscible treating solution phase. The Kraemer patent describes that the mixer can have one or more mixing stages and can be a co-current mixer.
[0011 ] U. S. 5,250,181 to Falkiner et al, assigned to the same entity as the present invention, describes a process for reducing the elemental sulfur content of a hydrocarbon fuel comprising mixing the hydrocarbon fuel with water, inorganic caustic and an aliphatic mercaptan in amounts effective to form after completion of mixing an aqueous layer containing polysulfides and a layer having a reduced elemental sulfur level fuel and recovering the treated fuel.

-S-SUMMARY OF THE INVENTION
[0012] The present invention provides an improved method for reducing elemental sulfur and total sulfur levels to levels generally not readily achievable by prior art processes. The present invention method allows reduction of the total sulfur while also removing the elemental sulfur in refined fuel products that are transported via crude pipelines.
[0013] The invention relates to a process for removing elemental sulfur as well as reducing the total sulfur level in hydrocarbon fuel products that are transported via crude pipelines. One embodiment of the invention removes elemental sulfur from pipeline transported fuels to meet current and future corrosion and future low sulfur fuel product specifications. Generally, the invention includes mixing the sulfur containing hydrocarbon fuel with an alkali solution containing an alkali metal sulfide. The alkali solution can be an aqueous-alkali solution, an alcohol-akali solution or a mixture thereof. An aromatic mercaptan may be added to the aqueous-alkali solution or the hydro-carbon stream to further improve the overall process performance. The two phases can be mixed using any conventional mixing means which includes but is not limited to, mechanically-agitated tank mixers, in-line static mixers, in-line dynamic mixers and ultrasonic mixers. After adequately mixing the two phases, the majority of the aqueous-alkali solution is separated from the hydrocarbon phase. The hydrocarbon phase, which contains a residual amount of entrained alkali solution, is then passed through a packed bed of solids. The packed bed of solids facilitates the extraction of elemental sulfur from the fuel phase into the alkali phase containing the alkali metal sulfide.

[0014] In one embodiment of the invention a gasoline stream is contacted with an aqueous solution of sodium hydroxide and sodium sulfide. The method further comprises mixing said contacted gasoline stream and aqueous solution of sodium hydroxide and sodium sulfide at ambient temperature with a mechanically agitated tank to form an intimate gasoline/aqueous-alkali/alkali-metal mixture. The mixture is fed to a settler to separate said mixture into a caustic stream and an overhead gasoline stream. The overhead gasoline stream which contains a residual amount of entrained aqueous-alkali/alkali-metal solution is directed into a bed of sand. The bed of sand removes elemental sulfur from the gasoline as well as the entrained aqueous-alkali/alkali-metal solution.
[0015] One advantage of the present invention is that unlike prior art methods the present invention removes elemental sulfur without the formation of di-and tri-sulfides which are soluble in the fuel product. The present invention, unlike prior art, lowers the total sulfur level in the fuel.
[0016] Another advantage of the present invention over prior art methods is that the present invention can be used to completely extract elemental sulfur from fuels into the aqueous-alkali/alkali-metal-sulfide solution without the addition of heat. As a result, both the capital and operating costs of the present invention are generally lower.
[0017] Yet another advantage of the present invention is that it provides a treated product without picking up free water from the recirculating alkaline solution because the present invention method can be operated at ambient conditions. Operating at higher than ambient temperature generally results in free water formation in the product when it is cooled in the product tanks.

Processes that operate at higher than ambient temperatures require a product dryer such as a salt drier for example, to remove free water. Product dryers increase both the operating and capital cost of the process. Other advantages exist and will become apparent from the following detailed description of the preferred embodiments of the invention.
DESCRIPTION OF THE FIGURES
[0018] Figure I shows the elemental sulfur content in a gasoline stream as it is processed through a mixer, a caustic settler, and a caustic sand filter, accord-ing to one embodiment of the present invention.
[0019] Figure 2 is a simplified schematic of an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
(0020] The invention relates to a method for removing elemental sulfur and reducing the total sulfur in fuel products, especially in pipeline-transported hydrocarbon fuel products. The method comprises contacting the fuel product with an immiscible treating solution comprising water or immiscible alcohol, alkali-metal, and a sulfide or a hydrosulfide. An aromatic mercaptan may be added to either the aqueous-alkali solution, alcohol-alkali solution or the hydrocarbon stream to improve the performance. Examples of alkali-metal include but are not limited to, sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH). An immiscible alcohol can be an alcohol, a mixture of alcohols or a mixture of alcohol and water which is _g_ immiscible in the fluid to be treated. Examples of immiscible alcohols include but are not limited to, methanol, ethanol, propanol and butanol. The hydrocarbon fuel product and the aqueous-alkali or alcoholic-alkali solution can be blended by any suitable conventional mixing device. Preferably, the mixing is accomplished in a continuous mode without the use of any moving mechanical stirring devices, for example, by combining the two streams and directing the combined stream through a static inline mixer. Other examples of mixing devices include but are not limited to, mechanically agitated tanks, dynamic in-line mixers and ultrasonic mixers. After adequately mixing the two phases, the majority of the aqueous-alkali or alcohol-alkali solution is separated from the hydrocarbon phase. The hydrocarbon phase, which contains a residual amount of entrained aqueous-alkali or alcohol-alkali solution, is then passed through a packed bed of solids. The packed bed of solids facilitates the extraction of elemental sulfur from the hydrocarbon fuel phase as well as removes the entrained aqueous-alkali or alcohol-alkali solution. The solids in the packed bed are sized to maximize the surface area for contacting between the hydrocarbon fuel phase and aqueous alkali or alcohol alkali solution phase without creating an excessive pressure drop.
[0021] Two parameters used to measure the effectiveness of a process to remove elemental sulfur as well as lower the total sulfur level in the product are percent elemental sulfur conversion (S° Converted, %) and percent total sulfur removed (S Removed, % of max). These performance indicators are calculated as follows:
S° Converted, % - ( (S°fd - S°pd) / S°fd ~ x S Removal, % max - ~ (S fd - Spd) / S°fd ~ x 100 (2) where: S°fd = elemental sulfur in the feed, mg/I
S°pd = elemental sulfur in the product, mg/1 S fd = total sulfur in the feed, mg/1 Spd = total sulfur in the product, mg/1 [0022) The present invention method achieves S° Converted and S Removed values greater than about 90% and greater than about SO%, respectively. Prior art methods achieve lower S° Converted and S Removed values and often times even negative S Removed values because the addition of mercaptan and similar organic compounds to the hydrocarbon fuel under certain conditions may increase the total sulfur in the fuel product significantly above the levels of total sulfur in the feed.
[0023) Unlike prior art methods, the use of a packed-bed of solids provides an effective surface area for extracting the elemental sulfur into a caustic phase containing the Na2S without significant formation of di- and tri-sulfides which are soluble in gasoline. It is believed that the extracted elemental sulfur reacts with the alkali metal sulfide such as sodium sulfide according to the following reaction:
Na2S + x S° ~ Na2SX+I (3) [0024) Effective extraction conditions for the packed bed of solids may include an operating temperature ranging from about 0°F (-18°C) to about 180°F
(80°C), and more preferably from about 40°F (5°C) to about 90°F (30°C).
Effective extraction conditions also include a residence time from about 0.1 to about 100 minutes, and more preferably from about 1 to about 10 minutes.

Furthermore, the mass flux rate of the packed bed of solids may range from about 0.1 to about 100 usgal/ftz, and more preferably from about 1 to about usgal/ft2 [0025] The treated fuel product is substantially free of elemental sulfur meaning that it has less than about 1 wppm elemental sulfur, and less than about 100 wppm total sulfur, more preferably less than about 0.5 wppm elemental sulfur, and less than about SO wppm total sulfur, and most preferably less than about 0.1 wppm elemental sulfur and less than about 30 wppm total sulfur.
[0026] Unlike prior art processes that employ aliphatic mercaptans the present invention prevents or suppresses the formation of di- and tri-sulfides that may occur, for example, according to the following reaction:
4 RSH + 3 S° + 4 NaOH --~ RSSR + RSSSR + 2 Na2S + 4 H20 (4) wherein R is an alkyl group.
(0027] The present process is directed to the removal of elemental sulfur from organic fluids such as hydrocarbon fuels (e.g., gasoline, kerosene, diesel, jet), fuel blending components such as octane improvers (ethers such as MTBE), mixtures thereof, liquefied petroleum gas (LPG), solvents, and other petroleum streams transported in pipelines which are otherwise used for the transportation of sour hydrocarbon streams such as crude oil.
[0028] The caustic 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.
(0029] The sulfide may be monosulfides and polysulfides of metals from Groups I and II of the Periodic Table. Examples of sulfides include Na2S, K2S, Li2, 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.
[0030] Alcohols may be used such as methanol, ethanol, propanol, ethylene glycol, propylene glycol and the like and alcohols 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, for example, from 0 to about 90 vol% of the water may be replaced with alcohol.
[0031] Fuels which may be treated in accordance with the invention include fuels containing elemental sulfur where the elemental sulfur is detrimental to the performance of the fuel. The fuels 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. 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.

[0032] Other fluids may also be treated such as 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 tertiarybutyl ether, methyl tertiary-amyl ether, methyl tertiary-hexyl ether, ethyl tertiary-butyl ether, n-propyl tertiary-butyl ether, isopropyl tertiary-amyl ether. Also, mixtures of these ethers and hydrocarbons may be treated in accordance with the invention.
[0033] 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 less than about 0.5 mg sulfur per liter, preferably less than about 0. I mg sulfur per liter or lower.
[0034] In general, the process of the invention involves the addition to the hydrocarbon fluid to be treated of effective amounts of alkali-metal, water and a sulfide. Optionally an aromatic mercaptan and/or an alcohol-alkali solution may be added. A suitable mixing device is used to intimately mix the two phases.
After mixing the two phases, the majority of the aqueous-alkali solution is separated from the hydrocarbon fluid. The hydrocarbon fluid, which contains a residual amount of entrained aqueous-alkali solution, is then passed through a packed bed of solids. The packed bed of solids facilitates the extraction of elemental sulfur from the hydrocarbon fluid. The separated aqueous-akali layer may be recycled back to the mixing zone for contact with fresh hydrocarbon fluid containing elemental sulfur 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.

[0035] The proportion of water, alkali, and sulfide to be mixed may vary within wide limits. Typically, the aqueous treating solution contains alkali in the range of about 0.01 to about 20M, the sulfide concentration is from about 0.2 to about ZOM. The relative amount of the aqueous-alkali-sulfide treating, and the hydrocarbon fluid to be treated may also vary within wide limits. Usually about 0.05 to about 10, more usually, about 0.1 to about 1.0 volumes of aqueous treating solution will be used per volume of hydrocarbon fluid to be treated.
[0036] Referring now to Figure 2, one embodiment of the present invention method is illustrated. An aqueous caustic solution of an alkali metal sulfide is added through line 2 to a hydrocarbon fuel containing elemental sulfur (line 1 ).
The combined stream 3 is mixed using a mixer (4). The mixer can be any conventional mixer sized and designed to effectively mix the aqueous caustic solution with the hydrocarbon fuel. Examples of mixers include mechanically agitated tanks, static in-line mixers, dynamic in-line mixers or ultrasonic mixers.
[0037] The mixture is then transported via line 5 to a separator or settler (6) which separates the majority of the aqueous caustic solution into stream 11 from the hydrocarbon fluid (stream 7). The separator can be any conventional two-phase separator. The hydrocarbon fluid (stream 7) which contains a residual amount of entrained aqueous-caustic solution is then passed through a packed bed of solids (8). The packed bed of solids facilitates the extraction of elemental sulfur from the fuel phase into the caustic phase.
[0038] Suitable solids for the packed bed (8) are any solid materials that have high surface area. Examples include but are not limited to, sand, carbon, and alumina. The solids are sized to maximize the available surface area without creating excessive pressure drop. The packed bed of solids facilitates extraction of the elemental sulfur from the fuel phase into the caustic phase by providing sufficient surface area for the two phases to come into contact.
[0039] Treated hydrocarbon fluid from the packed bed (stream 9) typically contains less than 0.5 mg/1 of elemental sulfur. The residual caustic phase (stream 10) is typically combined with the caustic phase ( 11 ) from the separator (6) and recycled via stream 12 to stream 2 to further treat fresh hydrocarbon fluid containing elemental sulfur (stream 1 ).
[0040] Optionally, an aromatic mercaptan such as thiophene may also be added to the aqueous or hydrocarbon stream. Addition of an aromatic mercaptan may improve the performance by accelerating the transfer of elemental sulfur from the hydrocarbon fluid to the caustic phase.
[0041] Although the exact mechanism for the extraction of elemental sulfur is not known, it is believed that the bed of solids when coated with the aqueous-alkali/alkali-metal-sulfide solution provides an effective surface or contact area for the transfer of elemental sulfur from the fuel into the aqueous-alkali solution.
The high surface area in the packed bed of solids allows the extraction of elemental sulfur to proceed at ambient temperatures without the addition of heat.
[0042] The following examples further illustrate the invention and should not be construed as limiting the scope of the invention which is delineated in the claims.

EXAMPLES
Example 1 [0043] 40 kB/D of regular gasoline (RUL) containing approximately 22 mg/1 of elemental sulfur is mixed with 20 kB/D of 25 Be caustic containing 1.5 wt%
Na2S. The mixture is fed to a mechanically agitated mixing vessel (10 ft.
diameter by 60 ft. high) containing six mixing impellers 4 ft. in diameter operated at 120 rpm. The residence time of the mixture in the vessel is 20 minutes while the operating temperature is approximately 20°C. The gasoline caustic mixture is then fed to a caustic settler where most of the caustic is allowed to settle out to the bottom while the overhead gasoline fraction flows to a vessel filled with a 3 ft. bed of sand, referred to as a sandfilter. The residence and mass flux rate of the hydrocarbon fluid through the bed of sand is 11 minutes and 2 usgpmlft2, respectively. Residual caustic entrained in the gasoline from the caustic settler settles out in the sandfilter. The residence time of the gasoline in the caustic settler is 30 minutes while the residence time of the gasoline in the sandfilter vessel is 42 minutes.
[0044] The profile of elemental sulfur content in the gasoline through the mixer, caustic settler and caustic sandfilter is shown in Figure 1. Figure 1 shows that the elemental sulfur level in the treated product from the mixer asymptotically reaches a level of approximately 7 mg/l. Although there is very little if any change in the elemental sulfur level of the gasoline through the caustic settler, there is a significant drop in the elemental sulfur level in the treated product leaving the caustic sandfilter. These data indicate that at the same operating temperature, the sandfilter can extract a significant amount of elemental sulfur into the caustic that could not be removed by the conventional mixer (mechanically agitated tank).
[0045] Table 1 summarizes the results for Example 1. As shown, the treated product from the vessel containing the bed of sand contains no elemental sulfur as well as no di and trisulfides. All of the elemental sulfur is extracted into the caustic and none of the elemental sulfur is converted to di- and trisulphides.
The total sulfur in the product is effectively reduced due to the removal of the elemental sulfur from the gasoline feed.

Results from Example 1 Product Feed from Sandfilter Elemental Sulfur, mg/1 22 0 Total Sulfur, mg/I 289 257 Di + Trisulfides, mg/1 0 0 Elemental Sulfur Converted, % (Equation [ 1 ]) N/a 100 Sulfur Removal, % of maximum (Equation [2]) N/a 110 Example 2 (0046) A gasoline containing 16.1 mg/1 of elemental sulfur is fed to a packed bed of sand at a rate of 20 cc/minute. The packed bed is 3 ft. long and has a diameter of 0.65 inches. The sand bed is operated at a temperature of 24°C. The residence time and mass flux rate through the bed of sand is 9.8 minutes and 2.3 usgpm/ft2, respectively. The elemental sulfur in the treated product is 15.9 mg/l.

Examine 3 (0047) A 0.65" diameter by 3' long packed bed of sand is pre-soaked with a caustic solution containing 19 wt% NaOH. A gasoline containing 16.1 mg/1 of elemental sulfur was fed up-flow to the sand bed at a rate of 20 cc/minute.
The sand bed is operated at a temperature of 25°C. The residence time and mass flux rate through the bed of sand is 9.8 minutes and 2.3 usgpm/ftZ, respectively.
The elemental sulfur in the treated product is 15.7 mg/l.
Example 4 [0048] A 0.65" diameter by 3' long packed bed of sand is pre-soaked with a caustic solution containing 19 wt% NaOH and 1.5 wt% Na2S. A gasoline containing 17.0 mg/1 of elemental sulfur was fed up-flow to the sand bed at a rate of 20 cc/minute. The sand bed is operated at a temperature of 25°C. The residence time and mass flux rate through the bed of sand is 9.8 minutes and 2.3 usgpm/ft2, respectively. The elemental sulfur in the treated product is 12.0 mg/l.

Results from Examples 2, 3 and 4 Example 2 Example 3 Example 4 Sand Condition No Caustic Caustic Caustic No Na2S No Na2S Na2S
Feed Elemental Sulfur, mg/1 16.1 16.1 17.0 Product Elemental Sulfur, mg/1 15.9 15.7 12.0 Elemental Sulfur Converted, 1.1 2.5 29.1 (Equation [ 1 ]) [0049] Examples 2, 3 and 4 illustrate the effect of pre-soaking the sand with caustic and Na2S solutions on the ability of the sand bed to remove elemental sulfur from the gasoline. Table 2 summarizes the results from Examples 2, 3 and 4. As shown, very little if any elemental sulfur is converted when the sand is not pre-soaked with both caustic and Na2S. The data indicate that the sand must be coated with both caustic and Na2S before a substantial amount of elemental sulfur can be removed from the gasoline.
Example 5 [0050] Gasoline and caustic solution are pumped at 47°C to a mechanically agitated tank at a rate of 183 cc/minute and 93 cc/minute, respectively. The gasoline contains 15.2 mg/1 of elemental sulfur. The caustic contains 19 wt%
NaOH and 1.5 wt% Na2S and has previously processed approximately 3000 cc of gasoline per cc of caustic. The mechanically agitated tank is 4" in diameter and 2' long. The tank contains six 1.5" diameter impellers operated at 671 rpm.
Example 6 [0051] The gasoline and caustic mixture from the mechanically agitated tank in Example 5 is separated in a 6" diameter by 3' long settler. The gasoline with some entrained caustic is fed upflow to the sand bed containing 304 cc of sand in a 1.4" diameter by 12" long vessel. The mass flux rate and residence time of the gasoline in the sand bed is 4.6 usgpm/ft2 and 1.6 minutes, respectively. The sand bed is operated at approximately 20°C.

Results from Examples 5 and 6 Example 5 Example 6 MAT*

Gasoline Treatment MAT* plus Sand Bed Feed Elemental Sulfur, mg/1 15.2 15.2 Product Elemental Sulfur, mg/1 1.1 0 Feed Total Sulfur, mg/1 20 20 Product Total Sulfur, mg/I 6 5 Elemental Sulfur Converted, % 93 100 (Eqn. [ 1 ]) Sulfur Removal, % of maximum (Eqn.92 99 [2]) * MAT = mechanically agitated tank [0052) Examples 5 and 6 illustrate the effect of treating the gasoline in a mechanically agitated tank (MAT) and treating the gasoline in a MAT plus a sand bed. Table 3 compares the results from Examples 5 and 6. As shown, although the MAT is able to convert 93% of the elemental sulfur and remove 92% of the maximum sulfur, the MAT plus the sand bed is able to convert 100%
of the elemental sulfur as well as remove 99% of the maximum sulfur.
Importantly, the MAT plus the sand bed is able to achieve the elemental sulfur specification of < 0.5 mg/1 in the treated gasoline while the MAT alone is not.
Example 7 (0053) Both the gasoline and caustic solutions are by-passed around the mechanically agitated tank in Example 5. The gasoline and caustic solutions are blended together at 22°C and at a rate of 89 cc/minute and 96 cc/minute, respectively. The gasoline contains 16.6 mg/1 of elemental sulfur while the caustic contains 19 wt% NaOH and 1.5 wt% Na2S and has previously processed approximately 3000 cc of gasoline per cc of caustic. The gasoline and caustic mixture is separated in the settler in Example 6. The gasoline with some entrained caustic is fed upflow to the sand bed in Example 6. The mass flux rate and residence time of the gasoline in the sand bed is 2.2 usgpm/ft2 and 3.4 minutes, respectively. The sand bed is operated at approximately 20°C.

Results from Examules 6 and 7 Example 7 Example 6 MAT*
Gasoline Treatment Sand Bed plus Sand Bed Feed Elemental Sulfur, mg/1 16.6 15.2 Product Elemental Sulfur, mg/1 5.1 0 Elemental Sulfur Converted, % (Equation [ 1 )) 69 100 * MAT = mechanically agitated tank [0054) Examples 6 and 7 illustrate the effect of treating the gasoline in a sand bed alone and treating the gasoline in a mechanically agitated tank (MAT) plus a sand bed. Table 4 compares the results from Examples 6 and 7. As shown, the sand bed only converts on 69% of the elemental sulfur while the MAT plus the sand bed is able to convert 100% of the elemental sulfur. These date indicate that gasoline and caustic solutions must first be adequately mixed in order to achieve the best sand bed performance.

Example 8 [0055] Gasoline and caustic solution are pumped at 4°C to a mechanically agitated tank at a rate of 189 cc/minute and 97 cc/minute, respectively. The gasoline contains 21.8 mg/1 of elemental sulfur while the caustic contains 19 wt% NaOH and 1.5 wt% Na2S and has previously processed approximately 4450 cc of gasoline per cc of caustic. The mechanically agitated tank is 4" in diameter by 2' long and contains six 1.5" diameter impellers operated at 671 rpm.
Example 9 [0056) The gasoline and caustic mixture from the mechanically agitated tank in Example 8 is separated in a 6" diameter x 3' long settler operated at 4°C. The gasoline with some entrained caustic is fed upflow to the sand bed containing 304 cc of sand in a 1.4" diameter x 12" long vessel. The mass flux rate and residence time of the gasoline in the sand bed is 4.6 usgpm/ft2 and 1.6 minutes, respectively. The sand bed is operated at approximately 4°C.

Results from Examples 8 and 9 Example 8 Example 9 MAT*

Gasoline Treatment MAT* plus Sand Bed Feed Elemental Sulfur, mg/1 21.8 21.8 Product Elemental Sulfur, mg/1 20.4 0 Feed Total Sulfur, mgll 61 61 Product Total Sulfur, mg/1 64 43 Elemental Sulfur Converted, % (Eqn.6 100 [ 1 ]) Sulfur Removal, % of maximum (Eqn.-14 83 [2]) * MAT = mechanically agitated tank [0057) Examples 8 and 9 illustrate the effect of treating the gasoline in a mechanically agitated tank (MAT) and treating the gasoline in a MAT plus a sand bed when both are operated at 4°C. Table 5 compares the results from Examples 8 and 9. As shown, the MAT at 4°C converts very little elemental sulfur and consequently removes very little of the total sulfur. However, at 4°C
the MAT plus the sand bed is able to convert 100% of the elemental sulfur as well as remove 83% of the maximum sulfur. Importantly, the MAT plus the sand bed is able to achieve the elemental sulfur specification of < 0.5 mg/1 in the treated gasoline at 4°C while the MAT alone is not. The excellent performance of the MAT plus a sand bed at these low temperatures allows the process to operate at ambient conditions in locations such as Vancouver, British Columbia.
Consequently, no additional capital and operating costs are required to heat the process.

Claims (14)

1. A method for removing sulfur from a hydrocarbon stream, the method comprising:
mixing said hydrocarbon stream with an immiscible alkali solution containing an alkali metal sulfide and an alkali metal hydroxide;

separating the majority of the alkali solution from the hydrocarbon phase; and treating the recovered hydrocarbon phase containing a residual amount of entrained alkali solution in a packed bed of solids comprising sand, carbon or alumina to produce a hydrocarbon product which has less than 0.5 wppm of elemental sulfur and a sulfur content of less than 15 wppm; and wherein the hydrocarbon product has a lower elemental sulfur content than the recovered hydrocarbon phase.

2. The method of claim 1, wherein the packed bed of solids comprises carbon or alumina.

3. The method of claim 1 or 2, wherein said hydrocarbon stream is a pipeline transported gasoline, diesel fuel, kerosene or jet fuel, and said immiscible alkali solution is an aqueous alkali solution, an alcohol alkali solution, or a mixture thereof.

4. The method of claim 3, wherein said aqueous-alkali solution contains an aromatic mercaptan.

5. The method of any one of claims 1 to 3, wherein an aromatic mercaptan is added to said hydrocarbon stream.

6. The method of any one of claims 1 to 5, wherein said mixing comprises using a mechanically agitated tank operated at mixing energies ranging from 2 to 200 hp/kusgal and at a temperature ranging from 0°F to 180°F.

7. The method of any one of claims 1 to 6, wherein said effective mixing conditions include a residence time of from 0.5 to 100 minutes.

8. The method of any one of claims 1 to 7, wherein said separating step includes feeding said mixture in a settler, holding said mixture into said settler for 1 to 100 minutes to allow the caustic to settle out to the bottom of the settler while the overhead hydrocarbon stream flows to said packed bed of solids.

9. The method of claim 1, wherein said packed bed of solids is a vessel filled with sand and allows a residence time of from 0.1 to 100 minutes.

10. The method of claim 1, wherein said packed bed of solids is a vessel filled with sand and allows a mass flux rate from 0.1 to 100 usgal/ft2.

11. The method of any one of claims 1 to 10, wherein said mixing occurs in an inline mixer providing a residence time of from 0.1 seconds to 10 minutes.

12. The method of any one of claims 1 to 11, wherein said hydrocarbon stream is a pipeline gasoline having a sulfur content of 30 to 100 wppm as measured by ASTM 5453.

13. The method of claim 1, wherein said hydrocarbon stream is a pipeline diesel having a sulfur content of 15 to 100 wppm as measured by ASTM 5453.

14. A method for removing sulfur from a gasoline stream, the method comprising:
contacting said gasoline stream with an aqueous solution of sodium hydroxide containing sodium sulfide;
mixing said contacted gasoline stream and aqueous solution of sodium hydroxide at ambient temperature to form a mixture;
feeding said mixture to a settler;
separating said mixture into a caustic stream and a treated gasoline stream;
and treating said gasoline stream containing a residual amount of entrained caustic in a packed-bed of solids consisting of alumina, alumina promoted metals, carbon, zeolites, ion exchange resins, silica gel, and mixtures thereof to produce a gasoline product which has less than 0.5 wppm of elemental sulfur and a sulfur content of less than 15 wppm; and wherein the gasoline product has a lower elemental sulfur content than the treated gasoline stream.