Process for reducing the level of elemental sulfur in hydrocarbon streams

Abstract

A process for reducing the level of elemental sulfur from sulfur-containing hydrocarbon streams, particularly refined fuel streams such as gasoline that is transported through a pipeline. A mercaptan compound is mixed with the stream prior to, or after, the stream is pipelined.

Description

FIELD OF THE INVENTION

[0002] This invention relates to a process for reducing the level of elemental sulfur from sulfur-containing hydrocarbon streams, particularly refined fuel streams such as gasoline that is transported through a pipeline. A mercaptan compound is mixed with the stream prior to, or after, the stream is pipelined.

BACKGROUND OF THE INVENTION

[0003] It is well known that elemental sulfur in hydrocarbon streams, such as petroleum streams, is corrosive and damaging to metal equipment, particularly copper and copper alloys. Sulfur and sulfur compounds may be present in varying concentrations in refined petroleum streams, such as in gasoline 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.

[0004] Various techniques have been reported for removing elemental sulfur from petroleum products. For example, U.S. Pat. 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. Pat. 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. Pat. 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. Pat. 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. Pat. 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 with sulfur to form 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 increasing the economics and efficiency of elemental sulfur removal from hydrocarbon streams that pick-up sulfur when transported in pipelines.

SUMMARY OF THE INVENTION

[0009] In accordance with the present invention, there is provided a process for reducing the level of elemental sulfur in a hydrocarbon stream containing same, which process comprises treating said hydrocarbon stream with an effective amount of a mercaptan compound.

[0010] In a preferred embodiment of the present invention the mercaptan is mixed with the hydrocarbon stream prior to its being transported through a pipeline.

[0011] In another preferred embodiment of the present invention the mercaptan is mixed with the hydrocarbon stream after it has been transported through a pipeline.

[0012] In still another preferred embodiment of the present invention the mercaptan is selected from the group consisting of aliphatic and aromatic mercaptans.

[0013] In yet another preferred embodiment of the present invention the mercaptan is used in a concentration from about 1 to about 1000 wppm.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Hydrocarbon streams that are treated in accordance with the present invention are preferably refined hydrocarbon streams containing elemental sulfur, particularly those wherein the sulfur has been, or will be, picked-up when the stream is transported through a pipeline. Preferred streams are also those wherein the elemental sulfur 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. Naphtha boiling range streams can comprise any one or more refinery streams boiling in the range from about 10° C. to about 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. Non-limiting examples of hydrocarbon feed streams boiling in the distillate range include diesel fuels, jet fuels, heating oils, and lubes. Such streams typically have a boiling range from about 150° C. to about 600° C., preferably from about 175° C. to about 400° C.

[0015] The hydrocarbon streams can contain quantities of elemental sulfur as high as 1000 mg sulfur per liter, typically from about 10 to about 100 mg per liter, more typically from about 10 to 60 mg per liter, and most typically from about 10 to 30 mg per liter. Such streams can be effectively treated in accordance with this invention to reduce the elemental sulfur contamination to less than about 10 mg per liter, preferably to less than about 5 mg sulfur per liter, or lower. Preferred hydrocarbon streams are those streams that have become contaminated with elemental sulfur as a result of being transported in a pipeline that was previously used to transport sour hydrocarbon streams, such as sour petroleum crudes. Residual sulfur from the sour crudes will contaminate the pipeline. Non-limiting examples of such streams that can be treated in accordance with the present invention include gasoline, jet fuel, diesel fuel, kerosene and dialkyl ethers containing same. Alkyl ethers 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-amyl ether. Mixtures of these ethers and hydrocarbon streams may also be treated in accordance with this invention.

[0016] The mercaptan that is mixed with the sulfur-containing stream is an organo 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 about 16 carbon atoms. Thus, the radical may be, for example methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, t-butyl, amyl, 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 about 80 wt. %, more preferably by at least about 90 wt. %, and most preferably by at least about 95 wt. %, of the elemental contaminants. This amount of mercaptan compound will typically range from about 1 wppm to about 1000 wppm, preferably from about 10 wppm to about 100 wppm. In terms of mole ratios, the amount of mercaptan compound will range from about 0.2 to about 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 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 about ambient temperature (about 22° C.) to about 100° C., or higher. Substantially atmospheric pressures are suitable, although pressures may, for example, range up to about 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 about 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 device, 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.

[0019] The following examples are illustrative of the invention and are not to be taken as limiting in any way.

EXAMPLE 1

[0020] Thiophenol was added to a tank containing gasoline with 21 mg/l of elemental sulfur (S°). The molar ratio of thiophenol to elemental sulfur was 2.0. The solution was mixed for 5 minutes using a recirculation pump. The elemental sulfur level in the mixture was monitored over time. After 16 days the elemental sulfur level dropped from 21 to 9.8 mg/l as shown in Table 1 below.

TABLE 1
Effect of Thiophenol Addition to Gasoline Containing Elemental Sulfur
Time	Temperature	S°	S° Conv.*	Total Sulfur
(Days)	(° C.)	(mg/l)	(%)	(mg/l)
0	12-15	21.3	0	108
2.0	12-15	18.8	11.7	—
9.9	12-15	11.2	47.4	—
15.9	0	9.8	54.0	120
20.8	23	9.8	54.0	—
*S° Conversion = [S° (in feed) − S° (in product)]/S° (in feed) *100

[0021] Sulfur species analysis of the mixture after 21 days showed the presence of diphenol-disulphide that was not present in the fresh feed.

EXAMPLE 2

[0022] Propyl mercaptan was added to an amber glass bottle containing gasoline with 24 mg/l of elemental sulfur. The molar ratio of propyl mercaptan to elemental sulfur was 1.5. The solution was mixed for one minute by shaking. The elemental sulfur level in the mixture was monitored over time. After 5 days the elemental sulfur level dropped from 24 to 1 mg/l as shown in Table 2 below.

TABLE 2
Effect of Propyl Mercaptan Addition to Gasoline Containing
Elemental Sulfur
Time	Temperature	S°	S° Conv.	Total Sulfur
(Days)	(° C.)	(mg/l)	(%)	(mg/l)
0	22	24.1	0	96
3.0	24	3.4	85.9	—
4.0	25	3.9	83.8	—
5.0	23	1.1	95.4	86
6.0	222	1.1	95.4	—
9.8	23	1.1	95.4	86

[0023] Sulfur species analysis of the mixture after 10 days showed the presence of dipropyl-disulphide and dipropyl-trisulphide that were not present in the fresh feed. Although the sulfur speciation data indicates the formation of polysulfides the exact mechanism is not understood.

Claims

1. A process for reducing the level of elemental sulfur in hydrocarbon stream containing same, which process comprises treating said hydrocarbon stream with an effective amount of a mercaptan compound.

2. The process of claim 1 wherein said hydrocarbon stream is treated with said mercaptan compound prior to being transported through a pipeline.

3. The process of claim 1 wherein said hydrocarbon stream is treated with said mercaptan compound while being transported through a pipeline.

4. The process of claim 1 wherein said hydrocarbon product stream is treated with said mercaptan compound after being transported through a pipeline.

5. The process of claim 1 wherein said mercaptan compound is represented by the formula RSH, where R represents an organic radical that may be alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl or arylalkyl having from 1 to about 16 carbon atoms.

6. The process of claim 1 wherein said mercaptan compound is used in a concentration of from about 1 to about 1000 wppm.

7. The process of claim 1 wherein the hydrocarbon product stream is selected from the group consisting of gasoline boiling range streams and distillate boiling range streams.

8. The process of claim 1 wherein the hydrocarbon product stream is a dialkyl ether having 1 to 7 carbon atoms in each alkyl group.

9. The process of claim 8 wherein the dialkyl ether is selected from the group consisting of methyl tertiary-butyl ether, methyl tertiary-amyl ether, methyl tertiary-hexyl ether, ethyl tertiary-butyl ether, n-propyl tertiary-butyl ether, and isopropyl tertiary-amyl ether.

10. The process of claim 1 wherein the sulfur content of the hydrocarbon product stream before being treated with the mercaptan compound is up to about 1000 mg/l.

11. A process for reducing the level of elemental sulfur in naphtha boiling range streams containing same, which process comprises treating said naphtha boiling range stream with an effective amount of a mercaptan compound represented by the formula RSH, where R represents an organic radical that may be alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl or arylalkyl having from 1 to about 16 carbon atoms.

12. The process of claim 11 wherein said hydrocarbon stream is treated with said mercaptan compound prior to being transported through a pipeline.

13. The process of claim 11 wherein said hydrocarbon stream is treated with said mercaptan compound while being transported through a pipeline.

14. The process of claim 11 wherein said mercaptan compound is used in a concentration of from about 1 to about 1000 wppm.