IMPROVED PERFORMANCE OF SULFIDE SCAVENGER

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority benefit of U.S. Provisional Patent Application Serial No. 62 / 370,308 filed August 3, 2016.FIELD OF INVENTION

[0002] The present disclosure relates to methods for removing sulfides from fluid streams.BACKGROUND OF THE INVENTION

[0003] Hydrogen sulfide is a clear toxic gas with a foul odor. It is also highly flammable. The Environmental Protection Agency and other regulatory agencies worldwide strictly control the release of hydrogen sulfide into the environment. Hydrogen sulfide is often present in well water, waste water, and other aqueous streams. Hydrogen sulfide may also be present in industrial process streams such as crude oil and natural gas reserves, and must be removed before using.

[0004] The removal of hydrogen sulfide from industrial process streams presents a challenge in many industries. Generally, hydrocarbon streams can be treated with chemical scavengers to remove sulfides. These chemicals are called scavengers or sweetening agents. Certain aldehydes are known to be useful for this purpose. However, the use of aldehydes, such as glyoxal, can cause increased corrosion and damage to the metals of processing and refinery equipment.

[0005] Conventionally, the addition of surfactants, neutralizing agents and buffers, and corrosion inhibitors have been used to enhance the performance of glyoxal based scavengers, and to reduce the corrosion associated with their use. Patent application WO2013 / 049027 A1 relates to methods and scavenger compositions for removing hydrogen sulfide from liquid hydrocarbon media, the method comprising adjusting a pH value of a glyoxal solution to a pH in a range of 2.5 to 6.0 and dispersing the adjusted glyoxal solution in the liquid hydrocarbon media.SUMMARY OF THE INVENTION

[0006] The present invention relates to a method for removing sulfide in a fluid hydrocarbon stream as disclosed in the appended claims.

[0007] A method for removing sulfide in an industrial process fluid comprises obtaining a measurement of a specific gravity of the industrial process fluid, obtaining a measurement of a specific gravity of a scavenger composition comprising at least one aldehyde or at least one hydrotriazine; reducing a settling velocity of the scavenger composition in the industrial process fluid by adjusting the specific gravity of the scavenger composition to within about fifteen percent or less of the specific gravity of the industrial process fluid, and adding to the industrial process fluid an effective amount of the adjusted scavenger composition.

[0008] The aldehyde can comprise at least one of formaldehyde, glyoxal, glutaraldehyde, acrolein, glyoxylic acid, and combinations thereof. The weight percent (wt%) of the aldehyde is from about 1 percent by weight to about 25 percent by weight of a total weight of the sulfide scavenger solution. The aldehyde can also be present from about 5 percent by weight to about 20 percent by weight of a total weight of the solution. A method for removing sulfide in an industrial process fluid comprises decreasing the specific gravity of the scavenger composition by adding a solvent in a quantity sufficient to cause the specific gravity of the scavenger composition to be within about fifteen percent or less of the specific gravity of the industrial process fluid.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] This invention will be further described in the appended drawings wherein: Fig. 1 is a graphical representation of the results obtained upon use of a sulfide scavenger in bunker fuel as referred to in Example 1; Fig. 2 is a graphical representation of the results obtained upon use of a sulfide scavenger in naphtha as reported in Example 2; and Figs. 3A and 3B are graphical representations of the corrosion test results obtained upon use of a sulfide scavenger as reported in Example 3. DETAILED DESCRIPTION

[0010] The method for reducing sulfides from a fluid stream can be used to reduce sulfides, including organic sulfides and hydrogen sulfide (H 2 S) in an industrial process fluid, also referred to herein as a fluid stream, and a target industrial process stream. A fluid stream encompasses a liquid stream. The fluid stream of the invention is a fluid hydrocarbon stream. Hydrocarbon streams can include, but are not limited to, unrefined and refined hydrocarbon products, derivatives from petroleum or the liquefaction of coal, naphtha, wellhead condensate, crude oil or distillates such as gasolines, bunker fuels, distillate fuels, oils and residual fuels.

[0011] The fluid streams can be treated continuously or in a batch process near a wellhead. Continuous treatment installations near the wellhead can be used to inject scavengers directly into the hydrocarbon pipeline. The injection system can include a chemical injection pump or piping tees to introduce the scavengers into the pipeline. A length of the pipeline allows for contact between the scavenger and the sulfide. The scavengers can be used neat or diluted with water, glycol, glycol ethers, or alcohols.

[0012] The various examples provide for an improved sulfide scavenger, also referred to herein as a scavenger, or scavenger composition, with increased scavenging activity, reduced reaction times, and reduced corrosion to processing equipment.

[0013] The method for removing sulfide in an fluid hydrocarbon stream includes adjusting the specific gravity of the scavenger composition by decreasing the specific gravity of the sulfide scavenger by adding a solvent in a quantity sufficient to cause the specific gravity of the sulfide scavenger to be within about fifteen percent or less of the specific gravity of the fluid stream. The solvent can include water, alcohols, glycols, glycol ethers, and combinations thereof.

[0014] In an embodiment, the specific gravity of the scavenger composition is adjusted to within about five percent or less of the specific gravity of the fluid hydrocarbon stream. In other embodiments, the specific gravity of the scavenger composition is adjusted to within about one percent or less of the specific gravity of the fluid hydrocarbon stream.

[0015] The aldehydes which can be utilized in the practice of the method of the disclosure include, but are not limited to, formaldehyde, glyoxal, glutaraldehyde, acrolein, glyoxylic acid, and combinations thereof. Most any aldehyde that can be employed in an aqueous solution and is effective at sulfide scavenging can be utilized. Glyoxal is a water-soluble aldehyde and can include oligomers of glyoxal. Glyoxal is commercially available as a 40 weight percent aqueous solution.

[0016] The aldehyde is present from about 1 percent by weight to about 25 percent by weight, based on the total weight of the reaction composition. In another embodiment, the aldehyde is present from about 5 percent by weight to about 20 percent by weight.

[0017] A solvent is used to adjust the specific gravity of the sulfide scavenger composition. The sulfide scavengers are miscible in water; therefore, suitable solvents include water and water-miscible solvents. Specific examples of suitable solvents include, but are not limited to, water, alcohols, glycols, and glycol esters.

[0018] The solvent can be blended with the scavenger composition in any conventional manner. In one embodiment, the adjusted scavenger composition can be mixed into the fluid stream. In another embodiment, the adjusted scavenger composition can be dispersed with the fluid stream as the fluid stream is transported through a pipe or tube. The adjusted scavenger composition can be added in one or more batch modes, and repeated additions can be made.

[0019] In one embodiment, the solvent can comprise at least one member selected from the group consisting of water, alcohols, glycols, and glycol ethers. There is no limit on how much solvent can be used. In an embodiment, the solvent can be present from about 10 percent by weight to about 90 percent by weight, based on the total weight of the scavenger composition. In another embodiment, the solvent can be present from about 1 percent by weight to about 25 percent by weight. In another embodiment, the solvent can be present from about 50 percent by weight to about 75 percent by weight. In yet another embodiment, the solvent can be present from about 5 percent by weight to about 10 percent by weight, based on the total weight of the scavenger composition.

[0020] In the method of the invention, a settling velocity of the sulfide scavenger in fluid hydrocarbon stream is reduced by adjusting a specific gravity of a solution comprising at least one of an aldehyde and hexahydrotriazine to within about fifteen percent or less of a specific gravity of the fluid hydrocarbon stream.

[0021] The specific gravity of the solution can be adjusted to within about five percent or less of the specific gravity of the fluid hydrocarbon stream. In other embodiments, the specific gravity of the solution is adjusted to within about one percent or less of the specific gravity of the fluid hydrocarbon stream. The sulfide scavenger can include a non-ionic surfactant, and a quaternary ammonium surfactant.

[0022] A transition metal salt can include a cation member, for example, zinc, iron, copper, molybdenum, cobalt, manganese, and combinations thereof, and at least one anion member, for example, chloride, acetate, nitrate, nitrite, carbonate, citrate, phosphate, sulfate, sulfite, gluconate, and combinations thereof.

[0023] The hexahydrotriazine can include a reaction product with any of monoethanolamine, methylamine, methoxypropylamine, isopropanolamine and combinations thereof. The hexahydrotriazine can include monoethanolamine hexahydrotriazine, and methylamine hexahydrotriazine.

[0024] The method for removing sulfide in a fluid hydrocarbon stream comprises: obtaining a measurement of the specific gravity of the industrial process fluid, obtaining a measurement of the specific gravity of a scavenger composition, reducing the settling velocity of the scavenger composition in the industrial process fluid by adjusting the specific gravity of the scavenger composition to within about five percent or less of the specific gravity of the industrial process fluid, adding to the industrial process fluid in an effective amount of the adjusted scavenger composition. Another embodiment discloses a method for removing sulfide in an industrial process fluid wherein the specific gravity of the scavenger composition to within about one percent or less of the specific gravity of the industrial process fluid.

[0025] The amount of sulfide scavengers added to a fluid stream will depend on the application and amount of sulfide scavenging required. In one embodiment, the sulfide scavenger is added to the fluid stream in an amount ranging from about 10 to about 100,000 ppm by volume of the fluid stream. In another embodiment, the sulfide scavenger is added to the fluid stream in an amount ranging from about 100 to about 50,000 ppm by volume of the fluid stream. Alternatively, the sulfide scavenger is added to the fluid stream in an amount ranging from about 600 to about 3,000 ppm by volume of the fluid stream.

[0026] While not being bound by any theory, it is nevertheless believed that the adjusting the specific gravity of the scavenger employed in the method of the present disclosure works in at least two ways to remove sulfide and thus prevent corrosion. Firstly, it is believed that matching the specific gravity of the scavenger to the process fluid allows additional time and opportunity for reaction of the scavenger with the H 2 S in the target fluid. Secondly, it is believed that the increased reaction of the scavenger with the hydrogen sulfide results in less scavenger available to react with the vessel thereby preventing, or at least minimizing, this corrosion mechanism.

[0027] In order that those skilled in the art will be better able to practice the present disclosure, the following examples are given by way of illustration and not by way of limitation.EXAMPLESEXAMPLE 1

[0028] With reference to FIG. 1, in this example two experiments were conducted utilizing sour bunker fuel at 75 °C as the target fluid, and scavenger formulas which included an aldehyde. The aldehyde was glyoxal. The specific gravity of the target fluid was 0.99.

[0029] A first experiment utilized a glyoxal based scavenger Formula 1. The scavenger Formula 1 was 40% by weight aqueous glyoxal having a specific gravity of 1.26. The difference in specific gravity between the target fluid and the scavenger Formula 1 was 0.27. It can be seen from FIG. 1 that the H 2 S level was reduced to < 15 ppm by volume, as measured in the vapor phase, at approximately 600 ppm of active glyoxal.

[0030] A second experiment utilized a glyoxal based scavenger Formula 2. The specific gravity of the scavenger Formula 2 was 1.04. Formula 2 was prepared by adding a solvent to Formula 1 in an amount effective to decrease the specific gravity to 1.04. The solvent used was water. Formula 2 was a 6-fold dilution of Formula 1. The difference in specific gravity between the target fluid and the scavenger Formula 2 was 0.05. It can further be seen from FIG. 1, that the H 2 S vapor was reduced to near zero ppm by volume, as measured in the vapor phase, at approximately 200 ppm of active glyoxal.

[0031] The difference in specific gravity between Formula 2 and the target fluid is five times lower than that of Formula 1. That is, 0.05 as compared to 0.27. While not wishing to be bound by any theory, it is nevertheless believed that the decreased difference in specific gravity between the scavenger Formula 2 and the target fluid resulted in a decreased settling rate of the scavenger formula in the target fluid, thereby providing additional time and opportunity for reaction of the scavenger with the H 2 S in the target fluid.

[0032] In viscous fluid dynamics, the Archimedes number is used to determine the motion of fluids due to density differences. The decreased difference in specific gravity between the scavenger Formula 2 and the target fluid decreased the Archimedes number of the resulting mixture of the target fluid and the scavenger, thereby reducing settling time by slowing down the motion of fluids due to density differences, and providing additional time and opportunity for reaction of the scavenger with the H 2 S in the target fluid.EXAMPLE 2

[0033] With reference to FIG. 2, in this example four experiments were conducted utilizing sour naphtha distillate at 32 °C (90 °F) as the target fluid and four scavenger formulas each having a different specific gravity. The specific gravity of the target fluid was 0.70.

[0034] A first experiment was conducted utilizing a triazine based scavenger Formula 3. The specific gravity of the scavenger Formula 3 was 1.10. The difference in specific gravity between the target fluid and the scavenger Formula 3 was 0.40. It can be seen from FIG. 2 that the H 2 S level was reduced from approximately 21.5 ppm, as measured in the vapor phase, to < 3 ppm by volume at approximately 50 ppm of active Formula 3.

[0035] A second experiment was conducted utilizing a triazine based scavenger Formula 4. The specific gravity of the scavenger Formula 4 was 1.01. The difference in specific gravity between the target fluid and the scavenger Formula 4 was 0.31. Formula 4 was prepared by adding a solvent to Formula 3 in an amount effective to decrease the specific gravity to 1.01. The solvent used was water. Formula 4 was a 6-fold dilution of Formula 3. It can further be seen from FIG. 2, that the H 2 S vapor was reduced from approximately 21.5 ppm by volume, as measured in the vapor phase, to < 4 ppm at approximately 12 ppm of active Formula 4.

[0036] A third experiment was conducted utilizing a glyoxal based scavenger Formula 5. The specific gravity of the scavenger Formula 1 was 1.26. The difference in specific gravity between the target fluid and the scavenger Formula 1 was 0.56. It can be seen from FIG. 2 that the H 2 S level was reduced from approximately 21.5 ppm by volume, as measured in the vapor phase, to < 7 ppm at approximately 49 ppm of active Formula 5.

[0037] A fourth experiment was conducted utilizing a glyoxal based scavenger Formula 6. The specific gravity of the scavenger Formula 6 was 1.04. Formula 6 was prepared by adding a solvent to Formula 5 in an amount effective to decrease the specific gravity to 1.04. The solvent used was water. Formula 6 was a 6-fold dilution of Formula 5. The difference in specific gravity between the target fluid and the scavenger Formula 6 was 0.34. It can further be seen from FIG. 2, that the H 2 S vapor was reduced from approximately 21.5 ppm by volume, as measured in the vapor phase, to < 1 ppm at approximately 42 ppm of active Formula 6.EXAMPLE 3

[0038] In this example, corrosion tests were performed by holding steel corrosion coupons at 77 °C for approximately six days. A first steel corrosion coupon 016 was held in a scavenger Formula 8. The glyoxal based scavenger Formula 8 was 40% by weight aqueous glyoxal having a specific gravity of 1.26.

[0039] A second steel corrosion coupon 015 was held in a process fluid including scavenger Formula 7. The specific gravity of the glyoxal based scavenger Formula 7 was 1.04. Formula 7 was prepared by adding a solvent to glyoxal based Formula 8 in an amount effective to decrease the specific gravity to 1.04. The solvent used was water. Formula 7 was a 6-fold dilution of Formula 8.

[0040] Corrosion rate can be determined through mass loss balance. This technique is suitable for generalized and localized corrosion and can be described as follows. Localized pitting and general corrosion were evaluated through surface examination before and after the trial. This exam was recorded using a digital camera with a magnification lens. This method is useful for evaluating the corrosive effect of a scavenger solution, particularly when localized corrosion has occurred.

[0041] FIG. 3A is a magnified digital photo of steel corrosion coupons 015 and 016 prior to the corrosion test. FIG. 3B is a magnified digital photo of steel corrosion coupons 015 and 016 after being held at 77 °C in a process fluid including the Formulas 7 and 8, respectively, for approximately six days.

[0042] Results of the corrosion test are shown in Table 1, and FIGS. 3A and 3B. The steel test coupons 015 and 016 were weighed at the beginning and at the end of the trial. Visual examination of the surfaces of the coupons indicated the presence of localized or pitting corrosion on steel test coupon 016 as demonstrated in FIG. 3B. The corrosion rate, was determined as mils per year of loss of metal. The corrosion rate data for these steel test coupons 015 and 016 are given in Table 1. TABLE 2Solvent Concentration. of glyoxal (%) Specific. Gravity. of scavenger Δ sp. gr. (between scavenger & fluid) % density difference Vapor H 2 S ppm @ 110 °C (± 200 ppm) nonenonenone00%2700water391.260.2424%2000water19.51.130.1111%1600water131.090.077%1600water6.51.040.022%1800glycerol6.51.260.2424%2500methanol6.50.870.1515%2500

[0043] The Examples clearly demonstrate that the adjustment of specific gravity by the addition of a solvent is effective at mitigation of corrosion by glyoxal. Corrosion generally occurs when the metal is contacted by the scavenger composition as it settles out of the fluid stream. Reducing the settling time of the scavenger in the fluid stream not only provides additional time and opportunity for reaction of the scavenger with the H 2 S, but also reduces the duration of the contact between the scavenger with the metal, thereby reducing the corrosion rate.

Claims

1. A method for removing sulfide in a fluid hydrocarbon stream, comprising: obtaining a measurement of a specific gravity of the fluid hydrocarbon stream; obtaining a measurement of a specific gravity of a scavenger composition; reducing a settling velocity of the sulfide scavenger composition in the fluid hydrocarbon stream by adjusting the specific gravity of the sulfide scavenger composition to be within fifteen percent or less of a specific gravity of the fluid hydrocarbon stream; and adding to the fluid hydrocarbon stream an effective amount of the adjusted scavenger composition, wherein (1) the scavenger composition comprises at least one aldehyde; or (2) the scavenger composition comprises at least one hexahydrotriazine, and wherein a solvent is used to adjust the specific gravity of the sulfide scavenger composition; wherein the at least one aldehyde is present from 1 percent by weight to 25 percent by weight of a total weight of a sulfide scavenger composition.

2. The method as in claim 1, wherein the solvent comprises at least one member selected from the group consisting of water, alcohol, glycol, and glycol ether.

3. The method as in claim 1, wherein the aldehyde comprises glyoxal.

4. The method as in claim 1, wherein the aldehyde is present from 5 percent by weight to 20 percent by weight.

5. The method as in claim 1, wherein the hexahydrotriazine comprises a reaction product with at least one member selected from the group consisting of monoethanolamine, methylamine, methoxypropylamine, isopropanolamine and combinations thereof.

6. The method as in claim 1, wherein the adjusted sulfide scavenger composition is added to the fluid hydrocarbon stream in an amount ranging from 10 ppm to 100,000 ppm by volume of the fluid hydrocarbon stream.