WO2024023215A1

WO2024023215A1 - Method for scavenging mercaptans in a hydrocarbon fluid

Info

Publication number: WO2024023215A1
Application number: PCT/EP2023/070838
Authority: WO
Inventors: Gijsbertus Cornelis Spruijt
Original assignee: Wrt BV
Current assignee: Wrt BV
Priority date: 2022-07-28
Filing date: 2023-07-27
Publication date: 2024-02-01
Anticipated expiration: 2025-01-28
Also published as: NL2032631B1

Abstract

The present invention relates to a method for scavenging mercaptans in a hydrocarbon fluid, comprising contacting the hydrocarbon fluid with an aqueous scavenging composition comprising an alcohol, an aqueous alkaline reagent and an effective scavenging amount of a phthalocyanine catalyst comprising disulfoacid of cobalt dichlorodihydroxyphthalocyanine mixed with disodium sulfate and potassium bromide, wherein the ratio of alkaline reagent to ethanol, by mass, is from 1:3 to 1:4; and the phthalocyanine catalyst is dissolved in ethanol in an amount of 1.0 to 1.5 mg/l.

Description

Title: METHOD FOR SCAVENGING MERCAPTANS IN A HYDROCARBON FLUID

Technical Field

The present invention relates to a method for scavenging mercaptans in a hydrocarbon fluid, comprising contacting the hydrocarbon fluid with an aqueous scavenging composition. As a result, light mercaptans in sour hydrocarbon are separated and heavy mercaptans are catalytically oxidized to disulfide oils using an aqueous treatment solution containing a chelated polyvalent metal catalyst.

Background Art

Mercaptans can cause many problems ranging from malodors to metal corrosion. Because of the volatility of mercaptans, they tend to evolve into vapor spaces, where their offensive odors create problems in and around storage areas and throughout pipelines and shipping systems used for transportation. The treatment of a hydrocarbon fluid containing undesirable acidic species such as mercaptans is known and can be performed using either an extraction or a conversion process.

A catalytic chemical process was developed by UOP, referred to as the Merox process, which is used in oil refineries and natural gas processing plants to remove mercaptans from LPG, propane, butanes, light naphthas, kerosene and jet fuel by converting them to liquid hydrocarbon disulfides. The Merox process requires an alkaline environment which, in some process versions, is provided by an aqueous solution of sodium hydroxide (NaOH), a strong base, commonly referred to as caustic. In other versions of the process, the alkalinity is provided by ammonia, which is a weak base.

The conversion processes are known as “sweetening” processes because they results in products which no longer have the sour, foul odors of mercaptans and hydrogen sulfide. The liquid hydrocarbon disulfides may remain in the sweetened products. These may be used as part of the refinery or natural gas processing plant fuel, or they may be processed further.

The most common mercaptans removed are:

Methanethiol - CH3SH [m-mercaptan]

Ethanethiol - C2H5SH [e- mercaptan]

1 -Propanethiol - C3H7SH [n-P mercaptan] • 2-Propanethiol - CH3CH(SH)CH3 [2C3 mercaptan]

• Butanethiol - C4H9SH [n-butyl mercaptan]

• tert-Butyl mercaptan - C(CH3)3SH [t-butyl mercaptan]

• Pentanethiol - C5H11SH [pentyl mercaptan]

In particular, high molecular weight mercaptans (C4 and higher) are difficult to convert.

Mercaptan scavengers are commercially available to sweeten fuels. A successful scavenger is based on IVKAZ™, which is a phthalocyanine catalyst comprising disulfoacid of cobalt dichlorodihydroxyphthalocyanine mixed with disodium sulfate and potassium bromide; and further comprising caustic soda (50%) and ethanol, employed in amounts of 0.6 mg, 0.84 I and 0.2 I. This scavenger is pumped into a hydrocarbon fluid, and together with the ethanol acts to oxidize the common mercaptans into disulfides. Additionally, an oxidizing agent may be present. However, the sour liquid hydrocarbon may contain entrained oxygen or air in sufficient concentration to accomplish the desired sweetening. The oxidizing agent may also be used during the regeneration process.

A description of the demercaptanization of gas condensate with IVKAZ catalyst in a pilot plant scale is described by Maryam Ghaedian et al, in Petroleum & Coal 54(4), 379-384, 2012, Available online at www.vurup.sk/petroleum-coal. Further information may be found in RU2241732, which provides a method for purification of hydrocarbonaceous raw material or commercial hydrocarbon fractions from mercaptans, in particular from high-boiling tertiary mercaptans. The method realizes oxidation of mercaptans by oxygen-bearing gas in an alkaline medium in presence of a phthalocyanine catalyst, ethanolamine and a promoting additive.

Basu B et al, “Merox and related metal phthalocyanine catalyzed oxidation processes” Catalysis Reviews, Vol. 35, No. 4, 571-609 (1993) explains that alkyl and aromatic mercaptans are among important organic sulfur compounds distributed in petroleum products. The mercaptans cause foul odor and are corrosive toward metals. In addition, mercaptans may cause oxidative deterioration as well as inhibit the performance of various additives (TEL, antioxidants) in finished products. Therefore, it is necessary to remove them, either by extractive processes or by converting them into innocuous disulfides. Such processes are usually referred to as “sweetening.” Likewise US3352777 describes the oxidation of mercaptans, wherein in the US patent the acceleration of the rate of oxidation of mercaptans in contact with phthalocyanine catalyst is achieved by means of a specific salt. Whereas the use of an alcohol is mentioned, these documents d not disclose that further improvement may be achieved with a reduced amount of scavenger. Further information may be fund in Vil’danov, A.F., Bazhirova, N.G., Mazgarov, A.M. et al. Experience with the operation of units at the Omsk Oil Refinery for removing sulfur compounds from the butane-butylene fraction and waste water with the use of homogeneous and heterogeneous catalysts. Chem Technol Fuels Oils 49, 204-210 (2013). https://doi . orq/10.1007/s 10553-013-0432-x. In this paper data is reported that attests to the successful operation of the butane-butylene fraction demercaptanizing unit of the gas fractionating section of the KT-1/1 plant and the unit for demercaptanizing the unsaturated stabilizer overhead stream (reflux) of the gas purifying and gas fractionating section of the catalytic cracking plant 43-103. In the demercaptanization process, the alkali solution was regenerated using homogeneous catalyst of the trademark IVKAZ.

There remains a need for enhanced reduction of mercaptans in fuels, in particular high molecular weight mercaptans (C4 and higher) with a reduced amount of scavenger as additive.

Summary of the Invention

The current invention relates to a method for scavenging mercaptans in a hydrocarbon fluid, comprising contacting the hydrocarbon fluid with an aqueous scavenging composition comprising an alcohol, an aqueous alkaline reagent and an effective scavenging amount of a phthalocyanine catalyst comprising disulfoacid of cobalt dichlorodihydroxyphthalocyanine mixed with disodium sulfate and potassium bromide, and optionally a source of oxygen, wherein the ratio of alkaline reagent to ethanol, by mass, is from 1 :3 to 1 :4, and the phthalocyanine catalyst is dissolved in ethanol in an amount of 1.0 to 1.5 mg/l, preferably from 1.1 to 1.3 mg/l.

Detailed description of the invention

The current method is similar to the conventional Merox process for extraction and removal of mercaptans from crude oil, crude oil emulsions, oilfield condensate, petroleum residua and refined fuels including liquefied petroleum gases (LPG), such as propane, butanes and mixtures of propane and butanes. More specifically, the hydrocarbon fluids to which the method herein may be applied include, but are not limited to, crude oil, oil field condensates (e.g. naphtha, etc.), residual fuels, petroleum distillates (e.g. gasoline, kerosene, diesel, etc.) light hydrocarbons (e.g. propane, butane, etc.), aromatic solvents (e.g. toluene, xylene, etc.) and paraffinic solvents (e.g. pentane, heptane, etc.), renewable fuels such as biodiesel, and mixtures thereof. Further, the hydrocarbon fluids may contain oxygenated compounds such as alcohols, esters, glycols, ethers and the like and mixtures thereof. The aqueous caustic solution containing the scavenger catalyst reacts with mercaptans in the hydrocarbon fluids and extracts them. The reaction that takes place in the extractor is:

2 RSH + 2 NaOH 2 NaSR + 2 H₂O

In the above reaction, RSH is a mercaptan and R signifies an organic group such as a methyl, ethyl, propyl or other group.

The second step is referred to as regeneration and it involves heating and oxidizing of the caustic solution leaving the extractor. The oxidations results in converting the extracted mercaptans to organic disulfides (RSSR) which are liquids that are water-insoluble and are then separated and decanted from the aqueous caustic solution. The reaction that takes place in the regeneration step is:

4NaSR + O₂ + 2H₂O 2RSSR + 4NaOH.

After decantation of the disulfides, the regenerated "lean" caustic solution is recirculated back to the top of the extractor to continue extracting mercaptans.

The net overall Merox reaction covering the extraction and the regeneration step may be expressed as:

4 RSH + O₂ 2 RSSR + 2 H₂O.

Technical details of the demercaptanization process may also be found in the article in Petroleum & Coal 54(4), 379-384, 2012, mentioned above. Moreover, methods for scavenging mercaptans from hydrocarbons are disclosed in various patents, such as US8679203B2, RU2656100C2, or LIS20210198583 and references described therein, which involve adding to the hydrocarbon fluid an effective scavenging amount of an aqueous scavenging composition.

The scavenging method of the present invention can be carried out at normal atmospheric or elevated pressure. Also, the scavenging method of the present invention can be carried out at temperatures in the range of -50° C. through 900° C., in the range of -50° C. through room temperature, in the range of room temperature through 900° C., and at room temperature. Preferably, the temperature is in the range of -20° C. through 100° C. The method can even be carried out at higher temperatures, although such temperatures are not characteristic in petroleum extraction and treatment, or for the scavenging of petroleum products downstream from heat exchangers of the installation. Keeping in mind that the temperature limits of the hydrocarbon raw material being processed in systems for treatment of crude petroleum or gas, or in feeding petroleum products from a plant downstream from a cooler, are usually in the range of 30° C. to 60° C., the scavenger composition of the present invention can be used at temperatures of raw material being processed in this range of 30° C. to 60° C. When being supplied to the well, the scavenger composition of the present invention can even be used at product extraction temperatures up to 90° C. or more. The scavenger composition of the present invention can also be used at lower temperatures, for example, down to -5° C., under conditions of storage of petroleum in reservoirs in cold climate conditions. The scavenger composition of the present invention can also be used at even lower temperatures, and the inventors do not restrict the present invention to a particular indicated temperature below which the method is not applicable. However, the treatment time increases at lower temperatures. To shorten the treatment time, it may be necessary to increase the expenditure of reagent. Thus, the applicability of the method will depend on the conditions of each particular case, and the inventors do not herein restrict the area of application of the composition of the present invention to a lower temperature limit of -5° C., but rather indicate that this is a low temperature as a reference point for the primary range of applications.

It will be appreciated that it is not necessary for all of the mercaptans present in the hydrocarbon fluids to be reacted and/or removed for the method herein to be considered successful. The method has accomplished a goal when the amounts of mercaptan are reduced as a consequence of being contacted with the scavenging composition described herein.

The current invention accordingly relates to a method for scavenging mercaptans in a hydrocarbon fluid, comprising contacting the hydrocarbon fluid with an aqueous scavenging composition comprising an alcohol, an aqueous alkaline reagent and an effective scavenging amount of a phthalocyanine catalyst comprising disulfoacid of cobalt dichlorodihydroxyphthalocyanine mixed with disodium sulfate and potassium bromide, wherein the ratio of alkaline reagent to ethanol, by mass, is from 1 :3 to 1 :4; and the phthalocyanine catalyst is dissolved in ethanol in an amount of 1.0 to 1.5 mg/l.

Preferably, alkaline reagent is caustic soda, more preferably is caustic soda at 50%mass (having a density of about 1.15 g/ml).

Preferably, the ratio of alkaline reagent to ethanol, by mass, is from 1 :3.2 to 1 :3.6, more preferably from 1 :3.3 to 1 :3.5, still more preferably from 1 :3.40 to 1.3.45. When using Caustic Soda at 50%mass, this corresponds to about 0.3I caustic soda on about 0.75I ethanol (both ± 0.05 I). In other words, .0.31 NaOH (50%) is 0.3 x 1.15 x 50% = 0.1725 g whereas 0.75I EtOH equals 0.75 x 0.789 = 0.59175. The ratio is therefore 1 : 3.43 Preferably, the phthalocyanine catalyst is dissolved in ethanol in an amount of 1.1 to 1.3 mg/l. For instance, on about 0.75I ethanol (± 0.05I) about 0.9 mg phthalocyanine catalyst (± 0.05 mg) may be used.

The phthalocyanine catalyst preferably comprises 70-75 %mass disulfoacid of cobalt dichlorodihydroxyphthalocyanine mixed with 20-25% mass disodium sulfate and further comprising 0.1-0.5 %mass potassium bromide as promoting additive. Preferably, the catalyst that is employed is the catalyst that is available as IVKAZ® catalyst, which is an improved Russian analogue of the Merox WS (manufactured by Honeywell UOP, USA).

The invention is illustrated by the following examples.

Examples

Three different hydrocarbon fractions containing mercaptans were tested.

Materials used:

As shown in Table 1 , a commercial mercaptan scavenger, MSC1 , or the mercaptan scavenger according to the invention, MSC2, was used in the indicated dosages. The liquid phase mercaptan (RH) proportion after 48 and 96 hours was noted. The results are listed in Table 1. Table 1

Results

The test results are not yet optimized. Still, it may be seen from Table 1 that the mercaptan levels using MSC2 as compared to the higher dosage levels of MSC1 were equal or even better.

Claims

CLAIMS A method for scavenging mercaptans in a hydrocarbon fluid, comprising contacting the hydrocarbon fluid with an aqueous scavenging composition comprising an alcohol, an aqueous alkaline reagent and an effective scavenging amount of a phthalocyanine catalyst comprising disulfoacid of cobalt dichlorodihydroxyphthalocyanine mixed with disodium sulfate and potassium bromide, and optionally a source of oxygen, wherein the ratio of alkaline reagent to ethanol, by mass, is from 1 :3 to 1 :4; and the phthalocyanine catalyst is dissolved in ethanol in an amount of 1.0 to 1.5 mg/l. The method of claim 1 , wherein the alkaline reagent is caustic soda, more preferably is caustic soda at 50%mass, having a density of about 1.15 g/ml. The method of claim 1 or 2, wherein the ratio of alkaline reagent to ethanol, by mass, is from 1 :3.2 to 1 :3.6, more preferably from 1 :3.3 to 1 :3.5, still more preferably from 1 :3.40 to 1.3.45. The method of claim 2, wherein the alkaline reagent is caustic soda at 50%mass, used in an amount of 0.3 ± 0.05 I caustic soda to 0.75± 0.05 I ethanol. The method of anyone of claims 1-4, wherein the phthalocyanine catalyst is dissolved in ethanol in an amount of 1.1 to 1.3 mg/l. The method of anyone of claims 1-4, wherein the phthalocyanine catalyst is dissolved in ethanol in an amount of 0.9 ± 0.05 mg phthalocyanine catalyst on 0.75 ± 0.05 I ethanol. The method of anyone of claims 1-6, wherein the method is applied to crude oil, oil field condensates, residual fuels, petroleum distillates, light hydrocarbons, aromatic solvents and paraffinic solvents, renewable fuels, and mixtures thereof. The method of claim 7, wherein the hydrocarbon liquid is prewashed to remove any H₂S.