A continuous extractive desulfurization process and system for a hydrocarbon stream

Abstract

The present application relates to a continuous extractive desulfurization method and system for hydrocarbon stream, which comprises: (1) alkali extraction of the hydrocarbon stream with extractive alkali liquor to obtain hydrocarbon stream product and mercaptide-containing alkali liquor; (2) oxidation of the mercaptide-containing alkali liquor with oxidizing gas to obtain disulfide-containing alkali liquor after separation of excess oxidizing gas; (3) separation of the to-be-separated material to obtain disulfide stream and lean alkali liquor; (4) counter-extraction of the lean alkali liquor with selective solvent to obtain regenerated alkali liquor and disulfide-containing selective solvent; (5) fractional distillation separation of the to-be-distilled material to obtain regenerated selective solvent and disulfide product; the to-be-separated material in step (3) further comprises at least part of the disulfide product obtained from step (5). The present application can more effectively remove disulfide in the alkali liquor, and obtain hydrocarbon stream product with lower sulfur content and high-purity disulfide product.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of refining hydrocarbon materials, and in particular to a method and system for continuous extractive desulfurization of a hydrocarbon stream. BACKGROUND

[0002] Alkaline extraction is a traditional method for refining hydrocarbon materials, and is widely used in the desulfurization refining of low-carbon light hydrocarbon materials such as natural gas, liquefied petroleum gas, light gasoline, naphtha, alkanes, olefins, etc. that contain acidic sulfides. The method is to contact the hydrocarbon fluid with an alkaline solution, and the acidic sulfides in the hydrocarbon stream, mainly mercaptans, are removed from the hydrocarbon stream by reacting with the alkaline solution to form mercaptide salts.

[0003] The alkaline solution containing mercaptide salts cannot be directly discharged, as this is neither economical nor environmentally friendly. Oxidation is usually used to oxidize the mercaptide salts to disulfides, thereby regenerating the alkaline solution containing mercaptide salts (see USP 2853432). Specifically, this method oxidizes the mercaptide salts dissolved in the used alkaline solution to disulfides by injecting air and an oxidation catalyst into the used alkaline solution, thereby regenerating the alkaline solution. Thereafter, the regenerated alkaline solution is separated from the disulfides therein by sedimentation separation and / or extraction with an organic hydrocarbon solvent to continue using the regenerated alkaline solution to remove mercaptans from the hydrocarbon stream, thereby greatly reducing the discharge of waste alkali.

[0004] The existing alkaline liquid extraction desulfurization technology includes the following successive basic steps: (1) extraction, (2) oxidation, (3) phase separation, (4) back extraction. In the extraction step, alkaline liquid (including regenerated alkaline liquid) is contacted with a hydrocarbon stream containing mercaptans and reacts with mercaptans to form mercaptide, which is dissolved in the alkaline liquid; in the oxidation step, the alkaline liquid containing mercaptide from the extraction step is mixed with an injected oxidizing gas and an oxidation catalyst to oxidize the mercaptide in the alkaline liquid to disulfide, thereby regenerating the alkaline liquid, wherein the oxidation catalyst is a widely known metal phthalocyanine, such as sulfonated cobalt phthalocyanine, poly cobalt phthalocyanine. The metal phthalocyanine catalyst is usually injected into the oxidation step intermittently or continuously with fresh alkaline liquid (commercially available metal phthalocyanine catalyst usually exists in the form of a powdery solid or a liquid mixture); in the phase separation step, the regenerated alkaline liquid from the oxidation step is separated from the mixture of disulfide and oxidizing gas by sedimentation, on the one hand to release excess oxidizing gas, and on the other hand to separate the alkaline liquid from the disulfide which is aggregated into a phase, so as to remove the disulfide. Due to the small density difference between the disulfide and the alkaline liquid, the disulfide is usually difficult to be completely separated and removed by being aggregated into a phase in the phase separation step, which is limited by the relatively short sedimentation time. Therefore, the back extraction step is applied. In the back extraction step, the alkaline liquid from the phase separation step is mixed with an organic hydrocarbon solvent to back extract the remaining disulfide in the alkaline liquid into the organic hydrocarbon solvent, and then the regenerated alkaline liquid is separated from the disulfide-containing solvent by sedimentation, and the regenerated alkaline liquid treated by back extraction is returned to the extraction step for continuous use. In order to enhance the effect of hydrocarbon stream desulfurization, an organic liquid additive with a back extraction effect and / or an oxidation effect, such as a low-carbon alcohol, can be added to the alkaline liquid.

[0005] In addition, if the disulfide cannot be completely removed from the alkaline liquid, so that the regenerated alkaline liquid still contains residual disulfide, the disulfide in the regenerated alkaline liquid may be back extracted into the hydrocarbon stream when the regenerated alkaline liquid is returned to the extraction step for continuous use. Therefore, the organic solvent back extraction method is usually used to extract and remove the disulfide, that is, the organic solvent is contacted with the alkaline liquid which has absorbed the mercaptan and has been oxidized, so that the disulfide is transferred into the organic solvent, thereby the alkaline liquid basically no longer contains disulfide and can be better used for the extraction desulfurization of the hydrocarbon stream. The back extraction solvents used in the literature are mostly naphtha fractions, gasoline fractions, etc. The hydrocarbon back extraction solvent used to absorb the disulfide is usually sent to an additional hydrogenation device for desulfurization treatment. However, when the back extraction solvent contains aromatic hydrocarbons, it is easy to emulsify with the alkaline liquid, and even after water washing, it is difficult to wash away the trace amount of alkaline liquid, which is extremely easy to cause the hydrogenation catalyst to be poisoned and inactivated during hydrogenation treatment. There are also hydrocarbon back extraction solvents sent back to the catalytic cracking device for treatment, and cracked at high temperature in the catalytic cracking device. However, the trace amount of alkaline liquid carried by the back extraction solvent is also harmful to the catalytic cracking catalyst. This makes the treatment of waste back extraction solvent a problem that is not easy to solve for the refinery.

[0006] In addition, in the back extraction step, the alkali liquor oxidized and regenerated usually cannot completely remove the disulfide produced from the regenerated alkali liquor, and often has a large residual amount, which makes the regenerated alkali liquor returned to the extraction system when used, easily transfer the disulfide into the hydrocarbon stream, resulting in the reduction of the desulfurization rate of the hydrocarbon stream extraction, and even the abnormal phenomenon of the increase of sulfur content.

[0007] In addition, before the regenerated alkali liquor returned to the extraction system is contacted with the hydrocarbon stream containing mercaptan, there are often still trace amounts of oxidizing gas, which makes part of the mercaptan in the extraction system be oxidized into disulfide and still remain in the hydrocarbon stream after extraction. For this reason, the patent CN200510132299.7 uses nitrogen replacement to remove the oxidizing gas carried in the regenerated alkali liquor before back extraction, but often the replacement is not complete, especially when the back extraction solvent carries oxidizing gas (for example, naphtha and gasoline stored in the refinery tank farm are used as back extraction solvents, which are easy to contact air), which may affect the deep desulfurization of the hydrocarbon stream.

[0008] In summary, how to find a continuous extraction desulfurization method and system of hydrocarbon stream, so that the regenerated alkali liquor returned for the extraction process does not contain sulfide and oxidizing gas, to improve the desulfurization effect of the hydrocarbon stream is a technical problem to be solved at present. SUMMARY

[0009] The present application provides a continuous extraction desulfurization method and system of hydrocarbon stream, the purpose is to make the alkali extraction better separation and purification of alkali liquor, so that the regenerated alkali liquor does not contain sulfide and oxidizing gas, and then significantly improve the desulfurization effect of the hydrocarbon stream.

[0010] In the first aspect, the present application relates to a continuous extraction desulfurization method of hydrocarbon stream, the continuous extraction desulfurization method comprises the following steps:

[0011] (1) contacting the hydrocarbon stream with the extraction alkali liquor to perform alkali extraction, obtaining a hydrocarbon stream product and a sulfidic alkali liquor;

[0012] (2) contacting the sulfidic alkali liquor from step (1) with an oxidizing gas to perform oxidation, after separating the excess oxidizing gas, obtaining a disulfide-containing alkali liquor;

[0013] (3) separating the material to be separated containing the disulfide-containing alkali liquor from step (2) to obtain a disulfide stream and a lean alkali liquor;

[0014] (4) contacting the lean alkali liquor from step (3) with a selective solvent to perform back extraction, obtaining a regenerated alkali liquor and a disulfide-containing selective solvent;

[0015] (5) fractionally separating the material to be fractionally separated containing at least part of the disulfide-containing selective solvent from step (4) to obtain a regenerated selective solvent and a disulfide product;

[0016] wherein the extractive caustic solution in step (1) comprises the regenerated caustic solution from step (4); and the material to be separated in step (3) further comprises at least part of the disulfide product from step (5).

[0017] In a second aspect, the present application relates to a continuous extractive sweetening system of a hydrocarbon stream, comprising a caustic extraction unit, an oxidation unit, a separation unit, a back extraction unit and a fractionation column;

[0018] The caustic extraction unit is provided with a hydrocarbon stream inlet line, an extractive caustic solution inlet and a hydrocarbon stream product outlet line, the mercaptide-containing caustic solution outlet of the caustic extraction unit is communicated with the mercaptide-containing caustic solution inlet of the oxidation unit through a mercaptide-containing caustic solution line, and the mercaptide-containing caustic solution line is provided with an oxidizing gas inlet;

[0019] The disulfide-containing caustic solution outlet of the oxidation unit is communicated with the disulfide-containing caustic solution inlet of the separation unit through a disulfide-containing caustic solution line;

[0020] The separation unit is provided with a disulfide stream outlet and a lean caustic solution outlet, and the lean caustic solution outlet is communicated with the lean caustic solution inlet of the back extraction unit through a lean caustic solution line;

[0021] The back extraction unit is provided with a selective solvent inlet line, a regenerated caustic solution outlet line and a disulfide-containing selective solvent outlet line, and the disulfide-containing selective solvent outlet line is communicated with the material to be fractionated inlet line of the fractionation column;

[0022] The regenerated caustic solution outlet line of the back extraction unit is communicated with the extractive caustic solution inlet of the caustic extraction unit;

[0023] The fractionation column is provided with a regenerated selective solvent outlet and a disulfide outlet, and the disulfide outlet is communicated with the disulfide inlet of the separation unit through a circulating disulfide line.

[0024] Advantages:

[0025] The present application adopts multi-stage treatment of the caustic solution containing sulfur by disulfide and selective solvent, so as to obtain regenerated caustic solution containing no sulfide and oxidizing gas for the extractive refining of the hydrocarbon stream; the disulfide in the caustic solution can be removed more effectively, the continuous extractive sweetening of the hydrocarbon stream is promoted to be more effective, the hydrocarbon stream product with lower sulfur content is obtained, and the disulfide product with high purity is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a structural schematic diagram of a specific embodiment of the continuous extractive sweetening system of the present application;

[0027] Figure 2 This is a schematic diagram of a specific embodiment of a continuous extraction and desulfurization system for hydrocarbon streams according to the present invention;

[0028] Explanation of reference numerals in the attached figures

[0029] 1. Pre-alkali washing unit; 2. Alkali extraction unit; 3. Oxidation unit; 4. Separation unit.

[0030] 5. Back-extraction unit; 6. Fractionating column;

[0031] 1a Original hydrocarbon inlet, 1b Pre-alkali washing alkali inlet pipeline,

[0032] 1c circulating alkali solution pipeline, 1d hydrocarbon inlet pipeline;

[0033] 2a Inlet for extraction alkali solution; 2b Outlet pipeline for hydrocarbon product; 2c Pipeline for alkali solution containing thiols.

[0034] 3a Oxidizing gas inlet, 3b Tail gas outlet, 3c Alkali solution containing disulfide pipeline;

[0035] 4a Lean alkali solution pipeline; 4b Disulfide logistics outlet;

[0036] 5a has a selective solvent inlet line, and 5b has a disulfide selective solvent outlet line.

[0037] 5c circulation pipeline, 5d regenerated alkali solution outlet pipeline;

[0038] 6a Inlet pipeline for material to be fractionated; 6b Outlet pipeline for regenerated selective solvent.

[0039] 6c Disulfide outlet, 6d Circulating disulfide pipeline,

[0040] 6e disulfide product export pipeline. Detailed Implementation

[0041] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0042] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0043] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0044] In a first aspect, the present application relates to a continuous extractive sweetening process of a hydrocarbon stream, the continuous extractive sweetening process comprising the steps of:

[0045] (1) contacting the hydrocarbon stream with an extractive caustic to perform an alkaline extraction, to obtain a hydrocarbon stream product and a caustic containing mercaptan salt;

[0046] (2) contacting the caustic containing mercaptan salt from step (1) with an oxidizing gas to perform an oxidation, to obtain a caustic containing disulfide after separation of excess oxidizing gas;

[0047] (3) separating a material to be separated comprising the caustic containing disulfide from step (2) to obtain a disulfide stream and a lean caustic;

[0048] (4) contacting the lean caustic from step (3) with a selective solvent to perform a back extraction, to obtain a regenerated caustic and a selective solvent containing disulfide;

[0049] (5) separating a material to be fractionated comprising at least part of the selective solvent containing disulfide from step (4) to obtain a regenerated selective solvent and a disulfide product;

[0050] wherein the extractive caustic in step (1) comprises the regenerated caustic from step (4); and the material to be separated in step (3) further comprises at least part of the disulfide product from step (5).

[0051] It is to be understood that the extractive caustic in step (1) can comprise fresh caustic and regenerated caustic from step (4). The caustic used in the present application includes any known organic or / and inorganic basic reagent having the ability to extract mercaptans from gasoline. The ideal caustic is generally an aqueous solution of alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. If necessary, aqueous solutions of alkaline earth metal hydroxides such as calcium hydroxide, barium hydroxide, ammonia and aqueous solutions of organic quaternary ammonium bases can be used. Additives such as low carbon alcohols: methanol, ethanol, isopropyl alcohol, etc., nitrogen-, phosphorus-, oxygen-, sulfur-, arsenic-, antimony-containing compounds and various basic nitrogen compounds, etc. can be added to the basic reagent, the amount of which is generally not more than 200 μg / g. The particularly ideal caustic used in the present application is about 1% to 50% (by weight) of sodium hydroxide solution, potassium hydroxide solution, preferably 5% to 25% (by weight) of sodium hydroxide solution.

[0052] After the oxidation of step (2), in addition to the obtained alkali liquor containing disulfide, there can be residual oxidizing gas (tail gas), which can be treated by a subsequent liquid separation tank and light hydrocarbon recovery device for clean emission, or sent to the flue gas desulfurization system of the catalytic cracking device for incineration treatment, or recycled after pressurization. The separation in step (3) can use separation methods such as sedimentation separation and phase separation. After step (4), the residual disulfide (including residual oxidizing gas) in the poor alkali liquor is transferred into the selective solvent, and the obtained disulfide-containing selective solvent contains the residual oxidizing gas in the poor alkali liquor, and the obtained regenerated alkali liquor basically does not contain disulfide and oxidizing gas, which can be better returned to step (1) as an extraction alkali liquor.

[0053] It is particularly important to note that the inventors of the present application have innovatively found that by setting step (5), the fractionation and separation of the material to be fractionated containing at least part of the disulfide-containing selective solvent obtained from step (4) can simultaneously obtain regenerated selective solvent and disulfide product, and the obtained disulfide product can be partially returned to step (3) to mix with the disulfide-containing alkali liquor obtained from step (2) as the material to be separated for the separation in step (3), which greatly improves the separation degree of disulfide and poor alkali liquor, making the separation of the two more thorough, and then performing the subsequent step (4) counter-extraction, so that the obtained regenerated alkali liquor basically does not contain sodium mercaptan, disulfide and oxidizing gas, thereby obtaining regenerated alkali liquor without disulfide and oxidizing gas. Such regenerated alkali liquor is returned to step (1) as an extraction alkali liquor, which greatly improves the desulfurization effect of the hydrocarbon stream, significantly reduces the sulfur content of the obtained hydrocarbon stream product, and significantly improves the sulfur removal rate.

[0054] According to a preferred embodiment of the continuous extraction desulfurization method according to the first aspect of the present application, in step (4), the selective solvent comprises the regenerated selective solvent obtained from step (5) and optionally part of the disulfide-containing selective solvent obtained from step (4); and / or,

[0055] The disulfide-containing selective solvent obtained from step (4) used for fractionation and separation in step (5) accounts for 1% to 100% of the total volume of the disulfide-containing selective solvent obtained from step (4).

[0056] It should be noted that the selective solvent comprises optionally part of the disulfide-containing selective solvent obtained from step (4), wherein optionally part means that it can not contain (0 part) the disulfide-containing selective solvent obtained from step (4), or any part of the disulfide-containing selective solvent obtained from step (4).

[0057] It should be noted that in one case, the disulfide-containing selective solvent from step (4) can be divided into two parts, one part continues to be subjected to the fractionation separation in step (5), and the other part is subjected to the counter-extraction in step (4) after being contacted with the alkali-lean solution from step (3) as the selective solvent. Alternatively, in another case, the disulfide-containing selective solvent from step (4) is subjected to the fractionation separation in step (5) in its entirety, and the regenerated selective solvent obtained is returned to step (4) in its entirety as the selective solvent for the counter-extraction. In this way, the desulfurization method of the present application can be well operated in a self-circulation manner, and is a continuous counter-extraction desulfurization method, and such an arrangement can further improve the desulfurization effect while saving energy, and at the same time, a hydrocarbon stream product with lower sulfur content and a disulfide product with higher purity can be obtained.

[0058] It should be noted that in step (4), a part of the sulfur-containing selective solvent (disulfide-containing selective solvent) from the sulfur-containing selective solvent (disulfide-containing selective solvent) in contact with the alkali solution circulation is separated out to step (5) for fractionation, and the amount of the sulfur-containing selective solvent (disulfide-containing selective solvent) separated out is not specifically limited, as long as it ensures that step (5) is effectively and continuously operated to the minimum extent, and the sulfur-free selective solvent (regenerated selective solvent) obtained from step (5) is returned to step (4) in its entirety as the selective solvent for circulation, for example, 1% to 100% by volume of the sulfur-containing selective solvent (disulfide-containing selective solvent) from the sulfur-containing selective solvent (disulfide-containing selective solvent) in contact with the alkali solution circulation can be separated out to step (5) for fractionation, and the sulfur-free selective solvent (regenerated selective solvent) obtained after fractionation is returned to step (4) in its entirety, as long as the volume ratio of the alkali solution (alkali-lean solution) to the selective solvent in step (4) is within the required range.

[0059] According to a preferred embodiment of the continuous counter-extraction desulfurization method according to the first aspect of the present application, in step (4), the selective solvent further comprises a low-carbon liquid hydrocarbon for desulfurization;

[0060] The low-carbon liquid hydrocarbon is selected from a combination of one or more of C3 to C6 liquid hydrocarbons;

[0061] The low-carbon liquid hydrocarbon does not contain hydrogen sulfide and mercaptan.

[0062] It should be noted that the low-carbon liquid hydrocarbon is substantially free of hydrogen sulfide and mercaptan, and can be selected from any monomer liquid hydrocarbon with carbon number of 3-6 or mixed liquid hydrocarbon, such as refinery carbon three, carbon four, carbon five, carbon six or mixed fraction, light naphtha, light gasoline, etc. The "substantially free of hydrogen sulfide and mercaptan" means that no hydrogen sulfide and mercaptan is detected according to known detection method, or the content (sulfur basis) of hydrogen sulfide and mercaptan is below the lower limit of detection.

[0063] It should be noted that the back-extraction solvent or selective solvent used in the prior art back-extraction is often naphtha, gasoline, etc. Such selective solvent for back-extraction not only has general effect on back-extraction of disulfides, but also has complex treatment process of the selective solvent containing disulfides obtained by back-extraction.

[0064] The present inventors have found, in the process of years of research and development, that the desulfurized C3-C6 liquid hydrocarbon substantially free of hydrogen sulfide and mercaptan, especially the desulfurized C3, C4 or C5 hydrocarbon substantially free of hydrogen sulfide and mercaptan, is used as a newly introduced selective solvent, and then a part of the selective solvent containing disulfides obtained by back-extraction in step (4) is used as a selective solvent for back-extraction in step (4), another part of the selective solvent containing disulfides obtained by back-extraction in step (4) is subjected to fractional separation in step (5), the regenerated selective solvent obtained in step (5) is used as a selective solvent for back-extraction in step (4), and the disulfide product obtained in step (5) is mixed with the alkaline solution containing disulfides obtained in step (2) to be used as a material to be separated for separation in step (3). The whole process forms a continuous extraction desulfurization method of hydrocarbon flow which can operate in a self-circulation mode, and the desulfurization effect is significantly improved.

[0065] The desulfurized C3, C4 or C5 hydrocarbon substantially free of hydrogen sulfide and mercaptan obtained by back-extraction is used as a newly introduced selective solvent, and the low-carbon liquid hydrocarbon containing disulfides obtained by back-extraction is separated from the low-carbon liquid hydrocarbon by boiling point difference in step (5), and the low-carbon liquid hydrocarbon can be recycled as a selective solvent for back-extraction without being sent to another device for treatment (such as hydrogenation treatment, etc.), which greatly reduces the treatment difficulty and improves the desulfurization effect.

[0066] It is to be noted that in the preferred embodiment, the selective solvent in step (4) comprises three parts: the first part is the desulfurized low carbon liquid hydrocarbon as mentioned above, such as C3, C4 or C5 hydrocarbon which is substantially free of hydrogen sulfide and mercaptan and is first introduced into the counter-extraction process as the basic selective solvent, the second part is the partially disulfide-containing selective solvent obtained from step (4), and the third part is the regenerated selective solvent obtained from step (5), i.e. the selective solvent in the second and third parts is the selective solvent produced in the desulfurization process and recycled for use.

[0067] According to a preferred embodiment of the continuous counter-extraction desulfurization method according to the first aspect of the present application, in step (5), the material to be fractionated further comprises the disulfide stream obtained from step (3).

[0068] and / or,

[0069] The continuous counter-extraction desulfurization method further comprises a pre-alkali washing step before step (1):

[0070] The original hydrocarbon stream is subjected to pre-alkali washing to obtain the hydrocarbon stream in step (1).

[0071] It is to be noted that the disulfide stream obtained from step (3) is mixed with the optional part of the disulfide-containing selective solvent obtained from step (4) to form the material to be fractionated in step (5), and the fractionation separation in step (5) produces the regenerated selective solvent and the disulfide product.

[0072] Firstly, the disulfide stream obtained from step (3) is subjected to the fractionation in step (5) to obtain a disulfide product with higher purity, and the desulfurization process of the hydrocarbon stream produces two products: the hydrocarbon stream product and the disulfide product.

[0073] Secondly, a part of the disulfide product obtained from step (3) by the fractionation in step (5) can play a role similar to that of the selective solvent, and the mixture of the part and the disulfide-containing caustic solution obtained from step (2) is subjected to the separation in step (3) to greatly improve the separation degree of the lean caustic solution and the disulfide, and reduce the sulfur content and the oxidizing gas content in the regenerated caustic solution obtained subsequently to further improve the desulfurization effect.

[0074] It is to be noted that the pre-alkali washing can further improve the desulfurization effect before the alkali extraction in step (1).

[0075] According to a specific embodiment of the continuous counter-extraction desulfurization method according to the first aspect of the present application, the original hydrocarbon stream is selected from at least one of natural gas, liquefied petroleum gas, light naphtha, light gasoline and C1-C6 low carbon hydrocarbon.

[0076] It should be noted that the original hydrocarbon stream used in the continuous extraction desulfurization method of the present application can be selected from one or more combinations of the above-mentioned natural gas, liquefied petroleum gas, light naphtha, light gasoline and C1-C6 low carbon hydrocarbons containing mercaptans, but is not limited to the above-mentioned, and can also be selected from other materials to be desulfurized containing mercaptans.

[0077] According to a specific embodiment of the continuous extraction desulfurization method according to the first aspect of the present application, the conditions for performing the alkali extraction in step (1) include:

[0078] The temperature is -5°C to 100°C, preferably 25°C to 50°C;

[0079] The pressure is 0.1 MPa to 4.0 MPa, preferably 0.1 MPa to 2.0 MPa;

[0080] The volume ratio of the extraction alkali solution in the hydrocarbon stream is 1% to 50%, preferably 5% to 40%;

[0081] and / or,

[0082] The conditions for performing the oxidation in step (2) include:

[0083] The temperature is -5°C to 100°C, preferably 25°C to 80°C;

[0084] The pressure is 0.1 MPa to 2.0 MPa, preferably 0.1 MPa to 1.0 MPa;

[0085] The oxidizing gas is selected from at least one of oxygen, air and oxygen-enriched air; the amount of the oxidizing gas is greater than or equal to 1 to 20 times, preferably 2 to 10 times, the theoretical chemical requirement amount of the oxidizing gas required for oxidizing the mercaptide contained in the mercaptide-containing alkali solution into disulfide.

[0086] It should be noted that controlling the conditions for alkali extraction in step (1) as described above is conducive to maintaining the hydrocarbon stream in a liquid state, and for liquefied petroleum gas (LPG) as the hydrocarbon stream in step (1), the pressure is selected to be between 1.0 MPa and 2.0 MPa; the pressure in step (2) is preferably 0.1 MPa to 0.8 MPa; by controlling the conditions for alkali extraction in step (1) and oxidation in step (2) as described above, the desulfurization effect of the continuous extraction desulfurization method of the present application is further improved.

[0087] It should be noted that the theoretical requirement of oxidizing gas is calculated based on the requirement of 0.25 mole of oxygen for oxidizing one mole of mercaptan salt to disulfide, and the amount of oxidizing gas is more preferably 2 to 4 times the theoretical requirement. In step (2), in order to completely oxidize the mercaptan salt in the mercaptan salt-containing alkaline solution to disulfide, the alkaline solution needs to be heated to a temperature ensuring the catalytic oxidation to proceed, and thus the temperature can be higher than that in step (1), and the pressure should be lower than that in step (1). The excess oxidizing gas after the contact is released from the top of the oxidation tower used for the oxidation, and is cleaned and discharged after being treated by a subsequent liquid separator and a light hydrocarbon recovery device, or is sent to a flue gas desulfurization system of a catalytic cracking device for incineration treatment, or can be recycled after being pressurized.

[0088] It should be noted that in step (2), a catalyst for catalyzing the oxidation reaction needs to be present when the mercaptan salt-containing alkaline solution is contacted with the oxidizing gas for oxidation, and the catalyst can be a metal phthalocyanine catalyst, preferably a cobalt phthalocyanine compound such as sulfonated cobalt phthalocyanine or poly cobalt phthalocyanine as the oxidation catalyst. The cobalt phthalocyanine catalyst can be used by being dissolved in the alkaline solution or forming a stable emulsion in the alkaline solution, and the content in the alkaline solution when used can be 5 μg / g to 1000 μg / g, preferably 10 μg / g to 400 μg / g.

[0089] The cobalt phthalocyanine catalyst can also be used in the form of a supported fixed bed by being supported on a porous material such as activated carbon, and the content of the cobalt phthalocyanine catalyst supported on the activated carbon carrier when used can be 0.01% to 10%, preferably 0.05% to 1.0%, and various compounds containing nitrogen, phosphorus, oxygen, sulfur, arsenic, antimony and various basic nitrogen compounds can be used as catalytic aids on the supported catalyst. Preferably, a supported fixed bed catalyst is used.

[0090] According to another specific embodiment of the continuous extraction desulfurization method according to the first aspect of the present application, the conditions for performing the separation in step (3) include:

[0091] the temperature is -5°C to 80°C, preferably 25°C to 50°C;

[0092] the pressure is 0.1 MPa to 2.0 MPa, preferably 0.1 MPa to 1.0 MPa;

[0093] in the material to be separated, the volume ratio of the disulfide product from step (5) to the disulfide-containing alkaline solution from step (2) is 1:(0.01 to 100), preferably 1:(0.1 to 10);

[0094] and / or,

[0095] the conditions for performing the back extraction in step (4) include: ​

[0096] The temperature is -5°C to 80°C, preferably 25°C to 50°C;

[0097] The pressure is 0.1 MPa to 2.0 MPa, preferably 0.1 MPa to 1.0 MPa;

[0098] The volume ratio of the low-carbon liquid hydrocarbon as the selective solvent to the alkali-lean solution from step (3) is 1:(0.01-100), preferably 1:(0.1-10).

[0099] It should be noted that the pressure in step (3) is more preferably not more than 0.5 MPa, and the pressure in step (4) is more preferably not more than 0.5 MPa, so as to obtain a better desulfurization effect; by controlling the conditions of separation in step (3) and counter-extraction in step (4) as described above, the desulfurization effect of the continuous counter-extraction desulfurization method of the present application is further improved.

[0100] It should be noted that the separation in step (3) is preferably carried out by sedimentation separation, and after sedimentation, the disulfide stream is sent to a fractionating column for fractionation or concentration treatment in step (5). The time of the sedimentation separation is usually not less than 15 min, preferably not less than 45 min, and more preferably not less than 90 min. The selection of the pressure in step (4) should ensure that the selective solvent exists in a liquid state, and at the same time, it is relatively low and is comparable to that in step (3).

[0101] It should be noted that the continuous counter-extraction desulfurization method of the hydrocarbon stream of the first aspect of the present application can be implemented based on the continuous counter-extraction desulfurization system of the hydrocarbon stream of the second aspect of the present application, but is not limited to being implemented only by the continuous counter-extraction desulfurization system of the hydrocarbon stream of the second aspect of the present application. The continuous counter-extraction desulfurization method of the first aspect of the present application can also be implemented based on other devices, systems, etc., and all fall within the protection scope of the present application.

[0102] As a preferred embodiment, the disulfide-containing alkali solution from step (2) is cooled before step (3) is carried out, so as to reduce the volatilization of the disulfide stream and hydrocarbon gas as much as possible. Similarly, the pressure in step (3) can be selected to be lower than that in step (2).

[0103] According to a specific embodiment of the continuous counter-extraction desulfurization method of the first aspect of the present application, the purity of the disulfide product from step (5) is not less than 99%; and / or,

[0104] The sulfur content of the hydrocarbon stream product from step (1) is not more than 10 μg / g.

[0105] It should be noted that the regenerated selective solvent from step (5) is substantially free of disulfides and oxidizing gases.

[0106] In a second aspect, the present application relates to a continuous extractive desulfurization system of a hydrocarbon stream, such as Figure 1 or 2, the continuous extractive desulfurization system comprising an alkali extraction unit 2, an oxidation unit 3, a separation unit 4, a back extraction unit 5 and a fractionation column 6;

[0107] The alkali extraction unit 2 is provided with a hydrocarbon stream inlet line 1d, an extract alkali inlet 2a and a hydrocarbon stream product outlet line 2b, and the mercaptide-containing alkali outlet of the alkali extraction unit 2 is communicated with the mercaptide-containing alkali inlet of the oxidation unit 3 through a mercaptide-containing alkali line 2c, and the mercaptide-containing alkali line 2c is provided with an oxidizing gas inlet 3a;

[0108] The disulfide-containing alkali outlet of the oxidation unit 3 is communicated with the disulfide-containing alkali inlet of the separation unit 4 through a disulfide-containing alkali line 3c;

[0109] The separation unit 4 is provided with a disulfide stream outlet 4b and a lean alkali outlet, and the lean alkali outlet is communicated with the lean alkali inlet of the back extraction unit 5 through a lean alkali line 4a;

[0110] The back extraction unit 5 is provided with a selective solvent inlet line 5a, a regenerated alkali outlet line 5d and a disulfide-containing selective solvent outlet line 5b, and the disulfide-containing selective solvent outlet line 5b is communicated with the material to be fractionated inlet line 6a of the fractionation column 6;

[0111] The regenerated alkali outlet line 5d of the back extraction unit 5 is communicated with the extract alkali inlet 2a of the alkali extraction unit 2;

[0112] The fractionation column 6 is provided with a regenerated selective solvent outlet 6b and a disulfide outlet 6c, and the disulfide outlet 6c is communicated with the disulfide inlet of the separation unit 4 through a circulating disulfide line 6d.

[0113] It should be noted that in the alkali extraction unit 2, the mercaptan-containing hydrocarbon stream to be desulfurized enters the alkali extraction unit 2 through the hydrocarbon stream inlet line 1d, the extract alkali enters the alkali extraction unit 2 through the extract alkali inlet 2a, the mercaptan-containing hydrocarbon stream contacts with the extract alkali, and the mercaptan in the hydrocarbon stream reacts with the extract alkali to form mercaptide, i.e. through the alkali extraction process of the alkali extraction unit 2, a mercaptide-containing alkali is obtained.

[0114] The mercaptide-containing alkali obtained by the alkali extraction unit 2 flows to the oxidation unit 3 through the mercaptide-containing alkali line 2c, and the oxidizing gas enters the oxidation unit 3 through the oxidizing gas inlet 3a, and often a metal phthalocyanine catalyst is also provided in the oxidation unit 3, the mercaptide in the mercaptide-containing alkali contacts with oxygen and completes the oxidation reaction under the catalysis of the catalyst, and the mercaptide is converted into disulfide in the organic phase, and the oxidation process of the oxidation unit 3 obtains a disulfide-containing alkali.

[0115] The disulfide-containing alkaline liquor from the oxidation unit 3 flows into the separation unit 4 through the disulfide-containing alkaline liquor pipeline 3c, and the partial disulfide product from the fractionating column 6 flows into the separation unit 4 through the disulfide outlet 6c and the circulating disulfide pipeline 6d, and after the disulfide-containing alkaline liquor from the oxidation unit 3 and the disulfide product from the fractionating column 6 are contacted, a separation process is carried out, and a poor alkaline liquor and a disulfide-containing stream are obtained.

[0116] The obtained poor alkaline liquor flows into the back extraction unit 5 through the poor alkaline liquor pipeline 4a, and at the same time, the selective solvent flows into the back extraction unit 5 through the selective solvent inlet pipeline 5a; after a back extraction process, a regenerated alkaline liquor and a disulfide-containing selective solvent are obtained. The obtained regenerated alkaline liquor flows into the alkaline extraction unit 2 through the regenerated alkaline liquor outlet pipeline 5d and the extraction alkaline liquor inlet 2a for recycling as the extraction alkaline liquor. The obtained disulfide-containing selective solvent flows into the fractionating column 6 through the disulfide-containing selective solvent outlet pipeline 5b and the material to be fractionated inlet pipeline 6a for fractionation. In the fractionating column 6, the disulfide is concentrated at the bottom by virtue of the difference in boiling points, and the regenerated selective solvent is discharged from the top.

[0117] It should be noted that in the continuous extraction desulfurization system of the hydrocarbon stream of the present application, the disulfide outlet 6c of the fractionating column 6 is communicated with the disulfide inlet of the separation unit 4 through the circulating disulfide pipeline 6d, so that after the disulfide-containing alkaline liquor from the oxidation unit 3 is contacted with the disulfide product from the fractionating column 6, a separation in the separation unit 4 is carried out, which greatly improves the separation effect of the poor alkaline liquor and the disulfide, and the separation is more thorough, and further, the regenerated alkaline liquor obtained after the back extraction unit 5 does not contain sulfides and oxidizing gas, and the desulfurization effect of the continuous extraction desulfurization system is significantly improved.

[0118] According to a specific embodiment of the continuous extraction desulfurization system according to the second aspect of the present application, the selective solvent inlet pipeline 5a of the back extraction unit 5 is communicated with the disulfide-containing selective solvent outlet pipeline 5b;

[0119] and / or,

[0120] The selective solvent inlet pipeline 5a of the back extraction unit 5 is communicated with the regenerated selective solvent outlet 6b of the fractionating column 6 through the circulating pipeline 5c.

[0121] It is to be noted that part of the selective solvent containing disulfides from the back extraction unit 5 can be used as the selective solvent in the back extraction unit 5 in turn through the selective solvent outlet line 5b and the selective solvent inlet line 5a. The regenerated selective solvent from the fractionating column 6 is used as the selective solvent in the back extraction unit 5 through the regenerated selective solvent outlet 6b, the circulation line 5c and the selective solvent inlet line 5a. The continuous extraction desulfurization system of the present application can be operated in a self-circulation mode, saving energy and further improving the desulfurization effect.

[0122] According to another specific embodiment of the continuous extraction desulfurization system of the second aspect of the present application, the selective solvent inlet line 5a of the back extraction unit 5 is provided with a low-carbon liquid hydrocarbon inlet;

[0123] and / or,

[0124] The disulfide stream outlet 4b of the separation unit 4 is in communication with the material to be fractionated inlet line 6a of the fractionating column 6;

[0125] and / or,

[0126] The continuous extraction desulfurization system is further provided with a pre-alkali washing unit 1, which is provided with an original hydrocarbon stream inlet 1a, a pre-alkali washing lye inlet line 1b, a circulation lye line 1c, a post-pre-alkali washing lye outlet and a hydrocarbon stream outlet; the hydrocarbon stream outlet is in communication with the hydrocarbon stream inlet line 1d of the alkali extraction unit 2; the post-pre-alkali washing lye outlet is in communication with the pre-alkali washing lye inlet line 1b through the circulation lye line 1c; the pre-alkali washing lye inlet line 1b is in communication with the original hydrocarbon stream inlet 1a;

[0127] and / or,

[0128] The oxidation unit 3 is further provided with a tail gas outlet 3b;

[0129] and / or,

[0130] The fractionating column 6 is further provided with a disulfide product outlet line 6e in communication with the disulfide outlet 6c.

[0131] It is to be noted that the low-carbon liquid hydrocarbon as the newly introduced selective solvent can enter the selective solvent inlet line 5a through the low-carbon liquid hydrocarbon inlet and then enter the back extraction unit 5. The disulfide stream from the separation unit 4 can flow to the fractionating column 6 through the disulfide stream outlet 4b and the material to be fractionated inlet line 6a to be separated together with the selective solvent containing disulfides from the back extraction unit 5, obtaining the disulfide product and the regenerated selective solvent.

[0132] By setting up the pre-alkali washing unit 1, the alkali extraction of the hydrocarbon stream from the pre-alkali washing unit 1 into the alkali extraction unit 2 can further improve the desulfurization effect. Excess or residual oxidizing gases in the oxidation unit 3 can be discharged through the tail gas outlet 3b. Excess oxidizing gases can be treated by subsequent separators and light hydrocarbon recovery devices before being discharged cleanly, or sent to the flue gas desulfurization system of the catalytic cracking unit for incineration, or they can be recycled after pressurization. A portion of the disulfide product obtained from the fractionation tower 6 can be partially discharged through the disulfide product outlet pipeline 6e, or, after appropriate treatment, can be used as the final disulfide product.

[0133] According to a specific embodiment of the continuous extraction desulfurization system of the second aspect of the present invention, the conditions of the fractionation tower 6 include:

[0134] The temperature at the top of the tower is 35℃~80℃, preferably 40℃~65℃;

[0135] The pressure at the top of the tower is 0.15 MPa to 2.20 MPa, preferably 0.35 MPa to 1.20 MPa;

[0136] The temperature at the bottom of the tower is 55℃~150℃, preferably 60℃~130℃.

[0137] It should be noted that setting the above conditions in fractionation tower 6 can further improve the desulfurization effect of the system.

[0138] It should be noted that the continuous extraction desulfurization system for hydrocarbon streams described in the second aspect of the present invention can be implemented using the continuous extraction desulfurization method for hydrocarbon streams described in the first aspect of the present invention, but it is not limited to the continuous extraction desulfurization method for hydrocarbon streams described in the first aspect. Other methods can also be used, all of which fall within the protection scope of the present invention.

[0139] The operation process of the continuous extraction and desulfurization system for hydrocarbon streams in this application is described below:

[0140] like Figure 1 As shown in Figure 2, firstly, in the pre-alkali washing unit, the original hydrocarbon stream is mixed with fresh alkali solution from the pre-alkali washing alkali inlet line 1b and / or circulating alkali solution flowing out of the pre-alkali washing unit 1 from the circulating alkali solution line 1c, and then enters the pre-alkali washing unit 1 through the original hydrocarbon stream inlet 1a. Hydrogen sulfide (and some mercaptans) in the hydrocarbon stream are removed. The scheme with the pre-alkali washing step is the preferred scheme, achieving better desulfurization results.

[0141] Then, the hydrocarbon stream from which hydrogen sulfide is removed flows into the base extraction unit 2 through the hydrocarbon stream inlet pipeline 1d, and is countercurrently contacted with fresh alkaline liquor from the alkaline liquor inlet 2a and / or regenerated alkaline liquor from the regenerated alkaline liquor outlet pipeline 5d (communicating with the alkaline liquor inlet 2a) of the back extraction unit 5 in the base extraction unit 2, and mercaptans in the hydrocarbon stream are absorbed by the alkaline liquor to form mercaptide, and the hydrocarbon stream from which hydrogen sulfide and mercaptans are removed becomes a product and flows out from the hydrocarbon stream product outlet pipeline 2b at the top of the base extraction unit 2 to become a desulfurized product (hydrocarbon stream product).

[0142] The alkaline liquor in which mercaptans are absorbed, i.e., the mercaptide-containing alkaline liquor (rich alkaline liquor), leaves the base extraction unit 2 from the mercaptide-containing alkaline liquor pipeline 2c, and after being mixed with oxidizing gas (such as air) from the oxidizing gas inlet 3a, flows into the oxidation unit 3, and under the action of the fixed-bed oxidation catalyst, i.e., the metal phthalocyanine supported catalyst, loaded in the oxidation unit 3, the mercaptide in the mercaptide-containing alkaline liquor (rich alkaline liquor) is oxidized by the oxidizing gas to form disulfide, and the disulfide is transferred into the disulfide stream, and the alkaline liquor is preliminarily regenerated and becomes disulfide-containing alkaline liquor. The excess air tail gas after the preliminary regeneration of the alkaline liquor is released from the tail gas outlet 3b at the top of the oxidation unit 3, and after being treated by a subsequent liquid separation tank and a light hydrocarbon recovery device, it is discharged clean, or is sent to a catalytic cracking device for incineration treatment.

[0143] The disulfide-containing alkaline liquor from the oxidation unit 3 leaves the oxidation unit 3 from the disulfide-containing alkaline liquor pipeline 3c, and after being mixed with the disulfide product from the circulating disulfide pipeline 6d at the bottom of the fractionating column 6, it flows into the separation unit 4 for separation operation. It needs to be emphasized that the present inventors have innovatively found that during or before the separation process in the separation unit 4, by contacting the disulfide product obtained by fractionation in the fractionating column 6 with the disulfide-containing alkaline liquor from the oxidation unit 3, the phase separation process of disulfide and alkaline liquor can be greatly promoted, the separation process is significantly better and more thorough, and the desulfurization effect of the entire system is greatly improved, which is ingenious and has a significant effect.

[0144] In the separation unit 4, the lean alkaline liquor in the lower layer flows into the back extraction unit 5 from the lean alkaline liquor pipeline 4a at the bottom of the separation unit 4, and the disulfide stream in the upper layer flows out from the disulfide stream outlet 4b and can flow to the fractionating column 6 for subsequent fractionation treatment.

[0145] In the back-extraction unit 5, the lean caustic solution from the lean caustic solution line 4a is contacted with the selective solvent from the selective solvent inlet line 5a and separated after the contact, the selective solvent can include a combination of one or more of fresh selective solvent (such as desulfurized low carbon liquid hydrocarbon substantially free of hydrogen sulfide and mercaptan), the disulfide-containing selective solvent from the disulfide-containing selective solvent outlet line 5b, and the regenerated selective solvent from the regenerated selective solvent outlet 6b. The residual disulfides (including residual oxidizing gas) in the lean caustic solution are transferred into the selective solvent, the selective solvent that has absorbed the disulfides (including residual oxidizing gas) flows out from the disulfide-containing selective solvent outlet line 5b, and can be sent to the fractionation column 6 for fractionation, or be divided into two parts, one part is returned to the back-extraction unit 5 for back-extraction, and the other part is sent to the fractionation column 6 for subsequent fractionation treatment. The regenerated caustic solution substantially free of oxidizing gas and disulfides from the back-extraction unit 5 flows out through the regenerated caustic solution outlet line 5d and the extraction caustic solution inlet 2a in turn and is returned to the caustic extraction unit 2 for recycling.

[0146] In the fractionation column 6, the disulfide stream from the separation unit 4 through the disulfide stream outlet 4b and at least part of the disulfide-containing selective solvent from the back-extraction unit 5 through the disulfide-containing selective solvent outlet line 5b are mixed and then enter the fractionation column 6 through the material to be fractionated inlet line 6a, the selective solvent and the disulfides are separated by the difference in boiling point, the regenerated selective solvent free of disulfides and oxidizing gas flows out from the regenerated selective solvent outlet 6b at the top of the fractionation column, and then is returned to the back-extraction unit for recycling, and the concentrated disulfide product free of oxidizing gas is divided into two parts, one part flows into the separation unit 4 through the circulating disulfide line 6d and is contacted with the disulfide-containing caustic solution from the disulfide-containing caustic solution line 3c and then is separated, achieving recycling, and the other part flows out through the disulfide product outlet line 6e and is treated to become a disulfide product after appropriate treatment, and is utilized.

[0147] As can be seen from the above, in the continuous extraction desulfurization method or system of the present application, the disulfide product generated by fractionation is contacted with the disulfide-containing caustic solution and then undergoes a phase separation process, the disulfide-containing selective solvent generated by back-extraction can be partially recycled for back-extraction, and the regenerated selective solvent obtained by fractionation can be recycled for back-extraction, the entire process can form a closed loop system with self-circulation, energy is saved, and the desulfurization effect is significantly improved.

[0148] The contacting described in the present application can use various columns, devices known in the industry, such as a perforated plate extraction column, a packed extraction column, a fiber membrane contactor, a static mixing contactor, a jet contactor, a rotating gravity contactor, etc.

[0149] The present application is further illustrated in detail by the following examples, but is not limited to the present application.

[0150] The examples are intended to generally represent the flow of a preferred embodiment of the present application, and are not intended to give details of the containers, heaters, coolers, pumps, compressors, valves, control equipment for the process, etc., which are basic to those skilled in the art. The examples are intended to illustrate the present application, and are not intended to limit the present application in any way.

[0151] Example 1

[0152] The hydrocarbon stream to be desulfurized was light catalytic cracking gasoline, and its basic properties are shown in Table 1. Among them, the determination of sulfur content used ultraviolet fluorescence method, and the determination of mercaptan used potentiometric titration method.

[0153] Table 1

[0154] Density (20) / (g / cm 3 )]]> Distillation / °C Sulfur content / (μg / g) Mercaptan sulfur content / (μg / g) 0.6350 34～70 65 60

[0155] The continuous extraction desulfurization system shown in Figure 1 or Figure 2 The hydrocarbon stream in Table 1 - light catalytic cracking gasoline was desulfurized using the continuous extraction desulfurization system shown in

[0156] A 15% (by weight) NaOH solution was used in the alkali extraction unit, the volume ratio of alkali solution to hydrocarbon stream was 1:9, the temperature was room temperature, and the pressure was 0.50 MPa. The hydrocarbon stream product after completing alkali extraction in the alkali extraction unit flowed out from the hydrocarbon stream product outlet pipeline 2b, and the obtained mercaptide-containing alkali solution entered the oxidation unit.

[0157] In the oxidation unit, a metal phthalocyanine supported oxidation catalyst was loaded, with activated carbon (provided by Beijing Guanghua Crystal Activated Carbon Factory, model GH-8) as the carrier, sulfonated cobalt phthalocyanine as the main active component, content 0.5%, and dodecyl dimethyl benzyl ammonium chloride (content 1%) and isopropyl amine (content 5%) as the auxiliary active component, content based on the mass of the carrier. The preparation process of the catalyst is as follows: according to the target loading, respectively configure the dilute ammonia solution of sulfonated cobalt phthalocyanine, the mixed solution of dodecyl dimethyl benzyl ammonium chloride and isopropyl amine, and adsorb activated carbon in equal volume, and dry treatment each time by rotary evaporator.

[0158] In the oxidation unit, the amount of air injected is 4 times the theoretical chemical requirement for oxidizing the mercaptide contained in the mercaptide-containing alkaline solution from the alkaline extraction unit into disulfide, which is equivalent to a volume ratio of air to mercaptide-containing alkaline solution (from the alkaline extraction unit) of about 1:1 under standard conditions, the alkaline solution oxidation temperature is 50°C, and the pressure is 0.40 MPa. After oxidation, the excess air tail gas is separated out and sent to the flue gas desulfurization system of the catalytic cracking device for incineration.

[0159] After that, the disulfide-containing alkaline solution (from the oxidation unit) is cooled to room temperature and mixed with the disulfide product from the fractionating column at a volume ratio of 10:1 and then flows into the settling separation unit after mixing. The disulfide and the alkaline solution are separated, and a disulfide stream and a lean alkaline solution are obtained. The obtained lean alkaline solution enters the back-extraction unit, and the obtained disulfide stream enters the fractionating column. The temperature in the settling separation unit is 50°C, and the pressure is 0.30 MPa.

[0160] In the back-extraction unit, the inlet pressure is 0.30 MPa, and the selective solvent contacts the lean alkaline solution (from the separation unit) at room temperature, and the circulating volume ratio of the selective solvent to the lean alkaline solution is 1:1. The selective solvent used is a refinery carbon tetramer that is substantially free of hydrogen sulfide and mercaptans. After the selective solvent contacts the lean alkaline solution, it is separated to obtain a disulfide-containing selective solvent and a regenerated alkaline solution. The obtained disulfide-containing selective solvent is divided into two parts, one part of the disulfide-containing selective solvent is returned to the back-extraction unit for recycling, and the other part of the disulfide-containing selective solvent is mixed with the disulfide from the settling separation unit and then flows into the fractionating column for fractionation. In the disulfide-containing selective solvent obtained from the back-extraction unit, the volume ratio of the part returned to the back-extraction unit for recycling to the part entering the fractionating column for fractionation is 1:1 (i.e., the part entering the fractionating column for fractionation accounts for 50% of the total volume of the disulfide-containing selective solvent obtained from the back-extraction unit). The obtained regenerated alkaline solution is returned to the alkaline extraction unit for recycling.

[0161] In the fractionating column, the top pressure is 0.5 MPa, the top temperature is 51.5°C, the bottom temperature is 90°C, and the reflux ratio is 1.0. The disulfide stream from the separation unit and the part of the disulfide-containing selective solvent from the back-extraction unit are fractionated and separated in the fractionating column, and the regenerated selective solvent is obtained at the top, and the disulfide product is obtained at the bottom. The obtained regenerated selective solvent is returned to the back-extraction unit for recycling, and the obtained disulfide product is partially returned to the separation unit to contact the disulfide-containing alkaline solution for the separation process, and the other part of the disulfide product can be output.

[0162] The results show that after the treatment, the sulfur content in the light gasoline flowing out of the hydrocarbon stream product outlet pipeline 2b is reduced to 5 μg / g, not only the mercaptans are completely removed, but also the sulfur content is greatly reduced (the sulfur content reduction of the light gasoline is equivalent to the sulfur content of the mercaptan before the desulfurization treatment). The regenerated alkali solution obtained from the back extraction unit is detected to have no sodium mercaptide (determined by potentiometric titration), indicating that the alkali solution containing mercaptide is completely regenerated, and the regenerated alkali solution obtained by back extraction also has no disulfide, indicating that the regenerated alkali solution returned to the alkali extraction step does not contain disulfide and oxidizing gas, so there is no case that the regenerated alkali solution carries disulfide into the light gasoline in the alkali extraction step, and there is also no case that part of the mercaptans in the light gasoline are oxidized to disulfide by the oxidizing gas carried by the regenerated alkali solution and still remain in the light gasoline. The obtained disulfide product is colorless and transparent, and the purity is not less than 99%.

[0163] Example 2

[0164] The hydrocarbon stream to be desulfurized is liquefied petroleum gas, density (20°C): 0.557 g / cm 3 , sulfur content: 215 μg / g (determined by ultraviolet fluorescence method).

[0165] The continuous extraction desulfurization system shown in Figure 1 or Figure 2 is used for desulfurization treatment of the above hydrocarbon stream-liquefied petroleum gas. The pre-alkali washing alkali solution is a 5% (by weight) NaOH solution, and the alkali solution dosage is 5% of the weight of the raw material (the hydrocarbon stream to be desulfurized). The hydrocarbon stream after pre-alkali washing enters the alkali extraction unit.

[0166] In the alkali extraction unit, the alkali solution used is a 15% (by weight) NaOH solution. In the alkali extraction unit, the volume ratio of the alkali solution to the raw material (the hydrocarbon stream obtained from the pre-alkali washing unit) is 3:7, the temperature is room temperature, and the pressure is 1.6 MPa. The rest is the same as in Example 1. The desulfurization results are shown in Table 2.

[0167] The results show that after the treatment, the sulfur content in the liquefied petroleum gas is reduced to 3 μg / g. The regenerated alkali solution is detected to have no sodium mercaptide (determined by potentiometric titration), indicating that the alkali solution containing mercaptide is completely regenerated, and the regenerated alkali solution obtained by back extraction also has no disulfide, indicating that the regenerated alkali solution returned to the extraction step basically does not contain disulfide and air.

[0168] Comparative Example 1-2

[0169] Comparative Example 1 and Comparative Example 2 use Figure 1 or Figure 2The continuous extraction desulfurization system of the hydrocarbon stream shown is used to desulfurize the hydrocarbon stream of Example 1, i.e. light catalytic cracking gasoline, and the hydrocarbon stream of Example 2, i.e. liquefied petroleum gas, respectively. The operating conditions used, the catalysts used are the same as those of Example 1 and Example 2, respectively, no selective solvent anti-extraction of disulfides is used (no anti-extraction unit 5 is used for anti-extraction), and no fractionation process is carried out by the fractionation column, and no part of the disulfide product produced by fractionation is returned to be separated after being contacted with the disulfide-containing lye. After oxidation of the lye, the lye is separated from the excess oxidizing gas and disulfides by natural sedimentation to obtain regenerated lye, which is returned to the lye extraction unit for recycling. The desulfurization results are shown in Table 2.

[0170] Compared with Example 1, the light gasoline treated in Comparative Example 1 has a greatly reduced content of mercaptans, but the desulfurization effect is not ideal, part of the mercaptan sulfur is converted into disulfides and remains in the product after desulfurization, which may be due to the fact that the regenerated lye carries a small amount of air back to the extraction system, causing part of the mercaptans to be oxidized in the extraction unit and remain in the product after desulfurization, or it may be because the regenerated lye carries a small amount of disulfides back to the extraction unit, and then the disulfides are transferred into the product after desulfurization.

[0171] Compared with Example 2, the liquefied petroleum gas treated in Comparative Example 2 still has a relatively large amount of sulfides, and the reason is the same as that of Comparative Example 1.

[0172] Table 2

[0173]

[0174] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "back", "left", "right" and the like indicate the orientation or positional relationship based on the working state of the present application, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as limiting the present application in terms of indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0175] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood in a broad sense. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0176] The above describes the present application in combination with the preferred embodiments, but these embodiments are only exemplary and serve only to illustrate. On this basis, various substitutions and improvements can be made to the present application, and these all fall within the scope of protection of the present application.

Claims

1. A process for the continuous extractive desulfurization of a hydrocarbon stream, characterized in that, The continuous extractive desulfurization method comprises the following steps: (1) contacting a hydrocarbon stream with an extractive alkali solution to perform alkaline extraction, to obtain a hydrocarbon stream product and a sulfidic alkali solution containing mercaptides; (2) contacting the sulfidic alkali solution containing mercaptides from step (1) with an oxidizing gas to perform oxidation, and after separation of excess oxidizing gas, obtaining a disulfide-containing alkali solution; (3) separating a material to be separated containing the disulfide-containing alkali solution from step (2) to obtain a disulfide stream and a lean alkali solution; (4) contacting the lean alkali solution from step (3) with a selective solvent to perform reverse extraction, to obtain a regenerated alkali solution and a disulfide-containing selective solvent; (5) separating a material to be fractionated containing at least part of the disulfide-containing selective solvent from step (4) to obtain a regenerated selective solvent and a disulfide product; wherein the extractive alkali solution in step (1) contains the regenerated alkali solution from step (4); the material to be separated in step (3) further contains at least part of the disulfide product from step (5), and in the material to be separated, the volume ratio of the disulfide product from step (5) to the disulfide-containing alkali solution from step (2) is 1:(0.01-100); and in step (4), the selective solvent contains low-carbon liquid hydrocarbons free of hydrogen sulfide and mercaptans in desulfurization, and the low-carbon liquid hydrocarbons are selected from a combination of one or more of C3-C6 liquid hydrocarbons.

2. The continuous extractive desulfurization method according to claim 1, characterized by, in step (4), the selective solvent contains the regenerated selective solvent from step (5) and part of the disulfide-containing selective solvent from step (4); and / or, the disulfide-containing selective solvent from step (4) used to perform the fractionation separation in step (5) accounts for 1%-100% of the total volume of the disulfide-containing selective solvent from step (4).

3. The continuous extractive desulfurization method according to claim 1, characterized by, in step (5), the material to be fractionated further contains the disulfide stream from step (3); and / or, the continuous extractive desulfurization method further comprises a pre-alkali washing step before step (1): performing pre-alkali washing on an original hydrocarbon stream to obtain the hydrocarbon stream in step (1).

4. The continuous extractive desulfurization method according to claim 3, characterized by, The original hydrocarbon stream is selected from at least one of natural gas, liquefied petroleum gas, light naphtha, light gasoline and C1-C6 low-carbon hydrocarbons.

5. The continuous extractive desulfurization process according to claim 1, characterized in that, The conditions for performing the alkaline extraction in step (1) include: the temperature is -5°C-100°C; the pressure is 0.1 MPa-4.0 MPa; the volume ratio of the extractive alkali solution in the hydrocarbon stream is 1%-50%; and / or, The conditions for performing the oxidation in step (2) include: the temperature is -5°C-100°C; the pressure is 0.1 MPa-2.0 MPa; the oxidizing gas is selected from at least one of oxygen and air; the amount of the oxidizing gas is greater than or equal to 1-20 times the theoretical chemical requirement for oxidizing the sulfidic alkali solution containing mercaptides into disulfides.

6. The continuous extractive desulfurization process according to claim 1, characterized in that, The conditions for performing the separation in step (3) include: the temperature is -5°C-80°C; the pressure is 0.1 MPa-2.0 MPa; The volume ratio of the disulfide product from step (5) to the disulfide-containing alkaline liquor from step (2) in the material to be separated is 1:(0.1-10); and / or, The conditions for performing the back extraction in step (4) include: The temperature is -5℃-80℃; The pressure is 0.1MPa-2.0MPa; The volume ratio of the low-carbon liquid hydrocarbon as the selective solvent to the poor alkaline liquor from step (3) is 1:(0.01-100).

7. The continuous extractive desulfurization process according to claim 1, characterized in that, The purity of the disulfide product from step (5) is not less than 99%; and / or, The sulfur content of the hydrocarbon stream product from step (1) is not more than 10μg / g.

8. The continuous extractive desulfurization method according to claim according to claim 1, characterized in that, The conditions for performing the alkaline extraction in step (1) include: The temperature is 25℃-50℃; The pressure is 0.1MPa-2.0MPa; The volume proportion of the extraction alkaline liquor in the hydrocarbon stream is 5%-40%; and / or, The conditions for performing the oxidation in step (2) include: The temperature is 25℃-80℃; The pressure is 0.1MPa-1.0MPa; The oxidizing gas is selected from at least one of oxygen and oxygen-enriched air; The amount of the oxidizing gas is greater than or equal to 2-10 times the theoretical chemical requirement for oxidizing the mercaptide in the mercaptide-containing alkaline liquor into disulfide.

9. The continuous extractive desulfurization process according to claim 1, characterized in that, The conditions for performing the separation in step (3) include: The temperature is 25℃-50℃; The pressure is 0.1MPa-1.0MPa; The volume ratio of the disulfide product from step (5) to the disulfide-containing alkaline liquor from step (2) in the material to be separated is 1:(0.1-10); and / or, The conditions for performing the back extraction in step (4) include: The temperature is 25℃-50℃; The pressure is 0.1MPa-1.0MPa; The volume ratio of the low-carbon liquid hydrocarbon as the selective solvent to the poor alkaline liquor from step (3) is 1:(0.1-10).

10. A continuous extractive desulfurization system for a hydrocarbon stream, characterized by, The continuous extraction desulfurization system comprises an alkaline extraction unit (2), an oxidation unit (3), a separation unit (4), a back extraction unit (5) and a fractionating column (6); The alkaline extraction unit (2) is provided with a hydrocarbon stream inlet pipeline (1d), an extraction alkaline liquor inlet (2a) and a hydrocarbon stream product outlet pipeline (2b), the mercaptide-containing alkaline liquor outlet of the alkaline extraction unit (2) is communicated with the mercaptide-containing alkaline liquor inlet of the oxidation unit (3) through a mercaptide-containing alkaline liquor pipeline (2c), and the mercaptide-containing alkaline liquor pipeline (2c) is provided with an oxidizing gas inlet (3a); The disulfide-containing alkaline liquor outlet of the oxidation unit (3) is communicated with the disulfide-containing alkaline liquor inlet of the separation unit (4) through a disulfide-containing alkaline liquor pipeline (3c); The separation unit (4) is provided with a disulfide stream outlet (4b) and a poor alkaline liquor outlet, and the poor alkaline liquor outlet is communicated with the poor alkaline liquor inlet of the back extraction unit (5) through a poor alkaline liquor pipeline (4a); The back extraction unit (5) is provided with a selective solvent inlet pipeline (5a), a regenerated alkali liquor outlet pipeline (5d) and a disulfide-containing selective solvent outlet pipeline (5b); the disulfide-containing selective solvent outlet pipeline (5b) is communicated with the feed material inlet pipeline (6a) of the fractionating column (6); The regenerated alkali liquor outlet pipeline (5d) of the back extraction unit (5) is communicated with the extraction alkali liquor inlet (2a) of the alkali extraction unit (2); The fractionating column (6) is provided with a regenerated selective solvent outlet (6b) and a disulfide outlet (6c), which is communicated with the disulfide inlet of the separation unit (4) through a circulating disulfide pipeline (6d).

11. The continuous extractive desulfurization system according to claim 10, characterized in that, The selective solvent inlet pipeline (5a) of the back extraction unit (5) is communicated with the disulfide-containing selective solvent outlet pipeline (5b); And / or, The selective solvent inlet pipeline (5a) of the back extraction unit (5) is communicated with the regenerated selective solvent outlet (6b) of the fractionating column (6) through a circulating pipeline (5c).

12. The continuous extractive desulfurization system according to claim 10, characterized in that, The selective solvent inlet pipeline (5a) of the back extraction unit (5) is provided with a low-carbon liquid hydrocarbon inlet; And / or, The disulfide flow outlet (4b) of the separation unit (4) is communicated with the feed material inlet pipeline (6a) of the fractionating column (6); And / or, The continuous extraction desulfurization system is further provided with a pre-alkali washing unit (1), which is provided with an original hydrocarbon flow inlet (1a), a pre-alkali washing alkali liquor inlet pipeline (1b), a circulating alkali liquor pipeline (1c), a pre-alkali washing alkali liquor outlet and a hydrocarbon flow outlet; the hydrocarbon flow outlet is communicated with the hydrocarbon flow inlet pipeline (1d) of the alkali extraction unit (2); the pre-alkali washing alkali liquor outlet is communicated with the pre-alkali washing alkali liquor inlet pipeline (1b) through the circulating alkali liquor pipeline (1c); the pre-alkali washing alkali liquor inlet pipeline (1b) is communicated with the original hydrocarbon flow inlet (1a); And / or, The oxidation unit (3) is further provided with a tail gas outlet (3b); And / or, The fractionating column (6) is further provided with a disulfide product outlet pipeline (6e) communicated with the disulfide outlet (6c).

13. The continuous extractive desulfurization system according to claim 10, characterized in that, The conditions of the fractionating column (6) include: The temperature at the top of the column is 35-80℃; The pressure at the top of the column is 0.15-2.20 MPa; The temperature at the bottom of the column is 55-150℃.

14. The continuous extractive desulfurization system according to claim 10, characterized in that, The conditions of the fractionating column (6) include: The temperature at the top of the column is 40-65℃; The pressure at the top of the column is 0.35-1.20 MPa; The temperature at the bottom of the column is 60-130℃.

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