Hydrocarbon stream extraction desulfurization method and system combined with gasoline production

Abstract

The invention relates to a hydrocarbon stream extraction desulfurization method and system combined with gasoline production. The method comprises the following steps: (1) carrying out alkali extraction on a hydrocarbon stream to obtain a hydrocarbon stream product and a mercaptan-containing alkali solution; (2) oxidizing the thiol-containing alkali liquor to obtain disulfide-containing alkali liquor; (3) contacting the disulfide-containing alkali liquor with a first selective solvent, and separating to obtain lean alkali liquor and the first disulfide-containing selective solvent; (4) contacting the lean alkali liquor with a second selective solvent for reverse extraction to obtain regenerated alkali liquor and a second disulfide-containing selective solvent; (5) fractionating the low-carbon liquid hydrocarbon and / or at least part of the hydrocarbon flow product to obtain a C5 fraction, and using the C5 fraction as a second selective solvent; the first selective solvent in the step (3) comprises part of the second disulfide-containing selective solvent. The hydrocarbon stream product with lower sulfur content is obtained, and the disulfide-containing selective solvent is absorbed in gasoline and then is subjected to desulfurization refining, so that the C5 fraction is converted into the gasoline fraction to be utilized.

Description

Technical Field

[0001] The invention relates to the technical field of hydrocarbon material refining, and in particular to a hydrocarbon stream extraction and desulfurization method and system combined with gasoline production. Background Art

[0002] Alkali extraction is a traditional method for refining hydrocarbon materials. It is widely used in the desulfurization and refining of low-carbon light hydrocarbon materials such as natural gas, liquefied petroleum gas, light gasoline, naphtha, alkanes, olefins, etc. containing acidic sulfides. The method is to contact the hydrocarbon fluid with alkali solution, and the acidic sulfides mainly composed of mercaptans in the hydrocarbon stream react with the alkali solution to form mercaptides and are removed from the hydrocarbon stream.

[0003] If the alkali solution containing mercaptide salt is directly discharged, it is neither economical nor in line with environmental protection requirements. Usually, an oxidation method is used to oxidize the mercaptide salt into disulfide so that the alkali solution containing mercaptide salt is regenerated (see U.S. Patent No. 2853432). Specifically, the method injects air and an oxidation catalyst into the used alkali solution to oxidize the mercaptide salt dissolved in the alkali solution into disulfide, thereby regenerating the alkali solution. However, the alkali solution after oxidation and regeneration contains disulfide. If it is circulated for alkali extraction of hydrocarbon streams, the hydrocarbon streams will absorb the disulfide and make it difficult to reduce its sulfur content or even increase it. For this reason, it is necessary to separate the regenerated alkali solution from the disulfide therein by sedimentation separation and / or organic hydrocarbon solvent back extraction so that the regenerated alkali solution can continue to be used for removing mercaptans in the hydrocarbon stream and effectively reduce the sulfur content in the hydrocarbon stream, thereby greatly reducing the discharge of spent alkali.

[0004] The existing alkaline solution extraction desulfurization technology includes the following basic steps in succession: (1) extraction, (2) oxidation, (3) phase separation, and (4) back extraction. In the extraction step, the alkaline solution (including the regenerated alkaline solution) contacts the hydrocarbon stream containing mercaptans and reacts with the mercaptans to form mercaptides, which are dissolved in the alkaline solution; in the oxidation step, the alkaline solution containing mercaptides from the extraction step is mixed with the injected oxidizing gas and oxidation catalyst to oxidize the mercaptides in the alkaline solution to disulfides, thereby regenerating the alkaline solution, wherein the oxidation catalyst is a well-known metal phthalocyanine, such as sulfonated cobalt phthalocyanine and polyphthalocyanine cobalt. Usually, the metal phthalocyanine catalyst is intermittently or continuously injected into the oxidation step along with fresh alkali solution (commercially available metal phthalocyanine catalyst is usually in the form of powdered solid or liquid mixture); in the phase separation step, the regenerated alkali solution from the oxidation step and the mixture of disulfide and oxidizing gas are separated by sedimentation, on the one hand, to release the excess oxidizing gas, and on the other hand, to separate the alkali solution from the disulfide aggregated into phases, so as to achieve the purpose of removing the disulfide. Due to the small density difference between disulfide and alkali solution, it is usually difficult to aggregate the disulfide into phases and completely separate and remove it in the phase separation step of sedimentation due to the relatively short sedimentation time. For this reason, the back extraction step is applied. In the back extraction step, the alkali solution from the phase separation step of sedimentation is mixed with an organic hydrocarbon solvent so that the remaining disulfide in the alkali solution is back extracted into the organic hydrocarbon solvent so that the regenerated alkali solution and the disulfide-containing solvent are separated from each other, and the regenerated alkali solution treated by back extraction is returned to the extraction step for continued use. In order to enhance the desulfurization effect of hydrocarbon streams, organic liquid additives with extraction and / or oxidation-assisting effects, such as low-carbon alcohols, may be added to the alkali solution.

[0005] The stripping solvents used in the literature are mostly naphtha fractions, gasoline fractions, etc. The stripping solvent is usually sent to the hydrogenation unit for desulfurization treatment after absorbing disulfides. However, due to the influence of the trace amount of alkali liquid carried, especially for the stripping solvent containing aromatics and easily emulsified, it is difficult to wash away the trace amount of alkali liquid carried even with water washing, which can easily lead to poisoning and deactivation of the hydrogenation catalyst during hydrogenation treatment. There are also methods that send hydrocarbon stripping solvents back to the catalytic cracking unit for treatment and high-temperature cracking in the catalytic cracking unit. However, the stripping solvent carrying trace amounts of alkali liquid will also be seriously harmful to the catalytic cracking catalyst. This makes the treatment of waste stripping solvents a problem that is not easy to solve in refineries.

[0006] In addition, in the back-extraction step, the disulfides produced after the oxidation regeneration of the alkali solution are usually not completely removed from the regenerated alkali solution, and there is often a large amount of residual content. This makes it easy for the regenerated alkali solution to transfer disulfides into the hydrocarbon stream when it is returned to the extraction system for use, resulting in a decrease in the desulfurization rate of the hydrocarbon stream extraction, and even the abnormal phenomenon of increased sulfur content.

[0007] In addition, before the regenerated alkali solution returns to the extraction system and contacts the hydrocarbon stream containing mercaptans, there are often trace amounts of oxidizing gases remaining, which causes some mercaptans to be oxidized to disulfides in the extraction system and remain in the hydrocarbon stream after extraction. For this reason, patent CN 200510132299.7 uses nitrogen replacement to remove the oxidizing gases carried in the regenerated alkali solution before back extraction, but the replacement is often not complete, especially when the back extraction solvent carries oxidizing gases (for example, naphtha and gasoline stored in the refinery tank area are used as back extraction solvents and are easily exposed to air), which is likely to affect the deep desulfurization of the hydrocarbon stream.

[0008] In summary, how to better treat the alkali solution after alkali extraction in the desulfurization process of hydrocarbon streams to obtain regenerated alkali solution free of sulfides and oxidizing gases for recycling, so as to significantly improve the desulfurization effect, and how to better treat the selective solvent for absorbing disulfides, are technical problems that need to be solved urgently. Summary of the invention

[0009] The present invention provides a hydrocarbon stream extraction desulfurization method and system combined with gasoline production, the purpose of which is to better treat the alkali liquor after alkali extraction so that the recycled regenerated alkali liquor does not contain sulfide and oxidizing gas, thereby improving the desulfurization effect and better treating the selective solvent that absorbs disulfide.

[0010] In a first aspect, the present invention relates to a hydrocarbon stream extractive desulfurization method associated with gasoline production, the hydrocarbon stream extractive desulfurization method comprising the following steps:

[0011] (1) contacting a hydrocarbon stream with an extraction alkali solution in an alkali extraction unit to perform alkali extraction to obtain a hydrocarbon stream product and a mercaptan-containing alkali solution;

[0012] (2) contacting the mercaptan-containing alkali solution from step (1) with an oxidizing gas in an oxidation unit for oxidation, and separating the remaining oxidizing gas to obtain a disulfide-containing alkali solution;

[0013] (3) contacting and separating the disulfide-containing alkali solution from step (2) with a first selective solvent in a separation unit to obtain a lean alkali solution and a first disulfide-containing selective solvent;

[0014] (4) contacting the lean alkali solution from step (3) with a second selective solvent in a stripping unit and stripping the solution to obtain a regenerated alkali solution and a second disulfide-containing selective solvent;

[0015] (5) subjecting the low-carbon liquid hydrocarbons and / or at least a portion of the hydrocarbon stream product obtained from step (1) to a decarbonization five fractionation tower to obtain a decarbonization five fraction and a remaining fraction;

[0016] Wherein, the extraction alkali solution in step (1) comprises the regenerated alkali solution obtained from step (4); the first selective solvent in step (3) comprises part of the second disulfide-containing selective solvent obtained from step (4); and the second selective solvent in step (4) comprises the C5 fraction obtained from step (5).

[0017] In a second aspect, the present invention relates to a hydrocarbon stream extraction and desulfurization system combined with gasoline production, characterized in that the hydrocarbon stream extraction and desulfurization system comprises:

[0018] Alkali extraction unit, oxidation unit, separation unit, back extraction unit and decarbonization five fractionation tower;

[0019] The alkali extraction unit is provided with a hydrocarbon stream inlet pipeline, an extraction alkali solution inlet, a hydrocarbon stream product outlet and a mercaptan-containing alkali solution outlet;

[0020] The mercaptoalkoxide alkali solution inlet of the oxidation unit is connected to the mercaptoalkoxide alkali solution outlet of the alkali extraction unit through a mercaptoalkoxide alkali solution pipeline, and the mercaptoalkoxide alkali solution pipeline is provided with an oxidizing gas inlet; the oxidation unit is also provided with a residual oxidizing gas outlet and a disulfide-containing alkali solution outlet;

[0021] The disulfide-containing alkali solution inlet of the separation unit is connected to the disulfide-containing alkali solution outlet of the oxidation unit, and the separation unit is provided with a first selective solvent inlet, a lean alkali solution outlet and a first disulfide-containing selective solvent outlet; the first disulfide-containing selective solvent outlet is connected to the raw material inlet of the absorption stabilization system of the catalytic cracking unit;

[0022] The lean alkali solution inlet of the back-extraction unit is connected to the lean alkali solution outlet of the separation unit, and the back-extraction unit is provided with a second selective solvent inlet pipeline, a second disulfide-containing selective solvent outlet and a regeneration alkali solution outlet pipeline; the second disulfide-containing selective solvent outlet is connected to the first selective solvent inlet of the separation unit through a selective solvent pipeline; the regeneration alkali solution outlet pipeline is connected to the extraction alkali solution inlet of the alkali extraction unit;

[0023] The decarbonization five fractionation tower is provided with an inlet for materials to be fractionated, an outlet pipeline for the carbon five fraction and an outlet for the remaining fraction; the outlet pipeline for the carbon five fraction is connected to the second selective solvent inlet pipeline of the back extraction unit.

[0024] Beneficial effects:

[0025] The hydrocarbon stream extraction and desulfurization method combined with gasoline production of the present invention uses the C5 fraction as a selective solvent to carry out back extraction of alkali solution, and can obtain regenerated alkali solution free of sulfide and oxidizing gas for recycling, thereby significantly improving the desulfurization effect and obtaining a high-quality hydrocarbon stream product with a lower sulfur content. The disulfide-containing selective solvent produced in the separation step is absorbed into gasoline and then subjected to desulfurization and refining, so that the C5 fraction is converted into a gasoline fraction for utilization after absorbing disulfide. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of a specific embodiment of a hydrocarbon stream extraction and desulfurization system combined with gasoline production according to the present invention;

[0027] Figure 2 It is a structural schematic diagram of another specific embodiment of a hydrocarbon stream extraction desulfurization system combined with gasoline production according to the present invention;

[0028] Description of reference numerals:

[0029] 1 Pre-alkali washing unit, 2 alkali extraction unit, 3 oxidation unit, 4 separation unit,

[0030] 5 back extraction unit, 6 decarbonization five fractionation tower;

[0031] 1a original hydrocarbon stream inlet pipeline, 1b pre-alkali wash alkali solution inlet pipeline, 1c circulating alkali solution outlet, 1d hydrocarbon stream inlet pipeline;

[0032] 2a extraction alkali liquor inlet, 2b hydrocarbon stream product outlet, 2c mercaptan salt alkali liquor pipeline;

[0033] 3a oxidizing gas inlet, 3b residual oxidizing gas outlet, 3c disulfide-containing alkali solution outlet;

[0034] 4a is an outlet for lean alkali solution, 4b is an outlet for the first disulfide-containing selective solvent;

[0035] 5a second selective solvent inlet pipeline, 5b second disulfide-containing selective solvent outlet,

[0036] 5c selective solvent pipeline, 5d regeneration alkali solution outlet pipeline;

[0037] 6a is the inlet of the material to be fractionated, 6b is the outlet of the remaining fraction, 6c is the outlet pipeline of the C5 fraction. DETAILED DESCRIPTION

[0038] The present application is further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present application will become clearer and more specific.

[0039] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0040] In addition, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0041] In a first aspect, the present invention relates to a hydrocarbon stream extractive desulfurization method associated with gasoline production, the hydrocarbon stream extractive desulfurization method comprising the following steps:

[0042] (1) contacting a hydrocarbon stream with an extraction alkali solution in an alkali extraction unit to perform alkali extraction to obtain a hydrocarbon stream product and a mercaptan-containing alkali solution;

[0043] (2) contacting the mercaptan-containing alkali solution from step (1) with an oxidizing gas in an oxidation unit for oxidation, and separating the remaining oxidizing gas to obtain a disulfide-containing alkali solution;

[0044] (3) contacting and separating the disulfide-containing alkali solution from step (2) with a first selective solvent in a separation unit to obtain a lean alkali solution and a first disulfide-containing selective solvent;

[0045] (4) contacting the lean alkali solution from step (3) with a second selective solvent in a stripping unit and stripping the solution to obtain a regenerated alkali solution and a second disulfide-containing selective solvent;

[0046] (5) subjecting the low-carbon liquid hydrocarbons and / or at least a portion of the hydrocarbon stream product obtained from step (1) to a decarbonization five fractionation tower to obtain a decarbonization five fraction and a remaining fraction;

[0047] Wherein, the extraction alkali solution in step (1) comprises the regenerated alkali solution obtained from step (4); the first selective solvent in step (3) comprises part of the second disulfide-containing selective solvent obtained from step (4); and the second selective solvent in step (4) comprises the C5 fraction obtained from step (5).

[0048] It should be noted that the first disulfide-containing selective solvent obtained from step (3) can also be partially returned to step (3) for use as the first selective solvent. The extraction alkali solution may include any known organic and / or inorganic alkaline reagent that has the ability to extract mercaptans from gasoline. The ideal alkali solution is generally an aqueous solution of an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. If necessary, an aqueous solution of an alkaline earth metal hydroxide such as calcium hydroxide and barium hydroxide, ammonia water, and an aqueous solution of an organic quaternary ammonium base can be used. Auxiliary agents can be added to the alkaline reagent, such as low-carbon alcohols: methanol, ethanol, isopropanol, etc., nitrogen, phosphorus, oxygen, sulfur, arsenic, antimony, etc. The amount of the alkali solution used in the present invention is preferably about 1% to 50% (by weight) sodium hydroxide solution or potassium hydroxide solution, preferably 5% to 25% (by weight) sodium hydroxide solution.

[0049] It should be noted that in the hydrocarbon stream extraction and desulfurization method combined with gasoline production of the present invention, the hydrocarbon stream containing mercaptan is subjected to alkali extraction in step (1), and mercaptan reacts with alkali solution to be converted into mercaptide salt to obtain mercaptan salt alkali solution, and mercaptan in the hydrocarbon stream is converted into mercaptide salt and removed to obtain hydrocarbon stream product. In step (2), mercaptan salt alkali solution undergoes oxidation reaction with oxidizing gas under the catalysis of oxidation catalyst, mercaptide salt is converted into disulfide, and disulfide-containing alkali solution is obtained; at the end of step (2), there may be excess oxidizing gas, and the excess oxidizing gas can be discharged after being treated in subsequent liquid separator and light hydrocarbon recovery device, or sent to the flue gas desulfurization system of catalytic cracking device for incineration treatment, or can be recycled after being pressurized. In step (3), disulfide-containing alkali solution is contacted with a first selective solvent that does not contain oxidizing gas so that at least part of disulfide is absorbed by the first selective solvent, thereby obtaining lean alkali solution and a first disulfide-containing selective solvent. The obtained lean alkali solution may still contain disulfides. After the back extraction in step (4), the disulfides remaining in the lean alkali solution are absorbed by the second selective solvent to obtain regenerated alkali solution and a second disulfide-containing selective solvent. The obtained regenerated alkali solution is returned to step (1) for use as extraction alkali solution.

[0050] It is important to point out that, firstly, the inventors of the present application have innovatively discovered in their long-term research and development of hydrocarbon stream desulfurization that by setting up step (5), low-carbon liquid hydrocarbons substantially free of hydrogen sulfide and mercaptan and / or at least a portion of the hydrocarbon stream product obtained from step (1) are subjected to a fractionation process of decarbonizing the five carbon fraction, thereby obtaining a five carbon fraction substantially free of hydrogen sulfide and mercaptan and free of oxidizing gases; and when performing the back extraction of step (4), the five carbon fraction from step (5) is used as the second selective solvent for back extraction to absorb disulfides in the lean alkali solution, thereby more thoroughly removing disulfides and oxidizing gases in the lean alkali solution, obtaining a regenerated alkali solution free of sulfides and oxides, and significantly reducing the sulfur content of the resulting hydrocarbon stream product.

[0051] The low-carbon liquid hydrocarbons in step (5) may be low-carbon liquid hydrocarbons that are substantially free of hydrogen sulfide and mercaptan from other units in the refinery, i.e., a combination of one or more of liquefied petroleum gas that is substantially free of hydrogen sulfide and mercaptan, crude mixed C3 hydrocarbons and C4 hydrocarbons, crude mixed C4 hydrocarbons, and mixed liquid hydrocarbons of C1 to C6; or the raw material for the fractionation process in step (5) may be the hydrocarbon stream product obtained in step (1), or a mixture of the hydrocarbon stream product in step (1) and low-carbon liquid hydrocarbons that are substantially free of hydrogen sulfide and mercaptan from other units in the refinery. In the mixture of the hydrocarbon stream product of step (1) and the low-carbon liquid hydrocarbons from other equipment of the refinery that are substantially free of hydrogen sulfide and mercaptan, the volume proportion of the hydrocarbon stream product of step (1) is not limited. For example, the hydrocarbon stream product obtained from step (1) with a volume proportion of 2%, 5%, 8%, 10%, 12%, 15%, 17%, 20%, 25%, 30%, 32%, 35%, 40%, 45%, etc. can be subjected to the fractionation process of the decarbonization five fraction in the decarbonization five fractionation tower in step (5) to obtain the carbon five fraction. Since the hydrocarbon stream product of step (1) is substantially free of hydrogen sulfide and mercaptan, when it is used independently as the raw material of the decarbonization five tower, the carbon five fraction obtained after fractionation is also substantially free of hydrogen sulfide, mercaptan, and oxidizing gas.

[0052] The sulfide contained in the C5 fraction fractionated by the decarbonized five fractionation tower is not limited, as long as it basically does not contain hydrogen sulfide and mercaptan. The "basically does not contain hydrogen sulfide and mercaptan" means that hydrogen sulfide and mercaptan cannot be detected according to known detection methods, or the content of hydrogen sulfide and mercaptan (in terms of sulfur) is below the lower limit of detection; and the amount of sulfide accumulated during the contact between the C5 fraction and the alkali solution is not limited, as long as it is ensured that the regenerated alkali solution after desulfurization basically does not contain disulfide and oxidizing gas, thereby greatly improving the effective utilization rate of the alkali solution and the desulfurization effect, greatly reducing the sulfur content in the obtained hydrocarbon stream product, and also greatly reducing the external discharge treatment of the second disulfide-containing selective solvent (reverse extraction solvent). In addition, the hydrocarbon stream product obtained from step (1) can be optionally partially subjected to the decarbonized five fraction fractionation process of step (5) together with low-carbon liquid hydrocarbons, so that the entire hydrocarbon stream extraction desulfurization method forms a closed cycle.

[0053] Secondly, when performing the separation in step (3), the disulfide-containing alkali solution from step (2) is first contacted with the first selective solvent, i.e., the second disulfide-containing selective solvent at least partially obtained from step (4), and then subjected to sedimentation separation or phase separation, and subsequent back extraction, so that the obtained regenerated alkali solution does not contain sulfides and oxidizing gases, and the sulfur content of the obtained hydrocarbon stream product can be further reduced.

[0054] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method of the first aspect of the present invention, the second selective solvent in step (4) further comprises part of the second disulfide-containing selective solvent obtained from step (4).

[0055] It should be noted that in the hydrocarbon stream extraction desulfurization method of the present invention, the second disulfide-containing selective solvent obtained from step (4) can be divided into two parts, one part is used as the second selective solvent to continue the back extraction of step (4), and the other part is used as the first selective solvent to continue the separation of step (3). Firstly, it can not only better regenerate the alkali solution and improve the desulfurization effect to obtain a hydrocarbon stream product with a lower sulfur content, but also make the entire hydrocarbon stream extraction desulfurization method better self-circulating to save energy. Thirdly, the second disulfide-containing selective solvent produced in step (4) does not need to rely on an external treatment system, which greatly reduces the external discharge treatment of the second disulfide-containing selective solvent (back extraction solvent).

[0056] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method of the first aspect of the present invention, step (3) further includes the following steps after the separation:

[0057] The first disulfide-containing selective solvent is intermittently or continuously mixed with the raw material of the absorption stabilization system of the catalytic cracking unit and then separated, and the first disulfide-containing selective solvent is absorbed into the stabilized gasoline, and then desulfurized and refined to obtain low-sulfur gasoline;

[0058] The sulfur content of the low-sulfur gasoline is not more than 10 μg / g.

[0059] The inventors of the present application have also innovatively discovered in the long-term research and development of hydrocarbon stream desulfurization that the first disulfide-containing selective solvent from step (3) is mixed with the raw material of the absorption stabilization system of the catalytic cracking unit and then separated, and the first disulfide-containing selective solvent is absorbed into the stable gasoline, and becomes a part of the stable gasoline after absorption (no secondary cracking is required), and then undergoes desulfurization and refining to obtain low-sulfur gasoline. The operation of the absorption stabilization system and the desulfurization and refining operation of the stable gasoline are carried out in a conventional manner, preferably by selective hydrogenation, and the sulfur content of the gasoline product after desulfurization is not more than 10μg / g. The sulfur-containing gasoline becomes a low-sulfur gasoline product after the well-known desulfurization and refining operation (such as selective hydrodesulfurization), and the sulfur content of the low-sulfur gasoline product is not more than 10μg / g. In this way, the C5 fraction in the low-carbon mixed liquid hydrocarbons of the refinery is used as the second selective solvent (reverse extraction solvent) and then transferred into gasoline to obtain maximum utilization. In short, the C5 fraction separated from the liquid hydrocarbons of the refinery can be converted into a gasoline fraction after absorbing disulfide and utilized. This utilization method has greatly reduced disadvantages compared with the prior art method of directly sending it to an additional hydrogenation unit for treatment and the method of returning it to the catalytic cracking unit to mix with the catalytic feed for catalytic cracking reaction for secondary cracking.

[0060] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method according to the first aspect of the present invention, the hydrocarbon stream extraction desulfurization method further comprises a pre-alkali washing step before step (1):

[0061] Contacting the original hydrocarbon stream with a pre-alkaline washing alkali solution to perform pre-alkaline washing to obtain the hydrocarbon stream described in step (1);

[0062] The raw hydrocarbon stream is selected from at least one of natural gas, liquefied petroleum gas, light naphtha, light gasoline and C1-C6 low-carbon hydrocarbons.

[0063] It should be noted that the desulfurization effect can be further improved by providing a pre-alkali washing step, and a hydrocarbon stream product with a lower sulfur content can be obtained. The original hydrocarbon stream can be selected from the above-mentioned mercaptan-containing natural gas, liquefied petroleum gas, etc., but is not limited.

[0064] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method described in the first aspect of the present invention, the low-carbon liquid hydrocarbons in step (5) are selected from one or more combinations of liquefied petroleum gas, crude mixed C3 hydrocarbons and C4 hydrocarbons, crude mixed C4 hydrocarbons and mixed liquid hydrocarbons of C1 to C6.

[0065] It should be noted that the low-carbon liquid hydrocarbons may be low-carbon liquid hydrocarbons from other equipment in the refinery that are substantially free of hydrogen sulfide and mercaptans. The low-carbon liquid hydrocarbons include but are not limited to the above-mentioned liquefied petroleum gas and mixed liquid hydrocarbons of C1 to C6.

[0066] Using the carbon five fraction obtained by the fractionation process of the above-mentioned low-carbon liquid hydrocarbons in step (5) to remove the carbon five fraction as the second selective solvent for the back extraction in step (4) can greatly improve the effective utilization rate of the alkali solution and the desulfurization effect, thereby greatly reducing the sulfur content in the obtained hydrocarbon stream product.

[0067] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method according to the first aspect of the present invention, in step (1), the conditions for performing the alkaline extraction include:

[0068] The temperature is -5°C to 100°C, preferably 25°C to 50°C;

[0069] The pressure is 0.1MPa to 4.0MPa, preferably 0.1MPa to 2.0MPa;

[0070] The volume proportion of the extracted alkali solution in the hydrocarbon stream is 1% to 50%, preferably 5% to 40%.

[0071] It should be noted that when the hydrocarbon stream is liquefied petroleum gas (LPG), the pressure is preferably 1.0 MPa to 2.0 MPa. In the hydrocarbon stream extraction desulfurization method of the present invention, the sulfur content of the obtained hydrocarbon stream product can be further reduced by controlling the temperature and pressure of the alkali extraction in step (1) as above.

[0072] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method according to the first aspect of the present invention, in step (2), the conditions for performing the oxidation include:

[0073] The temperature is -5°C to 100°C, preferably 25°C to 80°C;

[0074] The pressure is 0.1MPa to 2.0MPa, preferably 0.1MPa to 1.0MPa;

[0075] The oxidizing gas is selected from one or more combinations of oxygen, air and oxygen-enriched air;

[0076] The amount of the oxidizing gas used is greater than or equal to 1 to 20 times the theoretical chemical demand of the oxidizing gas required to oxidize the mercaptide contained in the mercaptide-containing alkali solution into disulfide, preferably 2 to 10 times the theoretical chemical demand.

[0077] It should be noted that in step (2), the pressure is more preferably 0.1 MPa to 0.8 MPa. The theoretical demand for the oxidizing gas is calculated based on the fact that 0.25 moles of oxygen are required for each mole of mercaptide to be oxidized to form disulfide, and the amount of the oxidizing gas is more preferably 2 to 4 times the theoretical demand. In order to completely oxidize the mercaptide in the mercaptide-containing alkali solution to disulfide, the mercaptide-containing alkali solution needs to be heated to a temperature that ensures catalytic oxidation. Therefore, the temperature in step (2) can be higher than that in step (1), while the pressure can be lower than that in step (1).

[0078] In step (2), when the mercaptan salt in the mercaptan salt alkali solution is subjected to oxidation reaction with the oxidizing gas, the oxidation catalyst may be a metal phthalocyanine catalyst, preferably a cobalt phthalocyanine compound such as sulfonated cobalt phthalocyanine or polycobalt phthalocyanine as the oxidation catalyst. The cobalt phthalocyanine catalyst may be used by dissolving in the alkali solution or forming a stable emulsion in the alkali solution, and the content in the alkali solution when used is 5 μg / g to 1000 μg / g, preferably 10 μg / g to 400 μg / g. The cobalt phthalocyanine catalyst may also be used by being supported on a porous material such as activated carbon in the form of a supported fixed bed, and the content of the cobalt phthalocyanine catalyst supported on the activated carbon carrier when used is 0.01% to 10%, preferably 0.05% to 1.0%, and the supported catalyst may be a catalyst containing nitrogen, phosphorus, oxygen, sulfur, arsenic, antimony, etc. Compounds and various basic nitrides are used as catalyst promoters. Preferably, cobalt phthalocyanine supported fixed bed catalyst is used.

[0079] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method according to the first aspect of the present invention, in step (3), the conditions for performing the separation include:

[0080] The temperature is -5°C to 80°C, preferably 25°C to 50°C; the pressure is 0.1MPa to 2.0MPa, preferably 0.1MPa to 1.0MPa; the volume ratio of the second disulfide-containing selective solvent obtained from step (4) as the first selective solvent to the disulfide-containing alkali solution is 1:(0.01 to 100), preferably 1:(0.1 to 10); and / or,

[0081] In step (4), the conditions for performing the back extraction include:

[0082] The temperature is -5°C to 80°C, preferably 25°C to 50°C; the pressure is 0.1MPa to 2.0MPa, preferably 0.1MPa to 1.0MPa; the volume ratio of the C5 fraction as the second selective solvent to the lean alkali solution obtained from step (3) is 1:(0.01 to 100), preferably 1:(0.1 to 10).

[0083] It should be noted that by controlling the temperature and pressure of the oxidation in step (2), the separation in step (3) and the stripping in step (4) as above, it is more conducive to preparing a regenerated alkaline solution that does not contain sulfides and oxidizing gases, and can further prepare a high-quality hydrocarbon stream product with a lower sulfur content.

[0084] The separation method in step (3) is preferably carried out by sedimentation separation, and the sedimentation separation time is usually not less than 15 minutes, preferably not less than 45 minutes, and preferably not less than 90 minutes. As a preferred embodiment, after the oxidation in step (2) is completed, the disulfide-containing alkali solution is cooled, and then the separation in step (3) is carried out, so that the volatilization of the disulfide flow and the hydrocarbon gas can be reduced as much as possible. The pressure in step (3) is preferably less than that in step (2). The pressure in steps (3) and (4) is more preferably 0.1MPa to 0.5MPa.

[0085] The contact described in the present invention can adopt various towers and devices known in the industry, such as perforated plate extraction tower, packed extraction tower, fiber membrane contactor, static mixing contactor, jet contactor, rotary gravity contactor, etc.

[0086] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method of the first aspect of the present invention, the sulfur content of the hydrocarbon stream product obtained from step (1) is not more than 10 μg / g.

[0087] In a second aspect, the present invention relates to a hydrocarbon stream extraction desulfurization system associated with gasoline production, such as Figure 1 As shown in 2, the hydrocarbon stream extraction desulfurization system comprises:

[0088] Alkali extraction unit 2, oxidation unit 3, separation unit 4, back extraction unit 5 and decarbonization five fractionation tower 6;

[0089] The alkali extraction unit 2 is provided with a hydrocarbon stream inlet pipeline 1d, an extraction alkali solution inlet 2a, a hydrocarbon stream product outlet 2b and a mercaptan-containing alkali solution outlet;

[0090] The mercaptoalkoxide alkali solution inlet of the oxidation unit 3 is connected to the mercaptoalkoxide alkali solution outlet of the alkali extraction unit 2 through a mercaptoalkoxide alkali solution pipeline 2c, and an oxidizing gas inlet 3a is provided on the mercaptoalkoxide alkali solution pipeline 2c; the oxidation unit 3 is also provided with a residual oxidizing gas outlet 3b and a disulfide-containing alkali solution outlet 3c;

[0091] The disulfide-containing alkali solution inlet of the separation unit 4 is connected to the disulfide-containing alkali solution outlet 3c of the oxidation unit 3, and the separation unit 4 is provided with a first selective solvent inlet, a lean alkali solution outlet 4a and a first disulfide-containing selective solvent outlet 4b; the first disulfide-containing selective solvent outlet 4b is connected to the raw material inlet of the absorption stabilization system phase of the catalytic cracking unit;

[0092] The lean alkali solution inlet of the back extraction unit 5 is connected to the lean alkali solution outlet 4a of the separation unit 4, and the back extraction unit 5 is provided with a second selective solvent inlet pipeline 5a, a second disulfide-containing selective solvent outlet 5b and a regeneration alkali solution outlet pipeline 5d; the second disulfide-containing selective solvent outlet 5b is connected to the first selective solvent inlet of the separation unit 4 through a selective solvent pipeline 5c; the regeneration alkali solution outlet pipeline 5d is connected to the extraction alkali solution inlet 2a of the alkali extraction unit 2;

[0093] The decarbonization five fractionation tower 6 is provided with an inlet 6a for materials to be fractionated, a C5 fraction outlet pipeline 6c and a residual fraction outlet 6b; the C5 fraction outlet pipeline 6c is connected to the second selective solvent inlet pipeline 5a of the back-extraction unit 5.

[0094] It should be noted that the inlet 6a of the material to be fractionated of the decarbonization five-cent fractionation tower 6 can also be connected to the hydrocarbon stream product outlet 2b, so that part of the hydrocarbon stream product can enter the decarbonization five-cent fractionation tower 6 for decarbonization five-cent fractionation to obtain the carbon five fraction and then use it as the second selective solvent of the back-extraction unit.

[0095] The hydrocarbon stream flows into the alkali extraction unit 2 through the hydrocarbon stream inlet pipeline 1d, contacts with the extraction alkali solution flowing into the extraction alkali solution inlet 2a for alkali extraction, and the obtained hydrocarbon stream product is output through the hydrocarbon stream product outlet 2b. The obtained mercaptoalkoxide alkali solution flows through the mercaptoalkoxide alkali solution pipeline 2c to the mercaptoalkoxide alkali solution inlet of the oxidation unit 3 and then enters the oxidation unit 3.

[0096] The oxidizing gas flows into the oxidation unit 3 through the oxidizing gas inlet 3a and the mercaptan-containing alkali solution pipeline 2c. The oxidizing gas contacts the mercaptan-containing alkali solution in the oxidation unit 3, and the mercaptan is oxidized into disulfide. The obtained disulfide-containing alkali solution flows into the separation unit 4 through the disulfide-containing alkali solution outlet 3c of the oxidation unit 3 and the disulfide-containing alkali solution inlet of the separation unit 4, and the remaining oxidizing gas leaves the oxidation unit 3 through the remaining oxidizing gas outlet 3b.

[0097] The disulfide-containing alkali liquid flowing into the separation unit 4 contacts with the first selective solvent flowing in through the first selective solvent inlet, and the disulfide is absorbed into the first selective solvent. After sedimentation separation, the obtained lean alkali liquid flows into the reverse extraction unit 5 through the lean alkali liquid outlet 4a, and the obtained first disulfide-containing selective solvent flows out through the first disulfide-containing selective solvent outlet 4b and enters the catalytic cracking unit and the absorption stabilization system after the catalytic cracking reactor is configured. The first disulfide-containing selective solvent is absorbed in the stabilized gasoline, and the stabilized gasoline is desulfurized and refined after being discharged to obtain a low-sulfur gasoline with a sulfur content of not more than 10 μg / g.

[0098] In the back-extraction unit 5, the lean alkali solution contacts the second selective solvent from the second selective solvent inlet pipeline 5a, so that the disulfide remaining in the lean alkali solution is absorbed by the second selective solvent to obtain regenerated alkali solution and a second disulfide-containing selective solvent. The obtained regenerated alkali solution flows into the alkali extraction unit 2 through the regenerated alkali solution outlet pipeline 5d and the extraction alkali solution inlet 2a and is recycled as the extraction alkali solution. The obtained second disulfide-containing selective solvent flows into the separation unit 4 through the second disulfide-containing selective solvent outlet 5b, the selective solvent pipeline 5c and the first selective solvent inlet and is recycled as the first selective solvent.

[0099] The low-carbon liquid hydrocarbons can enter the decarbonization five fractionation tower 6 through the material inlet 6a for fractionation, and the C5 fraction obtained by the fractionation of the decarbonization five fraction in the decarbonization five fractionation tower 6 can flow into the back-extraction unit 5 through the C5 fraction outlet pipeline 6c and the second selective solvent inlet pipeline 5a for use as the second selective solvent.

[0100] It should be emphasized that, firstly, the alkali liquor after alkali extraction is subjected to multi-stage ingenious treatment through the hydrocarbon stream extraction desulfurization system of the present invention, and the obtained regenerated alkali liquor does not contain sulfide and oxidizing gas. The obtained regenerated alkali liquor is returned to the alkali extraction unit 2 through the regenerated alkali liquor outlet pipeline 5d and the extracted alkali liquor inlet 2a for recycling, which can greatly reduce the amount of fresh alkali liquor used, and at the same time the desulfurization effect is significantly improved, and the sulfur content of the obtained hydrocarbon stream product is low. Secondly, the C5 fraction outlet pipeline 6c is connected with the second selective solvent inlet pipeline 5a of the stripping unit 5, so that the C5 fraction from the decarbonization fractionation tower 6 is returned to the stripping unit 5 as the second selective solvent for recycling, and the disulfide and oxidizing gas remaining in the lean alkali solution can be more thoroughly stripped into the C5 fraction, so that the obtained regenerated alkali solution does not contain sulfide and oxidizing gas. Thirdly, the second disulfide-containing selective solvent outlet 5b is connected with the first selective solvent inlet of the separation unit 4 through the selective solvent pipeline 5c, and the discharge amount of the disulfide-containing C5 fraction can be greatly reduced, avoiding complicated external treatment.

[0101] According to a specific embodiment of the hydrocarbon stream extraction desulfurization system according to the second aspect of the present invention, the second selective solvent inlet pipeline 5a of the stripping unit 5 is connected to the second disulfide-containing selective solvent outlet 5b; and / or,

[0102] The hydrocarbon stream extraction and desulfurization system is also provided with a pre-alkali washing unit 1, and the pre-alkali washing unit 1 is provided with an original hydrocarbon stream inlet pipeline 1a, a pre-alkali washing alkali solution inlet pipeline 1b, a circulating alkali solution outlet 1c and a hydrocarbon stream outlet after pre-alkali washing; the pre-alkali washing alkali solution inlet pipeline 1b is connected to the circulating alkali solution outlet 1c, and the pre-alkali washing alkali solution inlet pipeline 1b is connected to the original hydrocarbon stream inlet pipeline 1a; the hydrocarbon stream outlet after pre-alkali washing is connected to the hydrocarbon stream inlet pipeline 1d of the alkali extraction unit 2.

[0103] It should be noted that the second selective solvent inlet pipeline 5a of the stripping unit 5 is connected to the second disulfide-containing selective solvent outlet 5b, so that the second disulfide-containing selective solvent produced by the stripping unit 5 is all returned to the hydrocarbon stream extraction and desulfurization system for recycling, a part of it is returned to the stripping unit 5 for recycling as the second selective solvent, and the other part is returned to the separation unit 4 for recycling as the first selective solvent, without the need for external treatment equipment for treatment, and the whole system forms a better self-circulation.

[0104] By providing the pre-alkali washing unit 1, the sulfur content of the hydrocarbon stream product obtained from the hydrocarbon stream product outlet 2b can be further reduced, thereby obtaining a hydrocarbon stream product with higher quality.

[0105] According to a specific embodiment of the hydrocarbon stream extraction desulfurization system according to the second aspect of the present invention, the top temperature of the decarbonization five fractionation tower 6 is 35°C to 80°C, preferably 40°C to 65°C; the top pressure is 0.15MPa to 2.20MPa, preferably 0.35MPa to 1.20MPa; the bottom temperature is 55°C to 150°C, preferably 60°C to 130°C.

[0106] It should be noted that by controlling the temperature and pressure of the decarbonization pentahydrogen fractionation tower 6 as above, it is beneficial to the fractionation process of the low-carbon liquid hydrocarbons and an optional portion of the hydrocarbon stream product obtained from the alkali extraction unit 2 to obtain a carbon pentahydrogen fraction free of sulfides and oxidizing gases, so as to better obtain a carbon pentahydrogen fraction free of sulfides and oxidizing gases for use as the second selective solvent of the back-extraction unit 5, so as to better prepare a regenerated alkali solution free of sulfides and oxidizing gases.

[0107] The operation process of the hydrocarbon stream extraction and desulfurization system combined with gasoline production of the present application is described below:

[0108] The original hydrocarbon stream (for example, catalytic liquefied petroleum gas, distilled from the absorption stabilization system of the catalytic device and after the hydrogen sulfide is removed by the amine removal system) passes through the original hydrocarbon stream inlet pipeline 1a and is mixed with the fresh alkali solution from the pre-alkali washing alkali solution inlet pipeline 1b and / or the circulating alkali solution from the pre-alkali washing unit 1 from the circulating alkali solution outlet 1c, and then enters the pre-alkali washing unit 1, and the trace hydrogen sulfide (and part of the mercaptan) in the original hydrocarbon stream is removed.

[0109] The hydrocarbon stream flowing out of the pre-alkali washing unit 1 flows into the alkali extraction unit 2 through the hydrocarbon stream inlet pipeline 1d, and is countercurrently contacted with the fresh alkali solution entering through the extraction alkali solution inlet 2a, and / or the regenerated alkali solution which basically no longer contains disulfide and oxidizing gas from the regenerated alkali solution outlet pipeline 5d (connected to the extraction alkali solution inlet 2a) in the alkali extraction unit 2, and the mercaptans in the hydrocarbon stream are absorbed by the alkali solution to form mercaptides, and the hydrocarbon stream from which hydrogen sulfide and mercaptans are removed becomes a hydrocarbon stream product, which flows out from the hydrocarbon stream product outlet 2b at the top of the alkali extraction unit 2 as a desulfurized product (hydrocarbon stream product).

[0110] The alkali liquor that has absorbed mercaptans, i.e., the mercaptol-containing alkali liquor (rich alkali liquor), leaves the alkali extraction unit 2 from the mercaptol-containing alkali liquor pipeline 2c, and is mixed with the oxidizing gas (e.g., air) entering through the oxidizing gas inlet 3a, and then flows into the oxidation unit 3. Under the action of the fixed-bed oxidation catalyst, i.e., the metal phthalocyanine-supported catalyst loaded in the oxidation unit 3, the mercaptol salts in the mercaptol-containing alkali liquor (rich alkali liquor) are oxidized into disulfides by the oxidizing gas (e.g., air), and the excess oxidizing gas is discharged through the residual oxidizing gas outlet 3b, and is cleanly discharged after being treated in the subsequent liquid separator and light hydrocarbon recovery device, or is sent to the flue gas desulfurization system of the catalytic cracking unit for incineration treatment, or can be recycled after being pressurized.

[0111] The disulfide-rich alkali liquor from which the excess oxidizing gas is separated flows out through the disulfide-containing alkali liquor outlet 3c, mixes with the first selective solvent from the selective solvent pipeline 5c and flows into the separation unit 4, and the disulfides in the alkali liquor are transferred into the first selective solvent. The first disulfide-rich selective solvent obtained after separation is discharged from the first disulfide-containing selective solvent outlet 4b, sent to the catalytic cracking unit and the absorption stabilization system arranged after the catalytic cracking reactor, and absorbed into the stable gasoline; the absorption stabilization system is operated in a conventional manner, so that the selective solvent and disulfide are absorbed into the stable gasoline, and the subsequent desulfurization refining operation is carried out together with the stable gasoline. The desulfurization refining operation of the stable gasoline is carried out in an industrially known manner to reduce the sulfur content to below 10μg / g to meet the requirements of the gasoline standard.

[0112] The lean alkali solution flowing out of the separation unit 4 is mixed with the second selective solvent for stripping without oxidizing gas from the second selective solvent inlet pipeline 5a through the lean alkali solution outlet 4a and flows into the stripping unit 5. In the stripping unit 5, the residual disulfide and the remaining oxidizing gas contained in the lean alkali solution are absorbed by the second selective solvent. After stripping, the lean alkali solution becomes a regenerated alkali solution, and the second selective solvent becomes a second disulfide-containing selective solvent. The second disulfide-containing selective solvent flows out through the second disulfide-containing selective solvent outlet 5b, a part of the second disulfide-containing selective solvent is returned to the stripping unit 5 for recycling through the second selective solvent inlet pipeline 5a, and the other part of the second disulfide-containing selective solvent enters the separation unit 4 through the selective solvent pipeline 5c and the first selective solvent inlet, and contacts with the disulfide-containing alkali solution rich in disulfide from which the excess oxidizing gas is separated and then separated. The obtained regenerated alkali solution enters the alkali extraction unit 2 through the regenerated alkali solution outlet pipeline 5d and the extracted alkali solution inlet 2a for recycling.

[0113] When the hydrocarbon stream extraction desulfurization system of the present application starts to operate, the second selective solvent flowing into the stripping unit 5 through the second selective solvent inlet pipeline 5a comes from the bottom effluent of the decarbonization five fractionation tower 6 - the C5 fraction, and the C5 fraction flows out through the C5 fraction outlet pipeline 6c and flows into the stripping unit 5 through the second selective solvent inlet pipeline 5a. The material to be fractionated entering the decarbonization five fractionation tower 6 through the material to be fractionated inlet 6a can be low-carbon liquid hydrocarbons from a refinery that are substantially free of hydrogen sulfide and mercaptan, or can be at least a portion of the hydrocarbon stream products flowing out through the hydrocarbon stream product outlet 2b, or can be a mixture of low-carbon liquid hydrocarbons from a refinery that are substantially free of hydrogen sulfide and mercaptan and a portion of the hydrocarbon stream products flowing out through the hydrocarbon stream product outlet 2b.

[0114] The present invention is further described in detail below by way of examples, but the present invention is not limited thereto.

[0115] The examples are intended to generally represent the process of a preferred embodiment of the present invention, and are not intended to give details of the vessels, heaters, coolers, pumps, compressors, valves, process control equipment, etc., which are basic equipment for those skilled in the art. The examples given are intended to illustrate the present invention, but are not intended to limit the present invention in any way.

[0116] Example 1

[0117] The hydrocarbon stream to be desulfurized is light catalytic cracking gasoline, and its basic properties are shown in Table 1. The sulfur content is determined by ultraviolet fluorescence method, and the mercaptan is determined by potentiometric titration method.

[0118] Table 1

[0119] <![CDATA[Density (20 °C) / (g / cm 3 )]]> Distillation range / ℃ Sulfur content / (μg / g) Thiol sulfur content / (μg / g) 0.6344 32～77 57 52

[0120] use Figure 1 or Figure 2 The flow chart shown in the figure carries out desulfurization treatment on the hydrocarbon stream - light catalytic cracking gasoline in Table 1, but no pre-alkali washing is carried out. The light catalytic cracking gasoline is brought into contact with the NaOH solution in the alkali extraction unit for alkali extraction. The NaOH solution with a concentration of 15% (by weight) is used. In the alkali extraction unit, the volume ratio of the extraction alkali liquid to the hydrocarbon stream is 1:9, the temperature is room temperature, and the pressure is 0.50 MPa. After alkali extraction, hydrocarbon stream products and mercaptoalkoxide alkali liquid are obtained; the hydrocarbon stream products flow out from the hydrocarbon stream product outlet 2b, and the mercaptoalkoxide alkali liquid enters the oxidation unit.

[0121] In the oxidation unit, under the catalysis of the catalyst, the mercaptan salt alkali solution is contacted with the oxidizing gas-air, so that the mercaptan salt is oxidized to disulfide, and the disulfide-containing alkali solution is obtained. The metal phthalocyanine type oxidation catalyst is loaded, with activated carbon (provided by Beijing Guanghua Jingke Activated Carbon Factory, brand GH-8) as the carrier, sulfonated cobalt phthalocyanine as the main active component, with a content of 0.6%, and dodecyl dimethyl benzyl ammonium chloride (content 1%) and isopropanolamine (content 5%) as auxiliary active components. The preparation process of the catalyst is as follows: according to the target loading, the dilute ammonia solution of sulfonated cobalt phthalocyanine, the mixed solution of dodecyl dimethyl benzyl ammonium chloride and isopropanolamine are respectively prepared, and the activated carbon is adsorbed in equal volumes successively, and each time it is dried by a rotary evaporator.

[0122] In the oxidation unit, the amount of air injected is 4 times the theoretical chemical demand, which is equivalent to a volume ratio of air to mercaptan-containing alkali solution of about 0.8:1 under standard conditions, an alkali solution oxidation temperature of 50°C, and a pressure of 0.40MPa. After oxidation, excess air tail gas is separated and sent to the flue gas desulfurization system of the catalytic cracking unit for incineration.

[0123] Then, the disulfide-containing alkali liquid from which the excess air tail gas is separated contacts with the first selective solvent and flows into the separation unit, and the volume ratio of the first selective solvent to the disulfide-containing alkali liquid is 1:10. The first selective solvent is the second disulfide-containing selective solvent from the back extraction unit. The conditions in the separation unit are: temperature of 50°C and pressure of 0.30MPa.

[0124] In the separation unit, a lean alkali solution and a first disulfide-containing selective solvent are separated. The first disulfide-containing selective solvent is separated from the lean alkali solution and sent to a catalytic cracking unit and an absorption stabilization system arranged after the catalytic cracking reactor, so that the selective solvent and disulfide are mixed with the raw materials of the absorption stabilization system and then separated and absorbed into the stable gasoline, and the subsequent desulfurization and refining operation is carried out together with the stable gasoline. The desulfurization and refining operation of the stable gasoline is carried out by selective hydrogenation to reduce its sulfur content to less than 10 μg / g. The lean alkali solution obtained by separation enters the back-extraction unit, and the second selective solvent also enters the back-extraction unit.

[0125] In the back-extraction unit, the inlet pressure of the back-extraction unit is 0.30MPa, and the second selective solvent without oxidizing gas contacts with the lean alkali solution at room temperature. During the contact, the circulation volume ratio of the second selective solvent (the carbon five fraction separated by the decarbonization five fractionation tower) to the lean alkali solution is 1:1. After that, the second selective solvent is separated from the lean alkali solution to obtain a second disulfide-containing selective solvent and a regenerated alkali solution. The second selective solvent for absorbing disulfides adopts the carbon five fraction that is basically free of hydrogen sulfide, mercaptan and oxidizing gas separated by the decarbonization five fractionation tower from the low-carbon liquid hydrocarbons of the refinery. The operating conditions for fractionating the low-carbon liquid hydrocarbons of the refinery through the decarbonization five fractionation tower may include: tower top pressure 0.5MPa, tower top temperature 51.5℃, tower bottom temperature 90℃, and reflux ratio 1.0. The raw material of the decarbonization five fractionation tower is a mixed liquid light hydrocarbon (C3~C5) that is basically free of hydrogen sulfide and mercaptan.

[0126] The second disulfide-containing selective solvent obtained by back extraction is divided into two parts, one part is returned to the back extraction unit as the second selective solvent for recycling, and the other part is returned to the separation unit as the first selective solvent to contact with the disulfide-containing alkaline solution rich in disulfide from which excess air tail gas is separated.

[0127] The regenerated alkali solution obtained by back extraction is returned to the alkali extraction unit for recycling.

[0128] The results show that after treatment, the sulfur content in light gasoline is reduced to 5μg / g. Not only is the mercaptan completely removed, but the sulfur content is also greatly reduced (the sulfur content reduction value of light gasoline is equivalent to the mercaptan sulfur content before desulfurization treatment). No sodium mercaptide is detected in the regenerated alkali solution obtained by back extraction (determined by potentiometric titration), indicating that the mercaptan-containing alkali solution is completely regenerated, and no disulfide is detected in the regenerated alkali solution obtained by back extraction, indicating that the regenerated alkali solution returned to the alkali extraction unit does not contain disulfide or oxidizing gas. Therefore, in the alkali extraction step, the regenerated alkali solution will not carry disulfide and transfer to the light gasoline, nor will part of the mercaptan in the light gasoline be oxidized to disulfide and remain in the light gasoline).

[0129] Example 2

[0130] The hydrocarbon stream to be desulfurized is liquefied petroleum gas, density (20℃): 0.5558g / cm 3 , Sulfur content: 320μg / g (UV fluorescence method).

[0131] use Figure 1 or Figure 2 The flow chart shown in the figure is used to desulfurize the above hydrocarbon stream-liquefied petroleum gas. The hydrocarbon stream is first pre-washed with alkali and then subjected to alkali extraction. The concentration of the pre-washing alkali solution is 5% (by weight), and the amount of alkali solution is 5% of the weight of the raw material, i.e., the hydrocarbon stream. In the alkali extraction unit, the concentration of the alkali solution used is 15% (by weight), the volume ratio of the alkali solution to the raw material, i.e., the hydrocarbon stream, 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.

[0132] The results show that after treatment, the sulfur content in the liquefied petroleum gas dropped to 6μg / g. No sodium mercaptide was detected in the regenerated alkali solution (determined by potentiometric titration), indicating that the alkali solution containing mercaptans was completely regenerated, and no disulfide was detected in the regenerated alkali solution obtained by back extraction, which also shows that the regenerated alkali solution returned to the alkali extraction unit basically does not contain disulfide and air.

[0133] Comparative Example 1-2

[0134] use Figure 1 The flow chart shown in or 2 is used to desulfurize the hydrocarbon stream-light catalytic cracking gasoline of Example 1 and the hydrocarbon stream-liquefied petroleum gas of Example 2. The operating conditions and catalysts used are the same as those of Example 1 and Example 2, except that the second selective solvent is not used for the back extraction process, and the decarbonization five distillation tower is not used. After the alkali liquid oxidation, the alkali liquid and the excess oxidizing gas are separated by natural sedimentation. The first selective solvent is not used to contact the disulfide-containing alkali liquid obtained from the oxidation unit. The desulfurization results are shown in Table 2.

[0135] Compared with Example 1, although the content of mercaptan in the light gasoline treated in Comparative Example 1 is greatly reduced, the desulfurization effect is not ideal, and part of the mercaptan sulfur is converted into disulfide and remains in the desulfurized product. This may be because the regenerated alkali solution carries a trace amount of air back to the alkali extraction unit, causing part of the mercaptan to be oxidized in the alkali extraction unit and remain in the desulfurized product. It may also be because the regenerated alkali solution carries a trace amount of disulfide back to the alkali extraction unit and then transfers the disulfide into the desulfurized product.

[0136] Compared with Example 2, the liquefied petroleum gas treated in Comparative Example 2 still has more sulfides remaining, and the reason is the same as that in Comparative Example 1.

[0137] Table 2

[0138]

[0139]

[0140] In the description of the present application, it should be noted that the terms "upper", "lower", "inside", "outside", "front", "back", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships in the working state of the present application. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present application.

[0141] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "install", "connect", and "connect" should be understood in a broad sense. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0142] The present application has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and serve only as an illustration. On this basis, various replacements and improvements may be made to the present application, all of which fall within the scope of protection of the present application.

Claims

1. A method for extractive desulfurization of hydrocarbon streams in combination with gasoline production, characterized in that: The hydrocarbon stream extraction desulfurization method comprises the following steps: (1) contacting a hydrocarbon stream with an extraction alkali solution in an alkali extraction unit to perform alkali extraction to obtain a hydrocarbon stream product and a mercaptan-containing alkali solution; (2) contacting the mercaptan-containing alkali solution from step (1) with an oxidizing gas in an oxidation unit for oxidation, and separating the remaining oxidizing gas to obtain a disulfide-containing alkali solution; (3) contacting and separating the disulfide-containing alkali solution from step (2) with a first selective solvent in a separation unit to obtain a lean alkali solution and a first disulfide-containing selective solvent; (4) contacting the lean alkali solution from step (3) with a second selective solvent in a stripping unit and stripping the solution to obtain a regenerated alkali solution and a second disulfide-containing selective solvent; (5) subjecting the low-carbon liquid hydrocarbons and / or at least a portion of the hydrocarbon stream product obtained from step (1) to a decarbonization five fractionation tower to obtain a decarbonization five fraction and a remaining fraction; Wherein, the extraction alkali solution in step (1) comprises the regenerated alkali solution obtained from step (4); the first selective solvent in step (3) comprises part of the second disulfide-containing selective solvent obtained from step (4); and the second selective solvent in step (4) comprises the C5 fraction obtained from step (5).

2. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: The second selective solvent in step (4) further comprises a portion of the second disulfide-containing selective solvent obtained in step (4).

3. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: Step (3) further comprises the following steps after the separation: The first disulfide-containing selective solvent is intermittently or continuously mixed with the raw material of the absorption stabilization system of the catalytic cracking unit and then separated, and the first disulfide-containing selective solvent is absorbed into the stabilized gasoline, and then desulfurized and refined to obtain low-sulfur gasoline; The sulfur content of the low-sulfur gasoline is not more than 10 μg / g.

4. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: The hydrocarbon stream extraction desulfurization method further comprises a pre-alkali washing step before step (1): Contacting the original hydrocarbon stream with a pre-alkaline washing alkali solution to perform pre-alkaline washing to obtain the hydrocarbon stream described in step (1); The raw 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 hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: The low-carbon liquid hydrocarbons in step (5) are selected from one or more combinations of liquefied petroleum gas, crude mixed C3 hydrocarbons and C4 hydrocarbons, crude mixed C4 hydrocarbons and mixed liquid hydrocarbons of C1 to C6.

6. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: In step (1), the conditions for carrying out the alkaline extraction include: The temperature is -5°C to 100°C, preferably 25°C to 50°C; The pressure is 0.1MPa to 4.0MPa, preferably 0.1MPa to 2.0MPa; The volume proportion of the extracted alkali solution in the hydrocarbon stream is 1% to 50%, preferably 5% to 40%.

7. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: In step (2), the conditions for carrying out the oxidation include: The temperature is -5°C to 100°C, preferably 25°C to 80°C; The pressure is 0.1MPa to 2.0MPa, preferably 0.1MPa to 1.0MPa; The oxidizing gas is selected from one or more combinations of oxygen, air and oxygen-enriched air; The amount of the oxidizing gas used is greater than or equal to 1 to 20 times the theoretical chemical demand of the oxidizing gas required to oxidize the mercaptide contained in the mercaptide-containing alkali solution into disulfide, preferably 2 to 10 times the theoretical chemical demand.

8. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: In step (3), the conditions for carrying out the separation include: The temperature is -5°C to 80°C, preferably 25°C to 50°C; the pressure is 0.1MPa to 2.0MPa, preferably 0.1MPa to 1.0MPa; the volume ratio of the second disulfide-containing selective solvent obtained from step (4) as the first selective solvent to the disulfide-containing alkali solution is 1:(0.01 to 100), preferably 1:(0.1 to 10); and / or, In step (4), the conditions for performing the back extraction include: The temperature is -5°C to 80°C, preferably 25°C to 50°C; the pressure is 0.1MPa to 2.0MPa, preferably 0.1MPa to 1.0MPa; the volume ratio of the C5 fraction as the second selective solvent to the lean alkali solution obtained from step (3) is 1:(0.01 to 100), preferably 1:(0.1 to 10).

9. The hydrocarbon stream extraction and desulfurization method according to claim 1, characterized in that: The sulfur content of the hydrocarbon stream product obtained from step (1) is not greater than 10 μg / g.

10. A hydrocarbon stream extraction and desulfurization system combined with gasoline production, characterized in that: The hydrocarbon stream extraction and desulfurization system comprises: Alkali extraction unit (2), oxidation unit (3), separation unit (4), back extraction unit (5) and decarbonization five-fractionation tower (6); The alkali extraction unit (2) is provided with a hydrocarbon stream inlet pipeline (1d), an extraction alkali solution inlet (2a), a hydrocarbon stream product outlet (2b) and a mercaptan-containing alkali solution outlet; The mercaptan-containing alkali solution inlet of the oxidation unit (3) is connected to the mercaptan-containing alkali solution outlet of the alkali extraction unit (2) via a mercaptan-containing alkali solution pipeline (2c), and the mercaptan-containing alkali solution pipeline (2c) is provided with an oxidizing gas inlet (3a); the oxidation unit (3) is also provided with a residual oxidizing gas outlet (3b) and a disulfide-containing alkali solution outlet (3c); The disulfide-containing alkali solution inlet of the separation unit (4) is connected to the disulfide-containing alkali solution outlet (3c) of the oxidation unit (3), and the separation unit (4) is provided with a first selective solvent inlet, a lean alkali solution outlet (4a) and a first disulfide-containing selective solvent outlet (4b); the first disulfide-containing selective solvent outlet (4b) is connected to the raw material inlet of the absorption stabilization system of the catalytic cracking unit; The lean alkali solution inlet of the back-extraction unit (5) is connected to the lean alkali solution outlet (4a) of the separation unit (4); the back-extraction unit (5) is provided with a second selective solvent inlet pipeline (5a), a second disulfide-containing selective solvent outlet (5b) and a regeneration alkali solution outlet pipeline (5d); the second disulfide-containing selective solvent outlet (5b) is connected to the first selective solvent inlet of the separation unit (4) via a selective solvent pipeline (5c); the regeneration alkali solution outlet pipeline (5d) is connected to the extraction alkali solution inlet (2a) of the alkali extraction unit (2); The decarbonization five fractionation tower (6) is provided with an inlet (6a) for the material to be fractionated, a C5 fraction outlet pipeline (6c) and a residual fraction outlet (6b); the C5 fraction outlet pipeline (6c) is connected to the second selective solvent inlet pipeline (5a) of the back extraction unit (5).

11. The hydrocarbon stream extraction and desulfurization system according to claim 10, characterized in that: The second selective solvent inlet pipeline (5a) of the stripping unit (5) is connected to the second disulfide-containing selective solvent outlet (5b); and / or, The hydrocarbon stream extraction desulfurization system is further provided with a pre-alkali washing unit (1), wherein the pre-alkali washing unit (1) is provided with an original hydrocarbon stream inlet pipeline (1a), a pre-alkali washing alkali solution inlet pipeline (1b), a circulating alkali solution outlet (1c) and a hydrocarbon stream outlet after pre-alkali washing; the pre-alkali washing alkali solution inlet pipeline (1b) is connected to the circulating alkali solution outlet (1c), and the pre-alkali washing alkali solution inlet pipeline (1b) is connected to the original hydrocarbon stream inlet pipeline (1a); and the hydrocarbon stream outlet after pre-alkali washing is connected to the hydrocarbon stream inlet pipeline (1d) of the alkali extraction unit (2).

12. The hydrocarbon stream extraction and desulfurization system according to claim 10, characterized in that: The top temperature of the decarbonization five fractionation tower (6) is 35°C to 80°C, preferably 40°C to 65°C; the top pressure is 0.15MPa to 2.20MPa, preferably 0.35MPa to 1.20MPa; the bottom temperature is 55°C to 150°C, preferably 60°C to 130°C.

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