A process and system for the extraction desulfurization of hydrocarbon streams in conjunction with gasoline production

Abstract

The present invention relates to a method and system for extracting and desulfurizing a hydrocarbon stream in combination with gasoline production, which comprises: (1) base extraction of the hydrocarbon stream to obtain a hydrocarbon stream product and a sulfidic base solution; (2) oxidation of the sulfidic base solution to obtain a disulfidic base solution; (3) contacting the disulfidic base solution with a first selective solvent and separating to obtain a lean base solution and a first disulfidic selective solvent; (4) contacting the lean base solution with a second selective solvent for back extraction to obtain a regenerated base solution and a second disulfidic selective solvent; (5) fractionating low carbon liquid hydrocarbons and / or at least part of the hydrocarbon stream product to obtain a C5 fraction, and using the C5 fraction as the second selective solvent; the first selective solvent in step (3) comprises part of the second disulfidic selective solvent. The present invention obtains a hydrocarbon stream product with lower sulfur content, and the disulfidic selective solvent is absorbed in gasoline and then subjected to desulfurization refining, so that the C5 fraction is converted into a gasoline fraction for utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refining hydrocarbon materials, and in particular to a method and system for extracting and desulfurizing hydrocarbon streams in combination with gasoline production. BACKGROUND

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

[0003] The alkaline solution containing mercaptide cannot be directly discharged as it is neither economical nor environmentally friendly. The method of oxidation is usually used to oxidize the mercaptide to disulfide so as to regenerate the alkaline solution containing mercaptide (see USP 2853432). Specifically, the method oxidizes the mercaptide dissolved in the used alkaline solution to disulfide by injecting air and an oxidation catalyst into the used alkaline solution, so as to regenerate the alkaline solution. However, the regenerated alkaline solution contains disulfide, and if it is recycled for alkaline extraction of the hydrocarbon stream, the hydrocarbon stream will absorb the disulfide, making it difficult to reduce the sulfur content of the hydrocarbon stream, and even increasing the sulfur content. Therefore, it is necessary to separate the regenerated alkaline solution from the disulfide therein by sedimentation separation and / or organic hydrocarbon solvent back extraction, so as to continue to use the regenerated alkaline solution to remove mercaptan in the hydrocarbon stream while effectively reducing the sulfur content in 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 the 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 mixture of regenerated alkaline liquid, disulfide and oxidizing gas from the oxidation step is separated 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 sedimentation 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 sedimentation 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, so as to separate the regenerated alkaline liquid from the disulfide-containing solvent, and the regenerated alkaline liquid treated by back extraction is returned to the extraction step for continuous use. In order to enhance the desulfurization effect of the hydrocarbon stream, an organic liquid additive with a back extraction assisting effect and / or an oxidation assisting effect, such as a low-carbon alcohol, can be added to the alkaline liquid.

[0005] The back extraction solvents used in the literature are mostly naphtha fractions, gasoline fractions and the like. After the back extraction solvents are used to absorb disulfide, they are usually sent to a hydrogenation device for additional desulfurization treatment. However, due to the influence of trace alkaline liquid, especially for the back extraction solvents which are easy to emulsify due to the presence of aromatic hydrocarbons, even after water washing, the trace alkaline liquid is difficult to be washed out, which easily leads to the poisoning and deactivation of the hydrogenation catalyst during hydrogenation treatment. There are also hydrocarbon back extraction solvents sent back to a catalytic cracking device for treatment, and high-temperature cracking in the catalytic cracking device. However, the trace alkaline liquid carried by the back extraction solvents is also harmful to the catalytic cracking catalyst. This makes the treatment of waste back extraction solvents a problem that is not easy to solve for a refinery.

[0006] In addition, in the back extraction step, the disulfide produced after the oxidation and regeneration of the alkaline liquid is usually not completely removed from the regenerated alkaline liquid, and there is often a large amount of residual disulfide, which makes the regenerated alkaline liquid return to the extraction system for use, and the disulfide is easily transferred into the hydrocarbon stream, resulting in a decrease in the extraction desulfurization rate of the hydrocarbon stream, and even an abnormal phenomenon of an increase in sulfur content.

[0007] In addition, the regenerated alkali liquor still contains trace amounts of oxidizing gas before it is returned to the extraction system and contacted with the hydrocarbon stream containing mercaptans, which causes some mercaptans to be oxidized to disulfides in the extraction system and remain in the hydrocarbon stream after extraction. To this end, patent CN 200510132299.7 uses nitrogen replacement to remove the oxidizing gas carried by the regenerated alkali liquor before back extraction, but the replacement is often incomplete, 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 can affect the deep desulfurization of the hydrocarbon stream.

[0008] In summary, in the desulfurization process of the hydrocarbon stream, how to better treat the alkali liquor after alkali extraction to obtain regenerated alkali liquor free of sulfides and oxidizing gas for recycling use to significantly improve the desulfurization effect, and how to better treat the selective solvent that absorbs disulfides, are technical problems that need to be solved. SUMMARY

[0009] The present application provides a hydrocarbon stream extraction desulfurization method and system combined with gasoline production, which aims to better treat the alkali liquor after alkali extraction, so that the regenerated alkali liquor for recycling use is free of sulfides and oxidizing gas, thereby improving the desulfurization effect, and better treating the selective solvent that absorbs disulfides.

[0010] In a first aspect, the present application relates to a hydrocarbon stream extraction desulfurization method combined with gasoline production, which comprises the following steps:

[0011] (1) contacting a hydrocarbon stream with an extraction alkali liquor in an alkali extraction unit to perform alkali extraction, to obtain a hydrocarbon stream product and a sulfidic alkali liquor;

[0012] (2) contacting the sulfidic alkali liquor from step (1) with an oxidizing gas in an oxidation unit to perform oxidation, and after separating out the remaining oxidizing gas, obtaining a disulfidic alkali liquor;

[0013] (3) contacting the disulfidic alkali liquor from step (2) with a first selective solvent in a separation unit and performing separation, to obtain a lean alkali liquor and a first disulfidic selective solvent;

[0014] (4) contacting the lean alkali liquor from step (3) with a second selective solvent in a back extraction unit and performing back extraction, to obtain a regenerated alkali liquor and a second disulfidic selective solvent;

[0015] (5) subjecting low-carbon liquid hydrocarbon and / or at least part of the hydrocarbon stream product from step (1) to a decarboxylation five fraction distillation process in a decarboxylation five fraction column, to obtain a decarboxylation five fraction and a remaining fraction;

[0016] wherein the extractive alkali in step (1) comprises the regenerated alkali from step (4); the first selective solvent in step (3) comprises the second selective solvent comprising disulfides from step (4); and the second selective solvent in step (4) comprises the carbon five fraction from step (5).

[0017] In a second aspect, the present application relates to a hydrocarbon stream extractive desulfurization system associated with gasoline production, characterized in that the hydrocarbon stream extractive desulfurization system comprises:

[0018] an alkali extraction unit, an oxidation unit, a separation unit, a reverse extraction unit, and a carbon five fraction distillation column;

[0019] the alkali extraction unit is provided with a hydrocarbon stream inlet pipeline, an extractive alkali inlet, a hydrocarbon stream product outlet, and a mercaptide-containing alkali outlet;

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

[0021] the disulfide-containing alkali inlet of the separation unit is connected to the disulfide-containing alkali outlet of the oxidation unit, and the separation unit is provided with a first selective solvent inlet, a lean alkali 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 stabilizing system of the catalytic cracking device;

[0022] the lean alkali inlet of the reverse extraction unit is connected to the lean alkali outlet of the separation unit, and the reverse extraction unit is provided with a second selective solvent inlet pipeline, a second disulfide-containing selective solvent outlet, and a regenerated alkali 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; and the regenerated alkali outlet pipeline is connected to the extractive alkali inlet of the alkali extraction unit;

[0023] the carbon five fraction distillation column is provided with a material to be distilled inlet, a carbon five fraction outlet pipeline, and a residual fraction outlet; and the carbon five fraction outlet pipeline is connected to the second selective solvent inlet pipeline of the reverse extraction unit.

[0024] Beneficial effects:

[0025] The present application is a hydrocarbon stream extraction desulfurization method combined with gasoline production, which uses carbon five fraction as a selective solvent for back extraction of alkaline solution, can obtain regenerated alkaline solution without sulfides and oxidizing gas for recycling, significantly improves desulfurization effect, obtains high-quality hydrocarbon stream product with lower sulfur content, and absorbs the selective solvent containing disulfides generated in the separation step in gasoline and then performs desulfurization refining, so that the carbon five fraction is converted into gasoline fraction after absorbing disulfides and is utilized. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0028] BRIEF DESCRIPTION OF DRAWINGS:

[0029] 1 pre-washing unit, 2 alkaline extraction unit, 3 oxidation unit, 4 separation unit,

[0030] 5 back extraction unit, 6 decarbonization five fraction column;

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

[0032] 2a extraction alkaline solution inlet, 2b hydrocarbon stream product outlet, 2c sulfide-containing alkaline solution pipeline;

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

[0034] 4a poor alkaline solution outlet, 4b first disulfide-containing selective solvent outlet;

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

[0036] 5c selective solvent pipeline, 5d regenerated alkaline solution outlet pipeline;

[0037] 6a to-be-fractionated material inlet, 6b remaining fraction outlet, 6c carbon five fraction outlet pipeline. DETAILED DESCRIPTION

[0038] The present application will be further described in detail below by means of the accompanying drawings and examples. Through these descriptions, the features and advantages of the present application will become more apparent.

[0039] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations. Although various aspects of embodiments are illustrated and described herein, unless specifically stated otherwise, the various aspects of embodiments are not necessarily mutually exclusive, but can be combined with each other in various ways.

[0040] Moreover, the technical features involved in the different embodiments described below can be combined with each other as long as there is no conflict.

[0041] In a first aspect, the present application 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 extractive lye in an alkali extraction unit to perform alkali extraction, to obtain a hydrocarbon stream product and a sulfidic lye containing;

[0043] (2) contacting the sulfidic lye containing obtained from step (1) with an oxidizing gas in an oxidation unit to perform oxidation, and after separating out the remaining oxidizing gas, obtaining a disulfide lye containing;

[0044] (3) contacting the disulfide lye containing obtained from step (2) with a first selective solvent in a separation unit to perform separation, to obtain a lean lye and a first disulfide lye containing selective solvent;

[0045] (4) contacting the lean lye obtained from step (3) with a second selective solvent in a reverse extraction unit to perform reverse extraction, to obtain a regenerated lye and a second disulfide lye containing selective solvent;

[0046] (5) subjecting low carbon liquid hydrocarbon and / or at least part of the hydrocarbon stream product obtained from step (1) to a decarboxylation five fraction distillation process in a decarboxylation five fraction distillation column, to obtain a decarboxylation five fraction and a remaining fraction;

[0047] wherein the extractive lye in step (1) comprises the regenerated lye obtained from step (4); the first selective solvent in step (3) comprises part of the second disulfide lye containing selective solvent obtained from step (4); and the second selective solvent in step (4) comprises the decarboxylation five fraction obtained from step (5).

[0048] It should be noted that the first disulfide-containing selective solvent obtained from step (3) can be partially returned to step (3) for use as the first selective solvent. The extraction alkaline solution may include any known organic and / or inorganic alkaline reagent capable of extracting thiols from gasoline. Ideally, the alkaline solution is generally an aqueous solution of an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, etc. If desired, aqueous solutions of alkaline earth metal hydroxides such as calcium hydroxide, barium hydroxide, ammonia, and organic quaternary ammonium bases may be used. Additives such as lower alcohols (methanol, ethanol, isopropanol, etc.) and substances containing nitrogen, phosphorus, oxygen, sulfur, arsenic, and antimony may be added to the alkaline reagent. The amount of such compounds and various basic nitrides added is generally not more than 200 μg / g. A particularly ideal alkaline solution for use in this invention is a sodium hydroxide solution or a potassium hydroxide solution of about 1% to 50% (by weight), preferably a sodium hydroxide solution of 5% to 25% (by weight).

[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 thiols undergoes alkaline extraction in step (1). After the thiols react with the alkaline solution, they are converted into thiolates, resulting in an alkaline solution containing thiolates. The thiols in the hydrocarbon stream are converted into thiolates and removed, yielding the hydrocarbon stream product. In step (2), the alkaline solution containing thiolates undergoes an oxidation reaction with oxidizing gases under the catalysis of an oxidation catalyst. The thiolates are converted into disulfides, resulting in an alkaline solution containing disulfides. At the end of step (2), there may be excess oxidizing gases. The excess oxidizing gases can be treated by a subsequent separator and light hydrocarbon recovery device for clean discharge, or sent to the flue gas desulfurization system of the catalytic cracking unit for incineration, or they can be recycled after pressurization. In step (3), the alkaline solution containing disulfides is contacted with a first selective solvent that does not contain oxidizing gases, so that at least part of the disulfides are absorbed by the first selective solvent, resulting in a lean alkaline solution and a first selective solvent containing disulfides. The resulting lean alkali solution may still contain disulfides. After the reverse extraction in step (4), the remaining disulfides in the lean alkali solution are absorbed by the second selective solvent to obtain the regenerated alkali solution and the second disulfide-containing selective solvent. The resulting regenerated alkali solution is returned to step (1) for use as the extraction alkali solution.

[0050] It is important to note that, first, the present inventor has found, in the long-term research and development of hydrocarbon stream desulfurization, that setting step (5) to subject the low-carbon liquid hydrocarbon substantially free of hydrogen sulfide and mercaptan and / or at least part of the hydrocarbon stream product from step (1) to a decarboxylic pentane fraction fractionation process to obtain a decarboxylic pentane fraction substantially free of hydrogen sulfide and mercaptan and also free of oxidizing gas; and when performing the reverse extraction of step (4), the decarboxylic pentane fraction from step (5) is used as the second selective solvent for the reverse extraction to absorb the disulfide in the lean alkali solution, which can more thoroughly remove the disulfide and oxidizing gas in the lean alkali solution to obtain regenerated alkali solution free of sulfide and oxidizing gas, thereby significantly reducing the sulfur content of the obtained hydrocarbon stream product.

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

[0052] The sulfides contained in the C5 fraction separated from the decarburized C5 fraction column are not limited, as long as they are substantially free of hydrogen sulfide and mercaptans. By "substantially free of hydrogen sulfide and mercaptans", it is meant that no hydrogen sulfide and mercaptans are detected according to known detection methods, or the content of hydrogen sulfide and mercaptans (calculated as sulfur) is below the lower limit of detection. Moreover, the amount of sulfides accumulated during the contact of the C5 fraction with the lye is not limited, as long as it ensures that the regenerated lye after desulfurization is substantially free of disulfides and oxidizing gases, thereby substantially increasing the effective utilization of the lye and the desulfurization effect, substantially reducing the sulfur content in the obtained hydrocarbon stream product, and substantially reducing the discharge treatment of the second disulfide-containing selective solvent (back-extraction solvent). Furthermore, the hydrocarbon stream product obtained from step (1) can be optionally partially subjected to the fractionation process of the decarburized C5 fraction in 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 lye obtained from step (2) is first contacted with the first selective solvent, i.e., at least part of the second disulfide-containing selective solvent obtained from step (4), and then subjected to sedimentation separation or phase separation, and subsequent back-extraction, which can make the regenerated lye free of sulfides and oxidizing gases, and further reduce the sulfur content in the obtained hydrocarbon stream product.

[0054] According to a specific embodiment of the hydrocarbon stream extraction desulfurization method according to the first aspect of the present application, 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 application, the second disulfide-containing selective solvent obtained from step (4) can be divided into two parts, one part continues to perform back-extraction in step (4) as the second selective solvent, and the other part continues to perform separation in step (3) as the first selective solvent. Firstly, it can better regenerate the lye, improve the desulfurization effect, and obtain a hydrocarbon stream product with lower sulfur content. Secondly, it can better operate the entire hydrocarbon stream extraction desulfurization method in a self-circulating manner to save energy. Thirdly, the second disulfide-containing selective solvent produced in step (4) can be processed without the aid of external systems, thereby substantially reducing the 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 according to the first aspect of the present application, step (3) further comprises the following steps after the separation:

[0057] separating the first disulfide-containing selective solvent from the feedstock of the absorption-stabilization system of the catalytic cracking unit after mixing the first disulfide-containing selective solvent with the feedstock of the absorption-stabilization system of the catalytic cracking unit, the first disulfide-containing selective solvent being absorbed into the stabilized gasoline, and then performing desulfurization refining 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 further innovatively found that, after separating the first disulfide-containing selective solvent from the feedstock of the absorption-stabilization system of the catalytic cracking unit after mixing the first disulfide-containing selective solvent with the feedstock of the absorption-stabilization system of the catalytic cracking unit, the first disulfide-containing selective solvent being absorbed into the stabilized gasoline, and then performing desulfurization refining to obtain low-sulfur gasoline. The operation of the absorption-stabilization system and the desulfurization refining operation of the stabilized gasoline are performed in a conventional manner, preferably in a selective hydrogenation manner, and the sulfur content of the desulfurized gasoline product is not more than 10 μg / g. The sulfur-containing gasoline is converted into a low-sulfur gasoline product after the well-known desulfurization refining operation (for example, selective hydrogenation desulfurization), and the sulfur content of the low-sulfur gasoline product is not more than 10 μg / g. In this way, the carbon five fraction in the low-carbon mixed liquid hydrocarbon in the refinery is used as a second selective solvent (counter-extraction solvent) and then transferred into gasoline to maximize the use, and in general, the carbon five fraction separated from the liquid hydrocarbon in the refinery is converted into a gasoline fraction after absorbing disulfides and used, and this use has greatly reduced disadvantages compared with the prior art in which the carbon five fraction is directly sent to an additional hydrogenation device for treatment or returned to the catalytic cracking unit to be mixed with the catalytic feedstock for catalytic cracking reaction to perform secondary cracking.

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

[0061] contacting the original hydrocarbon stream with a pre-alkaline washing lye to perform pre-alkaline washing, to obtain the hydrocarbon stream in step (1);

[0062] 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.

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

[0064] According to one embodiment of the hydrocarbon stream extraction desulfurization method of the first aspect of the present application, the low carbon liquid hydrocarbon in step (5) is selected from one or more of the group consisting of liquefied petroleum gas, crude mixed C3 hydrocarbon and C4 hydrocarbon, crude mixed C4 hydrocarbon, and mixed liquid hydrocarbon of C1 to C6.

[0065] It is to be noted that the low carbon liquid hydrocarbon can be low carbon liquid hydrocarbon from other devices of a refinery, which is substantially free of hydrogen sulfide and mercaptan, and includes, but is not limited to, the above-mentioned liquefied petroleum gas and mixed liquid hydrocarbon of C1 to C6, etc.

[0066] The carbon five fraction obtained from the fractionation process of the above-mentioned low carbon liquid hydrocarbon in step (5) is used as the second selective solvent for the reverse extraction in step (4), which can greatly improve the effective utilization rate of the lye and the desulfurization effect, and greatly reduce the sulfur content in the obtained hydrocarbon stream product.

[0067] According to one embodiment of the hydrocarbon stream extraction desulfurization method of the first aspect of the present application, in step (1), the conditions for the base extraction include:

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

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

[0070] The volume ratio of the extraction lye in the hydrocarbon stream is 1% to 50%, preferably 5% to 40%.

[0071] It is to 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 application, by controlling the temperature and pressure and other conditions of the base extraction in step (1) as above, the sulfur content of the obtained hydrocarbon stream product can be further reduced.

[0072] According to one embodiment of the hydrocarbon stream extraction desulfurization method of the first aspect of the present application, in step (2), the conditions for the oxidation include:

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

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

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

[0076] The amount of the oxidizing gas is greater than or equal to 1 to 20 times the stoichiometrically required amount of the oxidizing gas for oxidizing the mercaptide contained in the mercaptide-containing alkaline solution to disulfide, and is preferably 2 to 10 times the stoichiometrically required amount.

[0077] Note that in the step (2), the pressure is more preferably 0.1 MPa to 0.8 MPa. The stoichiometrically required amount of the oxidizing gas is calculated based on the fact that 0.25 mole of oxygen gas is required per mole of mercaptide to be oxidized to disulfide, and the amount of the oxidizing gas is more preferably 2 to 4 times the stoichiometrically required amount. In order to completely oxidize the mercaptide contained in the mercaptide-containing alkaline solution to disulfide, the mercaptide-containing alkaline solution needs to be heated to a temperature at which catalytic oxidation is ensured, and therefore the temperature in the step (2) can be higher than that in the step (1), and the pressure in the step (2) can be lower than that in the step (1).

[0078] In the step (2), the oxidizing catalyst used when the mercaptide contained in the mercaptide-containing alkaline solution is oxidized with the oxidizing gas can be a metal phthalocyanine catalyst, and a cobalt phthalocyanine compound such as sulfonated cobalt phthalocyanine or a poly cobalt phthalocyanine is preferably used as the oxidizing catalyst. The cobalt phthalocyanine catalyst can be used by being dissolved in the alkaline solution or by being used in the form of a stable emulsion in the alkaline solution, and the content of the cobalt phthalocyanine catalyst in the alkaline solution when used is 5 μg / g to 1000 μg / g, and preferably 10 μg / g to 400 μg / g. The cobalt phthalocyanine catalyst can also be used in the form of a fixed bed in which the catalyst is 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 is 0.01% to 10%, and preferably 0.05% to 1.0%, and a compound containing nitrogen, phosphorus, oxygen, sulfur, arsenic, antimony, and various basic nitrogen compounds, etc. can be used as a catalytic aid on the supported catalyst. A cobalt phthalocyanine supported fixed bed type catalyst is preferably used. In the step (2), the oxidizing catalyst used when the mercaptide contained in the mercaptide-containing alkaline solution is oxidized with the oxidizing gas can be a metal phthalocyanine catalyst, and a cobalt phthalocyanine compound such as sulfonated cobalt phthalocyanine or a poly cobalt phthalocyanine is preferably used as the oxidizing catalyst. The cobalt phthalocyanine catalyst can be used by being dissolved in the alkaline solution or by being used in the form of a stable emulsion in the alkaline solution, and the content of the cobalt phthalocyanine catalyst in the alkaline solution when used is 5 μg / g to 1000 μg / g, and preferably 10 μg / g to 400 μg / g. The cobalt phthalocyanine catalyst can also be used in the form of a fixed bed in which the catalyst is 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 is 0.01% to 10%, and preferably 0.05% to 1.0%, and a compound containing nitrogen, phosphorus, oxygen, sulfur, arsenic, antimony, and various basic nitrogen compounds, etc. can be used as a catalytic aid on the supported catalyst. A cobalt phthalocyanine supported fixed bed type catalyst is preferably used.

[0079] According to one embodiment of the hydrocarbon stream extraction desulfurization method according to the first aspect of the present application, in the step (3), the conditions under which the separation is performed include:

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

[0081] In the step (4), the conditions under which the back extraction is performed include:

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

[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 back extraction in step (4) as above, it is more favorable to produce the regenerated alkali liquor free of sulfides and oxidizing gas, and further to produce the high-quality hydrocarbon stream product with lower sulfur content.

[0084] The separation in step (3) is preferably carried out by sedimentation separation, and the time of the sedimentation separation is usually not less than 15 min, preferably not less than 45 min, and most preferably not less than 90 min. As a preferred embodiment, after the oxidation in step (2) is completed, the dithioalkali liquor is cooled, and then the separation in step (3) is carried out, so as to reduce the volatilization of the dithioalkali stream and the hydrocarbon gas as much as possible. The pressure in step (3) is preferably lower than that in step (2). The pressure in steps (3) and (4) is more preferably 0.1 MPa to 0.5 MPa.

[0085] The contact according to the present application can be carried out in various columns, vessels, etc. 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.

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

[0087] According to a second aspect, the present application relates to a hydrocarbon stream extraction desulfurization system associated with gasoline production, as shown in Figure 1 or 2, which comprises:

[0088] an alkali extraction unit 2, an oxidation unit 3, a separation unit 4, a back extraction unit 5, and a decarburization five fraction column 6;

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

[0090] The mercaptide-containing alkali liquor inlet of the oxidation unit 3 is connected to the mercaptide-containing alkali liquor outlet of the alkali extraction unit 2 through a mercaptide-containing alkali liquor pipeline 2c, and the mercaptide-containing alkali liquor pipeline 2c is provided with an oxidizing gas inlet 3a; the oxidation unit 3 is further provided with a residual oxidizing gas outlet 3b and a dithioalkali liquor outlet 3c;

[0091] The disengaging unit 4 is connected to the outlet 3c of the oxidizing unit 3, and is provided with a first selective solvent inlet, a lean caustic outlet 4a and a first selective solvent outlet 4b containing disulfide; the first selective solvent outlet 4b is connected to the raw material inlet of the absorption stabilization system of the catalytic cracking device;

[0092] The disengaging unit 4 is connected to the outlet 3c of the oxidizing unit 3, and is provided with a first selective solvent inlet, a lean caustic outlet 4a and a first selective solvent outlet 4b containing disulfide; the first selective solvent outlet 4b is connected to the raw material inlet of the absorption stabilization system of the catalytic cracking device;

[0093] The decarburized C5 fractionating column 6 is provided with a material to be fractionated inlet 6a, a C5 fraction outlet pipeline 6c and a remaining 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 material to be fractionated inlet 6a of the decarburized C5 fractionating column 6 can also be connected to the hydrocarbon stream product outlet 2b, so that part of the hydrocarbon stream product enters the decarburized C5 fractionating column 6 for decarburized C5 fractionation, and the C5 fraction is used as the second selective solvent of the back-extraction unit.

[0095] The hydrocarbon stream flows into the caustic extraction unit 2 through the hydrocarbon stream inlet pipeline 1d, and is contacted with the extraction caustic liquid flowing into the extraction caustic liquid inlet 2a for caustic extraction; the obtained hydrocarbon stream product is output through the hydrocarbon stream product outlet 2b, and the obtained mercaptide-containing caustic liquid flows into the oxidizing unit 3 through the mercaptide-containing caustic liquid pipeline 2c after flowing into the mercaptide-containing caustic liquid inlet of the oxidizing unit 3.

[0096] The oxidizing gas flows into the oxidizing unit 3 through the oxidizing gas inlet 3a and the mercaptide-containing caustic liquid pipeline 2c, and the oxidizing gas is contacted with the mercaptide-containing caustic liquid in the oxidizing unit 3, so that the mercaptide is oxidized into disulfide; the obtained disulfide-containing caustic liquid flows into the disengaging unit 4 through the disulfide-containing caustic liquid outlet 3c of the oxidizing unit 3 and the disulfide-containing caustic liquid inlet of the disengaging unit 4; the remaining oxidizing gas exits the oxidizing unit 3 through the remaining oxidizing gas outlet 3b.

[0097] The alkali liquor containing disulfide flowing into the separation unit 4 is contacted with the first selective solvent flowing in through the first selective solvent inlet, the disulfide is absorbed into the first selective solvent, and after sedimentation separation, the obtained poor alkali liquor flows out through the poor alkali liquor outlet 4a into the back extraction unit 5, and the obtained first selective solvent containing disulfide flows out through the first selective solvent containing disulfide outlet 4b and enters the absorption stabilization system after the catalytic cracking device and the catalytic cracking reactor, the first selective solvent containing disulfide is absorbed in the stabilized gasoline, and after the stabilized gasoline is discharged, desulfurization refining is carried out to obtain low-sulfur gasoline with a sulfur content of not more than 10 μg / g.

[0098] In the back extraction unit 5, the poor alkali liquor is contacted with the second selective solvent from the second selective solvent inlet pipeline 5a, so that the residual disulfide in the poor alkali liquor is absorbed by the second selective solvent, and the regenerated alkali liquor and the second selective solvent containing disulfide are obtained, the obtained regenerated alkali liquor flows into the alkali extraction unit 2 through the regenerated alkali liquor outlet pipeline 5d and the extraction alkali inlet 2a to be used as the extraction alkali, and the obtained second selective solvent containing disulfide flows into the separation unit 4 through the second selective solvent containing disulfide outlet 5b, the selective solvent pipeline 5c and the first selective solvent inlet to be used as the first selective solvent.

[0099] The low-carbon liquid hydrocarbon can enter the decarburization five-fraction column 6 through the material to be fractionated inlet 6a, and the carbon five fraction obtained by the fractionation of the decarburization five fraction of the decarburization five-fraction column 6 can flow into the back extraction unit 5 through the carbon five fraction outlet pipeline 6c and the second selective solvent inlet pipeline 5a to be used as the second selective solvent.

[0100] It is particularly important to note that, first, the alkali liquor after alkali extraction is subjected to multi-stage ingenious treatment by the hydrocarbon stream extraction desulfurization system, the obtained regenerated alkali liquor does not contain sulfides and oxidizing gas, the obtained regenerated alkali liquor returns to the alkali extraction unit 2 through the regenerated alkali liquor outlet pipeline 5d and the extraction alkali inlet 2a to be used in circulation, which can greatly reduce the amount of fresh alkali liquor, and at the same time, the desulfurization effect is significantly improved, and the sulfur content of the obtained hydrocarbon stream product is low. Second, the carbon five fraction outlet pipeline 6c is connected with the second selective solvent inlet pipeline 5a of the back extraction unit 5, so that the carbon five fraction from the decarburization five-fraction column 6 returns to the back extraction unit 5 to be used in circulation as the second selective solvent, which can more thoroughly back extract the residual disulfide and oxidizing gas in the poor alkali liquor into the carbon five fraction, so that the obtained regenerated alkali liquor does not contain sulfides and oxidizing gas, and third, the second selective solvent containing disulfide outlet 5b is connected with the first selective solvent inlet of the separation unit 4 through the selective solvent pipeline 5c, the discharge amount of the carbon five fraction containing disulfide can be greatly reduced, and complex external treatment is avoided.

[0101] According to a specific embodiment of the hydrocarbon stream extractive desulfurization system of the second aspect of the present application, the second selective solvent inlet pipeline 5a of the back-extraction unit 5 is in communication with the second disulfide-containing selective solvent outlet 5b; and / or,

[0102] The hydrocarbon stream extractive desulfurization system is further provided with a pre-alkali washing unit 1, which is provided with an original hydrocarbon stream inlet pipeline 1a, a pre-alkali washing lye inlet pipeline 1b, a circulating lye outlet 1c, and a post-pre-alkali washing hydrocarbon stream outlet; the pre-alkali washing lye inlet pipeline 1b is in communication with the circulating lye outlet 1c, and the pre-alkali washing lye inlet pipeline 1b is in communication with the original hydrocarbon stream inlet pipeline 1a; the post-pre-alkali washing hydrocarbon stream outlet is in communication with 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 back-extraction unit 5 is in communication with the second disulfide-containing selective solvent outlet 5b, so that the second disulfide-containing selective solvent produced by the back-extraction unit 5 is returned to the hydrocarbon stream extractive desulfurization system for recycling, part of which is returned to the back-extraction 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 devices, and the entire system forms a self-circulation system.

[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, and a hydrocarbon stream product with higher quality can be obtained.

[0105] According to a specific embodiment of the hydrocarbon stream extractive desulfurization system of the second aspect of the present application, the overhead temperature of the decarburized C5 fractional column 6 is 35-80°C, preferably 40-65°C; the overhead pressure is 0.15-2.20 MPa, preferably 0.35-1.20 MPa; and the bottom temperature is 55-150°C, preferably 60-130°C.

[0106] It should be noted that by controlling the temperature and pressure of the decarburized C5 fractional column 6 as above, the fractional process of the C5 fraction of the low-carbon liquid hydrocarbon and the optional part of the hydrocarbon stream product obtained from the alkali extraction unit 2 is facilitated, and the C5 fraction free of sulfides and oxidizing gases is better obtained as the second selective solvent of the back-extraction unit 5, so as to better prepare the regenerated lye free of sulfides and oxidizing gases.

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

[0108] The raw hydrocarbon stream (e.g. catalytically liquefied petroleum gas, distilled from the absorption-stabilization system of the catalytic unit and after removal of hydrogen sulfide by the amine removal system) enters the pre-wash unit 1 through the raw hydrocarbon stream inlet line 1a after mixing with fresh caustic from the pre-wash caustic inlet line 1b and / or recycled caustic from the recycled caustic outlet 1c. Trace amounts of hydrogen sulfide (and a portion of mercaptans) in the raw hydrocarbon stream are removed.

[0109] The hydrocarbon stream exiting the pre-wash unit 1 flows through the hydrocarbon stream inlet line 1d into the caustic extraction unit 2, where it is contacted countercurrently with fresh caustic entering through the extraction caustic inlet 2a and / or regenerated caustic from the regenerated caustic outlet line 5d (in communication with the extraction caustic inlet 2a) that is substantially free of disulfides and oxidizing gases. Mercaptans in the hydrocarbon stream are absorbed by the caustic to form mercaptide salts, and the hydrogen sulfide and mercaptan-removed hydrocarbon stream becomes the hydrocarbon stream product that exits the caustic extraction unit 2 from the hydrocarbon stream product outlet 2b at the top of the caustic extraction unit 2 as a desulfurized product (hydrocarbon stream product).

[0110] The caustic that has absorbed the mercaptans, i.e. the mercaptide salt-containing caustic (rich caustic), exits the caustic extraction unit 2 through the mercaptide salt-containing caustic line 2c and is mixed with oxidizing gas (e.g. air) entering through the oxidizing gas inlet 3a before flowing into the oxidation unit 3. Under the action of the fixed-bed oxidation catalyst, i.e. the metal phthalocyanine supported catalyst, packed in the oxidation unit 3, the mercaptide salts in the mercaptide salt-containing caustic (rich caustic) are oxidized by the oxidizing gas (e.g. air) to disulfides. The excess oxidizing gas is discharged through the excess oxidizing gas outlet 3b, treated by a subsequent separation tank and light hydrocarbon recovery device, and then discharged cleanly, or sent to the flue gas desulfurization system of the catalytic cracking unit for incineration, or recycled after being pressurized.

[0111] The disulfide-rich disulfide-containing caustic, from which the excess oxidizing gas has been separated, exits through the disulfide-containing caustic outlet 3c and is mixed with the first selective solvent from the selective solvent line 5c before flowing into the separation unit 4. The disulfides in the caustic are transferred into the first selective solvent. The first disulfide-rich selective solvent containing disulfides obtained by separation is discharged from the first disulfide-containing selective solvent outlet 4b and sent to the absorption-stabilization system of the catalytic cracking unit and arranged after the catalytic cracking reactor. The absorption-stabilization system operates in a conventional manner so that the selective solvent and disulfides are absorbed into the stabilized gasoline, and the stabilized gasoline undergoes subsequent desulfurization refining operations. The desulfurization refining operation of the stabilized gasoline is selected in an industrial manner known in the art to reduce the sulfur content to below 10 μg / g to meet the requirements of the gasoline standard.

[0112] The lean caustic solution from the separation unit 4 is mixed with the second selective solvent from the second selective solvent inlet line 5a at the lean caustic solution outlet 4a and flows into the back-extraction unit 5. In the back-extraction unit 5, the residual disulfides and the residual oxidizing gas contained in the lean caustic solution are absorbed by the second selective solvent. After the back-extraction, the lean caustic solution becomes a regenerated caustic solution, while the second selective solvent becomes a second disulfide-containing selective solvent. The second disulfide-containing selective solvent flows out of the second disulfide-containing selective solvent outlet 5b, and a portion of the second disulfide-containing selective solvent is recycled to the back-extraction unit 5 through the second selective solvent inlet line 5a, while another portion of the second disulfide-containing selective solvent is introduced into the separation unit 4 through the selective solvent line 5c and the first selective solvent inlet, and is contacted with the disulfide-containing caustic solution outlet 3c, which is the disulfide-enriched disulfide-containing caustic solution from which the excess oxidizing gas is separated, and then is separated. The regenerated caustic solution obtained is introduced into the caustic extraction unit 2 through the regenerated caustic solution outlet line 5d and the extraction caustic inlet 2a, and is recycled.

[0113] When the hydrocarbon stream extraction desulfurization system of the present application is started, the second selective solvent flowing into the back-extraction unit 5 through the second selective solvent inlet line 5a is obtained from the carbon pentane fraction, which is the bottom stream of the decarbonization five fraction column 6, and flows out of the carbon pentane fraction outlet line 6c and into the back-extraction unit 5 through the second selective solvent inlet line 5a. The material to be fractionated introduced into the decarbonization five fraction column 6 through the material to be fractionated inlet 6a can be a low-carbon liquid hydrocarbon substantially free of hydrogen sulfide and mercaptan from a refinery, can be at least a portion of the hydrocarbon stream product flowing out of the hydrocarbon stream product outlet 2b, or can be a mixture of the low-carbon liquid hydrocarbon substantially free of hydrogen sulfide and mercaptan from a refinery and a portion of the hydrocarbon stream product flowing out of the hydrocarbon stream product outlet 2b.

[0114] The present application is further illustrated in detail by the following examples, but is not limited to the examples.

[0115] 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 vessels, 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.

[0116] Example 1

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

[0118] Table 1

[0119] Density (20°C) / (g / cm 3 )]]> Distillation / °C Sulfur content / (μg / g) Mercaptan sulfur content / (μg / g) 0.6344 32～77 57 52

[0120] use Figure 1 or Figure 2 The flowchart shown illustrates the desulfurization treatment of the hydrocarbon stream from Table 1—light catalytic cracking gasoline—except for pre-alkali washing. The light catalytic cracking gasoline is then introduced into an alkali extraction unit where it is contacted with a NaOH solution for alkali extraction. A 15% (by weight) NaOH solution is used. In the alkali extraction unit, the volume ratio of the extraction alkali solution to the hydrocarbon stream is 1:9, the temperature is ambient, and the pressure is 0.50 MPa. After alkali extraction, a hydrocarbon stream product and a thiol-containing alkali solution are obtained; the hydrocarbon stream product flows out through hydrocarbon stream product outlet 2b, and the thiol-containing alkali solution enters the oxidation unit.

[0121] In the oxidation unit, under the catalysis of the catalyst, the thiolate-containing alkaline solution comes into contact with the oxidizing gas—air—to oxidize the thiolate to disulfide, yielding a disulfide-containing alkaline solution. A metal phthalocyanine-type oxidation catalyst is loaded, using activated carbon (provided by Beijing Guanghua Jingke Activated Carbon Factory, grade GH-8) as a support, with sulfonated cobalt phthalocyanine as the main active component (0.6%), and dodecyl dimethyl benzyl ammonium chloride (1%) and isopropanolamine (5%) as co-active components. The catalyst preparation process is as follows: According to the target loading, dilute ammonia solution of sulfonated cobalt phthalocyanine and a mixed solution of dodecyl dimethyl benzyl ammonium chloride and isopropanolamine are prepared separately. Equal volumes of activated carbon are then adsorbed sequentially, and each time the solution is dried using a rotary evaporator.

[0122] In the oxidation unit, the injected air volume is four times the theoretical chemical requirement, equivalent to a standard air-to-thiol salt volume ratio of approximately 0.8:1. The alkali oxidation temperature is 50°C, and the pressure is 0.40 MPa. 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 alkaline solution from the excess air tail gas is contacted with the first selective solvent and flows into the separation unit. The volume ratio of the first selective solvent to the disulfide-containing alkaline solution is 1:10. The first selective solvent is the second disulfide-containing selective solvent from the reverse extraction unit. The conditions in the separation unit are: temperature 50°C, pressure 0.30 MPa.

[0124] In the separation unit, the lean caustic solution and the first disulfide-containing selective solvent are separated. The first disulfide-containing selective solvent is separated from the lean caustic solution and sent to the catalytic cracking unit and disposed in the absorption-stabilization system after the catalytic cracking reactor, so that the selective solvent and the disulfide are mixed with the feedstock of the absorption-stabilization system and then separated to be absorbed into the stabilized gasoline, and then subjected to subsequent desulfurization refining operation with the stabilized gasoline. The desulfurization refining operation of the stabilized gasoline is performed by selective hydrogenation, so that the sulfur content is reduced to less than 10 μg / g. The lean caustic solution separated is sent to the back-extraction unit, and the second selective solvent is also sent to the back-extraction unit.

[0125] In the back-extraction unit, the inlet pressure of the back-extraction unit is 0.30 MPa, the second selective solvent without oxidizing gas is contacted with the lean caustic solution at normal temperature, the circulation volume ratio of the second selective solvent (the C5 fraction separated by the C5 fractionation column) to the lean caustic solution is 1:1, then the second selective solvent is separated from the lean caustic solution, and the second disulfide-containing selective solvent and the regenerated caustic solution are obtained. The second selective solvent for absorbing disulfide is the C5 fraction separated by the C5 fractionation column, which is a low-carbon liquid hydrocarbon in a refinery and is substantially free of hydrogen sulfide, mercaptan and oxidizing gas. The operating conditions of the C5 fractionation column for fractionating the low-carbon liquid hydrocarbon in the refinery can include: a column top pressure of 0.5 MPa, a column top temperature of 51.5°C, a column bottom temperature of 90°C, and a reflux ratio of 1.0. The feedstock of the C5 fractionation column is mixed liquid light hydrocarbon (C3-C5) substantially 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 for recycling as the second selective solvent, and the other part is returned to the separation unit to contact with the disulfide-rich disulfide-containing caustic solution separated from the excess air tail gas.

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

[0128] The results show that after treatment, the sulfur content in the light gasoline is reduced to 5 μg / g, not only the mercaptan is completely removed, but also the sulfur content is greatly reduced (the sulfur content reduction value of the light gasoline is equivalent to the mercaptan sulfur content before desulfurization treatment). The regenerated caustic solution obtained by back-extraction cannot detect sodium mercaptide (determined by potentiometric titration), which indicates that the caustic solution containing mercaptan is completely regenerated, and the regenerated caustic solution obtained by back-extraction also cannot detect the presence of disulfide, which indicates that the regenerated caustic solution returned to the caustic extraction unit does not contain disulfide and does not contain oxidizing gas, so there is no situation that the regenerated caustic solution carries disulfide into the light gasoline in the caustic extraction step, and there is also no situation that part of the mercaptan in the light gasoline is oxidized to disulfide and remains in the light gasoline.

[0129] Example 2

[0130] The hydrocarbon stream to be desulfurized is liquefied petroleum gas, with a density (20℃) of 0.5558 g / cm³. 3 Sulfur content: 320 μg / g (ultraviolet fluorescence method).

[0131] use Figure 1 or Figure 2 The flowchart shown illustrates the desulfurization treatment of the aforementioned hydrocarbon stream-liquefied petroleum gas. The hydrocarbon stream undergoes pre-alkali washing followed by alkali extraction. The pre-alkali washing alkali concentration is 5% (by weight), and the alkali usage is 5% of the weight of the raw material, i.e., the hydrocarbon stream. In the alkali extraction unit, the alkali concentration used is 15% (by weight), the volume ratio of alkali to raw material (hydrocarbon stream) is 3:7, the temperature is ambient, and the pressure is 1.6 MPa. The remaining steps are the same as in Example 1. The desulfurization results are shown in Table 2.

[0132] The results showed that the sulfur content in the liquefied petroleum gas was reduced to 6 μg / g after treatment. Sodium thiolate was undetectable in the regenerated alkali solution (determined by potentiometric titration), indicating complete regeneration of the thiol-containing alkali solution. Furthermore, no disulfides were detected in the regenerated alkali solution obtained after back-extraction, further demonstrating that the regenerated alkali solution returned to the alkali extraction unit was essentially free of disulfides and air.

[0133] Comparative Examples 1-2

[0134] use Figure 1 The flowcharts shown in Example 2 illustrate the desulfurization treatment of the hydrocarbon stream from Example 1 (light catalytic cracking gasoline) and the hydrocarbon stream from Example 2 (liquefied petroleum gas). The operating conditions and catalysts used were the same as in Examples 1 and 2, except that the second selective solvent was not used for the back-extraction process, and the decarbonization five-fractionation tower was not used. After alkaline oxidation, the alkaline solution and excess oxidizing gas were separated by natural sedimentation. The first selective solvent was not used to contact the disulfide-containing alkaline solution obtained from the oxidation unit. The desulfurization results are shown in Table 2.

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

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

[0137] Table 2

[0138]

[0139]

[0140] In the description of the present application, it needs to be explained 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 do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0141] In the description of the present application, it needs to be explained that the terms "mounting", "connecting", "connection" should be understood in a broad sense unless otherwise specifically defined and limited. 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.

[0142] 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, which all fall within the protection scope of the present application.

Claims

1. A process for the extraction desulfurization of hydrocarbon streams associated with gasoline production, characterized in that, The hydrocarbon stream extraction desulfurization method comprises the following steps: (1) contacting the hydrocarbon stream with an extraction lye in an alkali extraction unit to perform alkali extraction, to obtain a hydrocarbon stream product and a sulfidic lye containing solution; (2) contacting the sulfidic lye containing solution from step (1) with an oxidizing gas in an oxidation unit to perform oxidation, and after separating the remaining oxidizing gas, a disulfide lye containing solution is obtained; (3) contacting the disulfide lye containing solution from step (2) with a first selective solvent in a separation unit to perform separation, to obtain a lean lye and a first disulfide containing selective solvent; (4) contacting the lean lye from step (3) with a second selective solvent in a reverse extraction unit to perform reverse extraction, to obtain a regenerated lye and a second disulfide containing selective solvent; (5) subjecting low carbon liquid hydrocarbon and / or at least part of the hydrocarbon stream product from step (1) to a decarboxylation five fraction distillation process in a decarboxylation five fraction column, to obtain a five fraction and a remaining fraction; wherein the extraction lye in step (1) comprises the regenerated lye from step (4); the first selective solvent in step (3) comprises part of the second disulfide containing selective solvent from step (4); and the second selective solvent in step (4) comprises the five fraction from step (5); wherein the low carbon liquid hydrocarbon in step (5) is selected from one or more combinations of liquefied petroleum gas, crude mixed C3 hydrocarbon and C4 hydrocarbon, crude mixed C4 hydrocarbon, and mixed liquid hydrocarbon of C1-C6; and the volume ratio of the five fraction as the second selective solvent in step (4) to the lean lye from step (3) is 1:(0.01-100).

2. The hydrocarbon stream extractive desulfurization method according to claim 1, characterized by, The second selective solvent in step (4) further comprises part of the second disulfide containing selective solvent from step (4).

3. The hydrocarbon stream extractive desulfurization method of claim 1, wherein Step (3) further comprises the following steps after the separation: intermittently or continuously mixing the first disulfide containing selective solvent with the raw material of the absorption stabilization system of a catalytic cracking device to perform separation, the first disulfide containing selective solvent is absorbed into the stabilized gasoline, and then desulfurization refining is performed to obtain low sulfur gasoline; the sulfur content of the low sulfur gasoline is not more than 10 μg / g.

4. The hydrocarbon stream extractive desulfurization process of claim 1, wherein, The hydrocarbon stream extraction desulfurization method further comprises a pre-alkali washing step before step (1): contacting the original hydrocarbon stream with a pre-alkali washing lye to perform pre-alkali washing, to obtain the hydrocarbon stream in step (1); the original hydrocarbon stream is selected from at least one of natural gas, liquefied petroleum gas, light naphtha, light gasoline, and low carbon hydrocarbon of C1-C6.

5. The hydrocarbon stream extractive desulfurization process of claim 1, wherein, In step (1), the conditions for performing the alkali extraction include: the temperature is -5℃-100℃; the pressure is 0.1 MPa-4.0 MPa; the volume ratio of the extraction lye in the hydrocarbon stream is 1%-50%.

6. The hydrocarbon stream extractive desulfurization process of claim 1, wherein, In step (2), the conditions for performing the oxidation include: the temperature is -5℃-100℃; the pressure is 0.1 MPa-2.0 MPa; the oxidizing gas is selected from one or a combination of both of oxygen and air; The amount of the oxidizing gas is greater than or equal to 1 to 20 times the theoretical chemical requirement amount of the oxidizing gas required for oxidizing the mercaptide contained in the mercaptide-containing alkaline solution into disulfide.

7. The hydrocarbon stream extractive desulfurization method of claim 1, wherein In step (3), the conditions for performing the separation include: The temperature is -5℃ to 80℃; the pressure is 0.1MPa to 2.0MPa; the volume ratio of the second disulfide-containing selective solvent obtained from step (4) to the disulfide-containing alkaline solution as the first selective solvent is 1:(0.01 to 100); and / or, In step (4), the conditions for performing the back extraction include: The temperature is -5℃ to 80℃; the pressure is 0.1MPa to 2.0MPa; the volume ratio of the carbon five fraction as the second selective solvent to the lean alkaline solution obtained from step (3) is 1:(0.1 to 10).

8. The hydrocarbon stream extractive desulfurization method of claim 1, wherein, The sulfur content of the hydrocarbon stream product obtained from step (1) is not more than 10μg / g.

9. The hydrocarbon stream extractive desulfurization method of claim 1, wherein, In step (1), the conditions for performing the alkaline extraction include: The temperature is 25℃ to 50℃; The pressure is 0.1MPa to 2.0MPa; The volume proportion of the extraction alkaline solution in the hydrocarbon stream is 5% to 40%.

10. The hydrocarbon stream extractive desulfurization process of claim 1, wherein, In step (2), the conditions for performing the oxidation include: The temperature is 25℃ to 80℃; The pressure is 0.1MPa to 1.0MPa; The oxidizing gas is selected from one or a combination of both of oxygen and oxygen-enriched air; The amount of the oxidizing gas is greater than or equal to 2 to 10 times the theoretical chemical requirement amount of the oxidizing gas required for oxidizing the mercaptide contained in the mercaptide-containing alkaline solution into disulfide.

11. The hydrocarbon stream extractive desulfurization process in accordance with claim 1 wherein, In step (3), the conditions for performing the separation include: The temperature is 25℃ to 50℃; the pressure is 0.1MPa to 1.0MPa; the volume ratio of the second disulfide-containing selective solvent obtained from step (4) to the disulfide-containing alkaline solution as the first selective solvent is 1:(0.1 to 10); and / or, In step (4), the conditions for performing the back extraction include: The temperature is 25℃ to 50℃; the pressure is 0.1MPa to 1.0MPa; the volume ratio of the carbon five fraction as the second selective solvent to the lean alkaline solution obtained from step (3) is 1:(0.1 to 10).

12. A hydrocarbon stream sweetening system in conjunction with gasoline production, characterized by, The hydrocarbon stream extraction desulfurization system comprises: The alkaline extraction unit (2), the oxidation unit (3), the separation unit (4), the back extraction unit (5) and the decarburization five fraction distillation column (6); The alkaline extraction unit (2) is provided with a hydrocarbon stream inlet pipeline (1d), an extraction alkaline solution inlet (2a), a hydrocarbon stream product outlet (2b) and a mercaptide-containing alkaline solution outlet; The mercaptide-containing alkaline solution inlet of the oxidation unit (3) is communicated with the mercaptide-containing alkaline solution outlet of the alkaline extraction unit (2) through a mercaptide-containing alkaline solution pipeline (2c), and the mercaptide-containing alkaline solution pipeline (2c) is provided with an oxidizing gas inlet (3a); the oxidation unit (3) is further provided with a residual oxidizing gas outlet (3b) and a disulfide-containing alkaline solution outlet (3c); The disengaging unit (4) is connected with the outlet (3c) of the oxidizing unit (3) and provided with a first selective solvent inlet, a poor lye outlet (4a) and a first selective solvent outlet (4b) containing disulfide; the first selective solvent outlet (4b) is connected with the raw material inlet of the absorption stabilizing system of the catalytic cracking device; The disengaging unit (4) is connected with the outlet (3c) of the oxidizing unit (3) and provided with a first selective solvent inlet, a poor lye outlet (4a) and a first selective solvent outlet (4b) containing disulfide; the first selective solvent outlet (4b) is connected with the raw material inlet of the absorption stabilizing system of the catalytic cracking device; The disengaging unit (4) is connected with the outlet (3c) of the oxidizing unit (3) and provided with a first selective solvent inlet, a poor lye outlet (4a) and a first selective solvent outlet (4b) containing disulfide; the first selective solvent outlet (4b) is connected with the raw material inlet of the absorption stabilizing system of the catalytic cracking device; 13. The hydrocarbon stream extractive desulfurization system of claim 12, wherein, The disengaging unit (4) is connected with the outlet (3c) of the oxidizing unit (3) and provided with a first selective solvent inlet, a poor lye outlet (4a) and a first selective solvent outlet (4b) containing disulfide; the first selective solvent outlet (4b) is connected with the raw material inlet of the absorption stabilizing system of the catalytic cracking device; The hydrocarbon stream extraction desulfurization system is further provided with a pre-alkali washing unit (1) which is provided with an original hydrocarbon stream inlet pipeline (1a), a pre-alkali washing lye inlet pipeline (1b), a circulating lye outlet (1c) and a post-pre-alkali washing hydrocarbon stream outlet; the pre-alkali washing lye inlet pipeline (1b) is connected with the circulating lye outlet (1c) and the original hydrocarbon stream inlet pipeline (1a); the post-pre-alkali washing hydrocarbon stream outlet is connected with the hydrocarbon stream inlet pipeline (1d) of the alkali extraction unit (2).

14. The hydrocarbon stream extractive desulfurization system of claim 12, wherein, The overhead temperature of the decarburized C5 fractionating column (6) is 35-80℃, the overhead pressure is 0.15-2.20MPa and the bottom temperature is 55-150℃.

15. The hydrocarbon stream extractive desulfurization system of claim 12, wherein, The overhead temperature of the decarburized C5 fractionating column (6) is 40-65℃, the overhead pressure is 0.35-1.20MPa and the bottom temperature is 60-130℃.

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