Sodium-free alkali micro-slag mercaptan removing method for liquefied petroleum gas refining

Abstract

The invention relates to a sodium-free alkali micro-residue mercaptan removal method for liquefied petroleum gas refining, which is used for removing organic sulfides in liquefied petroleum gas. The method comprises the following steps: reacting mercaptan with a desulfurizing agent to form mercaptide, dissolving the mercaptide in the desulfurizing agent, and extracting and removing the mercaptan from the liquefied gas. According to the sulfur-containing desulfurizer, sulfide is oxidized to form disulfide in the presence of a catalyst, and then reverse extraction is performed, so that the desulfurizer is regenerated. According to the invention, while deep desulfurization of liquefied gas is realized, since a sodium-free alkali desulfurizer technology is adopted, almost no alkali residue is discharged in the use process, consumption of alkali liquor is reduced, alkali consumption and residue discharge are reduced to one twentieth of the original residue discharge amount, and the method has remarkable energy-saving and emission-reducing effects and very considerable economic benefits and social and environmental protection benefits.

Description

Technical Field

[0001] The invention belongs to the field of deep desulfurization and refining of liquefied gas in the process of petroleum refining, and relates to a sodium-alkali-free micro-slag desulfurization method for liquefied petroleum gas refining. Background Art

[0002] Liquefied petroleum gas mainly comes from associated gas in oil and gas fields and by-product gas in refineries. Liquefied petroleum gas is stored in liquid form and used in gaseous form. Liquefied petroleum gas can be divided into two categories according to its use: chemical use and fuel use. In the chemical industry, liquefied petroleum gas is separated into ethylene, propylene, butylene, butadiene, etc., which can be directly used to produce synthetic plastics, synthetic rubber, synthetic fibers, and produce medicines, explosives, dyes and other products. In terms of fuel, due to its high calorific value, no smoke and dust, no carbon slag, and easy operation and use, it has been widely used in production and life fields, such as industrial and commercial fuel, automobile fuel, and civilian fuel.

[0003] The main components of liquefied gas obtained from the refinery are one or more of propane, propylene, butane, and butene, and are also mixed with a small amount of pentane, pentene and trace sulfide impurities. If the unrefined liquefied gas is directly used for processing or use, it will cause environmental pollution, equipment corrosion, and catalyst deactivation of downstream devices. For liquefied gas, in addition to removing hydrogen sulfide, it is further treated with sweetening. Therefore, sweetening and refining of liquefied gas has become an indispensable and important step in the oil refining process. Only in this way can qualified raw materials be provided for subsequent chemical plants.

[0004] The removal of organic sulfur is an important unit in the liquefied gas refining process. Among the organic sulfur, the highest proportion is mercaptan sulfur, accounting for about 90% of all organic sulfur, while the remaining sulfides are mainly carbonyl sulfide and methyl sulfide.

[0005] Many domestic refineries’ liquefied gas desulfurization units mainly use the “Merox method” or similar desulfurization processes. The liquefied gas desulfurization unit uses the Merox method alkali-washing desulfurization process, which mainly includes pre-alkali washing, two-stage fiber membrane extraction desulfurization, water washing and refining, and three-phase mixed oxidation regeneration process. Taking advantage of the two characteristics of the weak acidity of mercaptans and the easy oxidation of mercaptan anions to generate disulfide compounds, the reaction equation is as follows:

[0006] RSH (oil phase) + NaOH (water phase) -> RSNa + H2O (removal of mercaptan sulfur from oil products)

[0007] 2RSNa (water phase) + 1 / 2O2 + H2O ——> RSSR (oil phase) + 2NaOH (removal of thiol anions from the base)

[0008] The reaction has the following characteristics:

[0009] (1) Thiols are insoluble in water, and the generated sodium thiolate reaction needs to be carried out in an alkaline solution (aqueous phase);

[0010] (2) Sodium thiolate is oxidized to disulfide and then precipitated from the alkali solution, which requires dissolved oxygen in the circulating agent;

[0011] (3) The regeneration reaction requires higher and longer-lasting catalyst activity.

[0012] Problems with current refinery liquefied gas desulfurization technology:

[0013] After the desulfurization system has been running for a period of time, the circulating alkali solution will enrich organic matter, inorganic salts and other harmful substances to a certain concentration, and the effective alkali concentration of the alkali solution will drop significantly, which will reduce the desulfurization effect or even make it ineffective. Therefore, the capacity of inorganic salts in traditional extraction alkali solution is limited, and the salting-out effect is obvious. With the continuous formation and accumulation of salts, the efficiency of extracting mercaptans with alkali solution will decrease and the extraction activity will gradually be lost. In order to compensate for the decline in regeneration effect and maintain the desulfurization activity, it is necessary to regularly replace and update the system alkali solution and add a large amount of various functional additives to reduce the accumulated salt in the system.

[0014] Moreover, organic matter and other impurities enriched in the circulating alkali solution will cause the alkali solution to foam, which in turn causes the oil carried by the circulating alkali solution to be carried to the downstream unit by the liquefied gas, resulting in unqualified MTBE sulfur content. The enriched organic impurities are mainly additive degradation products, amine liquid and back-extracted oil. The sodium carbonate generated by the reaction of carbon dioxide in the injected non-purified air with the alkali solution, the hydrogen sulfide entrained in the liquefied gas, and the inorganic salts such as sodium thiosulfate and sodium sulfide gradually produced during the circulation of the alkali solution will also cause the alkali solution concentration to decrease, accelerating the precipitation and inactivation of salts.

[0015] During the recycling process of alkali solution, after the concentration of harmful substances (including organic matter and inorganic salts) reaches a certain value, the effective alkali concentration continues to decrease. When it reaches a certain concentration, the effect of alkali solution on desulfurization is significantly reduced and ineffective. The salt content that ordinary extraction alkali solution can accommodate is very limited, the salting-out effect is obvious, and regeneration is difficult. The alkali solution will gradually lose its extraction activity. In order to maintain the desulfurization activity, the system alkali solution needs to be replaced regularly, and the desulfurization alkali residue is discharged.

[0016] For example, a refinery with an annual liquefied gas processing capacity of 100,000 tons produces up to 700 tons of alkali residue in the sweetening unit. When the sulfur content of the liquefied gas raw material increases and varies greatly, alkali replacement and alkali residue discharge become more frequent, which not only consumes a large amount of alkali solution, but also increases the amount of alkali residue discharged, increases the treatment burden of the sewage treatment plant, and causes odor pollution.

[0017] Therefore, it is of great significance to reduce the emission of alkali residue in the desulfurization process, improve the desulfurization efficiency, and develop micro-slag desulfurization technology for liquefied petroleum gas refining. Summary of the invention

[0018] The present invention relates to a sodium-free alkali micro-slag desulfurization method for liquefied petroleum gas refining, which is used for removing organic sulfides in liquefied gas. The invention content includes that the technology utilizes mercaptan to react with a desulfurizer to form mercaptide salts, and the mercaptide salts are dissolved in the desulfurizer, so that mercaptan is extracted and removed from the liquefied gas. The sulfur-containing desulfurizer is extracted, and in the presence of a catalyst, the sulfide is oxidized to form disulfide, and then reversely extracted, and the desulfurizer is regenerated. While realizing the deep desulfurization of liquefied gas, the present invention adopts the sodium-free alkali desulfurizer technology, and almost no alkali slag is discharged during use, and the consumption of alkali solution is reduced at the same time. The alkali consumption and slag discharge are reduced to one twentieth of the original slag discharge amount, which has a significant energy-saving and emission reduction effect, and the economic benefits and social and environmental protection benefits are very considerable.

[0019] The present invention is based on the actual use of refineries and the analysis of the principles of existing desulfurization technology. The essential reasons for the low desulfurization efficiency and large amount of alkali residue of existing desulfurization technology are as follows:

[0020] (1) The solubility of sodium hydroxide solution is limited, especially when there is a lot of sodium carbonate and sulfate in the solution, which leads to supersaturation of sodium hydroxide. As the device circulates, it precipitates under certain conditions and produces a large amount of alkaline slag.

[0021] (2) The catalyst circulates with the alkali solution. When sodium thiolate enters the alkali solution, the sodium thiolate and the residual oxygen in the alkali solution are partially oxidized to disulfide under the action of the catalyst, causing part of the disulfide to enter the liquefied gas again, resulting in low desulfurization efficiency of the liquefied gas.

[0022] (3) The sulfonated cobalt phthalocyanine catalyst currently used is a homogeneous catalysis with high catalytic efficiency. However, the solution aggregates and precipitates in the solution, resulting in a decrease in catalytic activity. It also causes the precipitation of sodium hydroxide and the generation of a large amount of alkaline residue.

[0023] Based on the above analysis, the purpose of the present invention is to provide a new desulfurization process that produces almost no alkali residue, has a better desulfurization effect, and has a total sulfur removal effect - a sodium-free alkali micro-slag desulfurization method. This technology adopts a variety of innovative technologies to solve the problems of large alkali consumption, large alkali residue discharge, high total sulfur content caused by disulfide backflow into liquefied gas, and large catalyst loss in traditional desulfurization technology, which is of great significance for promoting the green and efficient development of liquefied gas desulfurization process.

[0024] The specific innovations of this technology include:

[0025] (1) Optimization of the desulfurization process: In order to prevent mercaptans from being oxidized in the alkali solution and then returning to the oil phase, a alkali separation process is proposed, that is, the catalyst and alkali solution separation technology. Mercaptan conversion extraction is carried out in the extraction tower, and the extraction tower is a packed tower; the oxidation regeneration process of the desulfurizer adopts a fixed bed packed tower, which is designed as a two-stage packing form, the upper stage is a solid-supported desulfurization catalyst, and the lower stage is granular coconut shell activated carbon; the solid-supported desulfurization catalyst in the upper stage is a catalyst for the reaction of mercaptide salt to disulfide. When the sulfur-containing desulfurizer flows through the catalyst bed, the oxidation reaction is quickly completed, and then when the desulfurizer passes through the coconut shell activated carbon at the lower end, it is desalted and impurities are removed, and deep purification is obtained.

[0026] (2) Specialized immobilized desulfurization catalyst: A new carrier modification technology is used to prepare modified activated carbon. Then, combined with bonding technology, modified cobalt phthalocyanine is connected to the carrier to form a modified activated carbon-bonded cobalt phthalocyanine structure to obtain an immobilized desulfurization catalyst.

[0027] (3) Supporting special desulfurization solvent UPC-K40: Using sodium-free strong alkali to replace conventional sodium hydroxide can significantly reduce the generation of alkali residues, and has a strong salt tolerance to extend the service life of alkali solution.

[0028] (4) At the same time, an organic base is used to further increase the alkalinity of the solution, thereby providing a reaction process for the thiol to sodium thiolate.

[0029] (5) Add sulfur-loving and pollutant-absorbing components, use the similar compatibility principle of polar solvents and induced polarization to increase the dissolved raw materials, and strengthen the affinity and solubility of desulfurization solvents for sulfides. In addition, strong polar solvents have a volume-increasing effect on pollutants, reduce salting-out effects, and reduce the generation of alkali slag.

[0030] (6) By adding a phase transfer catalyst, the sulfide is promoted to diffuse from the desulfurization solvent phase to the stripping agent phase, thereby achieving rapid regeneration of the desulfurization solvent.

[0031] (7) In order to prevent the formation of impurities and improve the oxidation efficiency, pure oxygen is used as the oxidant in the oxidation regeneration tower.

[0032] The technical process of the present invention is as follows:

[0033] like Figure 1As shown, the mercaptan-containing liquefied gas from the upstream is mixed with the lean desulfurizer in a mixer, and then contacted in a countercurrent in an extraction tower (T1) to perform an extraction reaction, whereby the mercaptan is converted into mercaptide salts and enters the desulfurizer phase; the liquefied gas leaves the extraction tower from the top of the tower and enters a liquefied gas settling tank (V1) to further separate the desulfurizer, and then the obtained refined liquefied gas leaves the device; the rich desulfurizer is extracted from the bottom of the extraction tower, mixed with oxygen, back-extraction oil and other materials, and then enters an oxidation regeneration tower (T2), which is loaded with a solid-supported desulfurization catalyst; under the action of the catalyst, the mercaptide salts are oxidized to generate disulfide The mixture then enters the primary extraction settling tank (V2) for oil-agent two-phase sedimentation separation, and the obtained lean desulfurizer is returned to the extraction tower. The extracted oil of part of the mixed desulfurizer from the primary extraction settling tank enters the secondary stabilization settling tank (V3) for further sedimentation separation of insoluble matter, desulfurizer and extraction agent to obtain lean desulfurizer; the lean desulfurizer and the supplemented part of the desulfurizer are mixed and returned to the extraction tower for recycling; the obtained rich extraction agent leaves the sweetening device, and the insoluble matter is discharged from the sweetening device after a certain degree of accumulation;

[0034] The back-extraction agent in the sodium alkali-free micro-slag desulfurization technology of the present invention is a mixture of reformed gasoline rich in aromatics and mixed xylene, and the mixing volume ratio is 1:10 to 10:1; the volume purity of the oxidant oxygen used in the oxidation regeneration of the desulfurizer is above 99.9%;

[0035] In the sodium alkali-free micro-slag desulfurization technology of the present invention, the desulfurizer oxidation regeneration process adopts a packed fixed bed reactor, the upper section is filled with a solid-supported cobalt phthalocyanine catalyst, and the lower section is granular coconut shell activated carbon; wherein the preparation method of the solid-supported cobalt phthalocyanine catalyst is:

[0036] The first step is carrier activation: the granular activated carbon is vacuum dried at 180°C for 4 hours; then it is impregnated with a 10% to 30% potassium hydroxide solution for 12 hours; after filtering and drying, a modified carrier is obtained;

[0037] The second step is the synthesis of cobalt phthalocyanine: take a certain amount of phthalic anhydride, urea, ammonium molybdate, and cobalt acetate, grind them evenly and put them into a beaker, heat until the urea is dissolved, mix the reactants thoroughly and evenly, and then heat until they are melted; after reacting for 12h to 24h, take out the crude product obtained by cooling the beaker, boil it with 1M hydrochloric acid for 30 minutes, filter it, wash the product with ethanol and acetone in turn, and finally wash it with distilled water until it is neutral; after drying, dissolve the crude product in 98% concentrated sulfuric acid by mass, filter it with a glass sand core funnel, dilute the filtrate with ice water, precipitate and dry it to obtain a blue-purple solid for the synthesis of cobalt phthalocyanine;

[0038] The third step is sulfonation: take a certain amount of cobalt phthalocyanine and concentrated sulfuric acid or fuming sulfuric acid, add them to a round-bottom flask, add until they are melted, take them out after 3h to 12h and cool them naturally, slowly pour the product into ice water containing saturated sodium chloride, filter, wash with ice water until neutral, precipitate a blue-purple solid, then wash with anhydrous ethanol and acetone 2 to 3 times in sequence, and vacuum dry at room temperature for 24 hours to obtain sulfonated cobalt phthalocyanine;

[0039] The fourth step is carboxylation: take a certain amount of sulfonated cobalt phthalocyanine, add oxalic acid and malonic acid as raw materials, add a small amount of NHS (N-hydroxysuccinimide) and DCC (dicyclohexylcarbodiimide), in a phosphorus buffer with a pH of about 7.2, the reaction temperature is 40°C to 80°C, and the reaction is carried out for 12h to 48h; then the reaction mixture is slowly poured into ice water containing saturated sodium chloride, filtered, washed with ice water until neutral, precipitated blue-purple solid, and then washed with anhydrous ethanol and acetone for 2 to 3 times in sequence, and vacuum dried at room temperature for 24 hours to obtain carboxylated sulfonated cobalt phthalocyanine;

[0040] The fifth step is bonding and immobilization: adding an aqueous solution containing 1wt% to 5wt% of carboxylated sulfonated cobalt phthalocyanine into a container containing a modified carrier, and impregnating the carrier in a ratio of 0.1wt% to 5wt% of the active component of carboxylated sulfonated cobalt phthalocyanine to the carrier; the impregnation solution is allowed to stand at 70°C for 24h to 72h; then filtered and dried at 100°C under vacuum to obtain an immobilized cobalt phthalocyanine catalyst;

[0041] The desulfurization solvent UPC-K40 used in the sodium-free alkali micro-slag desulfurization technology of the present invention is a high-efficiency desulfurization solvent that does not contain sodium hydroxide, and comprises components such as non-sodium strong alkali, organic alkali, sulfur-loving and pollutant-absorbing solvent and phase transfer surfactant, and the rest is water;

[0042] The non-sodium strong base component is a mixture of one or more of potassium hydroxide, barium hydroxide and lithium hydroxide, with the added mass fraction being 20 to 60%;

[0043] Organic base component: one or more of triethylamine, triethanolamine, diethanolamine, benzylamine and tert-butylamine, with the added mass fraction being 2-20%;

[0044] Sulfur-loving and pollutant-absorbing components: one or more of ethanol, butanol, acetone, dioxane, ethylene glycol, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, methyl ethyl ketone, glycerol, propylene glycol, ethylene glycol methyl ether and ethylene glycol monobutyl ester, with the added mass fraction being 0.5 to 10%;

[0045] Phase transfer surfactant component: one or more of benzyltrimethylammonium hydroxide, tetrabutylammonium hydroxide, hexadecyltrimethylammonium bromide, bisdecyldimethylammonium bromide, dimethylbenzylammonium chloride, Span-80, Span-60, Tween-80 and Tween-60, with the added mass fraction being 0.001-1%.

[0046] Advantages of the present invention:

[0047] In the sodium-free alkali micro-slag sweetening technology, the catalyst uses a fixed-bed immobilized cobalt phthalocyanine catalyst, which has high catalytic activity, low loss rate, and avoids premature oxidation of mercaptides. At the same time, a special UPC-K40 sweetening solvent is used to replace ordinary extraction alkali solution + deodorization refining liquid. UPC-K40 sweetening solvent is compounded by non-sodium strong alkaline substances, highly active alkaline solvents and a variety of functional components. It has high sweetening effect, high ion solubility, reduced salting-out effect, and reduced solvent consumption, achieving the purpose of reducing or zero alkali residue emissions. The main technical features are as follows:

[0048] (1) The oxidation regeneration tower adopts a fixed bed reactor, in which a special solid-supported cobalt phthalocyanine catalyst is loaded to achieve agent-base separation, reduce the amount of disulfide entering the oil phase again, and further reduce the sulfur content of liquefied gas.

[0049] (2) A special method is used to prepare a firmly loaded and highly active desulfurization immobilized catalyst, which provides desulfurization activity and prolongs the service life of the catalyst, while preventing the catalyst in the solution from catalyzing the oxidation reaction of mercaptans, thereby preventing the premature generation of disulfides, which in turn causes the disulfides to re-enter the liquefied gas.

[0050] (3) The use of a special desulfurization solvent improves the comprehensive performance of the circulating solvent in extraction and regeneration, and strengthens the recycling agent's ability to extract mercaptans and the solvent regeneration activity;

[0051] (4) The oxidation regeneration tower is loaded with catalysts and fillers in two sections. The upper section is a solid-supported desulfurization catalyst, and the lower section is granular coconut shell activated carbon. The catalytic reaction occurs rapidly. At the same time, the activated carbon in the lower section can adsorb some of the dissociated active components to prevent them from entering the desulfurization solvent system.

[0052] (5) Using pure oxygen instead of traditional air as the oxidant can prevent impurities such as carbon dioxide from reacting with the desulfurizer to form insoluble substances, and can also improve the oxidation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a process flow chart of the desulfurization process of the present invention, which reflects the connection relationship between each reactor and separator. Due to space limitations, only the main equipment and connection relationships can be listed.

[0054] The main materials are: a: stripping agent; b: oxygen; c: raw liquefied gas; e: fresh sweetening solvent; f: tail gas; g: a small amount of insoluble matter; h: rich stripping agent;

[0055] Main tower types: T1: extraction tower; T2: oxidation regeneration tower

[0056] Main tank types: V1: liquefied gas stabilization tank; V2: primary sedimentation tank; V3: secondary sedimentation tank; V4: new agent tank;

[0057] Main pumps: P1: rich desulfurizer extraction pump; P2: new desulfurizer addition pump; P: lean desulfurizer circulation pump;

[0058] Figure 2 The desulfurization effects of the embodiments and comparative examples are compared, wherein A1 and A2 are embodiments 1 and 2, and B1, B2 and B3 are comparative examples 1, 2 and 3, respectively.

[0059] Figure 3 The salt tolerance effects of the embodiments and comparative examples are compared, wherein A1 and A2 are embodiments 1 and 2, and B1, B2, and B3 are comparative examples 1, 2, and 3, respectively. Example

[0060] The technical content and effects of the present invention are further illustrated below in conjunction with embodiments, but the scope of the present invention is not limited thereby.

[0061] Embodiment 1:

[0062] The mercaptan-containing liquefied gas from the upstream is mixed with the lean desulfurizer in a mixer, and then contacted in countercurrent in an extraction tower (T1) to undergo an extraction reaction, whereby mercaptan is converted into mercaptide salts and enters the desulfurizer phase; the liquefied gas leaves the extraction tower from the top of the tower and enters a liquefied gas settling tank (V1) to further separate the desulfurizer, and then the obtained refined liquefied gas leaves the device; the rich desulfurizer is extracted from the bottom of the extraction tower, mixed with oxygen, back-extraction oil and other materials, and then enters an oxidation regeneration tower (T2), which is loaded with a solid-supported desulfurization catalyst; under the action of the catalyst, the mercaptide salts are oxidized to generate disulfides, At the same time, disulfide is extracted to the oil phase; then the mixture enters the primary extraction settling tank (V2) for oil-agent two-phase sedimentation separation, and the obtained lean desulfurizer is returned to the extraction tower, and the extracted oil of part of the mixed desulfurizer from the primary extraction settling tank enters the secondary stabilization settling tank (V3) for further sedimentation separation of insoluble matter, desulfurizer and extraction agent to obtain lean desulfurizer; wherein the lean desulfurizer and the supplemented part of the desulfurizer are mixed and returned to the extraction tower for recycling; the obtained rich extraction agent leaves the sweetening device, and the insoluble matter is discharged from the sweetening device after a certain degree of accumulation;

[0063] The back-extraction agent in the sodium alkali-free micro-slag desulfurization technology of the present invention is a mixture of reformed gasoline rich in aromatics and mixed xylene, and the mixing volume ratio is 1:1; the volume purity of the oxidant oxygen used in the oxidation regeneration of the desulfurizer is above 99.9%;

[0064] In the sodium alkali-free micro-slag desulfurization technology of the present invention, the desulfurizer oxidation regeneration process adopts a packed fixed bed reactor, the upper section is filled with a solid-supported cobalt phthalocyanine catalyst, and the lower section is granular coconut shell activated carbon; wherein the preparation method of the solid-supported cobalt phthalocyanine catalyst is:

[0065] The first step is carrier activation: the granular activated carbon is vacuum dried at 180°C for 4 hours; then it is impregnated with a 20% potassium hydroxide solution by mass for 12 hours; after filtration and drying, a modified carrier is obtained;

[0066] The second step is the synthesis of cobalt phthalocyanine: take a certain amount of phthalic anhydride, urea, ammonium molybdate, and cobalt acetate, grind them evenly and put them into a beaker, heat until the urea is dissolved, mix the reactants thoroughly and evenly, and then heat until they are melted; after reacting for 12h to 24h, take out the crude product obtained by cooling the beaker, boil it with 1M hydrochloric acid for 30 minutes, filter it, wash the product with ethanol and acetone in turn, and finally wash it with distilled water until it is neutral; after drying, dissolve the crude product in 98% concentrated sulfuric acid by mass, filter it with a glass sand core funnel, dilute the filtrate with ice water, precipitate and dry it to obtain a blue-purple solid for the synthesis of cobalt phthalocyanine;

[0067] The third step is sulfonation: take a certain amount of cobalt phthalocyanine and concentrated sulfuric acid, add them to a round-bottom flask, add until they are melted, take them out after 3h to 12h and cool them naturally, slowly pour the product into ice water containing saturated sodium chloride, filter, wash with ice water until neutral, precipitate a blue-purple solid, then wash with anhydrous ethanol and acetone 2 to 3 times in sequence, and vacuum dry at room temperature for 24 hours to obtain sulfonated cobalt phthalocyanine;

[0068] The fourth step is carboxylation: take a certain amount of sulfonated cobalt phthalocyanine, add oxalic acid as a raw material, add a small amount of NHS (N-hydroxysuccinimide) and DCC (dicyclohexylcarbodiimide), in a phosphorus buffer with a pH of about 7.2, the reaction temperature is 40°C to 80°C, and the reaction is carried out for 12h to 48h; then the reaction mixture is slowly poured into ice water containing saturated sodium chloride, filtered, and washed with ice water until neutral, a blue-purple solid is precipitated, and then washed with anhydrous ethanol and acetone for 2 to 3 times in sequence, and vacuum dried at room temperature for 24 hours to obtain carboxylated sulfonated cobalt phthalocyanine;

[0069] The fifth step is bonding and immobilization: adding an aqueous solution containing 1 wt% of carboxylated sulfonated cobalt phthalocyanine to a container containing a modified carrier, and impregnating the carrier in a ratio of 2 wt% of the carboxylated sulfonated cobalt phthalocyanine active component to the carrier; the impregnation solution is allowed to stand at 70° C. for 24 h to 72 h; then filtered and dried at 100° C. under vacuum to obtain an immobilized cobalt phthalocyanine catalyst;

[0070] The desulfurization solvent UPC-K40 used in the sodium-free alkali micro-slag desulfurization technology of the present invention is a high-efficiency desulfurization solvent that does not contain sodium hydroxide, and comprises components such as non-sodium strong alkali, organic alkali, sulfur-loving and pollutant-absorbing solvent and phase transfer surfactant, and the rest is water;

[0071] The non-sodium strong base component is potassium hydroxide, and the added mass fraction is 40%;

[0072] Organic base components: triethylamine and triethanolamine, with a mass ratio of 1:1 and an added mass fraction of 10%;

[0073] Sulfur-loving and pollution-absorbing components: dioxane, ethylene glycol, dimethyl sulfoxide, tetrahydrofuran, the added mass fraction is 10%, and the mass ratio of the four is 0.5:1:1:0.1;

[0074] Phase transfer surfactant component: benzyltrimethylammonium hydroxide, the added mass fraction is 0.01%.

[0075] The reverse extraction agent in the sodium alkali-free micro-slag sweetening technology of the present invention is a mixture of reformed gasoline rich in aromatics and mixed xylene, and the mixing volume ratio is 10:1.

[0076] Embodiment 2:

[0077] The mercaptan-containing liquefied gas from the upstream is mixed with the lean desulfurizer in a mixer, and then contacted in countercurrent in an extraction tower (T1) to undergo an extraction reaction, whereby mercaptan is converted into mercaptide salts and enters the desulfurizer phase; the liquefied gas leaves the extraction tower from the top of the tower and enters a liquefied gas settling tank (V1) to further separate the desulfurizer, and then the obtained refined liquefied gas leaves the device; the rich desulfurizer is extracted from the bottom of the extraction tower, mixed with oxygen, back-extraction oil and other materials, and then enters an oxidation regeneration tower (T2), which is loaded with a solid-supported desulfurization catalyst; under the action of the catalyst, the mercaptide salts are oxidized to generate disulfides, At the same time, disulfide is extracted to the oil phase; then the mixture enters the primary extraction settling tank (V2) for oil-agent two-phase sedimentation separation, and the obtained lean desulfurizer is returned to the extraction tower, and the extracted oil of part of the mixed desulfurizer from the primary extraction settling tank enters the secondary stabilization settling tank (V3) for further sedimentation separation of insoluble matter, desulfurizer and extraction agent to obtain lean desulfurizer; wherein the lean desulfurizer and the supplemented part of the desulfurizer are mixed and returned to the extraction tower for recycling; the obtained rich extraction agent leaves the sweetening device, and the insoluble matter is discharged from the sweetening device after a certain degree of accumulation;

[0078] The reverse extraction agent in the sodium alkali-free micro-slag desulfurization technology of the present invention is a mixture of reformed gasoline rich in aromatics and mixed xylene, and the mixing volume ratio is 2:1; the volume purity of the oxidant oxygen used in the oxidation regeneration of the desulfurizer is above 99.9%;

[0079] In the sodium alkali-free micro-slag desulfurization technology of the present invention, the desulfurizer oxidation regeneration process adopts a packed fixed bed reactor, the upper section is filled with a solid-supported cobalt phthalocyanine catalyst, and the lower section is granular coconut shell activated carbon; wherein the preparation method of the solid-supported cobalt phthalocyanine catalyst is:

[0080] The first step is carrier activation: the granular activated carbon is vacuum dried at 180°C for 4 hours; then it is impregnated with a 10% to 30% potassium hydroxide solution for 12 hours; after filtering and drying, a modified carrier is obtained;

[0081] The second step is the synthesis of cobalt phthalocyanine: take a certain amount of phthalic anhydride, urea, ammonium molybdate, and cobalt acetate, grind them evenly and put them into a beaker, heat until the urea is dissolved, mix the reactants thoroughly and evenly, and then heat until they are melted; after reacting for 12h to 24h, take out the crude product obtained by cooling the beaker, boil it with 1M hydrochloric acid for 30 minutes, filter it, wash the product with ethanol and acetone in turn, and finally wash it with distilled water until it is neutral; after drying, dissolve the crude product in 98% concentrated sulfuric acid by mass, filter it with a glass sand core funnel, dilute the filtrate with ice water, precipitate and dry it to obtain a blue-purple solid for the synthesis of cobalt phthalocyanine;

[0082] The third step is sulfonation: take a certain amount of cobalt phthalocyanine and fuming sulfuric acid, add them to a round-bottom flask, add until they are melted, take them out after 3h to 12h and cool them naturally, slowly pour the product into ice water containing saturated sodium chloride, filter, wash with ice water until neutral, precipitate a blue-purple solid, then wash with anhydrous ethanol and acetone 2 to 3 times in sequence, and vacuum dry at room temperature for 24 hours to obtain sulfonated cobalt phthalocyanine;

[0083] The fourth step is carboxylation: take a certain amount of sulfonated cobalt phthalocyanine, add malonic acid as a raw material, add a small amount of NHS (N-hydroxysuccinimide) and DCC (dicyclohexylcarbodiimide), in a phosphorus buffer with a pH of about 7.2, the reaction temperature is 40°C to 80°C, and the reaction is carried out for 12h to 48h; then the reaction mixture is slowly poured into ice water containing saturated sodium chloride, filtered, and washed with ice water until neutral, a blue-purple solid is precipitated, and then washed with anhydrous ethanol and acetone for 2 to 3 times in sequence, and vacuum dried at room temperature for 24 hours to obtain carboxylated sulfonated cobalt phthalocyanine;

[0084] The fifth step is bonding and immobilization: adding an aqueous solution containing 2 wt% of carboxylated sulfonated cobalt phthalocyanine to a container containing a modified carrier, and impregnating the carrier according to the ratio of the carboxylated sulfonated cobalt phthalocyanine active component to 2 wt% of the carrier; the impregnation solution is allowed to stand at 70° C. for 24 h to 72 h; then filtering and drying at 100° C. under vacuum to obtain an immobilized cobalt phthalocyanine catalyst;

[0085] The desulfurization solvent UPC-K40 used in the sodium-free alkali micro-slag desulfurization technology of the present invention is a high-efficiency desulfurization solvent that does not contain sodium hydroxide, and comprises components such as non-sodium strong alkali, organic alkali, sulfur-loving and pollutant-absorbing solvent and phase transfer surfactant, and the rest is water;

[0086] The non-sodium strong base component is a mixture of potassium hydroxide and lithium hydroxide, with a mass ratio of 10:1 and a total added mass fraction of 30%;

[0087] Organic base component: two of triethylamine and benzylamine, with a mass ratio of 5:1 and an added mass fraction of 15%;

[0088] Sulfur-loving and pollutant-absorbing components: dioxane, ethylene glycol, dimethyl sulfoxide, dimethylformamide and ethylene glycol monobutyl ester, with a mass ratio of 1:1:1:1:1, and a total added mass fraction of 8%;

[0089] Phase transfer surfactant components include tetrabutylammonium hydroxide, hexadecyltrimethylammonium bromide and Span-80, the three components have the same mass, and the total mass fraction added is 0.01%.

[0090] The reverse extraction agent in the sodium alkali-free micro-slag desulfurization technology of the present invention is a mixture of reformed gasoline rich in aromatics and mixed xylene, and the mixing volume ratio is 5:1.

[0091] Comparative Example 1:

[0092] The desulfurization method is the same as that in Example 1, except that the desulfurization solvent is replaced with a sodium hydroxide solution having a mass fraction of 30%.

[0093] The desulfurization method is the same as that in Example 1, except that the desulfurization solvent is replaced with a potassium hydroxide solution having a mass fraction of 30%.

[0094] The desulfurization method is consistent with that in Example 1. The desulfurizer oxidation regeneration process adopts a packed fixed bed reactor, except that the immobilized cobalt phthalocyanine catalyst is replaced with a common activated carbon-supported cobalt phthalocyanine catalyst.

[0095] Performance evaluation of examples and comparative examples

[0096] (1) Evaluation method of liquefied gas desulfurization performance:

[0097] The desulfurization performance of naphtha-simulated liquefied gas was evaluated. The mass content of mercaptan sulfur in the simulated liquefied gas was about 100 μg / g, including 20wt% of ethyl mercaptan sulfur, 20wt% of n-propyl mercaptan sulfur, 30wt% of n-butyl mercaptan sulfur, and 30wt% of tert-butyl mercaptan sulfur. The desulfurizers of Example 1, Example 2 and Comparative Example 1 were used to extract the simulated oil. After extraction, the residual sulfide composition and sulfur content were tested, and the desulfurization rate was calculated.

[0098] (2) Evaluation method of desulfurization solvent salt tolerance:

[0099] Take 50mL of the sweetening alcohol solvent of Example 1, Example 2 and Comparative Example 1, add simulated alkali slag (including sodium carbonate and sodium sulfate solid powder) to the sweetening alcohol solvent in an amount under constant stirring, stir for 10 minutes, let stand for 10 minutes, and observe the turbidity of the solution. Then compare the amount added when turbidity occurs, and evaluate the solid precipitation after filtering, and evaluate the slag resistance of the sweetening alcohol solvent by the amount of simulated alkali slag added.

[0100] (3) Comparison of liquefied gas desulfurization performance and salt tolerance between the embodiment and the comparative example

[0101] Table 1 Laboratory test evaluation of desulfurization effect and salt tolerance comparison

[0102]

[0103]

[0104] The results of the sweetening test evaluation were evaluated by laboratory test, and the embodiment had higher mercaptan desulfurization rate and isomerized mercaptan desulfurization rate than the comparative example, indicating that the present technology and the immobilized catalyst have good conversion ability for improving mercaptan conversion, especially isomerized mercaptan that is difficult to convert, so the sweetening performance is high. It was found by the salt tolerance experiment that the embodiment had a significantly high salt tolerance compared with the comparative example one, proving that the sweetening solvent UPC-K40 has good solubility to alkali residues, and in the process of dissolving alkali residues, the important role played by each component in the sweetening agent. In the actual application of sweetening, a large amount of by-product alkali residues can be accommodated to keep the sweetening device running for a long period of time. The sodium-free alkali micro-slag sweetening method of the present invention has significant advantages in terms of sweetening efficiency, salt tolerance, and reducing alkali residue solid waste.

Claims

1. A sodium-free alkali-free micro-slag desulfurization method for liquefied petroleum gas refining, the process flow is as follows: as shown in FIG1, the mercaptan-containing liquefied gas from the upstream is mixed with the lean desulfurizer in a mixer, and then countercurrently contacted in an extraction tower (T1) to perform an extraction reaction, and the mercaptan is converted into mercaptide salt and enters the desulfurizer phase; the liquefied gas leaves the extraction tower from the top of the tower, enters the liquefied gas settling tank (V1) to further separate the desulfurizer, and then the refined liquefied gas leaves the device; the rich desulfurizer is extracted from the bottom of the extraction tower, mixed with oxygen, back-extraction oil and other materials, and then enters the oxidation regeneration tower (T2), which is loaded with a solid-supported desulfurization catalyst; under the action of the catalyst, the mercaptide salt is oxidized to generate disulfide, and the disulfide is back-extracted to the oil phase; then the mixture The two phases enter the primary reverse extraction settling tank (V2) for oil-agent two-phase sedimentation separation, and the obtained lean desulfurizer is returned to the extraction tower. The reverse extraction oil of part of the mixed desulfurizer coming out of the primary reverse extraction settling tank enters the secondary stabilization settling tank (V3) for further sedimentation separation of insoluble matter, desulfurizer and reverse extraction agent to obtain lean desulfurizer; wherein the lean desulfurizer and the supplemented part of the desulfurizer are mixed and returned to the extraction tower for recycling; the obtained rich reverse extraction agent leaves the sweetening device, and the insoluble matter is discharged from the sweetening device after a certain degree of accumulation; in the method, the reverse extraction agent is a mixture of reformed gasoline rich in aromatics and mixed xylene, and the mixing volume ratio is 1:10 to 10:1; the volume purity of the oxidant oxygen used in the oxidation regeneration of the desulfurizer is above 99.9%.

2. A sodium-free alkali-free micro-slag desulfurization method for liquefied petroleum gas refining according to claim 1, characterized in that: The desulfurizer oxidation regeneration process adopts a packed fixed bed reactor, the upper section is filled with solid-supported cobalt phthalocyanine catalyst, and the lower section is granular coconut shell activated carbon; the preparation method of the solid-supported cobalt phthalocyanine catalyst is: The first step is carrier activation: the granular activated carbon is vacuum dried at 180°C for 4 hours; then it is impregnated with a 10% to 30% potassium hydroxide solution for 12 hours; after filtering and drying, a modified carrier is obtained; The second step is the synthesis of cobalt phthalocyanine: take a certain amount of phthalic anhydride, urea, ammonium molybdate, and cobalt acetate, grind them evenly and put them into a beaker, heat until the urea is dissolved, mix the reactants thoroughly and evenly, and then heat until they are melted; after reacting for 12h to 24h, take out the crude product obtained by cooling the beaker, boil it with 1M hydrochloric acid for 30 minutes, filter it, wash the product with ethanol and acetone in turn, and finally wash it with distilled water until it is neutral; after drying, dissolve the crude product in 98% concentrated sulfuric acid by mass, filter it with a glass sand core funnel, dilute the filtrate with ice water, precipitate and dry it to obtain a blue-purple solid for the synthesis of cobalt phthalocyanine; The third step is sulfonation: take a certain amount of cobalt phthalocyanine and concentrated sulfuric acid or fuming sulfuric acid, add them to a round-bottom flask, add until they are melted, take them out after 3h to 12h and cool them naturally, slowly pour the product into ice water containing saturated sodium chloride, filter, wash with ice water until neutral, precipitate a blue-purple solid, then wash with anhydrous ethanol and acetone 2 to 3 times in sequence, and vacuum dry at room temperature for 24 hours to obtain sulfonated cobalt phthalocyanine; The fourth step is carboxylation: take a certain amount of sulfonated cobalt phthalocyanine, add oxalic acid and malonic acid as raw materials, add a small amount of NHS (N-hydroxysuccinimide) and DCC (dicyclohexylcarbodiimide), in a phosphorus buffer with a pH of about 7.2, the reaction temperature is 40°C to 80°C, and the reaction is carried out for 12h to 48h; then the reaction mixture is slowly poured into ice water containing saturated sodium chloride, filtered, washed with ice water until neutral, precipitated blue-purple solid, and then washed with anhydrous ethanol and acetone for 2 to 3 times in sequence, and vacuum dried at room temperature for 24 hours to obtain carboxylated sulfonated cobalt phthalocyanine; The fifth step is bond immobilization: adding an aqueous solution containing 1wt% to 5wt% of carboxylated sulfonated cobalt phthalocyanine into a container containing a modified carrier, and impregnating the carrier in a ratio of 0.1wt% to 5wt% of the active component of carboxylated sulfonated cobalt phthalocyanine to the carrier; the impregnation solution is allowed to stand at 70°C for 24h to 72h; then filtered and dried at 100°C under vacuum to obtain an immobilized cobalt phthalocyanine catalyst.

3. A sodium-free alkali-free micro-slag desulfurization method for liquefied petroleum gas refining according to claim 1, characterized in that: The desulfurization solvent UPC-K40 used in the sodium-free alkali micro-slag desulfurization technology is a highly efficient desulfurization solvent that does not contain sodium hydroxide, and contains components such as non-sodium strong alkali, organic alkali, sulfur-loving and pollutant-absorbing solvent and phase transfer surfactant, and the rest is water; (1) The non-sodium strong base component is a mixture of one or more of potassium hydroxide, barium hydroxide, and lithium hydroxide, with the added mass fraction being 20 to 60%; (2) Organic base component: one or more of triethylamine, triethanolamine, diethanolamine, benzylamine and tert-butylamine, with a mass fraction of 2 to 20%; (3) Sulfur-loving and pollutant-absorbing components: one or more of ethanol, butanol, acetone, dioxane, ethylene glycol, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, methyl ethyl ketone, glycerol, propylene glycol, ethylene glycol methyl ether and ethylene glycol monobutyl ester, with the added mass fraction being 0.5 to 10%; (4) Phase transfer surfactant component: one or more of benzyltrimethylammonium hydroxide, tetrabutylammonium hydroxide, hexadecyltrimethylammonium bromide, bis(decyldimethylammonium bromide), dimethylbenzylammonium chloride, Span-80, Span-60, Tween-80 and Tween-60, with the added mass fraction being 0.001 to 1%.

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