Process for the hydrodeolefinization and hydrodesulfurization of liquefied gases

Abstract

This invention discloses a liquefied petroleum gas (LPG) hydrodeolefins desulfurization process, characterized by the following steps: incoming LPG is pressurized and mixed with hydrogen, then heated and vaporized before entering a hydrorefining reactor; the hydrorefining reaction gas from step 1) enters a low-pressure separator after heat exchange and cooling; low-density gas generated at the top of the low-pressure separator is pressurized and mixed with fresh hydrogen from outside the unit to form mixed hydrogen; the hydrorefined LPG at the bottom of the low-pressure separator is pressurized and sent to an LPG desulfurization tower; in the LPG desulfurization tower, LPG and amine solution are contacted counter-currently to remove most of the hydrogen sulfide from the reaction gas, and the LPG exiting from the top of the tower enters a fine desulfurization tank; after the fine desulfurization tank uses a desulfurizing agent to adsorb and remove residual hydrogen sulfide from the LPG, the refined LPG is sent to a LPG separation unit.

Description

Technical Field

[0001] This invention relates to liquefied petrochemical technology for hydrogenation refining of liquefied petroleum gas (LPG), specifically to a process for hydrogenation of LPG to remove olefins and desulfurize. Background Technology

[0002] Liquefied petroleum gas (LPG) is a fundamental chemical feedstock in the petrochemical industry. LPG obtained from oil refineries primarily consists of one or two of propane, propylene, butane, and butene, and is also mixed with small amounts of pentane, pentene, and trace amounts of sulfide impurities. LPG associated with oil and gas fields contains virtually no olefins; its main components are ethane, propane, butane, and other alkanes, but it does contain small amounts of hydrogen sulfide and organic sulfur. The C3 and C4 hydrocarbons in LPG are important raw materials in the light hydrocarbon processing industry chain and can be used to produce chemical products such as ethylene, propylene, maleic anhydride, succinic anhydride, BDO, PBS, MTBE, acrylonitrile, and propylene oxide. When liquefied petroleum gas (LPG) is used as feedstock in alkane cracking units, olefins undergo polymerization, cyclization, condensation, and coking reactions in the cracking furnace. When used as feedstock in alkane dehydrogenation units, olefins cause catalyst carbon buildup. When used as feedstock in n-butane to maleic anhydride units, olefins cause hot spots in the catalyst bed and reactor overheating. Furthermore, sulfur in LPG can lead to catalyst poisoning and substandard products in downstream units. The LPG used in this invention patent is primarily byproduct of catalytic cracking and coking units, as well as light hydrocarbons produced as byproducts from oil and gas fields. Only after de-olefinification and desulfurization refining can LPG be used as a higher-value chemical feedstock.

[0003] The sulfides contained in liquefied petroleum gas (LPG) are mainly hydrogen sulfide and mercaptans, and also contain small amounts of carbonyl sulfides, thioethers, and disulfides to varying degrees. Hydrogen sulfide is mainly removed by absorption with alkanolamine solution, while mercaptan removal has always been a challenge in LPG desulfurization and a focus of research and development both domestically and internationally.

[0004] US Patent 2882224 discloses the Merox process, a technology developed by UOP (United Oil Products) for refining light petroleum products using alkali solutions. The basic principle of this technology is to add sulfonated cobalt phthalocyanine or polycobalt phthalocyanine catalyst to an aqueous NaOH solution. This causes thiols in the liquefied petroleum gas (LPG) to react with NaOH to form sodium thiolate, which is then transferred to the alkali solution. Under the action of the sulfonated cobalt phthalocyanine catalyst, air is introduced to oxidize the sodium thiolate into disulfides. After separation, the alkali solution can be regenerated and recycled. However, this technology consumes large amounts of caustic soda and catalyst, and the alkali solution needs frequent replacement. This not only results in a large amount of alkali residue being discharged, but also in insufficient desulfurization depth and difficulty in separating disulfides from the oxidizing regenerator alkali solution, often leading to excessive total sulfur content in the refined LPG. To address the aforementioned issues, UOP has continuously improved its Merox technology, and has developed a series of LPG desulfurization processes, which have been disclosed in patents US2988500, US3108081, US4049572, and US4626341. The overall technological advancements have been to reduce the amount of caustic alkali used and increase the desulfurization rate.

[0005] Chinese Patent 103965984A discloses a method for catalytic desulfurization of liquefied petroleum gas (LPG). In this method, LPG is mixed with hydrogen and subjected to a thioetherification reaction in a reactor, converting the reactive unsaturated hydrocarbons (thiols) in the LPG into high-boiling-point thioether compounds, while selectively saturating some dienes. However, this method requires the prior removal of hydrogen sulfide and carbonyl sulfide, and the olefins in the LPG cannot be completely saturated, making it unsuitable for refining LPG that requires the removal of olefins and hydrogen sulfide.

[0006] To address the issue of alkaline discharge, Chinese patent CN1702157A discloses a method for refining liquefied petroleum gas (LPG). This method first removes hydrogen sulfide from the LPG using an alkanolamine solution, then decarbonylates the LPG through hydrolysis to generate hydrogen sulfide and carbon dioxide. The LPG then passes through a desulfurizing agent bed to remove hydrogen sulfide. A liquid oxygenating agent, tert-butyl peroxide, is added to oxidize thiols to disulfides. Finally, gas fractionation and distillation are performed to obtain refined LPG and a heavy fraction enriched with disulfides. While this method can relatively completely convert thiols in LPG by controlling the amount of oxygenating agent added, the decomposition of tert-butyl peroxide to produce isobutanol poses difficulties for the separation and purification of the LPG product and may adversely affect its further processing and utilization. Furthermore, the removal of hydrogen sulfide, carbonyl sulfide, and thiols from the LPG requires three different methods, resulting in a complex process, large equipment footprint, and high energy consumption.

[0007] Chinese patent CN117757537 A discloses a method for deep desulfurization of liquefied petroleum gas (LPG). This method first uses an alkanolamine solution to remove hydrogen sulfide from the LPG. Then, the LPG and hydrogen are fed together into a reactor for hydrodesulfurization. After desulfurization, the LPG enters a separator for gas-liquid separation. The separated liquid phase enters an alkanolamine absorption tower to absorb the sulfides produced in the reaction. This method uses a two-stage process for removing hydrogen sulfide with alkanolamine solutions, which is lengthy and cannot guarantee deep removal of hydrogen sulfide. Furthermore, the catalyst used in this method has a low olefin saturation rate, making it unsuitable for LPG refining applications requiring deep olefin removal and desulfurization.

[0008] Chinese patent CN115216333 A discloses a method for deep desulfurization of liquefied petroleum gas (LPG). In this method, LPG and hydrogen undergo a selective desulfurization reaction in a fluidized bed reactor. The resulting gas is discharged from the top of the reactor and enters an alkanolamine absorption tower to remove hydrogen sulfide, yielding the desulfurized LPG product. However, this method requires a reactor temperature of 50–150°C. Direct entry of the reaction gas into the alkanolamine absorption tower leads to severe foaming within the tower. The reaction pressure is 0.3 MPa–2.0 MPa. At lower pressures, both LPG and hydrogen are in the gaseous phase, making separation difficult. Deep cryogenic treatment is required to condense the LPG into a liquid, thus rendering this method impractical for industrial application.

[0009] Olefin hydrogenation saturation is the most effective method for removing olefins. Chinese patent CN106753561A discloses a method for preparing ethylene cracking feedstock by hydrogenating liquefied petroleum gas (LPG). In this method, LPG and hydrogen flow concurrently through a hydrogenation reactor, where an olefin saturation reaction takes place. This method can remove olefins from LPG, but it is not suitable for processing sulfur-containing LPG. On the one hand, the sulfur compounds in LPG can poison precious metal catalysts; on the other hand, this method does not address the removal of sulfur components from LPG. Summary of the Invention

[0010] This invention proposes a method for desulfurization of liquefied petroleum gas (LPG) by hydrotreating to remove olefins. The crude LPG undergoes reactions such as olefin saturation and mercaptan conversion under the conditions of hydrorefining catalyst and hydrogen to produce feedstock for downstream light hydrocarbon deep processing units, thereby solving the technical problems of low desulfurization depth and inability to simultaneously remove olefins and desulfurize in the existing technology.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] The method for desulfurization of liquefied petroleum gas by hydrotreating olefins is characterized by the following steps:

[0013] 1) Imported liquefied gas is pressurized and mixed with hydrogen, then heated and vaporized before entering the hydrorefining reactor;

[0014] 2) The hydrogenation reaction gas from the hydrorefining reactor in step 1) enters the low-pressure separator after heat exchange and cooling;

[0015] 3) The low-pressure gas generated at the top of the low-pressure separator is pressurized and then mixed with fresh hydrogen from outside the unit to become mixed hydrogen; the hydrogenated liquefied gas at the bottom of the low-pressure separator is pressurized and then sent to the liquefied gas desulfurization tower.

[0016] 4) In the LPG desulfurization tower, LPG and amine solution come into countercurrent contact to remove most of the hydrogen sulfide from the reaction gas. The LPG coming out from the top of the tower enters the fine desulfurization tank.

[0017] 5) After the desulfurization tank uses a desulfurizing agent to adsorb and remove residual hydrogen sulfide from the liquefied gas, the refined liquefied gas is sent to the liquefied gas separation unit.

[0018] The method for hydrodeolefins and desulfurization of liquefied petroleum gas (LPG) of the present invention is further characterized in that: the LPG feedstock in step 1) is one or more of the LPG by-products of catalytic cracking, coking and other units, and light hydrocarbons by-products of oil and gas fields.

[0019] The liquefied petroleum gas (LPG) hydrodeolefins desulfurization method of the present invention is further characterized in that: before the external LPG is mixed with hydrogen, it is first dehydrated to remove free water and solid particles.

[0020] The present invention relates to a method for desulfurization and deolefin removal via liquefied petroleum gas (LPG) hydrotreating, characterized in that: the hydrorefining reactor is a fixed-bed reactor, and the LPG and hydrogen are in a gaseous state within the reactor. Each reactor inlet is equipped with a feed gas phase distributor, through which the mixed LPG is uniformly introduced into the catalyst zone of the reactor.

[0021] The liquefied petroleum gas (LPG) hydrodeolefins desulfurization method of the present invention is further characterized in that: the inlet temperature of the hydrorefining reactor is 200–320°C, the reaction pressure is 2.5–3.5 MPaG, the hydrogen-to-oil volume ratio is 20–100, and the volume hourly space velocity (VHSV) of the reaction feed relative to the catalyst is 2.0–15.0 h⁻¹. -1 .

[0022] The liquefied petroleum gas (LPG) hydrodeolefins desulfurization method of the present invention is further characterized in that: in step 1), the LPG is pressurized and mixed with hydrogen, then heated and vaporized by a reaction effluent / mixed feed heat exchanger, and heated to a higher temperature by a reaction feed heater before entering the hydrorefining reactor. Multiple reaction effluent / mixed feed heat exchangers are connected in series, divided into a feed vaporization zone and a heating zone.

[0023] The method for desulfurization of liquefied petroleum gas (LPG) by hydrotreating olefins is further characterized in that: in step 3), the low-pressure gas generated at the top of the low-pressure separator is pressurized by a circulating hydrogen compressor and then mixed with fresh hydrogen from outside the device to become mixed hydrogen; the hydrotreated LPG at the bottom of the low-pressure separator is pressurized by a LPG booster pump and then sent to the LPG desulfurization tower.

[0024] The method for desulfurization and deolefin removal by hydrotreating liquefied petroleum gas (LPG) of this invention is further characterized in that: the hydrogenation reaction gas in step 2) is cooled by an air cooler + a cold medium cooler. The low-pressure separator operates at a temperature of 20–45°C and a pressure of 2.0–3.0 MPaG; the low-pressure separator is equipped with internal separation components to enhance gas-liquid two-phase separation and reduce the amount of light hydrocarbons carried in the circulating hydrogen and the amount of hydrogen carried in the refined LPG product.

[0025] The method for desulfurization of liquefied petroleum gas (LPG) by hydrotreating olefins is further characterized in that the amine liquid used in the LPG desulfurization tower is one or more of monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), and N-methyldiethanolamine (MDEA).

[0026] The liquefied petroleum gas hydrodeolefins desulfurization process of the present invention is further characterized in that: the fine desulfurization tank is a liquid phase adsorption desulfurization, and the fine desulfurization tank is set as one or two. When two tanks are set, they can be switched in series or in parallel. The tank is filled with zinc oxide or iron oxide desulfurizing agent.

[0027] The raw materials of this invention are one or more of the following: liquefied petroleum gas (LPG) produced by catalytic cracking and coking units in refineries, and light hydrocarbons produced by oil and gas fields. After the LPG desulfurization tower removes the hydrogen sulfide carried by it, the raw materials are pressurized by the feed pump, mixed with hydrogen, and then enter the hydrorefining reactor for olefin saturation, removal of mercaptans and other impurities, etc. The hydrogen sulfide generated by the hydrorefining reaction is removed by the desulfurization reactor. The reaction products are then heat-exchanged and cooled before entering the low-pressure separator for gas-liquid separation to obtain refined hydrorefined LPG.

[0028] The method of the present invention has the following advantages compared with the prior art:

[0029] 1) The hydrorefining reactor carries out olefin saturation and hydrodesulfurization reactions to remove impurities such as olefins and mercaptans from liquefied petroleum gas.

[0030] 2) A combined process of hydrodesulfurization, amine absorption of hydrogen sulfide, and adsorbent fine desulfurization is adopted to ensure deep desulfurization effect.

[0031] 3) The reaction effluent increases the cooling of the cold medium, enhances the separation effect of circulating hydrogen and refined liquefied gas, and improves the hydrogen purity in the circulating hydrogen. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the liquefied petroleum gas (LPG) hydrodeolefins desulfurization process.

[0033] The attached figures are labeled as follows: 1-Feed pump; 2-Reaction effluent / mixed feed heat exchanger; 3-Reaction heater; 4-Hydrorefining reactor; 5-Reaction effluent air cooler; 6-Reaction effluent cooler; 7-Low-pressure separator; 8-Circulating hydrogen compressor; 9-Liquefied gas booster pump; 10-Liquefied gas desulfurization tower; 11-Fine desulfurization tank. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings:

[0035] Example 1

[0036] Reference Figure 1 The process involves pressurizing the raw material liquefied gas via feed pump 1, mixing it with circulating hydrogen, and then heating it through reaction effluent / mixed feed heat exchanger 2 and reaction feed heater 3 before sending it to the hydrorefining reactor 4. The hydrorefining reactor is mainly filled with refining catalyst. Under the action of the catalyst, olefins in the liquefied gas undergo a hydrogenation saturation reaction, and thiols are hydrogenated to produce hydrogen sulfide. After the reaction, the high-temperature gas phase is cooled by the reaction effluent / mixed feed heat exchanger 2, the reaction effluent air cooler 5, and the reaction effluent cooler 6, and then enters the low-pressure separator 7 for gas-liquid separation. The gas phase coming out of the top of the low-pressure separator is pressurized by the circulating hydrogen compressor 8 and mixed with fresh hydrogen from outside the unit before returning to the reaction system. The liquid phase coming out of the bottom of the low-pressure separator is pressurized by the LPG booster pump 9 and sent to the LPG desulfurization tower 10. In the LPG desulfurization tower, the LPG and amine liquid come into countercurrent contact to remove most of the hydrogen sulfide from the reaction gas. The LPG coming out of the top of the tower enters the fine desulfurization tank 11. After the residual hydrogen sulfide in the LPG is removed by the desulfurizing agent, the refined LPG is sent to the LPG separation unit.

[0037] In this embodiment, the olefin content in the liquefied petroleum gas feedstock is 1.65 wt%, the total sulfur content is 200 μg / g, and the organic sulfur content is 128 μg / g. The hydrogen-to-oil volume ratio in the hydrorefining reaction feedstock is 40, the reaction temperature is 260°C, the reaction pressure is 2.75 MPaG, and the feedstock volume hourly space velocity is 5.0 h⁻¹. -1 The low-pressure separator operates at a temperature of 40°C and a pressure of 2.4 MPaG; the hydrogen purity in the circulating hydrogen is 60%; and the desulfurization tower for liquefied gas operates at a pressure of 3.7 MPaG.

[0038] Table 1 Product indicators obtained from Example 1

[0039] project index Alkenes, μg / g ≯1000 Total sulfur, μg / g ≯0.5 <![CDATA[H2S,μg / g]]> ≯0.5 <![CDATA[H2S,μg / g]]> ≯0.5

[0040] The above are merely typical embodiments of the present invention. Those skilled in the art can make appropriate modifications and improvements based on them, but they are substantially the same as the present invention and also fall within the protection scope of the present invention.

Claims

1. A process for the hydrodeolefinic desulphurization of liquefied gases, characterized in that Includes the following steps: 1) Imported liquefied gas is pressurized and mixed with hydrogen, then heated and vaporized before entering the hydrorefining reactor; 2) The hydrogenation reaction gas from the hydrorefining reactor in step 1) enters the low-pressure separator after heat exchange and cooling; 3) The low-pressure gas generated at the top of the low-pressure separator is pressurized and then mixed with fresh hydrogen from outside the unit to become mixed hydrogen; the hydrogenated liquefied gas at the bottom of the low-pressure separator is pressurized and then sent to the liquefied gas desulfurization tower. 4) In the LPG desulfurization tower, LPG and amine solution come into countercurrent contact to remove most of the hydrogen sulfide from the reaction gas. The LPG coming out from the top of the tower enters the fine desulfurization tank. 5) After the desulfurization tank uses a desulfurizing agent to adsorb and remove residual hydrogen sulfide from the liquefied gas, the refined liquefied gas is sent to the liquefied gas separation unit.

2. The method for hydrotreating olefins and desulfurizing liquefied petroleum gas according to claim 1 is further characterized in that: the liquefied petroleum gas feedstock in step 1) is one or more of the liquefied petroleum gas by-products of catalytic cracking, coking and other units, and light hydrocarbons by-products of oil and gas fields.

3. The method for desulfurization of liquefied petroleum gas by hydrotreating olefins according to claim 1 is further characterized in that: before the imported liquefied petroleum gas is mixed with hydrogen, free water and solid particles are removed.

4. The method for desulfurization of liquefied petroleum gas by hydrotreating olefins according to claim 1, further characterized in that: the hydrorefining reactor is a fixed-bed reactor, and each reactor inlet is equipped with a feed gas phase distributor, through which the mixed liquefied petroleum gas is uniformly introduced into the catalyst zone of the reactor.

5. The method of claim 1, further characterized in that the hydrogenation reactor inlet temperature is 200 to 320 °C, the reaction pressure is 2.5 to 3.5 MPaG, the hydrogen to oil volume ratio is 20 to 100, and the reaction feed volume space velocity relative to the catalyst is 2.0 to 15.0 h -1 .

6. The method for desulfurization of liquefied petroleum gas by hydrotreating olefins according to claim 1 is further characterized in that: in step 1), after the liquefied petroleum gas is pressurized, it is mixed with hydrogen, heated and vaporized by the reaction effluent / mixed feed heat exchanger, and heated by the reaction feed heater before entering the hydrorefining reactor.

7. The liquefied gas hydrodeolefins desulfurization method according to claim 6 is further characterized in that: multiple reaction effluent / mixed feed heat exchangers are connected in series and divided into a feed vaporization zone and a heating zone.

8. The method for desulfurization of liquefied gas by hydrotreating olefins according to claim 1 is further characterized in that: the hydrogenation reaction gas in step 2) is cooled by an air cooler + a cold medium cooler.

9. The method for desulfurization of liquefied gas by hydrotreating olefins according to claim 1, further characterized in that: the low-pressure separator operates at a temperature of 20-45°C and an operating pressure of 2.0-3.0 MPaG; the low-pressure separator is equipped with internal separation components.

10. The method for desulfurization of liquefied gas by hydrotreating olefins according to claim 1, further characterized in that: the fine desulfurization tank is a liquid phase adsorption desulfurization tank, and the fine desulfurization tank is set to one or two units.

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