Method for lightening naphtha

Abstract

The invention discloses a method for lightening naphtha. The method comprises the following steps: 1) mixing a naphtha raw material with hydrogen-rich gas, and contacting the obtained mixture with a modification catalyst for modification treatment to obtain a modified product; and 2) separating the modified product obtained in the step 1) to respectively obtain a cracking raw material, a mixed aromatic hydrocarbon product and a circulating material, and circulating the circulating material to the step 1). According to the method disclosed by the invention, the naphtha raw material can be converted into a high-quality cracking raw material mainly containing propane in a high-selectivity manner, and efficient lightening of naphtha is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for lightening naphtha, in particular, to a method for lightening naphtha to produce high-quality steam cracking feedstock, while byproducting mixed aromatic hydrocarbons and other chemical raw materials, belonging to the field of petroleum and chemical industry. BACKGROUND

[0002] In recent years, with the rapid development of clean energy, the energy consumption structure has undergone profound changes, and the contradiction of excess refining capacity is becoming increasingly severe. "Oil conversion" has become one of the main directions of the transformation and development of the refining industry. How to increase the production of high-quality chemical raw materials and reduce the production cost of olefins and aromatic hydrocarbons has become a challenge on the "oil conversion" road of the current and future refining industry.

[0003] Ethylene is the leading product of the petrochemical industry, and the ethylene production is an important indicator of the development level of a country's petrochemical industry. Steam cracking is the main production process of ethylene, and ethane, propane, light hydrocarbon, light naphtha, naphtha, light diesel, hydrogenated tail oil, etc. are usually used as cracking raw materials. The product distribution and yield of different types of cracking raw materials are significantly different. For example, the double olefin (ethylene and propylene) yield of naphtha cracking is about 40%-50%, the ethylene yield of ethane cracking is up to 78%, and the double olefin yield of propane cracking is up to 60%. Studies have shown that the higher the content of n-alkanes in the cracking raw material, the lower the content of aromatic hydrocarbons, and the higher the degree of lightening, the more beneficial it is to increase the yield of high-value low-carbon olefins and reduce the production of low-value tar.

[0004] For a steam cracking unit, the quality of the raw material is a key factor affecting the cost. For an ethylene unit using naphtha as the raw material, the raw material accounts for about 80% of the total cost, and the quality of the raw material has a significant impact on the economic benefits of the enterprise. In China, most of the cracking units use naphtha as the raw material, so it is increasingly important for the petrochemical industry to improve the overall utilization rate of cracking raw materials and the yield of high-value products by modifying naphtha.

[0005] Many technical solutions have been proposed for the modification of naphtha, including catalytic cracking, hydrogenation (desulfurization), hydroisomerization, and aromatization of naphtha alone or with carbon four liquefied gas under hydrogen or non-hydrogen conditions, and the production of propane, etc. Among them, the aromatization modification technology has strong raw material adaptability, the reaction system is non-hydrogen and can be operated at low pressure, the device investment is less, the energy consumption is low, and it can effectively convert refinery naphtha and low-carbon hydrocarbons, but the yield and octane value of the liquid product are low.

[0006] CN112209794A provides a method for producing propylene by combining light hydrocarbon reforming and propane dehydrogenation. The method is to combine light hydrocarbon reforming and propane dehydrogenation to produce propylene, which includes light hydrocarbon reforming reaction zone and propane dehydrogenation reaction zone, and the light hydrocarbon reforming product and the propane dehydrogenation product enter the common product recovery and separation system, and the separated and recovered light hydrocarbon is recycled as the raw material for light hydrocarbon reforming, and the propane is recycled as the raw material for propane dehydrogenation.

[0007] CN110947417A discloses a catalyst for producing propane and gasoline from paraffin. The catalyst comprises a composite carrier and a rare earth oxide content of 0.1-2.0 mass% based on the carrier, and the composite carrier comprises 5-85 mass% ZSM-5 zeolite, 5-85 mass% MCM-41 zeolite and 5-40 mass% alumina. The catalyst is used for producing propane and gasoline from straight-run naphtha under non-hydrogen conditions, and the propane yield is below 40%.

[0008] CN101747933A discloses a method for naphtha and light hydrocarbon aromatization and reforming. The method carries out aromatization and reforming reaction of naphtha and C3-C5 light hydrocarbon under hydrogen condition, and converts low octane naphtha and low carbon hydrocarbon into high octane gasoline components and high-quality liquefied gas.

[0009] CN113385215A discloses a preparation method and application of a catalyst for hydrogen reforming to produce propane. The method uses a modified core-shell structure SAPO-34 / ZSM-5 composite molecular sieve catalyst to produce propane by catalytic cracking of light hydrocarbon under hydrogen condition, but when used for naphtha hydrogen reforming, the propane yield is below 40%, which still needs to be further improved. SUMMARY

[0010] In view of the problems existing in the prior art, the present application provides a method for lightening naphtha. The method can selectively convert naphtha (mainly C 12 The following hydrocarbons) into high-quality cracking raw materials containing C2-C3 alkanes, while producing oil products, mixed aromatic hydrocarbons, etc., which can be used as chemical raw materials or mixed with other gasoline components to improve the octane number of gasoline.

[0011] The present application provides a method for lightening naphtha, comprising the following steps:

[0012] 1) The naphtha raw material is mixed with hydrogen-rich gas, and the obtained mixture is contacted with a reforming catalyst to carry out reforming treatment, to obtain a reforming product;

[0013] 2) The reforming product obtained in step 1) is separated to obtain a cracking raw material, a mixed aromatic hydrocarbon product and a circulating material, respectively, wherein the circulating material is circulated to step 1).

[0014] Further, the naphtha feedstock in step 1) is selected from at least one of straight-run gasoline, hydrocracking gasoline, catalytic cracking gasoline, hydrocoking gasoline, reforming overhead oil, reforming raffinate oil, condensate oil, pyrolysis gasoline and pyrolysis gasoline raffinate oil.

[0015] Further, in the naphtha feedstock in step 1), the initial boiling point is 30-120°C and the final boiling point is 120-220°C.

[0016] Further, in the naphtha feedstock in step 1), the nitrogen mass content is 0.1-10 ppm. Preferably, when the nitrogen mass content in the naphtha feedstock is above 3 ppm, first denitrification treatment is performed before step 1). The denitrification treatment method is preferably adsorption denitrification. The adsorption denitrification can use conventional adsorption denitrification agents, such as one or more of acid-treated X-type molecular sieve, Y-type molecular sieve, L-type molecular sieve and ZSM-5-type molecular sieve, and the acid treatment can use at least one of inorganic acids such as phosphoric acid, nitric acid, sulfuric acid, etc. For example, the denitrification adsorbent described in CN201010543689.4.

[0017] Further, the adsorption denitrification conditions include: temperature 20-150°C, pressure 0.5-15 MPa, volume space velocity 0.5-5 h -1 .

[0018] Further, the upgrading treatment in step 1) can use a fixed bed or a fluidized bed.

[0019] Further, the upgrading treatment conditions in step 1) include: mass space velocity of naphtha feedstock 0.3-2 h -1 , reaction temperature 280-450°C, preferably 320-380°C, reaction pressure 0.5-3.0 MPa, preferably 1.0-2.0 MPa, hydrogen-rich gas to naphtha feedstock hydrogen / oil volume ratio 0.2-3.0:1.

[0020] Further, the hydrogen-rich gas in step 1) is at least one of hydrogen, hydrogen-methane mixture and hydrogen-rich dry gas. The hydrogen content in the hydrogen-rich gas is 50% or more.

[0021] Further, the upgrading catalyst in step 1) is a molecular sieve catalyst, and the molecular sieve is selected from at least one of ZSM-5 molecular sieve, Y-type molecular sieve, β molecular sieve, mordenite, SAPO-34 molecular sieve, preferably ZSM-5 molecular sieve. In the upgrading catalyst, the mass content of the molecular sieve is 70% or more, preferably 75% or more, and further preferably 80% or more.

[0022] Further, preferably, the modified catalyst is a metal-modified ZSM-5 molecular sieve catalyst.

[0023] Further, preferably, the content of the modified metal is 1%-10% based on the mass of the metal-modified ZSM-5 molecular sieve catalyst, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and any value in the range formed by any two of these values.

[0024] Further, the modified catalyst can further contain a binder, and the binder can be alumina. The binder accounts for 20% or less of the mass of the modified catalyst, and preferably 12%-20%.

[0025] Further, in the ZSM-5 molecular sieve, the molar ratio of SiO2 / Al2O3 is 50-250, and the total specific surface area is 300-500 m 2 / g, wherein the external specific surface area accounts for 33%-45% of the total specific surface area, and preferably 34%-45%, for example, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, and any value in the range formed by any two of these values.

[0026] Further, the ZSM-5 molecular sieve is a nanosheet agglomerate, the particle size of the nanosheet is 20-300 nm, the thickness is 10-100 nm, and the particle size of the agglomerate is 0.3-10 μm.

[0027] Further, the ZSM-5 molecular sieve is preferably a hydrogen-type ZSM-5 molecular sieve.

[0028] Further, the preparation method of the metal-modified ZSM-5 molecular sieve catalyst comprises: preparing a ZSM-5 molecular sieve catalyst, and then loading a metal component to obtain a metal-modified ZSM-5 molecular sieve catalyst.

[0029] Further, preferably, the preparation method of the ZSM-5 molecular sieve catalyst comprises: mixing the ZSM-5 molecular sieve and optional forming aids such as binders, peptizing acids and the like to form, drying and calcining to obtain a ZSM-5 molecular sieve catalyst intermediate, and then ammonium exchanging, drying and calcining to obtain the ZSM-5 molecular sieve catalyst. The preparation method of the ZSM-5 molecular sieve comprises: preparing a seed gel, mixing a second silicon source, an aluminum source, a second template agent, a second alkali source, water and the seed gel to obtain a synthesis liquid, and then performing a crystallization treatment to obtain the ZSM-5 molecular sieve. The molar ratio of the second silicon source (calculated as SiO2), the aluminum source (calculated as Al2O3), the second template agent T2, the second alkali source (calculated as an oxide) and water is as follows: SiO2:Al2O3=(30-260):1, SiO2:T2:second alkali source:H2O=1:(0.02-0.10):(0.07-0.12):(15-30). The amount of the seed gel (calculated as SiO2) is 1%-20% of the mass of the second silicon source (calculated as SiO2), and preferably 3%-10%.

[0030] Further, in the preparation method of the ZSM-5 molecular sieve, the second template agent is an organic amine, and preferably at least one of ethylenediamine, triethylamine, n-butylamine, tetrapropylammonium hydroxide, tetrapropylammonium bromide and cyclohexylamine. The second silicon source is at least one of silica sol, water glass, white carbon black and silica gel. The aluminum source is at least one of sodium aluminate, aluminum sulfate and aluminum isopropoxide. The second alkali source is sodium hydroxide.

[0031] Further, the crystallization treatment is performed under a closed condition at a temperature of 125-180°C for 16-60h.

[0032] Further, the preparation method of the seed gel comprises: mixing a solid silicon source, a first template agent, a first alkali source and water to obtain the seed gel. The molar ratio of the solid silicon source (calculated as SiO2), the first template agent T1, the first alkali source (calculated as an oxide) and water is as follows: first alkali source:SiO2=0.05-0.10, T:SiO2=0.05-0.10, H2O:SiO2=5-30. The mixing condition is stirring at 40-120°C for 6-30h. The solid silicon source is silica gel powder with a particle size of 100-300 mesh, the first template agent is at least one of n-butylamine, tetrapropylammonium hydroxide and tetrapropylammonium bromide, and the first alkali source is sodium hydroxide.

[0033] In the above technical solution, the ZSM-5 molecular sieve is obtained by any separation method known in the art after the crystallization step. The separation method can be, for example, filtration, washing and drying of the obtained product mixture, and an optional calcination step. The filtration, washing and drying can be performed by any method known in the art. The filtration can be performed by suction filtration. The washing can be performed by using deionized water. The drying temperature is 40-150°C, preferably 50-120°C, and the drying time is 1-30 hours, preferably 3-20 hours. The purpose of the calcination is to remove the organic template and possible moisture, thereby obtaining the calcined molecular sieve. The calcination can be performed by any method known in the art, wherein the calcination temperature is 300-750°C, preferably 400-650°C, the calcination time is 1-12 hours, preferably 2-10 hours, and the calcination atmosphere is air or nitrogen.

[0034] Further, in the preparation method of the ZSM-5 molecular sieve catalyst, the ammonium exchange is performed by a conventional ammonium exchange method, and the purpose is to convert the ZSM-5 molecular sieve into a hydrogen type ZSM-5 molecular sieve.

[0035] Further, the drying and calcination after the shaping and the drying and calcination after the ammonium exchange can be performed by conventional methods and conditions. Generally, the drying conditions are as follows: the drying temperature is 80-150°C, and the drying time is 6-18 hours; and the calcination conditions are as follows: the calcination temperature is 500-600°C, and the calcination time is 2-6 hours.

[0036] Further, the method for loading the metal component can be an impregnation method, which can be a saturated impregnation method, a supersaturated impregnation method, etc. After the impregnation, drying and calcination are performed to obtain the metal-modified ZSM-5 molecular sieve catalyst. Generally, the drying and calcination can be performed by conventional methods and conditions, for example, the drying conditions are as follows: the drying temperature is 80-150°C, and the drying time is 6-18 hours; and the calcination conditions are as follows: the calcination temperature is 500-600°C, and the calcination time is 2-6 hours.

[0037] Further, the separation in step 2) can be performed by a rectification method, for example, a stabilizer column, a depropanizer column, and a light hydrocarbon removal column are provided to obtain a cracking raw material, a circulating material, and mixed aromatic hydrocarbons. The cracking raw material is mainly C2-C3 products (from the overhead gas phase product of the depropanizer column), wherein the proportion of propane is more than 95v%; the circulating material is mainly C4-C6 products (from the overhead gas phase product of the light hydrocarbon removal column); and the mixed aromatic hydrocarbons are C7 +The above product (from the liquid phase product at the bottom of the de-light hydrocarbon column). Optionally, a de-butane column can also be arranged between the de-propane column and the de-light hydrocarbon column for separating C4 in the product at the bottom of the de-propane column, the overhead product of the de-butane column mainly being C4, and n-C4 (normal butane) and i-C4 (isobutane) being obtained by further separation, wherein the n-C4 can be used as a cracking raw material, and the bottom product of the de-butane column enters the de-light hydrocarbon column, and the overhead gaseous phase product of the de-light hydrocarbon column mainly being C5-C6 is used as a circulating material together with the i-C4.

[0038] Further, after the naphtha raw material is mixed with the hydrogen-rich gas and the circulating material, the naphtha raw material is preferably first exchanged heat with the modified product obtained in step 1), and then heated to the modified reaction temperature, and then contacted with the modified catalyst. The heating can be performed by using a separate heating device.

[0039] Further, the modified product obtained in step 1) is first subjected to cooling treatment before being separated.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] (1) The present application converts the naphtha raw material into high-quality cracking raw material mainly composed of ethane and propane by lightening, and realizes efficient utilization of the naphtha.

[0042] (2) The present application can delay coking of the catalyst to a certain extent and prolong the single-pass operation cycle of the catalyst by lightening the naphtha raw material under the condition of hydrogen.

[0043] (3) The present application can greatly improve the yield of cracking raw material under the condition of low hydrogen / oil volume ratio (0.2-3.0) by using the catalyst in the process of hydrogenation of the naphtha.

[0044] (4) The present application preferably uses a metal-modified ZSM-5 molecular sieve catalyst, and the inventors have found that when the external specific surface area of the ZSM-5 molecular sieve accounts for 33% to 45%, and the metal is modified in a specific manner, the catalyst obtained can greatly improve the yield of cracking raw material under the condition of low hydrogen / oil volume ratio in the process of hydrogenation of the naphtha.

[0045] (5) The present application preferably uses a metal-modified ZSM-5 molecular sieve catalyst, wherein the ZSM-5 molecular sieve is prepared by using solid silica gel as a silicon source to prepare gel seeds, and the synthesis liquid containing the gel seeds is crystallized under suitable conditions to obtain the ZSM-5 molecular sieve. The ZSM-5 molecular sieve is particularly suitable as a component of a naphtha modification catalyst, and after being modified by a metal, the naphtha modification catalyst obtained can greatly improve the yield of cracking raw material under the condition of low hydrogen / oil volume ratio in the process of hydrogenation of the naphtha. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 A schematic diagram of the process flow for the inventive process is shown in Figure 1.

[0047] Figure 1 The labels are as follows: A. adsorption denitrogenation column, B. feed-reactant heat exchanger, C. heater, D. reforming reactor, E. stabilizer column, F. depropanizer column, G. de- light hydrocarbon column, 1. feedstock, 2. hydrogen-rich gas, 3. light gas (C1+C2 and small amount of H2), 4. cracked feedstock (C3 and small amount of C2), 5. recycle material (C4-C6), 6. C7 + stream;

[0048] Figure 2 XRD pattern of ZSM-5 molecular sieve obtained in Example 1.

[0049] Figure 3 SEM pattern of ZSM-5 molecular sieve obtained in Example 1.

[0050] Figure 4 XRD pattern of ZSM-5 molecular sieve obtained in Example 2.

[0051] Figure 5 SEM pattern of ZSM-5 molecular sieve obtained in Example 2.

[0052] Figure 6 XRD pattern of ZSM-5 molecular sieve obtained in Comparative Example 1.

[0053] Figure 7 SEM pattern of ZSM-5 molecular sieve obtained in Comparative Example 1.

[0054] Figure 8 XRD pattern of ZSM-5 molecular sieve obtained in Comparative Example 2.

[0055] Figure 9 SEM pattern of ZSM-5 molecular sieve obtained in Comparative Example 2.

[0056] Figure 10 XRD pattern of ZSM-5 molecular sieve obtained in Comparative Example 3.

[0057] Figure 11 SEM pattern of ZSM-5 molecular sieve obtained in Comparative Example 3.

[0058] Figure 12 XRD pattern of ZSM-5 molecular sieve obtained in Comparative Example 4.

[0059] Figure 13 SEM pattern of ZSM-5 molecular sieve obtained in Comparative Example 4. DETAILED DESCRIPTION

[0060] For better understanding of the present application, the present application is further illustrated below in connection with examples, but the scope of protection claimed by the present application is not limited to the scope of the expression of the examples.

[0061] In the present application, XRD is used to analyze the phase by Rigaku D / max-2004 X-ray powder diffractometer, Cu Kα radiation is used, tube pressure is 40 kV, tube flow is 100 mA, scanning range 2θ is 5-50°, scanning step is 0.02°.

[0062] In the present application, SEM is tested by NOVA Nano SEM450 ultra-high resolution field emission scanning electron microscope of FEI Company of the United States.

[0063] In the present application, the silicon aluminum ratio of the molecular sieve is determined by inductively coupled plasma method (ICP-AES). The experiment is carried out on Plasma-Spec-I inductively coupled plasma atomic emission spectrometer of item Labs Company of the United States.

[0064] In the present application, the specific surface area and external specific surface area results are obtained by specific surface area test (BET). The test is carried out on Micromeritics ASAP-2020 specific surface area and pore size analyzer. The sample is first activated at 300℃, and vacuumized to 5mHg, and then carried out at liquid nitrogen temperature.

[0065] The present application is further illustrated below in connection with examples. Figure 1 The method of the present application is described in detail. The method for lightening naphtha provided by the present application comprises: naphtha raw material 1 is first pretreated by adsorption denitrification in adsorption denitrification tower A, the pretreated raw material is mixed with hydrogen-rich gas 2, and then heated by raw material-reaction product heat exchanger B, and then heated by heater C, and then enters into modification reactor D to contact with modification catalyst for modification treatment to obtain modified product, the modified product is heated by raw material-reaction product heat exchanger B, and then enters into stabilizer tower E, light gas 3 (C1+C2 and a small amount of H2) is obtained at the top, the bottom material enters into depropanizer tower F, cracking raw material 4 (propane and a small amount of ethane) is obtained at the top, the bottom material enters into de-light hydrocarbon tower, circulating material 5 (C4-C6) is obtained at the top, C7 + stream 6 (mixed aromatic hydrocarbon product) is obtained at the bottom, wherein the circulating material is mixed with the pretreated raw material as the raw material of the modification reactor D.

[0066] Example 1

[0067] (1) ZSM-5 molecular sieve raw powder synthesis

[0068] A seed gel was prepared by stirring a mixture of silica powder (300 mesh), tetrapropylammonium bromide, sodium hydroxide and water at 80°C for 24 hours, with the molar ratio of n(SiO2):n(template agent):n(Na2O):n(H2O) being 1:0.05:0.08:15.

[0069] A mixture of silica powder (300 mesh), sodium aluminate, tetrapropylammonium bromide, sodium hydroxide and water was prepared with the molar ratio of n(SiO2):n(Al2O3) being 80, and n(SiO2):n(template agent):n(Na2O):n(H2O) being 1:0.06:0.10:29. After stirring at room temperature for 30 minutes, 5% of the seed gel (based on the mass of silica) was added to the mixture, and the mixture was stirred at room temperature for 3 hours. The mixture was then transferred to a stainless steel autoclave for crystallization at 175°C for 48 hours. The crystallized solution was recovered by sedimentation and filtration, and the solid was washed with deionized water until neutral. The dried solid was then calcined at 550°C for 4 hours in air to obtain a ZSM-5 molecular sieve (denoted as S1). 2 The BET results of the calcined S1 molecular sieve showed that the total specific surface area was 425.1 m2 / g, and the external specific surface area / total specific surface area was 34.4%.

[0070] The XRD pattern of the calcined S1 molecular sieve is shown in Figure 1. Figure 2 As can be seen from the XRD pattern, the molecular sieve has obvious ZSM-5 characteristic peaks.

[0071] The scanning electron micrograph of the calcined S1 molecular sieve is shown in Figure 2. Figure 3 As can be seen from the scanning electron micrograph, the ZSM-5 molecular sieve is a nanosheet agglomerate, with a particle size of 100-200 nm and a thickness of 20-50 nm. Figure 3

[0072] Figure 3 The markers in the figure represent the length of the nanosheet (L), the thickness of the nanosheet (T), and the particle size of the agglomerate (W).

[0073] (2) Catalyst synthesis

[0074] A catalyst intermediate A was obtained by kneading and extruding 300 g of the above-mentioned sodium-type ZSM-5 molecular sieve powder S1 and 120 g of alumina with the addition of 2 wt% dilute nitric acid solution, drying at 120°C for 10 hours, and calcining at 550°C for 4 hours.

[0075] ​Take 50 g of catalyst intermediate A, add 8 wt% ammonium acetate solution (liquid-solid volume ratio is 10), exchange at 80℃ for 1h, wash with water, dry at 120℃ for 10 hours, calcine at 550℃ for 4h, get ZSM-5 molecular sieve catalyst B;

[0076] Take 20g ZSM-5 molecular sieve catalyst B, and immerse it in an excess of an aqueous ammonium molybdate solution, dry it at 120℃ for 10 hours after immersion, and calcine it at 500℃ for 2h to obtain a 5wt% molybdenum metal modified molecular sieve catalyst C-1.

[0077]

Example 2

[0078] (1) ZSM-5 molecular sieve raw powder synthesis

[0079] Use silica gel powder (300 mesh) as the silicon source, tetrapropylammonium bromide as the template agent, and sodium hydroxide as the alkali source. The silicon source, template agent, alkali source, and water are mixed according to the ratio n(SiO2):n(template agent):n(Na2O):n(H2O)=1:0.03:0.10:15, and stirred at 80℃ for 24h to prepare a seed gel.

[0080] Mix the silica gel powder (300 mesh), sodium aluminate, tetrapropylammonium bromide, sodium hydroxide, and water according to the ratio n(SiO2):n(Al2O3)=225, n(SiO2):n(template agent):n(Na2O):n(H2O)=1:0.03:0.12:21. After stirring at room temperature for 30min, add 5% of the seed gel (based on the mass of silicon dioxide in the mixed solution) to the mixed solution, and stir at room temperature for 3 hours. Transfer the above mixture to a stainless steel high-pressure reaction kettle for crystallization treatment, crystallize at 125℃ for 24h, and then crystallize at 175℃ for 24h. The above crystallized solution is recovered by sedimentation / filtration, the solid is washed with deionized water until it is neutral, and then dried to obtain the molecular sieve raw powder (denoted as S2). Take part of the molecular sieve raw powder S2, calcine it in air at 550℃ for 4 hours, and the BET results of the calcined S2 molecular sieve show that the total specific surface area is 410m 2 / g, and the external specific surface area / total specific surface area=42.3%. The SiO2 / Al2O3 molar ratio of the calcined S2 molecular sieve is 210.

[0081] The XRD pattern of the calcined S2 molecular sieve is shown in Figure 4 From the XRD pattern, it can be seen that the molecular sieve has obvious ZSM-5 characteristic peaks.

[0082] The scanning electron microscope image of the calcined S2 molecular sieve is shown in Figure 5 From the scanning electron microscope image, it can be seen that the ZSM-5 molecular sieve is a nanosheet agglomerate, the particle size of the nanosheet is 100-300nm, the thickness is 20-50nm, and the particle size of the agglomerate is 1-5μm.

[0083] (2) Catalyst synthesis

[0084] The catalyst preparation procedure was the same as in Example 1, using molecular sieve S2 instead of molecular sieve S1 to obtain catalyst C-2.

[0085]

Example 3

[0086] The ZSM-5 molecular sieve raw powder synthesis procedure was the same as in Example 1 to obtain molecular sieve S1.

[0087] Catalyst synthesis:

[0088] Take 300 g of the above sodium type ZSM-5 molecular sieve raw powder S1 and add 120 g of alumina, knead and extrude into strips by adding 2 wt% dilute nitric acid solution, dry at 120°C for 10 hours, and calcine at 550°C for 4 hours to obtain catalyst intermediate A;

[0089] Take 50 g of catalyst intermediate A, add 8 wt% ammonium acetate solution (liquid to solid volume ratio of 10), exchange at 80°C for 1 hour, wash with water, dry at 120°C for 10 hours, and calcine at 550°C for 4 hours to obtain ZSM-5 molecular sieve catalyst B;

[0090] Take 20 g of ZSM-5 molecular sieve catalyst B, and immerse in an equal volume of gallium nitrate aqueous solution, dry at 120°C for 10 hours after immersion, and calcine at 550°C for 4 hours to obtain 6 wt% gallium metal modified molecular sieve catalyst C-3.

[0091]

Comparative Example 1

[0092] (1) ZSM-5 molecular sieve raw powder synthesis

[0093] Silica gel powder (300 mesh), sodium aluminate, tetrapropylammonium bromide, sodium hydroxide and water were prepared into a synthesis solution according to n(SiO2):n(Al2O3)=80, n(SiO2):n(template agent):n(Na2O):n(H2O)=1:0.06:0.10:29, and stirred at room temperature for 3 hours. The above mixture was transferred into a stainless steel high-pressure reaction kettle for crystallization treatment, and crystallized at 175°C for 48 hours. The crystallized solution was recovered by sedimentation / filtration, and the solid was washed with deionized water until neutral, and dried to obtain a molecular sieve raw powder (denoted as D1). Part of the molecular sieve raw powder D1 was calcined at 550°C in air for 4 hours. The BET results of the calcined D1 molecular sieve showed that the total specific surface area was 365 m 2 / g, and the external specific surface area / total specific surface area=24.3%.

[0094] The XRD pattern of the calcined D1 molecular sieve is shown in Figure 6 From the XRD pattern, it can be seen that the molecular sieve has obvious ZSM-5 characteristic peaks.

[0095] The scanning electron microscope of the D1 molecular sieve after calcination is shown in Figure 2. Figure 7 .

[0096] (2) Catalyst synthesis

[0097] The catalyst preparation procedure was the same as in Example 1, except that the molecular sieve D1 was used instead of the molecular sieve S1 to obtain catalyst C-D-1.

[0098]

Comparative Example 2

[0099] (1) ZSM-5 molecular sieve powder synthesis

[0100] The silica gel powder (300 mesh), sodium aluminate, tetrapropylammonium bromide, sodium hydroxide and water were prepared into a synthesis solution according to n(SiO2):n(Al2O3)=85, n(SiO2):n(template):n(Na2O):n(H2O)=1:0.05:0.08:29, stirred at room temperature for 30 min, then 5% of the mass of the silica source (calculated as silicon dioxide) in the synthesis solution was added to the ZSM-5 powder (SiO2 / Al2O3 molar ratio=168, purchased from Shanghai Fuxu Molecular Sieve Co., Ltd.), and stirred at room temperature for 3 hours. The above mixture was transferred into a stainless steel high-pressure reaction kettle for crystallization treatment, and crystallized at 175°C for 48h. The mother liquor was recovered by sedimentation / filtration, and the solid was washed with deionized water until neutral, and dried to obtain the molecular sieve powder (denoted as D2).

[0101] A part of the molecular sieve powder D2 sample was calcined at 550°C in air for 4 hours. The BET results of the D2 molecular sieve after calcination showed that the total specific surface area was 341 m 2 / g, and the external specific surface area / total specific surface area=22.1%.

[0102] The XRD pattern of the D2 molecular sieve after calcination is shown in Figure 4. Figure 8 From the XRD pattern, it can be seen that the molecular sieve has obvious ZSM-5 characteristic peaks.

[0103] The scanning electron microscope of the D2 molecular sieve after calcination is shown in Figure 5. Figure 9 .

[0104] (2) Catalyst synthesis

[0105] The catalyst preparation procedure was the same as in Example 1, except that the molecular sieve D2 was used instead of the molecular sieve S1 to obtain catalyst C-D-2.

[0106]

Comparative Example 3

[0107] (1) ZSM-5 molecular sieve powder synthesis

[0108] The synthesis solution was prepared by mixing silica gel powder (300 mesh), sodium aluminate, tetrapropylammonium bromide, sodium hydroxide and water in a ratio of n(SiO2):n(Al2O3)=85, n(SiO2):n(template):n(Na2O):n(H2O)=1:0.05:0.08:29. After stirring at room temperature for 30 min, D1 powder was added to the synthesis solution in an amount of 5% by mass of the silica source (as SiO2), and the mixture was stirred at room temperature for 3 h. The mixture was then transferred to a stainless steel autoclave for crystallization treatment at 175°C for 48 h. The crystallized solution was recovered by sedimentation / filtration, and the solid was washed with deionized water until neutral and dried to obtain the molecular sieve powder (denoted as D3). Part of the molecular sieve powder D3 was calcined in air at 550°C for 4 h. The BET results of the calcined D3 molecular sieve showed that the total specific surface area was 398 m 2 / g, and the external specific surface area / total specific surface area=27%.

[0109] The XRD pattern of the calcined D3 molecular sieve is shown in Figure 10 As can be seen from the XRD pattern, the molecular sieve has obvious ZSM-5 characteristic peaks.

[0110] The scanning electron micrograph of the calcined D3 molecular sieve is shown in Figure 11 .

[0111] (2) Catalyst synthesis

[0112] The catalyst was prepared according to the procedure of Example 1, using the molecular sieve D3 instead of the molecular sieve S1, to obtain the catalyst C-D-3.

[0113]

Comparative Example 4

[0114] (1) ZSM-5 molecular sieve powder synthesis

[0115] Silica sol (25% by mass of SiO2) was used as the silica source, tetrapropylammonium bromide was used as the template, and sodium hydroxide was used as the alkali source. The seed gel was prepared by stirring the silica source, template, alkali source and water at 80°C for 24 h in a ratio of n(SiO2):n(template):n(Na2O):n(H2O)=1:0.05:0.08:15.

[0116] A synthesis solution was prepared by mixing silica sol (25% silica by mass), sodium aluminate, tetrapropylammonium bromide, sodium hydroxide, and water at a ratio of n(SiO2):n(Al2O3) = 80 and n(SiO2):n(template):n(Na2O):n(H2O) = 1:0.05:0.08:29. After stirring at room temperature for 30 min, a seed gel was added at 5% of the silica source (based on silica) in the synthesis solution, and the mixture was stirred at room temperature for 3 h. The mixture was then transferred to a stainless steel high-pressure reactor for crystallization at 175 °C for 48 h. The crystallized solution was then subjected to sedimentation / filtration to recover the mother liquor. The solid was washed with deionized water until neutral and dried to obtain molecular sieve powder (denoted as D4). A sample of molecular sieve powder D4 was calcined in air at 550 °C for 4 h. The BET results of the calcined D4 molecular sieve showed a total specific surface area of ​​367 m². 2 / g, external specific surface area / total specific surface area = 23.0%.

[0117] XRD patterns of the calcined D4 molecular sieve are shown in Figure 1. Figure 12 As shown in the figure, the molecular sieve has obvious ZSM-5 characteristic peaks.

[0118] Scanning electron microscopy of calcined D4 molecular sieves is shown in Figure 1. Figure 13 .

[0119] (2) Catalyst Synthesis

[0120] The catalyst preparation steps are the same as in Example 1, except that molecular sieve D4 is used instead of molecular sieve S1 to obtain catalyst CD-4.

[0121]

Examples 4-6

[0122] Using C-1, C-2, and C-3 catalysts respectively, and hydrocracking light naphtha (distillation range 60-140℃, nitrogen content 2.5ppm) as feedstock, the following methods were employed: Figure 1 The process follows the same procedure but excludes adsorption denitrification tower A. The reforming reactor E is a fixed-bed reactor. The reaction temperature is 350℃, the reaction pressure is 1MPa, and the feed mass hourly space velocity (WHSV) is 1.5h⁻¹. -1 The hydrogen-to-oil volume ratio was 0.5:1. The yield of the top cracking feedstock of the propane stripper F is shown in Table 1, in which propane accounted for more than 95% of the volume content of the cracking feedstock.

[0123]

Example 7

[0124] Using C-1 as a catalyst and hydrocracking light naphtha (distillation range 60-140℃, nitrogen content 2.5ppm) as feedstock, the following process was employed: Figure 1 The process follows the same procedure but excludes adsorption denitrification tower A. The reforming reactor E is a fixed-bed reactor with a reaction temperature of 370℃, a reaction pressure of 1.2 MPa, and a feed mass hourly space velocity (WHSV) of 1.4 h⁻¹. -1, hydrogen oil volume ratio 0.2:1. The depropanizer F overhead pyrolysis feedstock yield was 80.6%, and the pyrolysis feedstock contained more than 95% propane by volume.

[0125]

Comparative Examples 7-10

[0126] Using C-D-1, C-D-2, C-D-3 and C-D-4 as catalysts, respectively, and using the same feedstock and evaluation method as in Examples 4-6. The depropanizer F overhead pyrolysis feedstock yield is shown in Table 1, and the pyrolysis feedstock contained more than 95% propane by volume.

[0127] Evaluation results of the catalysts of Examples 1-6

[0128]

[0129]

[0130] The above is only a specific embodiment of the present application, and is not intended to limit the present application in any form. Although the present application has been disclosed above with specific embodiments, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the present application, and any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present application are still within the scope of the present application.

Claims

1. A method for lightening naphtha, comprising the following steps: 1) mixing naphtha feedstock with hydrogen-rich gas, and contacting the mixture with a reforming catalyst to perform reforming treatment, to obtain a reforming product; 2) separating the reforming product obtained in step 1) to obtain a cracking feedstock, a mixed aromatic product and a recycle material, respectively, wherein the recycle material is recycled to step 1).

2. The method of claim 1, wherein, In step 1), the naphtha feedstock is selected from at least one of straight-run gasoline, hydrocracking gasoline, catalytic cracking gasoline, hydrocoking gasoline, reforming overhead, reforming raffinate, condensate, pyrolysis gasoline and pyrolysis gasoline raffinate; and / or, in the naphtha feedstock in step 1), the initial boiling point is 30-120°C, and the final boiling point is 120-220°C.

3. The method of claim 1, wherein, In the naphtha feedstock in step 1), the mass content of nitrogen is 0.1-10 ppm; preferably, when the mass content of nitrogen in the naphtha feedstock is more than 3 ppm, first performing denitrification treatment, and then performing step 1).

4. The method of claim 1, wherein, In step 1), the reforming treatment is performed in a fixed bed or in a fluidized bed.

5. The method according to claim 1 or 4, characterized in that, The modification treatment conditions in step 1) include a mass space velocity of the naphtha feed of 0.3-2 h -1 -1, a reaction temperature of 280-450°C, preferably 320-380°C, a reaction pressure of 0.5-3.0 MPa, preferably 1.0-2.0 MPa, and a hydrogen to oil volume ratio of the hydrogen-rich gas to the naphtha feed of 0.2-3.0:

1.

6. The method of claim 1, wherein, In step 1), the reforming catalyst is a molecular sieve catalyst, and the molecular sieve is selected from at least one of ZSM-5 molecular sieve, Y molecular sieve, β molecular sieve, mordenite and SAPO-34 molecular sieve, preferably ZSM-5 molecular sieve; preferably, in the reforming catalyst, the mass content of the molecular sieve is more than 70%.

7. The method of claim 6, wherein, The reforming catalyst is a metal-modified ZSM-5 molecular sieve catalyst; wherein the modified metal is at least one of molybdenum, zinc, copper, gallium and lanthanum, preferably at least one of molybdenum and gallium; preferably, the content of the modified metal is 1%-10% based on the mass of the metal-modified ZSM-5 molecular sieve catalyst.

8. The method of claim 7, wherein, The ZSM-5 molecular sieve has a molar ratio of SiO2 / Al2O3 of 50-250, a total specific surface area of 300-500 m2 / g, and an external specific surface area of 100-300 m2 / g, wherein the external specific surface area accounts for 33%-45%, preferably 34%-45%, of the total specific surface area. 2 / g, wherein the external specific surface area accounts for 33%-45%, preferably 34%-45%, of the total specific surface area.

9. The method according to claim 7 or 8, characterized in that, The ZSM-5 molecular sieve is a nanosheet agglomerate, the particle size of the nanosheet is 20-300 nm, the thickness is 10-100 nm, and the particle size of the agglomerate is 0.3-10 μm.

10. The method of claim 1, wherein, In step 2), the cracking feedstock is mainly C2-C3 product, wherein the content of propane is more than 95 v%, and the recycle material is mainly C4-C6 product.

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