Method for catalyzing high yield of low-carbon aromatic hydrocarbon by adopting catalyst containing Y-type molecular sieve and catalyst containing shape-selective molecular sieve

Abstract

The invention relates to the field of low-carbon aromatic hydrocarbon production, and discloses a method for catalyzing high yield of low-carbon aromatic hydrocarbon by adopting a catalyst containing a Y-type molecular sieve and a catalyst containing a shape-selective molecular sieve. The method comprises the following steps: carrying out hydrofining reaction on hydrogen, diesel oil and a hydrofining catalyst, and then treating, so that the total nitrogen content in the obtained hydrotreating effluent is lower than 50 mu g / g, the hydrotreating effluent and a first hydrocracking catalyst are subjected to a first hydrocracking reaction, a first product is obtained, the first hydrocracking catalyst comprises a first carrier and a first metal component, the first carrier contains a Y-type molecular sieve, and the first metal component is a VIB group metal component; the first product and a second hydrocracking catalyst are subjected to a second hydrocracking reaction, the second hydrocracking catalyst comprises a second carrier and a second metal component, and the second carrier contains an MFI molecular sieve; wherein the second hydrocracking reaction temperature is higher than the first hydrocracking reaction temperature. By adopting the method, high-yield low-carbon aromatic hydrocarbon can be obtained.

Description

Technical Field

[0001] The invention relates to the field of low-carbon aromatic hydrocarbon production, and in particular to a method for producing more low-carbon aromatic hydrocarbons by using a Y-type molecular sieve catalyst and a shape-selective molecular sieve catalyst. Background Art

[0002] With the development of the economy, the demand for aromatics has increased rapidly. At present, the demand for low-carbon aromatics in my country has exceeded 40 million tons / year. This makes it of practical economic value to convert heavy aromatics into low-carbon aromatics through hydrocracking. There are two major low-carbon aromatics in demand, and the products with industrial value are mainly benzene, toluene, xylene, ethylbenzene, etc. The most important use of benzene in industry is as a chemical raw material, such as styrene, phenol, cyclohexane, maleic anhydride, nitrobenzene, alkylbenzene, caprolactam, etc. The existing industrial methods are mainly separated from catalytic reforming production oil, coal tar, and cracking oil. It can also be obtained by disproportionation and toluene dealkylation reaction. These processes have the disadvantages of high reaction temperature (500-600℃) and complex raw materials.

[0003] CN201811264066.6 discloses a method for catalytic diesel hydroconversion to produce aromatics in maximum quantity, comprising the following steps: (1) high aromatic catalytic diesel is mixed with circulating hydrogen and enters a hydrofining reaction zone for reaction, wherein at least two catalyst beds are arranged in the hydrofining reaction zone, and the degree of sulfidation of the catalyst shows a decreasing trend along the logistics direction; (2) the generated oil obtained in step (1) enters a hydrocracking reaction zone and contacts with at least two sulfided hydrocracking catalysts to carry out a ring-opening conversion reaction of polycyclic aromatic hydrocarbons; (3) the generated oil obtained in step (2) is separated by a separation system to obtain gas, gasoline, and diesel fractions, and the diesel fraction is all recycled back to the hydrofining reaction zone; (4) naphtha obtained in step (3) enters an aromatics extraction device, and a BTX product is obtained by solvent extraction. The present invention uses hydrogenation catalysts with different degrees of sulfidation by grading to balance the initial activity of the catalyst, thereby solving the problem of long initial adjustment period and long-term low octane number of the main purpose product gasoline fraction in the process of technical application.

[0004] The above method uses a graded hydrocracking interval to obtain a certain amount of naphtha fraction with a high BTX content, but the refined hydrogenation products all enter the downstream process in sequence, so that the organic nitrogen in the raw material enters the hydrocracking catalyst bed containing the molecular sieve in the form of inorganic ammonia and organic nitrogen, and both inorganic ammonia and organic nitrogen will undergo adsorption reaction on the molecular sieve. Among them, the inorganic ammonia molecules will pass through the inner pores of the catalyst due to their small molecular diameter, and then adsorb on the acidic center on the inner surface of the catalyst, so that the cracking activity of the catalyst is weakened; the organic nitrogen molecules are easy to adsorb on the acidic center on the outer surface of the catalyst due to their large molecular diameter, thereby reducing the cracking activity of the catalyst macromolecules. In order to overcome these problems during the LCO hydrocracking reaction, a certain hydrogenation activity is usually maintained in the cracking section catalyst to make the catalyst activity more stable. By adopting a bimetallic design, the additive effect of the VIII group metal is used to maintain a certain hydrogenation activity. However, the yield of low-carbon aromatics in the final product is still limited, and the benzene yield is also relatively limited. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem that the yield of low-carbon aromatics in the existing process needs to be further improved, and to provide a method for producing more low-carbon aromatics by using a Y-type molecular sieve catalyst and a shape-selective molecular sieve catalyst. The method can obtain a higher yield of low-carbon aromatics.

[0006] In order to achieve the above object, the present invention provides a method for producing more low-carbon aromatics, which comprises the following steps:

[0007] (1) subjecting hydrogen and diesel to a hydrotreating catalyst for hydrotreating reaction, and then treating the resultant hydrotreating effluent so that the total nitrogen content in the effluent is less than 50 μg / g;

[0008] (2) subjecting the hydroprocessing effluent to a first hydrocracking reaction with a first hydrocracking catalyst to obtain a first product, wherein the first hydrocracking catalyst comprises a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Y-type molecular sieve and the first metal component is a Group VIB metal component;

[0009] (3) subjecting the first product obtained in step (2) to a second hydrocracking reaction with a second hydrocracking catalyst, wherein the second hydrocracking catalyst comprises a second carrier and a second metal component supported on the second carrier, wherein the second carrier comprises an MFI molecular sieve, and the second metal component comprises a Group VIB metal component and a Group VIII metal component;

[0010] Wherein, the reaction temperature of the second hydrocracking reaction is higher than the reaction temperature of the first hydrocracking reaction.

[0011] Through the above technical solution, the beneficial effects of the present invention include:

[0012] The method provided by the present invention first controls the total nitrogen content in the hydrotreatment effluent to be lower than 50 μg / g, then adopts a first hydrocracking catalyst containing a first carrier of a Y-type molecular sieve and a monometallic active component and a second hydrocracking catalyst containing a second carrier of an MFI-type molecular sieve and a bimetallic active component in a reasonable grading, performs a secondary continuous hydrocracking reaction and controls the temperature of the second hydrocracking reaction to be higher than the temperature of the first hydrocracking reaction, so that the yield of low-carbon aromatics in the obtained product is significantly improved. DETAILED DESCRIPTION

[0013] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0014] In the present invention, the dry basis of a substance refers to a solid product obtained by calcining the substance at 600° C. for 3 hours.

[0015] In the present invention, "optional" means not essential, and can be understood as including or not including.

[0016] In the present invention, the density of the diesel is the density at 20°C.

[0017] In one aspect, the present invention provides a method for producing more low-carbon aromatics, the method comprising the following steps:

[0018] (1) subjecting hydrogen and diesel to a hydrotreating catalyst for hydrotreating reaction, and then treating the resultant hydrotreating effluent so that the total nitrogen content in the effluent is less than 50 μg / g;

[0019] (2) subjecting the hydroprocessing effluent to a first hydrocracking reaction with a first hydrocracking catalyst to obtain a first product, wherein the first hydrocracking catalyst comprises a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Y-type molecular sieve and the first metal component is a Group VIB metal component;

[0020] (3) subjecting the first product obtained in step (2) to a second hydrocracking reaction with a second hydrocracking catalyst, wherein the second hydrocracking catalyst comprises a second carrier and a second metal component supported on the second carrier, wherein the second carrier comprises an MFI molecular sieve, and the second metal component comprises a Group VIB metal component and a Group VIII metal component;

[0021] Wherein, the reaction temperature of the second hydrocracking reaction is higher than the reaction temperature of the first hydrocracking reaction.

[0022] In the present invention, the total nitrogen content in the hydroprocessing effluent is less than 50 μg / g, preferably less than 30 μg / g. This preferred embodiment can reduce the inhibitory effect of inorganic ammonia generated by the hydroprocessing reaction on the metal active centers and the molecular sieve active centers.

[0023] The present invention has no particular limitation on the treatment method of step (1), and it may be, for example, water washing, filtration, steam stripping, etc., as long as the total nitrogen content is lower than the above range.

[0024] In the present invention, the reaction temperature of the second hydrocracking reaction is higher than the reaction temperature of the first hydrocracking reaction, preferably 5-30° C. This preferred embodiment is conducive to the first hydrocracking catalyst and the second hydrocracking catalyst to exert their respective advantages, synergistically act, and improve the yield of light aromatics.

[0025] In the prior art, the raw materials used usually include heavy and inferior fractions such as VGO, which contain a large amount of aromatics and cycloalkanes. These aromatics and cycloalkanes usually exist in the form of side chains, so as to maintain a certain distillation range in the mixture. The reaction occurring at the acid center in the conventional hydrocracking process is usually based on the positive carbon ion mechanism, and the feed macromolecules are converted into small molecules through ring opening and side chain breaking reactions. However, the carbon-carbon bond breakage in this process is usually based on Beta cracking, that is, the breakage of the ortho-position chemical bond of the positive carbon ion coordination chemical bond, which makes the reaction product of this process usually contain certain branches, and it is difficult to obtain low-branched or even unbranched low-carbon aromatic compounds (BTEX). The present invention uses the diesel fraction with lower density, lower distillation range, and higher content of cycloalkanes and aromatics to be more easily converted into low-carbon aromatics, significantly improving the selectivity of low-carbon aromatics. Preferably, the density of the diesel is 0.85-0.96g / cm 3 , can be 0.85g / cm 3 , 0.86g / cm 3 , 0.87g / cm 3 , 0.88g / cm 3 , 0.89g / cm 3 , 0.9g / cm 3 、0.91g / cm 3 , 0.92g / cm 3 、0.93g / cm 3 、0.94g / cm 3 , 0.95g / cm 3 , 0.96g / cm 3and any value in the range formed by any two of these point values.

[0026] Preferably, the distillation range of the diesel is 180-375°C.

[0027] Preferably, the content of paraffins in the diesel is less than 15 weight %, for example, it can be 14.5 weight %, 14 weight %, 13 weight %, 12 weight %, 11 weight %, 10 weight %, 9 weight %, 8 weight %, 7 weight %, 6 weight %, 5 weight %, 4 weight %, 3 weight %, 2 weight %, 1 weight % and any value in the range formed by any two of these point values.

[0028] The present invention has no particular limitation on the source of the diesel raw material, and any diesel that meets the above requirements is within the applicable scope of the present invention.

[0029] In the prior art, hydrocracking catalysts are usually designed with bimetallic active metal components, and the promoter effect of Group VIII metals is used to maintain a certain hydrogenation activity. The promoter effect of Group VIII metals on Group VI metals in the sulfided state causes the bimetallic sulfided metal system to produce a mutual support effect, thereby accommodating more active hydrogen, so that the monocyclic aromatic hydrocarbons in the reaction product are further saturated into cycloalkanes, so that the total yield of low-carbon aromatic hydrocarbons in the final product is still limited, and the benzene yield is also still limited. The first hydrocracking catalyst of the present invention, which first uses a first carrier containing a Y-type molecular sieve and a monometallic active component to cooperate with a first hydrocracking catalyst, and then uses a second carrier containing an MFI-type molecular sieve and a bimetallic active component to cooperate with a second hydrocracking catalyst, can effectively overcome the above-mentioned defects, and the yield of low-carbon aromatic hydrocarbons has been significantly improved, and the yield of benzene has also been significantly improved.

[0030] In the present invention, the first hydrocracking catalyst comprises a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Y-type molecular sieve and the first metal component is a Group VIB metal component.

[0031] According to the present invention, preferably, based on the total weight of the first hydrocracking catalyst, the content of the first metal component in the first hydrocracking catalyst, calculated as oxide, is 10-35 wt%, preferably 10-30 wt%.

[0032] According to the present invention, preferably, based on the total weight of the first hydrocracking catalyst, the content of the first carrier in the first hydrocracking catalyst is 65-90 wt %, preferably 70-90 wt %.

[0033] In the first hydrocracking catalyst, the sum of the contents of the various components is 100%.

[0034] According to the present invention, preferably, the VIB Group metal component is Mo and / or W, preferably W. This preferred embodiment is advantageous for suppressing the oversaturation of aromatics during the reaction and improving the selectivity of low-carbon aromatics.

[0035] According to the present invention, preferably, the SiO2 / Al2O3 molar ratio of the Y-type molecular sieve is 5-80, preferably 8-30.

[0036] According to the present invention, preferably, the specific surface area of ​​the Y-type molecular sieve is 500-800m 2 / g, preferably 500-750m 2 / g.

[0037] According to the present invention, preferably, the pore volume of the Y-type molecular sieve is 0.1-0.6 mL / g, preferably 0.2-0.5 mL / g.

[0038] The use of Y-type molecular sieves with the above characteristics is beneficial to improving the hydrocracking activity of aromatics above C8 in the diesel fraction, and is more conducive to obtaining low-carbon aromatics.

[0039] In the present invention, the type of the Y-type molecular sieve can be selected from a wide range of types, and can be various Y-type molecular sieves commonly used in the art. Preferably, the Y-type molecular sieve is an ion-modified Y molecular sieve and / or an ultra-stable Y molecular sieve.

[0040] Preferably, the ion modification includes at least one of rare earth ion modification, alkaline earth metal ion modification, transition metal ion modification and phosphorus modification.

[0041] Further preferably, the Y-type molecular sieve is USY molecular sieve. This preferred embodiment is beneficial to improving the ring-opening selectivity of di- / polycyclic aromatic hydrocarbons, thereby improving the yield of low-carbon aromatic hydrocarbons.

[0042] According to the present invention, preferably, in the first hydrocracking catalyst, the first carrier further contains a heat-resistant inorganic oxide.

[0043] The heat-resistant inorganic oxide of the present invention refers to a porous material with a maximum use temperature of not less than 600° C. The heat-resistant inorganic oxide can increase the strength of the hydrocracking catalyst and improve and adjust the physicochemical properties of the hydrocracking catalyst, such as improving the pore structure of the catalyst.

[0044] The present invention has a wide range of heat-resistant inorganic oxides, and various heat-resistant inorganic oxides commonly used in the art can be used. Preferably, the heat-resistant inorganic oxide is selected from at least one of silicon oxide, aluminum oxide, zirconium oxide and titanium oxide, preferably aluminum oxide.

[0045] Preferably, based on the total weight of the first carrier, the content of the Y-type molecular sieve is 40-90 wt%, preferably 50-80 wt%; the content of the heat-resistant inorganic oxide is 10-60 wt%, preferably 20-50 wt%.

[0046] The present invention has no particular limitation on the source of the first hydrocracking catalyst, which can be purchased from commercial sources or prepared by conventional methods in the art.

[0047] In the present invention, the second hydrocracking catalyst comprises a second carrier and a second metal component supported on the second carrier, wherein the second carrier contains an MFI type molecular sieve, and the second metal component comprises Group VIB and Group VIII metal components.

[0048] According to the present invention, preferably, based on the total weight of the second hydrocracking catalyst, the content of the second metal component in the second hydrocracking catalyst, calculated as oxide, is 5-30 wt%, preferably 10-30 wt%.

[0049] According to the present invention, preferably, the mass ratio of the VIB group metal component to the VIII group metal component, calculated as oxide, is 1:0.05-0.4, preferably 1:0.1-0.35.

[0050] In the present invention, the VIB group metal component can be a conventional choice in the art. Preferably, the VIB group metal component is Mo and / or W, preferably Mo. This preferred embodiment is beneficial to suppress the oversaturation of aromatics during the reaction and improve the selectivity of low-carbon aromatics.

[0051] In the present invention, the Group VIII metal component can be selected from conventional materials in the art. Preferably, the Group VIII metal component is Ni and / or Co.

[0052] According to the present invention, preferably, the second hydrocracking catalyst further contains promoter elements and organic additives.

[0053] According to the present invention, preferably, the auxiliary element is selected from at least one of phosphorus, fluorine and boron, preferably phosphorus.

[0054] According to the present invention, preferably, based on the total weight of the second hydrocracking catalyst, the content of the auxiliary agent is 0.1-10 wt % in terms of oxide.

[0055] According to the present invention, preferably, based on the total weight of the second hydrocracking catalyst, the content of the organic additive is 0.5-15 wt%.

[0056] In the second hydrocracking catalyst, the sum of the contents of the various components is 100%.

[0057] According to the present invention, preferably, the organic additive is an oxygen-containing organic compound and / or a nitrogen-containing organic compound, preferably at least one selected from alcohol compounds, carboxylic acid compounds and organic amine compounds.

[0058] The present invention has a wide range of selection for the type of the carboxylic acid compound, which can be various carboxylic acid compounds commonly used in the art. Preferably, the carboxylic acid compound is selected from at least one of acetic acid, maleic acid, oxalic acid, aminotriacetic acid, aminoacetic acid, citric acid, tartaric acid and malic acid.

[0059] The present invention has a wide range of alcohol compound types, which can be various alcohol compounds commonly used in the art. Preferably, the alcohol compound is selected from at least one of ethylene glycol, glycerol, polyethylene glycol, diethylene glycol and butanediol.

[0060] The present invention has a wide range of selection for the type of the organic amine compound, which can be various organic amine compounds commonly used in the art. Preferably, the organic amine compound is selected from at least one of ethylenediamine, diethylenetriamine, cyclohexanediaminetetraacetic acid, ethylenediaminetetraacetic acid and ammonium ethylenediaminetetraacetate.

[0061] According to the present invention, preferably, the SiO2 / Al2O3 molar ratio of the MFI type molecular sieve is 15-300, preferably 20-80.

[0062] According to the present invention, preferably, the specific surface area of ​​the MFI molecular sieve is 180-650m 2 / g, preferably 300-450m 2 / g.

[0063] According to the present invention, preferably, the pore volume of the MFI molecular sieve is 0.1-0.6 mL / g, preferably 0.2-0.5 mL / g.

[0064] The use of MFI molecular sieves with the above characteristics is beneficial to improving the selectivity of low-carbon aromatics.

[0065] In the present invention, the type of the MFI type molecular sieve can be selected in a wide range. Preferably, the MFI type molecular sieve is a ZSM-5 molecular sieve.

[0066] According to the present invention, preferably, in the second hydrocracking catalyst, the second carrier further contains a heat-resistant inorganic oxide.

[0067] The heat-resistant inorganic oxide of the present invention refers to a porous material with a maximum use temperature of not less than 600° C. The heat-resistant inorganic oxide can increase the strength of the hydrocracking catalyst and improve and adjust the physicochemical properties of the hydrocracking catalyst, such as improving the pore structure of the catalyst.

[0068] The present invention has a wide range of heat-resistant inorganic oxides, and various heat-resistant inorganic oxides commonly used in the art can be used. Preferably, the heat-resistant inorganic oxide is selected from at least one of silicon oxide, aluminum oxide, zirconium oxide and titanium oxide, preferably aluminum oxide.

[0069] According to the present invention, preferably, based on the total weight of the second carrier, the content of the MFI molecular sieve is 40-90 wt%, preferably 40-80 wt%; the content of the heat-resistant inorganic oxide is 10-60 wt%, preferably 20-60 wt%.

[0070] The present invention has no particular limitation on the preparation method of the above-mentioned second hydrocracking catalyst, as long as the second hydrocracking catalyst of the above-mentioned composition can be prepared. In order to further improve the catalytic performance of the second hydrocracking catalyst, the present invention also provides a preparation method of the above-mentioned second hydrocracking catalyst.

[0071] Preferably, the preparation method of the second hydrocracking catalyst comprises the following steps:

[0072] (a) mixing an MFI molecular sieve and an optional heat-resistant inorganic oxide precursor to prepare a second carrier;

[0073] (b) introducing the second metal component and optionally the auxiliary agent and optionally the organic additive onto the second support by impregnation.

[0074] In the present invention, the method for preparing the second carrier in step (a) is well known to those skilled in the art, and the present invention has no particular limitation on this. For example, the method in step (a) may include: mixing and molding the MFI molecular sieve with an optional heat-resistant inorganic oxide precursor, and then drying and calcining to obtain the second carrier. The heat-resistant inorganic oxide precursor may be a conventional choice in the art. The molding in step (a) may be carried out by any conventional method in the art, for example, the molding may be carried out by tablet molding, ball rolling molding or extrusion molding. The drying and calcining conditions in step (a) may be carried out by conventional methods in the art, and the present invention has no particular limitation on this.

[0075] The present invention also has no particular limitation on the shape of the second carrier, which may be spherical, bar-shaped (including solid or hollow bars), block-shaped, etc. The bar-shaped may be a clover-shaped, four-leaf clover-shaped, or other multi-leaf clover-shaped or deformed forms thereof.

[0076] According to the present invention, preferably, the process of step (b) comprises: impregnating the second support with an impregnation solution containing a second metal precursor, an optional auxiliary agent precursor and an optional organic additive, followed by drying and optionally calcining.

[0077] Preferably, the second metal precursor is a soluble compound of the second metal, preferably selected from at least one of an oxide of the second metal, an inorganic salt of the second metal, and an organic substance of the second metal. For example, the inorganic salt of the second metal may be selected from at least one of a nitrate of the second metal, a carbonate of the second metal, a basic carbonate of the second metal, a hypophosphite of the second metal, a phosphate of the second metal, a sulfate of the second metal, and a chloride of the second metal. The organic substituent in the organic substance of the second metal may be selected from at least one of a hydroxyl group, a carboxyl group, an amine group, a ketone group, an ether group, and an alkyl group.

[0078] The auxiliary agent precursor of the present invention can be any conventional choice in the art, as long as it contains an auxiliary agent, for example, a soluble salt of an auxiliary agent, an inorganic acid of an auxiliary agent, etc.

[0079] The present invention has no particular limitation on the order of adding the above substances in step (b), and they can be added together or separately. The present invention adopts the method of adding together as an example.

[0080] The present invention has no particular limitation on the type and amount of the solvent in the impregnation solution containing the second metal precursor, and the method can be carried out according to conventional methods in the art.

[0081] The present invention does not have any particular limitation on the contact temperature of step (b), which can be any temperature that the impregnation liquid can reach. There is no particular limitation on the contact time, as long as the required amount of metal precursor can be loaded on the carrier. In general, the higher the contact temperature and the greater the concentration of the impregnation liquid, the shorter the time required to reach the same impregnation amount (i.e., the weight difference between the carrier after impregnation and before impregnation); and vice versa. Once the required impregnation amount and conditions are determined, it is easy to select a suitable contact time. The specific operation of the impregnation method is well known to those skilled in the art, and the impregnation method can be a saturated impregnation method or a supersaturated impregnation method. There is no particular limitation on the environment of the impregnation method. According to conventional methods in the art, it can be carried out under sealed conditions or in an open environment. The lost solvent can be replenished during the contact process, or it can not be replenished. Various gases, such as air, nitrogen, water vapor, etc., can be introduced during the contact process, or no new components can be introduced.

[0082] The drying in step (b) is a conventional step for preparing a catalyst and is not particularly limited. For example, the drying conditions in step (b) may be: a temperature of 80-350°C, preferably 100-300°C; a time of 0.5-24 hours, preferably 1-12 hours. The calcination conditions in step (b) may be: a temperature of 350-600°C, preferably 400-550°C; a time of 0.2-12 hours, preferably 1-10 hours.

[0083] The present invention has a wide range of conditions for the hydrofining reaction, which can be carried out according to conventional methods in the art. Preferably, the conditions for the hydrofining reaction in step (1) include: a reaction temperature of 320-410°C; a reaction pressure of 4-18 MPa; a hydrogen-to-oil volume ratio of 300-800:1; a liquid hourly space velocity of 0.5-3h -1 .

[0084] The present invention has no particular limitation on the type of the hydrotreating catalyst, which can be selected conventionally in the art. The hydrotreating catalyst can be obtained commercially or prepared by conventional methods in the art.

[0085] According to the present invention, preferably, the conditions of the first hydrocracking reaction include: reaction pressure of 3-9 MPa; reaction temperature of 370-420°C; hydrogen-oil volume ratio of 300-900:1; liquid hourly space velocity of 0.5-3h -1 .

[0086] According to the present invention, preferably, the conditions of the second hydrocracking reaction include: reaction pressure of 3-9 MPa; reaction temperature of 375-440°C; hydrogen-oil volume ratio of 300-900:1; liquid hourly space velocity of 0.5-4h -1 .

[0087] In the present invention, the first hydrocracking catalyst and the second hydrocracking catalyst may be loaded in different reaction zones of the same reactor, or may be loaded in different reactors. The selection may be made according to actual conditions, and the present invention has no particular limitation on this.

[0088] The hydrocracking reaction of the present invention can be carried out in any reactor that is sufficient to allow the hydrocarbon feedstock to contact and react with the catalyst under hydrogenation reaction conditions, for example, it can be a fixed bed reactor, a moving bed reactor, an ebullating bed reactor or a slurry bed reactor, and the present invention has no particular limitation on this.

[0089] Preferably, the low-carbon aromatic hydrocarbons are C6-C8 aromatic hydrocarbons.

[0090] Preferably, the second hydrocracking reaction product is separated to obtain a light naphtha component and a gasoline fraction. The specific separation method can refer to conventional methods of those skilled in the art, such as fractional distillation, etc., which will not be described in detail in the present invention.

[0091] Preferably, the first hydrocracking catalyst and the second hydrocracking catalyst are presulfided before use.

[0092] The present invention has no particular limitation on the specific conditions of the pre-sulfurization, and the pre-sulfurization can be carried out according to the commonly used methods in the art.

[0093] The pre-sulfurization of the present invention can be carried out outside the vessel, or in-situ sulfidation can be carried out inside the vessel to convert it into a sulfide type.

[0094] The present invention will be described in detail below through examples.

[0095] In the following examples, the pore volume and specific surface area of ​​the molecular sieve are measured by a static low-temperature adsorption capacity method (using the national standard GB / T5816-1995 method) using an ASAP2400 automatic adsorption instrument from Micromertics Instruments, Inc., USA. The specific method is as follows: vacuum degassing for 4 h at 250°C and 1.33 Pa, using nitrogen as the adsorbate, contacting with the adsorbate at -196°C, and statically reaching adsorption equilibrium; the amount of nitrogen adsorbed by the adsorbent is calculated from the difference between the nitrogen intake and the amount remaining in the gas phase after adsorption, and then the pore size distribution is calculated using the BJH formula, and the specific surface area and pore volume are calculated using the BET formula;

[0096] The crystal structure of the molecular sieve was determined using a D5005 X-ray diffractometer from Siemens, Germany, using the industry standard SH / T0339-92 method. Experimental conditions: Cu target, Ka radiation, solid detector, tube voltage 40kV, tube current 40mA, step scan, step width 0.02°, prefabrication time 2s, scanning range 5°~70°. The diffraction angle position refers to the 2θ angle value of the highest value of the diffraction peak;

[0097] The silicon-aluminum ratio of the molecular sieve was determined by using a 3271E X-ray fluorescence spectrometer produced by Rigaku Corporation of Japan. The determination method is as follows: the powder sample was pressed into tablets, a rhodium target, a laser voltage of 50 kV, a laser current of 50 mA, a scintillation counter and a proportional counter were used to detect the intensity of the spectral lines of each element, and the external standard method was used to perform quantitative and semi-quantitative analysis of the element content.

[0098] The content of each component of the catalyst is calculated by the feed amount.

[0099] Example 1

[0100] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71 wt% on dry basis) and USY molecular sieve (85 wt% on dry basis, specific surface area of ​​568 m 2 / g, SiO2 / Al2O3 molar ratio of 23, pore volume of 0.40mL / g) were mixed, extruded into trilobal strips with a circumscribed circle diameter of 1.6 mm, dried at 120°C for 3h, and calcined at 550°C for 3h to obtain the first carrier. Then, it was impregnated with 75mL aqueous solution containing ammonium metatungstate, dried at 120°C for 3h, and calcined at 480°C for 4h to obtain the first hydrocracking catalyst C-USY-1. Its composition is shown in Table 1.

[0101] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71 wt% on dry basis) and ZSM-5 molecular sieve (95 wt% on dry basis, specific surface area 325 m 2 / g, silicon aluminum molar ratio of 23, pore volume of 0.28mL / g) were mixed, extruded into a trilobal strip with an circumscribed circle diameter of 1.6 mm, dried at 120°C for 3 hours, and calcined at 600°C for 3 hours to obtain a second carrier. At room temperature, 75mL of an aqueous solution containing molybdenum oxide, nickel carbonate with a nickel oxide weight content of 51%, phosphoric acid with a phosphorus oxide weight content of 61%, and citric acid was impregnated into the second carrier prepared by the above method, and dried at 120°C for 3 hours to obtain a second hydrocracking catalyst C-MFI-1. Its composition is shown in Table 1.

[0102] The preparation of the hydrorefined raw material (LCO-QD) described in Table 2 was carried out on a fixed bed hydrocracking unit using an industrial hydrorefining catalyst RS-2100 (produced by the Changling Catalyst Company), a reaction pressure of 6.4 MPa, a reaction temperature of 335°C, a hydrogen-to-oil volume ratio of 300, and a liquid hourly space velocity of 2 h -1 After the reaction is completed, the pressure is released to room temperature and pressure to obtain a liquid product, which is washed and filtered to obtain an oil phase (LCO-HT) with a total nitrogen content of 20 μg / g.

[0103] Along the logistics direction, C-USY-1 and C-MFI-1 were placed in two reactors in sequence on a fixed bed hydrocracking unit for two hydrocracking reactions. The above catalyst was subjected to programmed temperature sulfurization before use: using straight-run kerosene containing 2% dimethyl disulfide as sulfurized oil, the temperature was increased from 110°C to 230°C at a rate of 20°C / h, and maintained for 6 hours; then the temperature was increased to 360°C at a rate of 20°C / h, and maintained for 6 hours.

[0104] The reaction pressure is 6.4 MPa, the hydrogen-oil volume ratio is 600, the temperature of the first hydrocracking reaction is 400°C, and the liquid hourly space velocity of the first hydrocracking reaction is 1.67 h -1The temperature of the second hydrocracking reaction is 410°C, and the liquid hourly space velocity of the second hydrocracking reaction is 2h -1 The analysis results of the light naphtha fraction and gasoline fraction in the obtained product are shown in Table 3. Among them, the second hydrocracking reaction product is separated by fractionation, the cutting temperature of the light naphtha and gasoline fraction is 65°C, and the cutting temperature of gasoline and heavy components is 180°C, and the following embodiments are all.

[0105] Example 2

[0106] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71 wt% on dry basis) and USY molecular sieve (75 wt% on dry basis, specific surface area of ​​680 m 2 / g, silicon aluminum molar ratio of 11, pore volume of 0.36mL / g) were mixed, extruded into a trilobal strip with an circumscribed circle diameter of 1.6 mm, dried at 120°C for 3h, and calcined at 550°C for 3h to obtain the first carrier. Then, it was impregnated with 75mL of an aqueous solution containing 41.2g of ammonium metatungstate, dried at 120°C for 3h, and calcined at 480°C for 4h to obtain the first hydrocracking catalyst C-USY-2. Its composition is shown in Table 1.

[0107] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71 wt% on dry basis) and ZSM-5 molecular sieve (95 wt% on dry basis, specific surface area 423 m 2 / g, silicon aluminum molar ratio of 60, pore volume of 0.4mL / g) were mixed, extruded into trilobal strips with an circumscribed circle diameter of 1.6 mm, dried at 120°C for 3h, and calcined at 600°C for 3h to obtain a second carrier. At room temperature, 75mL of an aqueous solution containing molybdenum oxide, nickel carbonate with a weight content of 51% nickel oxide, phosphoric acid with a weight content of 61% phosphorus oxide, 20g of tartaric acid, and 3g of ethylene glycol was impregnated with the second carrier prepared by the above method, and dried at 120°C for 3h to obtain a second hydrocracking catalyst C-MFI-2. Its composition is shown in Table 1.

[0108] The feedstock (LCO-QD) described in Table 2 was hydrotreated in a fixed-bed hydrocracking unit using hydrotreating catalyst RS-2100 (produced by Catalyst Changling Branch), reaction pressure 6.4 MPa, reaction temperature 335 °C, hydrogen-to-oil volume ratio 300, liquid hourly space velocity 2 h -1 After the reaction is completed, the pressure is released to normal temperature and pressure to obtain a liquid product, and the liquid product is washed and filtered to obtain an oil phase (LCO-HT) with a total nitrogen content of 5 μg / g.

[0109] In a fixed bed hydrocracking unit, C-USY-2 and C-MFI-2 were placed in two reactors in sequence for hydrocracking reaction. Before using the above catalyst, the above catalyst was subjected to programmed temperature rise sulfurization: using straight run kerosene containing 2% dimethyl disulfide by mass as sulfurized oil, the temperature was raised from 110°C to 230°C at a rate of 20°C / h, and maintained for 6h; then the temperature was raised to 360°C at a rate of 20°C / h, and maintained for 6h.

[0110] Reaction pressure 8.5MPa, hydrogen-oil volume ratio 800, first hydrocracking reaction temperature 380℃, first hydrocracking reaction liquid hourly space velocity 1h -1 The second hydrocracking reaction temperature is 400°C, and the second hydrocracking reaction liquid hourly space velocity is 2h -1 The analysis results of the light naphtha fraction and gasoline fraction in the obtained product are shown in Table 3.

[0111] Table 1

[0112]

[0113] Example 3

[0114] The method of Example 1 was followed, except that the temperature of the second hydrocracking reaction was changed to 440° C. The results are shown in Table 3.

[0115] Example 4

[0116] The method of Example 1 was followed, except that the carrier of the first hydrocracking catalyst was a Y-type molecular sieve containing MoNi. Specifically, at room temperature, 75 mL of an aqueous solution containing 51% by weight of basic nickel carbonate containing molybdenum oxide and nickel oxide was impregnated into the USY-type molecular sieve described in Example 1, dried at 120° C. for 3 h, and calcined at 450° C. for 4 h to obtain a Y-type molecular sieve containing MoNi, wherein the mass content of nickel oxide was 2.6% and the mass content of molybdenum oxide was 9.2% based on the total mass of the Y-type molecular sieve containing MoNi, calculated as oxide. The evaluation results are shown in Table 3.

[0117] Comparative Example 1

[0118] The hydrocracking activity test was carried out on a fixed-bed hydrocracking unit using the feedstock (LCO-QD) described in Table 2. The refining section used the industrial catalyst RN-411 (produced by Sinopec Catalyst Changling Branch), and the cracking section used the industrial catalyst RHC-220 (produced by Sinopec Catalyst Changling Branch). The volume ratio of the refining catalyst to the cracking catalyst was 0.428, the reaction pressure was 6.4 MPa, the reaction temperature was 410°C, the hydrogen-to-oil volume ratio was 700, and the refined liquid hourly space velocity was 1.25 h -1The total nitrogen content at the outlet of the refining section was analyzed to be 187μg / g. The cracking reaction products were separated by fractionation, with the cutting temperature of light naphtha and gasoline fraction being 65℃ and the cutting temperature of gasoline and heavy fraction being 180℃.

[0119] The light naphtha fraction and gasoline fraction in the generated oil were subjected to PONA analysis, and the results are shown in Table 3.

[0120] Comparative Example 2

[0121] The method of Comparative Example 1 was followed, except that the cracking catalyst was replaced with RHC-210 industrial catalyst (produced by the Changling Catalyst Company). PONA analysis was performed on the light naphtha fraction and gasoline fraction in the generated oil. The results are shown in Table 3.

[0122] Comparative Example 3

[0123] The method of comparative example 1 was followed, except that the cracking catalyst was replaced with D-1. The preparation method of D-1 was as follows: 158 g of pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71 wt% on dry basis) and 422 g of ZSM-5 molecular sieve (produced by Sinopec Catalyst Jianchang Branch, with a specific surface area of ​​325 m 2 / g, framework silicon-aluminum ratio of 70, pore volume of 0.31mL / g, dry basis 80 wt%), extruded into a trilobal strip with a circumscribed circle diameter of 1.6 mm, dried at 120°C for 3h, and calcined at 600°C for 3h to obtain a carrier. After cooling to room temperature, 50g of the above-prepared carrier was impregnated with 60mL of an aqueous solution containing 13.7g of tungsten oxide and a weight content of 91% ammonium metatungstate, dried at 120°C for 3h, and calcined at 480°C for 4h to obtain catalyst D-1.

[0124] The light naphtha fraction and gasoline fraction in the generated oil were subjected to PONA analysis, and the results are shown in Table 3.

[0125] Comparative Example 4

[0126] The method of Example 1 was followed, except that C-USY-1 and C-MFI-1 were swapped, i.e., C-MFI-1 was used in the first hydrocracking reaction, and C-USY-1 was used in the second hydrocracking reaction. The results are shown in Table 3.

[0127] Table 2

[0128]

[0129] Table 3

[0130]

[0131]

[0132] It can be seen from the results in Table 3 that the method of the present invention can obtain significantly higher yields of light aromatics.

[0133] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for producing more low-carbon aromatics, characterized in that: The method comprises the following steps: (1) subjecting hydrogen and diesel to a hydrotreating catalyst for hydrotreating reaction, and then treating the resultant hydrotreating effluent so that the total nitrogen content in the effluent is less than 50 μg / g; (2) subjecting the hydroprocessing effluent to a first hydrocracking reaction with a first hydrocracking catalyst to obtain a first product, wherein the first hydrocracking catalyst comprises a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Y-type molecular sieve and the first metal component is a Group VIB metal component; (3) subjecting the first product obtained in step (2) to a second hydrocracking reaction with a second hydrocracking catalyst, wherein the second hydrocracking catalyst comprises a second carrier and a second metal component supported on the second carrier, wherein the second carrier comprises an MFI molecular sieve, and the second metal component comprises a Group VIB metal component and a Group VIII metal component; Wherein, the reaction temperature of the second hydrocracking reaction is higher than the reaction temperature of the first hydrocracking reaction.

2. The method according to claim 1, wherein: The density of the diesel is 0.85-0.96 g / cm 3 , the distillation range is 180-375°C, and the content of paraffin in the diesel is less than 15% by weight.

3. The method according to claim 1, wherein: Based on the total weight of the first hydrocracking catalyst, the first metal component content in the first hydrocracking catalyst, calculated as oxide, is 10-35 wt%, preferably 10-30 wt%; and / or Based on the total weight of the first hydrocracking catalyst, the content of the first carrier in the first hydrocracking catalyst is 65-90% by weight, preferably 70-90% by weight; Preferably, the VIB Group metal component is Mo and / or W, preferably W.

4. The method according to any one of claims 1 to 3, wherein: The SiO2 / Al2O3 molar ratio of the Y-type molecular sieve is 5-80, preferably 8-30; the specific surface area of ​​the Y-type molecular sieve is 500-800m 2 / g, preferably 500-750m 2 / g; the pore volume of the Y-type molecular sieve is 0.1-0.6mL / g, preferably 0.2-0.5mL / g; Preferably, the Y-type molecular sieve is USY molecular sieve.

5. The method according to any one of claims 1 to 4, wherein: In the first hydrocracking catalyst, the first carrier further comprises a heat-resistant inorganic oxide; Preferably, based on the total weight of the first carrier, the content of the Y-type molecular sieve is 40-90% by weight, preferably 50-80% by weight; the content of the heat-resistant inorganic oxide is 10-60% by weight, preferably 20-50% by weight; Preferably, the heat-resistant inorganic oxide is selected from at least one of silicon oxide, aluminum oxide, zirconium oxide and titanium oxide.

6. The method according to any one of claims 1 to 5, wherein: Based on the total weight of the second hydrocracking catalyst, the content of the second metal component in the second hydrocracking catalyst, calculated as oxide, is 5-30 wt%, preferably 10-30 wt%; Preferably, the mass ratio of the Group VIB metal component to the Group VIII metal component, calculated as oxide, is 1:0.05-0.4, preferably 1:0.1-0.35; Preferably, the VIB Group metal component is Mo and / or W, preferably Mo; Preferably, the Group VIII metal component is Ni and / or Co.

7. The method according to any one of claims 1 to 6, wherein: The second hydrocracking catalyst also contains promoter elements and organic additives; Preferably, based on the total weight of the second hydrocracking catalyst, the content of the additive is 0.1-10 wt % in terms of oxide; Preferably, the auxiliary element is selected from at least one of phosphorus, fluorine and boron, preferably phosphorus; Preferably, the content of the organic additive is 0.5-15 wt % based on the total weight of the second hydrocracking catalyst; Preferably, the organic additive is an oxygen-containing organic compound and / or a nitrogen-containing organic compound, preferably at least one selected from alcohol compounds, carboxylic acid compounds and organic amine compounds; Preferably, the carboxylic acid compound is selected from at least one of acetic acid, maleic acid, oxalic acid, aminotriacetic acid, aminoacetic acid, citric acid, tartaric acid and malic acid; Preferably, the alcohol compound is selected from at least one of ethylene glycol, glycerol, polyethylene glycol, diethylene glycol and butanediol; Preferably, the organic amine compound is selected from at least one of ethylenediamine, diethylenetriamine, cyclohexanediaminetetraacetic acid, ethylenediaminetetraacetic acid and ammonium ethylenediaminetetraacetate.

8. The method according to any one of claims 1 to 7, wherein: The SiO2 / Al2O3 molar ratio of the MFI molecular sieve is 15-300, preferably 20-80; the specific surface area is 180-650m 2 / g, preferably 300-450m 2 / g; the pore volume is 0.1-0.6mL / g, preferably 0.2-0.5mL / g; Preferably, the MFI type molecular sieve is a ZSM-5 molecular sieve; Preferably, in the second hydrocracking catalyst, the second carrier further comprises a heat-resistant inorganic oxide; Preferably, based on the total weight of the second carrier, the content of the MFI molecular sieve is 40-90% by weight, preferably 40-80% by weight; the content of the heat-resistant inorganic oxide is 10-60% by weight, preferably 20-60% by weight; Preferably, the heat-resistant inorganic oxide is selected from at least one of silicon oxide, aluminum oxide, zirconium oxide and titanium oxide.

9. The method according to any one of claims 1 to 8, wherein: The reaction temperature of the second hydrocracking reaction is 5-30° C. higher than the reaction temperature of the first hydrocracking reaction.

10. The method according to any one of claims 1 to 9, wherein: The conditions of the hydrotreating reaction in step (1) include: reaction temperature of 320-410°C; reaction pressure of 4-18 MPa; hydrogen-oil volume ratio of 300-800:1; liquid hourly space velocity of 0.5-3h -1 ; Preferably, the conditions of the first hydrocracking reaction include: reaction pressure of 3-9 MPa; reaction temperature of 370-420°C; hydrogen-oil volume ratio of 300-900:1; liquid hourly space velocity of 0.5-3h -1 ; Preferably, the conditions of the second hydrocracking reaction include: reaction pressure of 3-9 MPa; reaction temperature of 375-440°C; hydrogen-oil volume ratio of 300-900:1; liquid hourly space velocity of 0.5-4h -1 .

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