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

Abstract

The invention relates to the field of low-carbon aromatic hydrocarbon production, and discloses a method for catalytically producing high-yield low-carbon aromatic hydrocarbon by adopting a Beta-type molecular sieve-containing catalyst and a shape-selective zeolite-containing catalyst. The method comprises the following steps: carrying out hydrofining reaction on hydrogen and diesel oil fractions 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 Beta 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 first hydrocracking reaction temperature is higher than the second hydrocracking reaction temperature. According to the method, high-yield low-carbon aromatic hydrocarbon is 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 Beta-type molecular sieve catalyst and a shape-selective zeolite catalyst. Background Art

[0002] At present, my country has a large demand for C6-C8 low-carbon aromatics, and the main products with industrial value are 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. Para-xylene can be used as a raw material for PTA, and then produce polyester, spinning, polyester and other synthetic fiber products. The existing industrial methods for producing low-carbon aromatics are mainly separated from catalytic reforming production oil, coal tar, and cracking oil, and can also be produced through disproportionation and toluene dealkylation reactions. These processes have the disadvantages of high reaction temperature (500-600℃) and complex raw materials.

[0003] Industrial hydrocracking has the characteristics of low reaction temperature, simple feed and process. Its raw materials 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 breaking in this process is usually based on Beta cracking, that is, the breaking 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). This problem can be effectively avoided by using inferior diesel fractions rich in aromatics with a lower distillation range.

[0004] CN201310520012.2 discloses a method for producing high-octane gasoline components or BTX raw materials by hydro-reforming. In this method, low-quality diesel is mixed with hydrogen-rich gas and then enters the hydro-refining reaction zone, contacts and reacts with the hydro-refining catalyst, and the reaction effluent of the hydro-refining reaction zone enters the hydro-reforming reaction zone without any intermediate separation facilities, and contacts and reacts with the first hydro-reforming catalyst and the second hydro-reforming catalyst in turn, and the effluent of the hydro-reforming reaction zone is cooled and separated to obtain hydrogen-rich gas and liquid products. By adopting the method provided by the present invention, high-octane gasoline can be produced with low-quality diesel fraction as raw material, and the BTX content in the high-octane gasoline fraction can reach more than 40%.

[0005] The above method uses graded hydrocracking intervals to obtain a certain amount of naphtha fractions with a high BTX content, but the refined hydrogenated 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 reactions on the molecular sieve. Among them, inorganic ammonia molecules, due to their small molecular diameter, will pass through the pores in the catalyst and then adsorb on the acidic centers on the inner surface of the catalyst, thereby weakening the cracking activity of the catalyst; organic nitrogen molecules, due to their large molecular diameter, are easily adsorbed on the acidic centers on the outer surface of the catalyst, 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 promoter effect of Group VIII metals is used to maintain a certain hydrogenation activity. Due to the auxiliary effect of Group VIII metals on Group VI metals in the sulfided state, the catalyst has a higher hydrogenation function and a stronger ability to saturate aromatics. Due to the mutual support effect of the bimetallic sulfide metal system, the system may accommodate more active hydrogen, thereby promoting the reaction of saturation of aromatics to cycloalkanes, so that the total yield of aromatics in the final product is still limited. Summary of the invention

[0006] 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 Beta-type molecular sieve catalyst and a shape-selective zeolite catalyst. The method can obtain a higher yield of low-carbon aromatics.

[0007] In order to achieve the above object, the present invention provides a method for producing more low-carbon aromatics, which comprises the following steps:

[0008] (1) subjecting hydrogen and diesel fraction to a hydrotreating catalyst for hydrotreating reaction, and then treating the resultant hydrotreating effluent so that the total nitrogen content is less than 50 μg / g;

[0009] (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 Beta molecular sieve and the first metal component is a Group VIB metal component;

[0010] (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 VIB group and a VIII group metal component;

[0011] Wherein, the reaction temperature of the first hydrocracking reaction is higher than the reaction temperature of the second hydrocracking reaction.

[0012] Through the above technical solution, the beneficial effects of the present invention include:

[0013] The method provided by the present invention first controls the total nitrogen content in the hydroprocessing effluent to be lower than 50 μg / g, and then adopts a first hydrocracking catalyst composed of a first carrier containing a specific type of Beta molecular sieve and a monometallic active component and a second hydrocracking catalyst composed of a second carrier containing an MFI molecular sieve and a bimetallic active component, which are reasonably graded, to carry out secondary continuous hydrocracking reactions and control the temperature of the first hydrocracking reaction to be higher than the temperature of the second hydrocracking reaction, which is beneficial to improving the yield of low-carbon aromatics. DETAILED DESCRIPTION

[0014] 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.

[0015] 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.

[0016] In the present invention, "optional" means not essential, and can be understood as including or not including.

[0017] In the present invention, the density of the diesel fraction is the density at 20°C.

[0018] In one aspect, the present invention provides a method for producing more low-carbon aromatics, the method comprising the following steps:

[0019] (1) subjecting hydrogen and diesel fraction to a hydrotreating catalyst for hydrotreating reaction, and then treating the resultant hydrotreating effluent so that the total nitrogen content is less than 50 μg / g;

[0020] (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 Beta molecular sieve and the first metal component is a Group VIB metal component;

[0021] (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 VIB group and a VIII group metal component;

[0022] Wherein, the reaction temperature of the first hydrocracking reaction is higher than the reaction temperature of the second hydrocracking reaction.

[0023] In the present invention, the total nitrogen content in the hydroprocessing effluent is less than 50 μg / g, preferably less than 30 μg / g. By adopting this preferred embodiment, the inhibitory effect of inorganic ammonia generated by the hydroprocessing reaction on the metal active centers and the molecular sieve active centers can be reduced.

[0024] 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 in the obtained hydroprocessing effluent is less than 50 μg / g.

[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, which usually exist in the form of side chains, so as to maintain a certain boiling range in the mixture. The reaction occurring on 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 cleavage in this process is usually based on Beta cracking, that is, the cleavage of the ortho-position chemical bonds of the positive carbon ion coordination chemical bonds, which makes the reaction products 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 boiling range and higher aromatic and cycloalkanes content, so that the components in the diesel fraction are more easily converted into low-carbon aromatics, thereby improving the selectivity of low-carbon aromatics.

[0026] Preferably, the density of the diesel is 0.85-0.96 g / 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 3 and any value in the range formed by any two of these point values.

[0027] Preferably, the distillation range of the diesel is 180-375°C.

[0028] 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.

[0029] The present invention has no particular limitation on the source of the diesel raw material, and any diesel fraction that meets the above requirements is within the applicable scope of the present invention.

[0030] 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. Due to the promoter effect of Group VIII metals on Group VI metals in the sulfided state, the catalyst has a higher hydrogenation function and a stronger ability to saturate aromatics; due to the mutual support effect of the bimetallic sulfided metal system, more active hydrogen can be accommodated in the system, thereby promoting the reaction of saturation of aromatics to cycloalkanes, so that the total yield of aromatics in the final product is still limited. The first hydrocracking catalyst containing a first carrier of a Beta-type molecular sieve and a monometallic active component is first used, and then a second hydrocracking catalyst containing a second carrier of an MFI-type molecular sieve and a bimetallic active component is used. The above-mentioned defects can be effectively overcome, and the yield of low-carbon aromatics is significantly improved.

[0031] 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 Beta molecular sieve and the first metal component is a Group VIB metal component.

[0032] 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 5-30 wt%, preferably 10-25 wt%.

[0033] 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 70-95% by weight, preferably 75-90% by weight.

[0034] In the first hydrocracking catalyst, the sum of the contents of the various components is 100%.

[0035] 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.

[0036] According to the present invention, preferably, the SiO2 / Al2O3 molar ratio of the Beta molecular sieve is 5-300, preferably 25-150.

[0037] According to the present invention, preferably, the specific surface area of ​​the Beta molecular sieve is 150-450m 2 / g, preferably 300-450m 2 / g.

[0038] According to the present invention, preferably, the pore volume of the Beta molecular sieve is 0.1-0.6 mL / g, preferably 0.2-0.5 mL / g.

[0039] The use of Beta molecular sieves with the above characteristics is beneficial to improving the cracking activity, thereby increasing the relative content of low-carbon aromatic components in the gasoline fraction.

[0040] According to the present invention, preferably, in the first hydrocracking catalyst, the first carrier further contains a heat-resistant inorganic oxide.

[0041] 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.

[0042] 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.

[0043] According to the present invention, preferably, based on the total weight of the first carrier, the content of the Beta 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%.

[0044] The present invention has no particular limitation on the preparation method of the first hydrocracking catalyst, as long as the first hydrocracking catalyst of the above composition can be prepared, and the catalyst can be purchased commercially or prepared by conventional methods.

[0045] 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.

[0046] 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%.

[0047] 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 1:0.05-4, preferably 1:0.08-0.35.

[0048] 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.

[0049] 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.

[0050] According to the present invention, preferably, the second hydrocracking catalyst further contains a promoter element.

[0051] According to the present invention, preferably, the auxiliary element is selected from at least one of phosphorus, fluorine and boron, preferably phosphorus.

[0052] 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.

[0053] According to the present invention, preferably, the second hydrocracking catalyst further contains an organic additive.

[0054] 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%.

[0055] In the second hydrocracking catalyst, the sum of the contents of the various components is 100%.

[0056] According to the present invention, preferably, the organic additive is selected from at least one of alcohol compounds, carboxylic acid compounds and organic amine compounds.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] According to the present invention, preferably, the SiO2 / Al2O3 molar ratio of the MFI type molecular sieve is 15-300, preferably 20-80.

[0061] 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.

[0062] 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.

[0063] The use of MFI molecular sieves with the above characteristics is beneficial to further improve the selectivity of low-carbon aromatics.

[0064] 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.

[0065] According to the present invention, preferably, in the second hydrocracking catalyst, the second carrier further contains a heat-resistant inorganic oxide. The use of 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.

[0066] 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%.

[0067] The present invention has a wide range of choices for the types 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.

[0068] 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.

[0069] Preferably, the preparation method of the second hydrocracking catalyst comprises the following steps:

[0070] (a) mixing an MFI molecular sieve and an optional heat-resistant inorganic oxide precursor to prepare a second carrier;

[0071] (b) introducing the second metal component and optionally the auxiliary agent and optionally the organic additive onto the second support by impregnation.

[0072] 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.

[0073] 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.

[0074] Preferably, the process of step (b) comprises: contacting 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.

[0075] 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.

[0076] The auxiliary agent precursor of the present invention can be any conventional choice in the art, as long as it contains auxiliary agent elements, for example, soluble salts of auxiliary agents, inorganic acids of auxiliary agents, etc.

[0077] 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.

[0078] The present invention has no particular limitation on the type and amount of the solvent in the impregnation solution, and the impregnation solution can be prepared according to conventional methods in the art.

[0079] 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.

[0080] The drying and calcining in step (b) are conventional steps for preparing catalysts and are 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 calcining 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.

[0081] 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 .

[0082] The present invention has no particular limitation on the type of the hydrotreating catalyst, which can be any conventional catalyst in the art.

[0083] The hydrotreating catalyst of the present invention can be obtained commercially or prepared by conventional methods in the art.

[0084] According to the present invention, preferably, the reaction temperature of the first hydrocracking reaction is 5-30° C. higher than the reaction temperature of the second hydrocracking reaction. This preferred embodiment is conducive to the first hydrocracking catalyst and the second hydrocracking catalyst to exert their respective advantages, synergistically act, and further improve the yield of light aromatics.

[0085] According to the present invention, preferably, the conditions of the first hydrocracking reaction include: reaction pressure of 2-8 MPa; reaction temperature of 370-440°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 2-8 MPa; reaction temperature of 365-425°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 content and aluminum content of the molecular sieve were 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 was used, 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 catalyst components is calculated by the feed amount.

[0099] Example 1

[0100] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 68 wt% on dry basis) and Beta molecular sieve (85 wt% on dry basis, specific surface area 423 m 2 / g, SiO2 / Al2O3 molar ratio of 27, pore volume of 0.39mL / 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 the first carrier. The first carrier was impregnated with 152mL of an aqueous solution containing 55g of ammonium metatungstate, dried at 120°C for 3h, and calcined at 480°C for 4h to obtain the first hydrocracking catalyst C-Beta-1. The 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 of ​​336 m 2 / g, SiO2 / Al2O3 molar ratio of 26, pore volume of 0.29mL / 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 27.7g of molybdenum oxide, 15.1g of basic nickel carbonate with a nickel oxide weight content of 51%, 11.1g of phosphoric acid with a phosphorus oxide weight content of 61%, and 15.1g of citric acid 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-1. The 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 normal temperature and pressure to obtain a liquid product. The obtained liquid product 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-Beta-1 and C-MFI-1 are placed in two reactors in sequence on a fixed-bed hydrocracking unit for hydrocracking reaction. The above catalyst is subjected to programmed temperature sulfurization before use: straight-run kerosene containing 2% dimethyl disulfide by mass is used as the sulfurized oil, and the temperature is increased from 110°C to 230°C at a rate of 20°C / h and maintained for 6 hours; then the temperature is increased to 360°C at a rate of 20°C / h and maintained for 6 hours. The reaction pressure is 6.4MPa, the hydrogen-to-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 1.67h -1 The temperature of the second hydrocracking reaction is 390°C, and the liquid hourly space velocity of the second hydrocracking reaction is 2h -1The gasoline fraction analysis results in the obtained product are shown in Table 3. The second hydrocracking reaction product is separated by fractionation, the cutting temperature of 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.

[0104] Example 2

[0105] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 68 wt% on dry basis) and Beta molecular sieve (82 wt% on dry basis, specific surface area of ​​360 m 2 / g, SiO2 / Al2O3 molar ratio of 120, pore volume of 0.45mL / 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 the first carrier. The first carrier was impregnated with 152mL aqueous solution containing 55g ammonium metatungstate, dried at 120°C for 3h, and calcined at 480°C for 4h to obtain catalyst C-Beta-2. The composition is shown in Table 1.

[0106] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71 wt% on dry basis) and ZSM-5 molecular sieve (89 wt% on dry basis, specific surface area of ​​406 m 2 / g, silicon aluminum molar ratio of 65, pore volume of 0.37mL / 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 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, and 14g EDTA was impregnated with the second carrier prepared by the above method, and dried at 120°C for 3h to obtain catalyst C-MFI-2. The composition is shown in Table 1.

[0107] 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 normal temperature and pressure to obtain a liquid product. The obtained liquid product is washed and filtered to obtain an oil phase (LCO-HT) with a total nitrogen content of 14 μg / g.

[0108] Along the logistics direction, C-Beta-2 and C-MFI-2 were placed in two reactors in sequence on a fixed bed hydrocracking unit for hydrocracking reaction. 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.

[0109] The reaction pressure is 7.5 MPa, the hydrogen-to-oil volume ratio is 800, the temperature of the first hydrocracking reaction is 420°C, and the liquid hourly space velocity of the first hydrocracking reaction is 1.67 h -1 The temperature of the second hydrocracking reaction is 390°C, and the liquid hourly space velocity of the second hydrocracking reaction is 2h -1 The analysis results of the gasoline fraction 65-180°C in the obtained product are shown in Table 3.

[0110] Table 1

[0111]

[0112] Example 3

[0113] The method of Example 1 was followed, except that the temperature of the second hydrocracking reaction was changed to 360° C. The results are shown in Table 3.

[0114] Comparative Example 1

[0115] 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 -1 The total nitrogen content at the outlet of the refining section was analyzed to be 187 μg / g, and the gasoline fraction in the generated oil was analyzed by PONA, and the results are shown in Table 3. Among them, the cracking reaction products were separated by fractionation, and the cutting temperature between light naphtha and gasoline fraction was 65°C, and the cutting temperature between gasoline and heavy components was 180°C.

[0116] Comparative Example 2

[0117] The method of Comparative Example 1 was followed, except that the hydrocracking catalyst was replaced with RHC-210 industrial catalyst (produced by the Changling Catalyst Company).

[0118] The gasoline fraction in the generated oil was subjected to PONA analysis, and the results are shown in Table 3.

[0119] Comparative Example 3

[0120] 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 an circumscribed circle diameter of 1.6 mm, dried at 120°C for 3h, and calcined at 600°C for 3h to obtain a carrier. At 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.

[0121] The gasoline fraction in the generated oil was subjected to PONA analysis, and the results are shown in Table 3.

[0122] Comparative Example 4

[0123] The method of Example 1 was followed, except that C-Beta-1 and C-MFI-1 were swapped, i.e., C-MFI-1 was used in the first hydrocracking reaction, and C-Beta-1 was used in the second hydrocracking reaction. The results are shown in Table 3.

[0124] Table 2

[0125]

[0126] Table 3

[0127] Example No. <![CDATA[Weight yield of C6-C8 aromatics in gasoline fraction, %]]> Example 1 36.7 Example 2 38.8 Example 3 32.3 Comparative Example 1 10.1 Comparative Example 2 14.6 Comparative Example 3 16.8 Comparative Example 4 27.8

[0128] It can be seen from the results in Table 3 that, among the products obtained by the method of the present invention, the yield of low-carbon aromatics in the gasoline fraction is significantly higher.

[0129] 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 fraction to a hydrotreating catalyst for hydrotreating reaction, and then treating the resultant hydrotreating effluent so that the total nitrogen content 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 Beta 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 VIB group and a VIII group metal component; Wherein, the reaction temperature of the first hydrocracking reaction is higher than the reaction temperature of the second hydrocracking reaction.

2. The method according to claim 1, wherein: The density of the diesel fraction is 0.85-0.96 g / cm 3 , the distillation range is 180-375°C, and the content of paraffins in the diesel fraction 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 5-30 wt%, preferably 10-25 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 70-95% by weight, preferably 75-90% 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 Beta molecular sieve is 5-300, preferably 25-150; the specific surface area of ​​the Beta molecular sieve is 150-450m 2 / g, preferably 300-450m 2 / g; the pore volume of the Beta molecular sieve is 0.1-0.6mL / g, preferably 0.2-0.5mL / g; Preferably, 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 Beta 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.

5. The method according to any one of claims 1 to 4, 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 1:0.08-0.35; Preferably, the VIB Group metal component is Mo and / or W, preferably Mo; Preferably, the Group VIII metal component is Ni and / or Co.

6. The method according to any one of claims 1 to 5, wherein: The second hydrocracking catalyst further contains a promoter element; 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.

7. The method according to any one of claims 1 to 6, wherein: The second hydrocracking catalyst further contains an organic additive; 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 selected from at least one of an alcohol compound, a carboxylic acid compound and an organic amine compound; 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 claim 8, wherein: The preparation method of the second hydrocracking catalyst comprises the following steps: (a) mixing an MFI molecular sieve and an optional heat-resistant inorganic oxide precursor to prepare a second carrier; (b) introducing the second metal component and optionally the auxiliary agent and optionally the organic additive onto the second support by impregnation.

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 reaction temperature of the first hydrocracking reaction is 5-30°C higher than the reaction temperature of the second hydrocracking reaction; Preferably, the conditions of the first hydrocracking reaction include: reaction pressure of 2-8 MPa; reaction temperature of 370-440°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 2-8 MPa; reaction temperature of 365-425°C; hydrogen-oil volume ratio of 300-900:1; liquid hourly space velocity of 0.5-4h -1 .

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