Process for the catalytic production of low-carbon aromatics using a catalyst comprising a beta-type molecular sieve and a catalyst comprising a shape-selective zeolite

Abstract

The present application relates to the field of low carbon aromatic hydrocarbon production, and discloses a method for catalytically producing low carbon aromatic hydrocarbon by using a Beta-type molecular sieve catalyst and a shape-selective zeolite catalyst. The method comprises: hydrogenating and refining hydrogen and diesel fraction with a hydrogenation refining catalyst, and then treating the hydrogenation and refining effluent so that the total nitrogen content of the hydrogenation and refining effluent is less than 50 μg / g; first hydrocracking the hydrogenation and refining effluent with a first hydrocracking catalyst to obtain a first product, wherein 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 Group VIB metal component; and second hydrocracking the first product with a second hydrocracking catalyst, wherein 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. The method can obtain high yield of low carbon aromatic hydrocarbon.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low-carbon aromatic hydrocarbon production, and in particular to a method for catalytically producing low-carbon aromatic hydrocarbons using a Beta-type molecular sieve catalyst and a shape-selective zeolite catalyst. BACKGROUND

[0002] At present, the demand for C6-C8 low-carbon aromatic hydrocarbons is large in China, and the products with industrial value mainly include 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. P-xylene can be used as a raw material for PTA, and then polyester, spinning, and polyester synthetic fiber products are produced. The existing industrial methods for producing low-carbon aromatic hydrocarbons are mainly obtained by separation from catalytic reforming oil, coal tar, and cracking oil, and 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] Industrial hydrocracking has the characteristics of low reaction temperature, simple feed and process, etc. Its raw materials include VGO and other heavy and poor fractions, which contain a large amount of aromatic hydrocarbons and naphthenes. These aromatic hydrocarbons and naphthenes usually exist in the form of side chains, thereby maintaining a certain distillation range in the mixture. The reactions occurring on the acid centers in the conventional hydrocracking process are usually based on the mechanism of carbenium ions, 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 cleavage, i.e. the breaking of the ortho chemical bond of the carbenium ion coordination chemical bond, which makes the reaction products usually contain a certain amount of branches, and it is difficult to obtain low-carbon aromatic hydrocarbon compounds (BTEX) with low or even no branches. The problem can be effectively avoided by using a poor diesel fraction with lower distillation range and rich in aromatic hydrocarbons.

[0004] CN201310520012.2 discloses a hydro-upgrading method for producing high-octane gasoline components or BTX raw materials. The method mixes poor diesel with hydrogen-rich gas, and then the mixture enters a hydrofining reaction zone to contact and react with a hydrofining catalyst. The reaction effluent of the hydrofining reaction zone enters a hydro-upgrading reaction zone without any intermediate separation facility, and sequentially contacts and reacts with a first hydro-upgrading catalyst and a second hydro-upgrading catalyst. The effluent of the hydro-upgrading reaction zone is cooled and separated to obtain hydrogen-rich gas and liquid products. Using the method provided by the present application, high-octane gasoline can be produced from a poor diesel fraction as a raw material, and the content of BTX in the high-octane gasoline fraction can reach more than 40%.

[0005] The above method uses a staged hydrocracking section to obtain a certain amount of naphtha fraction with high BTX content, but the refined hydrocracking products are sequentially fed into the downstream process, so that the organic nitrogen in the raw material enters the molecular sieve-containing hydrocracking catalyst bed in the form of inorganic ammonia and organic nitrogen, and both inorganic ammonia and organic nitrogen will undergo adsorption reaction on the molecular sieve. The inorganic ammonia molecules will pass through the inner pores of the catalyst and then be adsorbed on the acid centers on the inner surface of the catalyst, so that the cracking activity of the catalyst is weakened; the organic nitrogen molecules are easily adsorbed on the acid centers on the outer surface of the catalyst, thereby reducing the cracking activity of the catalyst for large molecules. In order to overcome these problems in the LCO hydrocracking reaction process, a certain amount of hydrogenation activity is maintained in the cracking section catalyst to make the catalyst activity stability higher, and a bimetallic design is used to maintain a certain amount of hydrogenation activity by using the promoter effect of Group VIII metals. Due to the promoter effect of Group VIII metals on Group VI metals in the sulfided state, the catalyst has high hydrogenation function and strong aromatic saturation capacity; due to the mutual support effect of the bimetallic sulfided metal system, more active hydrogen can be contained in the system, thereby promoting the reaction of saturating aromatics to naphthenes, so that the total yield of aromatics in the final product is still limited. SUMMARY

[0006] The purpose of the present application is to overcome the problem of low yield of low-carbon aromatic hydrocarbons in the existing process, and to provide a method for catalytically producing low-carbon aromatic hydrocarbons using a Beta-type molecular sieve catalyst and a shape-selective zeolite catalyst. The method can obtain a high yield of low-carbon aromatic hydrocarbons.

[0007] In order to achieve the above-mentioned purpose, one aspect of the present application provides a method for producing low-carbon aromatic hydrocarbons, which comprises the following steps:

[0008] (1) hydrogen and diesel fraction are subjected to hydrofining reaction with a hydrofining catalyst, and then treated so that the total nitrogen content in the obtained hydroprocessing effluent is less than 50 μg / g;

[0009] (2) the hydroprocessing effluent is subjected to first hydrocracking reaction with a first hydrocracking catalyst to obtain a first product, the first hydrocracking catalyst comprising a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Beta-type 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, the second hydrocracking catalyst comprising a second support and a second metal component supported on the second support, wherein the second support contains a MFI type molecular sieve, and the second metal component comprises a Group VIB and a Group VIII metal component;

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

[0012] By the above technical solution, the beneficial effects of the present application include:

[0013] The method provided by the present application first controls the total nitrogen content in the hydroprocessing effluent to be lower than 50 μg / g, and then uses a first hydrocracking catalyst comprising a first support containing a Beta type molecular sieve and a single metal active component and a second hydrocracking catalyst comprising a second support containing a MFI type molecular sieve and a double metal active component to reasonably grade and perform secondary continuous hydrocracking reaction, and the temperature of the first hydrocracking reaction is controlled to be higher than the temperature of the second hydrocracking reaction, which is beneficial to improve the yield of low-carbon aromatic hydrocarbons. DETAILED DESCRIPTION

[0014] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The endpoints of the ranges and any values can be combined with other endpoints to form new ranges or values, which are also contemplated as disclosed herein.

[0015] In the present application, the dry basis of a substance refers to the solid product obtained by calcining the substance at 600℃ for 3 hours.

[0016] In the present application, "optional" means non-essential and can be understood as containing or not containing.

[0017] In the present application, the density of the diesel fraction is the density at 20℃.

[0018] In one aspect of the present application, a method for producing low-carbon aromatic hydrocarbons in large quantities is provided, which comprises the following steps:

[0019] (1) subjecting hydrogen and a diesel fraction to a hydrofining reaction with a hydrofining catalyst, and then performing a treatment so that the total nitrogen content in the obtained hydroprocessing effluent is lower than 50 μg / g;

[0020] (2) subjecting the hydrotreated effluent to a first hydrocracking reaction with a first hydrocracking catalyst to obtain a first product, the first hydrocracking catalyst comprising a first support and a first metal component supported on the first support, wherein the first support contains a Beta-type 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, the second hydrocracking catalyst comprising a second support and a second metal component supported on the second support, wherein the second support contains an MFI-type molecular sieve and the second metal component comprises a Group VIB and a Group VIII 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 application, the total nitrogen content in the hydrotreated effluent is less than 50 μg / g, preferably less than 30 μg / g. By using this preferred embodiment, the inhibition of the metal active sites and the molecular sieve active sites by the inorganic ammonia generated in the hydrofining reaction can be reduced.

[0024] The method for treating in step (1) is not particularly limited in the present application, for example, it can be water washing and filtration, stripping, etc., as long as the total nitrogen content in the obtained hydrotreated effluent is less than 50 μg / g.

[0025] In the prior art, the raw material usually comprises VGO and other heavy and poor quality fractions, containing a large amount of aromatic hydrocarbons and naphthenes. These aromatic hydrocarbons and naphthenes usually exist in the form of side chains, so that the mixture has a certain distillation range. The reactions occurring on the acid centers in the conventional hydrocracking process are usually based on the mechanism of carbenium ions, and the feedstock 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 cleavage, i.e. the breaking of the ortho chemical bond of the carbenium ion coordination chemical bond, which makes the reaction products usually contain a certain amount of branches, and it is difficult to obtain low-branch or even non-branch low-carbon aromatic hydrocarbon compounds (BTEX). In the present application, the diesel fraction with lower density, lower distillation range and higher content of aromatic hydrocarbons and naphthenes is used, so that the components in the diesel fraction are more easily converted into low-carbon aromatic hydrocarbons, and the selectivity of low-carbon aromatic hydrocarbons is improved.

[0026] Preferably, the density of the diesel is 0.85-0.96 g / cm 3 , 0.85 g / cm 3 , 0.86 g / cm 3 , 0.87 g / cm 3 , 0.88 g / cm 30.89 g / cm3 3 0.9 g / cm3 3 0.91 g / cm3 3 0.92 g / cm3 3 0.93 g / cm3 3 0.94 g / cm3 3 0.95 g / cm3 3 0.96 g / cm3 3 and any value in the range between any two of these point values.

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

[0028] Preferably, the diesel has a paraffin content of less than 15 wt%, for example, 14.5 wt%, 14 wt%, 13 wt%, 12 wt%, 11 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, and any value in the range between any two of these point values.

[0029] The diesel feedstock is not particularly limited in the present application, as long as the diesel fraction meets the above requirements.

[0030] In the prior art, the hydrogenation cracking catalyst usually adopts a bimetallic active metal component design, and utilizes the promoter effect of Group VIII metal to maintain a certain hydrogenation activity. Due to the promoter effect of Group VIII metal on Group VI metal in the sulfided state, the catalyst has a higher hydrogenation function and a stronger aromatic saturation capacity; 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 saturating aromatic hydrocarbons into naphthenes, so that the total yield of aromatic hydrocarbons in the final product is still limited. The first hydrogenation cracking catalyst comprising a first carrier containing a Beta-type molecular sieve and a single-metal active component and the second hydrogenation cracking catalyst comprising a second carrier containing an MFI-type molecular sieve and a bimetallic active component can effectively overcome the above-mentioned defects, and the yield of low-carbon aromatic hydrocarbons is significantly improved.

[0031] In the present application, the first hydrogenation cracking catalyst comprises a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Beta-type molecular sieve, and the first metal component is a Group VIB metal component.

[0032] According to the present application, preferably, the content of the first metal component in the first hydrogenation cracking catalyst is 5-30 wt%, preferably 10-25 wt%, based on the total weight of the first hydrogenation cracking catalyst.

[0033] According to the present application, preferably, the content of the first carrier in the first hydrocracking catalyst is 70-95% by weight, preferably 75-90% by weight, based on the total weight of the first hydrocracking catalyst.

[0034] In the first hydrocracking catalyst, the content of each component adds up to 100%.

[0035] According to the present application, preferably, the Group VIB metal component is Mo and / or W, preferably W. With this preferred embodiment, it is beneficial to inhibit excessive saturation of aromatics during the reaction and improve the selectivity of low-carbon aromatics.

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

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

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

[0039] The use of the Beta-type molecular sieve with the above characteristics is beneficial to improve the cracking activity and thus improve the relative content of low-carbon aromatic components in the gasoline fraction.

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

[0041] The heat-resistant inorganic oxide according to the present application refers to a porous material with a maximum use temperature of not less than 600℃. The heat-resistant inorganic oxide can improve 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 application has a wide range of selection for the type of heat-resistant inorganic oxide, 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 application, preferably, the content of the Beta-type molecular sieve is 40-90% by weight, preferably 40-80% by weight, and the content of the heat-resistant inorganic oxide is 10-60% by weight, preferably 20-60% by weight, based on the total weight of the first carrier.

[0044] The preparation method of the first hydrocracking catalyst is not particularly limited in the present application, and the first hydrocracking catalyst with the above composition can be prepared by commercial purchase or self-preparation by a conventional method.

[0045] In the present application, 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 a Group VIB metal component and a Group VIII metal component.

[0046] According to the present application, preferably, the content of the second metal component in the second hydrocracking catalyst is 5-30 wt%, preferably 10-30 wt% based on the total weight of the second hydrocracking catalyst in terms of oxides.

[0047] According to the present application, preferably, the mass ratio of the Group VIB metal component to the Group VIII metal component is 1:0.05-4, preferably 1:0.08-0.35 in terms of oxides.

[0048] In the present application, the Group VIB metal component can be a conventional selection in the art. Preferably, the Group VIB metal component is Mo and / or W, preferably Mo. With this preferred embodiment, it is beneficial to inhibit excessive saturation of aromatic hydrocarbons during the reaction process and improve the selectivity of low-carbon aromatic hydrocarbons.

[0049] In the present application, the Group VIII metal component can be a conventional selection in the art. Preferably, the Group VIII metal component is Ni and / or Co.

[0050] According to the present application, preferably, the second hydrocracking catalyst further contains an auxiliary element.

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

[0052] According to the present application, preferably, the content of the auxiliary element is 0.1-10 wt% based on the total weight of the second hydrocracking catalyst in terms of oxides.

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

[0054] According to the present application, preferably, the content of the organic additive is 0.5-15 wt% based on the total weight of the second hydrocracking catalyst.

[0055] In the second hydrocracking catalyst, the content of each component adds up to 100%.

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

[0057] The present application has a wide range of selection for the type of the carboxylic acid compounds, which can be various carboxylic acid compounds commonly used in the art. Preferably, the carboxylic acid compounds are at least one selected from the group consisting of acetic acid, maleic acid, oxalic acid, amino triacetic acid, amino acetic acid, citric acid, tartaric acid and malic acid.

[0058] The present application has a wide range of selection for the type of the alcohol compounds, which can be various alcohol compounds commonly used in the art. Preferably, the alcohol compounds are at least one selected from the group consisting of ethylene glycol, glycerol, polyethylene glycol, diethylene glycol and butanediol.

[0059] The present application has a wide range of selection for the type of the organic amine compounds, which can be various organic amine compounds commonly used in the art. Preferably, the organic amine compounds are at least one selected from the group consisting of ethylenediamine, diethylenetriamine, cyclohexanediaminetetraacetic acid, ethylenediaminetetraacetic acid and ethylenediaminetetraacetic acid ammonium.

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

[0061] According to the present application, preferably, the MFI type molecular sieve has a specific surface area of 180-650 m 2 / g, preferably 300-450 m 2 / g.

[0062] According to the present application, preferably, the MFI type molecular sieve has a pore volume of 0.1-0.6 mL / g, preferably 0.2-0.5 mL / g.

[0063] The use of the MFI type molecular sieve with the above characteristics is beneficial to further improve the selectivity of low-carbon aromatic hydrocarbons.

[0064] The present application has a wide range of selection for the type of the MFI type molecular sieve, preferably, the MFI type molecular sieve is ZSM-5 molecular sieve.

[0065] According to the present application, 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 improve 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 application, preferably, the content of the MFI type molecular sieve is 40-90 wt%, preferably 40-80 wt%, and the content of the heat-resistant inorganic oxide is 10-60 wt%, preferably 20-60 wt%, based on the total weight of the second carrier.

[0067] The present application has a wide range of selection for the type of heat-resistant inorganic oxide, 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 application does not have a particular limitation on the preparation method of the second hydrocracking catalyst, as long as the second hydrocracking catalyst with the above composition can be prepared. In order to further improve the catalytic performance of the second hydrocracking catalyst, the present application also provides a preparation method of the second hydrocracking catalyst.

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

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

[0071] (b) introducing a second metal component, and optionally an additive and an optional organic additive into the second carrier by impregnation method.

[0072] In the present application, the method for preparing the second carrier in step (a) is well known to those skilled in the art, and the present application does not have a particular limitation. For example, the method in step (a) can include: mixing the MFI molecular sieve with optional heat-resistant inorganic oxide precursor into a shape, and then drying and calcining to obtain the second carrier. The heat-resistant inorganic oxide precursor can be a conventional selection in the art. The shaping in step (a) can be performed by any method conventionally used in the art, for example, the shaping can be performed by tabletting, balling or extruding. The conditions of drying and calcining in step (a) can be performed by a method conventionally used in the art, and the present application does not have a particular limitation.

[0073] The present application also does not have a particular limitation on the shape of the prepared second carrier, which can be spherical, strip-shaped (including solid or hollow strip-shaped), block-shaped, etc. The strip-shaped can be clover-shaped, four-leaf clover-shaped and other multi-leaf clover-shaped and their deformations.

[0074] Preferably, step (b) comprises: contacting the second carrier with an impregnation solution containing a second metal precursor, and optionally an additive precursor and an optional organic additive, and then drying and optionally calcining.

[0075] Preferably, the second metal precursor is a soluble compound of the second metal, preferably at least one selected from the group consisting of an oxide of the second metal, an inorganic salt of the second metal, and an organic compound of the second metal. For example, the inorganic salt of the second metal can be at least one selected from the group consisting 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 compound of the second metal can be at least one selected from the group consisting of a hydroxyl group, a carboxyl group, an amine group, a ketone group, an ether group, and an alkyl group.

[0076] The promoter precursor of the present application can be a conventional selection in the art as long as it contains the promoter element. For example, a soluble salt of the promoter, an inorganic acid of the promoter, etc.

[0077] The present application does not have a particular limitation on the order of addition of the above-mentioned substances during step (b), and they can be added together or separately. The present application uses the mode of adding them together as an example.

[0078] The present application does not have a particular limitation on the type and amount of the solvent in the impregnation solution, and it can be performed according to a conventional method in the art.

[0079] The present application does not have a particular limitation on the temperature of the contacting in step (b), and it can be any temperature that the impregnation solution can reach. The present application also does not have a particular limitation on the time of the contacting, as long as the desired amount of the metal precursor is loaded on the support. Generally, the higher the temperature of the contacting and the greater the concentration of the impregnation solution, the shorter the time required to reach the same impregnation amount (i.e., the weight difference of the support after and before impregnation). Conversely, the lower the temperature of the contacting and the smaller the concentration of the impregnation solution, the longer the time required to reach the same impregnation amount. When the desired impregnation amount and conditions are determined, the appropriate contacting time can be easily selected. 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. The environment of the impregnation method is not particularly limited, and it can be performed under a sealed condition or in an open environment according to a conventional method in the art. The lost solvent can or can not be supplemented during the contacting. Any gas, such as air, nitrogen, water vapor, etc., can or can not be introduced during the contacting.

[0080] The drying and calcination in step (b) are conventional steps for preparing a catalyst, and they are not particularly limited. For example, the drying in step (b) can be performed at a temperature of 80-350°C, preferably 100-300°C, for a time of 0.5-24 hours, preferably 1-12 hours. The calcination in step (b) can be performed at a temperature of 350-600°C, preferably 400-550°C, for a time of 0.2-12 hours, preferably 1-10 hours.

[0081] The conditions of the hydrofining reaction can be selected in a wide range according to the conventional method in the art. Preferably, the conditions of the hydrofining reaction in step (1) include: the reaction temperature is 320-410℃; the reaction pressure is 4-18 MPa; the hydrogen / oil volume ratio is 300-800:1; the liquid hourly space velocity is 0.5-3h -1 .

[0082] The type of the hydrofining catalyst is not particularly limited in the present application, and can be selected according to the conventional method in the art.

[0083] The hydrofining catalyst can be obtained by commercial purchase or prepared by the conventional method in the art.

[0084] According to the present application, preferably, the reaction temperature of the first hydrocracking reaction is 5-30℃ higher than that of the second hydrocracking reaction. By using this preferred embodiment, the first hydrocracking catalyst and the second hydrocracking catalyst can play their respective advantages and synergize to further improve the yield of low-carbon aromatic hydrocarbons.

[0085] According to the present application, preferably, the conditions of the first hydrocracking reaction include: the reaction pressure is 2-8 MPa; the reaction temperature is 370-440℃; the hydrogen / oil volume ratio is 300-900:1; the liquid hourly space velocity is 0.5-3h -1 .

[0086] According to the present application, preferably, the conditions of the second hydrocracking reaction include: the reaction pressure is 2-8 MPa; the reaction temperature is 365-425℃; the hydrogen / oil volume ratio is 300-900:1; the liquid hourly space velocity is 0.5-4h -1 .

[0087] In the present application, the first hydrocracking catalyst and the second hydrocracking catalyst can be loaded in different reaction zones of the same reactor or in different reactors, which can be selected according to the actual situation, and the present application does not have a particular limitation in this regard.

[0088] The hydrocracking reaction can be carried out in any reactor that is sufficient to allow the hydrocarbon feedstock to contact with the catalyst under the hydrocracking conditions, such as a fixed bed reactor, a moving bed reactor, a boiling bed reactor or a slurry bed reactor, and the present application does not have a particular limitation in this regard.

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

[0090] Preferably, the product of the second hydrocracking reaction is separated to obtain a light naphtha component and a gasoline fraction. The specific separation method can be selected according to the conventional method of those skilled in the art, such as fractionation, and the present application does not further describe it in detail.

[0091] Preferably, the first and second hydrocracking catalysts are pre-sulfided before use.

[0092] The present application does not have specific limitations on the specific conditions of the pre-sulfidation, which can be carried out according to the methods commonly used in the art.

[0093] The pre-sulfidation of the present application can be carried out ex situ or in situ in the reactor to convert it into a sulfide type.

[0094] The present application 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 determined by static low-temperature adsorption capacity method using an ASAP2400 automatic adsorption instrument of the American Micromertics Instrument Company (according to the method of national standard GB / T5816-1995), the specific method being: vacuum degassing at 250℃ and 1.33Pa for 4h, contacting with the adsorbate at -196℃, and reaching static adsorption equilibrium; the amount of nitrogen adsorbed by the adsorbent is calculated from the difference between the nitrogen inlet amount and the residual amount in the gas phase after adsorption, and then the pore size distribution is calculated by BJH formula, and the specific surface area and pore volume are calculated by BET formula;

[0096] The crystal structure of the molecular sieve is determined by a D5005 X-ray diffractometer of the German Siemens Company, according to the method of industry standard SH / T0339-92. The experimental conditions are: Cu target, Ka radiation, solid detector, tube voltage 40kV, tube current 40mA, step scanning, step size 0.02°, pre-setting time 2s, scanning range 5°-70°. The diffraction angle position refers to the 2θ angle value of the highest peak of the diffraction peak;

[0097] The silicon content and aluminum content of the molecular sieve are determined by a 3271E X-ray fluorescence spectrometer of the Japanese Rigaku Electric Industry Co., Ltd., the determination method being: the powder sample is pressed into a tablet, rhodium target, laser voltage 50kV, laser current 50mA, the spectral line intensity of each element is detected by a scintillation counter and a proportional counter, and the element content is quantitatively and semi-quantitatively analyzed by an external standard method;

[0098] The catalyst component content is calculated by the amount of the raw material.

[0099] Example 1

[0100] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch Co., Ltd., trade name PB90, dry basis 68wt%) and Beta molecular sieve (dry basis 85wt%, specific surface area 423m 2A mixture of SiO2 / Al2O3 (molar ratio of 27, pore volume of 0.39 mL / g) was extruded into trilobal strips with an outer circle diameter of 1.6 mm, dried at 120 °C for 3 h, and calcined at 600 °C for 3 h to obtain the first support. The first support was impregnated with a 152 mL aqueous solution containing 55 g of ammonium metatungstate, dried at 120 °C for 3 h, and calcined at 480 °C for 4 h to obtain the first hydrocracking catalyst C-Beta-1. The composition is shown in Table 1.

[0101] Boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, 71% by weight on dry basis) was compared with ZSM-5 molecular sieve (95% by weight on dry basis, specific surface area of ​​336 m²). 2 The mixture (containing SiO2 / Al2O3 molar ratio of 26 and pore volume of 0.29 mL / g) was extruded into trilobal strips with an outer circle diameter of 1.6 mm, dried at 120 °C for 3 h, and calcined at 600 °C for 3 h to obtain the second support. At room temperature, the second support prepared by the aforementioned method was impregnated with a 75 mL aqueous solution containing 27.7 g molybdenum oxide, 15.1 g basic nickel carbonate (51% by weight), 11.1 g phosphoric acid (61% by weight), and 15.1 g citric acid, and dried at 120 °C for 3 h to obtain the second hydrocracking catalyst C-MFI-1. The composition is shown in Table 1.

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

[0103] Along the flow path, C-Beta-1 and C-MFI-1 catalysts were sequentially placed in two reactors in a fixed-bed hydrocracking unit for hydrocracking reactions. Before use, the catalysts underwent programmed temperature sulfidation: using straight-run kerosene containing 2% dimethyl disulfide as the sulfiding oil, the temperature was increased from 110°C to 230°C at a rate of 20°C / h and held for 6 hours; then increased to 360°C at a rate of 20°C / h and held for 6 hours. The reaction pressure was 6.4 MPa, the hydrogen-to-oil volume ratio was 600, the temperature of the first hydrocracking reaction was 400°C, and the liquid hourly space velocity (LHSV) of the first hydrocracking reaction was 1.67 h⁻¹. -1 The temperature of the second hydrocracking reaction is 390℃, and the liquid hourly space velocity (LHSV) of the second hydrocracking reaction is 2 h⁻¹. -1The results of the analysis of the gasoline fraction of the product obtained are shown in Table 3. The second hydrocracking reaction product was separated by fractionation, with the cut temperature of light naphtha and gasoline fraction being 65°C and the cut temperature of gasoline and heavy component being 180°C. The following examples are all based on this.

[0104] Example 2

[0105] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, dry basis 71 wt%) was mixed with ZSM-5 molecular sieve (dry basis 89 wt%, specific surface area 406 m 2 / g, SiO2 / Al2O3 molar ratio 65, pore volume 0.37 mL / g), extruded into tri-lobed strips with an inscribed circle diameter of 1.6 mm, dried at 120°C for 3 h, and calcined at 600°C for 3 h to obtain a second carrier. A 75 mL aqueous solution containing 51 wt% of molybdenum oxide, 61 wt% of nickel oxide, 14 g of EDTA, and 51 g of nickel carbonate hydroxide was used to impregnate the second carrier prepared by the method described above at room temperature, dried at 120°C for 3 h to obtain catalyst C-MFI-2. The composition is shown in Table 1.

[0106] Pseudo-boehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, dry basis 71 wt%) was mixed with ZSM-5 molecular sieve (dry basis 89 wt%, specific surface area 406 m 2 / g, SiO2 / Al2O3 molar ratio 65, pore volume 0.37 mL / g), extruded into tri-lobed strips with an inscribed circle diameter of 1.6 mm, dried at 120°C for 3 h, and calcined at 600°C for 3 h to obtain a second carrier. A 75 mL aqueous solution containing 51 wt% of molybdenum oxide, 61 wt% of nickel oxide, 14 g of EDTA, and 51 g of nickel carbonate hydroxide was used to impregnate the second carrier prepared by the method described above at room temperature, dried at 120°C for 3 h to obtain catalyst C-MFI-2. The composition is shown in Table 1.

[0107] The preparation of a hydrotreated feedstock was carried out on a fixed bed hydrocracking device using the feedstock (LCO-QD) described in Table 2, using an industrial hydrofining catalyst RS-2100 (produced by Sinopec Catalyst Changling Branch), 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 / g, SiO2 / Al2O3 molar ratio 65, pore volume 0.37 mL / g), extruded into tri-lobed strips with an inscribed circle diameter of 1.6 mm, dried at 120°C for 3 h, and calcined at 600°C for 3 h to obtain a second carrier. A 75 mL aqueous solution containing 51 wt% of molybdenum oxide, 61 wt% of nickel oxide, 14 g of EDTA, and 51 g of nickel carbonate hydroxide was used to impregnate the second carrier prepared by the method described above at room temperature, dried at 120°C for 3 h to obtain catalyst C-MFI-2. The composition is shown in Table 1.

[0108] Catalysts C-Beta-2 and C-MFI-2 were used in the fixed-bed hydrocracking unit in sequence in two reactors in the direction of the flow. The above catalysts were subjected to programmed temperature sulfidation before use: straight-run kerosene containing 2% by mass of dimethyl disulfide was used as the sulfidation oil, the temperature was raised to 230°C at a rate of 20°C / h from 110°C, and maintained for 6h; then the temperature was raised to 360°C at a rate of 20°C / h, and maintained for 6h.

[0109] The reaction pressure was 7.5 MPa, the hydrogen / oil volume ratio was 800, the temperature of the first hydrocracking reaction was 420°C, the liquid hourly space velocity of the first hydrocracking reaction was 1.67h -1 The temperature of the second hydrocracking reaction was 390°C, the liquid hourly space velocity of the second hydrocracking reaction was 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 raw material (LCO-QD) described in Table 2, the refining section used an industrial catalyst RN-411 (produced by Sinopec Catalyst Changling Branch), the cracking section used an 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 / oil volume ratio was 700, the liquid hourly space velocity of the refining section was 1.25h -1 The total nitrogen content at the outlet of the refining section was 187 μg / g, the PONA analysis of the gasoline fraction in the product oil was carried out, and the results are shown in Table 3. The cracking product was separated by distillation, the cutting temperature of the light naphtha and the gasoline fraction was 65°C, and the cutting temperature of the gasoline and the heavy component was 180°C.

[0116] Comparative Example 2

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

[0118] The PONA analysis of the gasoline fraction in the product oil was carried out, 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 by D-1, which was prepared as follows: 158 g of pseudoboehmite (produced by Sinopec Catalyst Changling Branch, trade name PB90, dry basis 71 wt%) was mixed with 422 g of ZSM-5 molecular sieve (produced by Sinopec Catalyst Changling Branch, specific surface area 325 m 2 / g, framework silica-alumina ratio 70, pore volume 0.31 mL / g, dry basis 80 wt%) and extruded into tri-lobal strips with an inscribed circle diameter of 1.6 mm, dried at 120°C for 3 h, and calcined at 600°C for 3 h to obtain a carrier. At room temperature, 50 g of the carrier prepared above was impregnated with a 60 mL aqueous solution containing 13.7 g of tungsten oxide with a weight content of 91% of ammonium metatungstate, dried at 120°C for 3 h, and calcined at 480°C for 4 h to obtain catalyst D-1.

[0121] The gasoline fraction in the product 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 interchanged, 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. Weight yield of C6-C8aromatics in gasoline distillate, % 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] As can be seen from the results in Table 3, the low-carbon aromatic hydrocarbons in the gasoline fraction have a significantly higher yield in the product obtained using the method of the present application.

[0129] The preferred embodiments of the present application have been described in detail above, but the present application is not limited thereto. Various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A process for the production of low carbon aromatic hydrocarbons, characterized in that, The method comprises the following steps: (1) hydrogen and diesel fraction are subjected to hydrofining reaction with a hydrofining catalyst, and then treated so that the total nitrogen content in the obtained hydrofining effluent is less than 50 μg / g; (2) the hydrofining effluent is subjected to first hydrocracking reaction with a first hydrocracking catalyst to obtain a first product, the first hydrocracking catalyst being a first carrier and a first metal component supported on the first carrier, wherein the first carrier contains a Beta-type molecular sieve, and the first metal component is a Group VIB metal component; (3) the first product obtained in step (2) is subjected to second hydrocracking reaction with a second hydrocracking catalyst, the second hydrocracking catalyst being 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 is a Group VIB and Group VIII metal component; the second hydrocracking reaction product is separated to obtain a light naphtha component and a gasoline fraction containing low-carbon aromatic hydrocarbons; wherein the reaction temperature of the first hydrocracking reaction is 5-30 °C higher than that of the second hydrocracking reaction.

2. The method according to claim 1, wherein The diesel fraction has a density of 0.85 to 0.96 g / cm3 at 20°C 3 , a distillation range of 180 to 375°C and a content of paraffins in the diesel fraction of less than 15 wt%.

3. The method of claim 1, wherein, the content of the first metal component in the first hydrocracking catalyst is 5-30% by weight based on the total weight of the first hydrocracking catalyst; and / or the content of the first carrier in the first hydrocracking catalyst is 70-95% by weight based on the total weight of the first hydrocracking catalyst.

4. The method of claim 3, wherein, the content of the first metal component in the first hydrocracking catalyst is 10-25% by weight based on the total weight of the first hydrocracking catalyst; and / or the content of the first carrier in the first hydrocracking catalyst is 75-90% by weight based on the total weight of the first hydrocracking catalyst.

5. The method according to claim 1, wherein the Group VIB metal component in the first hydrocracking catalyst is Mo and / or W.

6. The method according to claim 5, wherein the Group VIB metal component in the first hydrocracking catalyst is W.

7. The method according to any one of claims 1-6, wherein The SiO2 / Al2O3 molar ratio of the Beta-type molecular sieve is 5-300; the specific surface area of the Beta-type molecular sieve is 150-450 m 2 / g; and the pore volume of the Beta-type molecular sieve is 0.1-0.6 mL / g.

8. The method according to claim 7, wherein The SiO2 / Al2O3 molar ratio of the Beta-type molecular sieve is 25-150; the specific surface area of the Beta-type molecular sieve is 300-450 m 2 / g; and the pore volume of the Beta-type molecular sieve is 0.2-0.5 mL / g.

9. The method according to any one of claims 1-6, wherein the first carrier in the first hydrocracking catalyst further contains a heat-resistant inorganic oxide; the content of the Beta-type molecular sieve is 40-90% by weight based on the total weight of the first carrier; and the content of the heat-resistant inorganic oxide is 10-60% by weight based on the total weight of the first carrier; the heat-resistant inorganic oxide is selected from at least one of silicon oxide, aluminum oxide, zirconium oxide and titanium oxide.

10. The method according to claim 9, wherein the content of the Beta-type molecular sieve is 40-80% by weight based on the total weight of the first carrier; and the content of the heat-resistant inorganic oxide is 20-60% by weight based on the total weight of the first carrier.

11. The method according to any one of claims 1-6, wherein The content of the second metal component in the second hydrocracking catalyst is 5-30% by weight, based on the total weight of the second hydrocracking catalyst, in terms of oxides.

12. The method according to claim 11, wherein, The content of the second metal component in the second hydrocracking catalyst is 10-30% by weight, based on the total weight of the second hydrocracking catalyst, in terms of oxides.

13. The method according to any one of claims 1-6, wherein, The mass ratio of the Group VIB metal component to the Group VIII metal component in the second hydrocracking catalyst is 1:0.05-0.4, in terms of oxides.

14. The method according to claim 13, wherein, The mass ratio of the Group VIB metal component to the Group VIII metal component in the second hydrocracking catalyst is 1:0.08-0.35, in terms of oxides.

15. The method according to any one of claims 1-6, wherein, The Group VIB metal component in the second hydrocracking catalyst is Mo and / or W; The Group VIII metal component in the second hydrocracking catalyst is Ni and / or Co.

16. The method according to claim 15, wherein, The Group VIB metal component in the second hydrocracking catalyst is Mo.

17. The method according to any one of claims 1-6, wherein, The second hydrocracking catalyst further contains an auxiliary element; The content of the auxiliary element in the second hydrocracking catalyst is 0.1-10% by weight, based on the total weight of the second hydrocracking catalyst, in terms of oxides; The auxiliary element is selected from at least one of phosphorus, fluorine and boron.

18. The method according to claim 17, wherein, The auxiliary element is phosphorus.

19. The method according to claim 17, wherein, The second hydrocracking catalyst further contains an organic additive; The content of the organic additive in the second hydrocracking catalyst is 0.5-15% by weight, based on the total weight of the second hydrocracking catalyst; The organic additive is selected from at least one of an alcohol compound, a carboxylic acid compound and an organic amine compound.

20. The method according to claim 19, wherein, The carboxylic acid compound is selected from at least one of acetic acid, maleic acid, oxalic acid, amino triacetic acid, amino acetic acid, citric acid, tartaric acid and malic acid; The alcohol compound is selected from at least one of ethylene glycol, glycerol, polyethylene glycol and butanediol; The organic amine compound is selected from at least one of ethylenediamine, diethylenetriamine, cyclohexanediaminetetraacetic acid, ethylenediaminetetraacetic acid and ethylenediaminetetraacetic acid ammonium.

21. The method according to claim 19, wherein, The alcohol compound is diethylene glycol.

22. The method according to any one of claims 1-6, wherein, The MFI type molecular sieve has a SiO2 / Al2O3 molar ratio of 15-300; a specific surface area of 180-650 m 2 / g; and a pore volume of 0.1-0.6 mL / g.

23. The method according to claim 22, wherein, The MFI type molecular sieve has a SiO2 / Al2O3 molar ratio of 20-80; a specific surface area of 300-450 m 2 / g; and a pore volume of 0.2-0.5 mL / g.

24. The method according to any one of claims 1-6, wherein, The MFI type molecular sieve is ZSM-5 molecular sieve.

25. The method according to claim 19, wherein, In the second hydrocracking catalyst, the second carrier further contains a heat-resistant inorganic oxide; The content of the MFI type molecular sieve is 40-90% by weight, and the content of the heat-resistant inorganic oxide is 10-60% by weight, based on the total weight of the second carrier. The heat-resistant inorganic oxide is selected from at least one of silicon oxide, aluminum oxide, zirconium oxide and titanium oxide.

26. The method of claim 25, wherein, The content of the MFI type molecular sieve is 40-80% by weight, and the content of the heat-resistant inorganic oxide is 20-60% by weight, based on the total weight of the second carrier.

27. The method of claim 25, wherein, The preparation method of the second hydrocracking catalyst comprises the following steps: (a) mixing the MFI type molecular sieve with optional heat-resistant inorganic oxide precursors to form a second carrier; (b) introducing a second metal component, and optionally an additive and an optional organic additive onto the second carrier by an impregnation method.

28. The method of any one of claims 1-6, wherein, The conditions of the hydrofining 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 0.5-3 h -1 .

29. The method of any one of claims 1-6, wherein, The conditions of the first hydrocracking reaction include: reaction pressure of 2-8 MPa; reaction temperature of 370-440℃; hydrogen / oil volume ratio of 300-900:1; liquid hourly space velocity of 0.5-3h -1 ; The conditions of the second hydrocracking reaction include: a reaction pressure of 2-8 MPa; a reaction temperature of 365-425°C; a hydrogen to oil volume ratio of 300-900: 1; a liquid hourly space velocity of 0.5-4 h -1 .

Images