CN108970636B - Preparation method of benzene alkylation catalyst - Google Patents

Preparation method of benzene alkylation catalyst Download PDF

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CN108970636B
CN108970636B CN201810676030.2A CN201810676030A CN108970636B CN 108970636 B CN108970636 B CN 108970636B CN 201810676030 A CN201810676030 A CN 201810676030A CN 108970636 B CN108970636 B CN 108970636B
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CN108970636A (en
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郭洪臣
钱吉
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Dalian University of Technology
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    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
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    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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    • B01J37/0018—Addition of a binding agent or of material, later completely removed among others as result of heat treatment, leaching or washing,(e.g. forming of pores; protective layer, desintegrating by heat)
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Abstract

The invention belongs to the technical field of petrochemical catalysts, and provides a preparation method of a benzene alkylation catalyst, which comprises the following steps: selecting a low-silica-alumina ratio nano ZSM-5 molecular sieve as a matrix of the catalyst; deactivating the acid centers on the inner and outer surfaces of the low silica-alumina ratio nano ZSM-5 molecular sieve by using an alkali metal sodium ion solution; selectively exchanging and removing sodium ions on the outer surface of the molecular sieve by adopting ammonium bromide or ammonium chloride aqueous solution of tetraethyl quaternary ammonium cations or tetrapropyl quaternary ammonium cations, and recovering the acidic active center on the outer surface of the molecular sieve by removing the quaternary ammonium cations in subsequent roasting; and finally, drying and roasting. The modification method is simple and easy to implement, the used reagent is cheap, and the modification degree can be adjusted according to the physical property of the synthesized molecular sieve matrix and the ethylbenzene limit index. The alkylation reaction is carried out on the outer surface of the catalyst, the limitation of micropore diffusion is avoided, and the alkylation reaction can be carried out at a lower temperature.

Description

Preparation method of benzene alkylation catalyst
Technical Field
The invention belongs to the technical field of petrochemical catalysts, and relates to a preparation method of a benzene alkylation catalyst.
Background
Toluene and mixed xylene are both important raw materials for producing p-xylene (PX), and p-xylene is also an important aromatic chemical raw material, is mainly used for preparing Purified Terephthalic Acid (PTA) and further producing polyester, and is a tap of a polyester product chain. Toluene and mixed xylenes are obtained from the alkylation of benzene with methanol. With the increase of the yield of methanol in China and lower price, the application of methanol and benzene to produce toluene and xylene has industrial significance. But benzene and methanol are alkylated to simultaneously generate ethylbenzene, propyl benzene, methyl ethyl benzene, trimethyl benzene, tetramethyl benzene and other impurity aromatic hydrocarbons. Since ethylbenzene is very close to xylene boiling point, the presence of ethylbenzene in substantial quantities as a contaminant aromatic hydrocarbons will interfere with downstream applications of mixed xylenes. Therefore, for the alkylation of benzene and methanol, the yield of toluene and xylene is increased, and the content of ethylbenzene, which is an impurity aromatic hydrocarbon, is reduced.
At present, few reports are made on the alkylation reaction of benzene and methanol, and few reports are made on ZSM-5 zeolite molecular sieve catalysts. For example:
the Chinese invention patent (CN 2014/104226357A) discloses a hierarchical pore molecular sieve catalyst and preparation and application thereof. The method is technically characterized in that a synthesized multi-stage pore ZSM-5 molecular sieve is used as a carrier, and a loaded metal oxide (magnesium acetate) is used as a catalyst to carry out benzene and methanol alkylation reaction, so that the aim of improving the selectivity of a product is fulfilled. The reaction temperature is 400-500 ℃, the reaction pressure is 0.1-1.0MPa, and the total space velocity is 1-12h-1Benzene to methanol molar ratio of 0.6 to 1.2h, and xylene product selectivity of up to 35.33%, but the patent does not teach the formation of ethylbenzene impurities and solutions.
Chinese invention patent (CN 2015/104874418A) discloses a ZSM-5 molecular sieve catalyst for preparing xylene by catalyzing coking benzene and methanol and application thereof. The method is technically characterized in that the molecular sieve is impregnated by a solution of one or two metal elements of Mg, Zn, Gd, P, La, Ce, Mo and Ni. When the obtained catalyst is applied to the alkylation reaction of catalytic coking benzene and methanol to prepare xylene, the catalyst has the characteristics of high catalytic activity and stability and the like, but the patent does not describe the generation condition and the solution of ethylbenzene impurities.
Chinese patent application (CN 2015/104326855A) discloses a method for preparing toluene xylene by alkylating benzene and methanol. It is technically characterized by that it utilizes alkaline earth metal and rare earth metalModifying with magnetic metal, and adopting fluidized bed reaction process, co-feeding benzene and methanol, and contacting benzene and methanol with fluidized bed catalyst; wherein the reaction temperature is 300-600 ℃, and the reaction pressure is 0-1.0 MPa; the molar ratio of benzene to methanol is (0.3-3) to 1; the total mass space velocity of the benzene and the methanol is 0.5 to 10h-1. The method can achieve the conversion per pass of benzene of not less than 40 percent, the total selectivity of toluene and xylene in the product of not less than 80 percent and the total yield of not less than 32 percent. However, the patent does not teach the formation of ethylbenzene impurity and solution.
The Chinese invention patent (CN 2015/104909980A) discloses the application of a hierarchical pore Ti-ZSM-5 molecular sieve catalyst in the synthesis of toluene and xylene. The titanium-containing hierarchical pore Ti-ZSM-5 molecular sieve is technically characterized in that tetraethoxysilane, aluminum isopropoxide, tetraethyl tera, tetrapropylammonium hydroxide, hexadecyl trimethoxy silane and ethanol are adopted to obtain the titanium-containing hierarchical pore Ti-ZSM-5 molecular sieve through hydrothermal synthesis. The introduction of titanium is utilized to adjust the acidity of the catalyst, thereby adjusting the reaction performance. The reaction temperature is 400 ℃, the reaction pressure is normal pressure, and the total mass space velocity of the benzene and the methanol is 2.0h-1And the molar ratio of benzene to methanol is 1. When no titanium is contained, the conversion rate of benzene in the catalyst is 48.9 percent, and the selectivity of ethylbenzene is 4.1 percent; when the titanium content is 80%, the benzene conversion rate is 60%, and the ethylbenzene selectivity is reduced to 0.1%. The patent method mentions a solution for reducing ethylbenzene, but the solution is to synthesize a titanium-containing molecular sieve, use a high-price template agent tetrapropylammonium hydroxide in the synthesis, need to adopt hexadecyl trimethoxy silane, and have poor practicability. But this method has a different scientific principle from the present method.
Chinese patent (CN 2016/105728018A) discloses a ZSM-5 zeolite catalyst for benzene and methanol alkylation, a preparation method and application thereof. The method is technically characterized in that any one of gamma-Al 2O3 or eta-Al 2O3 and a hierarchical porous HZSM-5 molecular sieve are used as carriers, and an isometric impregnation method is adopted to load MgO. The reaction temperature of benzene and methanol is 400-500 ℃, the reaction pressure is 0.1-1 MPa, and the total mass airspeed is 1-8 h-1And the molar ratio of the benzene to the methanol is 0.8-1.2. The modified catalyst can improve the selectivity of toluene and xylene and increase the stability of zeolite, butThe patent does not teach the formation of ethylbenzene impurity and solution.
Chinese patent (CN 2016/105214714A) discloses a fluidized bed catalyst for preparing p-xylene with high selectivity by alkylating benzene and methanol and a preparation method thereof. The technological feature is that ZSM-5 molecular sieve with Si/Al ratio of 25-300 is used as mother body, and the fluid bed catalyst is obtained after modification by alkaline earth metal (Mg, Ca) and siloxane compound. The conversion per pass of benzene can reach more than 55 percent; the isomerization process is not needed, the obtained main product is p-xylene, the selectivity of the p-xylene in isomers is up to more than 95 percent, and the other part of intermediate product toluene is obtained. However, the patent does not teach the formation of ethylbenzene impurity and solution.
The Chinese patent (CN 2017/106853376A) discloses a preparation method and application of a catalyst for benzene and methanol alkylation reaction. The method is technically characterized in that lanthanum nitrate with the mass fraction of 3-10% and magnesium nitrate solution with the mass fraction of 1-9% are adopted to carry out equal-volume impregnation on the calcined molecular sieve, the calcined molecular sieve is kept stand for 18-24h in a closed container at room temperature, then the calcined molecular sieve is placed in a drying oven to be dried for 6h at the temperature of 90-100 ℃, and then the calcined molecular sieve is calcined for 4-8h at the temperature of 480-550 ℃ in a muffle furnace to obtain the La/MgZSM-5 molecular sieve catalyst. The conversion rate of benzene and the selectivity of p-xylene are improved after modification. However, the patent does not teach the formation of ethylbenzene impurity and solution.
Chinese patent (CN 2017/106866332A) discloses a catalyst for benzene and methanol alkylation reaction and application thereof. The method is technically characterized in that a microporous ZSM-5 molecular sieve with the silica-alumina ratio of 170-500 is used as a matrix, and a urea solution is used for modifying to obtain the hierarchical porous ZSM-5 molecular sieve with micropores and a large number of mesopores. And then impregnating the multistage pore ZSM-5 molecular sieve with a zinc nitrate or magnesium acetate solution, and drying and roasting to obtain the benzene and methanol alkylation reaction catalyst. Reaction conditions are as follows: the mol ratio of benzene to methanol is 1:1, the reaction pressure is normal pressure, the reaction temperature is 400-450 ℃, and the total mass space velocity is 2.0-3.0h-1. The method has the function of reducing the generation of ethylbenzene impurities. But this method has a different scientific principle from the present method.
Patent CN 2011/102101818AA process for synthesizing xylene by alkylating benzene and methanol is disclosed. The method is technically characterized in that the reaction temperature is 400-460 ℃, the reaction pressure is normal pressure, the molar ratio of benzene to methanol is 1:1, and the total mass space velocity is 3.3h-1During the process, the Mo and Ni modified HMCM-56 molecular sieve catalyst is adopted, so that the selectivity of toluene and xylene is more than or equal to 89%, and the single-pass conversion rate of benzene is more than or equal to 45%. The molecular sieve precursors employed in this process are different from the present invention. Poor regeneration performance of the HMCM-56 molecular sieve is to be solved.
Patent CN 2012/102600887 a describes a catalyst for producing xylene by alkylation of benzene with methanol. The technical scheme is characterized in that alkaline earth and rare earth metal elements are loaded on a hydrogen MCM-22 molecular sieve, so that the defects of low methanol alkylation utilization rate, low benzene conversion rate and low xylene selectivity in the application of the catalyst are well overcome. The reaction temperature mentioned in the examples was 420 ℃, the reaction pressure was 0.2MPa, the molar ratio of benzene to methanol was 2:1, and the space velocity was 3.0 h-1. The molecular sieve precursors employed in this process are different from the present invention. Also, the poor regeneration performance of the HMCM-22 molecular sieve is to be solved.
Patent CN 2016/105272797A, CN 2017/105315120 a describes a process for the alkylation of benzene with methanol. The method is technically characterized in that in the presence of the catalyst (containing H-type IM-5 molecular sieve), the reaction temperature is 300-5The selectivity of the low-carbon hydrocarbon is reduced, and the side reaction of the methanol is reduced. The molecular sieve precursors employed in this process are different from the present invention.
In addition to the above patents, some other patents describe the alkylation of benzene with methanol, focusing mainly on the process. For example: US 2016/0060187A, CN 2016/105503508A, US 2012/039992, US 2013217940A, WO 2013/009399 a1, US 2013/061345, WO 2014/058609, JP 10324649a and JP 9316011A, CN 2010/101628846A, CN 2010/101624327A, CN 2012/102746099A, CN 2014/103980080A, CN 2016/104326855A, CN 2016/104109065 a.
Disclosure of Invention
The invention provides a preparation method of a benzene and methanol alkylation catalyst. The method is simple and easy to implement, and has obvious effect on reducing the generation amount of ethylbenzene impurities in reaction products. We have found that when ZSM-5 molecular sieves are used as catalysts for the alkylation of benzene and methanol to produce toluene and xylene, the formation of ethylbenzene occurs predominantly at specific activity centers on the internal surface of the catalyst. Therefore, the method can reduce the generation amount of ethylbenzene impurities by modifying the active center on the inner surface of the catalyst. Specifically, the method comprises the steps of deactivating active centers on the inner surface and the outer surface of a ZSM-5 zeolite molecular sieve by adopting an alkali metal ion (lithium, sodium and potassium) solution with a specific concentration, exchanging alkali metal ions on the outer surface by using a quaternary ammonium salt with a molecular size larger than a pore channel of the ZSM-5 molecular sieve, and recovering the alkylation catalysis effect of the active centers on the outer surface, so that the purposes of inhibiting the catalysis effect on the inner surface and reducing the generation amount of ethylbenzene are achieved. In order to maintain sufficient activity of the catalyst, the ZSM-5 molecular sieve precursor used in the present invention has a low silica-alumina ratio and a nano-sized grain size.
The specific technical scheme of the invention is as follows:
a preparation method of a benzene alkylation catalyst comprises the following steps:
the first step is as follows: the low silica-alumina ratio nanometer ZSM-5 molecular sieve is used as the matrix of the catalyst.
The low silica alumina ratio nanometer ZSM-5 molecular sieve has the characteristics of large external surface area and more external surface acid centers. The low silica alumina ratio nanometer ZSM-5 molecular sieve has the following silica alumina ratio and grain size:
SiO2/Al2O3the selection ratio is less than or equal to 100, preferably less than or equal to 60;
the primary crystal size is selected to be less than or equal to 100 nanometers, preferably less than or equal to 50 nanometers;
although the primary crystal size of the nano ZSM-5 molecular sieve is not easily judged due to self-aggregation, the external specific surface area of the ZSM-5 molecular sieve having the primary crystal size is often more than 20% in the total specific surface area. In addition, it is to be understood that the ranges of the silica to alumina ratio and the crystal size of the ZSM-5 molecular sieve indicated in the present invention are favorable ranges, and that reducing the silica to alumina ratio and the crystal size of the molecular sieve beyond the ranges required by the present invention will be relatively favorable for preparing an alkylation catalyst with low ethylbenzene impurity.
The low silica alumina ratio nano ZSM-5 molecular sieve of the present invention is easily obtained for engineers in the field. For example, it can be obtained by hydrothermal synthesis according to the method disclosed in the following patents: 201110364516.0, 03111069.X, 201380066788.X, 201010261600.5 and the like.
The second step is that: and (3) deactivating the acid centers on the inner and outer surfaces of the low silica-alumina ratio nano ZSM-5 molecular sieve by using an alkali metal sodium ion solution with a specific concentration.
Before deactivating the molecular sieve, it is preferable to shape the molecular sieve to eliminate the inconvenience of filtering and washing the solid powder. The shaping process can be extrusion molding, rolling ball molding, spray molding or other common catalyst shaping modes. The shaped catalyst generally requires calcination to obtain sufficient mechanical strength during which the organic templating agent in the channels can be removed. The manner of shaping can be determined by an engineer familiar with the art by reference to the reported process in combination with the reactor configuration to be employed for benzene and methanol alkylation. Thus, the molecular sieve used for the formation may be a sodium type molecular sieve without removal of the organic templating agent. Of course, the molecular sieve which is used for removing the organic template agent in advance has no harm to the effect of the invention, but the template agent is removed in advance, so that one-time high-temperature roasting treatment is obviously added, and the preparation process is not easy to simplify and the processing cost is not reduced.
The deactivation process recommended by the present invention is as follows: firstly, preparing an aqueous solution by using soluble sodium salts such as sodium nitrate, sodium chloride and sodium sulfate, wherein the concentration range of sodium ions can be 0.05-1.0mol/L, and is preferably 0.3-0.6 mol/L; then the treating fluid and the formed molecular sieve are contacted according to the weight ratio of about 2:1-20:1, preferably 5:1-10: 1; in order to facilitate the sodium ions entering the pores of the molecular sieve and to displace a substantial portion of the protons therein, the deactivation process is preferably carried out in a hot solution to facilitate gas evolution and ion exchange within the pores. The temperature of the solution is preferably in the range of 30-90 ℃, preferably 50-80 ℃; the deactivation treatment time is preferably 0.5 hour or more, more preferably 3 hours or more. The whole process is carried out in the state of solution circulation flow or slow stirring, after the solution treatment is finished, the treatment liquid is poured, and the solid is directly dried and roasted.
In this step, other soluble salts of alkali metals may be used in place of the sodium salt. However, sodium salts are preferred in the present invention because they are generally inexpensive and readily available and the molecular sieve precursor is originally in the sodium form. Although alkaline earth metal ions, as well as transition metal ions and rare earth metal ions, are often used to modify molecular sieves and adjust acidity, the use of these ions is not recommended in the present invention because these divalent and trivalent ions can create acidic centers in the micropores in situ during the alkylation reaction in the presence of water, which is detrimental to modification purposes. In addition, the solution treatment is preferably carried out in a state where the solution is circulated or slowly agitated. In addition, the above solution treatment may be repeated as necessary until the acid center removal is satisfactory. Drying and calcination treatments after solution treatment are conventional and engineers familiar with the art may refer to drying and calcination procedures in acid exchange and ammonium exchange commonly used for the preparation of ZSM-5 catalysts. In addition, for the purpose of accumulating experience, an ammonia Temperature Programmed Desorption (TPD) method can be used for assisting in measuring the removal degree of the acid centers, so that parameters such as solution concentration, treatment time, treatment times and the like can be comprehensively selected according to reaction needs.
And thirdly, selectively exchanging and removing sodium ions on the outer surface of the molecular sieve by using an ammonium bromide or ammonium chloride aqueous solution of tetraethyl, tetrapropyl or tetrabutyl quaternary ammonium cations, and restoring the acidic active centers on the outer surface of the molecular sieve by removing the quaternary ammonium cations in subsequent roasting. The concentration of the quaternary ammonium cation is preferably 0.01mol/L or more, preferably 0.2 to 0.6 mol/L; the solution treatment is preferably in the range of 20-50 ℃, preferably 25-40 ℃; the time is preferably more than 0.5 hour, more preferably more than 2 hours; the whole process is carried out under the state that the solution circularly flows or is slowly stirred, and after the treatment is finished, the treatment solution is poured out. In addition, for experience accumulation, ammonia Temperature Programmed Desorption (TPD) and a di-tert-butylpyridine-infrared (di-tert-butylpyridine-IR) method can be used for assisting in determining the recovery of the acid centers on the outer surface, so that parameters such as solution concentration, treatment time and the like can be comprehensively selected according to reaction requirements.
And step four, finally, drying and roasting the catalyst obtained in the step three. This is a familiar operation mode for engineers in this field and will not be described in detail.
The invention has the advantages and benefits that the modification method is simple and easy to implement, the used reagent is cheap, and the modification degree can be adjusted according to the physical properties of the synthetic molecular sieve matrix and the ethylbenzene restriction index. The alkylation reaction is carried out on the outer surface of the catalyst, the limitation of micropore diffusion is avoided, and the alkylation reaction can be carried out at a lower temperature.
Drawings
FIG. 1(a) is a graph showing the results of TPD of the comparative example.
FIG. 1(b) is a graph showing the results of di-tert-butylpyridine-IR of the comparative example.
Fig. 2(a) is a graph showing the results of TPD before deactivation processing in example 1.
FIG. 2(b) is a graph showing the results of di-tert-butylpyridine-IR before deactivation treatment in example 1.
Fig. 3(a) is a graph showing the results of the TPD after deactivation process of example 1.
FIG. 3(b) is a graph showing the results of di-tert-butylpyridine-IR after deactivation treatment in example 1.
Description of the drawings: TPD is the total acidity of the inner and outer surfaces of the catalyst measured by ammonia gas, but weak acid is greatly influenced by metal ions. Characterization of the acidity of the external surface was determined using macromolecular pyridine (di-tert-butylpyridine) in the Infrared (IR) at 1550cm-1Is a characteristic peak of the catalyst B after absorbing the di-tert-butylpyridine.
Detailed Description
The present invention is further illustrated by the following specific examples, but the present invention is not limited to the following examples. Comparative examples
According to the method provided by patent 201110364516.0, ZSM-5 zeolite molecular sieve with low silica-alumina ratio is synthesized. The zeolite molecular sieve has the silica-alumina ratio of 20, 30, 40 and 60 and the grain size of about 50 nm (the specific surface area is shown in the table 1). Pseudo-boehmite is used as a binder, sesbania powder is used as a pore-forming agent, the dry basis weight percentage of the molecular sieve in the extruded strip-shaped granular catalyst is 80%, and the strip-shaped sodium type catalyst is obtained by extrusion molding, air drying, drying and roasting.
The extruded catalyst samples were prepared as a hydrogen catalyst according to conventional practice: the catalyst in hydrogen form was obtained by exchanging 3 times with a slow flowing ammonium nitrate solution (0.6mol/L) at room temperature for 2h, and its TPD and di-tert-butylpyridine were characterized by the results shown in FIG. 1 (Si/Al ratio of 30) for the total acidity and the external surface acidity of the catalyst. The hydrogen type catalyst is used for the gas phase alkylation reaction of benzene and methanol, the reaction temperature is 400 ℃, the reaction pressure is 1.0MPa, the benzene/methanol molar ratio is 2, and the total feeding mass space velocity is 2h-1Under the condition of (3), the benzene conversion rate is more than 28 percent, and the methanol conversion rate is more than 99 percent. Compared with the product composition after 48 hours of reaction, the percentage of ethylbenzene impurities in the carbon-eight aromatic hydrocarbon products of the catalyst with the silicon-aluminum ratio of 20, 30, 40 and 60 in turn accounts for 48.0%, 44.5%, 46.6% and 50.6% of the main xylene product.
Example 1
The benzene and methanol alkylation catalysts were prepared using the sodium catalyst in the form of strands (silica alumina ratio in the order of 20, 30, 40, 60) obtained by calcination after extrusion molding in the comparative examples as the precursor. Firstly, mixing the strip-shaped sodium catalyst and 0.6mol/L sodium nitrate solution according to the solid-to-liquid ratio of 1:5, refluxing for 3 hours at 50 ℃, filtering and drying. The same method is used for reflux treatment for 3 times, and the deactivated catalyst is obtained after filtration, drying and roasting, wherein the TPD and the di-tert-butylpyridine represent the total acidity and the outer surface acidity of the catalyst and have the results shown in figure 2 (silicon-aluminum ratio of 30). Secondly, mixing the deactivated catalyst with 0.6mol/L tetrapropylammonium bromide solution according to a solid-to-liquid ratio of 1:2, carrying out reflux treatment for 3h at room temperature, filtering, drying and roasting to obtain the alkylation catalyst, wherein TPD and di-tert-butylpyridine represent the total acidity and the external surface acidity of the catalyst and have the results shown in figure 3 (silicon-aluminum ratio of 30). The above catalyst was used in the gas phase alkylation of benzene and methanol under the same reaction conditions as in the comparative example. The product after 24 hours of reaction is analyzed and calculated, and the result shows that the conversion rate of benzene is more than 27 percent, the conversion rate of methanol is more than 99 percent, and the percentages of ethylbenzene impurities in the carbon eight aromatic hydrocarbon product in the xylene main product are 18.0 percent, 18.5 percent, 19.6 percent and 20.6 percent in sequence.
Example 2
Example 1 was repeated, with the strip-shaped sodium catalyst being deactivated by 2-fold recirculation with 0.6mol/L sodium nitrate solution, and the other conditions being unchanged. The obtained alkylation catalyst was used in the gas phase alkylation of benzene and methanol under the same reaction conditions as in the comparative example. The product after 24 hours of reaction is analyzed and calculated, and the result shows that the conversion rate of benzene is more than 27 percent, the conversion rate of methanol is more than 99 percent, and the percentages of ethylbenzene impurities in the carbon eight aromatic hydrocarbon product in the xylene main product are 34.0 percent, 33.5 percent, 33.6 percent and 36.6 percent in sequence.
Example 3
Example 1 was repeated, and the strip-shaped sodium-type catalyst was subjected to 1-time refluxing treatment with 0.6mol/L sodium nitrate solution, while the other conditions were not changed. The obtained alkylation catalyst was used in the gas phase alkylation of benzene and methanol under the same reaction conditions as in the comparative example. The product after 24 hours of reaction is analyzed and calculated, and the result shows that the conversion rate of benzene is more than 27 percent, the conversion rate of methanol is more than 99 percent, and the percentages of ethylbenzene impurities in the carbon eight aromatic hydrocarbon product in the xylene main product are 40.0 percent, 38.5 percent, 39.6 percent and 41.6 percent in sequence.
Example 4
Example 1 was repeated, and the number of times of the refluxing treatment of the 0.6mol/L tetrapropylammonium bromide solution was adjusted to 2 times, while the other conditions were not changed. The obtained alkylation catalyst was used in the gas phase alkylation of benzene and methanol under the same reaction conditions as in the comparative example. The analysis and calculation of the product after 24 hours of reaction show that the conversion rate of benzene is more than 28 percent, the conversion rate of methanol is more than 99 percent, and the percentages of the ethylbenzene impurities in the carbon-eight aromatic hydrocarbon product in the main product of the xylene are 17.8 percent, 18.0 percent, 19.0 percent and 19.6 percent in sequence.
Example 5
Example 4 was repeated, replacing the tetrapropylammonium bromide solution with tetrabutylammonium bromide solution, and the other conditions were unchanged. The obtained alkylation catalyst was used in the gas phase alkylation of benzene and methanol under the same reaction conditions as in the comparative example. The analysis and calculation of the product after 24 hours of reaction show that the conversion rate of benzene is more than 28 percent, the conversion rate of methanol is more than 99 percent, and the percentages of the ethylbenzene impurities in the carbon-eight aromatic hydrocarbon product in the main product of the xylene are 17.0 percent, 18.0 percent and 19.0 percent in sequence.
TABLE 1 specific surface area of ZSM-5 molecular sieves with different Si/Al ratios
Figure BDA0001709832770000091

Claims (8)

1. A preparation method of a benzene alkylation catalyst is characterized by comprising the following steps:
the first step is as follows: selecting a low-silica-alumina ratio nano ZSM-5 molecular sieve as a matrix of the catalyst;
the low silica alumina ratio nano ZSM-5 molecular sieve has the following silica alumina ratio and grain size:
SiO2/Al2O3the ratio selection is less than or equal to 100;
the primary crystal size is selected to be less than or equal to 100 nanometers;
the second step is that: deactivating the acid centers on the inner and outer surfaces of the low silica-alumina ratio nano ZSM-5 molecular sieve by using an alkali metal sodium ion solution;
firstly, using soluble sodium salt as a treatment solution, wherein the concentration of sodium ions is 0.05-1.0 mol/L; then the treatment liquid is contacted with the low-silica-alumina ratio nano ZSM-5 molecular sieve in the weight ratio of 2:1-20: 1; deactivating at 30-90 deg.c for over 0.5 hr; the whole process is carried out in the state that the solution circularly flows or is slowly stirred, after the solution treatment is finished, the treatment solution is poured, and the solid is directly dried and roasted;
selectively exchanging and removing sodium ions on the outer surface of the molecular sieve by adopting ammonium bromide of tetraethyl or tetrapropyl or tetrabutyl quaternary ammonium cations, and recovering an acidic active center on the outer surface of the molecular sieve by removing the quaternary ammonium cations in subsequent roasting; the concentration of the quaternary ammonium cation is more than 0.01 mol/L; treating at 20-50 deg.C for more than 0.5 hr; the whole process is carried out in the state that the solution circularly flows or is slowly stirred, and after the treatment is finished, the treatment solution is poured out;
and step four, finally, drying and roasting the catalyst obtained in the step three to obtain the benzene alkylation catalyst.
2. The production method according to claim 1,
the low silica alumina ratio nano ZSM-5 molecular sieve has the following silica alumina ratio and grain size:
SiO2/Al2O3the ratio selection is less than or equal to 60;
the primary crystal size is less than or equal to 50 nm.
3. The production method according to claim 1 or 2,
before deactivating the low silica alumina ratio nano ZSM-5 molecular sieve, molding and processing the low silica alumina ratio nano ZSM-5 molecular sieve;
the forming process is extrusion forming, rolling ball forming or spray forming.
4. The production method according to claim 1 or 2,
the deactivation processing conditions were further as follows:
firstly, using soluble sodium salt as a treatment solution, wherein the concentration of sodium ions is 0.3-0.6 mol/L; then the treatment liquid is contacted with the low-silica-alumina ratio nano ZSM-5 molecular sieve in a weight ratio of 5:1-10: 1; the deactivation treatment time is more than 3 hours at the temperature of 50-80 ℃; the whole process is carried out in the state that the solution circularly flows or is slowly stirred, after the solution treatment is finished, the treatment solution is poured, and the solid is directly dried and roasted;
the soluble sodium salt is sodium nitrate, sodium chloride or sodium sulfate prepared aqueous solution.
5. The production method according to claim 3,
the deactivation processing conditions were further as follows:
firstly, using soluble sodium salt as a treatment solution, wherein the concentration of sodium ions is 0.3-0.6 mol/L; then the treatment liquid is contacted with the low-silica-alumina ratio nano ZSM-5 molecular sieve in a weight ratio of 5:1-10: 1; the deactivation treatment time is more than 3 hours at the temperature of 50-80 ℃; the whole process is carried out in the state that the solution circularly flows or is slowly stirred, after the solution treatment is finished, the treatment solution is poured, and the solid is directly dried and roasted;
the soluble sodium salt is sodium nitrate, sodium chloride or sodium sulfate prepared aqueous solution.
6. The production method according to claim 1, 2 or 5,
the concentration of the quaternary ammonium cation is 0.2-0.6 mol/L; treating at 25-40 deg.C for more than 2 hr.
7. The production method according to claim 3,
the concentration of the quaternary ammonium cation is 0.2-0.6 mol/L; treating at 25-40 deg.C for more than 2 hr.
8. The production method according to claim 4,
the concentration of the quaternary ammonium cation is 0.2-0.6 mol/L; treating at 25-40 deg.C for more than 2 hr.
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