Bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes and preparation method and application thereof
阅读说明：本技术 用于正构烷烃直接芳构化的双金属无酸铝硅酸盐多孔复合材料及其制备方法和应用 (Bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes and preparation method and application thereof ) 是由 宋华 于 2020-03-30 设计创作，主要内容包括：本发明公开了一种用于正构烷烃直接芳构化的双金属无酸铝硅酸盐多孔复合材料及其制备方法和应用。该双金属无酸铝硅酸盐多孔复合材料是由具有活性位点的金属和非酸性多孔铝硅酸盐的基体材料,其中基体材料为包括ZSM-5型在内的分子筛。具有活性位点的金属是Pt,Pd,Na,K,Ca和Ba的一种或多种的混合物,每种金属在基体材料上的负载量是基体材料质量的0.1-10％。本发明制备的双金属无酸铝硅酸盐多孔复合材料能够实现多种烷烃(C<Sub>6</Sub>-C<Sub>10</Sub>)向芳烃等高附加值的化学品的转化,同时生产较少的焦炭。(The invention discloses a bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes and a preparation method and application thereof. The bimetallic acid-free aluminosilicate porous composite material is a matrix material of metal with active sites and non-acidic porous aluminosilicate, wherein the matrix material is a molecular sieve including ZSM-5 type. The metal having an active site is one of Pt, Pd, Na, K, Ca and BaOr a mixture of a plurality of metals, each metal being present in the matrix material in an amount of 0.1 to 10% by mass of the matrix material. The bimetallic acid-free aluminosilicate porous composite material prepared by the invention can realize various alkanes (C) 6 ‑C 10 ) Conversion to high value-added chemicals such as aromatics while producing less coke.)
1. Bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanesThe composite material is characterized in that the composite material is used for aromatization of alkane raw materials with the carbon chain length of 6-10, and the composite material is based on porous aluminosilicate with bimetallic load and has the following composition in molar ratio of wM1·xM2·ySiO2·zAl2O3Wherein w is 0-9.23 x 10-2，x＝0～3.09*10-2Y is between 4.36 x 10-2And 2.84 x 10-3，M1And M2Is any two of Pt, Pd, K, Na, Ca and Ba.
2. The method for preparing a bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes according to claim 1, which comprises the steps of:
1) preparing an organic template agent aqueous solution, wherein the mass fraction of the organic template agent is 10-40% of the aqueous solution, adding an aluminum source precursor, and uniformly stirring, wherein the content of the aluminum source precursor is determined by calculation according to the content of aluminum in the composite material;
2) adding the aqueous solution of the organic template agent and the precursor of the aluminum source into the raw material of the precursor of the silicon source and keeping stirring for 2 hours to obtain SiO2:Al2O3Mixtures in molar ratios ranging from 23:1 to 350: 1; after completely adding the silicon source precursor solution for 5-2400 minutes, obtaining a supersaturated solution along with the hydrolysis of the silicon source precursor, and then forming gel;
3) the gel obtained in the step 2) is reacted for 0.5 to 7 days at the temperature of 150-200 ℃ by a hydrothermal synthesis method to obtain high-purity crystalline powder, particles, aggregates or molded products, and the particle size range is 5 to 500 nm;
4) the product material still in solution is isolated by freeze drying and subsequently dried at a temperature above 75 ℃ and below 125 ℃ for a period of 3 to 24 hours at a pressure of 0.25 to 0.9 atm; after drying, calcining the product for 1-5 hours at the temperature of 400-;
5) and (3) carrying out metal loading on the carrier material obtained in the step 4), wherein the loaded metal is any two of Pt, Pd, K, Na, Ca and Ba, and the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes is prepared, wherein the metal loading is 0.1-10% by weight, and the precursor of the loaded metal is metal nitrate, sulfate or chloride.
3. The method for preparing the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes according to claim 2, wherein in step 2), after stirring for 1-60 minutes at room temperature, the silicon source precursor is added into the organic template aqueous solution containing the aluminum source precursor; in the preparation process of the partial bimetal acid-free aluminosilicate porous composite material, alkali metal or monovalent or divalent alkaline earth metal cations are added into an aqueous solution of an organic template and an aluminum source precursor, so that the content of the cations is between 10mg/g and 60 mg/g.
4. The method for preparing the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes according to claim 2, characterized in that in step 3), a microwave-assisted process is adopted.
5. The method for preparing a bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes according to claim 2, wherein in step 5), the temperature is maintained at 75-150 ℃ for 1-24 hours, and then the calcination is carried out in air or nitrogen atmosphere; the calcination temperature is 300-700 ℃ and the heating rate is 0.5-20 ℃/min because of different metal loading modes and different reaction conditions.
6. The method for preparing the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes according to claim 2, wherein the metal loading method used in step 5) comprises an initial wet impregnation method, a hydrothermal method, a current substitution method, a precipitation deposition method and a physical mixing method.
7. The bimetallic acid-free aluminosilicate porous composite for direct aromatization of n-alkanes of claim 1Use of a material, characterized in that the composite is used for the direct aromatization of n-alkanes, comprising C6-C10A plurality of alkanes or mixture thereof; and nitrogen, methane or hydrogen is used as a gas raw material, and is introduced into a reactor system simultaneously with the alkane raw material or before or after the alkane raw material reaches the reaction temperature, aromatization is carried out under the catalytic action, and the mass ratio of reactants to the bimetallic acid-free aluminosilicate porous composite material is 10:1 to 1: 10.
8. Use of the bimetallic acid-free aluminosilicate porous composite for direct aromatization of n-alkanes according to claim 7 characterized by the reactor system of one or more of the following combinations: batch reactors, continuous stirred reactors, continuous tubular reactors, packed bed reactors, semi-batch reactors, such as fixed bed, fluidized bed, moving bed, rotating bed, fluidized bed, and slurry reactors.
9. Use of the bimetallic acid-free aluminosilicate porous composite for direct aromatization of n-alkanes according to claim 7 characterized in that the reaction temperature is between 300 ℃ and 600 ℃.
10. Use of the bimetallic acid-free aluminosilicate porous composite for direct aromatization of n-alkanes according to claim 7 characterized in that the reaction pressure is between 1 and 200 atmospheres.
Technical Field
The invention belongs to the field of petroleum refining, and particularly relates to a bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes, and a preparation method and application thereof.
Background
Aromatic compounds such as benzene, toluene, ethylbenzene and xylene (BTEX) are important chemical raw materials and can be used for producing various important high polymer materials and chemicals. At present, the main way for preparing BTEX is to carry out catalytic reforming on petroleum raw materials such as naphtha, and the like, but the problems of low target product selectivity, high coking, quick catalyst inactivation and the like exist in the prior art, so that the important significance of optimizing the prior art is highlighted, and how to improve the production process of BTEX becomes a research hotspot which is continuous for many years in the chemical industry. In addition, as the amount of gasoline used as a fuel reaches a bottleneck due to environmental protection and other factors, there is an increasing interest in optimizing such processes and converting petroleum raw materials into chemical raw materials more efficiently, so as to produce high-value chemical raw materials by using the petroleum raw materials more and reduce the dependence on fuel use.
Conventional thermal cracking of petroleum feedstocks is often associated with lower energy efficiency and product selectivity, a problem which can be ameliorated and overcome by the use of catalysts (typically heterogeneous catalysts) in the reaction to increase the selectivity of the target product and the energy efficiency of the chemical process. In the catalytic cracking of petroleum feedstocks, heterogeneous catalysts based on molecular sieves are often used to promote the desired reaction. In fact, molecular sieves are one of the most widely used materials in hydrocarbon conversion. Among a plurality of molecular sieve materials, HZSM-5, which is aluminosilicate with a micropore MFI structure, is widely used for cracking and refining petrochemical products, and can effectively improve the octane number of petroleum refined products. Meanwhile, HZSM-5 has controllable cracking capacity and product selectivity, and the properties can be effectively adjusted by changing the acidity of zeolite by changing the ratio of silicon to aluminum. Through the loading of metal, the efficiency of the HZSM-5 catalyst can be further improved, and the stability of the catalyst can be greatly improved. For example, by adjusting product selectivity, polycyclic aromatic hydrocarbon compounds (C) are inhibited10+) The production of such products, which are of low commercial value and which may be coke precursors, can lead to significant improvements in the selectivity to the desired product and the lifetime of the catalyst. The acidity of the catalyst may also have a significant effect on its performance. For example, it is widely recognized as one of the most selective catalysts for direct aromatization of naphthaPt/K L, whichThe acid sites are occupied by K atoms, so that the cracking of the raw material carbon chains is inhibited, the oligomerization effect is avoided, and the generation of polycyclic aromatic hydrocarbon is reduced.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a bimetallic acid-free aluminosilicate porous composite material for direct aromatization of normal alkane, a preparation method and application thereof, wherein C can be prepared from C6-C10The alkane feed is efficiently converted to aromatic products.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme:
the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes is used for aromatization of alkane raw materials with carbon chain length of 6-10, and the composite material is based on bimetallic load porous aluminosilicate and has the following composition in molar ratio of wM1·xM2·ySiO2·zAl2O3Wherein w is 0-9.23 x 10-2，x＝0～3.09*10-2Y is between 4.36 x 10-2And 2.84 x 10-3，M1And M2Is any two of Pt, Pd, K, Na, Ca and Ba.
The preparation method of the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes comprises the following steps:
1) preparing an organic template agent aqueous solution, wherein the mass fraction of the organic template agent is 10-40% of the aqueous solution, adding an aluminum source precursor, and uniformly stirring, wherein the content of the aluminum source precursor is determined by calculation according to the content of aluminum in the composite material;
2) adding the aqueous solution of the organic template agent and the precursor of the aluminum source into the raw material of the precursor of the silicon source and keeping stirring for 2 hours to obtain SiO2:Al2O3Mixtures in molar ratios ranging from 23:1 to 350: 1; after completely adding the precursor solution of the silicon source for 5-2400 minutes, the supersaturated solution is obtained along with the hydrolysis of the precursor of the silicon sourceAnd a solution, then forming a gel;
3) the gel obtained in the step 2) is reacted for 0.5 to 7 days at the temperature of 150-200 ℃ by a hydrothermal synthesis method to obtain high-purity crystalline powder, particles, aggregates or molded products, and the particle size range is 5 to 500 nm;
4) the product material still in solution is isolated by freeze drying and subsequently dried at a temperature above 75 ℃ and below 125 ℃ for a period of 3 to 24 hours at a pressure of 0.25 to 0.9 atm; after drying, calcining the product for 1-5 hours at the temperature of 400-;
5) and (3) carrying out metal loading on the carrier material obtained in the step 4), wherein the loaded metal is any two of Pt, Pd, K, Na, Ca and Ba, and the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes is prepared, wherein the metal loading is 0.1-10% by weight, and the precursor of the loaded metal is metal nitrate, sulfate or chloride.
The further improvement of the invention is that in the step 2), after stirring for 1-60 minutes at room temperature, a silicon source precursor is added into an organic template agent aqueous solution containing an aluminum source precursor; in the preparation process of the partial bimetal acid-free aluminosilicate porous composite material, alkali metal or monovalent or divalent alkaline earth metal cations are added into an aqueous solution of an organic template and an aluminum source precursor, so that the content of the cations is between 10mg/g and 60 mg/g.
The invention has the further improvement that in the step 3), a microwave-assisted process is adopted.
The further improvement of the invention is that in the step 5), the temperature is kept for 1 to 24 hours at the temperature of 75 to 150 ℃, and then the calcination is carried out in the air or nitrogen atmosphere; the calcination temperature is 300-700 ℃ and the heating rate is 0.5-20 ℃/min because of different metal loading modes and different reaction conditions.
The further improvement of the invention is that in the step 5), the metal loading method comprises an initial wet impregnation method, a hydrothermal method, a current substitution method, a deposition precipitation method and a physical mixing method.
For direct arylation of n-alkanesUse of a structured bimetallic acid-free aluminosilicate porous composite for the direct aromatization of n-alkanes, comprising C6-C10A plurality of alkanes or mixture thereof; and nitrogen, methane or hydrogen is used as a gas raw material, and is introduced into a reactor system simultaneously with the alkane raw material or before or after the alkane raw material reaches the reaction temperature, aromatization is carried out under the catalytic action, and the mass ratio of reactants to the bimetallic acid-free aluminosilicate porous composite material is 10:1 to 1: 10.
In a further development of the invention, the reactor system comprises one or more of the following combinations: batch reactors, continuous stirred reactors, continuous tubular reactors, packed bed reactors, semi-batch reactors, such as fixed bed, fluidized bed, moving bed, rotating bed, fluidized bed, and slurry reactors.
A further development of the invention is that the reaction temperature is between 300 ℃ and 600 ℃.
A further development of the invention is that the reaction pressure is between 1 and 200 atmospheres.
The invention has at least the following beneficial technical effects:
in the alkane aromatization process, the selectivity of BTEX products such as benzene, toluene, ethylbenzene, xylene and the like is very high, the selectivity of aromatic hydrocarbon and polycyclic aromatic hydrocarbon with more side chains is inhibited, and the bimetallic acid-free aluminosilicate porous composite material has good atom economy; 2) according to the characteristics of the raw materials, factors such as metal load, reaction temperature and the like in the composite material reported by the invention can be adjusted, and the selectivity of target products including isomers in xylene can be adjusted; 3) the coke formation amount of the composite material reported by the invention is very low in the catalytic reaction process.
The bimetallic acid-free aluminosilicate porous composite material for direct aromatization of normal alkane prepared by the invention aims at the urgent practical requirements of petroleum refining industry, and refines and modifies the alkane-rich raw material into high-value-attached products such as aromatic hydrocarbon and the like. By using the catalyst composed of the bimetal modified non-acidic porous aluminosilicate, the normal alkane is subjected to dehydroaromatization reaction at proper temperature and pressure, and is converted into aromatic hydrocarbon compounds with high selectivity.
The preparation method of the bimetallic acid-free aluminosilicate porous composite material for direct aromatization of n-alkanes provided by the invention can obtain a molecular sieve pore channel structure with good crystallization performance, as shown in figure 1. The pore channel structure of the molecular sieve enables the bimetallic acid-free aluminosilicate porous composite material to have larger micropore surface area and external surface area, as shown in Table 4. When the bimetallic acid-free aluminosilicate porous composite material is used as a catalyst, the large micropore surface area and the external surface area enable alkane raw material molecules to be in high-efficiency contact with catalytic sites in the catalyst, and generation of a catalytic reaction target product is facilitated. The presence of bimetal in the acid-free aluminosilicate porous composite material adjusts the performance of the bimetallic acid-free aluminosilicate porous composite material catalyst from multiple aspects, for example, the presence of K and Na can adjust the acidity of the catalyst and inhibit the generation of alkane cracking reaction; the existence of Pt and Pd is beneficial to improving the dehydrogenation performance of the catalyst and promoting the activation of alkane molecules. Through optimization of the carrier hydrothermal synthesis time and conditions such as temperature, metal composition, metal loading mode, calcination temperature and pressure, calcination atmosphere and the like, a plurality of metals and a molecular sieve pore channel structure form a synergistic effect, and an activated active intermediate is subjected to aromatization reaction in the pore channels of the composite material to generate target products such as benzene, toluene, ethylbenzene, xylene and the like.
Drawings
FIG. 1 is an XRD spectrum of a catalyst based on a ZSM-5 type molecular sieve before and after an experiment;
FIG. 2 is a diagram showing product selectivity of n-octane, n-heptane and n-hexane under the action of different catalysts. Wherein the reaction involved is at 400 ℃ and N2The initial pressure was 145psig for 30 minutes. By varying the catalyst loading, the conversion was maintained between 21% and 28%. C6Closed-ring aromatization (C)6ring closure) reaction is shown in that two carbon atoms of C1 and C6 of each normal alkane are directly closed into a ring. C5Closed loop (C)5ring closure) to form cyclopentane and cyclopentene products. Dealkylation (dealkylation) reaction comprises the reaction ofMethane and aromatics produced upon loss of one or two methyl groups. Dehydrogenation (dehydrogenation) reactions refer to reactions that produce olefins. The post isomerization aromatization reaction refers to the production of meta-xylene and para-xylene from the isomerization and subsequent aromatization of the ring species. The standard deviation of the correlation data was +/-5%.
FIG. 3 is a distribution diagram of reaction products of n-octane under the action of different catalysts. Wherein Pt/KZSM-5 is loaded with potassium ions by ion exchange, and KX-10 to KX-60 contain 10mg/g to 60mg/g of potassium ions.
Detailed Description
The invention is further described below with reference to the following figures and examples.
Naphtha and alkane reforming catalysts commonly used in industry are mainly based on Mordenite type molecular sieves, ZSM-5 type molecular sieves, aluminum chloride and the like, and metals such as platinum or palladium and the like are used as active centers, but the application of the catalysts is limited by the characteristics of low target product selectivity, high coke rate and easy deactivation. In order to solve the problems, the invention shows a porous non-acidic carrier and shows high-efficiency catalytic performance including high selectivity to aromatic hydrocarbons such as BTEX after the carrier metal.
The catalyst of the invention can use various molecular sieve carriers, and the preferred matrix material is ZSM-5 type molecular sieve with larger BET surface area (509.2 m)2/g), in particular with a large micropore surface area (315.1 m)2In terms of/g). The ZSM-5 type molecular sieve can be prepared by hydrothermal synthesis. Firstly, adding a proper amount of aluminum source precursor into tetrapropylammonium hydroxide (TPAOH) solution which is continuously stirred at room temperature, and then continuously dropwise adding an organic silicon source precursor (such as tetraethyl orthosilicate (TEOS)) into the solution in which the aluminum source precursor is dissolved. The mass ratio of the added aluminum source precursor to the organic silicon source precursor is determined by the required SiO2/Al2O3Determined by the molar ratio, SiO2/Al2O3The molar ratio may be 23 to 350. With the hydrolysis process of the silicon source precursor, the solution gradually forms gel in the stirring process, and then is transferred to a hydrothermal synthesis kettle. Then the kettle is kept at a constant temperature for a period of time, and is cooled to a roomAfter warming, the solid was recovered by freeze drying. And drying the obtained solid at a specific temperature and pressure for a period of time, and calcining the dried solid at a high temperature in a specific atmosphere for a period of time to obtain a ZSM-5 sample.
The preferred catalyst for use in the present invention is a catalyst having a ZSM-5 sample as described above as the matrix material carrying an active metal species. The supported active metal species may be a mixture of one or more of Pt, Pd, K, Na, Ca and Ba. The loading amount of each active metal is 0.1-10% of the mass of the matrix material. After the catalyst is loaded with metal, the catalyst is firstly dried under heat preservation and calcined in a specific atmosphere, and then is reduced in the environment of pure hydrogen or mixed gas containing hydrogen to promote dispersion and reduction of active metal sites.
Preferred uses of the catalyst in the present invention include, but are not limited to, direct aromatization of n-alkanes. At a certain temperature and pressure, the aromatization reaction of alkane is catalyzed, and alkane raw materials are converted into aromatic hydrocarbon products with high added values.