Method of preparation of zeolite-containing catalyst for the aromatization of hydrocarbons

 

(57) Abstract:

Method of preparation of zeolite-containing catalyst for the aromatization of hydrocarbons, comprising preparing zeolite ZSm - 5 with a molar ratio of SiO2/Al2O3at least 80:1, alumets by dissolving aluminum metal in a mineral acid, followed by neutralization with a weak base Zola first stage, treatment with a strong mineral acid and evaporation of Zola in the second stage, a mixture of alumets with zeolite, the introduction of gallium compounds directly into the resulting suspension, a dispersion of a suspension in an aqueous solution of ammonia, heat treated spherical granules and drying. 5 C.p. f-crystals, 1 table.

The invention relates to the field of inorganic synthesis, particularly to a method of preparing zeolite-containing catalyst with a high silicon content, which can be used in industrial petrochemical processes, in particular in the process of aromatization of hydrocarbons.

The use of zeolite catalysis in the process of thermal conversion of low molecular weight alkanes to aromatic hydrocarbons is the most effective. However, this process protece the participating accelerated passivation its active centers. To restore the activity of the catalyst is necessary to conduct operations regeneration, which consists in burning out "coke" at high temperature oxygen. The stability of framework aluminosilicate catalyst during hard conditions of the process of transformation of low molecular weight paraffins to aromatic hydrocarbons and burning carbon deposits after the completion of the operating cycle creates ideal conditions for the development of industrial contacts with reliable performance.

From the prior art, it follows that the most active and selective in this process are the aluminosilicates family pentelow (2Sm or MFI), modified metal compounds, of which the most effective is gallium. So, in patents /1,2/ for flavoring paraffin hydrocarbons WITH3C8use kalisoderjasimi zeolite ZSm-5 with silicate module SiO2/Al2O320oC 70 1 (mol.). Kalisoderjasimi zeolite catalysts allow for the conversion of alkanes to aromatic hydrocarbons with a maximum selectivity, which in the case of use as a raw material of propane and stoiculescu alternating working and regeneration cycles, are however a number of disadvantages. First, the selectivity of the formation of the target aromatic hydrocarbons from alkanes far from theoretically possible, and, secondly, the duration mezhregionalnogo interval of operation of the catalyst is too small and is measured in several tens of hours. At the same time for a short working cycle of the catalyst, its activity is measured by the depth of the transformation of the raw material for the passage substantially reduced.

To reduce the rate of deactivation of the catalyst in the process of converting alkanes to aromatic hydrocarbons used a number of ways, based on different variants pre-treatment of the catalyst.

The authors of the famous fashion /4/ to achieve this goal is recommended to handle the aluminosilicate catalyst solutions of organic bases, carboxylic acids, glycols, phenol, or ether. The use of this technique allows to reduce the degree of reduction of the conversion of propane for 6 to 7 hours of continuous testing of Katalizator in the process of aromatization with 50 to 60% of abs. until 13 16% abs. The disadvantage of this method is the complexity and cost of the technology due to the introduction of additional processing stage catalyst d is S="ptx2">

In a known way /5/, selected as a prototype, with the aim of increasing the service life containing gallium zeolite catalyst by reducing coke formation in the process of aromatization of alkanes proposed modification of the catalytic compositions with phosphorus. It is assumed that the introduction of phosphorus compounds contributes to the transformation of the active centers of the binder (alumina), which is responsible for rapid coking of the catalyst, and the associated decrease in its activity. It is shown that the introduction of phosphorus compounds in the amount of 11 wt. in the calculation of the catalyst by reducing the concentration of coke on it after a test period of 100 h from 30.5% to 5.8% average conversion of raw materials to compare samples of the same and amounts to 45 wt. and the average selectivity of the formation of aromatic hydrocarbons in the modification increases from 54 to 57 wt. The disadvantage of this method is the use of additional reagents in the synthesis, leads to appreciation of the catalyst.

In addition, as shown in a known way /6/ detailing features of the preparation, use and regeneration of what and how /5/ catalyst t is t using oil as the dispersion medium, which leads to the need for operation periodic regeneration as pollution and disposal of waste water containing oil, at a later stage washing of the resulting spheres. Known molding technology requires the use of additional agent is hexamethylenetetramine (urotropine), partially decomposing in the process of dispersion in hot oil. Complete removal of organic components from the resulting spheres is at the stage of their initial calcination. Adopted in the known method the introduction of a promoter in the finished area of the media (zeolite-binder) leads to the need for additional secondary calcination of the finished catalyst and consequently the cleaning gas emissions after primary and secondary pokulok. In addition, there is a method of forming spherical catalyst includes a very long process of "aging" Almohades, which is 1 for 24 h in an oil bath or 6 h in ammonia. The duration of operation of aging leads to a periodicity of the molding process and a certain technological complications.

The technical problem faced by the authors of the image is cities with simplified technology, excluding the application of oil and hexamethylenetetramine in forming spheres, technology, cleaner, allowing the organization of a continuous process of forming spherical pellets of catalyst, manifesting in the aromatization reaction of low molecular weight alkanes high selectivity, stability, and activity. This goal is achieved by the proposed method for preparation of alumets, using the preparation of the catalyst the high-silica zeolite of type ZSm-5 with a characteristic silicate module and use as a forming medium of an aqueous solution containing ammonia, compounds of a number of ammonia or mixtures thereof.

In accordance with the method proposed catalytic system for the aromatization of hydrocarbons, in particular alkanes WITH3C4consists of a high-silica zeolite of type ZSm-5 having a molar ratio of SiO2/Al2O3more than 70: 1, Al2O3as a binder in a mass ratio of zeolite: binder in the range of 20oC 80:1 and the promoting additives in the form of compounds of gallium in the amount of 0.5 to 5.0 wt. in terms of metallic gallium.

The hallmarks from the way the prototype the following:

preparation Alu the stage with intermediate neutralization of a weak base Zola first stage, subsequent processing of a strong inorganic acid and evaporation of Zola in the second stage. The application of the proposed design technique allows to organize the technology of drip molding on a continuous circuit, eliminating the need for long-term operation of "aging" alumets, as in the known methods of drip molding (5,6);

use as aluminosilicate component of the catalyst is high-silica zeolite of type ZSm-5 with a molar ratio of SiO2/Al2O3more than 70: 1, synthesized under hydrothermal conditions from sources of silicon and aluminum in the presence of sodium hydroxide and ethanol as a structure-forming additives;

introduction gallium is used as the promoter in the catalyst composition at the stage of mixing the zeolite component with modified lumatrim the second stage before the surgery drip molding, and not by impregnation of a spherical carrier in a known manner. This technique allows you to abandon the operation of the intermediate calcination and what significantly has a positive influence on the process of forming spherical pellets.

use with drip molding as divenne to simplify and improve the environmental performance of the technological process, since the molding process is carried out in the absence of organic components, such as oil or methenamine.

Thus we can conclude according to the invention, the criterion of "novelty."

The materiality of the above-mentioned distinguishing features proved the following.

The first of these characteristics relates to the preparation stage of alumets. Known methods of preparation of spherical carriers, adsorbents or catalysts based on aluminum oxide provide application alumets obtained by direct dissolution of aluminum metal in the inorganic acid (5,6). As a direct result of the use of such Zola to ensure that the process of "aging" molded spheres in the dispersion medium of reaching in some cases days. This fact determines the frequency molding technology with all the negative consequences. To resolve their proposed method provides a new unknown in the prior art technology making alumets in two stages. Almasol the first stage is obtained by dissolving aluminum metal in a strong inorganic acid in a known manner. But then he Paley Sol is treated with a solution of the same mineral acid, followed by evaporation in the second stage up to a concentration of 60 to 110 g/L. for aluminum, the molar ratio of the acid anion to aluminum 0,7 1,37.

The proposed method for the preparation of alumets reduces the time drip molding the resulting gel-spheres up to 1 5 min, and carry out thereby a continuous molding technology, improving thus the porous structure of the obtained spherical particles.

Materiality use as aluminosilicate components of the catalyst the high-silica zeolite of type ZSm-5 with a molar ratio of SiO2O3more than 70 proven established by the inventors of fact significant dependence of the rate of coking of the catalyst not only on the characteristics of the active surface of the binder, the modification of which is directed supplementation of phosphorus compounds in the known solutions (5,6), but the ratio of SiO2/Al2O3in the zeolite matrix. This is illustrated by the examples in the table. The inventors have found that increasing this ratio, the stability of the catalyst by coking is significantly increased.

Essential to the achievement of the technical result and the method of introduction gallium promoter proposed by the authors of the invention. Izvestiya produce spherical catalyst;

introduction compounds of gallium in the intermediate stages of forming the gel spheres;

apply compound of gallium on the prepared spherical media zeolite-binder. This method of introduction of gallium given preference in obtaining spherical catalyst in the method of the prototype. The disadvantage of this method is the need for calcination of the catalyst after forming spheres, and after the introduction of gallium nitrate. To simplify technology for preparation of spherical catalyst and reduce energy consumption by the authors of the present invention prompted to enter the gallium nitrate in almasol at the stage of mixing with the zeolite directly in front drip molding. This technique not only eliminates the intermediate calcination of the gel spheres, but also has an impact on the stage of the drip molding, reducing the residence time of the granules in the dispersion medium, while maintaining performance properties of the catalyst.

The last of these distinctive characteristics are related to aspects of improvement of technology of preparation of spherical catalyst and is used as a dispersion medium with drip method formovannaja you can use any connection but preferably the nitrate, chloride, carbonate, sulfate, etc., the mixing Ratio of ammonium salts insignificant and is calculated in each case based on the desired concentration of ammonium ion in solution, the dissociation constants of salts and other factors. In comparison with known methods proposed technology not related to the use of organic reagents in the preparation of spherical catalyst such as oil, hydrocarbons, hexamethylenetetramine or urea. As well known technology has several disadvantages. In the process of drip molding hot oil, contacting the slurry of zeolite and binder in the presence of hexamethylenetetramine, constantly polluted suspension components and products of thermal decomposition of hexamine. This fact significantly complicates the technology of preparation of spherical catalyst, because it leads to the necessity of constant monitoring of physico-chemical characteristics of oil and its periodic regeneration. The use of oil as the dispersion medium leads to the appearance on the stage of washing the gel spheres of wastewater contaminated with oil, the disposal of which requires more readyasset increased requirements for manufacturing operations calcining the spherical catalyst.

The above-mentioned shortcomings devoid proposed by the authors of the invention "oil-free" scheme for the preparation of spherical catalyst, namely, that drip dispersion suspension alumetal-zeolite-gallium nitrate is carried out in an aqueous solution of ammonia. The absence in the schema of any organic components (oil and hexamethylenetetramine, in particular), gel-spheres catalyst and wastewater contaminated with oil, greatly simplifies the technology of preparation of the catalyst, makes it more environmentally friendly and reduces the cost of its implementation.

From the above it follows that to solve the problem only allows the implementation of all significant characteristics, thus we can conclude that the proposed solution meets the criterion of "inventive step".

The proposed method for the preparation of the catalyst in the aromatization of low molecular weight alkanes may be implemented on an industrial scale and is illustrated by the following examples of specific performance.

Example 1. Obtaining zeolite-active to the beginning of the aromatization catalyst.

The mould is made of steel and SN,8, NaAlO2, 225,1 g NaOH and 18.8 l of demineralized water, 2800 g of silica gel and 4 l2H5OH. The formed gel is homogenized and incubated at 150oC and stirring for 60 hours At the end of crystallization of the crystalline grain is separated from the mother liquor, washed with demineralized water and dried at 110oC for 6 h

Get a zeolite of type ZSm-5 chemical composition, wt. 90,7 SiO2, 1,7 Al2O3, 1,2 Na2O, 0.2 s and silicate module SiO2/Al2O3about 90 mol.).

The sodium form of the zeolite is subjected to the operation of ion exchange. With this purpose, 100 g of the zeolite is treated with 70oC under stirring for 3 h 600 g of a 10% aqueous solution of NH4NO3to a residual content of sodium in the zeolite 0.02 wt. The suspension of the zeolite is filtered, the zeolite is washed with demineralized water and dried at 110oC for 6 h

Example 2. Obtaining spherical catalyst.

100 g of aluminum powder is dissolved with stirring and a temperature of 65 to 70oC 4.5 DM310% solution of HNO3cool the solution to 20 25oC add 8 MD3distilled water, 0.5 DM325% solution of NH3, heated to 96 98oC and in the 09 DM3approximately 60% solution of HNO3, evaporated under stirring up to a volume of 1.5 to 2 DM3obtaining modified Zola, consistently contribute to the weight 53 g Ga(NO3)38H2O, 300 g of zeolite powder obtained in example 1, and again evaporated to about 0.9 DM3. The suspension is cooled to 30 to 40oC. Obtaining a gel-spheres carried out by dispersing the suspension of the secondary Sol-zeolite-gallium nitrate in 12% aqueous ammonia solution. Getting into the ammonia solution, the droplets solidify due to the hydrolysis reaction taking place in the volume drops. The time spent spheres in a solution of ammonia is 2 to 3 minutes After the separation of the spheres from ammonia latter is washed with demineralized water, dried by superheated steam with a temperature of 170 200oC and calcined 2 hours at 600oC.

The output of finished catalyst 480 hours the catalyst containing 2 wt. promoter in terms of metallic gallium at wt. the ratio of zeolite (chem. the composition in example 1): a binder in the form g Al2O360:40.

Testing of catalytic properties made in the conditions of example 2 catalysts in the reaction of aromatization of low molecular weight alkanes, carried out by the following method.

Prima 2, in the amount of 100 g load in the steel flow reactor setup, activate at 550oC in a stream of air for 2 h, rinsed with nitrogen and passed propane or butane, determining the conversion of the raw material, the selectivity of the formation of aromatic hydrocarbons and content of coke in the catalyst.

The test results presented in the table.

From the table it follows that, although the contents of the coke on the catalyst after completion of the test a few exceed the value given in the prototype, the selectivity of the formation of aromatic hydrocarbons from Bhutan is on the same level, and the average conversion of the raw material for 100 h in about 15 abs. more in the proposed method.

Thus, the proposed method for the preparation of the catalyst in the aromatization of hydrocarbon gases along with the technical advantages consisting in substantial simplification of the technological scheme, associated, mainly, with no need to use organic substances with drip molding in the scheme as a whole, the opportunity to implement technology on a continuous circuit, etc. provides equal conditions improved in comparison with the prototype performance setup Aromasin hydrocarbons, including the production of zeolite ZSM-5 with a molar ratio of SiO2/Al2O3at least 73:1, alumets obtained by dissolving aluminum metal in a strong inorganic acid, their subsequent mixing, droplet dispersion of the mixture in the dispersion medium, a modification of the obtained granules gallium and their heat treatment, characterized in that use almasol obtained in two stages with the neutralization of a weak base Zola first stage, followed by treatment with a strong mineral acid and evaporation of Zola in the second stage, the introduction of gallium compounds is carried out directly in the suspension of zeolite and alumets and dispersion is carried out in aqueous solution, ammonia or compounds his number or their mixtures with a concentration of ammonia of at least 6 wt. at a temperature of at least 10oC.

2. The method according to p. 1, characterized in that the use of zeolite ZSM-5 with a molar ratio of SiO2/Al2O380-100.

3. The method according to p. 1, characterized in that as a strong inorganic acid, nitric acid.

4. The method according to p. 1, characterized in that the neutralization Zola first stage hold water is 0 g/l, for aluminum, the molar ratio of the acid anion to aluminum 0,7 1,3.

5. The method according to p. 1, characterized in that compounds of some use ammonia chloride, nitrate, sulfate or ammonium carbonate.

6. The method according to p. 1, characterized in that the residence time of the droplets of the suspension in the dispersion medium is 1 to 5 minutes

 

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