RU2632911C1 - Catalyst of n-alkane hydroizomerization and method of its preparation - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: catalyst of the n-alkane hydroisomerization, which as an active component contains nanodispersed molybdenum carbide in the amount of 2.5-10.0 wt % of the total catalyst weight, as the acid support, the catalyst contains SAPO-31 crystalline silicoaluminophosphate with an ATO structure in the amount of 30-80%, as a binder, aluminium oxide in the amount of 20-70%, and a carbide precursor is introduced into the catalyst at the stage of the moulding mixture production for granulation.

EFFECT: high activity, selectivity and resistance to coke deactivation of catalysts in the hydroisomerization reaction of n-alkanes.

3 cl, 5 ex, 10 tbl

Description

The invention relates to the field of chemistry, namely to catalysts intended for the process of hydroisomerization of straight-run and hydrotreated diesel fractions, and can be used in the oil refining industry.

Hydroconversion processes of hydrocarbon fractions are fundamental for obtaining high-quality fuels that meet modern environmental and operational requirements.

Hydro-processing processes for hydrocarbon fractions include:

- hydrotreating of feedstock (desulfurization processes, purification of nitrogen compounds, hydrodeoxygenation, demetallization);

- hydrogenation of aromatic components of raw materials;

- hydrodecyclization of naphthenic components of raw materials;

- hydroisomerization and hydrocracking of paraffin and naphthenic components of raw materials.

The purpose of the hydroisomerization process is to obtain branched paraffins while maintaining the fractional composition of the resulting products, which in the case of hydroisomerization of gasoline fractions leads to an increase in octane number and a decrease in the content of aromatic components of gasoline. In the process of hydroisomerization of diesel fractions, their pour point decreases, thereby improving the operational characteristics of diesel fuel at low ambient temperatures. Moreover, a significant decrease in the pour point of hydroisomerized diesel fractions is not accompanied by a noticeable deterioration in their motor characteristics, since low-branched isoparaffins have high cetane numbers. Platinum-containing catalysts for the hydroprocessing of hydrocarbons are used in industry.

The role of platinum in the composition of hydroisomerization catalysts with high acidity of the support, on which the formation of the carbocation occurs directly on the acid centers of the catalyst, is reduced to the prevention of coke formation. On medium acid catalysts, such as zeolites and amorphous aluminosilicates, hydroisomerization proceeds according to a bifunctional mechanism, i.e. The process is initiated on metal particles, and the isomerization of the intermediate compounds proceeds on the acid surface of the catalyst. All supported platinum catalysts are, to one degree or another, bifunctional, especially on carriers with pronounced acidity. For strongly acid systems at low hydrocarbon conversion temperatures, the role of platinum is to activate hydrogen and to “timely” saturation of carbenium ions after their isomerization transformations with the formation of isoalkanes. The stability of the operation of such catalysts is due to the suppression of the formation of densification products at acid sites.

The disadvantage of platinum-containing hydroisomerization catalysts is a significant decrease in the hydrogenating activity of the platinum component in the presence of sulfur compounds contained in the hydroisomerization feedstock, which entails a decrease in the activity of the catalyst as a whole and its rapid coking. A significant decrease in the hydrogenating activity is explained by the fact that platinum even in the presence of a significant amount of hydrogen sulfurizes rather quickly, turning into sulfide, and the hydro-dehydrating activity of platinum sulfide is 2-3 orders of magnitude lower than the activity of metallic platinum. The need for preliminary hydrotreating of hydroisomerization feedstocks on platinum-containing catalysts significantly increases the cost of the process and limits their scope. Unlike metallic platinum, molybdenum and tungsten carbides are, firstly, more resistant to sulfur-containing compounds, and secondly, the specific activity of molybdenum carbides, hydroxycarbides and sulfides differs slightly and even in the case of partial sulfurization does not lead to a noticeable decrease in hydro-dehydrogenating activity.

A commercially attractive solution is the task of creating a sulfur-resistant highly stable hydroisomerization catalyst for diesel fractions based on an acid zeolite carrier modified with a sulfur-resistant hydro-dehydrogenating component that does not contain Group VIII metals - platinum, palladium, etc.

Interesting objects whose properties make it possible to consider them as promising hydro-dehydrogenating components of hydroisomerization catalysts are tungsten carbides and especially molybdenum carbides. Their ability to activate hydrogen and high activity in the hydrogenation of benzene, toluene, polycyclic aromatic hydrocarbons [Marquez-Alvarez C., Calridge J.B., York A.P.E., Sloan J., Green M.L.H. Studies in Surface Science and Catalysis. 1997. V. 106. P. 485-490; Choi J.-S., Bugli G., Djega-Mariadassou G.J. Catal. 2000. V. 193. P. 238-247; Usman M., Li D., Razzaq R., Yaseen M., Li Ch., Zhang S.J. Ind. Eng. Chem. 2015. V. 23. P. 21-26].

Molybdenum and tungsten carbides are active in the isomerization of n-paraffins [York A.P.E., Pham-Huu C., Del Gallo P., Ledoux M.J. Catal. Today. 1997. V. 35. P. 51-57; Ribeiro F.H., Boudart M., Dalla Betta R.A., Iglesia E. J. Catal. 1991. V. 130. P. 498-513; Liu P., Wu M., Wang J., Zhang W., Li Y. Fuel Process. Technol. 2015. V. 131. P. 311-316.], In the hydrodecyclization of naphthenes [Choi Y., Lee J., Shin J., Lee S., Kim D., Kyoo Lee J. Appl. Catal. A: General. 2015. V. 492. P. 140-150; Ardakani Sh. J., Smith K.J. Appl. Catal. A: General. 2011. V. 403. P. 36-47; Kim Y., Yun G., Lee Y. Catal. Commun. 2014. V. 45. P. 133-138.], In the hydrotreatment of hydrocarbon fractions [Furimsky E. Appl. Catal. A: General. 2003. V. 240. P. 1-28; Oyama S.T., Gott T., Zhao H., Lee Y.-K. Catal. Today. 2009. V. 143. P. 94-107].

In a number of works, it was shown that the molybdenum and tungsten carbides are close to the noble metals of group VIII in their catalytic properties in the isomerization reaction [York A.P.E., Pham-Huu C, Del Gallo P., Ledoux M.J. Catal. Today. 1997. V. 35. P. 51-57; Volpe L., Boudart M.J. Solid State Chem. 1985. V. 59. P. 348-356; Ledoux M.J., Pram Huu C., Guille J., Dunlop H.J. Catal. 1992. V. 134. P. 383-398].

Known methods for producing catalysts containing molybdenum or tungsten carbides can be divided into two groups, including:

- processing (carbonization) of the catalyst precursor, impregnated with a soluble compound of molybdenum or tungsten, at elevated temperatures in a medium containing hydrogen and a carbon source, usually C ₁ -C ₄ hydrocarbons, carbon monoxide, carbon dioxide;

- carbonization of a complex of molybdenum or tungsten with an organic ligand, which is a source of carbon, at elevated temperatures in a medium of hydrogen or inert gas.

The stabilizing effect of molybdenum and tungsten carbides was demonstrated during the hydroisomerization of paraffins in the presence of an activated carbon and chlorinated alumina catalyst modified with molybdenum and tungsten carbides [Patent US 6090992. Isomerization catalyst system, method of making and method of using such catalyst system in the isomerization of saturated hydrocarbons / An-hsiang Wu. Charles A. Drake; Phillips Petroleum Company; declared 12/08/1998; publ. 07/18/2000. Patent US 6,110,859. Hybrid catalyst system for converting hydrocarbons and a method of making and using such catalyst system / An-hsiang Wu, Charles A. Drake; Phillips Petroleum Company; declared 11/16/1998; publ. 08/29/2000]. A method of preparing a hydroisomerization catalyst consists in applying molybdenum or tungsten salts to γ-alumina, followed by calcination. The applied molybdenum or tungsten oxide is subjected to a thermally programmed carbonization step in a mixture of hydrogen and methane at temperatures of 600-1000 ° C (preferably 700-750 ° C) to obtain carbide dispersed on the surface of alumina. To form the acid properties of the catalyst after high-temperature treatment, it is additionally treated with a mixture of carbon tetrachloride and hydrogen vapors at a temperature of 300 ° C.

The use of a catalyst based on chlorinated alumina modified with molybdenum and tungsten carbides showed that its activity, selectivity, and stability during the isomerization of the pentane-hexane fraction are not inferior to those of the isomerization catalyst based on chlorinated alumina modified with platinum. The high stability of carbide modifiers with respect to impurities of sulfur-containing compounds in the isomerization feed is shown.

It is known to use zeolite catalysts modified with molybdenum and tungsten carbides in the hydroisomerization of C ₄ -C ₁₀ hydrocarbon fractions [Patent US 6124516. Catalyst composition and processes therefor and therewith / An-hsiang Wu. Charles A. Drake; Phillips Petroleum Company; declared 01/21/1999; publ. 09/26/2000]. In this case, molybdenum or tungsten salts are applied to highly siliceous zeolites of the types ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-35, ZSM-38. The method of deposition and thermoprogrammed carbonization is similar to the method described above for catalysts based on γ-alumina. The use of catalysts based on high-silica zeolites modified with molybdenum and tungsten carbides provides high activity and stability of the catalysts during the isomerization of the hydrocarbon fraction C ₄ -C ₁₀ in the presence of up to 40 ppmw nitrogen and up to 5000 ppmw sulfur compounds. It was shown that zeolite catalysts modified with molybdenum and tungsten carbides are significantly superior to platinum-containing catalysts in their resistance to catalytic poisons in hydroisomerization feedstocks.

The carbonization of a pre-prepared complex of molybdenum and citric acid at temperatures of 700-1000 ° C (optimal temperatures) in an inert gas atmosphere was used to prepare nanodispersed (<100 nm) molybdenum and tungsten carbides [Patent US 8158094. Methods of preparing metal carbides / Karen Swider Lyons. Arnold M. Stux: The United States Of America. As Represented By The Secretary Of The Navy; declared 05/12/2009; publ. 04/17/2012]. In accordance with this method, a complex is prepared from a solution of paramolybdate or ammonium paratungstate and citric acid in the range of molar ratios of 0.8-1.1, which is dried at 120 ° C and thermally programmed calcination to a temperature of 700-1000 ° C.

To prepare a catalyst containing the corresponding carbides dispersed on a porous carbon support, the carbonization process of supported tungsten or molybdenum guanidine complexes was used [Patent US 5573991. Preparation of metal carbide catalyst supported on carbon / Fawzy G. Sherif. Anantha N. Desikan: Akzo Nobel N.V .; declared 05/20/1994; publ. 12/12/1996]. In accordance with this method, the porous support is impregnated with a solution of the guanidine complex of molybdenum or tungsten in amyl alcohol. The impregnated carrier is dried at a temperature of 100-110 ° C and subjected to heat treatment at 550-600 ° C (optimal temperature range) in an inert atmosphere.

If we consider the two groups of catalysts identified by the carbonization method of the precursor, then it should be recognized that for the preparation of hydroisomerization catalysts, the relatively acceptable are the relatively low-temperature methods for producing carbides by the methods of thermoprogrammed synthesis and thermal decomposition of carbon-containing molybdenum and tungsten complexes, leading to the production of nanosized carbide particles with a dispersion of 4-30 nm and a specific surface area of 20-110 m ² / g. Such catalysts exhibit high resistance to catalytic poisons.

The main disadvantage of the considered examples of catalysts based on molybdenum and tungsten carbides is the relatively high carbonization temperature of metal carbide precursors, which can lead to irreversible changes in the phase composition, texture characteristics and acidity of the catalysts. The consequence of this is the insufficiently high activity and selectivity in the process of hydroisomerization of linear alkanes with high selectivity of side cracking reactions, as well as a high content of transition metals (up to 30 wt.%) On the surface of the acid carrier.

Thus, to create catalysts based on molybdenum and tungsten carbides supported on an acid support for the hydroisomerization of linear alkanes, it is necessary to use acid supports with an average strength of acid sites to reduce the undesired cracking reaction. In addition, it is necessary to use molybdenum or tungsten compounds, which allow carbonization at relatively low temperatures (<650 ° C), which allows nanosized carbide particles with a high specific surface to be obtained.

Closest to the technical nature of the claimed and achieved result are catalysts for hydroisomerization of aliphatic hydrocarbons described in US Pat. US No. 6124516, B01J 27/22, B01J 29/40, G10G 35/095, 09/26/2000, and the method of preparing nanodispersed (<100 nm) molybdenum and tungsten carbides described in US Pat. US No. 8158094, C01B 31/30, 04.17.2012.

The prototype catalyst contains, as an active component, molybdenum or tungsten carbides deposited on zeolites of the types ZSM-5, ZSM-8, ZSM-11, ZSM-12, ZSM-35, ZSM-38. The prototype catalyst is prepared by impregnation of zeolites with solutions of molybdenum or tungsten salts, followed by calcination. The deposited molybdenum or tungsten oxide is subjected to thermoprogrammed carbonization steps in a mixture of hydrogen and methane at temperatures of 600-1000 ° C, preferably 700-750 ° C, to obtain carbide dispersed on the surface of an acid carrier.

The main disadvantages of these catalysts are the high carbonization temperature of the precursor of molybdenum carbide (above 700 ° C), which does not allow to obtain nanosized carbides, as well as the high acidity of zeolite components, which leads to low selectivity of the hydroisomerization process due to the high activity in the process of alkane cracking, as well as non-optimal distribution of acid and hydro-dehydrogenation centers in a bifunctional catalyst. The non-optimal (uneven) distribution of acid and hydro-dehydrogenation centers in a bifunctional catalyst leads to an increase in selectivity for undesirable cracking products, rapid deactivation of acid centers with coke, and, as a result, to a low catalytic stability of the catalyst.

The invention solves the problem of developing an effective and stable catalyst for coke decontamination and a method for its preparation intended for carrying out the hydroisomerization of n-alkanes, as well as straight-run and hydrotreated diesel fractions.

This is achieved by a method of preparing a catalyst containing, as an active component, nanosized molybdenum carbide in an amount of 2.5-10.0 wt. %, as an acidic carrier, the catalyst contains crystalline silicoaluminophosphate SAPO-31 with the structure of the ATO, granulated with alumina.

The problem is also solved by a method of preparing a catalyst containing, as an active component, nanosized molybdenum carbide in an amount of 2.5-10.0 wt. %, characterized in that the carbide precursor is formed at the stage of preparation of the solution, which allows you to control the properties of the final product already at the stage of drying the catalyst. To achieve an optimal distribution of acid and hydro-dehydrogenation centers, the carbide precursor is introduced into the catalyst at the stage of preparation of the molding mixture for granulation, which makes it possible to distribute the future hydro-dehydrogenation component evenly on both the acid component of the catalyst and the binder.

EFFECT: high activity, selectivity and stability to coke deactivation of catalysts in the hydroisomerization reaction of n-alkanes, as well as straight-run and hydrotreated diesel fractions.

The problem is solved by the composition of the catalyst for the hydroisomerization of n-alkanes, characterized in that the catalyst contains crystalline silicoaluminophosphate SAPO-31 with an ATO structure in an amount of 30-80 wt. %, as a binder, alumina in an amount of 70-20 wt. %, and as an active component nanodispersed molybdenum carbide in an amount of 2.5-10.0 wt. % of the amount of acid carrier and binder.

Nanodispersed molybdenum carbide is characterized by a dispersion of 4-30 nm and a specific surface area of 20-110 m ² / g.

The problem is also solved by the method of preparation of the catalyst for the hydroisomerization of n-alkanes. The catalyst is prepared by mixing the precursor of molybdenum carbide, namely, the organic complex of ammonium paramolybdate with citric acid, with an acid carrier - crystalline silicoaluminophosphate SAPO-31 with the ATO structure and aluminum oxide as a binder, carbonization is carried out in a stream of hydrogen at a temperature of no higher than 600 ° C, in the result is a catalyst containing crystalline silicoaluminophosphate SAPO-31 with an ATO structure in an amount of 30-80 wt. %, aluminum oxide in an amount of 70-20 wt. % and nanosized molybdenum carbide in an amount of 2.5-10.0 wt. % of the sum of silicoaluminophosphate and alumina, nanosized molybdenum carbide is characterized by a dispersion of 4-30 nm and a specific surface area of 20-110 m ² / g.

The technical result is achieved by the fact that the proposed method for producing a catalyst allows to reduce the content of the transition metal on the surface of the carrier, to lower the temperature of molybdenum carbide formation to 500-600 ° C and to obtain nanosized molybdenum carbides uniformly distributed on the surface of both the acid carrier and the binder.

The proposed method for producing a bifunctional catalyst consists in preliminary synthesis at room temperature and mixing of an organic complex of ammonium paramolybdate with citric acid (CMO), adding this complex to the molding mixture in an amount of 2.5-10.0 wt. % of the mass of the future catalyst at the stage of preparing a molding mixture consisting of an acid carrier and a binder, subsequent molding, drying the granules in air and heat treatment in a hydrogen atmosphere at 500-600 ° C. The introduction of a solution of the organic complex of ammonium paramolybdate with citric acid (SMO) at the stage of preparation of the molding mixture makes it possible to distribute the future hydro-dehydrating component evenly on the acid component of the catalyst and on the binder and obtain bifunctional catalysts containing nanocrystalline molybdenum carbide, which are highly stable to coke deactivation . After molding, the bifunctional catalyst pellets were dried at 120 ° C in an oven for 7 hours. The dried catalyst was loaded into an isothermal flow reactor and purged with argon at a space velocity of 500 h ⁻¹ at room temperature and atmospheric pressure. After purging with argon, hydrogen was supplied at a space velocity of 500 h ⁻¹ and the temperature was raised at a rate of 3 ° C / min to 600 ° C. It was kept in a stream of hydrogen at 600 ° C for 2 h, after which it was cooled to room temperature.

The distinguishing features of this method are the uniform distribution of the carbide precursor on the surface of both the acid component of the catalyst and the binder, as well as the relatively low temperature for producing carbides by the methods of thermally programmed synthesis and thermal decomposition of carbon-containing molybdenum complexes, which leads to the production of nanosized carbide particles with a dispersion of 4-30 nm and specific a surface of 20-110 m ² / g.

Bifunctional catalysts based on molybdenum carbide and silicoaluminophosphate SAPO-31 with an ATO structure were prepared, containing various amounts of Al ₂ O ₃ as a binder. Different MoC _x contents (in terms of MoO ₃ ) were achieved using a solution of CMO of various concentrations.

Testing of the catalytic activity of the obtained samples in the n-decane isomerization reaction was carried out in a flow unit with a stainless steel reactor. Before conducting the experiments, the catalyst was preliminarily activated by treatment with hydrogen for one hour at 400 ° C and atmospheric pressure.

As a raw material for conducting catalytic tests, n-decane with a purity of 99.3% was used.

Catalyst studies were performed under the following conditions:

The reaction temperature is 300-380 ° C;

Pressure - 2.0 MPa;

Weighted feed rate - 1.0-3.0 h ^-1 ;

The consumption of hydrogen is 500 h ^-1 (by volume).

The invention is illustrated by the following examples.

Example 1 (comparative).

For the preparation of the catalyst, silicoaluminophosphate SAPO-31 granulated with 20% Al ₂ O ₃ , dried at 110 ° C for 7 hours and calcined at 550 ° C for 2 hours is used. The granular acid support is impregnated by moisture capacity with a CMo solution containing 7 % wt. MoC _x in terms of MoO ₃ . dried in air for 12 hours, then at 120 ° C in an oven for 7 hours. The dried catalyst was loaded into a flow isothermal reactor and purged with argon at a space velocity of 500 h ⁻¹ at room temperature and atmospheric pressure. After purging with argon, hydrogen is supplied with a space velocity of 500 h ⁻¹ and the temperature is increased at a rate of 3 ° C / min to 600 ° C. It is kept in a stream of hydrogen at 600 ° C for 2 hours, after which it is cooled to room temperature.

Determination of the catalytic activity of the obtained sample in the isomerization reaction of n-decane is carried out in a flow unit with a stainless steel reactor.

Before the experiment, the catalyst was preliminarily activated by treatment with hydrogen for 1 h at 400 ° C and atmospheric pressure.

Example 2

To prepare the molding mixture, silicoaluminophosphate SAPO-31 in an amount of 80%, calculated on the dry matter, reprecipitated aluminum hydroxide in an amount of 20% in terms of Al ₂ O ₃ , a CMo solution containing 7% wt. MoC _x in terms of MoO ₃ , distilled water in the amount necessary to achieve a total mass moisture content of 36-38%. After preparation of the plastic mass, the sample is formed into granules with a diameter of 2 mm and a length of 6 mm, dried in air for 12 hours, then at 120 ° C in an oven for 7 hours. The dried catalyst is loaded into a flow isothermal reactor and blown with argon with volumetric speed of 500 h ^-1 at room temperature and atmospheric pressure. After purging with argon, hydrogen is supplied with a space velocity of 500 h ⁻¹ and the temperature is increased at a rate of 3 ° C / min to 600 ° C. It is kept in a stream of hydrogen at 600 ° C for 2 hours, after which it is cooled to room temperature.

Determination of the catalytic activity of the obtained sample in the isomerization reaction of n-decane is carried out in a flow unit with a stainless steel reactor.

Before the experiment, the catalyst was preliminarily activated by treatment with hydrogen for 1 h at 400 ° C and atmospheric pressure.

Example 3

It differs in that for the preparation of the molding mixture, silicoaluminophosphate SAPO-31 is used in an amount of 30% in terms of dry matter, reprecipitated aluminum hydroxide in an amount of 70% in terms of Al ₂ O ₃ . The rest is carried out analogously to example 2.

Example 4

It differs in that for the preparation of the molding mixture, silicoaluminophosphate SAPO-31 is used in an amount of 50% in terms of dry matter, precipitated aluminum hydroxide in an amount of 50% in terms of Al ₂ O ₃ . The rest is carried out analogously to example 2.

Example 5

It differs in that for the preparation of the molding mixture, SAPO-31 silicoaluminophosphate is used in an amount of 30% in terms of dry matter, reprecipitated aluminum hydroxide in an amount of 70% in terms of Al ₂ O ₃ , and the granular acid carrier is impregnated by moisture content in a CMo solution containing 10.0% wt. MoC _x in terms of MoO ₃ . The rest is carried out analogously to example 2.

As can be seen from the above examples, the proposed catalysts are highly active in the process of hydroisomerization of n-decane. The most optimal content of the acid support (silicoaluminophosphate SAPO-31) in the catalyst is 30% wt. A bifunctional catalyst prepared on its basis using nanosized molybdenum carbide (MoC _x / SAPO-31), along with high activity, exhibits high selectivity and resistance to coke deactivation during hydroisomerization. During the 100 hours of the reaction, the activity and selectivity of the catalysts remained virtually unchanged, in contrast to the reference sample (Example 1).

Claims (3)

1. The catalyst for the process of hydroisomerization of n-alkanes containing, as an active component, molybdenum carbide supported on an acid carrier, characterized in that the catalyst contains crystalline silicoaluminophosphate SAPO-31 with an ATO structure in an amount of 30-80 wt. %, as a binder, alumina in an amount of 70-20 wt. %, and as an active component nanodispersed molybdenum carbide in an amount of 2.5-10.0 wt. % of the amount of acid carrier and binder. 2. The catalyst according to claim 1, characterized in that the nanosized molybdenum carbide is characterized by a dispersion of 4-30 nm and a specific surface area of 20-110 m ² / g. 3. A method of preparing a catalyst for the hydroisomerization of n-alkanes by applying an active component, molybdenum carbide, to an acid carrier, followed by carbonization, characterized in that the catalyst is prepared by mixing a molybdenum carbide precursor, namely, an organic complex of ammonium paramolybdate with citric acid, and an acid carrier, crystalline silicoaluminophosphate SAPO-31 with the ATO structure and aluminum oxide as a binder, carbonization is carried out in a hydrogen stream at a temperature of no higher than 600 ° To yield a catalyst comprising a crystalline silicoaluminophosphate SAPO-31 structure ATO in an amount of 30-80 wt. %, aluminum oxide in an amount of 70-20 wt. % and nanosized molybdenum carbide in an amount of 2.5-10.0 wt. % of the sum of silicoaluminophosphate and alumina, nanosized molybdenum carbide is characterized by a dispersion of 4-30 nm and a specific surface area of 20-110 m ² / g.