RU2486005C1 - Oxide catalyst for isomerisation of light gasoline fractions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to isomerisation catalysts. Described is a catalyst for isomerisation of light gasoline fractions, which contains tungsten-coated zirconium dioxide with platinum and aluminium oxide additives, with the following ratio of components in wt %: ZrQ₂=65.1-76.3; WO₄ ^2-=23.4-32.1; Al₂O₃=0.1-2.6; Pt=0.2, production of which involves precipitation of zirconium hydroxide from zirconyl chloride solution with ammonia solution, separating and washing the precipitate from chloride ions, drying, depositing tungstate anions, drying and calcining, followed by saturation with chloroplatinic acid solution, drying and calcining the catalyst.

EFFECT: catalyst having high catalytic activity is obtained.

5 cl, 1 tbl, 1 ex

Description

The invention relates to the field of oil refining and petrochemicals, specifically to a catalyst based on modified zirconia and to methods for its preparation. The catalyst is used for the isomerization of light gasoline fractions, in particular the skeletal isomerization of n-hexane and n-heptane.

The isomerization of light gasolines is one of the most promising processes for increasing the octane number of motor fuels; it allows one to obtain branched isomers with r.h. from linear C ₅ -C ₈ hydrocarbons with low octane numbers (r.h. 0-62). 92-105. The proportion of isomerization processes in Russia is 1.5%, while in the United States and Western Europe 4-5%. In connection with toughening environmental characteristics for motor fuels, in particular, limiting the content of high-octane aromatic hydrocarbons, the growth of isomerization products in commercial fuels in developed countries is planned to increase to 15%.

Currently, high-octane isocomponents in the production of high-grade gasolines are obtained by isomerization of light gasoline fractions on platinum-containing catalysts based on zeolites, chlorinated alumina and sulfated zirconia. A common drawback of these catalysts is that they are effective only in the isomerization of a narrow fraction of C ₅ -C ₆ alkanes and do not allow selective isomerization of alkanes with a longer hydrocarbon chain (with the lowest octane numbers) due to the intensification of the cracking reaction.

For low-temperature isomerization of long-chain alkanes, acid catalytic systems based on tetragonal zirconia modified with tungstate groups have attracted considerable attention in recent years.

A known method of preparing catalysts [Bray V.V., Levchuk N.N., Melezhik A.V., Patrilyak K.I. Influence of synthesis conditions for superacid WO _x / ZrO ₂ systems on their catalytic properties in the reaction of n-hexane isomerization // Catalysis and Petrochemistry. No. 5-6 (2000) S.59], containing tungsten zirconia, based on the precipitation of components in an aqueous solution using a return mother stream for irrigation. An aqueous solution of zirconyl chloride containing an additive of ammonium metatungstate was refluxed with slow introduction of ammonia. After cooling, the solutions are made alkaline with an ammonia solution to pH 9.2-9.6. The resulting precipitate is washed, dried and calcined. As the hydrogenation-dehydrogenating component of the catalyst, platinum is used, which is deposited from a solution of platinum hydrochloric acid, followed by calcination at a lower temperature.

The disadvantage of this method is the need for additional stages of boiling, alkalization of the solution and the difficulty of forming a homogeneous porous structure of the catalyst under conditions of a variable pH of precipitation of the precipitate.

A known method of preparing catalysts by introducing a solution of ammonium metatungstate at the stage of deposition of zirconium hydroxide. According to the method of [Cortes-Jacome MA, Toledo JA, Angeles-Chavez C., Aguilar M., Wang JA Influence of synthesis methods on tungsten dispersion, structural deformation, and surface acidity in binary WO ₃ -ZrO ₂ system // J. Phys . Chem. B. 109 (2005) P.22730], a solution of ammonium metatungstate is mixed with a solution of zirconium nitrate and precipitation is carried out with a solution of ammonia at pH 9.5-10. The precipitate is subjected to aging, drying and calcination at a temperature of 800 ° C.

The disadvantage of this method is the low specific surface area of 48 m ² / g, the total pore volume of 0.073 cm ³ / g and activity in the isomerization reaction of n-hexane. So, for example, at a pressure of 0.2 MPa, a temperature of 260 ° C, a volumetric feed rate of 2 h ^-1 and a molar ratio of hydrogen: feedstock equal to 8: 1, the degree of conversion of n-hexane is 5%.

A known method of producing tungsten - zirconium catalysts [Patent US 0119748 A1, C10G 11/00, publ. May 31, 2007], which is based on the preparation of a zirconium hydroxide precursor, from which, in subsequent stages, including the deposition of tungstate anions by wet impregnation and thermal activation, an active oxide phase is formed with modifying anions fixed to the surface.

The disadvantage of the catalyst and method for its preparation is low catalytic activity in the isomerization reaction of n-heptane. So at a reaction temperature of 160-180 ° C, the volumetric feed rate of n-heptane 0.6-2.14 h ^{-1 the} yield of heptane isomers does not exceed 50%.

The closest in technical essence is the catalyst and method for its preparation [h. No. WO 95/03262, C07C 5/13, C07C 5/22, publ. 07/19/1994]] which is a tungsten zirconia with platinum additives, the content of tungstate anions is 17.7 wt.%, Pt 0.5 wt.%. The catalyst is prepared by precipitating zirconium hydroxide from an aqueous solution of zirconyl chloride with a concentrated solution of ammonia hydrate. The precipitate obtained is separated from the mother liquor, washed from chloride ions, dried, impregnated with a solution containing tungstate anions, dried, calcined at a temperature of 825 ° C for 3 hours. The resulting carrier is impregnated with a solution of platinum hydrochloric acid. The catalyst is then calcined in a stream of air at 300 ° C for 2 hours.

The disadvantages of the catalyst and the method for its preparation include a low specific surface area of the catalyst (50 m ² / g) and low activity in the isomerization reactions of n-hexane and n-heptane. So, for example, when isomerization of n-heptane in a stream of hydrogen at atmospheric pressure, a temperature of 170 ° C, a volumetric feed rate of 1 h ^-1 and a molar ratio of hydrogen: n-heptane equal to 3: 1, the yield of heptane isomers is 30.2% .

Low activity and selectivity can be associated with the inhomogeneous porous structure of the dioxide due to its formation at a variable pH that varies during the deposition process from 1.5 to 9.0, and with the composition of the catalyst. In the initial period, the deposition occurs in a medium with a low pH value (1.5-2.0), in which, as shown in [Gavrilov V.Yu. Study of the microporous structure of zirconium dioxide // Kinetics and Catalysis. 41 (2000) P.786], a precipitate is formed mainly with small micropores. At pH greater than 7, mesopores necessary for the implementation of the catalytic reaction begin to form. The indices of the isomerizing activity of tungsten-zirconium catalysts are significantly affected by the content of tungsten anions and the phase composition of the catalyst. At the indicated tungstate anion content and calcination temperature of 825 ° С, the catalytically active tetragonal form of zirconium dioxide undergoes a partial phase transition to the monoclinic form, the process is accompanied by the appearance of the WO ₃ phase. Both components do not exhibit catalytic activity in the alkane isomerization reaction, and their presence in the composition of the catalytic composition leads to a decrease in the activity and selectivity of the catalysts.

The technical result of the invention is the development of an effective catalyst based on tungsten zirconia with the addition of aluminum and platinum, which has high catalytic activity in the process of skeletal isomerization of long chain alkanes, in particular n-hexane and n-heptane, and the development of a method for its production.

The technical result is achieved by the fact that the oxide catalyst for the isomerization of light gasoline fractions containing tungsten zirconia with additives of platinum and alumina in the following ratio, wt.%:

ZiO ₂ = 65.1-76.3;

WO ₄ ^2- = 23.4-32.1;

AlO ₃ = 0.1-2.6;

Pt = 0.2,

the preparation of which includes the precipitation of zirconium hydroxide from a solution of zirconyl chloride with an ammonia solution, separation and washing of the precipitate from chloride ions, drying, applying tungstate anions, drying and calcining, followed by impregnation with a solution of platinum chloride, drying and calcining the catalyst, characterized in that at the precipitation stage zirconium hydroxide is introduced aluminum by mixing solutions of zirconyl chloride and aluminum nitrate, followed by precipitation with ammonia solution, the deposition process is carried out At a constant pH of 9.5–9.8, the resulting precipitate is aged by aging in the mother liquor at room temperature.

And also by the fact that a constant pH is achieved by gradually and simultaneously pouring solutions of zirconyl chloride with the addition of aluminum nitrate and ammonia hydrate in a precipitation flask.

And also the fact that the deposition of tungstate anions is carried out by the moisture capacity of the obtained hydroxide from a solution of ammonium metatungstate at pH 6.

And also the fact that the calcination of the precipitate after applying tungstate anions is carried out at a temperature of 700-800 ° C.

And also the fact that it contains alumina.

The features distinguishing the claimed technical solutions from the prototype are not identified in other technical solutions when studying data and related fields of technology and, therefore, provide the claimed solutions with the criteria of "novelty" and "inventive step".

An example implementation of the method of producing an oxide catalyst

In a precipitation flask equipped with a mechanical stirrer, pour 200 ml of distilled water. A glass electrode connected to an ionomer for measuring pH is immersed in water. A 15% solution of zirconyl chloride containing an addition of aluminum nitrate and a 12.5% solution of ammonia hydrate are poured into the separatory funnels. When the stirrer is rotating, ammonia hydrate is added dropwise to a precipitation flask to pH 9.5. Then a mixture of a solution of zirconyl chloride with aluminum nitrate and ammonia hydrate are simultaneously added dropwise from both separatory funnels. The feed rate of the solutions is selected so that the pH is maintained within 9.5 ± 0.3. The deposition of a hydroxide precursor (a mixture of coprecipitated zirconium and aluminum hydroxides) is carried out for 35-45 minutes. After the mixture of solutions of zirconyl chloride and aluminum nitrate is completely drained, the flow of ammonia hydrate is stopped and the precipitate formed is aged in the mother liquor at room temperature for 3 hours. Then, the precipitate is washed with distilled water by decantation until a negative reaction to chloride ions in the wash water. Next, the precipitate is filtered off and dried in an oven at 110 ° С for 20 h. The dried hydroxide precursor is saturated with a solution of moisture capacity and saturated with ammonium metatungstate, the pH of the solution is adjusted to a value of 6 with ammonia hydrate. Then, the impregnated hydroxide is dried at 110 ° C for 2 hours and calcined in air at 700-800 ° C for 3 hours. The resulting oxide form is moisture-saturated with a solution of platinum chloride, dried at 110 ° C for 2 hours and a final calcination in air is carried out at temperature 500 ° С.

The composition, preparation conditions and properties of the oxide catalyst for isomerization of light gasoline fractions based on zirconia modified with tungstate anions, aluminum and platinum for skeletal isomerization of n-hexane and n-heptane into the corresponding skeletal isomers are shown in Table 1.

The porous structure of the catalyst (specific surface area, average diameter and pore volume) was studied on a Micromeritics ASAP 2040 apparatus using isotherms of low-temperature nitrogen adsorption. The phase composition was determined using X-ray diffraction patterns taken on PANalytical X'Pert PRO diffractometers with a PIXcel detector and a graphite monochromator and DRON-3, using filtered CuK _α radiation.

The catalytic activity in the isomerization reactions of n-hexane and n-heptane was determined on a BI-CATflow4-2 (A) automated plant with a flow reactor at atmospheric pressure. The tests were carried out on a 0.25-0.5 mm catalyst fraction selected by grinding compacted catalyst tablets. The loading of the catalyst into the reactor was 0.5-1.0 ml. Testing of the activity of the catalysts was carried out in a hydrogen medium at a volumetric flow rate of hydrocarbons for n-hexane 2 h ^-1 , reaction temperature 200 ° C, for n-heptane 1 h ^-1 and reaction temperature 170 ° C, the ratio of hydrogen: hydrocarbon was 3: 1 , The composition of the products was analyzed by gas chromatography using a flame ionization detector and a capillary column with squalane. The comparison of the catalysts by their activity was carried out after reaching the quasistationary regime, when the indicators did not change much in time.

The data presented in table 1 show that the proposed synthesis method and composition make it possible to obtain a catalyst that provides a high yield of hexane and heptane isomers with high selectivity for these products. So, according to the results No. 1, 4, 7, 9, 10 and 12 it is seen that the use of the catalyst obtained by the proposed method, with the content of components, wt.%: ZrO ₂ = 65.8-76.3; WO ₄ ^2- = 23.4-32.1; Al ₂ O ₃ = 0.1-1.9; Pt = 0.2 allows to increase the yield of isomers of hexane and heptane 1.7-2.9 times, compared with the prototype. So, for example, the yield of heptane isomers increases to 75.1 wt.% With selectivity for isomers 97.0% (pr.12). The proposed production method provides the formation of a homogeneous porous structure of hydroxide with a surface of 370-340 m ² / g, of which at the subsequent stages of deposition of tungstate anions at a concentration of 23.4-32.1 wt.% And thermal activation at a temperature of 700-800 ° C an oxide phase is formed with a surface of 78-65 m ² / g and a mesoporous structure with a narrow pore size distribution with a predominance of pores with sizes from 4 to 8 nm. The pore volume of the catalyst is in the range of 0.17-0.23 cm ³ / g Under these conditions, monophasic zirconia of tetragonal modification is formed with tungsten clusters fixed on the surface, which are formed as a result of heat treatment of a tungsten hydroxide precursor.

The specified characteristics of the catalyst are implemented in the stated conditions for the preparation of the catalyst. So when obtaining zirconium hydroxide in a variable pH value of the deposition without the aging stage, followed by calcination at a temperature of 825 ° C (pr.13 prototype), a catalyst is formed with a wide pore size distribution, with a substantial part of the porous volume (0.09 cm ³ / g) falls on micropores (with a size of less than 2 nm). The phase composition of such a catalyst is represented by a mixture of monoclinic and tetragonal forms of zirconium dioxide with a predominance of the latter, and also contains a phase of tungsten oxide (VI). The yield of hexane and heptane isomers on this catalyst is 20.2 and 30.2 wt.%, Respectively, with selectivity for the isomers of 85.5 and 78.2%.

Changing the order of platinum deposition, namely, impregnation with a solution of platinum hydrochloric acid of an anion-modified hydroxide precursor, followed by calcination at a temperature of 700 ° C, leads to a decrease in the catalytic activity of the synthesized composition (pr.2).

The catalytic properties are adversely affected by a change in the calcination temperature of the tungsten hydroxide precursor. A decrease in temperature to 600 ° C (Project 6) and an increase to 870 ° C (Project 8) leads to a decrease in the yield of hexane and heptane isomers by almost 1.5 times (Table 1).

As for the composition of the catalyst, according to the data in Table 1, the yield of hexane and heptane isomers is 35.1-52.3 wt.% And 50.1-76.1 wt.%, Respectively, with a ZrO ₂ content of 65.1-76.3 WO ₄ ^2- = 23.4-32.1, Al ₂ O ₃ = 0.1-2.6 and Pt = 0.2 wt.%. A change in the content of tungstate anions both in the direction of decreasing (D.3) and in the direction of increasing (D.5) leads to a decrease in the activity of the catalyst. With an increase in the alumina content (Pr.11), the yields of hexane and heptane isomers decrease by 22 and 13%, respectively.

The proposed method allows to obtain a catalyst with a surface of 68-78 m ² / g and a homogeneous mesoporous structure with a pore size mainly in the region of 5-8 nm. The pore volume of the catalyst is 0.17-0.23 cm ³ / g The phase composition of the catalyst is represented mainly by the tetragonal form of zirconium dioxide. The catalyst obtained by the proposed method provides a high yield of n-hexane and n-heptane isomers with high selectivity for these products.

Claims (5)

1. An oxide catalyst for the isomerization of light gasoline fractions containing tungsten zirconia with the addition of platinum and alumina in the following ratio of components, wt.%: ZrO ₂ 65.1-76.3; $$W{O}_{\mathrm{four}}^{2-}$$

23.4-32.1; Al ₂ O ₃ 0.1-2.6; Pt 0.2, the preparation of which includes the precipitation of zirconium hydroxide from a solution of zirconyl chloride with an ammonia solution, separation and washing of the precipitate from chloride ions, drying, applying tungstate anions, drying and calcining, followed by soaking in a solution of platinum-hydrochloric acid, drying and calcining catalyst, characterized in that at the stage of zirconium hydroxide precipitation, aluminum is introduced by mixing solutions of zirconyl chloride and aluminum nitrate, followed by precipitation with an ammonia solution, the deposition process bred at a constant pH of 9.5 to 9.8, and the resulting precipitate is subjected to aging by aging in the mother liquor at room temperature. 2. An oxide catalyst for the isomerization of light gasoline fractions according to claim 1, characterized in that a constant pH is achieved by gradually and simultaneously pouring zirconyl chloride solutions with the addition of aluminum nitrate and ammonia hydrate into a precipitation flask. 3. The oxide catalyst for the isomerization of light gasoline fractions according to claim 1, characterized in that the deposition of tungstate anions is carried out according to the moisture capacity of the obtained hydroxide from a solution of ammonium metatungstate at pH 6. 4. The oxide catalyst for the isomerization of light gasoline fractions according to claim 1, characterized in that the precipitate is calcined after applying tungstate anions at a temperature of 700-800 ° C. 5. The oxide catalyst for the isomerization of light gasoline fractions according to claim 1, characterized in that it contains aluminum oxide.