The preparation method of catalyst for the isomerization of n-butane isobutane

 

(57) Abstract:

The invention relates to a method of preparation of the catalyst of the isomerization of n-alkanes, in particular the skeletal isomerization of n-butane, and can be used in the petrochemical and refining industries. The inventive method for preparation of the catalyst of the isomerization of n-butane to isobutane by precipitation of zirconium hydroxide with ammonium hydroxide from a solution of nitrate Zirconia at a constant pH value, equal to 8.3-8.9, the separation of the hydroxide precipitate by filtration, drying, promotion nitrate of iron, drying, sulfation with sulfuric acid, drying sulfated hydroxide with the final annealing at a temperature of 600-700C. the constancy of the pH values at the stage of deposition of reach by simultaneous gradual addition in a precipitation flask 15% solution of nitric acid Zirconia and 12.5% solution of ammonium hydroxide. The catalyst contains zirconium oxide promoted with iron cations in the amount of 0.7-1.5 % and sulfate anions in the amount of 3.0-9.7 wt. % S04. The technical result is an increase of activity in the conversion of n-butane, the output of isobutane and exclusion stage of washing the hydroxide precipitate circondario n-alkanes, in particular skeletal isomerization of n-butane, and can be used in the petrochemical and refining industries.

Known methods [1, 2] preparation of oxide catalysts for the isomerization of n-alkanes from n-butane to n-hexadecane on the basis of oxides of metals (zirconium, tin, iron, titanium and other metals), modified anions SO2-4NGO2-4, WO2-4. The application of these anions on the surface of oxides attached to the catalyst's ability to carry out the skeletal isomerization of n-alkanes at low temperature (below 250-300C). Most high efficiency manifests zirconium oxide, modified sulfate groups [1].

The known method [3] obtain sulfated zirconium oxide by decomposition of zirconium sulfate Zr(SO4)24H2O at temperatures above 600C. The way tech has a small number of steps.

The disadvantage is the difficulty of controlling the magnitude of the surface porous structure and low activity in isomerization reactions. The maximum rate of isomerization of n-butane at 150C is only 1.5 10-3mol/GC.

Known methods of preparation of Katalizator the desired textural characteristics. According to the method of [4] sulfated zirconium oxide is applied on the fluorinated silicon oxide with high surface area and uniform pore structure represented by mesopores.

The disadvantage of this method is the need for additional special stages for the preparation of media, and the use of fluorinated medium, which is environmental and corrosion danger.

Known methods [1, 2, 5] preparation of sulfated zirconium oxide, based on the preparation of a precursor of zirconium hydroxide, which at the subsequent stages, including the promotion of a transition metal cations and anions dehydration and thermal activation to form an active oxide phase with a fixed surface modifying anions.

The closest in technical essence and the achieved effect is way [6] the preparation of the catalyst based on sulfated zirconium oxide, including deposition of zirconium hydroxide from an aqueous solution of chloride Zirconia the ammonium hydroxide, the aging of sludge, his separation from the mother liquor, washing chloride-ions, drying, impregnation with solutions of metal salts VII and VIII groups and sulfuric KIS is the gradual addition of a solution of ammonia to a solution of chloride of Zirconia to achieve pH values, equal to 8.

The disadvantages of the method include the need for careful cleaning of hydrated sediment from the chloride ions and the low activity and selectivity of the catalyst. Thus, the catalyst prepared by precipitation of zirconium hydroxide from a solution of chloride Zirconia at room temperature, its impregnation with a solution of nitrate of iron and 0.5 M sulfuric acid solution, drying at 100C and calcining at 700C, obtained the degree of conversion of n-butane 11.8% output by main product, the isobutane to 10.9%. Low activity and selectivity associated with inhomogeneous porous structure of the oxide due to its formation at variable pH value changing during deposition from 1.5 to 8.

In the initial period of the deposition of zirconium hydroxide is in an environment with low pH value (pH of the initial solution equal to 1.5 to 2.0), in which, as shown in [7], formed a precipitate with predominantly micropores small size. Only at pH more than 7 begin to form mesopores necessary for the implementation of catalytic reactions.

The proposed method for the preparation of the catalyst of the isomerization of n-butane to isobutane based on sulfated zirconium oxide includes the precipitation of the hydroxide zircon is .3-8.9, aging the precipitate in the mother solution at room temperature for 3 hours, drying, promotion nitrate of iron, drying and promotion of sulfate anions, drying to a final annealing at a temperature of 600-700C. A constant value of pH at the stage of deposition is supported by the gradual simultaneous prilipanie in a precipitation flask solutions of nitric acid Zirconia and ammonium hydroxide. The proposed method does not require a thorough cleaning of hydrated sediment, because the nitrate group is easily decomposed by calcination, allows to obtain sulfated zirconium oxide with high surface area and uniform mesoporous structure with a pore size predominantly in the range from 3 to 6 nm. The porosity of the catalyst is 0.18-0.25 cm3/g, the volume of micropores (smaller than 1.5 nm) does not exceed 0.002 cm3/, the Catalyst obtained by the proposed method provides high conversion of butane and high yield of isobutane.

The method of preparation of the catalyst is as follows.

In a precipitation flask containing 200 ml of distilled water, are added dropwise at the same time 15% solution of nitric acid Zirconia and 12.5% solution hydroxide ammoe pH (accuracy 0.2) in the range from 8.3 to 8.9. The entire deposition process is carried out for 35-45 min until complete removal of solution of nitrate Zirconia in the flask. During the whole period of deposition of the contents of the flask intensively stirred with a mechanical stirrer and pH control ionomers. After the deposition of the formed gel is subjected to aging for 3 hours at room temperature. The precipitate after aging is filtered off, dried at 110S, impregnated with a solution of nitrate of iron in the calculation of 0.7-1.5 wt.% Fe on zirconium oxide. The zirconium hydroxide. promoted iron salt, dried at 110S, impregnated with an aqueous solution of sulfuric acid, dried again at 110S for 18 h and calcined in air at a temperature in the region of 600-700C for 3 hours

The value of specific surface area of the catalysts was determined by the method of low-temperature adsorption of nitrogen on the installation ASAP 2010. The predominant pore size was calculated by the desorption branch of the isotherms.

Catalytic activity was determined in the reaction of isomerization of n-butane to isobutane. The tests were carried out on the installation of a flow-through reactor fraction 0.5-0.25 mm, selected by grinding the compressed tablets of the catalyst. The catalyst loading in the reactor was 0.5-yemei feed rate of n-butane 7.2 h-1The composition of the products was analyzed by gas chromatography using a flame ionization detector and capillary column with squalane.

The proposed method for the preparation of the catalyst based on sulfated Zirconia for skeletal isomerization of n-butane to isobutane is illustrated by the following examples.

Example 1.

Preparation of zirconium hydroxide. In a precipitation flask equipped with a mechanical stirrer, pour 200 ml of distilled water. In the water, submerge the glass electrode connected to ionomers for pH measurement. In a separating funnel pour a 15% solution of nitric acid Zirconia and 12.5% solution of NH4OH. During the rotation of the agitator in a precipitation flask is added dropwise a solution of ammonium hydroxide to a pH of 8.3. Then from both separating funnels simultaneously added dropwise a solution of nitric acid Zirconia and ammonium hydroxide. The feed rate of the solution are selected so that the pH was maintained within 8.30.2. The deposition process of the hydroxide is carried out within 35-45 minutes After complete draining solution of nitrate Zirconia (500 ml) submission NH4OH stop, and the formed precipitate of zirconium hydroxide is subjected stilnom Cabinet when 110S for 18 h, impregnated with a solution of Fe(NO3)3in the amount of 0.7% of Fe per ZrO2again dried at 110S for 18 hours the Dried product is impregnated with H2SO4containing 9.7% SO2-4per ZrO2and calcined in air at a temperature of C within 3 hours

The results determine the magnitude of the surface, the prevailing pore size and catalytic activity when S shown in the table.

Example 2.

The catalyst prepared according to example 1 with the difference that the pH at the stage of deposition support within 8.50.2 content SO2-4and Fe are 5.2% and 1.5%, respectively, and the temperature of annealing 600C.

The test results presented in the table.

Example 3.

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 8.70.2 content SO2-4and Fe are 3.0 and 1.5%, respectively, and the temperature of annealing 600C, and testing of catalytic activity performed at 200C.

The test results presented in the table.

Example 4.

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 8.90.2 content SO2-4and Fe are 9.7% and 1.5% respectively, the tion).

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 4.00.2 content SO2-4is 5.2%.

The test results presented in the table.

Example 6 (comparative).

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 6.002, content SO2-4and Fe are 5.2% and 1.5%, respectively, the temperature of annealing 600C, and testing of catalytic activity performed at 200C.

The test results presented in the table.

Example 7 (comparative).

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 7.50.2.

The test results presented in the table.

Example 8 (comparative).

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 9.80.2, the Fe content is 1.5%.

The test results presented in the table.

Example 9 (comparative).

The catalyst prepared according to example 1 with the difference that the pH is maintained within the range of 9.80.2 content SO2-4and Fe is 3.0% and 1.5%, respectively, the temperature of annealing 600C.

The test results presented in the table.

Example 10 (and the mixing add a 12.5% solution of NH4OH before reaching pH 8.0. The precipitate of zirconium hydroxide is washed by decantation with distilled water (3 times), filtered off, washed on the filter until a negative reaction to chloride ions (reaction with silver nitrate), and then dried at 100C for 24 hours of the Dried hydroxide impregnated with a solution of nitrate of iron (III) containing 3.0 wt.% Fe (calculated as ZrO2), dried at 100C for 5 h, annealed at 300C for 3 hours the resulting powder was impregnated with a solution of sulfuric acid containing 3.0 % SO2-4(calculated as ZrO2), dried at 100C for 24 h and calcined at 600C.

The results determine the magnitude of the surface, the prevailing pore size and catalytic activity when S shown in the table.

Example 11 (the prototype).

The catalyst prepared according to example 10 with the difference that the content SO2-4and Fe are 5.2% and 1.5%, respectively, the temperature of annealing 700C, and testing of catalytic activity performed at 200C.

The results determine the magnitude of the surface, the prevailing pore size and catalytic activity at 200C shown in the table.

Example 12 (comparative).

The catalyst goto is the SO2-4and Fe are 3.0% and 1.5%, respectively, the temperature of annealing 700C.

The results determine the magnitude of the surface, the prevailing pore size and catalytic activity are presented in the table.

The data presented in the table show that the proposed method allows to obtain a catalyst which provides high conversion in the conversion of n-butane with a high yield of the target product isobutane. Such results are achieved by precipitation of zirconium hydroxide from a solution of nitrate Zirconia at pH 8.3-8.9, maintaining constant during the entire deposition process of pH by the gradual and simultaneous addition of solutions of nitrate Zirconia and ammonium hydroxide in a precipitation flask.

Such deposition conditions ensure the formation of a homogeneous porous structure of the hydroxide with the surface 380-420 m2/g, from which the later stages of the promotion nitrate of iron and sulfuric acid at the indicated concentrations and thermal activation at a temperature of 600-700C phase is formed of zirconium oxide with a surface 96-112 m2/g and a mesoporous structure with a narrow distribution of pore size with a preponderance of long time with what size less than 1.5 nm) does not exceed 0.002 cm2/, High surface area and narrow pore size with a predominance of mesopores causing high catalytic activity and selectivity for isobutane. So, the value of the conversion of n-butane and the output of isobutane are at S 27.3-32,4% and 26.7-30.3% at 200C 43,3% and 42.4%, respectively (1-4).

These characteristics of the catalyst are implemented by precipitation at pH from 8.3 to 8.9. During the precipitation when the pH is less than 8.3 (5-7) and 8.9 (8-9) obtained catalysts with larger pore sizes (with a predominance then from 3 to 8 nm) and with a smaller surface area and catalytic activity. The precipitation of zirconium hydroxide at a variable pH value (for example, 10, 11 prototype) leads to the formation of the catalyst with a wide distribution of pore sizes (with a predominance then from 3 to 9 nm), while a significant portion of the porous volume (0.09 cm3/year) is attributable to micropores (less than 2 nm). The degree of conversion of n-butane and the output of isobutane on the catalysts obtained by alternating the pH value at the stage of precipitation of hydroxide (1.5 to 8), at a temperature T make up 24.8% and 22.7% (10) and 200C of 31.4 and 28.5 (11), respectively.

It is essential that in the proposed method, the deposition of hydrox is mywiki salts, because the nitrate group is easily decomposed in the subsequent calcination of the hydroxide. As shown by example 12 the presence of the chloride ions in the hydroxide of zirconium leads to sintering of the oxide surface by thermal activation and reduced conversion of butane and yield of isobutane.

Bibliography

1. Arata K. Preparation of superacids by metal oxides for reactions of butanes and pentanes //Applied Catalysis A: General 146 (1996), p. 3032.

2. Yadav, G. D., Nair J. J, Sulfated zirconia and its modified versions as promosing catalysts for industrial processes.//Microporous and Mesoporous Materials 33 (1999) 1.

3. The Kotsarenko N. S., Shmakova B. N. Catalytic properties of the products of thermal Zr(SO4)2. //Kinetics and catalysis, 43 (2002) 305-309.

4. Matsuhashi, H. Tanaka, M. Nakamura, H., Arata, K. Formation of acid sites in ordered pores of FSM-16 by modification with sulfated zirconia //Applied Catalysis. A: General. 208 (2001)1.

5. Ivanov, A. C., L. M. Kustov Solid supercolony on the basis of zirconium oxide: the nature of active centers and the isomerization of alkanes. //Russian chemical journal. XL1V. - 2. (2000). 21.

6. Patent JP 09103681, 1997.

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1. The preparation method of catalyst for the isomerization of n-butane to isobutane, including deposition of zirconium hydroxide hydroxide solution AMM, drying, impregnation of the dried hydroxide nitrate of iron and sulfuric acid, drying and calcination at a temperature of 600-700C, characterized in that the precipitation of zirconium hydroxide is carried out on the solution of nitrates of Zirconia at pH 8.3-8,9.

2. The method of preparation of the catalyst under item 1, characterized in that the pH value is maintained constant during the entire deposition process.

3. The method of preparation of the catalyst according to any one of paragraphs.1 and 2, characterized in that the constancy of the pH reached by the gradual and simultaneous addition of solutions of nitrate Zirconia and ammonium hydroxide in a precipitation flask.

 

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