BG65917B1 - Process of preparation of catalysts for the oxidation of methanol to formaldehyde based on iron and molybdenum oxides - Google Patents

Abstract

The method for the preparation of catalysts for the oxidation of methanol to formaldehyde, based on iron and molybdenum oxides, comprises mixture of initial solutions containing iron (III) chloride and ammonium paramolybdate, sodium molybdate and sodium wolframate at relatively lower temperatures. The iron (III) chloride containing solution has temperature ranging from 20 to 40 degrees C, and themolybdenum-containing solution û from 30 to 50 degrees C. Under these conditions a compact, easily washable sediment is formed and the molybdenum losses in the wash waters are reduced. The catalyst produced according to this process has low cost and higher activity and selectivity.

Description

Technical field

The invention relates to a process for the preparation of oxide catalysts for the oxidation of methanol to formaldehyde based on iron and molybdenum oxides.

BACKGROUND OF THE INVENTION

A method is known for the preparation of an oxide catalyst for oxidation of methanol to formaldehyde based on iron oxides and molybdenum by mixing water soluble iron salts and soluble molybdates (1).

There is also a method of preparing an oxide catalyst for the oxidation of methanol to formaldehyde on the basis of an iron-molybdenum catalyst, wherein some of the iron ions are replaced by ions of Cr, Co, Mi, Ni and the like. Usually, aqueous (III) chloride and ammonium paramolybdate solutions are used for precipitation.

It is also known that water-soluble molybdate obtained from the treatment of spent iron-molybdenum catalyst with sodium hydroxide (3) can be used.

The disadvantage of these methods is the high cost of the catalyst obtained due to the high energy consumption for heating the stock solutions, losses during the precipitation process from the finely dispersed colloidal solution obtained under these conditions and the difficult washing of the precipitated ions. Another disadvantage is the relatively low selectivity of the catalysts obtained.

SUMMARY OF THE INVENTION

The essence of the invention is a method in which a solution of iron (III) chloride with a concentration of 3 to 10 wt.% Is used as a starting material. % (solution A) and solution containing ammonium paramolybdate, sodium molybdate and sodium tungstate (solution B). The content of ammonium molybdate and sodium molybdate in solution B may vary from 0 to 10 wt. %, and of sodium tungstate - from 0 to 5 wt. %. Solution B may also contain water-soluble salts of chromium, manganese and cobalt in quantities of up to 2% by weight. %.

Sodium and ammonium molybdate may be commercially available or may be obtained by treating a spent catalyst with sodium hydroxide, ammonia or a mixture of the two in different proportions.

The preparation of the catalyst mass is accomplished by mixing the stock solutions at relatively low temperatures, with solution A at a temperature of 20 to 40 ° C and solution B at 30 to 50 ° C. These conditions ensure that a thick, easily washable sludge is obtained and molybdenum losses in the flushing water are reduced.

Further processing of the resulting catalyst mass includes filtration, drying at 50 to 200 ° C for 2 to 20 hours, tabletting and calcination after and / or before tableting at temperatures of 300 to 550 ° C for 4 to 24 h.

The advantages of the process according to the invention are the low cost, high activity and selectivity of the catalysts.

Embodiments of the invention

Comparative example (according to BG 60779 B1). Preparation of iron-molybdenum oxide catalyst by known method.

The catalyst is obtained by mixing aqueous solution of ferric chloride solution A, and aqueous ammonium paramolybdate solution B, and treating the resulting precipitate as follows:

Solution A: Dissolve 100 g of iron (III) chloride in 1.91 distilled water. By adding a 25% ammonia solution, the pH of the solution is 1.6.

Solution B: Dissolve 175 g of ammonium paramolybdate in 3.31 distilled water. The pH of the solution was 5.2 by the addition of nitric acid.

The two solutions were heated to 60 ° C and solution A was slowly added to solution B with continuous stirring. At the end of precipitation, the pH does not exceed 1.8.

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After standing overnight, the liquid phase over the precipitate was decanted, 51 distilled water was added and stirred for 30 min, then allowed to precipitate for 10 h. The operation is repeated 4 more times until the chlorine content of the solution is below 0.3 g per liter. After the last wash, the resulting precipitate was filtered off, dried at 110 ° C for 12 h, then quenched for 6 h at 300 ° C. The resulting dry mass was tableted in the form of 4x4 mm rings and a wall thickness of 1 mm and calcined at 500 ° C for 6 hours. The catalyst thus obtained has a mass of 146.2 g and a composition of 81.8 wt. % MoO ₃ and 18.2 wt. % Fe ₂ O ₃ .

Examples of the invention

Example 1. Preparation of an Oxide Iron-Molybdenum Catalyst According to the Invention Using Ammonium Paramolybdate and Sodium Molybdate

The catalyst is obtained by mixing an aqueous solution of ferric chloride solution A, and an aqueous solution of ammonium paramolybdate and sodium molybdate solution B, and treating the resulting precipitate as follows:

Solution A: Dissolve 100 g of iron (III) chloride in 1.91 distilled water. By adding a 25% ammonia solution, the pH of the solution is 1.6.

Solution B: 88 g of ammonium paramolybdate and 120 g of sodium molybdate are dissolved in 3.31 distilled water. The pH of the solution was 5.2 by the addition of nitric acid.

Solution B was heated to 50 ° C and solution A remained at room temperature. Solution A is slowly added to solution B with continuous stirring. At the end of precipitation, the pH does not exceed 1.8.

After standing overnight, the liquid phase over the precipitate was decanted, 51 distilled water was added and stirred for 30 min, then allowed to precipitate for 10 h. The operation is repeated 2 more times, with the chlorine ions content in the solution below 0.3 g per liter. After the last wash, the resulting precipitate was filtered off, dried at 110 ° C for 12 h, then quenched for 6 h at 300 ° C. The resulting dry mass was tableted in the form of 4x4 mm rings and a wall thickness of 1 mm and calcined at 500 ° C for 6 hours. The catalyst thus obtained has a mass of 152.5 g and a composition of 81.7 wt. % MoO ₃ and 18.3 wt. % Fe ₂ O ₃ .

EXAMPLE 2 Preparation of Oxide Iron-Molybdenum Catalyst According to the Invention Using Sodium Molybdate Prepared by Chemical Treatment of Exhaust Iron-Molybdenum Catalyst

The catalyst is obtained by mixing an aqueous solution of ferric (III) chloride solution A, and aqueous sodium molybdate solution B solution, and treating the resulting precipitate as follows:

Solution A: Dissolve 100 g of iron (III) chloride in 1.91 distilled water. By adding a 25% ammonia solution, the pH of the solution is 1.6.

Solution B: A solution of 86 g of NaOH in 0.9 l of distilled water was added to 190 g of spent iron-molybdenum catalyst containing MoO ₃ 75%, stirred for 2 h, then allowed to settle until complete precipitation. Fe (OH) ₃ . The clear liquid above the precipitate was decanted, after which the precipitate was filtered and washed with distilled water until the total volume of the filtrate and the wash water was 2.81. By adding nitric acid, the pH of the solution was 5.2, then distilled water was added to reach the final volume of the solution 3.31.

Solution B was heated to 45 ° C and solution A remained at room temperature. Solution A is slowly added to solution B with continuous stirring. At the end of precipitation, the pH does not exceed 1.8.

After standing overnight, the liquid phase over the precipitate was decanted, 51 distilled water was added and stirred for 30 min, then allowed to precipitate for 10 h. The operation is repeated 2 more times, with the chlorine ions content in the solution below 0.3 g per liter. After the last wash, the resulting precipitate was filtered off, dried at 110 ° C for 12 h, then quenched for 6 h at 300 ° C. The resulting dry mass was tableted in the form of 4x4 mm rings and a wall thickness of 1 mm and calcined at 500 ° C for 6 hours. That's right

65917 B1 The resulting catalyst has a mass of 154.4 g and a composition of 81.9 wt. % MoO ₃ and 18.1 wt. % Fe ₂ O ₃ .

Example 3 Preparation of Oxide Iron-Molybdenum Catalyst According to the Invention Using Ammonium Paramolybdate, Sodium Molybdate and Sodium Tungstate

The catalyst is obtained by mixing an aqueous solution of ferric chloride solution A, and an aqueous solution of ammonium paramolybdate and sodium molybdate solution B, and treating the resulting precipitate as follows:

Solution A: Dissolve 100 g of iron (III) chloride in 1.91 distilled water. By adding a 25% ammonia solution, the pH of the solution is 1.6.

Solution B: 88 g of ammonium paramolybdate, 110 g of sodium molybdate and 8 g of sodium tungstate are dissolved in 3.3 l of distilled water. The pH of the solution was 5.2 by the addition of nitric acid.

Solution B was heated to 45 ° C and solution A remained at room temperature. Solution A is slowly added to solution B with continuous stirring. At the end of precipitation, the pH does not exceed 1.8.

After standing overnight, the liquid phase over the precipitate was decanted, 51 distilled water was added and stirred for 30 min, then allowed to precipitate for 10 h. The operation is repeated 2 more times, with the chlorine ions content in the solution below 0.3 g per liter. After the last wash, the resulting precipitate was filtered off, dried at 110 ° C for 12 h, then quenched for 6 h at 300 ° C. The resulting dry mass was tableted in the form of 4x4 mm rings and a wall thickness of 1 mm and calcined at 500 ° C for 6 hours. The catalyst thus obtained has a mass of 154.2 g and a composition of 79.3 wt. % MoO ₃ and 18.1 wt.% Fe ₂ O ₃ and 2.6 wt. % WO ₃ .

Example 4. Preparation of Oxide Iron-Molybdenum Catalyst According to the Invention Using Ammonium Paramolybdate; sodium molybdate and chromium (III) nitrate.

The catalyst is obtained by mixing an aqueous solution of ferric (III) chloride solution A, and an aqueous solution of ammonium paramolybdate; sodium molybdate and chromium (III) nitrate - solution B, and treatment of the resulting precipitate as follows:

Solution A: Dissolve 100 g of iron (III) chloride in 1.91 distilled water. By adding a 25% ammonia solution, the pH of the solution is 1.6.

Solution B: Dissolve 88 g of ammonium paramolybdate, 110 g of sodium molybdate and 9 g of chromium (III) nitrate in 3.3 l of distilled water. The pH of the solution was 5.2 by the addition of nitric acid.

Solution B was heated to 45 ° C and solution A remained at room temperature. Solution A is slowly added to solution B with continuous stirring. At the end of precipitation, the pH does not exceed 1.8.

After standing overnight, the liquid phase over the precipitate was decanted, 51 distilled water was added and stirred for 30 min, then allowed to precipitate for 10 h. The operation is repeated 2 more times, with the chlorine ions content in the solution below 0.3 g per liter. After the last wash, the resulting precipitate was filtered off, dried at 110 ° C for 12 h, then quenched for 6 h at 300 ° C. The resulting dry mass was tableted in the form of 4x4 mm rings and a wall thickness of 1 mm and calcined at 500 ° C for 6 hours. The catalyst thus obtained has a mass of 152.6 g and a composition of 80.0 wt. % MoO ₃ and 18.1 wt. % Fe ₂ O ₃ and 1.9 wt. % Cr ₂ About ₃ .

Determination of catalytic properties of catalysts

In a flow-type reactor, 10 cm ³ of the catalyst obtained according to Example 1 and the catalysts obtained according to the invention described in Examples 2 to 5 are successively charged. Measurement of catalytic activity and selectivity is carried out at a catalyst bed temperature of 350 ° C, concentration of methanol in the alcohol-air mixture 6.0 vol. % and a volumetric rate of 16000 hr ¹ . The results obtained for total methanol conversion, conversion to formaldehyde, and formaldehyde selectivity for the catalysts obtained according to the described examples, as well as the same indicators for commercial catalysts produced by 4 different companies are presented in Table 1.

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Catalyst Conversion to formaldehyde Total conversion of methanol Selectivity Comparative example 90,0 97.0 92,7 (according to I6 60779B]) Example 1 92,1 98.4 93,6 Example 2 93,5 98.6 94.8 Example 3 93,8 99.0 94.7 Example 4 93,1 97.6 95,4 Commercial Catalyst # 1 * 88.1 99.0 89,0 №2 90.7 97.0 93,5 №3 90,9 96.5 94,2 №4 91,0 99.0 91,9 №5 89,3 96.1 92,9

♦ Commercial catalysts: № 1 - rings with dimensions 2,5 x 5,1 mm, № 2 - solid tablets with dimensions 3,2 x 3,5 mm, № 3 - rings with dimensions 3,5 x 4,3 mm, № 4 - rings with dimensions 3.6 x 4.2 mm, № 5 - rings with dimensions 4.8 x 5.0 mm.

Claims (1)

Claims A process for the preparation of an oxide catalyst for the oxidation of methanol to formaldehyde based on iron and molybdenum oxides, characterized in that a solution of ferric (III) chloride at a temperature of 20 to 40 ° C is mixed with a molybdenum solution with temperature from 30 to 50 ° C, the resulting precipitate is filtered off, dried at a temperature of 50 to 200 ° C for 2 to 20 hours, tableted and calcined from 300 to 550 ° C for 4 to 24 h, the molybdenum solution containing ammonium heptamolybdate and / or sodium molybdate up to 10 wt. %, sodium tungstate up to 5 wt. % and water soluble salts of chromium, manganese and cobalt up to 2 wt. %.