CS244033B1 - Method of multicomponent catalysts production for oxidation of aldehydes - Google Patents

Abstract

Process for the production of multi-component catalysts for the oxidation of aldehydes to carboxylic acids acid by mixing a homogeneous aqueous solution starting compounds of the active ingredients, which are oxides of molybdenum, vanadium and others promoter metals from I, V, and VIII. the Mendeleyev Periodic Group with the atomic ratio of molybdenum to vanadium 2: 1 to 12: 1 and atomic ratio of promoters to molybdenum is 0.01 to 0.5 with organic hydroxy acids selected from the group consisting of tartaric acid and citric acid in amounts 1-5 g-molecules per g-promoter promoter metal and adjusting the pH to 7 to 8 by addition ammonium hydroxide, such that the solution optionally with the addition of an inert carrier to a consistency of arocrocrystalline paste s-óbaaham 15 to 50 B by weight of moisture, ■ the paste is dried while calcining in a continuous a stirred dryer in a gas flue gas stream burner and / or air at temperature 250 to 350 ° C, the dust collected with * blends with tabletting additives, optionally added ammonium carbonate up to 40 B by weight the mixture is shaped into tablets, which are ignited with air access by the horse temperature of 300 to 400 eC for 5 to 24 hours. The method allows reproducibility of conditions individual manufacturing operations in industrial scale.

Description

The present invention relates to a process for the preparation of multi-component catalysts for the oxidation of aldehydes to carboxylic acids in the gas phase.

Multi-component catalysts based on mixed oxides of molybdenum, vanadium and other promoter metals of I., V. and VIII are commonly used for the catalytic ioxidation of aldehydes such as acrolein or natacrolaia to the corresponding carboxylic acids i.e. acrylic or methacrylic acid. of the Mendeleev Group of the Periodic System.

The basic drawback of all prior art catalyst preparation processes of this type is the poor reproducibility of the conditions of individual manufacturing operations on an industrial scale resulting in different catalytic properties of the individual batches of catalysts.

These multi-component catalysts are most often prepared by precipitation from solutions of soluble active ingredient compounds, with or without a carrier. After evaporation of the water, the obtained mass is further heat treated, the contained salts are thermally decomposed, the mixture is shaped and calcined to obtain the desired catalytic properties.

The main disadvantage of the most commonly used aethod is the high sensitivity of the precipitate composition to the order of the aà l ll solutions, the rate of dosing, the concentration of the solutions and the pH of the environment. ·

It is very difficult to maintain constant and reproducible precipitation conditions in a multi-component system and this is one of the causes of the inhomogeneity of the composition of the individual batches when preparing the catalyst on an industrial scale.

Significant advances in this direction are brought about by the use of coaplexing agents, as disclosed in U.S. Pat. No. 188,414, guaranteeing that all the components of the crystallisers are kept in a homogeneous solution until it is thickened into a microcrystalline paste. However, the above-mentioned AOs, like other known processes, do not sufficiently address the process of further thermal treatment of the thickened suspension (paste) under industrial conditions.

The starting materials for the preparation of catalysts for the oxidation of aldehydes are most commonly hexa-aryonic acid heptamolybdate, ammonium vanadate and nitrates of other promoting metals. The by-product of mixing their aqueous solutions is ammonium nitrate, which causes considerable difficulties in their further thermal treatment.

The thermal decomposition of ammonium nitrate is a highly exothermic process, which in the presence of metal salts proceeds autocatalytically. The heat released in this process can easily raise the temperature at the boundary, where decomposition becomes unmanageable and the catalyst at this stage is in danger of overheating, which in turn causes the loss of its good catalytic properties.

The presence of complexing agents further increases this risk and shifts the onset of thermal decomposition of NH4NO3 to lower temperatures. In this respect, the drying and kaleinization (thermal decomposition of salts) operation is a highly demanding operation requiring the corresponding technological equipment.

This opsracs from the conditions of AO 188 414 can only be carried out on a laboratory scale, where a relatively good heat dissipation from the dried and calcined matter can be guaranteed. Also, the other catalyst mass treatment process described in this AO is unsuitable for larger scale, since the proposed annealing of the catalyst in powdered form reduces the bottom layers of the material and is again feasible only in a small laboratory scale where sufficient air access to the entire annealed catalyst batch can be guaranteed.

Progress in comparison with the process for the production of the catalyst according to U.S. Pat. AO No. 188 414 consists not only in increasing the yield of useful aldehyde oxidation products by about -3%, as shown in Table I, but particularly in the fact that the process of the present invention is feasible on an industrial scale, while the process of preparing the catalyst of U.S. Pat. A0 No. 188 414 can be realized only in a small laboratory equipment.

SUMMARY OF THE INVENTION A process for the preparation of multi-component catalysts for the oxidation of aldehydes to carboxylic acids by mixing a homogeneous aqueous solution of the starting compounds of the active ingredients, which are the oxides of molybdenum, vanadium and other promoting metals of I., V. and VIII. of the Mendeleyev group of the Periodic System, wherein the atomic ratio of molybdenum to vanadium is 0.01 to 0.5 with organic hydroxy acids selected from the group comprising tartaric and citric acids in an amount of 1 to 5 g-molecules per 1 g-atom of promoting metal and adjusting the pH to The addition of ammonium hydroxide according to the invention consists in that the solution, optionally with the addition of an inert carrier, is thickened to a consistency of a microcrystalline paste containing 15 to 50% by weight of moisture, the paste is dried and calcined in a continuous stirred dryer in a flue gas stream. and / or air at 250 to 350 [deg.] C., the dust obtained is mixed with the additive additives, optionally up to 40% by weight of ammonium carbonate is formed and the mixture is shaped into tablets which are annealed under air at 300 to 400 ° C for 5 to 24 hours. The preferred shape of the tablets are 4 to 6 mm equilateral cylinders, preferably with an opening in the center.

This process of preparation of multi-component aldehyde oxidation catalysts guarantees the excellent catalytic properties of the catalysts and the perfect homogeneity of their individual batches for the following reasons:

The use of a combination of hydroxy acid and KHHOH ensures that the poly-component mixture of the active ingredients is kept in solution until it is concentrated to a paste with the desired moisture content, thereby achieving a perfect homogeneity of the mixture.

2. Appropriate combination of ertdothermal drying and exothermic calcination using a continuous stirred dryer with gaseous drying medium ensures perfect temperature control where the temperature of the dryer can be controlled within the required limits by selecting the moisture content in the paste, gaseous drying medium, which eliminates the possibility of unwanted overheating of the catalyst.

3. Easily maintaining constant operating conditions of the basic catalyst production operations then ensures perfect homogeneity and reproducibility of catalyst production in any amount.

4. Possible addition of ammonium carbonate before tabletting can then suitably influence the formation of the macroporous structure of the catalyst and thus eliminate the negative effect of internal diffusion on the selectivity of the oxidation reaction.

5. By shaping the catalyst into cylindrical form with an internal orifice, it is then possible to guarantee a better utilization of the catalyst internal surface, to reduce the cost of raw material production and to improve the hydrodynamic conditions in the reactor.

The catalysts produced according to the invention are characterized by high activity and selectivity in the oxidation of aldehydes. They can advantageously be used for the second oxidation stage in the process of producing acrylic acid from propene.

The catalyst prepared according to the present invention, when used for the oxidation of acrolein to acrylic acid, provides higher yields of acrylic acid under the same conditions than a catalyst of the same composition prepared on a laboratory scale according to No. AO No. 188 414 as shown in Table I below.

Table S. I

Catalyst according to AO 188 414 Catalyst of the invention acrolein conversion 95% 100% yield of acid acrylic 92% 95%

The actual process for preparing the catalyst of the present invention is further illustrated by the following example:

He did

Gradually prepare:

Solution A1 - 28 kg of hyxammonium heptamolybdate are dissolved in 132 l of water and 7.2 l of 26% ammonium hydroxide are added

Solution A2 - 4.6 kg of ammonium vanadate are dissolved in 222 l of water

Solution B1 - 8 kg of tartaric acid and 6.4 kg of cupric nitrate are dissolved in 43 l of water

Solution B2 - Dissolve 3 kg of tartaric acid and 2.7 kg of Selesium nitrate in 32 L of water.

Combining solutions A 1 and A 2 gives solution A. Combining solutions B 1 and B 2 gives solution B.

After mixing, the pH is adjusted to 7.3 with ammonium hydroxide. The resulting homogeneous solution is concentrated at 80-100 ° C to a paste with a minimum moisture content of 15% by weight. At the same time, the paste is pounded and calcined in a continuous stirred drier in a stream of natural gas and flue gas under the following conditions: air flow rate through the drier - 70 to 75 kg / h, duct outlet temperature + 300 ° C, hay gas consumption 2.5 m ^ / h, oven temp. shell temperature * 240 ° C.

Catalyst dust, after the addition of graphite and kaolin and 10 kg of ammonium carbonate, is tabletted into 6 x 3 mm cylinders with a 2 mm internal orifice and finally annealed in an air oven for 5 hours at 300 ° C and 10 hours at 350 Deň: 32 ° C.

Claims (1)

A process for the preparation of multi-component catalysts for the oxidation of aldehydes to carboxylic acids by mixing a homogeneous aqueous solution of the starting compounds of the active ingredients, which are the oxides of molybdenum, vanadium and other promoting metals of I., V. and VII. of the Mendeleyev periodic system, wherein the atomic ratio of molybdenum to vendan is 2: 1 to 12: 1 and the atomic ratio of promoters to molybdenum is 0.01 to 0.5 with organic hydroxy acids selected from the group comprising tartaric and citric acid in an amount of 1-5 g - a non-lg-etoma-promoting metal molecule and adjusting the pH to 7-8 by addition of ammonium hydroxide, characterized in that the rostok, optionally by addition of an inert carrier, is dried into a microcrystalline paste having a moisture content of 15-50% by weight; calcined in a continuous stirred drier in a flue gas stream of gas burner and / or air at a temperature of 250 to 350 ° C, the dust obtained is mixed with tableting ingredients, optionally up to 40% by weight of ammonium carbonate and formed into tablets which ee are pulled out of the access at 300 to 400 ° C for 5 to 24 hours.