CS207807B1 - Catalyser for preparation of the acryl acid and method of making the same - Google Patents

Description

The present invention relates to a catalyst for the preparation of acrylic acid by oxidation of acrolein with air and steam and to a process for its preparation.

It is known that catalytic gas phase oxidation of unsaturated carbonyl compounds to unsaturated carboxylic acids can be carried out on catalysts prepared specifically for this process. The composition and structure of the oxidation catalysts is still largely unknown. It is believed that individual oxides, mixtures or solid solutions, and optionally various salts of the iso- and heteropolyacids of molybdenum, vanadium, tungsten, chromium, iron, manganese, copper and other metal elements are present.

However, few catalysts containing the above elements are technically useful. This is mainly due to the properties of the feedstock to be processed and the operating conditions, such as high temperatures, long contact times, low conversion and selectivity to the desired product, unsatisfactory stability and catalyst life.

Among the many known catalysts for the oxidation of unsaturated carbonyl compounds to unsaturated carboxylic acids, for example for the oxidation of acrolein to acrylic acid, molybdenum-vanadium catalysts are most commonly used. Thus, Japanese Laid-open Patent Publication No. 68-09045 recommends a combination of Mo-V-0 and Al ₂ O ₃ ; DOS č.

924,496 protects the preparation of a MoV-O catalyst. which still contains germanium or tungsten. The preparation of the Mo-V-O catalyst is described in French Patent No. 1 520 089. Other patents, e.g.

050 155 are derived from the Mo-V-W-O system and further comprise antimony or Cu, Pb, Ag, Sn, Ti, Bi. DOS No. 2,303,383 protects a similar composition. Instead of antimony, other elements are used, for example, in DOS No. 1,908,965 iron or Mn, Ni. Cu and in DOS No. 2 004 874 then manganese, respectively. copper and chromium in DOS No. 2,152,037. Many patents also protect the use of supported catalysts. Silica, carborundum, is used as the carrier. diatomaceous earth, titanium dioxide and zirconium dioxide. The preparation of modified Mo-V-W-O catalyst on alumina with specific texture properties is particularly protected in DOS No. 2,152,037.

The process for the preparation of catalysts derived from the same basic type, e.g. Mo-V-W-O, is often different from one another. Accordingly, different catalytic effects can be observed under the conditions of catalytic oxidation of unsaturated carbonyl compounds. Most often, however, these catalysts are prepared by mixing solutions of the salts of the active elements at elevated temperature followed by evaporation of the solvent and decomposition of the catalyst dry matter by heat. The annealed mass is formed into particles of a regular shape.

It has now been found that generally known Mo-V-O and Mo-V-W-O catalysts can be further improved. According to the invention, the catalyst for the preparation of acrylic acid by oxidation of acrolein with air and water vapor in the gas phase consisting of molybdenum oxides Mo, vanadium V and tungsten W contains, in addition to the oxides of said metals in oxide form,

Mo ₁₂ V ₂ W ₀₁ . ₆ Ge _0S . ₅ Ox, where x depends on the atomic ratio of the elements present, and comprises a silicon carrier in the form of silica gel or 30% silica sol.

The process for the preparation of this catalyst consists in preparing an aqueous solution of molybdenum Mo, vanadium V, tungsten W by dissolving their oxides, ammonium salts or acids, optionally with the addition of concentrated ammonia, adding to the concentrated solution germanium Ge, the resulting mass is bent during

1.5 hours and either formed by extrusion, dried at 120 ° C, then successively at 160 ° C for 2 hours, at 200 ° C for 1 hour and finally at 350 ° C for 6 hours in a gas stream, or The kneaded catalyst mass is first dried and heat treated under the same conditions as the extrudates, then crushed, homogenized with graphite and tableted.

The lowering of the working temperature at a relatively short contact time allows the use of the catalyst according to the invention also advantageously in the treatment of a product which is produced, for example, by catalytic oxidation of propylene with air in the presence of water vapor in the gas phase on a special catalyst. Said product, besides acrolein as the main valuable component, also contains acrylic acid and acetic acid, unreacted propylene and oxygen, or other components such as nitrogen and water vapor. The gentle conditions under which the catalyst according to the invention operates have the effect of avoiding further oxidation of the acrylic acid entering the reactor simultaneously with acrolein and air.

For the preparation of the catalysts it is expedient to use ammonium oxides or molybdenum, vanadium and tungsten acids as starting materials. Germanium is added in the form of hydroxide, nitrate, acetate, oxalate, formate, citrate, all of which are easily decomposed into oxides and gases during heat treatment. Silicon is added as precipitated silica gel, silica sol, methyl silicate, ethyl silicate or colloidal silicon dioxide.

The annealed catalyst is expediently used to oxidize the unsaturated carbonyl compound in the gas phase at a reaction temperature of 210 to 320 ° C, preferably at 230 to 275 ° C. The composition of the incoming reaction mixture varies within wide limits of 1 to 10 mol%. unsaturated carbonyl compounds, e.g. acrolein, 5 to 15 mol%; of molecular oxygen, 20 to 60 mol%; water vapor and the remainder inert gases, or reaction products, resulting, for example, from the oxidation of propylene to acrolein in the previous oxidation stage. The reaction time of the reaction mixture (NTP) varies depending on the temperature and the composition of the reaction mixture between 0.5 and 20 seconds. The working pressure can vary from atmospheric up to 10 bar without deteriorating the catalytic properties. The oxidation can be carried out in a fixed bed or in a fluidized bed. When the oxidation is carried out with the catalyst in a fixed bed, preferably tubular reactors located in a circulating salt bath are used.

Catalyst efficiency is evaluated by parameters defined as follows:

Conversion% = moles of react. unsaturated carbonyl compounds mole of the unsaturated carbonyl compound

Selectivity to unsaturated carb. % = moles of unsaturated carboxylic acid formed moles of reacted unsaturated carbonyl compound

100 • 100

Yield of unsaturated carb. % conversion. selectivity

100 ALIGN!

The following examples illustrate the invention.

Example 1

106.2 g (NH ₄ ) ₆ Mo ₇ O ₂₄ .4 H ₂ O are dissolved with stirring in 600 ml of distilled water at 50 ° C. 11.7 g of NH4VO3 and 290 g of milled silica gel are added in portions. The suspension is evaporated to dryness with stirring, dried at 130 ° C, 2 hours at 160 ° C, Γ hour at 200 ° C. It is then crushed and scale with graphite. The porosity of the catalyst is 32%.

ml of the crushed catalyst was tested in a 14 mm stainless steel U-reactor. The reactor is heated in a molten salt bath at 375 ° C and activated in a 3 mol% mixture stream. acrolein, 31 mol%. air, 35 mol%. water vapor and nitrogen for 4 hours at a contact time of 1.8 seconds. The reaction temperature was then lowered to 350 ° C.

The acrolein conversion is 79.2%. The yields of acrylic acid and acetic acid are respectively 56.3% and 6.2%. The rest are CO and CO ₂ .

Example 2

106.2 g (NH ₄ ) ₆ Mo ₇ O ₂₄ .4 H ₂ O are dissolved with stirring in 600 ml of distilled water at 50 ° C. The solution was added portionwise

25.5 g of tungstic acid (90.5%), 11.7 g of NH ₄ VO _3, and concentrated aqueous ammonia solution in such an amount that all of the components have gone into solution. The solution is then metered with stirring

3.1 g GeO ₂ . The resulting suspension is concentrated under stirring, stirred with 405 g of 30% silica, dried at 130 ° C, 2 hours at 160 ° C and 1 hour at 200 ° C and finally calcined for 6 hours at 350 ° C in an inert gas stream. After grinding, the mass is granulated with graphite.

ml of crushed catalyst was tested as in Example 1 at 300 ° C.

The acrolein conversion is 92%. The yields of acrylic acid and acetic acid are respectively 83.5% and 1.1%.

Example 3

According to Example 2, a molybdenum solution is prepared.

Claims (3)

SUBJECT Catalyst for the preparation of acrylic acid by oxidation of acrolein with air and water vapor in the gas phase consisting of molybdenum oxides Mo, vanadium V and tungsten W, characterized in that, in addition to the oxides of said metals, it contains elements in the oxide form in proportions MO | ^ 2 VJL W _{of> 1} _ ₆ Ge _{0 <5} O _x, where x depends on the atomic ratio of the elements present, wherein the carrier contains silicon in the form of silica gel or silica sol 3Q%. 2. A process for the production of a catalyst as claimed in claim 1, wherein an aqueous solution of molybdenum Mo, vanadium V, tungsten W is prepared, dissolved in tungsten, tungsten and vanadium salts in 1 * x larger quantities. To the solution was added portionwise 64.7 g of Fe (NO _{3) 3} .9 H ₂ O dissolved in 500 ml of distilled water and 200 g of 3% silica sol. The suspension is evaporated to a thick powder with stirring. which is extruded into extrudates which are then dried at 130 ° C for 2 hours at 160 ° C, 1 hour at 200 ° C and finally ignite for 6 hours at 350 ° C. 5 ml of crushed catalysts were tested as in Example 1 at 275 ° C. the acrolein conversion is 98.4%. The yields of acrylic acid and acetic acid are respectively 88.7% and 1.9%. The rest are CO and CO ₂ . The porosity of the catalyst is 52.4%. INVENTION of their oxides, ammonium salts or acids, optionally with the addition of concentrated ammonia, to the concentrated solution is dosed with germanium Ge, bending the resulting mass for a period of time 1.5 hours and either formed by extrusion, dried at 120 ° C, then successively at 160 ° C for 2 hours, at 200 ° C for 1 hour and finally at 350 ° C for 6 hours in a gas stream, or The kneaded catalyst mass is first dried and heat treated under the same conditions as the extrudates, then crushed, homogenized with graphite and tableted.