DE2719299B2 - Process for the manufacture of a vanadium-molybdenum catalyst - Google Patents

Description

The invention relates to a process for the production of a vanadium-molybdenum catalyst of the type used in the production of maleic anhydride by the oxidation of benzene in the gas state. In this process, catalysts are usually used which contain vanadium pentoxide and molybdenum trioxide, the variable molar ratio MOO3 to V2O5 of which is usually within the limits of MoOj / V ₂ O ₅ = 0.3-1.2. In addition to the above-mentioned oxides, active vanadium molybdenum usually also contains, as promoters, oxides of elements such as Li, Na, K, Co, Ni, Fe, Cr, Cu, Ag, W, U, P, Te and Ta.

About the catalytic properties of vanadium-molybdenum catalysts decide: their chemical and phase composition, the applied carrier and its structure, type and concentration of Promoters and also the process used to produce it, which have a significant influence affects the quality of the catalysts.

These catalysts are most often by a corresponding application of the active composition on a produced a low specific surface area carrier. Usually come as a carrier Electric corundum, carborundum and sintered corundum from Λ-Αΐ2θ3 are possible.

In the case of the carrier contacts, the active material is applied to a carrier, ie the carrier is impregnated with a solution specially prepared for this purpose. This impregnation solution contains corresponding salts dissolved in aqueous solutions of mineral or organic acids. Sometimes the active material is applied to the carrier by the sintering process using an appropriate salt or oxide mixture. The catalysts obtained by impregnating the support with aqueous solutions are dried after the impregnation process has ended and then calcined, usually at a temperature of 320 to 450 ^° C.

All varieties of the stationary catalysts used in the process of partial oxidation of gaseous benzene must have a substantial mechanical strength and thermal stability since they under industrial operating conditions continuously for periods of 2-3 years in approximately 3 m thick catalyst beds at temperatures up to about 400 ⁰ C. , which can be even higher in the reaction zone, work.

Vanadium-molybdenum catalysts are often used to produce maleic anhydride Impregnating the carrier with a concentrated by dissolving vanadium pentoxide and molybdenum trioxide Hydrochloric acid in the hot state prepared solution. This way they become catalysts obtained with high activity and high persistence and it also becomes a uniform Distribution of the active material on the carrier granules and their good adhesion achieved.

During the dissolution of the vanadium pentoxide in concentrated hydrochloric acid, atomic chlorine is converted into Freedom set, which, as is well known, is chemically very active, which is why the chemical equipment used very high requirements in terms of their chemical resistance must be made, which accordingly high construction costs. In addition, concentrated hydrochloric acid sets free in the process set chlorine for the operating personnel working in the manufacture of the catalyst poses a potential hazard and also causes poisoning of the environment. For the reasons mentioned,

J5 d. H. for reasons of occupational safety and hygiene and also in order to reduce the production cost of the catalyst, it is desirable to have the Avoid using hydrochloric acid in the preparation of the catalyst. The procedure; en to manufacture of catalysts by impregnating a support with solutions obtained by dissolving the corresponding Vanadium and molybdenum salts and corresponding promoters are prepared, provides catalysts that in the oxidation of benzene to maleic anhydride give too low yields and therefore the dated Do not meet the requirements of the current technology for these catalysts. Catalysts produced in this way are therefore not used in industry.

Better, more active catalysts can be produced when using highly concentrated solvents aqueous solutions of certain organic acids, including oxalic acid, can be used. at Use of the latter is 3-6 moles of oxalic acid based on 1 mole of the imported vanadium pentoxide used. Admittedly, by choosing such concentrations of oxalic acid or another organic acid in the solution achieves good solubility of the introduced salts, but is thereby at the same time, on the last impregnation stage, the grains of carrier stick together or even bake together of the total catalyst mass produced. In addition, this manufacturing method achieved a low adhesive force between the active material and the carrier, which is not only the Production of the catalyst is also made more difficult, but also has adverse consequences in its industrial use in the stationary catalyst bed.

A method of the type described is also the one reproduced in DEPS 16 43 663. According to DE-PS 1643 663, a catalyst based on titanium dioxide, vanadium pentoxide and Molybdenum trioxide, the special characteristic of phosphorus pentoxide in an amount of 1.5 to 5.0 Contains percent by weight, produced by the fact that an aqueous solution of vanadium pentoxide and oxalic acid in a molar ratio of 1 to 5 with the other components titanium dioxide and molybdenum trioxide in solid form and secondary ammonium phosphate blended and the mixture thickened to a paste, from which one then the actual catalyst forms.

The catalyst produced in this way allows a Conversion of the benzene used to maleic anhydride up to a degree of conversion of 65 to To achieve 70% of theory. The manufacturing process with the sled is thickening and shaping laborious. It cannot be used to impregnate an inert carrier without being used to Caking of the carrier substance comes.

The invention is based on the object of a method for producing a vanadium-molybdenum analyzer by impregnating an inert porous support to provide that easily and inexpensively is to be carried out and after the catalysts are obtained that have a high degree of conversion of Benzene to maleic anhydride guarantee and under industrial conditions a long service life) o exhibit.

This object is in a method for producing one for the catalytic oxidation of Benzene to maleic anhydride in the gas state suitable vanadium-molybdenum catalyst by impregnation an inert porous support with a solution that contains the components of the catalytic mass such as vanadium and molybdenum salts in a ratio of molybdenum trioxides to vanadium pentoxide of 0.3-1.2 as well Contains promoters dissolved in water in the presence of organic, reducing substances, and then Evaporation of the volatile substances and calcining, solved according to the invention in that the aqueous solution organic substances with reducing properties such as corresponding acids and / or their ammonium salts are added in amounts of 0.4-1.2 moles of acid or salt to 1 mole of vanadium pentoxide will. It is particularly advantageous to use 0.6-1 mole of a reducing agent per 1 mole of vanadium pentoxide to add organic acid or its ammonium salt.

It has surprisingly been found that the hitherto customary dissolving of the catalyst components in highly concentrated mineral or organic acids can be replaced by the fact that the components in the essentially only in water with the addition of the specified small amount of reducing organic substances, such as in particular oxalic acid, citric acid, ascorbic acid, formic acid, maleic acid or their Ammonium salts are dissolved.

The catalysts obtained are notable for the degree of conversion of benzene to maleic anhydride of about 74-75 mol% with high resistance at the same time.

The impregnation solution for the carrier substance is prepared as follows: The ammonium salt of vanadium or the vanadium pentoxide is dissolved in hot water, then molybdic acid, its anhydride or its ammonium salt is dissolved in this solution, the ratio of MOO3 / V2O5 being within 0.3 -1.2 lies. However, it is particularly advantageous to use a catalyst in which the quantitative ratio of the oxides mentioned is within the limits of 03-0.6. Cu, Ag, K, Cd, Cr, W, U, Te and Ta added. These promoters are added in the form of readily soluble salts in which the second constituent is volatile under the conditions of the catalyst calcination, which takes place in the temperature range of 200-400 ° C. As a result, the salts of the metals mentioned are converted into oxides. A reducing agent in the form of a water-soluble organic substance, such as a corresponding organic acid or its ammonium salt, is also introduced into the finished solution in amounts of 0.4-1.2 mol, preferably 0.6-1.0 mol per 1 mol of the vanadium pentoxide present in the solution in the form of a corresponding soluble salt. The solution prepared in this way is used to ^{impregnate an inert, porous support rr:} «with a low specific surface area of the order of _{0.01-1 1} OmVg. The heated vessel in the rotating carrier with the impregnation solution is at a temperature of 60-200 ⁰ C is poured over. After all of the impregnation solution has been used up, the catalyst obtained is dried and calcined in the temperature range from 200-400 ° C.

The method according to the invention for the production of vanadium-molybdenum catalysts shows in comparison a number of advantages compared to the methods used so far:

The use of concentrated hydrochloric acid and other solvents that are cumbersome to use, harmful and expensive is avoided. Instead of this the constituents of the catalytic composition according to the invention are dissolved in hot water and then small, precisely defined amounts of organic substances with reducing properties are added to the solution such as oxalic acid or its ammonium salt, citric acid, maleic acid, ascorbic acid or its ammonium salts admitted.

This also makes the use of an expensive acid-resistant apparatus superfluous, whereby the inventive Method is much cheaper and compared to the known manufacturing process for Vanadium-molybdenum catalysts of this type are much more convenient. According to the invention Processes produced catalysts are characterized by good mechanical strength and good adhesion of the active composition on the carrier as well as characterized by long service life under the working conditions The use These catalysts guarantee that a high conversion of benzene into maleic anhydride is achieved.

The process for the preparation of catalysts containing vanadium molybdenum oxides used in the manufacture of maleic anhydride by oxidation of benzene in the gas state will be used below explained in more detail using examples

example 1

In 6 liters of water, 250 g of vanadium ammonium salt, 104 g of molybdic acid monohydrate, 12 g of nickel

- 6 H ₂ O. 133 g of sodium chloride, 3.9 g of phosphorus pentoxide and 91 g of oxalic acid dissolved. Tantalum pentachloride dissolved in 200 ml of absolute ethyl alcohol is then added to this solution. With the thus prepared solution, a is located in a rotating quartz vessel, consisting of sintered alumina carrier substance is poured over slowly, said vessel is heated with the flame of a gas burner so that the temperature of the medium is kept within the limits of 80- 100 ⁰ C. After consumption of the entire amount of the prepared impregnating solution, ie, after completion of carrier impregnation, the temperature of the rotating quartz vessel is slowly increased to 300-380 ⁰ C, wherein the catalyst obtained is calcined in 2-3 hours. The heating is then switched off and the rotating vessel is stopped about 15 minutes later. After cooling, the catalyst is sieved to remove contact dust and any lumps that may have arisen from agglomeration of granules

The catalyst obtained in this way is poured into a unitary reactor with a 3 m long tube which is heated with a molten bath. A mixture of gaseous benzene and air with a concentration of 42 g of benzene per m ^{3 of} air is passed through this reactor, the loading of 120 g of benzene per liter of catalyst in one hour.

The process is carried out at 300 ⁰ C.

With a total benzene conversion of 97 mol%, the yield of maleic anhydride is 75 Mol%.

Example 2

As in Example 1, the components of the active composition are dissolved in 6 liters of water, but the Oxalic acid has been replaced by 103 g of ammonium oxalate.

With the solution prepared in this way, which is otherwise used for the remaining parts of the Beatand in Example 1 Contains amounts, the carrier is impregnated. Then the catalyst obtained is as in Example 1 dried and calcined. When using this catalyst, a total benzene conversion of 97 * mol%, a maleic anhydride yield of 74 mol% is achieved.

Example 4

The components of the active material are dissolved in 6 liters of water as in Example 1, but this is Nickel nitrate has been replaced by 22 g of silver nitrate. With this solution, which is otherwise the remaining ingredients in contains the amounts given in Example I, was

Example 3

in 6 liters of water the individual components of the impregnation solution, as indicated in example 1, dissolved, however, the oxalic acid is replaced by 71 g of maleic anhydride been replaced. With the impregnation solution prepared in this way, the carrier becomes exactly as in Example 1 impregnated and the catalyst obtained is, as indicated there, dried and calcined. at Using this catalyst will benzene in the gas state with a total benzene conversion of 91 Mol% oxidized to maleic anhydride with an 86 mol% yield.

the carrier is impregnated. The obtained catalyst is dried and calcined as in Example 1. The thus produced catalyst has been obtained a yield of maleic anhydride of 73% by mole in your run at 300 ⁰ C process at a total benzene conversion of 97% MgI.

Example 5

ίο The individual components of the impregnation solution are dissolved in 6 liters of water as in Example 1, but the nickel nitrate has been replaced by 22 g of AgNO ₃ and no tantalum pentoxide was added.

With the solution prepared in this way, otherwise

contains the same amounts of other ingredients as in Example 1, the carrier is impregnated. The catalyst obtained is exactly the same as in the example! dried and calcined With the catalyst prepared in this way, a maleic anhydride yield of 66 mol% was achieved ^{in the process carried out at 420 ° C. with a total benzene conversion of 94 mol%.}

Example 6

The individual components of the impregnation solution are dissolved in 6 liters of water in the same way as in Example 1, but the nickel nitrate has been replaced by 22 g of AgNO ₃ and the oxalic acid by 103 g of the ammonium oxalate jo. The carrier is impregnated with the solution prepared in this way, which contains identical amounts of the remaining components as in Example 1. The catalyst obtained is dried and calcined as in Example 1.

Using the catalyst thus prepared, maleic anhydride is obtained with a yield of 73 mol% obtained with a total benzene conversion of 97 mol%.

Example 7

The individual components of the impregnation solution are dissolved in 6 liters of water as in Example 1. An additional 4 g of KNO _{3 are} added to this solution.

However, the solution does not contain tantalum pentoxide. With the solution prepared in this way, the identical amounts of Contains other components as in Example 1, the carrier is impregnated. The obtained catalyst is just like in example 1 dried and calcined.

When using this catalyst, maleic anhydride is obtained with a yield of 73 mol% in the process carried out at 400 ^{° C. with a total benzene conversion of 96 mol%.}

Example 8

As in Example 1, the individual components of the impregnation solution are dissolved in 6 liters of water, but without the addition of tantalum oxide. The nickel nitrate

bo is replaced by 17 g Cu (NO ₃ ) 2

With this solution, which contains identical amounts of other ingredients as in Example 1, the Impregnated carrier. The catalyst obtained is dried and calcined exactly as in Example 1.

b5 With this catalyst, a maleic anhydride yield of 68 mol% is achieved in the process carried out at 430 ^° C. with a total benzene conversion of 93 mol%.

Example 9
(Comparative example)

The impregnation solution was prepared as in Example 1, but instead of 91 g of oxalic acid, 27 g of oxalic acid (0.2 mol / 1 mol V ₂ O ₅ ) were added. The further procedure was as described in Example 1. The catalyst allowed it. Maleic anhydride to be obtained with a yield of 40 mol% with a total conversion of 62 mol%.

Example 10
(Comparative example)

The impregnation solution was prepared as in Example 1, but instead of 91 g of oxalic acid, 336 g of oxalic acid (2.5 mol / l mol V ₂ Os) were added. The further procedure was as described in Example I. The catalyst allowed it. Maleic anhydride to be obtained with a yield of 30 mol% with a total conversion of 45 mol%.

130111/115

Claims (3)

Patent claims: 1. Process for the preparation of one for the catalytic oxidation of benzene to maleic anhydride Vanadium-molybdenum catalyst suitable in the gas state by impregnating an inert one porous carrier with a solution that contains the components of the catalytic mass such as vanadium and molybdenum salts in a ratio of molybdenum trioxides to vanadium pentoxide of 0.3-1.2 as well as promoters in the presence of organic, reducing substances dissolved in water, and subsequent evaporation of the volatile substances and calcination, characterized in that that the aqueous solution organic substances with reducing properties such as Corresponding acids and / or their ammonium salts in amounts of 0.4-1.2 mol of acid or salt to 1 Added moles of vanadium pentoxide. 2. The method according to claim 1, characterized in that per 1 mol of vanadium pentoxide 0.6-1 mol a reducing organic acid or its ammonium salt can be added. 3. The method according to claim 1 or 2, characterized in that as reducing substances Oxalic acid, citric acid, ascorbic acid, formic acid, maleic acid or their ammonium salts be used.