DE2007795C3 - Process for increasing the effectiveness of bismuth molybdate supported catalysts, which may contain phosphorus - Google Patents

Description

U.

it can be subjected to activating heating following the calcination required for production in a known manner, or it can be treated ^{directly at 580 to 750 ° C. without prior calcination.} If a catalyst that has already been used is to be reactivated, the heating according to the invention is carried out directly.

It must be described as extremely surprising that by means of the process according to the invention an increase in the catalyst efficiency is achieved. Namely, if a bismuth phosphorus molybdate catalyst with about. 24.5 percent by weight bismuth, 14 percent by weight molybdenum and 0.3 percent by weight phosphorus, such as, for example, for the purpose of Acrylonitrile synthesis according to Example 1 of German Patent 11 27 351 is obtainable in this process is used for a longer period of time, there is a decrease leading to a gradual decrease in yield the catalytic activity with increasing running time at the same time a decrease in the specific Surface of the catalyst instead. The following Table I illustrates this process: a The decrease in the acrylonitrile yield after a period of 6 or 12 months is accompanied by a decrease in the specific surface area of the catalyst.

Table I.

Catalyst Fresh

6 months 12 months

Runtime runtime

30th

40

Specific 58 to 64 52 to 53 46 to 47 surface

(m ^a / g) Bi (%) 24 to 25 23.8 to 24.8 23.6 to

24.6

Mo (%) 13.5 to 14.5 13.3 to 14.3 13.2 to

14.2

Acrylonitrile 63 to 65 59 to 61 55 to 57 yield (%)

However, the inventive treatment of the catalyst at temperatures between 580 and 750 ° C leads also to a decrease in the specific catalyst surface, so that damage to the catalyst activity and a decrease in the yield of acrylonitrile was to be expected. That the inventive However, temperature treatment increases or restores the effectiveness of bismuth phosphorus molybdate catalysts would result was by no means predictable. This result was not to be expected insofar as it had been established is that the bismuth phosphorus molybdate catalyst at reaction temperatures above that for the Acrylonitrile synthesis required temperature and below the lower limit of the invention Temperature range is severely damaged in its activity.

Accordingly, heating at temperatures above 580 to about 75O ° C, which results in a further decrease in the specific catalyst surface, the effectiveness of the catalyst would further decrease. That achieved on the basis of the measure according to the invention The result is thus in marked contradiction to previously known observations and Results.

example 1

A bismuth phosphorus molybdate catalyst with 24.5 percent by weight bismuth, 14 percent by weight molybdenum and 0.3 percent by weight phosphorus, obtained according to Example 1 of German Patent 11 27 351, was used in a large-scale upright fluidized bed reactor in the customary manner for the synthesis of acrylonitrile. The acrylonitrile yield at the start of the experiment was 64%, the catalyst having a specific surface area of 58 m ² / g (Table II, column a). After a running time of 18 months, the acrylonitrile yield was 55%; the catalyst surface area had ^{dropped to 44 m 2} / g (Table II, column b). ^{After this running time of 18 months, the catalyst was heated to 550, 600, 650 and 700 °} C. for 5 hours in each case in the presence of air, and the values for the specific surface area and the acrylonitrile yield required to assess its activity (columns c to f of Table II ) determined by the following method:

With 720 g of catalyst (obtained according to Example 1 of German Patent 11 27 351) with a particle size of 10 to 100 μ. a mixture of 108 NL / h air, 19 g / h propylene (93%), 7.4 g / h ammonia and 7.8 g / h water is passed into a fluidized bed reactor with a diameter of 50 mm. The reaction temperature is 460 ⁰ C, the pressure in the reactor head is 0.2 to 0.3 atm. The reaction gases are passed through a cold 0.1 N HCl, the reaction products are absorbed there and analyzed by gas chromatography. The values for surface area and acrylonitrile yield of the catalyst in states c, d, e and f are shown in Table II below:

Table II

Condition of the catalyst
abcdef

Surface, m * / g 58 44 40 32 29 24 Acrylonitrile yield, 64 55 50 62 64 63

From Table II it can be seen that the temperature treatment at 55O ⁰ C (b catalyst after 18 months duration, column) a further reduction of the acrylonitrile yield of 55% is 50% (column c) result. In contrast, the catalyst to 600.650 and 700 ⁰ C (column d, e, and f) further heating reaches the original yield of acrylonitrile (column a) again, although the specific surface area according to d in the columns e and f values given in Compared to the original catalyst surface (column a) drops further.

The catalyst with the properties mentioned in column e of Table II shows with a further running time of 700 hours in the acrylonitrile synthesis no decrease in its activity.

Example 2

The catalyst described in Example 1 with a specific surface area of 58 m ² / g, which gives an acrylonitrile yield of 64% (cf. also column a in Table II), is in the fresh state, ie without it, it is already due to yield recovery and surface areas -

Subject to reduction-related running time, heated for 5 hours to 64O ° C and determined its activity as described in Example 1. While the specific surface area of the catalyst after the temperature treatment is 32 m ² / g, when the temperature-treated catalyst is used in the acrylonitrile synthesis, an acrylonitrile yield of 67% of theory is obtained.

Example 3

The catalyst with the properties shown in column a of Table II of Example 1 is, as shown in Table III below, ^{heated to 750, 800 and 850 °} C., used in the acrylonitrile synthesis and subjected to the yield determination according to Example 1:

Table III

temperature
750 ⁰ C

800 ⁰ C

850 ⁰ C

Time of treatment

30 min.

Acrylonitrile yield after 10 hours 64%
operation

Acrylonitrile yield after 100 hours 64%
operation

h 10 min.

up to 60% 62%

up to 59% 60%

30 min.

10 min.
57%

30 min. 51%

50 ° /

the active ingredient concentrations listed in Table IV

Example 4 trations produced and at 500 and 650 ⁰ C respectively

Treated for 5 hours and then, as in Example 1,

According to what is written in German patent specification 11 27 351 to determine the acrylonitrile yield Procedure, catalytic converters are tested with 30.

Table IV

Temperature treatment d e 5 hours at 650 ° C. i k 5 hours at 500 ^° C f g H ABC

Weight percent bismuth
Weight percent molybdenum
Weight percent phosphorus

Acrylonitrile yield (%)

24.5 20.0 10.0 20.0 30.0 24.5 20.0 10.0 20.0 30.0 14.0 11.5 6.0 14.0 14.0 14.0 11.5 6.0 14.0 14.0 0.3 0.3 0.2 0.3 0.3 0.3 0.3 0.2 0.3 0.3 64 58 49 60 59 66 to 65 62 to 65 65 67 63

The values shown in Table IV show that only in the case of the temperature treatment according to the invention the ratio in the active ingredient concentrations, in particular the ratio of the proportion of bismuth to molybdenum, can be varied within wide limits. The acrylonitrile yields obtained with the inventive Catalysts are obtained (columns g, h, i and k of Table IV, are only slightly reduced compared to the yield recorded in column f of Table IV, while the yields for catalysts which have not been heated by the method of the invention (acrylonitrile yields of columns b, c, d and ed: r Table IV) are in some cases considerably lower than those for the standard composition of the catalyst Acrylonitrile yield obtained in column a of Table IV. In addition, Table IV shows that a standard composition catalyst is 24.5 percent by weight bismuth, 14.0 percent by weight Molybdenum and 0.3 percent by weight of phosphorus provide higher acrylonitrile yields (column f opposite Column a of Table IV) if it is already at a temperature according to the invention during manufacture Area is heated.

Example

According to the method described in German Patent 11 27 351, Example 1, solutions of bismuth nitrate, ammonium molybdate and phosphoric acid are prepared and then applied to silica gel granules with a surface area of 160 m ² / g and a grain size of 10 to 120 μ. The catalysts are dried, every 5 hours, as described in Example 4, treated at 500 and 65O ⁰ C and, as described in Example 1, tested with regard to the acrylonitrile yield and specific surface area.

Example 6

The same catalysts as described in Example 5 are prepared, but without the addition of phosphorus. The acrylonitrile yields obtainable with these types of catalysts are those in Table V of Example 5 and have the values introduced in Table VI:

Table VI 24.5%
14.0% 10.0%
6.0% bismuth
molybdenum
₅ remainder: SiO ₂ 63.2 61 Yield (%)

Activation is achieved by heating at 650 ° C. for five hours.

Table V

Temperature treatment at 500 ⁰ C 5 hours at 650 ^° C 5 hours 10.0 24.5 10.0 % Bismuth 24.5 6.0 14.0 6.0 % Molybdenum 14.0 0.2 0.3 0.2 % Phosphorus 0.3 69 28 36 Specific surface according to temperature 55 treatment (m ² / g)

Acrylonitrile yield (%)

42

62

609 637/113

Claims (1)

The method according to the invention can be used Claim: both fresh and prepared in a known manner and unused £ ls also on used catalysts Process for increasing the effectiveness of sators whose effectiveness is due to their use in optionally phosphorus-containing bismuth 5 amoxidation processes, such as acrylonitrile synthesis, molybdate supported catalysts with a co- has already waned, composition of 10 to 30 percent by weight Wis- The active ingredient concentration on the carrier of the nrat, 6 to 18 percent by weight molybdenum, 0 to catalysts to be treated according to the invention, 1 percent by weight phosphorus and silicon dioxide can be varied within wide limits. Generally as a carrier substance, characterized in that the bismuth content is between about 10 and about, the catalysts are 0.5 to 30 percent by weight, the molybdenum content between 20 hours at temperatures between 580 and about 6 and about 18 percent by weight and the Phos-750 ⁰ C heated. phosphorus content between about 0 and 1 percent by weight. For example, method 15 of the present invention is applied to a catalyst that is 24 to 25 percent by weight Bismuth, 13.5 to 14.5 percent by weight Molybdenum and 0.2 to 0.4 weight percent phosphorus contains. For these shares are without further ado stronger fluctuations, especially with regard to the ao ratio of bismuth to molybdenum, what permissible however, this is not possible if the catalyst does not Bismuth, molybdenum and optionally phosphorus are subjected to the process according to the invention, containing supported catalysts are known. In this case, deviations from the above-mentioned in the production of.
niak and oxygen at elevated temperature and at The temperature range from 580 to 750 ⁰ C is for normal or elevated pressures in solid or flow to achieve the activation according to the invention on the bed used (see. German Patent 11 27 351). best suited; Tempe-specifically, particularly preferred is this process using temperatures from 620 to 670 ⁰ C. At temperatures above Wismutphosphormolybdat - supported catalysts 30 75O ⁰ C, z. B. at 800 ^° C., a treatment time for the industrial production of acrylonitrile (cf. activation can also be achieved; however, a very short Petroleum Refiner, No. 11, Nov. 1962, Vol. 41, p. 188 treatment time is then to be selected , so that the technical as well as Vol. 42, No. 11, Nov. 1963, p. 139; Chemical implementation is difficult. Week. ν. 28.1. 61, p. 39; Technical Week ν. 16. 8. 68, In general, the treatment time for the P. 28). 35 temperatures according to the invention 0.5 to 20 hours, In this process, the nitrile yield falls, as is often the case with catalytic production processes within the temperature range mentioned, with a lower temperature of 580 to 750 ° C. requiring a longer increasing running time due to a gradual catalyst heating time and with higher temperature exhaustion. In general, for the catalysis temperatures a shorter treatment time is required sator fatigue and the consequent off heated for 40 Preferably, the catalyst is 3 to yield decrease, the decrease of the specific upper 5 hours at 620 to 67o C. ⁰ area of the catalytic converter blamed. As a carrier for the catalysts to be treated In order to lower the acrylonitrile yield, silicon dioxide is generally used. The carrier amount avoid, it is also required, which is usually less than 85 percent by weight of the reaction of propylene, oxygen and ammonia required. Liehe reaction temperature in relatively narrow The catalyst can according to numerous known Keeping boundaries constant. It is generally the process to be produced. If it is to be used in a fixed bed -455 to 475 ° C and if possible not to overreact, then it is advisable to take steps (cf. 2. vses. Chim. O \ M. 14, [1969], the individual components 3, p. 274 to 280 \ Even a brief temperature to grind the catalyst mass and form pills or increase the temperature to, for example, 490 to 500 ⁰ C can deform balls If the catalyst is to be used in a fluidized bed or if an extremely fluidized bed is to be used for the catalyst in the fluidized bed or if an extremely fluidized bed is to be used, then the undesired process, which is achieved by spray drying in particular, is the undesirable process If a gel of the active ingredients and the carrier are advantageous, there is consequently great interest, the efficacy However, fluidized bed catalysts can also be provided by the ability, ie the activity and selectivity, of bismuth impregnation of the spheres with the active ingredient solution herphosphoromolybdate catalysts for the acrylonitrile. In all cases, the deformed synthesis should be increased or, if longer running and dried catalysts, a final time or excessive reaction temperatures already subjected to temperature treatment. A method to restore a certain catalyst fatigue with a decrease in yield after such catalysts are obtained. can, is in the German patent 11 27 351, It has now been found that the effectiveness is particularly described in Example 1,
of bismuth, molybdenum and optionally phosphorus 65 A pretreatment of the catalyst before the contained supported catalysts can increase if the process according to the invention is carried out, the catalysts are kept at temperature for 0.5 to 20 hours. If an unused catalyst is heated to temperatures between 580 and 750 ° C. subjected to the method according to the invention, so