DE2007795B2 - PROCESS FOR INCREASING THE EFFECTIVENESS OF ANISMUTOMOLYBDATE-CARRYING CATALYSTS, WHICH MAY CONTAIN PHOSPHORUS - Google Patents

Description

it can be subjected to the activating heating or directly without prior Cakinierung be treated hei 580 to 75O ⁰ C in connection with the required in a known manner for the production 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 the German Patent 11 27 351 is available, is used in this process for a long time, so takes place with the for gradual decrease in yield leading to decrease in catalytic activity with increasing Running time at the same time a decrease in the specific surface area of the catalyst stall. In the following Table I illustrates this process: a decrease in the acrylonitrile yield after 6 and 12 months, respectively Running time is accompanied by a decrease in the specific surface area of the catalytic converter.

Table 1

Catalyst Fresh 6 months 12 months, ₀

Lauizcit term

Specific 58 to 64 52 to 53 46 to 47 surface

(m ² / 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 (%)

40

The inventive treatment of the catalyst at temperatures between 580 and 750 ^° C. also leads to a decrease in the specific catalyst surface area, so that damage to the catalyst activity and a decrease in the acrylonitrile yield were to be expected. However, it was by no means foreseeable that the temperature treatment according to the invention would lead to an increase or restoration of the effectiveness of bismuth phosphorus molybdate catalysts. This result was also not to be expected since it has been found that the activity of the bismuth phosphorus molybdate catalyst is severely damaged at reaction temperatures above the temperature required for the acrylonitrile synthesis and below the lower limit of the temperature range according to the invention.

It must be accordingly expected that heating at temperatures above 5S0 would further reduce the Wirksanikcil of the catalyst to about 75O ⁰ C, the hai a further decrease in specific catalyst surface result. The result achieved on the basis of the measure according to the invention is therefore 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 ^s / 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). The catalyst was heated under this term of 18 months, respectively for 5 hours in the presence of air at 550, 600, 650 and 700 ⁼ C "and the 7UR assess its activity Wen required. For the specific surface area and the acrylonitrile yield (column C through 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 grain size from 10 to 100 μ is a mixture of 108 NL / h in a fluidized bed reactor with a diameter of 50 mm Air, 19 g / h propylene (93%), 7.4 g / h ammonia and 7.8 g / h water. The reaction temperature is 460 ° C, the pressure in the reactor head is 0.2 to 0.3 aiii. The reaction gases are passed through a cold 0, In-HCl passed, the reaction products are there absorbed 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 the following tables:

Table II

Condition of the catalyst

a b c d e f

Surface, m ² / 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 550 "C resulted in a further reduction in the acrylonitrile yield from 55" (catalyst after 18 months running time, column b) to 50 "" (column c). On the other hand, by further heating the catalyst to 600, 650 and 700 ^° C. (column d. E and f), the original yield of acrylonitrile (column a) is achieved again, although the specific surface area is as indicated in columns d, e and f Values in comparison to the original Kalalysatoroberfi surface (column a) decreases further.

The catalyst with the in column e of Table II does not show any properties mentioned in the acrylonitrile synthesis with a further running time of 700 hours Decline in its activity.

H e i s ρ i e 1 2

The catalyst described in Example 1 with the specific surface area 58 111 µg, which _{gives an acrylonitrile yield of 64 "u} (cf. also column a of Table 11), is used in the fresh state, ie without it, it is already

Subject to reduction-related running time, ^{heated to 640 0} C for 5 hours 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 in column a of table Ii of the example 1 presented properties is how

. . . '. i-_ τ., ΚοΙΙ, »TII nnfpfveiet. on 7SO RfW)

in the loigcnucn ι «^ -« - · - - <= - ^ > - · > -

and heated to 85O ° C, used in the acrylonite synthesis and according to Example 1 subjected to the design specification:

Table III

temperature
750 ° C

800 ⁰ C

Time of treatment

30 min.

Acrylonitrile yield after 10 hours 64%
operation

Acrylonitrile yield after 100 hours 64%
operation

_h 10 min. 30 min.

up to 60% 62% 58%

up to 59% 60% 56%

850 ° C

54 '

10 min. 30 min. 57% 51-

50 '·;

the active ingredient concentrations listed in Table IV made and at 500 and 650; C each

^{B p} 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 Catalysts are tested at 3 °.

Table IV

Temperature treatment b C. d e 5 hours at 650 ° C. i k 5 hours at 500 "C 20.0 10.0 20.0 30.0 f e H 20.0 30.0 a 11.5 6.0 14.0 14.0 24.5 20.0 10.0 14.0 14.0 Weight percent bismuth 24.5 0.3 0.2 0.3 0.3 14.0 11.5 6.0 0.3 0.3 Weight percent molybdenum 14.0 58 49 60 59 0.3 0.3 0.2 65 65 Weight percent phosphorus 0.3 66 to
67 65 62 to
63 Acrylonitrile yield (%) 64

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 that recorded in column f of Table IV Yield, while the yields for catalysts not heated according to the practice of the invention (acrylonitrile yields in columns h, c, d and c d: r Table IV) are sometimes considerably lower than that at Sianclard / usanimcnset / ung the catalyst preserved acrslniirilausbcuic of the column a dei Table IV. In addition, see Table IV / u, that a kalal \ s; ilor the standard / usanunenset / uiiL ' 24.5 weight pro / enl bismuth. I-1.0 (ieuiclits-

percent molybdenum and 0.3 percent by weight phosphorus provide higher acrylonitrile yields (column f opposite Column a of Table IV) if it has already been brought to a temperature according to the invention during manufacture Area heated wildly.

Example 5

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 Kicseigel granules with a surface area of 160 m ^a / g and a grain size of 10 to 120 μ. The catalysts wcrilen dried, every 5 hours, as described in Example 4, at 500 and 650 C and treated. as described in Hcispicll, ^{checked with regard to the Acrylniirilausbniu 1} and the specific surface.

Example 6

The same catalysts are prepared as described in Example 5, but without the addition of phosphorus, the _{remainder: SiO 2.} The acrylonitrile yields obtainable with these types of catalyst (%) are comparable to those shown in Table V of Example 5 and have the values introduced in Table VI:

Table VI 24.5% 10.0% bismuth 14.0% 6.0% molybdenum

63.2

61

Activation is achieved by heating to 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 (%)

47

62

Claims (1)

The method according to the invention can be used Claim: both fresh and prepared in a known manner and unused as well as used catalytic converters 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, Supported molybdate catalysts with a joint has already waned. composition of 10 to 30 percent by weight Wis- The active ingredient concentration on the carrier of the mut, 6 to 18 percent by weight molybdenum, 0 to catalysts to be treated according to the invention can 1 percent by weight phosphorus and silicon dioxide can be varied within wide limits. In general as a carrier substance, characterized by this, the bismuth content is between about 10 and about draws that the catalysts are 0.5 to 30 percent by weight, the molybdenum content between 20 hours to temperatures between 580 and about 6 and about 18 percent by weight and the phosphor 750 ° 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 ίο ratio of bismuth to molybdenum, what permissible however, this is not possible if the catalyst does not Bismuth, molybdenum and optionally phosphorus is subjected to the process according to the invention, Containing supported catalysts are known to In this case, deviations from the above lead in the production of α, / 3-unsaturated aliphatic catalyst composition to activity reductions Nitriles by reaction of olefins with ammonia and thus to reduced yields, niac and oxygen at elevated temperature and at The temperature range of 580 to 750 ° C is for normal or elevated pressures in the solid or flow, achieving the activation according to the invention on bed used (see German patent specification 11 27 351). best suited; Tempe - In particular, this method is used using temperatures from 620 to 670 ° C. At temperatures above of bismuth phosphorus molybdate - supported catalysts 30 750 ^c C, z. B. at 8GO ⁰ C, can also be another For the large-scale production of acrylonitrile (see. Achieve activation; however, then a very short one Petroleum Refiner, No. 11, Nov. 1962, Vol. 41, p. 188 treatment time to choose 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 drops, as is within the stated temperature range often in catalytic manufacturing processes, with a lower temperature of 580 to 750 ° C a longer one increasing running time due to gradual catalyst heating time and with higher tenipe exhaustion. In general, a shorter treatment time is required for the catalysts, Sator exhaustion and the resulting exhaustion. Preferably, the catalyst 3 to is heated decrease in prey the decrease in the specific upper 5 hours at 620 to 670 ⁰ C. area of the catalytic converter. As a support 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. The reaction temperature is relatively narrow. The catalyst can be kept constant according to numerous known limits. 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. Otsc. 14, [1969]) to precipitate the individual components together , No. 3, pp. 274 to 280). Even a short-term temperature to grind 50 catalyst mass and pills or increase the temperature to, for example, 490 to 500 ⁰ C can deform pebbles. You can also cause the previously significant and irreversible decrease in the formed carrier with the aqueous solution of the active acrylonitrile yield. Soaking substances is of course a matter of course. If the catalyst is to be used in fluidized bed or any decrease in catalyst efficiency is to be used in an extremely fluidized bed, then this is the undesirable process which, in particular, adversely affects the economic position by spray drying a solution or the economic viability of the process. If a gel of the active ingredients and the carrier is advantageous, there is consequently a great deal of interest, but also fluidized bed catalysts can by speed, ie the activity and selectivity, of bismuth impregnation of the spheres with the active solution herphosphoromolybdate catalysts for the acrylonitrile be asked. In all cases, the deformed synthesis should be increased or, if longer running and dried catalysts of a final time or excessive reaction temperatures, temperature treatment should already be reeducated. Towards a method to restore a certain catalyst fatigue with a decrease in the yield after such catalysts have occurred. 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 possibly phosphorus 65 A pretreatment of the catalyst before Containing supported catalysts can increase when carrying out the process according to the invention the catalysts for 0.5 to 20 hours on tempe- not necessary. Becomes an unused catalyst iaturen between 580 and 75O ^C C heated. subjected to the method according to the invention, so