DE1946225B2 - PROCESS FOR THE MANUFACTURING OF CATALYTICALLY EFFECTIVE MATERIAL - Google Patents

Description

The main patent 17 67 202 relates to a process for the production of a catalyst in which the catalytically active substance is applied in a finely divided state to a support by precipitating the catalytically active substance by means of hydroxyl ions in the presence of the support, drying the loaded support, optionally annealing and / or reduced by suspending the carrier in finely divided form in a dilute solution containing the metal ions of the catalytically active substance and, with heating and prolonged vigorous stirring, the catalytically active substance is precipitated by a chemical reaction known per se of Compounds also present in the solution homogeneously do not form hydroxyl ions faster than this by hydrolysis of an aqueous solution from 1 to 10 times the theory of the metal-related theory of the metal the case i:> i. iiiid ilen loaded "irai-raus the solution separated.

It is well known that in general it is catalytic! Activity of a catalyst of the size of the specific! Surface of the catalytically active material per portional. The size of the surface area per unit volume of catalyst has a direct influence on, among other things. cii: Size of the reactor in which the catalyst is used

ίο will. Because large reactors are generally difficult are to be operated, efforts are made to produce catalysts with a large specific active Surface. For this, however, the following is necessary:

! The catalytically active material must be in For π of fine particles are distributed on a carrier material. For technically well usable « For catalysts, a diameter of the catalytically active particles of 50 Å or less is recommended.

2. The active particles must be separated from one another and distributed homogeneously over the support surface. In this context , homogeneous distribution means that the density of the catalyst particles on the support surface is the same everywhere. The: is of great importance because in the case of a locally strong concentration of catalyst particles, these sinter together when heated, whereby the specific effective surface is considerably reduced.

3. The active particles must be for reaction participants be accessible and may e.g. B. from the during de:

During the manufacturing process, temporarily dissolved and subsequently reprecipitated carrier material cannot be included.

4. The carrier material must be loaded to a high degree with catalytically active material, e.g. B. ir a weight ratio of catalytically active: material to carrier of 1: 1 or higher.

5. The loaded carrier material must be easy to wear out solid bodies of uniform shape and dimensions can be deformed.

In addition, it should be possible to aul the catalyst easy to regenerate without sintering of the material.

Heat-resistant materials such as silicon dioxide are usually used as carriers for the catalytic particles

Aluminum oxide, titanium oxide and the like.

The method according to the parent application allows the production of catalytically active material, which the mentioned conditions is sufficient and with the simple metal salt solutions, such as sulfate, nitrate or chloride solution solutions are usable. The procedure is based on the Principle that when hydroxyl ions become homogeneous and gradually in the solution of the catalytically active Form material, any precipitation nuclei exclusively on the surface of a foreign substance

SS arise (in the present case on the one in the solution suspended carrier), and that the precipitate is bound to the carrier with a noticeable energy A prerequisite for this is that a homogeneous and gradual formation of hydroxyl ions takes place Homogeneous is understood to mean that the hydroxyl ion concentration is exactly the same in the entire solution even if arbitrarily small volume units are considered; gradual formation of hydroxyl ions means that the increase in concentration ever Unit of time is lower than the extent to which the to precipitating substance migrated from the solution to the surface of the carrier material. Any formation of nuclei in the solution outside the surface of the carrier

ί 9

Is thereby avoided.

Since the free energy and consequently.! As LosiichL · ::!. product of precipitation kenieii significantly higher in gis that of the filled particles, custom! um krin.sd.i., ·· V / eri of the hydroxyl ion con / .eniraiion, at which es /.;. formation of Präzipitationskeriien outside ck ■ <: surface of the support material is not to be th überschru if only the formation of Hydroxyüon ;;: takes place homogeneously and gradually in the solution and under unic monitorable conditions. For this homogeneous and gradual formation of hydroxyl ions , some methods are given in the Ha'ipt division, according to which the hydroxyl ions are introduced into the solution by chemical reactions.

The homogeneous and gradual increase in the hydroxyl ion concentration in the solution by adding an alkaline solution, which is necessary for carrying out the process, cannot, however, be easily achieved. The object of the invention is therefore, in a further development of the method according to your main patent, to show a possibility of working with the addition of an alkaline solution. The invention consists in that the slow and homogeneous increase of hydroxyl ions is generated by that one injects, with vigorous stirring, an alkaline solution gradually to the suspension of the support substance in the solution of the catalytically active substance. The alkaline solution is brought into contact with the suspension without another phase being in the immediate vicinity. In this way, an extraordinarily rapid distribution of the alkaline solution in the suspension is achieved in a surprisingly simple manner, without surface tension making the distribution more difficult, so that the hydroxyl ion concentration remains homogeneous, even with a gradual increase

The stirring intensity as well as the injection speed must exactly match that for the end result required total amount of alkaline solution to be reconciled. So it is desirable that the mean pH of the suspension does not rise more than 0.1 unit per minute during the precipitation and the deviation from the mean curve is no more than 0.05 pH unit.

An advantage of the present method over the method according to the main application, in which Urea or nitrite is used because the pH can be better monitored. if If necessary, the injection of alkaline solution can be stopped when the pH value is a certain one Size reached. The invention is particularly suitable for the large-scale application of the Procedure according to the main application. The gradient of the increase in hydroxyl ion concentration with the Time, as well as the relevant absolute values, can be programmed by comparing the observed pH values of the suspension with the amounts of alkaline solution to be injected in a simple manner monitor effectively. In addition, the formation of - in an absolute sense - large amounts of Hydroxyl ions can be avoided by slow chemical reactions at increased temperature. The present process can optionally be carried out at lower temperatures, wherein the duration of the precipitation process and the gradient of the pH value can be optimally adjusted.

The possibility of the exact setting of the DH value is important for the precipitation ;;; ii!>H;.i;:i'Lr !! ydroxyde, which are only insoluble in a limited range of the pl! Values. The .-; i! I. ' Ii. With aluminum and zinc hydroxide. which at - • i. hoii '.- iii Application of the pH value in the form of alumina! ι.'der /.inkat loose. In the method according to the Haupiar ^first message is the üildungsgeschwindigkeit hydro- -. \ Lion.-n controlled by the temperature da3 de · suspension of the support substance in the solution of the catalytically active component on a besiirnm- ·. set value. A sudden quenching of this suspension can only be achieved with great difficulty, so after reaching a certain pli-value the reaction still takes some time, as a result of which the pH-value continues to rise, which afterwards ¹ . - be; -;>: ίπ.

\) ü '. The present procedure is then used with advantage. when nitrite ion or ammonia together men rri'i the elements to be precipitated complexes · form when using urea and Natriumm y, tra difficulties arise. A solution of soda or sodium hydroxide may then be injected with advantage. Excellent results are also obtained for several elements with ammonia and ammonia carbonate. In some cases >% must be used to avoid insoluble ammonia compounds at an elevated temperature of e.g. B. 80 ⁰ C worked v / earth.

The alkaline solution is preferably injected in a known manner so that the solution is introduced through a thin line under the suspension level. To ensure that the alkaline solution is supplied with the desired uniformity, a gas-filled buffer vessel is installed in the feed line in front of the spray tube. The conditions under which some catalysts were prepared according to the present process are explained in more detail by means of examples.

In Figures 1 to 4 the precipitation process is ;;. illustrates, with the pH course during dei Addition of the precipitant is shown. The increase in pH, in some cases after being exceeded ten of the equivalence point occurred is indicated by dashed lines. For this purpose, the relevant ones are complete reproducible curves have been determined in separate experiments.

Example I Preparation of Nickel Catalysts

In the case of a low level of load on the carrier substance can: ·. the precipitation with ammonia at room temperature: ^ - take place; a high degree of loading is required. . * o the precipitation must stop at a higher temperature.

a) Bringing together H. "£

Ni (NO ₃ ) 2 · 6H ₂ O; 10 g of fumed silica _ ~ .c 600 cm ^{3 of} distilled water. The ratio of frilled Ni and S1O2 was 1: 3.4. With constant vigorous stirring, the mixture was then injected into the mixture at room temperature below the liquid level e:; ne 1 η ammonia solution in an amount of 6 irr; · 1 ~ per hour. E> s process was started when a pH value of -o? 8.9 canceled. The so loaded carrier -. :: »" was, after he had settled down, via sn

normal filter paper, with 1 liter of-di'iis · - tem water washed out and 20 Siurrden 'ier-.g rc: 12O ⁰ C dried the filtrate was clear and (ir ":".

The analysis showed the following composition of the material: Ni 18.1% by weight; SiO ₂ 61.7 wt%; NH ₃ 0.2 wt%; NO ₃ 2.9 wt%.

The course of the pH of the suspension as a function of time is shown in FIG. 1 shown. The ordinate is the pH value and the abscissa is the time in minutes. At the same time, the molar ratio between NH _{3 added} and Ni ⁺ + present is indicated on the abscissa. The addition of the ammonia solution begins at point A, the precipitation begins at point and is ended at point C. The mean increase in pH during precipitation was 0.008 units per minute with a maximum of 0.013 units per minute.

The X-ray diffraction test revealed two unidentifiable bands. The broadening of the X-ray reflections resulted in an average particle size of 44 A. After reducing the material in hydrogen for 72 hours at a temperature of 390 ° C., the preparation showed the X-ray diffraction diagram of nickel with broadened reflections. This broadened reflection resulted in an average particle size of 18 to 19 Å. Combined were 492.8 g Ni (NO _{1 I 2} · 6 H ₂ ; 80.3 g fumed silica and 4 liters of distilled water. The ratio Ni to SiO ₂ was 1.5: 1. With continued vigorous stirring, a 10 N ammonia solution was passed in at room temperature at an amount of 276 cm ³ per hour, the pH rising to 7.5 without that a Ni compound precipitated. The temperature was then increased to 100 ° C. During the preheating, the pH fell to 4.7.
The introduction of the 10 N ammonia solution was continued at the temperature of 100 ° C. until a pH value of 6.8 was reached and the liquid turned light blue because a nickel ammonium complex had formed. The experiment was stopped at this pH value. The carrier material loaded in this way, after it had settled, was filtered through normal filter paper, washed with 2 liters of distilled water and ^{dried at 100 °} C. for 20 hours.

The analysis showed the following composition of the material:

Ni 37.4 wt%; Sio ₂ 23.7% by weight, NH ₃ 0.3% by weight, NOi 9.1% by weight.

An x-ray diffraction test showed no identifiable pattern. An average particle size of 50-55 Å could be determined from the broadening of the X-ray reflections. After reducing the material in hydrogen for 72 hours at a temperature of 350 ° C., the specific nickel surface area was 63 m ² per g of nickel. After reduction at a temperature of 500 "C., this surface increased by up to 114 m ² per g of nickel. <*>

Example 11

Manufacture of iron catalysts

As can be seen from Examples Ua and b, at a high treatment temperature the dimensions of the precipitated iron oxide particles are smaller than at room temperature,
ii'i In 3 liters of distilled water \ g of fumed silica was suspended; the suspension was then boiled to remove undissolved oxygen. At a temperature of 85 ° C., 42 cm ^{3 of} a ferrochloride solution containing 2 g of iron were then added. With continued vigorous stirring, an oxygen-free ammonium carbonate solution containing 26 g of ammonium carbonate per liter was injected at the stated temperature below the liquid level at an amount of 500 cm ^{3 per hour.} This reagent was added over 17 minutes until the pH was 8.5. The carrier material loaded in this way, after it had settled, was passed through a normal paper filter for filtration, washed out with 1 liter of distilled water and dried at 100 ° C. for 24 hours *. The Filtrai was clear and colorless. The analysis showed the following composition: Fe 41.5% by weight; SiO ₂ 25.5 wt%; NH ₃ <0.1% by weight; CO ₂ 0.6 wt%; 6 Cl- <0.1 wt%.
An X-ray diffraction test showed that the presence of δ-FeOOH was by no means excluded. On the basis of the broadening of the X-ray reflections, an average particle size of 25 A could be determined,
b) 1 g of pyrogenic silica was suspended in 2 l of distilled water; then the suspension was boiled to remove undissolved oxygen. After cooling to room temperature, 42 cm ^{3 of} a ferrochloride solution containing 2 g of iron were added. An oxygen-free 0.25N sodium carbonate solution was injected under the surface of the liquid at room temperature with an amount of 500 cm ^{3 per hour with continuous vigorous stirring.} This reagent was added over 17 minutes until the pH was 9.2. After it had settled, the loaded carrier material was passed through normal filter paper for filtration, washed out with 1 liter of distilled water and dried for 72 hours at 100 ° C. The filtrate was clear and colorless even after 72 hours of exposure to air indicates the presence of unprecipitated ferrous chloride. The material had the following composition:
Fe 46.2 wt%; SiO ₂ 20.9 wt%; CO ₂ 2.6% by weight; CI- <0.1% by weight; NaO, 6% by weight.
FIG. 2 shows, in a manner similar to FIG. 1, the course of the pH value during the precipitation process. In this diagram, the pH value is plotted as the ordinate and the treatment time in minutes and the molar ratio between added Na ₂ COj and the presence of Fe ++ as the abscissa. The addition of the sodium carbonate solution begins at point A, the precipitation begins at point B and ends at point C. The mean increase in the pH value during the precipitation process was 0.08 units per minute with a maximum value of 0, 37 units per minute. The X-ray diffraction test did not produce an identifiable diagram. The broadening of the X-ray reflections indicated a mean particle size of 50 Λ.

Example III

1 production of zinc catalysts

31.6 g of ZnCl ₂ , 0.8 cn of concentrated HCl, 20 g of pyrogenic silica were brought together

Manufacture of tin catalysts

a) It was brought together
SnCU · 5H ₂ O; 75 g fumed silica
Liters of distilled water.

800 cm ^{3 of} distilled water. With constant vigorous stirring, a 1 η ammonia solution was ^{injected in an amount of 218 cm 3} per hour at room temperature below the liquid level. The solution was injected for 2 hours and 10 minutes until the suspension had a pH of 7.8. The experiment was discontinued at this value. The now loaded carrier material, after it had settled, was filtered through normal filter paper, ^{washed with 800 cm 3 of} distilled water and dried at 120 ° C. for 19 hours.

Analysis of the material obtained in this way showed a ratio of Zn to SiO ₂ of 1: 1. The course of the pH of the suspension over time is shown in FIG.

The pH value is plotted on the ordinate axis and the treatment time in minutes and the molar ratio between added NH ₃ and Zn ⁺ + present on the abscissa axis. The addition of the ammonia solution, as well as the precipitation, begins at point A. The precipitation ends at point B. The mean rise in pH was 0.03 units per minute during the precipitation. The precipitation is only complete in a pH range below 8. The method according to the invention followed here is particularly suitable for suddenly stopping the increase in the pH value after a value of 8 has been reached.

An X-ray diffraction test showed the presence of Zn ₅ (OH) ₈ Cl ₂ . An average particle size of 450 Å could be determined from the broadening of the X-ray reflections. Electron micrographs showed, however, that only a few large zinc-containing crystallites were present, while the vast majority of the zinc oxide was distributed in finely dispersed form over the carrier. These tiny zinc oxide particles were about 30 amps in size.

Example IV

15.0 g and 2 With constant vigorous stirring, a 1 η ammonia solution was injected at room temperature below the liquid level with a throughput of 500 cm ^{3 per hour.} After the pH had reached 3.1, the experiment was discontinued. The carrier material so loaded and sunk to the bottom was passed through a normal filter paper for filtration, washed out with 1 liter of water and dried at 120 ° C. for 20 hours. After annealing at a temperature of 45O ⁰ C following composition of the material could be detected with reference to an analysis of:
SnO ₂ 8.4 wt%; SiO ₂ 91.5 wt%.
An X-ray diffraction test showed no identifiable chart. As an electron microscopic examination showed, the particle size was 40 to 50 A. The course of the pH of the suspension as a function of time is shown in FIG. The pH value is plotted on the vertical axis and the treatment time and the molar ratio between added NH ₃ and Sn ^{4+ present on the horizontal axis.} The addition of the ammonia solution and the precipitation begin at point A; the precipitation process is ended at point B. The mean increase in pH was 0.03 units per minute with a maximum of 0.15 units per minute. In a separate experiment (dashed line in FIG. 4) the pH was increased further while the ammonia solution was continued to be injected. At a value of 7, all of the tin had dissolved again in the form of stannate. Here, too, the method according to the invention is particularly suitable for suddenly ending an increase in the pH value when a certain value is reached,
b) If the process for the production of tin catalysts is carried out at a temperature of 100 ° C., tin oxide particles with a particle size of only 10 Å are deposited on the carrier surface. The effect of the increase in temperature corresponds to that which is found in the precipitation before ferrohydroxide.

2 sheets of drawings Ϋ09 h33 /

Claims (4)

Claims-I. Method of making a l <ati ;! _; .-ütors, with which one “'Irksaine substance in A finely detailed state is applied to a '!' rager by precipitating the catalytically active substance by means of hydroxyl ions in the presence of the carrier, drying the loaded carrier, optionally glowing and / or reducing, in a dilute solution which contains the ivleiallionen of the catalytically active substance, suspended the carrier in finely divided form and with heating and prolonged vigorous stirring, the catalytically active substance is precipitated by the fact that by a known chemical reaction of compounds also present in the solution homogeneous hydroxyl ions are not formed faster than by hydrolysis of an aqueous solution of 1 to 10 times the theoretical amount of urea based on the catalytically active metal present in the solution is the case, and separates the loaded carrier from the solution, according to Patent P 17 67 202, characterized in that the slow and homogeneous increase in the hydroxyl ions is generated in that one below r vigorous stirring, an alkaline solution is gradually injected into the suspension of the carrier in the solution of the catalytically active substance. 2. The method according to claim 1, characterized in that the addition of the alkaline solution so is measured that the mean pH of the suspension during the formation of precipitation nuclei by a maximum of 0.1 units per minute increases and the deviations from the mean course are not more than 0.05 pH unit. 3. The method-according to claim: or 2, characterized characterized in that the measurement of the pH of the suspension and the injection of the alkaline Solution can be linked to one another by means of programming. 4. The method according to claim 1, 2 or 3, characterized in that the alkaline solution by a capillary ending below the liquid level of the suspension is injected.