JPS5920651B2 - Formaldehyde manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing methanol in the presence of a silver catalyst containing a component of particulate silver having a specific weight per unit cross-sectional area of the catalyst bed, a specific particle size, and a specific total surface area. This invention relates to a method for producing formaldehyde by oxidative dehydrogenation.

Ullmann's Encyclopedia der Technitzien Hemi, Volume 7, pages 659 et seq. describes various methods for the preparation of formaldehyde by oxidative dehydrogenation of methanol at elevated temperatures in the presence of a silver catalyst. has been done.

FIAT Report Haruka 999, pages 1-3, 10-15
It is described that the catalyst is arranged in a layer having a thickness of u. Particles having a size of 1.25 to 0.15 nm are used in a single layer, with larger particles lying below. The typical life of the catalyst is 6 months, but if methanol is used, which has a relatively high permanganate reactivity, the life can be reduced to 2 months or less. The methanol conversion is approximately 94%, and the formaldehyde yield is 82.5% of the theoretical value. BIOS Report ▲978, pages 2-6 describes a four-layer catalyst with the following composition, with the larger particles being at the bottom of the layers.

Particle size (1% by weight relative to total catalyst 0.158 The total layer thickness is approximately 1011, and the lifetime of the catalyst depends on the quality of methanol.

Purified methanol is used, and crude methanol is treated with permanganate and then distilled. According to the report, the catalyst typically has a lifespan of 6 months. Consistent with this, the above-mentioned FIAT report teaches that if methanol with high permanganate reactivity, i.e. crude methanol, is used, the lifetime is reduced to less than two months. In general, a yield of 82.2% of theory is obtained. German Patent No. 1,231,229 describes a catalyst arranged in two layers, the lower layer consisting of at least 50% by weight of crystals with a particle size of 1.25 to 511.

A crystal of 0.2 to 1 u is used as the upper layer. The height of the lower layer is chosen to be 15-50n. The height of the upper layer is 1 to 2u in Example 2. The life of this two-layer catalyst is described in Example 2 as 91 days, and the yield is 88.3% of the theoretical value. German Patent Application Publication No. 1
In the method described in No. 294360, at least 50% by weight of the lower layer consists of crystals with a particle size of 1 to 4 fins, and the upper layer consists of a two-layer catalyst consisting of crystals with a particle size of 0.1 to 0.911. used.

The thickness of the lower layer is 15-40" and the thickness of the upper layer is 0.75-31.
It is 1. As shown in the example, the lower layer is 1 to
94% by weight of the total catalyst with a particle size of 3TEL is used and a catalyst life of 70 days and a yield of 89% are obtained. In the production of formaldehyde, especially on an industrial scale, not only the individual operating results, e.g. the yield of the target substance, but also the best possible yield of the target substance and improved empty space when using crude methanol What is important is a process that provides high yields and a long catalyst life at the same time as the lowest possible proportions of methanol and of the acid formed by the reaction. The method has certain advantages,
For example, although the method described in German Patent Application No. 1294360 shows a high yield,
This is unsatisfactory in terms of the overall performance mentioned above. The overall performance, on the other hand, is limited in a blind manner by a number of interdependent factors, such as particle size, layer thickness, particle size distribution, pressure, temperature and catalyst loading. According to the state of the art, it is not possible to derive optimal values for the individual factors in this regard. In the method described in German Patent No. 1285995, 7/8 of the weight consists of silver crystals with a diameter of 0.75 to 3 #zl, and 1/8 consists of silver crystals with a particle size of 0.3 or less. A silver catalyst consisting of is used and the reaction gas is cooled very quickly so that the carbon monoxide content of the waste gas does not exceed 0.23% by volume.

To initiate the reaction, the silver catalyst must be heated by a heat source to at least 400-500 ml as shown in column 3, lines 40-42.
Must be preheated to 00°C. This patent teaches that particularly reducing the zone between the catalyst bed and the catalyst cooling device has good consequences for the performance of the process. This lesson is supported by examples using only catalysts according to the invention, but giving different residence times of the reaction gas in the cooling zone. According to German Patent Application No. 2,322,757, it is known that the reaction is carried out using a catalyst having a total layer thickness of 15 to 35 mm and having three or more silver crystal layers. , in which part of the layer contains 72.5-89% by weight of catalyst having particles with a particle size of 1-2.5 mm, and the other part of the layer contains particles with a particle size of 0.7 mm.
2.5-7.5% by weight of catalyst with particles of 5-1 and the remainder of the layer contains 8.5-20% by weight of catalyst with particles of particle size 0.2-0.751 Lm.

Compared to the four state-of-the-art methods mentioned at the outset, the method of the invention provides improved overall results with respect to yield, space-time yield and purity of the target product by simple and economical means, and especially Improved catalyst life is also obtained when using crude methanol. The lifetime of the catalyst is usually at least 100 days in the case of crude methanol and is longer than that of the catalyst of the process described in DE 1285995. This catalyst can be obtained by simple and economical means. Silver crystals of all particle sizes obtained during the production of granular silver by electrolysis are used. German patent number 1
Unlike the method of No. 285995, 0.3 to 0.7
It is shown that a particle size of 0.511 is used and particle sizes below 0.211 are not used. The catalyst according to the invention is described in German Patent No. 1,285,995, column 3, 40.
Judging from the description in lines ˜42, it is only necessary to preheat to 280-300'C by an external heat source to start the reaction. Control of the carbon monoxide content of the exhaust gas, which requires additional regulating and measuring equipment, is unnecessary. The inventors
have a particle size of 0.01 to 10μ, and 3 in 19
When carrying out the reaction with a catalyst containing a component of particulate silver with a total surface area of ~30 i in an amount of 1 to 20,009 g/w of catalyst bed cross section, methanol is added at elevated temperature in the presence of the silver catalyst. It has been found that formaldehyde can be advantageously obtained by oxidative dehydrogenation.

The inventors further found that the total layer thickness is 15-35 mm and has three or more layers of silver crystals, with some of the layers having grains with a grain size of 1-2.5 mm. A catalyst 72 having
．． 5 to 89% by weight, and the other part of the layer has a particle size of 0.75 to 1
2.5 to 7.5 wt.% of catalyst with particles of mm size and the rest of the layer contains 8.5 to 20 wt.% of catalyst with particles of particle size of 0.2 to 0.75 mm. It has been found that the method can be carried out particularly advantageously when a component of finely divided silver is added.

Viewed from the state of the art, the process according to the invention, in its preferred embodiment, improves the yield, space-time yield and purity of the target substance by simple and economical means compared to the four state-of-the-art processes mentioned at the beginning. It provides improved overall performance, as well as improved catalyst life especially when using crude methanol.

Also in a preferred embodiment and German Patent No. 12
In view of the process described in German Patent No. 85,995, the catalyst according to the invention has a longer life and, unexpectedly, a shorter life compared to the catalyst described in German Patent Application No. 2,322,757. do not have. In all embodiments, the process according to the invention has the advantage over all known processes that the catalyst only needs to be preheated to 180-240°C by an external heat source for the initiation of the reaction, which reduces equipment costs and energy consumption. This results in savings in costs and operating costs.

Control of the carbon monoxide content of the exhaust gas, which requires additional regulating and measuring equipment, is also unnecessary. The yield and space-time yield of this method are higher than the state of the art. All these favorable results are unexpected given the state of the art.

Because, according to the teachings of the above-mentioned German Patent Application, in connection with the first four publications mentioned, it should be expected that silver components with particularly relatively large particles would give rise to valuable catalysts. Because it was hot. In particular, according to the teachings of the above-mentioned published German patent application, contrary to the teaching of German Patent No. 1,285,995, the grain size is 0.2 m7! Components with a particle size of 0 are avoided and instead particles with a particle size of
．． 2~0.75m7! The components of L should be used. What was unexpected in this connection was that German patent no.
85995 and German Patent Application No. 2322
Lower preheat temperatures are obtained using a silver component having a significantly smaller particle size than that of the '757 patent. It was also reasonably assumed that fine particulate silver would increase the pressure drop over the catalyst and thereby reduce catalyst life. Suitable starting materials for the process are pure methanol, technical methanol, crude methanol prepared by high-pressure or low-pressure processes or preferably a mixture thereof with water, the concentration of the aqueous mixture being preferably between 50 and 95% by weight of methanol. , particularly preferably methanol 55-8
It may vary between 5% by weight.

In a preferred embodiment, German Patent Application Publication No. 1
277 834, DE 1 235 881 and DE 1 136 318, purified by separating the low-boiling fraction or by treatment with oxidizing agents and/or alkalis. Methanol is used. The crude methanol is fed to the reaction space in vapor form, preferably mixed with water vapor and optionally an inert gas.

For example, nitrogen is used as an inert gas for the method. As oxidizing agent it is possible to use pure oxygen as well as gases containing free oxygen, especially air.

Oxygen and methanol, usually in the form of air, are used in a molar ratio of preferably 0.25 to 0.6 mol of oxygen, especially 35 to 0.5 mol of O, per mole of methanol. Preferably the total amount of water vapor is less than 3.0 mol per mole of methanol, particularly preferably from 0.67 to 1.75 mol. Any silver catalyst can be used within a wide range,
Preferably all silver catalysts mentioned above for formaldehyde synthesis can be used.

The above particle diameters, particle sizes, silver amounts per layer, ratios of silver amounts in individual layers, layer thicknesses, number of layers, single layer catalysts and multilayer catalysts are preferably used. In a preferred embodiment, a multilayer catalyst is used as described in DE 23 22 757 A1. The total thickness of the catalyst is 15-35j! 11 preferably 20 to 30n.
Catalyst particles in the form of silver crystals are usually present in the catalyst of a vertically installed reactor and are arranged in the upper, middle and lower part of the entire bed, depending on the particle size. The starting mixture of methanol vapor and oxygen or air as well as optionally water vapor and an inert gas is generally introduced from the top down, so that the upper layer(s) at the same time means the part facing towards the starting mixture. do. In other designs of reactors or in other ways of introducing the starting mixture, the upper (or lower) part of the catalyst is All indications in the given text apply, e.g. in horizontally arranged reactors:
The designation upper (or lower) is used for the front (or rear) part of the catalyst. The lower part contains 72.5-89% by weight of the total catalyst particles, preferably 77.5-82.5% by weight, and the middle part contains 2.5-7.5% by weight of the total catalyst particles, preferably 4% by weight of the total catalyst particles. .5
~6.5% by weight and on top 8.5% of the total catalyst particles
~20% by weight, preferably 13-16% by weight is present. Particles in the lower layer are 1 to 2.5n1, particles in the middle layer are 0.7
5 to 1n1, and the particles in the upper layer have a particle size of 0.2 to 0.75n. Each layer section may consist of one or more layers, preferably one, two or three layers. Particularly advantageous are 4- to 7-layer catalysts, especially 4- or 5-layer catalysts.
layer catalyst. Each of these layers differs from the other layers in the grain size of the silver crystals and often also in the weight proportion of the total catalyst belonging to it. If the upper layer has two layers, the lower layer preferably contains 0.5-2% by weight
% and a particle size of 0.2 to 0.41, the upper layer thus has a proportion of 8 to 18% by weight and a particle size of 0.4 to 0.41.
75j! l! particles. If there are three layers in the upper layer, the weight percentage (particle size) in the total catalyst
Regarding lower layer 0.5-2% by weight (0.2-0.4n
), a middle layer of 5 to 10% by weight (0.4 to 0.611) and an upper layer of 3 to 8% by weight (0.6 to 0.75n) are preferred. Therefore, in the middle layer, the following relationship is preferable regarding the weight ratio (particle size). (a) In the case of two layers: 1.5-4.5% by weight (0.75-0.9%) of the upper layer and 1-3% (0.9-1%) by weight of the lower layer.

(b) In case of 3 layers: upper layer 0.5 to 1.5% by weight (0.5% to 1.5% by weight)
75-0.811), middle layer 1-3% by weight (0.8-0.
91t7! L) and lower layer 1-3% by weight (0.9-1%)
. In the lower layer, the following relationship is preferable. (c) 2
In case of layer: upper layer 7.5-22.5% by weight (1-1.75
sin) and lower layer 50-81.5% by weight (1-2.5 dew).

(d) In the case of 3 layers: upper layer 5-16.5% by weight (1-1
．． 511), middle layer 28-42% by weight (1.5-2.0 Hawk 1 and lower layer 28-42% by weight (2.0-2.5#!l)
.

The stacking of each layer is often regular, so that the thickness of the individual layers is the same over the entire cross section of the layer. The layer thickness in this case depends on the weight proportion mentioned above, based on the total catalyst, and on the size of the particles in each case. However, it is also possible to carry out an irregular stacking of all or several, preferably one, layer, for example to provide the main amount of catalyst particles in the center, on the sides or preferably on the periphery of the layer, so that the remaining layers It is also possible to distribute only a smaller remaining amount. In a preferred embodiment, several single layers or particularly preferably one
The single layer is in the form of an annular or crown-shaped layer with flat upper and lower surfaces of the layer (annular layer) only at the periphery of the catalyst zone, with an underlying regularly arranged and regular thickness. It is placed on top of a layer with The following arrangement is preferred. The upper layer (first layer) of the catalyst is surmounted by an annular layer at the periphery, preferably the diameter of the annular layer, i.e. the difference between the cross-sectional diameter of the entire catalyst and the inner diameter of the annular layer, is equal to the catalyst diameter, 1/100 of the diameter of the regular upper layer
It is 1/10. Particularly preferred is an arrangement in which an annular layer of this kind does not rest on top of the upper layer (first layer), but instead lies below it and thus on the underlying layer (second layer). The annular layer and the first layer or the annular layer, the first layer and the second layer then take the shape of a flat dish with an upwardly curved periphery. If the upper part has several layers, for example two or three layers, the annular layer can be placed below each layer of the upper part, for example under the second layer or the third layer. Since reaction tubes or tubular reaction chambers are usually used as reactors, such a periphery lies on the crown of the tube or on the inner tube wall outside the catalyst support. Particularly preferred catalysts have the following composition, the second layer being formed as an annular layer with a ring diameter corresponding to 1/60 of the catalyst diameter, and the first layer having a ring diameter corresponding to 1/60 of the catalyst diameter.
layer) and therefore above the third layer.

1st layer (top layer): 8-18% by weight of catalyst with particles with a particle size of 0.4-0.75 mm, 2nd layer: 8-18% by weight of catalyst with particles with a particle size of 0.2-0.
0.5 to 2% by weight of catalyst with particles of size 4, 3rd layer: 2.5 to 2% of catalyst with particles of particle size 0.75 to 1.0 m7n
7.5% by weight, 4th layer: 7.5-22.5% by weight of catalyst having particles with a particle size of 1.0-1.75 mm, 5th layer (bottom layer): particle size 1.0-2, Catalyst 50 with 5 mm particles
~81.5% by weight.

Preferably, the catalyst is loaded with 1 to 3, in particular 1.4 to 2.4, tons of methanol per hour of catalyst bed cross section.

For industrial implementation, catalyst bed diameters of at least 0.5 m are preferably employed, particularly preferably at least 1 to 3 m. The catalyst has a particle size of from 0.01 to 10 μ, preferably from 0.05 to 2 μ, especially from 0.1 to 1 μ, as well as from 3 to 1 g of finely divided silver.
A component of finely divided silver having a total surface area of 30 I, preferably 8 to 20 I, especially 11 to 16 I, is added in a proportion of 1 to 20,009, preferably 3 to 11,009, particulate silver per 1 I of cross section of the catalyst bed.
, especially in amounts of 250 to 10109.

This component can be mixed with the silver of the catalyst or with one, several or all catalyst layers during the production of single-layer or multi-layer catalysts. It can likewise be spread over the finished catalyst or on one, several or all catalyst layers after the catalytic silver has been introduced into the reaction chamber. The finely divided silver is therefore spatially distributed in the catalyst in the form of one or several layers.
Alternatively, it can be present in a single, few or multiple positions in the catalyst. Preferably, the particulate silver is uniformly distributed over the entire cross-section of the catalyst bed, with the silver preferably being distributed in thin stacked layers on top of a single-layer catalyst or on the top layer of a multi-layer catalyst, or in a number of multi-layer catalysts. Several layers or one layer are formed in the form of a stack on top of each other.

A preferred uniform distribution over the entire cross-section of the catalyst bed can also be achieved as follows. That is, when a component of particulate silver is well mixed with the total amount of catalyst or with one or several layers of catalyst, this component is statistically dispersed over some or all of the catalysts in the form of a large number of single particles. distribution, thus providing a homogeneous distribution of the components in the plane of the catalyst bed cross-section as well as in the direction of the reaction mixture being passed through. Finely divided silver can be produced by known methods, for example by appropriate crushing and sieving operations during silver production, or in the form of Ranni silver. The method for producing silver is described in Ullmann's Encyclopedia 1 der Technitzien Hemi, Volume 15, pp. 636-666.
Silver can also be obtained by precipitation from a suitable solution, such as a silver nitrate solution, using a precipitating agent such as hydrazine or formaldehyde, or by electrolysis. In a preferred embodiment, silver is precipitated onto a support material, such as a metal hydroxide such as aluminum hydroxide, for example by adding a reducing agent to a silver salt solution containing the support, and the support is then dissolved away.

Solvents for the supports include, for example, hydroxides, such as aqueous solutions of caustic soda or potassium hydroxide, or aqueous ammonia, and corresponding supports, for example, hydroxides of aluminum, cobalt, cadmium or nickel. Hydrazine, hydroxylamine or formaldehyde is preferably used as the reducing agent. In a particularly preferred embodiment, aluminum hydroxide is used as the finger body and the silver is precipitated onto this soil from an aqueous silver salt solution using hydrazine. 5-30% by weight silver nitrate solution, 10-50% by weight aqueous hydrazine hydrate solution and an amount of hydrazine of 0.5-1 mol per mol of silver nitrate,
and 300 to 1400% by weight silver precipitated on a support, especially an aluminum hydroxide support.

Precipitation is preferably carried out at a temperature of 15-35°C. The resulting suspension is filtered with suction, the filtrate residue is treated with the aqueous caustic solution described above and filtered with suction again. 1 to 10 equivalents of caustic solution are used.

Particularly advantageously, the caustic treatment of the milling residue is carried out several times, for example once with an aqueous solution of caustic soda or caustic potash, and then with aqueous ammonia, preferably at a temperature of 15 DEG to 35 DEG C. 1 per mole of metal hydroxide
~10 equivalents of caustic and 0.2-2 equivalents of ammonia are used. Preferably, 20 to 50% by weight of caustic soda or caustic potash aqueous solution and 2 to 10% by weight of aqueous ammonia are used. Precipitation or residual treatment is carried out under normal pressure or under pressure, continuously or discontinuously, preferably 2 to 1
It can be done in 20 minutes. Example 1(a) shows a particularly preferred embodiment of the production of finely divided silver. The oxidation is carried out by otherwise known means, for example by heating a mixture of methanol vapor and air, optionally an inert gas and preferably water vapor, in the amounts indicated, at a temperature of about 550 DEG to 800 DEG C., in particular The silver catalyst is conductive at a temperature of 650-730°C.

The method generally uses 0.5 to 2 atm, preferably 0.8 to 1 atm.
．． It is carried out continuously at a pressure of 8 atmospheres. In this case, the reaction gas leaving the catalytic zone is reduced within a short period of time, e.g.
Cooling to a temperature of 0° C. is advantageous. The cooled gas mixture is then preferably fed to an absorption column in which the formaldehyde is washed away from the gas mixture with water, preferably in countercurrent. Before the start of the reaction, the catalyst is preferably heated at 175-240°C, preferably 195-240°C, using a hot inert gas, preferably nitrogen or sooty combustion gas.
Heated to a temperature of 30°C.

The inert gas itself preferably has a temperature of 400-1300<0>C. This embodiment is advantageous over the use of indirect heating, for example electrical heating, especially when using large amounts of catalyst on an industrial scale. For example, the catalyst is heated to said low temperature using an inert gas, then the inert gas heating is stopped, and the gaseous starting mixture of methanol and steam in said amounts is heated to a temperature of 180-240'C. The prepared catalyst is preferably passed with a load of 0.04 to 1.0 tons of methanol per hour per TrI of catalyst bed cross section, then air is added to the starting mixture at said temperature and the reaction on the catalyst is started, then the catalyst is The loading of the gaseous mixture fed and the reaction temperature are increased and the reaction is finally carried out preferably at a temperature of 550 DEG to 800 DEG C. and a methanol loading of 1 to 3 tons per hour of catalyst bed cross section. The introduction of hot inert gas can also be continued during the introduction of methanol and steam, and the heating can be stopped after the introduction of air. Preferably, heating is stopped at or after the start of the reaction. After reaching a methanol load of 0.4 tons per hour per 1 TrI of catalyst bed at the latest,
Usually no more inert gas is introduced. The onset of the exothermic reaction is preferably confirmed by adding air to the starting mixture and checking the temperature change in the catalyst.

As soon as the reaction starts, a rise in temperature is observed;
If this is not the case, the temperature will be reduced by supplying cold air. The temperature is preferably measured in the catalyst by a thermocouple. Air is generally supplied from the start of the reaction by introducing it into the vaporous starting mixture and optionally into the bottoms of the evaporation column. After the start of the reaction, the temperature increases rapidly or slowly, preferably at 1
discontinuously or preferably continuously for 0 to 150 minutes,
Particularly advantageously, the temperature is increased by 1 to 30 °C per minute to 550 °C to 550 °C.
800°C, preferably 650-800°C, especially 650-800°C
It reaches 730℃.

The temperature increase can be achieved by indirect heating and/or preferably by increasing the amount of air accordingly. As well as the amount of air, the load of the total gaseous mixture is also increased. The amount of methanol vapor, water vapor and air passed is increased gradually, preferably until the final temperature is reached. However, it is also possible to carry out the feeding of the four components and thus the methanol charge in increasing quantities only after the final temperature has been reached. It is likewise possible to supply each component at different times and/or amounts. Compared to known methods, in the method of the present invention, not only is the temperature up to the start of the reaction lower, but the reaction once started can be maintained, and the reaction rate can be increased. Also, the heating time is short. silver 2001
Formaldehyde production plants with a catalyst amount of <g or more can also be heated to the above-mentioned temperatures without requiring the construction of larger heating equipment compared to known methods. The formaldehyde produced by the process of the invention is a disinfectant, tanning agent and reducing agent, and is also a valuable starting material for the production of synthetic resins, adhesives and plastics.

Applications are described in detail in the aforementioned volume of Ullmann's book, page 670. Parts in the following examples mean parts by weight.

Example 1 (a) Preparation of finely divided silver: 207.5 parts of Al(NO3)3.9H are dissolved in 200 parts by volume of water, and 25 parts by volume of concentrated aqueous ammonia (25% by weight) are added to form aluminum hydroxide. precipitates.

13 parts by volume of a 24% by weight hydrazine hydrate solution are added to this suspension. To a solution of 7 parts by volume of AgNO3 in 100 parts by volume of water, concentrated aqueous ammonia (25% by weight) is added (30 parts by volume) until the precipitate formed is dissolved again. This solution is gradually mixed into the suspension while stirring. The suspension is filtered by suction, suspended in 9 parts of 6N aqueous potassium hydroxide, and filtered again by suction. The P residue was washed with water, suspended in 9 parts of 5% by weight ammonia aqueous solution, filtered with suction, and diluted with methanol 2
Suspend in 7 parts, filter with suction and dry. (b)
Reaction: ″Using an apparatus with a methanol evaporator and an upright tubular reactor.

The reactor has at its top a feed inlet for the vaporous starting mixture and a reactor vault. The catalyst layer is below the top of the reactor, followed by a cooling zone below. This reactor is connected to an absorption column. The reactor is charged with a catalyst (0.187 parts) made from silver crystals having the following composition:

The second layer is spread over the third layer as an annular layer in the peripheral zone of the catalyst.

The diameter of the catalyst is 170CfL1 The inner diameter of the annular layer is 167 (7
It is L. In the center of the top layer there is a diameter of 34? of finely divided silver with a grain size of 0.1-1μ and a total surface area of 13,9 TI per finely divided silver 19? A circular layer of 4 g per meter of catalyst bed cross section is applied. The catalyst is heated to a temperature of 18'C for 177 minutes by passing hot nitrogen gas through it.

A mixture of 0.06 parts of methanol and 2 parts of water is heated to 95°C in an evaporator.

Steam exiting the evaporator at a temperature of 74°C enters the reactor cannula and flows through the catalyst. 0.6 parts of air per hour are then introduced into the liquid in the evaporator. The reaction is initiated when a mixture of air, steam and methanol is directed over the catalyst heated to 180°C. The temperature of the catalyst begins to rise. The air rate is 0.0% per hour at a catalyst temperature of 24°C.
Reduced to 336 copies. After 2 minutes, the catalyst temperature reaches 440°C.

Subsequently, over a period of 72 hours, the catalyst load was increased to 2.27 tons per hour of methanol, 9.3 tons per hour of air, and 3.43 tons per hour of steam per meter of catalyst bed cross section at a pressure of 1.4 atm before the catalyst. 'Produces a catalyst temperature of C.

The introduction of nitrogen is stopped at a methanol load of 0.3 tons per hour of catalyst bed cross section 1w1. The evaporator is fed and evaporated every hour with a mixture of 5.15 parts of methanol in the form of crude methanol containing 1.5% by weight of impurities, 3.43 parts of water and 9.3 parts of air.

The reaction is then carried out at 700° C. and 1.4 atm. The reaction mixture is then cooled to 150°C and dissolved in water. The waste gas contains 0.05% by weight of formaldehyde, 6.3% by weight of water vapor, 1.2% by weight of hydrogen, and 0.0% by weight of carbon monoxide.
3% by weight, 7.2% by weight of carbon dioxide and 84.9% by weight of nitrogen. 4.27 parts of formaldehyde (10
0%) was obtained, which is 88.0% compared to the theoretical value.
This corresponds to a yield of 4%.

The catalyst life is 110 days. The formaldehyde solution has a content of 3% by weight of methanol and 0.015% by weight of formaldehyde (calculated as 100%). Example 2 Using the same equipment as in Example 1, a catalyst from silver crystals (0.187 parts) having the following composition was added to the reactor:
Put in.

51 卜Jν′ [MiVv Symphony] The reaction is carried out in the same manner as in Example 1.

0 uniformly over the entire cross section of the catalyst in the top first layer.
Finely divided silver having a particle size of 1 to 1 .mu. and a total surface area of 11.1 mm per finely divided silver 19 is deposited in a uniform layer in an amount of 1000 g per m" of catalyst bed cross section.

The composition of the waste gas is the same as in Example 1. 40.8% by weight
4.26 parts of formaldehyde per hour (calculated as 100%) are obtained in the form of a formaldehyde solution of 4.26 parts per hour, corresponding to a yield of 88.2% of theory.

The catalyst life is 113 days. This formaldehyde solution has a content of 2.7% by weight of methanol and 0.016% by weight of formaldehyde (calculated as 100%). Example 3 The reaction is carried out analogously to Example 1 with the same amount of active silver distributed homogeneously over the entire catalyst by mixing.

Similar results to Example 1 are obtained. Comparative Example The reaction is carried out analogously to Example 2, but without the addition of finely divided silver.

Since no reaction occurs even with the addition of 0.6 parts of air at 180 DEG C., the air supply must be cut off and the catalyst must be heated to a further 10 DEG C. by supplying hot nitrogen gas. When the catalyst temperature is increased stepwise by 10°C until the reaction starts when air is added, a total heating time of 97 minutes and a heating temperature of 350°C is achieved before the reaction finally starts. I need. 4.24 parts of formaldehyde per hour (calculated as 100%) are obtained in the form of a 40.2% strength by weight formaldehyde solution, which corresponds to a yield of 87.8% of theory.

Claims (1)

[Claims] 1. A component of finely divided silver having a particle size of 0.01 to 10 μ and a total surface area of 3 to 30 m^2 per 1 g of 1 to 2000 g per 1 m^2 of the catalyst bed cross section. A process for the preparation of formaldehyde by oxidative dehydrogenation of methanol at elevated temperatures in the presence of a silver catalyst, characterized in that the reaction is carried out using a catalyst containing an amount of . 2 The total layer thickness is 15 to 35 mm, and has three or more layers of silver crystals, in which part of the layers has a grain size of 1
72.5-89% by weight catalyst with ~2.5 mm particles
, the other part of the layer contains 2.5-7.5% by weight of catalyst with particles with a particle size of 0.75-1 mm, and the rest of the layer contains particles with a particle size of 0.2-0.75 mm. Catalyst with 8.5
2. Process according to claim 1, characterized in that a component of particulate silver is added to the catalyst containing ~20% by weight.