DE10039753A1 - Production of ammonia for use in e.g. synthetic fertilizers, comprises forming silicon nitride from silicon (compound) and nitrogen, in the presence of a transition metal (oxide) catalyst, and reacting it with a strong base - Google Patents

Abstract

Production of ammonia (I) involves: (a) reacting silicon and/or its compounds (especially silicon-hydrogen compounds) with nitrogen in the presence of a transition metal element (or oxide) catalyst, at moderate temperature; and (b) reacting the obtained silicon nitride (Si3N4) with a strong base or its aqueous solution. Independent claims are included for two variations to the process, involving: (i) step (a) as above, followed by (b) reaction of the silicon nitride with carbon dioxide and water to give ammonium carbonate and silicon dioxide and (c) subjecting the ammonium carbonate to thermal decomposition or acid treatment to give (I); or (ii) step (a) as above, followed by (b) reaction of the silicon nitride with hydrofluoric acid to give (I).

Description

The present invention relates to a method for winning ammonia.

It is known to produce ammonia (NH ₃ ) in the Haber-Bosch process by reaction of nitrogen and hydrogen at high pressures, elevated temperature and using catalysts. This method has so far been the only way to get to relatively important nitrogen compounds, such as synthetic fertilizers and other nitrates, relatively easily.

The present invention is based on the object Process for the production of ammonia available len, which is carried out in a particularly economical manner ren leaves.

According to the invention, this object is achieved by a method with the following steps:

• a) reacting silicon and / or silicon compounds, in particular silicon hydrogen compounds, with nitrogen with the aid of a subgroup element or subgroup element oxide serving as catalyst to give silicon nitride (Si ₃ N ₄ ) at moderate temperatures; and
• b) reacting the silicon nitride obtained with a strong base or its aqueous solution to ammonia (NH ₃ ).

The method according to the invention consists of two steps. In a first step, silicon nitride is produced in a second step with a strong base or whose aqueous solution is converted to ammonia.

It is known to silicon nitride by heating silicon powder to 1350 ° -1450 ° C in a nitrogen atmosphere to manufacture. This method has the disadvantage that in As a result of heating to the temperatures mentioned, a re relatively high energy consumption is required.

In the method according to the invention, this is the starting point compound for the production of ammonia-serving silicon nitride catalytically by reaction of silicon and / or silicon compounds obtained with nitrogen. Surprisingly, it has been shown that using egg nes serving as a catalyst subgroup element or Subgroup element oxide silicon nitride at moderate tem temperatures (100-300 ° C) can be produced, the essential Lich below the range listed above. So is to initiate the reaction of the silicon with the Nitrogen just preheats the silicon and the Catalyst required. This is an activation  of the silicon for subsequent reaction with nitrogen reached in an exothermic way (from about 700 ° C), whereby very large large amounts of energy are released.

A subgroup element or minor is used as the catalyst group element oxide use. With subgroup elements are the corresponding elements of the subgroups of the periodic table of the elements. Subsidiary group Mentoxides are the oxides of these. Particularly good results can be used with the elements of the subgroup of Group I, namely Cu, Ag, Au, achieve the use of copper or copper oxide for particularly good results leads. Copper oxide (CuO) has proven to be particularly suitable not proven.

For the process according to the invention, Si are more elementary Form and / or Si compounds used. examples for Si compounds are silicon hydrogen compounds.

Further examples are silicon-metal compounds (silicides).

Furthermore, silicon alloys should also be included in the invention Procedures fall.

The silicon and / or the silicon compounds are preferably implemented as powder mixed or coated with the catalyst. A process variant is given before, in which a mixture of finely divided dust of Si and / or the Si compounds and the catalyst is preheated to about 200 ° C., whereby the reaction 3Si + 2N ₂ → Si ₃ N _{4 is} initiated.

The effect of the catalyst can be promoted by such for example zinc, zinc compounds, can be increased.  

In the manner described above, silicon ni trid in large quantities in a particularly economical way produce. There is a significant advantage of the method in that large amounts of energy are released, the ge can be used, for example as heating energy, to driving energy (internal combustion engine, rocket engine, jet engine etc.). Silicon nitride is therefore the starting point substance for the subsequent reaction to ammonia available in large quantities, either targeted can be produced or as a "waste product" at Be Driving such a drive occurs.

In the second step of the method according to the invention the silicon nitride obtained with a strong base or their aqueous solution converted to ammonia. Doing so preferably proceeded so that the catalytically obtained Silicon nitride from one for step a. reactor used discharged and into the strong base or its aqueous solution solution is entered. Preferably the silicon nitride with a hot base or a hot aqueous solution implemented from this.

According to a variant of the method, the process is catalytically won Silicon nitride with the strong base or its water Solution first converted to an amide, which then in an ammonium salt is transferred from which the ammonia is won.

NaOH, KOH or Ca (OH) ₂ are preferably used as the strong base. When implemented with these bases, further products are obtained which have numerous areas of application.

According to a second aspect of the present invention, the above-mentioned object is achieved by a method for the extraction of ammonia, which comprises the following steps:

• a) reacting silicon and / or silicon compounds, in particular silicon hydrogen compounds, with nitrogen with the aid of a subgroup element or subgroup element oxide serving as a catalyst to form silicon nitride (Si ₃ N ₄ ) at moderate temperatures;
• b) reacting the silicon nitride obtained with CO ₂ and H ₂ O to ammonium carbonate ((NH ₄ ) ₂ CO ₃ ) and silicon dioxide (SiO ₂ ); and
• c) Thermal decomposition of the ammonium carbonate or by adding a base to ammonia.

In this second method of the solution according to the invention is step a. with step a. of the above first procedure identical. In this respect, therefore, also apply all modifications given above, Eigen properties and advantages in relation to the production of Si licium nitride.

In a further step, the catalytically obtained Silicon nitride then with carbon dioxide and preferably hot ßem water converted to ammonium carbonate, which is then in a third step is decomposed to ammonia.  

According to a third aspect of the invention, the above object is achieved by a process for the extraction of ammonia, which comprises the following steps:

• a) reacting silicon and / or silicon compounds, in particular silicon hydrogen compounds, with nitrogen with the aid of a subgroup element or subgroup element oxide serving as a catalyst to form silicon nitride (Si ₃ N ₄ ) at moderate temperatures; and
• b) reacting the silicon nitride obtained with hydrofluoric acid (HF) to ammonia.

In this process too, step a. with the steps a. of the methods reproduced above are identical. It Therefore, all modifications, advantages apply here too and properties listed above in be train on the production of silicon nitride.

In step b. is now, however, with an acid, namely Hydrofluoric acid, worked to produce ammonia. Preferred two With this acidic decomposition, it becomes hot hydrofluoric acid or hot hydrogen fluoride used.

The silicon nitride obtained is expediently reacted with hydrofluoric acid to form ammonium hexafluorosilicate ((NH ₄ ) ₂ SiF ₆ ), from which ammonia and silicon tetrafluoride (SiF ₄ ) are obtained by heating.

The invention is illustrated below with the aid of an embodiment game described.

A mixture of fine Si powder and fine CuO powder was introduced into a horizontal reactor provided with heating rods. The reactor was then preheated to about 200 ° C. Air was then injected into the reactor. The Si ₃ N ₄ generated catalytically in this way was discharged from the reactor and introduced into hot sodium hydroxide solution. This produced sodium silicates and gaseous ammonia.

The term "moderate temperatures" used here refers at temperatures below 1000 ° C, in particular from 100-300 ° C, with a temperature of about 200 ° C particularly be is preferred.

The terms used "catalyst, catalysis, cataly table "do not rule out that the catalyst also in larger amounts than usual in catalytic reactions is set, for example in quantities up to 40% on silicon or the silicon compound.

Claims (9)

1. A process for the production of ammonia with the following steps:

• a) reacting silicon and / or silicon compounds, in particular silicon hydrogen compounds, with nitrogen with the aid of a catalyst as the catalyst or the subgroup element or subgroup element oxide to silicon nitride (Si ₃ N ₄ ) ₎ at moderate temperatures; and
• b) reacting the silicon nitride obtained with a strong base or its aqueous solution to ammonia (NH ₃ ).

2. The method according to claim 1, characterized in that the catalytically obtained silicon nitride from a for Step a. discharged used reactor and in the strong base or its aqueous solution entered becomes. 3. The method according to claim 1 or 2, characterized net that the catalytically obtained silicon nitride with the strong base or its aqueous solution first  is converted to an amide, which is then converted into an ammo nium salt is transferred from which the ammonia is obtained becomes. 4. Process for the production of ammonia with the following steps:

• a) reacting silicon and / or silicon compounds, in particular silicon hydrogen compounds, with nitrogen with the aid of a catalyst as the catalyst or the subgroup element or subgroup element oxide to silicon nitride (Si ₃ N ₄ ) at moderate temperatures; and
• b) reacting the silicon nitride obtained with CO ₂ and H ₂ O to ammonium carbonate ((NH ₄ ) ₂ CO ₃ ) and Siliciumdi oxide (SiO ₂ ); and
• c) decomposing the ammonium carbonate thermally or by adding a base to ammonia.

5. A process for the production of ammonia with the following steps:

• a) reacting silicon and / or silicon compounds, in particular silicon hydrogen compounds, with nitrogen with the aid of a catalyst as the catalyst or the subgroup element or subgroup element oxide to silicon nitride (Si ₃ N ₄ ) at moderate temperatures; and
• b) reacting the silicon nitride obtained with hydrofluoric acid (HF) to ammonia.

6. The method according to claim 5, characterized in that the silicon nitride obtained is reacted with hydrofluoric acid to form ammonium hexafluorosilicate ((NH ₄ ) ₂ SiF ₆ ), from which ammonia and silicon tetrafluotide (SiF ₄ ) are obtained by heating. 7. The method according to any one of the preceding claims, since characterized in that the silicon and / or the Silicon compounds as mixed with the catalyst tes or coated powder are implemented. 8. The method according to any one of the preceding claims, characterized in that a mixture of finely divided dust from silicon and / or the silicon compounds and the catalyst is preheated to about 200 ° C, whereby the reaction 3Si + 2N ₂ → Si ₃ N _{4 is} initiated. 9. Method according to one of the preceding claims, since characterized in that copper or Copper oxide is used.