Catalyst for the synthesis of ammonia from hydrogen and nitrogen

 

The invention relates to a catalyst for the synthesis of ammonia from hydrogen and nitrogen. Described is a catalyst for the synthesis of ammonia from hydrogen and nitrogen containing iron oxides and activators - oxides of cobalt, potassium, calcium, magnesium, aluminum, titanium with the following content of components in terms of metals, wt.%: cobalt is 0.1-0.3, potassium 0,4-0,5, calcium 1,6-1,8, magnesium 0.3 to 0.5, aluminium 1,5-1,8, titanium, 0.1 to 1.0, the rest is iron with natural impurities. The technical result is an increase in the activity of the catalyst. table 1.

The invention relates to a catalyst for the synthesis of ammonia from hydrogen and nitrogen.

The catalyst for ammonia synthesis plays an important role in the production of ammonia. It has an impact both on the economy and on the operating conditions of the installations for the production of ammonia.

Industrial catalysts for ammonia synthesis must meet several requirements, namely to have a high catalytic activity as possible at the lowest temperatures of the reaction in order to use the preferred thermodynamic equilibrium at low temperatures, good resistance to poisoning by oxygen-, chlorine - and sulfur-containing compounds, long term services which we gradually decreased from 250-350 bar up to 80-150 bar (25106-35106up to 8106-15106PA) due to the optimized operation of circuit synthesis, achieved with the help of new technology, particularly due to the manufacture of the Converter. Improvements in the front end circuit has radically reduced the content of catalytic poisons (oxygen-, sulfur - and chlorine-containing compounds) in Gaza, which is included in the Converter. However, the pressure drop of synthesis makes the necessary increase in the volume of catalyst in three or four times. Requirements to the quality of the catalyst also increases. It is obvious that a small improvement in catalytic activity of the catalyst can lead to large improvements in the modern contours of the synthesis of ammonia.

The catalyst precursor for the synthesis of ammonia, unrestored catalyst is made by melting iron oxides, mainly magnetite, and oxides or carbonates A1, K, CA and mg, the so-called activators. Melting is carried out in an electric furnace at a temperature above 1600oC. the Ratio of Fe2+/Fe3+in the melt is typically in the range of 0.5-0.75. The melt is then poured into metal trays, where it solidifies and cools.constituent of the grain size.

The catalyst precursor to restore the active iron catalyst "in situ" in the Converter synthesis of ammonia or used for the production of pre recovered catalyst by full recovery under optimized conditions in the reactor prior recovery. This material is pyrophoric, but after oxidation of the outer layer of active surface oxygen it can safely be kept in air at ambient temperature.

The activators mentioned above, containing A1, K, CA and mg are essential for the formation of a large surface of iron in the recovered catalyst and kinetics of formation of ammonia.

Since then, as initiated development of a catalyst, about 90 years ago, the concentration of such activators was optimized to obtain maximum activity and meet the additional requirements mentioned above. Additional improvements will probably only possible when adding new activators or new combinations of activators.

As a new activator was used cobalt oxide.

From U.S. patent 3839229 known catalyst for ammonia synthesis, which in cachesize and cobalt oxide, and the cobalt oxide is present in an amount of 5 to 10% weight. based on cobalt. In the catalyst additionally introduced activator selected from the group including aluminum oxide, silicon dioxide, zirconium dioxide, magnesium oxide, lime (Cao), potassium oxide and oxides of rare earth metals.

Another possible activator is titanium oxide. Only a small number of catalysts that use this activator, as described earlier. C. A. Abdukadirov and others in the journal "proceedings of the Moscow chemical-technological Institute, 1970, 2, 122-5, describe that the titanium oxide improves thermal stability, but reduces the activity.

The titanium oxide used as structural activator described M. E. Dry et. al ("Journal of Catalysis", 6, p. 194-199, 1966). The titanium oxide is not as effective as aluminum oxide relative to the surface area. This area and the amount of chemisorbed CO is usually increased with the content of the activator, but unlike other activators (Al2O3, MgO, CaO) TiO2has the maximum amount of chemisorbed CO at approximately 0.5 g-atom of cation per 100 g-atom Fe.

The main objective of the present invention is to develop a catalyst for ammonia synthesis with improved activaci concentrations of ammonia or higher activity at low temperatures.

The catalyst activity can be expressed in the form of the rate constant in the rate equation for this reaction synthesis. Speed is a function of temperature, pressure and composition of gas and decreases rapidly with increasing concentration of ammonia. Thus, most of the volume of the catalyst in the Converter synthesis will take up the ammonia in concentrations approaching the concentration at the outlet. Therefore, to improve the effectiveness of particular interest is the increase in the reaction rate at high ammonia concentrations.

As the equilibrium temperature decreases with increasing ammonia concentration, achieving higher conversion rates by increasing the reaction rate at high ammonia concentrations also means finding a catalyst with higher activity at low temperature.

To improve the catalytic activity, the inventors have produced a large number of samples of catalysts based on iron oxide with different activators in various concentrations. In addition to the usual activators mentioned above, tested new activators, in particular the oxides of cobalt and titanium.

The inventors have found that the reaction rate at high ammonia concentrations of hydrocarbons in the conventional activators.

The most preferred catalyst is obtained when the cobalt concentration is between 0.1 and 3.0 wt%. metal and when the concentration of titanium is between 0.1 and 1.0 wt%. metal.

The atomic ratio of Fe2+/Fe3+is between 0,5-0,65.

Thus, the present invention in a broad aspect will include a catalyst for the synthesis of ammonia from hydrogen and nitrogen containing iron oxides and activators, where promoters include oxides like cobalt and titanium in addition to the oxides of Al, K, CA and mg.

The invention is additionally illustrated by example.

Example Samples obtained by mixing iron ore, mainly magnetite, Fe3About4with activators. Such mixtures are then melted in a ceramic crucible in a laboratory furnace. The temperature of the support at approximately 1600oC. the Ratio of Fe2+/Fe3+regulate in the range of 0.5 to 0.65 by adding to the melt of metallic Fe.

The melt is then poured into a metal crucible and cooled.

The concentration of activators in the samples varies in accordance with the data below: - 0,4 - 0,5 Sa - 1,6 - 1,8 MD - 0,3 - 0,5 Al - 1,5 - 1,8 From - 0.10 to 3.00 for Ti - 0.14 to 0.95 Remainder is iron oxides with the natural use the/p> Samples (10 g each) experience together with a control (reference) samples in the microreactor. Control sample is a typical catalysts without the addition of cobalt oxide or titanium oxide.

Samples restore the flow of H2and N2in the ratio of 3:1 at a flow rate 33000 1/hour. The temperature rise is 3oS/h from 250 to 520oWith, and 520oWith support for 24 hours to ensure completeness of reaction.

The samples are then tested at a pressure of 50 bar (5106PA), the flow rate in the range of from 8000 to 50000 1/hour and at a temperature in the range from 350 to 420oC. the Incoming gas is an H2/N2=3/1 with the concentration of ammonia from 1.0 to 1.2% (vol.). The concentration of ammonia at the outlet is in the range from 4 to 9% (vol.).

Data obtained over a period of approximately 100 hours after initial stabilization in 24 hours or more, is used to calculate the parameters of the kinetic model of the reaction. The model is then further used to calculate the relative activity and relative reaction rate at higher ammonia concentrations than the concentration used in the test. In table presti and predicted relative reaction rate at higher concentrations of ammonia (20% NH3, 420oC), calculated using the kinetic model.

These tables show that the relative reaction rate is highest when high concentrations of ammonia (20%), while the cobalt oxide and the titanium oxide added as activators (compare samples 7-9 sample 1).

In addition, these tables show that by adding only or cobalt oxide, or titanium oxide together with other conventional activators achieved lower relative reaction rate at high ammonia concentrations (compare samples 2-3 and 4-6 sample 1).

In addition, these tables show that the activity increases when the temperature is reduced to 350oWhen as cobalt oxide, and titanium oxide added as an additional activators (see examples 7-9).

The example also shows that the activity increases with both at low and at high reaction temperature, when the activators are added as cobalt oxide, and titanium oxide.

Claims

Catalyst for the synthesis of ammonia from hydrogen and nitrogen containing iron oxides and activators - oxides of cobalt, potassium, calcium, magnesium, aluminum, featuring the comrade in terms of metals, wt.%:
Cobalt - 0,1-0,3
Potassium - 0,4-0,5
Calcium - 1,6-1,8
Magnesium - 0,3-0,5
Aluminum - 1,5-1,8
Titanium - 0,1-1,0
The rest is Iron with natural impurities

 

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