MXPA00008922A - Catalyst for the synthesis of ammonia from hydrogen and nitrogen - Google Patents

Abstract

The present invention relates to a catalyst for the synthesis of ammonia from hydrogen and nitrogen consisting of iron oxides and promoters where the promoters comprise oxides of both cobalt and titanium in addition to Al, K, Ca and Mg oxides, and where the concentration of cobalt is between 0. 1%and 3.0%by weight of metal and the concentration of titanium is between 0.1%and 1.0%by weight of metal.

Description

CATALYST FOR THE SYNTHESIS OF AMMONIA FROM HYDROGEN AND NITROGEN The present invention describes a catalyst for the synthesis of ammonia of hydrogen and nitrogen.

The ammonia synthesis catalyst plays an important role in the manufacture of ammonia. This affects both the economic conditions and the operation of the plants of a * m or n i a c o.

Industrial catalysts for ammonia synthesis must meet a number of requirements: high catalyst activity at the lowest possible reaction temperatures in order to take advantage of favorable thermodynamic equilibrium at low temperatures, good resistance to poisoning by compounds containing sulfur, chlorine and REF .: 123176 oxygen, a long life a high resistance marble In order to save the energy the synthesis pressure has been steadily reduced from 250-350 bar to 80-150 bar during the last 30 years due to the optimized operation of the loop synthesis made possible by the new technology, especially for the converter manufacturing. Improvements in the main end have drastically reduced the poisons content of the catalyst (compounds containing chlorine, sulfur and oxygen) in the gas inlet to the converter. However, the drop in the synthesis pressure requires 3 to 4 times the increase in the volume of the catalyst. The demands on the quality of the catalyst have also increased. Apparently small improvements in catalyst activity can lead to greater improvements in the operation of a modern ammonia loop synthesis.

The catalyst precursor of the ammonia synthesis, the non-reduced catalyst, is manufactured by melting iron oxides, mainly magnetite, and oxides or carbonates of aluminum, potassium, calcium and magnesium, of the so-called promoters. The melt is carried out in an electric furnace at a temperature above 1600 ° C. The Fe2 + / Fe3 + ratio in the melt is usually in the range of 0.5-0.75. The melt is then poured into metal trays where it solidifies and cools. The solid precursor is then broken, crushed and sieved to obtain the required grain size.

The precursor is reduced to an active iron catalyst "in situ" in the ammonia synthesis converter or used for the manufacture of the pre-reduced catalyst by a complete reduction under conditions used in a pre-reduction reactor. This material is pyrophoric, but after oxidation of the outer layer of the active surface with oxygen it can be safely handled in air at ambient temperatures.

The promoters mentioned above, which contain aluminum, potassium, calcium and magnesium, are essential for the formation of a long iron surface in the reduced catalyst and for the kinetics of ammonium co formation.

Since the development of the catalyst began, about 90 years ago, the concentration of these promoters has been used to obtain maximum activity to meet the additional requirements mentioned above. Additional improvements seem to be only possible when adding new promoters or new promoter combinations.

Cobalt oxide has been used as a new promoter.

From the patent US 3839229 an ammonia synthesis catalyst is known where the cobalt oxide is used as a promoter. The catalyst consists essentially of a solid solution of iron oxide and cobalt oxide and said cobalt oxide is present in an amount of 5 to 10 weight percent expressed as cobalt. The catalyst further includes a promoter selected from the group consisting of aluminum, silicon, zirconium, magnesium, lime (CaO), potassium oxide and rare earth metal oxides.

Another possible promoter is titanium oxide. Only some catalysts that use this promoter have been previously described. S.A. Abdukadyrova et al, which is in "Tr. Mosk Khim-Tekhnol, Inst. (1970), No. 2,122-5", discloses that titanium oxide improves thermal resistance but reduces activity.

The titanium oxide used as a structural promoter is described by M.E. Dry et al in "Journal of Catalysis", 6, page: 194-199, 1966. Titanium oxide is not as effective as aluminum oxide with respect to surface area. This area and the volume of CO normally adsorbed chemically increases with the content of the promoter, but in contrast to other promoters (A1203, MgO, CaO) Ti02 that have a maximum in the volume of CO chemically absorbed in about 0.5 grams of the cation per 100 grams of the iron atom.

The main objective of the present invention is to develop a catalyst for the synthesis of ammonia with improved activity.

The high activity can be used in two ways: a high reaction rate in high ammonia concentrations or a high activity at low temperatures.

The activity of the catalyst can be expressed with a ratio constant in a ratio equation for the synthesis reaction. The ratio is a function of the temperature, pressure and composition of the gas, and decreases rapidly with the increase in ammonia concentrations. In this way, a fraction load of the volume of the catalyst in a synthesis converter will have a concentration of ammonia approximate to the exit concentration. Consequently, to improve efficiency, the increase in the reaction rate at high concentrations of ammonia is of particular interest.

As the equilibrium temperature decreases with the increase in ammonia concentration, the investigation of a high conversion by increasing the reaction rate at high concentrations of ammonia also has the intention of investigating a catalyst with a high activity at low temperatures.

The inventors have manufactured many iron oxide samples based on catalysts with several promoters in various concentrations to improve the activity of the catalyst. In addition to the aforementioned conventional promoters, new promoters have been tested, in particular cobalt oxide and titanium oxide.

The inventors found that the reaction rate at high concentrations of ammonia increases by 10-20% when both titanium oxide and cobalt oxide are used as prornot ore together with conventional promoters.

The most preferred catalyst is carried out when the cobalt concentration is between 0.1% and 3.0% by weight of the metal and when the titanium concentration is between 0.1% and 1.0% by weight of the metal.

The atomic ratio of Fe 2+ / Fe 3+ is between 0.5-0.65.

The present invention thus in its very broad field comprises a catalyst for the synthesis of hydrogen and nitrogen ammonia consisting of iron oxide and promoters where the promoters comprise both cobalt and titanium oxides in addition to magnesium, calcium oxides, potassium and aluminum.

The present invention will be further explained in the appendix.

Example : The samples are made by mixing iron ore, mainly magnetite, Fe304, with promoters. These mixtures are melted in a ceramic crucible in a laboratory furnace. The temperature remains close to 1600 ° C. The Fe2 + / Fe3 + ratio is adjusted within 0.5 to 0.65 by adding iron metal to the melt.

The melt is then poured into an iron crucible and cooled.

The concentration of the promoters in the samples vary as shown in Table I: Table I The balance is between the oxides of iron with the natural impurities. The cooled samples are crushed and sieved to 0.4-0.63 mm particles for the test in a microreactor.

The samples, (each 10 g), are tested together with the reference sample in a microreactor. The reference sample is a conventional catalyst with no addition of titanium oxide or cobalt.

The samples are reduced in a flow of H2 and N2 in a ratio of 3/1 at a space velocity of 33000 1 / h. The increase in temperature is 3 ° C / h from 250 ° C to 520 ° C and 520 ° C is maintained for 24 hours to ensure a complete reduction.

The samples are then tested at a pressure of 50 bar, a space velocity in the range of 8000 to 50000 1 / h, and temperatures in the range of 350 ° C-420 ° C. The inlet gas is H2 / N2 = 3 / l with an ammonia concentration of 1.0 to 1.2% (vol.). The exit ammonia concentration is in the range of 4 to 9% (vol.).

The data obtained during a period of about 100 hours and after an initial stabilization of 24 hours or more, are used to calculate the parameters in a kinetic model for the reaction. The model is also used to calculate the relative activity and the relative reaction rate in high concentrations of ammonia more than those used in 1 to test.

The following table II shows the concentration of cobalt and titanium in several samples, the activities of the relative catalyst on average and the proportion of relative reaction predicted at high concentrations of ammonia (20% NH3, at 420 ° C) is calculated by the model kinetic.

Table II Table II shows that the relative reaction ratio is much higher than the high concentration of ammonia (20%) when both titanium oxide and cobalt oxide are added as promoters (compare samples 7-9 with sample 1) .

In addition, Table II shows that by adding either cobalt oxide or titanium oxide alone, together with the other conventional promoters, a low relative reaction ratio at a high concentration of ammonia is obtained (compare samples 2-3 and 4-6 with sample 1).

In addition, Table II shows that activity increases at temperatures below 350 ° C when both titanium oxide and cobalt oxide are added as extra promoters (see sample after 7-9).

The example also shows that the activity is increased at both high and low reaction temperatures when both the titanium oxide and the cobalt oxide are added as promoters.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (2)

1. A catalyst for the synthesis of ammonia from hydrogen and nitrogen consisting of iron oxides and promoters, characterized in that the promoters comprise oxides of both cobalt and titanium as well as oxides of aluminum, potassium, calcium and magnesium.

2. A catalyst for the synthesis of hydrogen and nitrogen ammonia according to claim 1, characterized in that the concentration of Cobalt is between 0.1% and 3.0% by weight of the metal and the concentration of titanium is between 0.1% and 1.0% by weight of the metal. twenty