EP4003590A1

EP4003590A1 - Process for producing catalysts for ammonia synthesis by reducing iron oxides

Info

Publication number: EP4003590A1
Application number: EP20739923.9A
Authority: EP
Inventors: Rene Eckert; Stephan J. REITMEIER; Stefan Maier
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 2019-07-24
Filing date: 2020-07-08
Publication date: 2022-06-01
Also published as: CA3140521C; CA3140521A1; CN114096348A; DE102019120012A1; WO2021013544A1; US20220250048A1

Abstract

The invention relates to a process for activating catalysts and catalyst precursors for ammonia synthesis, comprising the following process steps: (A) iron oxides are reduced to activate the catalysts by means of at least one reductive gas and by heating, (B) the concentration of the water formed in the gas phase during the reduction is measured by means of non-dispersive infrared spectroscopy (NDIR), and (C) the flow rate of the reductive gas and/or the heating rate is set in accordance with the concentration of the water that is formed.

Description

Process for the production of catalysts for the synthesis of ammonia

Reduction of iron oxides

description

In the production of catalysts or catalyst precursors based on iron oxides for the synthesis of ammonia, the iron oxides are usually reduced in reactors using reducing gases. A catalytically very active form of elemental iron is formed, in particular a form of body-centered cubic alpha iron. Such reduced iron catalysts are particularly good as

Catalysts for the ammonia synthesis, especially the Haber-Bosch synthesis are used.

During the reduction of the iron oxides, water is formed, but this can act as a catalyst poison. Therefore, in order to limit the amount of water formed during the reduction, the reduction process is often carried out very slowly and carefully. Furthermore, the concentration of the water formed is determined at regular intervals using the Ascarit method. In this analysis, the water content is determined by the fact that a defined amount of sample gas flows through an adsorbent, the adsorbent only adsorbing the water in the sample gas. The difference in weight of the adsorbent is then determined and the amount of water calculated using the measured volume flow. Such a method is very time-consuming and only provides information about the water content of the sample with a certain delay.

The object of the present invention is to provide a method for activating catalysts and catalyst precursors for ammonia synthesis which is improved with regard to the above-mentioned disadvantages. Furthermore, the use of an NDIR detector to determine the concentration of water during the reduction of iron oxides is described.

The present invention relates to a process for the activation of catalysts and catalyst precursors for ammonia synthesis, comprising the process steps:

(A) Iron oxides are reduced to activate the catalysts using at least one reducing gas and by means of heating,

(B) the concentration of the water formed during the reduction in the gas phase is measured by means of non-dispersive infrared spectroscopy (NDIR), and (C) the flow rate of the reducing gas and / or the heating rate are adjusted as a function of the concentration of the water formed.

The non-dispersive infrared spectroscopy (NDIR) is a

Spectrometric analysis of gases to be measured, in which infrared radiation of a defined wavelength is radiated into a sample. Depending on the concentration of the gas in the beam path, the IR beam is weakened by absorption. This creates pressure differences inside an opto-pneumatic receiver, an NDIR sensor, which can be converted into electrical voltage by microflow sensors, for example, and provides information about the amount of absorbing

Put gas molecules in the sample. With regard to the structure of the NDIR sensors, which are known to those skilled in the art, reference is made to the manual "XStream Gas Analyzers, XStream X2 Series" from Emerson Process Management GmbH & Co. OHG, May 2017 edition, sections 3.1.2 and 3.1.3 .

The determination of the concentration of the water by means of NDIR is directly possible and does not require complex analyzes in contrast to the conventional methods, so that the flow rate of the reducing gas and / or the heating rate can be set particularly easily depending on the concentration of the water in the reactor outlet gas, and so the generation of water concentrations harmful to the catalyst can be reduced during the reduction.

By means of the method according to the invention, the iron oxides can be prepared

Catalysts are produced or activated, and these are used directly after the activation for ammonia synthesis from synthesis gas, for example comprising a mixture of nitrogen and hydrogen. It is also possible, by means of the process according to the invention, to produce pre-reduced catalyst precursors which are first reduced under controlled conditions and then passivated in an oxidizing atmosphere before they are used as catalysts in the ammonia synthesis. These pre-reduced catalysts can be activated significantly faster and under milder conditions than the iron oxides.

Furthermore, in method step (C), the concentration of the water determined in method step (B) can be compared with a predetermined limit value for water. This can be carried out, for example, in such a way that a range is defined around the limit value and the flow rate of the reducing gas and / or the heating rate are set as a function of the measured water concentration so that the concentration increases Water is within the specified range around the limit value. Especially at the beginning of the process, the water concentration can fluctuate around the limit value and therefore also be outside this range. In particular, if the process is not yet stable, the water concentration can exceed the limit value by 200 ppmv (parts per million per volume) for a maximum of 1 hour or by 400 ppmv for a maximum of 20 minutes. As soon as the process is stable, the

Water concentrations are mainly within the range around the limit value.

In a further embodiment of the method according to the invention, in

Process step (C) carried out at least one of the following substeps:

(C1) the heating rate is increased if that determined in method step (B)

The concentration of water is below the range around the specified limit value, or

(C2) the flow rate is increased and / or the heating rate is decreased if the concentration of water determined in method step (B) is above the range around the predetermined limit value, or

(C3) the flow rate and / or the heating rate are maintained if the im

Method step (B) determined concentration of water is within the range around the predetermined limit value.

The inventors of the present invention have recognized that the concentration of the water formed during the reduction of the iron oxides in the gas phase should advantageously not exceed a limit of 4000 ppmv, preferably 3400 ppmv, more preferably 3200 ppmv, even more preferably 3000 ppmv. Reduced iron catalysts, which were activated at higher concentrations of water in the gas phase, usually show lower activities in the subsequent ammonia synthesis. Activation of the iron oxides with a higher proportion of water in the gas phase thus leads to

Catalysts which have lower activity in the subsequent ammonia synthesis, but at the same time a higher proportion of water enables faster and therefore more economical activation of the catalysts. In particular, the area around the

Limit selected from a group of ranges consisting of: ± 1000 ppmv, ± 800 ppmv, ± 600 ppmv, ± 400 ppmv, ± 300 ppmv, and ± 200 ppmv. The range is preferably ± 300 ppmv, more preferably ± 200 ppmv. A limit value of 3000 ppmv and a range of ± 600 ppmv are possible. A limit value of 3000 ppmv and a range of ± 200 ppmv are particularly preferred. The heating rate can be very high at low temperatures in the reactor system and can be up to 40 K / h especially at the beginning of the reduction. Conversely, the heating rate during the reduction of the iron oxides, as long as the concentration of water in the

desired range is in the range from 0 K / h to 2 K / h. The periods of time with these small heating rates can be up to 48 hours, depending on the flow rate and the catalyst volume.

According to an advantageous embodiment of the process according to the invention, this can be carried out as a continuous process, process steps (A), (B) and (C) being carried out continuously. It is thus possible in particular to determine the concentration of the water formed during the reduction in process step (B) by means of NDIR during the reduction of the iron oxides in process step (A) and to determine the flow rate of the reducing gas and within a short period of time in process step (C) / or adjust the heating rate accordingly. Thus, all process steps (A) to (C) can advantageously be carried out in parallel alongside one another or at the same time, which means a considerable time advantage compared to the conventional process in which the results of the Ascarit method must first be awaited. The concentration of the water in process step (B) can be measured continuously by means of NDIR (two measured values per second), while with the Ascarit method, a measured value is usually only available every 1 to 2 hours. Furthermore, depending on the water concentration determined in process step (B), the

Sub-steps (C1), (C2) or (C3) can be carried out several times in succession as required.

In a further variant of the method according to the invention, the measurement of the water formed during the reduction in method step (B) takes place in real time. This makes it possible to react immediately to changes in the concentration of the water formed and to adjust the flow rate and / or the heating rate accordingly. In this variant of the process according to the invention, it is possible to react to a change in the amount of water formed, in particular within a period of 1 to 10 minutes. Depending on the heating rate, the water concentration can rise from 0 ppmv to values of up to 3000 ppmv in a period of 0.5 h to 2 h. Usually the

Water concentration in process step (B) measured continuously by means of NDIR and checked every 15 min and, depending on the measured water concentration, the heating rate and / or the flow rate of the reducing gas in process step (C) is adjusted accordingly. A mixture comprising hydrogen and nitrogen is advantageously used as the reducing gas in a process according to the invention in process step (A), it being possible for ammonia to be formed during the reduction of the catalysts due to partial activation of the catalysts. In such a variant of the process according to the invention, the activation of the catalysts during the process can also be determined by the increasing content of ammonia formed in the gas phase. If the process according to the invention is carried out in a reactor which is also used for ammonia synthesis, the ammonia synthesis can be started particularly easily immediately after the activation of the catalysts has ended. The reducing gas can also contain noble gases such as argon. In particular, all of the noble gases present in the air can be present in the reducing gas. In addition, there may also be methane in the reducing gas, which was not converted during the reforming, the formation of hydrogen from methane.

In a further advantageous variant of the method according to the invention, in

Process step (B) the concentration of the water formed during the reduction in a wavelength range from 2.6 μm to 3 gm, preferably in the range from 2.7 to 2.8 μm, more preferably in the range from 2.75 μm to 2.79 measured pm. The concentration of water is usually measured at wavelengths of about 6 pm, but in this wavelength range the interference with absorption bands of ammonia is particularly large. In order to reduce this overlap, measurements are therefore preferably made in the above-specified wavelength range from 2.6 μm to 3 μm.

In method step (B) it is particularly advantageous to use an NDIR device for measuring the water formed, in which the absorption bands of ammonia are in the wavelength range from 2.6 pm to 3 pm, more preferably in the range from 2.75 pm to 2.79 pm are deducted by means of calibration. For example, calibration curves can be created for calibration by means of experimental data in which gas samples with approximately 0% by volume to 20% by volume of ammonia were measured by means of NDIR. These calibration curves allow the background signal of ammonia in the above given

Determine the wavelength range depending on the concentration of ammonia and take this into account when analyzing the water in this wavelength range. The inventors of the present method have found that during the reduction of the iron oxides with a mixture of hydrogen and nitrogen, ammonia can be formed in amounts of 0% by volume to 20% by volume, with the proportion of ammonia in the gas phase increasing as the reduction progresses. In method step (B), the concentration of the ammonia formed in the course of the reduction can also be determined particularly advantageously by means of NDIR. A

Determination of the ammonia, which can also be formed in the course of the reduction in the presence of nitrogen in the gas phase, can particularly advantageously provide information about the course of the activation of the catalysts or catalyst precursors. The concentration of ammonia formed in the gas phase can be determined in a particularly simple manner, analogously to the determination of water in the gas phase by means of NDIR, which enables the values to be determined particularly quickly. In particular, it is possible to determine ammonia simultaneously in a sample together with water by means of NDIR, the concentration of the ammonia advantageously in one

Wavelength range from 10.8 gm to 1 1, 2 gm, preferably at 1 1 pm is determined. In this area, water does not absorb any IR radiation, so the concentration increases

Ammonia can be determined particularly easily without a necessary correction of the values.

In a further advantageous variant of the process according to the invention, the reduction in process step (A) is carried out in a reactor which, via pipe feed lines for feeding in the reducing gas and pipe outlets for discharging a

Has gaseous reaction mixture from the reduction, which contains, inter alia, the water formed in the reduction and any ammonia formed. The

Pipe discharge lines have a sample line at the reactor outlet for taking a sample for the NDIR measurement. The test line is advantageously thermally insulated and possibly also has an additional heating device that ensures that the

Temperature in the sample line does not decrease too much. A drop in temperature causes water to condense, which would falsify the measurement results obtained by NDIR. If the sample to be measured is taken directly at the reactor outlet, heat losses in the reactor outlet line do not yet play such a major role. in the

With such a variant of the method according to the invention, a sample of the gas phase to be analyzed can be taken particularly easily via the sample line and the concentration of water and / or the concentration of ammonia can be determined particularly reliably by means of NDIR.

In particular, a sample to be analyzed can be expanded to a pressure of about 0.01 to 2 barg (0.01 to 2 bar above normal pressure) and the water content and / or ammonia content can then be determined by means of NDIR. Under these conditions, the dew point of the sample gas is reduced from about 70 ° C to 80 ° C before the expansion to 0 ° C 10 ° C, preferably to about 10 ° C after relaxation, the temperature in the NDIR device usually being 40 ° C to 50 ° C. The gas mixture to be measured may have a maximum temperature of 60 ° C, with the minimum temperature just above the

May be dew point. Furthermore, the sample gas stream to be analyzed can also be filtered in order to prevent the NDIR detector from being contaminated. The same flow rate is advantageously always set during the measurement in order to obtain better reproducible measurement results. The flow rate during the NDIR measurement can in particular be in the range from 0.2 l / min to 1.5 l / min, preferably 1.5 l / min.

In a further variant of the method according to the invention, the

Reduction formed ammonia and / or water removed from the reactor in process step (C) and condensed by means of a cooler. This enables water and any ammonia formed to be withdrawn from the reduction process in a particularly simple manner and thus to prevent an accumulation of water during the reduction process.

In method step (C), the temperature of the cooler can also be set so that it is at least 10 K, preferably at least 5 K, above the freezing point of the aqueous ammonia solution. In such a method, on the one hand, the temperature of the cooler can be set in such a way that disadvantageous freezing of the cooler is prevented, but on the other hand the temperature of the cooler is nevertheless lowered to such an extent that reliable condensation of water and / or ammonia or an aqueous

Ammonia solution is quite possible. Because of the particularly easy and quick

NDIR measurements of water and / or ammonia to be carried out can be the

Process parameters for the reduction, for example the pressure, the temperature and the flow rate, are adapted to the respective measured concentrations of water and / or ammonia in the gas phase in order to enable reliable condensation.

The at least one reducing gas, for example comprising a mixture of nitrogen and hydrogen, can be fed back into the reduction process in a particularly simple manner after the water and / or ammonia have been cut off. Since during the

Reduction process not all of the reducing gas is consumed, such a variant of the method according to the invention is particularly economical.

For the process according to the invention, a reactor system can be used in process step (A) which comprises a reactor for reducing the iron oxides, which

Having pipe feed lines for feeding the reducing gas and pipe discharge lines for discharging a gaseous reaction mixture from the reduction. In particular, the Reactor system have a gas circuit in which the gaseous reaction mixture derived from the reactor is fed back to the reduction process via the pipe feed lines after separation of water and / or ammonia. Such a reactor system can in particular be a reactor for ammonia synthesis, in which the catalyst is obtained from catalyst precursors by means of activation by reduction before being put into operation. Alternatively, the reactor system can also be a reactor which was designed for reducing the catalysts and from which the catalyst precursors can be removed and transported away after the reduction and possible passivation has taken place.

In a further embodiment of the process according to the invention, in particular magnetite or wustite or a combination thereof, preferably wustite, can be used as iron oxides in process step (A). Magnetite is a mixed iron oxide with the general chemical composition Fe ₃ Ü ₄ and contains divalent and

trivalent iron. In contrast, it concerns with wustite to iron (II) oxide FeO, which may also have a non-stoichiometric composition RDI O _x.

In process step (A), the temperature during the reduction can be set to a range from 360 ° C. to 450 ° C., preferably a range from 370 ° C. to 400 ° C. (for wustite). At these temperatures, a reduction of

Iron oxides, for example wustite or magnetite, can be carried out.

The inventors have found that the reduction of wüstite already at lower

Temperatures of about 370 ° C to 400 ° C expires. Water is released during the reduction. In contrast, for the reduction of magnetite under

Water release temperatures of over 400 ° C, especially in the range of 420 ° C to 460 ° C. Thus, effective control of the process via the heating rate and / or the flow rate is particularly advantageous when reducing Wustite, in order to prevent the concentration of water in the gas phase from increasing too much even at lower levels

To prevent temperatures.

In process step (C) the flow rate (gas hourly space velocity; ghs \ / ') in particular to values from 1000 h ¹ to 70,000 h ¹ , preferably from 3000 h ¹ to 60,000 h ¹ . The pressures in process step (A) can be set to values of 60 bar to 600 bar, preferably 60 bar to 300 bar, more preferably 60 bar to 180 bar, further preferably 80 bar to 150 bar. At the beginning, the pressures are around 80 bar, while at

progressive reduction pressures of up to 600 bar, preferably up to 300 bar are possible In method step (A), the reduction can in particular be carried out in a system which has a heating device for heating the at least one reducing gas. The heating device can either be present in the reactor or outside the reactor, as shown in FIG. 1. The heating device can, for example, also be a heat exchanger in which heat is transferred from the reactor space to the reducing gas to be newly added. A heating device is necessary in particular at the beginning of the method according to the invention in order to achieve the temperatures necessary for the reduction. As the

Process according to the invention, in process step (A), the proportion of the heating device in the total heat balance can decrease and the proportion of the heat of reaction from the formation of ammonia can increase, with the result that the flow rate can be increased.

In a further embodiment of the process according to the invention, the catalysts and / or catalyst precursors are in a process step (D) from the

Process step (C) exposed to an oxidizing gas to form a protective layer on the catalysts and / or catalyst precursors. In particular, a gas mixture comprising oxygen or air can be used as the oxidizing gas. It is particularly advantageous if the composition of the gas is changed after the reduction is complete and, for example, an oxidizing gas comprising nitrogen and air is supplied so that a passivation layer is formed on the reduced catalysts by means of oxidation. Before starting up a reactor for ammonia synthesis, these catalyst precursors can be subjected to a short reduction step in a particularly simple manner and then used as catalysts for ammonia synthesis.

The present invention also relates to the use of an NDIR detector to determine the concentration of the water that is during the reduction of

Forms iron oxides in the activation of catalysts and catalyst precursors for ammonia synthesis.

In particular, with such a use, the concentration of the water can be determined in real time. The reduction can take place by means of a reducing gas, and the flow rate and / or the heating rate of the reducing gas in

Can be adjusted depending on the concentration of the water formed. Incidentally, all of the embodiments already mentioned above with regard to the method for activating the catalysts can also be implemented in the context of the use of an NDIR detector.

In the following, the invention is to be explained in more detail using exemplary embodiments and figures. Show it:

1 shows a reactor system for carrying out a method according to the invention, FIGS. 2 and 3 flow diagrams for the determination of water and ammonia by means of NDIR and the subsequent process steps for controlling the method,

Figures 4 and 5 show the effects of water content in reducing the

Iron oxides on the catalytic activity, and

FIG. 6 shows a diagram of the measurement of the water content during the reduction of iron oxides by means of NDIR.

Figure 1 shows schematically a reactor system for carrying out a method according to the invention. A reactor 10 is provided which has several catalyst beds 10A. The iron oxides to be reduced are located in the catalyst beds 10A. The reactor 10 has a pipe system 60 with pipe feed lines 60A, via which the at least one reducing gas is fed into the reactor, and pipe outlets 60B via which the gaseous reaction mixture of the reduction is discharged from the reactor so that the gas in the reactor Can circulate. The direction of the arrows indicates the

Direction of circulation of the gases in the reactor system. During the reduction of the iron oxides, the at least one reducing gas can be heated by means of a heating device 50. There is also an NDIR sensor 5, which measures the water content and / or the ammonia content of the reaction gases at the pipe outlet 60B

Can measure the reduction process. For this purpose, there is an insulated and heatable pipe 6 on the pipe outlet 60B. The pipeline 6 can have a thermal insulation or a heating device, which can serve to keep the temperature of the gas mixture to be analyzed high enough to avoid condensation of the water and thus falsification of the NDIR measurement result. The pressure in the pipe outlet 6 is gradually reduced to 1 to 2 barg and then to 0.01 to 0.5 barg for the NDIR measurement.

The course of an embodiment of the process according to the invention in this reactor system is explained in more detail below. The at least one reducing gas, which preferably comprises hydrogen and nitrogen, can be compressed by means of a compressor 25 via a gas supply line 60C and then introduced into the interior of the reactor 10 via a pipe supply line 60A. At the start of the process, the gas mixture can be brought to the required temperature, for example up to 450 ° C., preferably to 370 ° C. to 390 ° C., via the heating device 50, and then passed through the catalyst beds 10A. Control fittings 15 are provided throughout the system to adjust the gas flow. The size of the catalyst beds 10A increases the further downstream the catalyst beds are arranged in the reactor 10. During the reduction, that resulting from the reduction becomes

Gas mixture containing water and / or ammonia as well as unreacted hydrogen and nitrogen, led out of the reactor via the pipe discharge line 60B. The water and / or ammonia content of this gas mixture is then determined by means of the NDIR sensor 5, which is connected at the reactor outlet via a pipe 6 to the pipe line 60B. The gas mixture resulting from the reduction can then at least partially release the heat that is still present via a heat exchanger 40. The gas mixture is then passed into a waste heat boiler 20, in which it gives off further heat to water, which is passed through the waste heat boiler. This water is introduced into the waste heat boiler 20 by means of a connection 21 and as water vapor from the

Waste heat boiler discharged via connection 22. The steam can be used, for example, to increase the energy efficiency and thermal efficiency of the entire system for operating the compressors by means of steam turbines. The gas mixture can then give off further heat via further heat exchangers 40 or via ammonia coolers 40A, so that a mixture of ammonia and / or water can then be separated in separator 30. The separated water / ammonia mixture can then be removed from the system via the discharge line 30A. The reducing gas mixture containing hydrogen and nitrogen can then be used again

Compressor 25 are fed to in a further cycle to reduce the

Iron oxides to be used.

Depending on the concentrations of water and / or ammonia in the system determined by the NDIR sensor 5, the flow rate of the reducing gas and / or the heating rate can be set accordingly, so that the

The concentration of the water formed is within a range around a certain limit value. Furthermore, the temperature in the separator 30 can also be adjusted by means of the NDIR sensor 5 so that ammonia does not freeze out, which would impair the operation of the separator. FIG. 2 shows a flow diagram for the processes and partial steps that follow after the water determination by means of an NDIR sensor. In this embodiment, the limit value for the concentration of water in the gas phase can be, for example, 3000 ppmv and the range around the limit value can be ± 200 ppmv. Starting with the elements provided with the reference numerals 80, 81, the water content determined by means of NDIR is first read off on the analyzer of the reactor system and the value is compared with the limit value. Depending on the result of the comparison, there are then three different sub-steps (C1), (C2) or (C3). If it is determined that the measured value is more than 200 ppmv above the limit value, the flow rate is increased or the meat rate is decreased (82A) in a method step (C2). Thus, the concentration of the water formed in the gas phase can either be reduced by setting a higher flow rate, which leads to a more rapid dilution of the water concentration in the gas phase, or the reduction is lowered by lowering the meat rate. If it is determined that the measured value is more than 200 ppmv below the limit value, the

Checked the reduction status in the catalyst bed of the reactor (82B), which can be done, for example, by determining the temperature of the catalyst bed or if the

reducing gas contains nitrogen and hydrogen via the ammonia concentration takes place in the gas phase. For temperature measurement, temperature sensors can be present at the inlet and outlet of the catalyst beds. The reduction of a catalyst bed can be regarded as complete when the ammonia concentration does not increase further at constant pressure and temperature. If it is found that the reduction in

If the catalyst bed has not yet ended, the meat rate can then be increased in a process step (C1) (83B). If it is found that the concentration of water in the gas phase is within a range of ± 200 ppmv around the limit value, the flow rate and / or the meat rate can be maintained in a partial step (C3) (82C).

If it is found that the reduction of the iron oxides in a catalyst bed has already taken place completely, it can be checked whether there are further catalyst beds with iron oxides to be reduced in the reactor (83A). If this is not the case, the reduction is ended (84) or if there are further catalyst beds, the

The inlet temperature of the subsequent bed can be increased by closing a valve in order to start the reduction of the next catalyst bed (85). The meat rate can be adjusted by adjusting the control valve.

FIG. 3 shows in a flow diagram the processes and partial steps occurring after the determination of the ammonia. For this purpose, the concentration is activated in a first step (90) Ammonia is determined in the gas phase and then depending on the process parameters such as pressure, water content in the gas phase and temperature, the freezing point of the aqueous ammonia solution present is calculated (91).

The temperature of the cooling device is then compared with the calculated freezing point of the aqueous ammonia solution (92) and various partial steps are carried out depending on the result. The partial method steps can in particular be a method step (C4) in which the temperature of the cooling device is increased if the temperature of the cooling device is less than 5 K above the calculated freezing point of the aqueous ammonia solution (92B). There is also the possibility of further lowering the temperature of the cooling device in a method step (C5) if the

The cooler temperature is more than 10 K above the calculated freezing point of the aqueous ammonia solution. It is first determined whether the system allows the temperature of the cooler to be lowered further (92C). Many systems do not allow the temperature to drop any further, especially when the cooler temperature is already at -20 ° C

Cooler temperature. Depending on whether a further reduction is possible, either the cooler temperature is then reduced further (92D) or the operating parameters are changed

retained (92E). Such a method shown in FIG. 3 with the corresponding sub-steps makes it possible to condense water and / or ammonia from the gas phase in a particularly reliable manner and at the same time to prevent the cooling device from freezing. If the cooler temperature is in a range of 5 to 10 ° C above the freezing point of the aqueous ammonia solution, the cooler temperature can be maintained (92A).

Figure 4 shows in a diagram the experimentally determined temperature profile and the experimentally determined water content in volume% in the gas phase with a reduction of iron oxides with a synthesis gas that contains 76.5% hydrogen, 22.5% nitrogen and 10% argon (each volume% ) contains. The iron oxides were reduced for different times at different flow rates of the synthesis gas, whereby by increasing the

Flow rate of the water content in the gas phase can be reduced. The one with 100

The curve designated here shows the course of the water content as a function of the temperature with a reduction over 25 hours and a flow rate of 250 l / h. The curve labeled 101 shows the course of the water concentration in the gas phase with a 30-hour reduction with a flow rate of 400 l / h. The course of the

The water concentration for a 30-hour reduction with a flow rate of 400 l / h is characterized by the curve labeled 102. A further reduction over a period of 40 hours with a flow rate of 1200 l / h was also carried out (curve labeled 103). It can be clearly seen that with increasing flow rate the The concentration of the water decreases due to the dilution effect caused by newly emerging gas, but on the other hand the period of time required for the reduction increases. FIG. 4 also shows that by increasing the flow rate, the maximum concentration of the water formed can be successively reduced from very high values of around 12000 ppmv at a flow rate of 250 l / h, so that concentrations finally increase at a flow rate of 1200 l / h formed water of less than 1500 ppmv can be achieved, which no longer impair the catalytic activity of the catalysts or catalyst precursors formed.

FIG. 5 shows the experimentally determined catalytic activity of six different catalysts based on Wustite, which differ during the reduction

Water levels below 2000 ppmv to 8000 ppmv have been exposed. It can be clearly seen that with increasing water content, in particular from a limit value of about 4000 ppmv, the catalytic activity decreases by about 5% to 10%.

FIG. 6 shows the course of the water concentration (curve labeled 110) in the gas phase at the reactor outlet in ppmv and the temperature curve (curve labeled 120) over a certain period t. The water concentration was measured by means of an NDIR sensor. Iron oxides based on Wustite were reduced at a pressure of 90 bar in a hydrogen-containing atmosphere at a flow rate of 1200 NL / h (NL = standard liters (volume at 1013.25 mbar and 0 ° C)). It can be clearly seen that at the beginning of the reduction the temperatures and the water content in the gas phase are still relatively low and, with increasing time, due to the increasing temperature

Reduction rate increases, which leads to a higher water content at the reactor outlet. Finally, a maximum of the water content is reached, the water content then decreasing again at the reactor outlet due to the decreasing reduction rate.

It can be clearly seen that the water content in the

Gas phase of more than 3000 ppmv or more than 3500 ppmv can be measured. Such high water contents can be effectively prevented by a method according to the invention for activating iron oxides.

The invention is not restricted by the description based on the exemplary embodiments. Rather, the invention encompasses any new feature and any combination of

Features, which in particular includes any combination of features in the claims, even if this feature or this combination itself is not explicitly specified in the claims or exemplary embodiments.

Claims

1. Process for activating catalysts and catalyst precursors for

Ammonia synthesis, comprising the process steps:

(A) Iron oxides are being used to activate the catalysts

at least one reducing gas and reduced by means of heating,

(B) the concentration of that formed during the reduction in the gas phase

Water is measured using non-dispersive infrared spectroscopy (NDIR), and

(C) the flow rate of the reducing gas and / or the heating rate are in

Adjusted depending on the concentration of the water formed.

2. The method according to claim 1, wherein in method step (C) the concentration of the water determined in method step (B) is compared with a predetermined limit value for water.

3. The method according to claim 2, wherein in step (C) at least one of the

the following partial steps are carried out:

(C1) the heating rate is increased if that determined in method step (B)

The concentration of water is below a range around the specified limit value, or

(C2) the flow rate is increased and / or the heating rate is decreased if the concentration of water determined in method step (B) is above a range around the predetermined limit value, or

(C3) the flow rate and / or the heating rate is maintained if the im

Process step (B) determined concentration of water within a

Range is around the specified limit value.

4. The method according to any one of claims 2 or 3, wherein the limit value is selected from a range between 3000 ppmv to 4000 ppmv, and preferably 3400 ppmv, more preferably 3200 ppmv, even more preferably 3000 ppmv.

5. The method according to any one of claims 2, 3 or 4, wherein the area around the

Limit around is selected from a group of ranges consisting of:

± 1000 ppmv, ± 800 ppmv, ± 600 ppmv, ± 400 ppmv, ± 300 ppmv or ± 200 ppmv, the range preferably being ± 300 ppmv, more preferably ± 200 ppmv.

6. The method according to any one of claims 1, 2, 3, 4 or 5, wherein the process steps (A), (B) and (C) are carried out continuously.

7. The method according to any one of claims 1 to 6, wherein the measurement of the water formed during the reduction in process step (B) takes place in real time.

8. The method according to any one of claims 1 to 7, wherein in step (B) the concentration of the water formed during the reduction in one

Wavelength range of 2.6 to 3 gm, preferably 2.7 to 2.8 gm, more preferably 2.7 pm is measured.

9. The method according to any one of claims 1 to 8, wherein in process step (A) a mixture comprising hydrogen and nitrogen is used as the reducing gas and ammonia is formed during the reduction of the catalysts.

10. The method according to any one of claims 1 to 9, wherein in method step (B) for measuring the water formed, an NDIR device is used in which absorption bands of ammonia are calculated out by means of a calibration in the wavelength range from 2.6 pm to 3 pm.

1 1. Process according to one of Claims 1 to 10, the concentration of the ammonia formed in the course of the reduction being determined by means of NDIR in process step (B).

12. The method according to any one of claims 1 to 1 1, wherein in the course of the reduction

ammonia and / or water formed is condensed by means of a cooler.

13. The method according to claim 12, wherein in method step (C) the temperature of the cooler is set so that the temperature is at least 10 K, preferably at least 5 K above the freezing point of the aqueous ammonia solution.

14. The method according to any one of claims 1 to 13, wherein magnetite or wustite or a combination thereof, preferably wüstite, is used as iron oxides.

15. The method according to any one of claims 1 to 14, wherein the temperature im

Process step (A) is set to a temperature in the range from 360 ° C to 450 ° C, preferably in the range from 370 ° C to 400 ° C.

16. The method according to claim 14, wherein in process step (A) wustite is used as iron oxide and is heated to a temperature in the range from 370 ° C to 400 ° C.

17. The method according to any one of claims 1 to 16, wherein in method step (B) a mixture comprising hydrogen and nitrogen is used as the reducing gas and an aqueous ammonia solution is condensed out during the reduction.

18. The method according to any one of claims 1 to 17, additionally comprising the

Process step (D), wherein the catalysts and / or catalyst precursors from process step (C) are exposed to an oxidizing gas to form a protective layer on the catalysts and / or catalyst precursors.

19. Use of an NDIR detector to determine the concentration of water that occurs during the reduction of iron oxides when activating

Forms catalysts and catalyst precursors for the synthesis of ammonia.

20. Use according to claim 19, wherein the reduction by means of at least one

reducing gas takes place, and the flow rate and / or the heating rate of the reducing gas can be adjusted depending on the concentration of the water formed.