DE2821972A1 - PROCESS FOR PRODUCING AMMONIA - Google Patents

Description

description

The invention relates to the synthesis of ammonia from molecular nitrogen and hydrogen using a new one Catalyst as well as new methods based on this catalyst. Ammonia is an important raw material in chemical Industry, especially for the production of synthetic fertilizers. Agricultural research has shown that nitrogen is an indispensable component of crops. The main source of such nitrogen is currently Ammonia. One of the main goals of chemical technology in the field of fertilizers is the production of ammonia at higher speeds and thus at correspondingly lower costs.

Known methods of producing ammonia from gaseous nitrogen and hydrogen use iron catalysts of different types. However, such catalysts require high temperatures and pressures, so that expensive Relatively low capacity facilities are required. Furthermore, these catalysts become relatively quick when required Temperatures and pressures consumed according to various degradation mechanisms.

Ammonia synthesis research towards room temperature synthesis in aqueous solutions in which either biological "nitrogen fixation conditions" are simulated or a metal salt or a complex is used as a catalyst together with a reducing agent, have already been carried out. The investigations of aqueous systems are still in the basic research stage, because still no process could be commercialized; however, it was found that the metals of heterogeneous catalyst Ren, which are able to catalyze ammonia at high temperatures from gaseous nitrogen and hydrogen, too catalyze ammonia synthesis when they are present as a salt or complex in aqueous solutions.

809847/1032

Gaseous nitrogen and hydrogen can theoretically be combined at room temperature and atmospheric pressure to produce ammonia with an equilibrium yield of 95.5% based on thermodynamic calculations, but so far there is neither a catalyst nor a method for ammonia synthesis at room temperature for the production of ammonia from gaseous nitrogen and Hydrogen at technically interesting speeds. It has therefore hitherto been necessary to maintain higher temperatures in the synthesis of ammonia in order to achieve satisfactory reaction rates. The iron catalysts previously used are capable no significant amounts of ammonia from gaseous nitrogen and hydrogen at temperatures below about 360 ⁰ C to produce. Even higher temperatures are therefore required to achieve acceptable yields. On the other hand, however, higher temperatures result in a drastic reduction in the thermodynamic equilibrium yield of the reaction due to its exothermic nature. A reduction in the equilibrium yields with increasing temperatures can only be partially compensated for by increasing the working pressure, the required pressures largely approaching the load limits of the systems as they are currently available in industry.

Known processes for the synthesis of ammonia from gaseous nitrogen and hydrogen over conventional iron catalysts are carried out at temperatures of about 500 ⁰ C. The equilibrium yield of the reaction at this temperature at only 1 atmosphere pressure is well below 0.2%. Higher pressures in the region of 150 atmospheres are therefore maintained in order to compensate for the low yield at ambient pressure. Such high pressures result in high investment and operating costs. Furthermore, the equilibrium yields achieved at such elevated pressures are usually below 25%. This means that a considerable part of the effluents from the reaction vessels has to be recycled one or more times, which significantly increases the production costs, both in terms of additional systems and long-term use.

809847/103 2

2S21972

operating times contributes to the separation and recycling of the product stream.

Due to the thermodynamic and kinetic discussed above Reasons are the cost of producing ammonia by known methods is very high, with relatively low production rates and expensive investments have to be accepted. The cost of iron catalyst itself is also considerable, mainly because special manufacturing processes have to be used, to improve the catalytic properties of iron. Therefore, you need additional components called promoters are added to the iron. In most cases, both the iron and the promoters need to be on a special carrier in such a way that there is sufficient contact between these components and the gaseous reactants is possible, which in turn is very expensive.

The above-described disadvantages of the previously known reactions between nitrogen and hydrogen over known ones Catalysts are eliminated by the invention. The new catalyst according to the invention allows for the first time compliance with significantly lower working temperatures and pressures, while still achieving technically interesting production rates. At such temperatures and pressures the equilibrium yields fall in the range of 30 to 60% so that the actual yields are markedly improved will. This new catalyst consists of titanium dihydride, either alone or in conjunction with a binary alloy of iron and titanium in a 1: 1 ratio . In certain circumstances the binary alloy alone can be used as a catalyst.

Those achievable using this new catalyst at a given temperature and pressure Reaction rates are at least a factor of 10 and sometimes several tens of factors above the reaction

809847/1032

tion speeds that can be achieved using known catalysts and processes. Consequently, the Ammonia production costs are significantly reduced. Further the required equipment is less costly due to the lower working pressures involved in the selected ones Working temperatures can be maintained. In addition, the catalyst itself does not pose many of the problems with which the known catalysts were affected, for example the problems of sintering and physical disintegration. Rather, it was found that the catalytic Activity of the titanium catalyst used according to the invention with aging in the presence of the hydrogen component the reactant atmosphere increases. This increase in yield is the result of cracks in the catalyst particles are formed, both microscopic cracks (surface cracks) and macroscopic cracks (cracking smaller particles), which increases the active surface area of the catalyst. It also takes place in lesser Extent of poisoning or deactivation of the catalyst by covering the adsorbing sites with adsorption of impurities normally present in the technically available nitrogen and hydrogen reactants. With appropriate control of the process conditions activation of the catalyst bed can be carried out simultaneously with the production reaction.

The invention therefore relates to the creation of a new process for the production of ammonia from hydrogen and nitrogen, yields are achieved which are higher than the previously achievable yields. The invention is a catalytic process for the production of ammonia from gaseous hydrogen and nitrogen created, which with essential increased production rates works. It also becomes an economical method of producing ammonia from Gaseous hydrogen and nitrogen created, which at lower temperatures and pressures than they were previously possible works, the process and operating costs are significantly reduced. According to the invention, ammonia is under

809847/1032

Manufactured using a catalyst that is resistant to contamination poisoning, as is normally the case present in technically available hydrogen and nitrogen reactant gases. The inventive catalytic The process requires higher ammonia production rates at ambient temperature than previously possible. The inventive Catalyst also favors the synthesis of ammonia in aqueous solutions, the molecular hydrogen and Contain nitrogen. In addition, a metal compound is identified by the invention, which the chemical bonds of nitrogen and hydrogen molecules being able to loosen or break open, with such a connection used as a catalyst to produce ammonia from molecular hydrogen and nitrogen. Furthermore, through The invention created a catalyst which can be easily and economically treated with a bimetallic alloy and possibly using other components to further promote the catalytic reaction. Through the Invention, a technical process for the catalytic production of ammonia is provided, with the cost for the catalyst itself are significantly lower than the costs of the catalysts previously known for such processes .

The catalyst of the present invention consists of titanium hydrides, mainly titanium dihydride, which is a stable compound. It has been found that titanium metal reacts with hydrogen to form an extremely active catalyst for its production combined by ammonia from gaseous nitrogen and hydrogen. Furthermore, the reaction seems to be accelerated, when the hydrogenated titanium is associated with a binary alloy of iron and titanium, particularly as hydrogenated Titanium phase in the iron-titanium alloy (which can itself be converted into iron-titanium anhydride). Under certain circumstances the alloy itself can also be used as a catalyst.

809847/1032

The specific alloy associated with the hydrogenated titanium in accordance with this preferred embodiment has a titanium: iron molar ratio of 1.0 and is available from the International Nickel Company. This alloy is described in more detail in a book entitled "Constitution of Binary Alloys", First Supplement, edited by RP Elliot and published by McGraw-Hill, New York, New York, 1965 and in an article by Reilly et al which will be discussed in more detail below. This alloy is produced of relatively pure iron and titanium by a melting method, which requires temperatures of 1500-1900 ⁰ C. Although this alloy can be made from technical iron, the purity of electrolyte iron is preferred.

The combined catalyst can be made by the same process as the binary alloy, as an alloyed one Mixture containing more than 1 mole of titanium per mole of iron, providing a mass consisting of two phases, namely the intermediate metal compound with a titanium: iron molar ratio of 1 and pure titanium, the latter being converted to titanium dihydride in an initial hydrogenation stage will. Titanium dihydride is a stable compound that persists as such during the production process, and is continuously activated (decontaminated) as long as it is in contact with significant amounts of hydrogen.

The following composition ranges for hydrogenated titanium associated with an iron-titanium 1: 1 compound require an appreciable catalytic activity on the union of molecular hydrogen and nitrogen to produce Generation of ammonia and are given in the order of increasing activity for this reaction: 0.1 mol hydrogenated Ti to 1 mole of FeTi, 1 mole of hydrogenated Ti to 1 mole of FeTi and 2 moles of hydrogenated Ti to 1 mole of FeTi. The bigger the Amount of titanium that is associated with the alloy, the greater the reaction rate and the

809847/1032

prey to ammonia synthesis. With catalyst masses that are richer of titanium dihydride are as a molar ratio of 2: 1 do not appear to be commercially available at present due to manufacturing difficulties corresponding iron-titanium alloys occur. It can be assumed, however, that even higher catalytic reaction rates Can be achieved when larger amounts of free titanium with the iron titanium compound or others Alloys are associated. Therefore, the invention encompasses the full range of free titanium containing compositions. Taking into account the above, the catalyst preferred according to the invention has 2 moles of hydrogenated Titanium associated with a carrier made of a binary alloy of titanium and iron in a molar ratio of 1: 1.

The catalysts according to the invention are active for ammonia formation at all temperatures around and above 180 ^° C. and at all pressures at and above atmospheric pressure. The higher the temperature or the pressure, or the higher these two parameters, the greater the achievable reaction rates. The upper limits with regard to temperature and pressure for the production reactions are only drawn by the physical parameters of the system used.

Hydrogenated titanium appears to develop increased catalytic activity when combined with the iron titanium bimetal compound alloyed or otherwise associated. Although the bimetal compound itself shows some catalytic activity, titanium dihydride is regarded as the more catalytically active component. Further information regarding the respective properties each of these compounds can be found in an article entitled "Formation and Properties of Iron Titanium Hydride "and published by J. J. Reilly and R. H. Wiswall, Jr. (Brookhaven National Laboratory) in" Inorganic Chemistry ", Volume 13, No. 1, 1974 on pages 218 bis 222 is published. Also in this context is on

809847/1032

the book by W. M. Müller et al. "Metal hydrides" published by Academic Press, New York, New York, 1968.

The titanium metal, either alone or together with the bimetal alloy, is first cleaned with hydrogen of the material and to form titanium dihydride, preferably in a separate series of steps is carried out prior to using this compound as a catalyst for carrying out the ammonia production reaction. Through the hydrogenation stages, the reaction-inhibiting ones become first oxides and other impurities are removed from the catalyst particles, followed by titanium dihydride and iron titanium anhydrides in the case of association with the bimetal alloy.

The catalyst mass should be used in the form of individual particles of relatively small size (less than 16 mesh). The particles are then coated with an oxide layer. In this state, the metal does not form hydride, which is the active compound as a catalyst. These activation steps also remove other impurities on the surface and inside, such as carbon and nitrogen compounds and adsorbed gases other than nitrogen and hydrogen. The initial cleaning of the particles and the formation of the catalyst are preferably carried out by exposing a bed of titanium in the form of individual particles to the action of hydrogen gas at temperatures between 200 and 400 ^° C. and pressures between 10.5 and 14 kg / cm ² , absolute (150 to 200 psia) for an extended period of time. The reactant gases are then passed through the bed to run the production reaction.

Is the catalyst with the binary iron-titanium-1: 1 alloy then the initial treatment is followed by degassing and then optionally pressurizing the Catalyst bed with hydrogen at a much higher pressure

809847/1032

and degassing the hydrogen for sequential hydrogenation and dehydrogenation of the alloy. By this method, the catalyst particles deposited on a carrier are broken into smaller particles, with many cracks being formed in the surface of each particle. This noticeably increases the reactive surface area of the catalyst bed. The dehydrogenation cycle is carried out at about 200 ^° C. or above, preferably at about 400 ^° C. Degassing is done by purging with pure helium at approximately atmospheric pressure. The hydrogenation cycle is generally carried out at ambient temperature (20 to 25 ° C) and under a pressure of 70 kg / cm ² , absolute (1000 psia). Optionally, and preferably because of the possibility of impurities in the helium, the degassing is carried out in such a way that a slight vacuum of 25 to 50 mm of water is created in the reaction vessel which contains the catalyst bed. This size reduction process is preferably continued until the average particle size becomes 200 mesh or less.

Subsequent to the steps for preparing the catalyst, a gaseous feed stream of nitrogen and hydrogen is continuously passed over the catalyst bed to carry out a production reaction which is carried out under such temperature and pressure conditions as are most expedient for the desired ammonia yield in the product. Considerable product yields can be achieved at temperatures of only 180 ^° C. and pressures of atmospheric pressure. Technical yields generally require higher temperatures between 275 and 325 ° C. and higher pressures between 35 and 105 kg / cm ² , absolute. Even higher temperatures and pressures increase the reaction rates, but such pressures are limited by the process equipment. Furthermore, higher temperatures can have detrimental effects on the ammonia synthesis reaction in that the rate of ammonia dissociation into nitrogen and oxygen becomes undesirable. In other words, this means that

809847/1032

Excessively high temperatures can reverse the synthesis reaction due to thermodynamic limitations that affect the exothermic nature of the reaction decrease. At temperatures and pressures within the ranges given above yields of approximately 100% of the theoretical yield can be achieved.

Is the hydrogen partial pressure in the reaction vessel the same or greater than the equilibrium dissociation pressure of iron titanium anhydride, and the catalyst is associated with the binary 1: 1 alloy, then this alloy phase becomes iron titanium anhydride converted, which is a stable compound only under such conditions. If the catalyst bed is degassed, then this hydride compound converts to the binary alloy, thereby promoting the breaking up of the particles will. It is believed, however, that the catalytic reaction itself is not inhibited by the hydride form of the intermetallic compound when such pressures in the production process be applied. The partial pressure of the hydrogen to be used at a given temperature The hydride state of the alloy can be obtained from the equilibrium dissociation pressure of the iron titanium anhydride at this temperature, the latter relationship being given in the literature. Regarding the specific Temperature and pressure relationship as used according to the invention refer to the article "Formation and Properties of Iron Titanium Hydride" mentioned above, to point out.

The preferred method for both making the combined form of the catalyst and then making it of ammonia is described below. A catalyst bed made from commercially available particles of titanium and iron, which have been alloyed in a ratio of 3: 1 is filled into a conventional reaction vessel, such as, for example is currently used for the production of ammonia with known catalysts. This mass contains one

809847/1032

Titanium metal phase, which is an iron-titanium 1: 1 compound phase is associated, there being 2 moles of free titanium per mole of carrier compound.

The reaction vessel is then heated and degassed in a manner that is applied at 400 ⁰ C a vacuum for approximately 6 to 8 hours to desorb and for expelling the polluting gases. Following the degassing, the reaction vessel, while it is kept at 400 ^° C., is pressurized with hydrogen (14 kg / cm ² , absolute) and kept at this temperature and at this pressure until the formation of titanium dihydride has ended, which takes about 4 to 6 hours. The catalyst generation process also removes the oxide films as well as other adsorbed impurities from the catalyst, thereby increasing the diffusion of hydrogen into the alloy and allowing the reactant gases to be adsorbed during the production reaction. The initial hydrotreatment is best carried out such that the hydrogen gas is confined to the reaction vessel in a static state and non-flowing pure hydrogen is used which could result in excessive temperatures in the hydride formation reaction. After the oxide films have been removed, titanium dihydride begins to form in the presence of the hydrogen, releasing heat which is sufficient to noticeably increase the reactor temperature. If the reactor temperature begins to drop to the externally maintained temperature (400 ^° C.), then the formation of the titanium dihydride catalyst has ended.

A method of increasing the activity of the supported catalyst thus formed is then begun by allowing the reactor to cool to about ambient temperature (20-25 ° C) while a vacuum is continuously applied over the catalyst bed to remove the hydrogen. After reaching ambient temperature the reaction vessel is again pressurized with hydrogen to a pressure above the equilibrium dissociation pressure the hydride form of the iron titanium alloy

809847/1032

tion is at the prevailing temperature. A hydrogen pressure of 70 kg / cm ^{2 is} absolutely sufficient to carry out this hydrogenation step at conventional ambient temperatures. After this pressure treatment has been carried out for a period of about 1/2 hour / the reactor is ^{heated again to about 400 °} C., whereupon it is allowed to cool immediately after it has reached that temperature, a slight vacuum during heating and cooling is maintained to remove the hydrogen in a dehydrogenation step. These hydrogenation and dehydrogenation cycles break up the catalyst particles without destroying the integral bond between the titanium hydride phase and the intermetallic compound phase. The cycles are preferably repeated until the desired particle size has been achieved. This usually takes 3 to 4 cycles, depending on the original particle size and the dimensions of the catalyst bed. The catalyst is then ready for the production reaction.

Subsequent to the last dehydrogenation stage of the size reduction process, the reactor is ^{heated to 300 °} C. and brought to 80 atm with hydrogen. A mixture of reactants of 1 mole nitrogen and 3 moles hydrogen is then introduced into the reaction vessel. The product stream is withdrawn continuously at a flow rate which is defined by the space velocity (ratio of the feed rate to the total weight of the catalyst). This space velocity should not ^{exceed 500 m 3} / h / t catalyst, determined under standard conditions with regard to temperature and pressure. A variety of other feed mixtures can be used, for example hydrogen to nitrogen molar ratios of 2: 1 or 1: 1 can be maintained. However, it is desirable to always maintain a sufficient amount of hydrogen in the feed stream to achieve continuous activation of the catalyst.

809847/1032

Higher space velocities and corresponding feed velocities are also possible, but can lower yields can be achieved, with a higher energy is required to operate the pumps. Faster However, throughputs and lower yields can overall depending on the optimal parameters of the separation and the recycling plant used to handle the product effluent from the reaction vessel, be more economical.

The product stream exiting the catalyst bed contains the nitrogen and hydrogen reactants and the ammonia product. If necessary, the ammonia can be separated off from the product stream in a conventional manner, whereupon the reactants are returned to the reaction vessel. Such a separation method is to cool the product stream to a temperature between 25 and 100 ⁰ C, such temperatures are usually low enough to completely condense the ammonia product, whereupon the stream is sent through a condensate separator and the gaseous effluent consisting of unreacted nitrogen and hydrogen exists, is fed back to the reaction vessel. The actual condensate temperature in this case depends on economic considerations, taking into account the cooling, heating and pumping required, as well as the partial pressure of the ammonia in the product stream. Part of the ammonia product can also be recycled, depending on the Separation system parameters.

In addition to the embodiment described above, there are also other embodiments are also possible. For example, can the hydrogen and nitrogen reactants are contacted with the catalyst while these reactants are in one other physical state than in the gas state. For example, aqueous solutions and other carrier-containing free nitrogen and hydrogen molecules in contact

809847/1 032

brought with the catalyst or passed over it, the hydrogen and nitrogen reacting to produce ammonia. All such procedures fall within the Scope of the invention.

It is of course possible to use different features of the described to fall back on specific embodiment, for example on one of the various masses of titanium dihydride with intermediate metal compounds of iron and titanium, also on various combinations of temperature and pressure. It is also possible to use titanium dihydride and / or the intermediate metal compound to combine with known catalytically active metals for this reaction, for example with Ruthenium and osmium, either in the form of mixtures or multi-component alloys (e.g. ternary, quaternary or higher alloys), or to associate the titanium dihydride with other intermetallic compounds, or furthermore, to apply the catalytic masses to an inert support material or another substrate.

Many other procedural stage changes are possible. Such changes are within the scope of the invention. For example, the activation of the catalyst, at a slower rate, can be carried out in this way that it is exposed to the action of hydrogen in the feed stream itself, especially when the product stream is to be recycled until the desired product content has been achieved. The above The description therefore shows only one preferred embodiment of the invention, so that other embodiments also fall within the scope of the invention.

809847/1032

Claims (11)

MÜLLER-BORE DEUFEL SCB'.GN HBRTEL PAT E N TAjSTWA LT ii DR. WOLFGANG MÜLLER-BORE (PATENT ACQUISITION FROM t927-197S) DR. PAUL DEUFEL. D1PL.-CHEM. DR. ALFRED SCHÖN. D1PL.-CHEM. WERNER HERTEL, DIPL.-PHYS. R 1183 THE RAFEL INDUSTRIAL GROUP, LTD. Reid House, Hamilton, Bermuda / USA Process for the production of ammonia Patent claims 1. A process for the production of ammonia, characterized in that that nitrogen and hydrogen in synthesis ratios under synthesis conditions with a catalyst which is an alloy of titanium and iron in a molar ratio of total titanium Total iron greater than 1.0, and then such a titanium-iron alloy to the action of hydrogen is exposed under hydrogenation conditions, the amounts of titanium and iron as well as the alloying conditions are such that an alloy is obtained which contains both an iron-titanium intermetallic compound and contains free titanium in amounts effective to catalyze the conversion of nitrogen and hydrogen to ammonia 8 0 9 8 A 7/1 0 3 2 ORIGINAL INSPECTED MUNICH 86 -SIEBERTSIR. 4 · POST BOX 880720 ■ CABLE: MTTEBOPAT · TEL. (089) 474005 TELEX 5-24285 are sam, furthermore the hydrogenation conditions are such that at least a portion of the free titanium hydrogenates will. 2. The method according to claim 1, characterized in that
the alloy of the action of hydrogen under one
Is exposed to pressure at least equal to the equilibrium dissociation pressure of iron titanium anhydride at the prevailing temperature of the alloy. 3. The method according to claim 1, characterized in that the intermediate metal compound has a molar ratio of titanium to
Has iron, which is substantially equal to 1.0. 4. The method according to claim 1, characterized in that the hydrogenation conditions are the alloy of
Exposure to hydrogen at an elevated temperature
and subject to pressure to remove oxides from exposed surfaces. 5. The method according to claim 1, characterized in that a molar ratio of total titanium to total iron in the alloy of at least 1.1 is observed. 6. The method according to claim 1, characterized in that the synthesis conditions provide a catalyst ^{temperature of at least 180 0} C and the reactants are under a total pressure of at least 1 atmosphere. 7. The method according to claim 1, characterized in that the amount of hydrogen to the amount of nitrogen corresponds to at least a molar ratio of 3: 1, and the synthesis conditions provide that the catalyst with a gaseous mixture of the reactants in an amount of not
more than 500 m ^{3 of} gas / hour / ton of catalyst, measured under standard temperature and pressure conditions, is contacted. 809847/1032 " 8. The method according to claim 1, characterized in that the Hydrogenation conditions are such that essentially all of the free titanium is converted to titanium dihydride. 9. The method according to claim 1, characterized in that the Hydrogenation conditions are such that the alloy has both an iron titanium anhydride phase and a separate titanium hydride phase contains. 10. The method according to claim 1, characterized in that the production of the catalyst consists in a granulate subjecting the alloy to the action of hydrogen at a pressure at least equal to the equilibrium dissociation pressure of iron titanium anhydride at the prevailing temperature of the granulate is to initiate hydrogenation to alloy, and to degas the granules under dehydration conditions in which the granules are broken down into smaller particles break. 11. The method according to claim 10, characterized in that the action of hydrogen on the granules has a first Provides stage in which the granules the action of gaseous hydrogen under conditions of elevated temperature as well as pressure used to remove oxides from the exposed alloy surfaces sufficient. 8 0 9 8 L 7/1 0 3 2