Haber process for ammonia production

For these reasons and due to its low aciditymagnesium oxide has proven to be a good choice of carrier. Carriers with acidic properties extract electrons from ruthenium, make it less reactive, and have the undesirable effect of binding ammonia to the surface. Catalyst poisons lower catalyst activity. They are usually impurities in the synthesis gas.

Permanent poisons cause irreversible loss of catalytic activity, while temporary poisons lower the activity while present. Sulfur compounds, phosphorus compounds, arsenic compounds, and chlorine compounds are permanent poisons. Oxygenic compounds like water, carbon monoxidecarbon dioxideand oxygen are temporary poisons. Although chemically inert components of the synthesis gas mixture such as noble gases or methane are not strictly poisons, they accumulate through the recycling of the process gases and thus lower the partial pressure of the reactants, which in turn slows conversion.

Haber process for ammonia production: The process combines nitrogen from

The reaction is an exothermic equilibrium reaction in which the gas volume is reduced. The equilibrium constant K eq of the reaction see table and obtained from:. Since the reaction is exothermicthe equilibrium of the reaction shifts at lower temperatures to the ammonia side. Furthermore, four volumetric units of the raw materials produce two volumetric units of ammonia.

According to Le Chatelier's principlehigher pressure favours ammonia. High pressure is necessary to ensure sufficient surface coverage of the catalyst with nitrogen. Even though the catalyst greatly lowers the activation energy for the cleavage of the triple bond of the nitrogen molecule, high temperatures are still required for an appropriate reaction rate.

The inert components, especially the noble gases such as argonshould not exceed a certain content in order not to reduce the partial pressure of the reactants too much. To remove the inert gas components, part of the gas is removed and the argon is separated in a gas separation plant. The extraction of pure argon from the circulating gas is carried out using the Linde process.

Modern ammonia plants produce more than tons per day in one production line. The following diagram shows the set-up of a modern designed in the early s by Kellogg [ 59 ] "single-train" Haber—Bosch plant:. Depending on its origin, the synthesis gas must first be freed from impurities such as hydrogen sulfide or organic sulphur compounds, which act as a catalyst poison.

Haber process for ammonia production: The Haber-Bosch process is

High concentrations of hydrogen sulfide, which occur in synthesis gas from carbonization coke, are removed in a wet cleaning stage such as the sulfosolvan processwhile low concentrations are removed by adsorption on activated carbon. To produce hydrogen by steam reforming, methane reacts with water vapor using a nickel oxide-alumina catalyst in the primary reformer to form carbon monoxide and hydrogen.

The methane gas reacts in the primary reformer only partially. To increase the hydrogen yield and keep the content of inert components i. The secondary reformer is supplied with air as the oxygen source. Also, the required nitrogen for the subsequent ammonia synthesis is added to the gas mixture. In the third step, the carbon monoxide is oxidized to carbon dioxidewhich is called CO conversion or water-gas shift reaction.

Carbon monoxide and carbon dioxide would form carbamates with ammonia, which would clog as solids pipelines and apparatus within a short time. In the following process step, the carbon dioxide must therefore be removed from the gas mixture. In contrast to carbon monoxide, carbon dioxide can easily be removed from the gas mixture by gas scrubbing with triethanolamine.

The gas mixture then still contains methane and noble gases such as argon, which, however, behave inertly. The gas mixture is then compressed to operating pressure by turbo compressors. The resulting compression heat is dissipated by heat exchangers ; it is used to preheat raw gases. The actual production of ammonia takes place in the ammonia reactor.

The first reactors were bursting under high pressure because the atomic hydrogen in the carbonaceous steel partially recombined into methane and produced cracks in the steel. Bosch, therefore, developed tube reactors consisting of a pressure-bearing steel tube in which a low-carbon iron lining tube was inserted and filled with the catalyst. Hydrogen that diffused through the inner steel pipe escaped to the outside via thin holes in the outer steel jacket, the so-called Bosch holes.

The development of hydrogen-resistant chromium-molybdenum steels made it possible to construct single-walled pipes. Modern ammonia reactors are designed as multi-storey reactors with a low-pressure drop, in which the catalysts are distributed as fills over about ten storeys one above the other. The gas mixture flows through them one after the other from top to bottom.

Cold gas is injected from the side for cooling. A disadvantage of this reactor type is the incomplete conversion of the cold gas mixture in the last catalyst bed. Alternatively, the reaction mixture between the catalyst layers is cooled using heat exchangers, whereby the hydrogen-nitrogen mixture is preheated to the reaction temperature.

Reactors of this type have three catalyst beds. In addition to good temperature control, this reactor type has the advantage of better conversion of the raw material gases compared to reactors with cold gas injection. Uhde has developed and is using an ammonia converter with three radial flow catalyst beds and two internal heat exchangers instead of axial flow catalyst beds.

This further reduces the pressure drop in the converter. The reaction product is continuously removed for maximum yield. The ammonia also condenses and is separated in a pressure separator. Unreacted nitrogen and hydrogen are then compressed back to the process by a circulating gas compressorsupplemented with fresh gas, and fed to the reactor.

The mechanism of ammonia synthesis contains the following seven elementary steps :. Transport and diffusion the first and last two steps are fast compared to adsorption, reaction, and desorption because of the shell structure of the catalyst. It is known from various investigations that the rate-determining step of the ammonia synthesis is the dissociation of nitrogen.

Since the adsorption of both molecules is rapid, it cannot determine the speed of ammonia synthesis. In addition to the reaction conditions, the adsorption of nitrogen on the catalyst surface depends on the microscopic structure of the catalyst surface. Iron has different crystal surfaces, whose reactivity is very different. The Fe and Fe surfaces have by far the highest activity.

The explanation for this is that only these surfaces have so-called C7 sites — these are iron atoms with seven closest neighbours. The adsorption of nitrogen is similar to the chemisorption of carbon monoxide. Since the nitrogen is isoelectronic to carbon monoxide, it adsorbs in an on-end configuration in which the molecule is bound perpendicular to the metal surface at one nitrogen atom.

A comparison with vibration spectra of complex compounds allows the conclusion that the N 2 molecule is bound "side-on", with an N atom in contact with a C7 site. This structure is called "surface nitride". The surface nitride is very strongly bound to the surface. Infrared spectroscopically detected surface imides NH adsurface amides NH 2,ad and surface ammoniacates NH 3,ad are formed, the latter decay under NH 3 release desorption.

On the basis of these experimental findings, the reaction mechanism is believed to involve the following steps see also figure : [ 67 ]. Experimental evidence points to reaction 2 as haber process for ammonia production slow, rate-determining step. This is not unexpected, since that step breaks the nitrogen triple bond, the strongest of the bonds broken in the process.

As with all Haber—Bosch catalysts, nitrogen dissociation is the rate-determining step for ruthenium-activated carbon catalysts. The active center for ruthenium is a so-called B5 site, a 5-fold coordinated position on the Ru surface where two ruthenium atoms form a step edge with three ruthenium atoms on the Ru surface. An energy diagram can be created based on the Enthalpy of Reaction of the individual steps.

Haber process for ammonia production: The Haber process can

The energy diagram can be used to compare homogeneous and heterogeneous reactions: Due to the high activation energy of the dissociation of nitrogen, the homogeneous gas phase reaction is not realizable. The catalyst avoids this problem as the energy gain resulting from the binding of nitrogen atoms to the catalyst surface overcompensates for the necessary dissociation energy so that the reaction is finally exothermic.

Nevertheless, the dissociative adsorption of nitrogen remains the rate-determining step: not because of the activation energy, but mainly because of the unfavorable pre-exponential factor of the rate constant. Although hydrogenation is endothermic, this energy can easily be applied by the reaction temperature about K. When first invented, the Haber process competed against another industrial process, the cyanamide process.

However, the cyanamide process consumed large amounts of electrical power and was more labor-intensive than the Haber process. When you are reading this page, if you find that you aren't understanding the effect of changing one of the conditions on the position of equilibrium or on the rate of the reaction, come back and follow up these links.

The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas methane into ammonia. The reaction is reversible and the production of ammonia is exothermic. The catalyst is actually slightly more complicated than pure iron. It has potassium hydroxide added to it as a promoter - a substance that increases its efficiency.

The pressure varies from one manufacturing plant to another, but is always high. You can't go far wrong in an exam quoting atmospheres. This figure also varies from plant to plant. The mixture of nitrogen and hydrogen going into the reactor is in the ratio of 1 volume of nitrogen to 3 volumes of hydrogen. Avogadro's Law says that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

That means that the gases are going into the reactor in the ratio of 1 molecule of nitrogen to 3 of hydrogen. In some reactions you might choose to use an excess of one of the reactants. You would do this if it is particularly important to use up as much as possible of the other reactant - if, for example, it was much more expensive. That doesn't apply in this case.

Haber process for ammonia production: The Haber process ; Stage one,

There is always a down-side to using anything other than the equation proportions. If you have an excess of one reactant there will be molecules passing through the reactor which can't possibly react because there isn't anything for them to react with. Save my name, email, and website in this browser for the next time I comment. Table of Contents Toggle.

Interesting Science Videos. Jyoti Bashyal Jyoti Bashyal, a graduate of the Central Department of Chemistry, is an avid explorer of the molecular realm. Fueled by her fascination with chemical reactions and natural compounds, she navigates her field's complexities with precision and passion. Outside the lab, Jyoti is dedicated to making science accessible to all.

This is achieved using heaters and pumps or compressors. During the chemical reaction, natural gas reacts with air to produce ammonia and water. The iron catalyst accelerates the chemical reaction. The reactor is a key component of the Haber-Bosch process for ammonia production. It is a closed vessel in which natural gas is mixed with air and subjected to high temperatures and pressures to promote the chemical reaction that produces ammonia and water.

The size and capacity of the reactor will depend on the amount of ammonia to be produced. Reactor sizes can range from small laboratory reactors to large industrial reactors. Reactors can also have different shapes and designs, depending on the needs and requirements of the process. In the Haber-Bosch process, the reactor is a key component, and it must be properly designed and constructed to ensure the efficiency and safety of the process.

The reactor must be able to withstand the high temperatures and pressures necessary to promote the chemical reaction and must also have safety measures in place to prevent accidents. Once the ammonia is produced, it is separated from the water and purified by distillation to remove impurities and contaminants. To separate the ammonia from the water, the mixture is heated at a high temperature so that the ammonia evaporates.

The evaporated ammonia is collected and condensed, forming droplets of pure ammonia liquid. The water does not evaporate at the same temperature as the ammonia and remains at the bottom of the vessel. Once the ammonia has been separated from the water, it is necessary to purify it to remove impurities and contaminants. Chemical and physical processes such as fractional distillation, filtration, and precipitation can be used for this purpose.