Haber Process - Ammonia Industrial Production, Manufacturing Process

Ammonia is a leading chemical industry in the world because ammonia is used to prepare more chemicals and has uses in laboratory scale too. In this tutorial we are going to cover followings of ammonia production.

Explanation of ammonia
Manufacturing process of ammonia starting from raw materials to final product
Uses of ammonia in the chemical industry and laboratories

Explanation of ammonia gas

Ammonia is compound which has molecular formula of NH₃. It is a colourless gas at room temperature. In laboratories, ammonia is met as aqueous ammonium hydroxide (NH₄OH) solution. Ammonia is a very toxic compound and have to use it very carefully to prevent injuries.

Preparation of ammonia gas in the laboratory

Chemistry of ammonia

Ammonia is a very toxic, sharp suffocating odor, colourless gas. Ammonia is basic gas and it is found as aqueous ammonium hydroxide solution in the laboratory. Ammonia dissolve very well in water.

Manufacturing process of ammonia, Haber process

In this section, we discuss how raw materials are converted to ammonia and what conditions (optimum conditions) should be maintained to get desired product. Reactions involving in ammonia production is explained with each step.

Raw Materials in Haber process

Extracting raw materials from sources

Nitrogen is derived from air.
Hydrogen is derived from natural gas or petroleum refining.

Obtaining nitrogen gas from air

Pressure and temperature of air is increased. Then air can be converted to liquid phase. That liquid air is done fractional distillation. From this method N₂ is separated.

Obtain hydrogen gas from natural gas

Natural gas is a hydrocarbon mainly containing methane (CH₄) gas.
In our case, methane gas is reacted with steam.
Reaction is occurred in the range of 700-1000 ⁰C temperature with help of catalyst.
This complete reaction is endothermic reaction.

CH_4(g) + H₂O_(g) → CO_(g) + 3H_2(g)

CO + H₂O_(g) → H_2(g) + CO_2(g)

Hydrogen and nitrogen reaction

Hydrogen and nitrogen react with each other and give ammonia as the product. But this reaction is a reversible one. After starting the reaction, it will start the backward reaction after sometime to give back hydrogen and nitrogen gases. Forward reaction is an exothermic reaction.

Heat of Reaction

Standard enthalpy of the reaction is -46 kJ mol^-1. This value is important in designing a new haber process plant to calculate energy requirement of the process.

Reactor conditions

Reversible Reaction
Needs Catalyst (contain iron in the catalyst)

Catalysts used in haber process

Iron Oxide. K₂O_(s) , Al₂O_3(s) are used as catalyst developers.
Iron dust. K₂O_(s) , Mo or Ca are used as catalyst developers.

Temperature in haber process

Forward reaction is a exothermic one. Therefore using low temperature will increase the forward reaction and give higher percentage of ammonia. But having low temperature will reduce the reaction rate. So, manufactures have to wait much time to take the product. By considering both product amount and production rate, temperature is decided.

400⁰C - 450⁰C temperature is applied.

Pressure in haber process

In forward reaction, two molecules are given by reacting four molecules. ( one N₂ molecule + three H₂ molecules). Therefore pressure is decreased due to reduction of number of molecules. With that, volume is decreased due to decrease of number of molecules. So increasing the pressure will bring the reaction more forward (producing more NH₃). But Equipments which are affordable to high pressure are expensive. Also to generate high pressure, cost is high.

Therefore Around 200 atm pressure should be maintained inside the reactor.

Ammonia preparing reaction

Exothermic reaction

1:3 N₂ : H₂ volume ratio

Reaction does not come to completeness. Hence there are remaining N_2(g) & H_2(g) with NH_3(g) in the product. Product is cooled here. When product is being cooled ammonia becomes to liquid state from gaseous state. But N_2(g) & H_2(g) are in gaseous state.

As the final product liquid ammonia is separated.

Unreacted nitrogen and ammonia is resent to the react.

Equilibrium of hydrogen and nitrogen reaction

Can obtain more ammonia, increasing reactants?

Excess reactants will bring equilibrium constant to the right. Hence more N_2(g) & H_2(g) will give more NH_3(g).
But more reactants will increase the pressure in the reactor. Therefore affordable devices have to be applied for high pressure. This results high cost.
And also adding more reactants will cost more money.

Can obtain more ammonia, decreasing temperature?

Decreasing Temperature means of decrease of Heat in the reactor
Forward reaction of NH₃ production is exothermic reaction.
Therefore removing heat from the reactor will bring equlibrium constant to the right giving large NH_3(g) product.
Decrease of heat results decrease of energy in reactants.
To Happen a reaction, moleculers should have activaton energy. Otherwise, molecules which have activation energy will only react.
Decrease of energy causes decrease of number of molecules which have activation energy.
Therefore, the reaction rate will fall. It means ammonia product in a unit time (per day , per month )will be decreased.
Manufactures can't wait long time.
Then very low temperature can't be applied.

Uses of Ammonia

Ammonia has so many uses in industrial scale and domestic scale.

For urea production
For nitric acid production
For explosive material Industry
Fertilizer Production
To prevent coagulation of natural latex.
As a refrigerant
As a disinfectant

Environmental pollution of Ammonia Industry

Ammonia industry may cause several environmental pollution due to its products and physical conditions.

Adding NH_3(g) gas into atmosphere will pollute air.
Ammonia dissolves in water and water become basic. This will kill fishes in the rivers and other water streams.
Due to high temperatures, heat is added to the environment. Temperature of environment will be increased.
Carbon dust is released to the environment due to obtaining H₂ from petroleum.
If H₂ is obtained from NaCl_(aq) electrolysis, atmosphere can be polluted by releasing Cl₂.

How is ammonia separated from unreacted nitrogen and hydrogen?

Boiling point of ammonia is higher than both hydrogen and nitrogen. So we can easily liquidize ammonia by pressurizing while hydrogen and nitrogen remain as gaseous state. So liquid nitrogen can be separated from unreacted hydrogen and nitrogen.

Improve efficiency of the plant

Haber process is performed at 530-560 ⁰C temperature. Therefore, products coming out of the reactor have a large heat. This heat can be used pre-heat the reactants, nitrogen and hydrogen. This will reduce energy requirement of the plant and economical.

Can we implement haber process in a petroleum plant?

In petroleum refining plant, hydrogen gas and ammonia gas are produced as a result of refining. But, that produced ammonia is exists as aqueous solution with HCl. So ammonia reacts with HCl and produce ammonium chloride ( NH₄Cl ). If we want to recover ammonia from ammonium chloride, we can add aqueous NaOH to the aqueous NH₄Cl solution under heating.

What is the source of hydrogen in haber process

Hydrogen gas is produced mainly in the petroleum industry to the world. This hydrogen gas is stored and used for many industrial applicaations.

Why is iron powder used in the manufacture of ammonia?

In use of catalyst or catalyst developer, we have to increase surface area to increase the efficiency of catalyst pprocess. Then When iron powder is used because they have a larger surface area than a iron piece.

in haber's process hydrogen is obtained by reacting methane

Hydrogen gas can be obtained by Steam-Methane Reforming. Following reactions occur in this process.

CH_4(g) + H₂O_(g) = CO(g) + H_(g)
Produced hydrogen should be separated from a separation process.

what is the gaseous product of the haber process?

Ammonia is the gaseous product of the haber process. It is the final product of haber process.

Is haber process endothermic?

Reaction of nitrogen and hydrogen is an exothermic reaction (at standard state, it's value is -46 kJ mol^-1 ). So we can say, haber process reaction is an exothermic reaction.

production of ammonia from nitrogen and oxygen

Oxygen is no used as a raw material in the production of ammonia. But, in the nitrogen separtaion, oxygen gas also can be separated.

What raw materials are used as a source of hydrogen and nitrogen in the production of ammonia in the haber process?

Hydrogen: From petroleum industry
Nitrogen: By fractional distillation of liquid air.