Haber process - ammonia production, manufacturing process

Ammonia is a leading chemical industry in the world. Because ammonia is used to prepare other chemicals and has its uses. In this tutorial we are going to cover followings.

  • Explanation of ammonia
  • Manufacturing process of ammonia starting from raw materials
  • Uses of ammonia in the industry

Explanation of ammonia

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

Amoonia reactions and preparing

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

  1. Nitrogen Gas - N2(g)
  2. Hydrogen Gas H2(g)

Extracting raw materials from other 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).
  • In our case methane gas is reacted with steam.
  • Reaction is done in between 700-1000 0C with help of catalyst.
  • This complete reaction is endothermic.

CH4(g) + H2O(g) → CO(g) + 3H2(g)

CO + H2O(g) → H2(g) + CO2(g)


Hydrogen and nitrogen reaction

Hydrogen and nitrogen react and give ammonia. But this reaction is a reversible one. After starting the reaction, it will start the backward reaction to give hydrogen and nitrogen. Forward reaction is a exothermic.

Hydrogen and nitrogen reaction

Heat of Reaction

Standard enthalpy of the reaction is -46 kJ mol-1. This value is important in designinga new plant.



Reactor conditions

  • Reversible Reaction
  • Needs Catalyst (contain iron in the catalyst)

Catalysts used in haber process

  1. Iron Oxide. K2O(s) , Al2O3(s) are used as catalyst developers.
  2. Iron dust. K2O(s) , Mo or Ca are used as catalyst developers.

Temperature

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, 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 forward reaction, two molecules are given by reacting four molecules. ( one N2 molecule + three H2 molecules). Therefore pressure is decreased, 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 given.


Ammonia preparing reaction

Exothermic reaction

1:3 N2 : H2 volume ratio

Reaction does not come to completeness. Hence there are remaining N2(g) & H2(g) with NH3(g) in the product. Product is cooled here. When product is being cooled ammonia becomes to liquid state from gaseous state. But N2(g) & H2(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 N2(g) & H2(g) will give more NH3(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 NH3(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.
Haber process - Ammonia production

Uses of Ammonia

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

Environmental pollution of Ammonia Industry

  • Adding NH3(g) gas into atmosphere will pollute air.
  • Ammonia dissolves in water and water become basic.
  • Dissolving ammonia in water, water is polluted.
  • 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.



Can we implement haber process in a petroleum plant?

In petroleum refining plant, H2 gas and NH3 are produced in petroleum refining. But ammonia is in aqueous state and with HCl. So NH3 exists as ammonium chloride ( NH4Cl ). If we want to recover ammonia from ammonium chloride, we can add aqueous NaOH to the aqueous NH4Cl solution with 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.

  • CH4(g) + H2O(g) = CO(g) + H(g)
  • Produced hydrogen should be separated from a separation 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.



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.


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