AMMONIA

Objectives:i. Outline the steps in the manufacture of

ammonia from its elements, by the Haber Process.

ii. Discuss the uses of ammonia

iii. Assess the impact of the ammonia industry on the environment

The Haber Process

Step1: Manufacture of hydrogen

Hydrogen is made form natural gas by steam reforming

Ni catalyst

CH4(g) + H2O(g) ----------> CO(g) + 3H2(g) 100oC, 50 atm

Gaseous Products are mixed with more steam

CO(g)+3H2(g) +H2O (g) Fe2O3 catalyst CO2(g) +4H2(g)

CO2 is removed by dissolving it in H2O under pressure

Step2: Manufacture of Nitrogen

Nitrogen is made by fractional distillation of liquid air or by burning hydrogen in air.

2H2(g) + O2(g) + N2(g) 2H2(g) + N2(g)

Step 3: Manufacture of AmmoniaDry nitrogen and hydrogen are mixed in volume

proportions of 1:3, pressurized to 200 atm and passed over an iron catalyst at 500 °C

N2(g) +3H2(g) Fe catalyst , 500°C, 200 atm

2NH3(g)

The ammonia is liquefied by cooling and separated from any unreacted gases which are recycled.

Le Chetalier’s Principal:PRESSURE-increasing the pressure causes

the equilibrium position to move to the right resulting in a higher yield of ammonia since there are more gas molecules on the left hand side of the equation (4 in total) than there are on the right hand side of the equation (2). Increasing the pressure means the system adjusts to reduce the effect of the change, that is, to reduce the pressure by having fewer gas molecules.

TEMPERATURE-Decreasing the temperature causes the equilibrium position to move to the right. Resulting in a higher yield of ammonia since the reaction is exothermic (releases heat). The system will produce more heat since energy is a product of the reaction. and therefore will produce more ammonia gas .

Rate Considerations:CATALYST- ensures that the reaction is fast

enough for a dynamic equilibrium to be set up within the very short time that the gases are actually in the reactor.

PRESSURE- increasing the pressure brings the molecules closer together. In this particular instance, it will increase their chances of hitting and sticking to the surface of the catalyst where they can react. The higher the pressure the better in terms of the rate of a gas reaction.

TEMPERATURE- a higher temperature is used to speed up the reaction which results in a lower yield of ammonia. Increasing the temperature, more reactant molecules have sufficient energy to overcome the energy barrier. A temperature range of 400-500°C is a compromise designed to achieve an acceptable yield of ammonia (10-20%) within an acceptable time period.

SUMMARY OF THE HABER PROCESS

Uses Of Ammonia

Agriculture and Fertilizer Industry: Can be applied directly to the soil as liquid

ammoniaCan be used to produce fertilizers such as

urea, ammonium and nitrate salt. As a source of protein in livestock feeds for

cattles, sheep and goats.

Chemical Industry:To manufacture nitric acid which is used to

make explosivesTo neutralize acid constituents of crude oil and

to protect equipment from corrosionAs a refrigerant because it easily liquefied by

compression or cooling and absorbs large amount of heat from its surroundings

The manufacture of certain products such as sulfa drugs, vitamins and cosmetics

Weak ammonia solutions are also widely used as commercial and household cleaners and detergent.

Impacts of the Ammonia Industry on

the Environment

Plants and Animals: Ammonium nitrate fertilizers are water

soluble and easily washed out from farmlands into waterways. When this occurs over a period of time, it leads to a rapid algal growth known as EUTROPHICATION. This prevents light from reaching lower plants in the water. The plants die and bacteria uses the dissolve oxygen . Without oxygen, aquatic organisms also die.

Humans.Humans:

HIGH CONCENTRATION

LOW CONCENTRATION

TREATMENT

Inhalation Immediate burning of the nose, throat and respiratory tract.

Coughing, nose and throat irritation.

Dispense humidified oxygen, bronchodilators and airway management.

Skin/ Eye contact Severe injury and burns permanent eye damage or blindness.

Rapid skin or eye irritation

Decontaminate eyes with copious amounts of water.

Ingestion Corrosive damage to the mouth, throat and stomach.In infants, nitrates easily combine with heamoglobin resulting in methaemoglobinaemia syndrome.Nitrates are carcinogenic- they react with amines in the diet to form carcinogenic compounds.

Ingested ammonia is diluted with milk or water

Past Paper Question June 2004 Unit 2, Paper 1 Module 3, Question 8