Industrial Chemistry: Manufacturing Processes, Catalysis and Important Industrial Products
Industrial chemistry applies the principles of chemistry on a large scale to convert raw materials into useful products. It stands behind the fertilisers that grow our food, the fuels that run our vehicles, the plastics and fibres in our homes, the cement and glass in our buildings, and the medicines that treat disease. It combines chemistry with chemical engineering, economics, safety and environmental protection.
For candidates preparing for APSC, ADRE, DHS, DME, SSC, Railways, NEET and other examinations in Assam, industrial chemistry is a practical and scoring topic. The questions usually concern the raw materials, the conditions and the products of the major manufacturing processes, along with the role of catalysts. Many of these processes are important to Assam, which has petroleum refining, tea processing and a growing fertiliser and cement industry. This article presents a complete deep-study revision of the subject.
Basic Terms
- Raw material: the naturally occurring or partially processed substance from which an industrial product is made.
- Catalyst: a substance that increases the rate of a reaction without being consumed, by providing an alternative path of lower activation energy.
- Promoter: a substance that increases the efficiency of a catalyst without itself being a catalyst.
- Catalytic poison: a substance that reduces or destroys the activity of a catalyst.
- Yield: the amount of product actually obtained, expressed as a percentage of the theoretical maximum.
- By-product: a secondary product formed along with the main product in a process.
- Calcination: heating an ore in the absence of air to remove volatile matter and decompose carbonates and hydroxides.
- Roasting: heating an ore in the presence of air to convert a sulphide to an oxide.
- Smelting: the reduction of a metal oxide to the metal in a furnace, using a suitable reducing agent along with flux.
- Flux: a substance added to combine with impurities and form a fusible slag.
- Slag: the molten waste material formed by the combination of flux with gangue, which is removed from the furnace.
- Cracking: the breaking of large hydrocarbon molecules into smaller, more useful ones by heat or a catalyst.
Core Concepts and Formulas
- Haber process for ammonia: nitrogen plus three volumes of hydrogen gives two volumes of ammonia, over an iron catalyst at about 400 to 500 degrees Celsius and 200 atmospheres, with molybdenum as a promoter.
- Contact process for sulphuric acid: two volumes of sulphur dioxide plus one volume of oxygen gives two volumes of sulphur trioxide, over a vanadium pentoxide catalyst at about 400 to 450 degrees Celsius.
- Ostwald process for nitric acid: four volumes of ammonia plus five volumes of oxygen gives four volumes of nitric oxide and six volumes of water, over a platinum or rhodium gauze catalyst at about 800 degrees Celsius.
- Solvay process for sodium carbonate: sodium chloride plus ammonia plus carbon dioxide plus water gives sodium bicarbonate and ammonium chloride; the bicarbonate is then heated to give sodium carbonate, carbon dioxide and water.
- Chlor-alkali process: two moles of sodium chloride solution on electrolysis give two moles of sodium hydroxide, one mole of chlorine and one mole of hydrogen.
- Percentage yield = actual yield divided by theoretical yield, multiplied by one hundred.
- Atom economy = mass of desired product divided by total mass of all products, multiplied by one hundred.
- According to Le Chatelier's principle, high pressure favours the formation of ammonia and of sulphur trioxide, because the forward reaction reduces the number of gas molecules.
- The rate of an industrial reaction is increased by using a catalyst, increasing the temperature within the safe limit and increasing the surface area of the reactants.
- In the manufacture of glass, the raw materials are silica, sodium carbonate and calcium carbonate, with small amounts of other oxides added for colour or special properties.
- In the manufacture of cement, the main raw materials are limestone and clay, which are heated in a rotary kiln to form clinker, and gypsum is added during grinding to control setting time.
Raw Materials, Unit Operations and Chemical Processes
Every industry begins with raw materials and converts them into products through a series of steps. The raw materials may be obtained from the earth, the sea, the air or from agriculture. Common unit operations include crushing, grinding, screening, mixing, heating, cooling, filtration, distillation, evaporation, drying and crystallisation, while the chemical processes include oxidation, reduction, neutralisation, hydrolysis, electrolysis and polymerisation. The choice of conditions, such as temperature, pressure and catalyst, is decided by thermodynamics and kinetics together.
An industrial process must be safe, economical and environmentally acceptable. The designer aims for a high yield, high atom economy, low energy consumption and the least possible waste and pollution. Excess heat may be recovered, by-products may be sold or recycled, and the catalyst is chosen to be selective and long-lasting. In this way, the principles of green chemistry and of chemical engineering are applied together.
Catalysis
Catalysis is the heart of industrial chemistry. A catalyst speeds up a reaction by lowering the activation energy, and it remains chemically unchanged at the end. Homogeneous catalysts are in the same phase as the reactants, while heterogeneous catalysts are in a different phase, usually a solid in contact with gases or liquids. The contact process, the Haber process, the Ostwald process and catalytic cracking all depend on solid catalysts.
The activity of a catalyst can be enhanced by promoters and reduced by poisons. For example, molybdenum acts as a promoter for the iron catalyst in the Haber process, and sulphur compounds poison the catalyst in many processes, which is why the feed gases are purified first. Catalysts are widely used in petroleum refining, in the manufacture of polymers, in exhaust treatment in vehicles and in the production of many fine chemicals. Their use reduces energy demand and waste.
Extraction of Metals
The extraction of metals follows the general sequence of concentration of the ore, conversion to the oxide, reduction to the metal and refining. Concentration removes the gangue by hand picking, gravity separation, froth flotation, magnetic separation or leaching. The concentrated ore is then roasted or calcined to give the oxide, which is reduced using carbon, carbon monoxide, hydrogen or a more reactive metal, or by electrolysis in the case of highly reactive metals.
Aluminium is extracted from bauxite by the Bayer process for purification followed by electrolysis of alumina dissolved in molten cryolite. Iron is extracted from haematite in a blast furnace, where the ore is reduced by carbon monoxide and the impurities are removed as slag by limestone. Copper is extracted by roasting and smelting followed by electrolytic refining, which also produces high-purity copper for electrical use. The refining step may involve distillation, liquation, electrolysis, zone refining or vapour phase refining.
Manufacture of Sulphuric Acid
Sulphuric acid is called the king of chemicals because of its enormous range of uses. It is manufactured by the contact process. First, sulphur or a sulphide ore is burnt in air to give sulphur dioxide, which is purified to remove dust and arsenic impurities that would poison the catalyst. The purified gas, mixed with air, is then passed over a vanadium pentoxide catalyst at about 400 to 450 degrees Celsius, where sulphur dioxide is oxidised to sulphur trioxide. The reaction is exothermic and reversible, and the conditions are chosen to give a good yield at a reasonable rate.
Sulphur trioxide is absorbed in concentrated sulphuric acid to form oleum, which is then diluted with water to give sulphuric acid of the required strength. The acid is used in the manufacture of fertilisers, in petroleum refining, in the pickling of steel, in lead-acid batteries, in the production of dyes, drugs and detergents, and in many other industries. Because of its corrosive nature, careful handling and safety measures are essential.
Manufacture of Ammonia
Ammonia is manufactured by the Haber process, one of the most important reactions in the world because ammonia is the starting material for nearly all nitrogen fertilisers. Nitrogen from the air and hydrogen, usually obtained from natural gas or water gas, are mixed in the ratio of one to three by volume, compressed to about 200 atmospheres and passed over a promoted iron catalyst at about 400 to 500 degrees Celsius. The reaction is reversible and exothermic, and the yield of ammonia increases with pressure and decreases with temperature.
According to Le Chatelier's principle, a moderate temperature is used because a very high temperature would reduce the yield even though it would speed up the reaction, and the catalyst makes the reaction fast enough at this temperature. The ammonia formed is separated by cooling and liquefaction, and the unreacted gases are recycled. Ammonia is used to make urea, ammonium sulphate, ammonium nitrate and many other fertilisers, and also in the manufacture of nitric acid and in refrigeration.
Nitric Acid, Sodium Carbonate and the Chlor-Alkali Process
Nitric acid is made by the Ostwald process. Ammonia is oxidised over a hot platinum or rhodium gauze catalyst to nitric oxide, which is cooled and further oxidised to nitrogen dioxide, and this is absorbed in water to give nitric acid. Nitric acid is used in the manufacture of fertilisers, explosives and dyes.
Sodium carbonate is manufactured by the Solvay process. Brine is saturated with ammonia and carbon dioxide, giving sodium bicarbonate, which is filtered and heated to give sodium carbonate. The by-product ammonium chloride is used as a fertiliser, and the carbon dioxide is recycled. Sodium hydroxide and chlorine are produced together by the electrolysis of brine in the chlor-alkali process, giving three important products: sodium hydroxide, chlorine and hydrogen.
Fertilisers, Cement, Glass and Polymers
Fertilisers supply the nitrogen, phosphorus and potassium that crops need. Nitrogenous fertilisers include urea, ammonium sulphate and ammonium nitrate; phosphatic fertilisers are made from rock phosphate; and potassic fertilisers come from potassium salts. The excessive use of fertilisers causes water pollution and eutrophication, so balanced application is essential.
Cement is made by heating limestone and clay in a rotary kiln to form clinker, which is then ground with gypsum. Glass is made by heating silica with sodium carbonate and calcium carbonate, and the type of glass is varied by changing the composition. Polymers such as polythene, polyvinyl chloride, nylon and bakelite are made by addition or condensation polymerisation, and they are used in packaging, fibres, pipes and countless other products. Petroleum refining separates crude oil into useful fractions by fractional distillation, and cracking converts heavy fractions into lighter and more valuable ones.
Safety, Health and the Environment
Industrial chemistry carries responsibilities as well as benefits. Factories handle corrosive acids, toxic gases, flammable solvents and high pressures and temperatures, so proper design, protective equipment, training and emergency planning are essential. The Bhopal gas tragedy is a reminder of the consequences of inadequate safety. Effluents and emissions must be treated before release, and solid and hazardous wastes must be disposed of safely.
Green chemistry offers a way forward by encouraging the use of safer chemicals, renewable raw materials, catalysts, energy-efficient processes and the prevention of waste. Continuous improvement in technology, strict regulation and public awareness together ensure that industry serves society without harming the environment or human health.
How Numerical Problems Are Solved
Industrial chemistry numericals usually involve yield, atom economy and stoichiometry. To find the percentage yield, divide the actual mass of the product obtained by the theoretical mass calculated from the balanced equation and multiply by one hundred. To find atom economy, divide the molar mass of the desired product by the total molar mass of all the products formed and multiply by one hundred. For process problems, first write the balanced equation, convert the given mass or volume of the raw material into moles, apply the stoichiometric ratio to find the theoretical moles of the product, and then convert to mass. For gas reactions, remember that volume ratios equal mole ratios at the same temperature and pressure. Always keep the units consistent and check the answer for practical sense.
Examination Trends
In state recruitment examinations, industrial chemistry questions are largely factual: the raw materials, catalysts, conditions and products of the contact, Haber, Ostwald, Solvay and chlor-alkali processes, and the manufacture of cement, glass and fertilisers. In NEET, questions often test the catalyst used, the optimum conditions, or the reason for a particular choice in the light of Le Chatelier's principle. Assertion-reason and matching items are frequent. Numerical questions on yield and atom economy also appear, so the basic formulas must be ready.
Common Mistakes to Avoid
- Mixing up the catalysts of the Haber, contact and Ostwald processes.
- Confusing roasting with calcination, which differ in the presence or absence of air.
- Forgetting that the Haber process uses high pressure because the forward reaction reduces the number of gas molecules.
- Assuming that a higher temperature always gives a better yield in a reversible exothermic reaction.
- Confusing a promoter with a catalyst poison.
- Mixing up the products of the chlor-alkali process.
- Ignoring the role of gypsum in controlling the setting time of cement.
- Reporting yield or atom economy without multiplying by one hundred.
How to Prepare This Topic
- Learn the general sequence of extraction of metals and the meaning of concentration, roasting, calcination, smelting and refining.
- Prepare a table of the major processes with their raw materials, catalyst, conditions and products.
- Understand the role of catalysts, promoters and poisons, along with the industrial importance of catalysis.
- Apply Le Chatelier's principle to explain the optimum conditions chosen in each reversible process.
- Relate industrial chemistry to the economy and environment of Assam, such as petroleum refining, tea processing and fertiliser production, and revise previous years' papers.
Frequently Asked Questions
What is the Haber process and why is it important?
The Haber process manufactures ammonia by combining nitrogen and hydrogen over a promoted iron catalyst at about 400 to 500 degrees Celsius and 200 atmospheres. It is important because ammonia is the starting material for almost all nitrogenous fertilisers, and it is a classic example of the industrial application of Le Chatelier's principle.
Why is sulphuric acid called the king of chemicals?
Because it is used in an enormous number of industries, including fertilisers, petroleum refining, steel pickling, dyes, drugs, detergents and lead-acid batteries. Its production is often taken as an indicator of a country's industrial development.
What is the difference between roasting and calcination?
Roasting is the heating of an ore in the presence of air to convert a sulphide ore into its oxide, while calcination is the heating of an ore in the absence of air to remove volatile impurities and to decompose carbonates and hydroxides into oxides.
What is a promoter and how is it different from a catalyst?
A promoter is a substance that increases the efficiency of a catalyst but has little activity of its own. A catalyst speeds up the reaction by itself. For example, molybdenum promotes the iron catalyst in the Haber process, while a catalytic poison, such as a sulphur compound, decreases the activity of the catalyst.
What is atom economy and why does it matter?
Atom economy is the ratio of the mass of the desired product to the total mass of all the products formed, expressed as a percentage. A high atom economy means that a larger fraction of the raw materials ends up in the useful product and less appears as waste, which is important for economic and environmental reasons.