Chemical Inorganic Industries Study Notes for Chemical Engineering

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Chemical inorganic industries play a vital role in our modern society, contributing to the production of a wide range of essential materials and substances. Chemical engineering, as a field of study, encompasses the principles and practices involved in the design, operation, and optimization of chemical processes in these industries. The study of chemical inorganic industries focuses on the production, purification, and utilization of inorganic compounds, which are substances that lack carbon atoms in their molecular structure. This branch of chemical engineering covers various industrial sectors, including metallurgy, ceramics, glass, cement, fertilizers, and more.

In order to understand and excel in this field, it is crucial for chemical engineering students to have a strong foundation in the principles of inorganic chemistry and materials science. This includes topics such as crystal structures, phase diagrams, reaction kinetics, thermodynamics, and process control. The study notes for chemical inorganic industries provide a comprehensive overview of the fundamental concepts and practical applications relevant to this area of chemical engineering. These notes cover a wide range of topics, including the production processes of inorganic compounds, their physical and chemical properties, the selection and design of reactors, separation techniques, environmental considerations, and safety protocols.

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What is the Meaning of the Chemical Inorganic Industries?

The term chemical inorganic industries refers to a sector of the chemical industry that focuses on the production, processing, and utilization of inorganic chemicals. Inorganic chemicals are substances that do not contain carbon atoms bonded to hydrogen atoms, unlike organic chemicals.

Chemical inorganic industries encompass a wide range of activities, including the extraction of raw materials, such as minerals and ores, and the subsequent manufacturing of inorganic compounds. These compounds can be used as raw materials in various industries or as finished products themselves.

Examples of inorganic chemicals produced by this industry include acids (such as sulfuric acid and hydrochloric acid), alkalis (such as sodium hydroxide and potassium hydroxide), salts (such as sodium chloride and calcium carbonate), fertilizers (such as ammonium nitrate and phosphates), metals (such as aluminum and copper), and many others.

Chlor-Alkali Industry

The Chlor-Alkali industry in India forms an important component of the basic chemicals industry, comprising around 74% of the production of the basic chemical in India. Caustic soda, soda ash, and chlorine alongside hydrogen and hydrochloric acid comprise the components. These chemicals find their applications in a number of industries such as textiles, chemicals, paper, PVC, water treatment, alumina, soaps & detergents, glass, and chlorinated paraffin wax, among others. The demand for the two subs increased significantly registering a respectively, over the past five years.

The Chlor-Alkali Industry in the country produces mainly Caustic Soda, Chlorine, and Soda Ash. The products of the industry are of vital importance and their uses are:

Use of Caustic Soda

  • Soaps and Detergent Industry
  • Pulp and Paper Industry
  • Textile Processing Industry
  • Pharmaceuticals

Use of Chlorine

  • The by-product of the Caustic Soda Industry is very important for the manufacturing of PVC, one of the five major Thermoplastic Commodity Plastics. Besides this, it is used in the disinfection of drinking water and pharmaceutic industries. Because of the strong oxidizing properties of Chlorine, it is effectively used to control bacteria and viruses in drinking water that can cause devastating illnesses such as Cholera.
  • The use of Chlorine is very of floods. 85% of the pharmaceuticals rely on Chlorine Chemistry including medicines that treat heart disease, cancer, AIDS, and many other life-threatening diseases. Chlorine tablets are also used by public health workers in rural areas.

Use of Soda Ash

  • It is used in Glass Industry, Soaps & Detergents, Silicates, and various other Chemical Industries.

Highlights of Processes for Chloralkali/Caustic Soda

The Chloralkali process (also Chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride solution (brine). Depending on the method, several products besides hydrogen can be produced. If the products are separated, chlorine and sodium hydroxide (caustic soda) are the products; by mixing, sodium hypochlorite or sodium chlorate is produced, depending on the temperature.

  • There are three basic processes for the electrolytic production of chlorine, the nature of the cathode reaction depends on the specific process. These three processes are the diaphragm cell process(Griesheim cell, 1885), the mercury cell process (Castner-Kellner cell, 1892), and the membrane cell process (1970). Each process represents a different method of keeping the chlorine produced at the anode separate from the caustic soda and hydrogen produced, directly or indirectly, at the cathode.
  • The basic principle in the electrolysis of a sodium chloride solution is the following:
    • At the anode, chloride ions are oxidized and chlorine (Cl2) is formed.
    • At the cathode: In the mercury process a sodium/mercury amalgam is formed and hydrogen (H2) and hydroxide ions (OH-) are formed by the reaction of the sodium in the amalgam with water in the denuder. In membrane and diaphragm cells, water decomposes to form hydrogen (H2) and hydroxide ions (OH-) at the cathode.
  • The main characteristics of the three electrolysis processes are presented in the Table below




Caustic quality

High, <30 ppm NaCl 5-150 pg Hg/l (Before treatment the Hg level is between 2.5-25 mg Hg/l)

1.0-1.5% by weight NaCl

(Before treatment the NaCl content is about 18%) 0.1% NaCl

Not suitable for some applications

High, <50 ppm NaCl

Caustic concentration


12%, requires a concentration of 50% for some applications

33%,requires concentration

to 50% for some applications

Chlorine quality

Contains low levels of oxygen (< 0.1%) and hydrogen

Oxygen content between 1.5-2.5%

Oxygen content between 0.5% and 2%, depending on whether an acidified electrolyte is used

Brine feedstock


purification is required but depends on the purity of the salt or brine used

Some purification is required but depends on the purity of the salt or brine used

 Very high-purity brine is required as impurities affect Membrane performance

Various Chemical Processes Production of Soda Ash

Le Blanc Process

  •  Reactions

2NaCl + H2SO4 ———— ► N2SO4+ 2 HCl

4C + NaSO4 ———— ► NaS + 4CO

Na2S + CaCO3—————-► Na2CO3 + CaS

  • A mixture of equivalent quantities of salt and concentrated sulphuric acid is heated in a cast iron salt cake furnace. Hydrochloric acid gas is given off and sodium hydrogen sulfate is formed.
  • The gas is dissolved in water and the mixture is raked and transferred to the muffle bed reverberatory furnace where it is subjected to stronger heat. Here sodium sulfate called salt cake is formed.

Dual Process

  • In this process, ammonium chloride is produced as a coproduct in equivalent quantities and differs from the conventional, Solvay process and it does not recycle ammonia.

Solvay process or Ammonia-soda process

  • The ammonia-soda process is the dominant technology used throughout the world, hence this process is selected for the production of soda ash.
  • Chemical reactions- Overall reaction

CaCO3 + 2NaCl ——————-> Na2CO3 + CaCl2

 This reaction takes place in a number of steps

CaCO3 —————————————->CaO + CO2

  • Brine Preparation
    • Sodium chloride solutions are occasionally available naturally but are more often obtained by solution mining of salt deposits to give raw, near-saturated brine containing low concentrations of impurities such as magnesium and calcium salts.
  • Ammonia Absorption
    • The strong brine is saturated with ammonia gas in the absorption tower.
    • The ammonia, recycled from various process steps, contains water vapor and carbon dioxide.
    • During ammoniation, the brine requires cooling (approx 1650 MJ/t or 394 kcal/kg of product soda ash).
    • The absorption operation is generally carried out at atmospheric pressure. The brine descends through the main part of the absorber counter-current to the rising ammoniacal gases.
    • The temperature of inlet brine is about 300C and that of exit is about 36 to 420C.
  • Precipitation of Bicarbonate
    • The ammoniated brine from the absorber coolers is pumped to the top of one column in a block of columns used to precipitate bicarbonate.
    • This column which has been fouled or partially plugged with sodium bicarbonate after several days of crystallization is referred to as a cleaning column.
    • Lime kiln gas, compressed to about 414 kPa (60psi), enters the bottom of the cleaning column and bubbles up through the solution to absorb most of the carbon dioxide.
    • The concentration of carbon dioxide in the liquor is kept below the precipitation concentration. Relatively little cooling is required. The scale is dissolved off the cooling surfaces of the cleaning column by the fresh ammoniated brine, assisted by gas agitation.
    • The liquor leaving this column is fed in parallel to the top of the remaining columns into the block.
    • A stronger carbon dioxide gas made up of a mixture of kiln gas and bicarbonate calciner gas is fed to this crystallizing or making columns and bubbles up through the solution.
    • This process precipitates sodium bicarbonate and is accompanied by the evolution of considerable heat which must be removed to improve yield.
  • Filtration of Bicarbonate
    • The slurry, collected from the crystallizing towers, is fed to continuous vacuum filters or centrifuges which separate the crystals from the filter liquor.
    • The filter cake is carefully washed with fresh water to control the residual chloride to meet customer specifications.
    • The dewatering characteristics of the bicarbonate crystals are very dependent on operating conditions in the crystallizing columns.
    • Air drawn through the vacuum filter (or the vent gas from the centrifuge operation) is returned to the absorption section.
  • Recovery of Ammonia
    • The filtered liquor contains unreacted sodium chloride and substantially all the ammonia with which the brine was originally saturated, present as fixed and free ammonia.
    • The fixed ammonia or ammonium chloride corresponds stoichiometrically to the sodium bicarbonate that had been precipitated.
    • Free ammonia includes ammonium hydroxide, bicarbonate, carbamate, and several possible carbon compounds of ammonia that decompose at moderate temperatures.
    • Before preheating, sulfide solution may be added for corrosion protection. The sulfide is distilled for eventual absorption by the brine in the absorber.
    • The filtered liquor is preheated by indirect contact with the gases leaving the distiller.
  • Lime Preparation
    • The most suitable limestone, hard and strong with low concentrations of impurities, is graded to a reasonably uniform coarse size.
    • Although other fuels may be used, the limestone is usually mixed with about 7% metallurgical-grade coke or anthracite and then burned in vertical shaft kilns.
    • Air is admitted continuously into the bottom of the kiln and gas is sucked off the top.
  • Calcining the Bicarbonate to Soda Ash
    • To prevent dilution of the decomposition gases, the crude filtered bicarbonate is continuously calcined by indirect heating.
    • Various techniques are used to heat the material which is recycled after compression to enrich the makeup kiln-gas feed to the carbonation operation.
    • The hot soda ash discharged from the calciner is cooled, screened, and packaged or shipped in bulk.
    • This product, called light ash because of its low bulk density, is converted to dense ash.
  • By-Products
    • Calcium Chloride
      • Relatively few synthetic soda ash plants recover calcium chloride and most of those that do utilize only a small part of the total amount available in the distiller waste.
      • To produce calcium chloride, the distiller waste liquor is settled and then evaporated in multiple-effect evaporators.
      • During concentration, most of the sodium chloride separates.
      • The remaining solution is further concentrated to the equivalent of CaCl2.2H2O.
      • This solution is cooled, forming flakes that are dried in a rotary dryer, giving a product sold as 77-80% calcium chloride.
    • Ammonium Chloride
      • Ammonium chloride is the principal salt present in the mother liquor from the crude sodium bicarbonate filtration in the ammonia-soda process.
      • Small amounts have been produced in soda ash plants by carbonation of the filter liquor, concentration, and crystallization of the ammonium chloride.
      • Most of the demands in the United States are low – tonnage.
      • The end uses are primarily in dry cells and fluxing agents.
  • Advantages of the Solvay process
    • Can use low-grade brine
    • Less electric power
    • Fewer corrosion problems
    • No co-products to dispose of
    • Does not require ammonia plant investment
  • Disadvantages of the Solvay process
    • Higher salt consumption
    • Higher investment in ammonia recovery units versus crystallization units for ammonium chloride
    • Waste disposal of calcium chloride brine stream
    • More steam consumption
    • Higher capacity plant for economic break-even operation.

Sulphuric Acid


  • The largest sulphuric acid consumer is the fertilizer industry.
  • Sulphuric acid is used with phosphate rock in the manufacture of phosphate fertilizers.
  • Smaller amounts are used in the production of ammonium and potassium sulfate.
  • It is also used as an acidic dehydrating agent in organic chemical and petrochemical processes, as well as in oil refining.
  • In the metal processing industry,
    • sulphuric acid is used for pickling and descaling steel;
    • for the extraction of copper, uranium, and vanadium from ores; and
    • in non-ferrous metal purification and plating.
  • In the inorganic chemical industry, it is used most notably in the production of titanium dioxide.

 Production of Sulphuric Acid

 Raw Material

  • Liquid sulfur is a product of the desulphurization of natural gas and crude oil by the Claus Process, with the cleaning of coal flue gas as a second source.
  • The third way is the melting of natural solid sulfur (Frasch-process) but this is not in frequent use because there are many difficulties in removing the contaminants

Conversion of SO2 into SO3

  • The design and operation of sulphuric acid plants are focused on the following gas phase chemical equilibrium reaction with a catalyst:-

SO2 + (1/ 2)O2 ———— ► SO3

  • Both thermodynamic and stoichiometric considerations are taken into account in maximizing the formation of S03. The Lechatelier Principle is usually taken into account in deciding how to optimize the equilibrium.
  • The contact process uses the V2O5 catalyst
  • For S02/S03 systems, the following methods are available to maximize the formation of S03
  • Removal of heat – a decrease in temperature will favor the formation of S03 since this is an exothermic process
  •  Increased oxygen concentration
  •  Removal of S03 (as in the case of the double absorption process) Raised system pressure
  •  Selection of the catalyst to reduce the working temperature (equilibrium) Increased reaction time
  •  Optimum overall system behavior requires a balance between reaction velocity and equilibrium.

Dilution of absorber acids

  • The acid produced, normally 95.5%-96.5% or 98.5%-99.5%, is diluted with water or steam condensate down to the commercial concentrations: 25%, 37%, 48%, 78%, 96%, and 98% H2SO4.
  • The dilution can be made in a batch process or continuously through in-line mixing

SO2 -Stripping

  • A small amount of air is blown through the warm acid in a column or tower to reduce the remaining SO2 in the acid to < 20mg The air containing SO2 is returned to the process.


  • When producing sulphuric acid by the contact process an important step is to produce sulfur trioxide by passing a gas mixture of sulfur dioxide and oxygen over a catalyst according to the equation

SO2 + (1/ 2)O2 ———— ► SO3

  • Today vanadium pentoxide is used almost exclusively.
  • Commercial catalysts contain 4-9 wt % vanadium pentoxide, V2O5, as the active component, together with an alkali metal.
  • Normally potassium sulfate is used as a promoter but in recent years also cesium sulfate has been used.
  • Cesium sulfate lowers the melting point, which means that the catalyst can be used at lower temperatures. The carrier material is silica in different forms of sulfate promoters.

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