Chapter 15: Common Chemical Industries in Pakistan

Substances added to soil to provide essential elements (N, P, K) for plant growth.

• Nutrients:
  • Micro-nutrients: Required in small amounts (6g-200g/acre). e.g., B, Cu, Fe, Mn, Zn, Mo, Cl.
  • Macro-nutrients: Required in large amounts (5kg-200kg/acre). e.g., N, P, K, Ca, Mg, S.
• Qualities: Water soluble, stable, cheap, readily available to plants, should not harm soil pH.

• Nitrogenous Fertilizers: Supply Nitrogen. e.g., Urea (46% N), Ammonium Nitrate (33% N). Urea manufacturing: Ammonia + CO2 -> Ammonium Carbamate -> Urea.
• Phosphatic Fertilizers: Supply Phosphorus. e.g., Calcium Super Phosphate, Diammonium Phosphate (DAP - 16% N, 48% P2O5).
• Potassium Fertilizers: Supply Potassium. e.g., Potassium Nitrate (KNO3).

Cement: Material obtained by heating calcareous and argillaceous materials. Portland Cement: Mixture of lime, silica, iron oxide, and alumina.

• Raw Materials: Limestone (Calcareous), Clay (Argillaceous), Gypsum.
• Manufacturing (Wet Process):
  • Crushing & Grinding: Raw materials ground to form Slurry.
  • Rotary Kiln: Long cylinder with different zones.
    • Drying Zone (500°C): Moisture removal.
    • Decomposition Zone (800°C): CaCO3 -> CaO + CO2.
    • Burning Zone (1500°C): Clinker formation (Calcium silicates/aluminates).
    • Cooling Zone (150-200°C): Clinkers cooled.
  • Grinding: Clinker mixed with 2% Gypsum and ground to powder.
• Setting of Cement: Hydration and hydrolysis reactions. Gypsum prevents rapid setting. Forms colloidal gel -> Crystallization -> Hardening.

Paper: Network of cellulosic fibers deposited from aqueous suspension.

• Raw Materials:
  • Non-Woody: Wheat straw, Rice straw, Bagasse, Cotton, Grasses.
  • Woody: Poplar, Eucalyptus, Douglas fir.
• Manufacturing (Neutral Sulphite Semi-Chemical Process - NSSC):
  • Raw Material Preparation: Cutting, Cleaning (Dry/Wet).
  • Digestion: Cooked with Sodium Sulphite (buffered with Na2CO3) in digester to remove lignin.
  • Blow Tank: Cooked material verified.
  • Washing: Black liquor removed.
  • Bleaching: Chlorine dioxide or Sodium hypochlorite used to whiten pulp (remove residual lignin).
  • Paper Making: Stock preparation -> Fourdrinier Machine (Flow spreader -> Head box -> Wire section -> Press section -> Dryer section -> Calender -> Reel).