Petrochemicals

• Petrochemicals


  Chemicals obtained from or derived from petroleum
• Petroleum (crude oil or mineral oil)

  A dark, viscous oily liquid found below the earth's crust, obtained by the mining process
• Natural gas


  A mixture of naturally occurring hydrocarbons like methane, ethane, propane, butanes, pentanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulphide, helium
• Dry natural gas


  • No oil, only gas in a petroleum well
• Wet natural gas


  • Natural gas occurs along with petroleum in oil wells, consists of a mixture of methane and higher hydrocarbons
• Compressed Natural Gas (CNG)

  Natural gas compressed at very high pressure, used as a fuel in place of petrol, diesel and LPG
• Liquefied Natural Gas (LNG)


  Natural gas which has been cooled down to liquid form for ease of storing and transporting, consists mainly of methane
• Liquefied Petroleum Gas (LPG)


  Petroleum gas which has been liquefied under pressure, a mixture of butane, propane, propene and ethane
• Coal


  A combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams, mainly composed of carbon
• Classification of coal based on carbon content

  • Anthracite
  • Bituminous
  • Sub-bituminous
  • Lignite
• Carbonization of Coal (Coking)


  Destructive distillation of coal to give coal gas, ammonia, coal tar, and coke
• Fractions of Coal Tar

  • Light oil (benzene, toluene, xylenes)
  • Middle oil (phenol, naphthalene, cresol)
  • Heavy oil (anthracene, phenanthrene)
  • Pitch (non-volatile carbon)
• Soft coke, hard coke, semicoke

  Types of coke obtained from carbonization of bituminous coal
• Petroleum (crude oil or mineral oil) is a dark viscous liquid occurring underground at depths of several thousand feet, associated with sand and located under different layers of rocks
• Distillation


  With respect to boiling point
• 1 kg = 22 pound
• Pale gas


  Carbon monoxide, 0
• Petrochemicals


  Alternate Sources
• Hard coke is used in metallurgy. The yield of tar is about 75-80 lbs per ton and the tar has higher percentage of aromatic hydrocarbons.
• High temperature carbonisation


  1. Produce high grade coke to serve metallurgical purposes

  2. Hard coke obtained is used in metallurgy

  3. Soft coke obtained is used as domestic fuel, for making water gas and acetylene
• Low temperature carbonisation


  Produces semicoke or smokeless fuel which can be easily converted into motor fuel
• Crude oil or petroleum

  • Dark viscous liquid occurring underground at depths of several thousand feet
  • Associated with sand and located under different layers of rocks
  • Deep well has to be drilled through the overlying layers till the oil bearing strata is reached
  • Petroleum is then raised to the surface by using suitable pumps and transported to refineries through pipes
• Composition of crude petroleum

  • Aliphatic hydrocarbons
  • Cycloalkanes
  • Aromatic compounds
  • Organic compounds of sulphur
  • Organic compounds of nitrogen
• Impurities in crude petroleum

  • Compounds like chlorophyll, haemin, green colouring matter of plants and red colouring matter of animals
  • Optically active organic compounds
• Mining of petroleum


  • Depth of petroleum deposits varies from place to place, generally found in porous strata beneath the impervious rock at depths of about 500 to 5000 feet
  • Brought to the surface by artificial drilling
  • Oil rushes out through these holes due to the pressure of natural gas but as the pressure of the gas subsides, air pressure is applied to force the oil out of the well
  • The crude oil thus obtained is sent to refineries through pipe lines
• Refining of petroleum


  • Crude oil or petroleum as pumped out of the oil well is a dark viscous liquid with an unpleasant odour because of the presence of sulphur compounds
  • It also contains impurities of sand and brine or sea water
  • It has to be processed or refined before being put to commercial use
  • The process of separating petroleum into useful fractions and the removal of undesirable impurities is called refining
  • Refining of petroleum is done by fractional distillation
• Fractions obtained from petroleum

  • Petroleum gas
  • Crude Naptha
  • Petrol or gasoline
  • Benzine
  • Kerosene oil
  • Fuel oil
  • Lubricating oil
  • Paraffin wax
• Purification of petroleum fractions

  • Essential to remove undesirable odours, make them stable to air oxidation and free them from corrosive constituents
  • Process of purification differs from fraction to fraction and also on the end use of fraction
• Cracking


  1. Decomposition of less volatile higher hydrocarbons into more volatile lower hydrocarbons with the application of strong heat

  2. Increases the yield and quality of gasoline

  3. Large hydrocarbon molecule break up to give hydrocarbons with lesser number of carbon atoms
• Mechanism of cracking


  • Various atoms in a molecule are held together by chemical bonds associated with certain amount of bond energy
  • On heating, the kinetic energy of the molecules increases and overcomes the bond energy causing the molecule to break up or the carbon to carbon bond to rupture
  • The free radical fragments stabilize by redistribution and readjustment of their valencies and hydrogen atoms
  • Stabilization is sometimes accompanied by rearrangement and isomerisation
• Changes occurring during cracking

  • Formation of a mixture of large number of hydrocarbons having lower boiling points than the initial hydrocarbon
  • Straight chain hydrocarbons are converted to branched chain hydrocarbons by isomerization
  • Ring closure or cyclization of aliphatic alkanes
  • Saturated hydrocarbons are converted to unsaturated hydrocarbons
• Types of cracking


  • Thermal cracking - carried out by the application of heat and pressure only
  • Catalytic cracking - carried out in the presence of catalysts
• Reforming or Aromatisation


  1. Process for obtaining aromatic hydrocarbons from aliphatic and alicyclic hydrocarbons

  2. Aliphatic and alicyclic alkanes containing six to eight carbon atoms are heated at about 670 K in the presence of palladium, platinum or nickel as catalyst

  3. Cyclisation and dehydrogenation take place, e.g. n-hexane changes into benzene and n-heptane changes into toluene
• Octane number


  • Measure of the knocking quality of a fuel in internal combustion engines
  • Isooctane (2,2,4 trimethylpentane) has an octane number of 100, n-heptane has an octane number of 0
  • Branched chain hydrocarbons have higher octane numbers and eliminate knocking
• Combustion engines


  Combustion of vapourised gasoline and air is used for producing power
• If a low quality fuel is used, the fuel does not burn smoothly
• Knocking


  Violent metallic sound produced occasionally due to irregular burning of fuel mixture
• A fuel which produces minimum knocking is considered as a good quality fuel
• Straight chain alkanes are found to be very poor fuels, and cause the engine to knock, while the branched chain hydrocarbons eliminate the knocking considerably
• Octane number


  Measure of the knocking quality of a fuel