Petrochemicals

• Petrochemicals


  Chemicals derived from petroleum or natural gas
• Petrochemicals manufacturing


  1. Derived from feedstock and utilized to produce petrochemical intermediates

  2. Primary Petrochemicals

  3. Intermediate Petrochemicals and Derivatives

  4. Downstream Petrochemicals

  5. Methane-derived Petrochemicals
• Primary Petrochemicals


  • Aromatics (Benzene, Toluene, Xylene)
  • Olefins (Ethene, Propene, Butadiene)
  • Methanol
• Ethylene


  An essential primary chemical material, dominates >75% of global petrochemical production
• Ethylene-derived Petrochemicals


  • Ethanol
  • Ethylene oxide
  • Dichloroethane
  • Vinyl chloride
  • Polyethylene
  • Ethyl benzene
• Propylene


  Can be produced by splitting naphtha or by pyrolyzing natural gas
• Propylene-derived Petrochemicals


  • Isopropyl alcohol
  • Polypropylene
  • Cumene (isopropyl benzene)
  • Crude glycerol
• Benzene-derived Petrochemicals


  • Ethyl benzene and cumene
  • Chlorobenzene
  • Nitrobenzene
  • Cyclohexane
  • Linear alkyl benzenes (LAB)
  • Branched alkyl benzenes (BAB)
• Desalting (dehydration)


  1. Chemical desalting

  2. Electrostatic separation
• Chemical desalting

  Water and chemical surfactants (demulsifiers) are added to the crude oil, the mixture is heated to dissolve salts and other impurities into the water and then held in a tank where they settle, wastewater is discharged and the desalted crude oil is sent to the atmospheric crude distillation tower
• Electrostatic desalting


  Uses an electric field to separate the salt and water from the crude oil
• Inadequate desalting process can lead to corrosion, plugging, equipment fouling and catalyst poisoning in processing units
• Refinery operations


  • Distillation
  • Cracking
  • Reforming
• Fractional distillation of crude oil

  Separates materials based on their volatility
• Physical and chemical processes for crude oil refining

  • Physical (Distillation, Solvent extraction, Propane deasphalting, Solvent dewaxing, Blending)
  • Chemical (Hydrotreating, Catalytic reforming, Catalytic cracking, Hydrocracking, Catalytic dewaxing, Alkylation, Polymerization, Isomerization)
  • Thermal (Visbreaking, Delayed coking, Flexicoking)
• Blending and distribution


  1. Various fractions are stored in intermediate tanks, blended into marketable products for loading onto railcars, trucks, or ships, and distributed to gas stations or industries

  2. Blending can be done in-line through a manifold system or batch blended in tanks and vessels

  3. Additives are added during and/or after blending to provide specific properties
• Distillation

  A process in which a liquid or vapour mixture of two or more substances is separated into its component fractions of desired purity by applying and removing heat
• Distillation working mechanism


  The vapour of a boiling mixture will be richer in the components that have lower boiling points (Light keys), when this vapour is cooled and condensed, the condensate will contain more volatile components, while the original mixture will contain less volatile components (Heavy keys)
• Types of distillation columns

  • Batch or differential
  • Continuous columns
• Classification of distillation columns


  • Binary column (feed contains only two components)
  • Multi-component column (feed contains more than two components)
  • Multi-product column (column has more than two product streams)
  • Extractive distillation (extra feed appears in the bottom product stream)
  • Azeotropic distillation (extra feed appears at the top product stream)
  • Tray column (trays used to hold up the liquid)
  • Packed column (packings used to enhance vapor-liquid contact)
• Basic operation of a distillation column

  1. Feed is introduced to the feed tray, dividing the column into a top (enriching or rectification) and bottom (stripping) section

  2. Heat is supplied to the reboiler to generate vapour which moves up the column

  3. Vapour exits the top and is cooled in a condenser, some of the condensed liquid is recycled back as reflux, the rest is the distillate or top product

  4. The liquid removed from the reboiler is the bottom product
• Atmospheric distillation


  The feedstock flows to a direct-fired crude charge heater into the vertical distillation column just above the bottom, as the hot vapour rises in the tower, its temperature is reduced, heavy fuel oil or asphalt residue is taken from the bottom, and various major products like kerosene, gasoline, and uncondensed gases are drawn off at successively higher points
• Vacuum distillation


  Reduced pressure is required to further distill the residuum or topped crude from the atmospheric tower without thermal cracking, the principles resemble fractional distillation but with larger diameter columns to maintain comparable vapour velocities at the reduced pressures
• Propane deasphalting


  Liquid propane is used as a solvent to extract asphaltenic materials (aromatic compounds, 'coke-precursors') from heavier distillation products, alkanes dissolve in propane whereas asphaltenic materials do not
• Solvent extraction and dewaxing


  Removes unsaturated, aromatic hydrocarbons from lubricant and grease stocks by dissolving or precipitating them, using solvents like phenol, furfural, and cresylic acid
• Aromatic solvent extraction unit is used for solvent extraction
• Solvent dewaxing is a method of refining lubricating oils as well as a host of other refinery stocks
• Solvent extraction


  Separates aromatics, naphthenes, and impurities from the product stream by dissolving or precipitation
• Solvent extraction


  1. Feedstock is first dried

  2. Treated using a continuous countercurrent solvent treatment operation

  3. Washed with a liquid in which the substances to be removed are more soluble than in the desired resultant product

  4. Selected solvents are added to cause impurities to precipitate out of the product

  5. Solvent is separated from the product stream by heating, evaporation, or fractionation

  6. Residual trace amounts are subsequently removed from the raffinate by steam stripping or vacuum flashing

  7. Electric precipitation may be used for the separation of inorganic compounds

  8. Solvent is regenerated for reuse in the process
• Most widely used extraction solvents


  • Phenol
  • Furfural
  • Cresylic acid
• Other solvents less frequently used

  • Liquid sulfur dioxide
  • Nitrobenzene
  • 2,2' dichloroethyl ether
• The selection of specific processes and chemical agents depends on the nature of the feedstock being treated, the contaminants present, and the finished product requirements
• Solvent dewaxing


  1. Mixing the feedstock with a solvent

  2. Precipitating the wax from the mixture by chilling

  3. Recovering the solvent from the wax and dewaxed oil for recycling by distillation and steam stripping
• Solvents used in solvent dewaxing


  • Toluene
  • Methyl ethyl ketone (MEK)
• Other solvents sometimes used in solvent dewaxing


  • Benzene
  • Methyl isobutyl ketone
  • Propane
  • Petroleum naphtha
  • Ethylene dichloride
  • Methylene chloride
  • Sulfur dioxide
• There is a catalytic process used as an alternate to solvent dewaxing
• Thermal cracking


  When a hydrocarbon is heated to a sufficiently high temperature
• Pyrolysis


  Thermal cracking, especially when coal is the feedstock
• Steam cracking


  Thermal cracking when steam is used
• Visbreaking


  A mild form of thermal cracking that lowers the viscosity of heavy crude oil residues without affecting the boiling point range