LIQUID FUELS

Petroleum

Petroleum means ‘rock oil’, as it is found underground in porous rocks. It is often used synonymously for ‘crude oil’, ‘crude petroleum‘ or simply ‘oil’. Petroleum is a dark coloured liquid with the potential to release energy to generate heat through combustion and is the source of a wide range of industrial liquid fuels for process heating and power generation. Though its composition varies with geological location, a general indication of the chemical composition (by weight) of petroleum would be as follows: C(84%), H(14%), S(1–3%), N(<1%), O(<1%), metals and salts (<1%). The value of petroleum is high due to its ease of storage, transportation, utilization, high stored-energy density and relative ease of conversion to thermal energy. The primary use of petroleum fuel is for transportation, with industrial process heating and power applications also accounting for significant consumption.

The major source of liquid fuels is crude petroleum; other sources are shale and tar sands. Synthetic hydrocarbon fuels such as gasoline and methanol can be made from coal and natural gas. Ethanol, which is used as an automotive fuel, is derived from vegetable matter.

Crude petroleum and refined products are a mix of a wide variety of hydrocarbons: aliphatic (straight or branched chained paraffins and olefins), aromatics (closed rings, six carbons per ring with alternate double bonds joining the ring carbons, with or without aliphatic side chains) and naphthenic or cycloparaffins (closed single-bonded carbon rings, five to six carbons). Refining is required to yield marketable products that are separated by distillation into fractions including a specific boiling range. Further processing (such as cracking, reforming, and alkylation) alters molecular structure of some of the hydrocarbons and enhances the yield and properties of the refined products.