Fossil Fuels Hydrocarbons Combustion  Elmhurst College
Natural Gas Gasoline Compounds  Combustion Energy  Chemistry Department
Gasoline Distill Oil Refinery Convert Oil Refinery  Virtual ChemBook

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Conversion Oil Refining

Although all fractions of petroleum find uses, the greatest demand is for gasoline. One barrel of crude petroleum contains only 30-40% gasoline. Transportation demands require that over 50% of the crude oil be converted into gasoline. To meet this demand some petroleum fractions must be converted to gasoline.

Catalytic Cracking: breaking down large molecules of heavy heating oil into smaller gasoline molecules.

The most widely used conversion method is called catalytic cracking because it uses heat and pressure to "crack" heavy hydrocarbon molecules into lighter ones. The cracking reaction is very endothermic, and requires a large amount of heat. Another problem is that reaction quickly fouls the Silica (SiO2) and alumina (Al2O3) catalyst by forming coke on its surface.

For example if eicosane (C-20) is heated to about 500 C the covalent carbon-carbon bonds begin to break during the cracking process. Many kinds of compounds including alkenes are made during the cracking process. Alkenes are formed because there are not enough hydrogens to saturate all bonding positions after the carbon-carbon bonds are broken.

 Hydroprocessing applies the same principles but uses a different catalyst, slightly lower temperatures, much greater pressure and hydrogen to obtain chemical reactions of breaking down large molecules of heavy heating oil into smaller gasoline molecules. It also converts aromatics to cyclic alkanes, olefins to alkanes.

Hydroprocessing first involves the addition of hydrogen atoms to molecules without actually breaking the molecule into smaller pieces at temperatures of about 325 degrees Celsius and pressures of about 50 atmospheres. Many catalysts will work, including; nickel, palladium, platinum, cobalt, and iron. Then hydrocracking breaks longer molecules into smaller ones at temperatures over 350 degrees Celsius and pressures up to 200 atmospheres. In both cases, very long residence times (about an hour) are required because of the slow nature of the reactions.



Alkylation or "polymerization" - forming longer molecules from smaller ones. Another process is isomerization where straight chain molecules are made into higher octane branched molecules.

The reaction requires an acid catalyst (sulfuric acid, H2SO4 or hydrofluoric acid, HF) at low temperatures (1-40 degrees Celsius) and low pressures (1-10 atmospheres). The acid composition is usually kept at about 50% making the mixture very corrosive.

Example 1

Quiz 1

 Quiz 2
 Catalytic Reforming uses heat, moderate pressure and fixed bed catalysts to turn naphtha, short carbon chain molecule fraction, into high-octane gasoline components - mainly aromatics. Because the reactions which produce higher octane compounds (aliphatic in this case) are endothermic (absorb heat) additional heaters are installed between reactors to keep the reactants at the proper temperature. The catalyst is a platinum (Pt) metal on an alumina (Al2O3) base.

Example 1

Quiz 1

 Example 2

 Quiz 2

 Example 3

Quiz 3