Chemistry of Crude Oil and Cracking

Crude Oil

• Crude oil is a mixture of hydrocarbons
• Hydrocarbons are made of carbon and hydrogen
• Crude oil is separated into different hydrocarbon fractions by fractional distillation
• The oil is heated until most of it turns into gas
• The gases enter a fractionating column
• The column has a temperature gradient (hot at the bottom, cooler at the top)
• Longer hydrocarbons have higher boiling points and condense at lower temperatures/near the bottom
• Shorter hydrocarbons have lower boiling points and condense at higher temperatures/near the top
• Bubble caps prevent separated liquids from mixing
• Each fraction contains a mixture of hydrocarbons with similar boiling points

Cracking

• Long-chain hydrocarbons have high boiling points and are viscous
• Shorter hydrocarbons have lower boiling points and are thinner
• Cracking is a thermal decomposition process; breaking down molecules via heating
• Cracking is used to produce shorter, more useful hydrocarbon molecules
• Cracking conditions include heat (600°C-700°C) and a catalyst (alumina or silica)
• The reaction produces shorter alkane and alkene molecules

Combustion

• Combustion is a reaction involving a substance and oxygen
• Burning hydrocarbons releases energy as heat
• Complete combustion (plenty of oxygen) produces carbon dioxide and water
• Incomplete combustion (not enough oxygen) produces carbon monoxide and soot
• Carbon monoxide is toxic and can be lethal
• Acid rain is formed when sulfur dioxide and nitrogen oxides mix with water in clouds

Alkanes

• Alkanes are saturated hydrocarbons (single bonds only)
• Alkanes have the general formula C_nH_2n+2
• The first five alkanes are methane, ethane, propane, butane, and pentane
• Alkanes combust completely when enough oxygen is present

Halogens and Alkanes

• Halogens (chlorine and bromine) react with alkanes in the presence of UV light
• This substitution reaction replaces hydrogen atoms in the alkane with halogen atoms
• The reaction produces a haloalkane and hydrogen halide

Alkenes

• Alkenes are unsaturated hydrocarbons (double bonds)
• Alkenes have the general formula C_nH_2n
• The first three alkenes are ethene, propene, and butene
• Alkenes can undergo addition reactions (halogens react with alkenes by adding across the double bond, forming dihaloalkenes)
• Alkenes undergo complete combustion in sufficient oxygen

Alcohols

• Alcohols have the -OH functional group
• The general formula for alcohols is C_nH_2n+1OH
• Alcohols with one -OH group are called monohydric alcohols
• Alcohols can be oxidised to form carboxylic acids, using an oxidising agent

Esters

• Esters are formed from alcohols and carboxylic acids
• Esters have the -COO- functional group
• Esters are usually fragrant and volatile
• The process of forming an ester with an acid catalyst needs an alcohol and a carboxylic acid to form an ester and water.

Addition Polymers

• Polymers are large molecules made of small repeating units (monomers)
• Addition polymers are formed from unsaturated monomers (alkenes)
• Addition polymerisation involves the monomers joining together, opening the double bond
• Example monomers include ethene, propene, and chloroethene
• Example polymers include poly(ethene) and poly(propene).
• Polymers are difficult or impossible to decompose and are therefore often problematic for the environment

Condensation Polymers

• Condensation polymers are formed when two monomers react together
• Condensation polymers often involve the loss of water as a byproduct
• Monomers contain groups for reacting with other molecules (e.g., alcohols, dicarboxylic acids)
• An example is Polyester.

Explore the fascinating processes involved in crude oil, focusing on its composition, fractional distillation, and the cracking process. Understand how different hydrocarbons are separated and transformed, leading to the production of more useful molecules. This quiz delves into the practical applications of chemistry in the oil industry.