Crude Oil and Fractional Distillation Flashcards
What are alkanes?
Saturated hydrocarbons with C-C and C-H single bonds only, and with the general formula CnH2n+2
What is the main source of alkanes?
Crude oil
What is a homologous series?
A set of organic compounds with the same functional group. The compounds differ in the length of their hydrocarbon chain.
Describe the process of catalytic cracking and the types of compounds formed.
- Takes place at a lower temperature (450 degrees C) and at a pressure of just over atmospheric pressure.
- Using a zeolite catalyst made of silicon dioxide and aluminium oxide.
-Products: cycloalkanes, branched alkanes and aromatic compounds.
Describe the process of thermal cracking and the types of compounds formed.
-Alkanes are heated up to a high temperature (900 degrees C), under high pressure (up to 70 atmospheres). Carbon-carbon bonds break in such a way that one electron from the pair in the covalent bonds goes to each carbon atom.
A High number of alkenes are formed, alkanes and sometimes hydrogen has.
What are the commercial benefits of cracking?
- To make products which are in greater demand
- To make alkenes, which are more reactive than alkanes
How might SO2 be formed when fuels are burned and how can it be removed from flue gases?
- Produced from sulfur-containing impurities present in crude oil. Sulfur dioxide can combine with water vapour in the air to form sulfuric acid.
- Can be removed by flue gas desulfurization- chimneys use calcium oxide or calcium carbonate to absorb the SO2 and form gypsum (CaSO4) which is used as plaster.
How are unburned hydrocarbons produced? How can its emissions be reduced?
- By incomplete combustion. They contribute to photochemical smog.
- Unburned hydrocarbons and nitrogen oxide can be reacted in a catalytic converter to form nitrogen, carbon dioxide and water
C8H18 + 25NO = 12.5 N2 + 8CO2 + 9H2O
How is carbon monoxide formed? How can its emissions be reduced?
- By incomplete combustion
- Can be removed by using a catalytic converter, which converts carbon monoxide and nitrogen oxide to form nitrogen gas and carbon dioxide:
2CO(g) + 2NO(g) = N2(g) + 2CO2(g)
How are nitrogen oxides formed? How can its emissions be reduced?
-Produced when there’s enough energy for N2 and O2 in the air to combine. This happens in a petrol engine when sparks ignite the fuel. They can react with water vapour and oxygen in the air to form nitric acid so they contribute to acid rain and photochemical smog.
-2CO(g) + 2NO(g) = N2(g) + 2CO2(g)
C8H18 + 25NO = 12.5 N2 + 8CO2 + 9H2O
How are alkanes separated from crude oil?
- By fractional distillation.
- The crude oil is heated and vaporized in a furnace and passed into a fractioning tower which gets cooler as you go up the tower.
- The vapours pass up the tower via a series of trays containing bubble caps until they arrive at a tray that is sufficiently cool- at a lower temp than their boiling point. They condense to liquids.
- The liquids on each tray are piped off.
- The shorter hydrocarbons condense in the trays nearer to the top of the tower, where it’s cooler, because they have lower boiling points.
What is often done to the thick residue that collects at the base of the tower (tar or bitumen) and why?
- Can be used for road surfacing.
- Often is further processed to give more valuable products because supply often exceeds demand.
Why are high temperatures required for cracking?
To break the strong C-C/C-H covalent bonds.
What property of alkanes allows them to be separated by fractional distillation?
Different boiling points.
What is a fraction?
-A mixture of hydrocarbons with similar boiling points collected during fractional distillation of crude oil.
