Industrial Cracking Flashcards
Why are longer chains fractions from crude oil less economically valuable?
They are less useful compared to shorter chain hydrocarbons which are in higher demand
What process is used to convert longer chain hydrocarbons into shorter ones?
Cracking
What are the two main advantages of cracking?
- Produce more useful short chains, such as petrol
- Produce alkenes, which are more reactive than alkanes
What is cracking?
Cracking is the process of breaking down long - chain hydrocarbons into shorter, more useful molecules, including alkanes and alkenes
Why are alkenes valuable to the chemical industry?
They are used as chemical feedstock and to make alkenes
Define “chemical feedstock”
It is a starting material supplied to industries to make different products
Why do alkanes require harsh conditions to break down?
Alkanes are very unreactive due to the strong C-C and C-H bonds, so high temperature and catalysts are needed for cracking
What happens to carbon - carbon bonds during this reaction?
The bonds break so that one electron from the covalent bond goes to each carbon atom
What are the products of thermal cracking?
Short chain alkanes + alkenes
What gas can also be produced during thermal cracking?
Hydrogen gas can be produced
Why does thermal cracking produce alkenes?
There are not enough hydrogen atoms to form only alkanes, so at least one product must have a C=C bond, making it an alkene
What are the products of catalytic cracking?
The products are usually motor fuels, aromatic hydrocarbons, cyclic alkanes and branched alkanes
Why can’t two alkanes be produced from the breaking of long chain alkanes into short chain alkanes?
There are not enough hydrogen atoms available to form two alkanes
What type of compound is always produced in addition to an alkane during thermal cracking?
An alkene
Can carbon - carbon bonds break at any point during the thermal cracking reaction?
Yes, any number of carbon - carbon bond may break and the chain does not need to break in the middle
What are the conditions required for catalytic cracking?
Catalytic cracking occurs at lower temps, lower pressures, using zeolite catalysts
Why are zeolite catalysts effective for cracking?
They have a honeycomb structure with a large surface area and are acidic, which helps break bonds efficiently
What are the conditions required for thermal cracking?
High temperatures (700-1200K) and high pressure
How are the products from cracking separated?
The products are separated by fractional distillation
What state are the products from catalytic cracking mostly in?
The products are mostly gases, showing they have chain length of less than C5
The decolourisation of bromine solution is a test for a carbon-carbon double bond, showing that the product contains alkenes.
What is the main difference between thermal cracking and catalytic cracking?
Thermal cracking uses high temperatures and pressures, while catalytic cracking occurs at lower temperatures with a zeolite catalyst
