Industrial cracking Flashcards
What does “cracking” mean?
Braking long chain hydrocarbons into shorter lengths
What is the products from cracking?
Short chain alkanes and alkenes
What does chemical feedstock mean?
Something that supplies an industry with the starting materials to make different products.
What are the two ways for cracking?
Thermal cracking
Catalytic cracking
Describe the steps for thermal cracking?
First the alkane must be heated at a high temperature (700-1200 K) and high pressure (up to 7000 kPa)
This makes the carbon-carbon bond break in such a way that one electron from the pair in the covalent bond goes to each carbon atom.
So two short chains are produced, each ending in a carbon atom with an unpaired electron.
What are the unpaired valance electrons (fragments) called?
Free radicals
Are free radicals reactive or under-reactive?
They are highly reactive
During thermal cracking there is not enough hydrogens to form two alkanes. Instead what must be formed?
One of the chains must form a carbon-carbon double bond and become an alkene
Draw a diagram for the process of thermal cracking
Check page 196
During thermal cracking the alkanes are kept under the specific conditions for a very short amount of time (usually 1 second). Why is that?
To avoid too much decomposition, as the chain can split at any time.
In what conditions does catalytic cracking take place?
Under lower temperatures (720 K) and lower pressure (but still more than atmospheric pressure), along with a zeolite catalyst
What catalyst is used in catalytic cracking?
A zeolite
What king of structure does a zeolite catalyst have?
A honeycomb structure
What does the honeycomb structure provide the zeolite catalyst?
A very large surface area
Are zeolite catalysts alkali or acidic?
Acidic
