Topic 1 (production): DP 1: (2) identify the industrial source of ethylene from the cracking of some of the fractions from the refining of petroleum Flashcards
What feature of ethene means that it can be used to produce/manufacture polyethylene and many key intermediate products?
Ethene’s double bond means that it can be used to produce/manufacture polyethylene and many key intermediate products
What two things are Ethene produced from?
Natural gas or Crude oil
What is the main method used to produce unsaturated hydrocarbons?
Thermal cracking of suitable feedstock, typical feedstock include:
a) Ethane and propane from natural gas
b) Fractional distillation of crude oi using naptha or gas oil fractions
What is the correlation between hydrocarbons being in higher demand and their molecular size?
the ones in higher demand generally have higher molecular weight
Define catalytic cracking
Catalystic cracking is the process by which fractions of higher molecular weight are broken down into fractions of lower molecular weights
What are Zeolites?
Zeolites are the inorganic compounds that are used as catalysts in the process of catalytic cracking
How is the process of catalytic cracking carried out molecularly?
- Alkanes with 15 to 25 carbon atoms per molecule are broken into two smaller molecules, one an alkane and the other an alkene.
- The alkene further splits into smaller alkenes until ethylene, propene, or a combination of both is formed.
What process is also carried out to meet the demands of ethylene given that catalytic cracking is not enough?
some fractions of petroleum are decomposed completely to produce ethylene through steam thermal cracking.
Define steam thermal cracking
The process in which ethane gas or larger hydrocarbons are mixed with steam and passed through hot metal coils, producing ethylene. at around 700-1000 degrees celsius.
How is Crude oil used to procure ethylene and other low weight hydrocarbons?
- Crude oil is separated by fractional distillation into
“fractions”, producing a large fraction of low-worth alkanes with 15 or more carbon atoms - These large molecules (high molecular weight= high BP) are broken into smaller molecules (low
molecular weight= lower BP) by cracking, which can be done by heating (Thermal cracking) or by the use
of a Zeolite catalyst (Cat Cracking) in the absence of oxygen - covalent bonds are broken.
Why are catalysts used in cracking?
Catalysts require extremely high temperatures and using a catalyst allows for this to happen at a much lower temp (500 degrees Celsius)
What the products of cracking?
Ethene, other alkenes and unbranched alkanes (C8H18). Alkenes are produced
because there are no atoms to occupy the bond positions that are created.
What happens when the mixture is cracked?
the mixture is fed back into the fractional distillation process. Many of the smaller
molecules end up in the valuable petrol or diesel fractions.
