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Cracking hydrocarbons
Thermal cracking and catalytic cracking are two types of hydrocarbon cracking used to produce lighter fractions from heavier fractions. Thermal cracking uses high temperatures and pressures to produce alkenes and alkanes, while catalytic cracking uses lower temperatures and a zeolite catalyst to produce motor fuels and aromatic hydrocarbons. Both cracking methods allow the production of lighter, more valuable fractions in higher demand to meet consumer needs.
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Cracking hydrocarbons
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- 4. Types of Cracking Thermal Cracking Catalytic Cracking •High Temperatures (up to 1000 C) •High Pressures (7000kPa) • High Temperatures (around 450 C) • Slight Pressures • Uses Zeolite Catalyst (compounds of aluminium/ silicon/oxygen) Catalyst : - Speeds up Rate of Reaction - Lowers Temperature and Pressure = Cuts cost
- 5. Thermal Cracking Produces LOTS of ALKENESand ALKANES By adjusting the conditions ( changing heat and pressure ) the proportion of alkane to alkenes can be changed, depending on what's more desired Used to produce lots of valuable products e.g. polymers, such as poly(ethene), in plastics manufacture Some of the smaller molecules formed by cracking are used as fuels
- 6. Catalytic Cracking Makes mostly Motor Fuelsand Aromatic Hydrocarbons Aromatic compounds have double benzene rings Uses a Zeolite catalyst: oHas microscopic pores which give it a large Surface area: Speeds up Rate of Reaction, = Cuts cost oCatalyst also Lowers Temperature and Pressure Catalytic cracking produces more branched, cyclic & aromatic hydrocarbons than thermal cracking = more useful for making motor fuels than unbranched hydrocarbons
- 7. Supply and Demand• GreaterDemand for Lighter Fractions (e.g. Petrol) than for heavy fractions • Fractional distillation can’t meet these demands • So Cracking converts heavy fractions into lighter, more valuable, fractions e.g. petrol & ethene decane ethene octane e.g.
- 8. Why are lighter fractionsmore in demand? lighter fractions = shorter branched alkanes= lower boiling point = more volatile (vaporize more easily) good for making petrol VERY IN DEMAND so to meet demand less needed fractions ( heavier fractions) are cracked
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