Chapter 3Thermal Cracking of Hydrocarbons
Thermal Cracking of Hydrocarbons Chapter 3
Thermal Cracking of HydrocarbonsRawmaterials of petroleumhvdrocarbons areheated athightemperatures (750-900C), so that hydrocarbon moleculesproceed the dehydrogenation or chain scission reactions togenerate small molecular weight alkenes, alkanes and otherhydrocarbons with different molecular weight.This process is called thermal cracking of hydrocarbons.Rawmaterials:Natural gas, Refinery gas, Light oil, Diesel, Heavy oil, etc.Lower molecular alkanes:Ethane,PropaneMainproducts:EthenePropene、ButadieneBenzene,Toluene,Xylenes
Raw materials： Natural gas, Refinery gas, Light oil, Diesel, Heavy oil, etc. Lower molecular alkanes: Ethane, Propane Main products： Ethene、Propene、Butadiene Benzene、Toluene、Xylenes Thermal Cracking of Hydrocarbons Raw materials of petroleum hydrocarbons are heated at high temperatures (750-900℃), so that hydrocarbon molecules proceed the dehydrogenation or chain scission reactions to generate small molecular weight alkenes, alkanes and other hydrocarbons with different molecular weight. This process is called thermal cracking of hydrocarbons
3.1 Chemical reactions of thermal cracking process-,Reactionrulesof thermal cracking ofhydrocarbons>The thermal cracking process of hydrocarbons is verycomplex,andproducts arealsovery complex evenif purecomponentis cracked.>Thermal cracking of hydrocarbons contains the reactions ofdehydrogenation, chain scission,isomerization, cyclization,disproportionation,polymerization,coking,diene synthesisetc.1.Cracking reaction ofalkanesThe cracking reactions of normalalkanemainlycontain the dehydrogenationreactionand the chain scissionreaction.The dehydrocyclizationmay occurforthe alkaneswithcarbonatomnumber≥C5
3.1 Chemical reactions of thermal cracking process 一、Reaction rules of thermal cracking of hydrocarbons 1. Cracking reaction of alkanes The cracking reactions of normal alkane mainly contain the dehydrogenation reaction and the chain scission reaction. The dehydrocyclization may occur for the alkanes with carbon atom number ≥ C5. ➢The thermal cracking process of hydrocarbons is very complex, and products are also very complex even if pure component is cracked. ➢Thermal cracking of hydrocarbons contains the reactions of dehydrogenation, chain scission, isomerization, cyclization, disproportionation, polymerization, coking, diene synthesis, etc
Dehydrogenationreaction :C,H2n+2C,H2n+H2(CleavageofCHbond)Chain scission reaction :C,H2n+2CmH2m+ C,H2k+2m+k=nDehydrocyclization reactionCH3CH2CH3CH2CH3+H2CH2CH2CH2CH2CH2CH2
Dehydrogenation reaction ： CnH2n+2 CnH2n+H2 （Cleavage of C—H bond ） Chain scission reaction ： CnH2n+2 CmH2m+ CkH2k+2 m＋k=n Dehydrocyclization reaction
Comparison of various bond energy键能/键能/碳氢键碳碳键(kJ /mol)(k//mol)426.8CH3--CH3346HC--H405.8CH3—CH2--CH3343.1CH,CH2--H397.5CHCH2---CH2CH3338.9CH3CH2CH2--HCH,CH2CH2—CH3(CH)2CH—H384.9341.8CH3CHaCH2CH2CH2--H393.2CH3CH2CH--HHCC-CH3376.6314.6CH3CH3364(CH)3C—H325.1CH,CH2CH2--CH2CH2CH3378.7CH3CH(CH3)CH(CH)CH310.9CH (般)
1.各种键能比较 Comparison of various bond energy