Cracking Question (1 Viewer)

[Anthel]

Hey guys,

I have a chemistry question. I already know what cracking is, but I just want to know how Ethylene is formed by catalytic cracking.

 

[Anthel]

Ok.. I know now

Ethene can be produced form the catalytic cracking of decane

decane --> ethylene + 2-methylheptane

C10H22 (I) --> C2H4(g) + C8H18 (I)

 

[snowflakeptical]

I hopefully I can explain this properly. The larger hydrocarbons separated through fractional distillation are then circulated with the catalyst (zeolite) in the catalytic cracker. Zeolite has pores in which the reactant molecules are absorbed and catalysed. The size of these pores control the end product. Then the cracked molecules are fed back into the fractional distillation process. The smaller molecules include ethene aka ethylene.

e.g. c6h14 ---> c4h10 + c2h4


edit: yep just remember zeolite

 

[Anthel]

Yes! I saw zeolite in my textbook too! It was missing in my chemistry notes so i was kinda confused. You just made it simpler, thanks for that.

 

[tyrone97]

The reactant doesn't have to be from decane specifically - it can be any long chain HC. The only restriction is that a long chain hydrocarbon alkane must decompose into smaller units (USUALLY two smaller units - one alkane and one alkene). Eg. pentane ---> ethene + propane. Also there are different types of cracking: one of them is thermal cracking which uses higher temperatures in comparison to catalytic. Refer to Jacaranda for this section - it is one of the better textbooks for POM.

 

[dan964]

Catalytic cracking
Uses a zeolite catalyst (don't confuse with Ziegler-Natta)
Conducted at lower temperatures than steam cracking
(check with textbook can't remember off top of head)
140kPa though