Daily Question (November 18): Ethane and propane cracking problem

This is a very complex topic, as the cracking of hydrocarbons is generally considered to follow a free radical reaction mechanism, and it requires thorough study. The relationship between propane cracking and the yield of ethylene depends mainly on residence time and cracking temperature; a shorter residence time and a higher cracking temperature result in more ethylene production, while conversely, more propylene is produced.

This post was last edited by VinDin on 2010-11-19 at 10:42. I haven’t worked on this problem for a long time, so the answers below are likely very incorrect; now they include some random and unclear ideas as well. During the cracking of ethane, free radicals are generated, leading to dehydrogenation reactions, and these reactions combine with individual ethane molecules to form propylene, thereby enabling chain growth； During the cracking of propane, C2 and C free monomer groups are generated; when these two C free radicals polymerize, C2H4 is formed along with the release of hydrogen. I just thought about it for a moment; I’d better write down the equation to understand it better. 1. C2H6 → 2CH3 (individual groups); 2CH3 + 2C2H6 → 2C3H6 + 3H2. Specifically, it is CH3* + C2H6 → CH4 + C2H5*.
2. C3H8 → C2H5* + CH3*; CH3* + CH3* → C2H4 + H2. Hmm, the answers are probably incorrect; I hope experts can provide some guidance.

This post was last edited by yanran88 on 2010-11-20 at 12:25. Daily Question (November 18): Why can propylene be obtained from ethane cracking? Why is the yield of ethylene higher than that of propylene in propane cracking? Propylene cannot be produced in a single reaction of ethane cracking, but in a second reaction, an ethyl radical and a methyl radical can combine to form propane, which can then be dehydrogenated to produce propylene; there are also other ways to generate propylene. During propane cracking, the C—C bond breaks more easily than the C—H bond; therefore, propane cracking first produces ethane and methane, with ethane then undergoing dehydrogenation to form ethylene. Secondly, propane is dehydrogenated to produce propylene; therefore, the yield of ethylene is actually higher than that of propylene.

I’d like to ask gently: regarding the issue mentioned by the original poster, has industrialization been achieved yet?

After decades of industrialization, the circulating gas furnace is used to crack mixtures of propane and ethane

Currently, the ethylene yield from the ethylene cracking feedstocks used in China is around 33%, while the yield of diolefins is approximately 46%; in other words, the ethylene yield is always higher than that of propylene.

Industrialization came early; it seems you’ve never been involved in ethylene production. :lol

Thank you, think, think, think, think, thank you!

I’ve studied it; I worked in a pyrolysis facility for six or seven years without ever thinking about such issues. I guess I didn’t study it deep enough