Octane numbers

[gml5121]

What are the main reactions in a reformer that contribute to higher octane numbers? I know a reformer converts low octane cycloalkanes to high octane aromatics and in the process produces hydrogen that can be used in other hydrogen addition units but what are the reactions?

 

[georgeverghese]

You mean what are the "other " reactions?

Isomerisation of straight chain alkanes (to branched alkanes) and dehydrocyclization of alkanes also leads to higher octane rating. The preference these days is to reduce the extent of the dehydrogenation of naphthenes into aromatics reactions and increase the isomerisation reactions for HSE reasons ( minimise human exposure to BTX vapors)

Any naphthene that has a boiling point between 180 and 400degF may be dehydrogenated in the reformer into the corresponding aromatic. These reactions are endothermic.

 

[EmmanuelTop]

The Octane number improvement reactions are:

- Dehydrogenation of Naphthenes to Aromatics
- Dehydrocyclization of Paraffins to Aromatics
- Dehydroisomerization of alkyl-cyclopentanes to Aromatics
- Isomerisation of Paraffins and Naphthenes

There are other (undesirable) reactions, mainly comprising of cracking and hydrocracking of paraffin molecules.
See more at:

http://nptel.ac.in/courses/103107082/module6/lecture6/lecture6.pdf

http://nopr.niscair.res.in/bitstream/123456789/17620/1/JSIR 62(10) 963-978.pdf

https://repositories.tdl.org/ttu-ir/bitstream/handle/2346/12491/31295009895953.pdf?sequence..

Dejan IVANOVIC
Process Engineer, MSChE