ABSTRACT

Propagation: . k2 R + M RH + M Chain transfer

(3.3)

,8--scission M ka R + Olefin (3.4)

Termination: Radical + Radical k4 Products (3.5)

Reaction (3.4) is called ,8--scission because the C-C bond {3 to the radical center (i.e. two carbons away) breaks to form an olefin and a smaller alkyl radical. For example, the n-nonane radical would decompose via ,8--scission as follows:

Ethylene formation

(3.7)

35 r-----------------------------------------~

• 8.63 [J 6.58

~ 5

n-alkanes

0 ~--~----~-----L-----L----~----J---~----~ 0 2 4 6 8 10 12 14 16

Reactions of parent radicals:

Termination Reactions:

reactions of n--alkanes (n-C16 for example)

(a)

(e)

(f)

H2 Pressure Temp, ·c Products No 101.3 kPa >700 Light olefins, coke No 3-7 MPa 430 Alkanes and olefins No 14 MPa 430 Alkanes and olefins Yes 14 MPa 430 Alkanes, less olefins

(3.8)

At high pressures, the olefins can undergo addition reactions with radicals:

Hydrogen abstraction

~+R·---+~+RH (3.10)

!3-scission

(3.11)

Addition

(3.12)

~+. (3.14)

(3.15)

hydrocracking can form naphthenes from aromatic compounds.