656
The Chemistry and Technology of Petroleum
is the conversion (reforming, molecular rearrangement) of n-hexane to cyclohexane or cyclohexane
to benzene. These processes reform or rearrange one particular molecular type to another, thereby
changing the properties of the product relative to the feedstock. Such processes are conducive to
expansion of the utility of petroleum products and to sales.
It is, therefore, the purpose of this chapter to present the concepts behind these secondary processes with specific examples of those processes that have reached commercialization. It must be
understood that the process examples presented here are only a selection of the total number available. The choice of a process for inclusion here was made to illustrate the different process types
that are available.
24.2 REFORMING
When the demand for higher-octane gasoline developed during the 1930s, attention was directed to
ways and means of improving the octane number of fractions within the boiling range of gasoline.
Straight-run gasoline, for example, frequently had a low octane number and any process that would
improve the octane number would aid in meeting the demand for higher quality (higher octane
number) gasoline. Such a process, called thermal reforming, was developed and used widely but to
a much lesser extent than thermal cracking.
Upgrading by reforming is essentially a treatment to improve a gasoline octane number and may
be accomplished in part by an increase in the volatility (reduction in molecular size) or chiefly by
the conversion of n-paraffins to iso-paraffins, olefins, and aromatics and the conversion of naphthenes to aromatics (Table 24.1). The nature of the final product is of course influenced by the source
(and composition) of the feedstock. In thermal reforming, the reactions resemble the reactions that
occur during gas oil cracking: that is, molecular size is reduced, and olefins and some aromatics
are produced.
Gasoline has many specifications that must be satisfied before it can be sold on the market. The
most widely recognized gasoline specification is the octane number, which refers to the percentage
TABLE 24.1
Structure and Octane Numbers of Selected Hydrocarbons
Compound
Compound
Formula
Formula
Structure
Structure
RON
RON
n-Hexane
Cyclohexane
1-Hexane
25
100
106
72
118
2,2,4-Trimethylpentane
(Isooctane)
2,4,4-Trimethy l-pentane
(Isooctane)
Cis 1,3-dimethylcyclohexane
1,3-Dimethylbenzene
76
83
123 (est.)
C 6 H 14
C 8 H 18
C 8 H 16
C 8 H 16
C 8 H 10
CH 3 (CH 2 ) 4 CH 3
CH 3
CH 3 CH 3
CH 3
CH 3
CH 3
CH 3
CH 3
CCH 2 CCH 3
CH 3
CHCH 3
CH 3
CH 2
CH 3 CCH 2
CH 2 -CH(CH 2 ) 3 CH 3
C 6 H 12
C 6 H 12
C 6 H 6
Benzene
The Chemistry and Technology of Petroleum
is the conversion (reforming, molecular rearrangement) of n-hexane to cyclohexane or cyclohexane
to benzene. These processes reform or rearrange one particular molecular type to another, thereby
changing the properties of the product relative to the feedstock. Such processes are conducive to
expansion of the utility of petroleum products and to sales.
It is, therefore, the purpose of this chapter to present the concepts behind these secondary processes with specific examples of those processes that have reached commercialization. It must be
understood that the process examples presented here are only a selection of the total number available. The choice of a process for inclusion here was made to illustrate the different process types
that are available.
24.2 REFORMING
When the demand for higher-octane gasoline developed during the 1930s, attention was directed to
ways and means of improving the octane number of fractions within the boiling range of gasoline.
Straight-run gasoline, for example, frequently had a low octane number and any process that would
improve the octane number would aid in meeting the demand for higher quality (higher octane
number) gasoline. Such a process, called thermal reforming, was developed and used widely but to
a much lesser extent than thermal cracking.
Upgrading by reforming is essentially a treatment to improve a gasoline octane number and may
be accomplished in part by an increase in the volatility (reduction in molecular size) or chiefly by
the conversion of n-paraffins to iso-paraffins, olefins, and aromatics and the conversion of naphthenes to aromatics (Table 24.1). The nature of the final product is of course influenced by the source
(and composition) of the feedstock. In thermal reforming, the reactions resemble the reactions that
occur during gas oil cracking: that is, molecular size is reduced, and olefins and some aromatics
are produced.
Gasoline has many specifications that must be satisfied before it can be sold on the market. The
most widely recognized gasoline specification is the octane number, which refers to the percentage
TABLE 24.1
Structure and Octane Numbers of Selected Hydrocarbons
Compound
Compound
Formula
Formula
Structure
Structure
RON
RON
n-Hexane
Cyclohexane
1-Hexane
25
100
106
72
118
2,2,4-Trimethylpentane
(Isooctane)
2,4,4-Trimethy l-pentane
(Isooctane)
Cis 1,3-dimethylcyclohexane
1,3-Dimethylbenzene
76
83
123 (est.)
C 6 H 14
C 8 H 18
C 8 H 16
C 8 H 16
C 8 H 10
CH 3 (CH 2 ) 4 CH 3
CH 3
CH 3 CH 3
CH 3
CH 3
CH 3
CH 3
CH 3
CCH 2 CCH 3
CH 3
CHCH 3
CH 3
CH 2
CH 3 CCH 2
CH 2 -CH(CH 2 ) 3 CH 3
C 6 H 12
C 6 H 12
C 6 H 6
Benzene