657
Product Improvement and Treating
by volume of iso-octane in a mixture of iso-octane and heptane in a reference fuel that when tested
in a laboratory engine, matches the antiknock quality, as measured for the fuel being tested under
the same conditions. The octane number posted at the gasoline pump is actually the average of the
Research Octane Number (RON) and Motor Octane Number (MON), commonly referred to as
(R + M)/2. RON and MON are two different test methods that quantify the antiknock qualities of
a fuel. Since the MON is a test under more severe conditions than the RON test, for any given fuel,
the RON is always higher than the MON.
Unfortunately, the desulfurized light and heavy naphtha fractions of crude oils have very low
octane numbers. The heavy naphtha fraction has an octane number on the order of 50 (R + M)/2.
Reforming is the refinery process that reforms the molecular structure of the heavy naphtha to increase
the percentage of high-octane components while reducing the percentage of low-octane components.
When lead was phased out of gasoline (Chapter 26), the only way to produce high-octane-number
gasolines is to use inherently high-octane hydrocarbons or to use alcohols (often referred to as
oxygenates) (Table 24.2). The ether derivatives are also high-octane oxygenates (Table 24.3) and
have been used widely as additives. The ethers may be produced at the refinery by reacting suitable
alcohols such as methanol and ethanol with branched olefins from the fluid catalytic cracker, such
TABLE 24.2
Oxygenates Allowed in Gasoline
Oxygenate
Maximum, Vol %
Methanol
3
Ethanol
5
Isopropyl alcohol
10
Isobutyl alcohol
10
tert-Butyl alcohol
7
Ether (5 or more C atoms)
15
Other oxygenates
10
TABLE 24.3
Various Oxygenates Used in Gasoline
Ethanol (EtOH)
129
118
119
112
34.73
18.15
15.66
15.66
Name
Formula
Structure
Oxygen
Content
Mass %
Blending
Research Octane
Number (BRON)
Methyl tertiary-butyl
ether (MTBE)
Ethyl tertiary-butyl
ether (ETBE)
Tertiary-amyl methyl
ether (TAME)
C 2 H 6 O
C 5 H 12 O
C 6 H 14 O
C 6 H 14 O
CH 3
CH 3 O C
CH 3 O C
CH 3 CH 2 O C
CH 3
CH 3
CH 3
CH 3
CH 3
CH 3
CH 3
CH 2 CH 3
CH 2 CH 2 OH
Product Improvement and Treating
by volume of iso-octane in a mixture of iso-octane and heptane in a reference fuel that when tested
in a laboratory engine, matches the antiknock quality, as measured for the fuel being tested under
the same conditions. The octane number posted at the gasoline pump is actually the average of the
Research Octane Number (RON) and Motor Octane Number (MON), commonly referred to as
(R + M)/2. RON and MON are two different test methods that quantify the antiknock qualities of
a fuel. Since the MON is a test under more severe conditions than the RON test, for any given fuel,
the RON is always higher than the MON.
Unfortunately, the desulfurized light and heavy naphtha fractions of crude oils have very low
octane numbers. The heavy naphtha fraction has an octane number on the order of 50 (R + M)/2.
Reforming is the refinery process that reforms the molecular structure of the heavy naphtha to increase
the percentage of high-octane components while reducing the percentage of low-octane components.
When lead was phased out of gasoline (Chapter 26), the only way to produce high-octane-number
gasolines is to use inherently high-octane hydrocarbons or to use alcohols (often referred to as
oxygenates) (Table 24.2). The ether derivatives are also high-octane oxygenates (Table 24.3) and
have been used widely as additives. The ethers may be produced at the refinery by reacting suitable
alcohols such as methanol and ethanol with branched olefins from the fluid catalytic cracker, such
TABLE 24.2
Oxygenates Allowed in Gasoline
Oxygenate
Maximum, Vol %
Methanol
3
Ethanol
5
Isopropyl alcohol
10
Isobutyl alcohol
10
tert-Butyl alcohol
7
Ether (5 or more C atoms)
15
Other oxygenates
10
TABLE 24.3
Various Oxygenates Used in Gasoline
Ethanol (EtOH)
129
118
119
112
34.73
18.15
15.66
15.66
Name
Formula
Structure
Oxygen
Content
Mass %
Blending
Research Octane
Number (BRON)
Methyl tertiary-butyl
ether (MTBE)
Ethyl tertiary-butyl
ether (ETBE)
Tertiary-amyl methyl
ether (TAME)
C 2 H 6 O
C 5 H 12 O
C 6 H 14 O
C 6 H 14 O
CH 3
CH 3 O C
CH 3 O C
CH 3 CH 2 O C
CH 3
CH 3
CH 3
CH 3
CH 3
CH 3
CH 3
CH 2 CH 3
CH 2 CH 2 OH