easily into the respiratory tract and are retained longer. Particulate matter also
contributes to haze.
Ozone. This photochemical oxidant is found in the atmosphere from ground
level to 6 miles above the ground and again in the stratosphere 6–30 miles above the
earth. At ground level, ozone, together with nitrogen oxides, volatile organic
compounds, and sunlight are the major constituents of “smog.” Ozone is a strong
oxidant that damages lung tissue and reduces lung function.
Meeting the Gasoline Parameters
Prior to 1990, the performance and emission characteristics of motor fuels were
mainly the responsibility of the engine manufacturers with some notable changes
imposed on the gasoline manufacturers. Notable among the restrictions imposed on
the refineries in the gasoline manufacture was the restriction on the use of TEL
(tetra ethyl lead) as an octane enhancer. The EPA (Environmental Protection
Agency) had, as early as 1970, enforced a program to reduce the addition of lead
so that even before 1990, there was available only “no lead” or “unleaded” gasoline
for road vehicles. The “Clean Air Act” of 1990 however put the onus on the
gasoline manufacturers for meeting the act’s requirements. In North America,
programs to introduce reformulated gasoline were launched. This RFG allowed
the performance of the gasoline to be retained while reducing the harmful emissions
caused by the traditional octane enhancers such as aromatics (from reformates) and
olefins (from cracked naphtha).
Reducing aromatics in gasoline. The most stringent environmental restriction
imposed on aromatics in gasoline is on benzene. This component in benzene has
now been reduced to levels below 1.0 % vol in the product. Refining processing
philosophy has undergone some extensive changes to meet this single requirement.
The following steps have been taken in part or as a whole to meet this change:
• Reducing reformer severity. This also reduces the quantity of the heavier
aromatics.
• Reducing the final boiling point of the gasoline. This essentially reduces the
amount of the heavier aromatics in the gasoline.
• Increasing the quantity of isoparaffin. This is accomplished by saturating the
benzene ring and isomerization of the naphthenes to isoparaffins.
• Reducing the aromatics in the cracked naphtha stock. Catalytic cracker naphtha
is high in olefins in the front end but high in aromatics in the back end. The
reduction of aromatics from this source is accomplished by lowering the cut’s
final boiling point.
• Aromatic extraction using an extraction process similar to that used in producing
the petrochemical aromatic complex feed (e.g., the sulfolane process). Only
about 20 of the largest refineries in North America have this extraction facility
however.
Reducing the olefins in gasoline. Almost all the olefins and sulfur in the gasoline
pool come from the catalytic cracker naphtha with a relatively small amount from
Petroleum Products and a Refinery Configuration
73
contributes to haze.
Ozone. This photochemical oxidant is found in the atmosphere from ground
level to 6 miles above the ground and again in the stratosphere 6–30 miles above the
earth. At ground level, ozone, together with nitrogen oxides, volatile organic
compounds, and sunlight are the major constituents of “smog.” Ozone is a strong
oxidant that damages lung tissue and reduces lung function.
Meeting the Gasoline Parameters
Prior to 1990, the performance and emission characteristics of motor fuels were
mainly the responsibility of the engine manufacturers with some notable changes
imposed on the gasoline manufacturers. Notable among the restrictions imposed on
the refineries in the gasoline manufacture was the restriction on the use of TEL
(tetra ethyl lead) as an octane enhancer. The EPA (Environmental Protection
Agency) had, as early as 1970, enforced a program to reduce the addition of lead
so that even before 1990, there was available only “no lead” or “unleaded” gasoline
for road vehicles. The “Clean Air Act” of 1990 however put the onus on the
gasoline manufacturers for meeting the act’s requirements. In North America,
programs to introduce reformulated gasoline were launched. This RFG allowed
the performance of the gasoline to be retained while reducing the harmful emissions
caused by the traditional octane enhancers such as aromatics (from reformates) and
olefins (from cracked naphtha).
Reducing aromatics in gasoline. The most stringent environmental restriction
imposed on aromatics in gasoline is on benzene. This component in benzene has
now been reduced to levels below 1.0 % vol in the product. Refining processing
philosophy has undergone some extensive changes to meet this single requirement.
The following steps have been taken in part or as a whole to meet this change:
• Reducing reformer severity. This also reduces the quantity of the heavier
aromatics.
• Reducing the final boiling point of the gasoline. This essentially reduces the
amount of the heavier aromatics in the gasoline.
• Increasing the quantity of isoparaffin. This is accomplished by saturating the
benzene ring and isomerization of the naphthenes to isoparaffins.
• Reducing the aromatics in the cracked naphtha stock. Catalytic cracker naphtha
is high in olefins in the front end but high in aromatics in the back end. The
reduction of aromatics from this source is accomplished by lowering the cut’s
final boiling point.
• Aromatic extraction using an extraction process similar to that used in producing
the petrochemical aromatic complex feed (e.g., the sulfolane process). Only
about 20 of the largest refineries in North America have this extraction facility
however.
Reducing the olefins in gasoline. Almost all the olefins and sulfur in the gasoline
pool come from the catalytic cracker naphtha with a relatively small amount from
Petroleum Products and a Refinery Configuration
73