413
Introduction to Refining Processes
The degree of octane number improvement depended on the extent of conversion but was not
directly proportional to the extent of crack per pass. However, at very high conversions, the production of coke and gas became prohibitively high. The gases produced were generally olefinic and the
process required either a separate gas polymerization operation or one in which C 3 –C 4 gases were
added back to the reforming system.
More recent modifications of the thermal reforming process due to the inclusion of hydrocarbon
gases with the feedstock are known as gas reversion and polyforming. Thus, olefinic gases produced
by cracking and reforming can be converted into liquids boiling in the gasoline range by heating
them under high pressure. Since the resulting liquids (polymers) have high octane numbers, they
increase the overall quantity and quality of gasoline produced in a refinery.
15.8.2.2 Catalytic Reforming
The catalytic reforming process was commercially nonexistent in the United States prior to 1940. The
process is really a process of the 1950s and showed phenomenal growth in 1953–1959 time period.
Like thermal reforming, catalytic reforming converts low-octane gasoline into high-octane gasoline (reformate). When thermal reforming could produce reformate with research octane numbers of
65–80 depending on the yield, catalytic reforming produces reformate with octane numbers on the
order of 90–95. Catalytic reforming is conducted in the presence of hydrogen over hydrogenation–
dehydrogenation catalysts, which may be supported on alumina or silica–alumina. Depending on
the catalyst, a definite sequence of reactions takes place, involving structural changes in the feedstock. This more modern concept actually rendered thermal reforming somewhat obsolescent.
The commercial processes available for use can be broadly classified as the moving-bed, fluidbed, and fixed-bed types. The fluid-bed and moving-bed processes used mixed non-precious metal
oxide catalysts in units equipped with separate regeneration facilities. Fixed-bed processes use predominantly platinum-containing catalysts in units equipped for cycle, occasional, or no regeneration.
Catalytic reformer feeds are saturated (i.e., not olefinic) materials; in the majority of cases that
feed may be a straight-run naphtha but other by-product low-octane naphtha (e.g., coker naphtha)
can be processed after treatment to remove olefins and other contaminants. Hydrocracker naphtha
that contains substantial quantities of naphthenes is also a suitable feed.
Dehydrogenation is a main chemical reaction in catalytic reforming, and hydrogen gas is consequently
produced in large quantities. The hydrogen is recycled though the reactors where the reforming takes
place to provide the atmosphere necessary for the chemical reactions and also prevents the carbon from
being deposited on the catalyst, thus extending its operating life. An excess of hydrogen above whatever
is consumed in the process is produced, and, as a result, catalytic reforming processes are unique in that
they are the only petroleum refinery processes to produce hydrogen as a by-product.
Catalytic reforming usually is carried out by feeding a naphtha (after pretreating with hydrogen
if necessary) and hydrogen mixture to a furnace where the mixture is heated to the desired temperature, 450°C–520°C (840°F–965°F) and then passed through fixed-bed catalytic reactors at hydrogen
pressures of 100–1000 psi (7–68 atm) (Figure 15.12). Normally, pairs of reactors are used in series
with heaters are located between adjoining reactors in order to compensate for the endothermic
reactions taking place. Sometimes as many as four or five reactors are kept on stream in series while
one or more are being regenerated.
The on-stream cycle of any one reactor may vary from several hours to many days, depending on
the feedstock and reaction conditions.
15.8.3 CAtAlysts
The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired
reformate. The catalysts used are principally molybdena–alumina, chromia–alumina, or platinum on
a silica–alumina or alumina base. The non-platinum catalysts are widely used in regenerative process
Introduction to Refining Processes
The degree of octane number improvement depended on the extent of conversion but was not
directly proportional to the extent of crack per pass. However, at very high conversions, the production of coke and gas became prohibitively high. The gases produced were generally olefinic and the
process required either a separate gas polymerization operation or one in which C 3 –C 4 gases were
added back to the reforming system.
More recent modifications of the thermal reforming process due to the inclusion of hydrocarbon
gases with the feedstock are known as gas reversion and polyforming. Thus, olefinic gases produced
by cracking and reforming can be converted into liquids boiling in the gasoline range by heating
them under high pressure. Since the resulting liquids (polymers) have high octane numbers, they
increase the overall quantity and quality of gasoline produced in a refinery.
15.8.2.2 Catalytic Reforming
The catalytic reforming process was commercially nonexistent in the United States prior to 1940. The
process is really a process of the 1950s and showed phenomenal growth in 1953–1959 time period.
Like thermal reforming, catalytic reforming converts low-octane gasoline into high-octane gasoline (reformate). When thermal reforming could produce reformate with research octane numbers of
65–80 depending on the yield, catalytic reforming produces reformate with octane numbers on the
order of 90–95. Catalytic reforming is conducted in the presence of hydrogen over hydrogenation–
dehydrogenation catalysts, which may be supported on alumina or silica–alumina. Depending on
the catalyst, a definite sequence of reactions takes place, involving structural changes in the feedstock. This more modern concept actually rendered thermal reforming somewhat obsolescent.
The commercial processes available for use can be broadly classified as the moving-bed, fluidbed, and fixed-bed types. The fluid-bed and moving-bed processes used mixed non-precious metal
oxide catalysts in units equipped with separate regeneration facilities. Fixed-bed processes use predominantly platinum-containing catalysts in units equipped for cycle, occasional, or no regeneration.
Catalytic reformer feeds are saturated (i.e., not olefinic) materials; in the majority of cases that
feed may be a straight-run naphtha but other by-product low-octane naphtha (e.g., coker naphtha)
can be processed after treatment to remove olefins and other contaminants. Hydrocracker naphtha
that contains substantial quantities of naphthenes is also a suitable feed.
Dehydrogenation is a main chemical reaction in catalytic reforming, and hydrogen gas is consequently
produced in large quantities. The hydrogen is recycled though the reactors where the reforming takes
place to provide the atmosphere necessary for the chemical reactions and also prevents the carbon from
being deposited on the catalyst, thus extending its operating life. An excess of hydrogen above whatever
is consumed in the process is produced, and, as a result, catalytic reforming processes are unique in that
they are the only petroleum refinery processes to produce hydrogen as a by-product.
Catalytic reforming usually is carried out by feeding a naphtha (after pretreating with hydrogen
if necessary) and hydrogen mixture to a furnace where the mixture is heated to the desired temperature, 450°C–520°C (840°F–965°F) and then passed through fixed-bed catalytic reactors at hydrogen
pressures of 100–1000 psi (7–68 atm) (Figure 15.12). Normally, pairs of reactors are used in series
with heaters are located between adjoining reactors in order to compensate for the endothermic
reactions taking place. Sometimes as many as four or five reactors are kept on stream in series while
one or more are being regenerated.
The on-stream cycle of any one reactor may vary from several hours to many days, depending on
the feedstock and reaction conditions.
15.8.3 CAtAlysts
The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired
reformate. The catalysts used are principally molybdena–alumina, chromia–alumina, or platinum on
a silica–alumina or alumina base. The non-platinum catalysts are widely used in regenerative process