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The Chemistry and Technology of Petroleum
after removal of hydrogen sulfide. The liquid product is passed into a stripping tower where steam
removes dissolved hydrogen and hydrogen sulfide and, after cooling, the product is taken to product
storage or, in the case of feedstock preparation, pumped to the next processing unit.
15.7.2.1 Hydrofining
Hydrofining is a process that first went on-stream in the 1950s and is one example of the many
hydroprocesses available. It can be applied to lubricating oils, naphtha, and gas oils. The feedstock
is heated in a furnace and passed with hydrogen through a reactor containing a suitable metal oxide
catalyst, such as cobalt and molybdenum oxides on alumina. Reactor operating conditions range
from 205°C to 425°C (400°F–800°F) and from 50 to 800 psi and depend on the kind of feedstock
and the degree of treating required. Higher-boiling feedstocks, high sulfur content, and maximum
sulfur removal require higher temperatures and pressures.
After passing through the reactor, the treated oil is cooled and separated from the excess hydrogen
which is recycled through the reactor. The treated oil is pumped to a stripper tower where hydrogen
sulfide, formed by the hydrogenation reaction, is removed by steam, vacuum, or flue gas, and the
finished product leaves the bottom of the stripper tower. The catalyst is not usually regenerated;
it is replaced after about a year’s use.
15.8 REFORMING
15.8.1 HIstorICAl develoPment
When the demand for higher-octane gasoline developed during the early 1930s, attention was
directed to ways and means of improving the octane number of fractions within the boiling range of
gasoline. Straight-run (distilled) gasoline frequently had very low octane numbers, and any process
that would improve the octane numbers would aid in meeting the demand for higher octane number
gasoline. Such a process (called thermal reforming) was developed and used widely, but to a much
lesser extent than thermal cracking. Thermal reforming was a natural development from older thermal cracking processes; cracking converts heavier oils into gasoline, whereas reforming converts
(reforms) gasoline into higher-octane gasoline. The equipment for thermal reforming is essentially
the same as for thermal cracking, but higher temperatures are used.
15.8.2 modern ProCesses
15.8.2.1 Thermal Reforming
In carrying out thermal reforming, a feedstock such as 205°C (400°F) end-point naphtha or a
straight-run gasoline is heated to 510°C–595°C (950°F–1100°F) in a furnace, much the same as a
cracking furnace, with pressures from 400 to 1000 psi (27–68 atm). As the heated naphtha leaves
the furnace, it is cooled or quenched by the addition of cold naphtha. The material then enters a
fractional distillation tower where any heavy products are separated. The remainder of the reformed
material leaves the top of the tower to be separated into gases and reformate. The higher octane
number of the reformate is due primarily to the cracking of longer-chain paraffins into higheroctane olefins.
The products of thermal reforming are gases, gasoline, and residual oil or tar, the latter being
formed in very small amounts (about 1%). The amount and quality of the gasoline, known as reformate, is very dependent on the temperature. A general rule is, the higher the reforming temperature,
the higher the octane number, but the lower the yield of reformate.
Thermal reforming is less effective and less economical than catalytic processes and has been
largely supplanted. As it used to be practiced, a single-pass operation was employed at temperatures
in the range of 540°C–760°C (1000°F–1140°F) and pressures of about 500–1000 psi (34–68 atm).
The Chemistry and Technology of Petroleum
after removal of hydrogen sulfide. The liquid product is passed into a stripping tower where steam
removes dissolved hydrogen and hydrogen sulfide and, after cooling, the product is taken to product
storage or, in the case of feedstock preparation, pumped to the next processing unit.
15.7.2.1 Hydrofining
Hydrofining is a process that first went on-stream in the 1950s and is one example of the many
hydroprocesses available. It can be applied to lubricating oils, naphtha, and gas oils. The feedstock
is heated in a furnace and passed with hydrogen through a reactor containing a suitable metal oxide
catalyst, such as cobalt and molybdenum oxides on alumina. Reactor operating conditions range
from 205°C to 425°C (400°F–800°F) and from 50 to 800 psi and depend on the kind of feedstock
and the degree of treating required. Higher-boiling feedstocks, high sulfur content, and maximum
sulfur removal require higher temperatures and pressures.
After passing through the reactor, the treated oil is cooled and separated from the excess hydrogen
which is recycled through the reactor. The treated oil is pumped to a stripper tower where hydrogen
sulfide, formed by the hydrogenation reaction, is removed by steam, vacuum, or flue gas, and the
finished product leaves the bottom of the stripper tower. The catalyst is not usually regenerated;
it is replaced after about a year’s use.
15.8 REFORMING
15.8.1 HIstorICAl develoPment
When the demand for higher-octane gasoline developed during the early 1930s, attention was
directed to ways and means of improving the octane number of fractions within the boiling range of
gasoline. Straight-run (distilled) gasoline frequently had very low octane numbers, and any process
that would improve the octane numbers would aid in meeting the demand for higher octane number
gasoline. Such a process (called thermal reforming) was developed and used widely, but to a much
lesser extent than thermal cracking. Thermal reforming was a natural development from older thermal cracking processes; cracking converts heavier oils into gasoline, whereas reforming converts
(reforms) gasoline into higher-octane gasoline. The equipment for thermal reforming is essentially
the same as for thermal cracking, but higher temperatures are used.
15.8.2 modern ProCesses
15.8.2.1 Thermal Reforming
In carrying out thermal reforming, a feedstock such as 205°C (400°F) end-point naphtha or a
straight-run gasoline is heated to 510°C–595°C (950°F–1100°F) in a furnace, much the same as a
cracking furnace, with pressures from 400 to 1000 psi (27–68 atm). As the heated naphtha leaves
the furnace, it is cooled or quenched by the addition of cold naphtha. The material then enters a
fractional distillation tower where any heavy products are separated. The remainder of the reformed
material leaves the top of the tower to be separated into gases and reformate. The higher octane
number of the reformate is due primarily to the cracking of longer-chain paraffins into higheroctane olefins.
The products of thermal reforming are gases, gasoline, and residual oil or tar, the latter being
formed in very small amounts (about 1%). The amount and quality of the gasoline, known as reformate, is very dependent on the temperature. A general rule is, the higher the reforming temperature,
the higher the octane number, but the lower the yield of reformate.
Thermal reforming is less effective and less economical than catalytic processes and has been
largely supplanted. As it used to be practiced, a single-pass operation was employed at temperatures
in the range of 540°C–760°C (1000°F–1140°F) and pressures of about 500–1000 psi (34–68 atm).