Page 94 - Synthetic Fuels Handbook

FUELS FROM PETROLEUM AND HEAVY OIL 81

reforming produces reformate with octane numbers on the order of 90 to 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, fluid bed, and fixed bed types. The fluid bed and moving bed processes used mixed
nonprecious 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 con-
taminants. 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 extend-
ing 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 to 520°C (842–968°F), and then passed through fixed bed
catalytic reactors at hydrogen pressures of 100 to 1000 psi (7–68 atm) (Fig. 3.12). Normally
several reactors are used in series with heaters 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 is being regenerated.

Reactor Reactor Reactor
Feedstock

Furnace Furnace Furnace

Light
hydrocarbons
Hydrogen
recycle
Fractionator

Separator
Reformate
FIGURE 3.12 Catalytic reforming.