c. Catalytic Cracking Process. In the catalytic cracking process, several different materials are used as
catalysts, but the most common is a fine sand-like porous material. As cracking takes place, carbon is deposited
on the surface of the catalyst. This carbon is burned off after which the catalyst can be used again and again. The
removal of carbon from the catalyst is known as regeneration. 'The catalyst flows continuously between the two
process stages of reaction and regeneration, propelled by gases. Because the catalyst flows like a liquid, the
process is called fluid catalytic process.
(1) A single hydrocarbon molecule can be cracked into smaller molecules that produce a greater
volume of material than the original molecule. This increase in volume is the result of changing the molecular
structure of the hydrocarbons.
(2) In 1909, one barrel of crude oil produced these fractions. You can see that only 11 percent of the
volume became gasoline. Through the cracking process, refineries can now produce more than three times the
1909 yield of gasoline.
d. Polymerization. Whereas the process of cracking breaks down large, complicated molecules into,
simpler ones, the process of polymerization combines small molecules into larger ones. Specifically, light olefins
are combined to form hydrocarbons of high molecular weight. Thus, the refiner uses byproduct gases to produce
a wide variety of products ranging from liquids used as blending in gasolines, to solids which can be used as
plasticizers. Polymerization of propylene and butylene in a mixture to produce a constituent of motor gasoline is
the most common polymerization operation. The process most commonly used employs phosphoric acid as a
catalyst. The product of the reaction is a mixture of heptenes and other olefins.
e. Alkylation. Alkylation, like polymerization, is a process whereby hydrocarbons are combined. In the
alkylation process, however, paraffinic hydrocarbon (generally considered nonreactive) is combined with an
olefin to produce a paraffin of branched structure, a highly desirable component of both automotive and aviation
gasolines. The result of this combination is known as alkylate. The help of a catalyst is necessary to bring about
the reaction.
(1) The process of alkylation makes possible the combination of some of the natural and stable light
hydrocarbons with the less stable gases produced by cracking. This process was developed during World War II
to increase the availability of source materials required for the manufacture of aviation gasoline. At that time, the
process was used primarily to produce aviation alkylate from isobutane and butylene; but propylene, ethylene, and
pentylene can also be alkylated with isobutane.
(2) There are two types of alkylation processes in wide use:
Sulfuric acid process
Hydrofluoric acid process
f. Hydrogenation.
The hydrogenation process adds hydrogen to the hydrocarbon molecule.
Hydrogenation may be either nondestructive or destructive. In the former, hydrogen is added to the molecule
only if, and where unsaturated with respect to hydrogen exists. The boiling range of the product resulting from
nondestructive hydrogenation, is substantially the same as that of the charge stock. Nondestructive hydrogenation
is usually carried out at pressures ranging between 200 and 400 PSI. Destructive hydrogenation requires much
higher presses. Catalyst is required for both types of hydrogenation.
QM5200
20-6
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