513
19
Catalytic Cracking
19.1 INTRODUCTION
Catalytic cracking is a conversion process that can be applied to a variety of feedstocks ranging
from gas oil to heavy oil and in a variety of configuration (Speight and Ozum, 2002; Letzsch, 2009).
Fluid catalytic cracking units are currently in place in ∼400 refineries around the world, and the
units are considered to be one of the most important achievements of the twentieth century.
Basically, catalytic cracking is similar to thermal cracking, but it differs only in the usage of a
catalyst that is not (in theory) consumed in the process, and it is one of the several practical applications used in a refinery that employs a catalyst to improve process efficiency. The original incentives
to develop cracking processes arose from the need to increase gasoline supplies and to increase
the octane number of gasoline, while maintaining yield from high-boiling stocks using catalysts
(Chapter 1; Germain, 1969). Since cracking could virtually double the volume of gasoline from a
barrel of crude oil, the purpose of cracking was completely justified.
This history of catalytic cracking started in the early part of the twentieth century (Table 19.1).
In the 1930s, thermal cracking units produced about half of the total gasoline manufactured,
the octane number of which was about 70 compared to 60 for straight-run gasoline. These were
usually blended together with light ends and sometimes with polymer gasoline and reformate
to produce gasoline base stock with an octane number of about 65. The addition of tetraethyl
lead (ethyl fluid) increased the octane number to about 70 for the regular grade gasoline and
80 for premium grade gasoline. The thermal reforming and polymerization processes that were
developed during the 1930s could be expected to further increase the octane number of gasoline
to some extent, but something new was needed to break the octane barrier that threatened to
stop the development of more powerful automobile engines. In 1936, a new cracking process
opened the way to higher-octane gasoline and this process was known as catalytic cracking,
since that time the use of catalytic materials in the petroleum industry has spread to other processes (Bradley et al., 1989).
The last 70 years have seen substantial advances in the development of catalytic processes
(Luckenbach et al., 1992). This has involved not only rapid advances in the chemistry and physics
of the catalysts themselves but also major engineering advances in the reactor design, for example,
the evolution of the design of the catalyst beds from fixed beds to moving beds to fluidized beds as
well as the different designs of the fluidized bed reactors currently used in catalyst chemistry and
physics, and bed designs have allowed major improvements in the process efficiency and product
yields (Sadeghbeigi, 1995).
An important purpose evolved from the ability of cracked gasoline to resist detonation that is
the cause of knocking in automobile engines. In the early days of automobile engine development,
straight-run gasoline had a lower end point (165°C, 330°F) than that of cracked gasoline (205°C,
400°F) and, furthermore, did not color when exposed to sunlight. Similar exposure caused the
cracked gasoline to turn brown, and hence, straight-run gasoline was regarded as the premium
material.
Gasoline is now mostly produced by either the catalytic cracking processes or by reforming
processes. In catalytic cracking, the petroleum (or petroleum-derived feedstock) is fed into a reaction vessel containing a catalyst. In reforming processes (Chapter 24), naphtha (refined or unrefined), which is produced by catalytic cracking of higher molecular weight feedstocks, is heated
19
Catalytic Cracking
19.1 INTRODUCTION
Catalytic cracking is a conversion process that can be applied to a variety of feedstocks ranging
from gas oil to heavy oil and in a variety of configuration (Speight and Ozum, 2002; Letzsch, 2009).
Fluid catalytic cracking units are currently in place in ∼400 refineries around the world, and the
units are considered to be one of the most important achievements of the twentieth century.
Basically, catalytic cracking is similar to thermal cracking, but it differs only in the usage of a
catalyst that is not (in theory) consumed in the process, and it is one of the several practical applications used in a refinery that employs a catalyst to improve process efficiency. The original incentives
to develop cracking processes arose from the need to increase gasoline supplies and to increase
the octane number of gasoline, while maintaining yield from high-boiling stocks using catalysts
(Chapter 1; Germain, 1969). Since cracking could virtually double the volume of gasoline from a
barrel of crude oil, the purpose of cracking was completely justified.
This history of catalytic cracking started in the early part of the twentieth century (Table 19.1).
In the 1930s, thermal cracking units produced about half of the total gasoline manufactured,
the octane number of which was about 70 compared to 60 for straight-run gasoline. These were
usually blended together with light ends and sometimes with polymer gasoline and reformate
to produce gasoline base stock with an octane number of about 65. The addition of tetraethyl
lead (ethyl fluid) increased the octane number to about 70 for the regular grade gasoline and
80 for premium grade gasoline. The thermal reforming and polymerization processes that were
developed during the 1930s could be expected to further increase the octane number of gasoline
to some extent, but something new was needed to break the octane barrier that threatened to
stop the development of more powerful automobile engines. In 1936, a new cracking process
opened the way to higher-octane gasoline and this process was known as catalytic cracking,
since that time the use of catalytic materials in the petroleum industry has spread to other processes (Bradley et al., 1989).
The last 70 years have seen substantial advances in the development of catalytic processes
(Luckenbach et al., 1992). This has involved not only rapid advances in the chemistry and physics
of the catalysts themselves but also major engineering advances in the reactor design, for example,
the evolution of the design of the catalyst beds from fixed beds to moving beds to fluidized beds as
well as the different designs of the fluidized bed reactors currently used in catalyst chemistry and
physics, and bed designs have allowed major improvements in the process efficiency and product
yields (Sadeghbeigi, 1995).
An important purpose evolved from the ability of cracked gasoline to resist detonation that is
the cause of knocking in automobile engines. In the early days of automobile engine development,
straight-run gasoline had a lower end point (165°C, 330°F) than that of cracked gasoline (205°C,
400°F) and, furthermore, did not color when exposed to sunlight. Similar exposure caused the
cracked gasoline to turn brown, and hence, straight-run gasoline was regarded as the premium
material.
Gasoline is now mostly produced by either the catalytic cracking processes or by reforming
processes. In catalytic cracking, the petroleum (or petroleum-derived feedstock) is fed into a reaction vessel containing a catalyst. In reforming processes (Chapter 24), naphtha (refined or unrefined), which is produced by catalytic cracking of higher molecular weight feedstocks, is heated