481
18
Thermal Cracking
18.1 INTRODUCTION
Distillation (Chapter 17) has remained a major refinery process and a process to which just about
every crude oil that enters the refinery is subjected (Speight and Ozum, 2002, and references cited
therein). However, not all crude oils yield the same distillation products. In fact, the nature of the
crude oil dictates the processes that may be required for refining. And balancing product yield with
demand is a necessary part of refinery operations.
After 1910, the demand for automotive fuel began to outstrip the market requirements for kerosene, and refiners were pressed to develop new technologies to increase gasoline yields. The earliest
process, called thermal cracking, consisted of heating heavier oils (for which there was a low market
requirement) in pressurized reactors and thereby cracking, or splitting, their large molecules into
the smaller ones that form the lighter, more valuable fractions such as gasoline, kerosene, and light
industrial fuels.
Gasoline manufactured by the cracking process performed better in automobile engines than
gasoline derived from distillation of unrefined petroleum. The development of more powerful aircraft engines in the late 1930s gave rise to a need to increase the combustion characteristics of
gasoline and spurred the development of lead-based fuel additives to improve engine performance.
During the 1930s and World War II, improved refining processes involving the use of catalysts
led to further improvements in the quality of transportation fuels and further increased their supply.
These improved processes, including catalytic cracking of heavy oil (Chapters 19 and 22), alkylation, polymerization, and isomerization (Chapter 24), enabled the petroleum industry to meet the
demands of high-performance combat aircraft and, after the war, to supply increasing quantities of
transportation fuels for public and military use.
The 1950s and 1960s brought a large-scale demand for jet fuel and high-quality lubricating oils.
The continuing increase in demand for petroleum products also heightened the need to process a
wider variety of crude oils into high-quality products. Catalytic reforming of naphtha (Chapter 24)
replaced the earlier thermal reforming process and became the leading process for upgrading fuel
qualities to meet the needs of higher compression engines. Hydrocracking, a catalytic cracking
process conducted in the presence of hydrogen (Chapter 22), was developed to be a versatile manufacturing process for increasing the yields of either gasoline or jet fuels.
Balancing product yield and market demand, without the manufacture of large quantities of fractions having low commercial value, has long required processes for the conversion of hydrocarbons of
one molecular weight range and/or structure into some other molecular weight range and/or structure.
Basic processes for this are still the so-called cracking processes in which relatively high-boiling constituents are cracked (thermally decomposed) into lower molecular weight, lower boiling molecules,
although reforming, alkylation, polymerization, and hydrogen-refining processes have wide applications in producing premium-quality products (Hsu and Robinson, 2006; Gary et al., 2007).
It is generally recognized that the most important part of any refinery is its gasoline (and liquid fuels) manufacturing facilities; other facilities are added to manufacture additional products as
indicated by technical feasibility and economic gain. More equipment is used in the manufacture
of gasoline, the equipment is more elaborate, and the processes more complex than for any other
product. Among the processes that have been used for liquid fuels production are thermal cracking,
catalytic cracking, thermal reforming, catalytic reforming, polymerization, alkylation, coking, and
18
Thermal Cracking
18.1 INTRODUCTION
Distillation (Chapter 17) has remained a major refinery process and a process to which just about
every crude oil that enters the refinery is subjected (Speight and Ozum, 2002, and references cited
therein). However, not all crude oils yield the same distillation products. In fact, the nature of the
crude oil dictates the processes that may be required for refining. And balancing product yield with
demand is a necessary part of refinery operations.
After 1910, the demand for automotive fuel began to outstrip the market requirements for kerosene, and refiners were pressed to develop new technologies to increase gasoline yields. The earliest
process, called thermal cracking, consisted of heating heavier oils (for which there was a low market
requirement) in pressurized reactors and thereby cracking, or splitting, their large molecules into
the smaller ones that form the lighter, more valuable fractions such as gasoline, kerosene, and light
industrial fuels.
Gasoline manufactured by the cracking process performed better in automobile engines than
gasoline derived from distillation of unrefined petroleum. The development of more powerful aircraft engines in the late 1930s gave rise to a need to increase the combustion characteristics of
gasoline and spurred the development of lead-based fuel additives to improve engine performance.
During the 1930s and World War II, improved refining processes involving the use of catalysts
led to further improvements in the quality of transportation fuels and further increased their supply.
These improved processes, including catalytic cracking of heavy oil (Chapters 19 and 22), alkylation, polymerization, and isomerization (Chapter 24), enabled the petroleum industry to meet the
demands of high-performance combat aircraft and, after the war, to supply increasing quantities of
transportation fuels for public and military use.
The 1950s and 1960s brought a large-scale demand for jet fuel and high-quality lubricating oils.
The continuing increase in demand for petroleum products also heightened the need to process a
wider variety of crude oils into high-quality products. Catalytic reforming of naphtha (Chapter 24)
replaced the earlier thermal reforming process and became the leading process for upgrading fuel
qualities to meet the needs of higher compression engines. Hydrocracking, a catalytic cracking
process conducted in the presence of hydrogen (Chapter 22), was developed to be a versatile manufacturing process for increasing the yields of either gasoline or jet fuels.
Balancing product yield and market demand, without the manufacture of large quantities of fractions having low commercial value, has long required processes for the conversion of hydrocarbons of
one molecular weight range and/or structure into some other molecular weight range and/or structure.
Basic processes for this are still the so-called cracking processes in which relatively high-boiling constituents are cracked (thermally decomposed) into lower molecular weight, lower boiling molecules,
although reforming, alkylation, polymerization, and hydrogen-refining processes have wide applications in producing premium-quality products (Hsu and Robinson, 2006; Gary et al., 2007).
It is generally recognized that the most important part of any refinery is its gasoline (and liquid fuels) manufacturing facilities; other facilities are added to manufacture additional products as
indicated by technical feasibility and economic gain. More equipment is used in the manufacture
of gasoline, the equipment is more elaborate, and the processes more complex than for any other
product. Among the processes that have been used for liquid fuels production are thermal cracking,
catalytic cracking, thermal reforming, catalytic reforming, polymerization, alkylation, coking, and