401
Introduction to Refining Processes
When kerosene was the major product, gasoline was the portion of crude petroleum too volatile
to be included in kerosene. The refiners of the 1890s and early 1900s had no use for it and often
dumped an accumulation of gasoline into the creek or river that was usually nearby. As the demand
for gasoline increased with the onset of World War I and the ensuing 1920s, more crude oil had to
be distilled not only to meet the demand for gasoline but also to reduce the overproduction of the
heavier petroleum fractions, including kerosene.
The problem of how to produce more gasoline from less crude oil was solved in 1913 by the
incorporation of cracking units into refinery operations in which fractions heavier than gasoline
were converted into gasoline by thermal decomposition. The early (pre-1940) processes employed
for gasoline manufacture were processes in which the major variables involved were feedstock type,
time, temperature, and pressure and which need to be considered to achieve the cracking of the
feedstock to lighter products with minimal coke formation.
As refining technology evolved throughout this century, the feedstock for cracking processes
became the residuum or heavy distillate from a distillation unit. In addition, the residual oils produced as the end products of distillation processes, and even some of the heavier virgin oils, often
contain substantial amounts of asphaltic materials, which preclude use of the residuum as fuel oils
or lubricating stocks. However, subjecting these residua directly to thermal processes has become
economically advantageous, since, on the one hand, the end result is the production of lower-boiling
salable materials and, on the other hand, the asphaltic materials in the residua are regarded as the
unwanted coke-forming constituents.
As the thermal processes evolved and catalysts were employed with more frequency, poisoning
of the catalyst with a concurrent reduction in the lifetime of the catalyst became a major issue for
refiners. To avoid catalyst poisoning, it became essential that as much of the nitrogen and metals
(such as vanadium and nickel) as possible should be removed from the feedstock. The majority of
the heteroatoms (nitrogen, oxygen, and sulfur) and the metals are contained in, or associated with,
the asphaltic fraction (residuum). It became necessary that this fraction be removed from cracking
feedstocks.
With this as the goal a number of thermal processes, such as tar separation (flash distillation),
vacuum flashing, visbreaking, and coking, came into wide usage by refiners and were directed at
upgrading feedstocks by the removal of the asphaltic fraction. The method of deasphalting with
liquid hydrocarbon, gases such as propane, butane, or iso-butane, became a widely used refinery
operation in the 1950s and was very effective for the preparation of residua for cracking feedstocks.
In this process, the desirable oil in the feedstock is dissolved in the liquid hydrocarbon, and asphaltic materials remain insoluble.
Operating conditions in the deasphalting tower depend on the boiling range of the feedstock and
the required properties of the product. Generally, extraction temperatures can range from 55°C to
120°C (130°F–250°F) with a pressure of 400–600 psi. Hydrocarbon/oil ratios of 6:1–10:1 by volume
are normally used.
15.5.2 modern ProCesses
15.5.2.1 Thermal Cracking
One of the earliest conversion processes used in the petroleum industry is the thermal decomposition of higher-boiling materials into lower-boiling products. This process is known as thermal
cracking and the exact origins of the process are unknown. The process was developed in the early
1900s to produce gasoline from the unwanted higher-boiling products of the distillation process.
However, it was soon learned that the thermal cracking process also produced a wide slate of products varying from highly volatile gases to nonvolatile coke.
The heavier oils produced by cracking are light and heavy gas oils as well as a residual oil that
could also be used as heavy fuel oil. Gas oils from catalytic cracking were suitable for domestic
Introduction to Refining Processes
When kerosene was the major product, gasoline was the portion of crude petroleum too volatile
to be included in kerosene. The refiners of the 1890s and early 1900s had no use for it and often
dumped an accumulation of gasoline into the creek or river that was usually nearby. As the demand
for gasoline increased with the onset of World War I and the ensuing 1920s, more crude oil had to
be distilled not only to meet the demand for gasoline but also to reduce the overproduction of the
heavier petroleum fractions, including kerosene.
The problem of how to produce more gasoline from less crude oil was solved in 1913 by the
incorporation of cracking units into refinery operations in which fractions heavier than gasoline
were converted into gasoline by thermal decomposition. The early (pre-1940) processes employed
for gasoline manufacture were processes in which the major variables involved were feedstock type,
time, temperature, and pressure and which need to be considered to achieve the cracking of the
feedstock to lighter products with minimal coke formation.
As refining technology evolved throughout this century, the feedstock for cracking processes
became the residuum or heavy distillate from a distillation unit. In addition, the residual oils produced as the end products of distillation processes, and even some of the heavier virgin oils, often
contain substantial amounts of asphaltic materials, which preclude use of the residuum as fuel oils
or lubricating stocks. However, subjecting these residua directly to thermal processes has become
economically advantageous, since, on the one hand, the end result is the production of lower-boiling
salable materials and, on the other hand, the asphaltic materials in the residua are regarded as the
unwanted coke-forming constituents.
As the thermal processes evolved and catalysts were employed with more frequency, poisoning
of the catalyst with a concurrent reduction in the lifetime of the catalyst became a major issue for
refiners. To avoid catalyst poisoning, it became essential that as much of the nitrogen and metals
(such as vanadium and nickel) as possible should be removed from the feedstock. The majority of
the heteroatoms (nitrogen, oxygen, and sulfur) and the metals are contained in, or associated with,
the asphaltic fraction (residuum). It became necessary that this fraction be removed from cracking
feedstocks.
With this as the goal a number of thermal processes, such as tar separation (flash distillation),
vacuum flashing, visbreaking, and coking, came into wide usage by refiners and were directed at
upgrading feedstocks by the removal of the asphaltic fraction. The method of deasphalting with
liquid hydrocarbon, gases such as propane, butane, or iso-butane, became a widely used refinery
operation in the 1950s and was very effective for the preparation of residua for cracking feedstocks.
In this process, the desirable oil in the feedstock is dissolved in the liquid hydrocarbon, and asphaltic materials remain insoluble.
Operating conditions in the deasphalting tower depend on the boiling range of the feedstock and
the required properties of the product. Generally, extraction temperatures can range from 55°C to
120°C (130°F–250°F) with a pressure of 400–600 psi. Hydrocarbon/oil ratios of 6:1–10:1 by volume
are normally used.
15.5.2 modern ProCesses
15.5.2.1 Thermal Cracking
One of the earliest conversion processes used in the petroleum industry is the thermal decomposition of higher-boiling materials into lower-boiling products. This process is known as thermal
cracking and the exact origins of the process are unknown. The process was developed in the early
1900s to produce gasoline from the unwanted higher-boiling products of the distillation process.
However, it was soon learned that the thermal cracking process also produced a wide slate of products varying from highly volatile gases to nonvolatile coke.
The heavier oils produced by cracking are light and heavy gas oils as well as a residual oil that
could also be used as heavy fuel oil. Gas oils from catalytic cracking were suitable for domestic