433
16
Refining Chemistry
16.1 INTRODUCTION
Crude oil is rarely used in its raw form but must instead be processed into its various products,
generally as a means of forming products with hydrogen content different from that of the original
feedstock. Thus, the chemistry of the refining process is concerned primarily with the production of
not only better products but also salable materials.
Crude oil contains many thousands of different compounds that vary in molecular weight from
methane (CH 4 , 16) to more than 2000 (Boduszynski, 1987, 1988; Speight, 1994). This broad range in
molecular weights results in boiling points that range from −160°C (−288°F) to temperatures on the
order of nearly 1100°C (2000°F). Many of the constituents of crude oil are paraffins. Remembering
that the word paraffin was derived from the Latin parum affinis meaning little affinity or little
reactivity, it must have come as a great surprise that hydrocarbons, paraffins included, can undergo
a diversity of reactions, thereby influencing the chemistry of refining depending upon the source of
the crude oil (Smith, 1994; Laszlo, 1995; Yen, 1998).
The major refinery products are liquefied petroleum gas (LPG), gasoline, jet fuel, solvents, kerosene, middle distillates (known as gas oil outside the United States), residual fuel oil, and asphalt.
In the United States, with its high demand for gasoline, refineries typically upgrade their products
much more than in other areas of the world, where the heavy end products, like residual fuel oil, are
used in industry and power generation.
Understanding refining chemistry not only allows an explanation of the means by which these
products can be formed from crude oil but also offers a chance of predictability. This is very necessary
when the different types of crude oil accepted by refineries are considered. And the major processes
by which these products are produced from crude oil constituents involve thermal decomposition.
There are various theories relating to the thermal decomposition of organic molecules and this
area of petroleum technology has been the subject of study for several decades (Hurd, 1929; Fabuss
et al., 1964; Fitzer et al., 1971). The relative reactivity of petroleum constituents can be assessed on
the basis of bond energies, but the thermal stability of an organic molecule is dependent upon the
bond strength of the weakest bond. And even though the use of bond energy data is a method for
predicting the reactivity or the stability of specific bonds under designed conditions, the reactivity of a particular bond is also subject to its environment. Thus, it is not only the reactivity of the
constituents of petroleum that is important in processing behavior, it is also the stereochemistry of
the constituents as they relate to one another that is also of some importance (Chapters 12 and 13).
It must be appreciated that the stereochemistry of organic compounds is often a major factor in
determining reactivity and properties (Eliel and Wilen, 1994).
In the present context, it is necessary to recognize that (parum affinis or not) most hydrocarbons decompose thermally at temperatures above about 650°F (340°C), so the high boiling points
of many petroleum constituents cannot be measured directly and must be estimated from other
measurements. And in the present context, it is as well that hydrocarbons decompose at elevated
temperatures, thereby lies the route to many modern products. For example, in a petroleum refinery,
the highest value products are transportation fuels:
1. Gasoline (boiling range: 35°C–220°C, 95°F–425°F)
2. Jet fuel (boiling range: 175°C–290°C, 350°F–550°F)
3. Diesel (175°C–370°C, 350°F–700°F)
16
Refining Chemistry
16.1 INTRODUCTION
Crude oil is rarely used in its raw form but must instead be processed into its various products,
generally as a means of forming products with hydrogen content different from that of the original
feedstock. Thus, the chemistry of the refining process is concerned primarily with the production of
not only better products but also salable materials.
Crude oil contains many thousands of different compounds that vary in molecular weight from
methane (CH 4 , 16) to more than 2000 (Boduszynski, 1987, 1988; Speight, 1994). This broad range in
molecular weights results in boiling points that range from −160°C (−288°F) to temperatures on the
order of nearly 1100°C (2000°F). Many of the constituents of crude oil are paraffins. Remembering
that the word paraffin was derived from the Latin parum affinis meaning little affinity or little
reactivity, it must have come as a great surprise that hydrocarbons, paraffins included, can undergo
a diversity of reactions, thereby influencing the chemistry of refining depending upon the source of
the crude oil (Smith, 1994; Laszlo, 1995; Yen, 1998).
The major refinery products are liquefied petroleum gas (LPG), gasoline, jet fuel, solvents, kerosene, middle distillates (known as gas oil outside the United States), residual fuel oil, and asphalt.
In the United States, with its high demand for gasoline, refineries typically upgrade their products
much more than in other areas of the world, where the heavy end products, like residual fuel oil, are
used in industry and power generation.
Understanding refining chemistry not only allows an explanation of the means by which these
products can be formed from crude oil but also offers a chance of predictability. This is very necessary
when the different types of crude oil accepted by refineries are considered. And the major processes
by which these products are produced from crude oil constituents involve thermal decomposition.
There are various theories relating to the thermal decomposition of organic molecules and this
area of petroleum technology has been the subject of study for several decades (Hurd, 1929; Fabuss
et al., 1964; Fitzer et al., 1971). The relative reactivity of petroleum constituents can be assessed on
the basis of bond energies, but the thermal stability of an organic molecule is dependent upon the
bond strength of the weakest bond. And even though the use of bond energy data is a method for
predicting the reactivity or the stability of specific bonds under designed conditions, the reactivity of a particular bond is also subject to its environment. Thus, it is not only the reactivity of the
constituents of petroleum that is important in processing behavior, it is also the stereochemistry of
the constituents as they relate to one another that is also of some importance (Chapters 12 and 13).
It must be appreciated that the stereochemistry of organic compounds is often a major factor in
determining reactivity and properties (Eliel and Wilen, 1994).
In the present context, it is necessary to recognize that (parum affinis or not) most hydrocarbons decompose thermally at temperatures above about 650°F (340°C), so the high boiling points
of many petroleum constituents cannot be measured directly and must be estimated from other
measurements. And in the present context, it is as well that hydrocarbons decompose at elevated
temperatures, thereby lies the route to many modern products. For example, in a petroleum refinery,
the highest value products are transportation fuels:
1. Gasoline (boiling range: 35°C–220°C, 95°F–425°F)
2. Jet fuel (boiling range: 175°C–290°C, 350°F–550°F)
3. Diesel (175°C–370°C, 350°F–700°F)