371
14
Instability and Incompatibility
14.1 INTRODUCTION
The study of the properties of petroleum would not be complete without some attention to the
phenomena of instability and incompatibility. Both result in the formation of degradation products
or other undesirable changes in the original properties of petroleum products. And it is the analytical methods that provide the data that point to the reason for problems in the refinery or for the
failure of products to meet specifications and to perform as desired.
As already stated (Chapter 1), petroleum products have been in use for over 5000 years
(Abraham, 1945; Forbes, 1958a,b, 1959; James and Thorpe, 1994). Certain derivatives of petroleum
(the nonvolatile residua and asphalt) could be used for caulking and as an adhesive for jewelry or for
construction purposes as well as the use of asphalt for medicinal purposes. Other derivatives (the
volatile naft or naphtha) were sued as incendiary materials or as illuminants.
Current refineries are a complex series of manufacturing plants that can be subdivided into
(1) separation processes, (2) conversion processes, and (3) finishing processes (Chapter 15).
Incompatibility can occur many of these processes, and the product can also exhibit incompatibility and instability. Furthermore, there are a myriad of other products that have evolved
through the short life of the petroleum industry. And the complexities of product composition
have matched the evolution of the products (Hoffman, 1992). In fact, it is the complexity of product composition that has served the industry well and, at the same time, had an adverse effect on
product use.
Product complexity and the means by which the product is evaluated (ASTM, 2012) have made
the industry unique among industries. But product complexity has also brought to the fore issues
such as instability and incompatibility. Product complexity becomes even more disadvantageous
when various fractions from different types of crude oil are blended or are allowed to remain under
conditions of storage (prior to use) and a distinct phase separates from the bulk product. The adverse
implications of this for refining the fractions to salable products increase (Batts and Fathoni, 1991;
Por, 1992; Mushrush and Speight, 1995).
Therefore, it is appropriate here to define some of the terms that are used in the liquid fuels field
so that their use later in the text will be more apparent and will also alleviate some potential for misunderstanding. The general scientific areas of instability and incompatibility are complex and have
been considered to be nothing better than a black art because not all of the reactions that contribute
to instability and incompatibility have been defined (Wallace, 1964). Nevertheless, recent studies
over the past three decades have made valuable contributions to our understanding of instability and
incompatibility in fuels. But, for the most part, gaps remain in our knowledge of the chemistry and
physics of instability and incompatibility.
Briefly, the term incompatibility refers to the formation of a precipitate (or sediment) or separate
phase when two liquids are mixed. The term instability is often used in reference to the formation
of color, sediment, or gum in the liquid over a period of time and is usually due to chemical reactions, such as oxidation, and is chemical rather than physical. This term may be used to contrast the
formation of a precipitate in the near term (almost immediately).
The phenomenon of instability is often referred to as incompatibility, and more commonly
known as sludge formation, and sediment formation, or deposit formation. In petroleum and its
products, instability often manifests itself in various ways (Table 14.1) (Stavinoha and Henry, 1981;
14
Instability and Incompatibility
14.1 INTRODUCTION
The study of the properties of petroleum would not be complete without some attention to the
phenomena of instability and incompatibility. Both result in the formation of degradation products
or other undesirable changes in the original properties of petroleum products. And it is the analytical methods that provide the data that point to the reason for problems in the refinery or for the
failure of products to meet specifications and to perform as desired.
As already stated (Chapter 1), petroleum products have been in use for over 5000 years
(Abraham, 1945; Forbes, 1958a,b, 1959; James and Thorpe, 1994). Certain derivatives of petroleum
(the nonvolatile residua and asphalt) could be used for caulking and as an adhesive for jewelry or for
construction purposes as well as the use of asphalt for medicinal purposes. Other derivatives (the
volatile naft or naphtha) were sued as incendiary materials or as illuminants.
Current refineries are a complex series of manufacturing plants that can be subdivided into
(1) separation processes, (2) conversion processes, and (3) finishing processes (Chapter 15).
Incompatibility can occur many of these processes, and the product can also exhibit incompatibility and instability. Furthermore, there are a myriad of other products that have evolved
through the short life of the petroleum industry. And the complexities of product composition
have matched the evolution of the products (Hoffman, 1992). In fact, it is the complexity of product composition that has served the industry well and, at the same time, had an adverse effect on
product use.
Product complexity and the means by which the product is evaluated (ASTM, 2012) have made
the industry unique among industries. But product complexity has also brought to the fore issues
such as instability and incompatibility. Product complexity becomes even more disadvantageous
when various fractions from different types of crude oil are blended or are allowed to remain under
conditions of storage (prior to use) and a distinct phase separates from the bulk product. The adverse
implications of this for refining the fractions to salable products increase (Batts and Fathoni, 1991;
Por, 1992; Mushrush and Speight, 1995).
Therefore, it is appropriate here to define some of the terms that are used in the liquid fuels field
so that their use later in the text will be more apparent and will also alleviate some potential for misunderstanding. The general scientific areas of instability and incompatibility are complex and have
been considered to be nothing better than a black art because not all of the reactions that contribute
to instability and incompatibility have been defined (Wallace, 1964). Nevertheless, recent studies
over the past three decades have made valuable contributions to our understanding of instability and
incompatibility in fuels. But, for the most part, gaps remain in our knowledge of the chemistry and
physics of instability and incompatibility.
Briefly, the term incompatibility refers to the formation of a precipitate (or sediment) or separate
phase when two liquids are mixed. The term instability is often used in reference to the formation
of color, sediment, or gum in the liquid over a period of time and is usually due to chemical reactions, such as oxidation, and is chemical rather than physical. This term may be used to contrast the
formation of a precipitate in the near term (almost immediately).
The phenomenon of instability is often referred to as incompatibility, and more commonly
known as sludge formation, and sediment formation, or deposit formation. In petroleum and its
products, instability often manifests itself in various ways (Table 14.1) (Stavinoha and Henry, 1981;