Page 19 - Synthetic Fuels Handbook

FUEL SOURCES 7

In addition to this definition, there are several tests that must be carried out to deter-
mine whether or not, in the first instance, a resource is a tar sand deposit (Speight, 2001
and references cited therein). Most of all, a core taken from a tar sand deposit, the bitumen
isolated therefrom, are certainly not identifiable by the preliminary inspections (sight and
touch) alone.
In the United States, the final determinant is whether or not the material contained
therein can be recovered by primary, secondary, or tertiary (enhanced) recovery methods
(US Congress 1976).
The relevant position of tar sand bitumen in nature is best illustrated by comparing its
position relevant to petroleum and heavy oil. Thus, petroleum is referred to generically as
a fossil energy resource that is derived from organic sediment (Fig. 1.2) and is further clas-
sified as a hydrocarbon resource.

Gas Natural gas

Naturally-occurring
hydrocarbons
Associated gas
Organic Liquid Petroleum Crude oil
sediments Heavy oil
Tar sand bitumen

Lignite Conversion required
Subbituminous to produce
Coal
Bituminous hydrocarbons
Soild Anthracite
Oil shale
FIGURE 1.2 Informal classification of organic sediments by their ability to produce hydrocarbons.

The inclusion of tar sand bitumen, coal, and oil shale kerogen in this subdivision of
organic sediments is automatic since these two natural resources (coal and oil shale kerogen)
will produce hydrocarbons by thermal decomposition (high-temperature processing). Thus,
if either coal and/or oil shale kerogen is to be included in the term hydrocarbon resources,
it is more appropriate that they be classed as hydrocarbon-producing resources.
It is incorrect to refer to tar sand bitumen as tar or pitch. In many parts the name bitu-
men is used as the name for road asphalt. Although the word tar is somewhat descriptive
of the black bituminous material, it is best to avoid its use with respect to natural materials.
More correctly, the name tar is usually applied to the heavy product remaining after the
destructive distillation of coal or other organic matter. Pitch is the distillation residue of
the various types of tar.
Physical methods of fractionation of tar sand bitumen can also produce the four generic
fractions: saturates, aromatics, resins, and asphaltenes. However, for tar sand bitumen, the
fractionation produces shows that bitumen contains high proportions of the molecularly
complex asphaltene constituents and resin constituents, even in amounts up to 50 percent
w/w (or higher) of the bitumen with much lower proportions of saturates and aromatics
than petroleum or heavy oil. In addition, the presence of ash-forming metallic constituents,
including organo-metallic compounds such as, vanadium and nickel, is also a distinguish-
ing feature of bitumen.