Page 114 - Synthetic Fuels Handbook

100 CHAPTER THREE

matter of selecting and blending various petroleum fractions to meet definite specifica-
tions, and the production of a homogeneous, stable fuel oil requires experience backed by
laboratory control.

3.5.3 Solid Fuels
Coke is the residue left by the destructive distillation of petroleum residua. That formed in
catalytic cracking operations is usually nonrecoverable, as it is often employed as fuel for
refinery processes.
The composition of petroleum coke varies with the source of the crude oil, but in gen-
eral, large amounts of high-molecular-weight complex hydrocarbons (rich in carbon but
correspondingly poor in hydrogen) make up a high proportion. The solubility of petroleum
coke in carbon disulfide has been reported to be as high as 50 to 80 percent, but this is in
fact a misnomer, since the coke is the insoluble, honeycomb material that is the end product
of thermal processes.
Petroleum coke is employed for a number of purposes, but its chief use is in the manu-
facture of carbon electrodes for aluminum refining, which requires a high-purity carbon—
low in ash and sulfur free; the volatile matter must be removed by calcining. In addition to
its use as a metallurgical reducing agent, petroleum coke is employed in the manufacture
of carbon brushes, silicon carbide abrasives, and structural carbon (e.g., pipes and Rashig
rings), as well as calcium carbide manufacture from which acetylene is produced:

Coke → CaC
2
CaC + H O → HC ≡ CH
2
2
Marketable coke is coke that is relatively pure carbon and can be sold for use as fuel
or for the manufacture of dry cells, electrodes, and the likes. Needle coke (acicular coke)
is a highly crystalline petroleum coke used in the production of electrodes for the steel
and aluminum industries. Catalyst coke is coke that has deposited on the catalysts used
in oil refining, such as those in a catalytic cracker. This coke is impure and is only used
for fuel.
Coke may be used to make fuel gases such as water gas and producer gas. From which, in
turn, synthesis gas can be manufactured leading to a variety of other liquid fuel products.
Water gas is a mixture of carbon monoxide and hydrogen, made by passing steam over
red-hot coke. Producer gas is a mixture of carbon monoxide, hydrogen, and nitrogen and is
manufactured by passing air over red-hot coke (or any carbon-based char)

3.6 REFERENCES

ASTM: Annual Book of Standards, American Society for Testing and Materials, West Conshohocken,
Pa., 2007.
Bland, W. F. and R. L. Davidson: Petroleum Processing Handbook, McGraw-Hill, New York, 1967.
Dickenson, R. L., F. E. Biasca, B. L. Schulman, and H. E. Johnson: Hydrocarbon Processing, 76(2),
1997, p. 57.
Dunning, H. N. and J. W. Moore: “Propane Removes Asphalts from Crudes,” Petroleum Refiner, 36(5),
1957, pp. 247–250.
Gary, J. H., and G. E. Handwerk: Petroleum Refining: Technology and Economics, 4th ed., Marcel
Dekker Inc., New York, 2001.
Gruse, W. A. and D. R. Stevens: Chemical Technology of Petroleum, McGraw-Hill, New York, 1960.