Ikelic - Alliance Digital Repository

COAL
from Western coal has been wasted, being
burned together with coal for electric power gen
eration. Based on coal production data from the
Utah region, it is estimated that at least
200 million pounds per year of fossil resin from
the Wasatch Plateau coal field is being used as
fuel ($0.01 per pound) for electric power genera
tion rather than being used as a chemical com
modity ($0.50 per pound). This practice repre
sents an inappropriate use of a valuable
resource. Improved process technology for the
recovery
the University
of fossil resin is under development at
of Utah and includes selective flota
tion of fossil resin from fine coal streams and sol
vent refining
of the fossil resin concentrate to
produce a premium resin product.
Selective Flotation
Several new flotation technologies have been
developed and a number of papers and research
reports have been published. Three United
States patents which describe the new flotation
technologies have been granted. Of these, selec
tive resin flotation by pH control appears to be
the most economical and practical process. This
resin separation technology is based on the find
ings that the heterocoagulation between resin
and coal particles, which contributes to the inef
ficiency of resin separation from coal, can be con
trolled by pH adjustment. In this regard, the state
of dispersion and coal hydrophobicity can be
controlled for selective resin flotation if the pH is
adjusted to an appropriate level, between pH 8
and 12, depending on the resinous coal type and
previous treatment.
The results from pilot-plant testing of two Utah
resinous coal samples (CO-OP Mines and UP&L
Mines)
have demonstrated the success of this
new flotation technology. Specifically, the proof-
of-concept continuous flotation circuit (about
0.1 tons per hour) resulted In fossil resin recovery
with the same separation efficiency as was ob
tained in laboratory bench-scale testing (more
than 80 percent recovery at about 80 percent
concentrate grade). Secondly, the testing of this
technology
has proved that the selective resin
flotation process is sufficiently profitable to justify
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the development of a fossil resin industry based
on this new flotation process.
Another approach is based on the discovery that
controlled surface oxidation can be used to ac
centuate the difference in hydrophobicity be
tween resin and the parent coal.
Finally, the selective fossil resin flotation can be
accomplished in both a multistage conventional
flotation circuit and in a flotation column. Of par
ticular interest in column flotation is the oppor
tunity to control the chemistry of the system with
the wash water; under these conditions excellent
separation efficiencies can be achieved.
Solvent Refining of Fossil Resin Concentrates
Because light-colored or yellow resin is
preferable and of greater commercial value than
the dark-colored resins, particularly in the ink in
dustry, solvent refining is a necessary step to
purify
resin concentrates and produce a light-
colored resin product.
A detailed study of batch solvent refining of resin
concentrates from the Wasatch Plateau coal is in
progress at the University of Utah to evaluate the
effect of refining conditions on the extraction
yield and product quality during various solvent
extraction processes. These solvent-refined
products are being characterized with respect to
their physical/chemical properties.
Solvent extraction studies indicate that two major
factors contribute to the natural color variation of
the fossil resin:
- Relative
-
abundance of chromophores
(mostly
pounds)
polar and unsaturated com
Finely dispersed inclusions of coal col
loids (< 100 microns)
The hexane-, heptane-, and ethyl acetate-
extracted resins appear light-yellow in color while
the toluene-extracted resin exhibits a significantly
darker color. Of the four solvents, the resin con-
THE SYNTHETIC FUELS REPORT, JANUARY 1995