United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S2-85/045 May 1985
>&EPA Project Summary
Laboratory Evaluation of Critical
Fluid Extractions for
Environmental Applications
Richard P. deFilippi and Marie E. Chung
The objective of this program was to
determine the technical feasibility of
the use of critical fluids (condensed
gases or supercritical fluids) as extract-
ing solvents to treat oily industrial
wastes. The process has the potential
for recovering by-product values from
the wastes to offset the operating cost
of the treatment. Wastes studied were:
oily mill scale from the steel industry,
oil-laden bleaching clays from specialty
oil and vegetable oil decolorization and
clarification, and lube-oil/water waste
emulsions from metal working in the
aluminum and steel industries. Steel
mill scales were successfully de-oiled to
below 0.1 wt %, using condensed-gas
hydrocarbon and halocarbon solvents
for extraction. The recovered oil met
acceptable fuel specifications. The iron
value of the de-oiled scale and the fuel
value of the oil would provide sufficient
credits to permit an attractive payout on
the investment in treating equipment.
Spent bleaching clays, used to proc-
ess silicone oils and vegetable (soybean)
oil, were treated with hydrocarbon and
halocarbon solvents: most of the oil (up
to 100%) was recovered. An analyzed
silicone oil met product specifications.
The cost of a critical-fluid-based extrac-
tion plant of representative capacity
would pay out favorably due to credits
for recovered oil.
Waste lube oil emulsions from alum-
inum-can forming and combined steel
mill operations were de-oiled using CO2
as a solvent near its critical point.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
In recent years, several studies have
been conducted by the U.S, EPA for uses
of critical-fluid extraction for waste treat-
ment. As a solvent extraction, the process
has unique advantages in facilitating
recovery of by-products and minimizing
solvent residues because of the high
solvent volatility. Prior studies sponsored
by EPA and others have focused on
coupling extraction with adsorption; i.e.,
using critical fluids to strip and regenerate
adsorbents wh ich selectively trap organic
pollutants from liquid and vapor effluents.
More recently, the direct extraction of
liquid and solid wastes has been con-
sidered, including a range of applications
of critical-fluid extraction to environ-
mental problems. From these, three major
industrial sectors have emerged as pri-
mary areas for further evaluation, ac-
cording to two criteria: the magnitude of
the environmental problem, and econom-
ics sufficiently favorable to permit suc-
cessful introduction of the technology
commercially.
The objective of the EPA program,
based on discussions with industry, was
to determine the technical feasibility, at
bench scale, of the use of critical-fluid
extraction to treat: steel-mill oily wastes,
vegetable- and specialty-oil processing
wastes, and machining-oil emulsion
wastes. Also, preliminary information on
the economics of this process was to be
obtained including the recovery of by*
product values.
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Steel Mill Scale De-Oiling
The steel industry is a major producer
of oil-containing solid wastes. While a
broad range of scale and sludges are
produced, the major volume problem is
mill scale, amounting to 4,-5% of the total
raw steel production. Mill scale is waste
iron oxides, partly contaminated with
lubricating oils, scraped from the surfaces
of formed steel such as rolling stock. Its
oil content varies, but can run as high as
several percent for the composite scale
•for a total mill, and much higher for
certain operations. About half the mill
scale produced is recycled to sinter plants
for return to the blast furnace; the other
half is stockpiled. About 11% of all
lubricants purchased by^ steel mills, ujti-
mately become the Diffraction of mill
scale. Mill scale fines, 80-85% of the total
mill scale, have an oil content significantly
high to adversely affect sinter plant
operations. The oil is volatilized during
sintering and recondenses in the sinter-
plant off-gas. Without treatment, the
gaseous effluent can produce a visible
plume; with baghouses, the oil can con-
dense and impair operations. Several de-
oiling methods have been tested: water-
washing using hot alkaline solution,
thermal incineration, and liquid solvent
washing using a chlorinated hydrocarbon
to extract the oil, and then distilling to
recover the solvent.
Bleaching Clay De-Oiling
The refining of certain synthetic and
natural oils includes a processing step to
decolorize, or bleach, the refined product
using special clays. Treated like this are
specialty oils (including high-value fluids
such as silicones) and large volumes of
crude vegetable oils, such as soybean,
corn, cottonseed, peanut, and sunflower.
The clay is mixed with the oil, and the
spent clay is filtered from the clarified oil.
The resulting clay filter cake contains
about 30-60% occluded oil, representing
a pollution problem and a yield loss.
Waste-Oil/Water Emulsion
De-Oiling
•Waste-oil/water emulsions from in-
dustrial processes may be derived from a
wide range of sources. Common among
these are waste lubricating emulsions in
the metal machining and forming indus-
tries. For these laboratory studies, two
types of wastes were selected for testing
critical-fluid solvent extraction for oil
-removal: ^aluminunr-*can-forming opera™
tions and various steel mill operations.
Each sample was extracted with at least
one of the following solvents: COz, pro-
pane, Solvent-12, and Solvent-500.
Conclusions
Steel mill scales containing several
percent oil can be de-oiled to levels
acceptable, for, sinter-plant feed, using
condensed gas solvents such as propane
and dichlorodifluoromethane (Solvent-
12).
The quality of oil extracted from oil mill
scale meets acceptable fuel specifica-
tions.'A preliminary economic evaluation
shows that credits for de-oiled mill scale
and fuel-quality oil provide an attractive
payout for a plant de-oiling 90,000 metric
tons/year of 5%-oil mill scale feed.
Oil laden spent clays from decolorizing
and clarifying silicone oils and soybean
oil can be de-oiled using condensed
propane'and halocarbons such as Solvent-
12 and a mixture of Solvent-12 with 1,1-
difluoroethane (Solvent-500).
Extracted silicone oil from spent clay
TrfeFpfoducT specifications. Preliminary
economics for a plant treating 300,000
Ib/yr (136,000 kg/yr) indicated that a
favorable payout could be achieved from
recovered oil credits. Waste lube-oil
emulsions from aluminum-can forming
were de-oiled using C02 as an extraction
solvent; however, hydrocarbon and halo-
carbon solvents were unsuccessful.
R, P. deFilippi and M. E. Chung are with Arthur D. Little, Inc., Cambridge, MA
02140.
Bruce A. Tichenor is the EPA Project Officer (see below).
The complete report, entitled "Laboratory Evaluation of Critical Fluid Extractions
for Environmental Applications," (Order No. PB 85-189 843/AS; Cost: $11.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161 • ...
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
* U.S. GOVERNMENT PRINTING OFFICE: 1985-559-O16/27066 j
United States
Environmental Protection
Agoncy
Center for Environmental Research
Information '
Cincinnati OH 45268
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