United States
Environmental Protection
Agency
Municipal Environmental Research ^
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-010 Jan. 1984
&ERA Project Summary
Conversion of Sewage Sludge to
Oil by Hydroliquefaction
Wilmer L. Kranich and Atal E. Eralp
A study was undertaken to determine
the feasibility of converting municipal
wastewater sludges into oil under
hydrogen pressure. In a laboratory
autoclave, raw and digested sludges
were subjected to 14 MPa (2000 psig)
total pressure for 20 to 90 minutes.
Aqueous suspensions were treated at
about 300°C, and predried sludge sus-
pended in an oil carrier was reacted at
about 425°C. When the predried sludge
solids were suspended in an oil carrier,
50 percent of the organic content of
sludge was converted into pentane-
soluble oil; but significant amounts of
oil were not produced under the condi-
tions studied when the sludge solids
were slurried in water. A commercial
plant using the oil carrier process
scheme would be complex with high
capital and operating costs. Conse-
quently, further development work on
hydro-liquefaction of sewage sludge is
not recommended.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory, Cincinnati. OH.
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
This study was undertaken to assess
the feasibility of converting municipal
wastewater sludge to liquid and gaseous
fuels through reactions with hydrogen at
high pressure and temperature. The work
was based on earlier experiments carried
out in the Resource Recovery Laboratory
at the Worcester Polytechnic Institute. In
the earlier studies ft-cellulose and
powdered newspaper were used to model
the behavior of combustible municipal
solid waste (J. A. Kaufman and A. H.
Weiss; 1975; Solid Wastes Conversion:
Cellulose Liquefaction; NTIS Report PB
235-509, National Technical Information
Service, Springfield, Virginia 22161).
These studies involved the hydrolique-
faction and hydrogasification over nickel
catalysts of cellulosic substances slurried
in paraffin oil at temperatures of 350° to
450°C under hydrogen pressure in the
range of 3 to 8 MPa (1150 psig). Under
such conditions, up to 90 percent of
cellulosic substances can beconvertedto
gaseous and liquid fuels. The background,
techniques, and experimental equipment
associated with the cellulose and lignite
liquefaction studies have been applied in
the present investigation to the hydro-
liquefaction and gasification of sewage
sludge.
Experimental Procedures
For this study, raw and digested
sludges were collected from the Deer
Island Sewage Treatment Plant in Mas-
sachusetts. These samples were used in
experiments either as aqueous suspen-
sions as received or as suspensions of
dried sludge solids slurried in anthracene
or paraffin oil.
Experiments were carried out in an
autoclave under hydrogen pressure. The
principal apparatus consisted of a
magnetically stirred batch autoclave.
Maximum safe pressure that could be
applied to this autoclave was 14 MPa
(2000 psig). Auxiliary equipment
included a hydrogen-feed system, a
slurry-feed device, pressure and
temperature recorder-controllers, a wet-
test meter for measuring the off-gas, and
analytical equipment for determining the
mass and composition of the liquid and
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gaseous products. Conditions for
experiments are listed in Table 1.
the
Table 1. Conditions for the Oil and Water
Slurry Experiments
Experiment
Oil slurry
Water slurry
Initial H2 Operating
pressure tempera-
(MPa) ture (°C)
8.3 (1200 psig) 425
3,5 (500 psig) 300
With the total pressure limited to 14 MPa
(2000 psig), it was necessary to use lower
initial hydrogen pressures and
temperatures for the water slurry experi-
ments because of the vapor pressure
generated by the water. The conversion
nearly reached its maximum after about
20 min at reaction temperature; little
further conversion was observed after 30
mm.
Results are evaluated in terms of the
total fractional conversion of the toluene-
insoluble organic feed into oils (pentane-
soluble substancesjand into other
substances. These are calculated by the
following relationships:
Conversion to Pentane-Soluble Oil, XQ =
(weight of oils in
product slurry)
(weight of oils in
- sewage sludge and
carrier oil) x 100
(weight of organic toluene-insolubles in
sewage sludge)
Conversion of Toluene-insolubles, XT! =
(weight of organic (weight of organic
toluene-insolubles - toluene-insolubles
in sewage sludge) in product slurry) x 100
(weight of organic toluene-insolubles
in sewage sludge)
Thus Xo represents the net oil yield per
unit of insoluble organic material in
sewage sludge, and XTI represents the
conversion of the insoluble organic
material in sewage sludge to all liquidand
gaseous products.
Results and Conclusions
1. Raw sewage sludge and sludge
settled in digesters can be largely
converted to liquid and gaseous
products by heating the water slurry
to about 300°C under its vapor
pressure. Conversion of up to 90
percent of the toluene-insoluble
organic feed can be achieved
with or without added hydrogen.
Neither sodium carbonate, sodium
molybdate, nor nickel carbonate
catalyst significantly alters the
result.
2. Significant amounts of pentane-
soluble oils were not produced from
the water-slurried sludge under any
of the conditions studied
3. If raw or settled digester sludge, or
the final effluent sludge from the
digesters is dried, ground, and"
slurried in a carrier oil, up to 90
percent of the toluene-insoluble
organic content can be converted in
20 min in the presence of hydrogen
at a total initial pressure of 8.3 MPa
(1200 psig) and a temperature of
about 425°C.
4. Under these conditions, up to 50
percent of the material so converted
may be recovered as pentane-
soluble oils or asphaltenes.
5. Great complexity and high projected
investment and operating costs of a
commercial plant are indicated by
the results obtained here for dried
sludge slurried with oil. These re-
sults do not encourage further
development work on hydrolique-
faction of sewage sludge.
The full report was submitted in fulfill-
ment of Cooperative Agreement No.
80739001 by Worcester Polytechnic
Institute, Worcester, MA, under the
sponsorship of the U.S. Environmental
Protection Agency.
Wilmer L. Kranich is with Worcester Polytechnic Institute, Worcester, MA 01609.
Atal E. Eralp is the EPA Project Officer (see below).
The complete report, entitled "Conversion of Sewage Sludge to OilbyHydrolique-
faction." (Order No. PB 84-133 768; Cost: $8.50. 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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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