United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S7-84-008 Oct. 1984
Project Summary
Conversion of Organic Wastes to
Unleaded, High-Octane Gasoline
James P. Diebold, Charles B. Benham, and G. D. Smith
The possibility of converting organic
waste material into high-value liquids,
such as gasoline, diesel fuel, fuel oils.
and premium-quality lubricating oils,
was the impetus for this project which
demonstrated the compatibility of two
technologies previously considered to
be unrelated-trie pyrolysis of organic
wastes and the low-pressure polymeri-
zation of low-molecular-weight hydro-
carbons to form polymer gasoline.
Specifically, this project developed a
muttistep chemical process to convert
solid organic materials; into a liquid
hydrocarbon product-high-octane
gasoline. Through selective pyrorysis,
organic wastes were converted into
gases rich in reactive hydrocarbons.
The pyrolysis gases were compressed
and purified, resulting in three gaseous
streams: carbon dioxide; byproduct fuel
gases (hydrogen, methane, and carbon
monoxide); and reactive hydrocarbons.
The latter stream was sent to the
polymerization reactor where high-
octane gasoline was formed. A bench-
scale system demonstrated the selective
pyrolysis, the gas purification, and the
polymerization aspects of the process.
The report projects that about 0.28
liters (0.074 gallons) per kilogram ot
organic material can be produced from
municipal trash with this process.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Cincinnati,' OH.
to announce key findings of the
research project that is fully document-
ed in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
In 1973, an economical process to
convert organic waste material into
gasoline was identified at the Naval
Weapons Center (NWC), where a project
was conducted to evaluate the feasibility
of energy independence for remote mili-
tary installations in the course of that
project, utilization of the energy content
of trash was evaluated. Two approaches
were considered.
1. pyrolysis of wastes to form reactive
hydrocarbons (e.g., ethylene), and
their subsequent purification and
conversion to a synthetic
. hydrocarbon gasoline which could
then be substituted for gasoline
derived from petroleum sources
with no changes in storage
facilities, engine design, toxicity, or
performance; and
2. pyrolysis of wastes to form synthetic
gas composed of carbon monoxide
and hydrogen with subsequent
catalytic conversion to methanol,
which could then be used as a
gasoline substitute after some
distribution system and engine
modifications.
Both of these processes appeared
to have considerable merit as eco-
nomical methods to dispose of
waste materials while producing an
energy product.
The critical technology that this
program needed to demonstrate was in
the area of selective pyrolysis of cellulosic
organic waste materials into gases
containing large amounts of olefins and
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their subsequent processibility. If the
selective pyrolysis could be verified and
demonstrated, then the remainder of the
process to make gasoline was seen as
relatively straightforward, based, as it
was, on industrial success with similar
processes; i.e., the parallel process of an
oil refinery. The most significant
difference, of course, would be the use of
cellulosic waste material rather than
crude oil as feed stock.
Pyrolysis
The handling of nonuniform waste
solids is an order of magnitude more
difficult than fluids. The capability of the
pilot plant to operate on a wide variety of
feedstocks will require a flexible system.
Part of the design information required
would be the characteristics of the
potential feedstocks with regard to
particle size, shape, moisture, etc. The
design of the equipment to fluidize the
solid feed would be critical to the success
of the pilot plant, since many organic
wastes tend to become fibrous when
finely ground and are therefore difficult
to fluidize. Once the feed is finely ground
andfluidized in the grinder, it may be best
to keep it flowing. Multi-training grinding
equipment with its reserve capacity
would be preferable to holding bins for
the ground material.
The organic feedstock, finely ground
and fluidized, would be pneumatically
transported to the pyrolysis reactor which
is envisioned as a number of long, red-hot
stainless steel tubes heated to a
temperature between 70Q°C to 800°C
inside a furnace fired by char and
byproduct gases. As is common in refin-
ery practice, the tube diameter would be
less than 10 centimeters. To obtain the
desired throughput, a multitude of tubes
are placed in parallel as in the petrochem-
ical industry cracking crude oil to make
ethylene. A key objective of the pilot-plant
phase is determination of the fluidized
solids stream's ability to divide into a
multitude of smaller streams to feed into
the individual pyrolysis tubes without
plugging them.
Efficient recovery of the energy content
of the pyrolysis stream leaving the reactor
is dictated by the large amount of steam
needed; such a recovery process is
routinely practiced in ethylene plants. For
the trash-to-gasoline process, a high-
temperature heat exchanger would be
required to reduce the pyrolysis stream
temperature from about 760°C to about
200°C. The pyrolysis stream temperature
cannot be lowered much below 200°C
without risk of condensing tar vapors that
could foul the heat exchanger surfaces
and cause the heat exchanger to plug up.
The presence of the char and dirt in the
pyrolysis stream would create the very
high heat-transfer rates experienced
with a fluidized bed, and also would
prevent coke from fouling the heat trans-
fer surfaces. The very fine char would be
removed from the pyrolysis stream in
parallel, small-diameter cyclones after
the stream had passed through the heat
exchanger. The diameter of the cyclones
must be kept small to retain the fine char.
The gas stream would be cooled rapidly
by spraying "quench water" into it. This
step causes the tar to condense into small
droplets rather than to adhere to the heat-
exchanger surfaces. Part of the hot
quench water can be recycled through
the heat exchanger as a supply of
superheated dilution steam for pyrolysis.
The steam will be further superheated in
the pyrolysis furnace.
Low-Pressure Gas Cleanup
After the pyrolysis gases are cooled,
the small remaining tar mist must be
removed prior to compression. This is a
relatively persistent tar mist, which may
require a scrubbing tower in conjunction
with the quench system. To increase the
degree of cleanup, the mist-laden
pyrolysis gas stream may require
electrostatic ionization prior to scrubbing.
Bench-scale experience has indicated
that although a second-stage scrubber
followed by a demisting cyclone was
helpful, the pyrolysis gas still needed to
be filtered before entering the compres-
sor. Unfiltered pyrolysis gases had a
tendency to cause the compressor valves
to gum up and stick. The cleanup of the
pyrolysis stream to remove residual char
and tar with well-designed scrubbers will
be one of the important aspects of the
pilot plant tests.
To compress the pyrolysis gases from
about atmospheric pressure up to above
3100 kPa (450 psig) for storage, a three-
stage reciprocating compressor was
used. Pyrolysis-gas-storage pressures of
up to 9300 kPa (1350 psi) were used.
Normally, very little condensate was
recovered from the intercoolers, although
significant amounts of aqueous and
organic condensates were recovered
from the storage tank where the
compressed gas was allowed to cool to
ambient temperatures. The organic
fraction is dark in color, but has a very low
viscosity and may contain primarily low-
molecular-weight aromatics; e.g.,
benzene, toluene, and xylenes. This
organic phase is referred to as "pyrolysis
gasoline" in the ethylene industry and
may be formed by the polymerization and
dehydrogenation of olefins during the
pyrolysis operation. This pyrolysis
gasoline will be used both as the lean oil
makeup for the hydrocarbon absorber,
and as a high octane (100+) blending
component for the final gasoline product.
The pyrolysis gasoline will be sent to the
lean-oil cleanup distillation column for
purification. The aqueous phase of the
compressor condensate may have use in
the final stage of the gas scrubbing
operation.
High Pressure Gas Purification
The gas-purification section separates
the pyrolysis gases into three separate
streams: carbon dioxide; byproduct gases
containing hydrogen, carbon monoxide,
and methane; and product gases
containing ethylene, propylene, and
butylene. The hot-carbonate system was
successfully piloted in the early 1950s.
Although stainless steel reboiler, valves,
and pumps are recommended, the
remainder of the hot-carbonate system
can be made of steel if a small amount of
potassium dichromate is used to
passivate the solution. To avoid the inad-
vertent precipitation of abrasive potassi-
um bicarbonate in the current bench-
scale project, a solution of 25% potas-
sium carbonate was selected. This
concentration is nearly as effective as
more concentrated solutions which
easily precipitate to plug transfer lines if
cooled slightly. To increase the efficiency
of absorption and regeneration, modern
installations add proprietary additives to
the carbonate solutions. These
proprietary additives may or may not be
more effective than the small amount of
contamination present in the pyrolysis
gases since the bench-scale system
worked so well.
Polymerization
In the early 1930s, the petroleum
industry began to commercially crack
heavy feedstocks in order to make more
gasoline. A major byproduct of this
operation was the production of low-
molecular-weight gases such as ethylene,
propylene, and butylene. Research soon
showed that the byproduct gases could be
readily polymerized to form even more
gasoline. This research was soon com-
mercialized both with and without
catalysts and was common until the
petrochemical market for olefins
developed in the 1950s.
The thermal or noncatalytic approach
was selected for the organic-waste-to-
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gasoline program because of the high
ethylene content of the pyrolysis gases.
The conditions required to polymerize
ethylene with phosphoric or sulfuric acid
catalysts are very severe relative to those
used to polymerize propylene ot butylene.
A series of catalytic polymerization
reactors with increasingly severe
conditions might have to be employed to
successfully polymerize the olefins. Also
the acid catalyst is difficult to maintain in
the active state at the temperature
required to polymerize ethylene. In
contrast, although requiring higher
temperatures and pressures, the thermal
polymerization preferentially polymerizes
ethylene, which is the major
component of the purified pyrolysis
gases. Chosen early in the program,
thermal polymerization still appears to be
the best method. When an impure,
randomly contaminated feedstock such
as organic wastes is used, there is no
concern about removing all of the
possible catalyst poisons. The scale-up of
the thermal polymerizing reactor is
expected to present a very low risk, as it
would be similar to previously
commercialized reactors. The reactor
probably would consist of a tube and shell
heat exchanger followed by a soaker
chamber.
Product
The present project's laboratory-work
confirmed the ease of thermal
polymerization with pure ethylene. The
1935-era octane values are 10 to 15 units
lower than today's values-this project's
polymer gasoline had an unleaded motor
octane of 90 compared with the 75 to 80
range of the 1935 era. After a single
distillation, it appears that the polymer
gasoline product probably will have an
unleaded octane rating and distillation
characteristics suitable for the United
States market. At present United States'
gasoline consumption rates, the market
impact of the gasoline produced from
organic wastes will be relatively small,
posing no immediate danger of market
depression.
Thermal polymerization of ethylene
and other ofef ins also produces synthetic
oils having excellent viscosity character-
istics. For example, the lubricating oils
formed by thermal polymerization of
ethylene, propylene, 1-butene, 2-pen-
tene, or 1 -hexene all had pour points less
than -32°C (-25°F). When cracked
paraffin wax, consisting primarily of
alpha olefins, was used as the feedstock,
the pour point was -34°C (-30°F) and the
viscosity index was 137. Temperatures
up to 450°C (850°F) and pressures up to
about 17,000 kPa (about 2500 psi)
required very short residence to avoid
product degradation. Attempts to further
thermally polymerize a previously
thermally polymerized gasoline fraction
resulted in a very low oil yield, indicating
that extended residence time in the origi-
nal polymerization to form gasoline will
not significantly affect the oil yields at the
moderate temperature of 320°C and
extended reaction time of 9.5 hours.
The market for byproduct lubricating oil
may be considerably more difficult to
exploit than the gasoline market due to
public consciousness of the brand names
of lubricating oils. Extensive testing will
be needed before the byproduct oil can
be compared with the leading synthetic
oils made from chemically pure feed-
stocks, although fairly simple laboratory
tests can easily verify its general
suitability as a lubricant.
Economic Scale-Up
Considerations
Municipal Waste Feedstock
To determine the economic feasibility
of the process to convert municipal trash
into gasoline required a long list of
assumptions. For the use of municipal
trash as feedstock, it was assumed that
the trash contained 60% dry organic
material, 13% inorganics (iron, aluminum,
and glass), and the balance moisture. A
credit of $4.85 per tonne ($4.40 per ton)
of trash processed was assumed for the
value of the reclaimed metals and glass.
A yield of 45 gallons of hydrocarbon
liquids per ton of raw trash processed
was assumed and referred to simply as
"gasoline." The relative economics of the
process were taken to be a function of
capital cost, plant size, gasoline
(hydrocarbon) value, and the dump fee
per ton of trash credited to the process.
The plant size can be expressed in terms
of the population served by the process,
by assuming a daily per capita trash
generation rate of 2.25 kg/day (2.5 tons
daily per 1000 people).
An in-house preliminary economic
evaluation was made by identifying the
major equipment items and estimating
the installed cost and operating cost. This
study indicated that a 91 -tonne/day
(100-ton/day) plant would involve a
capital cost of $6.32 million and an
annual operating cost of $815,000 in
early 1978 dollars. To verify this analysis,
the sponsor (EPA) let a contract to DOW
Chemical Company, Freeport, TX, to
conduct an independent process
evaluation. Dow's preliminary cost
estimate for a 91-tonne/day (100-ton/
day) plant was $7.6 million capital costs
and $873,000 annual operating costs in
early 1978 dollars. Most of the 17% extra
capital cost identified by Dow was related
to process changes that had occurred
since the original in-house study had
been completed. To obtain extrapolations
of the Dow cost estimates, the capital
costs were scaled using 0.65 as the
exponential scaling factor, whereas 0.20
was used as the labor scaling factor. It is
interesting to keep in mind that petroleum
prices are widely predicted to inflate at
annual rates of 3 to 7% faster than the
overall economy, due to the projected
increase in deeper wells and offshore rigs
needed to maintain oil production rates.
At 3% compounded for 10years, gasoline
value would increase by 34%, whereas at
7% annual increase it would double in 10
years. The gasoline value to be
considered is the local wholesale value,
not the much lower value often quoted at
a world-scale refinery located in some
large seaport or oilfield. By extrapolation
it can be shown that the larger the plant
size, the more economical the gasoline to
produce.
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James P. Diebold, Charles B. Benham, and G. D. Smith are with the Naval
Weapons Center, China Lake. CA 93555.
Walter W. Liberick, Jr., is the EPA Project Officer (see below).
The complete report, entitled "Conversion of Organic Wastes to Unleaded, High-
Octane Gasoline," (Order No. PB84-148 865; Cost: $14.50, 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:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
U.S. GOVERNMENT PRINTING OFFICE; 1984 - 559-016/7841
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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POSTAGE & FEES PAI
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PERMIT No. G-35
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