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
     BULK RATE
POSTAGE & FEES PAI
        EPA
  PERMIT No. G-35
Official Business
Penalty for Private Use $300

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