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[SANET-MG] plastic into oil
http://www.i-sis.org.uk/WPIO.phpISIS Press Release 29/11/05
Waste Plastics into Oil
What if the mountains of plastic wastes that blight our landscapes and
beaches spewing poisons from incinerators and landfills could be
transformed overnight into combustible gas and diesel oil. Dr. Mae-Wan Ho
A fully referenced version of this paper is posted on ISIS members’
website. Details here
As the price of oil and gas soar, alternative energy sources are rapidly
becoming cost-effective by comparison. One attractive option that has
emerged is diesel oil from waste plastics.
Chinese oil refinery used waste plastics
The first report of turning plastic wastes into oil came in 2001 from
the People’s Daily, China’s English language newspaper . An oil
refinery in Hunan province had succeeded in processing 30 000 tonnes of
plastic wastes into 20 000 tonnes of gasoline and diesel oil that
satisfied the provincial standards. Wang Xu, who built the refinery in
1999, started experimenting with waste plastic processing in the 1980s,
and later teamed up with Hunan University doctoral tutor Zeng Guangming
who gave him scientific advice on decomposing plastic wastes. This may
be one reason why China has been importing enormous amounts of plastic
wastes (“Redemption from the plastic wasteland”, this series).
Although no details were given on the technology used, it is most likely
based on thermal depolymerization, a process for breaking down organic
wastes under heat and pressure into light crude oil, which has been
studied in the West since the 1970s . It mimics the natural
geological processes thought to be involved in producing fossil fuels.
Under high pressure and heat, long chain polymers of carbon, hydrogen
and oxygen decompose into short-chain petroleum hydrocarbons in a matter
of hours. Until quite recently, however, the artificial process was far
from energy-efficient, as more energy had to be put in than was
produced, and the product, a crude oil, was also full of impurities.
In the 1980s, Illinois microbiologist Paul Baskis in the United States
modified the process to produce a lighter, cleaner oil, but failed to
convince investors until 1996, when a company called Changing World
Technologies began development with Baskis to make the process
commercially viable .
Changing World Technologies opened a demonstration plant in
Philadelphia, Pennsylvania, and in 2001, the first full-scale plant was
built in Carthage, Missouri, and the company applied to patent a
“thermal conversion process” (TCP) for converting organic wastes, such
as pig manure, into oil and other products.
Turkey offal into diesel oil and fertilizer
The first pilot TCP plant was built to treat turkey offal, which it
succeeded in converting to diesel fuel, along with fertilizer and
absorbent carbon. The full-scale plant, located in Carthage, Missouri,
can process up to 191 tonnes of turkey wastes a day .
(The TCP plant looks like a small refinery operation, and it is likely
that, given the earlier report from China, existing oil refineries could
easily be converted into TCP plants.)
Processing is divided into two main stages. In the first stage, the
turkey waste is pulped into a slurry and heated at a pressure of 40 bar
(1 bar ~ 1 atmosphere) to 200-300C. The solids are separated and the
liquid is ‘flashed’ to a lower pressure to separate the oil from water.
The oil is then heated in a second stage reactor to a higher temperature
around 500C to ‘crack’ it into light hydrocarbon oil, leaving a solid
product. Recovered from the first stage are solid minerals and a liquid
concentrate rich in nitrogen and other nutrients. From the second stage,
fuel gas, carbon, and diesel oil are recovered. The fuel gas produced is
a mixture of methane, carbon monoxide, carbon dioxide and low molecular
weight hydrocarbons. The oil contains predominantly straight chain
hydrocarbons with a chain length between 15 and 20.
One advantage of TCP is that it claims to break down the prion proteins
associated with mad cow disease - which survives normal boiling or
autoclaving - and is therefore suitable for treating slaughterhouse
wastes, disinfecting the wastes at the same time that biodiesel, gas
fuels and fertilizers are produced. However, no evidence was presented
for this claim.
The process also appears to be energy efficient and environmentally
friendly in a lifecycle audit . The audit did not include energy and
carbon emission costs involved in building the TCP plant, however.
From an input of 191 tonnes of wet turkey offal per day (50 percent
moisture) plus 3.0 tonnes of sulphuric acid and 91.2MJ of grid
electricity, the output are 2506 GJ of diesel oil, 274GJ fuel gas, 30.6
tonnes liquid nitrogen fertilizer, 7.5 tonnes mineral fertilizer, 6.1
tonnes of carbon and 79.9 m3 waste water.
There are no discharges to the atmosphere from the plant during the
processing. The only gaseous product is the medium to high heat-content
fuel-gas (heating values between 9 and 19 MJ/m3) used for heat in
processing, or as fuel for a boiler or turbine. Emissions from the
turbine have been independently verified to be in compliance with the
Clean Air Act. The oil product is typically a light hydrocarbon similar
to diesel fuel that could be used as heating oil or converted into
higher value products.
There are two types of fertilizers/soil amendments produced by the TCP:
Res minerals and Res liquid concentrate . Both are produced from food
and agricultural wastes such as turkey offal, feathers, bones, pig
manure, used cooking oil and slaughterhouse waste. Res minerals consist
of N, P K, and Ca, representing nearly 30 percent of the total
fertilizer, the rest is made up of organic material such as
carbohydrates, amino acids, fatty acids and moisture (40 percent).
The Res liquid concentrate is a mixture rich in nitrogen that also
contains phosphorus, potassium, sulphur and trace minerals, similar to a
fish emulsion, and is rich in amino acids and derivatives.
The products leave the unit at about 100C after heat recovery. With full
heat recovery, the overall energy efficiency could be above 85 percent
based on the heating value of the products and the dry weight of the
feedstock. In other words, it generates 467 percent more energy than it
takes to produce it; except that this figure leaves out energy needed to
construct the TCP plant.
For comparison, biofuel from maize crops, according to the latest study,
generates at best only 35 percent more energy than it takes to produce
, and has the added disadvantage that growing crops for biofuels uses
up valuable agricultural land that could produce food.
Each tonne wet weight of turkey wastes processed was estimated to save
more than a tonne of carbon dioxide equivalents in green house gas
emissions, largely on account of the savings due to substituting for diesel.
There were various setbacks experienced by the Carthage plant . The
plant was shut down for a period due to reported noxious smell, though
it could not be confirmed to have come from the plant. In addition, the
oil produced by the plant did not qualify as a biofuel for tax purposes,
and so the plant did not qualify for the $42 per barrel of No. 2 oil in
tax credits. But the definitions have since been changed to allow
explicitly for diesel generated from thermal depolymerization process,
taking effect at the end of 2005.
Despite the setbacks, the process appears cost effective. In January
2005, the Carthage plant was producing refined No. 2 oil (used for
diesel and gasoline) for about $80/barrel, compared to the on-highway
prices for diesel in the US at $101/barrel or $2.40/gallon (8 August
2005), which is likely to continue to rise.
Bench pilot for plastic wastes
Changing World Technologies aims to tackle plastic wastes next . A
major source of plastic wastes comes from some 15 million cars that are
de-registered in the US each year, 95 percent shredded to recover
metals, leaving a ‘shredder residue’ of fluff 25 percent by weight
that’s buried in landfills. Most of this two million tonnes of shredder
residue is plastic: polyurethane foams and rubber.
In a pilot bench experiment, the company demonstrated the conversion of
two different mixtures of shredder residue (see Table 1) into a variety
of products including light hydrocarbon oil. The two mixtures of
shredder residues differed both in their composition of solids and in
the amount of moisture. They were first screened to remove a small
portion of the inorganic material (mainly iron oxides and small pieces
of glass and rocks) that would not fit in the bench-scale reactor.
The bench reactors were capable of operating at temperatures above 900C
and pressures above 138 atmospheres.
In SR #1 the polymers that make up the rubber and plastics were mostly
transformed into the hydrocarbon oil, which is similar to diesel, with a
small fraction going to the 2nd stage gas. The first stage gas was
primarily carbon dioxide. But the second stage was rich in hydrocarbons
and would support combustion. It had a heating value of approximately 80
percent that of natural gas. The yield of hydrocarbon oil was 41.9
percent of the total input mass or 65 percent of the initial weight of
solids. Less than 20 percent of the solids went into the carbon matrix.
For SR #2, which contained more water, oil yield was 29.8 percent of
overall mass, or 52.7 percent of the initial solid matter. The carbon
matrix yield was 32 percent of the solids.
The two samples of fuel gas were quite similar, as were the diesel oil
Shredder residue is often contaminated with toxic chemicals such as PCB
(polychlorinated biphenyls) and heavy metals. The samples treated were
spiked with water containing PCB. The PCB was largely degraded in the
process. The heavy metals arsenic, barium cadmium, chromium, copper,
lead, mercury, silver and zinc were detected, mainly concentrated in the
carbon matrix. Selenium was not detected. Small amounts of zinc were
detected in the oil from SR #1, and zinc, chromium and lead in oil from
SR #2. Practically no bromine (from polybrominated flame retardant) were
found in oils, but ended up in the water and the carbon matrix.
TCP and similar processes look promising both for extending the use of
oil by recycling mixed plastics wastes and for turning food and
agricultural wastes into renewable fuel and saving on greenhouse gas
emissions, though certain questions remains unanswered.
The Institute of Science in Society, PO Box 32097, London NW1 OXR
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