Waste Plastics into Oil

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ISIS 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

<m.w.ho

 

A fully referenced version <http://www.i- sis.org.uk/full/WPIOFull.php> of this

paper is posted on ISIS members’ website. Details here

<http://www.i-sis.org.uk/membership.php>

 

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 [1]. 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

<http://www.i-sis.org.uk/RFTPW.php>”, 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 [2]. 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 [3].

 

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 [4].

 

(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 [5]. 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 m^3 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/m^3 ) 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 [6]. 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 [7], 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 [3]. 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.

 

The Institute of Science in Society, PO Box 32097, London NW1 OXR