Thermal depolymerization is a process for the reduction of complex organic materials (usually waste products of various sorts) into light crude oil. It mimics the natural geological processes thought to be involved in the production of fossil fuels. Under pressure and heat, long chain polymers of hydrogen, oxygen, and carbon decompose into short-chain petroleum hydrocarbons with a maximum length of around 18 carbons.
This is not a new technology; it is similar to the process that produced the fossil fuels used today. The difference is that where the geological process occurs over millions of years, the technological process occurs in a timeframe measured in hours.
Until recently the human process was not efficient enough to serve as a practical source of fuel - more energy was required than was produced. However, a new approach was developed by Illinois microbiologist Paul Baskis in the 1980s and refined over the next fifteen years that exceeded break-even. The technology was finally developed for commercial use in 1996 by Changing World Technologies. A demonstration plant was completed in 1999 in Philadelphia, and the first full-scale commercial plant was constructed in Carthage, Missouri, about 100 yards from ConAgra Foods' massive Butterball Turkey plant, where it will processes 200 tons of turkey waste a day.
Many methods to create hydrocarbons use a lot of energy to remove water from the materials. This method instead requires water, as the water both improves the heating process and supplies hydrogen and oxygen for the chemical reactions.
The feedstock material is first ground into small chunks, and mixed with water if it is especially dry. It is then fed into a reaction chamber where it is heated to around 250°C and subjected to 600 psi for approximately 15 minutes, after which the pressure is rapidly released to boil off most of the water. The result is a mix of crude hydrocarbons and solid minerals, which are separated out. The hydrocarbons are sent to a second-stage reactor where they are heated to 500°C, further breaking down the longer chains, and the resulting petroleum is then distilled in a manner similar to conventional oil refining. Working with turkey offal as the feedstock, the process proved to have energy efficiencies of approximately 85%; in other words, the energy required to process materials could be supplied by using 15% of the petroleum output. Higher efficiencies may be possible with drier and more carbon-rich feedstocks, such as waste plastic.
