Over the last few years, as costs of motor fuels climb ever higher and as concerns grow over the carbon footprint of waste products ranging from sewerage to plastics, the process of thermal depolymerization (the breakdown of complex  macromolecules which consist of repeating structural units into monomers or simple molecules capable of bonding to form polymers) has been increasingly applied as a solution for dealing with waste and thus has been increasingly in the news.  Through pyrolysis (the decomposition or transformation of certain compounds using heat in the absence of oxygen), polymers can be broken down and made available for reformulations.  Anhydrous pyrolysis which takes place in the absence of water is generally referred to simply as pyrolysis. (An industrial process for making charcoal from wood is an example.) The process of hydrous pyrolysis uses water in breaking down polymers into monomers.  Though plastics and waste-biomass pyrolysis will not take the place totally of petroleum drilling and refining for acquiring components for polymers for fuels and manufacturing, such recycled use will reduce the negative environmental impacts of these organic wastes. One tremendously important positive of depolymerization of plastics, for example, through pyrolysis is the elimination of CO2 and toxin emissions in their utilization as fuel.

Recently reported in the news and the subject of a YouTube sensation was the creation and use of a safe and effective relatively small machine that converts plastics to oil useable as a simple fuel for stoves and generators. This same oil can be refined for use as motor fuel.  The company that has developed and manufactures the machine (Blest Company of Japan) makes one of its machines available at about $12,700 (U.S.). This small machine is the one demonstrated in the YouTube video which at this writing has had 1,689,345 views. YouTube lists other videos on this particular machine and several more on the process it uses in general.

A similar process (using infrared energy for heating the plastic waste) is utilized by Envion which has established a $5 million facility opened in September of 2009 in Montgomery County, Maryland. The plant is capable of processing 6,000 tons of plastic annually into about one-million barrels of a light crude oil. Blended with other components the product can be sold as diesel or gasoline.

Researchers at the University of Warwick in Coventry, United Kingdom, have developed a process utilizing pyrolysis wherein various types of plastics can be broken down into a number of useful components, retrievable mostly through distillation. Processing plants envisioned by the Warwick researchers are projected to be able to deal with 10,000 tons of plastic waste per year and be very commercially profitable.

Not only plastics can be transformed into monomers for commercial purposes through thermal depolymerization but biomass as well. One of the most innovative uses of the technology is in the conversion of plant and animal refuse into oil. A commercial processing plant has been built by Renewable Environmental Solutions near the ConAgra Foods Butterball turkey plant in Carthage, Missouri, to process slaughter waste. ConAgra produces about 200 tons of waste daily from the slaughter of 30,000 turkeys. The thermal depolymerization plant built nearby is a joint venture of ConAgra and Changing World Technologies (CWT) of West Hempstead, New York. Estimates are that the plant can convert the waste into 500 barrels (21,000 US gallons) of oil daily.

Thermal depolymerization process (TDP) has been considered as an alternative for sewerage treatment in the United States, according to a 2007 article in USA Today.  Similarly,  a University of Illinois (Urbana-Champaign) research team, lead by Yuanhui Zhang, an agricultural engineering professor there, has been able to produce oil from hog manure through the use of a small-scale thermochemical reactor. Heat and pressure applied by the reactor decompose the long-chain hydrocarbons into shorter ones, rendering oil, methane, carbon dioxide, and water.  As the price of a barrel of imported oil gets higher, the more economical the production of thermal depolymerization of hog manure becomes, not only rendering valuable fuel but saving farmers an expensive waste-elimination problem and saving the environment from pollution. It is estimated that during the production cycle of one pig enough manure is excreted to be converted into 21 gallons of crude oil.

One of the limitations to the economic efficiency of the process of thermal depolymerization is the lack of sufficient cheap feedstocks. Agricultural plant and animal waste is often utilized in fertilizer, feeds, and feedstock for other industries. The current trend to develop and exploit certain high yield energy crops holds potential as feedstock for thermal depolymerization process oil.

The benefits of producing oil through thermal depolymerization are many. Besides the production of oil, there is the rendering of useful and mostly valuable by-products. To these benefits the positive environmental effects of utilizing and diminishing pollutants from our landscapes, our oceans, and our landfills can be added.  While the industry is not without some criticism, these negative concerns are mostly aimed at the environmental effects of human industrial activities in general.

[This article first appeared on Xomba in February 2011.]