Thermal depolymerization

Overview
Thermal depolymerization (TDP) is a process using hydrous pyrolysis for the reduction of complex organic materials (usually waste products of various sorts, often known as biomass and plastic) 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.

Similar processes
Thermal depolymerisation is similar to other processes which use superheated water as a major step in their processing to produce fuels, such as direct Hydrothermal Liquefaction and hydrous pyrolysis. Thermochemical conversion (TCC) can mean conversion of biomass to oils using superheated water, although it more usually is applied to fuel production via pyrolysis. The Thermal Conversion Process is another name for thermal depolymerisation. A company called Renewable Environmental Solutions (RES) was formed as a joint venture between ConAgra Foods and Changing World Technologies to operate the plant at Carthage, Missouri and the name of the process was changed.

EnerTech operates the "SlurryCarb" process, which uses similar technology to decarboxylate wet solid biowaste, which can then be physically dewatered and used as a solid fuel called E-Fuel. The plant at Rialto, California is said to be able to process 683 tons of waste per day.

The Hydro Thermal Upgrading (HTU) process was originally developed by Shell, and is now operated by Biofuel BV. It uses superheated water to produce oil from a range of biomass and domestic waste. A demonstration plant is due to start up in the Netherlands said to be capable of processing 64 tons of biomass (dry basis) per day into oil. Thermal depolymerisation differs in that it contains a hydrous process followed by an anhydrous cracking / distillation process, although upgrading of the raw HTU product is also possible.

History
Thermal depolymerization is similar to the geological processes that produced the fossil fuels used today, except that the technological process occurs in a timeframe measured in hours. Until recently, the human-designed processes were not efficient enough to serve as a practical source of fuel&mdash;more energy was required than was produced.

Many previous methods which create hydrocarbons through depolymerization used dry materials (or anhydrous pyrolysis), which requires expending a lot of energy to remove water. However, there has been work done on hydrous pyrolysis methods, in which the depolymerization takes place with the materials in water. In U. S. patent 2,177,557, issued in 1939, Bergstrom and Cederquist discuss a method for obtaining oil from wood in which the wood is heated under pressure in water with a significant amount of calcium hydroxide added to the mixture. In the early 1970s Herbert R. Appell and coworkers worked with hydrous pyrolysis methods, as exemplified by U. S. patent 3,733,255 (issued in 1973), which discusses the production of oil from sewer sludge and municipal refuse by heating the material in water, under pressure, and in the presence of carbon monoxide.

An approach that exceeded break-even was developed by Illinois microbiologist Paul Baskis in the 1980s and refined over the next 15 years (see U. S. patent 5,269,947, issued in 1993). The technology was finally developed for commercial use in 1996 by Changing World Technologies (CWT). Brian S. Appel (CEO of CWT) took the technology in 2001 and expanded and changed it into what is now referred to as TCP (Thermal Conversion Process), and has applied for several patents (see, for example, published patent application US 2004/0192980). A Thermal Depolymerization demonstration plant was completed in 1999 in Philadelphia by Thermal Depolymerization, LLC, and the first full-scale commercial plant was constructed in Carthage, Missouri, about 100 yards (100 m) from ConAgra Foods' massive Butterball turkey plant, where it is expected to process about 200 tons of turkey waste into 500 barrels (21,000 US gallons or 80 m³) of oil per day.

Theory and process
In the method used by CWT, the water improves the heating process and contributes hydrogen to the reactions.

In the CWT process, 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 (4 MPa) 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 mix of hydrocarbons is then distilled in a manner similar to conventional oil refining.

Working with turkey offal as the feedstock, the process proved to have yield efficiencies of approximately 85%; in other words, the energy contained in the end products of the process is 85% of the energy contained in the inputs to the process (most notably the energy content of the feedstock, but also including electricity for pumps and natural gas for heating). Alternatively, if one considers the energy content of the feedstock to be free (i.e., waste material from some other process), one could consider the energy efficiency of the process to be 560% (85 units of energy made available for 15 units of energy consumed). The company claims that 15 to 20% of feedstock energy is used to provide energy for the plant. The remaining energy is available in the converted product. Higher efficiencies may be possible with drier and more carbon-rich feedstocks, such as waste plastic.

By comparison, the current processes used to produce ethanol and biodiesel from agricultural sources have energy efficiencies in the 320% range when the energy used to produce the feedstocks is considered (in this case, usually sugar cane, corn, soybeans and the like). As these energy efficiencies include the energy cost to produce the feedstock, and the above thermal depolymerization process (TDP) energy efficiency does not, these values are not directly comparable.

The process breaks down almost all materials that are fed into it. TDP even efficiently breaks down many types of hazardous materials, such as poisons and difficult-to-destroy biological agents such as prions.

Carthage plant products
The yield from one U.S. ton (907kg) of turkey waste is 600 pounds (272 kg) petroleum, 100 pounds (45 kg) butane/methane, and 60 pounds ( 27kg ) minerals. In addition, the water is recycled back into the system for reuse.

The Carthage, MO plant produces API 40+, a high value crude oil comparable to diesel fuel. It contains light and heavy naphthas, a kerosene, and a gas oil fraction, with essentially no heavy fuel oils, tars, asphaltenes or waxes present.

The fixed carbon solids produced by the TDP process have multiple uses as a filter, a fuel source and a fertilizer. It can be used as activated carbon in wastewater treatment, as a fertilizer, or as a fuel similar to coal.

Advantages
The process can break down organic poisons, due to breaking chemical bonds and destroying the molecular shape needed for the poison's activity. It is highly effective at killing pathogens, including prions. It can also safely remove heavy metals from the samples by converting them from their ionized or organometallic forms to their stable oxides which can be safely separated from the other products.

Plants photosynthesize organic matter from water and carbon dioxide - which has been released into the atmosphere in large quantities from the burning of fossil fuels since the start of industrialization. At least in theory, these spent fossil fuels can be fully recycled by thermal depolymerization, using plant organic matter as input material.

Despite the somewhat similar output materials, the technical process of thermal depolymerization is quite different from biomass-to-liquid biofuel production, as the former yields mineral oils that can be refined into petrol, while the latter produces synfuels which are of inferior quality for current internal combustion engines.

Whether thermal depolymerization of plantstuffs can alleviate the growing scarcity of crude oil is unproven however. A potential benefit is that as opposed to animal waste, the water content of plant matierals - which typically is very high, in excess of 80 or even 90% - can be reduced by drying with less risk of spoilage. As noted above, the possibility of using plant matter as input material has been proven. It was found though that when using fairly pure cellulose fibers the output consists of considerably more natural gas than mineral oils, compared to other input materials.

Potential sources of waste inputs
The United States Environmental Protection Agency estimates that in 2001 there were 229 million tons of municipal solid waste, or 4.4 pounds generated per day per person in the USA. Industrial facilities in the USA create 7.6 billion tons of industrial wastes each year, however 97% of that waste is water, which means only 228 million tons of potential feedstock remains. In failing to mention the latter, Changing World Technologies tend to overestimate the potential benefit that the country may reap from wide-scale implementation of the process. However, this still works out to be 457 million tons of daily waste that could be converted into fuels.

Limitations
The process only breaks long molecular chains into shorter ones, so small molecules such as carbon dioxide or methane cannot be converted to oil through this process. However, the methane in the feedstock is recovered and burned to heat the water that is an essential part of the process. In addition, the gas can be burned in a gas turbine; connected to a generator, the electricity can also be sold to consumers and the heat from the engine is then used to heat the water. This also increases the efficiency of the process (already said to be over 85% of feedstock energy content).

Many agricultural and animal wastes could be processed, but many of these are already used as fertilizer, animal feed, and, in some cases, as feedstocks for paper mills or as boiler fuel.

Current status
Reports in 2004 claimed that the facility was selling products at 10% below the price of equivalent oil, but its production costs were low enough that the plant produced a profit. At the time it was paying for turkey waste (see also below).

The plant then consumed 270 tons of turkey offal (the full output of the turkey processing plant) and 20 tons of egg production waste daily. According to a 2/1/2005 article by Fortune Magazine, the Carthage plant was producing about 400 oilbbl/d of crude oil. This oil is being refined as No. 2 (a standard grade oil which is used for diesel and residential heating oil) and No. 4 (a lower grade oil used in industrial heating).

In April 2005 the plant was reported to be running at a loss. Further 2005 reports summarized some economic setbacks which the Carthage plant encountered since its planning stages. It was thought that concern over mad cow disease would prevent the use of turkey waste and other animal products as cattle feed, and thus this waste would be free. As it turned out, turkey waste may still be used as feed in the United States, so that the facility must purchase that feed stock at a cost of $30 to $40 per ton, adding $15 to $20 per barrel to the cost of the oil. Final cost, as of January 2005, was $80/barrel ($1.90/gal).

The above cost of production also excludes the operating cost of the thermal oxidizer and scrubber added in May 2005 in response to odor complaints (see below).

A biofuel tax credit of roughly $1 per US gallon (26 ¢/L) on production costs was not available because the oil produced did not meet the definition of "biodiesel" according to the relevant American tax legislation. The Energy Policy Act of 2005 specifically added thermal depolymerization to a $1 renewable diesel credit, which became effective at the end of 2005.

As reported on 04/02/2006 by Discover Magazine, the Carthage plant was producing 500 oilbbl/d of oil made from 270 tons of turkey guts and 20 tons of pig fat. A federal subsidy (the Energy Policy Act of 2005) allowed a profit of $4/barrel of output oil.

Company expansion
The company has explored expansion in California, Pennsylvania, and Virginia, and is presently examining projects in Europe, where animal products cannot be used as cattle feed. TDP is also being considered as an alternative means for sewage treatment in the United States.

Smell complaints
The pilot plant in Carthage was temporarily shut down due to smell complaints. It was soon restarted when it was discovered that few of the odors were generated by the plant. Furthermore, the plant agreed to install an enhanced thermal oxidizer and to upgrade its air scrubber system under a court order. Since the plant is located only four blocks from the tourist-attracting town center, this has strained relations with the mayor and citizens of Carthage.

According to a company spokeswoman, the plant has received complaints even on days when it is not operating. She also contended that the odors may not have been produced by their facility, which is located near several other agricultural processing plants.

In December 29, 2005, the plant was ordered by the state governor to shut down once again over allegations of foul odors as reported by MSNBC.

As of March 7, 2006, the plant has begun limited test runs to validate it has resolved the odor issue. .

As of August 24, 2006, the last lawsuit connected with the odor issue has been dismissed and the problem is acknowledged as fixed. In late November, however, another complaint was filed over bad smells. This complaint was closed on January 11th of 2007 with no fines assessed.

Status as of May 2008
A May 2003 article in Discover magazine stated, "Appel has lined up federal grant money to help build demonstration plants to process chicken offal and manure in Alabama and crop residuals and grease in Nevada. Also in the works are plants to process turkey waste and manure in Colorado and pork and cheese waste in Italy. He says the first generation of depolymerization centers will be up and running in 2005. By then it should be clear whether the technology is as miraculous as its backers claim."

However, as of May 2008, the only operational plant listed at the company's website is the initial one in Carthage, Missouri.