The possible ways in which a polymer can be degraded are:
Thermal: long drying time, long residence time in extruder or fuel transfer
Mechanics: grinding, friction in processing
Photochemistry
Chemical Radiation
Biological: microorganisms
Chemistry: hydrolytic agents, hydrolysis
The depolymerization is a special category of degradation, is the process that converts the polymer in a monomer, a mixture of monomers or oligomers. De-polymerization is a process of decomposition of the polymer chain to its monomers or oligomers. It is usually achieved with high temperature (thermal) or hydrolytic agents (chemical).
Commonly, thermal depolymerization is classified as the chemical reaction in which the polymer chain is converted to high temperature monomers.
Depolymerization occurs during the thermal decomposition of polimetilmetactilato (PMMA), the polystyrene (PS) and some resins of the methacrylate. In general, polymers generated by addition, can be depolymerized by high temperature while polymers of condensation such as polyamide (PA) and polyesters (PET, PBT) do not depolymerize thermally.
Chemical depolymerization is that chemical compounds containing active hydrogen atoms react with the polar groups in the main chains of the condensation polymer. Usually, this reaction is an acidic or basic hydrolysis (hydrogen bond break) of the bonds in the amide, ester or urethane.
Theory and Process
Previous techniques for cleaving hydrocarbon polymers have spent a great deal of energy to remove excess water. Thermal depolymerization, on the other hand, uses water to improve the heating process, and water also delivers hydrogen from its molecules to the reactions.
The feedstock is first ground and mixed with water if it is too dry. It is then heated to 250 ° C and subjected to a pressure of 4 MPa for about 15 minutes. Then the pressure drops rapidly, causing most of the water to evaporate. The result is a mixture of hydrocarbons and solids which are separated. Hydrocarbons are heated to 500 ° C again, causing further molecules to be cleaved. The resulting mixture of liquid hydrocarbons is distilled in a similar manner to conventional oil.
The company claims that the energy efficiency of this process is 560% (85 units of energy produced per 15 units of energy consumed). Higher efficiency can be achieved with carbon- rich drier inputs such as plastic waste.
For comparison, current methods used to produce biodiesel and bioethanol from agricultural sources have an energy efficiency of around 320%.
By means of thermal depolymerization, a variety of materials, including poisons and poorly degradable hospital waste, can be cleaved.
On the other hand, many possible agricultural waste that could serve as feedstock is already used as fertilizer, fuel, or animal feed.
Similar processes
Thermal depolymerisation is similar to other processes which use superheated water as a major step to produce fuels, such as direct Hydrothermal Liquefaction. These are distinct from processes using dry materials to depolymerize, such as pyrolysis. The term Thermochemical Conversion (TCC) has also been used for conversion of biomass to oils, using superheated water, although it is more usually applied to fuel production via pyrolysis. Other commercial scale processes include the "SlurryCarb" process operated by EnerTech, 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 in Rialto, California was designed to process 683 tons of waste per day. However, it failed to perform to design standards and was closed down. The Rialto facility defaulted on its bond payments and is in the process of being liquidated. The Hydro Thermal Upgrading (HTU) process uses superheated water to produce oil from 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.
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—more energy was required than was produced.
The first industrial process to obtain gas, diesel fuels and other petroleum products through pyrolysis of coal, tar or biomass was designed and patented in the late 1920s by Fischer-Tropsch. 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 and obtained several patents (see, for example, published patent 8,003,833, issued August 23, 2011). 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 (91 m) from ConAgra Foods' massive Butterball turkey plant, where it is expected to process about 200 tons of turkey waste into 500 barrels (79 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 Changing World Technologies (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 pressure vessel reaction chamber where it is heated at constant volume to around 250 °C. Similar to a pressure cooker (except at much higher pressure), steam naturally raises the pressure to 600 psi (4 MPa) (near the point of saturated water). These conditions are held for approximately 15 minutes to fully heat the mixture, after which the pressure is rapidly released to boil off most of the water (see: Flash evaporation). The result is a mix of crude hydrocarbons and solid minerals. The minerals are removed, and the hydrocarbons are sent to a second-stage reactor where they are heated to 500 °C, further breaking down the longer hydrocarbon chains. The hydrocarbons are then sorted by fractional distillation, in a process similar to conventional oil refining.
The CWT 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. 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 or woodgas for heating). If one considers the energy content of the feedstock to be free (i.e., waste material from some other process), then 85 units of energy are made available for every 15 units of energy consumed in process heat and electricity. This means the "Energy Returned on Energy Invested" (EROEI) is (6.67), which is comparable to other energy harvesting processes. Higher efficiencies may be possible with drier and more carbon-rich feedstocks, such as waste plastic.
By comparison, the current processes[specify] used to produce ethanol and biodiesel from agricultural sources have EROEI in the 4.2 range, when the energy used to produce the feedstocks is accounted for (in this case, usually sugar cane, corn, soybeans and the like). These EROEI values are not directly comparable, because these EROEI calculations include the energy cost to produce the feedstock, whereas the above EROEI calculation for thermal depolymerization process (TDP) does not.
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.
| Feedstock | Oils | Gases | Solids (mostly carbon based) | Water (Steam) |
|---|---|---|---|---|
| Plastic bottles | 70% | 16% | 6% | 8% |
| Medical waste | 65% | 10% | 5% | 20% |
| Tires | 44% | 10% | 42% | 4% |
| Turkey offal | 39% | 6% | 5% | 50% |
| Sewage sludge | 26% | 9% | 8% | 57% |
| Paper (cellulose) | 8% | 48% | 24% | 20% |
(Note: Paper/cellulose contains at least 1% minerals, which was probably grouped under carbon solids.)
Carthage plant products
As reported on 04/02/2006 by Discover Magazine, a Carthage, Missouri plant was producing 500 barrels per day (79 m3/d) of oil made from 270 tons of turkey entrails and 20 tons of hog lard. This represents an oil yield of 22.3 percent. The Carthage plant produces API 40+, a high value crude oil. It contains light and heavy naphthas, a kerosene, and a gas oil fraction, with essentially no heavy fuel oils, tars, asphaltenes or waxes. It can be further refined to produce No. 2 and No. 4 fuel oils.
TDP-40 Oil Classification by D-5443 PONA method
| Output Material | % by Weight |
|---|---|
| Paraffins | 22% |
| Olefins | 14% |
| Naphthenes | 3% |
| Aromatics | 6% |
| C14/C14+ | 55% |
| 100% |
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 likely to be 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.
Along with similar processes, it is a method of recycling the energy content of organic materials without first removing the water. It can produce liquid fuel, which separates from the water physically without need for drying. Other methods to recover energy often require pre-drying (e.g. burning, pyrolysis) or produce gaseous products (e.g. anaerobic digestion).
Potential sources of waste inputs
The United States Environmental Protection Agency estimates that in 2006 there were 251 million tons of municipal solid waste, or 4.6 pounds generated per day per person in the USA. Much of this mass is considered unsuitable for oil conversion.
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 combined heat and power plant, consisting of a gas turbine which drives a generator to create electricity, and a heat exchanger to heat the process input water from the exhaust gas. The electricity can be sold to the power grid, for example under a feed-in tariff scheme. This also increases the overall efficiency of the process (already said to be over 85% of feedstock energy content).
Another option is to sell the methane product as biogas. For example, biogas can be compressed, much like natural gas, and used to power motor vehicles.
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. Energy crops constitute another potentially large feedstock for thermal depolymerization.
Current status
Reports in 2004 claimed that the Carthage facility was selling products at 10% below the price of equivalent oil, but its production costs were low enough that it 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. In February 2005, the Carthage plant was producing about 400 barrels per day (64 m3/d) of crude oil.
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, allowing 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.
On 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 11 of 2007 with no fines assessed.
Status as of February 2009
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 August 2008, the only operational plant listed at the company's website is the initial one in Carthage, Missouri.
Changing World Technology applied for an IPO on August 12; 2008, hoping to raise $100 million.
The unusual Dutch Auction type IPO failed possibly because CWT has lost nearly $20 million with very little revenue.
CWT, the parent company of Renewable Energy Solutions, filed for Chapter 11 bankruptcy. No details on plans for the Carthage plant have been released.
In April 2013, CWT was acquired by a Canadian firm, Ridgeline Energy Services, based in Calgary.
Similar technologies
Plasma Converters use powerful electric arcs to reduce and extract energy from waste.
Wet oxidation
Hydrocracking
Source from Wikipedia
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