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Thermal depolymerization breaks down waste materials into crude petroleum products through hydrated pyrolysis. The process is efficient, with an EROEI rating of 6.67, and can handle a wide range of feedstocks. The resulting hydrocarbons can be further refined into different types of fuel oil, while residual solids can be used for various purposes. The process also has environmental benefits, such as breaking down heavy metal contamination and organic poisons.
Thermal depolymerization is an industrial process for breaking down various waste materials into crude petroleum products. This involves subjecting materials to elevated temperatures and pressures in the presence of water, thus initiating a process known as hydrated pyrolysis. The result is the depolymerization of long-chain polymer materials into short-chain monomers, in this case petroleum hydrocarbons. This is a highly accelerated artificial rendering of the process that formed fossil fuels in nature. A wide range of waste products, known as feedstocks, can be used in thermal depolymerization processes, including plastics and biomass.
The thermal depolymerization (TDP) process has been around for about 70 years, but it wasn’t considered viable until the late 1990s. This lack of profitability was the result of an unacceptable energy return on energy invested assessment (EROEI), i.e. measuring the amount of energy taken to produce the energy produced. Early methods required much more energy to produce than power generation, but they paved the way for modern systems that feature EROEI ratings of 6.67, or about 85 units of energy produced for every 15 consumed. Conventional agricultural production of biodiesel and ethanol have ratings of around 4.2, thus making the thermal depolymerization process an attractive option. In addition to its efficiency, the system has many other benefits, including the breakdown of heavy metal contamination into harmless oxides and the destruction of organic poisons and prions responsible for mad cow disease and Creutzfeldt-Jakob disease.
In practice, the hydrous pyrolysis process at the heart of thermal depolymerization is quite simple. The raw materials are first ground into small pieces and mixed with water. The mixture is then heated to 482°F (250°C) for about 15 minutes in a pressure vessel. The steam generated raises the pressure in the vessel to approximately 600 pounds per square inch (PSI) which, at the end of the heating process, is rapidly released. This causes the water to wither or evaporate rapidly, thus leaving solid residues and raw hydrocarbons.
These constituents are separated and the hydrocarbons collected for further refinement. This involves further heat treatment to 930°F (500°C) and sorting by fractional distillation. The results are light and heavy naphthas, kerosene and diesel fractions suitable for the production of different types of fuel oil. The residual solids remaining after the initial heat treatment can be used as fertilizers, filters, soil fuels, and activated carbon for wastewater treatment.
The list of raw materials suitable for TDP is extensive and includes waste plastics, tires, wood pulp, medical waste and rather nasty by-products such as turkey offal and sewer sludge. The efficiency of the thermal depolymerization process is further enhanced by the fact that process by-products such as methane, which cannot be broken down by depolymerization, are collected and used to power turbine generators to produce electricity for the plant or for the resale. Natural gas also has potential as biogas, a green alternative to conventional petrol.
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