Thermal depolymerization is an industrial process of breaking down various waste materials into crude oil products. The materials are subjected to high temperatures and pressure in the presence of water, thereby initiating hydrous pyrolysis. As a result, the long chain polymers of the materials are depolymerized into short chain monomers. It is said to mimic the natural geological processes thought to be involved in fossil fuel production.
Thermal depolymerization occurs in nature when an accumulated biomass is heated and pressurized in the earth's crust over millions of years. This biomass, also known as kerogen, is believed to react with clay mineral enzymes at temperatures below 200 °C (392 °F), which produces oil. This method is rapidly gaining a lot of attention world-wide as an alternative source of energy. It is particularly helpful as solid wastes contain carbon, which can be chemically transformed into liquid fuel.
Thermal Depolymerization Process
During thermal depolymerization process, the feedstock material is ground into tiny chunks and mixed with water. The mixture is then subjected to high pressure and heated at a constant volume to 250 °C (482 °F). As a result, crude hydrocarbons and solid minerals are produced, which are then separated using fractional distillation and oil refining techniques. Some of commonly used feedstock materials include corn, soya, sugarcane, tires, sewage sludge and medical wastes. Carthage plant products like aromatics, olefins, paraffins and naphthenes are also used.
The following are the three main steps involved in the thermal depolymerization process:
- Feedstock is heated under pressure and pulped into a water slurry.
- Slurry is subjected to low pressure and then oil is separated from water.
- Crude oil is heated to high temperature to obtain light carbons in a solid form.
The temperature of the initial phase will be in the range of 200 to 300 °C (392 to 572 °F) and the next phase will be around 500 °C (932 °F).
Benefits of Thermal Depolymerization
Thermal depolymerization process can breakdown organic poisons by breaking the chemical bonds and deforming the molecular shape required for the poison's activity. It can also eliminate heavy metals from the samples by converting the metals from their ionized forms to stable oxides that can be separated from the other products.
Using this process, the energy content of organic materials can be recycled without removing the water. Unlike other recovering methods like pyrolysis and burning, which require pre-drying or produce gaseous products, water is easily separated by liquid fuel in this method. TDP energy farms can also be used as a habitat for other species and as recreational space for people.
Limitations of Thermal Depolymerization
Thermal depolymerization process only breaks long molecular chains into short chains. As a result, small molecules like methane or carbon dioxide cannot be converted into oil using this process. Hence, there is a need for additional refining steps. In addition, as the process requires temperature greater than 400 °C (752 °F), toxic byproducts like furan and dioxin may be released in addition to methane and carbon dioxide.
The key applications of thermal depolymerization are as follows:
- Waste Reduction - Thermal depolymerization is a high heat process that involves physical and chemical changes resulting in total destruction of waste bringing a significant reduction in the volume and mass of the waste. It can treat a wide range of waste including biological, anatomical, plastics, glass and needles, etc.
- Oil Production – Researchers have produced oil from agricultural plant wastes like hog manure, animal wastes, plastics using thermal depolymerization method where the application of heat and pressure yields oil in addition to carbon dioxide, methane and water.
Besides reducing waste and by-products by using water as a medium, thermal depolymerization process also produces fuel resources that can benefit the world. Invaluable fuel products can be produced from organic waste and low quality feed stocks in an environment-friendly manner. It also yields clean crude oil products by removing sulfur and nitrogen compounds.
In a completely thermal depolymerization-based economy, the amount of CO2 produced by the burning of fuels is exactly balanced by the plants grown to be used for thermal depolymerization feedstock. The amount of energy hitting the Earth is about 5000 times more than the total amount of energy used by all human activity. Therefore, with an optimum use of the thermal depolymerization technology, the Earth might conveniently support ten times its current population at a high standard of living.
The technology is yet to make an impact as an alternative for producing liquid crude oil due to high cost of the entire process. Upon resolving this issue, thermal depolymerization could help bring the shortage of the dwindling fuel resources across the globe to an end.