Millions of tons of plastic and tyre waste are produced in the world every year. Most of these wastes are either burnt or used for filling land. Burning emits harmful gases and creates threats to the environment. Pyrolysis technology emerged as a solution for decomposing plastic and tyre waste. Pyrolysis involves carbonaceous material’s thermal decomposition in an oxygen free environment. In this process, the pressure of the system is not restricted by the pressure of water vapour. In other words, pyrolysis is the process of heating biomass without oxygen. This method is considered to be useful in reducing plastic and tyre wastes. It also allows recycling some useful energy stored in the biomass.
Application of pyrolysis helps to recover energy in plastic waste and tyre waste through chemical manipulation. Pyrolysis plastic recycling through pyrolysis process consists of several steps. All plastic waste needs to be sorted before putting it through the process. Mechanical recycling includes shredding of polymers and cryogenic grinding of plastics. Through pyrolysis process, the long chain molecules of polymer are cracked into smaller chains with the help of pressure and heat. Actually it is similar to nature’s process where the earth breaks down carbon and produces oil. This natural process takes millions of years. The process of plastic pyrolysis produces mainly three products: bio-oil, bio-char and syngas.
Bio-oil or pyrolysis oil can be considered as a substitute for industrial diesel. The plastic pyrolysis oil or tyre pyrolysis oil is also used in boilers, furnace, electric generators, diesel pumps, hot air/water generators, heaters, thermic fluids, and other equipment. Syngas is reused in pyrolysis plants and the bio-char or carbon black is put to use in plastic/rubber industries and also in inks, paints etc. High calorific value biomass can only be pyrolised in order to generate bio-oil.
Tyre recycling process through the pyrolysis involves heating of whole or shredded tyres without oxygen in a closed vessel reactor. Rubber polymers will break down and form smaller molecules. Vaporized smaller molecules are burnt further to produce bio-oil or pyrolysis oil. Solid, liquid and gaseous properties are derived from tyre pyrolysis process in accordance with the process conditions and feedstock used. A major issue related to tyre pyrolysis is the generation of solid stream, which constitutes about 40% of the total output. Steel from solid stream is removed with the help of magnets but the remaining bio-char has no value other than being a carbon fuel of lower grade.
Importance of waste tyre and plastic pyrolysis
The major advantage of the pyrolysis process is that it decomposes waste and produces valuable products. The pyrolysis process uses waste plastics and scarp tyre as biomass or feedstock. The pyrolysis process and output from this process are environment friendly. Pyrolysis can produce synthetic diesel fuel and thereby the dependency on fossil fuels can be reduced. Bio-oil can be used in pharmaceuticals. Further research can yield technology that can convert bio-oil and in the future it may become a substitute fuel for car engines. Bio-char or black carbon is considered as a useful fertilizer. Therefore all products from pyrolysis process are different forms of renewable energy.
Apart from this, the pyrolysis process and technology are economically viable as there will not be any scarcity for the availability of waste plastics and scrap tyres. This technology is modular and more flexible than incineration. The pyrolysis process will not produce any harmful gases or chemicals and the products offer a better solution for the recovery of natural resources. Improving the operations of pyrolysis can reduce a considerable amount of plastic and tyre wastes.
Challenges of waste tyre and plastic pyrolysis
Proper measures or steps should be taken in order to close all technical knowledge gaps existing in the pyrolysis industry. Availability of high-end infrastructure facility can be considered as another major challenge. The products from this process need to be stored on a long term basis. Governments should provide support for the development of pyrolysis technology. Apart from gaps related to technology, knowledge industries should address all major challenges related to operational performance. Upgrades and stability are necessary for the proper functioning of pyrolysis machines.