The photo is sourced from pstu.ru
The most common way plastic disposal method is mechanical processing; however, it is not possible of the plastic items consist of several different types of polymers or have various impurities. Often there is no other way to dispose of multi-layer plastics except for incineration, however, if polymers include halogens, sulfur or nitrogen, such incineration may damage the environment. The alternative is the re-use of polymers after recycling; however, often expensive equipment is required, which can be seen using the example of the worn-out tires.
Using the slow pyrolysis process may be a way out – this is combustion in the oxygen-free chamber with high temperature. The scientists of the Perm Polytechnical University used this method to recycle a hard polymer mix consisting of low-density polyethylene and polypropylene with the added contaminants in the form of pinewood shavings and sunflower oil. 20 grams of such mis was placed into a steel tubular reactor, which, in its turn, was put into the furnace and heated to very high temperatures. After the completion of the experiment, the reactor was removed from the furnace and cooled, and the mix was taken out for analysing it.
“As a result of pyrolysis of pure polyethylene and polypropylene with the impurities of wood shavings and oil under the temperatures of 510-590 °С and the processing time of 30-60 minutes, in all the cases we received liquids looking similar to petroleum products in terms of their colour and odour. Th received samples of pyrolysis fuel contain rather light fractions, which start vapourising under the room temperature already”, the Perm Polytechnical University is citing Marina Krasovskikh, the candidate of technical sciences.
The specific calorific capacity of the liquid received from the multi-layer polymers incineration, was between 50 and 56 megajoules (MJ) per kilogram, which is close to the amount of heat generated when combusting traditional liquid fuels. At the same time, the scientists also conducted an experiment with rubber granules from the worn-out tires with the addition of vegetable oils. Eventually, a bitumen-like product was received, which may be used as bitumen modifier for roads pavement.
In general, the pyrolysis used today mainly in petroleum and gas chemistry, may be widely adopted by the new energy. We are talking here not only about plastics recycling, but also about recovering metals from the used-up photovoltaic batteries. The specialists from Rosi Solar company proposed to use pyrolysis specifically for these purposes. In their opinion, it will allow for recovering silicon, silver and copper from photovoltaic panels (and these elements make up to 65% of such panels costs).
