Not so long ago, the use of recyclable materials and recycling of waste was associated with our fellow citizens with the past i.e with the Soviet practice of voluntary collection of scrap metal and waste paper, but today more and more often people associate these practices with the future. It is a kind of man-made analogue of the natural ecosystems with their "secrets" of maintaining a balance. But in fact, recycling is faced with a number of scientific, technological and even ethical issues.
Before starting the treatment of waste in an industrial scale, they are needed to be collected and that's the problem. The world produces annually about 30 million tons of waste plastics only, and only about 10% of them are recycled. In Russia, too, there are companies of such profile, but the "offer" of their services often exceeds demand. "One of the major incidents, which is told by the representatives of such companies in the media and at industry conferences - is that the facilities for the processing of polymers in Russia exceeds the volume of raw material they can find - told STRF.ru Aleksandr Tsygankov, Director of Development Charity Shop. - For example, a plant for the processing of PET "Plarus" from the Moscow region had to import recycled plastic from abroad to load their facilities. "
But today most of the polymers recycling» as a rule, means "burning", which leads to emissions of carbon dioxide and other oxides and unburned residues accumulation in atmosphere. All this is not only a waste of useful materials, but also the pollution of the environment.
But no less important is the problem of maximizing the usefulness of recycling itself. If we talk about plastic waste, the "output" in theory can possibly allow to obtain a wide range of fuel fractions, as well as composite materials and energy.
Now one of the most common and efficient processing of such complex plastics as rubber polymers is their fragmentation. The resulting rubber crumb is used in enterprises as reagent. But apart from the crumbs crushing leads to a "by-product" - polymer cord, which, together with the "entangled" crumbs makes up to 30% of raw materials. To recycle this mechanical processing is not enough.
Scientists from the Tver State Technical University under the guidance of Doctor of Technical Sciences, professor Yuriy Kosivtsova are sure that you can solve the problem by taking under control the processes that take place at high temperatures. In particular, this trend is being developed in the framework of the project "Development of technology for environmentally friendly recycling of plastic waste by a low-temperature catalytic pyrolysis to produce a combustible gas, liquid fuel fractions and composite materials for various applications", supported by the Federal Targeted Program "Research and Development" for 2014-2020.
Pyrolysis (destruction), which scientists rely upom is a chemical process in which organic (and many inorganic) compounds decompose under the influence of high temperatures and lack of oxygen.
"Pyrolysis is not the new technology - Kosivtsov said. Many people in the ancient caves used coal, and it is obtained by pyrolysis. We have improved the process of adding special catalysts, and designing an installation".
Indeed, the impact of high temperatures on the timber with a limited access of oxygen is known from ancient times. It was charcoal that our ancestors used as a fuel during Iron and Bronze Ages.
Improvements of this ancient skill produced by a team of TSTU led to the fact that in addition to the coal o of hydrogen is obtained from the reaction which in its pure form, is likely to become the basis for future energy.
"In fact as output we get two useful products - said the project manager. - This is the electrical energy that is produced directly in the installation and then fed into the grid. And carbon residue obtained after pyrolysis - low-grade coal, which can be used as an absorbent ".
In addition, scientists isolated liquid and gaseous fuel fractions which they are trying to maximize the output of reducing the share of solid reaction products.
But one of the major disadvantages of this process is that the useful yield is obtained in the pyrolysis reaction only at very high temperature, about 1000 ° C. To adapt this method for the production, the research team from the TSTU is improving the installation, and most importantly, looking for effective and yet inexpensive catalysts that will significantly reduce the reaction temperature.
As catalysts for the pyrolysis a variety of materials used: metal chlorides and silica-alumina catalysts, special clays, which are widely used for cracking. The former became the preferred variant of the scientists from TPGU, because such catalysts are not only highly effective but also available, and therefore inexpensive. Thanks to their use
pyrolysis temperature was reduced from 1100 ° C to 400-600 ° C, the useful output of the low-temperature pyrolysis increased by 10-30% depending on the kinds of catalysts and reaction time.
Operating temperature decrease means lowering the cost of the end product (it is possible to use smaller amount of heat resistant materials in the installation, and the energy costs for heating are reduced). This means greater viability of the technology.
Pyrolysis takes place, so to speak, in three stages. First, the polymer (which may be, for example, old tires, and there may be other polymers - the optimal catalysts can be selected for any raw garbage) breaks down into solid carbon residue, heavy and light hydrocarbons and gases: hydrogen, carbon monoxide gas, methane and others. Then successively heavy hydrocarbons are decomposed to lighter liquids, the latter become gases. The higher proportion of light and heavy fractions - the more is the reactions yield.
By the way, the plant generates heat also in a relatively cheap way - easily accessible diesel is used as fuel, however, the installation may work on other fuels.
This technology has been adopted by an industrial partner of the project - the company "Ekomashgrupp", one of the leading Russian suppliers of equipment for recycling of waste. There is already an order to purchase the plant. The company "Iskozh" in the Tver Region is considering the use of technology for the processing of rubber. "We have complete mutual understanding with our industrial partners ", - noted Kosivtsov.
Perhaps in the near future garbage will finally take its rightful place in the list of "raw material" resources.