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Abstract: In 1950, the world’s population of 2.5 billion produced 1.5 million tons of plastic; in 2016, a global population of more than 7 billion people produced over 320 million tons of plastic, and half of that is just single use plastic. [1] This is set to double by 2034. More than 8 million tonnes of plastic leaks into the ocean each year – equal to dumping a garbage truck of plastic every minute. [2]The issue of plastic pollution is gravely concerning and actions have been taken in the past, the problem still remains at large. It is now high time that we start searching for innovative ideas to counter this issue; Pyrolysis presents itself as just one such solution to this issue.
Introduction:Plastics have become an indispensable part in today’s world, due to their lightweight, durability, and energy efficiency, coupled with a faster rate of production and design flexibility; these plastics are employed in entire gamut of industrial and domestic areas; hence, plastics have become essential materials and their applications in the industrial field are continually increasing. At the same time, waste plastics have created a very serious environmental challenge because of their huge quantities and their disposal problems. Waste plastic pyrolysis not only can effectively solve the problem of plastic pollution, but also can alleviate the energy shortage to a certain extent. Recycling of waste plastics is expected to become the most effective way. Waste plastics’ recycling, regenerating, and utilizing have become a hot spot of research at home and abroad and gradually formed a new industry. Pyrolysis is the process of thermally degrading long chain polymer molecules into smaller, less complex molecules through heat. The process requires intense heat with shorter duration and in absence of oxygen. The three major products that are produced during pyrolysis are oil, gas and char which are valuable for industries especially production and refineries. Pyrolysis technology is very old and earlier it was first used for preparation of charcoal in Middle East and Southern Europe before 5500 years ago. In thermal degradation of plastics, temperature is one of the most significant operating parameters in pyrolysis since it controls the cracking reaction of the polymer chain. Different plastics have different degradation temperature depending on the chemical structure. For common plastics such as PET, HDPE and LDPE the thermal degradation temperature started at 350⁰C. Additionally, the operating temperature required relies strongly on the product preference. If gaseous or char product was preferred, higher temperature more than 500⁰C was suggested. If liquid was preferred instead, lower temperature in the range of 300-500⁰C was recommended and this condition is applicable for all plastics.
Materials used:
- Pyrometer for measuring high temperature
- Chamber with stand (12*12 Autoclave)
- Aluminum pipe tubes
- Portable burner stove (Electric heater can also be used)
- Check Valve
- Pressure meter
- Water as coolant
Cost for equipment is approximately NRs 15,000 ($135)
Material Description: For the purpose of this experiment, PET, HPDE, LDPE and Polystyrene were used. The plastics were cut manually into small strips ranging from 0.5 inches to 3 inches and were cleaned using water and detergent to remove any foreign impurities such as dirt, mud or oil. Washed out plastic were dried before using in the reactor. The appropriate moisture content was found to be lower than 20−25%.
Experimental Setup:
For our demonstration we designed and built our reactor by modifying a 12*12 autoclave, used for sterilizing medical equipment. The operating temperature of the reactor was >350 degree Celsius and the vessel was secured to be air-tight so that oxygen cannot enter the reactor. The oxygen initially present in the reactor is removed during the initial minutes of heating and the moisture is also dehydrated.The gases produced through plastic pyrolysis consist principally of hydrogen (H2), carbon dioxide (CO2), carbon monoxide (CO){in presence of Oxygen}, methane (CH4), ethane (C2H4), and butadiene (C4H6), with trace amounts of propane (CH3CH2CH3), propene (CH3CH=CH2), n-butane (CH3(CH2)2CH3), and other miscellaneous hydrocarbons.[14]The hot gases were then transported away from the reactor and heat source towards the coolant by using metal pipes. Metal piping, which has a much higher melting point, will be needed to ensure the gases are transported safely without any damage to the pipe itself.The final stage in the process was the cooling stage. At this point the material used to house the coolant will not matter. The coolant used was simply cold tap water.The hydrocarbon gases condense through the pipe and in the water; a layer of Pyrolysis Liquid Fuel (PLF) can be seen on the surface of the water. The PLF was extracted from the surface of the water by using a pipette. At optimum process conditions optimum liquid oil yield is 88%.
Conclusion: The worldwide plastic generation expanded over years because of the variety applications of plastics in numerous sectors that caused the accumulation of plastic waste in the landfill. The growing of plastics demand definitely affected the petroleum resources availability as non-renewable fossil fuel since plastics were the petroleum-based material. A few options that have been considered for plastic waste management were recycling and energy recovery technique. Nevertheless, several obstacles of recycling technique such as the needs of sorting process that was labour intensive and water pollution that lessened the process sustainability. As a result, the plastic waste conversion into energy was developed through innovation advancement and extensive research. Pyrolysis can indeed be the solution that the world has been looking for, with further research and industrial scale operations, the economy, efficiency and effectiveness of pyrolysis can greatly be increase.
Some images from the science fair:
