Polymers and plastics are crucial materials in many sectors of our economy, due to their numerous advantages. They also have some disadvantages, among the most important are problems with the recycling and disposal of used plastics. The recovery of waste plastics is increasing every year, but over 27% of plastics are landfilled. The rest is recycled, where, unfortunately, incineration is still the most common management method. From an economic perspective, waste management methods that lead to added-value products are most preferred—as in the case of material and chemical recycling. Since chemical recycling can be used for difficult wastes (poorly selected, contaminated), it seems to be the most effective way of managing these materials. Moreover, as a result this of kind of recycling, it is possible to obtain commercially valuable products, such as fractions for fuel composition and monomers for the reproduction of polymers. This review focuses on various liquefaction technologies as a prospective recycling method for three types of plastic waste: PE, PP and PS.
It is known that biogas without prior purification to biomethane is a commonly used fuel only for the stationary internal combustion engines but not for vehicle engines. The current study evaluates the use of biogas without its prior upgrading to biomethane as fuel for tractor engines. The following tests were carried out: biochemical methane potential tests, dynamometer engine tests, and field tests with the use of a tractor. The average methane content in biogas obtained from vegetable wastes exceeded 60%. The tests performed on the engine dynamometer showed that the engine powered by dual fuel worked stably when diesel was replaced by 40% biogas (containing 50% of CO2) or 30% methane. Dual fuel supplying of the engine caused an increase in the concentration of hydrocarbons and carbon monoxide in the exhaust gases and a decrease or no effect in the concentration of particulate matter and nitrogen oxides. It did not significantly affect the dynamics of the vehicle and its useful properties. Biogas that contains a maximum of 50% CO2 and from which H2S, moisture, and siloxanes have been largely removed, is suitable as a fuel for tractors. Such biogas can be obtained in biogas plants from different substrates, e.g., vegetable or agriculture wastes as well as biodegradable municipal wastes.
Waste products from the agriculture industry and other sectors are creating a waste problem with a negative environmental impact. Such effects can be minimized by further processing methods. One method, which is gaining increased importance around the world, is anaerobic digestion, for which biodegradable waste is a valuable source of raw material (Ryckebosch et al. 2011; Deublein, Steinhauser 2008). The paper discusses the technological process of biogas production, as well as the most commonly used methods of purification and refining. It also identifies the potential ways of using the resulting product (CHP, biofuels).
This research paper studied the environmental impact of using methane fuels for supplying internal combustion engines. Methane fuel types and the methods of their use in internal combustion engines were systematized. The knowledge regarding the environmental impact of using methane fuels for supplying internal combustion engines was analyzed. The authors studied the properties of various internal combustion engines used for different applications (specialized engines of power generators—Liebherr G9512 and MAN E3262 LE212, powered by biogas, engine for road and off-road vehicles—Cummins 6C8.3, in self-ignition, original version powered by diesel fuel, and its modified version—a spark-ignition engine powered by methane fuel) under various operating conditions in approval tests. The sensitivity of the engine properties, especially pollutant emissions, to its operating states were studied. In the case of a Cummins 6C8.3 modified engine, a significant reduction in the pollutant emission owing to the use of methane fuel, relative to the original self-ignition engine, was found. The emission of carbon oxide decreased by approximately 30%, hydrocarbons by approximately 70% and nitrogen oxide by approximately 50%, as well as a particulate matter emission was also eliminated. Specific brake emission of carbon oxide is the most sensitive to the operating states of the engine: 0.324 for a self-ignition engine and 0.264 for a spark-ignition engine, with the least sensitive being specific brake emission of nitrogen oxide: 0.121 for a self-ignition engine and 0.097 for a spark-ignition engine. The specific brake emission of carbon monoxide and hydrocarbons for stationary engines was higher in comparison with both versions of Cummins 6C8.3 engine. However, the emission of nitrogen oxide for stationary engines was lower than for Cummins engines.
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