Pirólise de resíduos plásticos visando à obtenção de produtos de alto valor agregado

Abstract

The increase in plastics consumption leads to increase the waste generation. Thus, the recycling of plastic materials has become increasingly important. The pyrolysis technique is one of the promising methods for recycling plastic waste. In pyrolysis, the material is thermally degraded in an inert atmosphere, providing liquid, solid and gaseous products. These products have a potential to be used as fuel and as feedstock for industry. This work aims to recycling polyolefins (HDPE, LDPE, LLDPE and PP) present in municipal solid waste by pyrolysis. The polymers were characterized by measuring the melting temperature through DSC analysis. The degradation profiles of each sample, useful for selecting the pyrolysis temperature, were obtained from thermogravimetric analysis. The evolved gas analysis results were compared to those obtained by TGA. The evolved gas analysis coupled to a mass spectrometer allowed the sample identification in a single analysis. Composition of the pyrolysis products at 450 °C, 475 °C and 500 °C was analyzed by Py-GC/MS. The pyrolysis of single and mixed plastics samples were performed in a batch reactor. Solid, liquid and gaseous yields were reported as a function of the temperature and the type of polymer. The liquid product was analyzed by FTIR analysis. DSC results showed endothermic peaks at characteristic melting points of the polymers. The graphic of LDPE sample suggests the presence of LLDPE and blends of both polymers. TGA and DTG curves indicated only one degradation step. Polypropylene sample degraded in a lower temperature range compared to the other polymers. The same behavior was observed in Py-EGA/MS results. A comparison of the thermograms and the resulting mass spectra with the GC/MS library confirmed the structure of each sample. Py-GC/MS analysis showed the formation of alkanes, alkenes and alkadienes. The increase in pyrolysis temperature led to the appearance of lower molecular chain compounds. This behavior was confirmed in batch experiments, in which the liquid and gaseous fractions were increased with temperature. The liquid yield was higher for PP pyrolysis. The additives present in polymer samples migrated to the pyrolysis products, requiring further purification steps. Analysis by FTIR confirmed the presence of unsaturated hydrocarbons. The similarity of PE and PP structures produced similar spectra. The spectrum of oil from mixed plastics reflects the degradation of each polymer.