Pyrolysis and combustion of municipal solid wastes:evaluation of synergistic effects using TGA-MS

A thermogravimetric methodology was developed to investigate and semi-quantify the extent of synergistic effects during pyrolysis and combustion of municipal solid waste (MSW). Results from TGA-MS were used to compare the pyrolysis and combustion characteristics of single municipal solid waste components (polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), branches (BR), leaves (LV), grass (GR), packaging paper (PK), hygienic paper (HP) and cardboard (CB)) and a mixture (MX) of PP, BR and CB. Samples were heated under dynamic conditions at 20°C/min from 25°C to 1000°C with the continuous record of their main evolved fragments. Synergistic effects were evaluated by comparing experimental and calculated weight losses and relative areas of MS peaks. Pyrolysis of the mixture happened in two stages, with the release of H2, CH4, H2O, CO and CO2 between 200 and 415°C and the release of CH4, CxHy, CO and CO2 between 415 and 525°C. Negative synergistic effect in the 1st stage was attributed to the presence of PP where the release of hydrocarbons and CO2 from BR and CB was inhibited, whereas positive synergistic effects were observed during the 2nd degradation stage. In a second part of the study, synergistic effects were related to the dependency of the effective activation energy (Eα) versus the conversion (α). Higher Eαs were obtained for MX during its 1st stage of pyrolysis and lower Eαs for the 2nd stage when compared to the individual components. On the other hand, mostly positive synergistic effects were observed during the combustion of the same mixture, for which lower Eαs were recorded

Thermal degradation kinetics of real-life reclaimed plastic solid waste (PSW) from an active landfill site:The mining of an unsanitary arid landfill

Landfilling is viewed nowadays as a serious threat associated with various burdens and stressors on the urban environment. To date, there is little information available on actual value of landfilled waste namely plastic solid waste (PSW) resulting from mining operations. In this work, PSW reclaimed from an active unsanitary landfill site (MAB) has been studied with the aim of determining its thermal profile and degradation behaviour for future utilisation in thermo-chemical conversion (TCC) processes. The materials were characterised by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) in accordance with internationally approved test methods in a simulated pyrolytic environment. In addition, chemical analysis using Fourier Transform Infrared Spectroscopy (FTIR) was applied to study the nature of the materials reclaimed. The degradation kinetics of the reclaimed PSW were studied with the aim of determining the apparent activation energy (Ea) of the pyrolytic reactions. The Ea values determined ranged from 199 to 266 kJ mol−1 which is in-line with pyrolytic reactions applicable for future use in fuel recovery units. TGA showed a clear shift in thermograms indicating a clear change in the degradation mechanism. The physico-chemical studies conducted on the materials also favours TCC treatment over other conventional end of life options such as physical (mechanical) recycling or incineration. The degradation mechanism was also determined from the Criado method showing that Avarami-Erofeve was the model that best represents PSW degradation. Overall, this work points towards future intervention schemes for reclaimed municipal solid waste (MSW) and in particular PSW favouring TCC technologies

Catalytic co-pyrolysis of biomass and waste plastics as a route to upgraded bio-oil

A two-stage reactor system consisting of co-pyrolysis of biomass and plastic in the 1st stage and catalytic upgrading (zeolite ZSM-5 catalyst) of the derived pyrolysis gases in the 2nd stage was used to investigate the yield and composition of the product gases and bio-oil. Biomass waste wood and waste plastics in the form of high density polyethylene, low density polyethylene, polypropylene, polystyrene and polyethylene terephthalate were used as feedstock. The addition of the plastics to the biomass with co-pyrolysis-catalysis, produced a higher CnHm gas yield compared with what would be expected by calculation, suggesting some interaction of the biomass and plastic. The presence of waste plastic resulted in a decrease in the relative proportion of oxygenated compounds in the product oil compared to pyrolysis of biomass alone; for example a reduction of >65% for biomass with polyethylene and polypropylene and >95% reduction for biomass with polystyrene. The fuel properties of the co-pyrolysis upgraded oil were improved compared to biomass alone; for example, the co-pyrolysis of polystyrene and biomass showed an improved relative proportion of compounds in the C5 ― C12 fuel range (76%). In terms of the ratio of biomass to plastic, even low quantities of plastic (9:1 biomass:plastic ratio) produced a lower relative proportion of oxygenated bio-oil compounds, for example biomass:polystyrene at a ratio of 9:1 reduced the relative proportion of oxygenated compounds in the product bio-oil by >55%