Thermal Pyrolysis of Polystyrene Aided by a Nitroxide End-Functionality Improved Process and Modeling of the Full Molecular Weight Distribution

A significantly improved thermal pyrolysis process for polystyrene (PS) is reported and mathematically modeled, including the description of the time evolution of the full molecular weight distribution of the polymer during its degradation by direct integration of the balance equations without simplifications. The process improves the styrene yield from 28–39%, reached in our previous report, to 58–75% by optimizing the heating ramp during the initial stage of the pyrolysis process. The process was tested at 390 and 420 °C on samples of conventional PS synthesized via free-radical polymerization (FRP) and PS with a nitroxide end-functionality synthesized via nitroxide mediated polymerization (NMP) with three levels of the nitroxide to initiator (N/I) molar ratio: 0.9, 1.1 and 1.3. The NMP-PS produced with N/I = 1.3 generates the highest styrene yield (75.2 ± 6.7%) with respect to the best FRP-PS yield (64.9 ± 1.2%), confirming the trends observed in our previous study. The mathematical model corrects some problems of a previous model that was based on assumptions that led to significant errors in the predictions; this is achieved by solving the full molecular weight distribution (MWD) without assumptions. The model provides further insight into the initial stages of the pyrolysis process which seem to be crucial to determine the chemical paths of the process and the styrene yield, as well as the influences of the initial heating ramp used and the presence of a nitroxide end-functionality in the polymer.

Effect of Heat of Reaction and Charring Properties on Heat Release Rate during Combustion

The heat release rate (HRR) of fires can be determined from the relationship between the thermal pyrolysis rate of combustibles and the effective heat of combustion. To accurately determine the thermal pyrolysis rate of combustibles, it is important to understand the heat of reaction of combustibles. However, this parameter is difficult to measure for combustibles, such as wood, that produce charring during combustion because they undergo a multi-step pyrolysis reaction. In this study, the ISO 5660-1 standard method was used to perform cone calorimetry experiments to understand how the HRR is affected by the heat of reaction heat and charring properties of combustibles. To this end, the HRR calculated using FDS computational analysis was compared to the measured value from the ISO 5660-1 cone calorimetry experiments. A dehydrated Douglas-fir, an evergreen tree of the pine family, was used as a combustible material. The cone calorimetry experiment and FDS computational analysis results confirmed that increases in the heat of reaction and charring properties were directly correlated with the decrease in the HRR.

A technology review of recycling methods for fiber-reinforced thermosets

The rapidly rising demand for fiber-reinforced plastics (FRPs) has led to large volumes of manufacturing and end-of-life waste. Recycling fiber-reinforced thermosets is very difficult owing to their complex structure and heterogeneity. Landfill and incineration have become the most commonly used methods for eliminating non-degradable FRP waste, which adversely affects the environment and ecology. The purpose of this review is to evaluate end-of-life FRP recycling technologies in terms of optimizing the reuse/recycling of resources and eliminating waste, thereby improving FRP waste management. The technical progress made in the recycling of thermosetting composites is reviewed, including mechanical, thermal (pyrolysis and fluidized-bed), and chemical (critical fluid and low-temperature solvent) methods. The technical feasibility of each method was compared, and the economic and environmental impacts were considered. The challenges and opportunities facing the establishment of a composite recycling market in the future are examined. Finally, we provide a comprehensive summary of the scope of each recycling method.

On the Mechanism of Methane Conversion in the Nonсatalytic Processes of Its Thermal Pyrolysis and Steam and Carbon Dioxide Reforming

A detailed kinetic modeling of the noncatalytic processes of thermal pyrolysis and steam and carbon dioxide reforming of methane revealed almost completely identical kinetics of the methane conversion in these processes. This suggests that, in the temperature range 1400–1800 K, the initial stage of conversion of methane in all these processes is its thermal pyrolysis. The modeling results agree well with the experimental data on methane pyrolysis. For the temperature range examined, the Arrhenius expressions (pre-exponential factors and activation energy) were obtained in the first-order kinetics approximation for the rate of methane conversion in the processes studied. The expressions derived may be useful for making preliminary estimates and carrying out engineering calculations.