Search

High- and low-density polyethylene (HDPE and LDPE) and polypropylene (PP) are the most common polymers among plastic waste as they have multiple commercial applications. This study focused on thermal degradation characteristics and kinetic of a plastic mixture with a composition of 92.5 wt% LDPE and 7.5% PP. Thermal decomposition characteristics of the plastic mixture was analysed through thermo-gravimetric analysis (TGA). The overall kinetic of the process was studied using the modified Coats−Redfern method and the Ozawa-Flynn-Wall (OFW) method. The apparent activation energy (E) and pre-exponential factor (A) obtained were 316.0 kJ/mol; 8.09E+21 min−1 and 311.5 kJ/mol; 4.35E+21 min−1, respectively. Slow pyrolysis of the analysed mixture was carried out in a semi-batch reactor under atmospheric pressure and nitrogen atmosphere and three different pyrolysis temperatures were investigated: 420 °C, 450 °C and 500 °C. H 2 , CH 4 , C 2 H 4 , C 2 H 6 and C 3 H 8 were the main components of the gas phase. Liquid (oil/wax phase) yields increased with increasing operative temperature from 42% at 420 °C to 62% at 500 °C. On the other hand, solid phase showed a specular behaviour compared to the oil/wax phase, decreasing from 21% to 5% in the considered temperature range. On the contrary, gas phase did not change much with pyrolysis temperature, with a decrease from 37% at 420 °C to 34% at 500 °C. Products' energy yields were also estimated at 420 °C. They ranged from 7.4% to 37.8% and 43.0% for solid, gas and oil fraction, respectively. Oil fraction collected from pyrolysis at 420 °C was also characterized. • Liquid yields increased with temperature from 42% at 420 °C to 62% at 500 °C. • Oil/wax phase properties and aspect showed significant variations with temperature. • Gas yield is maximum at 420 °C and slightly decreased with increasing temperature. • Produced liquid phase was mostly composed of aliphatic compounds. • At 420 °C most of the mixture initial energy content was divided between oil and gas fractions. [ABSTRACT FROM AUTHOR]

This work focuses on bitumen slow pyrolysis. Mass and energy yields of oil, solid and gas were obtained from pyrolysis experiments using a semi-batch reactor in a nitrogen atmosphere, under three non-isothermal conditions (maximum temperature: 450 °C, 500 °C and 550 °C). The effect of temperature on the product yields was discussed. The gas compositions were analysed using gas chromatography (GC) and the heating value of oil and solid residue was also measured. Using a thermo-gravimetric analyser, kinetic parameters were evaluated through Ozawa-Flynn-Wall (OFW) method. Results showed that oil yield is maximum at 500 °C (50%). Moreover, gas yield increased with increasing pyrolysis temperature from 18% to 36%. On the other hand, solid yield showed an opposite trend: it decreased from 39% to 32%. As regard energy yields, they showed a similar trend with the mass ones. H 2, CH 4 , C 2 H 4 , C 2 H 6 and C 3 H 8 are the main components of the produced gas phase. It has been noticed that the recovery of bitumen to liquid oil through pyrolysis process had a great potential since the oil produced had high calorific value comparable with commercial fuels. • Slow pyrolysis is a good alternative process in order to produce high added-value products from waste. • Oil yield is 50 %wt at 500 °C and produced oil had high HHV values (43–44 MJ/kg). • Gas yield is maximum at 550 °C and increased with increasing pyrolysis temperature. Produced gas phase was rich in light HC (C–C3) and H 2. • At 450 °C and 500 °C most of the bitumen energy content was concentrated in the oil fraction. • Results demonstrated that the produced pyrolysis gas could be sufficient enough to self-sustaining the process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Use of Volume of Fluid (VOF) method to model free surface dynamics in UUSTs. • Comprehensive assessment of suitable turbulence models for unbaffled stirred tank analysis. • Study of effects of impeller speed on vortex shape and aeration at different viscosities. • Prediction of Power Number (Np) and vortex shape in non-aerated and aerated conditions. • Prediction of cavities near the impeller blades in super-critical regime. The transition between non-aerated and aerated regimes in uncovered unbaffled stirred tanks (UUSTs) was investigated using computational fluid dynamics (CFD). The Volume of Fluid (VOF) method was employed to model the free surface dynamics under various operational conditions. The simulations were able to predict the peculiar experimentally observed behavior of UUSTs and revealed that at velocities below a critical threshold (N_ < _N crit) , the system remains non-aerated, while exceeding this threshold (N_ ≥ _N crit) induces bubble ingestion, leading to significant changes in power consumption and flow patterns. The CFD simulations accurately predicted the behaviour of the Power Number (Np) as well as the vortex shape inside the tank both in subcritical and supercritical regimes and showed good agreement with original experimental data and correlations from the literature. Additionally, the modeling of the aerated regime successfully predicted the vortex shape, the bubble dispersion within the tank, and the cavities formed behind the blades. [ABSTRACT FROM AUTHOR]

The interest in the process industry on unbaffled stirred tanks has greatly expanded in the last years because they may bring about significant advantages in a number of applications, including biochemical, food and pharmaceutical processes where the presence of baffles is undesirable for several reasons. Despite their application potential, unbaffled vessels still lack fundamental information, due to the fact that only recently their capabilities have started being dug out. The lack of information on scale up effects is possibly the main reason hindering practical applications. In this work the influence of vessel size and liquid viscosity on the mass transfer performance in unbaffled stirred vessels, is investigated. As regards the first issue (scale-up) quite surprisingly results show that comparable mass transfer coefficients may be obtained in larger vessels, for a given power input per unit volume, with typical k L a values up to 2 × 10 −3 s −1 in ungassed conditions and of 2 × 10 −2 s −1 in gassed conditions. This is opposite to expectations based on the fact that the exchange surface in subcritical conditions only grows with D 2 while volume grows with D 3 . Notably, the same result is obtained at an increased liquid viscosity (a feature often exhibited by biological cultivation broths) and confirms that unbaffled stirred tanks should be regarded as a strong candidate for industrial applications. Finally, also at the larger scale, in the super-critical regime unbaffled tanks are found to provide a performance comparable with that of standard (baffled & sparged) stirred tanks, hence resulting in a viable alternative to baffled tanks for all gas–liquid processes and bio-processes. [ABSTRACT FROM AUTHOR]