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This paper summarizes the results of one of the first comprehensive laboratory studies that was conducted to evaluate the effects of adding different contents of recycled polyethylene terephthalate (rPETE) as a modifier to an asphalt binder on the rheological and mechanical properties of the modified binder as well as on the agglomeration behavior between the rPETE and asphalt binder at a multiscale level. The high-temperature and low-temperature performances of the modified binder were investigated at the macro-scale and compared with those of the unmodified binder using dynamic shear rheometer (DSR) and bending-beam rheometer (BBR) rheological tests, as well as asphalt binder cracking device (ABCD) testing. The nano-scale evaluation of the binder properties, including the surface roughness, bonding energy, and reduced modulus, was accomplished using atomic force microscopy (AFM). The results indicated that the addition of rPETE enhanced the high- and intermediate-temperature rheological properties of the modified PG 64-22 binder. The low-temperature rheological properties and resistance to cracking decreased slightly with increasing rPETE content in the asphalt binder. However, this reduction was not remarkable when adding 4%, 8%, and 10% rPETE contents. The asphalt binder modified with 4% rPETE had a low-temperature grade of −22, similar to that of the unmodified binder, indicating that 4% rPETE can be added to the binder to improve its high- and intermediate-temperature properties without reducing its resistance to low-temperature damage. The AFM tapping-mode results indicated that the inclusion of rPETE in the asphalt binder improved the stiffness properties of the modified binder as compared with those of the control asphalt binder. In addition, the rPETE-modified binders showed rougher surfaces than the control binder. The addition of rPETE to the binder increased the values of the reduced modulus and bonding energy compared with those of the control binder.

 

Solvothermal liquefaction (STL) is a thermochemical conversion technique that employs solvents other than water to transform waste plastics into valuable compounds. The objective of this study was to explore the potential use of supercritical toluene, a nonpolar solvent, for the depolymerization of four electrical waste (e-waste) thermoplastics, namely polyamide (PA), polycarbonate (PC), polyoxymethylene (POM), and polyether ether ketone (PEEK), into liquid products. Depolymerization experiments were carried out in batch reactors at three reaction temperatures (325, 350, and 375 ◦C), and three residence times (1, 3, and 6 h). The findings revealed that increasing STL temperature and extending the reaction time enhances the depolymerization of e-waste thermoplastics. The highest STL conversation (100 %) was observed for POM, and the lowest STL conversation (32.23 %) was observed for PEEK. Additionally, the ultimate analysis showed that the liquid product obtained from STL at 375 ◦C and 6 h exhibited higher heating values (HHV) within the range of 31.43 to 35.31 MJ/kg. Thermogravimetric analysis (TGA) demonstrated that the boiling point distributions of liquid products are highly dependent on thermoplastic type. Finally, the reaction mechanisms of STL for PA, PC, POM, and PEEK were proposed based on gas chromatography-mass spectrometry (GCMS) analysis. 

The monumental challenge associated with food waste management has emphasized the dire need of upcycling it into useful materials, including ultraporous adsorbent. Among various technologies of maximizing porosity of such waste-derived porous sorbents, potassium hydroxide (KOH) activation of food waste hydrochar has emerged to be a prominent one. There are two different ways to synthesize ultraporous adsorbent, namely, direct chemical activation (DCA) and char impregnation (CI). This study aims in investigating the environmental impact comparison of DCA and CI using life cycle assessment (LCA). The results demonstrate that CI processes in an environmentally sound way for synthesizing ultraporous carbons from food waste, where freshwater ecotoxicity (57.2%) plays the major contributing role in environmental impact category, primarily due to acid neutralization in the mixer unit of the CI technique of activation. In addition, the dryer unit in the CI process, which is powered by natural gas combustion, was responsible for climate change impact category. Therefore, as an alternative, employment of renewable solar energy (from solar thermal power plant) was also investigated, and results highlighted the possibility of achieving reduced climate change and acidification potential. 

Shrimp shell is a popularly consumed seafood around the globe which generates a substantial quantity of solid wet waste. Hydrothermal carbonization (HTC) could be a viable pathway to convert wet shrimp shell waste into energy-dense hydrochar. The present study aims to assess the fuel properties, physicochemical attributes, and combustion properties of shrimp shell hydrochar generated with a wide range of HTC temperatures (110–290 °C). Results showed that a rise in carbonization rate results in a decline in mass yield to as low as 25.7% with the increase in HTC temperature. Thermogravimetric analysis indicates shrimp shell hydrochars to be more thermally stable than raw dried feedstock. Results from the bomb calorimeter report a maximum HHV of 27.9 MJ/kg for SS-290, showing a 13% increase in energy densification compared to raw shrimp shell. The slagging and fouling indices determined for the hydrochars further assisted in addressing the concern regarding increasing ash content changing from 17.0% to 36.6%. Lower ratings of the slagging index, fouling index, alkali index, and chlorine content for hydrochars at higher temperature indicate the reduced probability of reactor fouling during combustion. The findings of the analysis demonstrate that HTC is a promising approach for transforming shrimp shell waste into a potential fuel replacement.

 

In this study, carbon dots are synthesized hydrothermally from loblolly pine using top-down and bottom-up processes. The bottom-up process dialyzed carbon dots from hydrothermally treated process liquid. Meanwhile, hydrochar was oxidized into carbon dots in the top-down method. Carbon dots from top-down and bottom-up processes were compared for their yield, size, functionality, and quantum properties. Furthermore, hydrothermal treatment temperature and residence time were evaluated on the aforementioned properties of carbon dots. The results indicate that the top-down method yields higher carbon dots than bottom-up in any given hydrothermal treatment temperature and residence time. The size of the carbon dots decreases with the increase in reaction time; however, the size remains similar with the increase in hydrothermal treatment temperature. Regarding quantum yield, the carbon dots from the top-down method exhibit higher quantum yields than bottom-up carbon dots where the quantum yield reaches as high as 48%. The only exception of the bottom-up method is the carbon dots prepared at a high hydrothermal treatment temperature (i.e., 260 °C), where relatively higher quantum yield (up to 18.1%) was observed for the shorter reaction time. Overall, this study reveals that the properties of lignocellulosic biomass-derived carbon dots differ with the synthesis process as well as the processing parameters. 

This study focused on evaluating the reduction of chlorine content in waste polyvinyl chloride (WPVC) through high‐temperature catalytic hydrothermal treatment (HTT). Catalytic HTT experiments were carried out to evaluate the effect of noble metal catalysts (Ru/C, Pt/C, and Pd/C), residence time (0.5, 1, 2, and, 4 h), reaction temperature (300, 325, and 350°C), and catalyst loading (0, 5, and 10 wt%). The findings indicated that dechlorination efficiency can be achieved by 99.01% at 350°C and 1 h, with 10 wt% Pd/C loading. Based on chlorine balance, the chlorine content of the solid phase significantly decreased from 568.8 to 5.64 g kg⁻¹at the same condition. The catalytic HTT solid residue ash has low chlorine content under most operational conditions. These results suggest that catalytic HTT is an effective method to dechlorinate WPVC as a high‐halogenated waste plastic in order to reduce its harmful effect on the environment.