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    Co-combustion dynamics and products of textile dyeing sludge with waste rubber versus polyurethane tires of shared bikes
    (Elsevier Sci LTD, 2023) He, Yao; Chen, Xi; Tang, Xiaojie; Chen, Siqi; Evrendilek, Fatih; Chen, Tao
    The co-combustions of major waste streams such as textile dyeing sludge (TDS) and waste tires of shared bikes may reduce the dependence on fossil fuels, as well as enhance their circular management and the recovery of their value-added products. In this study, the ash-to-gas products, interaction effects, and reaction mechanisms of the co-combustions of TDS and waste tires were characterized. The mono-combustions included the three stages of water evaporation, volatiles release, and mineral decomposition for TDS and the five stages for both rubber (RT) and polyurethane (PUT) tires. The three substages of the main stage of volatiles release for TDS had the activation energy of 124.5, 144.9, and 167.5 kJ/mol and were best explained by the reaction mechanism models of D3, D5, and F2, respectively. The (co-)combustion performance indices rose with the increased heating rate. The blend of 25% TDS with 75% RT (TR) and 75% PUT (TP) led to the best co-combustion performance according to comprehensive combustion index, with TP outperforming TR. The co-combustions of TP and TR reduced the activation energy required for the main devolatilization stage reaction. There was no significant difference in the main reaction mechanisms between the co-combustions. The interaction between TDS and waste tires reduced the applied energy required for the main devolatilization stage. The co-combustions at the low temperature produced O-H, CH4, CO2, CO, SO2, NO, carbonyl products, olefin products, and ketones. The cocombustions increased the production of C-H, reduced SO2 release and the viscosity of their ashes, promoted the complete combustion of substances, and alleviated the scale and sintering issues regardless of TP versus TR and caused the early release of NO from TP. According to the thermodynamic equilibrium simulations, the TR cocombustion promoted the retentions of Ca, S, Si, and Fe, in particular, the fixation of S. The addition of PUT enhanced the combination of Ca and Si into CaSiO3. The optimization based on the artificial neural networks pointed to the temperature range of 400-800 oC and the TR co-combustion as the optimal operational conditions.
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    Converting and valorizing heavy metal-laden post-harvest hyperaccumulator (Pteris vittate L.) into biofuel via acid-pretreated pyrolysis and gasification
    (Elsevier Science SA, 2023) Huang, Shengzheng; Liu, Jingyong; Chen, Siqi; Wang, Jin; Chen, Zhibin; Evrendilek, Fatih
    Not only should post-harvest hyperaccumulators rich in heavy metals (HMs) be properly disposed to avoid secondary HMs pollution, but also they should be valorized to enhance circular economy. This study aimed to characterize how As-hyperaccumulator (Pteris vittate L.) (PV) pretreated with HCl or H3PO4 affected its physi-cochemical, HMs, decomposition, and volatile characteristics. The HCl-pretreated PV retained its original main components, physical properties, and chemical structures but introduced Cl to carbon chain, induced O loss, increased C content, and removed most minerals, in particular, alkali/alkaline earth metals. The favorable py-rolysis and gasification behaviors of PV were maintained via the HCl-pretreated PV, with the raised and nar-rowed temperature range of mass loss but with the increased energy demand for the decomposition. Compared with PV (276.74 kJ/mol), 5% HCl-pretreated PV reduced activation energy of its pyrolysis (260.62 kJ/mol). The H3PO4 pretreatment destroyed carbon chain, loaded phosphorus oxygen group, and removed more organics and minerals in PV than did the HCl-pretreated PV. This in turn allowed for an earlier start and finish of devolati-lization stage, an easier breaking of potential energy barrier, and improvement of reaction favorability. Unlike the two atmospheres, the acid pretreatments changed the temperature dependency of volatile products during the main reaction-temperature range. The volatile products which released from the pyrolysis and gasification at the temperature of maximum mass loss peak or 350 degrees C were collected. HCl-pretreated PV reduced the formation of ring-opening products, while H3PO4-pretreated PV emitted more aromatic compounds and selectively generated ketone, such as levoglucanone. More HMs were dissolved with the increased acid concentration, with HMs in HCl-pretreated PV being at a higher leaching concentration than those in the other treatments. H3PO4- pretreated PV retained As, Cd, and Pb at a low leachable rate. The best joint optimization was achieved with the combined settings of 5% HCl-pretreated PV or 10% H3PO4-pretreated PV at 10 degrees C/min in the N2 atmosphere. Overall, findings provide new insights into how to best manage and valorize post-harvest and HM-laden hyperaccumulators.