RESUMEN
Hydrothermal carbonization (HTC) is emerging as an effective technology to convert PVC into highly valuable materials via the removal of chlorine. This means that an in-depth understanding of HTC requires the hydrochar structure, thermal degradation behavior, and relationship between structure and thermal reactivity to be understood. In this work, two typical PVC waste materials were selected for HTC experiments at different temperatures. The structure of the hydrochar was characterized in detail by compositional analysis, FTIR spectroscopy, and 13C NMR analysis. Furthermore, the thermal degradation behavior of the hydrochar was analyzed. The changes after thermal degradation were used to establish a correlation with pyrolysis reactivity. The results showed that the C content and chemical structure of the hydrochar approached that of bituminous coal with increasing HTC temperature. Compared with the untreated PVC feedstock, the hydrochar exhibited higher levels of oxygen-containing functional groups on its surface, and its carbon skeleton structure changed from polymeric straight chains to short-chain paraffins, cycloalkanes, and aromatics. A negative correlation was observed between the CPI value of the hydrochar derived from SPVC and the HTC temperature. The structural evolution path of the hydrochar was altered by additives, which improved its thermal reactivity. These findings are expected to play a significant role in bridging the gap from the creation of a theoretical potential energy source to the development of a sustainable alternative renewable fuel.
RESUMEN
Rigid PVC plastics (R-PVC) contain large amounts of chlorine, and improper disposal can adversely affect the environment. Nevertheless, there is still a lack of sufficient studies on hydrothermal treatment (HTT) for the efficient dechlorination of R-PVC. To investigate the migration mechanism of chlorine during the HTT of R-PVC, R-PVC is treated with HTT at temperatures ranging from 220 °C to 300 °C for 30 min to 90 min. Hydrochar is characterized via Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. The results revealed that the hydrothermal temperature is the key factor that affects the dechlorination of R-PVC. Dramatic dechlorination occurs at temperatures ranging from 240 °C to 260 °C, and the dechlorination efficiency increases with the increase in the hydrothermal temperature. The main mechanism for the dechlorination of R-PVC involves the nucleophilic substitution of chlorine by -OH. CaCO3 can absorb HCl released by R-PVC and hinder the autocatalytic degradation of R-PVC; hence, the dechlorination behavior of R-PVC is different from that of pure PVC resins. Based on these results, a possible degradation process for R-PVC is proposed. This study suggests that HTT technology can be utilized to convert organochlorines in R-PVC to calcium chloride, achieving the simultaneous dechlorination of R-PVC and utilization of products.
RESUMEN
With the improvement of living standards, food waste (FW) has become one of the most important organic solid wastes worldwide. Owing to the high moisture content of FW, hydrothermal carbonization (HTC) technology that can directly utilize the moisture in FW as the reaction medium, is widely used. Under mild reaction conditions and short treatment cycle, this technology can effectively and stably convert high-moisture FW into environmentally friendly hydrochar fuel. In view of the importance of this topic, this study comprehensively reviews the research progress of HTC of FW for biofuel synthesis, and critically summarizes the process parameters, carbonization mechanism, and clean applications. Physicochemical properties and micromorphological evolution of hydrochar, hydrothermal chemical reactions of each model component, and potential risks of hydrochar as a fuel are highlighted. Furthermore, carbonization mechanism of the HTC treatment process of FW and the granulation mechanism of hydrochar are systematically reviewed. Finally, potential risks and knowledge gaps in the synthesis of hydrochar from FW are presented and new coupling technologies are pointed out, highlighting the challenges and prospects of this study.
RESUMEN
The organic solid waste (OSW) is a potential resource that loses its original value in people's daily production process. It can be used for secondary energy utilization through hydrothermal technology, which is similar to artificially simulating the natural coalification process. Co-hydrothermal carbonization (co-HTC) is a promising thermochemical conversion pathway, and advanced mechanisms can eliminate the drawbacks of single-feedstock hydrothermal carbonization (HTC). The preparation and production process of hydrochar can solve the problems of energy crisis and environmental pollution. This paper comprehensively reviews the key mechanisms of co-HTC to prepare solid fuels, and reviews the development process and practical application of hydrothermal technology. To begin with, the physical and chemical properties and combustion performance of co-hydrochar depend on the production method, process parameters, and selection of raw materials. The co-hydrochar usually has a higher HHV and a low atomic ratio of H/C and O/C, which improves combustion performance. Subsequently, the transformation path of the hydrothermal process of lignocellulosic and protein OSW was comprehensively expounded, and the reaction mechanism of the co-HTC of the two OSWs was effectively proposed. The effect of the ratio of different raw materials on the synergistic effect of co-HTC was also analyzed. Furthermore, the typical advantages and disadvantages of environmental safety, technical economy, and practical application in the co-HTC process are expounded. All in all, this review provides some foundations and new directions for the co-HTC of OSWs to prepare potential fuel. In addition, several prospects for the development and integrated application of co-HTC are presented in the future.
