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Hydrothermal carbonization (HTC) is a useful method to convert wet biomass to value-added products. Fruit waste generated in juice industries is a huge source of moist feedstock for such conversion to produce hydrochar. This paper deals with four types of fruit wastes as feedstocks for HTC; namely, rotten apple (RA), apple chip pomace (ACP), apple juice pomace (AJP), and grape pomace (GP). The operating conditions for HTC processing were 190 °C, 225 °C, and 260 °C for 15 min. For all samples, higher heating value and fixed carbon increased, while volatile matter and oxygen content decreased after HTC. Except for ACP, the ash content of all samples increased after 225 °C. For RA, AJP, and GP, the possible explanation for increased ash content above 225 °C is that the hydrochar increases in porosity after 230 °C. It was observed that an increase in HTC temperature resulted in an increase in the mass yield for RA and GP, which is in contrast with increasing HTC temperature for lignocellulose biomass. Other characterization tests like thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) also showed that the HTC process can be successfully used to convert fruit wastes into valuable products.

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Hydrothermal carbonization (HTC) is a promising thermochemical process for the conversion of biomass with high moisture content, and therefore, interest in the development of continuous technology is growing. However, the development of continuous HTC systems requires the in-depth understanding of reaction kinetics, heat transfer mechanisms, exothermic or endothermic nature of the reaction, effect of operational parameters, recyclability of process water, and variability in biomass feedstock. The current paper discusses the effects of recyclability of process water and particle size on the product yield. To investigate the water recycling effect, HTC experiments were performed on sawdust using recycled water in a batch reactor. Moreover, to study the particle size effect, 3 small reactors containing specific particle sizes of biomass were placed in a larger reactor simultaneously to ensure consistency in the process condition. The results showed that the process water recycling increases the mass yield and higher heating value (HHV) of the solid product by 12% and 2%, respectively, after the first recycle. Physicochemical properties of hydrochar were studied by carrying out the ultimate and proximate, HHV, thermogravimetric coupled with Fourier transform infrared spectroscopy, and Brunauer−Emmett−Teller analysis, and results are discussed. Regarding the particle size study, higher mass yield, a decrease in heating value, and an increase in total organic carbon in the process water were observed by increasing the particle size.

In recent years, hydrothermal carbonization (HTC) has been introduced as an attractive method for converting biomass into value-added products. The complex reaction chemistry and variable composition of biomass have, however, been barriers to find general equations for describing the HTC process. The goal of this study is to establish a link between the composition of biomass and the expected hydrochar from HTC. Based on the experimental design found from response surface methodology, the biomass components, namely pure cellulose, hemicellulose, and lignin, were submitted in different combinations into 39 HTC experiments with severity factors (SFs) of 3.83, 5.01, and 6.19. Using the experimental data, an attempt was then made to predict the mass yield, higher heating value (HHV), carbon content (C%), and energy recovery factor of the hydrochars according to the biomass composition and the process severity. The results revealed that the interactions between the biomass components do not have a major effect on the hydrochar characteristics, whereas the interaction between cellulose and SF is the most significant. Moreover, it was shown that, after the lignin content, the hemicellulose content has the highest positive impact on HHV and C% of the hydrochar. An optimization study showed that, with a focus on minimizing the SF while the HHV is maximized, biomass with a cellulose content of 40%, hemicellulose of 35%, and lignin of 25%, under the severity of 4.41 will be the most suitable case for HTC treatment. Finally, a comparison between the predictions and the experimental data in the literature suggests that the proposed equations can provide a good evaluation on the HTC of several biomass feedstocks, especially when the amount of ash and extractives are low.

Plastics are abundant and have a high energy content making their use in energy applications attractive. This article presents a review on plastic waste (PW) management by pyrolysis and gasification, which are two routes of thermochemical conversion (TCC) techniques. The conversion of PW and the application of its converted products are important steps towards reducing reliance on fossil fuel, enhancing closed-loop recycling of materials and circular economy. The review presented herein also focuses on product distribution and yields with emphasis on the energy content and potential integration to energy systems and grids. It is found that pyro-oils have properties similar to conventional fuels such as diesel and can partially substitute fossil fuels. In fact, the energy content of PW pyro-oils obtained by various researchers range from 41.10 -46.16 MJ kg -1 , which are close to the heating values of conventional fuels, thus are potential candidates for fuel applications. Typical treatment post conversion is also conducted to maintain the quality of the oil produced and the removal of sulphur content to conform with market standards. On the other hand, syngas produced during gasification possesses a lesser potential for fuel applications as its energy content may reach values as low as 20 MJ kg -1 in

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