This study compares the chemical and structural properties of the hydrochars prepared from microwave-assisted and conventional hydrothermal carbonizations of Prosopis africana shell, a waste plant material. The preparation involved heating the raw material in de-ionized water at 200 °C for 5-20 min, and 120-240 min in the microwave and conventional oven respectively. The prepared hydrochars were characterized using the scanning electron microscope, nitrogen sorption measurement, Fourier transform infrared spectroscopy, CHN analyzer, thermogravimetric analysis, and nuclear magnetic resonance. The results showed that the microwave-assisted hydrothermal carbonization process is fast in the carbonization of the Prosopis africana shell as shown by the level of conversion attained within the short time. This study presents new data on the comparison of the hydrochars from microwave-assisted and conventional hydrothermal carbonization processes of the same lignocellulosic material in terms of their properties.

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Hydrothermal carbonization has been used as a green and effective technique for the preparation of hydrochars from simple carbohydrates, such as glucose. The chemical and structural properties of hydrochars prepared from glucose have been studied. However, the energy properties of hydrochars prepared from microwaveassisted hydrothermal carbonization of glucose have not been studied. Thus, in this study, microwave-assisted hydrothermal carbonization of glucose, and the energy properties of the prepared hydrochars are reported. The preparation involved heating glucose in de-ionized water at 200°C for 5-60 min in a microwave oven. The prepared hydrochars were characterized using scanning electron microscope, nitrogen sorption measurement, Fourier transform infrared spectroscopy, elemental (CHN) analyzer, and nuclear magnetic resonance, and their energy properties studied. The result indicated that, in comparison with previous studies using the classical hydrothermal carbonization process, this approach reduced the processing time greatly from hours to 45 min, while the increase in higher heating value of the hydrochar when compared to that of the starting material was higher in this study than some value previously reported.

Hydrothermal carbonization of a waste biomass is a green and promising technique for improving its solid fuel properties, which does not require pretreatment procedure such as drying of the biomass. In this study, hydrothermal carbonization of rapeseed husk, a waste plant material was carried out under microwave heating and the effect of process parameters, such as the reaction temperature and the residence time on the mass yields and the energy properties of the hydrochars was studied. The procedure involved the heating of the feedstock in deionized water in a microwave oven at temperatures of 150 to 200 °C for a specified period of time. The results indicated that the mass yields decreased, as the reaction temperature and residence time were increased, which led to improvement in the energy properties of the prepared hydrochars. The reaction was rapid within the first 20 min, and stabilizes afterwards.The energy properties of the prepared hydrochars are consistent with previous studies, showing that the hydrochars have the potential of being used as solid fuel. The structural and morphological analysis carried out revealed that the feedstock was transformed during the process.

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A new microwave-assisted hydrothermal synthesis of carbon monolith is reported in this work. The process uses microwave heating at 100 °C under acidic condition by employing a triblock copolymer F127 as the template, and resorcinol-formaldehyde as the carbon precursor. Scanning electron microscopy, Fourier transform infrared spectroscopy, nitrogen sorption measurements, transmission electron microscopy, X-ray studies and thermogravimetic analysis were used to characterize the synthesized material. The carbon monolith is crack-free, mesoporous and has a high surface area of 697 /g. The results demonstrate that the microwave-assisted hydrothermal synthesis is a fast and simple approach to obtain carbon monoliths, as it reduces effectively the synthesis time from hours to a few minutes which could be an advantage in the large scale production of the material.

In this study, microwave-assisted hydrothermal carbonization of waste coconut shell (feedstock) is reported. It is a thermo-conversion technique in which the feedstock was transformed into energy-rich carbonaceous material under mild conditions. The process was conducted in a microwave oven by heating the waste coconut shell in deionized water inside a pressurized vessel. The effects of different process conditions on the product yields, and the energy properties of the hydrochars were studied by varying the reaction temperature from 150 -200 °C and residence time from 5 -30 min. The results showed that there was transformation of the feedstock in the process due to the decarboxylation, dehydration, and demethanation reactions. This led to changes in the chemical and structural compositions, as well as increase in the energy properties of the prepared hydrochars. The higher heating value increased from 15.06 MJ/Kg in the feedstock to 19.76 MJ/Kg in the hydrochar. The energy properties of the hydrochars prepared in this study showed that microwave-assisted hydrothermal carbonization process could be a technique for converting waste coconut shell into high value-added product.