Grape stem is a kind of agricultural and forestry waste. A fundamental understanding of grape stem pyrolysis behavior and kinetics is essential for its efficient thermochemical conversion. Thermogravimetric infrared spectroscopy and pyrolysis gas chromatography-mass spectrometry, combined with two model-free integral methods: Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were used to investigate the weight loss behavior, the distribution and content of rapid pyrolysis products, the release law of small molecule pyrolysis gases, and the pyrolysis activation energy during pyrolysis. The results showed that the main pyrolysis reaction temperature ranged from 240 °C to 690 °C. The pyrolysis reaction of grape stems at 200 °C to 700 °C was divided into three stages: 0.15 < α < 0.35, 0.35 < α < 0.65, and 0.65 < α < 0.75, which corresponded to the main pyrolysis stages of hemicellulose, cellulose, and lignin, respectively. The products of rapid pyrolysis at 290 °C were mainly composed of acids and sugars, while the products at 355 °C were mainly phenolics. This study aims to provide a theoretical reference for the pyrolysis gasification test of grape stem.
The kinetics of pyrolysis of apricot stone and its main components, i.e., lignin, cellulose, and hemicellulose, were investigated via distributed activation energy mode. Experiments were done in a thermogravimetric analyzer at heating rates of 10, 20, 30, and 40 K·min-1 under nitrogen. The activation energy distribution peaks for the apricot stone, lignin, cellulose, and hemicellulose were centered at 246, 318, 364, and 170 kJ·mol-1, respectively. The activation energy distribution for the apricot stone slightly changed; lignin exhibited the widest distribution; and cellulose exhibited the highest activation energy at a conversion degree (α) of less than 0.75. At low pyrolysis temperatures (400 K to 600 K), the pyrolysis of hemicellulose was the main pyrolysis reaction. The apparent activation energy for the apricot stone mainly depended on the pyrolysis of hemicellulose and a small amount of lignin, and the activation energy was low in the early stage of pyrolysis. With the continuous increase in the pyrolysis temperatures (600 K to 660 K), the thermal weight loss of cellulose and lignin was intense. The apparent activation energy for the apricot stone mainly resulted from the pyrolysis of cellulose and lignin, and a higher activation energy was observed in the later stage of pyrolysis.
Finding low-cost and environmentally friendly precursors that can maintain their electrochemical attraction natural texture properties while obtaining hierarchical porous carbons with high electrochemical performance is desirable for offering a leap forward in industrial applications. However, phenomena associated with the high microporosity of porous carbon remain. Herein, the protective effect of hydrothermal methods and the microporeforming ability of KOH were used. The as-synthesized porous carbon (PC-1) holds the natural texture property (the retention of texture property with apertures higher than 2 nm was up to 80%) and achieves three-dimensional (3D) architecture with hierarchical structures accompanied by an ultrahigh specific surface area (3559.45 m 2 /g). Benefiting from its texture properties, PC-1 possesses a high specific capacitance of 288.75 F/g at 0.5 A/g, excellent rate capability as high as 223.72 F/g at 10 A/g, and remarkable conductivity in a three-electrode system with a 6 M KOH electrolyte. In view of its environment friendliness, low cost, and excellent specific capacitance, PC-1 has promising applications in high-performance supercapacitors.
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