Effect of pyrolysis conditions on the improvement of the physicochemical structure of activated carbon obtained from Jixi bituminous coal

Abstract

Different pyrolysis conditions have been confirmed as a useful way to improve the physicochemical structure of Jixi bituminous char to obtain fully developed porosity after a low burn-off during activation. In this paper, a series of coalchar samples were prepared at different pyrolysis temperatures, rates, and residence times. The effect of the pyrolysis temperature on the physicochemical structure in coal char is important because it can control the breakage and recombination of different types of chemical bonds. The impact of the pyrolysis rate gradually increases with increasing temperature, indicating that its influence is closely related to the pyrolysis temperature. However, an extension of the residence time at different pyrolysis temperatures and rates can only help the evolution of the chemical structure. It was determined that the typical char (KJX800-40) produced by rapid pyrolysis at 800°C over a long residence time (40 min) is the most suitable for subsequent activation due to its disordered carbon structure, abundant initial pores, and active sites. The initial pores that developed in the KJX800-40 char facilitate the diffusion of activated gas to avoid serious carbon losses on the surface of the particles; alternatively, more active sites help the etching of the carbon structure to promote the rapid and continuous development of the micropores, following nonhierarchical development. On the basis of these results, a pyrolysis condition with a high S BET (859.14 m 2 /g)/burn-off ratio (25.2%) of 34.09 m 2 /(g•%) was identified.

Microwave-Assisted Hydrothermal Preparation of Corn Straw Hydrochar as Supercapacitor Electrode Materials

“…become more comfortable to escape from this free framework structure, resulting in the formation of pores of different sizes and shapes. 19 Also, the hydrothermal reaction is enhanced gradually by the extension of microwave radiation time from 40 to 100 min. 20 In this process, high-temperature and pressure water can also remove the impurities in the original pores of straw hydrochar to open some of the blocked pores.…”

“…The 002 and 100 peaks of HTC-40/70/100 are high and narrow, indicating the large size and good degree orientation of straw hydrochar. To further study the crystal structure changes of straw hydrochar and pyrochar, the 002 and 100 peaks of all samples are treated by the fitting method, and the specific parameters [such as layer distance ( d 002 ), stacking height ( L c ), width ( L a ), and layer number ( N = L c / d 002 )] are calculated by the Bragg law and Scherrer formula, 19 as shown in Table 1 .…”

“…Then, a lot of volatile components (such as CO, CO 2 , C x H y , etc.) become more comfortable to escape from this free framework structure, resulting in the formation of pores of different sizes and shapes . Also, the hydrothermal reaction is enhanced gradually by the extension of microwave radiation time from 40 to 100 min .…”

“…However, AC-1000­(K) presents a small number of microcrystalline layers at high temperatures. With the increase of heat treatment temperature from 500 to 1000 °C, the condensation, aromatization, and dehydrogenation of hydrogenated aromatics of straw pyrochar can lead to the formation of more microcrystalline layers . However, AC-500/800/1000­(K) contains only a small area and few layers of microcrystalline layers, which is related to the release of more potassium-based compounds in an open environment.…”

Effect of Physical and Mechanical Activation on the Physicochemical Structure of Coal-Based Activated Carbons for SO2 Adsorption

“…In this work, Jixi bituminous coal with particle sizes of 200-350 µm was obtained from the northeast of China. In order to eliminate the interference of minerals in the raw material, Jixi bituminous coal was treated sequentially using 30 wt % hydrofluoric acid (HF) and 5 mol•L −1 hydrochloric acid (HCl) following the steps in the literature [30]. Then, the acid-treated samples were washed using deionized water and dried in an oven at 90 • C for 12 h. The proximate analysis and elemental analysis of the acid-treated samples (JX) were given in Table 1.…”