In this work, the influence of KCl concentration on the gasification characteristics of lignite coal char between 800–1100 °C is studied through the experiments of temperature programmed gasification and isothermal gasification using a thermogravimetric analyzer. The gasification kinetics, characteristic parameters, and the reaction mechanism of catalytic gasification is explored using the random pore model (RPM). In view of temperature programmed gasification, the gasification rate of coal char is relatively slow when the temperature is below 700 °C, and only when the temperature is higher than 700 °C, the gasification starts to accelerate. Results show that with the existence of a catalyst, the temperature required for gasification reaction is reduced and the gasification reaction rate is increased. Furthermore, the higher concentration of KCl leads to the shorter half reaction time, the higher gasification rate, and the stronger catalysis. In addition, the activation energy of AW-char (the char from acid-washed coal) is the highest, while the activation energy and the energy level required for the gasification reaction are reduced by adding KCl. Based on the analysis of the catalytic mechanism, it is found that the unified mechanism of catalytic gasification of alkali and alkaline earth metals is applicable for the KCl catalysis on coal char gasification.

In this study, thermogravimetric analysis (TGA) with a final temperature of 1000°C at a heating rate of 10°C/min and rapid pyrolysis are used to analyze the catalytic pyrolysis effect of CaCl₂ and NiCl₂ on lignite samples, mainly including pyrolysis reaction analysis and tar product distribution. To avoid the influence of minerals on the pyrolysis reaction, acid-washed coal is selected and mixed with metal cations for further analysis. The TGA results show that when mixed with 6 wt. % Ca or Ni, the weight loss rate of acid-washed lignite increases from 46.46% to 59.76% and 54.66%, respectively. At pyrolysis temperatures above 600°C, the performance on coal pyrolysis transformation of Ca is significantly better than that of Ni. The effect of the catalyst on coal pyrolysis could be divided into three stages. Due to catalysis, the pyrolysis of the most unstable structure of coal is advanced to the first stage, which makes the second stage show a certain catalytic inhibition. Kinetic analysis reveals that the activation energy of pyrolysis is obviously reduced by catalysts, and comparatively, the most energy is needed at the second stage. The tar mainly contains substances with 5 to 16 carbon atoms, and aromatic hydrocarbons, as the main components, account for more than 90% of the tar composition. The yield of light aromatic compounds increases with the catalysts Ca and Ni, while the yield of polycyclic aromatics decreases.

In this work, the effect of temperature on the pyrolysis products of two typical coal samples, namely, bituminous coal and subbituminous coal, is studied by using a tube furnace with the highest working temperature of 1700°C. The temperature range is set to 1000–1400°C to obtain ultrahigh temperature conditions. Proximate analyses and ultimate analyses are performed to obtain the basic characteristics of raw coal samples. In the pyrolysis process, the tube furnace is preheated to the target temperature, prior to the coal samples and as the quartz tube being pushed into the constant temperature zone of the tube furnace. The yields and release rate of the light volatile gas (LVG), the calorific value, the distribution of LVG, and pyrolysis products are evaluated. Additionally, the impact of temperature on LVG is discussed in-depth. The amount of volatile gas increased by 1.25 and 1.38 times for ZD coal and DT coal, respectively, with increasing temperature. Our results show that increased temperature has a positive impact on the acceleration of the cracking and raises the gross output of volatile gas. The H₂ yield is approximately 50–70% of LVG, and the CO₂ and CO show opposite variations with temperatures due to the conversion of the oxygen atoms in the gas. The output of CH₄ is inhibited due to the presence of the carbon deposition reaction in the high-temperature pyrolysis, resulting in increasing H₂ yield. Additionally, the yields of char and tar decrease with increasing temperature.

Sludge-based activated carbons (SACs) prepared from sewage sludge and corn straw, were modified by ferric nitrate, and the unmodified SAC and modified SAC were used as the adsorbing agent to treat the landfill leachate, the elimination capacity for chemical oxygen demand (COD) and organic matter in leachate were studied. Based on this, the physicochemical properties of SACs and the components changes in leachate were analyzed and characterized by X-ray photoelectron spectroscopy and three-dimensional fluorescence spectroscopy. The results showed that under optimal experimental conditions, the elimination capacities of SAC372 for COD, biological oxygen demand over 5 days, and NH₄⁺–N in the leachate were 81.58%, 54.73%, and 69.08%, respectively; while the adsorption capacities of modified SAC for these three substances were 86.25%, 63.51%, and 79.15%, respectively. The ferric nitrate modification improved the ability of SAC to eliminate COD and organic matter from leachate slightly, and made the adsorption occurred easily. The adsorption process of unmodified SAC was dominated by multi-layer adsorption, while the adsorption process of modified SAC was dominated by monolayer adsorption. The mass fraction of Fe (2p) in modified SAC remarkably increased, from 0.70% to 26.01%, organic functional groups certain phase of Fe oxides with different valence states were generated in SAC, which provided a substrate for iron–carbon micro electrolysis. After adsorbed by unmodified SAC and modified SAC adsorption, the total fluorescence intensity of in the leachate increased by 17.01% and 116.84%, respectively. Both two SACs could decompose the humic acid-like substances into aromatic protein organic compounds, and modified SAC could further decompose the soluble microbial byproduct-like substances.