This study aims to cognize the evolution of char structure during Co-Ca catalyzed coal hydrogasification and its influence on gas-solid hydrodynamics of gasifier. Co-Ca catalyzed coal hydrogasification was carried out in a pressurized bubbling fluidized bed at 1123 K and 3 MPa. The results showed that the initial 5 min of coal hydrogasification can be considered as coal hydropyrolysis period. Particle size increased during coal hydropyrolysis, reduced when carbon conversion lied below 69% and then remained basically stable during char hydrogasification. The apparent particle density decreased progressively. Micropores were formed in abundance during coal hydropyrolysis and then decreased gradually during char hydrogasification. Whereas mesopores kept increasing and the macropores firstly increased then collapsed with carbon conversion. The simulation results of gasifier suggested that more particles aggregated at the bottom of the gasifier during coal hydropyrolysis, and the gas-solid flow state changed increasingly from bubbling to turbulent during char hydrogasification.

The pressurized hydrogasification/catalytic hydrogasification behaviors of naphthalene as a coal-based model compound were investigated for the first time in a batch reactor. The composition of products was roundly analyzed by gas chromatography (GC), gas chromatography-mass spectrometer (GC-MS) and laser desorption time-of-flight mass spectrometry (TOF-MS). Based on the product analysis results, the detailed reaction pathways for naphthalene hydrogasification and the effects of cobalt on reaction pathways were elucidated. Naphthalene first destabilized during hydrogasification. Subsequently, the destabilized naphthalene either underwent stepwise hydrocracking by active hydrogen atoms to ultimately produce benzene and methane, or formed naphthalene free radicals to initiate condensation. Cobalt can regulate products distribution to boost methane, benzene and toluene yield by facilitating active hydrogen generation, despite it had a limited ability to facilitate the naphthalene destabilization at temperature below 700 degrees C. Whereas above 750 degrees C, cobalt can promote naphthalene destabilization, thereby remarkably enhancing the conversion of naphthalene. Furthermore, cobalt intensified condensation leading to a shift of molecular mass distribution of condensation products from 252 500 Da to 750 - 2000 Da. These phenomena supported similar findings in coal catalytic hydrogasification. The rise in temperature, initial H2 pressure (P0), and cobalt content all facilitated the cobalt catalyzed naphthalene hydrocracking to gaseous product, with temperature exerting a particularly significant effect. This trend was similar with cobalt catalyzed coal hydrogasification. For example, when temperature increased from 650 degrees C to 750 degrees C, naphthalene conversion improved from 21.2 % to 49.6 %, and gas yield rose from 2.6 % to 29.4 % at 1 % Co and 1.3 MPa P0. The investigation serves to shed light on the molecular-level understanding of the mechanism underpinning coal hydrogasification.

Hydrogasification (C + H2 -> CH4) is a crucial reaction for obtaining CH4 from coal or biomass. However, the reaction is sluggish in the absence of a suitable catalyst. Cobalt is more catalytically active than iron, nickel, and alkali metals, but is expensive. To improve the process economy, catalyst recycling was investigated with a focus on cobalt and calcium (Co-Ca) catalyzed coal hydrogasification. The results revealed that Co existed as metallic state in the gasified residue, and it was strongly associated with Ca compounds. Co-Ca as nitrate and acetate exhibited significantly higher activity than that of chloride and sulfate. Nitrate acid (HNO3) can effectively leach Co and Ca from the residue, as the leaching efficiencies of Co and Ca exceeded 99.7 % and 98.0 %, respectively. Additionally, seventeen mineral impurity elements were extracted from the residue. With repeated recycling, the majority of impurities accumulated in the recovered catalyst and exhibited distinct effects on its activity. Al impurity demonstrated its ability to significantly lower the Co-Ca activity, whereas Fe, K, Na, Mg, P, and S could not. Because impurities inhibited Co reducibility, the catalytic performance of recovered Co-Ca decreased with each recycling. Inspired by the results, the proposed HNO3 leaching procedure was optimized using two-step precipitations for impurities removal, and a high activity of recovered catalyst was achieved. This study provides some insights into the recovery, deactivation, and regeneration of cobalt catalyst employed for coal or biomass hydrogasification.

Catalytic hydrogasification (C + H2 & RARR; CH4) is an efficient process for methane production from coal. To reduce reactant hydrogen cost, cheap crude gas from coal gasifier without further treatment is proposed to replace hydrogen for the process. In this study, the effect of steam in crude gas on Co-Ca bimetal catalyzed coal hydrogasification was investigated using H2 and steam mixtures (H2 + steam) in a fluidized bed reactor, with 5% to 30% steam addition. The result demonstrated that the product distribution in H2 + steam was determined by coupled reactions of hydrogasification and steam gasification. A 95.1% carbon conversion with a 68.8% CH4 selectivity was achieved in H2 + 10% steam at 900 degrees C and 4 MPa. The reaction heat released by hydrogasification can be in situ absorbed through steam gasification, realizing heat utilization in H2 + steam. Co-Ca exhibited activity for both the reactions. However, the presence of steam significantly inhibited Co-Ca activity toward hydrogasification. The inhibition mechanism was that the preferentially adsorbed H2O, OH, and O species on cobalt surface blocked the dissociative adsorption of H2 molecules. The study provides an insight for developing an inexpensive and effective process for coal to clean fuels.

The coal-fired power generation is still the most important electricity generation technology in China. The emission of pollutants during the coal combustion process has severely hindered the sustainable development of coal-fired power plant. The key to solving these problems is to promote the clean and efficient use of coal. Power generation from oxidation of coal in supercritical water is an efficient and environmentally clean combustion technology of coal. The energy of coal oxidation is directly transmitted to water without heat transfer surfaces. In addition， nearly pure CO 2 can be separated from the expanded stream. The effects of mineral removal on coal structure， oxidation reaction characteristics of ashless Xichagou coal and the transformation of carbon， sulfur and nitrogen in supercritical water have been investigated. The results showed that demineralization had little effect on the structure of Xichagou coal. The gas phase products were mainly CO 2 during supercritical water oxidation， no polluting gases such as NO x and SO x were generated. Small amount of CO and H 2 were detected at temperatures lower than 500 ℃. When the final reaction temperature exceeds 500 ℃， the converted carbon was completely oxidized to carbon dioxide. The conversion of carbon， nitrogen， and sulfur in coal increased with the increase offinal temperature and the amount of oxidant. At 550 ℃ and the oxidant was 1.4 times of stoichiometry， the conversion of C， N and S reached 97.08%， 94.52% and 94.41%， respectively.

Coal catalytic hydrogasification (CCHG) is a promising approach for producing substituted natural gas by using pure hydrogen as a gasifying agent. If pure hydrogen could be replaced by cheaper crude gas from the coal gasifier, the economy of CCHG would be significantly improved. However, the composition of crude gas is complicated because in addition to H-2, CO, CO2 and H2O are contained in it. To preliminarily investigate the influence of CO2 in the feed gas on CCHG, a mixture of H-2 and CO2 with a CO2 concentration of 10% (denoted as H-2 + CO2) was used for Co-Ca catalyzed coal hydrogasification at 850 C and 3 MPa in a fluidized bed reactor. The results showed that the concurrence of coal hydrogasification with CO2 methanation produced CH4 efficiently. The CH4 yield (based on the carbon in coal) increased from 77.4% for pure H2 to 188% for H-2 + CO(2)within 120 min. More than 90% CO2 in situ conversion and 72.3% coal conversion were achieved. The catalytic effect of the Co-Ca loaded coal considerably improved the CH4 selectivity of CO2 methanation from 43.5% to 82.7%. The forms of Co and Ca in H2 + CO2 were consistent with those in pure hydrogen. The slow coal hydrogasification rate in H-2 + CO2 was mainly attributed to the two-fold effects of CO2 methanation: the decrease in the partial hydrogen pressure and the competitive adsorption behavior of H-2 and CO (a by-product of CO2 methanation) molecules on the cobalt active surface. This work provides a unique approach for simultaneously realizing the conversion of coal and the utilization of CO2.