Modification mechanism of caking and coking properties of Shenmu subbituminous coal by low-temperature rapid pyrolysis treatment

Shenmu(SM)subbituminous coal without caking property was treated by low-temperature rapid pyrolysis(LTRP)to modify its caking and coking properties.The treated samples were characterized by Fourier transform infrared spectrometry,vitrinite reflectance,and X-ray diffraction to determine the modification mechanism.Moreover,caking index(G)and coking indices(mechanical strength,coke reactivity,and coke strength after reaction)were employed to evaluate caking and coking properties,respectively.The results showed that SM coal was gradually upgraded with increasing processing temperature.Furthermore,the G values for the treated samples were significantly higher than that for SM coal,and G reached the maximum value at 450℃,implying the modification of caking property and the existence of an optimum temperature(450℃).Additionally,laboratory coking determinations showed that LTRP increased the mechanical strength of coke and coke strength after reaction and decreased coke reactivity when the treated coals were used in the coal blends instead of raw SM coal.Overall,LTRP treatment is effective to improve the caking and coking properties of SM coal.A mechanism was proposed for the modification.Suitable upgrading degree with suitable molecular masses and some releasable hydrogen-rich donor species present within the coal,which dominate the development of caking property,is important.

Formation mechanism of solid product produced from co-pyrolysis of Pingdingshan lean coal with organic matter in Huadian oil shale

A mixture of Pingdingshan lean coal and acid-treated Huadian oil shale was co-pyrolyzed in a drop-tube fixed-bed reactor in the temperature range of 300℃–450℃.To reveal the formation mechanism of the solid co-pyrolysis product,changes in some physicochemical properties were investigated,using analysis by X-ray diffraction,X-ray photoelectron spectroscopy,scanning electron microscopy,pore analysis,thermogravimetry,and electron spin resonance.X-ray diffraction showed that the lattice plane spacing for the co-pyrolyzed mixture decreased from 0.357 nm to 0.346 nm and the average stacking height increased from 1.509 nm to 1.980 nm in the temperature range of 300°C–450°C,suggesting that pyrolysis treatment increased its degree of metamorphism.The amount of oxygen-containing functional groups and pore volume decreased with increasing temperature.Thermogravimetry and electron spin resonance results showed that synergistic effects occurred during the co-pyrolysis process.A formation mechanism for the solid product was proposed.Hydrogen-rich radicals generated from the pyrolysis of the oil shale were trapped by hydrogen-poor macromolecular radicals of the intermediate metaplast produced from coal pyrolysis,thereby increasing the yield of solid product.

Single-Ni-atoms on nitrogenated humic acid based porous carbon for CO_(2)electroreduction

tWe proposed a facile synthesis of single-Ni-atom catalysts on low-cost porous carbon using a calcina-tion method at the temperatures of 850-1000°C,which were used for CO_(2)electrochemical reduction to CO.The porous carbon was prepared by carbonizing cheap and abundant humic acid.The structural characterizations of the as-synthesized catalysts and their electrocatalytic performances were analyzed.The results showed that the single-Ni-atom catalyst activated at 950°C showed an optimum catalytic performance,and it reached a CO Faradaic efficiency of 91.9%with a CO partial current density of 6.9 mAcm^(-2)at-0.9 V vs.reversible hydrogen electrode(RHE).Additionally,the CO Faradaic efficiency and current density of the optimum catalyst changed slightly after 8 h of continuous operation,suggesting that it possessed an excellent stability.The structure-activity relations indicate that the variation in the CO_(2)electroche-mical reduction performance for the as-synthesized cataly-sts is ascribed to the combined effects of the increase in the content of pyrrolic N,the evaporation of Ni and N,the decrease in pore volume,and the change in graphitization degree.