Jianli Yang

Transformation behavior of trace elements during coal pyrolysis

Transformation behavior of trace elements during pyrolysis of three Chinese coals at temperatures up to 1000 °C was studied. Effects of temperature, atmosphere (N 2 and H 2 ), and coal type on release of As, Pb, Cr, Cd and Mn were examined. Experiments were carried out in a fixed bed quartz reactor with a heating rate of 20 °C/min. Results show that bleeding ratios of As, Pb, Cr, Cd and Mn increase with increasing pyrolysis temperature. H 2 atmosphere promotes the release of these elements. Among the trace elements studied, Pb is the most volatile element; Cr and Mn are relatively non-volatile. However, the volatility of these elements varies with coal type. This suggests that these elements are present in various compounds in the coals and the distribution of the element in the compounds is different. Distribution of the forms for these elements in Yima coal and char was analyzed.

Characteristics of residues from thermal and catalytic coal hydroliquefaction

Abstract The properties of residues from thermal or catalytic coal hydroliquefaction experiments were characterised by the ultimate, proximate analyses. The relations between the properties of the residues and the liquefaction reaction conditions, such as temperature, time, catalyst, H-donor solvent and atmosphere were investigated. Variations in H/C ratio and organic volatile matter (OVM) content of the residues with liquefaction conditions and coal conversion were studied. Results show that liquefaction temperature and time are main factors that control the organic properties of the residues. The roles of the Fe–S catalyst and H-donor solvent are to reduce the proportion of condensation products in the residue rather than increase the extent of polymerisation. Consequently, coal liquefaction conversion is improved by 100% by the catalyst, but H/C ratio and OVM content of the residues are not significantly decreased.

Characteristics and carbonization behaviors of coal extracts

Abstract N -methyl pyrrolidone (NMP) raw coal extract (EXT), hydrogenated coal extract (HEXT) and the blend of EXT and HEXT in NMP (BLD), from two bituminous coals, were studied. The extracts were carbonized in both tube-bomb and a temperature programmable furnace. Elemental analysis, FTIR spectroscopy and optical microscopy techniques were employed to characterize the extracts and the carbonization residues. It was found that the extracts resembled petroleum-derived pitches in the hydrogen content and (C/H) atomic ratio. Higher oxygen and nitrogen contents differentiated the coal extracts from commercial petroleum pitch. More carbon and hydrogen, and lesser oxygen and sulfur differentiated HEXT from EXT. The ratios of integrated IR band intensity for aromatic and aliphatic CH stretching indicate that the relative content of aliphatic hydrogen in EXT is higher than in HEXT. HEXT contains comparatively more aromatic hydrogen, a feature necessary for thermal stability and fluidity during carbonization. BLD materials are at a place somewhere in between. Kinetic modeling of the aliphatic hydrogen change during carbonization reveals that EXT has high carbonization rate and low apparent activation energy. This can be related to the optical texture size of carbonization residues. The residues made from EXTs exhibited fine mosaic optical texture and limited mesophase development. HEXTs were readily converted into highly anisotropic coke. BLDs produced carbonization residues with intermediate properties. Extracts with similar activation energies produced similar residues in the same coal series. The degree or extent of anisotropy displayed by the carbonization residues was found to be dependent on the relative distribution of aromatic and aliphatic hydrogen.

Improvement and characterization of an impregnated iron-based catalyst for direct coal liquefaction

Abstract An impregnation method to prepare an active iron-based catalyst for direct coal liquefaction was improved. With the same catalytic activity, the water usage in the improved method is only 1% of that used in the unmodified method. The improved method not only simplifies the impregnation procedure and reduces cost, but also generates small catalyst particle size on coal surface. Water in the coal promotes thermal liquefaction, but deactivates the impregnated catalyst (possibly due to the adsorption of H 2 O molecular on the catalyst surface). Electron probe microanalysis (EPMA), X-ray diffraction (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS) analyses show that the catalyst precursors prepared by both methods are in nanometer size and highly dispersed on coal surface. The irons deposited on coal surface are not only in sulfide forms, but also coordinate with oxygen from moisture- and oxygen-containing groups of coal. The impregnated iron may be composed of FeOOH and FeS or in the forms of Fe–O–S or Fe–S–O. The iron transforms to crystalline pyrrhotite in coal liquefaction.

Promotion of Ferrous Sulfate Catalyst by Sulfur for Hydrogenation of Coal

Sulfur released from five Chinese coals and an USA coal in hydrogen was correlated with the catalytic activity of an impregnated ferrous sulfate for hydrogenation of the coals. The hydrogenation was carried out at a high or ambient pressure. Sulfur released from the coals into the gas phase at the ambient pressure was monitored online with a flame photometric detector. The data indicate that the catalytic activity of the impregnated ferrous sulfate was promoted by the sulfur released from the coals. The promotion ability is proportional to the amount of sulfur released for the lower sulfur coals generally and levels out for the higher sulfur coals. The promotive effect of sodium sulfide on the activity of ferrous sulfate shows the similar behavior. Additional sulfur, no matter added or released, does not improve the catalytic activity further significantly for the higher sulfur coals. The results partially explain the difference in the catalytic activity of ferrous sulfate and effectiveness on added sulfur for different coals.

Dynamic Behaviors of Sulfur Evolved in the Gas Phase from Pyrolysis of Six Chinese Coals

Dynamic behaviors of gaseous sulfur-containing compounds evolved from pyrolysis of six Chinese coals were studied in the temperature range of up to 800°C under N2 and H2. The released amount of total sulfur-containing gases was traced by an online flame photometric detector (FPD). Simultaneously, the changes of different sulfur forms, including H2S, SO2, COS and CS2, also were investigated using an online mass spectrometer (MS). FPD results show that the effect of H2 on gaseous sulfur evolved is complex, which promoted certain peak and suppresses other peaks. Based on the data from MS, it is suggested that a series of competitive reactions between active sulfur and other active matters during pyrolysis may impact on the sulfur form in gas phase. Interactions between active sulfur-containing intermediates and the coal matrix are attributed to be the main factor determining the dynamic behavior.

Effects of Organic Gaseous Additives on Desulfurization of Coal during Pyrolysis

Sulfur removal from coal prior to combustion is an ideal form of sulfur emission control. Pyrolysis is likely to be an effective way to transform sulfur in coal to gas and liquid phases and to generate chars of low sulfur for clean combustion. This article presents recent research on the effects of organic additives on sulfur removal from a Spanish coal and 3 Chinese coals (Yanzhou, Datong, and Xianfeng) by pyrolysis. The coal samples were pyrolyzed in a fixed-bed reactor in a temperature range up to 700°C. Ethanol or acetone was introduced to a pyrolysis atmosphere. It was observed that the introduction of the organic reagents in pyrolysis altered the behavior of sulfur removal as well as the evolution of volatile matter from coals, which resulted in lower sulfur content chars and higher char yields than that in hydrogen and nitrogen. The desulfurization efficiency increases with increasing ethanol or acetone addition. For Datong coal, the promotion of ethanol and acetone on sulfur removal was the most remarkable. Based on XPS information, the promotive effect is contributed to selective oxidation of organic sulfur.

Hg0 Removal by Activated Coke Supported Metal Oxide Catalysts

Gas-phase elemental mercury (Hg0) removal by activated coke (AC) supported metal oxide catalysts MxOy/AC (MxOy=MnO2, Fe2O3, CuO) were studied under N2+HCl atmosphere and compared with that by AC. The influences of MxOy loading, temperature and Hg0 concentration on Hg0 removal were investigated. The results indicate that the capabilities of MxOy/AC for Hg0 removal were much higher than that of AC, indicating the important role of MxOy. The capabilities were found to follow the trend MnO2/AC > Fe2O3/AC > CuO/AC, which was corresponding to the oxidation activities of MxOy. The Hg0 removal capability of MnO2/AC increased with an increase of the MnO2 loading (1-10 wt.%) and temperature (120-200 °C). Scanning electron microscope-energy dispersive X-ray analysis confirmed the correlation between MnO2 and Hg adsorbed over MnO2/AC.