Dr Wei Xie

The thermal stabilities of humic acids (HAs) are critical for its effective utilization and relate closely with raw lignites. Thus, this work is to study the relationship of thermal stability between lignites and its derived HAs using Thermogravimetry¿Fourier Transform Infrared Spectroscopy (TG-FTIR) and Differential Scanning Calorimetry Measurement (DSC) techniques. The TG-FTIR results indicated that the intensities of peaks from the evolution gases (H2O, CO2, CO, CH4) during thermal treatment of Zhaotong lignite (ZL) and its derived HAs (denoted as ZLHA) are higher compared with the Mile lignite (ML) and its derived HA (denoted as MLHA). TG-FTIR and DSC measurements of lignites showed that the thermal stability of ML is better than that of ZL, and the more oxygen containing functional groups existed in ZL. Similarly, the results indicated that the contents of oxygen containing functional groups of ZLHA are higher than that of MLHA. On the other hand, DSC experimental data showed that the MLHA has smaller peaks on the DSC profiles, which showed that MLHA has longer aliphatic chain and less oxygen containing functional groups. Briefly, the results obtained from TG-FTIR and DSC measurement are consistent. The thermal stabilities of HAs are highly associated with the physicochemical property of raw lignites.

Thermoplasticity is a determining factor for the development of the coke structure and coke strength. Mobile phase, whether vaporizable or not, may significantly affect thermoplasticity during coal coking. This work studies the effect of the mobile phase, including the volatile tar and extractable metaplast generated from one bituminous coking coal, on the thermo-swelling of the raw coal. The volatile tar was collected when the raw coal was heated from room temperature to 450 °C at a heating rate of 5 °C/min, while the metaplast was extracted from the heated char. Molecular properties of the tar and metaplast were characterized using a laser desorption/ionization-time of flight-mass spectrometry technique (LDI-TOF-MS). Thermo-swelling of the raw coal and its blends with the volatile tar and extractable metaplast was investigated using a computer-aided thermal analysis (CATA). The volatile (C and H) evolution rate of the heating coal samples was tracked using a dynamic elemental thermal analysis (DETA), and the weight loss rate was investigated using thermogravimetric analysis (TGA). It was found that the extracted metaplast has a higher molecular weight distribution than that of the volatile tar. The swelling and thermal changes of the heating coal increased with the addition of tar or metaplast. The weight loss rate prior to coal swelling increased with the additives, while the raw coal showed a higher volatile release after maximum swelling than the blends. The addition of metaplast into the raw coal led to greater swelling, increased exothermicity, and resulted in a higher thermal conductivity than the addition of volatile tar during the primary devolatilization, particularly when the additive was 20 wt % in the blend. Different influences of thermoplasticity of the blends indicated that the interactions between the additive and the coal are affected by the molecular weight distribution of the additive. These findings will aid in the selection of the additive for improving thermoplasticity of low-caking coals to benefit coke production.

A suit of nitrogen-dried maceral concentrates derived from a coking coal and a non-coking coal was investigated to reveal the impact of varying coal main organic constituent, the vitrinite, on their thermoplasticity and pyrolysis products. The thermoplastic development of maceral concentrates during pyrolysis was evaluated via their thermo-swelling and dynamic volatile release. These measurements were then linked to molecular weight distributions of vaporised tars and tetrahydrofuran (THF) extracts obtained from heat-treated samples. Regardless of the vitrinite content, only coking macerals agglomerated during pyrolysis while non-coking macerals retained their powdered structure. This result indicated that although concentrating the vitrinite could alter the extent of coal thermoplasticity, such process could not grant or remove thermoplasticity from a maceral concentrate. This was reflected in the similar molecular weight distribution of solvent extracts produced between the parent coals and their concentrates. In specific, coking concentrates generated extractable materials with a relatively more complex structure, consisting of a bimodal molecular weight distribution with 12¿14 Da repeating structures at <600 Da and 24 Da reoccurring units between 600 and ~1500 Da. Solvent extracts isolated from non-coking concentrates, on the other hand, possessed a unimodal molecular weight distribution with only 12¿14 Da repeating structures extending to ~800 Da. The absence of high-range molecular weight materials (the 24 Da repeating units) in non-coking coal and its concentrates was speculated to play a vital role to their inability to exhibit thermoplastic behaviour during pyrolysis.

This work has used high range imaging mass spectrometry to study a coal sample that has undergone heating with a temperature gradient. A custom made hotplate was heated to 1000°C and the coal was allowed to heat naturally through conduction to produce a large thermal gradient typical of conditions in a coke oven. The sample was quenched, sectioned and analysed using laser desorption time of flight imaging mass spectrometry (LDI-TOF-IMS) to study the molecular changes that occur within the plastic layer and in the semi-coke. The raw coal was observed to have a molecular weight range between 500 and 20,000 Da with a peak occurring at 2000 Da. The plastic layer was observed to have a prevalence for increasing 500-1000 Da structures though this formed part of the larger molecular weight range. Resolidification of the plastic layer coincided with a rise in 4000 Da structures. The semi-coke spectrum had a series of repeating peaks separated by 24 Da extending from 1000 Da to 3000 Da. This was considered evidence of broad molecular ordering. A second phenomenon was observed in the semi-coke associated with low range molecular weights (50-300 Da). This appeared as high intensity signals in a molecular range typically considered as ion fragments (being too low in size to remain in the high vacuum environment). It was speculated that these low range structures may be associated with the coking of volatile tars exiting the hot-side of the plastic layer through high temperature semi-coke. Overall, this preliminary work provides a novel methodology to study the heating impacts during coking on a molecular level.

A hierarchically porous activated carbon (HPAC) with high surface area (3064¿m2/g) and large pore volume (2.319¿cm3/g) was prepared from lignite using KOH as activation agent by microwave heating. Nitrogen adsorption¿desorption at -196¿°C, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy were used to characterize the HPAC. Because of its high surface area, macro¿meso¿micro hierarchically porous structure and oxygen-enriched surface, the HPAC exhibits excellent electrochemical performance in terms of specific capacitance, energy density and cycling stability as electrode material for supercapacitors. The HPAC showed a high specific capacitance of 390¿F/g in aqueous electrolyte at a current density of 50¿mA/g and 94.1¿% of the initial specific capacitance was retained after 2000 cycles. Furthermore, this HPAC displayed a high specific capacitance of 198¿F/g in an organic electrolyte.

The thermoplastic development of an Australian coking coal was investigated by linking thermal swelling with changes in molecular weight of its pyrolysis products. Coal thermal swelling was investigated together with volatiles evolution and characterization of generated volatiles (including volatile tar and light gases). The molecular weight distributions of coal and its solvent extracts were measured by using laser desorption/ionization time of flight mass spectroscopy (LDI-TOF-MS). Solvent extraction (by acetone and tetrahydrofuran (THF)) was initially used on the raw coal to aid interpretation of thermoswelling by volumetric expansion measurements. The removal of ~2% solvent-soluble matter from the raw coal (the mobile phase) reduced its swelling extent during heating by up to 22% (from 86% down to 68% and 64% for acetone- and THF-residues, respectively). Volatile release after solvent treatment remained unaffected. This suggested that the majority of the coals swelling behavior could be attributed to the formation of heat-generated liquid matter (the Metaplast) during pyrolysis. Broad molecular weight changes were found in the solvent extractable component (metaplastic material extracted by acetone and THF) of the semicoke. Prior to softening (350 °C), the extractable components were composed of molecules mainly <500 Da. The upper limit in molecular weight distribution of solvent extracts increased significantly to 1800 Da at the onset of swelling (400-450 °C) and decreased back to ~500 Da at the end of swelling (500 °C). The spectra showed that the volatile tar and acetone extract (the light solvent extract) consisted of similar repeating structures separated 12-14 Da apart. As the treatment temperature increased, the molecular weight distribution of volatile tar increased in molecular mass, approaching that of the acetone extract distribution (~600 Da). The THF extract molecular weight distribution was a mixture of 12-14 and 24 Da repeating units which only became apparent at molecular weight above 600 Da. The LDI-TOF-MS analysis of the solid coal showed that it contained a distribution of molecular structures centered at 2000 Da and spanning between 500 and 7000 Da. This raw coal spectrum also contained multiple repeating mass lines every 24 Da apart. Overall, these results suggested that the coal consisted of complicated structures which subsequently degraded into smaller fragments capable of forming a complex intermediate liquid phase and a distribution of lighter volatile tar species.

Dynamic measurements of physical, chemical and thermal changes in the transformation of coal maceral concentrates were made during heating at a rate of 10°C/min to 1000°C. The endothermic and exothermic processes were identified by measurements of apparent specific heat while the fluidity was indicated by the estimated thermal conductivity. Measurements of swelling and bed permeability were made, with continuous quantitative elemental analysis of gases and tars as they evolved. Data for two coal concentrates of high and moderate vitrinite indicate that the same reactions and events are occurring for the two samples, but to a greater extent for the high vitrinite sample. The research has noted the significance of evolved tars in the early events, being the lowest temperature event identified, with rapid tar evolution prior to the onset of swelling associated with permeability change. Further tar release and gas evolution is associated with a rapid swelling event, this event being substantially greater for the high vitrinite sample. The data has also quantified contraction at higher temperatures following swelling which is associated with the release of hydrogen containing gases. Evolved tars from the high vitrinite sample showed elevated H/C ratio indicating that vitrinite tars appear to be more aliphatic than those evolved from inertinite. A comparison of measured swelling with estimated volumetric flow rate of the volatiles has indicated that thermo-expansion of coal utilised up to 21% of the volatiles to drive bubble growth. This utilisation rate varied significantly across the plastic temperature range.

© 2015 Elsevier B.V. Mesoporous activated carbons (ACs) were successfully prepared from lignite using KOH as activation agent at the temperature above 700°C. The pore structure and surface chemistry of the as-prepared ACs were characterized by means of nitrogen adsorption-desorption, X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The results show that such prepared mesoporous ACs have a high specific surface area (~3036m²·g^-1) with a hierarchical macro-meso-micro-pore structure and oxygen-enriched surface. The electrochemical performances of the ACs as electrode materials for electrochemical capacitors (ECs) were assessed by galvanostatic charge-discharge, cyclic voltammetry and cycling durability tests. It was demonstrated that the mesoporous ACs produced in this study possessed a maximum specific capacitance of 355F·g^-1 and 196F·g^-1 in 3M KOH aqueous and 1M (C<inf>2</inf>H<inf>5</inf>)<inf>4</inf>NBF<inf>4</inf>/PC organic electrolytes, respectively, at a current density of 50mA·g^-1, and exhibited a desirable energy and power density with a superior cycling performance. The excellent capacitive behavior of the prepared mesoporous ACs in aqueous system is attributed to their unique macro-meso-micro-hierarchical pore structure with high surface area and oxygen-containing surface. Their superb electrochemical performance in the organic electrolyte is attributed to their well-developed mesoporous structure.

A fundamental study was undertaken to characterize the changes in solvent-extracted matter formed during the thermoplastic phase of coking. Coal samples were heated to fixed temperatures within the pyrolytic plastic range of 400-500 °C, and the volatile material was extracted in a two-stage extraction with acetone (light extract) and then tetrahydrofuran (THF heavy extract). The extracted material was analyzed using laser desorption ionization (time-of flight) mass spectrometry (LDI-TOF-MS). The LDI-TOF-MS results showed that three extracted fractions could be broadly classified here as overlapping molecular weight ranges as volatile tars (200-450 Da), light acetone-soluble extract (250-500 Da), and heavy THF-soluble extract (300-1200 Da). A further class of compounds was identified from THF extraction of the raw coal in the range of 600-2500 Da that required higher laser powers to ionize and was not observed in the thermally generated samples. Negligible changes were observed in the composition of the acetone-soluble extracts with temperature, while the THF-soluble extract showed smaller proportions of larger molecules with higher treatment temperatures. It was observed that each molecular weight spectrum showed repeating structural units forming peaks every 12-14 Da (homologous series), with distributions of species around each peak. The volatile tar and acetone-soluble material shared common repeating structures also evident in the raw coal extract. This suggested that the material in this fraction was thermally stable over the analyzed temperature range. The repeating features of the THF-soluble extract species appeared to be structurally different. Overall, this work has indicated that development of extractable matter expected to be associated with fluidity during coking and subsequent resolidification relies on <1000 Da compounds. The results showed that >600 Da compounds are thermally sensitive. Compounds with molecular weights of <450 Da may be removed during coking, possibly as a vapor, resulting in a reduction in fluidity. There has been speculation that the thermally stable (acetone-soluble) material identified in both raw coal extract and those from thermally treated samples may be capable of undergoing a phase change to initiate plastic deformation.

A new technique that allows dynamic measurement of thermal properties, expansion and the elemental chemistry of the volatile matter being evolved as coal is pyrolysed is described. The thermal and other properties are measured dynamically as a function of temperature of the coal without the need for equilibration at temperature. In particular, the technique allows for continuous elemental characterisation of tars as they are evolved during pyrolysis and afterwards as a function of boiling point. The technique is demonstrated by measuring the properties of maceral concentrates from a coal. The variation in heats of reaction, thermal conductivity and expansion as a function of maceral composition is described. Combined with the elemental analysis, the results aid in the interpretation of the chemical processes contributing to the physical and thermal behaviour of the coal during pyrolysis. Potential applications in cokemaking studies are discussed. © 2013 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. All rights reserved.

A novel technique is described which provides quantitative and continuous analysis of light gas and condensable tar components as they are evolved in terms of carbon, hydrogen and oxygen. The technique has also been used to directly characterise the total tar sample in terms of carbon distribution and boiling point. It has been found that changes to the dynamic tar-H/C ratio correspond well with particular temperatures measured by Geiseler Plastometer for softening, maximum fluidity and re-solidification. This technique can enhance the chemical understanding of mechanisms occurring during de-polymerisation and cross-linking of coal (i.e. metaplast development and the transfer of hydrogen) while also monitoring tar evolution. A tar collection and re-vaporisation method provides a means of identifying tar groups that contribute towards the metaplast phase and temperatures at which they evolve. Both methods are unique in studying chemical aspects of coal and tar behaviour with heating, in a field based on thermo-physical techniques (e.g. H1 NMR, high temperature rheology, Geiseler plastometry, dilatation). Overall, the Dynamic Elemental Thermal Analysis (DETA) technique can give new insight into the fundamental mechanisms prevalent in coal pyrolysis and provides quantitative chemical assessment of tar nature (i) during the heating of coal and (ii) as a final (total) condensed product. © 2012 Elsevier Ltd. All rights reserved.

A fundamental study on the behaviour of heating coal macerals has been undertaken using two novel thermal analysis techniques. The apparent specific heat was determined during heating using an inverse calorimetric method (computer aided thermal analysis, CATA) and combined with pressure and displacement measurements to correlate endothermic and exothermic behaviour with measurement of swelling. The second technique used a post-oxidation stage to combust the tars and gases into products which were analysed. This method was used to study the elemental character of volatiles release from coal maceral concentrates in terms of carbon and hydrogen. Extents of swelling and exothermicity during primary devolatilisation were found to be correlated with vitrinite content and were associated with tar evolution. For the highest vitrinite fraction (of 86.4% vitrinite) swelling was initiated at the same temperature range for exothermic reactions, and maximum swelling coincided with the peak release of light gases. Tar evolution was found to change in chemical character (as defined by H/C ratio) during progressive heating, initially rising in the early stages of tar formation (<430°C) to a maximum of 1.24, then gradually decreasing to a minimum of 0.64 at 550°C. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Using different size range of flying ash samples from gangue thermal power plant of Liaoning Fuxin as carrier, Fe-Ce oxide as active component, Kaolin as binder, through mechanical mixing, forming, drying and high temperature calcination, columnar samples are prepared. In the condition of 120°C, drying for 4h,then calcining in 700°C for 8h, the iron-cerium-based sorbents for hot coal gas desulphurization were prepared using coal ash as the support and the sorbents and coal ash are characterized by means of numerous analytical methods such as composition analysis, XRD and SEM. The results clearly indicate that the sorbents prepared using coal ash as the support demonstrate high reactivity and high resistance to attrition during sulfidation during the temperature range of 400 °C to 600°C.

The paper proposed a two-step desulphurization process using iron-based high temperature sorbents for removal of hydrogen sulfide from hot coal gases after coal gasification. The authors use the mixture of iron oxide with other metal oxides (e.g. Ce) supported by ash from a coalgangue- fired power plant to prepare high temperature desulphurization sorbents. The two-step desulphurization process is comprised of a first-stage desulphurization of removing majority of sulfur followed by a second-stage desulphurization to remove the remaining sulfur species. The process is integrated with effective sulfur recovery through direct elemental sulfur production during the regeneration of Fe/Ce based sorbents. Preliminary studies on sulfidation using a quartz fixed-bed reactor demonstrated that the Fe/Ce-based sorbents prepared in this study was able to remove >97% sulfur in the temperature range of 400-600°C. Simultaneous removal of organic and inorganic sulfur species was achieved.

Coal will continue to dominate China s energy supply in the future. The mining of coal creates large amount of gangue which not only occupies a large area of land but also generate environmental problems. On the other hand, coal gangue is a low calorific fuel which should be utilized properly. A few small power plants are current running or under construction in China. However, due to its high ash content, coal gangue generates a large amount of ash when it is combusted in power plants. The ash from power stations not only contributes to emissions of fine particulates in the air but also results in the contamination of soil. The utilization of coal gangue ash is therefore important to reduce China s environmental pollution. In this paper, current status of the research and development of gangue ash utilization in China is reviewed. The gangue ash has found its application in a wide range of areas, such as road construction, chemicals, agriculture fertilizers, etc. Some ash samples were collected by the authors from a coal gangue fired power plant in Fuxin, northeast China. Characteristics of the ash were analyzed by using XRD, SEM, Laser sizer and other techniques. Because of its physical structure (e.g., large surface area and porosity) and its composition (i.e., containing mainly SiO2, Al2O3 and CaO) the gangue ash has a potential in the application of iron-based sorbents for high temperature removal of hydrogen sulfide from coal gas. A desulphurization sorbent was prepared by using the mixture of iron oxide and the gangue ash collected from the power plant. The structure and property of the surbent were examined using XRD, SEM and other techniques.