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A model carbon prepared from phenolic resin was O2-activated and then impregnated with Ca, Cu or Zn to clarify chlorine behavior in coal utilization. Ease of interaction between HCl and the carbon material was enhanced at 100–300 °C. The concentration at which HCl reacted with Ca, Cu and Zn was high. The surface chloric species that were generated by reaction of the carbon substrate with HCl were studied using X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). XPS measurements suggested the presence of inorganic chloride and organic chlorine species after reaction with HCl. When the carbon samples were washed after the HCl reaction, most of the HCl was eluted. Chemically adsorbed HCl species were also detected by TPD measurement; the presence of inorganic chloride, organic chlorine and chemically adsorbed HCl species were indicated. No correlation was determined between the amount of organic chlorine species generated and the number of activated carbon sites at 100 °C. However, the amount of organic chlorine at 300 °C indicated a tendency to increase with the number of carbon sites, and the surface functional oxygen groups acted as sites for the generation of C-Cl bonds. As a result, possible scheme for the generation of organic chlorine species at low temperature by reaction between HCl and the metal-doped (Ca, Cu or Zn) carbon is discussed.

Calcium ion exchange was performed in Indonesian low-rank coal using saturated aqueous solutions of Ca(OH)2 at 30.0 ± 0.1 °C without pH adjustment. The Ca2+ concentration and pH were monitored during ion exchange. A coal product was obtained with 3.2 mass% Ca2+. Gasification of the ion-exchanged samples was conducted in a circulating dual bubbling fluidized bed (CDBFB) reactor at 700 °C, 800 °C, and 900 °C. Coal carbon conversion into carbonaceous gases (CO, CO2, CH4, and C2 hydrocarbons) using the Ca2+-exchanged coal achieved 78% at 900 °C in the CDBFB. The Ca catalyst led to the greatest rate enhancement at 800 °C, resulting in a twofold increase in the gas product yield compared to that without Ca. A comparison of carbon conversion between the CDBFB and fixed-bed reactors revealed that the conversion value using the CDBFB at 700 °C was very small. Regarding an examination of this influence in detail, it seems that the existing H2 adhered primarily to the active sites of the char, and the use of Ca2+-exchanged coal led to a reverse shift reaction.

A model carbon prepared from phenolic resin was activated with O2 and then impregnated with Ca, Cu, or Zn to examine the relationship between the amount of HCl desorbed from carbon samples containing various metals in this lower temperature range (100 and 300 °C) and clarified the effect of active sites on HCl adsorption. The results showed that interactions between HCl and carbon were enhanced at temperatures in the range of 100–300 °C and that the amount of HCl reacted was increased by doping with these metals. The different HCl concentration profiles at 100 and 300 °C were obtained with a greater overall decrease in HCl at the lower temperature (100 °C). Those are attributed to increased physical adsorption of HCl at 100 °C. The mass of HCl reacted increased in the order of Cu < Ca < Zn at 300 °C and Ca < Cu < Zn at 100 °C, and HCl reacted at 300 °C was evidently more stable than that reacted at 100 °C. Organochlorine compounds, chemisorbed HCl, and inorganic chlorides were all identified on the carbon...

Pyrolysis of 29 coals with carbon contents of 71–92 mass% on a dry, ash-free basis (daf) has been performed mainly in a temperature-programmed mode at 10°C/min up to 800°C with a flow-type fixed bed quartz reactor, and some factors controlling HCl formation have been examined. The rate profiles of HCl formation exhibit at least three distinct peaks at around 260–360, 470–510 and 580–630°C, and the lowest temperature peak is present for 8 coals alone, whereas the middle and highest temperature peaks are common with almost all of the coals. The HCl profile is also affected by the size of coal particles and the height of coal particles in the fixed bed. Yields of HCl and char-Cl at 800°C for 28 coals except an American bituminous coal are 44–95 and 4–54%, respectively, and tar-Cl is as low as ≤ 7% in all cases. The chlorine distribution is almost independent of the heating rate in the range of 2.5–400°C/min and has no distinct relationship with carbon or chlorine content in coal, but HCl tends to increase with increasing amount of (Na + 2Ca) in coal with a corresponding decrease in char-Cl. When an Indonesian sub-bituminous coal is injected into an O2-blown entrained bed gasifier under pressure, there is an almost 1:1 relationship between carbon and nitrogen conversions, whereas the sulfur and chlorine are enriched in the remaining char, and the degree of the enrichment is higher with chlorine. The method of evaluating coal-Cl forms quantitatively using model chlorine compounds is proposed.

Ca2+ and Na+ cations were separately or consecutively ion-exchanged with an Indonesian low-rank coal using saturated aqueous solutions of Ca(OH)2 and/or soda ash at 20–40 °C without pH adjustment. This was done by adding aqueous solutions of the soda ash and/or calcium hydroxide to a dispersion of coal particles in deionized water, while monitoring the Na+ and Ca2+ concentrations and pH of the resulting mixture. A 3.5 mass % Ca2+-exchanged coal, a 1.6 mass % Na+-exchanged coal and a 3.8 mass % Ca2+- and 1.0 mass % Na+-exchanged coal were obtained. The catalytic pyrolysis and subsequent gasification of these ion-exchanged specimens were performed in a fixed bed quartz reactor at 650, 700, or 750 °C. X-ray diffraction analyses of the samples pyrolyzed at 700 °C found no evidence of Na or Ca species, indicating that these were present as nanoscale particles. The Ca2+/Na+-exchanged coal underwent steam gasification more readily than the other samples, with complete char conversion of this material following 1...

Catalytic decomposition of toluene (C6H5CH3) or benzene (C6H6) with inexpensive limonite ores, composed mainly of goethite (α-FeOOH), was examined using a vertical, cylindrical flow fixed-bed quartz reactor to develop a novel method of removing biomass-derived tar components. The unsupported limonite catalyst was active for the decomposition of 480 ppm of C6H5CH3 and 1700 ppm of C6H6 in 15 vol % H2O/45 vol % H2/He, leading to C6H5CH3 and C6H6 conversions at 500 °C of nearly 100 and 97%, respectively. When the C6H5CH3 decomposition temperature was increased from 500 to 800 °C, the overall reaction path changed from demethylation to hydrocracking and then to steam reforming. A honeycomb-supported limonite catalyst also was effective and achieved nearly complete C6H5CH3 conversion at 600 °C. In addition, the honeycomb-supported catalyst promoted C6H6 conversion of nearly 100% without carbon deposits at 700 °C in 15 vol % H2O/20 vol % H2/26 vol % CO/20 vol % CO2/5 vol % CH4 that was designed to simulate raw f...

Ion-exchange reactions of brown and sub-bituminous coals with natural soda ash, composed of >99% Na2CO3, have been studied at 20–40 °C without any pH-adjusting reagents, and the pyrolysis and subsequent steam gasification of the resulting Na+-exchanged coals have been conducted using a fixed-bed quartz reactor at 700 °C. When the Na+ concentration and pH of an aqueous mixture of coal and soda ash are monitored during the ion-exchange process, both values decrease at a greater rate with brown coal with a higher content of COOH groups, indicating that ion exchange of Na+ with H+ of the COOH group is the predominant process. About 65% of COOH can be exchanged with Na+ ions under optimal conditions, irrespective of the coal type. The reactivity of these raw coals in steam at 700 °C is similar, with char conversions of less than 20 mass %, even after 2 h of reaction. Exchanged Na promoted the gasification of both coals at this temperature, but the rate profiles were different: conversion of brown coal increase...

Secondary reactions of hydrogen chloride (HCl) during high-temperature combustion processes were elucidated using a model carbon prepared from a commercially available phenol resin. This resin was O2-activated, followed by doping with K+, Ca2+, Cu2+, or Zn2+, and subsequently exposed to a stream of 100 ppm of HCl in N2 at 500 °C, during which HCl reacts with the carbon samples to form surface chlorine species. In the absence of metal cations, the extent of reaction increases almost linearly up to 500 °C as the number of carbon active sites, determined by temperature-programmed desorption, increases. The addition of Ca, Cu, or Zn but not K significantly promotes the formation of carbon sites as well as the reaction with HCl, with the latter effect increasing in the order of Ca < Cu < Zn on a molar basis. Cl 2p X-ray photoelectron spectroscopy (XPS) data show that inorganic chlorides of Ca, Cu, and Zn are formed and that the organic Cl/C ratio is 2.0–2.3 times greater when using these additives. It is thus ...

Catalytic decomposition of 2000 ppm NH 3 with an Australian limonite ore, which is composed mostly of goethite (α-FeOOH), has been studied from a viewpoint of hot gas cleanup with a vertical, cylindrical quartz reactor at 750–850 °C under a high space velocity of 45,000 h −1 . It has already been reported that the limonite achieves the almost complete decomposition of NH 3 in inert He at 500 °C and shows very stable performance in the reaction at 750 °C in the coexistence of 50–500 ppm H 2 S or at 850 °C in the presence of fuel gas components produced in an air-blown coal gasification process. In the coexistence of a high concentration of syngas (50% CO/25% H 2 ) produced with an O 2 -blown coal gasifier, the limonite is deactivated almost completely because of the remarkable occurrence of carbon deposition from the CO. On the other hand, the addition of small amounts of CO 2 and H 2 O, which are always included in actual coal-derived fuel gas, to the syngas improves the activity of the limonite, and conversions of NH 3 –N 2 at 750 and 850 °C become about 65% and almost 100% without carbon deposition, respectively. When several limonite-based catalysts with alkali metal and alkaline earth metal cations are prepared by the impregnation method and then used in the NH 3 decomposition at 750 °C in 50% CO/25% H 2 /5% CO 2 /3% H 2 O, fine particles of MgO derived from Mg cations can work more effectively as the promoter, and the 3 mass% Mg-added limonite maintains the high and stable NH 3 conversion of almost 100% for 25 h. In this case, no significant carbon deposition takes place. It is probable that MgO with strong basicity suppresses the carbon formation from CO, and that the limonite-based composite catalyst thus shows the superior performance in the decomposition of NH 3 in syngas-rich fuel gas that simulates product gas in O 2 -blown coal gasification.

The effect of Ca catalysts prepared from CaCO 3 on the steam gasification of Indonesian subbituminous coal at 700–800 °C is examined. The char obtained by pyrolyzing the coal with 0.59 wt.% of Ca (dry basis) showed conversions in steam gasification at 750 and 800 °C of around 70 and 90 wt.% (dry ash and catalyst free basis), which were 2 and 1.5 times larger than those of the coal without the Ca catalyst, respectively. The activity of this Ca catalyst was as high as that prepared using an aqueous solution of Ca(OH) 2 . The TPD and XRD measurements demonstrated that the Ca catalyst from CaCO 3 was initially present in the ion-exchanged form, and as a finely dispersed calcium species after pyrolysis. These results confirm that CaCO 3 is effective as a catalyst raw material in the steam gasification of subbituminous coal, even at low catalyst loadings.

Cost of catalysts is a crucial factor in realizing coal catalytic gasification process. In this study, inexpensive raw materials, soda ash (Na 2 CO 3 ) and slaked lime (Ca(OH) 2 ), were selected as catalyst precursors, and Na-, Ca- and Ca/Na-loaded coals were prepared by an ion-exchange procedure using a sub-bituminous coal (Adaro coal, Indonesia). These coal samples were rapidly pyrolyzed and in-situ gasified in an atmospheric drop-tube reactor (DTR) at 850–1000 °C under a steam partial pressure of 0.05 MPa. The Na and Ca catalysts showed remarkable activity for gasification, and the Ca/Na-loaded coal exhibited the highest reactivity among the coal samples prepared. The char yield of the Ca/Na-loaded coal at 1000 °C was as low as 17.6 mol-C per 100 mol-C of coal, and more than 70% (on carbon basis) of its primary char was gasified within 3 s. At 900 °C, the coal with Ca-loading of 3.2 wt.% showed catalytic activity higher than the coal with Ca-loading of 0.52 wt.%. At 950 and 1000 °C, however, the coal with the lower Ca-loading showed higher activity. The XRD analysis suggested that the Ca catalyst with the lower loading was more resistant to coarsening along with the progress of char gasification.

In order to understand chlorine chemistry in coal pyrolysis, the dynamics of HCl evolution and changes in chlorine functional forms during temperature-programmed pyrolysis of eight Argonne premium coal samples have been examined with an online HCl-monitoring technique and by the Cl 2p X-ray photoelectron spectroscopy (XPS) method. The rate profiles of HCl evolved show at least three distinct peaks at 390, 520, and 600 °C, and the presence of these peaks depends strongly on the type of coal. The HCl peak at 390 °C appears with four coals alone and becomes considerably small by water washing, whereas the high-temperature peaks above 450 °C observed with almost all of the coals do not change significantly after washing. Yields of HCl up to 1000 °C are in the range of 50–90% in many cases, and the yield tends to decrease with increasing atomic Ca/Cl ratio in coal. The chlorine XPS analyses show that the chlorine in each coal is enriched at the surface and composed of inorganic and organic functional forms. Th...

Decomposition of pyrrole or pyridine with iron catalysts supported on carbons has been studied with a cylindrical quartz-made pulse reactor, into which liquid pyrrole or pyridine is injected as a pulse, in order to develop a novel hot gas cleanup method of removing the nitrogen present in tar as N 2 . The catalyst is mainly prepared by heating FeOOH precipitated onto powdery cellulose from FeCl 3 solution. Nanoscale iron catalysts with the average particle sizes of 25–30 nm can promote decomposition reactions of the N-containing heterocyclic compounds in inert gas at >500 °C and provide N 2 yields of 40–45% after the almost complete decomposition of pyrrole at 600 °C or pyridine at 650–700 °C. Iron catalyst with the mean size of 100–500 nm, prepared from Fe(NO 3 ) 3 impregnated with a commercial activated carbon, is also active for the decomposition of the heterocyclic N-compounds, but it is almost inactive for N 2 formation, the yields being as low as less than 2% in all cases. The increase in the number of pulses lowers the catalytic activity of iron nanoparticles for N 2 formation, whereas in situ H 2 treatment at 500 °C after reaction can restore it to the almost original state. On the basis of the above-mentioned results, it is likely that the activity of iron catalyst for N 2 formation from pyrrole or pyridine is very sensitive to the iron particle size, and the in situ H 2 treatment is effective for recovery of the decreased catalytic performance.

Polyacrylonitrile-derived activated carbon as a model of coal char has been heated in high-purity He at 10 °C/min up to 1000 °C with a flow-type fixed bed quartz reactor, and the catalysis of N 2 formation by precipitated iron has been investigated by use of XPS, TEM and XRD methods. Fine iron particles with the average size of 15 nm increase remarkably the formation rate between 600 and 1000 °C, and N 2 yield up to 1000 °C reaches about 65% at 1.9 mass% Fe. The XPS and XRD measurements after heat treatment exhibit that nitrogen functionality does not change significantly, but carbon crystallization occurs through the dissolution of iron nanoparticles into the carbon substrate. The in situ XRD analyses during heating reveal the formation of austenite that is solid solution of Fe and N (and/or C). Interestingly, the catalysis of N 2 formation by iron and the formation of austenite occur at almost the same temperature range of 600–1000 °C. It is thus likely that nanoscale iron particles move in the carbon matrix and react with heterocyclic nitrogen in order to produce the solid solution, which is subsequently decomposed into N 2 .

Activated carbons (ACs) with very high specific surface areas up to approximately 900 m2/g and total pore volume up to 0.5 cm3/g were produced from a Canadian peat through chemical activation using either H3PO4 or ZnCl2 as the activation agent, followed by activation/carbonization in air at 450 °C for 45 min. ZnCl2 was found to be more effective for developing microporous structures in the ACs, while H3PO4 is more efficient in developing the mesopores. Demineralization of the AC precursor to remove intrinsic minerals greatly affected the development of pore structures during the activation process. The AC derived from the demineralized peat activated by ZnCl2 attained the highest BET surface area with significantly increased micro-/mesopores.

The functionalities of the fluorine and carbon present in fly ashes formed in pulverized coal combustion have been studied with X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques. The ash samples include 20–130 μg/g-dry and 0.4–4.1 mass%-dry of fluorine and carbon elements, respectively, and these components are enriched at the outermost layer of the ash surface. The F consists of both inorganic and organic functionalities, and the proportion of the latter is as high as 84–98 mol%. The C has different types of surface oxygen species, such as carboxyl, lactone/acid anhydride and phenolic groups, and most of these groups decompose to CO 2 or CO up to 700 °C to yield carbon active sites. When the amount of the O-functional forms increases, the content of organic C–F forms tends to increase almost linearly. On the basis of the above results, it may be speculated as one possibility that the formation of covalent C–F bonds takes place mainly through secondary reactions between gaseous F-containing compounds (HF and/or F 2 ) in flue gas and carbon active sites produced below 700 °C downstream of coal-fired boilers.

Biomass gasification produces a low to medium-BTU product gas (or syngas) containing primarily CO2, H2, CO, CH4 and (C2 + C3), as well as some contaminants such as tars, NH3, H2S and SO2. In order to achieve better efficiencies of the syngas applications, these contaminants must be removed before the syngas is used for internal combustion, gas engines, and in particular for fuel cells and methanol synthesis. Compared with the wet scrubbing technology, hot-gas cleanup technology to remove tar, ammonia and other contaminants at the “hot” state is more advantageous with respect to energy efficiencies. This paper provides an overview on recent advances in catalysts for hot-gas removal of tar and ammonia from biomass gasification. The review focuses on the recent development and applications of dolomite catalysts, iron-based catalysts, nickel and other metal supported catalysts, and the novel carbon-supported catalysts for hot-gas tar removal and ammonia decomposition. The barriers in applications of hot-gas cleanup processes and catalysts for full-scale biomass gasification, and areas for future research, are also discussed.

Two novel carbon-based Ni/Fe catalysts were developed and tested for catalytic decomposition of ammonia into N2 and H2. These catalysts were prepared using a mesoporous activated carbon (AC) support derived from a Canadian peat by H3PO4 activation. The newly developed catalysts proved to be highly active for ammonia decomposition. The conversion of 2000 ppm NH3 diluted in helium over the Fe catalyst reached as high as 90% at 750 °C and at the space velocity of 45,000 h−1, compared with only about 15% with the activated carbon alone without metal loading. The new catalyst of Fe/AC was also much more active than the Fe catalyst supported on a commercial activated carbon reported previously. In addition, the new Fe/Ni catalysts showed superior performance with respect to their resistance to catalyst deactivation. Both catalysts remained active as the reaction time increased up to 10 h without showing a sign of deactivation. Fresh and spent catalysts were characterized by XRD and XPS. A cycle mechanism, involving both metal phosphides and metal nitrides, was proposed for the NH3 decomposition reactions over these new Fe/Ni catalysts.

Leaching behavior of the boron (B) and fluorine (F) present in fly ashes formed in pulverized coal combustion has been studied with a batch-type quartz vessel under the conditions of 25 °C and a solution to solid ratio of 100 ml/g according to the Dutch Standard NEN 7341 method (availability test). When each ash sample is stirred in ultra pure water without any acids, the pH of the resulting aqueous mixture is as high as 11-12 in every case, whereas the leaching of B-containing ions or F- ions depends strongly on the type of the ash, and the corresponding leaching extent after 60 min-stirring is in the range of 20 % to 65 % and 15 % to 45 %, respectively. In the experiments at a constant pH of 1.5-9.0 of a fly ash with relatively-high B (1000 μg/g-dry) and F (130 μg/g-dry) contents, more than 70 % of B in the ash is leached rapidly within 10 min, and the rate is larger at a lower pH condition. The leaching of F- ions also occurs within 10 min, and the extent depends significantly on pH and increases in the order of pH 9.0 (32 %) ≈ pH 5.6 (35 %) < pH 1.5 (72 %) < pH 3.0 (80 %). The concentration of the B or F present in each ash sample after acid leaching at pH 1.5 - 2.0 is less than the corresponding regulation limit for water pollution. Several factors determining the leachability of these elements are investigated.

The fate of coal-N in the fixed-bed pyrolysis of 25 coals with 62−81 wt % (daf) C has been studied with a quartz reactor at 1000 °C under ambient pressure to examine the effects of metal cations present naturally in these coals on the partitioning of coal-N into N2, NH3, HCN, tar-N, and char-N. Nitrogen mass balances for all runs fall within the reasonable range of 100 ± 5%, and N2 is the predominant product for all of the coals. As the N2 yield increases, the sum of NH3, HCN, and tar-N is unchanged significantly, whereas the char-N yield decreases almost linearly, showing that most of N2 originates from char-N. When eight kinds of inherent metals, such as Na, Mg, Al, Si, K, Ca, Fe, and Ti, are determined by the conventional method and related with the N2 yield, there exists a strong, direct correlation between the Fe content and N2 formation for low-rank coals with less than 75 wt % (daf) C. Transmission electron microscopy coupled with an energy-dispersive analysis of X-rays (TEM−EDAX) measurements afte...

The present review paper highlights on the recent progress in Japan on the hot gas cleanup of HCl, H2S and NH3 in raw fuel gas for coal-based, combined cycle power generation technologies. It has been shown that NaAlO2, prepared by mixing Na2CO3 solution with Al2O3 sol, can reduce HCl in an air-blown gasification gas from the initial 200 ppm to

The present review focuses on elucidating the chemistry of nitrogen release during coal pyrolysis, in particular, on making clear catalytic roles of inherent Ca and Fe ions in not only the partitioning of volatile-N to tar-N, HCN, NH 3 and N 2 but also the conversion of char-N to N 2 . In slow heating rate pyrolysis of low-rank coals at 1000 °C with a fixed bed reactor, the demineralization with acid washing increases tar-N and HCN, but it decreases NH 3 . On the other hand, the ion-exchange of Ca 2+ ions with the demineralized coals shows the nearly reverse effect on the distribution of these nitrogen species, though the physical mixing of Ca(OH) 2 is almost ineffective. Since the sum of tar-N, HCN and NH 3 is unchanged significantly in any cases, it is likely that Ca cations, which exist originally in the ion-exchanged forms, can control the partitioning of volatile-N to tar-N, HCN, and NH 3 . The Fe 3+ ions precipitated on the demineralized coals catalyze the decomposition of tar-N, HCN and NH 3 into N 2 . The evolution of N 2 from coal-N occurs even in the absence of any metal cations added. The extent is generally larger with a lower rank coal, at a slower heating rate and a higher temperature, and at a longer solid residence time when coal is rapidly pyrolyzed. N 2 yield at 1350 °C reaches about 70% at maximum. Since a strong reverse correlation exists between N 2 and char-N, N 2 originates predominantly from char-N (and/or precursors). Demineralization of low-rank coals decreases N 2 , whereas subsequently added Fe or Ca cations enhance N 2 mainly at ≤ 1000 °C or ≥ 1000 °C, respectively. As the sum of naturally present Fe and Ca cations increases, N 2 yield at 1350 °C tends to increase up to about 1 mass%. It can be proposed that fine particles of metallic Fe and CaO, which are formed from these inherent ion-exchanged cations, promote efficiently N 2 formation from char-N through solid–solid interactions with heterocyclic nitrogen forms in char matrix.

Catalytic performance of limonite in the decomposition of 2000 ppm NH 3 in the presence of a small concentration of H 2 S has been studied with a cylindrical quartz reactor at a high space velocity of 45000 h − 1 to examine the sulfur tolerance of the limonite catalyst. It is not poisoned apparently by 50–500 ppm H 2 S at 750 °C, but the remarkable sulfur poisoning is observed at 2000 ppm H 2 S. In the coexistence of 100 ppm H 2 S, conversion of NH 3 to N 2 decreases gradually with time after 10 h at 650 °C, whereas the limonite maintains the high conversion of almost 100% for 50 h at 750 °C. The SEM-EDX measurements after reaction show that the surface composition at 750 °C is richer in metallic Fe, which may be produced by the reaction of NH 3 and/or H 2 with FeS formed. Commercially-available FeS promotes the decomposition of NH 3 diluted with inert gas at 750 °C, and the FeS is partly transformed into H 2 S and α-Fe in this process. Possible mechanisms for the decomposition of NH 3 in the presence of H 2 S with the limonite are discussed on the basis of the results of some model experiments.

Catalytic decomposition of 2000 ppm NH 3 in different atmospheres with an Australian α-FeOOH-rich limonite ore at 750-950 °C under a high space velocity of 45000 h-1 has been studied with a cylindrical quartz reactor to develop a novel hot gas cleanup method of removing NH 3 from fuel gas produced in an air-blown coal gasification process for an integrated gasification combined cycle (IGCC) technology. The limonite shows very high catalytic activity for the decomposition of NH 3 diluted with inert gas at 750 °C, regardless of whether the catalyst material is subjected to H 2 reduction before the reaction or not. Conversion of NH 3 to N 2 over the reduced limonite reaches ≥99% at 750-950 °C, and the catalyst maintains the high performance for about 40 h at 750 °C. When the decomposition reaction is carried out in the presence of fuel gas components, the coexistence of syngas (20% CO/10% H 2 ) causes not only the serious deactivation of the limonite catalyst but also the appreciable formation of deposited carbon and CO 2 . On the other hand, the addition of 10% CO 2 or 3% H 2 O to the syngas improves the catalytic performance and concurrently suppresses the carbon deposition almost completely, and the NH 3 conversion in the 3% H 2 O-containing syngas reaches about 90% and almost 100% at 750 and 850 °C, respectively. Influential factors controlling the catalytic activity of the limonite ore in the coexistence of fuel gas components are discussed on the basis of the results of the powder X-ray diffraction measurements, thermodynamic calculations, and some model experiments.

Functional forms of the unburned carbon present in six kinds of coal fly ashes have been examined mainly by the temperature-programmed desorption (TPD)/temperature-programmed oxidation (TPO) and laser Raman spectroscopy (LRS) methods. The carbon contents of the ash samples range from 0.4 to 4.1 mass%. The LRS analysis shows that the C consists of both amorphous and crystallized forms, and the proportion of the former is as large as 50-65 C%. Further, the TPD measurement exhibits that the C contains several types of surface oxygen species, such as carboxyl and lactone/acid anhydride groups, which can readily be decomposed into CO2 up to 700 °C to provide active carbon sites. The results of the TPD also indicate that the ashes have surface CaCO3, and most of this species can be converted to CaO and CO2 around 600-700 °C. Interestingly, there is a significant correlation between organic fluorine concentrations and carboxyl/lactone/acid anhydride groups or surface CaCO3 contents in the ash samples. It might thus be possible that the formation of organic F forms proceeds through gas-solid-solid interactions among HF (and/or F2) in flue gas, active carbon sites and surface Ca species produced around 600-700 °C downstream of coal-fired boilers.

Aiming to understand the formation mechanism of dioxins in the iron ore sintering process, dust samples obtained from some windboxes of a commercial iron ore sintering plant have been characterized with a powder X-ray diffraction (XRD), by the transmission electron microscope (TEM) equipped with an electron energy loss spectroscopy (EELS), and by the temperature-programmed desorption (TPD) and temperature- programmed oxidation (TPO) techniques. The elemental and XRD analyses reveal that the content of the Cl present in the samples ranges from 0.075 mass%-dry to 5.1 mass%-dry and tends to be higher at smaller dust particles, and that some of the Cl exists as KCl with the average crystalline size between 40 nm and 50 nm. Dust samples also contain a significant amount of unburned carbon, and the smallest dust particles

The fate of the chlorine and fluorine present in a sub-bituminous coal from Indonesia during pyrolysis and gasification has been studied with fixed and entrained bed reactors. The rate profile for HCl evolved in the temperature programmed pyrolysis exhibits the main and shoulder peaks at 480 and 600 °C, respectively. Model experiments and subsequent Cl 2p XPS measurements show that HCl reacts with metal impurities and carbon active sites at 500 °C to be retained as inorganic and organic chlorine forms, from which HCl evolves again at elevated temperatures. It is suggested that the HCl observed in the coal pyrolysis may originate from the above-mentioned chlorine functionalities formed by secondary reactions involving the nascent char. In the CO2 gasification of the 900 °C char at 1000 °C and 2.5 MPa, any measurable amounts of HCl and HF could not be detected even at a high conversion of 75 wt% (daf), suggesting the accumulation of these halogens in the residual char. When the coal is injected into an O2-blown, entrained bed gasifier at 1200–1400 °C under 2.6 MPa, the partial oxidation proceeds to a larger extent at a higher O2/coal ratio, whereas the chlorine and fluorine are enriched in the remaining char, and the extent of the enrichment at the latter stage of gasification is larger with the fluorine. The XPS measurements of the chars reveal the presence of the broad F 1 s peak, which can cover a wide range of binding energies attributable to inorganic and organic fluorine. The halogen enrichment during gasification is discussed in terms of secondary reactions of HCl and HF with char.

Catalytic NH3 decomposition with limonite rich in α-FeOOH has been studied as a hot gas cleanup method to remove a low concentration of NH3 from fuel gas produced in coal gasification. Fine particles of metallic Fe formed from α-FeOOH achieve the almost complete decomposition of 2000 ppm NH3 to N2 at 500°C under a high space velocity of 45,000 h−1 and show the stable catalytic performance for 50 h. The predominant catalytic mechanism involving the formation and subsequent decomposition of Fe nitrides may be proposed on the basis of the XRD and TPD results.

A novel hot gas cleanup method to decompose a low concentration of NH3 to N2 with metal cations present inherently in low rank coals has been studied with a quartz reactor under the conditions of 750–850 8C, 0.1 MPa and high space velocity of 45,000 h K1 . Each coal is pyrolyzed at 900 8C to prepare the char, which is subjected to the decomposition of 2000 ppm NH3 after pretreatment with H2. All of five chars examined promote NH3 decomposition in inert gas, but the promotion effect depends strongly on the kind of char and can correlate more closely with the Fe content than with the Ca content. This result may indicate that the Fe plays a crucial role in the reaction. A commercial activated carbon with a very low Fe content of !0.05 wt% exhibits lower conversion of NH3 to N2 than five chars. The TEM pictures reveal the formation of nanoscale particles of Fe and Ca components on a brown coal char that provides the largest catalytic performance. The char maintains the high conversion level of 80% during 25 h reaction at 750 8C and achieves the complete decomposition of NH3 at 850 8C. The co-feeding of a mixture of H2, CO, and CO2 does not change significantly the catalytic activity of the char at a steady state, whereas the coexistence of 2000 ppm H2S lowers it in the whole range of time on stream. It is proposed by combining the XRD and TPD observations with our previous results that the catalytic decomposition of NH3 in inert gas with the chars derived from low rank coals proceeds through two cycle mechanisms involving iron metal, iron nitrides, CaO and CaCN2. q 2005 Elsevier Ltd. All rights reserved.

The evolution of HCl during pyrolysis of 16 coals with different ranks at a heating rate of 10 °C/min has been studied with an online monitoring method. Approximately 50%−95% of total chlorine is converted to HCl up to 800 °C, and the remainder is mostly retained in the char, which leads to a strong reverse correlation between the two. As the sum of Na and Ca naturally present in coal increases, the amount of HCl tends to decrease. The temperature dependence of the rate of HCl evolved differs with each coal and shows at least four peaks at 280, 360, 480, and 580 °C. The former two peaks are present for two coals alone, whereas the higher temperature HCl formation at ≥450 °C is common for almost all of the coals. The HCl peaks at 280 and 360 °C are considerably small by water washing. When model chlorine compounds added to activated carbon, such as hydrated NaCl, hydrated CaCl2, and organic hydrochlorides, are pyrolyzed in the same manner as above, HCl formation occurs dominantly between 250 and 450 °C in ...

An experimental study was conducted to clarify the suppression effect of nitrogen-containing compounds, that is, ammonia and urea, on the formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) through the de novo synthesis reaction. In the experiment, graphite and copper chloride contained in a mixture were used as sources of carbon and chlorine, respectively. The granulated sample mixture was charged as a packed-bed in the glass tube and heated at 300 degrees C in the flow of Ar-O2 gas mixture. In some cases, urea was added as aqueous solution to the sample, while ammonia was added to the gas flowed through the sample bed. The amount of PCDD/Fs formed decreases significantly by the addition of both ammonia and urea. Particularly, the addition of urea reduces the amount of PCDD/Fs discharged in the outlet gas by approximately 90%. The oxidation rate of carbon in the early stage of the experiment, that is, the heating period, is promoted bythe addition of nitrogen-containing compounds. However, soon afterthe temperature reaches 300 degrees C, the formation rate becomes lower than that of the case without the addition of nitrogen-containing compounds. On the other hand, organic compounds containing amino (-NH2) or cyanide (-CN) groups and those containing nitrogen within the carbon ring frame were detected in the outlet gas in the case of urea addition. Typically observed aromatic compounds are chlorobenzonitriles, chlorobenzeneamines, and chloropyridines. This suggests a possibility that hydrogen and/or chlorine combined with PCDD/Fs are also substituted by such nitrogen-containing groups, and this decreases the formation rate of their frame of carbon rings. This phenomenon was also consistent with the fact that a significant reduction was observed in the amount of PCDD/Fs released to the outlet gas when urea was added.

N 2 formation during pyrolysis of Mg-, Ca-, Sr- and Ba-loaded low rank coal at 1200 °C has been examined with a fixed bed quartz reactor in an inert atmosphere. At 10 °C/min, the Ca, Sr and Ba, except for Mg, increase considerably the formation rate between 850 and 1100 °C, and N 2 yield reaches > 60% at 1200 °C. The increase in the yield is almost equal to the decrease in yield of the corresponding char-N, which means that the Ca, Sr and Ba can enhance N 2 formation from char-N (and/or precursors) through solid phase reactions. In addition, all of the alkaline earth metals used promote secondary decomposition reactions of tar-N to NH 3 . When the effects of some factors on the catalytic activity of the Ca for N 2 formation are examined, pyrolysis temperature, heating rate and the sulfur in coal affect its performance. The in situ X-ray diffraction (XRD) measurements reveal that the Ca, Sr and Ba added are transformed to nanoscale particles of CaO, SrO and BaO with the mean crystalline sizes of 20-40 nm during heating at 900 °C where their activity for N 2 formation appears significantly. The oxides also enhance not only the proportion of crystallized carbon but yields of both H 2 and CO. These observations suggest strong interactions between fine particles of the oxides and char substrate. The mechanism of N 2 formation is discussed in terms of solid-solid reactions of CaO, SrO or BaO with heterocyclic nitrogen forms in char.

Mesoporous molecular sieves (MCM-41 and SBA-15) with different pore diameters have been studied as supports of high loading of Co catalysts, and the performances in FT synthesis have been examined with a fixed bed stainless steel reactor at 2.0 MPa for the purpose of efficient production of C10–C20 fraction as the main component of diesel fuel. The method of exchanging template ions in uncalcined MCM-41 with Co2+ ions is effective for holding 10–20% Co within the mesopores while keeping the structure regularity of MCM-41 to some extent, compared with the conventional impregnation method using calcined MCM-41. At 523 K, CO conversion and selectivity to C10–C20 hydrocarbons are both higher at larger loading of 20% Co for the exchanged catalysts with pore diameters of 2.7–2.9 nm. When four kinds of 20% Co/SBA-15 with the diameters of 3.5–13 nm, prepared by the impregnation method using an ethanol solution of Co acetate, are used in FT synthesis at 523 K, the catalyst with the diameter of 8.3 nm shows the largest CO conversion, which is higher than those over MCM-41 supported Co catalysts. At a lower temperature of 503 K, however, the acetate-derived Co is almost inactive. In contrast, the use of Co nitrate alone or an equimolar mixture of the acetate and nitrate as Co precursor drastically enhances the reaction rate and consequently provides high space–time yield (260–270 g C/kgcat h) of C10–C20 hydrocarbons. The X-ray diffraction and temperature-programmed reduction measurements show that the dependency of the catalytic performance of 20% Co/SBA-15 on its precursor originates probably from the differences in not only the reducibility of the calcined catalyst but also the dispersion of metallic Co. Catalyst characterization after FT synthesis strongly suggests the high stability of the most effective Co/SBA-15 in the dispersion and reducibility of the oxide species and in the mesoporous structure.

Decomposition of NH3 to N2 with Fe and Ca catalysts supported on brown coal chars has been studied with a cylindrical quartz reactor from a viewpoint of hot gas cleanup. The catalyst is prepared by pyrolyzing a brown coal with Fe or Ca ions added. In the decomposition of 2000 ppm NH3 diluted with He at 750 °C and at a space velocity of 45,000 l/h, 2–6 wt% Fe catalysts are more active than not only 6 wt% Ca catalyst but also 8 wt% Fe catalyst loaded on a commercial activated carbon. The transmission electron microscope observations show that fine iron particles with the sizes of 20–50 nm account for the higher catalytic performances. When reaction temperature is increased to 850 °C, all of Fe and Ca catalysts on the chars achieve complete decomposition of NH3. The co-feeding of H2 with 2000 ppm NH3 improves the performance of the 2% Fe catalyst at 750 °C, but contrarily the coexistence of syngas (CO/H2=2) deactivates it remarkably, whereas the addition of CO2 to syngas restores the catalytic activity of the Fe to the original state without syngas. The powder X-ray diffraction and temperature programmed desorption measurements strongly suggest that the Fe and Ca catalysts promote NH3 decomposition through cycle mechanisms involving the formation of N-containing intermediate species and the subsequent decomposition to N2.

Hydrocracking of petroleum asphaltene with Fe and Ni catalysts loaded on SBA-15 supports has been carried out with a stainless autoclave at 573 K in pressurized H 2 . Asphaltene conversion with 10 wt.% Fe catalysts with average pore diameters of 4.5–15 nm increases with increasing pore diameter up to 12 nm and reaches about 70%, but levels off beyond this value. Maltene yield shows the same dependency on the diameter and the highest value of 40% at 12–15 nm. When metal loading in the Fe catalyst with the pore diameter of 12 nm is varied between 4 and 30 wt.%, asphaltene conversion and maltene yield are the largest at 4 and 10% Fe, respectively, indicating the presence of the optimum Fe loading for maltene formation. The use of the 10% Ni catalyst in place of the 10% Fe catalyst lowers the conversion slightly but improves selectivity to maltene greatly. This means that the Ni is suitable for selective conversion of asphaltene to maltene, probably because of higher hydrogenation ability. The X-ray diffraction (XRD) measurements of toluene-insoluble (TI) fractions recovered after hydrocracking and the analyses of SO 2 evolved during the temperature-programmed oxidation (TPO) reveal the formation of Fe–S and Ni–S phases as surface species. The catalysis of asphaltene conversion by the sulfided forms is discussed.

Pyrolysis of five coals has been carried out at 1000−1350 °C and different heating rates with fixed-bed and free-fall reactors to examine carbon structures in devolatilized chars. The X-ray diffraction measurements show the formation of crystallized carbon with turbostratic structures, depending strongly on coal type and severity of pyrolysis. The proportion of the carbon with low rank coals decreases by demineralization with acid washing but contrarily increases by subsequent addition of Ca2+ ions, irrespective of heating rate, and a small amount of 0.5−1 wt % Ca works efficiently. It is thus likely that Ca2+ ions naturally present as ion-exchanged forms in low rank coals determine dominantly the extent of carbon crystallization at higher temperatures. The Ca added is transformed to fine particles of CaO upon pyrolysis, and a larger amount of CO is formed in the presence of the Ca. A mechanism for the Ca-enhanced carbon crystallization is discussed in terms of solid−solid interactions between CaO particl...

Nitrogen release from two low rank coals during rapid pyrolysis at 1300 °C has been studied with a graphite-made drop tube reactor, in which a graphite filter is installed for controlling a residence time of coal particles. Nitrogen distribution depends strongly on the time. At 0 s, 60−65% of coal-N is retained in the chars, and the rest is released as tar-N, HCN, NH3, and N2. When the time is prolonged to 120 s, N2 yield increases dramatically and reaches 40−55%, whereas char-N decreases mainly. There is the reverse time dependence between N2 and char-N. Demineralization with HCl washing decreases N2 but increases char-N, and the addition of 1 wt % Ca to the demineralized coal shows almost the reverse effect on N2 and char-N. The deconvolution results of C(002) XRD lines reveal that the proportion of crystallized carbon in every char increases with increasing time. The linear relationship between the proportion and N2 yield exists among all of the samples used, which strongly suggests that N2 formation f...

Fischer−Tropsch (FT) synthesis with Co catalysts supported on mesoporous silica (SBA-15) with narrow pore size distribution has been carried out with a fixed bed stainless steel reactor at 503 K and 2.0 MPa. When 20 mass % Co is supported on SBA-15 with an average pore diameter of 8.6 nm by using an ethanol solution of Co acetate, nitrate, or an equimolar mixture of these compounds, denoted as Co(20A), Co(20N), or Co(10A+10N), respectively, the Co(20A) is almost inactive in FT synthesis, whereas the Co(20N) and Co(10A+10N) drastically enhance CO conversion, which reaches 85−90%. Such differences arise partly from the formation of less or more reducible Co species. The latter two catalysts show selectivity to C10−C20 hydrocarbons of 30−32 C-mol % and provide high space-time yields of this fraction as the main component of diesel fuel, 260−270 g-C/kg-catalyst·h. The yield with the Co(20N) catalyst depends on the amount and has a maximal value of 350 g-C/kg-catalyst·h. The N2 adsorption, X-ray diffraction, a...

Binary oxides of Ca-Ce, Ca-Cr, and Ca-Mn exhibit good performance and similar kinetic behavior in the conversion of CH4 to C2 hydrocarbons with CO2, whereas the corresponding Sr- and Ba-containing catalysts show lower activity in C2 formation except for Sr-Mn and Ba-Mn oxides. The Sr-Mn oxide provides even higher C2 yield than the Ca-containing catalysts. Characterization reveals that solid solution and composite oxides comprising Ca2+ species and the redox component (Ce, Cr, or Mn) exist at a steady state of reaction and probably account for the synergy in C2 formation over the Ca-containing catalysts. On the other hand, Sr and Ba carbonates are formed along with Ce, Cr, or Mn oxides during the reactions over Sr- and Ba-containing oxides. The carbonates, however, can react with MnO to form SrMnO2.5 and BaMnO2.5, the probable active species for CH4 activation over the Sr-Mn and Ba-Mn catalysts.

Pyrolysis of 10 coals with carbon contents of less than 80 wt%(daf) has been studied with a fixed bed quartz reactor to examine mainly nitrogen release from char-N without volatile matters. When temperature is raised from 1000 to 1350 °C, N 2 yield increases but char-N decreases for all the coals used. There is a strong reverse correlation between N 2 and char-N, which points out that most of N 2 arises from char-N via solid phase reactions. NH 3 is also formed from char-N at high temperatures of ≥1000 °C. In the pyrolysis of low rank coals, demineralization by HCl washing increases yields of tar-N, HCN and char-N, but decreases NH 3 and N 2 . The addition of 3 wt% Ca to the demineralized coals shows almost the reverse effect. The XRD measurements after pyrolysis at 1000–1350 °C reveal that the Ca exists predominantly as CaO with the average crystallite size of 25–65 nm and promotes carbon crystallization. As the extent of crystallized carbon increases, N 2 yield increases remarkably. It is likely that the highly dispersed CaO catalyzes efficiently conversion reactions of char-N to N 2 in the process of carbon crystallization. The reaction mechanism is discussed in term of interactions between CaO particles and char-N.

Formation of N2 during temperature programmed pyrolysis at 10 °C/min of low rank coals up to 1350 °C has been studied with a fixed bed quartz reactor. When Ca2+ ions are exchanged with the raw or demineralized coals by using a saturated aqueous solution of Ca(OH)2, the Ca enhances the formation rate mainly at around 820 or 850–1100 °C, respectively. The determination of mineral components removed by demineralization strongly suggests that the low temperature enhancement for the raw coals arises from synergistic effect between naturally present Fe ions and the added Ca. On the other hand, the rate increase observed for the demineralized coals in the higher temperature region originates from the intrinsic activity of the Ca catalyst. The X-ray diffraction (XRD) measurements after pyrolysis of the demineralized coals reveal that the average crystallite sizes of CaO derived from the exchanged Ca2+ are as small as 30–50 nm and the Ca promotes carbon crystallization upon pyrolysis. It is likely that fine particles of CaO catalyze N2 formation at 850–1100 °C through solid-phase reactions of heterocyclic nitrogen forms in char.

Binary oxides, mainly Ca-Mn, Sr-Mn and Ba-Mn, have been studied as catalysts for the coupling of CH 4 to C 2 hydrocarbons (C 2 H 6 and C 2 H 4 ) using CO 2 as oxidant. At temperatures of ≧840°C, the Ca-Mn catalyst exhibits quite similar performances to those of other Ca-containing binary oxide catalysts (Ca-Ce, Ca-Cr and Ca-Zn) reported previously; C 2 selectivity and yield at 850°C increase remarkably with increasing partial pressure of CO 2 , and apparent activation energies observed over these catalysts are roughly the same (190–220 kJ mol −1 ). When the temperature is decreased from 840 to 825°C, CH 4 conversion and C 2 selectivity over the Ca-Mn catalyst abruptly drop; here a discontinuous change also is seen in the Arrhenius plots. On the other hand, the Sr-Mn and Ba-Mn catalysts show different kinetic features from the Ca-Mn system; C 2 selectivity at 850°C changes only slightly with partial pressure of CO 2 , and the activation energies are constant over the whole temperature range examined and notably lower. Characterizations reveal that solid solution of Ca 0.48 Mn 0.52 O is the main phase for the Ca-Mn catalyst after reaction at 850°C, while, at 800°C, some Ca 2+ ions separate from the solid solution to form CaCO 3 , which covers the catalyst surface. Such a difference probably accounts for the discontinuous change in the catalytic behavior with temperature. With the Sr-Mn and Ba-Mn catalysts, SrCO 3 and BaCO 3 are formed along with MnO after reaction, and the carbonates are suggested to react with MnO to form SrMnO 2.5 and BaMnO 2.5 in the conversion process of CH 4 with CO 2 . The mechanism for C 2 formation involving SrMnO 2.5 and BaMnO 2.5 as intermediates is discussed.

Several types of SBA-15 with pore diameters of 3.6–12 nm have been synthesized under different reaction conditions, followed by air calcination, and utilized as supports for loading 10–20 mass% Co catalysts. Post-synthesis heat treatment after reaction at 308 K is more effective for increasing the pore diameter and volume of SBA-15 than the addition of trimethylbenzene before reaction. The combination of the two results in the formation of SBA-15 with large pore diameter but broad size distribution and less organized structures. When an acetone, ethanol, or water solution of Co(NO 3 ) 2 is used as a precursor for impregnation with SBA-15 with pore diameter of 3.6 nm, the average crystalline size of Co 3 O 4 observed at 10 mass% Co exceeds the pore diameter irrespective of the kind of the solvent. On the other hand, the use of an ethanol solution of Co(CH 3 COO) 2 or an acetone solution of (CH 3 COCHCOCH 3 ) 2 Co provides no X-ray diffraction peaks of Co 3 O 4 even at loading as high as 20 mass% Co, and catalyst addition considerably decreases the pore volume of SBA-15 support regardless of the pore diameter. These observations strongly suggest that Co catalysts exist as nanosized clusters inside the mesopores. The SAXS measurements show that the hexagonal mesoscopic organization of the SBA-15 support with pore diameter of 5.5 nm is almost retained even after addition of 20 mass% Co. The 20 mass% Co/SBA catalysts are also tested preliminarily in Fischer–Tropsch synthesis under 503–523 K and 2.0 MPa.

The effects of Ca catalysts on nitrogen release during heat treatment of polyacrylonitrile-derived carbon and pyrolysis of low rank coals have been studied with a fixed bed quartz reactor in a stream of high purity He. In the temperature-programmed treatment at 10 °C/min of the carbon with 3 wt % Ca, the Ca promotes N2 formation at 850−1000 °C and the catalytic effect is larger at a higher temperature. When a low rank coal, after demineralization and subsequent addition of 3 wt % Ca, is pyrolyzed in the same manner as above, the Ca enhances the rate of N2 formation at 850−1100 °C at largest by a factor of 15. In the fast heating pyrolysis at 400 °C/min of the demineralized samples, the Ca at loading of 1−3 wt % also increases N2 yields at 1200−1350 °C irrespective of type of coal. These observations and nitrogen distribution indicate that the N2 increased by Ca addition arises mainly from solid-phase reactions of heterocyclic nitrogen forms. The X-ray diffraction measurements after heat treatment and pyro...