Tetsuo Yamada

Effect of demineralization on the hydrogasification reactivity of iron-loaded birch char

Abstract Iron-loaded raw and demineralized birch chars were hydrogasified in a thermobalance to examine the influence of ash removal on their reactivities at 700 and 800°C. Demineralization was so effective in enhancing the reactivity in the low-temperature region that 4 wt% iron loading gave a conversion of 90 wt% at 700°C. The increased catalytic effect of iron in the absence of wood ash can be explained by the formation of finer metallic iron particles during the gasification. The loss in the catalytic activity of iron due to calcium and silica as the main ash components was investigated by X-ray diffraction and X-ray photoelectron spectroscopy. It is proposed that calcium and silica form calcium iron oxides and iron silicates during carbonization, inhibiting the reduction of iron oxide to metal with catalytic activity at low temperatures. However, the ash plays quite a different role at higher temperatures. Its presence was beneficial for the formation of catalytically active metallic iron, whereas demineralized char rapidly lost reactivity in this region, owing to accelerated sintering of metallic iron particles.

Nickel-catalyzed carbonization of wood for coproduction of functional carbon and fluid fuels I: production of crystallized mesoporous carbon

Japanese larch wood loaded with nickel (1%–4%) alone or with nickel and calcium (0.25%–1.5%) was carbonized at 800°–900°C for 0–120min with a heating rate of 5°–20°C min−1 in a helium flow of 5.8−46.4 ml STP cm−2 min−1 to examine the influence of these variables on the crystallization of carbon (the formation of T component) and the development of mesoporosity. From the obtained results, reaction conditions suitable for effective production of carbon with the dual functions of adequate electroconductivity and adsorption capacity in liquid phase were established, thereby explaining the factors that govern the process. It was also confirmed that mesopore having a diameter of about 4 nm was selectively produced at the cost of specific (BET) surface area in parallel with the formation of T component. This result provided good insight into how the simultaneous dual function could be realized.

Influence of calcium on the catalytic behavior of nickel in low temperature hydrogasification of wood char

Abstract Demineralized birch char co-loaded with nickel and calcium was hydrogasified to examine the catalytic behavior of the binary system at temperatures below 700°C. The activity of nickel was determined by the amount of co-existing calcium, and it became a maximum at a given ratio of calcium to nickel. This can be explained by the two roles of calcium: (1) retardation of nickel sintering and (2) inhibition of the formation of catalytically active nickel species. Calcium was considered to interact with nickel to form a certain double oxide of calcium and nickel, whereby both actions occur. On the basis of this assumption, the function of calcium for nickel- and iron-catalyzed hydrogasifications of wood char is discussed.

Catalytic activity of physically-mixed nickel compounds on the CO2 gasification of phenol-formaldehyde resin char

Abstract In order to account for the various activities of different nickel compounds in low temperature catalytic gasification of carbon the reducibility of individual nickel compounds in carbon dioxide to metallic was studied by thermogravimetry and the behaviour of mixture of nickel salts with a phenol-nickel formaldehyde resin char was investigated by temperature-programmed X-ray diffraction analysis. A correlation was found between the order of reducibility of the nickel salts and their order of activity in catalytic gasification. Low temperature gasification up to 98 wt% was demonstrated for char mixed with nickel acetate (up to 9/10 wt% Ni), which suggests that there may be good prospects for finding a method of complete gasification with nickel.

Catalytic activities of ion-exchanged nickel and iron in low temperature hydrogasification of raw and modified birch chars

Abstract Raw, HNO3 oxidized and carboxymethylated birch woods loaded with nickel or iron by the ion-exchange method were carbonized at 500 °C in a flow of nitrogen, and the resulting chars were hydrogasified in a thermobalance to examine their reactivities below 700 °C. The amounts of ion-exchanged metals on raw char were too small to give high gasification reactivity. However, oxidized and carboxymethylated woods with increased ion-exchange capacity produced much more reactive chars. Both nickel and iron exhibited larger catalytic activities on carboxymethylated chars than on oxidized chars, because better metal dispersion could be achieved on carboxymethylated wood with its larger cation exchangeability. It was noteworthy that only 1 wt% loading of iron, as well as nickel, on carboxymethylated char was sufficient to attain a gasification of 90 wt% at 700 °C. It was also noted that the catalytic effect, up to 600 °C, of iron on the gasification of oxidized and carboxymethylated chars was larger than that of nickel. This is ascribed to two factors; greater catalytic activity of metallic iron formed during the gasification than that of nickel metal, and low ash level in the chars. Above 600 °C, however, serious loss of activity of the iron was observed in the absence of wood ash. This showed the different influence of wood ash on the catalysis of iron in the low and high temperature regions.

Hydrogasification of wood for high heating-value gas production X: Effect of pretreatment of Japanese oak bark by HNO3 oxidation on subsequent iron-catalyzed hydrogasification

Japanese oak bark, which is one of the most difficult woody biomass materials for iron-catalyzed lowtemperature (<700°C) hydrogasification, was subjected to HNO3 oxidation as the pretreatment after prewashing with water. The effect was compared with that of HCl demineralization from four points of view: (1) removal of catalyst poisons; (2) development of porosity in the cell tissue; (3) introduction of ion-exchanged iron; and (4) reduction of nitrogen and sulfur. It was found that HNO3-oxidized oak bark char loaded with iron by the ion-exchange method gave a satisfactory reactivity in agreement with the corresponding larch bark char previously used. Also, the oak bark char contained only small amounts of nitrogen and sulfur. These situations confirmed the high suitability of oxidation pretreatment combined with water prewashing for woody biomass.

Contact between catalyst and carbon in the tin- and lead- catalyzed gasification of carbon with carbon dioxide

Abstract The wettability and distribution of tin and lead metals on a phenol-folmaldehyde resin char were investigated by means of contact angle measurement and microscopic analysis. The wettability on the pelletized char was not so significant. However, stannic oxide was found to be distributed around a tin catalyst particle. This can be considered a result of the vapor phase transport of stannous oxide and its oxidation by CO 2 . Stannous oxide was formed through a red-ox type catalysis cycle. On the other hand, in the case of lead-catalyzed gasification, the mobile species was the lead metal itself. Thus, the high catalytic activity of tin and lead metals was appropriately ascribed to an intimate contact between the catalyst and the carbon substrate caused by the vapor phase transportation of stannous oxide and lead metal.

Effect of pretreatment of oak bark to develop porosity in the cell tissue on subsequent iron-catalysed hydrogasification

Abstract Oak bark was immersed in boiling water or extracted with supercritical carbon dioxide in the presence of water to develop porosity in the cell tissue before iron catalyst was loaded by wet impregnation. The iron-loaded bark was carbonized at 500°C, and the resulting char was hydrogasified in a thermobalance to measure the reactivity by the temperature-programmed method. The reactivity up to 700°C was higher than that of raw bark char at 5 wt% iron loading because of improved dispersion of the metal particles. Supercritical extraction was superior to boiling in its effect. These pretreatments following demineralization with HCl enhanced the activity of iron to a greater degree, so that demineralized and extracted char with 5 wt% iron gave a conversion of 90% at 700°C. Demineralized and boiled char also exceeded demineralized char in reactivity at the same iron loading. These results showed the significance of development of porosity for higher catalytic activity of iron in subsequent gasification. The X-ray diffraction intensity of metallic iron was found to be useful for judging its dispersion on bark char containing a large amount of mineral matter.

Nickel-catalyzed carbonization of wood for coproduction of functional carbon and fluid fuels II: improved fuel quality of oil fraction and increased heating value of gas fraction

The yields and properties of oil and gas fractions coproduced during carbonization of larch wood loaded with Ni 2%, Ni 2%+Ca 1%, and Ni 4% and without catalyst (None) at 700°–900°C were examined to clarify the catalytic effect in terms of conversion into fluid fuels. The net calorific value of oil occurred mainly below 500°C and increased in the order None < Ni 2% < Ni 4% < Ni 2%+Ca 1%, while the yield decreased in this order. The same order held for the production of gases enriched with hydrogen at 500°–700°C. Even above 800°C, markedly promoted evolution of hydrogen took place for all catalyst systems. These observations confirmed the effectiveness of nickel-catalyzed carbonization at 900°C, particularly Ni 2%+Ca 1%, for both upgrading of oil and gaseous fractions, although the quality of oil was not satisfactory. The catalysis of nickel with and without calcium is discussed on the basis of the modified Broid-Shafizadeh scheme, and the scheme was altered to adapt to the high temperature region where oil was no longer produced.

Chemical characterization of unburned carbon in coal fly ashes by use of TPD/TPO and LRS methods.

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.