This article is made freely available as part of this journal's Open Access: ID | Phuong ManuscriptRef.1-ajiras030616 JAPAN6 |
Afiliation: 1. Nagasaki University | Graduate School of Fisheries and Environmental Sciences | Nagasaki | Japan | 2. Tokyo University of Agriculture and Technology | Faculty of Agriculture | Tokyo | Japan |
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ABSTRACT Background: Characterisation of the pore structure of biochar is important to their application in soil. For most cases, the biochar’s pore structure is strongly affected by the original biomass feedstock and pyrolysis temperature. Objectives: The aims of this study were to investigate whether the porous structure of biochars & their surface area affected by the different parts of rice plant (straw and husk), different rice varieties and different pyrolysis temperature. Methods: In this study, Koshihikari straw and husk obtained from Japan and IR50404 straw and husk obtained from Vietnam were pyrolysed under the temperature range of 300ºC – 800ºC. The surface physical properties was assessed through N2 adsorption and I2 adsorption. Results: The comparative N2 adsorption isotherms illustrated the pore filling of micropores (type I) and capillary condensation (type IV) of biochars. In general, the adsorption volumes of N2 increased as the pyrolytic temperature increased, reached a maximum at 700ºC, then finally decreased at 800ºC. The majority of studied biochars were in the range of 1.2- 9.9 nm, and biochars showed a tendency to smaller pore sizes as pyrolysis temperature increased. Most of surface area were occupied by micropores in biochars; however, the volumes of meso- and macropores were larger than volumes of micropores in many cases. BET surface area and iodine number showed well correlation to each other, increased with pyrolysis temperature, but not similar numbers. Rice-straw-based-biochar conventionally host more micropores, total pore volume, BET surface area and higher iodine numbers than rice-husk-based-biochar. Biochars produced from Vietnamese rice-residue showed a better adsorption capacity (due to a higher surface area) than from Japan. SEM analysis slightly indicated surface area and porosity changes with changing temperature. Conclusions: Differences in porous properties and surface area were observed among rice-husk-biochars and among rice-straw-biochars. Additionally, different parts of rice plant will have different adsorption capacities, which may due to the differences in cell wall compositions of rice straw and rice husk, differences in functional groups on the biochars’ surface, and also differences in the ash content of biochars. Keywords: rice straw, rice husk, adsorption isotherm, surface area, iodine number.
