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Fast Pyrolysis of Rice Husk in a Fluidized Bed: Effects of the Gas Atmosphere and Catalyst on Bio-oil with a Relatively Low Content of Oxygen Sirimirin Meesuk,* Jing-Pei Cao, Kazuyoshi Sato, Yukiko Ogawa, and Takayuki Takarada Department of Chemical and Environmental Engineering, Gunma University, 1-5-1 Tenjin-cho, Kiryu 376-8515, Japan ABSTRACT: The pyrolysis of rice husk is carried out in a fluidized-bed reactor at atmospheric pressure. The effects of pyrolysis parameters, i.e., gas atmosphere and catalyst, on the carbon conversion of rice husk and composition of bio-oils are studied. The experiments with catalysts under a hydrogen atmosphere to produce bio-oils with a much lower oxygen content compared to those under a nitrogen atmosphere are performed. The results show that the oxygen content of bio-oils is markedly reduced because the oxygenated hydrocarbons are hydrocracked, resulting in the formation of H2O, CO, and CO2, when catalysts are introduced under a nitrogen atmosphere and decreases even more under a hydrogen gas atmosphere (hydropyrolysis). The oxygen content of bio-oil under a hydrogen atmosphere decreases from over 31.1% without a catalyst to 25.91, 20.51, 26.51, and 10.1% with Ni/Al2O3, Ni/LY, dolomite, and CoMo/Al2O3, respectively. The use of CoMo/Al2O3 and Ni/LY catalysts under a hydrogen atmosphere shows high activity to decrease the oxygen content, which leads to a higher heating value and more aromatic hydrocarbons. These experiments indicate that catalytic hydropyrolysis is suitable for producing bio-oils with a lower molecular weight and high aromatic hydrocarbons, which are possible to use as a potential liquid fuel and chemical feedstock.
1. INTRODUCTION Currently, biomass is increasingly recognized as an interesting alternative energy source partly because of its origin, which mainly comes from plants and animals. The energy stored in a biomass is a renewable energy that can be converted into fuel with less pollution and global-warming-inducing gases compared to existing fossil fuels.1,2 Rice husk is an abundant biomass resource in Japan. It has been used as a feedstock for pyrolysis because of its high content of organic compounds (cellulose, hemicellulose, and lignin), high energy content, and steady supply from rice plants. Many researchers have been studying fast pyrolysis of rice husk.35 Recently, fast pyrolysis in a high heat-transfer rate to biomass particles, short residence time ( Ni/LY > Ni/ Al2O3 > dolomite > sand. The highest aromatic hydrocarbons are obtained with CoMo/Al2O3, and this increase is due to the decrease in the oxygenated compound content. The high aromatic hydrocarbon production may be linked to the active metal content and the specific surface area of the catalyst, which has a relatively high catalyst activity. It can be concluded that pyrolysis with CoMo/Al2O3 under a hydrogen atmosphere is suitable for obtaining a high yield of hydrocarbon compounds, such as BTX and naphthalene.11 An interesting result is that of Ni/LY, and a plausible explanation is that the Ni catalyst catalyzes the hydrogenation
of phenol or phenol precursors or, in other words, it inhibits the formation or degradation of phenol.32 Nickel can considerably help decrease the hydrodeoxygenation process cost and is wellknown for being active in hydrogenation.25 It can be concludedz that Ni/LY is also an interesting alternative because it can be used to improve the quality of the bio-oil product. These results indicate that the hydrogen atmosphere with catalysts gives light oil with a low heteroatom content. Furthermore, these suggest that the outcome in terms of oxygen removal in bio-oil, although structurally different depending upon the type of catalyst used, could be achieved for biomass pyrolysis.
’ CONCLUSION Fast pyrolysis of rice husk is investigated using a fluidized-bed reactor under different gas atmospheres and with different catalysts. The results reveal that a lower molecular weight of bio-oils and several aromatic hydrocarbons are obtained with pyrolysis under a hydrogen atmosphere. Catalysts are used in this study to decrease the oxygen content of the bio-oils. Best results are obtained with Ni/LY and CoMo/Al2O3 under a hydrogen atmosphere; this is possibly due to the ability of these catalysts to promote the hydrodeoxygenation of primary pyrolysis vapors, producing bio-oils containing lower amounts of oxygenated compounds of about 20.15 and 10.10%, respectively. However, Ni/LY is deemed more favorable than CoMo/Al2O3 in terms of the production cost of the bio-oil. ’ AUTHOR INFORMATION Corresponding Author
*Telephone: +81-277-30-1452. Fax: +81-277-30-1454. E-mail:
[email protected] or
[email protected].
’ ACKNOWLEDGMENT This work has been supported by the Department of Chemical and Environmental Engineering, Gunma University, Kiryu, Japan. The authors express their gratitude to Natthaya Punsuwan for her helpful advice. 4120
dx.doi.org/10.1021/ef200867q |Energy Fuels 2011, 25, 4113–4121
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