ARTICLE pubs.acs.org/EF
Study of Catalytic Hydropyrolysis of Rice Husk under Nickel-Loaded Brown Coal Char 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 hydropyrolysis of rice husk was carried out in a fluidized-bed reactor. To determine the optimal condition for the bio-oil yield and investigate the effects of an inexpensive nickel-loaded Loy Yang brown coal (Ni/LY) char activity on the product yield and composition, the non- catalytic hydropyrolysis was tested under different reaction conditions (gas flow rate, static bed height, and temperature). The maximum bio-oil yield of 47.06% was obtained at a gas flow rate of 2 L/min, a static bed height of 5 cm, and a temperature of 500 °C. In the presence of the catalyst, the bio-oil yields markedly reduced, while the gas yield and water content showed an opposite trend. The influence of the catalyst was to convert the oxygen content in bio-oil to the formation of H2O, CO, and CO2. The oxygen content of bio-oils decreased, whereas the higher heating value of bio-oils increased when increasing the volume fraction of Ni/LY char. The bio-oil with the lowest oxygen content (20.7 wt %) and the highest heating value (30 MJ/kg) was obtained with a 75% volume fraction of the catalyst. The catalytic hydropyrolytic oil contained more aromatic hydrocarbons with slightly reduced oxygenated compounds than the non-catalytic hydropyrolytic oil. The high amount of aliphatic and aromatic hydrocarbons was obtained from hydropyrolysis, with the volume fraction of Ni/LY char >50%. The results indicated that the bio-oils from the hydropyrolysis, using Ni/LY char, contained more aromatic hydrocarbons with slightly reduced oxygenated compounds and can be used as liquid fuel and chemical feedstock.
1. INTRODUCTION Biomass is a renewable energy resource and consists of carbon, hydrogen, oxygen, and nitrogen, which can be converted into fuels and chemical feedstock. In comparison to a fossil fuel power plant, the use of biomass is more environmentally friendly and reduces global warming. Rice husk is a major agricultural component, which is currently produced every year in Japan and 100 million tons/year around the world.1,2 Rice husk contains a great quantity of organic compounds (i.e., cellulose, hemicelluloses, and lignin). It could be considered a potential source of renewable energy based on the benefits of both energy recovery and environmental products.3 Fast pyrolysis at a moderate temperature with a very short residence time (50% gave a high potential of biooil with high aliphatic and aromatic hydrocarbons and low oxygenated compounds. Dundich et al.11 have reported that the deoxygenation of aliphatic and aromatic oxygen-containing compounds to corresponding hydrocarbons can be efficiently performed on a nickel catalyst. Similar to previous work on the composition of biomass hydropyrolytic oil, the aliphatic and aromatic compounds were increased when the catalyst was present.30 3.3.3. Functional Group Compositional Analysis. The FTIR spectra of the bio-oils obtained from hydropyrolysis using a 75% volume fraction of Ni/LY char and without the catalyst at a gas flow rate of 2 L/min, static bed height of 5 cm, temperature of 500 °C, and heating rate of 10 °C/min are shown in Figure 10. The noncatalytic hydropyrolytic oil showed a strong adsorption band between 3600 and 3200 cm 1 representing O H vibrations, CdO stretching vibrations between 1750 and 1650 cm 1, and C O stretching vibrations between 950 and 1300 cm 1 and indicated the oxygenated compounds, such as phenol, alcohol, esters, carboxylic acids, ketones, and aldehydes. However, these oxygenated compound peaks are also present in the catalytic hydropyrolysis oil, suggesting that the Ni/LY char does not completely remove the oxygenated compounds in bio-oil. For the non-oxygenated compounds, the C H stretching vibrations between 2800 and 3000 cm 1, deformation vibrations between 1350 and 1475 cm 1, absorption peaks between 1575 and 1625 cm 1 and between 675 and 900 cm 1 indicating alkane and alkene have been detected at high concentrations in catalytic hydropyrolytic oil whereas low concentrations in noncatalytic 5442
dx.doi.org/10.1021/ef201266b |Energy Fuels 2011, 25, 5438–5443
Energy & Fuels
ARTICLE
’ ACKNOWLEDGMENT This work was supported by the Department of Chemical and Environmental Engineering, Gunma University, Kiryu, Japan. ’ REFERENCES
Figure 10. FTIR spectra of bio-oils.
hydropyrolysis oil. The adsorption peaks of aromatic compounds, i.e., the adsorption bands between 3000 and 3050 cm 1, between 1450 and 1600 cm 1, and between 700 and 900 cm 1, showed a markedly increase after the catalyst. These results indicated that the presence of the catalyst can produce bio-oil with relatively high alkene groups, single rings, aromatic hydrocarbons, and low oxygenated compounds compared to no catalyst.31 Overall, it has been shown that the Ni/LY char has great influence on hydropyrolysis of biomass. There is a decrease in the bio-oil yield after the catalysis, while an improved product is obtained with low oxygen content and high aromatic content, which might be used as a potential liquid fuel and chemical feedstock.
4. CONCLUSION Fast hydropyrolysis of rice husk was investigated using a fluidized-bed reactor for different gas flow rates, static bed heights, and bed material temperatures. The bio-oil product first increased and then decreased when there was an increased gas flow rate from 1.5 to 2.5 L/min. As for the effect of the static bed height, the bio-oil yield decreased when the static bed height was increased to 10 cm because of the longer residence time, resulting in the decrease of the bio-oil yield and the increase of the gas yield. At the higher temperatures, the result found that the bio-oil yield decreased when the temperature increased. The optimal conditions for the bio-oil yield were found to be 500 °C with a gas flow rate of 2 L/min and static bed height of 5 cm without the catalyst. The performed catalyst for hydropyrolysis was found to be attractive for decreasing the oxygen content in the bio-oil by converting the oxygen to form H2O, CO, and CO2 via hydrocracking and deoxygenation reactions to obtain bio-oil with a relatively low oxygen content compared to noncatalytic hydropyrolysis. The oxygenated compounds decreased, while aliphatic and aromatic hydrocarbons slightly increased, when the volume fractions of Ni/LY char increased. It is concluded that the preparation of an inexpensive Ni/LY char by the ion-exchange method could be used to improve the quality of bio-oil to a level suitable for the production of a liquid fuel and chemical feedstock.
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dx.doi.org/10.1021/ef201266b |Energy Fuels 2011, 25, 5438–5443
