Idzumi Okajima

Energy conversion of biomass with supercritical and subcritical water using large-scale plants

Exploiting unused or waste biomass as an alternative fuel is currently receiving much attention because of the potential reductions in CO2 emissions and the lower cost in comparison to expensive fossil fuels. If we are to use biomass domestically or industrially, we must be able to convert biomass to high-quality and easy-to-use liquid, gas, or solid fuels that have high-calorific values, low moisture and ash contents, uniform composition, and suitable for stored over long periods. In biomass treatment, hot and high-pressure water including supercritical and subcritical water is an excellent solvent, as it is clean and safe and its action on biomass can be optimized by varying the temperature and pressure. In this article, the conversion of waste biomass to fuel using hot and high-pressure water is reviewed, and the following examples are presented: the production of large amounts of hydrogen from waste biomass, the production of cheap bioethanol from non-food raw materials, and the production of composite powder fuel from refractory waste biomass in the rubble from the Great East Japan Earthquake. Several promising techniques for the conversion of biomass have been demonstrated in large-scale plants and commercial deployment is expected in the near future.

Recycling of Carbon Fiber Reinforced Plastics Using Subcritical Water

The decomposition of carbon fiber reinforced plastics (CFRP) was carried out to recover phenolic monomers and carbon fiber (CF) using subcritical water. The total yield of phenolic monomers reached 70.9% at 673K, 20MPa, 45min and 2.5wt% potassium carbonate catalyst. The tensile strength of the recovered CF was about 15% lower than that of a virgin one and it might be acceptable level for industrial use such as filler in polymers. The functional groups on the surface of the recovered CF decreased, comparing with a virgin one. Therefore the oxidation treatment of the recovered CF might be required, when we try to reuse it.

Energy Conversion of Biomass and Recycling of Waste Plastics Using Supercritical Fluid, Subcritical Fluid and High-Pressure Superheated Steam

Abstract Utilization of unused or waste biomass as fuels is receiving much attention owing to the reduction of CO2 emission and the development of alternative energy to expensive fossil fuels. On the other hand, the recycling of waste plastics is important for the prevention of the exhaustion of fossil resources. In this chapter, typical several examples of the energy conversion of biomass and the recycling of waste plastics using supercritical fluid, subcritical fluid, and high-pressure superheated steam were introduced: (1) bioethanol production from paper sludge with subcritical water, (2) hydrogen production from various biomass with high-pressure superheated steam, (3) production of composite solid fuel from waste biomass and plastics with subcritical water, (4) waste treatment and recovery of thermal energy with high-pressure superheated steam oxidation, (5) recycling of carbon fiber-reinforced plastic with high-pressure superheated steam and supercritical alcohol, (6) recycling of laminate film with subcritical water, and (7) recycling of cross-linked polyethylene with supercritical methanol.

Gasification and Hydrogen Production from Waste Biomass with High Pressure Superheated Steam

High pressure superheated steam above the critical temperature (374oC) and below the critical pressure (22.1MPa) of water was used to produce hydrogen gas from waste biomass efficiently. The targets are large amount of waste biomass such as livestock excrement and paper sludge. We investigated the effects of reaction temperature, pressure, time, catalyst and molar ratio of water to carbon in biomass on the decomposition efficiency of waste biomass and the productivity of hydrogen. Almost 100% of the decomposition efficiency and 1350-1550cm3 of hydrogen production per gram of dry biomass were realized in the presence of KOH catalyst at 700oC, 10MPa, 20min and 20 of molar ratio of water to carbon in biomass.

Decomposition and Detoxification of Chlorinated Organic Compounds Using Supercritical Water Oxidation

超臨界水酸化による有機塩素系農薬とダイオキシン類の分解・無害化を検討した。有機塩素系農薬の2, 4, 5-Tと2, 4-Dは600℃, 25MPa, 30分, 過剰過酸化水素比1.4 (2, 4, 5-T) および1.1 (2, 4-D) の条件で分解率99.99%以上とほぼ完全に分解した。また600℃, 30分の条件で2, 4-Dの超臨界水酸化, 超臨界水加水分解および熱分解の分解生成物を比較したところ, 超臨界水酸化では中間生成物は検出されなかったが, 超臨界水加水分解ではフェノール等が生成し, 熱分解ではさらに多環芳香族化合物も生成した。ダイオキシン類の超臨界水酸化について, 各同族体の分解率は温度および圧力の増加とともに上昇した。一方, 毒性が強い四塩素化物や五塩素化物は化学的に安定なので, 中間生成物として残存する傾向があることが明らかになった。すべてのダイオキシン類同族体は600℃, 25MPa, 30分, 過剰過酸化水素比10, 000の反応条件で99.999%以上分解した。