Shuntaro Tsubaki

Microwave-assisted hydrolysis of biomass over activated carbon supported polyoxometalates

Activated carbon supported polyoxometalates (AC-POMs) were used for acceleration of hydrolysis of biomass under microwave irradiation. Microwaves exhibited a higher saccharification rate for cellobiose and green seaweed (Monostroma latissimum) over AC-POMs than conductive heating by 1.25 to 1.55-fold. The activity of the AC-POMs was positively correlated with the dielectric loss of the catalysts, suggesting that microwave susceptibility of AC-POMs is relevant to the enhancement of catalysis under microwave irradiation.

Microwave-Induced Biomass Fractionation

Microwave irradiation initiates molecular motions of dipoles and electrolytes in a solution and directly generates heat from inside of the irradiated materials. The unique heating property of microwave irradiation is expected to boost hydrothermal fractionation of useful chemicals from biomass. This chapter summarizes the effects of the exploitation of microwave irradiation on biomass fractionation regarding the following three topics: (1) the fundamentals of the dielectric heating and microwave-assisted chemical reactions, (2) the effects of microwave irradiation on hydrothermal treatment of model compounds of biomass, and (3) the practical applications of microwave irradiation on fractionation processes of lignocellulose and food-waste biomass.

Enhancement of anodic current attributed to oxygen evolution on α-Fe2O3 electrode by microwave oscillating electric field.

Various microwave effects on chemical reactions have been observed, reported and compared to those carried out under conventional heating. These effects are classified into thermal effects, which arise from the temperature rise caused by microwaves, and non-thermal effects, which are attributed to interactions between substances and the oscillating electromagnetic fields of microwaves. However, there have been no direct or intrinsic demonstrations of the non-thermal effects based on physical insights. Here we demonstrate the microwave enhancement of oxidation current of water to generate dioxygen with using an α-Fe2O3 electrode induced by pulsed microwave irradiation under constantly applied potential. The rectangular waves of current density under pulsed microwave irradiation were observed, in other words the oxidation current of water was increased instantaneously at the moment of the introduction of microwaves, and stayed stably at the plateau under continuous microwave irradiation. The microwave enhancement was observed only for the α-Fe2O3 electrode with the specific surface electronic structure evaluated by electrochemical impedance spectroscopy. This discovery provides a firm evidence of the microwave special non-thermal effect on the electron transfer reactions caused by interaction of oscillating microwaves and irradiated samples.

Microwave-Driven Biorefinery for Utilization of Food and Agricultural Waste Biomass

Abstract Food and agricultural waste biomass are potentially valuable feedstock for the production of bio-based and renewable chemicals and materials. Microwave irradiation enhances chemical reactions by directly affecting catalysts and substrates due to molecular motions of dipoles and electrolytes in a solution. The unique heating phenomenon of microwaves is expected to accelerate hydrothermal treatment of food and seaweed biomass. This chapter summarizes recent advances in the microwave-assisted conversion process of the waste biomass such as extraction of value-added chemicals and hydrolysis of polysaccharides from waste biomass. The specific effects of microwave irradiation on hydrothermal treatment of biomass are also discussed based on the fundamentals of the dielectric heating and microwave-assisted chemical reactions.

Microwave-Assisted Water Extraction of Carbohydrates From Unutilized Biomass

Abstract Microwaves provide rapid and efficient water extraction of carbohydrates because microwaves directly generate heat by dipole rotations of water molecules. Microwaves penetrate into biomass substrates and generate heat from within, thus enhancing the extraction efficiency of the components contained in the plant bodies. In addition, water under high temperature and pressurized condition enables extraction and autohydorolysis of polysaccharides without using hazardous chemicals. This chapter, therefore, summarizes fundamentals and applications of water extraction of carbohydrates from unutilized biomass (agricultural wastes, food wastes and seaweeds) using microwaves under hydrothermal condition. The dielectric properties relevant for water extraction of polysaccharides are also discussed to understand the heating mechanism of the mixture of water and biomass.

Catalytic Hydrolysis of Polysaccharides Derived from Fast-Growing Green Macroalgae

Green macroalgae, such as Ulva spp., has a higher growth rate than terrestrial lingocellulosic biomass, which often leads to serious environmental issues such as green tide. So, it is a promising feedstock for biorefineries. Hiraoka produced Ulva with reproducible compositions and sizes by our original cultivation method. The macroalgae contained approximately 35u2005wtu2009% of a soluble polysaccharide called ulvan, which is a sulfated glucuronorhamnan polysaccharide. The catalytic conversion of extracted ulvan was performed under hydrothermal conditions at 130u2009°C by using solid acid catalysts. The Amberlystu200570 catalyst has a stable structure and gave monosaccharides in quantitative yield, predominantly in the form of rhamnose. The Amberlystu200570 catalyst showed higher activity than sulfonated activated‐carbon (AC‐SO3H) in the hydrothermal conversion of ulvan, although Amberlystu200570 showed lower catalytic activity than AC‐SO3H in the hydrolysis of starch.

Catalysis of polyoxometalates under microwave irradiation and their dielectric properties

Summary form only given. Polyoxometalates (POMs) is a unique metallic cluster that exhibit very strong acidic and oxidative catalysis with less corrodibility. In this paper, we report two examples of POM reaction systems under microwave irradiation based on the microwave absorption mechanisms of POM-based catalysts. The microwave-susceptive solid catalyst exhibits non-equilibrium local heating in the vicinity of the catalyst and facilitates heterogeneous chemical reactions at milder condition than conventional heating. The POMs (phosphotungstic and silicotungstic acids) were, therefore, supported on activated carbons as microwave susceptors to enhance microwave absorption of the solid catalyst. Then, the POM based solid catalysts were applied for hydrolysis of biomass under microwave irradiation. The carbon-supported POMs exhibited higher activity on hydrolysis of cellobiose and green seaweeds than conventional heating. The dielectric loss of carbon-supported POMs exhibited positive correlation with saccharification rate indicating that direct microwave absorption by the solid catalyst was important to enhance the reactions. In the case of homogeneous system, oxidation of benzyl alcohols in DMSO was conducted by using POM (phosphomolybdic acid) under three microwave frequencies in ISM bands (915 MHz, 2.45 GHz and 5.8 GHz). We found that the selectivity to benzaldehyde was enhanced at 915MHz and 5.8 GHz rather than 2.45 GHz by 18.6% and 31.8%, respectively. The dielectric measurement using the coaxial probe method revealed that absorption of POM-DMSO system at 915MHz and 5.8 GHz were due to ionic conduction of POMs and dipolar dielectric loss of DMSO, respectively. The results suggested that different microwave-absorption mechanism of POM-DMSO system have led to different oxidation catalysis.

Study on metal refining process of Sc metal using by microwave irradiation

High-Sc-content ScAlN thin films have attracted significant attention because of their strong piezoelectricity. Akiyama et al. found that the piezoelectricity of ScAlN thin films increases monotonically with increasing Sc concentration, r. The piezoelectricity reaches a maximum at r = 43 at%, at which point the piezoelectric coefficient, d33, is five times that of pure AlN. Hashimoto et al. reported that a surface acoustic wave (SAW) resonator based on the ScAlN/6H-SiC structure exhibited resonance Q, anti-resonance Q, and K2 values of 340, 240, and 4.5%, respectively, at 3.8 GHz. These values suggest that a ScAlN thin film on a hard substrate should be a suitable SAW wideband filter substrate for next-generation wireless communication systems.