Motonobu Goto

Green materials synthesis with supercritical water

This paper describes the chemistry of green materials synthesized with supercritical fluids. First, the properties and some specific features of supercritical water are summarized. Then, supercritical hydrothermal synthesis of nanoparticles is explained, and various applications of green materials are described. The surface control of nanoparticles in supercritical water is also explained. Green processes involving chemical recycling of waste polymers and a combination of hydrothermal synthesis and supercritical water oxidation are also discussed. Finally, commercialization of supercritical water processes is discussed.

Shrinking-core leaching model for supercritical-fluid extraction

Abstract Extraction or leaching of a solute from a solid material is a process involving mass transfer in the solid matrix. When the solute content in the solid material is sufficiently large as compared to the solubility in fluid phase, the process is similar to that of irreversible desorption. The shrinking-core model was applied to the modeling of the extraction process. The model including axial dispersion in the extraction column was solved numerically. Quasi-steady-state solution without axial dispersion was derived, and the accuracy was discussed in comparison with the numerical solutions. The model calculations gave a good agreement with the experimental extraction curve reported in literature.

Value-added subcritical water hydrolysate from rice bran and soybean meal

New value-added product was derived from agricultural by-products: rice bran and soybean meal by means of subcritical water (SW) hydrolysis. The effect of temperature (200-220 degrees C), reaction time (10-30 min), raw material-to-water weight ratio (1:5 and 2:5), was determined on the yields of protein, total amino acids, and reducing sugars in the soluble products. The suitable hydrolysis time was 30 min and the proper weight ratio of the raw material-to-water was 1:5. The reaction temperature suitable for the production of protein and amino acids was 220 degrees C for raw and deoiled rice bran, 210 degrees C for raw soybean meal, and 200 degrees C for deoiled soybean meal. The products were also found to have antioxidant activity as tested by ABTS(.)(+) scavenging assay. In addition, sensory evaluation of milk added with the hydrolysis product of deoiled rice bran indicated the potential use of the product as a nutritious drink.

The use of psychrometric charts for the optimisation of a thermal swing desiccant wheel

Abstract An effective prediction is proposed to estimate the optimal rotation speed and performance of a rotary adsorber, in which simultaneous enthalpy and humidity changes are dealt with separately by visualising changes of state of product or exhaust air on a psychrometric chart. Assuming that the adsorbent rotor is completely regenerated to equilibrium with the regeneration air during the corresponding period, the optimal rotation speed corresponds to the region of the short time adsorption in which penetration theory holds and enthalpy exchange between both streams through the adsorbent rotor follows the behaviour of a rotary sensible heat exchanger at lower revolution rates. The change of the product/exhaust air condition with increasing rotational speed is presented as a set of simple equations. Also, by considering the relative humidity of product air and that of regeneration air to be almost the same at a sufficiently high flow rates of regeneration air, an optimal rotation speed and the product air condition are easily found by simple calculation. In comparison with experiments, the proposed method gives a rotational speed near the “optimum” and the humidity and temperature of the product air are predicted almost exactly.

Pressurized hot water extraction of anthraquinones from the roots of Morinda citrifolia

This study examines pressurized hot water extraction of anthraquinones from dried roots of Morinda citrifolia (Noni). The effects of various operating conditions such as water temperature (110, 170, and 220 °C), and water flow rate (2, 4, and 6 mL min−1) on extraction yield and extraction rate were determined. At 220 °C, the extraction yield was the highest and was approximately 43.6 mg g−1. Subcritical water extraction at 4 mL min−1 or higher was found to be able to recover all the antraquinones present in the roots within 3 h of extraction, even at 170 °C. Pressure had no significant effect on the results for the range of temperatures studied. The flow rate of 6 mL min−1 resulted in the highest extraction rate, but the extraction efficiency, as measured by the amount of anthraquinones extracted per unit volume of water was lower than that of 4 mL min−1. Anthraquinones solubility in pressurized hot water was determined. The results indicate a presence of a mass transfer limitation in the extraction process from solid matrix.

Chemical compositions and antioxidant properties of essential oils from nine species of Turkish plants obtained by supercritical carbon dioxide extraction and steam distillation

Chemical compositions and antioxidant activities of essential oils from nine different species of Turkish plants, namely Melissa officinalis L., Rosmarinus officinalis L., Cuminum cyminum L., Piper nigrum L., Lavandula stoechas spp., Foeniculum vulgare, Pimpinella anisum L., Thymus serpyllum and Liquidamber orientalis Mill., were studied. Essential oils were obtained by supercritical carbon dioxide (SCCO2) extraction and steam distillation, and were analyzed by gas chromatography–mass spectrometry. The antioxidant activities of SCCO2 extraction and steam distillation extracts were tested by means of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Essential oils extracted by SCCO2 and steam distillation showed different compositions in different species. In the DPPH assay, R. officinalis, C. cyminum, P. anisum, T. serpyllum and L. orientalis essential oils obtained by SCCO2 extraction showed higher antioxidant activity than steam distillation extracts, with radical scavenging activities ranging from 87.1±0.23% to 92.0±0.34% compared with the butylated hydroxytoluene positive control (91.4±0.21%).

Supercritical CO2 extraction of essential oils and cuticular waxes from peppermint leaves

Essential oils and cuticular waxes were extracted from peppermint leaves with supercritical carbon dioxide in a semicontinuous-flow extractor. The effects of CO 2 flow rate and pressure on the extraction rate were studied within the flow rate range of (4.1-9.8)X10 -5 kg/s and the pressure range of 10-30 MPa. Flow rate effect indicated that the intraparticle diffusion resistance was not dominant in this process. The extraction rate of cuticular waxes increased remarkably with the pressure, whereas that of essential oils was almost constant as compared with cuticular waxes. The concentration of cuticular waxes at the exit of the extractor was close to the solubility of triacontane while that of essential oils was much lower than the solubility of 1-menthol.

Parabolic profile approximation (linear driving-force model) for chemical reactions

Abstract The parabolic approximation for the concentration profile inside a particle yields a substantial simplification in computations. The linear driving-force model for combined internal diffusion and external mass transfer arises from the approximation. We have applied this approximation to consider the time dependence of two cases of isothermal, irreversible, first-order chemical reaction in a spherical particle and in a slab: (1) when the reactant is a nondiffusing (adsorbed or solid) component initially inside the particle and the products diffuse out of the particle (e.g. for a reaction extraction), and (2) when the reactant is diffusing into the particle (e.g. for a catalytic reaction). The approximation is found to be satisfactory over a wide range of parameters for case (1). For case (2), however, the accuracy of the approximation is limited to small Biot numbers and Thiele moduli.

Depolymerization of polyethylene terephthalate in supercritical methanol

The degradation of polyethylene terephthalate (PET) in supercritical methanol was investigated with the aim of developing a process for chemical recycling of waste plastics. A batch reactor was used at temperatures of 573–623 K under an estimated pressure of 20 MPa for a reaction time of 2–120 min. PET was decomposed to its monomers, dimethyl terephthalate and ethylene glycol, by methanolysis in supercritical methanol. The reaction products were analysed using size-exclusion chromatography, gas chromatography–mass spectrometry, and reversed-phase liquid chromatography. The molecular weight distribution of the products was obtained as a function of reaction time. The yields of monomer components of the decomposition products including by-products were measured. Continuous kinetics analysis was performed on the experimental data.

Frontal analysis of protein adsorption on a membrane adsorber

The adsorption behaviour of two kinds of proteins, myoglobin and ovalbumin, with a membrane adsorber, DEAE MemSep 1000 (Millipore), was studied in comparison with a bead-based packed-bed adsorber, DEAE Sephacel (Pharmacia-LKB), by means of frontal analysis. Adsorption isotherms were obtained by integrating the breakthrough curves for various feed concentrations. Adsorption isotherms were expressed by the Langmuir equation and the adsorption capacity for the membrane adsorber was smaller than that for the packed-bed adsorber. The breakthrough curves of myoglobin for the membrane adsorber were independent of the flow-rate, but those of ovalbumin were affected by the flow-rate. Abnormal behaviour was observed for the adsorption of ovalbumin on a membrane adsorber. With the packed-bed adsorber, the breakthrough curves for both proteins were significantly affected by the flow-rate. A mathematical model for the membrane adsorber involving axial dispersion and adsorption kinetics was derived. The model simulated the breakthrough curves for myoglobin well. Axial dispersion was dominant for the membrane adsorber whereas intraparticle diffusion was dominant for the packed-bed adsorber.