Showing papers by "Shiro Saka published in 2003"

Pyrolysis behavior of levoglucosan as an intermediate in cellulose pyrolysis: polymerization into polysaccharide as a key reaction to carbonized product formation

Abstract: Pyrolysis behavior of levoglucosan (1,6-anhydro-β-d-glucopyranose), the major anhydromonosaccharide formed during cellulose pyrolysis, was studied at 250°–400°C under nitrogen. The pyrolysis products were found to change stepwise: levoglucosan → MeOH-soluble fraction (lower-molecular-weight products and oligosaccharides) → water-soluble fraction (polysaccharides) → insoluble fraction (carbonized products). From the present experimental results, a pathway of cellulose pyrolysis via anhydromonosaccharide is proposed including polymerization to polysaccharides (a reversible reaction) as a key reaction to carbonized product formation.

Comparison of the decomposition behaviors of hardwood and softwood in supercritical methanol.

Abstract: The chemical conversion of Japanese beech (Fagus crenata Blume) and Japanese cedar (Cryptomeria japonica D. Don) woods in supercritical methanol was studied using the supercritical fluid biomass conversion system with a batch-type reaction vessel. Under conditions of 270°C/27 MPa, beech wood was decomposed and liquefied to a greater extent than cedar wood, and the difference observed was thought to originate mainly from differences in the intrinsic properties of the lignin structures of hardwood and softwood. However, such a difference was not observed at 350°C/43 MPa, and more than 90% of both beech and cedar woods were effectively decomposed and liquefied after 30 min of treatment. This result indicates that the supercritical methanol treatment is expected to be an efficient tool for converting the woody biomass to lower-molecular-weight products, such as liquid fuels and useful chemicals.

Reactivity of lignin in supercritical methanol studied with various lignin model compounds

Abstract: Behavior of lignin in supercritical methanol (250–270°C, 24–27 MPa) was studied by using lignin model compounds at the tin bath temperature of 270°C with a batch-type reaction vessel. Guaiacol and veratrole were selected as a guaiacyl type of aromatic ring in lignin, while 2,6-dimethoxyphenol and 1,2,3-trimethoxybenzene as a syringyl one. In addition, biphenyl and β-O-4 types of dimeric lignin model compounds were, respectively, studied as condensed and ether linkages between C6-C3 phenyl propane units. As a result, both guaiacyl and syringyl types of aromatic rings were very stable, and the biphenyl type was comparatively stable under supercritical conditions of methanol. However, β-ether linkage in the phenolic β-O-4 model compound was cleaved rapidly into guaiacol and coniferyl alcohol, which was further converted to its γ-methyl ether. Non-phenolic β-O-4 model compound was, on the other hand, converted initially into its α-methyl ether and degraded further to produce guaiacol. These lines of evidence imply that in lignin macromolecules, the new phenolic residues are continuously formed and depolymerized repeatedly in supercritical methanol into the lower molecular products, mainly by the cleavage of the dominant β-ether structure in lignin.

Reaction behavior of lignin in supercritical methanol as studied with lignin model compounds

Abstract: The reaction behavior and kinetics of lignin model compounds were studied in supercritical methanol with a batch-type supercritical biomass conversion system. Guaiacol, veratrole, 2,6-dimethoxyphenol, and 1,2,3-trimethoxybenzene were used as model compounds for aromatic rings in lignin. In addition, 5-5, β-1, β-O-4, and α-O-4 types of dimeric lignin model compounds were used as representatives of linkages in lignin. As a result, aromatic rings and 5-5 (biphenyl)-type structures were stable in supercritical methanol, and the β-1 linkage was not cleaved in the β-1-type structure but converted rapidly to stilbene. On the other hand, β-ether and α-ether linkages of β-O-4 and α-O-4 lignin model compounds were cleaved rapidly, and these compounds decomposed to some monomeric compounds. Phenolic compounds were found to be more reactive than nonphenolic compounds. These results indicate that cleavages of ether linkages mainly contribute to the depolymerization of lignin, whereas condensed linkages such as the 5-5 and β-1 types are not cleaved in supercritical methanol. Therefore, it is suggested that the supercritical methanol treatment effectively depolymerizes lignin into the lower-molecular-weight products as a methanol-soluble portion mainly by cleavage of the β-ether structure, which is the dominant linkage in lignin.

Photocatalytic activity of TiO2 crystallite-activated carbon composites prepared in supercritical isopropanol for the decomposition of formaldehyde

Abstract: An effort was made to develop photocatalytic TiO2 crystallite–activated carbon (TiO2-AC) composites from tetraisopropyl titanate (TPT)-soaked activated carbon in supercritical isopropanol. It was subsequently found that TPT in supercritical isopropanol could be effectively converted to the anatase form of the TiO2 crystallites. The prepared composites, composed of activated carbon as an adsorbent and the anatase form of TiO2 as a photocatalyst, were evaluated for their adsorption capacity and subsequent photocatalytic activity against formaldehyde, one of the harmful air pollutants in the environment. As a result, the supercritically treated TiO2–AC composites, particularly at 300°C and 350°C, had much higher formaldehyde-decomposing ability compared to a noncomposite comprising a simple mixture of activated carbon and TiO2 granules. This indicates that the supercritical treatment can be effective for preparing the photocatalytic composites that have a high synergetic effect of adsorption and photocatalytic decomposition of formaldehyde for environmental cleaning.

Process for producing fatty acid alkyl ester composition

Abstract: A process for producing a fatty acid alkyl ester composition in a reaction system in which water and a free fatty acid are present. It eliminates problems in the alkali catalyst method in current use which are associated with catalyst separation/recovery and excess catalyst consumption by a free fatty acid contained in a starting material. It further eliminates problems concerning the necessity of a large excess of an alcohol in the conventional supercritical methanol method. The process, which is for producing a fatty acid alkyl ester composition from one or more fat compounds comprising a fatty acid glyceride and/or a fatty acid, is characterized by reacting the fat compounds under the conditions of a temperature of 100 to 370°C and a pressure of 1 to 100 MPa in the presence of an alcohol and/or water.

Method for hydrolyzing polysaccharide substance

Abstract: PROBLEM TO BE SOLVED: To provide a method for hydrolyzing a polysaccharide substance, by which saccharides such as glucose can selectively and efficiently be produced from a polysaccharide substance such as cellulose in semi-critical or supercritical water as a solvent. SOLUTION: This method for hydrolyzing the polysaccharide substance, comprising bringing the polysaccharide substance such as cellulose into contact with the semi-critical or supercritical water, is characterized by making a quinone compound coexistent in the reaction system. Thereby, the polysaccharide substance can selectively and quickly be hydrolyzed. COPYRIGHT: (C)2005,JPO&NCIPI

Method for producing fatty acid alkyl ester composition

Abstract: An object of the present invention is to solve a problem of separation and recovery of catalysts present in an alkali metal catalytic method currently often used, a problem of excess consumption of a catalyst by a free fatty acid in a raw material, and other problems, and to solve a problem of the presence of a large excess amount of alcohol in a conventional supercritical methanol method, and to provide a method for producing a fatty acid alkyl ester composition in a reaction system containing water and free fatty acid present. The present invention has attained the above-mentioned object by provided a method for producing a fatty acid alkyl ester composition using fats and oils containing a fatty acid glyceride and/or fatty acid, wherein alcohol and/or water is allowed to co-exist with the above-mentioned fats and oils and the reaction is conducted under conditions of a temperature of 100° C. to 370° C. and a pressure of 1 to 100 MPa.