Quantifying rate enhancements for acid catalysis in CO 2 -enriched high-temperature water

Thermodynamic calculations revealed that 10 to 100-fold increases in reaction rate are obtainable with added CO 2 (0.1–1 MPa) for an acid-catalyzed reaction in high-temperature liquid water (HTW) that is first order in H + concentration. These calculations suggest that CO 2 is most effective as a rate-enhancing additive in HTW at lower temperatures (150–200°C). When compared with increased temperature as a competitive option for accelerating acid-catalyzed reactions in HTW, CO 2 addition generally carries a lower pressure penalty (and no temperature penalty) for the model acid-catalyzed reaction with activation energies of up to 35 kcal/mol. An experimental survey revealed that CO 2 addition is effective for achieving increased reaction rates for dibenzyl ether hydrolysis in HTW, but that bisphenol A cleavage, methyl benzoate hydrolysis, and o -phthalic acid decarboxylation were not significantly impacted by added CO 2 . This behavior is consistent with previous results for these reactions wherein mineral acid, rather than CO 2 , was added to lower the pH. A summary of experimental results reported for reactions in CO 2 -enriched HTW revealed that product yields of some reactions can be increased by a factor of 23 with added CO 2 . Taken collectively, these results suggest that CO 2 addition may be a practical technique for making HTW more attractive as a reaction medium for acid-catalyzed organic synthesis. © 2007 American Institute of Chemical Engineers AIChE J, 2008Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57897/1/11392_ftp.pd

Crosslink Density Changes during the Hydrolysis of Tridimensional Polyesters

The hydrolysis of almost ideal networks based on macrodiols of average molar mass about 2 kg mol 1, with L¼18 ester groups per chain is studied. Tensile testing is used to evaluate the crosslink density through the statistical theory of rubber elasticity at two temperatures and three values of relative humidity. A kinetic model for ester consumption including an autocatalysis term is proposed and combined with two original approaches for modeling the crosslink density changes. This allows kinetic parameters of hydrolysis to be determined, and very good predictions are obtained for the variations of crosslink density (or elastic modulus) in the three aging conditions considered. The initial curvature of elastic modulus versus time is predicted positive for weak autocatalysis and negative for strong autocatalysis. The obtained conversion ratio at degelation is found to decrease sharply with the number of esters per elastically active chaincontrat de recherche SAFRAN - ART

アリンカイスイ エノ シボウサン ノ ヨウカイド ト シボウサン エステル ノ カスイ ブンカイ

京都大学0048新制・課程博士博士(農学)甲第10886号農博第1392号新制||農||888(附属図書館)学位論文||H16||N3897(農学部図書室)UT51-2004-G733京都大学大学院農学研究科食品生物科学専攻(主査)教授 安達 修二, 教授 井上 國世, 教授 北畠 直文学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDA

Properties of Extract from Okara by Its Subcritical Water Treatment

Okara was treated with subcritical water at temperatures ranging from 170 to 260°C for various times. After clarification, the extracts were analyzed for their protein and carbohydrate contents, DPPH radical scavenging activity, and antioxidative activity. The carbohydrate content significantly decreased with the increasing treatment temperature and time. The protein content, however, increased with the increasing treatment temperature and slightly decreased with a heating time longer than 10 min. The extract obtained from the subcritical water treatment at 240°C for 5 min, which would be used to evaluate the antioxidative activity, provided the relatively highest radical scavenging activity and the activity tended to decrease with the prolonging heating time and temperature. The extract also exhibited a suppressive activity to the autoxidation of linoleic acid with the increasing weight ratio of the extract to linoleic acid. The results clearly showed okara still contained highly valuable substances for human consumption

Isomerization and epimerization of glucose and galactose in arginine solution and phosphate buffer under subcritical fluid conditions

Reaction of glucose or galactose was performed in arginine solution or phosphate buffer (pH 7.0) using a batch reactor at 110°C. The yields of products, pH, and absorbances at 280 and 420 nm were measured during the reaction. Fructose, mannose, and allulose were formed from glucose; tagatose, talose, and sorbose were done from galactose. The reaction proceeded more rapidly in arginine solution than in phosphate buffer. In arginine solution, yields of fructose and tagatose were 20% and 16%, respectively, after 30-min reaction; in phosphate buffer, they were 14% and 10%, respectively. However, in both reaction media, the pH drop and increase in absorbances continued even after the yield became almost constant. The absorbance increased particularly in the latter half of the reaction due to formation of browning products. Therefore, to avoid browning, the reaction should be stopped as soon as possible after the yield approaches its maximum value

Isomerization of maltose to maltulose by microwave heating, using arginine as a catalyst

Microwave heating was applied to isomerize maltose to maltulose, using arginine as a catalyst. The initial molar ratio of arginine/maltose was kept constant at 0.05. Maltulose yields of 0.28-0.30 were achieved within 90-400 s, dependent on the microwave power and the volume of the substrate solution but not on the initial concentration of maltose, indicating that isomerization of maltose by microwave heating is highly productive. Independent of the power of the microwave oven and the volume of the substrate solution, the fraction of remaining maltose, the yield of maltulose, the pH of the reaction mixture, and its absorbance at 280 and 420 nm could be expressed as a function of energy density, which was defined as the amount of energy absorbed per unit volume of the reaction mixture. This indicates that the operating conditions for the isomerization of maltose to maltulose by microwave heating can be determined based on the energy density. Practical applications: Isomerization of aldose saccharides to their rare keto-isomers in the presence of arginine in a heated aqueous solution is a green and effective process. To further improve the process efficiency, microwave heating can be employed. This study also demonstrated that a so-called “energy density” can be used to determine the operating condition for the isomerization of sugar by microwave heating

Compositions, flavour and antiradical properties of products from subcritical water treatment of raw Isada krill

Comparative analysis of subcritical water (SCW) treatment and ambient pressure boiling one of raw Isada krill was performed for the nutritive, flavour and antiradical properties of krill extracts and residues as well as the molecular mass and odour intensity of the extract. SCW treatment was performed for 10 min in a batch-type vessel in the temperature range of 100–240 °C, using a 1:1 weight ratio of raw krill to water. Higher protein and lipid contents were obtained by SCW treatment relative to boiling. The lipid content of the SCW extracts increased with increasing treatment temperature. Protein was the main component in these extracts, and the highest protein content was achieved by SCW treatment at 200 °C. High-molecular-mass species decomposed under SCW treatment at high temperatures with consequent generation of smaller molecules. The antiradical activity of the SCW extract, determined by DPPH and ABTS assays, increased with increasing treatment temperature. The krill extracts and residues exhibited shrimp-like flavour, and the most desirable flavour was obtained by SCW treatment at 140 °C or 160 °C for 10 min. The treatment would be applicable for the production of seasonings from Isada krill

Subcritical Water Treatment for Producing Seasoning From Semidried Isada Krill

Semidried Isada krill (Euphausia pacifica) was treated with boiling water and subcritical water at 100–240C for 10 min with a semidried krill to a water ratio of 8/52 w/v to produce seasoning. The protein concentration, lipid content and odor concentration of the extract increased after increasing the treatment temperature. The highest protein content of the extract (0.047–0.049 kg/kg-extract) was obtained by subcritical water treatment at 180 or 200C. Compounds with lower molecular mass were detected in the extracts derived from subcritical water treatment at temperatures higher than 160C. The extract prepared by subcritical water treatment at 160 and 180C received the high score in the flavor preference test by a group of panelists. Treatment at temperatures lower and higher than 160–180C, respectively, conferred undesirable fishy and smoky or burnt odors to the extracts and residues

Decomposition kinetics of glucose and fructose in subcritical water containing sodium chloride

The kinetics of the decomposition and isomerization of glucose and fructose in pure water and water containing sodium chloride (1–20 % w/w) under subcritical conditions at 180–220 °C was investigated. The addition of sodium chloride in subcritical water accelerated the decrease of glucose, and the rate was expressed by the Weibull equation. Although the isomerization of glucose to fructose was observed in parallel with decomposition, the yield of fructose was lower at higher sodium chloride concentrations. Mannose was also formed from glucose with very low yield. It was seen that fructose decomposed much faster than glucose, in pure and salty subcritical water. The decomposition of fructose obeyed first-order kinetics in the initial stages of the reaction and could be expressed by the autocatalytic model in the later stages. The formation of glucose and mannose from fructose was not observed under any of the conditions investigated