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Subcritical Water (subcritical + water)
Selected AbstractsSUBCRITICAL WATER EXTRACTION OF CAFFEINE FROM BLACK TEA LEAF OF IRANJOURNAL OF FOOD PROCESS ENGINEERING, Issue 3 2008ANVAR SHALMASHI ABSTRACT This study examines subcritical water extraction (SCWE) of caffeine from black tea leaf. The effects of various operating conditions such as water temperature (100, 125, 150 and 175C), water flow rate (1, 2 and 4 g/min), mean particle size (0.5, 1 and 2 mm) on extraction yield and rate were determined. SCWE at 175C, water flow rate of 2 g/min and mean particle size of 0.5 mm were found to be able to recover 3.82% (w/w) of caffeine present in the black tea leaf within 3 h of extraction. In comparison to the SCWE, conventional hot water extraction showed 3.30% (w/w) extraction yield. It was found also that pressure had no effect on extraction yield and rate. PRACTICAL APPLICATIONS Recently, subcritical water has become of great interest as an alternative solvent for extraction of natural active compounds. Subcritical water, as a green solvent, can be used in many different fields of applications. In recent years, extraction of flavors, fragrances and antioxidant components from plant materials, and hydrolysis of carbohydrates, vegetable oils and fatty acids have been widely investigated by many researchers. Using subcritical water for analytical purposes, for soil remediation and applying it as a reaction media are some other interesting fields for practical applications. Subcritical water is an excellent solvent for caffeine as well as many other organic compounds but is safer than the organic solvents that are used for caffeine extraction. [source] Evaluation of 08CH18N10T stainless steel corrosion in subcritical water by electrochemical noise analysisMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2008P. Ku Abstract The corrosion behaviour of pressurized water reactor (PWR) steam generator tube material (08CH18N10T steel) was studied by electrochemical noise (EN) measurements and electrochemical impedance spectroscopy in high-temperature water at 280,°C and 8 MPa. Long-term measurements were performed in two electrolytes: (i) deionised water alkalized to pH25,=,9.5 by KOH; (ii) the same electrolyte with 200 ppm of chlorides added (as KCl). The noise data were processed by two filtering methods and the noise resistance and spectral noise resistance values were calculated. Different contributions to the total impedance were identified and the polarization resistance values were calculated from EIS data. Noise and polarization resistances were compared and the influence of filtering methods was discussed. Instantaneous corrosion data were transformed to integral ones and comparison with mean corrosion current estimated from the oxide thickness was made. It was confirmed that the crucial point of EN analysis is selection of proper cut-off frequency in high-pass fast Fourier transform (HP-FFT). [source] Subcritical Water Reaction Behavior of D -Glucose as a Model Compound for Biomass Using Two Different Continuous-Flow Reactor ConfigurationsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2009T. Saito Abstract Recently, cellulosic materials have been considered as a useful resource for the recovery of valuable chemicals and liquid fuels, etc. Cellulose is a homopolymer of D -glucose, which is often used as a model compound for biomass. Reactions of D -glucose in subcritical water as the reaction solvent were conducted using a single-flow-type reactor (S1) and an admixture-type reactor with feed and preheated-water flow (S2) at temperatures from 200 to 240,°C, pressures from 15 to 20 MPa, residence times from 40 to 120 s, and initial feed concentrations of 1.5,10 wt %. D -Glucose was converted into aldehydes, organic acids and furans, with mainly organic acids obtained at 240,°C. D -Glucose decomposition using reactors S1 and S2 revealed that the conversion rate of D -glucose was promoted more using S2 than by S1. The yield of furans with S1 was higher than with S2, while the yield of organic acids from S1 was lower than that from S2. [source] | ||||||||||