The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
Refat M. Hassan - One of the best experts on this subject based on the ideXlab platform.
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Kinetics and mechanistic approach to the Chromic Acid oxidation of l-tryptophan with a spectral detection of chromium(III) product
Journal of Saudi Chemical Society, 2016Co-Authors: Ahmed Fawzy, Refat M. Hassan, Sheikha S. Ashour, M. A. Musleh, Basim H. AsgharAbstract:Abstract The kinetics of Chromic Acid oxidation of l -tryptophan in H 2 SO 4 medium at a constant ionic strength of 0.6 mol dm −3 and at 25 °C have been investigated spectrophotometrically. The reaction exhibits a 3:2 stoichiometry (tryptophan:Chromic Acid). The reaction shows a first order dependence on [Chromic Acid], a fractional-first order dependence on [tryptophan] and fractional-second order dependence on [Acid]. Increasing ionic strength and dielectric constant had no significant effect on the oxidation rate. The final oxidation products of tryptophan were identified as the corresponding aldehyde (indole-3-acetaldehyde), ammonium ion and carbon dioxide. A spectral evidence for the formation of chromium(III) product was obtained. The experimental results suggest formation of an intermediate complex between the protonated tryptophan and Chromic Acid which decomposes in the rate-determining step to yield the products. The mechanism of such reaction has been proposed. The thermodynamic parameters with respect to the first step of the suggested mechanism were evaluated and discussed.
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kinetics and mechanism of oxidation of chondroitin 4 sulfate polysaccharide by Chromic Acid in aqueous perchlorate solutions
Carbohydrate Polymers, 2013Co-Authors: Refat M. Hassan, Ishaq A. Zaafarany, Samia M Ibrahim, Abdelrahman A Dahy, Fahd A Tirkistani, Hideo D. TakagiAbstract:The kinetics of Chromic Acid oxidation of chondroitin-4-sulfate polysaccharide as sulfated carbohydrates at a constant ionic strength of 4.0 mol dm(-3) has been investigated, spectrophotometrically. The reaction kinetics showed a first-order dependence in Chromic Acid and fractional-first-order kinetics with respect to the chondroitin-4-sulfate concentration. The influence of [H(+)] on the reaction rates showed that the oxidation process is Acid-catalyzed. Added Mn(2+) ions indicated the formation of Cr(IV) as intermediate species. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The kinetic parameters have been evaluated and a tentative reaction mechanism in good consistent with the kinetic results obtained is discussed.
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Acid-catalyzed oxidation of carboxymethyl cellulose polysaccharide by Chromic Acid in aqueous perchlorate solutions. A kinetics study
Catalysis Communications, 2010Co-Authors: Refat M. Hassan, Saddek M. Ahmed, Ahmed Fawzy, Doaa A. Abdel-kader, Yasuhisa Ikeda, Hideo D. TakagiAbstract:Abstract The Acid-catalysis of Chromic Acid oxidation of carboxymethyl cellulose (CMC) as a polysaccharide in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm−3 have been investigated spectrophotometrically. The experimental results showed first-order kinetics in Chromic Acid and fractional first-order dependence with respect to [CMC]. A kinetic evidence for the formation of 1:1 complex between Chromic Acid and CMC was revealed. The hydrogen ion dependence of the reaction rates showed that the oxidation process is Acid-catalyzed. Induced polymerization of acrylonitrile indicated that the oxidation process proceeds by free-radical mechanism. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is suggested.
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Acid-catalysis of Chromic Acid oxidation of kappa-carrageenan polysaccharide in aqueous perchlorate solutions
Journal of Molecular Catalysis A-chemical, 2008Co-Authors: Ishaq A. Zaafarany, Khalid S. Khairou, Refat M. HassanAbstract:Abstract The Acid-catalyzed oxidation of kappa-carrageenan (KCAR) polysaccharide as a natural polymer by Chromic Acid in aqueous perchloric Acid at a constant ionic strength of 4.0 mol dm −3 have been investigated spectrophotometrically. A first-order reaction in Chromic Acid and a fractional-order with respect to KCAR concentrations were revealed. A kinetic evidence for the formation of 1:2 complex between Chromic Acid and KCAR is presented. The influence of hydrogen ion concentrations on the reaction rates showed that the oxidation process is Acid-catalyzed. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is discussed.
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Kinetics and mechanism of oxidation of poly(vinyl alcohol) macromolecule by Chromic Acid in aqueous perchloric Acid
European Polymer Journal, 2001Co-Authors: M. I. Abdel-hamid, Gamal A. Ahmed, Refat M. HassanAbstract:Abstract The kinetics of Chromic Acid oxidation of poly(vinyl alcohol) (PVA), a synthetic polymer, in perchlorate media at a constant ionic strength of 1.0 mol dm −3 has been studied spectrophotometrically. A first-order reaction in Chromic Acid and a fractional order with respect to PVA concentration were observed. The reaction was found to be Acid catalyzed. Kinetic evidence for the formation of an intermediate complex between the Chromic Acid and PVA is presented. A mechanism consistent with the kinetic results is suggested.
Matthias Wessling - One of the best experts on this subject based on the ideXlab platform.
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Chromic Acid recovery by electro-electrodialysis. I. Evaluation of anion-exchange membrane
Journal of Membrane Science, 2005Co-Authors: Ines Frenzel, H. Holdik, Dimitrios Stamatialis, Gérald Pourcelly, Matthias WesslingAbstract:Electro-electrodialysis (EED) is a promising technology for economic recovery of Chromic Acid in plating shops. It could potentially achieve Chromic Acid recovery, removal of metallic impurities and purification of static rinses in one step. There are however, process limitations. These are mainly, the poor stability of the applied anion-exchange membrane (AEM) against the oxidative Chromic Acid solution and the increase of the AEM resistance, especially at the starting phase of the process, due to the formation of polychromates in the membrane. In this work, various AEM are investigated for Chromic Acid recovery. The membrane fumasep® FAP (FuMA-Tech GmbH) seems to be the most efficient. Its current efficiency is much higher than those previously reported in the literature. Furthermore, the fumasep® FAP is used for process optimisation experiments. The process performance depends on the concentration gradient between product (anolyte) and central compartment (exhausted rinse water) and the temperature. Our results show that batch processing is recommended and the chromate transfer rates through the AEM could be significantly increased when increasing the temperature up to 50 °C. Finally, low initial current density (10?20 mA cm?2), feed flow rate higher than 7 cm s?1 could help overcoming the process limitations attributed to high AEM resistance.
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Chromic Acid recovery by electro-electrodialysis. II. Pilot scal process, development, and optimization
Separation and Purification Technology, 2005Co-Authors: Ines Frenzel, H. Holdik, Dimitrios Stamatialis, Gérald Pourcelly, Matthias WesslingAbstract:Electro-electrodialysis is a promising technology for Chromic Acid recovery and static rinse water purification. It combines the recovery of the plating chemicals from rinse water, the elimination of metallic impurities from the process and rinse water treatment in one step. Previous industrial use was restricted due to non-resistant anion-exchange membranes and process ineffectiveness. In this work, a stable and economical process is developed and high-quality Chromic Acid is recovered using a new oxidative stable anion exchange membrane (AEM Fumasep® FAP, FuMA-Tech GmbH). The membrane stability and performance is evaluated by a long-term experiment for 400 h. Recovery rates were determined for batch and continuous operation and at different operation temperatures. The highest Chromic Acid production was reached by batch processing at 40 °C. Both measures increase significantly the chromate transfer and result in lower equipment size and operational costs
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Chromic Acid recovery by electro-electrodialysis
Separation and Purification Technology, 2005Co-Authors: Ines Frenzel, H. Holdik, Dimitrios Stamatialis, Gérald Pourcelly, Matthias WesslingAbstract:Electro-electrodialysis is a promising technology for Chromic Acid recovery and static rinse water purification. It combines the recovery of the plating chemicals from rinse water, the elimination of metallic impurities from the process and rinse water treatment in one step. Previous industrial use was restricted due to non-resistant anion-exchange membranes and process ineffectiveness. In this work, a stable and economical process is developed and high-quality Chromic Acid is recovered using a new oxidative stable anion exchange membrane (AEM Fumasep® FAP, FuMA-Tech GmbH). The membrane stability and performance is evaluated by a long-term experiment for 400 h. Recovery rates were determined for batch and continuous operation and at different operation temperatures. The highest Chromic Acid production was reached by batch processing at 40 °C. Both measures increase significantly the chromate transfer and result in lower equipment size and operational cost
Qiwei Pan - One of the best experts on this subject based on the ideXlab platform.
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surface modification of ultra high molecular weight polyethylene fibers by Chromic Acid
Surface and Interface Analysis, 2016Co-Authors: Li Meng, Lun Wang, Qiwei PanAbstract:Ultra-high molecular weight polyethylene (UHMWPE) fibers were modified by Chromic Acid. The effects of surface modification were evaluated with Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electron microscope (SEM). The results showed that both the content of O-containing functional groups and surface roughness of modified fibers increased. The polar groups on the modified fiber surface decreased the contact angles with water and ethylene glycol, as evidenced by contact angle measurement. The tensile test results showed the strength and the elongation at break of UHMWPE fibers decreased but the modulus increased after Chromic Acid modification. Copyright © 2016 John Wiley & Sons, Ltd.
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Surface modification of ultra‐high molecular weight polyethylene fibers by Chromic Acid
Surface and Interface Analysis, 2016Co-Authors: Li Meng, Lun Wang, Qiwei PanAbstract:Ultra-high molecular weight polyethylene (UHMWPE) fibers were modified by Chromic Acid. The effects of surface modification were evaluated with Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), contact angle measurement, and scanning electron microscope (SEM). The results showed that both the content of O-containing functional groups and surface roughness of modified fibers increased. The polar groups on the modified fiber surface decreased the contact angles with water and ethylene glycol, as evidenced by contact angle measurement. The tensile test results showed the strength and the elongation at break of UHMWPE fibers decreased but the modulus increased after Chromic Acid modification. Copyright © 2016 John Wiley & Sons, Ltd.
Ines Frenzel - One of the best experts on this subject based on the ideXlab platform.
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Chromic Acid recovery by electro-electrodialysis. I. Evaluation of anion-exchange membrane
Journal of Membrane Science, 2005Co-Authors: Ines Frenzel, H. Holdik, Dimitrios Stamatialis, Gérald Pourcelly, Matthias WesslingAbstract:Electro-electrodialysis (EED) is a promising technology for economic recovery of Chromic Acid in plating shops. It could potentially achieve Chromic Acid recovery, removal of metallic impurities and purification of static rinses in one step. There are however, process limitations. These are mainly, the poor stability of the applied anion-exchange membrane (AEM) against the oxidative Chromic Acid solution and the increase of the AEM resistance, especially at the starting phase of the process, due to the formation of polychromates in the membrane. In this work, various AEM are investigated for Chromic Acid recovery. The membrane fumasep® FAP (FuMA-Tech GmbH) seems to be the most efficient. Its current efficiency is much higher than those previously reported in the literature. Furthermore, the fumasep® FAP is used for process optimisation experiments. The process performance depends on the concentration gradient between product (anolyte) and central compartment (exhausted rinse water) and the temperature. Our results show that batch processing is recommended and the chromate transfer rates through the AEM could be significantly increased when increasing the temperature up to 50 °C. Finally, low initial current density (10?20 mA cm?2), feed flow rate higher than 7 cm s?1 could help overcoming the process limitations attributed to high AEM resistance.
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Chromic Acid recovery by electro-electrodialysis. II. Pilot scal process, development, and optimization
Separation and Purification Technology, 2005Co-Authors: Ines Frenzel, H. Holdik, Dimitrios Stamatialis, Gérald Pourcelly, Matthias WesslingAbstract:Electro-electrodialysis is a promising technology for Chromic Acid recovery and static rinse water purification. It combines the recovery of the plating chemicals from rinse water, the elimination of metallic impurities from the process and rinse water treatment in one step. Previous industrial use was restricted due to non-resistant anion-exchange membranes and process ineffectiveness. In this work, a stable and economical process is developed and high-quality Chromic Acid is recovered using a new oxidative stable anion exchange membrane (AEM Fumasep® FAP, FuMA-Tech GmbH). The membrane stability and performance is evaluated by a long-term experiment for 400 h. Recovery rates were determined for batch and continuous operation and at different operation temperatures. The highest Chromic Acid production was reached by batch processing at 40 °C. Both measures increase significantly the chromate transfer and result in lower equipment size and operational costs
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Chromic Acid recovery by electro-electrodialysis
Separation and Purification Technology, 2005Co-Authors: Ines Frenzel, H. Holdik, Dimitrios Stamatialis, Gérald Pourcelly, Matthias WesslingAbstract:Electro-electrodialysis is a promising technology for Chromic Acid recovery and static rinse water purification. It combines the recovery of the plating chemicals from rinse water, the elimination of metallic impurities from the process and rinse water treatment in one step. Previous industrial use was restricted due to non-resistant anion-exchange membranes and process ineffectiveness. In this work, a stable and economical process is developed and high-quality Chromic Acid is recovered using a new oxidative stable anion exchange membrane (AEM Fumasep® FAP, FuMA-Tech GmbH). The membrane stability and performance is evaluated by a long-term experiment for 400 h. Recovery rates were determined for batch and continuous operation and at different operation temperatures. The highest Chromic Acid production was reached by batch processing at 40 °C. Both measures increase significantly the chromate transfer and result in lower equipment size and operational cost
Hideo D. Takagi - One of the best experts on this subject based on the ideXlab platform.
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kinetics and mechanism of oxidation of chondroitin 4 sulfate polysaccharide by Chromic Acid in aqueous perchlorate solutions
Carbohydrate Polymers, 2013Co-Authors: Refat M. Hassan, Ishaq A. Zaafarany, Samia M Ibrahim, Abdelrahman A Dahy, Fahd A Tirkistani, Hideo D. TakagiAbstract:The kinetics of Chromic Acid oxidation of chondroitin-4-sulfate polysaccharide as sulfated carbohydrates at a constant ionic strength of 4.0 mol dm(-3) has been investigated, spectrophotometrically. The reaction kinetics showed a first-order dependence in Chromic Acid and fractional-first-order kinetics with respect to the chondroitin-4-sulfate concentration. The influence of [H(+)] on the reaction rates showed that the oxidation process is Acid-catalyzed. Added Mn(2+) ions indicated the formation of Cr(IV) as intermediate species. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The kinetic parameters have been evaluated and a tentative reaction mechanism in good consistent with the kinetic results obtained is discussed.
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Acid-catalyzed oxidation of carboxymethyl cellulose polysaccharide by Chromic Acid in aqueous perchlorate solutions. A kinetics study
Catalysis Communications, 2010Co-Authors: Refat M. Hassan, Saddek M. Ahmed, Ahmed Fawzy, Doaa A. Abdel-kader, Yasuhisa Ikeda, Hideo D. TakagiAbstract:Abstract The Acid-catalysis of Chromic Acid oxidation of carboxymethyl cellulose (CMC) as a polysaccharide in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm−3 have been investigated spectrophotometrically. The experimental results showed first-order kinetics in Chromic Acid and fractional first-order dependence with respect to [CMC]. A kinetic evidence for the formation of 1:1 complex between Chromic Acid and CMC was revealed. The hydrogen ion dependence of the reaction rates showed that the oxidation process is Acid-catalyzed. Induced polymerization of acrylonitrile indicated that the oxidation process proceeds by free-radical mechanism. The kinetic parameters have been evaluated and a tentative reaction mechanism consistent with the kinetic results is suggested.