Totally found 282 items.

  • [期刊] Effects of acetic acid addition methods on butyl acetate enzymatic synthesis
    Butyl acetate is a versatile chemical due to its excellent solvency for polymers, resins, and oils. In this work, the butyl acetate synthesis was studied by the esterification of n-butanol with acetic acid using the commercial immobilized lipase Novozym (R) 435. The acetic acid and n-butanol concentrations have to be limited in the enzymatic synthesis of this ester due to the deleterious effects caused by these reagents on the enzyme. Three methods of acetic acid addition (single, stepwise and continuous addition) were investigated to minimize the acid concentration. A significant drop on acid conversion was observed in the presence of a higher concentration of the reagents when single or stepwise acid addition was used. However, a solvent-free system using a continuous addition of acetic acid favored butyl acetate synthesis, reaching a conversion of 84% at 60 degrees C, employing 5 wt% of enzyme and n-butanol/acetic acid final molar ratio equal to 1/1.
  • [期刊] Hexavalent chromium removal by polyacrylic acid-grafted Macadamia nutshell powder through adsorption-reduction mechanism: Adsorption isotherms, kinetics and thermodynamics
    Hydrochloric acid-treated Macadamia nutshell (AMM) powder was grafted with acrylic acid monomers at different doses of 0.5, 1.0 and 2.0 M to incorporate the carboxylic groups on its surface. The grafted materials were labeled 0.5 GAM, 1 GAM and 2 GAM signifying the grafting ratios. The incorporation of acrylic acid was demonstrated by an increase in oxygen content from 0.18% to 1.20% in the elemental analysis. The splitting and shifting of the alcohol intermolecular bonded -OH functional groups at 3330 cm(-1) to 3396 and 3321 cm(-1) observed after grafting was further proof of the addition of acrylic acid. Scanning electron microscopy (SEM) images revealed that the materials exhibited stacked sheets with spherical halo openings typical of biomaterials. The maximum conditions for chromium(VI) removal were obtained at pH 2, 180 min contact time, 7.5 g/L adsorbent dosage concentration and a temperature of 40 degrees C. The adsorption mechanism was best described by the monolayer sorption postulated by Langmuir with reported adsorption capacity of 39.21 mg/g. The best fit for the kinetic data was obtained with the pseudo-second-order rate model suggesting a chemisorption nature of interaction. Accordingly, the thermodynamic factors were feasible, spontaneous and endothermic. The acrylic acid-functionalized Macadamia adsorbent showed greater potential compared to other biosorbents in the removal of hexavalent chromium from aqueous solution in the presence of competing anions.
  • [期刊] Hexavalent chromium removal by polyacrylic acid-grafted Macadamia nutshell powder through adsorption-reduction mechanism: Adsorption isotherms, kinetics and thermodynamics
    Hydrochloric acid-treated Macadamia nutshell (AMM) powder was grafted with acrylic acid monomers at different doses of 0.5, 1.0 and 2.0 M to incorporate the carboxylic groups on its surface. The grafted materials were labeled 0.5 GAM, 1 GAM and 2 GAM signifying the grafting ratios. The incorporation of acrylic acid was demonstrated by an increase in oxygen content from 0.18% to 1.20% in the elemental analysis. The splitting and shifting of the alcohol intermolecular bonded -OH functional groups at 3330 cm(-1) to 3396 and 3321 cm(-1) observed after grafting was further proof of the addition of acrylic acid. Scanning electron microscopy (SEM) images revealed that the materials exhibited stacked sheets with spherical halo openings typical of biomaterials. The maximum conditions for chromium(VI) removal were obtained at pH 2, 180 min contact time, 7.5 g/L adsorbent dosage concentration and a temperature of 40 degrees C. The adsorption mechanism was best described by the monolayer sorption postulated by Langmuir with reported adsorption capacity of 39.21 mg/g. The best fit for the kinetic data was obtained with the pseudo-second-order rate model suggesting a chemisorption nature of interaction. Accordingly, the thermodynamic factors were feasible, spontaneous and endothermic. The acrylic acid-functionalized Macadamia adsorbent showed greater potential compared to other biosorbents in the removal of hexavalent chromium from aqueous solution in the presence of competing anions.
  • [期刊] Effects of acetic acid addition methods on butyl acetate enzymatic synthesis
    Butyl acetate is a versatile chemical due to its excellent solvency for polymers, resins, and oils. In this work, the butyl acetate synthesis was studied by the esterification of n-butanol with acetic acid using the commercial immobilized lipase Novozym (R) 435. The acetic acid and n-butanol concentrations have to be limited in the enzymatic synthesis of this ester due to the deleterious effects caused by these reagents on the enzyme. Three methods of acetic acid addition (single, stepwise and continuous addition) were investigated to minimize the acid concentration. A significant drop on acid conversion was observed in the presence of a higher concentration of the reagents when single or stepwise acid addition was used. However, a solvent-free system using a continuous addition of acetic acid favored butyl acetate synthesis, reaching a conversion of 84% at 60 degrees C, employing 5 wt% of enzyme and n-butanol/acetic acid final molar ratio equal to 1/1.
  • [期刊] Kinetic study of isopropyl palmitate synthesis catalyzed by lipases immobilized on a magnetic copolymer support
    Synthesis experiments of isopropyl palmitate, an emollient ester, were conducted using various reactant molar ratios and enzyme concentrations. Reactions were catalyzed by Candida rugosa or Penicillium camemberti lipases immobilized on magnetic poly(styrene-co-divinylbenzene). A kinetic model for the esterification reaction was developed based on a ping-pong bi-bi mechanism and validated with the experimental data obtained herein. Systems with different catalysts were compared, and correlations were found between parameters. Satisfactory predictions were obtained through curve fitting (R-2 of 0.89 for C. rugosa and R-2 of 0.92 for P. camemberti).
  • [期刊] Evolution mechanism of active groups and thermal effects of Chinese lignite in low-temperature oxidation
    The evolution of active groups at low temperature was examined using Chinese lignite by infrared technology and X-ray photoelectron spectroscopy (XPS). The results showed that the hydroxyl, aliphatic ether, methylene, and methyl groups played important roles in the low-temperature oxidation of lignite below 200 degrees C. Carbonyl and carboxyl groups were important intermediates. Thus, a multi-step evolution mechanism involving the hydroxyl, aliphatic ether groups, and alkane was reasoned to describe the low-temperature oxidation of lignite. In addition, according to the oxidation kinetics experiment and the evolution laws of the active groups, the ratios of the reaction lines were determined considering the accuracy of thermal effects. The thermal effects and the heat release intensities of each temperature interval were obtained based on the evolution mechanism and the reaction ratios. The shortest spontaneous combustion period of lignite was calculated and compared with the experimental value, which proved that the reasoned evolution mechanism of the active groups and the calculations of the thermal effects were reliable.
  • [期刊] Kinetic study of isopropyl palmitate synthesis catalyzed by lipases immobilized on a magnetic copolymer support
    Synthesis experiments of isopropyl palmitate, an emollient ester, were conducted using various reactant molar ratios and enzyme concentrations. Reactions were catalyzed by Candida rugosa or Penicillium camemberti lipases immobilized on magnetic poly(styrene-co-divinylbenzene). A kinetic model for the esterification reaction was developed based on a ping-pong bi-bi mechanism and validated with the experimental data obtained herein. Systems with different catalysts were compared, and correlations were found between parameters. Satisfactory predictions were obtained through curve fitting (R-2 of 0.89 for C. rugosa and R-2 of 0.92 for P. camemberti).
  • [期刊] A facile one pot synthesis of highly stable PVA-CuO hybrid nanofluid for heat transfer application
    In this paper, we report in-situ preparation of polyvinyl alcohol (PVA)-copper oxide (CuO) nanocomposite by sol-gel method and the preparation of highly stable PVA-CuO hybrid nanofluid. This novel method combines the advantages of both the single step and two step methods of preparation of nanofluid. The prepared nanofluid is found to be stable up to 12 months under static conditions. Fourier Transform Infrared (FTIR) spectroscopy and X-Ray Diffraction (XRD) pattern confirmed the formation of monoclinic CuO and the interaction between PVA and CuO nanoparticles. The nanofluid was characterized by Transmission Electron Microscope (TEM) and it revealed the formation of ribbon shaped CuO embedded in PVA. High resolution TEM (HRTEM) image shows that the nanoribbons are actually made up of about 4 nm sized CuO crystallites. Stability of the nanofluids for various concentrations of the PVA was investigated by Zeta Potential measurements, UV-Vis spectroscopy, and photo capturing methods. It shows that 0.5 wt% PVA-CuO hybrid nanofluid results in highest stability. Particle size analysis using Dynamic Light Scattering (DLS) showed that 0.125 wt% of PVA resulted in large agglomerates due to insufficient capping. Thermal conductivity of the nanofluid was also measured using hot wire method and it showed enhancement over the base fluid.
  • [期刊] Investigation of crystal growth of borax in single and dual impeller batch cooling crystallizer
    The purpose of this work was to investigate and compare the influence of fluid flow in a single and dual impeller batch cooling crystallizer on crystal growth kinetics of borax decahydrate. Examinations were conducted in a crystallizer of 15 dm(3) stirred by a single pitched blade turbine and straight blade turbine as well as their dual configurations. Kinetics parameters of crystal growth determined at applied mixing conditions were correlated with hydrodynamic conditions. In this paper, hydrodynamics was characterized by mixing time, which was experimentally determined, and by fluid flow patterns, which were simulated by the means of computational fluid dynamic (CFD). It was found that although the crystal growth in all systems investigated was controlled by the integration mechanism, the crystal growth rate constant changed significantly with impeller configuration. Regarding the characteristics of the final product, a dependence of the crystal size distribution on the fluid flow pattern was noticed while the number of impellers did not affect the product properties. On the other hand, mixing efficiency differed significantly with the type and number of impellers.
  • [期刊] Production of racemic acetoin by fermentation using Lactobacillus casei
    An aqueous two-phase system (ATPS) was used to extract enantioenriched acetoin produced by Lactobacillus casei using an isopropyl alcohol/potassium carbonate mixture. Saturation of the aqueous layer with potassium carbonate (40% w/w) at 50 degrees C with stirring for 2 h led to racemization of acetoin with a 50/50 ratio of the R/S enantiomers, respectively. Racemization of acetoin was found to be dependent primarily on increasing pH, while elevated temperatures (50 degrees C) also had an effect on the rate of racemization of acetoin in alkaline environments. Extraction with isopropyl alcohol (35% v/v), allowed a recovery of 94.3% of acetoin after 12 h of separation time. This paper shows that natural enantioenriched acetoin produced by fermentation is susceptible to racemization when an ATPS is used for downstream processing.
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