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Reaction Stages (reaction + stage)
Selected AbstractsCuring kinetics of boron-containing phenol,formaldehyde resin formed from paraformaldehydeINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2002Yanfang Liu A boron-containing phenol,formaldehyde resin (BPFR) was synthesized from boric acid, phenol, and paraformaldehyde. The curing reaction of BPFR was studied by Fourier-transform infrared spectrometry and differential scanning calorimetry. According to the heat evolution behavior during the curing process, several influencing factors on isothermal curing reaction were evaluated. The results show that the isothermal kinetic reaction of BPFR follows autocatalytic kinetics mechanism, and kinetic parameters m, n, k1, and k2, were derived, respectively. In the latter reaction stage, the curing reaction becomes controlled mainly by diffusion. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 638,644, 2002 [source] Kinetic study of the thermal degradation of poly(aryl ether ketone)s containing 2,7-naphthalene moietiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Si-Jie Liu Abstract The degradation of poly(aryl ether ketone) containing 2,7-naphthalene moieties was subjected to dynamic and isothermal thermogravimetry in nitrogen and air. The dynamic experiments showed that the initial degradation temperature, temperature for 5% weight loss, and temperature corresponding to the maximum degradation rate of poly(aryl ether ketone) containing 2,7-naphthalene moieties were a little higher than those of poly(ether ether ketone) and almost independent of the 2,7-naphthalene moiety content. The thermal stability of poly(aryl ether ketone) containing 2,7-naphthalene moieties in air was substantially less than that in nitrogen, and the degradation mechanism was more complex. The results obtained under the isothermal conditions were in agreement with the corresponding results obtained in nitrogen and air under the dynamic conditions. In the dynamic experiments, the apparent activation energies for the degradation processes were 240 and 218 kJ/mol in nitrogen and air for the second reaction stage as the heating rate was higher than 5°C/min. In the isothermal experiments, the apparent activation energies for the degradation processes were 222 and 190 kJ/mol in nitrogen and air, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Statistical analysis of catalyst degradation in a semi-continuous chemical production processJOURNAL OF CHEMOMETRICS, Issue 8 2001Eleftherios Kaskavelis Abstract The effect of decaying catalyst efficacy in a commercial-scale, semi-continuous petrochemical process was investigated. The objective was to gain a better understanding of process behaviour and its effect on production rate. The process includes a three-stage reaction performed in fixed bed reactors. Each of the three reaction stages consists of a number of catalyst beds that are changed periodically to regenerate the catalyst. Product separation and reactant recycling are then performed in a series of distillation columns. In the absence of specific measurements of the catalyst properties, process operational data are used to assess catalyst decay. A number of statistical techniques were used to model production rate as a function of process operation, including information on short- and long-term catalyst decay. It was found that ridge regression, partial least squares and stepwise selection multiple linear regression yielded similar predictive models. No additional benefit was found from the application of non-linear partial least squares or Curds and Whey. Finally, through time series profiles of total daily production volume, corresponding to individual in-service cycles of the different reaction stages, short-term catalyst degradation was assessed. It was shown that by successively modelling the process as a sequence of batches corresponding to cycles of each reaction stage, considerable economic benefit could be realized by reducing the maximum cycle length in the third reaction stage. Copyright © 2001 John Wiley & Sons, Ltd. [source] Exploration of the morphological transition phenomenon of polyaniline from microspheres to nanotubes in acid-free aqueous 1-propanol solution in a single polymerization processPOLYMER INTERNATIONAL, Issue 9 2010Yu-Fong Huang Abstract Polyaniline micro- or nanostructures have been widely investigated due to their unique physical and chemical properties. Although several studies have reported the synthesis of polyaniline microspheres and nanotubes, their mechanisms of formation remain controversial. This study reports our observation of the morphological transition of polyaniline from microspheres to nanotubes in a single polymerization process and also tries to propose their mechanisms of formation. The polymerization of aniline monomer in acid-free aqueous 1-propanol solutions (1 and 2 mol L,1) produces polyaniline microspheres and nanotubes at different reaction stages through a morphology transition process with treatment using ultrasound. In the initial reaction stage, Fourier transform infrared spectra indicate that the aniline monomers form phenazine-like units, producing polyaniline microspheres with an outside diameter of 1,2 µm. The hydrogen bonds between 1-propanol and polyaniline serve as the driving force for the polyaniline chains to build microspheres. As the reaction continues, observation indicates the microspheres decompose and reform one-dimensional nanotubes. In this stage, a structure consisting of a head of phenazine-like units and a tail of acid-doping para -linked aniline units develops. The protonation of the para -linked aniline units provides the driving force for the formation of nanotubes through a self-curling process. We report here the unique morphology transition of polyaniline from microspheres to nanotubes in a single polymerization process. The results indicate that the structural change of polyaniline leads to this morphological change. The mechanisms of formation of the microspheres and nanotubes in a polymerization process are also well explained. Copyright © 2010 Society of Chemical Industry [source] Computational study on the comparative synthesis of energetic FOX-7 derivativesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4 2010Min-Hsien Liu Abstract Ethene and two kinds of nitrating reagents (HNO3 and N2O5) were included in respective molecular systems, which progressed through a two-stage electrophilic and free radical nitrosubstitution, resulting in the corresponding nitroethene compounds. Subsequent halogenation (using Cl2 and Br2) and amination (using ammonia) were then performed, also by electrophilic and radical substitution, to produce the target 1,1-diamino-2,2-dinitroethene (FOX-7) derivatives. All transition state species were identified using a two- or three-structure Synchronous Transit-Guided Quasi-Newton between the Cartesian coordinates of the related molecular systems at specific reaction stages. The modeling results suggest that N2O5 is the better agent for nitration and bromine is suitable for use in halogenation. The comparable activation energies throughout the reaction stages were considered to imply the most feasible pathways of FOX-7 synthesis. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Statistical analysis of catalyst degradation in a semi-continuous chemical production processJOURNAL OF CHEMOMETRICS, Issue 8 2001Eleftherios Kaskavelis Abstract The effect of decaying catalyst efficacy in a commercial-scale, semi-continuous petrochemical process was investigated. The objective was to gain a better understanding of process behaviour and its effect on production rate. The process includes a three-stage reaction performed in fixed bed reactors. Each of the three reaction stages consists of a number of catalyst beds that are changed periodically to regenerate the catalyst. Product separation and reactant recycling are then performed in a series of distillation columns. In the absence of specific measurements of the catalyst properties, process operational data are used to assess catalyst decay. A number of statistical techniques were used to model production rate as a function of process operation, including information on short- and long-term catalyst decay. It was found that ridge regression, partial least squares and stepwise selection multiple linear regression yielded similar predictive models. No additional benefit was found from the application of non-linear partial least squares or Curds and Whey. Finally, through time series profiles of total daily production volume, corresponding to individual in-service cycles of the different reaction stages, short-term catalyst degradation was assessed. It was shown that by successively modelling the process as a sequence of batches corresponding to cycles of each reaction stage, considerable economic benefit could be realized by reducing the maximum cycle length in the third reaction stage. Copyright © 2001 John Wiley & Sons, Ltd. [source] Interaction of separation and reactive stages on ETBE reactive distillation columnsAICHE JOURNAL, Issue 3 2004Budi H. Bisowarno Abstract Reactive distillation is a favorable alternative to conventional series of reactor-distillation processes for ether productions. However, the design of such columns is complicated due to the interaction between vapor-liquid equilibrium and reaction rates. There are conflicting reports on whether adding excessive separation stages degrade the column performance. A comparison is made of several designs of single and double feed reactive distillation columns for ETBE production to investigate the effects of separation and reaction stages on the overall performance. The explanations are presented using simulation results, whose mathematical models are written in the Aspen Plus environment. The results confirm that a conservative approach by adding extra separation and reaction stages can be applied to reactive distillation design. However, output multiplicity may be observed for longer column and should be considered in the early design phase. © 2004 American Institute of Chemical Engineers AIChE J, 50: 646,653, 2004 [source] Solid-State Synthesis of Nanocrystalline BaTiO3: Reaction Kinetics and Powder PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2008Maria Teresa Buscaglia The formation of BaTiO3 nanoparticles by a solid-state reaction between nanocrystalline raw materials BaCO3 and TiO2 was studied as a function of temperature (400°,800°C), time (1,24 h), and titania particle size (15 and 30 nm). The reaction starts at 500°C and a high reaction rate is already observed at 600°C for the finest titania, with up to 90% conversion after 2 h. Two main reaction stages were observed at 600°,700°C. The first step is dominated by nucleation and growth of BaTiO3 at the TiO2,BaCO3 contact points and at the TiO2 surface. Surface diffusion of BaCO3 is, most likely, the prevailing mass transport mechanism responsible for the rapid formation of BaTiO3, even in the absence of a significant contribution from lattice diffusion. The second stage begins when the residual TiO2 cores are completely covered by the product phase. For longer times, the reaction can only proceed by the slower lattice diffusion, resulting in a strong decrease of the reaction rate. Single-phase BaTiO3 nanopowders with a specific surface area of 12,15 m2/g, an average particle size of 70,85 nm, a relative density of 96.5%,98.3%, and a tetragonality of 1.005 were obtained by calcination at 700°,800°C. Critical parameters in the preparation of ultrafine powders by solid-state reactions are the particle size of both raw materials, the absence of large hard agglomerates, and the homogeneity of the mixture. The use of fine raw materials and optimization of the reaction conditions make mechanical activation unnecessary. [source] Exploration of the morphological transition phenomenon of polyaniline from microspheres to nanotubes in acid-free aqueous 1-propanol solution in a single polymerization processPOLYMER INTERNATIONAL, Issue 9 2010Yu-Fong Huang Abstract Polyaniline micro- or nanostructures have been widely investigated due to their unique physical and chemical properties. Although several studies have reported the synthesis of polyaniline microspheres and nanotubes, their mechanisms of formation remain controversial. This study reports our observation of the morphological transition of polyaniline from microspheres to nanotubes in a single polymerization process and also tries to propose their mechanisms of formation. The polymerization of aniline monomer in acid-free aqueous 1-propanol solutions (1 and 2 mol L,1) produces polyaniline microspheres and nanotubes at different reaction stages through a morphology transition process with treatment using ultrasound. In the initial reaction stage, Fourier transform infrared spectra indicate that the aniline monomers form phenazine-like units, producing polyaniline microspheres with an outside diameter of 1,2 µm. The hydrogen bonds between 1-propanol and polyaniline serve as the driving force for the polyaniline chains to build microspheres. As the reaction continues, observation indicates the microspheres decompose and reform one-dimensional nanotubes. In this stage, a structure consisting of a head of phenazine-like units and a tail of acid-doping para -linked aniline units develops. The protonation of the para -linked aniline units provides the driving force for the formation of nanotubes through a self-curling process. We report here the unique morphology transition of polyaniline from microspheres to nanotubes in a single polymerization process. The results indicate that the structural change of polyaniline leads to this morphological change. The mechanisms of formation of the microspheres and nanotubes in a polymerization process are also well explained. Copyright © 2010 Society of Chemical Industry [source] | |||||||||||||