Nonisothermal Conditions (nonisothermal + condition)

Distribution by Scientific Domains

Selected Abstracts

Preparation and thermal decomposition reaction kinetics of a dysprosium(III) p -chlorobenzoate 1,10-phenanthroline complex

Jian Jun Zhang
The title complex [Dy(p -ClBA)3Phen]2·2H2O was synthesized, where p -ClBA is p -chlorobenzoate and Phen is 1,10-phenanthroline. The complex was characterized by various techniques including elemental analysis, IR, XRD, and molar conductance. The thermal decomposition of the complex was studied under the nonisothermal condition by TG-DTG and IR techniques. The kinetic parameters of dehydration process were obtained from the analysis of DSC curves of the complex by the NL-DIF and Popescu methods, respectively. © 2007 Wiley Periodicals, Inc. 40: 66,72, 2008 [source]

Theoretical and visual study of bubble dynamics in foam injection molding

Mehdi Mahmoodi
This article presents an experimental observation and a theoretical prediction of bubble dynamics in foam injection molding process with a main focus on the cell collapse phenomenon under pressure. Using a visualizing setup, cell growth behavior under a nonisothermal condition was monitored. In conjunction with the growth behavior, dynamics of cell collapse under different pressures and the effect of growing time on collapse behavior and final cell size were studied. Theoretical simulation of bubble behavior included power law model, which predicted bubble dynamics during foaming process. The results show that collapse phenomenon strongly depends on both exerted holding pressure and growth time. The presented model can also give a reasonable prediction of growth and collapse of cells and could give insight to control of cell size in injection foaming process. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers [source]

Moisture curing kinetics of isocyanate ended urethane quasi-prepolymers monitored by IR spectroscopy and DSC

Ana Luísa Daniel-da-Silva
Abstract The study of the kinetics of the curing of isocyanate quasi-prepolymers with water was performed by infrared spectroscopy and differential scanning calorimetry. The influence of the free isocyanate content, polyol functionality, and of the addition of an amine catalyst (2,2,-dimorpholinediethylether) in the reaction kinetics and morphology of the final poly(urethane urea) was analyzed. A second-order autocatalyzed model was successfully applied to reproduce the curing process under isothermal curing conditions, until gelation occurred. A kinetic model-free approach was used to find the dependence of the effective activation energy (Ea) with the extent of cure, when the reaction was performed under nonisothermal conditions. The dependence of Ea with the reaction progress was different depending on the initial composition of the quasi-prepolymer, which reveals the complexity of the curing process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

Kinetic study of the curing of mixtures of DGEBA and five-membered cyclic carbonates with lanthanum triflate as cationic initiator

Roser Cervellera
Abstract Mixtures of diglycidylether of bisphenol A (DGEBA) with 1,3-benzodioxolane-2-one (CC) or 4-phenoxymethyl-1,3-dioxolane-2-one (PGEC) were cured in the presence of lanthanum triflate. FTIR/ATR was used to study the evolution of carbonate and epoxide groups to follow the reactive processes that take place during curing. DSC was applied to study the thermal characteristics of the curing process and to determine the glass-transition temperatures of the cured materials. The kinetics of the curing was studied isothermally by means of FTIR and the kinetic model was selected through the isokinetic relationships. DSC experiments were used to study the kinetics in nonisothermal conditions by means of isoconversional procedures and the Coats,Redfern and Criado methodologies. By TMA we could monitor the evolution of the shrinkage during isothermal curing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2875,2884, 2007 [source]

Theoretical study of a membrane reactor for the water gas shift reaction under nonisothermal conditions

AICHE JOURNAL, Issue 12 2009
María E. Adrover
Abstract A simulation of a membrane reactor for the water gas shift reaction is carried out by means of a 1D pseudo-homogeneous nonisothermal mathematical model. The composite membrane consists of a dense layer of Pd (selective to H2) supported over a porous ceramic layer. The effect of temperature, overall heat-transfer coefficient, and mode of operation on the membrane reactor performance and stability are analyzed, and the results obtained are compared with those corresponding to a reactor with no hydrogen permeation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Measuring velocity distributions of viscous fluids using positron emission particle tracking (PEPT)

AICHE JOURNAL, Issue 7 2004
S. Bakalis
Abstract Positron emission particle tracking (PEPT) can be used to trace the path of a radioactive particle within opaque fluids in pilot-scale equipment; the method can track particles through several centimeters of metal. PEPT has been successfully used to follow isokinetic tracers in viscous fluids and thus to measure velocity distributions under both isothermal and nonisothermal conditions in pipe flow. The accuracy of the method decreased as the measured velocities increased; the faster the particle traveled, the less accurate its detection. For velocities of up to 0.5 m/s the accuracy of the method was acceptable. Agreement between experimentally measured and theoretical velocity distributions was very good, for a range of fluids and process conditions. As tracer particles are used, there were problems ensuring that all parts of the measurement volume were sampled. This is possible to overcome to an extent by adjusting particle size; 600-,m tracers did not pass within 1 mm from the tube wall, whereas 240-,m particles passed much closer to the boundaries of the flow. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1606,1613, 2004 [source]

Online estimation and control of polymer quality in a copolymerization reactor

AICHE JOURNAL, Issue 5 2002
Myung-June Park
The validity of an online state estimator for a semi-batch MMA/MA solution copolymerization reactor was established using online densitometer and viscometer. Using the conventional extended Kalman filter (EKF) as the state estimator, the experiment was conducted under both isothermal and nonisothermal conditions for application to the control of copolymer properties. Further analysis was made by using ofline measurement data for the mol fraction of MMA in the remaining monomers and the solid content. The EKF was found to provide a good estimate for the state of the copolymerization system. A model predictive controller was designed and implemented to obtain copolymers with uniform copolymer composition and the desired weight average molecular weight by adopting the feed flow rate of MMA and the reaction temperature as control inputs. The controller was proven effective with a satisfactory performance for the control of polymer properties in the semi-batch copolymerization reactor. [source]

Wide-ranging molecular mobilities of water in active pharmaceutical ingredient (API) hydrates as determined by NMR relaxation times

Sumie Yoshioka
Abstract In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin,spin relaxation and spin,lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed 1H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin,spin relaxation time (T2) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T2 may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T2 was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T2. A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:4258,4268, 2008 [source]

Prediction of the relaxation behavior of amorphous pharmaceutical compounds.


Abstract Variability in the time to crystallization is a major technical and economic hurdle in using amorphous solids in dosage forms. It is hypothesized that amorphous solids "age", and that the older they are, the more relaxed they are and the higher the probability of crystallization. At present, there is no method that allows the "effective age" of an amorphous raw material to be assessed relative to its unrelaxed initial condition. A method has been developed that may satisfy this unmet need and provide a first step in subsequent investigation of the crystallization "event". This method consists of using master curves to enable the determination of the effective age (,aging') of an amorphous compound given normal excursions in storage conditions. The present study shows that master curves can be prepared for different storage conditions and subsequently be used to predict the relaxation or aging behavior of amorphous compounds with expected variations in storage conditions. Given the constraint that the system remain within the area enclosed by the equilibrium supercooled liquid line and the glass on the enthalpy,temperature diagram, experimental results using indomethacin and salicin as model compounds show that master curves can be used to predict aging behavior under nonisothermal conditions, with temperature excursions as large as 10°C. The nonisothermal relaxation behavior can be modeled by combining the Kohlrausch,Williams,Watts (KWW) stretched exponential function, the relaxation function, and a shift factor. In addition, a model was developed that extends the range of applicability to time/temperature regions in which partial crystallization occurs. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:1464,1472, 2003 [source]

Isothermal and nonisothermal crystallization kinetics of nylon 10 12

Yongjin Li
This article studied the crystallization behaviors of a newly industrialized polyamide, Nylon 10 12, under isothermal and nonisothermal conditions from the melt. A differential scanning calorimeter (DSC) was used to monitor the energetics of the crystallization process. During isothermal crystallization, relative crystallinity develops in accordance with the time dependence described by the Avrami equation with the exponent n=2.0. For nonisothermal studies, several different analysis methods were used to describe the crystallization process. The experimental results show that the Ozawa approach cannot adequately describe the nonisothermal crystallization kinetics. However, Avrami treatment for nonisothermal crystallization is able to describe the system very well. The calculated activation energy is 264.4 KJ/mol for isothermal crystallization by Arrhenius form and 235.5 KJ/mol for nonisothermal crystallization by Kissinger method. [source]

Nonisothermal Bioreactors in the Treatment of Vegetation Waters from Olive Oil: Laccase versus Syringic Acid as Bioremediation Model

Angelina Attanasio
Laccase from Trametes versicolor was immobilized by diazotization on a nylon membrane grafted with glycidil methacrylate, using phenylenediamine as spacer and coupling agent. The behavior of these enzyme derivatives was studied under isothermal and nonisothermal conditions by using syringic acid as substrate, in view of the employment of these membranes in processes of detoxification of vegetation waters from olive oil mills. The pH and temperature dependence of catalytic activity under isothermal conditions has shown that these membranes can be usefully employed under extreme pH and temperatures. When employed under nonisothermal conditions, the membranes exhibited an increase of catalytic activity linearly proportional to the applied transmembrane temperature difference. Percentage activity increases ranging from 62% to 18% were found in the range of syringic acid concentration from 0.02 to 0.8 mM, when a difference of 1°C was applied across the catalytic membrane. Because the percentage activity increase is strictly related to the reduction of the production times, the technology of nonisothermal bioreactors has been demonstrated to be an useful tool also in the treatment of vegetation waters from olive oil mills. [source]

Production of Low-Lactose Milk by Means of Nonisothermal Bioreactors

Valentina Grano
The effect of the immobilization time on the activity of immobilized ,-galactosidase from K. lactis was investigated. Six biocatalytic membranes, different only for the time of the enzyme immobilization, were obtained by using nylon membranes grafted with glycidyl methacrylate (GMA) and activated by hexamethylenediamine (HMDA) and glutaraldehyde (Glu), used as spacer and coupling agent, respectively. Comparison between the isothermal and nonisothermal yield of these biocatalytic membranes was carried out in the process of lactose hydrolysis in milk. All of the results, reported as a function of the immobilization time, have evidenced the influence of our variable parameter on the activity of the catalytic membranes. The membrane giving highest yield under isothermal and nonisothermal conditions was that obtained with 2 h of immobilization time. The industrial application of these membranes has been discussed in terms of percentage reduction of the production times. [source]

From Time Temperature Integrator Kinetics to Time Temperature Integrator Tolerance Levels: Heat-Treated Milk

Wendie L. Claeys
Six milk compounds were studied as potential intrinsic time temperature integrators (TTIs) for the assessment of heat-treated milk. These include the enzymes alkaline phosphatase and lactoperoxidase, the whey protein ,-lactoglobulin and the chemical compounds hydroxymethylfurfural, lactulose and furosine. In previous research the inactivation/denaturation/formation kinetics of these compounds were analyzed under isothermal and nonisothermal conditions and evaluated for variability of the milk composition. The present paper focuses on the implementation of the TTIs. TTIs are validated with respect to microbiological indices and quality attributes, and a quantitative relationship between the denaturation, inactivation or formation of the TTIs and technological processes is established by construction of general time temperature tolerance (TTT) diagrams. In these diagrams temperature time combinations are presented, which lead to the same formation, inactivation or denaturation of TTIs, or result in the same level of microbiological destruction or quality degradation of the product. TTT-diagrams are very informative since they allow visualization of the impact of a thermal process on milk and evaluation of criteria for evaluating milk authenticity (conformity of the product with the terminology applied). Moreover, the optimum combination of temperature and time of heating may be readily deduced from these diagrams. [source]