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Exothermic Reaction (exothermic + reaction)
Selected AbstractsDevelopment of an Industrial Multi-Injection Microreactor for Fast and Exothermic Reactions , Part IICHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2008D. M. Roberge Abstract A Grignard reaction performed in a microreactor is presented. The reaction is of type A (highly exothermic and very rapid) and has a low yield which is attributed to a hot spot formed in the mixing zone of the reactor. The reaction yield could be significantly increased by applying the multi-injection principle, leading to better thermal control in the microreactor. Nevertheless, the microreactor plays a major role in reducing the magnitude of the hot spot. Knowing this, it was possible to design and construct an industrial microreactor with significant advantages such as modularity, high flow rate operation, and low investment expenditure (pumps and flow controller minimization). [source] Thermodynamics of the folding of D-glyceraldehyde-3-phosphate dehydrogenase assisted by protein disulfide isomerase studied by microcalorimetryFEBS JOURNAL, Issue 15 2001Yi Liang Thermodynamics of the refolding of denatured d -glyceraldehyde 3-phosphate dehydrogenase (GAPDH) assisted by protein disulfide isomerase (PDI), a molecular chaperone, has been studied by isothermal microcalorimetry at different molar ratios of PDI/GAPDH and temperatures using two thermodynamic models proposed for chaperone,substrate binding and chaperone-assisted substrate folding, respectively. The binding of GAPDH folding intermediates to PDI is driven by a large favorable enthalpy decrease with a large unfavorable entropy reduction, and shows strong enthalpy,entropy compensation and weak temperature dependence of Gibbs free energy change. A large negative heat-capacity change of the binding, ,156 kJ·mol,1·K,1, at all temperatures examined indicates that hydrophobic interaction is a major force for the binding. The binding stoichiometry shows one dimeric GAPDH intermediate per PDI monomer. The refolding of GAPDH assisted by PDI is a largely exothermic reaction at 15.0,25.0 °C. With increasing temperature from 15.0 to 37.0 °C, the PDI-assisted reactivation yield of denatured GAPDH upon dilution decreases. At 37.0 °C, the spontaneous reactivation, PDI-assisted reactivation and intrinsic molar enthalpy change during the PDI-assisted refolding of GAPDH are not detected. [source] Rate constant estimation for C1 to C4 alkyl and alkoxyl radical decompositionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2006H. J. Curran Rate coefficients for alkyl and alkoxy radical decomposition are important in combustion, biological, and atmospheric processes. In this paper, rate constant expressions for C1C4 alkyl and alkoxy radicals decomposition via ,-scission are recommended based on the reverse, exothermic reaction, the addition of a hydrogen atom or an alkyl radical to an olefin or carbonyl species with the decomposition reaction calculated using microscopic reversibility. The rate expressions have been estimated based on a wide-range study of available experimental data. Rate coefficients for hydrogen atom and alkyl radical addition to an olefin show a strong temperature curvature. In addition, it is found that there is a correlation between the activation energy for addition and (i) the type of atom undergoing addition and (ii) whether this radical adds to the internal or terminal carbon atom of the olefin. Rate coefficients for alkoxy radical decomposition show a strong correlation to the ionization potential of the alkyl radical leaving group and on the enthalpy of reaction. It is shown that the activation energy for alkyl radical addition to a carbonyl species can be estimated as a function of the alkyl radical ionization potential and enthalpy of reaction. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 250,275, 2006 [source] Theoretical studies of mechanisms of cycloaddition reaction between difluoromethylene carbene and acetoneINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2007Xiu Hui Lu Abstract Mechanisms of the cycloaddition reaction between singlet difluoromethylene carbene and acetone have been investigated with the second-order Møller,Plesset (MP2)/6-31G* method, including geometry optimization and vibrational analysis. Energies for the involved stationary points on the potential energy surface (PES) are corrected by zero-point energy (ZPE) and CCSD(T)/6-31G* single-point calculations. From the PES obtained with the CCSD(T)//MP2/6-31G* method for the cycloaddition reaction between singlet difluoromethylene carbene and acetone, it can be predicted that path B of reactions 2 and 3 should be two competitive leading channels of the cycloaddition reaction between difluoromethylene carbene and acetone. The former consists of two steps: (i) the two reactants first form a four-membered ring intermediate, INT2, which is a barrier-free exothermic reaction of 97.8 kJ/mol; (ii) the intermediate INT2 isomerizes to a four-membered product P2b via a transition state TS2b with an energy barrier of 24.9 kJ/mol, which results from the methyl group transfer. The latter proceeds in three steps: (i) the two reactants first form an intermediate, INT1c, through a barrier-free exothermic reaction of 199.4 kJ/mol; (ii) the intermediate INT1c further reacts with acetone to form a polycyclic intermediate, INT3, which is also a barrier-free exothermic reaction of 27.4 kJ/mol; and (iii) INT3 isomerizes to a polycyclic product P3 via a transition state TS3 with an energy barrier of 25.8 kJ/mol. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Quantitative framework for reliable safety analysisAICHE JOURNAL, Issue 1 2002Haitao Huang The effectiveness of any methodology used to identify hazards in chemical processes affects both safety and economics. To achieve maximum safety at minimum cost, a conservative, but realistic, analysis must be carried out. An approach to hazard identification is proposed based on a detailed process model which includes nonlinear dynamics and uncertainty. A new modeling framework, the region-transition model (RTM), is developed, which enables the simulation of regions of the operating space through an extension of the hybrid state transition system formalism. The RTM is illustrated on a nonlinear batch reactor with parameter uncertainty. A safety-verification algorithm identifies regions of the input space (initial conditions and external inputs) which guarantee safe operation. The algorithm is successfully applied to three examples: a tank with overflow and underflow, a batch reactor with an exothermic reaction, and a CSTR with feed preheating. [source] Differing Expansion Contributions of Three Investment Materials Used for Casting TitaniumJOURNAL OF PROSTHODONTICS, Issue 5 2009Danny Low BDS, MScDent, MScMed Abstract Purpose: This laboratory study aimed at investigating the effect of setting expansion (SE), which could enlarge a wax pattern by concurrent exothermic reaction. Materials and Methods: Two phosphate-bonded investment materials (Rematitan Plus, T-invest C & B) and alumina-magnesia-based investment material (Titavest CB) were subjected to setting temperature and SE measurements (n = 10). Full-crown wax patterns were prepared from metal dies having the same design. Crown castings (n = 6) were made using a one-chamber high-pressure casting machine. Commercially pure titanium ingot (Japanese Industrial Standard Class II) was used for each casting. Dimensional accuracy of the cast crowns was expressed by marginal discrepancy for a pair of wax pattern and casting prepared from the same die. All results were then subjected to regression analysis. Results: Rematitan Plus gave the highest setting temperature (about 70°C) and the highest SE (1.16 ± 0.01%) almost concurrently. The result was that Rematitan Plus produced oversized crowns from the lowest thermal expansion (TE) value (0.53 ± 0.05%) reducing the linear correlation to 0.80 (p < 0.05). No significant linear relationship was found between SE of investment material and crown-casting accuracy. Conclusions: The almost concurrent occurrence of high SE and high setting temperature generation in Rematitan Plus enlarged the wax pattern and effectively supplemented its low TE to produce oversized crowns. Despite this adverse effect, the correlation between TE and crown accuracy was still high. It is generally expected that the TE values given by manufacturers predict crown accuracy, when uniform TE, small SE, and minimum heat generation during setting are assured. [source] Preparation and adsorption of novel cellulosic fibers modified by , -cyclodextrinPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2008Youyi Xia Abstract Novel cellulosic fibers modified by , -cyclodextrin (CFEC) were prepared for adsorption for heavy metal ions like copper (II) and organic dye like neutral red from their aqueous solutions. The modified cellulosic fibers gave higher copper ion adsorption, and showed copper ion uptake values of 6.24,mg/g at 293°C, as against no adsorption for unmodified cellulosic fibers. Adsorption isotherm model indicated the adsorption of the novel modified fibers for heavy metal ions best fitted for Langmiur model. The adsorption was an exothermic reaction, and the reaction caloric was 6.295,kJ/mol. Copper ions could form a 7:4 complex with , -cyclodextrin (, -CD). The novel modified cellulosic fibers could also form inclusion complexes with neutral red via , -CD molecules. In addition, it was found that the novel modified cellulosic fibers had nearly the same mechanical and thermal properties as the unmodified cellulosic fibers because the modification did not destroy the main chain of cellulose molecules. Copyright © 2008 John Wiley & Sons, Ltd. [source] Theoretical Study on the Mechanism of the Cycloaddition Reaction between Methylidenesilene and EthyleneCHINESE JOURNAL OF CHEMISTRY, Issue 3 2006Xiu-Hui Lu Abstract The mechanism of a cycloaddition reaction between singlet methylidenesilene and ethylene has been investigated with MP2/6-31G, and B3LYP/6-31G, methods, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. Energies of the involved conformers were calculated by CCSD(T)//MP2/6-31G, and CCSD(T)//B3LYP/6-31G, methods, respectively. The results show that the dominant reaction pathway of the cycloaddition reaction is that a complex intermediate is firstly formed between the two reactants through a barrier-free exothermic reaction of 13.3 kJ/mol, and the complex is then isomerized to a four-membered ring product P2.1 via a transition state TS2.1 with a barrier of 32.0 kJ/mol. [source] Microwave-Assisted Synthesis of Fine Particle Oxides Employing Wet Redox MixturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Solomon Sundar Manoharan Interaction of electromagnetic radiation with a physical mixture of metal nitrates and amides/hydrazides is observed to initiate high-temperature reactions, useful for realizing several high-temperature ceramic materials. A judicious choice of such redox mixtures undergoes exothermic reactions when they couple with microwave radiation. The coupling of electromagnetic radiation with metal salts and amides/hydrazides depends on the dielectric properties of the individual components in the reaction mixture. The approach has been used to prepare ,-Fe2O3, Fe3O4, MgCr2O4, ,-CaCr2O4, and La0.7Ba0.3MnO3. [source] Thermal control system for thick composite laminates based on forecastingPOLYMER COMPOSITES, Issue 1 2004Daniel D. Shin A forecast-based thermal control system was developed to cure thick composite laminates that produced large exothermic reactions. The system used process simulation models for heat transfer and compaction to predict future cure conditions at a designated forecast time so that the system can respond to avoid approaching adverse conditions. The thermal control system derived cure cycles that eliminated exotherms and maintained uniform through-the-thickness temperature gradient for 3-cm thick AS4/35016 laminates. The on-line results indicated that cure cycles were slightly different from off-line simulation results, mainly because of the slow response of the hot press. Nevertheless the system was able to satisfy the cure criteria under such unforeseen circumstances, which demonstrated the flexibility of the forecasting method. [source] Soret Diffusion and Non-Ideal Dufour Conduction in Macroporous Catalysts with Exothermic Chemical Reaction at Large Intrapellet Damköhler NumbersTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007Laurence A. Belfiore Abstract The adiabatic temperature rise in catalytic pellets is predicted from a modified version of the Prater equation. Onsager reciprocal relations for coupled heat and mass transfer are violated in an analysis of thermal diffusion in macroporous catalysts with exothermic chemical reaction when Dufour conduction (i.e., the diffusion-thermo effect) is neglected. In this contribution, Dufour conduction is analyzed for both ideal and non-ideal pseudo-binary gas mixtures that simulate the production of methanol from carbon monoxide and hydrogen. In the diffusion-controlled regime at large intrapellet Damköhler numbers where intermolecular collisions provide the dominant resistance to mass transfer within the catalytic pores, temperatures in the catalytic core could be much greater than predictions based on the original Prater equation when the Prater number exceeds 0.30. The molecular flux of thermal energy includes Fourier's law, the interdiffusional flux, and Dufour conduction. Diffusional mass flux includes Fick's law and the Soret effect. All physicochemical properties of the reactive gas mixture exhibit temperature dependence. There is essentially no difference between maximum intrapellet temperature predictions that include or neglect ideal Dufour conduction when external catalytic surface temperatures range from 300-400 K and thermal diffusion enhances the flux of "smaller" reactants toward the centre of the catalyst. For "large-molecule reactants" that participate in exothermic reactions, thermal diffusion opposes Fick's law and Dufour conduction opposes Fourier's law. Under these conditions, it is demonstrated that core temperatures are overestimated by neglecting both off-diagonal coupling mechanisms (i.e., Soret diffusion and Dufour conduction). Prater numbers greater than unity and unrealistically high gas pressures are required to distinguish between maximum intrapellet temperatures for ideal and real gas simulations, where the latter consider two-body interactions for Lennard-Jones molecules in the virial equation of state. On prédit l'augmentation de la température adiabatique dans les pastilles catalytiques à partir d'une version modifiée de l'équation de Prater. Les relations réciproques d'Onsager pour le transfert de chaleur et de matière couplé sont violées dans une analyse de la diffusion thermique dans les catalyseurs macroporeux avec réaction chimique exothermique lorsque la conduction de Dufour (p.ex., l'effet de thermo-diffusion) est négligée. Dans cet article, on analyse la conduction de Dufour pour des mélanges de gaz pseudo-binaires idéaux et non idéaux qui simulent la production de méthanol à partir d'oxyde de carbone et d'hydrogène. Dans le régime à diffusion contrôlée à grand nombre de Damköhler entre les pastilles pour lesquels les collisions entre les molécules fournit la résistance dominante au transfert de matière à l'intérieur des pores catalytiques, les températures dans le noyau catalytique pourraient être bien plus grandes que les prédictions basées sur l'équation de Prater originale lorsque le nombre de Prater excède 0,30. Le flux moléculaire de l'énergie thermique inclut la loi de Fourier, le flux interdiffusionnel, et la conduction de Dufour. Le flux massique diffusionnel inclut la loi de Fick et l'effet Soret. Toutes les propriétés physicochimiques du mélange de gaz réactif montre une dépendance thermique. Il n'y a essentiellement pas de différence entre les prédictions des températures maximales entre les pastilles qui incluent ou négligent la conduction de Dufour idéale quand les températures de surface catalytiques externes sont comprises entre 300 et 400 K; la diffusion thermique améliore le flux des réactifs «plus petits» vers le centre du catalyseur. Pour les «réactifs composés de grandes molécules» qui participent aux réactions exothermiques, la diffusion thermique s'oppose à la loi de Fick et la conduction de Dufour à la loi de Fourier. Dans ces conditions, il est démontré que les températures de noyau sont surestimées en négligeant les deux mécanismes de couplage hors-diagonales (c.à-d. la diffusion de Soret et la conduction de Dufour). Des nombres de Prater plus grands que l'unité et des pressions de gaz élevées peu réalistes sont nécessaires pour distinguer les températures maximales entre les pastilles entre les simulations de gaz idéales et réelles, en considérant pour ces dernières les interactions à deux corps pour les molécules de Lennard-Jones dans l'équation d'état du viriel. [source] Guidance on Safety/Health for Process Intensification including MS Design; Part I: Reaction HazardsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 11 2009O. Klais Abstract The implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher space-time yields, higher temperatures, and a confined reaction volume comprises new risks, such as runaway reactions, decomposition, and incomplete conversion of reactants. Simplified spreadsheet calculations enable an estimation of the expected temperature profiles, conversion rates, and consequences of potential malfunction based on the reaction kinetics. The analysis illustrates that the range of optimal reaction conditions is almost congruent with the danger of an uncontrolled reaction. The risk of a spontaneous reaction with hot spots can be presumed if strong exothermic reactions are carried out in micro-designed reactors. At worst, decomposition follows the runaway reaction with the release of noncondensable gases. Calculations prove that a microreactor is not at risk in terms of overpressure as long as at least one end of the reactor is not blocked. [source] Explosionstypen und ihre Zuordnung zu Rechtsvorschriften,CHEMIE-INGENIEUR-TECHNIK (CIT), Issue 7 2004B. Reimer Prof. Abstract Schadensexplosionen werden durch einen spontanen und erheblichen Druckaufbau verursacht, der auf chemische Reaktionen oder physikalische Prozesse zurückzuführen ist. Explosionsfähige Reaktionssysteme können in der Gasphase, aber auch im festen oder flüssigen Zustand bzw. in Mischphasen auftreten. Für die sicherheitstechnische Charakterisierung derartiger Systeme stehen anerkannte Untersuchungsmethoden zur Verfügung. In der Stoff wandelnden Industrie sind solche physikalischen Explosionen von Bedeutung, bei denen der Druckaufbau durch einen spontanen Stoffübergang vom flüssigen in den gasförmigen Zustand hervorgerufen wird. Ausführliche Rechtsvorschriften, ergänzt durch technische Regeln, existieren bezüglich der Brennstoff/Luft-Gemische, die unter atmosphärischen Bedingungen auftreten. Auch der Umgang mit explosionsgefährlichen Stoffen ist im Sprengstoffgesetz und den diesbezüglichen Verordnungen detailliert geregelt. Die anderen explosionsfähigen Reaktionssysteme fallen in den Geltungsbereich der Gefahrstoffverordnung, wenn eine kritische Mengenschwelle überschritten wird, in den der Störfallverordnung. Die konstruktiven Anforderungen, die Arbeitsmittel bezüglich des Explosionsschutzes zu erfüllen haben, sind in Verordnungen zum Geräte- und Produktsicherheitsgesetz geregelt. Types of Explosions and their Relations to Legislative Regulations Explosions in industrial plants and equipments are the result of chemical reactions or physical processes which are connected with a pressure build-up. Chemical explosions are caused by exothermic reactions in the gas phase, the condensed phase or in hybrid phases. In the chemical industry such physical explosions are of importance, due to a spontaneous transition of matter from the liquid to the gas phase. There are some legislative regulations which concern the explosion prevention and protection. The most important are the Equipment Safety Act and the Explosivs Act with their ordinances; the Ordinance on Dangerous Substances and the Hazardous Incident Ordinances. Important for the protection against explosive atmospheres is the "Betriebssicherheitsverordnung". [source] |