Experimental setup to study catalysts by combined pulse microcatalytic and ESR spectroscopic methods

A setup consisting of an ESR spectrometer and a pulse microcatalytic installation is suggested for simultaneous kinetic and spectral measurements directly in catalytic processes.

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Electrochemical heat flow calorimeter

A device designed for research of heat phenomena occurring in chemical power sources (CPS) is described. The device includes two functional blocks: electrochemical and calorimetrical, operating under single control, which allows simultaneously performing electrochemical and calorimetric measurements. The calorimetric block is a heat flow calorimeter. The calorimetric chamber design provides the possibility of studying thermal processes in laboratory electrochemical cells and CPS of planar, disk, and prismatic design. The absolute measurement error of the heat flow is ±50 μW at the resolution of 1 μW. The operating temperature range of the calorimetric chamber is 0–90°C. The basis of the electrochemical block is a module of a four–range potentiostat–galvanostat. The maximum polarizing current of the potentiostat is ±200 mA at the maximum voltage on the auxiliary electrode of ±10 V. Multiuser remote access from the user computers over Ethernet to the device is provided for control and treatment of experimental data. Digital deconvolution filters allowing to compensate the response rate of the heat flow meter are used for processing primary data of calorimetric measurements.     

Temperature measurements with a differential calorimeter

A differential microcalorimeter was used for the reading of transition temperatures. The inherent factors in both the instrument and the sample which may introduce variables in temperature measurements carried out with the calorimeter were studied together with modifications of the reading methods. An accurate technique is described for the preparation of the sample and measurement of temperature. The proposed method, when applied to organic standards of very high and of decreasing purity, gives an accuracy of temperature reading in the order of ±0.1°, and confirms a relationship between experimental and theoretical values.

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Zusammenfassung Ein Differentialmikrokalorimeter wurde zur Bestimmung der Übergangstemperaturen angewandt. Man untersuchte die Faktoren sowohl seitens des Instruments wie der Probe, durch welche Variablen in den mit dem Kalorimeter ausgeführten thermometrischen Messungen eingeführt werden können, weiterhin wurden Modifikationen der Ablesemethoden vorgeschlagen. Ein sicheres Verfahren zur Probebereitung und Temperaturmessung wird beschrieben. Die Methode gab bei der Anwendung von organischen Standardstoffen sehr hoher und minderer Reinheit eine Genauigkeit von ±0.1°.

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Résumé On a utilisé un microcalorimètre pour la détermination des températures de transition. On a étudié les facteurs inhérents à la fois à l'instrument et à l'échantillon, susceptibles d'introduire des variations dans les mesures thermométriques et l'on a proposé des modifications. On décrit une technique précise pour préparer l'échantillon et mesurer la température. La méthode proposée, appliquée à des étalons organiques de très haute pureté, ainsi que de pureté moins élevée, donne une précision de l'ordre de ±0.1° dans la lecture de la température et confirme une relation entre les valeurs expérimentales et théoriques.

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The authors wish to thank Prof. G. Milazzo of the Istituto Superiore di Sanitgt (Rome) for assistance in the work.     

An isothermal heat flow calorimeter for large-volume applications

Design, construction, calibration, and testing of a new isothermal heat flow calorimeter suitable for investigation of large-volume specimens are presented. The measuring vessel has the volume of 1370?cm³, and the calorimeter allows for the measurement at surrounding air temperatures of 5?C60?°C. A practical application of the device is demonstrated at the determination of specific hydration heat of cement paste and concrete with silica-aggregate size of up to 16?mm, having the same water/cement ratio. The differences over the whole measuring time period of about 100?h are lower than 2% which indicates a good potential of the calorimeter for the measurement of total hydration heat of composite materials. A reference measurement of hydration heat of cement paste using common isothermal heat flow calorimeter with the measuring vessel of 1?cm³ shows an agreement within ±7%, which seems acceptable, taking into account the heat transport processes in the far larger specimens. The designed calorimeter may find use in future also in other applications where larger specimens are required, such as the measurement of adsorption heat, solution heat, various reaction heats, and enthalpy of liquid?Csolid transition in heterogeneous systems with large representative elementary volumes.     

Inductive heating with magnetic materials inside flow reactors

Superparamagnetic nanoparticles coated with silica gel or alternatively steel beads are new fixed-bed materials for flow reactors that efficiently heat reaction mixtures in an inductive field under flow conditions. The scope and limitations of these novel heating materials are investigated in comparison with conventional and microwave heating. The results suggest that inductive heating can be compared to microwave heating with respect to rate acceleration. It is also demonstrated that a very large diversity of different reactions can be performed under flow conditions by using inductively heated flow reactors. These include transfer hydrogenations, heterocyclic condensations, pericyclic reactions, organometallic reactions, multicomponent reactions, reductive cyclizations, homogeneous and heterogeneous transition-metal catalysis. Silica-coated iron oxide nanoparticles are stable under many chemical conditions and the silica shell could be utilized for further functionalization with Pd nanoparticles, rendering catalytically active heatable iron oxide particles.     

Low-temperature adiabatic calorimeter with a built-in cryo-refrigerator

An adiabatic calorimeter was constructed for heat-capacity measurement between 13.8 and 350 K. The cryogenic temperature was produced by a cryo-refrigerator built into the cryostat. This made it possible to make a prolonged experiment at low temperatures without an external supply of liquid helium or liquid hydrogen. With precautions against possible adverse effects of the mechanical vibration of the refrigerator, the accuracy and precision of the calorimeter as proved by measurements on standard reference benzoic acid were comparable with those of the best low-temperature adiabatic calorimeters. Satisfactory performance of the present apparatus has been demonstrated by detection of a glass transition of CsNO₂(c) around 40 K.     

Liquid flow inside a cylindrical capillary with walls covered with a porous layer (Gel)

Viscous incompressible liquid flow in a long cylindrical capillary, the internal surface of which is covered with a permeable porous layer, is studied within the frameworks of three mathematical models. In the first model, the liquid flow in the porous layer is described by the Brinkman equation; according to the second one, the presence of the porous layer is taken into account using the Navier slip boundary conditions; and, in the third model, the Navier condition is imposed on the porous layer-liquid interface, with the flow inside the porous layer being excluded. The theoretical predictions are compared with the experimental data that one of us has obtained for liquid flow rates in porous capillaries. The validity and appropriateness of the application of the proposed models are discussed.     

Entropy generation analysis for nanofluid flow inside a duct equipped with porous baffles

Journal of Thermal Analysis and Calorimetry - In this research, a numerical simulation is performed to investigate thermal and viscous irreversibilities for Al2O3–water nanofluid inside a...     

Continuous flow ozonolysis in a laboratory scale reactor

Several important types of ozonolysis reactions have been performed in a continuous flow device that is able to perform both the ozonolysis and quenching steps in flow mode. This technique allows safe and scalable ozonolysis reactions to be performed on a laboratory scale.     

Decarboxylative biaryl synthesis in a continuous flow reactor

A practical protocol was developed that allows performing decarboxylative cross-coupling reactions in continuous flow reactors. Various biaryls were thus synthesized from aromatic carboxylic acids and aryl triflates using a Cu/Pd-catalyst system.     

Simplifying the setup for vacuum‐outlet GC: Using a restriction inside the injection port

The application of vacuum GC has several advantages over pressurized GC. One of the key characteristics is that the optimal gas velocity is very high. Combined with short capillary columns of wide internal diameter, this results in short analysis times using standard GC‐MS equipment. To make vacuum GC possible using a GC‐MS system, a restriction must be positioned at the injection side of the column. This restriction is usually made of deactivated 0.1 mm i.d. fused‐silica tubing which is coupled to the analytical column. Such restrictions will work, but practical challenges are found in coupling, reducing dead volume and robustness. A new way of making restrictions is by incorporating the restriction into the injection port. Using well‐defined short pieces of fused silica with internal diameter of 0.025 mm, one can make a restriction using a Press‐Tight® type connector, and position this inside the injection port. By doing this, the restriction is very short and at high temperature all the time. Activity plays a minimal role, and also leaks will not be an issue as the coupling is in 100% inert gas. Data obtained using this concept is promising as vacuum GC becomes easier and more robust.     

Study of a transferred-arc plasma reactor with a converging wall and flow through a hollow cathode

In this paper the behavior of an arc in a transferred-arc plasma reactor with a converging wall geornetrr and flow through a hollow cathode is investigated numerically with emphasis on the fluid dynamics. The general conservation equations and auxiliary relations for the calculation domain are established based on reasonable assumptions Then, the coupled nonlinear differential equations are solved with suitable boundary conditions and temperature-dependent argon plasma properties at atmospheric pressure, by employing an efficient finite-difference method. The results, for a hollow cathode geornetrr with low injection flow rates, clear/y demonstrate the existence of the Maecker elect which is responsible Joy the formation of two recirculation zones. As the plasma gas flow rate is increased, the downstream recirculation zoner is swept away leaving only an upstream recirculation zone.     

A modular flow reactor for performing Curtius rearrangements as a continuous flow process

The use of a mesofluidic flow reactor is described for performing Curtius rearrangement reactions of carboxylic acids in the presence of diphenylphosphoryl azide and trapping of the intermediate isocyanates with various nucleophiles.     

Spectrophotometric flow injection determination of l-ascorbic acid with a packed reactor containing ferric hydroxide

A flow injection system with spectrophotometric detection is proposed for determining l-ascorbic acid in pharmaceutical formulations. In this system a column containing Fe(OH)(3) immobilized in polyester resin (packed reactor) is inserted before the detector. Fe(III)-1,10-phenanthroline complex is reduced by l-ascorbic acid to produce Fe(II)-1,10-phenanthroline complex which is monitored at 510 nm. Under the optimum analytical conditions, the linearity of the calibration equation for l-ascorbic acid ranged from 5.0x10(-6) to 6.0x10(-5) M of added amount. The detection limit was 5.0x10(-7) M and recoveries between 98.5-102.0% were obtained. No interference was observed from the common excipients of pharmaceutical formulations and other active substances such as acetylsalicylic acid, caffeine and thiamine.     

Evaluation of a biological aneroid microbomb calorimeter with calcium carbide

A robust, inexpensive commercial microbomb combustion calorimeter, which has previously only been used with biological samples, has been evaluated for applications involving inorganic materials. The calorimeter has been calibrated extensively using N.P.L. standardised benzoic acid, and has been evaluated with calcium carbide. Measurements on the combustion of calcium carbide were made using the carbide alone, and using benzoic acid, graphite and calcium as addition agents. The calorimeter is shown to have an uncertainty of ±1.3% (2 × standard deviation of mean) in calibration. The measurements on the combustion of calcium carbide have a total uncertainty of the order of ±7% (2 × standard deviation of mean), which is shown to be too large to permit any significant determination of the enthalpy of formation of the carbide. The potential applications of this calorimeter are outlined.     

A simple continuous flow microwave reactor

A new simple procedure for microwave-assisted organic synthesis under continuous flow processing has been developed for use in a monomodal microwave synthesizer with direct temperature control using the instrument's in-built IR sensor. This design makes optimum use of the standing wave cavity to improve the energy efficiency of microwave-assisted flow reactions.