Modem Calorimeters

W. P. White. The Modem Calorimeter. Chemical Catalog Company New York, 1928. 

The modem calorimeters can be equipped with numerous additional installations enabling a number of different feed modes, other processes control strategies, such as pH-value dependent, or the simultaneous measurement of additional properties, such as... 

Between 1881 and 1905, Berthelot and co-workers developed the first combustion calorimeter, precursor of the modem calorimeters with static bomb [27-30]. 

Adiabatic calorimeters have only become possible with advanced designs for electrical temperature measurement and the availability of regulated electrical heating. The first adiabatic calorimeter of this type was described by Nemst in 1911 [9]. Special equipment is needed for low-temperature calorimetry, below about 10 K as are described in Sect. 4.3. Modem calorimeters [10-13] are more automated than the adiabatic calorimeter shown in Fig. 4.33, but the principle has not changed from the original design by Nemst. 

Some classical texts on calorimetry are White WP (1928) The Modem Calorimeter. Chem Catalog Co, New York. Swietoslawski W (1946) Microcalorimetry. Reinhold Publ, New York. Sturtevant JM (1971) Calorimetry. In Weissberger A Rossiter BW, eds. Techniques of Chemistry Vol I, Part V. Wiley-Interscience, New York. 

Modem calorimeters permit relatively rapid and truly precise measurement of heat exchanges in a wide variety of reactions. Since heat evolution is proportional to the conversion (extent of reaction) in a chemical, physical, or biological reaction, calorimetric measurement constitutes one method for quantitative evaluation of the reaction itself. Measurement is possible not only of the total heat (and therefore the total conversion) of a reaction but also of the course of the reaction... 

White, W.P. (1928) The Modem Calorimeter, American Chemical Society Monograph Series No. 42, The Chemical Catalog Company,... 

Very few modem calorimeters employ mercury-in-glass thermometers. The limit of accuracy of the most accurate instrument of this type, the Beckmann thermometer, is about 0.001 K it is easily broken, and subject to errors caused by exposed stem, pressure, sticking of the mercury column, and drift in calibration. 

The development of modem calorimeters not only enables the enthalpy changes occurring in adsorption and desorption to be measured incrementally, to obtain differential enthalpies of adsorption, but also the kinetics of the processes can be followed at the same time. Such data, in association with the established characterization methods of (a) surface area, using different adsorbates, (b) PSDs and (c) TPD provide a comprehensive knowledge of the properties of an activated carbon. 

Calorimetry is an important technique in biology as well as in chemistry. The inventor of the calorimeter was Antoine Lavoisier, who is shown in the illustration. Lavoisier was a founder of modem chemistry, but he also carried out calorimetric measurements on biological materials. Lavoisier and Pierre Laplace reported in 1783 that respiration is a very slow form of combustion. Thus, calorimetry has been applied to biology virtually from its invention. 

The design and operation of solution calorimeters is an extensive topic. Reference (125) reviews modem calorimetry and identifies earlier discussions. The thermometric titration type of calorimeter has been perfected during the past fifteen or twenty years. It is especially useful for measuring heats of reaction that take place in several steps. The availability of advances in thermometry has had a major effect on calorimetry. 

Using modem isothermal calorimeters, experiments with a reproducibility better than 20 mj can be achieved. This is therefore the value one has to compare with the expected immenion energy in order to predict the feasibiHty of an experiment and to estimate the sample mass to be used. The immersion energies range between a few mj/m (water/Teflon) and a few hundred mj/m (specially carbons in organic solvents, but also inorganic oxides in water). Up to a few hundred miUigrams of sample can be introduced in the bulb. 

Given the availability of modem instrumentation, the contemporary chemist is spared the meticulous and laborious procedures followed in early hydrogen thermochemistry (see, for example, Kistiakowsky, et al., 1935, 1936). Only two more recent hydrogen calorimeter implementations are recommended to the scientist who wishes to pursue this line of research, one a commercial instrument (Tronac Inc. Orem, UT, USA) and one that can be constructed from standard laboratory equipment with a few modifications. 

The heat capacity of Th02 was determined in an adiabatic calorimeter from 10.2 to 305.4 K. The heat capacity and entropy at 298.15 K were calculated to be (61.76 + 0.06) and (65.24 + 0.08) JK mol respectively when corrected for the modem atomic weight of thorium, these become 61.74 and 65.23 J K mol. The sample of thoria used was ground from electrically-fused material, and was analysed to have a Th content of (87.54-87.93) mass% (theoretical 87.88). Chemical analysis showed the total content of lanthanide elements to be < 150 ppm, similar to the total content of other metals, measured spectroscopically. 53 heat capacity measurements were made, extending from 10.2 to 305.4 K. For the entropy calculations, the heat capacity was extrapolated to 0 K using a Debye function. The heat capacity and entropy from this excellent study were adopted by the review. 

The first requirement is mainly important for the assessment of chemical reactions. In the overwhelming majority of chemical processes, not only the chemical conversion into the single desired product takes place. Instead, the desired reaction is accompanied by numerous parallel and consecutive reactions. Under the defined operating conditions resulting from the optimization work, the effect of these simultaneous reactions on yield and selectivity has been minimized by the choice of mode of operation (continuous, batch or semibatch) and of process parameters, such as pressure, temperature, concentration, pH-value, mass flow rates etc. A performance of the safety tests under conditions deviating fi-om those chosen for the plant process would inadvertently favour those secondary reactions in a different manner. Values for the gross value of heat output and reaction rate obtained this way would not be suitable for any process safety evaluation. Modem reaction calorimeters, like those commercially available today, enable the conduction of experiments with sufficient similarity to actual plant conditions. 

Modem reaction calorimetry is the method of choice for the experimental characterization of normal operating conditions. Today, such measuring devices are available commercially as well as self-made in many different designs and their description can be found in the literature [e.g. 60,61,62,63]. The key input to this development was given by Regenass 1979, when he developed the first so-called bench-scale calorimeter [64]. 

Fig. 4-67. Schematic drawing of the measuring set up of a modem reaction calorimeter...

A third way of measuring the heat exchanged in a passive diathermal calorimeter is to make use, in the surrounding thermostat, of a peripheral liquid flow (usually water) whose temperature change is determined. This is the principle followed by Junkers flame calorimeter [39], the Picker liquid mixing calorimeter [40], and modem reaction calorimeters developed for safety studies of chemical reactions. 

Modem adiabatic calorimeters employ a technique whereby the enthalpy of vaporization is measured under conditions in which a measured amount of electrical energy is supplied to a heater immersed in the sample to compensate for the heat absorbed by the substance during the evaporation and hence the temperature is kept constant. The main differences among adiabatic calorimeters are that the vapour flows out of the calorimeter at atmospheric pressure (those of Mathews and Fehlandt [65]), into a vacuum, [67,69-71] into a gas stream [68], or into a closed recirculation system with continuous fluid flow [66]. 

Wang, Q.G. Zhang, J. 2003. Principle and application on cone calorimeter. Modem scientific instruments (6) 36-39. 

A modem adiabatic calorimeter is described by Gmelin E, Rodhammer P (1981) Automatic Low Temperature Calorimetry for the Range 0.3- 320 K. J Phys E, Instrument. 14 223-238. 

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