Isothermal flow calorimeter

Christensen, J. J., and R. M. Izatt. 1984. An isothermal flow calorimeter designed for high temperature, high-pressure operation. Thermochimica Acta. 73 117-129. 

Gmehling (1993) measured excess enthalpies of mixing of different liquids in a commercial isothermal flow calorimeter (Hart Scientific 7501) with an uncertainty of less than 1%. The flow mixing tube was thermostatized by constant Peltier cooling and controlled electrical pulse heating to keep the temperature constant. 

Device for Continuous Reaction 2.2.1 Isothermal Flow Calorimeter TKR... 

A survey of the literature shows that although very different calorimeters or microcalorimeters have been used for measuring heats of adsorption, most of them were of the adiabatic type, only a few were isothermal, and until recently (14, 15), none were typical heat-flow calorimeters. This results probably from the fact that heat-flow calorimetry was developed more recently than isothermal or adiabatic calorimetry (16, 17). We believe, however, from our experience, that heat-flow calorimeters present, for the measurement of heats of adsorption, qualities and advantages which are not met by other calorimeters. Without entering, at this point, upon a discussion of the respective merits of different adsorption calorimeters, let us indicate briefly that heat-flow calorimeters are particularly adapted to the investigation (1) of slow adsorption or reaction processes, (2) at moderate or high temperatures, and (3) on solids which present a poor thermal diffusivity. Heat-flow calorimetry appears thus to allow the study of adsorption or reaction processes which cannot be studied conveniently with the usual adiabatic or pseudoadiabatic, adsorption calorimeters. In this respect, heat-flow calorimetry should be considered, actually, as a new tool in adsorption and heterogeneous catalysis research. 

It appears therefore that during the operation of all usual calorimeters, temperature gradients are developed between the inner vessel and its surroundings. The resulting thermal head must be associated, in all cases, to heat flows. In isoperibol calorimeters, heat flows (called thermal leaks in this case) are minimized. Conversely, they must be facilitated in isothermal calorimeters. All heat-measuring devices could therefore be named heat-flow calorimeters. However, it must be noted that in isoperibol or isothermal calorimeters, the consequences of the heat flow are more easily determined than the heat flow itself. The temperature decrease... 

Since heat exchange between the calorimeter vessel and the heat sink is not hindered in a heat-flow calorimeter, the temperature changes produced by the thermal phenomenon under investigation are usually very small (less than 10 4 degree in a Calvet microcalorimeter, for instance) (23). For most practical purposes, measurements in a heat-flow calorimeter may be considered as performed under isothermal conditions. 

Chemical composition was determined by elemental analysis, by means of a Varian Liberty 200 ICP spectrometer. X-ray powder diffraction (XRD) patterns were collected on a Philips PW 1820 powder diffractometer, using the Ni-filtered C Ka radiation (A, = 1.5406 A). BET surface area and pore size distribution were determined from N2 adsorption isotherms at 77 K (Thermofinnigan Sorptomatic 1990 apparatus, sample out gassing at 573 K for 24 h). Surface acidity was analysed by microcalorimetry at 353 K, using NH3 as probe molecule. Calorimetric runs were performed in a Tian-Calvet heat flow calorimeter (Setaram). Main physico-chemical properties and the total acidity of the catalysts are reported in Table 1. 

The rate of isothermal heat evolution in lignocellulosic sheet material was studied at temperatures between 150 and 230°C using a labyrinth air flow calorimeter and commercial hardboards, medium density boards and laboratory hardboards of holocellulose, bleached kraft and groundwood, the latter with and without fire retardants. 

Such basic data are here presented from isothermal measurements on 5 by 90 cm lignocellulosic and cellulosic strips up to 13 mm thick. A suitable labyrinth air flow calorimeter operating at temperatures up to 250°C was built for these fairly large size samples. (7)... 

The isothermal and isoperibol calorimeters are well suited to measuring heat contents from which heat capacities may be subsequently derived, while the adiabatic and heat-flow calorimeters are best suited to the direct measurement of heat capacities and enthalpies of transformation. 

The enthalpy change associated with formation of a thermodynamically ideal solution is equal to zero. Therefore any heat change measured in a mixing calorimetry experiment is a direct indicator of the interactions in the system (Prigogine and Defay, 1954). For a simple biopolymer solution, calorimetric measurements can be conveniently made using titra-tion/flow calorimeter equipment. For example, from isothermal titration calorimetry of solutions of bovine P-casein, Portnaya et al. (2006) have determined the association behaviour, the critical micelle concentration (CMC), and the enthalpy of (de)micellization. 

Further developments in calorimetry include the invention of the twin- calorimeter" by Joule (1845) and its modification by Pfaundler (1869XRef 25,p 543) "phase- change calorimer (isothermal) of Bunsen(Ref 15,p 796 Ref 25,p 547) "labirinth flow calorimeter (Ref 25,p 549) "adiabatic calorimeter (nonisothermal), first used by Richards in 1905 (Ref 15,p 797) and modified by Yost, Osborne others (Ref 25,p 550)(See also Ref 3,p ll6)(Parr adiabatic calorimeter is described in Refs 16 29) "constant- temperature- enviroment calorimeter", first used by Nemst in 1907, was modified by Giauque in 1923(Ref 15>p 797)... 

Regenass [10] reviews a number of uses for heat flow calorimetry, particularly process development. The hydrolysis of acetic anhydride and the isomerization of trimethyl phosphite are used to illustrate how the technique can be used for process development. Kaarlsen and Villadsen [11,12] provide reviews of isothermal reaction calorimeters that have a sample volume of at least 0.1 L and are used to measure the rate of evolution of heat at a constant reaction temperature. Bourne et al. [13] show that the plant-scale heat transfer coefficient can be estimated rapidly and accurately from a few runs in a heat flow calorimeter. 

As stated earlier, adsorption measurements should preferably be amplified by (micro-)calorlmetry. A relatively old example where this has been done concerns the adsorption of a homologous series of fatty acids from heptane on hematite (a- FCjOg) using a flow calorimeter ). All isotherms are of the L-type and so were the curves. Over a range of coverages, excluding low 0... 

In the same vein, fig. 2.28 Illustrates the adsorption of long chain n-alkanes from n-heptane on different grades of graphite, to compare their surface properties. One of these adsorbents, Vulcan 3G, was a standard sample especially prepared under lUPAC auspices. The enthalpies were measured as displacement enthalpies in a flow calorimeter. All enthalpy and adsorption isotherms are S-shaped. In fig. 2.28a, right, is plotted as a function of for the... 

Fig. 12. Double isothermal wire calorimeter probe for low pressure flow system.

Flow calorimetric measurements of the isothermal Joule-Thomson coefficient of a vapour also provide information on gas non-ideality which is fiee from adsorption errors. Basically, all that is required is a fixed-throttle flow calorimeter, free of heat leaks, fitted with an electric heater as shown in Figure 9 so that isothermal measurements can be made [77-alb/wor]. 

A flow calorimeter for measurement of the isothermal Joule-Thomson coefficient of vapours has been described by Francis, McGlashan, and Wormald and an apparatus said to be useful for studies on mixtures has been described by Dawe and Snowdon, but very few measurements of ft for mixtures have been... 

The three types of isothermal heat flow calorimeters described above can be used to measure heat flow in semi-batch reactions, where one or more reactants are charged to the reactor and the other reactants are added at controlled rates throughout the reaction. With careful design the heat flow calorimeters can simulate process variables such as feed rate, stirring, distillation and reflux . 

Stockton et al, 1986. North American Thermal Analysis Conf September 1986. Wright, T.K. and Butterworth, C.W., 1987, Isothermal heat flow calorimeter. Hazards from Pressure, Symposium Series No. 102, 85-96 (IChemE, Rugby, UK). Regenas, W., 1979, Am Chem Soc Symp Ser No. 65, 37-49. 

Heat flow calorimetry is often used to determine the heat profile of the desired reaction and, from this, the heat of reaction. These calorimeters are best operated in an isothermal mode as it is often difficult to interpret the resulting heat profile curve when there is a heating stage with a batch reaction. The heat profile obtained in such a case has a distinct curve due to the heating and it is necessary to repeat the experiment, as closely as possible but without any reaction taking place, in order to determine the baseline. Batch processes are therefore frequently converted to isothermal, semi-batch processes when using a heat flow calorimeter to determine the heat of reaction. 

This Dewar experiment showed that the overall process was in fact endothermic with a total heat uptake of around 100 kJ kg . The majority of the reaction took place during the heat-up phase as no further temperature change in the Dewar contents was observed during the hold period. The actual reaction between formaldehyde and the glycols is exothermic. This was demonstrated by the isothermal heat flow calorimeter experiment in which the acid catalyst was added not at the start but once the process was at 80°C. The relatively small exothermic peak, compared to that estimated theoretically, shows that the effect of the acid was to ensure that the reaction went to completion and that the reaction itself takes place without a catalyst. The reason for the difference between... 

Setaram C80 heat flow calorimeter sample mass, polyisocyanate 264 mg, polyol 292 mg crucible, mixing cell with metallic membrane isothermal at 80 °C, sensitivity 1 jiV. Initially, the two reagents are isolated by a membrane and stabilized in the calorimeter at 80 °C. The membrane is cut, and mixing is effected by manual rotation of the stirrer. 

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