Calorimetry adaptive

Different alternatives have been presented to circumvent this issue in heat flow calorimetry. A priori off-line determination of the dependence of UA [9], adaptive calorimetry using an additional off-line measurement [12] and cascade state estimation observers [14] proven to work, will be discussed in the following section. Obviously, another alternative is to use heat balance calorimetry and to solve the energy balances given by Equations 7.1 and 7.2 simultaneously to compute the evolution of the heat of reaction, Qp and the overall heat transfer coefficient, UA. This approach will be addressed in Section 7.2.3. 

The overall heat transfer coefficient can be estimated online by using an additional process measurement (e.g., gravimetric conversion or solids content) together with state (parameter) estimation techniques to update the value of the overall heat transfer coefficient. This approach referred as adaptive calorimetry has been mainly exploited by Fevotte and coworkers [12] to monitor emulsion (co) polymerization reactions. They used a dependence of U with conversion... 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

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. 

Fig. 2 Typical thermogram obtained using conventional differential scanning calorimetry on PNIPAM solution the temperature of maximum heat capacity (Tmax), the width of the transition at half-height (AT1/2), the heat of transition (AH), the difference in the heat capacity before and after the transition (ACp), and the demixing temperature (Tdem). (Adapted from Ref. [200])...

Fig. 6 Differential scanning calorimetry thermogram of 2,4-dinitrophenyl-2,4-dinitro-benzoate, illustrating the recrystallization of form IV into form III (Tl), the melting of forms III and II (T2 and T4), the solidification of the melts produced by T2 and T4 (T3 and T5), and the melting of form I (T6). (Data adapted from Ref. 46.)...

Fig. 12 Differential scanning calorimetry thermograms obtained for piretanide, as recrystallized from (a) f-butanol, (b) n-propanol, (c) i-propanol, and (d) IV V-dimethyl-formamide. (Data adapted from Ref. 34.)...

To 1-g sieved air-dry soil add 20 mL add extracting solution. Shake for 5 minutes and filter if filtrate is not clear, repeat filtration. The filtrate can be analyzed by calorimetry or ICP (adapted from Reference 10). 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

Figure 5.2 Experimental data for the PhO-H bond dissociation enthalpy, in solution (only photoacoustic calorimetry values) and in the gas phase. A recommended gas-phase value is indicated by the solid line and its error limit by dashed lines. Adapted from [75],...

Titration calorimetry is a method in which one reactant inside a calorimetric vessel is titrated with another delivered from a burette at a controlled rate. This technique has been adapted to a variety of calorimeters, notably of the isoperibol and heat flow types [194-198]. The output of a titration calorimetric experiment is usually a plot of the temperature change or the heat flow associated with the reaction or physical interaction under study as a function of time or the amount of titrant added. 

Figure 11.1 (a) Scheme of an isoperibol titration calorimetry apparatus A Dewar vessel B lid C stirrer D electrical resistance E thermistor F titrant delivery tube G O-ring seal, (b) Vessel for isothermal operation A stainless-steel, platinum, or tantalum cup B water-tight stainless steel container C heater D Peltier thermoelectric cooler E O-ring seal F heater and cooler leads. Adapted from [211],... 

The principles of titration calorimetry will now be introduced using isoperibol continuous titration calorimetry as an example. These principles, with slight modifications, can be adapted to the incremental method and to techniques based on other types of calorimeters, such as heat flow isothermal titration calorimetry. This method, which has gained increasing importance, is covered in section 11.2. 

As mentioned above, titration methods have also been adapted to calorimeters whose working principle relies on the detection of a heat flow to or from the calorimetric vessel, as a result of the phenomenon under study [195-196,206], Heat flow calorimetry was discussed in chapter 9, where two general modes of operation were presented. In some instruments, the heat flow rate between the calorimetric vessel and a heat sink is measured by use of thermopiles. Others, such as the calorimeter in figure 11.1, are based on a power compensation mechanism that enables operation under isothermal conditions. 

Figure 11.5 Typical curve for a continuous titration calorimetry study of an exothermic reaction, using the calorimeter of Figure 11.1 in the heat flow isothermal mode of measurement./ is the frequency of the constant energy pulses supplied to the heater C in Figure 11.1 b. Adapted from [196,197],...

Figure 6.3. Levitation of a molten metal in a radio-frequency field. The coil consists of water-cooled copper tubes. The counter winding above the sample stabilizes levitation. The same coils (and possibly additional ones) act as the induction heater. This technique has been applied to container-less melting and zone refining of metals and for drop calorimetry of liquid metals. It can be also used to decarburize and degas in ultrahigh vacuum mono-crystalline spheres of highly refractory metals (adapted from Brandt (1989)). The arrows indicate the instantaneous current flow directions in the inductors.

Figure 6. Calibration of heat generation from o-cresol by Pseudomonas metabolism as a standard plot for analysis of o-cresol alone and in o-cresol, vanillic acid mixtures, dependent on Pseudomonas adaptation in both calorimetry and stripping.

The idea of calorimetry is based on the chemical reaction characteristic of molecules. The calorimetry method does not allow absolute measurements, as is the case, for example, with volumetric methods. The results given by unknown compounds must be compared with the calibration curve prepared from known amounts of pure standard compounds under the same conditions. In practical laboratory work there are very different applications of this method, because there is no general rule for reporting results of calorimetric determinations. A conventional spectrophotometry is used with a calorimeter. The limitations of many calometric procedures lie in the chemical reactions upon which these procedures are based rather than upon the instruments available . This method was first adapted for quinolizidine alkaloid analysis in 1940 by Prudhomme, and subsequently used and developed by many authors. In particular, a calorimetric microdetermination of lupine and sparteine was developed in 1957. The micromethod depends upon the reaction between the alkaloid bases and methyl range in chloroform. 

FIGURE 3.1 Differential scanning calorimetry melting curves (scan rate 0.04°C/min) of trimyristin dispersions (10% triglyceride stabilized with different concentrations of tyloxapol) with different mean photon correlation spectroscopy z-average diameters. The raw material was dispersed in an aqueous phase containing 1% tyloxapol. (Adapted from [1]. Copyright 2000, American Chemical Society. With permission.)... 

This is the most common mode of addition. For safety or selectivity critical reactions, it is important to guarantee the feed rate by a control system. Here instruments such as orifice, volumetric pumps, control valves, and more sophisticated systems based on weight (of the reactor and/or of the feed tank) are commonly used. The feed rate is an essential parameter in the design of a semi-batch reactor. It may affect the chemical selectivity, and certainly affects the temperature control, the safety, and of course the economy of the process. The effect of feed rate on heat release rate and accumulation is shown in the example of an irreversible second-order reaction in Figure 7.8. The measurements made in a reaction calorimeter show the effect of three different feed rates on the heat release rate and on the accumulation of non-converted reactant computed on the basis of the thermal conversion. For such a case, the feed rate may be adapted to both safety constraints the maximum heat release rate must be lower than the cooling capacity of the industrial reactor and the maximum accumulation should remain below the maximum allowed accumulation with respect to MTSR. Thus, reaction calorimetry is a powerful tool for optimizing the feed rate for scale-up purposes [3, 11]. 

Physicochemical methods, i.e. adsorption of probe molecules followed by varied analytical techniques (gravimetry, chromatography, calorimetry, spectroscopic techniques, etc.) are currently used for estimating more precisely the concentration of the potential active sites.[34 36] However, very few methods are well adapted for this purpose most of the methods employed for the characterization of the acidity of solid catalysts lead to values of the total concentrations of the acid sites (Brpnsted + Lewis) and to relative data on their strength, whereas few of them discriminate between Lewis and Brpnsted acid sites. It is however the case for base adsorption (often pyridine) followed by IR spectroscopy, from which the concentrations of Brpnsted and Lewis sites can be estimated from the absorbance of IR bands specific for adsorbed molecules on Brpnsted or Lewis sites. 

Stavinoha and Kline (2001) adapted ASTM method D 6186 (Oxidation Induction Time of Lubricating Oils by Pressure Differential Scanning Calorimetry [P-DSC]) for analyzing the oxidative stability of SME treated with antioxidants. This report concluded that isothermal P-DSC analysis is suitable for screening the effectiveness of antioxidants for treating biodiesel. 

Phase-change adsorption calorimetry. This was the earliest type of diathermal-conduction calorimetry and was originally developed in the form of ice calorimetry by Lavoisier and Laplace (1783), who weighed the liquid water, and by Bunsen (1870), who measured the change of volume. Dewar (1904) devised an elegant adsorption calorimeter at liquid air temperature the heat was evaluated from the volume of air vaporized. Of course, the temperature of the calorimeter is imposed by the temperature of the phase change. Because these calorimeters lack adaptability and cannot be readily automated, they are mainly of historical interest. 

Immersion calorimetry can be used to study either the surface chemistry or the texture of active carbons. A sensitive Tian-Calvet microcalorimeter is adaptable for either purpose, the main difference being in the choice of wetting liquids. 

Fig. 3. Isothermal crystallization thermogram obtained by differential scanning calorimetry (DSC) indicating the determination of f, and reduced crystallinity (f) (adapted from Ref. 9).

Abbreviations DEA, dielectric analysis >OC. degree of crystallinity DSC, di erential scanning calorimetry LM, local mobility (secondary relaxations) SR, structural relaxation 7g, determination of glass transition temperature TSDC. thermally stimulated depolarization current spectroscopy XRD, X-ray difTractometry. Source Adapted from Ref. 15. 

It should be, however, noted that no apparatus or method can be considered universal in the domain of high-temperature mixing calorimetry, and adaptations should always be made in accordance with the particular requirements of the system under investigation. 

Two questions are raised by the tide of this main section and deserve being answered immediately, i.e., (i) why are we deahng with calorimetry and (ii) is immersion calorimetry reserved to pure hquids The answers are that (i) the heat exchanged on wetting is a precious data to be exploited, for sure (as we shall see), whereas (ii) the way devised to carry out a clean and precise immersion calorimetry experiment requests a pure hquid and is not adapted for the study of adsorption from solutions. In this section, we should certainly pay tribute to Zettlemoyer [2], who, with his coworkers, was the first to extensively apply immersion calorimetry for the study of adsorbents. 

Figure 12.1 Closed-system setup for immersion calorimetry of powders in a Tian-Calvet heatflow microcalorimeter. (Adapted from [7].)...

Figure 12.2 High-pressure liquid intrusion calorimetry setup for the determination of energies of wetting for nonwetting systems. (Adapted from [39].)...

Figure 12.4 Accessible surface area as a function of pore width for a set of activated charcoals (activation increases from Cl to C4). The liquids used for immersion calorimetry are, in order of increasing size benzene, methanol, isopropanol, cyclohexane, tertiary butanol, and a-pinene. (Adapted from [36].)...

Figure 12.7 Differential enthalpy of adsorption of iodine on two carhons (calorimetry). (Adapted from [63].)...

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