Isotherm static method

In slow pyrolysis, temperatures are generally lower than for flash pyrolysis, but residence time is longer. Meanwhile, there are two different methods. One method is the isothermal-static method where the charge is directly heated at a given temperature and maintained during a certain time while in the dynamic method (TGA) the charge is progressively heated. 

Static Methods for Measurement of Vapour Pressures 4.2.2.2 The Dew-point and Non-isothermal Isopiestic 68... 

This is easy to explain because values derived from the elution partial isotherm only pay regard to the amount adsorbed in the mesopores and the outer surface area. By contrast, the static method is not able to distinguish between these contributions and the micropore part of adsorption. Therefore the obtained values are higher but have no physical meaning whereas the elution values give a more realistic picture. The results for the standard carbon are very similar to the static values. This means that there are almost no micropores and the sorption processes take place in the mesopores and the outer surface area. This is confirmed by the huge difference in the thermodesorption peak of both materials. 

In principle, a continuous procedure can be used to construct the isotherm under quasi-equilibrium conditions the pure adsorptive is admitted (or removed) at a slow and constant rate and a volumetric or gravimetric technique used to follow the variation of the amount adsorbed with increase (or decrease) in pressure. A carrier gas technique, making use of conventional gas chromatrographic equipment, may be employed to measure the amount adsorbed provided that the adsorption of the carrier gas is negligible. In all types of measurement involving gas flow it is essential to confirm that the results are not affected by change in flow rate and to check the agreement with representative isotherms determined by a static method. 

An earlier study (Stavinoha and Howell, 2000) examined the effects of TBHQ and a-tocopherol on oxidative stability of SME from four different sources by non-isothermal P-DSC in static (zero air-purge) mode. P-DSC curves were analyzed by measuring the OT where P = 2000 kPa, initial temperature = 25 °C, and (S = 5°C/min. Results for two of the SME samples showed that addition of 2000 ppm a-tocopherol increased OT by -20 °C while addition of 2000 ppm TBHQ increased OT by -30 °C. Addition of the same concentration of a-tocopherol and TBHQ to the other two SME samples increased OT by -30 °C and -40 °C, respectively. Interpretation of these results suggested TBHQ was more effective at increasing relative resistance to oxidation of SME than a-tocopherol, a conclusion that was in accordance with those by Mittelbach and Schober (2003) for the isothermal Rancimat method. 

In this paper solubility measurements of synthetic and natural dyestuffs are presented using VIS-spectroscopy. The investigations concentrate on two different methods. I. P-carotene was measured as a function of temperature and pressure in near- and supercritical C02 (289 to 309 K, 10 to 160 MPa) and CC1F3 (297 to 326 K, 12 to 180 MPa), respectively, using a static method. II. Additionally, the solubilities of l,4-bis-(n-alkylamino)-9,10-anthraquinones (with n-alkyl = butyl, octyl) were determined with a dynamic method in temperature and pressure ranges from 310 to 340 K and 8 to 20 MPa, respectively this method permits a continuous purification from better soluble impurities as well as the measurement of solubilities at the same time. For both anthraquinone dyestuffs intersection points of the solubility isotherms were found in the plot of concentration versus pressure. This behavior can be explained by a density effect. 

The aim of the present paper was to investigate the structural and surface characteristics of two types of porous polymers. The sorption isotherms of nitrogen at 77 K, and benzene and water vapor at room temperature were measured by the static method. The specific surface areas, pore volumes and pore dimensions were derived for the investigated polymers from different experimental data. The structural characteristics of the investigated porous polymers differ considerably for various types of adsorbates and temperatures. The surface characterization of both resins was made by XPS method. 

Starch has been classified as a moderately hygroscopic material.f Water sorption studies have been conducted using static methods (saturated salt solutions in closed chambers) modified inverse frontal gas chromatography, and automated moisture balance systems. " The isotherms are typically type II curves exhibiting hysteresis, as shown in Fig. 5. Hysteresis in starch samples has been attributed to intra- and... 

Figure 2. Sorption Isotherm of Com Starch Determined at 25°C by Static Method.

Fig. 6.17 Principle of different static methods for isotherm determination.

The primary use of isotherm data measurements carried out on single-component elution profiles or breakthrough curves is the determination of the single-component adsorption isotherms. This could also be done directly, by conventional static methods. However, these methods are slow and less accurate than chromatographic methods, which, for these reasons, have become very popular. Five direct chromatographic methods are available for this purpose frontal analysis (FA) [132,133], frontal analysis by characteristic point (FACP) [134], elution by characteristic point (ECP) [134,135], pulse methods e.g., elution on a plateau or step and pulse method) [136], and the retention time method (RTM) [137]. 

It has been shown in many investigations that ECP, FA, and FACP give the same experimental isotherm as the static method. An example of such results is given in Figure 3.45a [8], which shows that data obtained by a static method and data derived by a dynamic (i.e., frontal analysis) method compare very well. 

Figure 3.45 A-(above) Comparison of isotherm measurement methods. Static methods and FA. RNase A on DuPont WCX-300, Langmuir isotherm, o, FA, a = 47.59 mg/mL, b = 0.5290 mL/mg , static method, a = G.37 mg/mL, h = 0.5234 mg/mL. Reproduced with permission from. -X. Huang and C. HorvAth,. Chromatogr., 406 (1987) 285 (Fig. 6).

There is a dearth of competitive adsorption data, in a large part because they are difficult to measme, but also because little interest has been devoted to them, as, until recently, there were few problems of importance whose solution depended on their understanding. Besides the static methods, which are extremely long and tedious and require a large amoimt of material, the main methods of measurement of competitive isotherms use column chromatography. Frontal analysis can be extended to competitive binary isotherms [14,73,93-99], as well as pulse techniques [100-104]. The hodograph transform is a powerful method that permits an approach similar to FACP for competitive binary isotherms [105,106]. 

Try to simulate mixture e q)eriments with single-component isotherms Determine component interactions only if necessary Check agreement between theoretical and e5q)erimental chromatograms Static methods... 

As shown in Figs. 17 and 18, some results on l,4-bis-(octylamino)-9,10-anthra-quinone (AQ08) obtained from the static method are plotted. Whereas the c p) isotherms in Fig. 17 intersect resulting in a complex temperature dependence, no intersection points are found for the c p) isotherms (Fig. 18). This makes clear that the dominant parameter for solubility is density, and that the unusual temperature dependence of the c p) isotherms mentioned above derives from the pVT behavior of CO2. For additional data and a detailed discussion see [40-42,45-47,76-80]. 

Examples of single-component and binary isotherms showing good agreement between the experimental isotherms determined by chromatographic and static methods are shown in Figure 8.8. It should be noted that this method is restricted to binary systems and cannot be easily extended to ternary or multicomponent mixtures. 

The theoretical basis for the chromatographic analysis of adsorption phenomena in gas and/or liquid phase was given by Don DeVault (ref. 1) and Glueckauf (ref. 2, 3). The mathematical procedure developed by these authors enables one to determine the adsorption isotherm of a solute from its elution profiles in column chromatography. The experimental procedure required for this method is far less laborious than those for the conventional static methods of adsorption measurement, and many experimental works have appeared since (ref. 4, 5). Many of these works, however, dealt with adsorption from gaseous phases, and applications to liquid phases are scarce (ref. 6, 7). 

The enthalpies of adsorption for carbon dioxide on active carbon were determined from adsorption isotherms at 25 and 30°C the values vary between 40 and 25 kJ mol with increase of coverage [89]. The differences from the static method results are 2 kJ mol". The results obtained for adsorption of argon, oxygen, nitrogen, carbon dioxide and methane on carbon and silica at infinite dilution do not agree with calorimetric and isosteric data, the difference reaching as much as 2 kJ mol" [90] (Table 4.8). Some contributions [88, 91, 92] mention greater precision... 

The method of determining adsorption isotherms described above is less accurate than frontal analysis, which is often preferred [133—144] because it ignores all kinetic factors and volume changes of the gas phase caused by adsorption of vapours. However it is considerably faster and simpler, and the adsorption isotherms it yields correspond to those of static methods provided that experimental conditions are so chosen that the errors are minimized [1,126]. Sinailarly, due to the short contact time of adsorbent and adsorbate, GSC allows the determination of adsorption isotherms whenever the injected substance undergoes both adsorption and dissolution in polymer provided that the latter process is slow. 

Application of the ebulliometric method at elevated pressures has already been discussed. The method has been used only occasionally, and most vapour-pressure measurements in the range now considered have been made by the static method in apparatus which is, in principle, the same as that used by Andrews for his work on the isotherms of carbon dioxide, and subsequently developed by Hannay and by Ramsay and Young. The sample is confined over mercury in a thick-walled glass tube sealed at its upper end, and the tube is attached to a steel U-tube containing mercury the pressure is transmitted through the mercury to the pressure gauge and a piston on a screw allows the level of the mercury, and hence the volume occupied by the sample, to be adjusted. The experimental tube is heated by means of a vapour jacket. (Alternatively, the glass tube itself may be bent into the form of a U, often then known as a Cailletet tube, and the apparatus is heated by immersion in a normal thermostat bath. )... 

Markowski et al. (44) have applied sandwich TLC for the evaluation of adsorption isotherms, comparing this method to the breakthrough and static methods. All three methods have given similar results. 

The CONTINUOUS FLOW method doses adsorptive onto the sample at a constant and pre-determined flow rate which is low enough to enable quasi-equilibration to occur. The flexibility of this technique is enhanced through the use of a mass flow controller,as is used in the OMNISORP instruments. Rouquerol et al (3) have shown that no appreciable difference is found in the isotherms when compared to static method if the correct mass flow controller setting is used. They also describe how this setting can be confirmed. Theoretically resolution with this method is infinite in practice it is normally unnecessary to exceed 1000 data points but the great advantage of this method is that it is fast. Analysis times are usually significantly less than with the static method. 

The TG-MS technique is extensively used to study the kinetics of the chemical reactions and to determine the kinetic parameters such as activation energy, E and pre-exponential factor, A and to determine the reaction mechanisms controlling the chemical reaction. Two methods, namely, isothermal (static or constant temperature) and non-isothermal (dynamic heating) are generally used for this purpose. 

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