Absorption isobar

It has been found that in the region of concentrations where two hydrogen-palladium alloys coexist (the perpendicular sections of the curves of Fig. 40) it is not possible to trace out the same isobaric curve on sorption and desorption. There is a hysteresis effect illustrated by Fig. 40. It is interesting to find in the study by Lombard, Eichner and Albert (96) that the permeability-temperature curve follows in an inverse manner the absorption isobar, there being a great increase in the permeability in the region 180-200° C. It may be that this rapid alteration in permeability marks the change from )ff-phase to a-phase alloy. 

It is shown in this section with the help of hydrogen sorption isobars on evaporated metal films sintered at various temperatures that the sorption process consists of absorption into the interior of the structure as well as of... 

In order to study the effect of absorption in the nickel-hydrogen system in more detail, Beeck et al. (11) have investigated the hydrogen sorption isobars between 20°K. and room temperature. As shown in Fig. 6, the solid curves represent the isobars for increasing and decreasing temperature. With increasing temperature (the part between 20 and 80°K. will be discussed later), sorption increases fast between 80 and... 

It is of interest to note that in the measurement of the hydrogen absorption on the ascending isobar of Fig. 6, a sudden desorption of hydrogen took place, after raising the temperature, followed by a slow... 

Before leaving the nickel experiments, it may be well to refer to the experiments on hydrogen adsorption variously reported in the literature. As an example, the work of Maxted and Hassid (13) had as its main objective the measurement of the slow activated adsorption of hydrogen on reduced nickel oxide catalysts. It has been proved by the foregoing that the slow adsorption is actually absorption. When plotting their data as isobars, as was done in Fig. 9, the similarity between these isobars and those obtained with sintered nickel films is evident. 

A further method separates the extracted substances by absorption. Basic for this method is that there should be a high solubility of extracted substances in the absorption material, and that the solubility of absorption substance in the circulation solvent should be as low as possible. Further, the absorption material must not influence the extract in a negative way and a simple separation of extract and absorption material has to be available. An ideal absorption material is therefore a substance which is present in the raw material. Most plant-materials contain water, which can act as a very successful absorption material. An ideal example is the separation of caffeine for the decaffeination of coffee and tea. On the one hand, water has a low solubility in CO2, and on the other, water-saturated CO2 is necessary for the process. The extracted caffeine is dissolved into water in the separator and caffeine can be produced from this water-caffeine mixture by crystallization. One advantage of this separation method is that the whole process runs under nearly isobaric conditions. 

Processes with high mass-flow rates, for example more than 40 t/h, have energy demands of a very high level. Especially for the decaffeination processes, in which several hundred - up to a thousand tons of CO2 are in circulation, isobaric processes were developed. In these processes, the extraction step and the separation step have nearly the same pressure and temperature. The separation of the dissolved substance from the CO2 in circulation is maintained by adsorption on activated charcoal, with an ion-exchanger, or by absorption in a washing column. 

The separation in the isobaric decaffeination processes is executed with absorption of caffeine, that means, the caffeine dissolved in CO2 is carried over into water by means of a packed washing column, or by adsorption with activated charcoal, but without recovery therefrom. Other separation methods under investigation are the use of membranes, since the difference in molecular weight between extract and solvent is high enough, or by the addition of substances of low solvent power. It is questionable whether the advantage of the possible isobaric process can compensate for the investment for the additional process steps required. 

A pronounced minimum in the freezing curve be occurs at approximately 0.3 K. As we have discussed earlier for 4He, this leads to the conclusion that Afus-Sm = AfUSi/m = 0 at the pressure minimum, in this case, 2.98 MPa. Below 0.3 K, the liquid has a lower entropy than the solid, and both the enthalpy and entropy of fusion are negative. It is an interesting exercise to start with liquid 3He at 7 = 0.1 K and p = 3 MPa and heat it isobarically. At about 0.6 K, the liquid solidifies with the absorption of heat. Heating the solid to 0.65 K causes it to melt, again with the absorption of heat ... 

Kamlet-Taft) hydrogen bond donation ability ultrasound absorption coefficient isobaric expansibility... 

The quantity t differs from r = tvS, the isobaric, adiabatic relaxation time, by the factor r /r = (C — Cvlb)/C . Both the sound-velocity dispersion and excess sound absorption a can be written in terms of r ... 

Assuming dilute solutions, Table 6.21 lists the equations for sizing absorbers and strippers in terms of a key component and Table 6.22 outlines the calculation procedure. In numbering the relationships in Table 6.21, A, S, P, and T means absorption, stripping, packed columns and tray columns, respectively. Processing dilute solutions implies that heat effects will be small, and therefore, the separation is essentially isothermal. If the column is both isothermal and isobaric, the equilibrium value will be constant. Also, dilute solution means that the gas and liquid flow rates will essentially be constant. In absorption, the gas flow rate is fixed and the liquid flow rate must be estimated, whereas in stripping the liquid flow rate is fixed and the gas flow rate must be estimated. 

The quantities a, c, f, F, r, and p are the thermal diffusivity, sound speed, heat capacity ratio, bulk viscosity coefficient, shear viscosity coefficient, and density of the sample, respectively and Eo, a, P and Cp are the energy fluence of the laser beam, the optical absorption coefficient, the volume expansion coefficient, and the isobaric heat capacity, respectively, of the fluid. Tlie first and second terms in Eq. 2 describe the time dependences of the thermal and acoustic modes of wave motion, respectively. Since the decays of the acoustic and thermal mode densities back to their ambient values take place on such different time scales (microsecond time scale for acoustic mode and millisecond time scale for thermal mode), they were recorded on the oscilloscope using different time bases. 

Figure 2. SFC chromatograms of a 2000 MW polystyrene oligomer mixture. Conditions n-pentane mobile phase at 210 C, 10 m X 100 Ji fused silica capillary column coated with a 0.25- Jm film of crosslinked 50% phenyl metbylphenylpoly-siloxane, UV-absorption at 205 nm, (A) linear pressure program from 34.6 atm (0.12 g/mL) to 60 atm at 0.15 atm/min after a 5-min isobaric period (B) asyoiptotic density program from 0.12 g/mL (34.6 atm) to 0.35 g/siL according to the...

Pressure-composition isotherms may be constructed under an isochoric constraint by adding hydrogen aliquots to the system and measuring the hydrogen absorption or desorption stepwise, or under an isobaric constraint by actively controlling the pressure over the sample to a constant value while the sample absorbs or desorbs. 

Portions of neutron powder diffraction patterns recorded on the high resoiution powder diffractometer (HRPD) instrument at ISIS (UK) from LaNis charged with deuterium in situ to approx. D/M = 0 to 0.6 in the a + p two-phase region. Dotted iine after muitipie pseudo-isobaric absorption steps. Soiid iine after a singie isochoric absorption step from D/M = 0. The iatter data are uninterpretabie except that they obviousiy represent regions of sampie with wideiy distributed iattice parameters. The highest peaks come from the aiuminium sampie ceii and demonstrate that the oniy difference between the two measurements is the state of the sampie. 

We will calculate the difference of the two entropy capacities Cp — Cy as our second example. These are the usual isobaric ( = ( p (at constant pressure) and the more rarely used isochoric capacity Qy (at constant volume). The latter must be smaller than C = Cp (as implied in Sect. 3.9), because the absorption of entropy is made more difficult if the change of volume (positive or negative) related to it is impeded. It makes no difference whether V and S are coupled in the same or in the opposite direction, i.e., F t S or F, S, ( p > Ov is always valid. To calculate the difference... 

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