Isothermal absorption

Discussion of the concepts and procedures involved in designing packed gas absorption systems shall first be confined to simple gas absorption processes without compHcations isothermal absorption of a solute from a mixture containing an inert gas into a nonvolatile solvent without chemical reaction. Gas and Hquid are assumed to move through the packing in a plug-flow fashion. Deviations such as nonisotherma1 operation, multicomponent mass transfer effects, and departure from plug flow are treated in later sections. 

DISCUSSION AND CONCLUSIONS In this study a general applicable model has been developed which can predict mass and heat transfer fluxes through a vapour/gas-liquid interface in case a chemical reaction occurs in the liquid phase. In this model the Maxwell-Stefan theory has been used to describe the transport of mass and heat. A film model has been adopted which postulates the existence of a well-mixed bulk and stagnant zones where the principal mass and heat transfer resistances are situated. Due to the mathematical complexity the equations have been solved numerically by a finite-difference technique. In this paper (Part I) the Maxwell-Stefan theory has been compared with the classical theory due to Pick for isothermal absorption of a pure gas A in a solvent containing component B. Component A is allowed to react by a unimolecular chemical reaction or by a bimolecular chemical reaction with... 

L. I. Katysheva, et ah, Calculation of two-phase non-isothermal absorption in a liquid film in downward co-current flow, Theor. Found. Chem. Eng.,... 

The property changes of the fluid as it flows through the individual piec of equipment may be shown as paths on a TS diagram, as illustrated in Fig. 8-The sequence of paths represents a cycle. Indeed, the particular cycle shown a Carnot cycle. In this idealization, step 1 2 is the isothermal absorption... 

Dry prod.discharge Ib/h % moisture 4.4 Is there some isothermal absorption known of the dry... 

In conclusion, the large differences between natural collagen and keratin must be emphasized both in terms of the isotherm absorption and the nature of fixation sites of the water. We have shown that the influence of chemical modifications gives results which can be explained in terms of the model we have proposed. 

Figure 12.2 Isothermal absorption and re-absorption curves for the bismaleimide epoxy resin Narmco Rigidite 5245 at 90% RH at 45 °C. Calculated theoretical Fickian first absorption and desorption curves are also shown [4].

In the case of isothermal absorption, the equilibrinm line is easily written with Hemy s law, which formulates a linear relationship between y and x. The molar fractions have to be replaced by the new molar loadings according to... 

The solubility reduction appears likely to severely curtail the absorption rate expected on the basis of isothermal absorption. From Fig. 3, the solubility of chlorine at 70 C is only 1/5th of that at the datum of 25 C, and the effective driving force would thereby be reduced by a factor of 5. 

Since an increase in the temperature from i,a to i.co occurs, this causes a decrease in the solvent absorption capacity of the soluted substance according to Henry s law. The absorption efficiency reduces due to an unfavorable equilibrium position at the higher temperature, (see Chapter 1.4.3.3). Consequently, isothermic absorption is aimed for in practice. The heat flux to be removed under isothermal absorption at (t / a = di u) follows from Eq. (3-7). 

We have used the term state of the system many times what is the state of a system The state of a system is rigorously defined through the state variables of the system. The state variables of any system are chosen according to the nature of the system. The state of a boiler can be described by temperature and pressure, a heat exchanger by temperature, a nonisother-mal reactor by the concentration of the different components and temperature, an isothermal absorption tower by the concentration of different components on different plates, a human body by blood pressure and temperature, flow through a pipe by the velocity as a variable varying radially and axially, and so on. 

Remember, though, that the old concept of the HETP (height equivalent to a theoretical plate) can be evaluated as equal to around 25 times the nominal size of the packing. Thus, we can quickly gain a rough estimation of the height of a distillation colunm or even an isothermal absorption column. However, this way of working is imprecise, because there is no rational justification for the concept of the HETP. 

Isothermal Absorption test can help especially in the surface characterization of the nanoclay, and also in the determination of the attachment of the surfactant to the clay. Presence of mono-, double- or tri-layers can be identified in the isothermal adsorption curve. 

Non isothermal phenom ia are present to scane extent in all gas absorption operations. As se i above the importance of the non isothermal effects arises from their influence on the mass transfer rate and, in the case of chemical absorption, from their influence on reaction rates and selectivities. This means that to neglect the boundary condition coiq>ling between solubility and interface temperature may lead to serious overestimates of the absorption rates and to model the non isothermal absorption process, it is necessary to consider the mass and energy balance equations simultaneously. Attention has been ccmsiderably focused both experimentally and theoretically on that important topic particularly during these 3 or 4 last years (14 -. ... 

---