Desorption of Carbon Dioxide

Carbon dioxide in aqueous solutions exist in three forms (i) physically dissolved CO2 (ii) bicarbonate ion HCOg and (iii) carbonate ion COj -. In the physiological range of pH the latter form can be neglected. The bicarbonate ion HCOg is produced by the following hydration reaction  

This reaction is rather slow in the absence of the enzyme carbonic anhydrase, which is usually the case with fermentation broths, although this enzyme exists in the red blood cells. Thus, any increase of for CO, desorption from fermentation broths due to simultaneous diffusion of HCO3 seems negligible. 

The values of k a for CO, desorption in a stirred-tank fermentor, calculated from the experimental data on physically dissolved CO, concentration (obtained by the above-mentioned method) and the CO2 partial pressure in the gas phase, agreed well with the k a values estimated from the k a for O, absorption in the same fermentor, but corrected for any differences in the liquid-phase diffusivities [11]. Perfect mixing in the liquid phase can be assumed when calculating the mean driving potential. In the case of large industrial fermentors, it can practically be assumed that the CO, partial pressure in the exit gas is in equilibrium with the concentration of CO, that is physically dissolved in the broth. The assumption of either a plug flow or perfect mixing in the gas phase does not have any major effect 

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Tadaki and Maeda (Tl) examined the desorption of carbon dioxide from water in a bubble-column and analyzed the experimental results under the assumption that while the gas phase moves in piston flow, the liquid undergoes axial mixing that can be characterized by the diffusion model. (Shulman and Molstad, in contrast, assumed piston flow for both phases.) Only poor agreement was obtained between the theoretical model and the experimental... 

To reduce to the simple rate Equation (2), it is necessary that some of the steps in the general scheme occur at a negligible or an extremely fast rate. It has been observed (37) that carbon monoxide gas is an immediate product of the chemisorption of carbon dioxide on carbon and that the adsorption of carbon dioxide is not reversible to give immediate desorption of carbon dioxide. Therefore, it may be assumed that the lives of CCCOs) and C(CO)x are short. Consequently, the general expressions can be simplified to... 

Wet oxidation of active carbon - desorption of carbon dioxide 19... 

Quinn R, Appleby JB, Mathias PM, and Pez GP. Liquid salt hydrate acid gas absorbents An unusual desorption of carbon dioxide and hydrogen sulfide upon solidification. Sep. Sci. Technol. 1995 30 1711-1723. 

Sircar, S. and Golden, T.C. Isothermal and isobaric desorption of carbon dioxide by purge. Industrial Engineering Chemistry Research, 1995, 34, 2881. 

The reactivity of carbon dioxide toward oxygen was also studied (25, 66). First, carbon dioxide was adsorbed on nickel oxide containing preadsorbed oxygen. The black color and the high electrical conductivity of the sample remain unaltered (25). However, a reaction does occur since a subsequent adsorption of carbon monoxide produces a desorption of carbon dioxide, while adsorption of carbon monoxide is impossible on a sample precovered by carbon dioxide (25). It is believed that... 

A to G (Fig. 33) were obtained by integration of curves A to G (Fig. 34). Evolution of the profile of the calorimetric curves indicates that the reactivity of the oxide toward carbon monoxide increases progressively with the extent of reduction. From curve A (Fig. 34), it appears that the reaction of dose A is a relatively slow exothermic process. Curves B to F (Fig. 34) are more complex. Analysis of these curves shows that three thermal phenomena occur during the reaction of doses B to F (i) a fast exothermic process whose intensity increases with the extent of reduction, (ii) a slower exothermic process similar to that observed for dose A, whose intensity decreases from curve B to F and, (iii) a slow endothermic process which is evidently the desorption of carbon dioxide. Both exothermic processes are related to the adsorption of carbon monoxide and to the surface reduction of the solid. 

Reduction of the oxide begins with some difficulty, in the absence of metal nuclei, and this accounts for the slow exothermic phenomenon whose intensity is maximum at the beginning of reduction and which results probably in the formation of metal nuclei on the oxide surface. Since the intensity of the fast exothermic phenomenon increases when the extent of reduction is larger, it must be related to a reduction process now occurring at the metal-oxide interface, carbon monoxide being adsorbed on metal crystallites. All carbon monoxide in dose G is adsorbed on the metal and reacts with nickel oxide at the metal-oxide interface since the slow exothermic phenomenon does not appear on curve G (Fig. 34). Calorimetric curves similar to curve G are obtained during the reaction of subsequent doses of carbon monoxide. Finally, it appears from curves B to G (Fig. 34) that desorption of carbon dioxide is a slower process than the adsorption of carbon monoxide and its interaction with nickel oxide. 

Also, the depletion of oxygen from the gas phase is rather low and usually compensated by the desorption of carbon dioxide. The methodology is attractive because it permits a separation of fluid dynamics (momentum balances, continuity equations, and turbulence model) from material balance equations for the state variables of interest. Figure 8 illustrates how results from the fluid dynamic simulations (mean velocities turbulent dispersion coefficient... 

The most common surface functionalities formed during the oxidation of graphite are carboxyl and carbonyl groups. The exact nature of the functional groups depends on the temperature, the concentration of the reactants and reaction products, and the reactivity of the defective site which varies for different types of defects. The decomposition of carboxylic acids and lactones occurs at low temperatures (<300°C) and leads mainly to desorption of carbon dioxide, whereas phenols and quinones favor formation of carbon monoxide (CO), but decompose only at elevated temperatures (>600°C). The exact decomposition/desorption temperatures strongly depend on the carbon material and values reported in literature vary substantially, as discussed in greater detail in the following sections. 

Kwong DWJ, Deleon N, Haller GL (1988) Desorption of carbon-dioxide molectrles from a Pt(l 11) surface a stochastic classical trajectory approach. Chem Phys Lett 144 533-540... 

Sun ZF, Yu KT (2002) Absorption and desorption of carbon dioxide in and from organic solvent effects of Rayleigh and Marangoni instability. Ind Eng Chem Res 41 1905-1913... 

Arsenite Solutions. Addition of essentially stoichiometric proportions of arsenic trioxide to aqueous sodiiun or potassium carbonate solutions results in a marked increase in the rate of absorption and desorption of carbon dioxide, as compared with conventional carbonate solutions. Figure 5-31 illustrates this phenomenon by comparing, qualitatively, the rate of absorption of carbon dioxide at 1 atm partial pressure and room temperature in 40% potassium carbonate and in a typical solution used in the Giarrunarco-Vetrocoke process (Riesen-feld and Mullowney, 1959). The effects of the more rapid absorption and desorption are appreciable savings in regeneration heat, reduction in equipment size, and production of treated gas of higher purity than is possible with ordinary hot carbonate solutions. 

The chemical reactions occurring during absorption and desorption of carbon dioxide can be symbolized by the following equations ... 

The second step consists of desorption of carbon dioxide according to... 

We wish to model growth for that we consider three steps taking place at the internal interface decomposition of COj" ion into adsorbed CO2, desorption of carbon dioxide, and disappearance of the defect accompanying the crystalUzation of the oxide. 

The second step is desorption of carbon dioxide and release of one adsorption... 

M. Simioni, S.E. Kentish, G.W. Stevens, Membrane stripping Desorption of carbon dioxide from alkali solvents, J. Memb. Sci. 378 (2011) 18-27. 

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