CO2 desorption rate

Fig. 9.23. Comparison of simulated absorption/desorption rates with experimental data of Hikita and Konishi [100] for SO2 absorption into aqueous Na2CC>3 solutions (adapted from Ref. [70]). (a) SO2 absorption rate (b) CO2 desorption rate.

We studied the behaviour of two 2 mm thick PUs sheets with two different initial CO2 concentrations Cj = 13.7% grav. and C2 = 3.8% grav., respectively (Fig. 4.76). After a period of time, the concentration of CO2 in the first case became equal to the initial concentration of the second case C2. Surprisingly, the further CO2 desorption rate for the first sample was not equal to the desorption rate observed in the second case, even though at that time, the CO2 content was equal in both cases. It was observed that the lower the initial concentration of CO2, the slower the rate of CO2 desorption (Fig. 4.76). 

Fig. 4.76 CO2 desorption rate for different PU sheet thickness and different initial CO2 content ...

FIGURE 9.15 Separation of poly(styrene-comethyl methacrylate)s on a silica gel column with 5 p.m particles using a solvent gradient including using chloroform with 3.5% ethanol added as the desorption promoting solvent and CO2. Flow rates CO2,0.5 mL/min chloroform with ethanol additive (0.25-2.5 mL/min in 30 min) at 333 K and back pressure 20 MPa. (Reprinted from E. Kawai et al., J. Chromatogr. A, 991 197 (2003). With permission.)... 

The expected areas of future expansion of EFLC are in the separation of highly polar solutes. Mixtures of 61.7/27.7/10.6 and 55.7/25/1/19.2 mol ratio methanol/H20/C02 were predicted to have dielectric constants of 38 and 34 [28], respectively. Ion-exchange EFLC should be viable in these and other higher polar EFL mixtures, such as acetontrile/H20/C02 and THF/H2O/CO2 mixtures. Ultra high-speed gradient separations may be possible in EFLC as a result of the fast desorption rate constants for solutes under EFLC conditions. 

As mentioned in Section 15.3.3, most CO2 in blood exists as HCO3". In evaluating the CO2 desorption performance of blood oxygenators, we must always consider the simultaneous diffusion of HCOg", the rate of which is greater than that of physically dissolved COg. Experimental data on the rates of CO2 desorption... 

At low temperature the surface is mainly covered by CO due to larger sticking coefficient then the dissociative adsorption of oxygen is limited. When the temperature increases, the CO coverage decreases due to the rise of the desorption rate, then oxygen can adsorb and react with adsorbed CO and the rate of CO2 production increases. At high temperature the desorption of CO becomes faster and limits the reaction rate. 

Erkey and Akgerman [8] reported an adsorption equilibrium constant for naphthalene in alumina pores filled with supercritical CO2. Analysis shows that this desorption equilibrium constant is simply proportional to the solubility of naphthalene in CO2 as measured by Tsekhanskaya et al. [9]. Hence, the desorption rate constant was estimated from the following type of correlation reported for the naphthalene-ethylene system by Tsekhanskaya et al. [9] ... 

Fig. 11. Experimental setup for the in situ detection of chemisorbed CO during catalytic combustion of CO on Pt using optical infrared-visible sum frequency generation (SFG) and mass spectrometry. A mode-locked Nd YAG laser system is used to provide the visible laser beam (second harmonic 532 nm) and to pump an optical parametric system to generate infrared radiation (wir) tunable with a pulse duration of 25 ps. MC monochromator, PMT Photomultiplier, AES Auger Electron Spectrometer, LEED Low Energy Electron Diffraction Spectrometer, QMS Quadrupole Mass Spectrometers for CO Thermal Desorption (TD) and CO2 production rate measurements.

In the following, we will discuss DMC simulations on the CO oxidation on the Pt(lOO) surface, that were done in our laboratories. The simulations show oscillations in the CO2 production rate as well as several types of spatio-temporal pattern formation. In essence, it is an extension of the ZGB model with desorption and diffusion of A, finite reaction rates and surface reconstruction. We will discuss it to illustrate the complexity of the models with which DMC simulations can be done nowadays. For clarity, we will stick to the A and B2 notation employed in the previous section. Species A corresponds to CO and B2 corresponds to 02- Furthermore, we will speak in terms of reaction rates instead of relative reaction probabilities. This terminology is entirely justified in the DMC approach that we used. 

The CO coverage is not inhibiting the adsorption of the other reactants now, since the higher temperature leads to a higher CO desorption rate. As a result, the lower concentrations of the reactants toward the outlet lead to decreasing adsorption rates and a lower production rate of CO2. This is in contrast to Fig. 6, in which an increasing CO2 production toward the outlet is shown. The surface reaction between NO and N is the most important step in the N2 formation in the first half of the reactor. In the last part, the recombination of two N adatoms becomes an extra and dominant contribution in the... 

A large amount of N2O was formed from the initial stage over LaM03 (M = Co, Mn, Fe, Cr, Ni) at 573 K. The time course of the NO+CO reaction (performed in a batch recirculation system) reflects this situation. These results support a two-step reaction pathway in which N2O is an intermediate for nitrogen formation, deal et al. (1994) confirm the role of N2O as intermediate in this reaction over perovskite oxides. They used steady-state isotopic transient kinetic analysis to study the mechanism of NO + CO reaction over LaCo03. They concluded that N2O was an intermediate in the formation of N2 at T < 873 K. They also concluded that at high temperature CO2 desorption became the rate-limiting step of the overall reaction. This is likely due to the rapid formation and slow decomposition of very stable carbonates on the perovskite surface as reported by Milt et al. (1996). 

Temperature-programmed desorption (TPD) is extensively applied for catalyst characterization. Commonly used molecules are NH3, H2, CO and CO2. From the desorption pattern much useful information can be obtained. TPD allows kinetic experiments in which the desorption rate from the surface is followed while the temperature of the substrate is increased continuously in a controlled way, usually in a linear... 

Generally, the catalytic reactions are controlled by several intermediate steps such adsorption, desorption and surface reaction [1]. For hydrogenation of CO2, it is so far believed that surface reaction is the ratecontrolling step [12-14]. Therefore, less attention has been paid to study the effect of adsorption and desorption rates on catalytic conversion of CO2 to hydrocarbons. This work is an attempt to study the effect of adsorption/desorption and surface reaction on hydrogenation of C020ver a newly developed Cu-aluminosilicate catalyst. 

Figure 7.5a shows molecular beam results on the temperature dependence of the steady-state rate of CO oxidation over a Pd(l 1 0) surface. At 300 K the reaction is Umited by oxygen adsorption because the surface is covered with COads In the temperature interval between 370 and 650 K, however, the rate for CO2 production increases rapidly, presumably because of desorption of some of the CO, which reduce the COads coverage on the surface. A bistability is seen in this temperature region, as indicated by the hysteresis in CO2 formation rate seen between experiments with increase and decrease of temperature (Figure 7.5a). As the temperature is increased, the transfer from the CO layer to the Oads layer is delayed, while when the temperature is decreased, the reverse is true. Local single oscillations are also seen for the CO2 rate at 372 and 382 K in the...

The only gas chromatographic method used for the measurement of diffusion coefficients of gases on solid surfaces is the RF-GC technique validating a recent mathematical analysis, also permitting the estimation of adsorption and desorption rate constants, local adsorbed concentrations, local isotherms, local monolayer capacities, and energy distribution functions." The RF-GC technique has been successfully applied for the time-resolved determination of surface diffusion coefficients for physically adsorbed or chemisorbed species of O2, CO, and CO2 on heterogeneous surfaces of Pt/Rh catalysts supported on Si02." All calculations for the... 

As before we tried to find a correlation between the rate of the CO2 desorption process and the 0- °° - time evolution achieved under the same conditions. The experiment was also performed on 2 mm thin PUs sheets. 

A series of remarks could be made according to equations 4.22 (a) and (b) CO2 appeared in PUs as time proceeded and consequently, its desorption depended both on the rate of the reactions and on the CO2 diffusion rate. 

Figure 6 shows the pressure dependence of diffusion coefficients calculated from permeation, sorption, and desorption rate curves for CO2 in PI2080. The average values of diffusion coefficients from sorption and desorption rate curves D y are in fair agreement with that from permeation rate curve D. The solid line in Figure 6 was computed from Equation 14... 

Figure 6. Pressure dependence of diffusion coefficients calcuiated from permeation ( -), sorption ((,)) and desorption (A) rate curves for CO2 in PI2080. 9 is average vaiue of diffusion coefficients from sorption and desorption rate curves at same pressure. The soiid iine is caicuiated from Equation 14 using parameters 0 in Tabie 1. The dotted line is calculated from Equation 15 using parameters in Table 1.

A number of reviews are available discussing the application of membrane contactors for acid gas removal (Li and Chen, 2005 Mansourizadeh and Ismail, 2009) [4] [7]. Most research activities described in the literature deal with use of membrane contactor for the removal of carbon dioxide. Most of the time alkanolamine solutions have been used for the selective removal of CO2 from various gas streams (Jamal et al. 2006 Wang et al. 2004) [2] [10]. The effect of the amine solvent, the operating conditions, and the membrane characteristies on the removal of CO2 has been studied by (Wang et al, 2004) [10]. Results for the kinetics for both the absorption and desorption rate of CO2 for different amine absorption liquids (MEA, DEA, MDEA) and AMP and mixtures of these absorption liquids have been reported by (Jamal et al., 2006) [2]. Also, the use of other types of absorption liquids has been studied. Results for different amino acid salt solutions as CO2 absorbent have been described by (Lu et al., 2009) [6]. The use of membrane contactors is not limited to the removal of CO2. Membrane contactors have also been applied to remove H2S and SO2 from different gas streams (Li et al. 2000) [5]. 

In Eqs. (1) and (2), J was the CO2 absorption or desorption rate (or flux) by ILs and Xa were the surface reaction mass transport rate constant and diffusion mass transport rate constant, respectively and, , and were the fugacities of CO2 in ILs at equflibrium, at the vapor—Hquid interface, and at the bulk phase of the ILs, respectively. 

The results registered for direct methanol and ethanol fuel cells operating at intermediate temperatures (up to about 150 °C) in combination with composite PFSA membranes with enhanced properties under these conditions indicate that this approach can provide a promising solution to increase performance by overcoming the low reaction oxidation rate of the organic fuel, enhance the desorption rate of the adsorbed organic residues thus enhancing the electrochemical stability, and may promote an increase of the CO2 yield in the case of ethanol-fed fuel cells. 

The liquid side volumetric physical mass transfer coefficient was determined from the desorption rate of oxygen. Detailed description of the experimental set up, procedure and analysis of data is given by Tosyali [30]. Methods of estimating the interfacial CO2 concentration, diffusivities of CO2 and OH in the liquid phase, reaction rate constant, which are all required in data analysis, can be found elsewhere [31, 32]. ... 

Fig. 8.3 Interfacial structure of CO2 desorption from stagnant ethyl acetate at 17 °C and N2 rate of 0.1 m /h [1]. a Beginning of formation, b Development, c Stable structure...

Okunev et al. [115] proposed an approximate analytical expression for the rate of CO2 desorption as a function of sorbent texture, temperature, CO2 pressure, particle size, and Sherwood number. The reaction was defined as ... 

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