Desorption carbon dioxide

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... 

The carbon monoxide reaction is well studied and the observed kinetics are well understood. Of particular interest is the so-called CO-inhibiting regime , characterized by carbon dioxide covering and blocking the surface, so that the reaction rate is governed by CO desorption rate (see original citations in [78]). 

After the catalyst was saturated with carbon dioxide, a temperature programmed desorption (TPD) was carried out by heating the sample in helium (40 cm3min 1) from room temperature to 873 K (10 Kmin 1). The mass spectrometer was used to follow water (mass 18), carbon monoxide (mass 28), carbon dioxide (mass 44) and oxygen (mass 32). 

Binax A process for removing carbon dioxide from methane from landfill by washing with water absorption takes place under pressure and desorption is done by an air blast at atmospheric pressure. Piloted at a wastewater treatment plant at Modesto, CA, in 1978. 

Carbon monoxide oxidation is a relatively simple reaction, and generally its structurally insensitive nature makes it an ideal model of heterogeneous catalytic reactions. Each of the important mechanistic steps of this reaction, such as reactant adsorption and desorption, surface reaction, and desorption of products, has been studied extensively using modem surface-science techniques.17 The structure insensitivity of this reaction is illustrated in Figure 10.4. Here, carbon dioxide turnover frequencies over Rh(l 11) and Rh(100) surfaces are compared with supported Rh catalysts.3 As with CO hydrogenation on nickel, it is readily apparent that, not only does the choice of surface plane matters, but also the size of the active species.18-21 Studies of this system also indicated that, under the reaction conditions of Figure 10.4, the rhodium surface was covered with CO. This means that the reaction is limited by the desorption of carbon monoxide and the adsorption of oxygen. 

Brady et al. [52] have discussed pressure-temperature phase diagrams for carbon dioxide polychlorobiphenyls and examined the rate process of desorption from soils. Supercritical carbon dioxide was used to extract polychlorobiphenyls and DDT and Toxaphene from contaminated soils. 

A new approach to the analysis of the carcinogenic TSNA in moist snuff tobacco is based on SFE with methanol-modified carbon dioxide. Extracted TSNA are trapped across a glass cartridge filled with Tenax GR, from which they are subsequently released by thermal desorption and analyzed by capillary GC-TEA LOD was <2 ng/g. The technique is fast, reproducible, highly selective and sensitive617. SFE with carbon dioxide was also used in the analysis of TSNA in smokeless tobacco. It revealed the presence of higher levels of 4-(methylnitrosamino)-l-(3-pyridyl)-l-butanone (300) than had been determined earlier by conventional methods618. 

Formic acid decomposes generally on metal surfaces to carbon dioxide and hydrogen. A thermal desorption study on Cu(l 10) showed that the reaction... 

The extraction of environmental or geological particulate matter with solvents, solvent mixtures or supercritical carbon dioxide is the preferred method, because it results in minimum alteration of its polar components, avoids hydrolysis of anhydrides, esters, etc. and is highly efficient for most organic compounds (even sugars). Other workers have reported the direct vaporization by thermal desorption or flash pyrolysis of organic compounds from particulate matter into GC, MS, or GC-MS instruments. Those methods work fine for neutral compounds (e.g. hydrocarbons) but should be used with caution when analyzing polar or labile compounds. 

Figure 6 shows the TPR spectra of adsorbed CO on nickel. The CO was desorbed mostly as the molecular form, whereas the amounts of desorbed carbon dioxide and methane were quite small. Thus, most of the CO adsorbed on nickel is in an undissociated state, and the extent of its adsorption is fairly weak, as the desorption is completed below 200 C. In contrast, the adsorption of methyl acetate on nickel is stronger than those of other reactants or products, as evaluated from the retention time in the nickel-activated carbon column shown in Table III. This fact suggests that most of the nickel is covered by methyl acetate and reaction products, and the coverage of adsorbed CO is quite low under the reaction conditions when the partial pressure of CO is close to that of methyl acetate. The carbonylation is therefore accelerated by increasing the CO/AcOMe ratio which increases the coverage of CO adsorbed competitively with methyl acetate. 

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T0141 Carbon Dioxide Pellet Surface Cleaning—General T0142 Carlo Environmental Technologies, Inc., Medium-Temperature Thermal Desorption (MTTD)... 

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The GEiM-lOOO low-temperature thermal desorption unit is an ex situ technology that treats soils contaminated with volatile organic compounds (VOCs). This process involves a countercurrent drum, pulse-jet baghouse, and a catalytic oxidizer mounted on a single portable trailer. As the soil is heated in the GEM-1000 unit, contaminants are vaporized. The contaminants are then directed to the system s catalytic oxidizer, which is designed to convert virtually all of the VOCs to carbon dioxide and water vapor. The oxidizer contains approximately 4.9 ft of noble metal catalyst and can destroy between 95 and 99% of the hydrocarbons when operating between 600 and 1250°F. 

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... 

As in the carbon-carbon dioxide reaction, mechanisms A and B can be treated for the cases where either the surface rearrangement or desorption of the carbon-oxygen complex is the slow step. This has no effect on the discussion except that the significance of the rate constant js in Equation (10) is altered, as previously discussed. 

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