Two-stage adsorption

Hobbs, S. and Barder, T. (1989) Two-stage adsorptive separation process for purifying 2,6 dimethylnaphthalene. US Patent 4,835,334. 

Benfield LoHeat System (UOP) [677], The high thermal efficiency of this two-stage adsorption process using lean and semi-lean solvent is achieved by recompression of the flash steam with an injector or a mechanical vapor compressor. UOP has also developed a number of other process configurations [404], [669], [678] -[680], The diethanolamine promoter enhances the mass transfer by carbamate... 

The condensation phase and reprocessing of the desorbate are carried out in the same manner as described for the single-stage plant. For example, a two-stage adsorption plant for the recovery of dichloromethane is able to clean a gas stream of3000 m /h to a residual solvent content of less than 20 mg/m. ... 

The adsorption of cationic polymers such as nonylphenol diethylamine, NP triethylamine, NP tetraethyl pentamine. Octyl phenol (OP) diethylene triamine, and OP tetraethylene pentamine from aqueous solutions on an activated carbon showed a two-stage adsorption. " low adsorptions the molecules were postulated to have flat orientation on the surface of the carbon. A reorientation of the molecules occurred in the second stage as the adsorption increased, until at saturation the molecules were almost perpendicular to the surface. The variation of heats of adsorption with surface coverage showed two inflections (Figure 7.26). 

Figure 3.32 Two Stage (Adsorption/Regeneration) System for Drying of Solvents...

The next step of water treatment is two-stage adsorption process, wha-eby the value of the residual concentration of organic substances is strongly reduced due to their physical adsorption on activated carbon and bio-oxidation by heterotrophic bacteria. The water is then drawn through fine filters, made of sand, to remove any remaining contaminants. After slow filter, the water is clear, colorless, without odor and taste. At that stage, the water is ready to be consumed. The water... 

An example of the time effects in irreversible adsorption of a surfactant system is shown in Fig. XI-8 for barium dinonylnapthalene sulfonate (an oil additive) adsorbing on Ti02 (anatase). Adsorption was ineversible for aged systems, but much less so for those equilibrating for a short time. The adsorption of aqueous methylene blue (note Section XI-4) on TiOi (anatase) was also irreversible [128]. In these situations it seems necessary to postulate at least a two-stage sequence, such as... 

Compounds having low vapor pressures at room temperature are treated in water-cooled or air-cooled condensers, but more volatile materials often requite two-stage condensation, usually water cooling followed by refrigeration. Minimising noncondensable gases reduces the need to cool to extremely low dew points. Partial condensation may suffice if the carrier gas can be recycled to the process. Condensation can be especially helpful for primary recovery before another method such as adsorption or gas incineration. Both surface condensers, often of the finned coil type, and direct-contact condensers are used. Direct-contact condensers usually atomize a cooled, recirculated, low vapor pressure Hquid such as water into the gas. The recycle hquid is often cooled in an external exchanger. 

A variant of the common Langmuir type models is obtained if it is assumed that both alkene molecules are chemisorbed (Langmuir adsorption) on the same active center. If it is further assumed that there are two different adsorption steps, the following set of reaction equations for the initial stages of the metathesis of propene is obtained ... 

COPISA [CO pressure induced selective adsorption] A process for separating carbon monoxide from the effluent gases from steel mills by a two-stage PSA unit. Developed jointly by Kawasaki Steel Corporation and Osaka Oxygen Industry. In the first stage, carbon dioxide is removed by activated carbon. In the second stage, carbon monoxide is removed by sodium mordenite. 

An SMB-type process has been disclosed to extract the 26DMN using liquid phase adsorption in a simulated moving bed two stage system [45, 46]. The source of the 26DMN is not specified but could be by one of the methods outlined by Lillwitz. Currently almost all separation of 26DMN is by crystallization. 

Instead of rotary pumps, large water jet, steam ejector, or water ring pumps can be used. For batch evacuation, and the production of hydrocarbon-free fore vacuum for sputter-ion pumps, adsorption pumps (see Section 2.1.8.1) are suitable. If the use of oil-sealed rotary vane pumps cannot be avoided, basically two-stage rotary vane pumps should be used. The small amount of oil vapor that backstreams out of the Inlet ports of these pumps can be almost completely removed by a sorption trap (see Section 2.1.4) Inserted In the pumping line. 

Calibration at a flow rate other than the flow rate associated with the adsorption or desorption peaks can lead to serious errors because the width of the peaks and therefore the peak areas are directly proportional to the flow rate. A good two-stage pressure regulator and needle valve provide adequately constant flow rates over the short time required for desorption and calibration. 

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