Regeneration method

The choice between the possible modes of regeneration, for any particular system, depends on economic factors as well as on technical considerations. For example, availability of a cheap source of steam or waste heat tends to favor thermal swing operation over the other alternatives. Nevertheless, there 

Thermal swing is probably the most common system. The temperature dependence of the adsorption equilibrium constant is governed by a vant Hoff equation [Eq. (2.20)]. Since adsorption is an exothermic process and since the more strongly adsorbed species generally have the higher heats of adsorption, a large decrease in the adsorbed phase concentration in equilibrium with a specified fluid concentration may be achieved by a comparatively modest increase in temperature. This means that at elevated temperatures the iso- 

TABLE 11.2. Summary of Factors Governing Choice of Regeneration Method 

Pressure swing Good where weakly adsorbed species is required in high purity Very low P may be required 

Displacemenl desorption Good for strongly held species Avoids risk of cracking reactions during regeneration Product separation and recovery needed (choice of desorbent is crucial) 

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Regeneration. In recent years, considerable effort has been expended to better understand and quantify the process of regeneration. Methods are available to predict thermal, purge, and steaming requirements. Models are available to simulate all of the regeneration types, temperature, pressure, and purge swings. 

Activated carbon adsorption generally uneconomical for removal of >1000 ppm contaminant from large stream unless bed regenerated steaming often easiest regeneration method but creates new wastewater problem usually 3—5 kg steam requited per kg of carbon for regeneration. 

Use closed-loop systems for pickling regenerate and recover acids from spent pickling liquor using resin bed, retorting, or other regeneration methods such as vacuum crystallization of sulfuric acid baths. 

The BiodeNOx process is a novel process concept to reduce NO emissions from flue gases of stationary sources like power plants and other industrial activities [1]. The concept combines a wet chemicd absorption process with a novel biotechnological regeneration method. In the wet chemical absorption step, flue gas components are absorbed into an aqueous solution of Fe"(EDTA) (EDTA= ethylme-diamino-tetraacetic acid). The following reactions take place ... 

Birgersson, H., Boutonnet, M., Klingstedt, F. et al. (2006) An investigation of a new regeneration method of commercial aged three-way catalysts, Appl. Catal. B Environ., 65, 93. 

Seelbach, K., Riebel, B., Hummel, W. etal. (1996) A novel, efficient regenerating method of NADPH using a new formate dehydrogenase. Tetrahedron Letters, 37, 1377-1380. 

It is possible that the regeneration method succeeds by removing short chain, inactive polymer fragments, which will be soluble in the aqueous medium. Once these smaller polymer chains have been removed, the bulk of the polymer is then able to reform its preferred tertiary structure, thus restoring its catalytic activity. The aqueous nature of the procedure may also aid regeneration by... 

Rigorous scale homogenization procedures lead to continuum models for the entire DPF (Bissett, 1984 Konstandopoulos et al., 2001, 2003) exploiting (as is common in continuum descriptions) a suitable scale disparity, namely the ratio of the channel hydraulic radius to the entire DPF diameter. The smallness of this parameter is invoked to formulate a perturbation expansion of the discrete multichannel equations. The continuum multichannel description of the DPF can accommodate various regeneration methods (thermal, catalytic and N02-assisted) and can provide spatio-temporal information of several quantities of interest (e.g. filter temperature, soot mass distribution, flow distribution, etc.) as illustrated in Fig. 38. 

Various glycol regeneration methods were considered, such as direct-fired glycol reboilers, o direct-fired indirect hot oil system, electricol heating ond waste heat recovery. A direct-fired in-direct hot oil system was finally selectd because it provided a safe, well proven regeneration system which could be accommodated within the platform space limitations. 

TABLE 1. FACTORS GOVERNING CHOICE OF REGENERATION METHOD... 

Design techniques for gas-phase adsorption range from empirical to theoretical. Methods have been developed for equilibrium, for mass transfer, and for combined dynamic performance. Approaches are available for the regeneration methods of heating, purging, steaming, and pressure swing. Several broad reviews have been published on analytical equations... 

The remaining polymerization route involves zero-valent nickel complexes and dihalide monomers. Variations of this route most often arise where different sources or regeneration methods of the active nickel species are utilized [82,199, 200-204]. A typical example is shown below in Scheme 51 in which poly(3-phe-nylthiophene) 50 is synthesized from the parent 2,5-dichlorothiophene. As with the Ullmann reaction, polymerization appears to be most compatible with ring systems containing electron-withdrawing substituents. 

Efficient Coenzyme-Regeneration Methods Should be Available... 

Generally, the nicotinamide coenzymes are not covalently bound to the enzyme. They are employed in enzyme assays and preparative applications by adding catalytical but optimized amounts, and they need to be recycled. For an economic process, an efficient regeneration method is a basic requirement. The necessary recycle number depends essentially on the value of the chiral product, generally the method should recycle the coenzyme 100-100,000 times ([42]). 

Process Liquid or gas phase" Adsorbent Selectivity Regeneration method... 

Apart from enzymatic cofactor regeneration, both chemical and electrochemical regeneration methods have attracted attention due to their greater flexibility. The electrochemical regeneration of cofactors has a few advantages, especially the use... 

Kula MR, Wandrey C (1988) Continuous enzymic transformation in an enzyme-membrane reactor with simultaneous NADH regeneration. Methods Enzy-mol 136 9-21... 

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