Regeneration conditions

There are several theories about the chemistry of vanadium poisoning. The most prominent involves conversion of VjOj to vanadic acid (H-iVO ) under regenerator conditions. Vanadic acid, through hydrolysis, extracts the tetrahedral alumina in the zeolite crystal structure, causing it to collapse. 

In commercial operations, catalyst activity is affected by operating conditions, feedstock quality, and catalyst characteristics. The MAT separates catalyst effects from feed and process changes. Feed contaminants, such as vanadium and sodium, reduce catalyst activity. E-cat activity is also affected by fresh catalyst makeup rate and regenerator conditions. 

Co(NH3)6 is effective for NO absorption, and O2 can enhance NO absorption as the result of oxidation reaction. Activated carbon is also active to maintain stability of NO absorption by turning the side reaction of Co complex oxidized into Co complex backward, and the suitable regeneration conditions are obtained. A laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

Regenerahility often is also a requirement. In the life cycle of a catalyst the most severe conditions are not always the reaction conditions regeneration conditions may well be more severe that the regular reaction conditions. Examples are hydrogenation catalysts that are regenerated by oxidative treatment in diluted oxygen. These catalysts must be resistant to oxidative treatment at high temperatures. This makes alumina a suitable carrier for these processes. 

For some applications, an adsorbent may be impregnated with a material that enhances its contaminant-removal ability. The improved effectiveness may be related to any of several mechanisms. The impregnating material may react with the vapor contaminant to form a compound or complex that remains on the adsorbent surface. Some impregnants react with the contaminant, or catalyze reactions of the contaminant with other gas constituents, to form less noxious vapor-phase substances. In some instances, the impregnant acts as a catalyst intermittently, for example, under regeneration conditions. In this case, the contaminant is adsorbed by physical adsorption and destroyed by a catalytic reaction during regeneration. 

There is a need for low-cost methane steam reforming catalysts that are active at low temperature and resistant to coke formation under membrane reactor conditions. Low-cost (Ni-based) catalysts are also needed that can withstand regeneration conditions in a sorption-enhanced reformer. 

In the majority of impurity removal processes, the adsorbent functions both as a catalyst and as an adsorbent (catalyst/adsorbent). The impurity removal process often involves two steps. First, the impurities react with the catalyst/adsorbent under specified conditions. After the reaction, the reaction products are adsorbed by the catalyst/adsorbent. Because this is a chemical adsorption process, a severe regeneration condition, or desorption, of the adsorbed impurities from the catalyst/adsorbent is required. This can be done either by burning off the impurities at an elevated temperature or by using a very polar desorbent such as water to desorb the impurities from the catalyst/adsorbent. Applications to specific impurities are covered in the followings section. The majority of industrial applications involve the removal of species containing hetero atoms from bulk chemical products as purification steps. 

Control of the regeneration conditions, together with a wide variety of modification, allows the production of a wide variety of products including high-wet modulus fibers, hollow fibers, crimped fibers, and flame-resistant fibers. While almost all rayon is produced using the... 

Stabilizing the Support Oxide. Promoter elements can be added to the support oxide resulting in a decreased Co compound formation with the support oxide. This is illustrated in Figure 3A. More specifically, strategies should be followed to avoid the formation of either cobalt titanate, cobalt silicate or cobalt aluminate as a result of Co solid-state diffusion under reducing or regeneration conditions in the subsurface of these support oxides. Some transition metals, for example Zr or La, could act in such a way. 

A related problem is the reduction in support surface area. This is especially a problem in the case of titania, where the anatase polymorph is only stable under oxidative regeneration conditions from about 400°C to 750°C. The addition of Si, Zr and Ta as promoter elements may avoid or diminish surface collapse of the support oxide. 

N diffuses into the structural pores of clinoptilolite 10 to 10 times faster than does CH4. Thus internal surfaces are kinetically selective for adsorption. Some clino samples are more effective at N2/CH4 separation than others and this property was correlated with the zeolite surface cation population. An incompletely exchanged clino containing doubly charged cations appears to be the most selective for N2. Using a computer-controlled pressure swing adsorption apparatus, several process variables were studied in multiple cycle experiments. These included feed composition and rates, and adsorber temperature, pressure and regeneration conditions. N2 diffusive flux reverses after about 60 seconds, but CH4 adsorption continues. This causes a decay in the observed N2/CH4 separation. Therefore, optimum process conditions include rapid adsorber pressurization and short adsorption/desorp-tion/regeneration cycles. 

Under NADPH-regenerating conditions, (99) was converted into geisso-schizine (101), which has been shown not to be a direct alkaloid precursor (for further discussion, see below). 

The fact that the slopes of the 6-plots for partially decoked samples are the same as those of the initial coked ones proves that under our regeneration conditions the internal micropore void volume is practically unchanged (this is confirmed by the quantities of xenon adsorbed at saturation (212K) which are virtually identical). Thus a large fraction of the carbonaceous residues (at least 50%) is located on the external surface of the crystallites. 

Generally, having a repetitively renewable sensing matrix is of great importance to a successful biosensor. In fact, most of the matrices presented in this contribution can be easily regenerated by harsh or mild regeneration conditions [11,16,18,25,26],... 

In a few cases it is possible to redisperse sintered materials on a catalyst The procedures involved are dependent on the nature of the system In typical examples, dispersion is increased by the formation of oxides or oxychlorides The operation involves careful control of regeneration conditions bearing in mind the nature of the catalyst, the IS, and the maximum allowable temperature under regeneration conditions... 

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