Water catalysts activation

For the catalyst system NdV/EASC/DIBAH the impact of water on monomer conversion, Mw, polydispersity and cis- 1,4-content was systematically studied (Table 16) [191], With increasing amounts of water catalyst activity passes through a maximum whereas Mw and Mw/Mn pass through a minimum. It has to be mentioned, however, that the overall effect of water on reaction rate and polymer properties are relatively small. In this study it is also shown that water has no influence on cis-1,4-contents [ 191],... 

The inactivity of pure anhydrous Lewis acid haUdes in Friedel-Crafts polymerisation of olefins was first demonstrated in 1936 (203) it was found that pure, dry aluminum chloride does not react with ethylene. Subsequentiy it was shown (204) that boron ttifluoride alone does not catalyse the polymerisation of isobutylene when kept absolutely dry in a vacuum system. However, polymers form upon admission of traces of water. The active catalyst is boron ttifluoride hydrate, BF H20, ie, a conjugate protic acid H" (BF20H) . 

SHica—alumina has been studied most extensively. Dehydrated sHica—alumina is inactive as isomerisation catalyst but addition of water increases activity until a maximum is reached additional water then decreases activity. The effect of water suggests that Brmnsted acidity is responsible for catalyst activity (207). SHica—alumina is quantitatively at least as acidic as 90% sulfuric acid (208). 

The alkoxy titanate compounds formed by reaction of one mole of tetraalkyl titanate with one mole of a dialkanolamine are excellent esterification catalysts for the manufacture of phthalate-based plasticizers (112). If a 1 1 molar mixture of alkanolamine and water is used ia place of the alkanolamine, oligomeric titanate complexes are formed, which have high catalyst activity and can be used as thixotropic additives to paints and other aqueous coating formulations (113). 

Carbon monoxide has been found to poison cobalt molybdate catalysts. It causes not only instantaneous deactivation but a cumulative deactivation as well. It should be removed from treat gas entirely or at least reduced to a very low value. Carbon dioxide also must be removed since it is converted to CO in the reducing atmosphere employed in Hydrofining. Liquid water can damage the structural integrity of the catalyst. Water, in the form of steam does not necessarily hurt the catalyst. In fact 30 psig steam/air mixtures are used to regenerate the catalyst. Also, steam appears to enhance the catalyst activity in... 

In addition to having the required spedfidty, lipases employed as catalysts for modification of triglycerides must be stable and active under the reaction conditions used. Lipases are usually attached to supports (ie they are immobilised). Catalyst activity and stability depend, therefore, not only on the lipase, but also the support used for its immobilisation. Interesterification reactions are generally run at temperatures up to 70°C with low water availability. Fortunately many immobilised lipases are active and resistant to heat inactivation under conditions of low water availability, but they can be susceptible to inactivation by minor components in oils and fats. If possible, lipases resistant to this type of poisoning should be selected for commercial operations. 

Water injection in a dehydrogenation process Improvement of catalyst activity through water injection 84... 

One of the key challenges for this process is dealing with the wide range of contaminants in the waste HBr stream. Both inorganic and organic contaminants may be present. These contaminants are typically reactants and products of the upstream bromination process which generated the waste HBr. In addition, they may include corrosion products of upstream equipment or ionic materials present in the water used to scrub the gaseous bromination process effluent. The main concerns about contaminants in the feed streams are their effect on catalyst activity and stability and their effect on bromine product quality. 

Fig. 11 High resolution XANES spectra collected at the GILDA BM8 heamline of the ESRF Grenoble (France) at liquid nitrogen temperatiu e on the TS-1 catalyst activated TS-1 catalyst (dotted line)-, after contact with anhydrous H2O2 from the gas phase (full line) after subsequent contact with water (scattered squares). Adapted from [50] with permission. Copyright (2004) by VCH...

Liquid catalyst Low thermal stability Soluble in water Low activity per weight Small pore size Low activity Deactivates in water, but not in organic phase Medium activity... 

While the control resins were deep red in color due to the presence of soluble porphyrin complexes, the methacrylate resins obtained after removal of the polyethylene-supported catalysts varied from light yellow to nearly water-white (APHA < 25). UV-Vis spectrophotometric analysis of the yellow resins indicated an absorption signal for the cobalt porphyrin complex Soret band (wavelength of cobalt(ll) porphyrin species appears at -415 nm free porphyrin ligand is formd at -423 tun). Resin samples that visttally appear as water-white show little or no porphyrin species present in the spectrum. Measured catalyst activity and PDl of the polyethylene-supported porphyrin complexes are in the expected range for soluble porphyrin CCT catalysts (PDl = M /Mn - 1.2- 2.0)." The screening resrrlts clearly... 

Periodically, a portion of the catalyst slurry is purged from the reactor for regeneration. In the catalyst regeneration process, the catalyst is washed with water to remove impurities that accumulate in the caustic phase. Most of the regenerated catalyst is returned to the reactor along with new catalyst. With this configuration, fresh catalyst can be added as required to maintain acceptable catalyst activity without the need to replace the entire reactor charge in a batchwise manner. 

Addition of ammonium hydroxide and water were explored to evaluate their influence upon catalyst activity and selectivity. The data in this study suggest that there was little influence of ammonium hydroxide on reaction rate and selectivity. The data, however, were not sufficient to definitively define the role of these additives and investigation of these effects will be the subject of future exploration. Examination of Figure 3 may lead to the conclusion that water is actually harmful to the life of the catalyst but such a preliminary hypothesis is overly simplistic, acknowledging that the ammonium hydroxide additive comprises 70% water. 

The initial screening of the resin catalysts was done in a batch reactor at supercritical for butene-1 conditions of temperature 155 °C, pressure of 1000 psig and at molar ratio of 1-butene water of 5.5. The reaction was stopped after predetermined period of time and the products analyzed. It was found that under the standard reaction conditions, for all of the catalysts studied, a constant concentration in the sec-butanol concentration was achieved within a 1-2 hour reaction time. Using only the linear section of the concentration-time plot, the one hour result was used to evaluate the catalyst activity, which was normalized as mmol of SBA/ per proton/ per hour (a), as mmol of product/ per gram of dry catalyst/ per hour (b) and mmol of product/ per ml of wet catalyst/ per hour (c). 

Stephens and co-workers (69) have found that the preheating of CdS specimens in an atmosphere of nitrogen (the purpose of preheating is to enrich a CdS specimen in an acceptor impurity) reduced the catalyst activity in relation to the photooxidation of water. 

Sc(OTf)3-catalyzed aldol reactions have been successfully performed in micellar systems (Scheme 15).59 The catalyst activity is remarkably enhanced by adding a small amount of a surfactant. Allylation60 and Mannich-type reactions61 also proceed smoothly in water in the presence of a catalytic amount of Sc(OTf)3 and a surfactant. 

---