Drop-in catalysts

Pressure drop in catalyst beds is governed by the same principles as in any flow system. Consequently, at very low flow, pressure drop is directly proportional to velocity, and at very high flow, to the square of velocity. These conditions correspond to the laminar and turbulent regimes of the flow. 

Neither Larson and Falconer [43] nor Blount and Falconer [54] definitely identified the compound or compounds responsible for the observed drop in catalyst activity during the photocatalytic oxidation of aromatic contaminants. Some possible intermediates, including benzaldehyde and benzoic acid, were considered, but were ruled out as being die species responsible for the apparent deactivation of the photocatalysts. 

Metallocenes are so-called drop-in catalysts. Only minor changes are required to retrofit commercial-scale reactors when metallocene catalysts are to be used. By the high-pressure... 

Reversible deactivation is affecting hydrothermal deactivation, via the deterioration of the coke selectivity of the catalyst and hence higher regenerator temperatures. This can continue until the regenerator reaches a new equilibrium, because of the drop in catalyst activity. 

Metallocene catalysts which are to be used as drop-in catalysts in existing plants for polyolefin production have to be heterogenized due to the fact that current... 

In the 1960s, Bl Paso employed pbo ]Aoric add deposited on kieselguhr around 325 C and about 6.10 Pa absolute. This catalyst is capable of converting the polyethylbenzenes, but their recycle results in a drop in catalyst activity due to the cracking reactions and the formation of coke deposits. 

TABLE 38 A Sharp Drop in Catalyst Porosity and Polymer Ml with Increasing Activation Temperature Indicates Sintering, Which is Inhibited if the Calcination Is Done in CO Rather Than Air or N2... 

Drop-in catalyst replacement for existing hydroprocessing reactors... 

The HAT series catalysts not only have exhibited excellent performance in the S-TDT process units, but also have been successfully used as a drop-in catalyst in many other company-licensed process units in China. 

Metallocenes immobilized on solid support materials have been successfully introduced in industry as polymerization catalysts for the production of new, application-oriented polymer materials (see also the contribution of Brintzinger and Fischer [29]). Industrial polymerization processes, which are carried out either as a slurry process in liquid propylene or as a gas-phase process, require that catalysts are used in the form of solid grains or pellets soluble metallocene catalysts thus have to be supported on a solid carrier (so-called drop-in catalysts). 

Preventing masking of active surface of catalysts in a fixed-bed reactor by filtering the incoming gas streams containing dust particles. This also minimizes pressure drop in catalyst beds and frequent shutdown of the catalytic reactor for screening of the bed is not required. 

The above examples have shown that there is considerable activity in searching for other ways to achieve separation of product and homogeneous catalysts. The improvements needed are the same for all reaction types, also reactions other than hydroformylation. Most of the new techniques have in common that not only the product, but also the starting material and byproducts are separated from the catalyst. This mixture of organic products needs further separation, but as we have seen in Chapter 8 separation of catalyst and byproducts such as heavy ends is an important issue in hydroformylation of simple alkenes. There may be a future for immobilized drop in catalysts as described above in the hydroformylation of fine chemicals. 

The dicationic complex [Ru(py-NHC)(terpy)(OH2)] (terpy=2,2 6, 2 -terpyridine) containing the bidentate pyridyl-NHC ligand 3-meth)d-l-(pyridine-2-yl)imidazol-2-ylidene catalyzed the epoxidation of terminal alkenes vrith Phi (OAc)2 in CH2CI2 at room temperature (Table 12.7). In an effort to make the system reusable, a solvent system comprising a 1.2 0.8 mixture of CH2Q2 and the ionic liquid [bmim] [PFg] was employed. Tests with cyclooctene showed that this allowed 10 consecutive epoxidation reactions to be carried out without any drop in catalyst performance [107]. 

Metallocene catalysts which are to be used as drop-in catalysts in existing plants for polyolefin production have to be heterogenized due to the fact that current technology is based on gas phase and slurry processes. Thus the metallocenes are to be fixed on a carrier. Carriers may be divided into three groups (1) metals have been used as fillers (2) inorganics like silica, aluminia, zeoliths or MgCl2 [470,476] and (3) organic materials like cyclodextrins [477], starch (as a filler) [478] and polymers (polystyrenes, polyamides) have been used to support either the metallocene or the cocatalyst. 

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