Catalysts selection basis

The experimental study of solid catalyzed gaseous reactions can be performed in batch, continuous flow stirred tank, or tubular flow reactors. This involves a stirred tank reactor with a recycle system flowing through a catalyzed bed (Figure 5-31). For integral analysis, a rate equation is selected for testing and the batch reactor performance equation is integrated. An example is the rate on a catalyst mass basis in Equation 5-322. 

So the competition will apparently continue, each refinery alkylation plant and catalyst selection being evaluated on an individual basis. 

These studies have demonstrated that the homogeneously catalyzed oxychlorination of ethylene to 1,2-dichloroethane is feasible under relatively mild operating conditions without the need for catalyst circulation and that selectivities better than 96% can be achieved in sustained operations. A rational basis for reactor design has been devised, taking into account such factors as ethylene- and oxygen-mass transfer rates, chemical kinetics, water vapor pressure over the catalyst, selectivity relation-... 

Studies of the stability of the Li/MgO catalyst woe conducted by KExperiments performed ova a quartz diluted 3.1% Li/MgO catalyst showed a significant drop in methane convosion, but it did not change the catalyst selectivity. The lithium content in the post-reaction samples was detmnined to be around 0.1 wt%. A white deposit found downstream fron the reacts exit was identified as liOH. FurthernKxe, it was detemiined that lithium formed silicates with the quartz chips used as diluent and widi the quartz walls of the reactor. On the basis of these experimental results, Korf... 

Naphthalene and its derivatives are one of the more dominant aromatics present in various diesel and jet fuel feedstocks. Therefore, several investigators have reported the influence of naphthalene on HDS of model compounds. One of the first reports was by Lo who found naphthalene to weakly inhibit the conversion and selectivity of the HDS of DBT. Similarly, LaVopa and Satterfield found little effect of naphthalene and phenanthrene on the HDS of thiophene. Other researchers have, however, found naphthalene to be a stronger inhibitor of HDS activ-ity. Nagai and Kabe, in fact, found naphthalene to significantly reduce catalyst selectivity for the hydrogenation pathway.Isoda et al., on the basis of similar selectivity inhibition, concluded that naphthalene severely inhibits the hydrogenation active sites in a... 

The compositional modulation technique has been applied to the Fischer-Tropsch synthesis (FTS) reaction [2-5], It was found that the cyclic feeding of CO/H2 had an influence on the selectivity of the FTS products. Among the conclusions was that for an iron catalyst the selectivity for methane increased under periodic operation compared to the steady state operation [5], In the study [5] it was found that the propane/propene ratio increased under periodic operation and the largest changes were with periods between one and ten minutes. Due to the limitations of the anal5dical technique utilized, they could not separate ethane and ethene so that the selectivity basis was for the C3 hydrocarbons. In this study the analytical procedure permitted analysis of products only to the Cg-compoimds. 

The selectivity of catalysts with respect to various functional groups may change upon attachment of a metal complex to a support. With soluble PdCl2(PPh3)2, conjugated dienes are more readily hydrogenated to monoenes than isolated dienes. The reverse is observed for the supported catalyst the basis for this reversal is not yet clear. 

The ammoxidation of propylene is carried out by feeding the olefin, air, ammonia and steam over a fixed or fluidized bed of catalyst at between 420 and 500°C. Several binary oxide systems, Bi-Mo, U-Sb (Sohio) and Sn-Sb (BP Chemicals), form the basis of commercial catalysts. Selectivities are now about 70% on propylene, with acetonitrile and HCN as byproducts. 

Acid catalysis using strong acid catalysts, especially 2eohtes which enhance selectivity because of pore si2e restrictions, has been used for a variety of alkenes and dienes (9—11). /-Butyltoluenediamine [106398-83-8] (/-BTDA) (C H gN2) is available on a semicommercial basis (12). 

The complexation procedure included addition of an equimolar amount of R,R-DBFOX/Ph to a suspension of a metal salt in dichloromethane. A clear solution resulted after stirring for a few hours at room temperature, indicating that formation of the complex was complete. The resulting solution containing the catalyst complex was used to promote asymmetric Diels-Alder reactions between cyclopen-tadiene and 3-acryloyl-2-oxazolidinone. Both the catalytic activity of the catalysts and levels of chirality induction were evaluated on the basis of the enantio-selectivities observed for the endo cycloadduct. 

Performance of an FCC unit is often maximized when the unit is operated against multiple constraints simultaneously. It is essential that the specified constraints allow for minimum comfort zones. An operator-friendly advanced control program, coupled with proper selection of catalyst formulation, would allow optimizing the performance of the unit on a daily basis. 

A detailed study of the dehydrogenation of 10.1 l-dihydro-5//-benz[6,/]azcpinc (47) over metal oxides at 550 C revealed that cobalt(II) oxide, iron(III) oxide and manganese(III) oxide are effective catalysts (yields 30-40%), but formation of 5//-dibenz[7),/]azepinc (48) is accompanied by ring contraction of the dihydro compound to 9-methylacridine and acridine in 3-20 % yield.111 In contrast, tin(IV) oxide, zinc(II) oxide. chromium(III) oxide, cerium(IV) oxide and magnesium oxide arc less-effective catalysts (7-14% yield) but provide pure 5H-dibenz[b,/]azepine. On the basis of these results, optimum conditions (83 88% selectivity 94-98 % yield) for the formation of the dibenzazepine are proposed which employ a K2CO,/ Mn203/Sn02/Mg0 catalyst (1 7 3 10) at 550 C. 

If, for the purpose of comparison of substrate reactivities, we use the method of competitive reactions we are faced with the problem of whether the reactivities in a certain series of reactants (i.e. selectivities) should be characterized by the ratio of their rates measured separately [relations (12) and (13)], or whether they should be expressed by the rates measured during simultaneous transformation of two compounds which thus compete in adsorption for the free surface of the catalyst [relations (14) and (15)]. How these two definitions of reactivity may differ from one another will be shown later by the example of competitive hydrogenation of alkylphenols (Section IV.E, p. 42). This may also be demonstrated by the classical example of hydrogenation of aromatic hydrocarbons on Raney nickel (48). In this case, the constants obtained by separate measurements of reaction rates for individual compounds lead to the reactivity order which is different from the order found on the basis of factor S, determined by the method of competitive reactions (Table II). Other examples of the change of reactivity, which may even result in the selective reaction of a strongly adsorbed reactant in competitive reactions (49, 50) have already been discussed (see p. 12). 

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