Reaction conditions, catalyst composition

Figure 1 Product distribution as a function of added triethylamine in the Ru/Rh/EtgN/HOAc catalyst composition. Reaction conditions Ru (2.0 mmol), Rh (0.2 mmol), glacial acetic acid (50 ml), 1000 atm CO/H2 (1 1), 230oC.

Figure Product distribution as a function of metal concentration in the Ru/Rh/Et3N/HOAC catalyst composition. Reaction conditions 1000 atm C0/H2(1 1), 230°C Ru Rh Et3N 10 1 10...

Fig. 23. Interaction between the catalyst TiCyEB/MgCL, and TEA effect of the contact time on the catalyst composition. (Reaction conditions T = 50 °C,TEA = 50 mmol/1, Ti = 7 mmol/1)...

We have shown that XANES spectra for catalysts can be obtained In two minutes. This enables us to spectroscopically monitor changes in catalyst composition in real time. Our controlled atmosphere cell allowed us to do these experiments on catalysts under reaction conditions. 

Although often it is considered that a single reaction mechanism occurs in the selective reduction of NO by ammonia, data show that instead different mechanisms are possible and that too depending on the type of catalyst and reaction conditions (feed composition, reaction temperature) - one mechanism may prevail over the others [31b], However, not considering this aspect and making extrapolation regarding the reaction mechanism from one catalyst to another or to different reaction conditions may lead to erroneous conclusions. In addition, it is important to consider all possible opportunities to develop new kinds of catalysts, for example, for the combined removal of NO and N20 from nitric acid plant emissions [25],... 

Butene as the feed alkene would thus—after hydride transfer—give 2,2,3-TMP as the primary product. However, with nearly all the examined acids, this isomer has been observed only in very small amounts. Usually the main components of the TMP-fraction are 2,3,3-, 2,3,4-, and 2,2,4-TMP, with the selectivity depending on the catalyst and reaction conditions. Consequently, a fast isomerization of the primary TMP-cation has to occur. Isomerization through hydride- and methyl-shifts is a facile reaction. Although the equilibrium composition is not reached, long residence times favor these rearrangements (47). The isomerization pathways for the TMP isomers are shown schematically in Fig. 3. 

Oxidation of organonitrogen compounds is an important process from both industrial and synthetic viewpoints . N-oxides are obtained by oxidation of tertiary amines (equation 52), which in some cases may undergo further reactions like Cope elimination and Meisenheimer rearrangement . The oxygenation products of secondary amines are generally hydroxylamines, nitroxides and nitrones (equation 53), while oxidation of primary amines usually afforded oxime, nitro, nitroso derivatives and azo and azoxy compounds through coupling, as shown in Scheme 17. Product composition depends on the oxidant, catalyst and reaction conditions employed. 

Substrate Catalyst precursor Reaction conditions Con- ver- sion Yield Hydroformylation products and isomeric composition Chiral reaction product Ref. 

Furthermore, because catalysts may undergo restructuring at elevated pressures and temperatures, (14,15,48,51,216,222) or even undergo changes in composition (55,60,252), the availability and nature of adsorption sites and adsorbate geometries at mbar pressures may be different from those existing under UHV, and the most incisive characterizations are those of catalyst under reaction conditions. 

All steam reforming catalysts in the activated form contain metallic nickel as active component, but the composition and structure of the support and the nickel content differ considerably in the various commercial brands. Thus the theoretical picture is less uniform than for the ammonia synthesis reaction, and the number of scientific publications is much smaller. The literature on steam reforming kinetics published before 1993 is summarized by Rostrup - Nielsen [362], and a more recent review is given by K. Kochloefl [422]. There is a general agreement that the steam reforming reaction is first order with respect to methane, but for the other kinetic parameters the results from experimental investigations differ considerably for various catalysts and reaction conditions studied by a number of researchers. 

The ammoxidation of toluenes substituted with electron-donating groups, for example hydroxy- and alkoxy-substituted toluenes is rather less selective. However, under carefully chosen conditions (choice of the catalyst, feed composition, reaction conditions) adequate yields of nitriles can be achieved. Stabihty of the catalyst performances is typically an issue. 

Most commercial processes nowadays use CH2O-CH3CHO-NH3 feed combinations to co-produce pyridine and 9-picoline [9]. Typically, a C1/C2 molar ratio of ca 1.0 is used, but lower ratios can be employed if more pyridine and -picoline are required [10,11], If available, acrolein (CH2=CHCHO) can be used instead of the C,-C2 components and this tends to produce a surplus of yff-picoline [3,9]. Addition of propionaldehyde to the C1-C2 feed can also be used to increase the amount of -picoline [12,13]. The yields of 1, 3, and higher alkylated pyridine by-products depends on feed composition, reaction conditions, and the choice of catalyst. 

The ionones possess odours which are reminiscent of violet, sometimes also with woody notes. Each isomer has its own combination of violet and wood character and small variations in the composition can have relatively large effects on the odour. The most valued odour is that of (Z)-a-wu-methylionone (8.58). The exact composition of the product mixture from any ionone synthesis of this type depends very much on the nature of the catalysts and reaction conditions employed. A vast amount of development work has gone into each step of the synthesis in order to optimise yield and product isomer ratio. All the companies which produce ionones have their own signature blends of isomers and the mixtures are available under many different trade names. For obvious reasons, much of the detail of development work and reaction and distillation conditions are kept as company secrets. Citral and the ionones are very important commercially, not just in their own right but also as intermediates in the synthesis of vitamins. Consequently, there is a large volume of published academic and patent literature on their synthesis. This will be considered in more detail in Chapter 9, in the context of factors concerning synthesis on commercial production scale. 

Measurements of are usually made at ambient conditions using simple gases such as N2, He, H2, and CO2. To predict for the same catalyst under reaction conditions, the effects of changes in temperature, pressure, and gas composition must be accounted for. One approach is to predict Dpore for the test gas (say. He) from Eqs. (4.5), (4.7), and (4.9) and to calculate r from Eq. (4.10) using measured values of and r. Then is predicted for the reactants at various reaction temperatures and pressures, and the same values of e and r are used to get from Eq. (4.10). The relative importance of Knudsen diffusion and bulk diffusion may change with reaction conditions, but and r should be constant. 

Table 4. Co/alumina Catalyst Case Study - Run summary of the effect of H2O for an alumina-supported 12% Co-catalyst [7]. Reaction conditions P, t = 19.7 atm, T = 210 C, space velocity = 2982 cm /gcat hr, feed composition = 63.9% H2,32.1% CO, 4.0% N2, H2/CO = 2.1.

Table 7. Run summary of the effect ofH20 for a titania-supported 10% Co-catalyst [17], Reaction conditions Ptot = 20 atm, T = 230°C, space velocity = varies, feed composition = 57.1% Hj, 28.6% CO, 14.3% Ar, Hj/CO = 2.0.

The important catalysts applied in this process are Lewis acids (promoted by hydrogen halide) and protic acids (61,77). Hydrogen fluoride and sulfuric acid are the preferred catalysts because they are handled more conveniently and can be reused. Of the reactants, alkanes and cycloalkanes with tertiary carbon atoms are the most reactive in the alkane-alkene reaction. The process may yield alkylates of markedly different product compositions, depending on the reactants, catalysts, and reaction conditions. Superacids may also be used as catalysts with signiflcant and characteristic differences in product distribution (63). 

Single-reaction-step processes have been studied. However, higher selectivity is possible by optimizing catalyst composition and reaction conditions for each of these two steps (40,41). This more efficient utilization of raw material has led to two separate oxidation stages in all commercial faciUties. A two-step continuous process without isolation of the intermediate acrolein was first described by the Toyo Soda Company (42). A mixture of propylene, air, and steam is converted to acrolein in the first reactor. The effluent from the first reactor is then passed directiy to the second reactor where the acrolein is oxidized to acryUc acid. The products are absorbed in water to give about 30—60% aqueous acryUc acid in about 80—85% yield based on propylene. 

Analysis of a method of maximizing the usefiilness of smaH pilot units in achieving similitude is described in Reference 67. The pilot unit should be designed to produce fully developed large bubbles or slugs as rapidly as possible above the inlet. UsuaHy, the basic reaction conditions of feed composition, temperature, pressure, and catalyst activity are kept constant. Constant catalyst activity usuaHy requires use of the same particle size distribution and therefore constant minimum fluidization velocity which is usuaHy much less than the superficial gas velocity. Mass transport from the bubble by diffusion may be less than by convective exchange between the bubble and the surrounding emulsion phase. 

The reaction conditions, formaldehyde-to-phenol ratios, and concentration and type of catalyst govern the mechanisms and kinetics of resole syntheses. Higher formaldehyde-to-phenol ratios accelerate the reaction rates. This is to be expected since phenol-formaldehyde reactions follow second-order kinetics. Increased hydroxymethyl substitution on phenols due to higher formaldehyde compositions also leads to more condensation products.55... 

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