Effectiveness of the catalyst

The expander turbine is designed to minimize the erosive effect of the catalyst particles stiU remaining in the flue gas. The design ensures a uniform distribution of the catalyst particles around the 360° aimulus of the flow path, optimizes the gas flow through both the stationary and rotary blades, and uses modem plasma and flame-spray coatings of the rotor and starter blades for further erosion protection (67). 

Although the point values of the rate diminish with p, in the steady state the rate of reaction equals the rate of diffusion at the mouth of the pores. The effectiveness of the catalyst is a ratio... 

The striking effect of the catalyst is exemplified by the reaction of pregna-4, 16-diene-3,20-dione (10) with benzyl mercaptan. In the presence of piperidine only conjugate addition occurs to give (11) whereas with pyridine hydrochloride only the 3-benzyl thioenol ether (12) is formed. In the presence of p-toluenesulphonic acid both reactions take place to yield (13). 

The effect of the catalyst-steroid ratio has been studied for the p-toluene-sulphonic acid-catalyzed ketalization of androst-4-ene-3,17-dione. Selective formation of the 3-monoketal is observed with the use of an equimolar amount of ethylene glycol and a low ratio of catalyst to steroid. ... 

Compared with the bonding groups (mol%) to aromatic ring of PS, the degree of acylation was observed when MA was used. These results was obtained by determination of kinetic parameters of PS with MA and AA under the same reaction conditions. As shown in Table 5, if the initial rate (Wo) and rate constant (K) of the acylation reaction between MA and AA are compared, the MA is almost 10-14 times higher than AA in the presence of BF3-OEt2 catalyst. This fact is due to the stretching structure of MA and the effect of the catalyst. 

For the reaction of stannic chloride with toluene (this aromatic being used here because of the lower effectiveness of the catalyst), different kinetics were obtained the rate expression being... 

Figure 8.59. Effect of the catalyst potential (UWR) on the C02, N2) N20 formation rates and the selectivity of NO reduction to N2. Conditions T=373°C, inlet composition p 0=1.34 kPa, p 0 =0.55 kPa.63 Reprinted with permission from Academic Press.

Strong effects of the catalyst on the regioselectivity have been observed in the cycloadditions of a variety of heterocyclic dienophiles. Some results of the BF3-catalyzed reactions of quinoline-5,8-dione (21) and isoquinoline-5,8-dione (22) with isoprene (2) and (E)-piperylene (3) [25], and of the cycloadditions of 4-quinolones (23a, 23b) as well as 4-benzothiopyranone (23c) with 2-piperidino-butadienes, are reported [26] in Scheme 3.8 and Equation 3.2. The most marked... 

The effect of the catalyst composition upon the catalyst activity, selectivity, and reaction pathways was examined using a conventional high pressure fixed reactor and a TAP reactor. Particular emphasis was placed upon the effect of Au and KOAc on the acceleration or impedance of the pathways associated with vinyl acetate synthesis. A summary of the key findings is given below ... 

Another, more semiempirical, method is to assume that the only effect of the catalyst is to change the binding to the surface entropy and solvation effects are taken to be the same as for the solvated spices. This assumes that the hydrogen bonds to, e.g., OH are the same as the hydrogen bonding to OH [Roques and Anderson, 2004]. We... 

Scheme 10.12 gives some examples of enantioselective cyclopropanations. Entry 1 uses the W.s-/-butyloxazoline (BOX) catalyst. The catalytic cyclopropanation in Entry 2 achieves both stereo- and enantioselectivity. The electronic effect of the catalysts (see p. 926) directs the alkoxy-substituted ring trans to the ester substituent (87 13 ratio), and very high enantioselectivity was observed. Entry 3 also used the /-butyl -BOX catalyst. The product was used in an enantioselective synthesis of the alkaloid quebrachamine. Entry 4 is an example of enantioselective methylene transfer using the tartrate-derived dioxaborolane catalyst (see p. 920). Entry 5 used the Rh2[5(X)-MePY]4... 

Since the initial work of Onto et al. (1) a considerable amount of work has been performed to improve our understanding of the enantioselective hydrogenation of activated ketones over cinchona-modified Pt/Al203 (2, 3). Moderate to low dispersed Pt on alumina catalysts have been described as the catalysts of choice and pre-reducing them in hydrogen at 300-400°C typically improves their performance (3, 4). Recent studies have questioned the need for moderate to low dispersed Pt, since colloidal catalysts with Pt crystal sizes of <2 nm have also been found to be effective (3). A key role is ascribed to the effects of the catalyst support structure and the presence of reducible residues on the catalytic surface. Support structures that avoid mass transfer limitations and the removal of reducible residues obviously improve the catalyst performance. This work shows that creating a catalyst on an open porous support without a large concentration of reducible residues on the Pt surface not only leads to enhanced activity and ee, but also reduces the need for the pretreatment step. One factor... 

The Effect of Catalyst Concentration The first parameter that was studied was the effect of the catalyst concentration. Samples impregnated with 1, 5, 10 and 15% tin as stannous chloride and a sample with no catalyst were hydrogenated at 450°C to investigate the effect that increasing catalyst concentration has on the composition of the oil (hexane soluble portion) formed. 

Since cA and T may vary from point to point within a catalyst particle (see Figure 8.9), the rate of reaction also varies. This may be translated to say that the effectiveness of the catalyst varies within the particle, and this must be taken into account in the rate... 

As an example, when automotive catalytic mufflers and converters were introduced many years ago, the automobile industry required the petrochemical industry to eliminate lead from gasoline since lead degraded and reduced the effectiveness of the catalyst and caused the destruction of the gasoline. One set of industrial compounds that can harm catalysts are halogens, a family of compounds that include chlorine, bromine, iodine, and fluorine. Bromine, while not prevalent in industry, is present in chemical plants. Freons are fluorine compounds. Silicone is another compound that is deleterious to catalysts. It is used as a slip agent, or a lubricant, in many industrial processes. Phosphorous, heavy metals (zinc, lead), sulfur compounds, and any particulate can result in shortening the life of the catalyst. It is necessary to estimate the volume or the amount of each of those contaminants, to assess the viability of catalytic technologies for the application. 

A gas oil is cracked at 630 C and 1 atm by passing vaporized feed through a bed of silica-alumina catalyst spheres with radius 0.088 cm. At a feed rate of 0.2 mol/(h)(cc catalyst bed) conversion was 50%. The reaction is pseudo first order. The effective diffusivity is 0.0008 cm2/s. As an approximation, assume a constant volumetric flow rate. Find the effectiveness of the catalyst. 

Fig. 2 Long time effect of the catalyst deactivation, Cc, on the concentrations Ca and Cp.

The effect of the catalyst concentration on the DP of the polymer was investigated at -78° with methyl chloride as solvent at isobutene concentrations of 0.643 and 0.25 mole fraction (approximately 9.5 and 4.6 mole/1) [53]. The catalyst concentration, given as wt.% A1C13 on isobutene (sic ), covers the range 1.5 x 10"3 to 10"1 in these units. Recalculation of the results shows that 1/DP increases linearly with [A1C13] up to a certain value and at higher values remains constant. This corresponds closely to the behaviour reported for the polymerisations of undiluted monomer [53] and can be explained in the same way (see p.159). 

---