Dehydrogenation reaction conditions

Dehydrogenation of n-butane was employed to evaluate the activities of the Fresh as well as the regenerated catalysis Before reaction, all samples wpre First, reduced at SSG C for 2 hours in flowing hydrogen. Dehydrogenation reaction conditions were 380°C, 0.1 MPa, H2/n-C4H o (molar ratio) = l and GHSV... 

Figure 1. Thermodynamic equilibrium conversion for different dehydrogenation reactions. Conditions P = bar, Hj/saturated hydrocarbon = 0 (calculations based on the software HSC Chemistry from Outokumpu Research Oy).

Another possible route for producing formaldehyde is by the dehydrogenation of methanol (109—111) which would produce anhydrous or highly concentrated formaldehyde solutions. Eor some formaldehyde users, minimization of the water in the feed reduces energy costs, effluent generation, and losses while providing more desirable reaction conditions. 

The reaction of androst-4-ene-3,17-dione with DDQ in refluxing benzene or dioxane leads to the A -3-ketone as the major product, although small amounts of A -3-ketone and A -3-ketone are also produced. The latter arises from the A -3-ketone, since the A -3-ketone is not dehydrogenated further under the usual reaction conditions. A -3-Ketone production is more favored in benzene than it is in dioxane substituents at C-6 can also influence this selectivity. A recent thorough investigation of the mechanism of dehydrogenation of 3-ketones under neutral and acidic condi-... 

The oxidation process uses air as the oxidant over a silver or copper catalyst. The conditions are similar to those used for the dehydrogenation reaction. 

Dehydrogenation. Under ideal conditions (i.e., a clean feedstock and a catalyst with no metals), cat cracking does not yield any appreciable amount of molecular hydrogen. Therefore, dehydrogenation reactions will proceed only if the catalyst is contaminated with metals such as nickel and vanadium. 

Example 10.6 A commercial process for the dehydrogenation of ethylbenzene uses 3-mm spherical catalyst particles. The rate constant is 15s , and the diffusivity of ethylbenzene in steam is 4x 10 m /s under reaction conditions. Assume that the pore diameter is large enough that this bulk diffusivity applies. Determine a likely lower bound for the isothermal effectiveness factor. 

In the present study our reaction system and sensitive anal3rtic technique allowed us to perform the HDN reaction of DHQ under such reaction conditions that only small amounts of Q, THQ-1, and OPA were formed (Table 1). This indicates that dehydrogenation of the carbocychc ring of DHQ was slow and could be neglected. Therefore, the reaction network can be simplified as in Fig. 2. 

The concentration of PB in the reaction products (Table 1) is too high to be accounted for by dehydrogenation of PCHE, especially in the absence of H2S, since at thermodynamic equilibrium the PCH/PB ratio sho lld be greater than 50 (15) under our experimental conditions. Furthermore, no toluene was observed in the simultaneous reaction of methylcyclohexene and DHQ under the same reaction conditions. Therefore, there must be another reaction path to accoimt for the formation of PB in the HDN products of DHQ. This second reaction path can only be the reaction of DHQ->THQl- OPA-> HC. It has been demonstrated that a relatively high concentration of PB is present in the HDN of OPA due to the direct hydrogenolysis of the C(sp-)-N bond of OPA (16). 

Reaction conditions were lOTorr CgHio, 200Torr H2, and 273-323 K for hydrogenation (400-443 K for dehydrogenation). Selectivity at 448K based on experimentally measured turnover frequencies (lOTorr CsHio, 200Torr H2). 

Figure 15. Turnover rate for cyclohexene hydrogenation and dehydrogenation as a function of particle size. Reaction conditions are lOTorr CeHio, 200 Torr H2, and 310K for hydrogenation and 448 K for dehydrogenation, respectively [18].

The dehydrogenation reaction was generally monitored by taking samples for reversed phase H PLC analysis. Diode array detectors for H PLC were relatively new at that time and proved valuable for quickly getting structural information on products of the reaction produced under different conditions. Key reaction parameters for adduct formation, overall concentration, BSTFA, TfOH, and DDQ charges, were optimized using a thermostated HPLC autosampler to sample reactions directly for analysis. Comparison of reaction profiles provided rate and reaction time information that was used to select a more limited number of reaction conditions that were scaled up to compare yields. 

Reactions over chromium oxide catalysts are often carried out without the addition of hydrogen to the reaction mixture, since this addition tends to reduce the catalytic activity. Thus, since chromium oxide is highly active for dehydrogenation, under the usual reaction conditions (temperature >500°C) extensive olefin formation occurs. In the following discussion we shall, in the main, be concerned only with skeletally distinguished products. Information about reaction pathways has been obtained by a study of the reaction product distribution from unlabeled (e.g. 89, 3, 118, 184-186, 38, 187) as well as from 14C-labeled reactants (89, 87, 88, 91-95, 98, 188, 189). The main mechanistic conclusions may be summarized. Although some skeletal isomerization occurs, chromium oxide catalysts are, on the whole, less efficient for skeletal isomerization than are platinum catalysts. Cyclic C5 products are of never more than very minor impor-... 

For 4-nitrophenyl 2-azadiene 617, vigorous reaction conditions are necessary (110°C, sealed tube, 25h) and give bicyclic product 619. The formation of this compound could be explained by [4+2] cycloaddition reaction leading to 618 followed by dehydrogenation (Scheme 99) <1994T12375, 2003H(61)493>. 

The most frequently used synthetic route to cycl[3.2.2]azines involves the reaction of an indolizine with a dienophile, for example, DMAD, in the presence of a dehydrogenating agent such as palladium-on-carbon (Scheme 85), although the scope of the reaction is limited by the presence of substituents in one or both of the reactants, and/or the reaction conditions. If C-3 and C-5 of the indolizine are unsubstituted, the cyclazine is the main product a 3,4-dihydrocyclazine may sometimes be isolated as a by-product (see below). 

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