Propane formation

The species participating in propane formation whose yield is not affected by the applied field must therefore by the methyl radical. We conclude that methane and methyl radicals are neutral products of ion-molecule sequences. 

In these studies it was also reported that butyraldehyde isomer ratios were increased by lowering the partial pressure of carbon monoxide, but that this decrease in Pco caused a dramatic and parallel increase in propane formation. It was concluded that propane was formed in lieu of isobutyraldehyde at low Pco. This effect is illustrated in Fig. 8. 

In addihon to shape selechvity and acid-site strength, other catalyst characteristics that influence the catalyhc performance of SAPO-34 have also been idenhfied. Variahon in the SAPO-34 gel composition and synthesis condihons have been were used to prepare samples with different median particle sizes and Si contents (Tables 15.3 and 15.4) [104]. In these samples the median parhcle size was varied from 1.4 to 0.6 xm, and the Si mole frachon in the product was varied from 0.14 down to 0.016. A comparison of samples B and E (which have similar parhcle size distributions) shows that reducing Si content decreases propane formation and increases catalyst life. A comparison of samples B and C (which have similar Si contents) illushates an increase in catalyst life with a reduchon in parhcle size. 

This can in pan be answered because Pt/alumina, e,g. EUROPT-3 (and Pt/Re/alumina) has also been studied [7]. In n-butane hydrogenolysis on Pt/alumina the accumulation of carbonaceous deposits on the catalyst surface suppressed ethane formation (i.e. relative to that of propane formation (i.e. S3), Thus for Pt/alutnina sites responsible for central C-C bond scission in n-butane may be selectively deactivated, e.g. at 603K sample S2 S3... 

However, this cannot be the mechanism for propane formation at 1470 A., since too little CH2 is produced as measured by CH4 in the products.128 The above mechanism undoubtedly contributes to propane formation at 1236 A., where methane formation and, therefore, CH2 production are greatly enhanced.13 ... 

Reaction-energy diagram for the first propagation step in the chlorination of propane. Formation of the secondary radical has a lower activation energy than does formation of the primary radical. 

Table 2 gives the yields of the various products in Co radiolysis of gaseous cyclopropane obtained by the several workers. It shows a good agreement of the yields of the main products obtained in the various studies. However, there are some disagreements, e.g. for propane or isobutane formation. The controversy concerning the G-value for propane formation can be explained if von Bunau and Kuhnert s system included small amounts of alkanes which were found to increase the yield of propane from 0.5 to 1.0. 

The conversion of n-hexane on ZnO/H-ZSM-5 catalysts was studied in the range of 2-32 h l volume velocity in a quartz microreactor at SOOT and 1 atm [1]. The selectivity of the lowest olefin formation has been shown to be slightly higher than that of paraffins. The lowest olefins and paraffins are formed in the process of hexane cracking. The selectivity of benzene, toluene, xylene methane, ethane, and propane formation rises with increasing hexane conversion in proportion to the contact time, as the selectivity of the olefin formation decreases. 

Only about 3wt% of ethane is observed in the steam cracking products, indicating that the formation of ethylene is the preferential fate of ethyl radicals. Note that most of ethane is formed via ethyl radical H-abstraction reactions, while less than 10% is due to the recombination reaction of methyl radicals. Similarly, propane formation is mostly due to the H-abstraction reactions of propyl radicals and only marginally to the recombination of methyl and ethyl radicals. 

Fig. 5. Effects of the addition of NO molecules upon the photolysis of 2-pentanone adsorbed on Vycor glass at 298 K (ethylene and propane formations) and 2-butanone (ethane formation) (amount of 2-pentanone adsorbed 3.29 x 10 mol/g, amount of 2-butanone 3.99 x 10 mol/g).

Fig. 8. Stern-Volmer plots for scavenging of the propane formation in the photolysis of 2-pentanone adsorbed on Vycor glass which had been degassed at various temperatures (a degassed at 573 K, b degassed at 773 K, c degassed at 973 K).

Propane Formation. Previous workers who report mechanisms for the formation of C3H8 (20, 28, 30, 44) invoke neutral-neutral reactions. From our results (Table III) these reactions account for only one-third of the C3H8 while two-thirds are caused by reactions involving CH/, CH3 and CH2+ (Table V). Recent work (2, 15, 37, 45, 47) in simple HC systems has demonstrated that the contribution of excited states of reactant ions to ion-molecule reactions cannot be neglected. Similar considerations are true for radical-radical and radical-molecule reactions (16). We postulate the following ion-molecule reaction involving CH4+. ... 

Propane formation occurs through a three-step process with hydrogenation of acetone on the platinum sites, dehydration of isopropanol on the acid sites and hydrogenation of propene on the platinum sites. 2-Methylpentane being a primary product results probably from propene dimerisation on the acid sites followed by hydrogenation. 

Decomposition. Equation 5.26 is the reverse of the formation reaction for C3H8(g), so the enthalpy change for this decomposition reaction is the negative of the AHf value for the propane formation reaction —AHj [C3Hg(g)]. 

The trend for propanal formation (Figure 15.15) agreed with that for hexanal (Figure 15.16). 

Another possible route to propanal formation is via the isomerization of the CH3CH2CH(00 )0C3H7 peroxy radical (see Collins et al., 2005, Orlando, 2007), and the discussion below on di-isopropyl ether oxidation] ... 

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