Secondary reactions of olefins

The reactions were carried out in a TEOM reactor where the weight of the catalyst bed is continuously recorded. The setup is similar to that described previously [8]. The methanol flow was controlled by a liquid flow controller while DME and propene were fed using gas flow controller. The MTO and DTO reactions were carried out at 425°C, WHSV=417h" and a methanol or DME partial pressure of 8 kPa, with helium as diluent. One DTO experiment was also performed at WHSV=600 h" to keep the residence time identical to those from the MTC) experiments. Such high space velocity and low partial pressure were used to avoid non-uniform coke distribution through the catalyst bed, and to keep the conversion well below 100% to minimize secondary reactions of olefins. 

Secondary Reactions of Olefins in Pyrolysis of Petroleum Hydrocarbons... 

For this model, the product distribution of FTS should be determined or influenced by not only the chain-growth factor a but also the secondary reaction of olefins (/ ), which can direct the design of FTS catalyst and engineering enlargement. However, the olefin readsorption mechanism model needs to be studied further to clarify the intrinsic product distribution of FTS. 

The major breakthrough in the catalytic asymmetric dihydroxylation reactions of olefins was reported by Jacobsen et al.55 in 1988. Combining 9-acetoxy dihydroquinidine as the chiral auxiliary with /V-methylmorphine TV-oxide as the secondary oxidant in aqueous acetone produced optically active diols in excellent yields, along with efficient catalytic turnover. 

Grubbs and co-workers have further investigated the influence of allylic substitution on E/Z diastereocontrol in olefin CM reactions using catalyst 5. In some cases, it was found that secondary and tertiary allylic alcohols could afford complete -selectivity, particularly when a cross-partner bearing allylic heteroatom substitution was used. Also, in contrast to the less reactive catalyst 2, catalyst 5 was found to promote the CM reaction of olefins bearing quaternary allylic substitution (Scheme 7). The cross-partners in these examples represent type III olefins with respect to 5 therefore, they can be applied either stoichiometrically or in excess without a reduction in yield. E/Z ratios of >20 1 were typically observed. 

The catalytic cracking of four major classes of hydrocarbons is surveyed in terms of gas composition to provide a basic pattern of mode of decomposition. This pattern is correlated with the acid-catalyzed low temperature reverse reactions of olefin polymerization and aromatic alkylation. The Whitmore carbonium ion mechanism is introduced and supported by thermochemical data, and is then applied to provide a common basis for the primary and secondary reactions encountered in catalytic cracking and for acid-catalyzed polymerization and alkylation reactions. Experimental work on the acidity of the cracking catalyst and the nature of carbonium ions is cited. The formation of liquid products in catalytic cracking is reviewed briefly and the properties of the gasoline are correlated with the over-all reaction mechanics. 

Accordingly, work has been done on series of n-paraffins,. isoparaffins, naphthenes, aromatics, and naphthene-aromatics which have been chosen as representative of the major components of petroleum. In addition, olefins, cyclo-olefins, and aromatic olefins have been studied as a means of depicting the important secondary reactions of the copious amounts of unsaturates produced in the majority of catalytic cracking reactions. A silica-zirconia-alumina catalyst was used principally it resembles closely in cracking properties typical commercial synthetic silica-alumina catalysts. 

Fundamental studies of catalytic cracking have led to the conclusion that the chief characteristics of the products may be traced to the primary cracking of the hydrocarbons in the feed stock and to the secondary reactions of the olefins produced both correspond to the ionic reaction mechanisms of hydrocarbons in the presence of acidic catalysts. The chemistry of both the hydrocarbons and catalysts dealt with here has advanced rapidly in the last decade. Nevertheless, much further exploration is required with respect to the nature of the catalyst and the properties of the hydrocarbons undergoing reaction. A promising field lies ahead for future research. 

Rabinovitch et al. (85) studied the reaction of H atoms with trans-ethylene-d2 as a function of ethylene pressure in the temperature range — 78 to 160°C. They were able to account for all secondary reactions of the hot ethyl radicals and to determine the rates of their decomposition (relative to stablization). Simultaneously they calculated the theoretical rates on the basis of the Rice-Ramsperger-Kassel theory of uni-molecular reactions, using expressions derived by Marcus (71), and found a reasonable agreement with the experimental values. Similar satisfactory agreements had been found previously by Rabinovitch and Die-sen (84) for hot sec-butyl radicals. Extensive studies of hot radicals produced by H or D atom additions to various olefins have been carried... 

Chiche et a/.[56] have studied the oligomerization of butene over a series of zeolite (HBeta and HZSM-5), amorphous silica alumina and mesoporous MTS-type aluminosilicates with different pores. The authors found that MTS catalyst converts selectively butenes into a mixture of branched dimers at 423 K and 1.5-2 MPa. Under the same reaction conditions, acid zeolites and amorphous silica alumina are practically inactive due to rapid deactivation caused by the accumulation of hydrocarbon residue on the catalyst surface blocking pores and active sites. The catalytic behaviour observed for the MTS catalyst was attributed to the low density of sites on their surface along with the absence of diffusional limitations due to an open porosity. This would result in a low concentration of reactive species on the surface with short residence times, and favour deprotonation and desorption of the octyl cations, thus preventing secondary reaction of the olefinic products. 

We conclude that linear and branched olefins and paraffins can be formed after one surface sojourn by termination of growing surface chains. Therefore, they are primary Fischer-Tropsch products (4,14). a-Olefins readsorb and initiate chains in a secondary reaction. Thus, olefins reenter the primary chain growth process and continue to grow. These chains ultimately terminate as olefins or paraffins, in a step that can resemble a secondary hydrogenation reaction because it leads to the net consumption of olefins and to the net formation of paraffins, but which proceeds via primary FT synthesis pathways. 

Water, a by-product of the FT synthesis reaction, inhibits secondary hydrogenation, hydroformylation, and oligomerization of a-olefins during FT synthesis. At sufficiently high pressures, CO also inhibits these secondary reactions. These olefins react more rapidly near atmospheric reactant pres-... 

Dimensional analysis of the coupled kinetic-transport equations shows that a Thiele modulus (4> ) and a Peclet number (Peo) completely characterize diffusion and convection effects, respectively, on reactive processes of a-olefins [Eqs. (8)-(14)]. The Thiele modulus [Eq. (15)] contains a term ( // ) that depends only on the properties of the diffusing molecule and a term ( -) that includes all relevant structural catalyst parameters. The first term introduces carbon number effects on selectivity, whereas the second introduces the effects of pellet size and pore structure and of metal dispersion and site density. The Peclet number accounts for the effects of bed residence time effects on secondary reactions of a-olefins and relates it to the corresponding contribution of pore residence time. 

Linear a-olefins together with linear paraffins are the main primary products. On Fe the olefin content in the fraction of linear hydrocarbons for small carbon numbers was found to be about 80% (Fig. 4), which is very close to their primary selectivity [6]. This can be due to the high potassium loading, which suppresses the secondary reactions of the olefins. With increasing CO2 content a slight increase of the olefin content is observed. This can be due to the increasing amount of water formed from the reaction with CO2 instead of CO. The effect of added water on the olefin selectivity for a potassium promoted fused iron catalyst has been reported earlier by Satterfield [7]. With increasing CO2 concentration in the reaction gas on Co no more olefins were present in the products. 

A very different situation was represented by the behavior of adsorbed vinyl acetate (13). The maximum quantity of this substrate which could be adsorbed at room temperature (1.28 mmole/gm), is considerably greater than for the other olefins and for oxygen. However, it turns out that most of this material could be recovered by desorption over the temperature range 100-200°C (see Figure 3). While complete mass balance could not be achieved, the only other products isolated on heating to as high as 340°C were acetaldehyde and acetic acid. Control experiments verified that these were not produced by secondary reaction of vinyl acetate at... 

Readsorption and secondary reactions of the intiailly produced ct-olefins is an important pathway in Fischer-Tropsch reactions on Fe single crystals Dwyer, D.J., and Somorjai, G.A., J. Catal., 56, 249, (1979). Schulz, H., and Achtsnit,... 

Mark and Rechnitz [3] systematized a vast amount of experimental material that can be used directly in KGCM. Some data are presented here that show the wide differences in organic compounds with regard to their kinetic characteristics. Table 2.1 [14] gives the relative rates of reaction of olefins with perbenzoic acid and Table 2.2 summarizes the rates of the etherification reaction of carboxylic acids with diphenyldiazomethane [15]. The tabulated data are indicative of large differences in organic compounds as far as their reactivity is concerned. The rates of reaction of some isomers differ so widely that one can, for example, analyse secondary and tertiary alkyl bromides in the presence of primary alkyl bromides in a reaction with silver nitrate [16]. It is possible to differentiate between CIS and trans isomers of 1,3-dienes by their reaction with dienophils (e.g., chloromethylene anhydride) because the cis isomer reacts much more slowly than the trans isomer [17]. 

In conclusion, it should be re-emphasized that the fragment ions from propene are very reactive towards propene and the reaction schemes of even the secondary reactions of these ions have not been completely estabished. We will see that the situation is the same for higher olefins. 

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