Butane alkene conversion

It is advantageous to pretreat butene feeds before alkylation.294-298 1,3-Butadiene is usually hydrogenated (to butenes or butane) since it causes increased acid consumption. The additional benefit of this process is that under hydrogenation conditions alkene isomerization (hydroisomerization) takes place, too. Isomerization, or the transformation of 1-butene to 2-butenes, is really attractive for HF alkylation since 2-butenes give better alkylate (higher octane number) in HF-cata-lyzed alkylation. Excessive 1,3-butadiene conversion, therefore, ensuring 70-80% isomerization, is carried out for HF alkylation. In contrast, approximately 20% isomerization is required at lower butadiene conversion for alkylation with H2SO4. 

The basic mechanism of hydrogenation is shown by the catalytic cycle in Fig. 7.3. This cycle is simplified, and some reactions are not shown. Intermediate 7.9 is a 14-electron complex (see Section 2.1). Phosphine dissociation of Wilkinson s complex leads to its formation. Conversion of 7.9 to 7.10 is a simple oxidative addition of H2 to the former. Coordination by the alkene, for example, 1-butene, generates 7.11. Subsequent insertion of the alkene into the metal-hydrogen bond gives the metal alkyl species 7.12. The latter undergoes reductive elimination of butane and regenerates 7.9. 

Note that although the conversion of 7.11 to 7.12 assumes anti-Markovnikov addition, the Markovnikov product also gives butane. Conversion of 7.9 to 7.11 could also take place by prior coordination of alkene followed by the oxidative addition of dihydrogen. Indeed this parallel pathway for the formation of 7.11 does operate. Like the equilibrium shown between RhClL3, 7.9, and the dimer [RhClL L, there is an equilibrium between 7.9 and the alkene coordinated complex RhCl(alkene)L2. 

The assertion by Centi et al. (30) that the reaction proceeds via a series of redox couples was based on experimental results obtained at high butane concentrations and high oxygen conversions. Under these conditions, many V " " sites are formed as the catalyst undergoes a partial reduction. Butane activation requires a couple, whereas the subsequent conversion to MA requires a couple. Alkenes from butane dehydro-... 

The Ruhrchemie/Rhone-Poulenc [1] process for the hydroformylation of short-chain alkenes such as propene and butene (cf. Section 2.4.1.1.3) combines a facile catalyst recycling with high selectivity and sufEcienfly high conversion rates to provide a commercially viable large-scale manufacturing process for butanal [2] and valeraldehyde [3]. Higher alkenes (> Cg) are not suitable for the RCH/RP process as run in Oberhausen. 

The ODH of ethane, propane, and butanes carried out over representative catalysts are given in Table 15.1 to Table 15.3, respectively. The coluums in the tables represent the following the chemical composition of the catalyst, the alkane to oxygen molar ratio, the contact time or equivalent representations, and the temperature of the reaction are given in columns one, two, three, and four the alkane conversion and alkene selectivity are given in columns five and six and the reference of the article is given in column seven. 

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