Propene production

Dimerization in concentrated sulfuric acid occurs mainly with those alkenes that form tertiary carbocations In some cases reaction conditions can be developed that favor the formation of higher molecular weight polymers Because these reactions proceed by way of carbocation intermediates the process is referred to as cationic polymerization We made special mention m Section 5 1 of the enormous volume of ethylene and propene production in the petrochemical industry The accompanying box summarizes the principal uses of these alkenes Most of the ethylene is converted to polyethylene, a high molecular weight polymer of ethylene Polyethylene cannot be prepared by cationic polymerization but is the simplest example of a polymer that is produced on a large scale by free radical polymerization... 

As a new kind of carbon materials, carbon nanofilaments (tubes and fibers) have been studied in different fields [1]. But, until now far less work has been devoted to the catalytic application of carbon nanofilaments [2] and most researches in this field are focused on using them as catalyst supports. When most of the problems related to the synthesis of large amount of these nanostructures are solved or almost solved, a large field of research is expected to open to these materials [3]. In this paper, CNF is tested as a catalyst for oxidative dehydrogenation of propane (ODP), which is an attractive method to improve propene productivity [4]. The role of surface oxygen annplexes in catalyzing ODP is also addressed. 

The simple hydrocarbon substrates included ethene, 1,2-propa-diene, propene and cyclopropane (22). Their reactivity with Sm, Yb and Er was surveyed. In contrast to the reactions discussed above, lanthanide metal vapor reactions with these smaller hydrocarbons did not provide soluble products (with the exception of the erbium propene product, Er(C H ) ). Information on reaction pathways had to be obtained primarily by analyzing the products of hydrolysis of the metal vapor reaction product. 

A more recent raw material for plasticizer alcohols is crack-C4 as a byproduct of steamcrackers in ethene/propene production. After extraction of butadiene for use and etherification of isobutene with methanol to methyl-tertiary-butylether MTBE as an octane enhancer, a stream is left containing 1-butene, 2-butene, and butanes, so-called raffinate II. Oligomerization of the butenes yields C8 olefin mixtures ( dibutene ) as the main product and the corresponding C12 olefins as the main byproduct (tributene). They are the... 

The addition to a carbon-carbon triple bond results in the formation of cyclo-propene products, and with diazoacetates the catalyst of choice for intermolecular addition is the dirhodium(II) carboxamidate 13 (e.g., Eq. 26). The reactions are general, except for phenylacetylene whose cyclopropene product undergoes [2 + 2]-cycloaddition, and selectivities are high. However, high selectivities have not been reported for reactions with allenes. 

In this 3-phcnylalkyne system the triple bond becomes incorporated into a cyclo-propene ring, whereas from the enynes 10 and 11 there is no sign of a vinylcyclo-propene product. The preference for reaction to take place at the alkene unit rather than at the alkyne unit in the photochemistry of enynes is seen again in the photochemistry of enepoly-yne chlorides, where only cyclopropyl chlorides are produced (equation 18). This preference is probably a reflection of the lower strain energy in a cyclopropane than in a cyclopropene ring. 

Reaction of Methyl Complexes with Propene. Products. 

After a switch from isopropanol - inert the outlet concentration of the alcohol falls quickly and desoiption from the S2-sites occurs resulting in a drastic increase of propene production whereas Ae ether formation slows down. At long cycle times the propene concentration... 

At short periods (Fig. 3A), the desorption time is insufficient and an important fraction of 82-sites are still blocked when the isopropanol feed is restored. Therefore, the propene production rate does not reach is maximum possible value and a considerable amount of ether is produced throughout the whole period. The oscillations are more symmetric and the production rate of ether is roughly proportional to the isopropanol concentration. 

At the same time the obtainable maximal productivity under periodic operation decreases with increasing space time as indicated in Fig. SB. This result is in line with the observation that the maximal transient propene production increases with decreasing space time and that the maximum is shifted to shorter times (Fig. 2). 

For the parent cyclopropane, the path to propene must be different than the concerted double rotation. For substituted cyclopropanes, however, it seems reasonable to propose that propene products arise from a 1,2-hydrogen shift of the biradical. We have noted earlier that 1,2-shifts are essentially never seen in simple radicals. Thus, the substantial driving force of forming a new C-C it bond makes this usually unfavorable process feasible. 

Various Nb containing catalysts were also studied for the ODH of propane. Smits and coworkers [61] observed that niobium oxide shows a very high selectivity in this reaction although the conversion was very low. The activity of the Nb containing catalysts was improved without diminishing its selectivity by adding elements, such as V, Cr, or Mo, all of which are reducible transition metals. For a series of V-based catalysts and at isoconversion levels ( 30% conversion), the propene selectivity for 1 1 Nb-V and Sb-V catalysts was 20 and 40%, respectively. The 1 1 Sb-V and 1 1 5 Nb-V-Si prepared via the nonhydrolytic method offer the best results in terms of propane conversion and propene yield. With the 1 1 5 Nb-V-Si catalysts the propene productivity of 0.23 kg of propene per kilogram of catalyst per hour was achieved at 823 K [62]. 

SveUe S, Olsbye U, Joensen F, Bjprgen M. Conversion of methanol to alkenes over medium- and large-pore acidic zeohtes steric manipulation of the reaction intermediates governs the ethene/propene product selectivity. J Phys Chem C 2007 111 17981. ... 

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