Disproportionation of propylene

Other. Ethylene can be produced by steam cocracking of propylene with ethane and propane. Ethylene and butenes can also be produced by catalytic disproportionation of propylene (108). 

Although ethylene is produced by various methods as follows, only a few are commercially proven thermal cracking of hydrocarbons, catalytic pyrolysis, membrane dehydrogenation of ethane, oxydehydrogenation of ethane, oxidative coupling of methane, methanol to ethylene, dehydration of ethanol, ethylene from coal, disproportionation of propylene, and ethylene as a by-product. 

Propylene Disproportionation. A commercial plant utilizing the disproportionation of propylene to ethylene was built in 1966 by Gulf Oil of Canada Ltd. utilizing technology developed by Phillips. 

Minachev, Eidus et al. (25) found that Ca, Ni, Co, and NdY zeolites were active in the disproportionation of propylene to ethylene and butenes. The process was accompanied by hydrogen rearrangement to form saturated hydrocarbons and condensation products. The selectivity in this reaction depends on the composition of the catalysts, their pretreatment, and the experimental conditions (26). 

Mol, Visser, and Boelhouwer 741 subjected 1,2-dimethyl-butane (ring structure of the suggested transition state for disproportionation of propylene) to rhenium oxide-alumina catalyst under conditions which propylene gives high disproportionation conversions. This compound was stable only at high temperatures (730 °C), where thermal cracking occurred, were olefins found. 

Lewis and Wills83) obtained initial differential rate data for the disproportionation of propylene over a C0O-M0O3 -Ala 03 catalyst. Temperatures of 394-478 °K and pressures of 1 to 9 atmospheres were used. The authors reported the experimental data were well correlated when it was assumed that a dual site surface reaction was the controlling step in the mechanism. 

The simplest example of alkene metathesis, the disproportionation of propylene to ethylene and 2-butene, was the first commercial application of this reaction. Changes in the relative economic value of... 

The disproportionation of propylene on supported tungsten oxide catalysts is thought to proceed via a cyclobutane intermediate as follows. 

In some bimolecular reactions like disproportionation of propylene to butylene and ethylene and hydrogenation of ethylene to ethane, a modified form of LHHW models has to be used. Here, the reaction is assumed to occur by a molecule of one of the reactants (say A) striking an obsorbed molecule of B (or another A). Thus the rate equation would be (or aPb if reacts... 

There are other commercial processes available for the production of butylenes. However, these are site or manufacturer specific, eg, the Oxirane process for the production of propylene oxide the disproportionation of higher olefins and the oligomerisation of ethylene. Any of these processes can become an important source in the future. More recentiy, the Coastal Isobutane process began commercialisation to produce isobutylene from butanes for meeting the expected demand for methyl-/ rZ-butyl ether (40). 

Disproportionation of Olefins. Disproportionation or the metathesis reaction offers an opportunity to convert surplus olefins to other desirable olefins. Phillips Petroleum and Institut Fransais du Petrc le have pioneered this technology for the dimerization of light olefins. The original metathesis reaction of Phillips Petroleum was intended to convert propylene to 2-butene and ethylene (58). The reverse reaction that converts 2-butene in the presence of excess ethylene to propylene has also been demonstrated (59). A commercial unit with a capacity of about 136,000 t/yr of propylene from ethylene via 2-butene has been in operation in the Gulf Coast since 1985 (60,61). In this process, ethylene is first dimerized to 2-butene foUowed by metathesis to yield propylene. Since this is a two-stage process, 2-butene can be produced from the first stage, if needed. In the dimerization step, about 95% purity of 2-butene is achieved at 90% ethylene conversion. 

A second route based on olefin disproportionation was developed by Phillips Petroleum (131). Here isobutylene reacts with propylene to form isoamylenes, which are dehydrogenated to isoprene. 2-Butene can be used in place of propylene since it also yields isoamylene and the coproduct propylene can be recycled. Use of mixed butylenes causes the formation of pentenes, giving piperjlene, which contaminates isoprene. 

Table 8-5 indicates the wide variety of catalysts that can effect this type of disproportionation reaction, and Figure 8-7 is a flow diagram for the Phillips Co. triolefm process for the metathesis of propylene to produce 2-butene and ethylene. Anderson and Brown have discussed in depth this type of reaction and its general utilization. The utility with respect to propylene is to convert excess propylene to olefins of greater economic value. More discussion regarding olefin metathesis is noted in Chapter 9. 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Although in general functionally-substituted olefins are unreactive, the disproportionation of acrylonitrile with propylene and of certain unsaturated fatty acid esters have been recently reported (8, 9). The disproportionation of acetylenes has been observed over heterogeneous catalysts (10). 

Falconer and Cvetanovic (40) attempted to obtain a more quantitative value for the fraction of nonterminal addition in the case of propylene. They produced hydrogen atoms by mercury photosensitized decomposition of H2, using at least 100 times as much H2 as C3H6 and total pressures of 40 and of 250 mm. Under these conditions the reactions of importance were the combination and disproportionation of the iso- and n-propyl radicals and their cross reactions, the combination of the two radicals with H atoms (assumed to be equally probable), and a very small amount of decomposition of hot n-propyl radicals. Disproportionation to combination ratios were taken as 1.64 for two iso-propyl, 1.14 for two w-propyl, and hence 1.39 was taken as the mean of the two values for one iso- and one n-propyl radical. Using these values and the analysis of the products, the nonterminal addition of H atoms to C3H6 and C3D6 was found to amount to 6 1%. 

Studies by Lapidus and coworkers 33) of the isomerization of w-butenes on nickel-zeolite catalysts indicate that some zeolite catalysts are active for the disproportionation of butenes to propylene and pentenes. 

Woody, Lewis, and Wills 72> studied the disproportionation of [1-14C] propylene over cobalt oxide-molybdate-alumina at 149 and 177 °C. Approximately equal amounts of radioactivity were found in the approximately equal molar quantities of ethylene and butene. These results are in agreement with those of Clark and Cook showing that double-bond isomerization was a factor in this temperature region. Woody and coworkers suggest that since the isomerization of the 2-butene product was negligible, an explanation of double-bond mobility as simple isomerization is probably an oversimplification. 

Isotopic experiments show that ethane is formed by association of methyl radicals. Propylene results from disproportionation of isopropyl... 

The latest industrial application of metathesis was developed by Phillips who started up a plant in late 1985 at Cbannelview, Texas, on the L ondell Petrochemical Complex with a production capacity of 135,000 t/year of propylene from ethylene. This facility carries out the disproportionation of ethylene and 2-butenes, in the vapor phase, around 300 to 350°C, at about 0.5.10 Pa absolute, with a VHSV of 50 to 200 and a once-througb conversion of about 15 per cent 2-butenes are themselves obtained by the dimerization of ethylene in a homogeneous phase, which may be followed by a hydroisomerization step to convert the 1-butene formed (see Sections 13.3.2. A and B). IFP is also developing a liquid phase process in this area. 

Disproportionation of primary Cy alkylate (from propylene) with isobutane under alkylation conditions probably accounts for the near-equal amounts of isopentane and isohexanes found in propylene alkylate. 

The second relevant phenomenon is the decrease of the overall rate or the increase of the decay rate which is often observed when the alkyl concentration increases beyond certain limits. According to some authors 88 11this may be due to the adsorption of the Al-alkyl on catalytic sites in competition with the monomer. Still others 92,95 107) attribute it to an overreduction of titanium. This seems plausible when considering the results obtained by Kashiwa78) who showed that Ti2+ is less active than Ti3+ or Ti4+ in ethylene polymerization and completely inactive in the polymerization of propylene. Keii98), in turn, based on the results of Fig. 32, hypothesizes that the decay rate is due to a bimolecular disproportionation of the Ti—R bonds, favored by Al-alkyl reversibly adsorbed on the catalyst surface. 

The measured reaction orders support the proposed mechanism. Path A is certainly first order in reactant. Paths B and C may be 1/2, first, or 3/2 order, depending on the termination reaction (15). Most likely, termination involves combination or disproportionation of small chain carrying radicals (CH3, C2H5 ). With first-order initiation, this would result in 3/2-order kinetics. The overall reaction order would then be somewhere between first (Mechanism A) and 3/2 (Mechanisms B and C). The measured order of 1.33 for dodecene agrees with this prediction. The fact that propylene and nonene are formed with reaction orders of 1.10 and 1.16 with respect to dodecene (Table III) supports the hypothesis that they are formed largely by a first-order decomposition. 

Redox processes involving 178 have also been studied.Anodic oxidation of thianthrene has been eifected in a wide variety of solvents. Use of trifluoracetic acid gives stable solutions of 178 and, if perchloric acid is included, the solid perchlorate salt may be isolated on evaporation of the solvent after electrolysis. Dichloromethane at low temperatures has been used and, at the opposite extreme, fused aluminum chloride-sodium chloride mixtures. " Propylene carbonate permits the ready formation of 178, whereas the inclusion of water in solvent mixtures gives an electrochemical means of sulfoxidizing thianthrene. Reversible oxidation of 178 to thianthrenium dication may be brought about in customary solvents such as nitriles, nitro compounds, and dichloromethane if the solvent is treated with neutral alumina immediately before voltammetry addition of trifluoracetic anhydride to trifluoracetic acid equally ensures a water-free medium. The availability of anhydrous solvent systems which permit the reversible oxidation and reduction of 178 has enabled the determination of the equilibrium constants for the disproportionation of the radical and for its equilibria with other aromatic materials. ... 

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