Phase isomerization

Zhu S-B, Lee J, Robinson G Wand Lin S H 1989 Theoretical study of memory kernel and velocity correlation function for condensed phase isomerization. I. Memory kernel J. Chem. Phys. 90 6335-9... 

Mobil s Vapor Phase Isomerization Process (MVPI)... 

A second Mobil process is the Mobil s Vapor Phase Isomerization Process (MVPI) (125,126). This process was introduced in 1973. Based on information in the patent Hterature (125), the catalyst used in this process is beHeved to be composed of NiHZSM-5 with an alumina binder. The primary mechanism of EB conversion is the disproportionation of two molecules of EB to one molecule of benzene and one molecule of diethylbenzene. EB conversion is about 25—40%, with xylene losses of 2.5—4%. PX is produced at concentration levels of 102—104% of equiHbrium. Temperatures are in the range of 315—370°C, pressure is generally 1480 kPa, the H2/hydrocatbon molar ratio is about 6 1, and WHSV is dependent on temperature, but is in the range of 2—50, although normally it is 5—10. 

Xylenes. The main appHcation of xylene isomers, primarily p- and 0-xylenes, is in the manufacture of plasticizers and polyester fibers and resins. Demands for xylene isomers and other aromatics such as benzene have steadily been increasing over the last two decades. The major source of xylenes is the catalytic reforming of naphtha and the pyrolysis of naphtha and gas oils. A significant amount of toluene and Cg aromatics, which have lower petrochemical value, is also produced by these processes. More valuable p- or 0-xylene isomers can be manufactured from these low value aromatics in a process complex consisting of transalkylation, eg, the Tatoray process and Mobil s toluene disproportionation (M lDP) and selective toluene disproportionation (MSTDP) processes isomerization, eg, the UOP Isomar process (88) and Mobil s high temperature isomerization (MHTI), low pressure isomerization (MLPI), and vapor-phase isomerization (MVPI) processes (89) and xylene isomer separation, eg, the UOP Parex process (90). 

Another example of catalytic isomerization is the Mobil Vapor-Phase Isomerization process, in which -xylene is separated from an equiHbrium mixture of Cg aromatics obtained by isomerization of mixed xylenes and ethylbenzene. To keep xylene losses low, this process uses a ZSM-5-supported noble metal catalyst over which the rate of transalkylation of ethylbenzene is two orders of magnitude larger than that of xylene disproportionation (12). 

The reaction is about 50% faster in ethoxyethanol than in decane. Calculate the activation parameters at 150°C. Although precisely comparable data are not available, for the gas-phase isomerization of norbomadiene is 50kcal/mol. Draw a sketch... 

Iso-Kel [Isomerization-Kellogg] A fixed-bed, vapor-phase isomerization process for making high-octane gasoline from aliphatic petroleum fractions. The catalyst is platinum on alumina. Developed by MW Kellogg. 

MVPI [Mobil vapor phase isomerization] A process for converting mixed xylene streams to />xylene, catalyzed by the zeolite ZSM-5. Invented by Mobil Corporation in 1973, later superseded by MHTI. See also LTI, MHTI, MLPI. 

A gas phase isomerization is catalyzed by porous spherical grains. In the absence of complicating factors the rate of chemical reaction is approximately zero order, that is,... 

One important application of analysis of variance is in the fitting of empirical models to reaction-rate data (cf. Section VI). For the model below, the analysis of variance for data on the vapor-phase isomerization of normal to isopentane over a supported metal catalyst (Cl)... 

Bowen, R.D. Stapleton, B.J. Williams, D.H. Nonconcerted Unimolecular Reactions of Ions in the Gas Phase Isomerization of Weakly Coordinated Carbonium Ions. J. Chem. Soc., Chem. Commun. 1978, 24-26. 

Reversing the CH=N group position in 477-5,6-benzoxazin-4-one should result in the same isomerization enthalpy as from HC(NMe)OMe to MeCHNOMe. The enthalpy of formation of the latter species was calculated to be —7.1 kJmoR from the high-level quantum chemical calculations of Reference 4. The enthalpy of formation of the former species is unknown. However, if we accept the gas phase isomerization enthalpy of dimethylamides to methyl imidates (69.6 13.4 kJmoR ) in equation 52 from Reference 75,... 

Phenylacetaldehyde can be obtained in high yield by vapor-phase isomerization of styrene oxide, for example, with alkali-treated silica-alumina [147]. Another process starts from phenylethane-l,2-diol, which can be converted into phenylacetaldehyde in high yield. The reaction is performed in the vapor phase in the presence of an acidic silica alumina catalyst [148]. 

A unique liquid-phase isomerization to produce m-xylene in the presence of HF-BF3 was developed by Mitsubishi288 on the basis of earlier work by Lien and McCaulay,83 who found that m-xylene forms the most stable a complex in HF-BF3 at low temperature. This complex selectively dissolves in the acid phase, allowing easy separation from the less stable other two isomers. The complex then is decomposed to produce pure m-xylene. 

Using the monomolecular rate theory developed by Wei and Prater, we have analyzed the kinetics of the liquid-phase isomerization of xylene over a zeolitic catalyst. The kinetic analysis is presented primarily in terms of the time-independent selectivity kinetics. With the establishment of the basic kinetics the role of intracrystalline diffusion is demonstrated by analyzing the kinetics for 2 to 4 zeolite catalyst and an essentially diffusion-free 0.2 to 0.4 m zeolite catalyst. Values for intracrystalline diffusivities are presented, and evidence is given that the isomerization is the simple series reaction o-xylene <= m-xylene <= p-xylene. 

Foote, Mallon, and Pitts48 report a gas-phase isomerization of benzene at 1849 A with a quantum yield of approximately unity, and tentatively identify the isomer as benzvalene although they suggest the... 

Salient features of the three commercialized processes are shown in Table VI. The Shell Development Co s liquid phase isomerization process uses an improved Friedel-Crafts catalyst system consisting of a solution of A1C13 in SbCl3 and uses HC1 as a promoter. This process was first evaluated in an existing isomerization unit in 1961 (26) giving it the... 

Butane vapor-phase isomerization a process for isomerizing n-butane to iso-butane using aluminum chloride catalyst on a granular alumina support and with hydrogen chloride as a promoter. 

The experimental Arrhenius activation energy and rate constant for the gas phase isomerization of methyl isocyanide have been reported (at the lowest pressure used) thus a = 36.27 kcal mol-1, i.e. 151.8 kJ mol-1, and log A = 10.46, i.e. A = 2.88 x 1010 s-1 [220]. We want to compare our calculated activation free energy with an experimental value, let us calculate AG from a and A. From the Arrhenius equation Eq. (5.174) and the Eyring equation Eq. (5.197) it follows that... 

Enthalpies of formation are from A. M. Rozhnov and T. N. Nesterova, Russ. J. Phys. Chem., 27, 1390 (1973). The dibromobutane gas-phase enthalpies were obtained from liquid-phase isomerization of the 1,2-species and semiempirical corrections to the 1,4-dibromobutane enthalpy of vaporization. The enthalpies of formation are (kJmol1) 1,2-dibromobutane [(1), -140 8 (g),-92.9]. 

Rate constants and activation energies for liquid- and gas-phase isomerization of a-pinene have been determined.310 The activity of metal sulphate monohydrates in isomerizing a-pinene is correlated with the strength of co-ordination of the water of crystallization to the metal ion.3" Pyrolysis of chrysanthanol acetate (217 R = Ac) gives citronellal and the (E)- and (Z)-3,7-dimethylocta-l, 6-dien-l -ol acetates in 20, 28, and 3% yields respectively formation of the enol acetates is consistent with a biradical or a concerted pathway.312 Further work directed towards C-l—C-7 bond pyrolysis of pinane derivatives shows C-l—C-7 C-l—C-6 bond cleavage ratios of 4 51 for (217 R = Ac), 13 22 for (217 R = H), 6 7 for (218 R = H), and 43 35 for (218 R = Me) the expected acyclic and cyclic alcohol, aldehyde, and ketone pyrolysis products are obtained.313 The ene reaction between /3-pinene and methyl... 

The enthalpies of combustion, formation, and isomerization of car-2-ene and car-3-ene have been reported 335 the activation energy for the titanium-catalysed first-order isomerization of car-3-ene into car-4-ene and various menthadienes is 20kcalmor1 at 150—160 °C.336 Isomerization of car-3-ene over metal oxide catalysts varies substantially depending upon the metal catalyst used 337 other Russian work reports diene formation from the vapour-phase isomerization of car-3-ene but this Reporter is unable to assess the significance of the work from Chemical Abstracts in the absence of the original paper.338... 

Table 15.2 Conversion and selectivities obtained with used zeolites in the liquid phase isomerization of isophorone oxide 23...

To our knowledge, no vapor phase isomerization utilizing heterogeneous catalysts has been previously described in the literature for this reaction. Continuous vapor phase reactions should be preferred over discontinuous liquid phase reactions, as this yields a higher efficiency (space time yield) as well as an easier separation of the catalyst from the reaction mixture. 

A general view of the used zeolites in the vapor phase isomerization and their conversions and selectivities is shown in Table 15.3. The blank test yields less than 2% conversion. 

Using zeolites with the same structure but in different ratios of Si02/Al203, we found an increased tendency towards selectivity to 24 with higher Si02/Al203 ratios, as was previously observed in liquid phase isomerization. All tested zeolites yielded high conversions, except for Na-ZSM-5 and silicalite. A shorter contact time seems to have a positive effect on the aldehyde formation, possibly due to reduced decarbonylation. The influence of solvents in the gas phase is similar to that of the liquid phase. Best yields were obtained with toluene, anisole and o-xylene. 

A number of papers have been published describing the thermal isomerization reactions of bicyclo[2.2.2]oct-2-ene, bicyclo[3.2.1]oct-2-ene, and norcamphene to bicyclo[3.3.0]octenes.149-152 The gas phase and solution phase isomerization of perhydroindane to a mixture of methyl substituted bicyclo[3.3.0]octanes has also... 

Lonza S.p.A. Furmaric acid Maleic anhydride Liquid-phase isomerization, two-step crystallization process 6 1991... 

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