Alumina, butene isomerization over

Figure 24 shows the cfs-butene isomerization over zinc oxide as a function of time at room temperature (7/). On a per unit area basis the initial rate at room temperature is 4 X 1010 molecules/sec cm2, a rate roughly one third that reported for alumina (69). Since the activation energy for alumina is less than that found for zinc oxide, this means that zinc oxide is comparable (on a per unit area basis) to alumina as an isomerization catalyst at slightly higher temperatures. 

B. Example of a Three Component System Butene Isomerization over Pure Alumina Catalyst... 

Fio. 10. Temperature dependence of relative rates of butene isomerization over palladium-alumina (31). Q 2-butene from 1-butene at 32 4% conversion. 3= tran -2-butene from cw-2-butene at 34 5% conversion =s SO mm, Ph,= 155 mm in each case). 

C2H2 —D2, cyclo-C3H6 — D2 and 1-butene isomerization over these alumina catalysts/ In the case of COS hydrolysis, a poisoning experiment showed that basic sites were essential/ ... 

Over silica-alumina, butene isomerizes on protonic acid sites which are originally present in small quantity on the surface or on protonic sites induced on Lewis acid sites. This conclusion was deduced from the tracer studies of Ozaki and Kimura and Hightower and Hall. The latter group carried out coisomerization of butene-rfs and butene-do and found that mixing of hydrogen isotope between the do and ds species took place in starting as well as in isomerized butene isomers to comparable extents. Their analysis demonstrated that the j r-butyl cations is the intermediate. The analysis has been further advanced by Misono et taking into account the stereochemistry of proton addition and abstraction shown by the model in Fig. 4. IB. 

Extrapolation of the rate data in Fig. 24 to zero conversion shows that the initial ratio of butene-1 to frans-butene formation is about unity. Thus, butene-1 is not an intermediate in the cis-trans isomerization and direct cis-trans isomerization occurs. Similar results are found for the heterogeneous base catalyzed isomerization over sodium on alumina (17). 

Tphe isomerization of olefins over acidic catalysts has been carefully A studied in the past few years. Hightower and Hall (1, 2) have studied the isomerization of n-butenes over silica-alumina. They were able to interpret their results in terms of a simple model involving the 2-butyl carbonium ion as a common intermediate. More recently Lombardo and Hall studied the isomerization of the same olefins over Na-Y-zeolite. They showed that the reaction was first order in conversion as well as time (3), that the isomers could be directly interconverted (4), and that activity sharply increased with water addition reaching a saturation value (5). There are, however, reports in the literature which are at variance with this idea. Dimitrov et al. (7, 8) explained their results for n-butene isomerization on Na-X-zeolite in terms of a free radical type mechanism. As discussed more thoroughly elsewhere (4) others have argued about the nature of catalytic activity on zeolites (9-13). 

In Section 3.5 recycle reactors and particularly a Berty reactor were described. At high impeller rotation speed, a Berty reactor should behave as a CSTR. Below are plotted the dimensionless exit concentrations, that is, C(t)/C°, of cis-2-butene from a Berty reactor containing alumina catalyst pellets that is operated at 4 atm pressure and 2000 rpm impeller rotation speed at temperatures of 298 K and 427 K. At these temperatures, the cis-2-butene is not isomerized over the catalyst pellets. At t = 0, the feed stream containing 2 vol % cis-2-butene in helium is switched to a stream of pure helium at the same total flow rate. Reaction rates for the isomerization of cis-2-butene into 1-butene and trans-2-butene are to be measured at higher temperatures in this reactor configuration. Can the CSTR material balance be used to ascertain the rate data ... 

Toluene reacts with carbon monoxide and butene-1 under pressure in the presence of hydrogen fluoride and boron trifluoride to give 4-methyl-j iYbutyrophenone which is reduced to the carbinol and dehydrated to the olefin. The latter is cycHzed and dehydrogenated over a special alumina-supported catalyst to give pure 2,6- dim ethyl n aph th a1 en e, free from isomers. It is also possible to isomerize various dim ethyl n aph th a1 en es to the... 

Isomerization of olefins can be accomplished also in the gas phase m a flow reactor with alumina or nickel oxide as catalyst Thus perfluoro 2-butene can be prepared by passing perfluoro-1 butene over these catalysts at 150-400 °C [79] Similar results may be obtained in an autoclave with the same catalysts Perfluoro-1 butene isomenzes almost quantitatively at 250 °C after 100 h to perfluoro-2-butene [20]... 

Melhyl-l-propanol Isobutyl Alcohol) and 2-Phenyl-1-propanol Herling and Pines (SO) studied the dehydration of 2-methyl-l-propanol and 2-phenyl-1-propanol. The two alcohols were passed over alumina under nonacidic conditions at temperatures of 350° and 270°, respectively (Tables III and IV). The 2-methyl-l-propanol underwent, in part, skeletal isomerization forming butenes, whereby the ratio of cisjtrans 2-butene produced was four to six times greater than the equilibrium ratio. The extent of skeletal isomerization depended to some extent on the method of preparation of the alumina. 

A high cisjtrans ratio of 4.4 was observed by Haag and Pines (95) in the isomerization of 1-butene over the same pure alumina (P) catalyst. Although the close agreement of the ratio in dehydration and isomerization may be coincidental, it was suggested that both reactions proceed through the same intermediate. 

To calculate L values using Table I we need forward reaction rates, the number of molecules converted per unit area per second. These reaction rates are most easily obtained at low conversions. But frequently—often for practical purposes—high conversions are reported. We have developed a method for the determination of site densities in a certain class of systems even though the conversion and back reaction are both large. Also, the method can be used under certain conditions even if product isomerization is involved. We shall describe the theory here and in Section III,B apply it to the isomerization of 1-butene to cis- and trans-2-butene over silica-alumina. Although in this article we do not use this method to analyze any other systems, we present it in some detail because it may have potential for further use. 

Although the catalyst results in the rapid formation of an equilibrium isomer distribution, Haag and Pines (11), as well as O Grady et al. (12), have found that the rate of formation of isomers differs considerably. Eunetic studies of the reaction of 1-butene over sodium on alumina show that in short contact times 1-butene is predominantly converted into cfs-2-butene rather than into the thermodynamically favored trans-2-butene. On longer contact with the catalyst, cfs-2-butene is converted to trans-2-butene in the amount expected from the equilibrium distribution. By assuming that the isomerization reaction is first order in each isomer, a... 

The most active heterogeneous catalysts that are effective at room temperature are alkali metals supported on activated alumina. Simple C4-Cg alkenes, for example, were shown to yield equilibrium mixtures in short contact time over sodium on alumina.112116 Partial conversion of 1-butene at low temperature and in very short contact time (—60°C, 14 s) led to the stereoselective formation of m-2-butene.112 The changes in isomeric composition in the transformation of 4-methyl-l-pentene112 are as follows ... 

The compensation trend present in data reported by Shannon et al. (285) for the isomerization of n-butenes over a number of different oxide catalysts is given in Table V, P (omitting from the calculation the point for MnO, which shows a marked deviation). Dehydrogenation of cyclohexane over oxides (286) exhibited similar behavior the calculated line is given in Table V, Q. Hydrocarbon exchange over alumina (287) also gave a slight compensation trend, for which e = 0.132 and ae = 0.024. 

The work of Misono et al. (55) illustrates how acid strength distributions for silica-alumina catalyst can be deduced from catalytic titration measurements by use of an appropriate series of reactants. Surface concentration of amine, pyridine in this case, was adjusted by proper choice of amine partial pressure and desorption temperature while carrier gas flowed over the catalyst sample. At each level of chemisorbed pyridine, pulses of the reactants were passed over silica-alumina at 200°C and the products analyzed. The reactants were t-butylbenzene, diisobutylene, butenes, and f-butanol. It was concluded that skeletal transformations require the presence of very strong acid sites, that double-bond isomerization occurs over moderately strong acid sites, and that alcohol dehydration can occur on weak acid sites. 

The isomerization of butene-1 and butene-2 has been studied over conventional ion exchange resins 110 in> as well as over the sulfonated and phosponated polyphenyls 110>. A careful kinetic study showed that the reaction over these materials as well as over silica-alumina catalysts goes by way of a common intermediate, which can be understood best as the secondary butyl carbonium ion. 

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. 

The process includes steps for isomerizing 1-butene into 2-butene at temperatures below 0 °C over alumina treated with alkaline metal and for disproportionating the 2-butene with isobutene over rhenium heptaoxide on alkaline-... 

These isomerizations, rearrangements, and cleavages are best explained by a carbonium-ion mechanism. Vapor-phase dehydration of alcohols over aluminum oxide greatly reduces the tendency for isomerization and rearrangement. The alcohol vapors are passed over the catalyst at 300-420°. In this manner, pure 1-butene is prepared from re-butyl alcohol and t-butylethylene is obtained from methyl-/-butylcatbinol (54%). The relative rates of dehydration of the simpler alcohols over alumina have been studied. The main side reaction is dehydration to ethers (method 118). 

This chemistry suggests a role for H2O as cocatalyst with the monovalent zeolites if the equilibrium is moved to the right in the presence of a base. In the present work, the effects of small deliberate replacements of Na by Ca ", of cation deficiency, and of H2O on the catalytic properties of Na-Y zeolite were studied. Also investigated was the possibility that carbonaceous residues form the catalytic sites, as was reported for the isomerization of n-butenes over silica-alumina catalysts (3, 8, 9). The isomerization of the n-butenes provided a useful tool for these studies because it follows first-order kinetics (10) and proceeds over Na-Y zeolite via the 5ec-butylcarbonium ion (11, 12). 

Hence, for the isomerization of butenes over pure alumina catalyst at 230° in an all glass flow reactor, the relative rate constants are... 

Fig. 11. The exchange of cts-2-butene and the deuterium content of the isomerized butenes as a function of percentage hydrogenation, over palladium-alumina at 18° (31).

The relative rate of isomerization of the butenes is small over platinum-alumina between 0 and 100° 31). Cis-2-butene undergoes cis-trans isomerization some fifteen times faster than the frans-isomer, while double-bond migration of 1-butene proceeds at an intermediate... 

The isomerization and exchange of the w-butenes over iridium-alumina has been investigated at and below room temperature (31). Rates of... 

These reactions have been studied 31) over rhodium-alumina between — 20 and 175°, and very marked changes of behavior have been observed in this temperature range. At low temperatures, relative rates of isomerization are small (see Fig. 18) and the behavior of rhodium is entirely reminiscent of that of platinum. However, with increasing temperature the relative rates of isomerization increase very quickly (see also Fig. 18), and above about 80° the behavior of rhodium is reminiscent of that of palladium. The course of the reaction of 1-butene with hydrogen at 166° is shown in Fig. 19 the initial transjcis ratio is about 1.6. 

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