Isomerization velocity

Upon variation of the stirring velocity between 500 and 1500 rpm the conversion of the olefin remained at the same high level and the selectivity to the linear aldehyde also remained constant. Obviously there is no mass transfer limitation in this two-phase reaction system. In comparison to the single-phase reaction in propylene carbonate as the only solvent [23], the selectivity decreases from 95% to 70%, which can be explained by the high concentration of the non-electron-donating solvent dodecane in the propylene carbonate phase. The presence of the dodecane leads to a decrease of the isomerization velocity, which results in a lower hnearity of the formed aldehydes. 

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... 

Detailed reaction dynamics not only require that reagents be simple but also that these remain isolated from random external perturbations. Theory can accommodate that condition easily. Experiments have used one of three strategies. (/) Molecules ia a gas at low pressure can be taken to be isolated for the short time between coUisions. Unimolecular reactions such as photodissociation or isomerization iaduced by photon absorption can sometimes be studied between coUisions. (2) Molecular beams can be produced so that motion is not random. Molecules have a nonzero velocity ia one direction and almost zero velocity ia perpendicular directions. Not only does this reduce coUisions, it also aUows bimolecular iateractions to be studied ia intersecting beams and iacreases the detail with which unimolecular processes that can be studied, because beams facUitate dozens of refined measurement techniques. (J) Means have been found to trap molecules, isolate them, and keep them motionless at a predetermined position ia space (11). Thus far, effort has been directed toward just manipulating the molecules, but the future is bright for exploiting the isolated molecules for kinetic and dynamic studies. 

For the n-Cq reforming and n-C[2 isomerization reactions the catalysts were run in a fixed bed micro reactor equipped with on-line GC analysis. The catalyst, together with a quartz powder diluent, was added to a 6 inch reactor bed. A thermocouple was inserted into the center of the bed. The catalysts were calcined at 350-500°C immediately prior to use and reduced in H2 at 350-500°C for 1 hour. n-Heptane or dodecane (Fluka, puriss grade) were introduced via a liquid feed pump. The mns were made at 100-175 psi with a H2/n-heptane (or n-Ci2) feed ratio of 7 and a weight hourly space velocity of 6-11. 

We compared Pt/silica-alumina, yttria-modified silica-alumina, and fluorided alumina for n-Ci2 isomerization. Not surprisingly, increasing yttria content lowers catalyst activity at a fixed space velocity (Fig. 10). The 9% Y203/Si-Al catalyst compares closely to the 1%F/Al203 catalyst in activity. Of the catalysts evaluated here, the 9%Y203-loaded Si-Al had higher isomerization selectivity at equal conversion (Fig. 11). 

Figure 6, Compilation of isomeric shifts in compounds. The data converted to scale and is indicated hy dashed lines. A positive velocity corresponds to the ZnTe source moving towards the absorber. Note lack of agreement between shifts for molecular iodine...

The key process variables for C8A isomerization are the temperature, pressure, weight- or Hquid-hourly space velocity (WHSV or LHSV) and hydrogen partial... 

A graphical procedure for characterizing isomerization mechanisms . The protocol uses data from product inhibition, and l/[v[p]=o vpjo] is plotted versus 1/[P] at various constant concentrations of the substrate (where Vp=o is the initial velocity in the absence of product and V[p]o is the initial velocity in the presence of product). Secondary and ternary replots allows one to characterize the mechanism . This procedure requires very accurate estimation of initial rates. 

In water, the isomeric cresols may eventually volatilize to the atmosphere, but volatilization is expected to be a slow process. Based on their Flenry s law constants, which range from 1.2x10 to 8.65x10 atm-m /molecule (Gaffney et al. 1987 Hine and Mookerjee 1975), the volatilization half-life from a model river 1 m deep, flowing at 1 m/sec, witha wind velocity of 3 m/sec can be estimated to range from approximately 30 to 41 days (Lyman et al. 1982). 

The other commercialized pentane isomerization process is that of the Standard Oil Co. (Indiana) (20). This process differs from the Indiana-Texas butane process in that the aluminum chloride is introduced as a slurry directly to the reactor and that about 0.5% by volume of benzene is added continuously in the feed to suppress side reactions. Temperature, catalyst composition, space velocity, and hydrogen chloride concentration are generally similar to those in the corresponding butane process, but the reactor pressure is about 100 pounds lower. The Pan American Refining Co. operated the Indiana pentane isomerization process commercially during the last nine months of the war and produced about 400 barrels of isopentane per calendar day. 

Fig. 2. Isomerization of n-heptane over mixtures of particles of silica-alumina and particles of inert-supported platinum (W5). The dashed lines represent conversions over platinum-impregnated silica-alumina. Conditions of runs 25 atm., Hj/nC = 4/1, space velocity = 0.7 g. nC7 per hour per gram of catalyst.

Eckstein (443) has prepared the isomeric derivatives of uridine-2 3 -0,0-cyclophosphorothioate where one or the other of the tw o free oxygen atoms is converted to a sulfur atom. The maximum velocity for the hydrolysis of these compounds is one-fifth that of U > p under comparable conditions while the Km value for one is identical to U > p and the other is larger by a factor of 8. 

The effect of pressure on the isomerization of n-heptane and n-octane was determined over the Pt//l-zeolite, Mo2C-oxygen-modified and M0O3-carbon-modified catalysts. The weight hour space velocity (WHSV) was changed with the pressure to keep the conversion at a similar level, enabling the effect on the isomerization selectivity and the product distributions to be seen. Other conditions were kept constant. 

The investigation of the isomerization process for the binaphtyl system in solution gives a reequilibration velocity time constant t = 0.3 ps for a viscosity 17 near to lcp and a value of 14 ps 1 for o>B.47... 

The amides of alkali and alkaline-earth metals catalyse hydrogen exchange in hydrocarbons even in the absence of liquid ammonia. For example, the heterogeneous deuterium exchange of benzene and 2-methylbutene-l occurs with a considerable velocity on solid KND2 and Ca(ND2)2 at 70°. This gives rise to the isomerization of 2-methyl-butene-1 to 2-methylbutene-2 (Shatenshtein et al., 1958a). 

A survey of literature exhibits the fact that up to now not much attention has been paid to the impact of porosity and velocity distribution on the analysis of fixed bed chemical reactors. Under non-uniform flow conditions Chaudhary et al. [8] compared measured and calculated concentration profiles for an isomerization reaction in an isothermal fixed bed chemical reactor... 

Smith and Lieber (36) reported that, although the use of alkali activated Raney nickel for the hydrogenation of carbonyl groups, it had a deterring effect on the reduction of aromatic nitro compounds. In particular, alkali retarded the reduction of nitrobenzene and the three isomeric sodium nitrobenzoates, whereas it increased the velocity of reduction of the methyl and ethyl esters of nitrobenzoic acid. 

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