Isomerization capacity

Finally, Ven yaminov et al. [338] compare a Sn/Sb = 4/1 catalyst with bismuth molybdate (2/3) at 450°C and note that the Sn—Sb catalyst is less hampered by a drop in selectivity at high degrees of conversion. On the other hand, lower yields are found in the oxidation of 2-butene (compared with 1-butene). The superiority of the bismuth molybdate catalyst in this respect is probably connected with its greater isomerizing capacity. 

Isomerization Today. Present isomerization capacity in the Western Hemisphere and Western Europe is estimated to be about 50,000 BPD basis information provided in Refs. 26 and 34. It is not known how many World War II plants may still be operating or are capable of being returned to service, but the number is believed to be very small. Near the end of World War II isomerization capacity peaked out at 45,000- 50,000 BPD of which slightly over 40,000 BPD consisted of n-butane isomerization. All of these installations used one of five processes employing aluminum chloride complexes (25). 

In Western Europe it is expected that new isomerization capacity may exceed alkylation installations since naphtha availability generally exceeds demand. By selecting isomerization over alkylation the octane number of the gasoline pool may be increased without increasing the volume. Moreover, olefinic charge stock avails for alkylation are considerably smaller in Europe since there are fewer catalytic cracking units per refinery than in the United States and Canada. It is predicted that C5, and to a lesser extent C5/C6 isomerization, will prevail over alkylation in Western Europe until more catalytic cracking units are installed and/or a shift in the demand for naphtha over fuel oil is experienced. 

Reduced Volatility—Volatility reductions would decrease gasoline volume and octane levels and produce excess light hydrocarbons. All gasoline producing facilities would, of course, have to be expanded to make up the volume loss, but greater increases in alkylation and isomerization capacity would be needed to raise octanes and utilize as much of the light hydrocarbons in gasoline as possible. 

Olefin Reductions—Alkylation capacity would increase with any reduction in olefin content because it would provide a way to use the C4 and some C5 olefins in gasoline. New isomerization capacity would be needed if substantial quantities of C5 and C6 olefins had to be removed. The C5/C6 olefins would have to be hydrogenated and isomerized to make up part of the octane loss. 

Reduced Aromatics—Substantial alkylation and isomerization capacity increases would have to accompany any reduction in aromatics content. With limits on aromatics concentration, alkylate and isomerate would be the major tools available for controlling octanes. 

With the start of World War II, several processes were developed to the point where commercialization was possible. The first commercial butane isomerization unit went on stream in the fall of 1941. Use of the process increased rapidly until by the end of the war, four years later, total isomerization capacity was 40,000 bbl./day (12). Soon after the end of hostilities most of these units were shut down as the need for aviation gasoline dropped. 

Bindungsfilhigkeit,/. combining capacity, combining power binding power, bindungsisomer, a. showing isomerism due to different modes of union of the atoms (sometimes merel3 to different positions of a double bond). 

Seeligmann, Torrilhon, and Falconnet, in a treatise on rubber published in France in 1896, recorded interesting early observations on the sol and gel components now known to be present in most specimens of undegraded raw rubber. They referred to them as the two isomeric hydrocarbides of rubber, one being the adhesive principle and the other the nervous principle. It was observed that the latter refused to dissolve on repeated treatment with fresh portions of solvent and that the approximate percentage of this constituent was roughly the same when different solvents were used to extract the soluble portion. The authors called attention also to the enormous swelling capacity of the nervous hydrocarbide. Vulcanization was attributed to a reaction of sulfur with the adhesive principle whereby the adhesive characteristics are suppressed or eliminated. 

Interestingly, we have recently identified a mutation of a tyrosine in the third intracellular loop of the hDAT that causes a major alteration in the conformational equilibrium of the transport cycle, and thus as such is comparable to mutants on G protein-coupled receptors causing constitutive isomerization of the receptor to the active state (66). Most importantly, this conclusion is based on the observation that mutation of the tyrosine completely reverts the effect of Zn2+ at the endogenous Zn2+ binding site in the hDAT (50,51) from potent inhibition of transport to potent stimulation of transport (Fig. 6). In the absence of Zn2+, transport capacity is reduced to less than 1% of that observed for the wild-type, however, the presence of Zn2+ in only micromolar concentrations causes a close to 30-fold increase in uptake (66). Moreover, it is found that the apparent affinities for cocaine and several other inhibitors are substantially decreased, whereas the apparent affinities for substrates are markedly increased (66). Notably, the decrease in apparent cocaine affinity was around 150-fold and thus to date the most dramatic alteration in cocaine affinity reported upon mutation of a single residue in the monoamine transporters (66). 

Most of the work with alumina was done, however, attempting to elucidate the nature of the catalytically active sites in dehydrated alumina. The catalytic activity of alumina is enhanced by treatment with hydrofluoric acid. Oblad et al. (319) measured a higher activity in the isomerization of 1- and 2-pentene. Webb (339) studied the effect of HF treatment on ammonia adsorption by alumina. There was no difference in the capacity. However, the ammonia was more easily desorbed at a given temperature from the untreated sample. Apparently, the adsorption sites grew more strongly acidic by the treatment. No NH4+ ions, only NHj molecules were detected by their infrared spectra, indicating that the ammonia was bound by Lewis acids rather than Bronsted acids. 

The rather low concentration of the desired p-xylene component in the Parex unit feed means a large fraction of the feed stock contains other A8 components that are competing for adsorption sites in the adsorbent zeoHte cages. Due to this typically lean feed, a significant hike in the Parex unit capacity can be obtained by even a small increase in the composition of the p-xylene. Techniques to increase the p-xylene feed concentration include greater dealkylation of the ethylbenzene in the Isomar unit by converting from an ethylbenzene isomerization catalyst to... 

Andrews, E J., Eynn, G., and Johnston, J. The heat capacities and heat of crystallization of some isomeric aromatic compounds, J. Am. Chem. Soc, 48(5) 1274-1287, 1926. 

---