Isomerization butane

Butane isomerization is usually carried out to have a source of isobutane which is often reacted with C3-C5 olefins to produce alkylate, a high octane blending gasoline [13]. An additional use for isobutane was to feed dehydrogenation units to make isobutene for methyl tert-butyl ether (MTBE) production, but since the phaseout of MTBE as an oxygenate additive for gasoline, this process has decHned in importance. Zeolitic catalysts have not yet been used industriaUy for this transformation though they have been heavily studied (Table 12.1). 

Zeolite S1O2/ Metal Feed H2/HC WHSV Temperature Pressure Conversion Product Notes Reference 

Paraffin isomerization of heavy alkane feeds is often used to alter the cloud or pour point of diesel or lube fractions. Catalysts for this reaction are almost always dual-function catalysts of Pt supported on a one-dimensional zeolite. Using a onedimensional zeolite allows control of the isomerized product to contain few branches, usually methyl branches (Table 12.4). 

5 n-Butane Isomerization. - Coke deposited on a sulfated zirconia catalyst during the isomerization of n-butane, was extracted with different solvents, and the coke left on the catalyst analysed by TPO . The extraction with pure solvents had the objective of assesing the functionality of the coke by its solubility in specific solvents. Solubility in hexane and benzene was practically zero. Methanol and piridine were more effective in the extraction. According to these results, the only conclusion the authors could draw was that the coke was not completely paraffinic. In the extraction with piridine, after solvent evaporation, the solid was analysed by FD-mass spectrometry. Fragments up to m/z = 2737 

Five processes for butane isomerization were in commercial use by the end of World War II. These processes differ primarily in the type of aluminum chloride catalyst used and in the method of contacting the hydrocarbon with the catalyst. Two are vapor-phase processes, which require periodic discard and replacement of the catalyst the other three are carried out in the liquid phase and have continuous catalyst addition and withdrawal. 

The Isocel process developed by the Shell Oil Company was the first isomerization process to reach commercialization and started operation 

Vapor-phase butane isomerization. Shell Isocel process. 

Liquid from the accumulator is pumped to the top of the hydrogen chloride stripping column, which has twenty bubble-cap trays and operates at 275 p.s.i. without external reflux. This permits recycling of the overhead stream which is largely hydrogen chloride without additional compression. 

Process Shell Anglo-Jersey U.O.P. Standard (Indiana)-Texas Shell 

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Z. Hong, K.B. Fogash, and J.A. Dumesic, Reaction kinetic behavior ofsulfated-zirconia catalysts for butane isomerization, Catalysis Today 51, 269-288 (1999). 

Activity in n-butane isomerization reaction of various alkaline salts of H3PW12O40 and H4SiWi2O40 was shown to be strongly dependent on the strength and number of accessible protons whereas the stability with time on stream was correlated to the presence of mesoporosity. For the liquid iC4/C4 continuous alkylation reaction, the strength and the number of acid sites appeared less important than the existence of mesoporosity indicating that the diffusion of the reactants and of the products plays an important role in this reaction. 

The activity and decay behaviour of the different porous heteropolycompounds were compared in two reactions requiring strong acid sites the n-butane isomerization and the isobutane/2-butene alkylation. Although these two reactions are important in the petroleum refining industry, n-butane isomerization is often used as a "test reaction" since it is known that this reaction requires very strong acid sites and only a limited number of oxides are active in this reaction, under mild conditions (T = 473 K). 

Catalytic activity in n-butane isomerization at 473 K after 4 min of time on stream. 

It is striking to observe that the most initially active samples were the most stable with time on stream in the n-butane isomerization. 

The ratio of the amount of n-butane-2-13C to the amount of isobutane produced was, provided measurements were made under conditions where secondary reactions were unimportant (i.e., initial reaction products), constant and independent of temperature, and this ratio was 1/4. At the same time, no scrambling of the 13C occurred i.e, all of the isotopically substituted molecules remained singly labeled. Anderson and Baker (68) speculated that the butane isomerization might have occurred by a recombination of adsorbed surface residues produced by fragmentation of the... 

Butamer [Butane isomerization] A process for converting n-butane into iso-butane conducted in the presence of hydrogen over a dual-functional catalyst containing a noble metal. Developed by UOP and licensed worldwide since 1959. In 1992, more than 55 units had been licensed. 

K. Tomishige, A. Okabe, and K. Fujumoto, Effect of hydrogen on n-butane isomerization over Pt/SOa -Zr02 and Pt/Si02 + S04 -Zr02, Appl. Catal. A 194, 383-393 (2000). 

These reactions can also be performed over a strong acid catalyst at reaction temperatures that are lower than over zeolites. Because of this, isomerization of M-butane over Zr02-supported sulfate catalysts was initially proposed by Hino and Arata. They proposed these catalysts as being effective in butane isomerization at room temperature, a reaction that does not take place, even in 100% sulphuric acid. For this reason, these catalysts were considered as solid superacids, since they are active and selective in the isomerization of n-butane to isobutane at... 

Isomerization, A process used to convert straight-chain to branch-chain hydrocarbons as in a butane isomerization plant. 

Asuquo, R.A., Eder-Mirth, G., and Lercher, J.A. (1995) n-butane isomerization over acidic mordenite. J. Catal,... 

Torr of H2 (630 equiv./M). Bottom curve weak butane isomerization into isobutane takes place. 

Fig. 6 FT-IR spectra of catalytic surface during n-butane isomerization at 323 K taken every 16 minutes. This shows the difference in IR spectra from before activation to during reaction. The black lines show the spectra first at the start of the reaction, and the next is at the maximum reaction rate. ...

Butane isomerization and pentane-hexane isomerization are the two most important isomerization processes. Isobutane is utilized primarily as alkylate feedstock. Isopentanes and isohexanes have become valuable high-octane blending components in gasoline. 

Butane isomerization is relatively straightforward. The butanes show no appreciable tendency to crack or disproportionate under isomerization conditions (6). 

The other vapor-phase butane isomerization process, developed cooperatively by the Anglo-Iranian Oil Co. and the Standard Oil Development Co., is somewhat similar to the Isocel process. In the AIOC-Jersey process (18), the reactor is initially filled with bauxite, and aluminum chloride is sublimed into the vaporized feed as necessary to maintain the desired catalyst activity. Upflow of vapor through the reactor is the customary arrangement. Since carry-over of aluminum chloride is not excessive at the usual rates of catalyst addition, about half of the commercial plants employing this process were not equipped with guard chambers. 

The butane isomerization process developed by the Universal Oil Products Co. is shown in Figure 4. In this process (3), the feed is maintained essentially in the liquid phase under pressure. Part of the feed is by-passed through a saturator, where it dissolves aluminum chloride. The feed later picks up hydrogen chloride and passes through the reactor, which is packed with quartz chips. Some insoluble liquid complex is formed, and this adheres to the quartz chips. The aluminum chloride in the feed is preferentially taken up by the complex, which thus maintains an active catalyst bed. The complex slowly drains through the reactor, losing activity en route. It arrives at the bottom in essentially spent condition and is discarded. Aluminum chloride carried overhead in the reactor products is returned to the reactor from the bottom of the recovery tower. The rest of the process is the same as in the vapor-phase processes. 

The third liquid-phase butane-isomerization process, shown in Figure 5, was developed by Shell as an improvement over the original intermittent vapor-phase process. 

A summary of commercial operations employing the five butane isomerization processes is given in Table II. The data represent typical wartime process operations rather than characteristics of any specific commercial plant. 

Table II. Typical Commercial Process Data for Butane Isomerization...

The 34 domestic commercial units employing these five butane-isomerization processes contributed substantially to the war effort. 

In the event of another major war, it is probable that all existing isomerization units would be reactivated and pushed to capacity. Although production of Grade 115/145 aviation fuel required by newer aircraft engines may place somewhat greater emphasis on aromatics, there would still be a demand for maximum alkylate production, and butane isomerization would again play an important role. Expansion of pentane and naphtha isomerization is somewhat less certain and would depend on future developments in aircraft fuels. 

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