Naphtha isomerization

The only commercial isomerization of light naphtha was carried out in two plants employing the Isomate process developed by the Standard Oil Company (Indiana). In this process (26), a feed containing normal pentane and low-octane-number hexanes is converted to isopentane and hexanes of higher octane number. Pentanes and hexanes in any ratio can be processed. By recycle of selected fractions of the product, concentrates of isopentane or of neohexane (2,2-dimethylbutane) and diisopropyl (2,3-dimethylbutane) can be made as the final products. 

Isomerized naphtha (isomate) flows from the reactor into the hot settler maintained at the temperature and pressure of the reactor. The 

The addition of aluminum chloride is a particularly difficult problem in the case of naphtha isomerization because the solid aluminum chloride must be transferred from atmospheric pressure to 700-800 p.s.i. it is not possible to add make-up aluminum chloride in solution as in the butane 

Typical operating conditions for processing hexanes or a mixture of pentanes and hexanes from Mid-Continent crude are  

Space velocity, vol. feed/hr./vol. catalyst Hydrogen added, cu.ft./bbl. 

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Jao, R.-M., Leu, L.-J., and Chang, J.-R. (1996) Effects of catalyst preparation and pretreatment on light naphtha isomerization over mordenite-supported Pt catalysts. Appl Catal A., 135, 301-315. 

Modern refining concepts-an update on naphtha-isomerization to modem gasoline manufacture. Catal. Today, 81 (1), 51-55. 

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. 

In the area of oil refining, a general lecture sets the scene for present and future challenges. It is followed by in-depth case studies involving FCC, hydrocracking and light naphtha isomerization. Also, an entire chapter is devoted to the often-overlooked subject of base oils. 

The latter conclusion is supported by the data of Table VI, which demonstrate that testing in a bench-scale and microflow reactor gives almost identical results for light naphtha isomerization over undiluted catalyst of actual size. The absence of a noticable effect of bed length and gas velocity is in line with the assumption that in this case extraparticle mass transfer effects are relatively unimportant, as discussed earlier. 

With properly designed equipment and careful execution of the tests, the accuracy of small-scale testing can be quite high. Table VII shows some data on the reproducibility of microflow tests on light naphtha isomerization carried out in several reactor units during a period of about half a year. The agreement between results of individual tests is sufficiently good for practical purposes of catalyst evaluation and optimization of process conditions. 

Table VIII compares microflow test results on light naphtha isomerization with catalyst performance as found in industrial plants. It can be seen that there is a satisfactory agreement between the activities found in laboratory tests and in commercial operation.

Table VI. Comparison of Test Results on Light Naphtha Isomerization in Bench-scale and Microflow Reactors...

Table VIII. Comparison of Microflow Test Results with Data from Commercial Plants on Light Naphtha Isomerization over Pt/H-Mordenite Catalysts...

A simple naphtha isomerization process has a feed of 10,000 barrels per day (bpd) of a 50 wt% mixture of n-hexane and methyl pentane. The feed is heated and sent to a reactor, where it is brought to equilibrium at 1300 kPa and 250°C. The reactor products are cooled to the dew point and fed to a distillation column operated at 300 kPa. The bottoms product of the distillation is rich in n-hexane and is recycled to the reactor feed. An overall conversion of n-hexane of 95% is achieved. 

The light naphtha isomerization process is more complex than the description given in Example 4.7. 

The maximum production of isohexanes is considered the practical parameter of choice upon which refiners base their selection of operating conditions in light naphtha isomerization. 

EMICT [ExxonMobil Isomerization Catalyst Technology] A naphtha isomerization process developed by ExxonMobil that uses sulfated zirconia with tungsten oxide. 

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