Light naphtha catalysts

Light naphtha containing hydrocarbons in the C5-C7 range is the preferred feedstock in Europe for producing acetic acid by oxidation. Similar to the catalytic oxidation of n-butane, the oxidation of light naphtha is performed at approximately the same temperature and pressure ranges (170-200°C and =50 atmospheres) in the presence of manganese acetate catalyst. The yield of acetic acid is approximately 40 wt%. 

Par-Isom [Paraffin isomerization] A process for isomerizing light naphtha in order to improve the octane number. The proprietary catalyst was developed by Cosmo Oil Company and Mitsubishi Heavy Industries, and the process was developed by UOP. The oxide catalyst is claimed to be more efficient than zeolite catalysts currently used for this process. 

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. 

Further research has been performed and is continued to be reported, mostly with zeolites unloaded or loaded with Pt, and Ga- and Zn-promoted H-ZSM-5 or H-[Al]ZSM-5 catalysts to clarify the details of the complex transformations taking place and make further improvements. In addition, new catalysts were studied and reported. Reference should also be made to work addressing the problems of the modification of catalyst features of ZSM-5404 and the development of a new light naphtha aromatization process using a conventional fixed-bed unit.405 406... 

Butane from natural gas is cheap and abundant in the United States, where it is used as an important feedstock for the synthesis of acetic acid. Since acetic acid is the most stable oxidation product from butane, the transformation is carried out at high butane conversions. In the industrial processes (Celanese, Hills), butane is oxidized by air in an acetic acid solution containing a cobalt catalyst (stearate, naphthenate) at 180-190 °C and 50-70 atm.361,557 The AcOH yield is about 40-45% for ca. 30% butane conversion. By-products include C02 and formic, propionic and succinic acids, which are vaporized. The other by-products are recycled for acetic acid synthesis. Light naphthas can be used instead of butane as acetic adic feedstock, and are oxidized under similar conditions in Europe where natural gas is less abundant (Distillers and BP processes). Acetic acid can also be obtained with much higher selectivity (95-97%) from the oxidation of acetaldehyde by air at 60 °C and atmospheric pressure in an acetic acid solution and in the presence of cobalt acetate.361,558... 

If benzene is the main product desired, a narrow light naphtha fraction boiling over the range 70 to 104°C is fed to the reformer, which contains a noble metal catalyst consisting of, for example, platinum-rhenium on a high-surface-area alumina support. The reformer operating conditions and type of feedstock determine the amount of benzene that can be produced. The benzene product is most often recovered from the reformate by solvent extraction techniques. 

The catalyst used in the mid-distillate and gas-oil hydrocracking was Harshaw 400T. The COED, H-Coal, and Synthoil samples were run over 1/8-in. extrudates the SRC II sample was run on 1/16-in. extrudates. The catalyst was presulfided in situ with 1% CS2 in a light naphtha. 

Phillips Petroleum Co. Olefins Light Hydrocarbons to light naphtha Dehydrogenation of light paraffins uses proprietary catalysts for high selecbvibes 2 1992... 

Chiyoda Corp. BTX Light naphtha, LPG and raffinate Zeolite catalyst and fixed-bed reactor produce petrochemical grade BTX 1 NA... 

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 VII. Reproducibility of Catalyst Testing in Microflow Reactors for Isomerization of Light Naphtha...

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

Deactivation of light naphtha aromatization catalyst based on zeolite was studied, by kinetic analysis, micropore volume analysis and model reactions. Coke accumulates at the entrance of zeolite channel, blocks it and hinders reactant molecule to access active sites in zeolite channel. Our own stabilization technique passivates coke-forming sites at the external surface of the zeolite. This minimizes the coke formation at the entrance of zeolite channel and increases on-stream stability. The stabilized catalyst enabled us to develop a new light naphtha aromatization process using an idle heavy naphtha reformer that is replaced by CCR process. 

Catalytic Activity Measurement. The reaction was carried out in a stainless steel microflow reactor. In each run, 2 g catalyst was placed in the reactor and heated to 520 °C under a nitrogen stream. The nitrogen stream was replaced by a light naphtha vapor fed by a micro plunger pump. The reaction was carried out at 520 °C, under various pressures and WHS Vs without any hydrogen addition. The products were analyzed periodically by gas chromatography. The properties of the light naphtha are shown in Table I. 

FUKASE ET AL. Deactivation of Light Naphtha Aromatization Catalyst 221... 

Stability of Various Catalysts. Experiments were conducted to investigate deactivation of the various catalysts. The conversion of light naphtha is defined here by the following equation ... 

Kinetics of Catalyst Deactivation. In order to study the kinetics of the deactivation of stabilized catalyst, we carried out several sets of experiment varying pressure, with constant space velocity and with constant contact time, respectively. We assumed that reaction rate of light naphtha conversion conforms to first-order kinetics with respect to light naphtha concentration and that the decreasing rate of active site, which is caused by coke deposition, is expressed by first order. Then catalyst activity is described as exponential deactivation (S). 

Figure 3. Variation of rate constant of light naphtha conversion with increasing pressure under constant space velocity over the stabilized catalyst.

Surface Characterization of the Stabilized Catalyst by Probe Molecule Reaction. HZSM-5 obtained from PQ Zeolite was chosen to study the mechanism of stabilization in light naphtha aromatization. The reactions of both molecules were carried out over stabilized and unstabilized HZSM-5. We assumed first order kinetics with respect to each reactant concentration and first order decay of each reaction, and calculated initial rate constants. Figure 6 shows the initial rate constants of cumene cracking and triisopropyl-benzene cracking over the stabilized and the unstabilized catalysts. 

On the basis of the results of the fundamental and scale-up studies, a 2,250 BSD demonstration plant was designed and was operated at Japan Energy s Mizushima Oil Refinery in Japan to aromatize light naphtha. The plant achieved long-term operation without any trouble. We confirmed the good stability of the catalyst (7 ). 

A new catalyst with long-term stability was developed for the aromatization of light naphtha. Our proprietary technique of steaming reduced acid site density of the external surface of the catalyst and minimized coke formation. The new catalyst enabled us to develop a new light naphtha aromatization (LNA) process using a conventional fixed bed unit. Idle heavy naphtha reformer can be converted to this process without large modification. 

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