M-Xylene conversion

The structure of SSZ-35 (IZA structure code STF) as viewed in the [001] direction is shown in Fig. 17. The dimensions of the 10-MR structures are 5.5 x 6.1 A and the diameter of the 18-MR structures is 12.5 x 9 A. This pore structure is in contrast to the structure of SSZ-44 (IZA structure code SFF) shown in Fig. 18, where the 10-MR structures are nearly spherical (5.8 A) and the 18-MR structures are slightly larger (12.9 x 9 A). These small differences in pore size apparently translate into startling differences in reactivity. A study of m-xylene conversion shows a high degree of isomerization versus disproportionation, which is consistent with a 10-MR pore system (47). The interesting data is the para to ortho selectivity in the isomerization products, where SSZ-44 exhibited a higher para/ortho... 

Fig. 9.5 Transformation of m-xylene over HMORIO and NaHMORlO samples. Disproportionation / Isomerisation rate ratio (D/I) versus m-xylene conversion (X%) on fresh and on deactivated catalysts HMORIO (0), 14NaHMOR ( ), 28NaHMOR (A), 45NaHMOR (+), 63NaHMOR (o)...

Sastre et aL [112] studied the isomerization of m-x>iene over OfBretite and observed monotonical increase in m-xylene conversion upon exdumge of the K -cations. This was ascribed to the increase of the concentration of the protons and the increase in accessibility of the pores, which resulted in a higher selectivity for the isomerisation reaction at the e q>aise of the disproportionation reactioiL Only a sHght increase in the p-xyloie in the fraction of oitho-and para-xylene was observed. Over Beta a maximum activity for the xylene isomersation was observed and this was explained by either a pos le existence of a eigistic effect between extra-framework aluminium and the fitunework Bronsted acid sites or a concentration effect [113]. 

In case of the m-xylene isomerization it should be noted that the m-xylene conversion is restricted to about 48 % for thermodynamical reasons. This equilibrium is practically reached for samples after 24 hcrystallization time. In case of the ethylbenzene it can be seen that the conversion... 

P-20 - Application of adsorption Dubinin-Radushkevich equation for study of -pentane and m-xylene conversion catalysts microporous structure S.B. Agayeva, B.A. Dadashev, S.I. Abasov andD.B. Tagiyev... 

Figure 1 shows that there is a very rapid deactivation of the USHY zeolite m-xylene conversion passes from 55% at 2 minutes to 3% at 75 minutes. This deactivation can be related to the retention of carbonaceous compounds on the zeolite ( coke ). The coke content of the zeolite first increases very rapidly with time-on-stream then more slowly. 

Fig.l. m-Xylene conversion and coke formation at 250°C over USHY as a function of time-on-stream (TOS). 

Chlorine-enhancement may offer a partial solution. The addition of the chlorinated olefin TCE, PCE, or TCP to air/contaminant mixtures has recently been demonstrated to increase quantum yields substantially [1, 2, 6]. We recently have extended this achievement [3], to demonstrate TCE-driven high quantmn efficiency conversions at a reference feed concentration of 50 mg contaminant/m air not only for toluene but also for other aromatics such as ethylbenzene and m-xylene, as well as the volatile oxygenates 2-butanone, acetaldehyde, butsraldehyde, 1-butanol, methyl acrylate, methyl-ter-butyl-ether (MTBE), 1,4 dioxane, and an alkane, hexane. Not 1 prospective contaminants respond positively to TCE addition a conventional, mutual competitive inhibition was observed for acetone, methanol, methylene chloride, chloroform, and 1,1,1 trichloroethane, and the benzene rate was altogether unaffected. 

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

M. Warman, Preparation of Trinitro-Meta-Xylene (TNX) , PATM 1728 (1966) [Reported is a procedure for the pilot plant prepn of TNX from m-xylene. The nitration of m-xylene is carried out in two stages 1) The conversion of m-xylene to 2-nitro-m-xylene using mixed add (sulfuric 59/nitric 25/w 16%) at 35 to 50°, and 2) The trinitration of 2-nitro-m-xylene to trinitro-m-xylene, again using mixed add (sulfuric 79/nitric 17.5/w 3.5%), at 95 to 102°. The author states that the overall yield of TNX from m-xylene is as high as 94%. One crystn of the crude product from acet is sufficient to raise the mp to the 182-83° value reported in the literature]... 

The linear" p-xylene can escape from the catalyst much more easily than the bent" m- or u-xylene (see Figs. I 4 and 1.5).- The o- and m-xylenes are trapped but not wasted. Under the acidic conditions of the catalyst they continue to rearrange, and whenever a p-xylene molecule is formed, it can pop out and leave the system. Conversion is thus essentially complete. Catalytic zeolites have been compared to enzymes because shape and size are crucial For the catalytic action of both.5 ... 

The possibility of using of aliphatic alcohols as hydrogen donors for the catalytic transfer reduction of nitro group over MgO was examined. Catalytic hydrogen transfer was found to be effective and selective method for reduction of nitrobenzene, A-nitrotoluene, A-chloronitrobenzene, 4-nitro-m-xylene, 3-nitro-styrene, 3-nitrobenzaldehyde, 1-nitropropane, and 1-nitrobutane. Conversion of starting nitro compound into desired product depended on the alcohol used as a donor. Adsorption of reactant and catalyst deactivation were studied by esr. New aspects of a role of one-electron donor sites in hydrogen transfer over MgD were demonstrated. 

Figure 3.1 Acetylation at 373 K with acetic anhydride of a series of aromatic compounds over HBEA-15 zeolite. Conversion (XSUB) of anisole ( ), 2-methoxynaphthalene (x), m-xylene ( ), toluene ( ), 2-methylnaphthalene (o) and fluorobenzene (a) versus time. Reprinted from Journal of Catalysis, Vol. 230, Guidotti et al. Acetylation of aromatic compounds with H-BEA zeolite the influence of the substituents on the reactivity and on the catalyst stability, pp. 375-383, Copyright (2005), with permission from Elsevier...

A representative mixture has the composition C6-C8 nonaromatics (20), benzene (12), toluene (18), ethylbenzene (7), p-xylene (10), m-xylene (20), o-xylene (13), all in wl%. The goal is the separation of benzene and p-xylene of high purity. The other aromatics should be recovered at convenient purity in view of selling or for further conversion into the main products. 

For example, for the conversion of dinitro- to trinitro-m-xylene, a mixture containing 9-10% of water at a temperature up to 100°C is used. 

More recent work of Kazanskff and Liberman (150,151) amends the view of the Zelinskil school that gem-substituted cyclohexanes are inert under dehydrogenation conditions over platinum. They established the conversion of 3,3-dimethylhexane into 1,1-dimethylcyclohexane under dehydrocyclization conditions as an intermediate step in the formation of aromatics (toluene and m-xylene) from that paraffin. Furthermore 1,1-dimethylcyclohexane was directly converted to aromatics, although at a lower rate than cyclohexanes with substituents attached to different carbon atoms. The mechanism of aromatization of paraffins on platinum was thus shown to involve the intermediate formation of a cyclohexane. 

In the present work we examine the microporosity of a TSLS complex formed from synthetic imogolite and natural montmorillonite. Nitrogen adsorption and desorption isotherms are reported and analyzed in terms of microporous volume and surface area. Also, the adsorption isotherm for an organic adsorbate, m-xylene, is reported. Preliminary FTIR results for the chemisorption of pyridine and catalytic studies of the dealkylation of cumene suggest that TSLS complexes are promising microporous acids for shape selective chemical conversions. 

The conversion of ortho- to meta- and para-xylene was carried out on a series of decationated catalysts which were subjected to thermal treatment at various temperatures. 10-/xl pulses of o-xylene were used, the catalyst amount was 300-350 mg, and the flow rate of the helium carrier gas was 50-100 ml/min. The products were analyzed on 7.8-benzoquinoline on Chromosorb W gas-chromatographic column. The m-xylene predominated over the para isomer. A small toluene production seemed to parallel that of isomerization. The conversion of xylene X... 

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