P-xylene and benzene

PX-Plus A process for disproportionating toluene to p-xylene and benzene. Developed by UOP in the 1990s. Competing technologies are Mobil s MSTDP and MTPX. Not commercialized as of 1997. 

GT-STDP A process for disproportionating toluene into p-xylene and benzene, using a high-silica zeolite catalyst. Operated in the vapor phase at 390 to 400°C. Developed by Indian Petrochemical and licensed to GT Technology. 

The significant finding was that the xylene fraction was 99% para. The other fractions are not lost. Toluene can be disproportionated to p-xylene and benzene with H-ZSM-5 treated with a little hexamethyldisiloxane to give 99% p-xylene, so that the usual separation of the ortho- and meta isomers with another zeolite would not be required.177 Benzene can be transalkylated with the higher aromatics to give toluene. Ethylbenzene can be isomerized to p-xylene. Ethylbenzene can be alkylated with ethanol in the presence of a modified ZSM-5 catalyst to produce p diethylbenzene with 97% selectivity.178... 

In Part 1(1) the temperature programmed desorption (tpd) of n-hexane and n-octane from the (Na, H) forms for ZSM-5, ZSM-11 and Theta-1 was reported. In Part 11(2) the tpd of p-xylene and benzene from the same zeolite samples was presented. In the latter study the desorption of p-xylene from ZSM-5 and ZSM-11 zeolites of varying Si/Al ratio was also included. In the present study the effect of different cations in the channels and intersections of ZSM-5, ZSM-11 and Theta-1 on the desorption of n-hexane is reported. 

Fig. 28 Co-diffusion of p-xylene and benzene. Uptake from a mixture of benzene and p-xylene as a function of the square root of time at 395 K but for two different partial pressures of benzene in the mixture. The overshooting of benzene sorption is clearly demonstrated (see text)...

All of the aromatic ketones and silanes were used as purchased from commercial sources. Tetrahydrofuran (THE) was purified prior to use by first drying over calcium hydride, then fractionally distilling. Alternatively, THE was distilled under nitrogen from sodium naphthalene complex. N,N,N, N -Tetramethylurea (TMU) was dried over calcium hydride and then fractionally distilled, while hexamethylphosphoramide was used as purchased. Magnesium metal was used in the form of 30 mesh shot. 2,3,5,6-Tetrachloro-1,4-benzoquinone used in the kinetic studies was recrystallized from acetone prior to use. Toluene, p-xylene, and benzene were dried by refluxing over calcium hydride followed by fractional distillation. Octamethylcyclotetra-siloxane (D ) was dried and purified by distillation at atmospheric pressure. The first and last fractions were discarded and the center fraction, boiling at 175-176°C, was used. Karstedt s catalyst was obtained from General Electric Silicone Products Business Division.Eiltrol-20 was used as purchased from the Eiltrol Company. Styrene monomer was freed from... 

Refer to Test Methods D 3797, D 3798, and D 4492 for determining the purity of oXylene, p-Xylene, and benzene, respectively. 

Silver trifluoroacetate is used in a one step synthesis of bicyclo[3 2 2]nona-6,8-diene-3-one from 2-methoxyallyl bromide and benzene [50] (equation 23) Analogous reactions of toluene, p-xylene, and mesitylene yield the corre spending substituted bicyclo[3 2 2]noiia-6,8-diene-3-ones [50]... 

The variation of amount of VOC adsorbed and the variation of BET surface area with modified contents were shown in Fig. 1. The optimum modified content was lwt% for benzene, toluene, p-xylene, methanol, ethanol and iso-propanol, but the amount of o-xylene, m-xylene, and MEK adsorbed were decreased with increasing modified contents. Interestingly, the amount of benzene, p-xylene, and ethanol adsorbed on lwt%-PA/AC was 1.5 to 2 times that on purified AC. The BET surface area of lwt%-PA/AC (1109m /g) took the maximum value. 

Cyclohexadienylidenes, disubstituted at the 4-position are expected to be kinetically more stable than the parent carbene, however, the rearrangement to benzene derivatives is still very exothermic. The gas phase chemistry of 4,4-dimethyl-2,5-cyclohexadienylidene Is was investigated by Jones et al.100,101 The gas phase pyrolysis of the diazo compound 2s produces a mixture of p-xylene and toluene, and by crossover experiments it was demonstrated that the methyl group transfer occurs intermolecularly via free radicals. Thus, the pyrolysis of a mixture of the dimethyl and the diethyl derivative 2s and 2t... 

Paracyclophane also has a compact structure in solution, as is readily seen on comparing its partition coefficient with that of p-xylene for the system octanol/water 32>. Rigid superposition of the benzene rings leads to an intramolecular delocalization of the hydrophobic -electron clouds and hence to an increased affinity for the aqueous phase. Accordingly, the logarithm of the partition coefficient is found to be smaller than the value observed for p-xylene, and not twice as large, as would be expected for completely hydrophobic surfaces. 

The values of Ogimachi etal. (1955) were related to the measurementsof Andrews and Keefer (1952) through p-xylene, since benzene itself was not measured by Ogimachi et al. 

More recently Hartog and Zwietering (103) used a bromometric technique to measure the small concentrations of olefins formed in the hydrogenation of aromatic hydrocarbons on several catalysts in the liquid phase. The maximum concentration of olefin is a function of both the catalyst and the substrate for example, at 25° o-xylene yields 0.04, 1.4, and 3.4 mole % of 1,2-dimethylcyclohexene on Raney nickel, 5% rhodium on carbon, and 5% ruthenium on carbon, respectively, and benzene yields 0.2 mole % of cyclohexene on ruthenium black. Although the cyclohexene derivatives could not be detected by this method in reactions catalyzed by platinum or palladium, a sensitive gas chromatographic technique permitted Siegel et al. (104) to observe 1,4-dimethyl-cyclohexene (0.002 mole %) from p-xylene and the same concentrations of 1,3- and 2,4-dimethylcyclohexene from wi-xylene in reductions catalyzed by reduced platinum oxide. 

Chemical/Physical. Under atmospheric conditions, the gas-phase reaction of o-xylene with OH radicals and nitrogen oxides resulted in the formation of o-tolualdehyde, o-methylbenzyl nitrate, nitro-o-xylenes, 2,3-and 3,4-dimethylphenol (Atkinson, 1990). Kanno et al. (1982) studied the aqueous reaction of o-xylene and other aromatic hydrocarbons (benzene, toluene, w and p-xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. The amount of cyanogen chloride formed increased at lower pHs (Kanno et al., 1982). In the gas phase, o-xylene reacted with nitrate radicals in purified air forming the following products 5-nitro-2-methyltoluene and 6-nitro-2-methyltoluene, o-methylbenzaldehyde, and an aryl nitrate (Chiodini et ah, 1993). 

In the presence of tellurium tetrachloride, aromatic hydrocarbons are alkylated with reactive alkylating agents such as benzylic or t-butyl alcohols and chlorides. The yields are high with toluene but only moderate for benzene, p-xylene and anisole. Equivalent and catalytic amounts of tellurium tetrachloride, respectively, are required for the alcohols and... 

In agreement with our aforementioned prediction, 98 and 99, both of which comprehend a secondary C2 axis, functioned as effective hosts for benzene, p-xylene, and 1,2,4-trimethylbenzene. " " On the contrary, the other benzo-fused derivatives of tetraphenylene, which are deprived of a secondary C2 axis, did not manifest any inelusion capacity in all solvents tested. ... 

The addition of BF3 OEt2 to a solution containing Ph3BiF2, allyltrimethylsilane and excess arenes induces a Friedel-Crafts-type allylation at low temperatures to yield allylarenes [36]. Benzene, toluene, anisole, p-xylene, and p-dimethoxyben-zene were all allylated with ease to give the corresponding allylation products, although diallylation could not be suppressed in the reaction with electron-rich... 

In early measurements the solubility of [C2CiIm][PFg] in aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene) and that of [C4QIm][PFg] in the same aromatic hydrocarbons, and in n-alkanes (pentane, hexane, heptane, and octane), and in cyclohydrocarbons (cyclopentane and cyclohexane) has been presented [96]. 

Figure 4 Temperature-programmed desorption/oxidation spectra for benzene, toluene, p-xylene, and mesitylene adsorbed on TiOi. (From Ref. 43.)...

Figure 19.12 (a) Experimental setup to determine the exchange dynamics of a combined NAPL-water system using the slow stirring method (SSM). (6) - (d) Measured and calculated aqueous concentrations of benzene m/p-xylene and naphthalene. The solid lines give the result of the linear bottleneck exchange model with an aqueous boundary layer thickness of 8bl = 2.4 x 1CT2 cm = 240 pm (adapted from Schluep et al., 2000). 

For m/p-xylene and naphthalene the aqueous equilibrium concentration (reached after about 2 days) agrees well with the calculated value, Ciw/NAPL. However, for benzene the measured value lies about 10% below the calculated equilibrium concentration (410 pg L-1). This discrepancy will be explained below (Answer d). 

Dimercury(I) n complexes are formed between aromatic compounds and Hg2(AsF6)2 in liquid S02 as solvent.113,121 Insoluble complexes with the ratio arene Hg2+ = 1 1 (arene = benzene, naphthalene, 2-methylnaphthalene, 2,6-dimethylnaphthalene, acenaphthene, fluor-anthrene, phenanthrene, anthracene, 9,10-dimethylanthracene or 1,3-dinitrobenzene) or 1 2 (arene = 9,10-benzophenanthrene) have been characterized by elemental analysis and, in some cases, by Raman spectrometry.113,120 The 13CNMR data allow the estimation of formation constants for the hexamethylbenzene, p-xylene and 1,4-dichlorobenzene complexes together with the chemical shifts for the bound substrates in these cases.121 Probably the coordination compounds of dimercury(I) salts with carbazole, dibenzofuran and diben-zothiophene are also n complexes.122... 

In a typical experiment, two solutions were prepared A - contained 0.3g p-xylene, 0.3g l,3-di(tri-fluoromethylbenzene, and 11.4g 1,3,5-tri-isopropyl-benzene B - contained l.Og n-nonane, l.Og mesitylene and 6.0g 1,3,5-tri-isopropylbenzene. 3.0g of solution A was added to l.Og H-ZSM-5 at room temperature the sorption of p-xylerie was monitored over a period of several hours by gas chromatography. When the sorption had reached a constant value, 0.6g of solution B was added. The resulting desorption of p-xylene and the adsorption of n-nonane was monitored by gas chromatography. In these experiments, the 1,3-di(trifluoro-methyl)benzene and mesitylene behaved exclusively as non-sorbing internal standards. 

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