M XYLENES AND ETHYLBENZENE

The halogen compounds used were methylene dichloride, chloroform, carbon tetrachloride, ethylene dichloride, ethyl bromide, ethylene dibromide, bromoform, methyl iodide, and ethyl iodide. The hydrocarbons selected for their interesting combustion properties were hexane, 2-methylpentane, 2,2-dimethylbutane, hex-l-ene, heptane, methylcyclo-hexane, isooctane, diisobutylene, benzene, toluene, m-xylene, and ethylbenzene. 

Using this approach, Tardif et al. (1997) simulated interactions occurring in a ternary mixture of toluene, m-xylene, and ethylbenzene. Then Haddad et al. (1999, 2000b) demonstrated that additional mixture components could be added to the model by simply incorporating mechanistic information on the new binary... 

Figure 21.6. PBPK model-based cancer risk assessment for lOppm of dichloromethane or 0.5 ppm of benzene alone or in mixture with lOppm each of toluene, m-xylene, and ethylbenzene (Mixture A) 5 ppm of toluene, 20 ppm of m-xylene and 40 ppm of ethylbenzene (Mixture B). Based on data from Haddad et al. (2001a).

Table 5. m-Xylene and Ethylbenzene Reactions with Medium Pore Size... 

Although the demand for p-xylene to produce terephthalic acid for fibers, and for o-xylene to obtain phthalic anhydride for the manufacture of plasticizers has risen considerably in recent decades, demand for m-xylene for the production of iso-phthalic add is relatively small. m-Xylene and ethylbenzene are therefore isomer-ized to o-and p-xylene. 

Monton, J. B. Llopis, F. J. Isobaric vapor-liquid equihbria of ethylbenzene + m-xylene and ethylbenzene + o-xylene systems at 6.66 and 26.66 kPa J. them. Eng. Data 1994,39, 50-52... 

XYLENES AND ETHYLBENZENE] (Supplement) m-Xylene [108-38-3], (See also 1,3-Dimethylbenzene.)... 

Monton and Llopis (1994) presented VLE data at 6.66 and 26.66 kPa for binary systems of ethylbenzene with m-xylene and o-xylene. The accuracy of the temperature measurement was 0.1 K and that of the pressure was 0.01 kPa. The standard deviations of the measured mole fractions were less than 0.001. The data at 26.66 for the ethylbenzene (1) - o-Xylene (2) are given in Table 15.8 and the objective is to estimate the NRTL and UNIQUAC parameters based on these data. 

An aromatic hydrocarbon feedstock consisting mainly of m-xylene is to be isomerised catalytically in a process for the production of / -xylene. The product from the reactor consists of a mixture of p-xylene, m-xylene, o-xylene and ethylbenzene. As part of a preliminary assessment of the process, calculate the composition of this mixture if equilibrium were established over the catalyst at 730 K. 

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]. 

Cannella, W.J. (1998) Xylenes and ethylbenzene. In Krosehwitz, J.l. Howe-Grant, M., eds, Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed., Supplement Vol., New York, John Wiley, pp. 831-863... 

The ultimate in xylene separation is claimed, however, by Hetzner (10), who first distills the mixture to remove o-xylene by taking m-p-xylene and ethylbenzene overhead in a column having about 35 to 60 theoretical plates. It is reported that concentrates containing up to 97% o-xylene have been produced by this process. The m-xylene, p-xylene, and ethylbenzene mixture is selectively sulfonated to remove m-xylene. In this operation, 2 moles of Sulfuric acid (96 to 98%) are added per mole of m-xylene in the mixture to be treated. After separation, the aqueous layer is hydrolyzed at 250° to 300° F. to recover a concentrate containing 90% or more m-xylene. The hydrocarbon layer is cooled to produce p-xylene crystals, which are separated by filtration or centrifugation. The 85 to 90% p-xylene concentrate is reprocessed to recover a final product containing 96% p-xylene. The mother liquor from the p-xylene crystallization contains impure ethylbenzene and is rejected from the system. 

When naphtha or naphthenic gasoline fractions are catalytically reformed, they usually yield a Cx aromatics stream that is comprised of mixed xylenes and ethylbenzene. It is possible to separate the ethylbenzene and o-xylene by fractionation. It is uneconomic to separate the m- and p-xylenes in this manner because of the closeness of their boiling points. To accomplish the separation, a Werner-type complex for selective absoiption of p-xylene from the feed mixture may be used. Or, because of the widely different freezing points of the two xylene isomers, a process of fractional crystallization may be used. To boost the p-xylene yield, die filtrate from the crystallization step can be catalytically isomerized. 

XYLENES AND ETHYLBENZENE. Xylenes and ethylbenzene (EB) are Cs aromatic isomers having the molecular formula CsHi... Tile xylenes consist of three isomers methyl groups on the benzene ring. The molecular structures are shown below. 

Many other hydrocarbons, o- and m-xylene, mesitylene, ethylbenzene, diphenyl, etc., can all be employed to give the corresponding aldehydes. The CHO group enters the para-position to the alkyl residue just as in the ketonic synthesis. Thus o-xylene gives 3 4-di-methyl-benzaldehyde. 

Fig. 1.4 double logarithmic plot of intrinsic viscosity [t ] (in dl g-1) vs. number average molecular weight M for poly(pentachlorophenyl methacrylate), (PPQPh) in o-dichlorobenzene ( ), o-xylene ( ), and ethylbenzene ( ). (From ref. [44])... 

Figure 2.7 Representation of the PBTK model developed for a mixture of 5 VOCs (m-xylene, toluene, ethylbenzene, benzene, and dichloromethane). All binary interactions that occur at the level of the rate of metabolism (RAM) are taken into account between the mixture constituents as shown by the dotted arrows. Because all chemicals interact by competitive inhibition, the Km of all mixture constituents is modulated by the presence of other chemicals as can be seen in the RAM equations. Cvl refers to venous blood concentrations. Vmax and Km refer to the maximal rate of metabolism and Michaelis affinity constant, respectively. Kuj is the constant describing competitive inhibition of the metabolism of chemical i by chemical j. (Figure adapted from Krishnan et al. [2002]).

It is obviously impossible to separate m-x ene and p-xylene by distillation, ance their boiling points differ by only (L8 C However, this separation method is feasible to isolate o-xylene and ethylbenzene, although supeifiactionations are required. Further more, the melting point of p-xylene is much higher than that of the other Cg compounds. This is why crystallization was initially employed to recover p-xylene from the mixture, which may be previously rid of ethylbenzene and o-xylene. 

As a rule, if the amount of o-xylene and ethylbenzene present in the feedstock rises, the temperature of formation of the m, p-xylenes eutectic decreases, as well as its p-xyleoe content Recover) is accordingly improved. 

Krishnan and colleagues developed an approach to the PBPK analysis of complex mixtures in which the toxicologic interactions of binary mixtures are first combined in the affected and modeled target tissue [30]. An example for a mixture of volatile organic chemicals (m-xylene, toluene, ethylbenzene, dichlo-romethane, and benzene) that interact via competitive inhibition was devel-oped.The approach requires thatPBPKmodels be available for each component models are interconnected by Kt values and, naturally, by substrate concentrations—here, in the liver. It is necessary that all binary interactions be characterized. For a mixture of n components, the number of binary interaction experiments performed to determine K, values will be n(n - 1)12. While not indicated, it seems that some reduction of resources would be... 

From the experimental data [44], the selectivity of the adsorbents was calculated as the relative retention volume of the separated species. It can be seen in Table 9 that Cs-CPM adsorbent possesses better selectivity than the Ca-CPM one with respect to the separation of the isomers of xylene and ethylbenzene with like properties. The results enabled us to conclude that the separation of the isomers of m- and p-cresol up to the purity degree of 99% can be achieved using the columns with the theoretical plates number (TPN) not exceeding 200, and that for the o- and m-isomers - employing the packed intermediate efficiency columns with TPN of 2000-2500. To separate the same pairs of the species using the Ca-CPM, the capillary columns with the TPN of 20000 were reqnired. 

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