A- -p-xylene

The blend membranes are permselective for different organic isomers. So, these could be used for the separation of n-propanol from a mixture of n-propanol (n-PrOH) and i-propanol (i-PrOH) [84] and the separation of p-xylene from a p-xylene and o-xylene mixture [35], It was evidenced that, in both cases, the separation was better by applying the evapomeation technique than that of the pervaporation. 

In this paper, observation results of defect healing of a p-xylene crystal are discussed. The crystal had been partially melted by a pressure decrease, and healing was caused by a slight re-appllcatlon of pressure. 

Figure 4. Healing behaviour of a p-xylene crystal In a 90% p-xylene mixture with elapsed time (Po 37MPa, P 4MPa, T=21 C).

Figure 6. Healing behaviour of a p-xylene crystal in a 70% p-xylene mixture (Po 62.9MPa, P 12MPa, T 19.8 C).

C, 10-50 atm). Xylene benzene ratios of 1-10 may be obtained. Metal catalysts were later replaced by zeolites.210,211,326-328 The most recent development is the Mobil selective toluene disproportionation process,329 which takes advantage of the high para shape selectivity of a zeolite catalyst.210 The catalyst activated by a novel procedure ensures a p-xylene content of up to 95%. After the successful com-mercialization at an Enichem refinery in Italy, the process is now licensed. The catalysts and technologies applied in toluene disproportionation may be also used for transalkylation324,325,331 [Eq. (5.74)] ... 

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 ... 

Fig. 69. Anaerobic catalytic photoreaction of p-xylene. (A) p-Xylene ( and O) ( + Pt02), 1,2-di-p-tolylethane. (From Ref. 408.)...

The point drops out of the common series, likely because the unit cell of 559b contains a p-xylene molecule... 

Process Economics Program Report SRI International. Menlo Park, CA, Isocyanates IE, Propylene Oxide 2E, Vinyl Chloride 5D, Terephthalic Acid and Dimethyl Terephthalate 9E, Phenol 22C, Xylene Separation 25C, BTX, Aromatics 30A, o-Xylene 34 A, m-Xylene 25 A, p-Xylene 93-3-4, Ethylbenzene/Styrene 33C, Phthalic Anhydride 34B, Glycerine and Intermediates 58, Aniline and Derivatives 76C, Bisphenol A and Phosgene 81, C1 Chlorinated Hydrocarbons 126, Chlorinated Solvent 48, Chlorofluorocarbon Alternatives 201, Reforming for BTX 129, Aromatics Processes 182 A, Propylene Oxide Derivatives 198, Acetaldehyde 24 A2, 91-1-3, Acetic Acid 37 B, Acetylene 16A, Adipic Acid 3 B, Ammonia 44 A, Caprolactam 7 C, Carbon Disulfide 171 A, Cumene 92-3-4, 22 B, 219, MDA 1 D, Ethanol 53 A, 85-2-4, Ethylene Dichloride/Vinyl Chloride 5 C, Formaldehyde 23 A, Hexamethylenediamine (HMDA) 31 B, Hydrogen Cyanide 76-3-4, Maleic Anhydride 46 C, Methane (Natural Gas) 191, Synthesis Gas 146, 148, 191 A, Methanol 148, 43 B, 93-2-2, Methyl Methacrylate 11 D, Nylon 6-41 B, Nylon 6,6-54 B, Ethylene/Propylene 29 A, Urea 56 A, Vinyl Acetate 15 A. 

Fig. 21.12. Sensitivity pattern of QCM coated with a p-xylene imprinted polyurethane to 0.1% solvent pulses. Other templates for the polymerisation results in increased sensitivity to the corresponding analyte and to sterically comparable neutral molecules.

Various processes have been developed by Chevron, Shell, Sinclair, Southern Petrochemical, etc., and particularly by IC1 (Imperial Chemical Industries), Maruxen (XIS process), which operates in the presence of steam at a ratio of 0.03 to 0.13 mol/ mol of xylenes feedstock, and ARCO, which proposes the permanent regeneration of its catalyst by using the moving bed technology. These processes are usually combined with a p-xylene recovery technique, generally by crystallization. The isomerization yield depends on the ethylbenzene content at the reactor inlet and on the desired target product, either p-xylene alone or o- and p-xy]enes simultaneously. 

Even more active was the in situ catalyst prepared from [Rh(l,5-hexadiene)Cl]2 and PPh3 with a low ratio of P/Rh = 1.2, and the use of a p-xylene/methanol solvent instead of benzene/methanol resulted in a further increase of activity (Table II). Both effects already have been observed 1,4) which shows that these may be characteristic for such rhodium, phosphine, and amine catalyst combinations. 

Fig. 1 Dianin s compound with p-xylene guest. (From Ref. [10].) (Top) Packing of six Dianin s host molecules around a p-xylene molecule, looking down the sixfold axis of the x-ray diffraction model (only part of each Dianin s inolecule is shown). (Bottom) Room-temperature C-CP/MAS spectrum showing the multiple splittings for the methyl groups (18 and 19. pointing into the cavity) that arise because the p-xylene molecule is static, and the sixfold symmetry is lost.

The crystallization processes used to produce p-xylene are generally carried out in two stages. The feedstock material is first dried to a residual water content of around 10 ppm, to avoid the formation of ice, then cooled to around -55 to -70 °C, and separated from the mother liquor in centrifuges or rotating vacuum drum filters. The mother liquor from the first stage is transferred to an isomerization unit. The crystallizate of the first stage with a p-xylene content of around 90% is melted, then cooled again and separated from the mother liquor. The purity of the produced p-xylene surpasses 99%. 

Calculate the SLE behavior of the binary system CCl4(A)-p-xylene (B) which forms an 1 1 adduct AB. Perform the calculation assuming ideal behavior using the following experimental melting temperatures and enthalpies of fusion [4] ... 

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