Xylene Molecules Research Articles

Dynamics of xylene molecules in zeolite NaY

The dynamics of p- and m-xylene in the cavities of zeolite NaY has been studied between 77 and 300 K. Three temperature regions with different types of motion are distinguished by analysis of the second moment of 1H nuclear magnetic resonance (NMR) signals. At temperatures up to 125 K the molecules are adsorbed in front of the SII′ Na cation. Between 125 and 250 K experimental data are best described by a tetrahedral jump model. Above 250 K enhanced mobility of the arenes is explained as continuous diffusion.

Transport and Isomerization of Xylenes over HZSM-5 Zeolites

The diffusion, adsorption, and reaction of xylenes on HSZM-5 was investigated by means of time-resolved in situ FTIR spectroscopy and gas chromatography. The different diffusion coefficients determined for the three sylene isomers ( p : o : m ≍ 1000:10:1) were found to influence the isomerization rate above 523 K under the reaction conditions employed. Below that temperature, reactant diffusion played a minor role. For all xylene molecules, the intramolecular mechanism of isomerization suffices to account for all observations. The selectivity of m -xylene isomerization was found to depend primarily upon the transition entropy (transition state selectivity). The selectivity in o - and p -xylene depends upon the surface concentration of the primary product, m -xylene. Its concentration is a function of the activity of the catalyst and the diffusional constraints m -xylene faces. The decrease of the effectiveness of ZSM-5 above 523 K due to reactant diffusional constraints can be seen in lower coverages of m - and o -xylene in comparison to p -xylene.

Dynamics of benzene and xylene molecules in the liquid state from the data of vibrational spectroscopy

Dynamics of benzene and xylene molecules in the liquid state from the data of vibrational spectroscopy

The Effects of Higher-boiling Compounds on the Liquid-phase Isomerization of m-Xylene over a Silica-Alumina Catalyst under Pressure

Abstract The liquid-phase isomerization of m-xylene was studied over a silica-alumina catalyst under pressure on the additions of 2% of 8 higher-boiling compounds and 20–50% of benzene to reactant m-xylene. The catalyst activity in the isomerization was not greatly affected by hexamethylbenzene, naphthalene, α-methylnaphthalene, diphenyl, or s-dibenzyl. On the other hand, the activity was greatly lowered by 1,6-dimethylnaphthalene, diphenylmethane, and anthracene. Moreover, a very rapid exchange reaction occurred between an aromatic ring of diphenylmethane and a reactant xylene molecule, while the content of the isomerization product decreased linearly with an increase in the amount of benzene. From these results, the chemisorption states of xylene were discussed as follows. Most xylene molecules may be deduced to be chemisorbed on acid sites by those benzene rings. On the other hand, the fact that diphenylmethane inhibits the isomerization implies the existence of such a chemisorption state of xylene as a methylbenzylcarbonium ion, which may be an intermediate in the disproportionation reaction of xylene. The acid sites available for the chemisorption of diphenylmethane and for the disproportionation were speculated to be common and to have both acidic characters, protonic and Lewis.

Crystal Structure of the Carbon Tetrabromide p-Xylene Complex

According to an x-ray diffraction study, crystals of the compound of carbon tetrabromide with p-xylene are orthorhombic, space group Cmcm, with a=8.48±0.03, b=8.89±0.03, and c=17.46±0.05 Å. With four molecules per cell, the density is calculated as 2.209 g cm—3. Each aromatic ring has a bromine atom on each face at a distance of 3.34 Å from the center of the ring. This configuration involving half of the bromine atoms is compatible with charge-transfer bonding. The structure consists of zigzag strings of alternate carbon tetrabromide and xylene molecules. Bond distances and angles within these molecules are normal with standard deviations of 0.02 to 0.05 Å for bond distances.

Dynamic Polarization in Asphaltene Solutions

Dynamic polarization experiments in solutions of asphaltene in xylene have been performed at both low and high magnetic fields. The interpretation of the experiments leads to the conclusion that the EPR line of the asphaltene is inhomogeneously broadened. The characteristics of the spin packet are deduced. In particular, the spin-packet width is found to be constant for many different experimental conditions. Specific information is obtained on the residence time of a xylene molecule on the asphaltene particle.