Search results for "Xylene"
showing 8 items of 58 documents
Macrocyclic (1,3)- and (1,4)-benzena-(1,4)-piperazinacyclophanes
1995
New large, up to 45-membered macrocycles were synthesised from piperazine and m- and p-2,6-bis(bromomethyl)xylene under high dilution conditions. X-ray structures of compounds 3a, 4a, 5a, and 8b were determined. Surprisingly, none of the macrocycles prepared showed any inclusion properties towards small guest molecules. Instead, the compounds were found to self-organize during the packing process into larger structures due to the complementary of the molecular skeletons. In the crystalline state 3a forms nets, where the macrocycles are bound by HCH…N interactions to each other. 4a exits in a dimeric structure, which, in turn, further extends to a sheet structure. The positively charged phan…
Benzene, toluene, ethyl benzene and xylenes in ambient air and Pinus sylvestris L. needles: a comparative study between Belgium, Hungary and Latvia
2001
Abstract Concentrations of benzene, toluene, ethyl benzene and xylenes (BTEX) in ambient air and in 1 yr old Pinus sylvestris pine needles were monitored along a busy road, petrol station and rural area of Belgium, Hungary and Latvia in a 1 yr period. To test P. sylvestris as a possible biomonitor for the BTEX concentrations, samples were taken in the four seasons. As the distribution of data was not normal, the level of pollution on different sites and seasons was compared and evaluated by non-parametric tests. The measured air concentrations did not differ significantly from one season to another throughout the year. There were, however, differences between sampling places. The C2-alkylbe…
Differential calorimetric enthalpies of adsorption ofp-xylene andm-xylene on y faujasites at 25°C
1997
The differential enthalpies of adsorption ofp-xylene andm-xylene on NaY, KY and BaY zeolites were measured by isothermal calorimetry coupled with isothermal volumetry at 25‡C. Whatever the zeolite, the enthalpies of adsorption ofp-xylene andm-xylene at low filling were of the same order of magnitude. They did not show significantly the effect of the dipolar moment ofm-xylene. Their absolute values varied in the sequence
On the Mechanism of Xylene Isomerization and its Limitations as Reaction Test for Solid Acid Catalysts
1993
The kinetics of the gas-phase isomerization of m-xylene, over a series of ultraestable Y zeolites, has been studied in a fixed-bed flow reactor under initial conditions. Using deuterated p-xylene as reactant it has been seen that more than 20% of the m- and o-xylene obtained, are formed via a bimolecular mechanism. The relative proportion of uni- to bimolecular mechanism depends on the zeolite composition. The relation between the turnover number, calculated from the kinetic rate constant for the unimolecular mechanism, and the framework Al content of the zeolite, was coincident with the topological zeolite model. Besides, the values of the adsorption constants indicate that dealumination h…
Sorption Kinetics of Benzene and p-Xylene on Template Supported Synthesized Gallosilicates
1993
Adsorption equilibria and kinetics of benzene and p-xylene on microporous gallosilicates (Ga-MFI) were measured piezometrically to ascertain the role of Ga in the system and to compare it with Ga-free MFI structures. The intracrystalline mobility of benzene follows a diffusional mechanism throughout the entire concentration range with an energy of activation that considerably exceeds that for the Ga-free species (78 kJmol−1 and 26 kJmol−1, respectively). For p-xylene, the kinetics indicate the existence of three sorption states. Sorbing species become highly immobile at a pore filling of ca n > 4 molecules per unit cell, i.e. in the range of concentration where isotherm hysteresis occurs. T…
Determination of the Pore Topology of Zeolite IM-5 by Means of Catalytic Test Reactions and Hydrocarbon Adsorption Measurements
2000
Abstract The pore topology of a recently synthesized zeolite IM-5 has been determined by means of catalytic test reactions, i.e., n -decane hydroisomerization–cracking, m -xylene isomerization–disproportionation, n -hexadecane isodewaxing, and adsorption–microcalorimetry of molecules with different sizes and shapes ( n -hexane, toluene, m -xylene, and 1,3,5 trimethylbenzene). It has been found that the channel network consists of a system of unidirectional 10 MR with lobes or side pockets, or crossing 10 membered ring pores with a pore diameter somewhat smaller than those in ZSM-5. This structure offers interesting shape selectivity features for catalytic reactions.
Absolute cross-sections for the nonresonant multi-photon ionization of toluene and xylene in the gas phase
2001
Abstract The absolute multi-photon ionization cross-section of the phenyl ring was determined by laser-ionization of toluene and xylene molecules in the gas phase. Excitation was achieved using nonresonant four-photon absorption of the frequency doubled light of a 10 ns pulsed Nd:YAG laser (532 nm). The resulting ions were stored in a Penning trap and detected by time-of-flight mass spectrometry. The values of the cross-sections are 1.4(3)×10 −42 cm 8 W −4 s −1 and 1.3(3)×10 −42 cm 8 W −4 s −1 for toluene and xylene, respectively.
Hazardous air pollutants and primary liver cancer in Texas.
2016
The incidence of hepatocellular carcinoma (HCC), the most common primary liver cancer, is increasing in the US and tripled during the past two decades. The reasons for such phenomenon remain poorly understood. Texas is among continental states with the highest incidence of liver cancer with an annual increment of 5.7%. Established risk factors for HCC include Hepatitis B and C (HBV, HCV) viral infection, alcohol, tobacco and suspected risk factors include obesity and diabetes. While distribution of these risk factors in the state of Texas is similar to the national data and homogeneous, the incidence of HCC in this state is exceptionally higher than the national average and appears to be di…