Concentrations Of O-xylene Research Articles

Sorption and Diffusion Properties of H- and Modified Forms of ZSM-5 Zeolites

The sorption properties of samples of H-ZSM-5 zeolite and their forms modified with P, B and Mg were determined by the physical adsorption of nitrogen and evaluated by BET isotherm and t-plot methods. The diffusivities of the samples were measured using a new flow gravimetric method involving the sorption of p- and o-xylenes. The BET specific surface area decreased from 358 m2/g to 35–90 m2/g mainly because of a decrease in micropore volume as determined by the t-plot method. The rate of sorption of p-xylene on all the samples investigated followed Fick's second law of diffusion, leading to an effective diffusivity of ca. 1.7 × 10−11 m2/s, irrespective of whether the H-form or the modified forms were investigated. The sorption isotherms for o-xylene showed some unusual steps. Values for the effective diffusivities decreased from 2.6 × 10−12 m2/s for the H-form to 2.0–2.3 × 10−12 m2/s for the modified forms. The equilibrium concentration of o-xylene at P/P0 = 0.1 was only 0.38–0.68 mol/unit cell, while that of p-xylene was 4.40–5.98 mol/unit cell.

Flüchtige organische Verbindungen (VOC) in Aussenluft. Messung und Dateninterpretation

A method for the automated and inattended measurement of aromatic and halogenated compounds in ambient air has been developed and tested. The method is based on trapping ambient air on an adsorption tube followed by thermal desorption and gaschromatographic analysis. After 1 1/2 years of measurements at a measurement site in the agglomeration of Zürich enough data are available to allow a characterization of the immission concentrations of benzene, toluene, ethylbenzene, m/p-xylene, o-xylene, dichlorodifluoromethane (FCKW - 12), 1,1,2-trichlorotrifluoroethane (FCKW-113), trichloromethane, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene, and tetrachloroethene.

Vehicle emissions as the major source of gaseous aromatic hydrocarbons at different locations in Germany

Fourteen gaseous aromatic hydrocarbons have been measured in four 1-month monitoring campaigns. Sampling locations included a rural site, a small town, an urban and an industrial site, all in western Germany. Twenty-four-hour samples were collected on activated charcoal, avoiding immediate traffic impact. Analyses were carried out by GC/ITD. Average concentrations of the total of all quantified compounds ranged from 2 μg/m 3 at the rural site to 17 μg/m 3 at the urban site. For source determination, the data were normalized by the respective o-xylene concentrations. Average values of normalized concentrations showed only small standard deviations and at all locations were similar to data found for highway tunnel exhaust air, thus indicating vehicle emissions as the common source.

Use of Branched .BETA.-Cyclodextrins as Separating Agents for Liquid-Liquid Extraction of Mixed Xylenes.

In order to develop industrial use of branched β-cyclodextrins (CDs), of which solubility in water is remarkably higher than that of unsubstituted β-CD, liquid-liquid extraction of xylene mixture, utilizing the inclusion by branched β-CDs, was examined. The inclusion selectivity to each guest species was in the following order: o-xylene_??_p-xylene>ethylbenzene>m-xylene. Thus, the use of branched β-CDs was found to be useful, in particular, for the separation of o-xylene. The complex formation reached a state of equilibrium in a few minutes. The effect of temperature on the composition and yield of the oil extracted was examined, which indicated that the inclusion at ordinary temperature was preferable. Repetition of inclusion complexation increased the concentration of o-xylene. The once used branched β-CD worked well for inclusion, after the release of guest species.

The Neurotoxicity of Organic Solvents, Studied with in Vitro Models

The present paper deals with the general anaesthetic effect of organic solvents. The emphasis is on cell membranes as models for predicting the adverse reactions of the human nervous system to organic solvents, and for studying the mechanisms of their anaesthetic action. Human and rat erythrocyte and platelet membranes, rat synaptosomal membranes and cultured neural cell membranes were exposed in vitro to various concentrations (3–30mM) of benzene, toluene, o-xylene and styrene in the incubation mixtures. After exposure to a solvent for 30 minutes, the membrane integral protein integrity was determined by measuring ATPase and acetylcholinesterase activities. All measurements were performed in triplicate from 3 or 4 independent experiments with each exposure of solvent and each membrane isolation. The enzyme inhibition was dose-dependent, and differed after solvent treatment in all membrane preparations tested in increasing order, as follows: benzene, toluene, styrene, o-xylene. The results support the protein theories on the mechanism of the anaesthetic action of various industrial organic solvents. The integral membrane proteins contain hydrophobic pockets which may bind anaesthetics, e.g. solvents which change the properties of integral enzymes. The effects of solvents in peripheral models are quite similar to those in neural membranes in vitro. Therefore, these membrane models can serve as test models when the narcotic potencies of the solvents are being evaluated, or at least for screening purposes and for studies of the mechanisms of solvent neurotoxicity.

Interference effects in trapping trace components from gases on tenax-GC : Sorption of benzen in the presence of n-butanol, o-xylene and n-pentane

Sorption equilibria were measured in systems of Tenax-GC and benzene- n- butanol—nitrogen, benzene— o-xylene—nitrogen and benzene— n-pentane—nitrogen gaseous mixtures at 19.9, 27.1 and 35δC. With all the systems the benzene (a model analyte) concentration was kept at 0.5 ppm and the concentrations of n-butanol, o-xylene and n-pentane (interferents) were varied over a range of four orders of magnitude. The dependences of the parition coefficient of benzene on the concentrations of the interferents are discussed in terms of the conservation and equilibration modes of concentrating trace substances in sorbent-packed trapping columns.

Atmospheric Hydrocarbon Concentrations in the Baltic Sea Area

Abstract During a marine research expedition in 1983 in the Baltic Sea area air samples were collected for the analysis of several organic and inorganic pollutants. The aim of the expedition was to obtain information on the airborne load in the sea as well as to measure the concentrations of the pollutants far away from source areas. In this paper the background concentrations of the primarily traffic originated aromatic hydrocarbons benzene, toluene and xylenes will be presented. The concentrations of benzene were from 0.2 to 2μg/m3, of toluene between 0.4–3μg/m3, of m-xylene 0.02–0.60μg/m3 while the concentrations of o-xylene were 0.01–0.1 μg/m3. The concentrations did not depend too much on the origin (continental/sea type) of the air masses. A weak minimum in the concentrations of the measured hydrocarbons was noticed in the central Baltic Sea area. When comparing lead concentrations in fine particles (< 2.5 μm) with those of benzene, toluene and m-xylene some coincidence between them could be observed.

Flow characteristics in a segmented closed-tube design for ion-mobility spectrometry

Closed-tube design with unidirectional flow of drift gas in ion-mobility spectrometry (i.m.s) was found to provide residence times for analyte from 10 s to 10 min based on drift gas flow rate. The volume of drift gas necessary to restore reactant ions completely to the original intensity, after addition of excess (>900 mg l −1) of analyte to the ion source, was three times the inner volume of the tube, regardless of flow rate. Contamination of the i.m.s. tube from analyte in the external atmosphere occurred readily in the open-tube design and in the closed-tube design with or without a slight vacuum attached to the tube. Rates of migration of analyte from outside to inside the tube were similar in all designs and the present closed-tube design was largely non-resistant to external contamination. Product-ion intensities for aromatic and polynuclear aromatic hydrocarbons were independent of drift flow rate from 100 to 800 ml min −1 in the closed-tube design with no formation of artifacts. Plots of ion intensity vs. concentration of o-xylene were linear int wo ranges, 0.05–0.08 μg l −1 and 0.1–2 μg l −1, with slopes of 1.2 × 10 −9 A l μg −1 in the first range and 1.0 × 10 −11 A l μg −1 in the second range. No changes in mobility of aromatic product-ion peaks were seen with increases in concentration when the analyte was added to the drift gas rather than near the reaction region in unidirectional flow.

Kinetics of the catalytic air oxidation of o-xylene over a commercial V 2O 5-TiO 2 catalyst

The gas-phase oxidation of o-xylene over a commercial V 2O 5-TiO 2 catalyst was studied in fixed bed non-isothermal reactor. The experiments were carried out at initial o-xylene concentrations which differed greatly from each other. The following reaction network was suggested. ▪ It is suggested to use the Langmuir-Hinshelwood kinetic model in which a surface reaction between o-xylene and oxygen, chemisorbed on separate active centres, is the limiting step. It seems that the redox model is not adequate for the kinetic description of o-xylene oxidation.

Benzene, toluene and xylene concentrations in car exhausts and in city air

The concentration of benzene, toluene, m-xylene and o-xylene in exhaust gases of passenger cars and in city air were investigated. The mean emissions of aromatic compounds from 31 cars subjected to a total of 107 ECE 15 test drives were: benzene 250± 100, toluene 350± 130, m-xylene 220±95 and o-xylene 95± 40 mg km −1. The results showed that 3–4 % of the aromatic compounds of the fuel were expelled unburnt with the exhaust gases. The corresponding concentrations of these aromatic compounds in city air during peak traffic periods (prevailing concentrations of carbon monoxide 10 ppm) were 100,140.60 and 30 μg m −3.

Studies on the embryotoxic effects of ortho-, meta- and para-xylene

CFY rats were exposed to inhalation of ortho-, meta-, or para-xylene at 150, 1500, or 3000 mg/m 3 concentration for 24 h/day from day 7 to day 14 of pregnancy. Additional groups of 3 rats were exposed to o-xylene at 150, 1500, or 3000 mg/m 3 concentrations for 2 h only on the 18th day of pregnancy. In this latter group of rats exposed to o-xylene 18th day of pregnancy, the o-xylene concentration in the blood of the rats was proportional to that in the atmosphere. The solvent crossed the placenta; it was present in the fetal blood and amniotic fluid. All the 3 xylene isomers inhaled at the highest concentration brought about toxic effects in the mother animals. All the 3 isomers brought about the retardation of fetal development: a decrease in the weight of the fetuses, an increase in the incidence of the symptoms of skeletal retardation, a decrease in the activity of different enzymes, succinic dehydrogenase, alkaline- and acid phosphatase and glucose 6-phosphatase, characteristic features of the functional maturity of the nephron. Retardation of the fetuses was dose-dependent, but also dependent on the chemical structure of the particular isomer; their effectiveness was para-, ortho- and meta-xylene in the decreasing order of potency. None of the isomers proved to be teratogenic. Meta- and para-xylene inhalation at the highest concentration increased the incidence of extra ribs. Preimplantation fetal loss was increased by meta- and para-xylene, meta-xylene at the highest concentration interfered with the process of implantation, while para-xylene exposure resulted in an increased postimplantation loss of the fetuses. Ortho-xylene inhalation was without effect on the incidence of the extra ribs, either on implantation, or on the pre- and postimplantation fetal losses.

The effects of water-soluble petroleum components on the growth of Chlorella vulgaris Beijerinck

The effects of the water-soluble components of petroleum on a selected algal test species, Chlorella vulgaris, have been investigated under controlled laboratory conditions. Aqueous extracts of seven different crude oils and one refined product exhibited marked differences in toxicity to Chlorella, resulting in a 5% to 41% reduction of cell numbers during the first 48 h. However, this toxicity was only of a short-term nature, apparently resulting in a lag phase prior to the onset of growth. Work with oil extracts allowed to evaporate for 0, 24, 48 or 120 h prior to their inoculation with algae, suggests that the observed toxicity of oil extracts is due to highly volatile compounds which are largely lost from the culture flasks during the first 25 h. Lower concentrations of benzene, toluene, o-xylene and napthalene resulted in a growth inhibition similar to that caused by crude oil. Higher concentrations caused total inhibition of growth. The growth rate of cells was normal once the lag phase had ended. A significant stimulation of growth was observed with three of the oil extracts after their toxic compounds had evaporated. It is not known at present if this stimulation is a reflection of an actual ability to utilise certain hydrocarbons heterotrophically from the extract. Other possible interpretations are discussed.