Showing papers on "Xylene published in 1993"

Kinetics of competitive inhibition and cometabolism in the biodegradation of benzene, toluene, and p‐xylene by two Pseudomonas isolates.

Abstract: Two Pseudomonas species (designated strains B1 and X1) were isolated from an aerobic pilot-scale fluidized bed reactor treating groundwater containing benzene, toluene, and p-xylene (BTX). Strain B1 grew with benzene and toluene as the sole sources of carbon and energy, and it cometabolized p-xylene in the presence of toluene. Strain X1 grew on toluene and p-xylene, but not benzene. In single substrate experiments, the appearance of biomass lagged the consumption of growth substrates, suggesting that substrate uptake may not be growth-rate limiting for these substrates. Batch tests using paired substrates (BT, TX, or BX) revealed competitive inhibition and cometabolic degradation patterns. Competitive inhibition was modeled by adding a competitive inhibition term to the Monod expression. Cometabolic transformation of nongrowth substrate (p-xylene) by strain B1 was quantified by coupling xylene transformation to consumption of growth substrate (toluene) during growth and to loss of biomass during the decay phase. Coupling was achieved by defining two transformation capacity terms for the cometabolizing culture: one that relates consumption of growth substrate to the consumption of nongrowth substrate, and second that relates consumption of biomass to the consumption of nongrowth substrate. Cometabolism increased decay rates, and the observed yield for strain B1 decreased in the presence of p-xylene.

Degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) by the lignin-degrading basidiomycete Phanerochaete chrysosporium.

Abstract: Degradation of the BTEX (benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes) group of organopollutants by the white-rot fungus Phanerochaete chrysosporium was studied. Our results show that the organism efficiently degrades all the BTEX components when these compounds are added either individually or as a composite mixture. Degradation was favored under nonligninolytic culture conditions in malt extract medium, in which extracellular lignin peroxidases (LIPs) and manganese-dependent peroxidases (MNPs) are not produced. The noninvolvement of LIPs and MNPs in BTEX degradation was also evident from in vitro studies using concentrated extracellular fluid containing LIPs and MNPs and from a comparison of the extents of BTEX degradation by the wild type and the per mutant, which lacks LIPs and MNPs. A substantially greater extent of degradation of all the BTEX compounds was observed in static than in shaken liquid cultures. Furthermore, the level of degradation was relatively higher at 25 than at 37 degrees C, but pH variations between 4.5 and 7.0 had little effect on the extent of degradation. Studies with uniformly ring-labeled [14C]benzene and [14C]toluene showed substantial mineralization of these compounds to 14CO2.

Kinetics of toluene alkylation with methanol over magnesium-modified ZSM-5

Abstract: The kinetics of toluene alkylation with methanol has been studied over both unmodified and Mg-modified ZSM-5 catalysts. On the basis of the product distribution obtained over the unmodified zeolite, the following secondary reactions have been considered: methanol dehydration, toluene disproportionation and xylene dealkylation. Power law and Langmuir-Hinshelwood-Hougen-Watson (LHHW) models have been tested for the main toluene alkylation reaction, the best fits to the experimental data being achieved with two models: a second-order power law model and a model based on the Rideal-like mechanism. The first one has been applied to the results obtained with the Mg-modified catalyst, including the effect of the diffusion rate, due to its simpler expression. Over this catalyst p-xylene is the only isomer present in the primary product, hence m- and o-xylene formation takes place by p-xylene isomerization on the external surface catalytic sites. Therefore, the kinetic model developed for the Mg-modified zeolite takes into account, as well as diffusional effects, the influence of p-xylene isomerization over the external zeolite surface, reproducing the experimental product distribution with an average relative error of 6.8%

Process for producing highly purified benzenedicarboxylic acid isomers

Abstract: Disclosed herein is a process for producing highly purified benzenedicarboxylic acid isomers without an additional catalytic reductive purification step, which comprises (a) an oxidation step wherein xylene isomer is oxidized with molecular oxygen or molecular oxygen containing gas in the presence of a catalyst system composed of cobalt, manganese, bromine and at least one selected from nickel, chromium, zirconium and cerium in lower aliphatic carboxylic acid; and (b) an extraction/post-oxidation step wherein the oxidation product is crystallized to give cake of crude benzenedicarboxylic acid isomer, the cake is reslurried by adding lower aliphatic carboxylic acid solvent thereto followed by heating in order to extract impurities contained therein into the solvent, and the resulting slurry is oxidized with said catalyst system at a temperature of 2°-80° C. lower than that of said heating, each of said oxidation and extraction/post-oxidation being carried out once or twice, provided that any one or both of said steps should be carried out twice. According to the invention, the solvent employed to extract impurities is recycled from the subsequent oxidation steps.

Active site dynamics of xylene hydroxylation by cytochrome P-450 as revealed by kinetic deuterium isotope effects

Abstract: The cytochrome P-450 catalyzed hydroxylation of o- and p-xylene and five deuterated derivatives of each has been investigated using phenobarbital-induced rat liver microsomes. All possible monohydroxylation products were observed but benzylic hydroxylation predominated strongly (88-96%). H/D discrimination was strongest when both isotopes were located on the same methyl group, less when they were located in different methyl groups on the same xylene molecule, and least when they were located in methyl groups on different molecules. Benzylic hydroxylation is subject to a large intrinsic (intramolecular) deuterium isotope effect (CH 3 /CD 3 =1.5-9.5), comprised of a large primary component (5.3-1.8) and a large normal α-secondary component (1.09-1.19)

Excretion of methylhippuric acids in urine of workers exposed to a xylene mixture: comparison among three xylene isomers and toluene

Abstract: The correlation between exposure to three xylene isomers and resulting urinary excretion of corresponding methylhippuric acid (MHA) isomers was studied among 175 Chinese workers of both sexes who had been predominantly exposed to xylenes (exposure to xylenes accounting for 70% or more of the total exposure on a ppm basis). Nonexposed controls (281 men and women) were also studied to define the background level of MHAs in urine. The solvent exposure of xylene-exposed workers during their workshift was monitored by diffusive sampling of breathing zone air, and MHAs in shift-end urine were determined by high-performance liquid chromatography. Regression analysis showed that the concentration of each MHA isomer correlated significantly with the time-weighted average intensity of exposure to the corresponding xylene isomer, and therefore the correlation between the sum of three xylene isomers in air and that of three MHA isomers in urine was also significant; the slope of the regression line was essentially the same among the three isomers. The calculated regression line suggested that the urinary MHA level after hypothetical exposure to xylenes at 100 ppm will be somewhat less than the proposed biological exposure index and biological tolerance value. Two social habits of smoking and drinking in combination suppressed the conversion of xylenes to MHAs in male workers.

Polypropylene compositions having good transparency and improved impact resistance

Abstract: Disclosed is a polymer composition containing: (A) from 70 to 98 parts by weight of a crystalline propylene homopolymer, or a crystalline random copolymer of propylene with ethylene and/or C 4 -C 10 α-olefins, containing from 0.5 to 10% by weight of ethylene and/or α-olefins [fraction (A)]; and (B) from 2 to 30 parts by weight of elastomeric copolymer of ethylene with one or more C 4 -C 10 α-olefins, containing from 60 to 85% by weight of ethylene, and partially soluble in xylene at 25° C. [fraction (B)]; wherein the composition has an intrinsic viscosity value in tetrahydronaphthalene at 135° C. of the fraction soluble in xylene at 25° C. ranging from 0.8 to 1.1 dl/g.

Recycling of polymers by pyrolysis

Abstract: The pyrolysis of plastic waste, scrap tires and other polymeric materials in a fluidized bed has been carried out based on a scale up program (laboratory plants 70 g/h, 500 g/h, 3000 g/h, and pilot plant 20-50 kg/h). The fluidized bed shows short residence times and high heat and mass transfers, and is heated indirectly up to 600-800°C. In the case of poly(methylmethacrylate) (PMMA) or polystyrene as feedstock up to 97 wt.% of the monomer can be recovered. Other polymers give a more unspecific product spectrum. Depending on the process parameters between 30 and 60% of the polymeric material could be recovered as oil which is comparable to that of a mixture of light benzene and bitumious coal tar if the pyrolysis gas is used as fluidizing gas. The other fractions are gas and a residue containing fillers and impurities (heavy metals). The gas fraction contains mainly methane, ethane, ethene, and propene, the oil fraction benzene, toluene, xylene, and naphthalene

Integrated selective adsorption and crystallization process for para-xylene recovery

Abstract: The eutectic limit of para-xylene crystallization is overcome by enriching the concentration of para-xylene of the crystallization feed. This is accomplished by passing the crystallization feed stream through a selective adsorption zone to produce a para-xylene-enriched stream and a para-xylene-depleted stream. The para-xylene-depleted stream is passed to an isomerization zone to re-equilibrate the xylene mixture, thereby producing additional para-xylene. The para-xylene-enriched stream is passed to a crystallization zone to produce high purity para-xylene. The result is an increase in the overall para-xylene recovery.

Cytogenetic effects of low-level exposure to toluene, xylene, and their mixture on human blood lymphocytes.

Abstract: The present study was undertaken to investigate, both in vitro and in vivo, the genotoxic potential of short-term low-level exposure to toluene, xylene, and their mixture, for which information is limited at the present time. Five adult healthy white men were exposed for 7 consecutive hours per day over 3 consecutive days to 50 ppm toluene and 40 ppm xylene either alone or in combination in a controlled exposure chamber. Such an exposure was repeated three times at intervals of 2 weeks. Blood samples were taken before and after the termination of such exposure. Three different cytogenetic end-points were evaluated using peripheral blood lymphocytes: number of sister chromatid exchanges (SCEs), cell cycle delay, and cell mortality. No significant effects on SCEs, cell cycle delay, and cell mortality were observed following such exposure to toluene or xylene or their mixture. Similarly, exposure of human blood lymphocytes in vitro to either toluene (0–2.5 mM) or xylene (0–2 mM) or their mixture for 72 h did not result in any significant cytogenetic effects at lower concentrations, while at higher concentrations, only cell mortality was found to be significantly affected. Thus our present study indicates that simultaneous exposure to low levels (within the admissible limits) of toluene, xylene, or their mixture for a short period does not pose any potential mutagenic threat to humans.

Method of removing hydrocarbon contaminants from air and water with organophilic, quaternary ammonium ion-exchanged smectite clay

Abstract: A method of removing hydrocarbon contaminants from air and a method of removing nonionic organic contaminants, particularly petroleum-derived aromatic contaminants that have a limited capacity to ionize in aqueous solution at substantially neutral pH, from water, by contacting the contaminants in the air or water with an organophilic clay that has been prepared by ion-exchange of an ion-exchangeable clay with a tetra short chain alkyl (C 1 -C 4 ) quaternary ammonium ion for use in removing air-laden contaminants; or a di- or tri- short chain alkyl (C 1 -C 4 ), with one or two mono- substituted or unsubstituted cycloalkyl moieties, or one or two mono-substituted or unsubstituted aryl or one or two alkaryl moiety quaternary ammonium ion for removing air and water-laden contaminants. The method is particularly adapted for removal of aromatic petroleum-based contaminants from water, such as benzene, toluene, xylene (o, m and p) ethylbenzene and naphthalene, and other water-contained petroleum constituents or derivatives that have a pKa in aqueous solution of at least about 10.

Crystallization process for para-xylene recovery using two-stage recovery section

Abstract: In a combination crystallization/xylene isomerization process for producing para-xylene crystals, the recovery section is modified to accommodate crystallizing and separating para-xylene crystals at two different temperatures (a higher temperature followed by a lower temperature). The benefit is a reduction in the overall energy cost of the process.

Kinetics of toluene disproportionation over unmodified and modified ZSM-5 zeolites

Abstract: The kinetics of toluene disproportionation has been studied over both unmodified and Si-Mg modified ZSM-5 catalysts using an integral reactor and taking into account the reversibility of the reaction. It has been found that xylene dealkylation is the major secondary reaction, whereas toluene dealkylation can be considered negligible. For the unmodified ZSM-5, heterogeneous models based as the alkyl-transfer mechanism allowed the experimental results to be fit better than first and second pseudohomogeneous models, the best concordance being obtained when toluene adsorption is assumed as the rate-limiting step. The corresponding kinetic equations has been further applied to the modified zeolite (SiMg/ZSM-5), leading to the development of a kinetic model which includes the effect of the toluene and p-xylene intracrystalline diffusion rate and the presence of nonselective acid sites on the external zeolite surface. This model describes adequately the selective formation of p-xylene over modified ZSM-5, reproducing the experimental product distribution with an average relative error of 2.8%

Mordenite catalysts in toluene synthesis

Abstract: In accordance with the the present invention, there is provided a process for the conversion of aromatic hydrocarbons including benzene to hydrocarbon components comprising primarily toluene. According to the invention, a catalyst reaction zone is established having a metal-loaded mordenite catalyst. A mixed feedstock of aromatic hydrocarbons, including benzene, xylene(s) and, optionally, ethylbenzene is introduced into the reaction zone and hydrogen is used as a cofeed to provide a reductive environment. The feedstock is contacted with the metal-loaded mordenite catalyst and the conversion of the aromatic hydrocarbon components is conducted under temperature and pressure conditions sufficient to effect the conversion of the feedstock to hydrocarbon components containing primarily toluene. Finally, the conversion product containing primarily toluene is recovered from the reaction zone.

Catalytic Cracking of Naphthalene on Dolomite

Abstract: Gasification of biomass and waste produces tar as an undesired byproduct. Previous studies have shown that dolomite is an effective catalyst for the reduction of the tar content in the gas. The result, compared to thermal cracking, is that the remainder of unconverted tar consists mainly of lighter aromatics, BTX (Benzene, Toluene, Xylene) and naphthalene instead of polyaromatics.

Concentrated liquid or gel light duty dishwashing detergent composition containing calcium xylene sulfonate

Abstract: Concentrated liquid or gel dishwashing detergent compositions containing from about 20% to about 95% surfactant and calcium ions. A substantial amount of the calcium ions is added as calcium xylene sulfonate for improved stability of the composition.