Showing papers on "Xylene published in 2011"

Metal-organic framework MIL-101(Cr) for high-performance liquid chromatographic separation of substituted aromatics.

Abstract: The diverse structures and pore topologies, accessible cages and tunnels, and high surface areas make metal–organic frameworks attractive as novel media in separation sciences. Here we report the slurry-packed MIL-101(Cr) column for high-performance liquid chromatographic separation of substituted aromatics. The MIL-101(Cr) packed column (5 cm long × 4.6 mm i.d.) offered high-resolution separation of ethylbenzene (EB) and xylene, dichlorobenzene and chlorotoluene isomers, and EB and styrene. The typical impurities of toluene and o-xylene in EB and styrene mixtures were also efficiently separated on the MIL-101(Cr) packed column. The column efficiencies for EB, m-dichlorobenzene, and m-chlorotoluene are 20000, 13000, and 10000 plates m–1, respectively. The relative standard deviation for five replicate separations of the substituted aromatics was 0.2–0.7%, 0.9–2.9%, 0.5–2.1%, and 0.6–2.7% for the retention time, peak area, peak height, and half peak width, respectively. The MIL-101(Cr) offered high affinit...

Catalytic oxidation of toluene and p-xylene using gold supported on Co3O4 catalyst prepared by colloidal precipitation method

Abstract: Gold supported on cobalt oxide has been successfully synthesized through a colloidal precipitation method and tested in toluene and p -xylene total oxidation. It has been demonstrated that the catalytic activity of Au/Co 3 O 4 for toluene and p -xylene oxidation is much higher than that of Au/Al 2 O 3 and Au/MgO in spite of its lower BET surface area and larger gold crystalline size. The enhanced catalytic activity in toluene and p -xylene oxidation has been linked to a high concentration of superficial electrophilic oxygen species and oxygen vacancies, which may be originated from a strong interaction in the colloidal Au–Co 3 O 4 system.

Adsorption of BTEX on Surfactant Modified Granulated Natural Zeolite Nanoparticles: Parameters Optimizing by Applying Taguchi Experimental Design Method

Abstract: In this paper, a novel adsorbent developed by means of granulating of natural zeolite nanoparticles (i.e., clinoptilolite) was evaluated for possible removal of the petroleum monoaromatics (i.e., benzene, toluene, ethylbenzene, and xylene, BTEX). To do this, the natural zeolite was ground to produce nanosized particulate, then modified by two cationic surfactants and granulated. The effect of various parameters including temperature, initial pH of the solution, total dissolved solids (TDS), and concentration of a competitive substance (i.e., methyl tert-butyl ether, MTBE) were studied and optimized using a Taguchi statistical approach. The results ascertained that initial pH of the solution was the most effective parameter. However, the low pH (acidic) was favorable for BTEX adsorption onto the developed adsorbents. In this study, the experimental parameters were optimized and the best adsorption condition by determination of effective factors was chosen. Based on the S/N ratio, the optimized conditions for BTEX removal were temperature of 40°C, initial pH of 3, TDS of 0 mg/L, and MTBE concentration of 100 µg/L. At the optimized conditions, the uptake of each BTEX compounds reached to more than 1.5 mg/g of adsorbents.

Solid particulate catalysts comprising bridged metallocenes

Abstract: A polypropylene homopolymer with a melting point of less than 147° C., a percentage of 2.1 errors of at least 1% and a xylene soluble fraction of less than 0.5 wt %.

Toluene Disproportionation and Methylation over Zeolites TNU-9, SSZ-33, ZSM-5, and Mordenite Using Different Reactor Systems

Abstract: An array of zeolites varying in the channel structural design and acidity was investigated in toluene methylation with methanol, together with toluene disproportionation, using fluidized-bed and fixed-bed reactors. The conversions of toluene in the methylation and disproportionation reactions in the fixed-bed reactor were higher than those in the fluidized-bed reactor over the zeolite based catalysts at similar reaction conditions. The unique pore architecture of zeolite TNU-9, with 10-ring channel systems, being slightly larger zeolite compared with ZSM-5, can offer new opportunities for toluene disproportionation, as well as for toluene methylation. The medium pore zeolite TNU-9 was found to possess the highest conversion in toluene disproportionation as compared with other zeolite based catalysts under study. In toluene methylation, the highest toluene conversion was achieved with mordenite based catalyst (MOR-A), while the xylene selectivity follows the order: ZSM-5 > TNU-9 > MOR-A > SSZ-33 > MOR-B. T...

Desilication of MOR zeolite: Conventional versus microwave assisted heating

Abstract: MOR zeolites were modified via desilication treatments with NaOH, under conventional and microwave heating. The samples were characterized by powder X-ray diffraction, 27 Al and 29 Si NMR spectroscopy, TEM and N 2 adsorption at −196 °C. The acidity of the samples and the space available inside the pores were evaluated through a catalytic model reaction, the isomerization of m -xylene, for which the profiles of the coke thermal decomposition were also analyzed. Powder X-ray diffraction and 29 Si and 27 Al MNR results show that in comparison with conventional heating, microwave irradiation (a less time consuming process) leads to identical amount of Si extraction from the zeolite framework. With this treatment, in addition to the customary mesopores development promoted by conventional heating, a partial conversion of the zeolite microporosity into larger micropores, is observed. The microwave irradiated and conventionally heated samples show different catalytic behavior in the m -xylene isomerization model reaction. It was observed that, by controlling the experimental conditions, it is possible to obtain samples with catalytic properties closer to the parent material, which is also confirmed by the respective coke analysis.

Metabolites indicate hot spots of biodegradation and biogeochemical gradients in a high-resolution monitoring well.

Abstract: Anaerobic degradation processes play an important role in contaminated aquifers. To indicate active biodegradation processes signature metabolites can be used. In this study field samples from a high-resolution multilevel well in a tar oil-contaminated, anoxic aquifer were analyzed for metabolites by liquid chromatography-tandem mass spectrometry and time-of-flight mass spectrometry. In addition to already known specific degradation products of toluene, xylenes, and naphthalenes, the seldom reported degradation products benzothiophenemethylsuccinic acid (BTMS), benzofuranmethylsuccinic acid (BFMS), methylnaphthyl-2-methylsuccinic acid (MNMS), and acenaphthene-5-carboxylic acid (AC) could be identified (BFMS, AC) and tentatively identified (BTMS, MNMS). The occurrence of BTMS and BFMS clearly show that the fumarate addition pathway, known for toluene and methylnaphthalene, is also important for the anaerobic degradation of heterocyclic contaminants in aquifers. The molar concentration ratios of metabolites and their related parent compounds differ over a wide range which shows that there is no simple and consistent quantitative relation. However, generally higher ratios were found for the more recalcitrant compounds, which are putatively cometabolically degraded (e.g., 2-carboxybenzothiophene and acenaphthene-5-carboxylic acid), indicating an accumulation of these metabolites. Vertical concentration profiles of benzylsuccinic acid (BS) and methyl-benzylsuccinic acid (MBS) showed distinct peaks at the fringes of the toluene and xylene plume indicating hot spots of biodegradation activity and supporting the plume fringe concept. However, there are some compounds which show a different vertical distribution with the most prominent concentrations where also the precursor compounds peaked.

Structure-reactivity relationship for aromatics transalkylation and isomerization process with TNU-9, MCM-22 and ZSM-5 zeolites, and their industrial implications

Abstract: TNU-9 is a medium pore zeolite with a complex tridimensional channel system. Its catalytic properties have been studied in some reactions that involve the BTX fraction, such as benzene and toluene alkylation with methanol, ethanol or isopropanol. These reactions use in practice medium pore zeolites such as ZSM-5 (MFI) or MCM-22 (MWW), and the selectivities obtained with TNU-9 are compared and analyzed from the point of view of the zeolite structure and pore topology, as well as from its possible industrial application. For benzene alkylation to give ethylbenzene (EB), TNU-9 is an active and selective catalyst with selectivities to EB much higher than ZSM-5 and close to those of the industrially relevant MCM-22. However, olefin oligomerization within the pores of TNU-9 occurs in a larger extension than with MCM-22, leading not only to some lower selectivity, but also to a faster catalyst deactivation. In the case of cumene formation, again the selectivity of TNU-9 to the desired product is higher than ZSM-5 but lower than MCM-22, owing to the formation of larger amounts of n-propylbenzene in the former as a result of its pore topology. Nevertheless, TNU-9 may be worth to be studied further for the disproportionation of toluene to give xylenes. In this case, its comparison with ZSM-5 appears of interest. By studying the alkylation of toluene with alcohols of different chain length, i.e. methanol, ethanol and isopropanol, it has been found that TNU-9 has an antagonistic behaviour, closer to ZSM-5 or MCM-22 depending on the activity or selectivity parameters considered that could be explained by its complex topology, formed by 10-ring tortuous channels with crosses as in ZSM-5, and large cavities as in MCM-22.

Influence of the Eluent in the MIL-53(Al) Selectivity for Xylene Isomers Separation

Abstract: Metal–organic framework MIL-53(Al) pellets were tested for selective adsorption and separation of xylene isomers with the aim of studying the influence of the solvent used at bulk concentrations. In this way, a set of single and multicomponent pulse experiments to measure selectivities was conducted, with iso-octane, n-hexane, and n-heptane as eluents, at 313 K. In order to complete this study, multicomponent breakthrough experiments were also performed, under the same conditions, in the presence of these three eluents, and the obtained selectivities were compared. MIL-53(Al) presented a preference for o-xylene over m-xylene and p-xylene in all experiments. The selectivity was higher when n-heptane was the eluent. For the breakthrough experiments that used n-heptane as the eluent, selectivities of 2.1 were obtained for o-xylene over m-xylene and over p-xylene. It was possible to conclude that the choice of eluent influences the adsorption selectivity and capacity of the adsorbent. This could result, among...

Equilibrium for the Reactive Extraction of Caproic Acid Using Tri-n-butyl Phosphate in Methyl Isobutyl Ketone and Xylene

Abstract: The recovery of caproic acid from the aqueous stream is of practical relevance due to its market value and the stringent environmental standards. The profound success of reactive extraction has bee...

Characterization of Aromatic Hydrocarbon Rading Bacteria from Petroleum Contaminated Sites

Abstract: Aromatic hydrocarbons such as benzene, hexane, toluene, naphthalene and xylene degrading bacteria such as Flavobacterium spp.1 & 2 and Pseudomonas spp.1 & 2 were isolated from petroleum contaminated soil samples. They were resistant to heavy metals such as lead, iron, zinc, cobalt and mercury. The optimum pH for hydrocarbon degradation by Flavobacterium spp.1 was 9. Flavobacterium spp.2, Pseudomonas spp.1 & 2 have shown optimum pH 7 for their degradation. The optimum temperature for hydrocarbon degradation by Flavobacterium spp.1 & 2 and Pseudomonas spp.1 & 2 were at 40˚C & 45˚C.

Selective Liquid Phase Adsorption and Separation of ortho-Xylene with the Microporous MIL-53(Al)

Abstract: Metal-organic framework MIL-53(Al) pellets were tested for the selective adsorption and separation of xylene isomers, in liquid phase and using n-heptane as eluent. The objective of this work is to assess relevant data for a posterior xylene isomers separation process design. In order to complete this study, single and multi-component breakthrough experiments were performed at 313 K, in the presence of n-heptane. MIL-53(Al) presented a preference for o-xylene over m-xylene and p-xylene in all experiments. The selectivities of 2.0 were obtained for o-xylene over m-xylene and over p-xylene. It is concluded that MIL-53(Al) may be used for separating o-xylene from the other xylene isomers, using n-heptane as desorbent. Supplemental materials are available for this article. Go to the publisher's online edition of Separation Science & Technology to view the free supplemental file.

Separation of xylene isomers through adsorption on microporous materials: a review

Abstract: Xylene is an aromatic hydrocarbon with a single ring and two methyl groups attached to this ring in positions 1-2, 1-3 and 1-4, called o-xylene, m-xylene, and p-xylene, respectively. Because of the similarities in their physicochemical properties, it is very difficult to obtain these isomers in a pure form. For this reason, numerous techniques have been developed with the objective of separating them. One technique is based on the adsorption of substances according to the adsorption heat observed during their interaction with the adsorbent. This review presents the main studies developed in recent years that seek to evaluate the potential of microporous materials in separating the different xylene isomers.

Catalytic transformation of methyl benzenes over zeolite catalysts

Abstract: Catalytic transformation of three methyl benzenes (toluene, m -xylene, and 1,2,4-trimethyl benzene) has been investigated over ZSM-5, TNU-9, mordenite and SSZ-33 catalysts in a novel riser simulator at different operating conditions. Catalytic experiments were carried out in the temperature range of 300–400 °C to understand the transformation of these alkyl benzenes over large pore (mordenite and SSZ-33) in contrast to medium-pore (ZSM-5 and TNU-9) zeolite-based catalysts. The effect of reaction conditions on the isomerization to disproportionation product ratio, distribution of trimethylbenzene (TMB) isomers, and p -xylene/ o -xylene ratios are reported. The sequence of reactivity of the three alkyl benzenes depends upon the pore structure of zeolites. The zeolite structure controls primarily the diffusion of reactants and products while the acidity of these zeolites is of a secondary importance. In the case of medium pore zeolites, the order of conversion was m -xylene > 1,2,4-TMB > toluene. Over large pore zeolites the order of reactivity was 1,2,4-TMB > m -xylene > toluene for SSZ-33 catalyst, and m -xylene ∼ 1,2,4-TMB > toluene over mordenite. Significant effect of pore size between ZSM-5 and TNU-9 was observed; although TNU-9 is also 3D 10-ring channel system, its slightly larger pores compared with ZSM-5 provide sufficient reaction space to behave like large-pore zeolites in transformation of aromatic hydrocarbons. We have also carried out kinetic studies for these reactions and activation energies for all three reactants over all zeolite catalysts under study have been calculated.

Low‐temperature growth of multi‐walled carbon nanotubes by thermal CVD

Abstract: Low-temperature thermal chemical vapor deposition (thermal CVD) synthesis of multi-walled carbon nanotubes (MWCNTs) was studied using a large variety of different precursor compounds. Cyclopentene oxide, tetrahydrofuran, methanol, and xylene: methanol mixture as oxygen containing heteroatomic precursors, while xylene and acetylene as conventional hydrocarbon feedstocks were applied in the experiments. The catalytic activity of Co, Fe, Ni, and their bi-as well as tri-metallic combinations were tested for the reactions. Low-temperature CNT growth occurred at 400 degrees C when using bi-metallic Co-Fe and tri-metallic Ni-Co-Fe catalyst (on alumina) and methanol or acetylene as precursors. In the case of monometallic catalyst nanoparticles, only Co (both on alumina and on silica) was found to be active in the low temperature growth (below 500 degrees C) from oxygenates such as cyclopentene oxide and methanol. The structure and composition of the achieved MWCNTs products were studied by scanning and transmission electron microscopy (SEM and TEM) as well as by Raman and X-ray photoelectron spectroscopy (XPS) and by X-ray diffraction (XRD). The successful MWCNT growth below 500 degrees C is promising from the point of view of integrating MWCNT materials into existing IC fabrication technologies. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Complete catalytic oxidation of o-xylene over CeO2 nanocubes.

Abstract: The activities of CeO 2 nanocubes calcined at different temperatures were tested for catalytic oxidation of o -xylene. Using CeO 2 nanocubes as catalysts, complete catalytic oxidation of o -xylene was achieved below 210°C. The CeO 2 nanomaterials were characterized by means of BET, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). From the TEM images, all CeO 2 nanocubes displayed cubic morphology irrespective of calcination temperature. The HRTEM images revealed that these nanocubes were enclosed by reactive {001} planes, which may contribute to the intrinsically catalytic property of o -xylene oxidation. The higher activity of CeO 2 nanocubes calcined at 550°C than those calcined at above 550°C was attributed to their smaller crystallite size and larger surface area. The influences of reaction conditions were also studied, which found that a higher reaction temperature was necessary for complete catalytic oxidation of o -xylene at higher weight hourly space velocity (WHSV) and o -xylene concentration.

Continuous synthesis of multiwalled carbon nanotubes from xylene using the swirled floating catalyst chemical vapor deposition technique

Abstract: This work reports the continuous and large-scale production of multiwalled carbon nanotubes (MWCNTs) from xylene/ferrocene in a swirled floating catalyst chemical vapor deposition reactor using argon as the carrier gas. The concentration of ferrocene used was 0.01 g/mL of xylene. In every run, 50-mL xylene gas was used together with xylene/ferrocene mixture injected into the reactor by means of a burette. The MWCNTs produced were characterized using the transmission electron microscopy (TEM) and Raman spectra. TEM analysis showed a poor production rate at 850 °C and a good production in the range of 900–1000 °C with optimal production rate at 950 °C. Furthermore, xylene/ferrocene mixture produced more MWCNTs at 950 °C with H:Ar (1:7) as the carrier gas. The diameters of the MWCNTs in the temperatures studied ranged from 15 to 95 nm with wall thicknesses between 0.5 and 0.8 nm.