Benzene Toluene Research Articles

Comparison of the efficiencies of modified clay with polyethylene glycol and tetradecyl trimethyl ammonium bromide for BTEX removal

Aims: In this study, the effectiveness of modified clay [montmorillonite (Mt)] with polyethylene glycol (PWG) and tetradecyl trimethyl ammonium bromide (TTAB) on the benzene, toluene, ethylbenzene and xylene (BTEX) removal from aqueous solution was investigated.Materials and Methods: The batch adsorption experiments including surfactant loading rates (0.2-4 cation exchange capacity [CEC] of the clay), contact time (0-24 h), pH (4-12) and adsorbate concentration (10-200 mg/L) were conducted at room temperature (25°C) with 100 mL of BTEX solution into a 200-mL conical flask and mixed by an orbital shaker (250 rpm for 24 h). Results: It was found that the optimum adsorption condition obtains for the surfactant loading rate of 200% clay CEC for both the adsorbents at the contact time of 24 h. The sorption capacity of BTEX by both the adsorbents was in order of benzene toluene ethylbenzene xylene. The results of both the adsorbents also showed that the pseudo-second-order kinetic model and Freundlich isotherm model fitted the experimental data better than of other kinetic and isotherm models, respectively.Conclusion: The adsorption capacity of TTAB-Mt (22.11 mg/g) was slightly higher than PEG-Mt (18.77 mg/g). With regard to lower toxic effects and lower cost of nonionic surfactants than the cationic type, using the nonionic modified Mt is preferred than cationic modified Mt for the removal of BTEX from aqueous solution.

Aromatization of Cyclopentane Over ZSM-5 Catalysts: A Proposal of Reaction Pathway

The conversion of cyclopentane over HZSM-5 and GaZSM-5 was studied at 500–600°C in a fixed bed flow reactor. The reaction over HZSM-5 showed that cyclopentane was first cracked to liquified petroleum gas (LPG) that consecutively aromatized to BTX and C9+ aromatics. While over GaZSM-5, cyclopentane preferred to oligomerize to larger intermediate namely cyclic hydrocarbon pool that could be converted to C9+ aromatics and then cracked to benzene toluene and xylene and LPG. The higher activity was obtained by lowering Si/Al ratio of the parent HZSM-5 and increasing reaction temperature.

Production of IL-10, TNF and IL-12 by Peripheral Blood Mononuclear Cells in Mexican Workers Exposed to a Mixture of Benzene–Toluene–Xylene

Occupational exposure to low-level benzene and the joint action of toluene-xylene probably cause effects on circulating monocytes immune response. We undertook this study to determine relationship between occupational exposure to benzene-toluene-xylene mixture (BTX) and IL-10, TNF and IL-12 production by peripheral blood mononuclear cells. Exposure was estimated in 54 workers from a paint company in Mexico City through BTX accumulated potential dose (BTX-APD). Two exposure groups were formed: high and low BTX-APD established with a cutoff point at ≥1.0 of BTX-APD, as a function of the geometric mean of the estimator's value distribution and the higher agreement between BTX-APD ≥1.0 and the areas referred as using (or not) organic solvents in the work process. IL-10, TNF and IL-12 concentrations were measured with ELISA. Through multiple linear regression models, the production of each of the proposed cytokines and of the whole set was assessed. Workers with high BTX-APD showed a significant reduction in TNF production (β = -1,196.0 pg/mL; p = 0.01); a reduction for IL-10 (β = -520.3; p = 0.13) and IL-12 (β = -843.3; p = 0.09) was also observed, although without statistical significance. TNF production assessed in workers with a high BTX-APD is lower than in those with a low BTX-APD, but not in IL-10 and IL-12 production.

Dynamic optimization of a dividing-wall column using model predictive control

Dividing-wall column (DWC) is one of the best examples of process intensification, as it can bring significant reduction in the capital invested as well as savings in the operating costs. Conventional ternary separations progressed from the (in-)direct sequences to thermally coupled columns such as Petlyuk configuration, and later to the DWC compact design that integrates the two distillation columns into a single shell. Nevertheless, this integration leads also to changes in the control and operating mode due to the higher number of degrees of freedom.In this work we explore the dynamic optimization and advanced control strategies based on model predictive control (MPC), coupled or not with PID. These structures were enhanced by adding an extra loop controlling the heavy component in the top of the feed side of the column, using the liquid split as manipulated variable, thus implicitly achieving energy minimization. To allow a fair comparison with previously published references, this work considers as a case-study the industrially relevant separation of the mixture benzene–toluene–xylene (BTX) in a DWC.The results show that MPC leads to a significant increase in performance, as compared to previously reported conventional PID controllers within a multi-loop framework. Moreover, the optimization employed by the MPC efficiently accommodates the goal of minimum energy requirements – possible due to the addition of an extra loop – in a transient state. The practical benefits of coupling MPC with PID controllers are also clearly demonstrated.

Hybrid organic–inorganic phenyl stationary phases for the gas separation of organic binary mixtures

Organic–inorganic hybrid silica xerogels are versatile materials that can be used in the separation/purification of gases and vapours. In the present study, hybrid xerogels were synthesised at pH 10 using phenyltriethoxysilane (PhTEOS) and tetraethoxysilane (TEOS) as silica precursors with 20, 40 and 70% PhTEOS molar ratios. The xerogels were characterised by helium pycnometry, FTIR, TGA–DSC, N 2 (77 K) and CO 2 (273 K) adsorption analyses. The retention time and selectivity of several binary mixtures were measured, including benzene–toluene, m-xylene–benzene, m-xylene–toluene, water–ethanol, and carbon tetrachloride–dichloromethane. The characterisation results reveal that the hybrid xerogels were mainly macroporous. For each adsorbate–adsorbent system, the retention time decreased with an increase in temperature, ruling out that activated diffusion was the primary mechanism of separation. The xerogel synthesised from 40% PhTEOS presented the greatest potential for the resolution of binary mixtures. It represents a trade-off between surface area and phenyl-group surface density. Aromatic substances had a stronger affinity for the hybrid xerogels than the other analytes due to the strong interaction between phenyl groups on the analyte and the stationary phase. Water–ethanol mixtures were effectively separated by the xerogel derived from 70% PhTEOS.

Aromatization of alkanes over Pt promoted conventional and mesoporous gallosilicates of MEL zeolite

Aromatization of hexane and propane was investigated over Pt promoted mesoporous gallium-containing HZSM-11 with controlled mesoporosity generated by desilication. Prepared catalysts were characterized by nitrogen adsorption, X-ray powder diffraction, scanning electron microscopy, Fourier transform infrared of chemisorbed pyridine, and NH 3 temperature programmed desorption confirming the development of intracrystalline mesoporosity of Ga-containing HZSM-11. The catalytic activities, which were compared in the aromatization of n-hexane and propane, increased upon desilication. The aromatization of n-hexane decreased in the following order, Pt/mesoporous GaZSM-11 ≫ Pt/conventional GaZSM-11 ≫ mesoporous GaZSM-11 > conventional GaZSM-11. Hexane conversion reached 70.1% over mesoporous Pt/GaZSM-11 with Si/Ga of 61, as compared with 29.6 and 24.9% for corresponding mesoporous and conventional GaZSM-11 (Si/Ga = 94), respectively, for experiments at liquid hour space velocity of 3.6 h −1, and 540 °C. Comparison of BTX (benzene–toluene–xylene) selectivity at the conversion level of ∼21.0% revealed that Pt/mesoporous GaZSM-11 is more selective than corresponding mesoporous and conventional GaZSM-11. The BTX selectivity over Pt/mesoporous GaZSM-11 (Si/Ga = 94), which showed strong dependence on the conversion, reached 28.2%, whereas over corresponding mesoporous and conventional GaZSM-11catalysts reached 19.1% and 5.5%, respectively. A higher conversion and better selectivity can be attributed to the improved accessibility to the active extra-framework Ga species owing to the generation of mesopores inside the zeolite particles and shortening the contact time. It is worth mentioning that the prepared catalysts exhibited quite low activity in propane aromatization but exhibiting similar trends as for hexane aromatization.

High-purity control of internal thermally coupled distillation columns based on nonlinear wave model

Internal thermally coupled distillation column (ITCDIC) is a frontier of energy saving distillation researches, which is a great improvement on conventional distillation column (CDIC). However its high degree thermal coupling makes the control design a bottleneck problem, where data-driven model leads to obvious mismatch with the real plant in the high-purity control processes, and a first-principle model which is comprised of complex mass balance relations and thermally coupled relations could not be directly used as control model for the bad online computing efficiency. In the present work, wave theory is extended to the control design of ITCDIC with variable molar flow rates, where a general nonlinear wave model of ITCDIC processes based on the profile trial function of the component concentration distribution is proposed firstly; combined with the thermally coupled relations, a novel wave model based generic model controller (WGMC) of ITCDIC processes is developed. The benzene–toluene system for ITCDIC is studied as illustration, where WGMC is compared with another generic model controller based on a data-driven model (TGMC) and an internal model controller (IMC). In the servo control and regulatory control, WGMC exhibits the greatest performances. Detailed research results confirm the efficiency of the proposed wave model and the advantage of the proposed WGMC control strategy.

Energy efficient control of a BTX dividing-wall column

Dividing-wall column (DWC) is considered nowadays the new champion in distillation, as it can bring substantial reduction in the capital invested as well as savings in the operating costs. This work presents the simulation results of energy efficient control and dynamics of a dividing-wall column (DWC). In order to allow a fair comparison of the results with previously published references, the case-study considered here is the industrially relevant ternary separation of the mixture benzene–toluene–xylene (BTX) in a DWC. Rigorous simulations were carried out in Aspen Plus and Aspen Dynamics. Several conventional control structures based on PID control loops ( DB/ LSV, DV/ LSB, LB/ DSV, LV/ DSB) were used as a control basis. These control structures were enhanced by adding an extra loop controlling the heavy component composition in the top of the prefractionator, by using the liquid split as an additional manipulated variable, thus implicitly achieving minimization of energy requirements. The results of the dynamic simulations show relatively short settling times and low overshooting especially for the DB/ LSV and LB/ DSV control structures. Moreover, the energy efficient control proposed in this work allows the operation of DWC with minimum energy requirements or maximum purity of products.

ESTIMATION OF MASS TRANSFER COEFFICIENTS IN A PACKED DISTILLATION COLUMN USING BATCH MODE

This research adopts the estimation of mass transfer coefficient in batch packed bed distillation column as function of physical properties, liquid to vapour molar rates ratio (L / V), relative volatility (α), ratio of vapour and liquid diffusivities (DV / DL), ratio of vapour and liquid densities (ρV / ρL), ratio of vapour and liquid viscosities (μV/ μL).The experiments are done using binary systems, (Ethanol Water), (Methanol Water), (Methanol Ethanol), (Benzene Hexane), (Benzene Toluene). Statistical program (multiple regression analysis) is used for estimating the overall mass transfer coefficient of vapour and liquid phases (KOV and KOL) in a correlation which represented the data fairly well.
 KOV = 3.3 * 10-10 α-0.7 (DV / DL) 0.65 (L / V) 3.5 (ρV / ρL) 1.25 (μV / μL) -5.0
 KOL = 2.8 * 10-6 α-0.95 (DV / DL) 0.03 (L / V) 1.15 (ρV / ρL )0.077 (μV / μL) -0.9
 In this research a method where the resistances to mass transfer in both phases are accounted for separately through the use of HTU-NTU model for each phase
 Z=HTUOV.NTUOV and Z=HTUOL.NTUOL
 Results show that both overall vapour and liquid mass transfer coefficient are increased with liquid to vapour molar rates ratio, vapour to liquid diffusivities ratio and vapor to liquid densities ratio, but decreased with increasing the relative volatility and vapour to liquid viscosities ratio.

Degradation of a benzene–toluene mixture by hydrocarbon-adapted bacterial communities

We examined the rate of degradation of a benzene–toluene mixture in aerobic microcosms prepared with samples of an aquifer that lies below a petrochemical plant (SIReN, UK). Five samples exposed to different concentrations of benzene (from 0.6 to 317 mg l−1) were used. Fast degradation (approx. 1–6 mg l−1 day−1) of both contaminants was observed in all groundwater samples and complete degradation was recorded by the seventh day except for one sample. We also identified the microbial community in each of the samples by culture-independent techniques. Two of the less impacted samples harbour the aerobic benzene degrader Pseudomonas fluorescens, while Acidovorax and Arthrobacter spp. were found in the most polluted sample and are consistent with the population observed in situ. Hydrogenophaga was found in the deepest sample while Rhodoferax spp. were recovered in an alkaline sample (pH 8.4) and may also be implicated in benzene degradation. Time series analysis shows that each of the samples has a different community but they remain stable over the degradation period. This study provides new information on a well not previously studied (no. 309s) and confirms that adapted communities have the ability to degrade hydrocarbon mixtures and could be used in further bioaugmentation approaches in contaminated sites.

Effects of co-exposure of benzene, toluene and xylene to Drosophila melanogaster: Alteration in hsp70, hsp60, hsp83, hsp26, ROS generation and oxidative stress markers

Benzene, toluene and xylene are monocyclic aromatic hydrocarbon compounds, used both as individual compound and as mixtures, in industry as well as household. Previous studies involving exposures to these compounds, individually, have shown that benzene was more toxic compared to toluene or xylene. Here, we tested a working hypothesis that toluene and/or xylene in a mixture containing benzene affect benzene induced toxicity in a non-target organism, Drosophila melanogaster. We exposed D. melanogaster larvae transgenic for hsp70, hsp83 or hsp26 and wild type (Oregon R strain) larvae to 25.0–100.0 mM benzene, 25.0–100.0 mM toluene and 25.0–100 mM xylene, individually or in mixtures. Subsequently, we examined the expression of stress genes (encoding heat shock proteins, hsps), generation of reactive oxygen species (ROS), induction of anti-oxidant stress markers and emergence of flies under treatment as well as control conditions. We observed that all these endpoints were significantly altered in all the treatment groups compared to their respective controls. However, the magnitude of toxicity of a benzene–toluene (BT) or benzene–xylene (BX) or benzene–toluene–xylene (BTX) mixture was significantly lower in the organism than that of individual chemical. Our results also show the modulation of toluene toxicity by xylene. Present study suggests antagonistic effect of xylene and toluene on benzene toxicity and additive/synergistic effect of xylene on toluene induced toxicity. Thus, expression of stress genes may be used as an assay for detection of early cellular toxicity. Further, our study supports the use of Drosophila as an alternative animal model for first tier screening of adverse effects of chemical mixtures.

Degradability of the three dimethyl phthalate isomer esters (DMPEs) by a Fusarium species isolated from mangrove sediment

Dimethyl phthalate esters (DMPEs) are common plasticizersand additives to improve flexibility and softness of plastic products(Cartwright et al., 2000; Wang et al., 2004; Xu et al., 2005). ThreeDMPE-isomers, namely dimethyl phthalate (ortho-DMP; ortho-arrangement of the two carboxyl groups), dimethyl isophthalate(DMI; meta-) and dimethyl terephthalate (DMT; para-), display dif-ferent physical and chemical properties and are used in differentindustrial applications. DMP is used as a plasticizer in cellulose es-ter-based plastics (cellulose acetate and cellulose butyrate; Stapleset al., 1997). In polyester-based products, such as tape for VCR cas-settes, synthetic textile fibers etc., DMI and DMT are used as inter-mediates for their synthesis (Lee et al., 1999; Wang and Gu,2006a,b). Phthalate esters (PAEs) occur ubiquitously in both aqua-tic and terrestrial environments (Gu et al., 2005), and foods (Peter-sen and Breindahl, 2000). Because they do not bond covalentlywith the resin, leaching and migration of PAEs from plastic materi-als into the environment are of major concern for the potentialhealth problems associated with these chemicals. PAEs may actas endocrine disruptors affecting the normal function of the repro-ductive system and development of humans and animals at verylow concentrations (Jobling et al., 1995; Colon et al., 2000; Guet al., 2005; Xu et al., 2005). As a result, six PAEs including DMPare listed as priority pollutants by the United States EnvironmentalProtection Agency (Gu et al., 2005).It is suggested that complete degradation of PAEs in the envi-ronment is via microbial mineralization (Staples et al., 1997; Guet al., 2005). Degradation of PAEs has been well documented inbacteria. Various PAE-degrading bacteria have been isolated fromactivated sludge, mangroves, soils, rivers, and the marine environ-ment (Vegaand Bastide, 2003; Changet al., 2004; Gu et al., 2005; Liet al., 2005a,b; Xu et al., 2005; Wang and Gu 2006a,b; Fang et al.,2007). Both Gram-positive and Gram-negative bacteria are respon-sible for the aerobic degradation of phthalic acid (PA) via differentpathways (Chang and Zylstra, 1998; Stingley et al., 2004). Severalfunctional operons involved in the metabolism of PA have beenidentifiedand characterizedin Arthrobacter keyseri12B, Mycobacte-rium vanbaaleniiPYR-1, Burkholderia cepacia DBO1 and other bacte-rial strains (Chang and Zylstra, 1998; Eaton, 2001; Stingley et al.,2004). However, degradation of PAEs by fungi has rarely beenshown. Fungi have been demonstrated to be potential degradersof a wide range of recalcitrant compounds, including polycyclicaromatic hydrocarbons (PAHs), benzene–toluene–ethylbenzene–xylenes (BTEX), chlorophenols, polychlorinated biphenyl, muni-tions waste, and pesticides (Tortella et al., 2005). Nevertheless,degradation of PAEs by fungi has been studied only to a limited ex-tent with Aspergillus niger and Sclerotium rolfsii (Sivamurthy et al.,1991; Ganji et al., 1995; Pradeepkumar et al., 2000). The role offungi on the environmental fate of PAEs remains largely unknown.Coastal wetlands, such as mangroves, are usually sinks of pollu-tants from the aquatic system (Tam et al., 2001; Ke et al., 2005).Mangrove microorganisms may play an important role in the fateoforganicpollutantsinaquaticenvironments.Anumberofbacterialspecies capable of degrading PAEs have been isolated from man-grove sediments, such as Pseudomonas fluorescens, Rhodococcus ru-ber, Pasturella multocida, and Sphingomonas paucimobilis (Li et al.,2005a,b;Xuetal.,2005;LiandGu,2006).However,therearenore-ports concerned with the degradation of PAEs by mangrove fungi.The Futain Mangrove Nature Reserve of Shenzhen, China, is on thesouthern border of Shenzhen, one of the cities with the most rapideconomic development in China. The Reserve is under increasingpollution pressure derived from intense urbanization of the city,The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only thosepapers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 42, 703–704).

Pd/Al 2O 3 catalyst for selective hydrogenation of benzene in benzene–toluene mixture

Pd/Al2O3 demonstrates (in comparison with Pt/Al2O3 and Ni/Al2O3) higher selectivity toward benzene hydrogenation in competitive hydrogenation of a benzene–toluene mixture, which can be enhanced (up to 76%) by the increase of overall reaction pressure up to 37 atm.

Analysis of mixtures of organic volatile compound in water by MIMS. Semiquantitative evaluation of data

Chemometric analysis of intensities of ion currents measured by MIMS was demonstrated on two mixtures: nonpolar mixture containing benzene–toluene–p-xylene (set I) and polar mixture containing methanol–ethanol–propan-1-ol (set II), both in water solutions. The acquired MIMS data were evaluated off-line using Solver, a tool of Microsoft Excel and then verified by calculation of relative concentrations of components in mixtures. For evaluation we considered the additivity of ion currents coming from fragmentation of components, independent vapor permeation of components through membrane and unimolecular conditions in ion source of MS. By using this evaluation analysis it is possible to determine relative concentrations of organic substances in mixture, which penetrated through the membrane, without any separation. Set I penetrated according to the model analysis and the obtained relative concentrations were in reasonable agreement with the preset values. On the contrary, for set II the agreement of adjusted and calculated relative concentrations was not achieved due to high dielectric permittivity of alcohols.

First steps of the reactions of alkanes and arenes with adamantyl cations in sulfuric acid in comparison with other reagents

Solutions of 1-adamantanol in sulfuric acid at T 85%) and arenes (ArH, [H2SO4] > 59%). The data on the kinetics, kinetic isotope effect (KIE), effects of the structure of RH and ArH and acidity of the medium, and the observation of 1,4-cis-dimethylcyclohexane isomerization indicate that adamanyl cations (Ad+) serve as reactive species. In the reactions with alkanes, the Ad+ cation abstracts the hydride ion from RH in the rate-determining step. Compensation dependences appear between the activaion parameters for the KIE and “effect 5/6” (ratio of the rate constants for the C–H bond cleavage in cyclopentane and cyclohexane) in the reactions of cycloalkanes with Ad+ and other electrophilic reagents, such as “anthracene” (An2)H+ and hydroxymethyl (CH2OH)+ cations and HgII ions, including the points of the lower selectivity limit (kH/kD) = 1.4, (“5/6”) = 1. In the reactions with the Ad+ cation, the bond selectivity 30: 20 of alkanes is higher, while 20: 20 is lower compared to other reagents. In the first case, the selectivity is probably determined predominantly by the energies of the cleaved C–H bonds, whereas in the second case it is determined by steric hindrances. Judging by the kinetic and selectivity data in the series benzene—toluene—o-xylene—m-xylene and the absence of the reaction with p-xylene, mesitylene, and pseudocumene, it can be concluded that the main contribution to the Ad+ + ArH interaction is made by adamantylation to the para- and meta-positions of the benzene ring, whereas the ortho-positions are inaccessible to the attack because of steric hindrances.

In-well air sparging efficiency in remediating the aquifer of a petroleum refinery site

Air sparging represents an innovative groundwater remediation technology, which has been proved to be capable of restoring aquifers that have been polluted by volatile and (or) biodegradable contaminants, such as petroleum hydrocarbons. This paper presents the design, the installation, and the pulsed operation of an in-well air sparging system at the site of a Greek petroleum refinery. The geographical position, the hydrologeoly, and the contamination features of the chosen study area develop special conditions that, along with the fact that the existing refinery is still active, greatly determine the applicability and the effectiveness of the specific technology. The area that was used for the application of the technology covered almost 600 m2 and included five air injection wells and four additional monitoring wells. The pulsed operation of the installed system lasted about 5 months and the results of frequent groundwater sampling and analysis indicate an important decline in total petroleum hydrocarbons (TPH) and benzene–toluene–ethylbenzene–xylene (BTEX) concentrations (up to 99%). However, prior to any attempt to expand the application of air sparging within the facilities of the refinery, special attention should be given to the eccentricities of the site and the ability of the technology to confront more persistent contaminants, such as methyl tertiary-butyl ether (MTBE).

Competitive Nitration of Benzene–Fluorobenzene and Benzene–Toluene Mixtures: Orientation and Reactivity Studies Using HPLC

In this experiment for the first-year organic laboratory mixtures of benzene�toluene and benzene�fluorobenzene are competitively nitrated using HNO3�acetic anhydride to determine the reactivity and orientation effects of CH3 and F, respectively. This experiment accomplishes the goals of studying these effects in a single laboratory session and using HPLC to analyze the reaction mixtures. Approximately one-half of the students nitrate the benzene�toluene mixture and find that the CH3 group activates and directs ortho�para. The other half nitrate the benzene�fluorobenzene mixture and find that fluorine deactivates slightly and directs ortho�para with a ratio much less than the statistically expected 2:1 value.

A nonequilibrium model for distillation processes

AbstractA general thermodynamic model is developed by combining organically the nonequilibrium thermodynamic analysis with the traditional METSH simulation of distillation processes. The model is capable of both simulating industrial distillation processes and analyzing energy consumptions of the processes. The benzene–toluene binary distillation is selected as the model system to test the theory, and the industrial‐scale tray column is studied in this work. The simulation results show that the tray structure and operation parameters have significantly influenced the entropy generation rate (EGR). It is also found that the development of vapor and liquid flow patterns on the industrial‐scale trays can enhance tray efficiency and result in evident reduction of the EGR. The model is suitable for tray design, column performance analysis, and energy consumption evaluation of distillation processes. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

Hydrothermal vent fluids from Middle Valley, a sediment-covered vent field located on the northern Juan de Fuca Ridge, were sampled in July, 2000. Eight different vents with exit temperatures of 186–281 °C were sampled from two areas of venting: the Dead Dog and ODP Mound fields. Fluids from the Dead Dog field are characterized by higher concentrations of ΣNH 3 and organic compounds (C 1–C 4 alkanes, ethene, propene, benzene and toluene) compared with fluids from the ODP Mound field. The ODP Mound fluids, however, are characterized by higher C 1/(C 2 + C 3) and benzene:toluene ratios than those from the Dead Dog field. The aqueous organic compounds in these fluids have been derived from both bacterial processes (methanogenesis in low temperature regions during recharge) as well as from thermogenic processes in higher temperature portions of the subsurface reaction zone. As the sediments undergo hydrothermal alteration, carbon dioxide and hydrocarbons are released to solution as organic matter degrades via a stepwise oxidation process. Compositional and isotopic differences in the aqueous hydrocarbons indicate that maximum subsurface temperatures at the ODP Mound are greater than those at the Dead Dog field. Maximum subsurface temperatures were calculated assuming that thermodynamic equilibrium is attained between alkenes and alkanes, benzene and toluene, and carbon dioxide and methane. The calculated temperatures for alkene–alkane equilibrium are consistent with differences in the dissolved Cl concentrations in fluids from the two fields, and confirm that subsurface temperatures at the ODP Mound are hotter than those at the Dead Dog field. Temperatures calculated assuming benzene–toluene equilibrium and carbon dioxide–methane equilibrium are similar to observed exit temperatures, and do not record the hottest subsurface conditions. The difference in subsurface temperatures estimated using organic geochemical thermometers reflects subsurface cooling processes via mixing of a hot, low salinity vapor with a cooler, seawater salinity fluid. Because of the disparate temperature dependence of alkene–alkane and benzene–toluene equilibria, the mixed fluid records both the high and low temperature equilibrium conditions. These calculations indicate that vapor-rich fluids are presently being formed in the crust beneath the ODP Mound, yet do not reach the surface due to mixing with the lower temperature fluids.

Competitive adsorption of a benzene–toluene mixture on activated carbons at low concentration

Previous studies of the adsorption of benzene and toluene at low concentration showed that both porosity and surface chemistry of the activated carbon play an important role. This paper analyses the adsorption behaviour of a mixture of VOCs (benzene–toluene) on AC, due to the lack of information regarding the adsorption of mixtures. Thus, the performance of chemically activated carbons, physically activated carbon with steam and commercial samples is studied. This study shows that chemically activated carbons have better performance than the other samples, showing much higher adsorption capacities, breakthrough times and separation times. Porosity is a key factor and those activated carbons with higher volumes of micropores exhibit higher adsorption capacities and breakthrough times. This work also analyses the state of the adsorbed phase resulting from the mixture adsorption and comparison of the composition of the adsorbed hydrocarbons with that predicted by the ideal adsorption solution theory (IAST), shows good agreement.