Seasonal and Spatial Variation of Polycyclic Aromatic Hydrocarbons in Vapor-Phase and PM2.5 in Southern California Urban and Rural Communities

Fifteen priority polycyclic aromatic hydrocarbons (PAHs) were measured in two rural communities (Atascadero and Lompoc) located several hundred km northwest of Los Angeles and in four urban communities 40–100 km downwind of Los Angeles (San Dimas, Upland, Mira Loma, and Riverside), during all seasons, from May 2001 to July 2002. PM_2.5 and vapor-phase PAHs were collected, on prebaked quartz fiber filters and PUF-XAD-4 resin, respectively, at 113 LPM, during 24 h periods, every eighth day, and quantified by HPLC-Fluorescence. At all sites vapor-phase PAHs contained > 99.9% of the total PAH mass and were dominated by naphthalene (NAP), which varied from about 60 ng m ^{? 3} in Lompoc, a community with light traffic, to ～580 ng m ^{? 3} in Riverside, a community traversed by ～200,000 vehicles day^{? 1}. During summer pollution episodes in urban sites, NAP concentrations reached 7–30 times annual averages. Except for summer episodes, concentrations of low MW PAHs showed small seasonal variations (～2 times higher in winter). Similar concentrations of particle-phase PAHs were observed at all sites except for Lompoc. Benzo[ghi]perylene (BGP), a marker of gasoline exhaust emissions, showed the highest concentration among particle-phase PAHs, varying from 23.3 pg m^?3 in Lompoc to 193 pg m^?3 in Mira Loma. Benzo[a]pyrene and indeno[1,2,3-cd]pyrene, found exclusively in the particle phase, were much higher in urban sites (～40–100 pg m^?3), than in Lompoc (～12 pg m^?3). Winter particle-phase PAHs were 2 to 14 times higher than summer levels. Particle-phase PAHs were negatively correlated with mean air temperature in urban sites (r = ?0.50 to ?0.75), probably resulting from surface inversions occurring during winter. The data suggest that in Southern California vehicular exhaust emissions are a major contributor to particle-phase PAHs.     

Electrochemical stability of carbon nanofibers in proton exchange membrane fuel cells

This fundamental study deals with the electrochemical stability of several non-conventional carbon based catalyst supports, intended for low temperature proton exchange membrane fuel cell (PEMFC) cathodes. Electrochemical surface oxidation of raw and functionalized carbon nanofibers, and carbon black for comparison, was studied following a potential step treatment at 25.0 °C in acid electrolyte, which mimics the operating conditions of low temperature PEMFCs. Surface oxidation was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Cyclic voltammograms clearly showed the presence of the hydroquinone/quinone couple. Furthermore, identification of carbonyl, ether, hydroxyl and carboxyl surface functional groups were made by deconvolution of the XPS spectra. The relative increase in surface oxides on carbon nanofibers during the electrochemical oxidation treatment is significantly smaller than that on carbon black. This suggests that carbon nanofibers are more resistant to the electrochemical corrosion than carbon black under the experimental conditions used in this work. This behaviour could be attributed to the differences found in the microstructure of both kinds of carbons. According to these results, carbon nanofibers possess a high potential as catalyst support to increase the durability of catalysts used in low temperature PEMFC applications.     

Use of peroxyacetic acid as green chemical on yield and sensorial quality in Watercress (Nasturtium officinale R. Br.) under soilless culture

The goal of this research was to evaluate the effect of different doses of peroxyacetic acid on the productivity of watercress (Nasturtium officinale R. Br.) cultivated hydroponically using a constant nutritive solution. Green chemistry in protected horticulture seeks compatibility with the environment through the creation of biodegradable byproducts. In hydroponics, appropriate doses of peroxyacetic mixtures deliver these byproducts while also oxygenating the roots. Watercress producers who recirculate the nutritive solution can use these mixtures in order to increase oxygenation in the hydroponic system. The experiment took place between August and December 2009, beginning with the planting of the watercress seeds and concluding with the completion of the sensory panels. A completely random design was used, including three treatments and four repetitions, with applications of 0, 20 and 40 mg L(-1) of the peroxyacetic mixture. Measured variables were growth (plant height, leaf length and stem diameter), yield (weight per plant and dry matter) and organoleptic quality (color and sensory panel). The application of 40 mg L(-1) of the peroxyacetic mixture had a greater effect on the growth and development of the plants, which reached an average height of 29.3 cm, stem diameter of 3.3 mm and leaf length of 7.6 cm, whereas the control group reached an average height of only 20.2 cm, stem diameter of 1.9 mm and leaf length of 5.7 cm. The application of the peroxyacetic mixtures resulted in an improvement in growth parameters as well as in yield. Individual weights achieved using the 40 mg L(-1) dose were 1.3 g plant(-1) in the control group and 3.4 g plant(-1) in the experimental group (62% yield increase). Sensory analysis revealed no differences in organoleptic quality.     

Hydrosoluble copolymers of acrylamide‐(2‐acrylamido‐2‐methylpropanesulfonic acid). Synthesis and characterization by spectroscopy and viscometry

Hydrosoluble copolymers containing sulfonic acid groups incorporated into a macromolecule were synthesized. The group of polymers studied was obtained by free radical solution polymerization, using potassium persulfate as an initiator. The copolymerization of the monomers 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) and acrylamide (AA) was carried out at different pH values of the reaction medium of the monomer mix. The copolymers were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR) and Fourier transform infrared spectroscopy (FTIR). The viscosity behavior of the copolymers in NaCl solution showed a dependency on the pH of the reaction medium, with higher pH leading to lower viscosities. The acidic conditions of this medium affect the initiator decomposition rate, which is a probable cause of the viscosity variation, and the extent of decomposition increases with increasing pH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 192–198, 2003     

Composite phenolic resin-based carbon molecular sieve membranes for gas separation

Composite carbon molecular sieve membranes (c-CMSM) were prepared from phenolic resin loaded with boehmite by a single dipping–drying–pyrolysis step. The composite membrane was analyzed by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, mercury porosimetry, CO₂ adsorption and permeation experiments. It was produced a 2 μm thick composite uniform layer on top of a α-Al₂O₃ support. The composite top layer exhibited nanowires of Al₂O₃ 1–2 nm thick and 10–30 nm long well dispersed in a microporous carbon matrix. The micropores network accounted for 63% of the total pore volume (DR isotherm). The c-CMSM exhibited ideal O₂/N₂ and C₃H₆/C₃H₈ permselectivities of 5 and 15, respectively. The performance of the c-CMSM for pair C₃H₆/C₃H₈ was above the upper bound curve for polymeric membranes, making it a promising vehicle for olefin purification.     

Detailed description of kinetic and reactor modeling for naphtha catalytic reforming

Kinetic and reactor modeling of catalytic reforming of naphtha is described in the present work. The development of a kinetic reforming model is reported with detail. The validation of the developed kinetic model with bench-scale isothermal reactor experiments is also carried out. The kinetic and reactor models are applied for the simulation of commercial semi-regenerative reforming unit. The effect of benzene precursors in the feed in both laboratory and commercial reactors is also simulated, and the use of the reactor model to predict other process parameters is highlighted.     

Broad-band electrical conductivity of carbon nanofibre-reinforced polypropylene foams

The influence of foaming a semi-crystalline polymer reinforced with different concentrations of carbon nanofibres (0–20 wt.%) on the formation of an electrically conductive network was studied at room temperature using an impedance analyzer over a wide interval of frequencies (from 10⁻² to 10⁶ Hz). Composites were prepared by melt-compounding using a twin-screw extruder, and later chemically foamed. Although composite materials displayed lower conductivities than expected, assuming a percolative behavior, foaming promoted a tunnel-like conduction at lower CNF concentrations than in the solids. At higher CNF concentrations, no great improvements were achieved as tunneling conduction decreased with increasing local crystallinity. Foams showed electrical conduction characteristics typical of a conductive random-distributed fibre-like system, while the behavior of the solids was closer to a system of spherical particles, related to CNF aggregation. The anisotropic cellular structure of the 20 wt.% CNF composite foamed by a physical foaming process disrupted the preferential in-plane CNF orientation attained during solid preparation, with these foams showing higher through-plane conductivity and more isotropic electrical properties than the chemically-foamed ones. It has been demonstrated that foaming PP–CNF composites resulted in the formation of a conductive network at lower CNF concentrations than in the solids, with foams showing the potential for use in conductive high-performance lightweight composite systems.     

New sensor network design and retrofit method based on value of information

Traditionally, the sensor network design procedure was based on positioning sensors so that certain network monitoring capabilities (e.g., observability, redundancy, and error detectability) of key variables are assured at minimum sensors cost. We present a new approach that is based on maximizing economic value of information minus cost instead of the traditional approach that requires the satisfaction of performance targets. This article presents the conceptual aspect and computation issues of this new approach: the connection between the new approach and the traditional minimum‐cost approaches is explored and the computational methods to solve the proposed problem are presented. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Competition between hydrotreating and polymerization reactions during pyrolysis oil hydrodeoxygenation

Hydrodeoxygenation (HDO) of pyrolysis oil is an upgrading step that allows further coprocessing of the oil product in (laboratory‐scale) standard refinery units to produce advanced biofuels. During HDO, desired hydrotreating reactions are in competition with polymerization reactions that can lead to unwanted product properties. To suppress this polymerization, a low‐temperature HDO step, referred to as stabilization, is typically used. Small batch autoclaves have been used to study at near isothermal conditions the competition between hydrotreating and polymerization reactions. Although fast polymerization reactions take place above 200°C, hydrogen consumption was already observed for temperatures as low as 80°C. Hydrogen consumption increased with temperature and reaction time; however, when the end temperature exceeded 250°C, hydrogen consumption achieved a plateau. This was thought to be caused by the occurrence of fast polymerization reactions and the refractivity of the products to further hydrotreating reactions. The effect of the gas–liquid mass transfer was evaluated by using different stirring speeds. The results of these experiments (carried out at 300°C) showed that in the first 5 min of HDO, gas–liquid mass transfer appears to be limiting the overall rate of hydrotreating reactions, leading to undesired polymerization reactions and product deterioration. Afterward, intraparticle mass transfer/kinetics seems to be governing the hydrogen consumption rate. Estimations on the degree of utilization (effectiveness factor) for industrially sized catalysts show that this is expected to be much lower than 1, at least, in the early stage of HDO (first 30 min). Catalyst particle size should, thus, be carefully considered when designing industrial processes not only to minimize reactor volume but also to improve the ratio of hydrotreating to polymerization reactions. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

Decomposition of Dolomite Monitored by Neutron Thermodiffractometry

Dolomite powder from Coín (Spain) was heated in air at a constant rate of 2°C/min to 1000°C, while neutron diffraction patterns were collected every 150 s. Rietveld refinement was applied and raw intensity data were used to monitor decomposition. The full process happened in two stages: dolomite decomposition to give calcite and periclase, and calcite breakup. The first stage activation energy was 47 kcal·mol⁻¹ from fitting to a contracting sphere model. The dolomite mean thermal expansion coefficients were (6.7 ± 0.4) × 10⁻⁶ and (2.7 ± 0.2) × 10⁻⁵ K⁻¹ along the a and c axes, respectively. Changes in the Ca–O and Mg–O bond distances were also measured.