Synthesis of α‐cellulose/polypyrrole composite for the removal of reactive red dye from aqueous solution: Kinetics and equilibrium modeling

In this work, a composite from α‐cellulose coated with conducting polypyrrole by in situ polymerization using potassium persulfate as oxidant was obtained. The composite was characterized by fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry, UV/Vis spectroscopy, and scanning electron microscopy (SEM) analysis showed homogeneous coating of α‐cellulose with polypyrrole (PPy) to produce a composite with a conductivity of 3.5 × 10⁻⁵ S/m. Batch aqueous adsorption experiments of the reactive red 120 (RR120) dye onto the synthesized material were conducted. The results showed that this composite is an efficient adsorbent for RR120 dye removal. For the adsorption experiments set to an initial pH of 3.9, the adsorption capacity was 15.6 mg of dye/g of composite for an equilibrium concentration (in the liquid) of RR120 dye equal to 1,000 mg/L, whereas a value of 96.1 mg of dye/g of composite was obtained when the solution pH was set to 2.0 for the same equilibrium concentration. When performing adsorption experiments using pure α‐cellulose, dye adsorption was insignificant at any pH value. Adsorption isotherm for RR120 was described by a typical Freundlich model. The transient adsorption of RR120 on the synthesized composite was described by a general three‐resistance model that includes the transport on the film that surrounds the composite particles, diffusion inside the particles, and adsorption on the surface of the particles. A fitting of the uptake curves was performed allowing the estimation of values for the effective diffusivity, D₀, and the adsorption rate coefficient, k₁. For the adsorption experiments with an initial pH value set to 3.9, D₀ was estimated as 1.05 × 10⁻¹⁰ m²/s, whereas k₁ was 1.65 × 10⁻⁴ Lⁿ/g mg^{n − 1} s; the corresponding values of k₁ at pH = 2 and 9.0 were 3.18 × 10⁻⁴ and 5.16 × 10⁻⁵, respectively. POLYM. COMPOS., 36:312–321, 2015. © 2014 Society of Plastics Engineers     

Characterization of palladium supported on sulfated zirconia catalysts by DRIFTS, XAS and n-butane isomerization reaction in the presence of hydrogen

Palladium supported on sulfated zirconia (PdSZ) has been characterized by the n-butane isomerization reaction in the presence of hydrogen, X-ray absorption spectroscopy (XAS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of adsorbed carbon monoxide. Catalyst calcination at 873 K followed by hydrogen reduction at 513 K results in the formation of 30–40 Å Pd metal clusters, but the surface can only weakly adsorb CO, though stronger than Pd-free, sulfated zirconia catalysts. In the presence of hydrogen, PdSZ has a lower n-butane isomerization activity than SZ, and the Pd function cannot stabilize the reaction at low H₂/n-butane ratios.     

High polymer/surfactant ratio in the seeded semicontinuous heterogeneous polymerization of vinyl acetate

Vinyl acetate (VAc) was polymerized by a seeded semicontinuous heterogeneous process. Stable latexes with a polymer/surfactant weight ratio of 65 were obtained, which is comparable with the highest value reported in the literature for emulsion polymerization but with the advantage of obtaining smaller particles (average diameter, D_p = 53 nm) which are similar to those obtained by microemulsion polymerization. The surfactant (sodium dodecylsulfate, SDS) concentration used in the recipe (0.32 wt%) is much lower than those typically used in microemulsion polymerization. Although molar masses increased during the continuous monomer addition period, they were small at the end of the reaction (M_n = 69 × 10³ g·mol^–1) and this was attributed to bimolecular termination inside the particles. The values of polymerization rate (R_p) and monomer addition rate (F_m) were nearly the same, indicating that polymerization was performed under monomer starved conditions. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

CPFD flow pattern simulation in downer reactors

This study contributes with a computational fluid dynamic simulation based on the numerical solution of continuity and momentum balance equations in a three‐dimensional (3‐D) framework. The proposed down flow gas–solid suspension model includes a unit configuration and C_D drag coefficients recommended for these units. Computational particle fluid dynamics (CPFD) calculations using suitable boundary conditions and a Barracuda (version: 14.5.2) software allow predicting local solid densification and asymmetric “wavy flows.” In addition, this model forecasts for the conditions of this study higher particle velocity than gas velocity, once the flow reaches 1 m from the gas injector. These findings are accompanied with observations about the intrinsic rotational character of the flow. CPFD numerical 3‐D calculations show that both gas and particle velocities involve the following: (a) an axial velocity component, (b) a radial velocity component (about 5% of axial velocity component), and (c) an angular velocity component. The calculated velocity components and the rotational flow pattern are established for a wide range of solid flux/gas flux ratios. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1635–1647, 2013     

Effect of operating conditions in removal of arsenic from water by nanofiltration membrane

The removal of arsenic from synthetic waters and surface water by nanofiltration (NF) membrane was investigated. In synthetic solutions, arsenic rejection experiments included variation of arsenic retentate concentration, transmembrane pressure, crossflow velocity and temperature. Arsenic rejection increased with arsenic retentate concentration. Arsenic was removed 93-99% from synthetic feed waters containing between 100 and 382 μg/L as V, resulting in permeate arsenic concentrations of about 5 μg/L. Under studied conditions, arsenic rejection was independent of transmembrane pressure, crossflow velocity and temperature. In surface water, the mean rejection of As V was 95% while the rejection of sulfate was 97%. The co-occurrence of dissolved inorganics does not significantly influence arsenic rejection. The mean concentration of As in collected permeated was 8 μg/L. The mean rejection of TDS, total hardness and conductivity were 75, 88 and 75% respectively.     

A review of the statistical turbulence theory required extending the population balance closure models to the entire spectrum of turbulence

The models for fluid particle breakage and coalescence due to turbulence are generally limited to the inertial subrange of isotropic turbulence and infinite Reynolds numbers. A rigorous procedure for extending the fluid particle breakage and coalescence closures to the entire spectrum of isotropic turbulence and for a wider range of Reynolds numbers can be established based on statistical turbulence theory. The modeling procedure consists of a three‐dimensional (3‐D) literature model energy spectrum for the dissipation, inertial, and energy containing subranges of isotropic turbulence, and an exact literature integral relation for determining the second‐order longitudinal structure function from the 3‐D energy spectrum. A review of the requisite statistical turbulence theory and the use of the model energy spectrum is provided, because the necessary details are not easily accessible in the chemical engineering literature and misconceptions are found in the publications of the previous modeling attempts. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1795–1820, 2016     

Anticoagulant, Antioxidant and Antitumor Activities of Heterofucans from the Seaweed Dictyopteris delicatula

In the present study, six families of sulfated polysaccharides were obtained from seaweed Dictyopteris delicatula by proteolytic digestion, followed by acetone fractionation and molecular sieving on Sephadex G-100. Chemical analyses demonstrated that all polysaccharides contain heterofucans composed mainly of fucose, xylose, glucose, galactose, uronic acid, and sulfate. The fucans F0.5v and F0.7v at 1.0 mg/mL showed high ferric chelating activity (～45%), whereas fucans F1.3v (0.5 mg/mL) showed considerable reducing power, about 53.2% of the activity of vitamin C. The fucan F1.5v presented the most prominent anticoagulant activity. The best antiproliferative activity was found with fucans F1.3v and F0.7v. However, F1.3v activity was much higher than F0.7v inhibiting almost 100% of HeLa cell proliferation. These fucans have been selected for further studies on structural characterization as well as in vivo experiments, which are already in progress.     

Corrosion behavior of Eurofer 97 and ODS-Eurofer alloys compared to traditional stainless steels

In the present work, the corrosion resistance of ferritic-martensitic EUROFER 97 and ODS-EUROFER steels was tested in solutions containing NaCl or H₂SO₄ and KSCN, both at 25 °C. The results were compared to those of AISI 430 ferritic and AISI 410 martensitic conventional stainless steels. The as-received samples were tested by electrochemical techniques, specifically, electrochemical impedance spectroscopy, potentiodynamic polarization curves, and double-loop electrochemical potentiokinetic reactivation tests. The surfaces were observed by scanning electron microscopy after exposure to corrosive media. The results showed that EUROFER 97 and ODS-EUROFER alloys present similar corrosion resistance but lower than ferritic AISI 430 and martensitic 410 stainless steels.