Elio E. Gonzo

Estimating correlations for the effective thermal conductivity of granular materials

Based on the well-known solution of Maxwell [1] for the thermal conductivity of dilute dispersions of spheres and the improved form of Maxwell’s equation developed by Chiew and Glandt [2], two general correlation for keff estimation are proposed. One of them apply to medium dense dispersions (0.15≤φ≥0.85) and the other one for dense porous materials (φ>0.9). Both correlating equations encompass a wide range of phase conductivity ratio values. The comparison with experimental measurements shows very good agreement.

Thermodynamics of the absorption of hydrocarbon vapors in polyethylene films

Abstract Solubility of n-butane, n-pentane, n-hexane and n-heptane vapors in polyethylene membranes was measured with an accurate gravimetric technique as a function of temperature, within the range of 258 to 318 K, and relative vapor pressure of hydrocarbons (up to 0.95). The results are analyzed with the scope of establishing a unique expression to predict the solubility of the hydrocarbon vapors. It is shown that such an expression exists and can be used with a fair degree of accuracy to estimate both solubility and solubility coefficients, in spite of the marked deviation of the experimental results from Henrys law. The effect of temperature over the whole range investigated is also well correlated, and the isoplethic heat of absorption was calculated, showing that its values are independent both of temperature and solubility. The Flory-Huggins theory was also used to analyze experimental results and the values of the interaction parameter were calculated, which can be used in turn to predict solubility and solubility coefficients of hydrocarbon vapors.

Acid-activated Carbons from Peanut Shells: Synthesis, Characterization and Uptake of Organic Compounds from Aqueous Solutions

Activated carbon with a high adsorption capacity for the removal of organic compounds from aqueous solutions was made from phosphoric acid-activated peanut shells. Adsorption isotherms for the uptake of phenol, iodine, Methylene Blue and tannic acid were obtained at 22°C. Freundlich, Langmuir and previously developed equation models all explained the experimental data satisfactorily. Further analysis using the Dubinin–Radushkevich equation showed that the maximum micropore volume accessible to the adsorbate decreased as the molecular size increased, suggesting a molecular sieve or gate effect. A comparison was made with the micropore volume as determined by nitrogen adsorption at −196°C. The results presented indicate that peanut shell residues provide a suitable option for the preparation of activated carbon with good surface properties and the ability to remove organic compounds from aqueous solutions.

The analysis of sorption data of organic vapors in polymeric membranes through novel theories

Abstract Analysis of sorption data of hydrocarbon vapors in polyethylene and polypropylene films using Flory-Huggins, UNIFAC. Michael-Hausslein and Flory-Rehner theories are presented. Basically two models are used, one deduced with UNIFAC and Michael-Hausslein (UNIFAC-M-H) approach and the other with UNIFAC and Flory-Rehner (UNIFAC-F-R) theory. Prediction of penetrant activity values through these theories fit quite well the experimental results with errors ranging between 4.7 and 10.8%. The mean arithmetic values of the fraction of elastically effective chain in the amorphous region are f =0.4915 and f =0.3354 for polypropylene (PP) and polyethylene (PE), respectively. The experimental results with polypropylene are correlated, establishing a unique expression to predict solubility and solubility coefficient. The dependence of solubility in polypropylene over the whole range of temperature it is also presented.

Kinetics of Phenol Removal from Aqueous Solution by Adsorption onto Peanut Shell Acid-activated Carbon

A pseudo-second-order rate equation describing the kinetic adsorption of phenol onto peanut shell acid-activated carbon at different initial concentrations, carbon dosages and particle sizes has been developed. The adsorption kinetics were followed on the basis of the amount of phenol adsorbed at various time intervals at 22°C. The rate constant and the equilibrium adsorption capacity were calculated. From these parameters, empirical correlations for predicting the equilibrium adsorption capacity as a function of the C0/D ratio, and for estimating the rate constant as a function of the relation D/(C0dp)0.5, were derived. This allowed a general rate expression for design purposes to be obtained which was valid for C0/D ≤ 1.5. The operation line for each case studied was constructed and the equilibrium adsorption capacity obtained. A comparison was undertaken with the experimental adsorption isotherm as previously determined. The effect of the initial phenol concentration, the carbon dose and the particle size on the initial adsorption rate was also analyzed.

Peanut Shell Activated Carbon: Adsorption Capacities for Copper(II), Zinc(II), Nickel(II) and Chromium(VI) Ions from Aqueous Solutions

The adsorption of copper(II), zinc(II), nickel(II) and chromium(VI) ions from aqueous solutions onto an activated carbon produced from peanut shell was studied as a function of the concentration of the ions and the pH value. The amounts of Cu(II), Zn(II) and Ni(II) ions adsorbed increased with increasing equilibrium pH of the solution, while the uptake of Cr(VI) ions decreased. For Cr(VI) ions, maximum uptakes were found at a pH below the point of zero charge of the adsorbent (pHpzc). The amount of metal cation adsorbed at a given equilibrium concentration increased in the order Ni(II) < Zn(II) < Cu(II). This metal ion uptake order may be explained from a consideration of the combined effects of the electronegativity of the metal ion and the first stability constant of the corresponding metal hydroxide. The activated carbon produced from peanut shell was an effective and economic adsorbent for the removal of metal cations at pH ≥ pHpzc and anions at pH ≤ pHpzc.

Continuum heterogeneous biofilm model-A simple and accurate method for effectiveness factor determination.

We present a novel analytical approach to describe biofilm processes considering continuum variation of both biofilm density and substrate effective diffusivity. A simple perturbation and matching technique was used to quantify biofilm activity using the steady‐state diffusion–reaction equation with continuum variable substrate effective diffusivity and biofilm density, along the coordinate normal to the biofilm surface. The procedure allows prediction of an effectiveness factor, η, defined as the ratio between the observed rate of substrate utilization (reaction rate with diffusion resistance) and the rate of substrate utilization without diffusion limitation. Main assumptions are that (i) the biofilm is a continuum, (ii) substrate is transferred by diffusion only and is consumed only by microorganisms at a rate according to Monod kinetics, (iii) biofilm density and substrate effective diffusivity change in the x direction, (iv) the substrate concentration above the biofilm surface is known, and (v) the substratum is impermeable. With this approach one can evaluate, in a fast and efficient way, the effect of different parameters that characterize a heterogeneous biofilm and the kinetics of the rate of substrate consumption on the behavior of the biological system. Based on a comparison of η profiles the activity of a homogeneous biofilm could be as much as 47.8% higher than that of a heterogeneous biofilm, under the given conditions. A comparison of η values estimated for first order kinetics and η values obtained by numerical techniques showed a maximum deviation of 1.75% in a narrow range of modified Thiele modulus values. When external mass transfer resistance, is also considered, a global effectiveness factor, η0, can be calculated. The main advantage of the approach lies in the analytical expression for the calculation of the intrinsic effectiveness factor η and its implementation in a computer program. For the test cases studied convergence was achieved quickly after four or five iterations. Therefore, the simulation and scale‐up of heterogeneous biofilm reactors can be easily carried out. Biotechnol. Bioeng. 2012; 109:1779–1790.

Catalytic reactivity of Cr/SiO2 in the liquid phase oxidation of cyclohexanol by tert-butyl hydroperoxide

Silica supported chromium is a heterogeneous, active and selective catalyst for the liquid phase oxidation of cyclohexanol by tert-butyl hydroperoxide (TBHP) in the presence or absence of oxygen. It is also active for the decomposition of TBHP. The reactivity at 70ºC and atmospheric pressure is higher than over other catalysts and the cyclohexanone selectivity is 100%.

Adsorption of Organic Compounds on Activated Carbon Derived from Peanut Shells. Potential Theory Correlation for Estimating Adsorption Capacities and Affinity Coefficients

Adsorption isotherms of eight organic contaminants (acetone, pyridine, phenol, iodine, Methylene Blue, Congo Red, Reactive Navy and tannic acid) onto an activated carbon obtained from peanut shells have been studied at 22°C. The experimental data were analyzed using the Polanyi Potential Theory and the Dubinin–Astakhov equation and collapsed into one general characteristic curve. This analysis allowed the affinity coefficient for each organic compound to be obtained using phenol as the reference substance. A useful correlation for the calculation of the affinity coefficient as a function of relative parachor is presented.

Effectiveness factors and selectivity for parallel catalytic reactions with Langmuir-Hinshelwood kinetics

Les reactions ont lieu dans un reacteur catalytique a lit fixe. Les calculs sont menes par la methode des perturbations