Alberto Cincotti

Sardinian natural clinoptilolites for heavy metals and ammonium removal: experimental and modeling

Sardinian natural clinoptilolites are examined to evaluate their adsorption for the metals, copper, cadmium, lead and zinc, as well as ammonium removal. The natural material is either used as received or once converted into the sodium form. Equilibrium data for each species and the natural material are obtained. The corresponding behavior is quantitatively correlated using classical isotherms, whose parameters are estimated by fitting the equilibrium data. Breakthrough experiments of lead solutions are also performed. Fixed-bed runs are simulated using a mathematical model which includes axial dispersion as well as a new approximate rate law for non-linear adsorption and diffusion in spherical adsorbent particle based on an equivalent film resistance model.

Effect of catalyst concentration and simulation of precipitation processes on liquid-phase catalytic oxidation of p-xylene to terephthalic acid

Abstract The influence of catalyst concentration, i.e. cobalt naphthenate, on product distribution and kinetic constants of the lumped kinetic scheme of liquid-phase p -xylene oxidation proposed in previous works (cf. Cao et al. , 1994a, b) is investigated. The experiments involving various levels of catalyst concentrations (from 1.67 to 33.3 × 10 −4 mol/kg l ) are conducted in an isothermal semi-batch oxidation reactor where both the gas and the liquid phase are well mixed. The dependence of the kinetic constants of the lumped kinetic scheme on the catalyst concentration is examined. In addition, the interaction between the chemical reactions of the lumped kinetic scheme for p -xylene oxidation to terephthalic acid and the precipitation kinetics of both 4-carboxybenzaldehyde and terephthalic acid is analyzed theoretically. A semi-batch gas-liquid reactor model which incorporates the description of the above phenomena allows us to identify their interplay.

Treatment and recycling of zinc hydrometallurgical wastes by self-propagating reactions

Abstract A novel technique for treating and recycling of a highly toxic solid waste from electrolytic zinc plants, i.e. goethite waste, is proposed. It consists of blending this waste with suitable amount of reducing agents (aluminum or aluminum and silicon) and ferric oxide, and igniting the resulting mixture so that a self-propagating reaction in the form of a combustion wave rapidly travels through the mixture without requiring additional energy. Reactants are converted into two solid products (P 1 and P 2 ) with different mass, composition and structure, and a gas constituted by SO 2 . Aluminum and silicon should be preferred as reducing agents, since the reaction product P 1 obtained in larger quantity, is constituted by an amorphous glassy structure of alumino-silicates which embodies heavy metals, such as Pb and Cd. Leaching tests of the reaction products P 1 are also performed to verify the possibility of their disposal. The solid product P 2 on the other hand may be recycled in the roasting unit of the industrial zinc production plant. A waste treatment process is also proposed.

Film model approximation for non-linear adsorption and diffusion in spherical particles

Abstract A new approximate rate law for non-linear adsorption and diffusion in a spherical adsorbent particle is developed based on an equivalent film resistance model. The approximation provides a quantitatively correct description of the effect of the adsorption isotherm for parallel pore and solid diffusion as well as of the effect of a variable adsorbed-phase diffusivity. In general, uptake curves calculated with this new approximation compare favorably with the numerical solution of the adsorption–diffusion equation in spherical coordinates producing results of accuracy similar to that obtained when the LDF approximation is used for systems with a constant diffusivity.

A methodology to investigate the intrinsic effect of the pulsed electric current during the spark plasma sintering of electrically conductive powders

Abstract A novel methodology is proposed for investigating the effect of the pulsed electric current during the spark plasma sintering (SPS) of electrically conductive powders without potential misinterpretation of experimental results. First, ensemble configurations (geometry, size and material of the powder sample, die, plunger and spacers) are identified where the electric current is forced to flow only through either the sample or the die, so that the sample is heated either through the Joule effect or by thermal conduction, respectively. These ensemble configurations are selected using a recently proposed mathematical model of an SPS apparatus, which, once suitably modified, makes it possible to carry out detailed electrical and thermal analysis. Next, SPS experiments are conducted using the ensemble configurations theoretically identified. Using aluminum powders as a case study, we find that the temporal profiles of sample shrinkage, which indicate densification behavior, as well as the final density of the sample are clearly different when the electric current flows only through the sample or through the die containing it, whereas the temperature cycle and mechanical load are the same in both cases.

A novel population balance model to investigate the kinetics of in vitro cell proliferation: Part I. model development

In biotechnology and biomedicine reliable models of cell proliferation kinetics need to capture the relevant phenomena taking place during the mitotic cycle. To this aim, a novel mathematical model helpful to investigate the intrinsic kinetics of in vitro culture of adherent cells up to confluence is proposed in this work. Specifically, the attention is focused on the simulation of proliferation (increase of cell number) and maturation (increase of cell size and DNA content) till contact inhibition eventually takes place inside a Petri dish. Accordingly, the proposed model is based on a population balance (PB) approach that allows one to quantitatively describe cell cycle progression through the different phases the cells of the entire population experienced during their own life. In particular, the proposed model has been developed as a 2D, multi‐staged, and unstructured PB, by considering a different sub‐population of cells for any single phase of the cell cycle. These sub‐populations are discriminated through cellular volume and DNA content, that both increase during the mitotic cycle. The adopted mathematical expressions of the transition rates between two subsequent phases and the temporal increase of cell volume and DNA content are thoroughly analyzed and discussed with respect to those ones available in the literature. Specifically, the corresponding uncertainties and pitfalls are pointed out, by also taking into account the difficulties and the limitations involved in the quantitative measurements currently practicable for these biological systems. A novel mathematical expression for contact inhibition in line with the PB model developed is also formulated, along with a proper comparison between modeled and measurable DNA distributions. The strategy for a reliable, independent tuning of the adjustable parameters involved in the proposed model along with its numerical solution is outlined in Part II of this work, where it is also shown how it can be profitably used to gain a deeper insight into the phenomena involved during cell cultivation under microgravity conditions. Biotechnol. Bioeng. 2012; 109:772–781.

Combustion synthesis of metal carbides: Part I. Model development

The definition of a rigorous theoretical framework for the appropriate physico-chemical description of self-propagating high-temperature synthesis (SHS) processes represents the main goal of this work which is presented in two sequential articles. In this article, a novel mathematical model to simulate SHS processes is proposed. By adopting a heterogeneous approach for the description of mass transfer phenomena, the model is based on appropriate mass and energy conservation equations for each phase present during the system evolution. In particular, it takes microstructural evolution into account using suitable population balances and properly evaluating the different driving forces from the relevant phase diagram. The occurrence of phase transitions is treated on the basis of the so-called enthalpy approach, while a conventional nucleation-and-growth mechanistic scenario is adopted to describe quantitatively the formation of reaction products. The proposed mathematical model may be applied to the case of combustion synthesis processes involving a low melting point reactant and a refractory one, as for the synthesis of transition metal carbides from pure metal and graphite. Thus, the model can be profitably used to gain a deeper insight into the microscopic elementary phenomena involved in combustion synthesis processes through a suitable combination of experimental and modeling investigations, as it may be seen in Part II of this work [J. Mater. Res. 20, 1269 (2005)].

FILM MODEL APPROXIMATION FOR PARTICLE-DIFFUSION-CONTROLLED BINARY ION EXCHANGE

A new rate expression for particle-diffusion-controlled ion exchange, based on an equivalent pseudosteady-state film resistance model, is developed. The rate expression approximates the electric field effects on intraparticle diffusion in spherical ion-exchangers. With regard to the prediction of batch exchange and column breakthrough curves for both irreversible and reversible processes, the model captures the essential traits of the coupled diffusion phenomenon described by the Nernst–Planck equation with results of accuracy comparable to that obtained when using the linear driving force approximation for systems with constant diffusivity. Numerical results for the exchange of two counterions of equal valence are presented as application examples for different mobility ratios and selectivity coefficients.

A simulation model for stem cells differentiation into specialized cells of non-connective tissues

A novel mathematical model to simulate stem cells differentiation into specialized cells of non-connective tissues is proposed. The model is based upon material balances for growth factors coupled with a mass-structured population balance describing cell growth, proliferation and differentiation. The proposed model is written in a general form and it may be used to simulate a generic cell differentiation pathway during in vitro cultivation when specific growth factors are used. Literature experimental data concerning the differentiation of central nervous stem cells into astrocytes are successfully compared with model results, thus demonstrating the validity of the proposed model as well as its predictive capability. Finally, sensitivity analysis of model parameters is also performed in order to clarify what mechanisms most strongly influence differentiation and cell types distribution.

A Simulation Model for the Growth of Engineered Cartilage on Polymeric Scaffolds

A mathematical model to simulate the growth of engineered cartilage on polymeric scaffold performed in rotating bioreactors has been developed. The model, based upon the material balance for the nutrient species (oxygen) and the primary extra-cellular matrix product (GAG), accounts for population balances to simulate cell proliferation and its distribution within the polymeric scaffold. A comparison between model results and literature experimental data in terms of GAG contents and its distribution within the tissue construct has been performed. All model parameters are taken from the literature except for the constant of the time rate of mass change appearing in the proposed population balance which has been adjusted to reproduce the experimental data concerning the tissue culture performed at 80 mm Hg of oxygen partial pressure. The predictive capability of the model has been also demonstrated by comparison with experimental data obtained for a different value of oxygen partial pressure (40 mm Hg).