Benedetta de Caprariis

Comparison of global models of sub-bituminous coal devolatilization by means of thermogravimetric analysis

Coal gasification and combustion are strongly dependent on devolatilization step. Aim of this work is to obtain the parameters of global kinetics of devolatilization of a sub-bituminous coal with high sulfur content. The kinetic parameters are obtained by means of TG experimental data, and applying different approaches to extrapolate the data to industrial relevant conditions. The simpler method is a model-free one which supposes a single step process whose Arrhenius kinetic parameters (A and Ea) have to be determined. Another common approach is the distributed activation energy model (DAEM) which assumes a series of first order parallel reactions occurring and sharing the same pre-exponential factor, A, with a continuous distribution of the activation energy. For the fitting of the experimental data, a numerical solution to DAEM and two approximate methods have been evaluated. Moreover, the results of these kinetic methods based on empirical approaches were compared with simulated data obtained using a more complex model based on percolation theory with cross-linking mechanism and vapor–liquid equilibrium (chemical percolation devolatilization, CPD model), which allows to simulate the coal pyrolysis from volatile yield data.

Kinetic analysis of biomass pyrolysis using a double distributed activation energy model

Pyrolysis is a fundamental step in thermochemical processes of biomass materials, so a suitable kinetic model is an essential tool to predict the evolution of the resulting products of reaction. However, many difficulties arise in modeling this process step due to the very high number of the involved reactions. In this work, a new double-Gaussian distributed activation energy model was applied in fitting the experimental data of olive residue pyrolysis obtained by thermogravimetric analysis. 2-DAEM formulation considers two sets of parallel reactions occurring and sharing the same pre-exponential factor, but shows different distributions of the activation energy, described by two separate Gaussian distributions that, in turn, grasp the two pyrolysis steps with a high accuracy. Since it is well known that in fitting all the kinetic parameters the pre-exponential factor results highly correlated with the activation energy, the former parameter was separately estimated as a linear combination of the values obtained for the three main biomass components, cellulose, hemicellulose and lignin.

Exoelectrogenic Activity of a Green Microalgae, Chlorella Vulgaris, in a Bio-photovoltaic Cells (bpvs)

Bio-photovoltaic cells (BPVs) are a new photo-bio-electrochemical technology for harnessing solar energy using the photosynthetic activity of autotrophic organisms. This is a new technology for the production of sustainable and “clean” energy.Currently power outputs from BPVs are generally low and suffer from scarce efficiencies. However, a better understanding of the electrochemical interactions between the autotrophic microorganisms and conductive materials will be likely to lead to increased power yields. In the current study, the green microalgae Chlorella vulgaris was investigated for exoelectrogenic activity.To assess the exoelectrogenic activity of C. vulgaris a particular bio-photovoltaic cell was designed and built. The most important element is represented by the electrode configuration, based on inexpensive materials, with the anode immersed in the cultural broth and the cathode exposed to the atmosphere. This configuration represents a very interesting simplification for the cell design, furthermore allowing a simple illumination of the algal culture via a light source positioned above the cell, perpendicular to the electrode surface.This new kind of bioelectrochemical system does not need organic substrate and mediators, and the net production of CO2 is zero.This device was then characterized by measuring the electrical performance of the BPV. A power density of 14 µW/m2 was recorded, revealing interesting potentialities for green unicellular algae fuelled BPVs.

CFD model of a spinning disk reactor for nanoparticle production

The use of a spinning disk reactor (SDR) was investigated for the continuous production of nanoparticles of hydroxyapatite. SDR is an effective apparatus for the production of nanoparticles by wet chemical synthesis. Rotation of the disc surface at high speed creates high centrifugal fields, which promote thin film flow with a thickness in the range 50 – 500 μm. Films are highly sheared and have numerous unstable surface ripples, giving rise to intense mixing. SDR performances are strongly affected by the adopted operating conditions such as the influence of rotation speed that determines the attainment of micro-mixing and the feeding point location that has a great influence on the particle size distribution of the product. The experimental device consists of a cylindrical vessel with an inner disk, 8.5 cm in diameter, made by PVC coated by an acrylic layer. The rotational velocity of the disc is controlled and ranges from 0 to 147 rad/s. The reagent solutions are fed over the disk at a distance of 5 mm from the disc surface through tubes, 1 mm in diameter. A computational fluid dynamic model, validated in a previous work, was used to optimize the operative conditions of SDR. Through the CFD model it is possible to analyse the hydrodynamic of the thin liquid film formed on the disk at different speed rotations and to individuate the best mixing conditions between the reagents varying the feeding point positions. The production of hydroxyapatite was also investigated adding the reaction kinetic to model the product formation in the liquid phase and the population balance equation to predict particle size distribution. The simulation results were compared with available experimental data showing that the CFD model is fully capable to describe the process and qualifies as a suitable engineering tool to perform the SDR process design.

The boundary flux: New perspectives for membrane process design

The Boundary Flux: New Perspectives for Membrane Process Design Marco Stoller*, Javier Miguel Ochando Pulido, Benedetta de Caprariis, Nicola Verdone, Luca Di Palma, Angelo Chianese University of Rome “La Sapienza”, Dept. Of Chemical Materials Environmental Engineering, Via Eudossiana 18, 00184 Rome, Italy University of Granada, Dept. Of Chemical Engineering, Granada, Spain marco.stoller@uniroma1.it