Nicola Verdone

Process optimisation in sunflower oil extraction by supercritical CO2

Abstract A continuous process for the extraction of sunflower oil using supercritical CO 2 , featuring multiple extractors, one oil separator and three cascaded CO 2 recovery vessels operating at different pressures, was devised and studied. For every single equipment of the plant making up the process a mathematical model was built. Experimental tests—consisting in measurements of oil solubility in supercritical CO 2 —were carried out in a laboratory-scale apparatus to characterise the behaviour of sunflower oil in the separation from the supercritical fluid. The mathematical model of the whole process was coded in the commercial gPROMS process modelling environment where both its simulation and optimisation—this latter assuming the overall oil production cost as the objective function—were carried out. The process- and economics-related results are discussed and compared with those obtained with traditional and cold-pressing extraction.

Production and characterization of adsorbent materials from sewage sludge by pyrolysis

The conventional sludge disposal options include landfill, application to farmland and forestry and incineration. However, since in the last decade sewage sludge and industrial sludge are being generated in increasing amounts due to the rapid urbanization and industrialization, a growing interest has been devoted in developing cost effective and renewable disposal alternatives. Among them, the manufacture of adsorbents to remove metals from water and wastewater appears to be promising, also considering the high cost of commercial carbons. In this paper copper, zinc and cadmium removal from wastewater using adsorbents produced from pyrolysis of sewage sludge is investigated in comparison with commercial adsorbents. The kinetic of the pyrolytic process was studied, and the adsorbents produced under different pyrolysis conditions were characterized. The adsorption capacity of the pyrolyzed material were estimated in batch tests performed in an activated sludge reactor. Results show that the adsorbent materials obtained by sewage sludge pyrolysis increased organic matter removal in activated sludge systems, and limited the inhibition effects of heavy metals. In addition, a chemical activation of the sludge before the pyrolysis resulted in an increase of the adsorption capacity of the obtained adsorbent.

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.

The effect of disk rotational speed on oxygen transfer in rotating biological contactors.

Lab-scale experiments using a synthetic wastewater were carried out to assess the influence of disk rotational speed on oxygen transfer rate in a RBC unit in the presence of biomass. The overall oxygen transfer coefficient (K(L)a) was computed. Five different disk rotational speeds were tested, in the typical RBC operating range (3-10 RPM). The soluble organic substrate was monitored through TOC analysis. Influent hydraulic organic loadings were in the range of 5.4-35.2 g TOC/m(2)d. The set of kinetic coefficients calculated fitting the experimental data by the selected model resulted in good agreement with the value reported in literature. A correlation for K(L)a as a function of disk rotational speed and disk diameter was obtained. Accordingly, a new expression of the enhancement factor of oxygen transfer was found, and compared to literature 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.

Biological denitrification of high-nitrate wastewaters: A comparison between three electron donors

Wastewaters discharged by several industrial activities, such as synthetic fibers, mineral processing, fertilizers, metal finishing, and ammunitions and explosives industries, have an high-salinity content and are characterized by a very high concentration of nitrates (more than 3 g/L). The treatment of these wastewaters generally deals in an anoxic biological process performed in activated sludge reactors (ASR). Due to the practical absence of an organic component, the treatment involves the addition of an external source of carbon, as electron donor for denitrification reactions. In addition, explosives industries wastewaters are characterized by low pH (2-3), since nitrates are generally discharged as nitric acid, and this induces a further difficulty in reactor operation, due to the extreme sensitivity of denitrifying biomass to pH conditions. In this paper the results of an experimentation performed in a laboratory scale anoxic ASR treating a highnitrate wastewater, simulating the explosives and ammunitions industries wastewaters, are presented and discussed. Three different carbon sources (methanol, acetic acid and sucrose) were compared, and the conditions to achieve the maximum removal of nitrogen were assessed. The ratio C:N to be maintained in the reactor to optimize cell growth and denitrification rate was also investigated.

EDTA Leaching of Copper from Contaminated Soils: Experimental Study and Transport Model Application for Parameters Estimation

EDTA columns extraction were performed on four artificially contaminated soils, followed by the percolation of pure water to ensure the removal of EDTA entrapped in soil. The investigated soils were characterized by a content of organic matter ranging from 1% to 25%. A mathematical model was developed for copper leaching from the soils. The correlation of experimental data shows that while the EDTA transport was not affected by the soil organic fraction, the simulated transport of Cu-EDTA complexes in solution exhibited a delay effect due to the chemical adsorption of such complexes onto the soil organic matter. The distribution coefficient (Kd ), between the solid and liquid phases showed a logarithmic increase when the organic content of soil increased. The columns hydrodynamic characteristics (αL ) and the kinetic coefficients (k) of chelant extraction were estimated independently for each soil. A correlation of kinetic coefficients data versus soils organic content was also proposed: experimental data showed, in the investigated range, a logarithmic dependence of k on the organic content of soil.

Treatment of Wastewater with High Inorganic Salts Content

The study deals with the waste disposal of an aqueous solution with a high salt content (about 5% sodium sulfate) and an organic fraction consisting primarily of naphthalenesulfonic acids. First, a process based on crystallization for the removal of sodium sulfate from the wastewater was developed, leading to a recovery of about 70% of the sodium sulfate. The wastewater with the residual salts content was fed to a batch mesophilic anaerobic digestion process. The acclimatization of a methanogenic consortium to different mixtures of the desalted wastewater and a growth substrate was studied. Complete acclimation of the biomass to the solution was observed over a broad range of wastewater amount in a growth medium (from 3.5 to 224 mL of wastewater per liter of feeding solution). After a suitable acclimation period of time the biomass was able to digest the pure wastewater up to an amount of 57.1 mL per liter of the feeding solution, obtaining total organic carbon (TOC) (mg/LC) removal rates of 0.04 kg TOC/k...

Metals extraction from contaminated soils: Model validation and parameters estimation

In this paper a mathematical model based on the axial dispersion theory is developed to estimate copper leaching from contaminated soils in the presence of iron and calcium as competitive cation. The model considered the transport by pore diffusion-dispersion and metal complexation by ions in solution and linked solute transport of EDTA and EDTA-metal chelates to the metal solubilization process. For model validation and parameter estimation, EDTA column’s extraction were performed on an artificially contaminated soil by both copper and iron: the extractions were followed by the percolation of pure water to ensure the removal of EDTA entrapped in soil. The coefficients of dispersion (L) were calculated from the breakthrough curves of bromide ion, and the transport of EDTA and the metalEDTA complexes was evaluated. The molar concentration profiles obtained as breakthrough curves were used to estimate the main parameters of the model. A good accordance with the experimental results was observed: the average standard deviation between predicted and experimental data was about 0.005 %. The correlation of experimental data shows that the simulated transport of metal-EDTA complexes in solution exhibited a delay effect due to the chemical adsorption of such complexes onto the soil organic matter.

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.