Francesco Pepe

Modeling carbon dioxide adsorption on polyethylenimine-functionalized TUD-1 mesoporous silica.

Samples of porous, foam-like TUD (Technische Universität Delft)-1 mesoporous silica were functionalized with polyethylenimine and were used as a substrate for CO(2) adsorption. Produced solids were characterized by means of electron microscopy, thermogravimetric analysis, and N(2) adsorption/desorption at 77K, in order to prove that polymer chains efficiently filled the pores of functionalized samples. CO(2) adsorption isotherms on polyethylenimine-containing TUD-1 were evaluated at T=298, 313, 328, and 348 K for pressures up to 100 kPa by means of a volumetric technique. The CO(2) adsorption capacity proved to be significantly dependent on temperature, with the highest capacity encountered at T=348 K. The experimental data for CO(2) adsorption were satisfactorily described by means of the Langmuir isotherm, and the dependence of the isosteric heat on the fractional coverage of the adsorbent was evaluated by means of the vant Hoff equation, showing values in the order of 80 kJ/mol for a fractional coverage of about 50%.

Iron-activated carbon nanocomposite: synthesis, characterization and application for lead removal from aqueous solution

The removal of Pb(II) ions from aqueous solution by adsorption on an Iron-Activated Carbon (IAC) nanocomposite was investigated. Removal studies were carried out in a batch system, and the effects of various operating parameters, such as solution pH, solid to liquid ratio and initial concentration were evaluated. Experimental design was carried out using central composite design (CCD) with response surface methodology (RSM). According to the RSM results, the optimum adsorption conditions for Pb(II) removal by IAC were pH = 6.5, solid to liquid ratio of 3 g L−1 and initial lead concentration of 10 mg L−1. Under these optimum operating conditions, 96.5% of Pb(II) was removed by the IAC nanocomposite. The equilibrium adsorption data were well described by the Freundlich isotherm. The maximum adsorption capacity of IAC was 121.9 mg g−1 for Pb(II). It was observed that the adsorption kinetics of Pb(II) on the IAC could be well analyzed with a pseudo-second-order model.

Pyrolysis, Combustion, and Fragmentation Model of Coal Particles: Preliminary Results

ABSTRACT A mathematical model has been developed to predict fragmentation of particles under a wide range of pyrolysis and combustion conditions. The model is an upgrade of a previous one that took into account only fragmentation during the heat up and devolatilization stage. The model calculates the temperature and oxygen profiles within the particle, the evolution of internal porosity as a consequence of both devolatilization and carbon combustion, the mechanical stress caused by temperature gradients, and by volatiles-generated overpressure inside the particles. Eventually the model calculates the probability of rupture of the particle based on the Weibull (1939) theory. The model has been used to simulate heating of coal particles under inert conditions at different heating rates and temperatures showing good agreement with previous work. The model has been further used to simulate heating under oxidative conditions in order to highlight the role of combustion on fragmentation phenomena.

Chemical modification of activated carbon surface with iron functional groups for efficient separation of vanadium: batch and column study

In this study, iron functional groups-impregnated activated carbon (IIAC) composite was prepared as a novel adsorbent for vanadium separation. Adsorption experiments were performed in batch and column systems, and the effects of various operating parameters, such as solution pH, initial concentration, contact time, and temperature, were evaluated. The kinetic data confirmed the validity of the pseudo-second-order kinetic model for vanadium adsorption on IIAC. The sorption equilibrium data were analyzed using Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. The results showed that IIAC has a vanadium ions adsorption capacity of 313xa0mgxa0g−1. The activation and thermodynamic parameters were determined using kinetics and equilibrium data. The experimental data of the column adsorption process were fitted by Thomas and BDST models. The results showed that Thomas model can well describe the breakthrough curves. The column experiments showed that IIAC composite has good adsorption performance for vanadium ions adsorption.

Chemical Looping Reforming: Impact on the Performances Due to Carbon Fouling on Catalyst

Abstract The paper presents a numerical analysis of an autothermal chemical looping reforming (CLR) process for hydrogen production. A packed–bed reactor has been simulated, which uses a Ni-based oxygen carrier. A one-dimensional pseudo-homogeneous model, validated with data available in literature is used to describe the overall process. The model accounts for different reactions taking place (methane and hydrogen oxidation, steam reforming, dry reforming, Ni and carbon oxidation by air), and simultaneously describes heat and mass transport. To take into account the catalyst fouling due to carbon deposition, CH 4 decomposition and carbon regasification by steam and CO 2 (Boudouard reaction) have been considered in the kinetic model, and a catalyst deactivation function has been introduced. By means of numerical simulations we highlight that carbon deposition gradually blocks catalyst active sites, leading to a progressive loss of catalytic activity. and we quantify the effects of catalyst poisoning on process performances.

Cation selectivity of a Ca2+ pre-exchanged clinoptilolite tuff

Abstract With the purpose to evaluate clinoptilolite for possible use in soil amendment strategies as a substitute of naturally occurring clay minerals, a marketed clinoptilolite-rich tuff coming from Anatolia, Turkey, was submitted, after exhaustive treatment with Ca 2+ solutions, to exchange tests towards some nutrient or noxious cations. Accordingly, time-dependant and equilibrium data of exchange reactions of Pb 2+ , Cu 2+ , Zn 2+ , Na + , K + and NH 4 + for Ca 2+ were collected and the corresponding thermodynamic and kinetic parameters were calculated following standard procedures. Results demonstrated an excellent to good propensity of Ca 2+ -clinoptilolite for K + , NH 4 + and Pb 2+ and a moderate affinity for the other three cations. The conclusion was that a Ca 2+ -rich clinoptilolite tuff can be considered as a good substitute for clay minerals to recover and/or rebuild degraded and depleted soils.

Nanoporous Materials as H2S Adsorbents for Biogas Purification: a Review

Biogas is one of the most promising renewable sources of energy. However, it is also a gas mixture containing acidic gases, such as H2S, useless for energetic purposes, environmentally harmful and damaging for energy conversion devices. This review focuses on nanoporous materials as adsorbents of H2S for biogas purification processes. Cation-exchanged zeolites and impregnated activated carbons have been thoroughly studied since many years for this application, providing good results, in particular for what concerns activated carbons, despite having a limited regenerability. Amino-functionalized ordered mesoporous silicas produced very interesting results, both in terms of adsorption performances and regeneration capacity, but they are largely untested in large-scale “real-life” applications, and deserve further investigations, in particular for H2S and CO2 discrimination. On the contrary, despite reporting very good results, there are only few papers dealing with H2S adsorption on nanoporous metal organic frameworks.

Packed bed sorption enhanced methane reforming on CaO/CuO/Al2O3(NiO) catalyst

Abstract An autothermal sorption-enhanced steam methane reforming in a packed-bed reactor for production of high-purity hydrogen was studied by means of 1D numerical model. The reactor utilises a CaO/CuO/Al2O3(NiO) catalyst. This process is characterised by a number of challenges, such as the choice of the operating conditions to ensure both a production of high-purity H2 stream and an autothermal sorbent regeneration stage. This paper addresses these challenges through numerical simulation. The results for the system cyclically operated in a packed-bed showed a methane conversion of 95%, and a hydrogen yield and selectivity around 3xa0molH2·molCH4-1 and 90%, respectively.

Management of Hazardous By-products of Urban Waste Incineration: Some Considerations on the Italian Situation

Abstract Incineration is regarded as a very efficient technique for municipal solid waste (MSW) management. However, the environmental impact of MSW incineration needs to be carefully taken into account. The most relevant problem originating from MSW incineration is flue gas treatment, since untreated incineration flue gas contains large amounts of macropollutants and micropollutants. Another issue is the disposal of solid by-products of the incineration process. MSW incinerators essentially produce two kinds of solid by-products, i.e., bottom ash and air pollution control (APC) residues. APC residues are regarded as a hazardous waste, and different management strategies have been proposed for their recovery or disposal. In Italy, where this material amounts to about 4xa0×xa0108xa0kg/year, the most common management strategy is disposal via landfilling after solidification with cement or other hydraulic binders. Solidification is usually performed off site, in plants collecting APC residues from different incinerators. Another significant management option is represented by recovery of solidified residues as backfilling material of spent salt mines located in Germany.

Kinetics of the Ba2+/Na+ exchange on a mixed phillipsite-chabazite-rich tuff

Abstract The kinetics of Ba 2+ /Na + ion exchange on a mixed tuff, containing both phillipsite and chabazite, was studied. A fixed bed experimental apparatus was used and the breakthrough curves were determined varying the Ba 2+ concentration in the inlet solution in the range 0.77-17.5 eq-m -3 . The experimental results showed that the tuff under consideration is very selective towards Ba 2+ , with very steep breakthrough curves. A diffusional model, based on the linear driving force (LDF) approximation, was used to interpret the experimental data. The model takes into account both fluid-particle and intra-particle resistances to diffusion, and considers the fact that the tuff contains different zeolites, having different ion exchange properties. Its use allowed to evaluate the internal and the external mass transfer coefficients, and it appeared that, except in one of the experimental runs, their values do not depend on the composition of the liquid phase, confirming the validity of the LDF approximation.