Chemical and structural characterization of V2O5/TiO2 catalysts

A series of V2O5/TiO2 samples was synthesized by sol-gel and impregnation methods with different contents of vanadia. These samples were characterized by x-ray diffraction (XRD), Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and electronic paramagnetic resonance (EPR). XRD detected rutile as the predominant phase for pure TiO2 prepared by the sol-gel method. The structure changed to anatase when the vanadia loading was increased. Also, anatase was the predominant phase for samples obtained by the impregnation method. Raman measurements identified two species of surface vanadium: monomeric vanadyl (V4+) and polymeric vanadates (V5+). XPS results indicated that Ti ions were in octahedral position surrounded by oxygen ions. The V/Ti atomic ratios showed that V ions were highly dispersed on the vanadia/titania surface obtained by the sol-gel method. EPR analysis detected three V4+ ion types: two of them were located in axially symmetric sites substituting for Ti4+ ions in the rutile structure, and the third one was characterized by magnetically interacting V4+ ions in the form of pairs or clusters. A partial oxidation of V4+ to V5+ was evident from EPR analysis for materials with higher concentrations of vanadium. (C) 2001 American Vacuum Society.

V(2)O(5)/TiO(2) catalytic xerogels raman and EPR studies

Raman spectroscopy and Electron Paramagnetic Resonance (EPR) studies were performed on a series of V(2)O(5)/TiO(2) catalysts prepared by a modified sol-gel method in order to identify the vanadium species. Two species of surface vanadium were identified by Raman measurements, monomeric vanadyls and polymeric vanadates. Monomeric vanadyls are characterized by a narrow Raman band at 1030 cm(-1) and polymeric vanadates by two broad bands in the region from 900 to 960 cm(-1) and 770 to 850 cm(-1). The Raman spectra do not exhibit characteristic peaks of crystalline V(2)O(5). These results are in agreement with those of X-ray Diffractometry (XRD) and Fourier Transform Infrared (FT-IR) previously reported (C.B. Rodella et al., J. Sol-Gel Sci. Techn., submitted). At least three families of V(4+) ions were identified by EPR investigations. The analysis of the EPR spectra suggests that isolated V(4+) ions are located in sites with octahedral symmetry substituting for Ti(4+) ions in the rutile structure. Magnetically interacting V(4+) ions are also present as pairs or clusters giving rise to a broad and structureless EPR line. At higher concentration of V(2)O(5), a partial oxidation of V(4+) to V(5+) is apparent from the EPR results.

Nb-containing hematites Fe2-xNbxO3: The role of Nb5+ on the reactivity in presence of the H2O2 or ultraviolet light

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Increase on incineration capacity and NOx control for air enrichment in the experimental simulation of aqueous residue incineration

An experimental investigation of air enrichment in a combustion chamber designed to incinerate aqueous residues is presented. Diesel fuel and liquefied petroleum gas (LPG) were used independently as fuels. An increase of 85% in the incineration capacity was obtained with nearly 50% O-2 in the oxidant gas, in comparison to incineration with air only. The incineration capacity continues increasing for enrichment levels above 50% O-2 , although at a lower pace. For complete oxy-flame combustion (100% O-2 ), the increase of the incineration capacity was about 110% relative to the starting conditions and about 13.5% relative to the condition with 50% O-2 . The CO concentration measured near the flame front decreases drastically with the increase of O-2 content in the oxidant gas. At the chamber exit, the CO concentration was always near zero, indicating that the chamber residence time was sufficient to complete fuel oxidation in any test setting. For diesel fuel, the NOx was entirely formed in the first region of the combustion chamber. For diesel fuel, there was some increase in the NOx concentration up to 35% of O-2 ; this increase became very sharp after that. From 60 ppm, at operation with air only, the NOx concentration raises to 200 ppm at 35% O-2 , and then to 2900 ppm at 74% O-2 . The latter corresponds to six times more NOx in terms of the ratio of mass of NO to mass of residue, compared to the situation of combustion with air only. For LPG, the NOx concentrations reached 4200 ppm at 80% O-2 , corresponding to nine times more, also in terms of the ratio of mass of NO to mass of residue, in comparison with combustion with air only. Results of different techniques used to control the NOx emission during air enrichment are discussed: (a) variation of the recirculated zone intensity, (b) increase of the spray Sauter mean diameter, (c) fuel staging, (d) oxidizer staging, and (e) ammonia injection. The present paper shows that NOx emission may be controlled without damage of the increase of incineration capacity by the enrichment and with low emission of partial oxidation pollutants such as CO.

Thermal behaviour of Tin(II) complex with 8-hydroxyquinolinate in the solid state

Tin(II) complexes with 8-hydroxyquinolinate in solid state have been obtained by adding aqueous ammonium to a solution containing stannous chloride and 8-hydroxiquinoline in medium of HCl and acetone up to pH 5 and 9, respectively. The products obtained show the same composition, Sn(C9H6ON)(2); however there are some differences regarding both the thermal behaviour in an oxidant atmosphere and morphology. These products were characterised by elemental and complexometric analysis, TG and DTA curves, infrared and X-ray diffractometry. TG curves show, above 448 K, the partial oxidation on air atmosphere of Sn(II) complexes to Sn(IV) complexes, SnO(C9H6ON)(2). This behaviour does not depend only on pH in which the compounds were obtained but also on the heating rate in TG curves. Sn(II) complexes volatilise almost completely on nitrogen atmosphere and partially on air atmosphere depending on the oxidation degree of the compound.

Oxidative dissolution of chalcopyrite by Thiobacillus ferrooxidans

The oxidative dissolution of research-grade chalcopyrite was characterized in respirometric and growth experiments with Thiobacillus ferrooxidans. In respirometric experiments with chalcopyrite, the pH of mineral salts medium increased to values that inhibited the oxygen uptake activity of T. ferrooxidans. In glycine-H 2SO 4 buffered medium the pH remained stable and oxygen uptake was not inhibited. In cultures growing with chalcopyrite as the sole source of energy, pH changes were only minor during the incubation. The redox potential values increased to about 600 mV during the bacterial oxidation of chalcopyrite in the presence and absence of additional Fe 2+, while they remained at about 350 mV in abiotic control flasks. Iron in chalcopyrite was solubilized and oxidized to Fe 3+ by T. ferrooxidans. In the abiotic controls, by comparison, less iron was solubilized and it remained as Fe 2+. Jarosite was a major solid- phase product in T. ferrooxidans cultures. The solub'flization of copper from chalcopyrite in inoculated flasks was enhanced in the presence of additional Fe 2+.Accumulation of S 0, reflecting partial oxidation of the S-entity of chalcopyrite, was apparent from the x-ray diffraction analysis of solid residues from the inoculated flasks as well the abiotic controls. © 1997 Elsevier B.V. All rights reserved.

A preliminary physicochemical, exergetic and economic study of hydrogen production utilizing glycerol

This work has as objective to demonstrate technical and economic viability of hydrogen production utilizing glycerol. The volume of this substance, which was initially produced by synthetic ways (from oil-derived products), has increased dramatically due mainly to biodiesel production through transesterification process which has glycerol as main residue. The surplus amount of glycerol has been generally utilized to feed poultry or as fuel in boilers, beyond other applications such as production of soaps, chemical products for food industry, explosives, and others. The difficulty to allocate this additional amount of glycerol has become it in an enormous environment problem, in contrary to the objective of biodiesel chain, which is to diminish environmental impact substituting oil and its derivatives, which release more emissions than biofuels, do not contribute to CO2-cycle and are not renewable sources. Beyond to utilize glycerol in combustion processes, this material could be utilized for hydrogen production. However, a small quantity of works (theoretical and experimental) and reports concerning this theme could be encountered. Firstly, the produced glycerol must be purified since non-reacted amounts of materials, inclusively catalysts, contribute to deactivate catalysts utilized in hydrogen production processes. The volume of non-reacted reactants and non-utilized catalysts during transesterification process could be reutilized. Various technologies of thermochemical generation of hydrogen that utilizes glycerol (and other fuels) were evaluated and the greatest performances and their conditions are encountered as soon as the most efficient technology of hydrogen production. Firstly, a physicochemical analysis must be performed. This step has as objective to evaluate the necessary amount of reactants to produce a determined volume of hydrogen and determine thermodynamic conditions (such as temperature and pressure) where the major performances of hydrogen production could be encountered. The calculations are based on the process where advance degrees are found and hence, fractions of products (especially hydrogen, however, CO2, CO, CH4 and solid carbon could be also encountered) are calculated. To produce 1 Nm3/h of gaseous hydrogen (necessary for a PEMFC - Proton Exchange Membrane Fuel Cell - containing an electric efficiency of about 40%, to generate 1 kWh), 0,558 kg/h of glycerol is necessary in global steam reforming, 0,978 kg/h of glycerol in partial oxidation and cracking processes, and 0,782 kg/h of glycerol in autothermal reforming process. The dry reforming process could not be performed to produce hydrogen utilizing glycerol, in contrary to the utilization of methane, ethanol, and other hydrocarbons. In this study, steam reforming process was preferred due mainly to higher efficiencies of production and the need of minor amount of glycerol as cited above. In the global steam reforming of glycerine, for one mole of glycerol, three moles of water are necessary to produce three moles of CO2 and seven moles of H2. The response reactions process was utilized to predict steam reforming process more accurately. In this mean, the production of solid carbon, CO, and CH4, beyond CO2 and hydrogen was predicted. However, traces of acetaldehyde (C2H2), ethylene (C2H4), ethylene glycol, acetone, and others were encountered in some experimental studies. The rates of determined products obviously depend on the adopted catalysts (and its physical and chemical properties) and thermodynamic conditions of hydrogen production. Eight reactions of steam reforming and cracking were predicted considering only the determined products. In the case of steam reforming at 600°C, the advance degree of this reactor could attain its maximum value, i.e., overall volume of reactants could be obtained whether this reaction is maintained at 1 atm. As soon as temperature of this reaction increases the advance degree also increase, in contrary to the pressure, where advance degree decrease as soon as pressure increase. The fact of temperature of reforming is relatively small, lower costs of installation could be attained, especially cheaper thermocouples and smaller amount of thermo insulators and materials for its assembling. Utilizing the response reactions process in steam reforming, the predicted volumes of products, for the production of 1 Nm3/h of H2 and thermodynamic conditions as cited previously, were 0,264 kg/h of CO (13% of molar fraction of reaction products), 0,038 kg/h of CH4 (3% of molar fraction), 0,028 kg/h of C (3% of molar fraction), and 0,623 kg/h of CO2 (20% of molar fraction). Through process of water-gas shift reactions (WGSR) an additional amount of hydrogen could be produced utilizing mainly the volumes of produced CO and CH4. The overall results (steam reforming plus WGSR) could be similar to global steam reforming. An attention must to be taking into account due to the possibility to produce an additional amount of CH4 (through methanation process) and solid carbon (through Boudouard process). The production of solid carbon must to be avoided because this reactant diminishes (filling the pores) and even deactivate active area of catalysts. To avoid solid carbon production, an additional amount of water is suggested. This method could be also utilized to diminish the volume of CO (through WGSR process) since this product is prejudicial for the activity of low temperature fuel cells (such as PEMFC). In some works, more three or even six moles of water are suggested. A net energy balance of studied hydrogen production processes (at 1 atm only) was developed. In this balance, low heat value of reactant and products and utilized energy for the process (heat supply) were cited. In the case of steam reforming utilizing response reactions, global steam reforming, and cracking processes, the maximum net energy was detected at 700°C. Partial oxidation and autothermal reforming obtained negative net energy in all cited temperatures despite to be exothermic reactions. For global steam reforming, the major value was 114 kJ/h. In the case of steam reforming, the highest value of net energy was detected in this temperature (-170 kJ/h). The major values were detected in the cracking process (up to 2586 kJ/h). The exergetic analysis has as objective, associated with physicochemical analysis, to determine conditions where reactions could be performed at higher efficiencies with lower losses. This study was performed through calculations of exergetic and rational efficiencies, and irreversibilities. In this analysis, as in the previously performed physicochemical analysis, conditions such as temperature of 600°C and pressure of 1 atm for global steam reforming process were suggested due to lower irreversibility and higher efficiencies. Subsequently, higher irreversibilities and lower efficiencies were detected in autothermal reforming, partial oxidation and cracking process. Comparing global reaction of steam reforming with more-accurate steam reforming, it was verified that efficiencies were diminished and irreversibilities were increased. These results could be altered with introduction of WGSR process. An economic analysis could be performed to evaluate the cost of generated hydrogen and determine means to diminish the costs. This analysis suggests an annual period of operation between 5000-7000 hours, interest rates of up to 20% per annum (considering Brazilian conditions), and pay-back of up to 20 years. Another considerations must to be take into account such as tariffs of utilized glycerol and electricity (to be utilized as heat source and (or) for own process as pumps, lamps, valves, and other devices), installation (estimated as US$ 15.000 for a plant of 1 Nm3/h) and maintenance cost. The adoption of emission trading schemes such as carbon credits could be performed since this is a process with potential of mitigates environment impact. Not considering credit carbons, the minor cost of calculated H2 was 0,16288 US$/kWh if glycerol is also utilized as heat sources and 0,17677 US$/kWh if electricity is utilized as heat sources. The range of considered tariff of glycerol was 0-0,1 US$/kWh (taking as basis LHV of H2) and the tariff of electricity is US$ 0,0867 US$/kWh, with demand cost of 12,49 US$/kW. The costs of electricity were obtained by Companhia Bandeirante, localized in São Paulo State. The differences among costs of hydrogen production utilizing glycerol and electricity as heat source was in a range between 0,3-5,8%. This technology in this moment is not mature. However, it allows the employment generation with the additional utilization of glycerol, especially with plants associated with biodiesel plants. The produced hydrogen and electricity could be utilized in own process, increasing its final performance.

Efeitos das variações sazonais do clima tropical úmido sobre as águas e sedimentos de manguezais do estuário do rio Marapanim, costa nordeste do Estado do Pará

ABSTRACT: To evaluate the short period climatic variations impact over Amazonic mangrove ecosystem, studies were carried out on the northeast coast of Para State. Sediments, surficial and interstitial waters were collected and examinated throughout salinity, pH and Eh (mV) measurements; mineralogical determination using X-ray diffraction and electronic microscopy. Chemical analysis of dissolved sulfides, sulfate and chloride, among others were made in samples collected seasonally, under spring and neap tides conditions. The seasonal chloride variations in the interstitial waters shows 20 g/l during the dry season and less of 10 g/l in the season; the concentration in surficial are higher at neap tides (rainy season) and spring tide (dry season). The dissolved sulfides were found only at 10 cm, indicating sediment exposure to the atmospheric oxygen advectives fluxes. The dissolved iron rates increases between 0-10 cm and the pH tends to neutrality. The saturation of interstitial waters at dry season is indicated by evaporitic minerals: gypsum and halite. The pluviometric variations are responsible by gradual changes in the nutrient and physical chemical properties of surficial and interstitial waters, into the saline equilibrium control at coastal waters, in the salinization and desalinization of sediments and the distribution of mangrove vegetation at the estuary. The prolonged exposure of sediments during the dry season and the morphological characteristics contribute to the total or partial oxidation of surficial sediments, modifying the mineralogy of sediments and the physical chemical characteristics of interstitial waters.

Synthesis of Carbon Nanomaterials through Up-Cycling Agricultural and Municipal Solid Wastes

This work addresses the synthesis of carbon nanomaterials (CNMs) by up-cycling common solid wastes. These feedstocks could supersede the use of costly and often toxic or highly flammable chemicals, such as hydrocarbon gases, carbon monoxide, and hydrogen, which are commonly used as feedstocks in current nanomanufacturing processes for CNMs. Agricultural sugar cane bagasse and corn residues, scrap tire chips, and postconsumer polyethylene (PE) and polyethylene terephthalate (PET) bottle shreddings were either thermally treated by sole pyrolysis or by sequential pyrolysis and partial oxidation. The resulting gaseous carbon-bearing effluents were then channeled into a heated reactor. CNMs, including carbon nanotubes, were catalytically synthesized therein on stainless steel meshes. This work revealed that the structure of the resulting CNMs is determined by the feedstock type, through the disparate mixtures of carbon-bearing gases generated when different feedstocks are pyrolyzed. CNM characterization was conducted by scanning and transmission electron microscopy as well as by Raman spectroscopy and by thermogravimetric analysis. Gas chromatography was used to characterize the gases in the synthesis chamber. This work demonstrated an alternative method for efficient manufacturing of CNMs using both biodegradable and nonbiodegradable agricultural and municipal carbonaceous wastes.

Thermal stability and the magnetic properties of hybrid vanadium oxide-tetradecylamine nanotubes

Vanadium oxide nanotubes (NTs) were synthesized by the sol-gel method followed by a long-term hydrothermal treatment. The obtained nanotubes have a multiwall structure, and 70% of vanadium ions are in the V4+ state. This percentage was derived by evaluating three components of the magnetic susceptibility; namely, (i) the paramagnetic Curie-Weiss behavior, (ii) antiferromagnetic dimers, and (iii) magnetic trimers. The as-made NTs were annealed in situ in the cavity of the electron paramagnetic resonance (EPR) spectrometer. The line shape changes irreversibly at 390 K, and the EPR susceptibility presents an anomaly at 425 K. These changes are interpreted as a partial oxidation of the V4+ ions and consequently a decrease in the concentration of the magnetic species. The quantification of the V4+ ions of the annealed NTs reveals a diminution to 39% of V4+, a weakening of the Curie-Weiss and antiferromagnetic dimers contributions, and the suppression of magnetic trimers. Vibrational studies confirm the decrease of V4+ amount. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4749417]

Functionalization of gold and silver nanoparticles with diphenyl dichalcogenides probed by surface enhanced Raman scattering

This paper describes a surface-enhanced Raman scattering (SERS) systematic investigation regarding the functionalization of gold (Au) and silver (Ag) nanoparticles with diphenyl dichalcogenides, i.e. diphenyl disulfide, diphenyl diselenide, and diphenyl ditelluride. Our results showed that, in all cases, functionalization took place with the cleavage of the chalcogenchalcogen bond on the surface of the metal. According to our density functional theory calculations, the molecules assumed a tilted orientation with respect to the metal surface for both Au and Ag, in which the angle of the phenyl ring relative to the metallic surface decreased as the mass of the chalcogen atom increased. The detected differences in the ordinary Raman and SERS spectra were assigned to the distinct stretching frequencies of the carbonchalcogen bond and its relative contribution to the ring vibrational modes. In addition, the SERS spectra showed that there was no significant interaction between the phenyl ring and the surface, in agreement with the tilted orientation observed from our density functional theory calculations. The results described herein indicate that diphenyl dichalcogenides can be successfully employed as starting materials for the functionalization of Au nanoparticles with organosulfur, organoselenium, and organotellurium compounds. On the other hand, diphenyl disulfide and diphenyl diselenide could be employed for the functionalization of Ag nanoparticles, while the partial oxidation of the organotellurium unit could be detected on the Ag surface. Copyright (C) 2011 John Wiley & Sons, Ltd.

Ni catalyst on mixed support of CeO2-ZrO2 and Al2O3: Effect of composition of CeO2-ZrO2 solid solution on the methane steam reforming reaction

In this study, catalysts containing 5 wt.% Ni deposited on a support composed of a CeO2-ZrO2 solid solution deposited on alumina were tested in the steam reforming of methane. The supports, with various ratios of Ce to Zr, were prepared by co-precipitation of the oxide precursors, followed by calcination in synthetic air. The catalysts were then prepared by Ni impregnation of the supports. The prepared solids were characterized by temperature-programmed reduction with H-2 (TPR-H-2), in situ X-ray diffraction (XRD) and X-ray absorption near-edge structure (XANES) spectroscopy. The XRD analysis confirmed the formation of a solid solution between ZrO2 and CeO2. In the catalytic tests, it was found that catalysts with higher Ce content did not exhibit deactivation during 6 h of reaction. The catalyst with highest Ce content, Ni(0.8Ce0.2Zr)AI, provided the best result, with the highest rate of conversion of methane and the lowest carbon deposition, which may be partly due to the smaller Ni-0 crystallites in this sample and also the segregated CeO2 particles may have favored H2O adsorption which could lead to higher C gasification. (C) 2012 Elsevier B.V. All rights reserved.

Catalysts for H2 production

The research of new catalysts for the hydrogen production described in this thesis was inserted within a collaboration of Department of Industrial Chemistry and Materials of University of Bologna and Air Liquide (Centre de Recherche Claude-Delorme, Paris). The aim of the work was focused on the study of new materials, active and stable in the hydrogen production from methane, using either a new process, the catalytic partial oxidation (CPO), or a enhanced well-established process, the steam methane reforming (SMR). Two types of catalytic materials were examined: 1) Bulk catalysts, i.e. non-supported materials, in which the active metals (Ni and/or Rh) are stabilized inside oxidic matrix, obtained from perovskite type compounds (PVK) and from hydrotalcite type precursors (HT); 2) Structured catalysts, i.e. catalysts supported on materials having high thermal conductivity (SiC and metallic foams). As regards the catalytic partial oxidation, the effect of the metal (Ni and/or Rh), the role of the metal/matrix ratio and the matrix formulation of innovative catalysts obtained from hydrotalcite type precursors and from perovskites were examined. In addition, about steam reforming process, the study was carried out first on commercial type catalysts, examining the deactivation in industrial conditions, the role of the operating conditions and the activity of different type of catalysts. Then, innovative materials bulk (PVK and HT) and structured catalysts (SiC and metallic foam) were studied and a new preparation method was developed.

Biomass Gasification - Process analysis and dimensioning aspects for downdraft units and gas cleaning lines

In such territories where food production is mostly scattered in several small / medium size or even domestic farms, a lot of heterogeneous residues are produced yearly, since farmers usually carry out different activities in their properties. The amount and composition of farm residues, therefore, widely change during year, according to the single production process periodically achieved. Coupling high efficiency micro-cogeneration energy units with easy handling biomass conversion equipments, suitable to treat different materials, would provide many important advantages to the farmers and to the community as well, so that the increase in feedstock flexibility of gasification units is nowadays seen as a further paramount step towards their wide spreading in rural areas and as a real necessity for their utilization at small scale. Two main research topics were thought to be of main concern at this purpose, and they were therefore discussed in this work: the investigation of fuels properties impact on gasification process development and the technical feasibility of small scale gasification units integration with cogeneration systems. According to these two main aspects, the present work was thus divided in two main parts. The first one is focused on the biomass gasification process, that was investigated in its theoretical aspects and then analytically modelled in order to simulate thermo-chemical conversion of different biomass fuels, such as wood (park waste wood and softwood), wheat straw, sewage sludge and refuse derived fuels. The main idea is to correlate the results of reactor design procedures with the physical properties of biomasses and the corresponding working conditions of gasifiers (temperature profile, above all), in order to point out the main differences which prevent the use of the same conversion unit for different materials. At this scope, a gasification kinetic free model was initially developed in Excel sheets, considering different values of air to biomass ratio and the downdraft gasification technology as particular examined application. The differences in syngas production and working conditions (process temperatures, above all) among the considered fuels were tried to be connected to some biomass properties, such elementary composition, ash and water contents. The novelty of this analytical approach was the use of kinetic constants ratio in order to determine oxygen distribution among the different oxidation reactions (regarding volatile matter only) while equilibrium of water gas shift reaction was considered in gasification zone, by which the energy and mass balances involved in the process algorithm were linked together, as well. Moreover, the main advantage of this analytical tool is the easiness by which the input data corresponding to the particular biomass materials can be inserted into the model, so that a rapid evaluation on their own thermo-chemical conversion properties is possible to be obtained, mainly based on their chemical composition A good conformity of the model results with the other literature and experimental data was detected for almost all the considered materials (except for refuse derived fuels, because of their unfitting chemical composition with the model assumptions). Successively, a dimensioning procedure for open core downdraft gasifiers was set up, by the analysis on the fundamental thermo-physical and thermo-chemical mechanisms which are supposed to regulate the main solid conversion steps involved in the gasification process. Gasification units were schematically subdivided in four reaction zones, respectively corresponding to biomass heating, solids drying, pyrolysis and char gasification processes, and the time required for the full development of each of these steps was correlated to the kinetics rates (for pyrolysis and char gasification processes only) and to the heat and mass transfer phenomena from gas to solid phase. On the basis of this analysis and according to the kinetic free model results and biomass physical properties (particles size, above all) it was achieved that for all the considered materials char gasification step is kinetically limited and therefore temperature is the main working parameter controlling this step. Solids drying is mainly regulated by heat transfer from bulk gas to the inner layers of particles and the corresponding time especially depends on particle size. Biomass heating is almost totally achieved by the radiative heat transfer from the hot walls of reactor to the bed of material. For pyrolysis, instead, working temperature, particles size and the same nature of biomass (through its own pyrolysis heat) have all comparable weights on the process development, so that the corresponding time can be differently depending on one of these factors according to the particular fuel is gasified and the particular conditions are established inside the gasifier. The same analysis also led to the estimation of reaction zone volumes for each biomass fuel, so as a comparison among the dimensions of the differently fed gasification units was finally accomplished. Each biomass material showed a different volumes distribution, so that any dimensioned gasification unit does not seem to be suitable for more than one biomass species. Nevertheless, since reactors diameters were found out quite similar for all the examined materials, it could be envisaged to design a single units for all of them by adopting the largest diameter and by combining together the maximum heights of each reaction zone, as they were calculated for the different biomasses. A total height of gasifier as around 2400mm would be obtained in this case. Besides, by arranging air injecting nozzles at different levels along the reactor, gasification zone could be properly set up according to the particular material is in turn gasified. Finally, since gasification and pyrolysis times were found to considerably change according to even short temperature variations, it could be also envisaged to regulate air feeding rate for each gasified material (which process temperatures depend on), so as the available reactor volumes would be suitable for the complete development of solid conversion in each case, without even changing fluid dynamics behaviour of the unit as well as air/biomass ratio in noticeable measure. The second part of this work dealt with the gas cleaning systems to be adopted downstream the gasifiers in order to run high efficiency CHP units (i.e. internal engines and micro-turbines). Especially in the case multi–fuel gasifiers are assumed to be used, weightier gas cleaning lines need to be envisaged in order to reach the standard gas quality degree required to fuel cogeneration units. Indeed, as the more heterogeneous feed to the gasification unit, several contaminant species can simultaneously be present in the exit gas stream and, as a consequence, suitable gas cleaning systems have to be designed. In this work, an overall study on gas cleaning lines assessment is carried out. Differently from the other research efforts carried out in the same field, the main scope is to define general arrangements for gas cleaning lines suitable to remove several contaminants from the gas stream, independently on the feedstock material and the energy plant size The gas contaminant species taken into account in this analysis were: particulate, tars, sulphur (in H2S form), alkali metals, nitrogen (in NH3 form) and acid gases (in HCl form). For each of these species, alternative cleaning devices were designed according to three different plant sizes, respectively corresponding with 8Nm3/h, 125Nm3/h and 350Nm3/h gas flows. Their performances were examined on the basis of their optimal working conditions (efficiency, temperature and pressure drops, above all) and their own consumption of energy and materials. Successively, the designed units were combined together in different overall gas cleaning line arrangements, paths, by following some technical constraints which were mainly determined from the same performance analysis on the cleaning units and from the presumable synergic effects by contaminants on the right working of some of them (filters clogging, catalysts deactivation, etc.). One of the main issues to be stated in paths design accomplishment was the tars removal from the gas stream, preventing filters plugging and/or line pipes clogging At this scope, a catalytic tars cracking unit was envisaged as the only solution to be adopted, and, therefore, a catalytic material which is able to work at relatively low temperatures was chosen. Nevertheless, a rapid drop in tars cracking efficiency was also estimated for this same material, so that an high frequency of catalysts regeneration and a consequent relevant air consumption for this operation were calculated in all of the cases. Other difficulties had to be overcome in the abatement of alkali metals, which condense at temperatures lower than tars, but they also need to be removed in the first sections of gas cleaning line in order to avoid corrosion of materials. In this case a dry scrubber technology was envisaged, by using the same fine particles filter units and by choosing for them corrosion resistant materials, like ceramic ones. Besides these two solutions which seem to be unavoidable in gas cleaning line design, high temperature gas cleaning lines were not possible to be achieved for the two larger plant sizes, as well. Indeed, as the use of temperature control devices was precluded in the adopted design procedure, ammonia partial oxidation units (as the only considered methods for the abatement of ammonia at high temperature) were not suitable for the large scale units, because of the high increase of reactors temperature by the exothermic reactions involved in the process. In spite of these limitations, yet, overall arrangements for each considered plant size were finally designed, so that the possibility to clean the gas up to the required standard degree was technically demonstrated, even in the case several contaminants are simultaneously present in the gas stream. Moreover, all the possible paths defined for the different plant sizes were compared each others on the basis of some defined operational parameters, among which total pressure drops, total energy losses, number of units and secondary materials consumption. On the basis of this analysis, dry gas cleaning methods proved preferable to the ones including water scrubber technology in al of the cases, especially because of the high water consumption provided by water scrubber units in ammonia adsorption process. This result is yet connected to the possibility to use activated carbon units for ammonia removal and Nahcolite adsorber for chloride acid. The very high efficiency of this latter material is also remarkable. Finally, as an estimation of the overall energy loss pertaining the gas cleaning process, the total enthalpy losses estimated for the three plant sizes were compared with the respective gas streams energy contents, these latter obtained on the basis of low heating value of gas only. This overall study on gas cleaning systems is thus proposed as an analytical tool by which different gas cleaning line configurations can be evaluated, according to the particular practical application they are adopted for and the size of cogeneration unit they are connected to.

Preparazione di catalizzatori strutturati per la reazione di ossidazione parziale del metano

Questo lavoro di tesi ha avuto come obiettivo la preparazione di catalizzatori attivi nella reazione di ossidazione parziale catalitica, CPO, del metano per produrre gas di sintesi. I catalizzatori sono stati preparati tramite sintesi elettrochimica di composti di tipo idrotalcite a base di Rh/Mg/Al utilizzando come supporto schiume metalliche costituite da FeCrAlY. L’impiego di questo tipo di supporto comporta una serie di vantaggi, dallo sviluppo del catalizzatore all’ottimizzazione del processo catalitico in termini di prestazioni catalitiche, diminuzione degli “hot spots” termici, diminuzione delle perdite di carico e costi del catalizzatore. La sintesi del catalizzatore è stata effettuata per mezzo di una cella elettrochimica innovativa, che lavora in flusso, e quindi permette la continua rigenerazione della soluzione di sintesi, a differenza di quanto avviene in una cella elettrochimica standard a singolo comparto. La precipitazione dei composti di tipo idrotalcite si ottiene grazie alla tecnica di elettrogenerazione di basi, ovvero grazie alla generazione di un pH basico all’interno della cella elettrochimica a seguito dell’applicazione di un potenziale catodico. Il pH generato è il parametro più importante e determina la natura e la qualità del materiale depositato. È sorta quindi la necessità di sviluppare un sensore potenziometrico miniaturizzato per la determinazione istantanea del pH durante la sintesi, da installare all’interno della schiuma stessa. È possibile correlare le prestazioni catalitiche dei catalizzatori sintetizzati con la cella elettrochimica in flusso, alle loro caratteristiche di morfologia superficiale ed alla composizione chimica, e confrontare le stesse prestazioni catalitiche con quelle ottenute sintetizzando i catalizzatori con la cella elettrochimica standard a singolo comparto.