Dipartimento di Ingegneria dell'Ambiente - Tesi di Dottorato

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Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Ingegneria per l'Ambiente e il Territorio e Ingegneria Chimica dell'Università della Calabria.

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Subject: search.filters.subject.Idrogeno

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    Renewable energy generation and hydrogen production from concentrated brine by reverse eectrodialysis
    (2016-02-26) Tufa, Ramato Ashu; Drioli, Enrico; Curcio, Efrem; Molinari, Raffaele
    Salinity Gradient Power-Reverse Electrodialysis (SGP-RE) is among the emerging membrane-based technologies for renewable energy generation. In RE, cation exchange membranes (CEM) and anion exchange membranes (AEMs) are alternatively aligned to create a high concentration compartment (HCC) and low concentration compartment (LCC). When the compartments are feed by a low concentration and high concentration solution, salinity gradient is created which initiates the diffusive flux of ions towards electrodes. Electricity is generated by the redox process occurring at the electrodes. The total voltage generated (open circuit voltage, OCV) is proportional to the number of membrane pairs (cells). One of the challenges pertaining to the Ohmic losses when using very low concentration salt solutions like river water can be reduced by working with highly concentrated brines (Chapter 1). Investigation of the performance of RE under realistic high-salinity conditions is crucial for implementation of RE under natural condition. The most abundant ions in natural waters involve sodium, magnesium, calcium, chloride, sulfate, and bicarbonate. Under this condition, the presence of multivalent ions, in particular Mg2+, have a lowering effect on OCV and hence a reduction of power density. This could be attributed to the enhancement of cell resistance in the presence Mg2+ ion resulting in an increase of membrane resistance. The SGP potential and comparable decrease in power density of RE operated with solutions mimicking real brackish water and exhaust brine from a solar pond depicts the pretreatment requirement in RE for better performance (Chapter 2). Seawater reverse osmosis (SWRO) is the most widespread technology for fresh water production in many parts of the world. Extensive research have been carried out to tackle the technological challenges coming along with the expansion of SWRO practice with time, specifically the reduction of energy consumption. The integrated application RE in desalination technologies in the logic of process intensification is an interesting approach towards low energy desalination. Simultaneous production of energy and desalted water is possible by hybrid application of Direct Contact Membrane Distillation (DCMD) and RE units operated on the retentate stream from a SWRO desalination plant. The use of concentrated brine for energy recovery also leads to Near-Zero Liquid Discharge from desalination systems. This avoids the adverse ecological effect of discharging hypersaline solution into natural water bodies. Thus, integrated application of RE with RO and DCMD for simultaneous water and energy production represent an innovative approach towards low energy desalination and Near-Zero Liquid Discharge paradigm (Chapter 3). The possibilitity to exploit the chemical potential of sulfate wastes by SGP-RE can be a promising alternative renewable energy source. The key challenge remains the property of membrane in sulphate solution. Although the trends in the variation of desirable membrane properties (high permselectivity and low resistance) in Na2SO4 test solutions with varying operating conditions remain similar with that of NaCl test solution, their performance is comparatively low. This has a negative impact on the performance of the RE mainly on the obtained OCV and power density. Hence, design of well optimized and high performance membranes is required for practical applicability of SGP-RE for renewable energy generation from sulfate bearing waste resources (Chapter 4). Ion exchanging membranes (IEMs) are key components in RE. Low resistance and highly permeable ion exchange membranes are required for optimal performance of RE system. For practical applications of RE under real condition, IEMs which are less susceptible to fouling are required. There is a potential risk of fouling (for example, scaling of sparingly soluble salts) of IEM operated in concentrated brine. Operations under real conditions also require feed quality control, as the presence of multivalent ions negatively impact RE performance. The variation in Total Organic Carbon (TOC) and Total Hardness (TH) of feed samples may alter the membranes physico-chemical and electrochemical properties. In addition, long term stability of IEMs in concentrated brine govern their life time. Investigation on fouling and stability of IEMS, specifically in concentrated brines, would be essential to set a clear pretreatment requirement for the performance of RE under natural conditions (Chapter 5). For techno-economic optimization and feasibility study of RE, performance of large scale (industrial scale) systems need to be investigated under varying experimental conditions. Comparative assessment of operating conditions like feed concentration, flow velocity and temperature in a small scale RE and large scale RE systems is essential. In general, the trends in OCV and power density for industrial scale operations remain more or less similar to that of membrane based water and energy technologies (based on the difficulties to meet sustainability criteria) helps in identification of technological gaps and strategic solution (Chapter 9). Future research on RE will be focusing on optimal design and development of high performance membrane in hyper-saline solution. This will extend from design of highly permeable and low resistance ion exchange membranes to the development of fouling resistant and stable membrane, particularly in concentrated brine. The relationship between physicochemical membrane properties and fouling tendency under hyper-saline environment need to be assessed. The effect of other multivalent ions in seawater like SO4 2- and Ca2+ on the performance of RE under extreme operating conditions should be clearly outlined. For integrated applications in desalination technologies, for example with DCMD, the risk of scaling and fouling for practical applications should be investigated deeply. Better membranes and module designs are required for membrane desalination systems in general. For efficient application of RE in hydrogen technologies, specifically with APE water electrolysis, development of highly conductive and durable anion selective membranes as well as highly active and stable catalysts in corrosive alkaline environment is of future research interest. Above all, well established technoeconomic evaluations of a standalone and integrated applications of RE is essential in order to evaluate the feasibility of scale-up and commercialization of the technology as a renewable energy source (Chapter 10).
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    Analysis of membrane reactor integration in hydrogen production process
    (2014-11-11) Mirabelli, Ilaria; Drioli, Enrico; Barbieri, Giuseppe; Molinari, Raffaele
    In the H2 production field, the membrane reactor (MR) technology is considered a promising and interesting technology. In this thesis work the integration in a small scale hydrogen generator of an MR, to carry out the water gas shift reaction (WGS), has been studied. In particular, the effect of MR integration from a systems perspective, i.e. specifically assessing the impact of MR on the whole process, has been investigated. A preliminary design of a pilot scale MR to produced 5 Nm3/h of H2 by reformate stream upgrading has been performed. A CO conversion of 95% and an hydrogen recovery yield of 90% have been fixed as minimum performance target of the WGS-MR. Depending on the system considered to promote the driving force for the permeation, three scenarios have been proposed: base, vacuum and sweep scenario. On the basis of results from a preliminary scenario screening, the required membrane area (ca. 0.179 m2), for vacuum and sweep scenarios, has been estimated by means of an MR modelling and simulation. The results obtained from the pilot scale have been used for the scale-up of the WGS-MR integrated in the 100 Nm3/h hydrogen production unit. The plant for the integrated process (reformer and WGS-MR) has been simulated by using the commercial simulation tool Aspen Plus®. The MR integration, actually, implies a re-design of the process downstream the WGS reactor. Since more than 90% of the produced H2 is directly recovered in the permeate stream, the PSA unit can be removed, leading to a more compact system. For the retentate stream post processing, the possibility to recover the CO2, by means of membrane gas separation technology has been proposed. The results for a two stages membrane separation unit confirmed the technological feasibility of the CO2 capture, achieving the CO2 purity target. Pursuing the logic of process intensification, the comparison with the reference technology (reformer, high temperature shift, PSA) showed as the WGS-MR integrated system results in a more “intensified” process since a higher H2 productivity, a smaller plant and an enhanced exploitation of raw materials are obtained. In addition, since the MR delivers a high-pressure CO2-rich stream, it provides an opportunity for small-scale CO2 capture and thus possible emission reduction. The possibility to extend the spectrum of MR application in reactions of industrial interest, where hydrogen is produced as by-product, has been also studied. In particular, as case study, the direct conversion of n-butane to isobutene has been analysed showing as, from a thermodynamic point of view, better performance (equilibrium conversion up to seven times higher than the one of a traditional reactor) can be obtained.
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    Graphene and titanium based semiconductors in photocatalytic hydrogen and oxygen generation and hydrogenation of organics also in membrane reactors
    (2013-11-12) Lavorato, Cristina; Molinari, Raffaele; Argurio, Pietro; Garcia, Hermenegildo
    The development of graphene (G)-based materials as photocatalysts has become in the last years of high interest due to their sustainability and flexibility in the modification and design, particularly in the field of photocatalytic generation of hydrogen. Carbon based materials are sustainable when they are derived from renewable biomass feedstocks. G is a versatile material allowing different modification strategies to improve its activity. Thus, the present thesis reports that inserting heteroatoms, adding semiconductors or changing the layers size, the activity of the materials prepared can be improved for different applications. Sun light is one of major renewable energy resource. The use of light as driving force for chemical reactions has attracted much attention of organic chemists. Heterogeneous photocatalysis is a discipline which includes a large variety of reactions, in particular hydrogen (considered the perfect renewable energy source in the future) and oxygen generation from water and hydrogenation of multiple bonds are the target of this PhD thesis. Photocatalytic reductions represent an alternative to conventional catalytic hydrogenation and it represent a more sustainable method to synthesize organic compounds under mild conditions in the presence of affordable photocatalysts. Photocatalytic processes in membrane reactors represent a technology of great scientific interest because it allows chemical reactions and separation processes to be accomplished in one step, which in turn results in lower processing cost and minimum environmental impact. The preparation and characterization of G-based semiconductors has been carried out in the first part of the Thesis and their photocatalytic activity for hydrogen and oxygen generation from water was determined in the second part. Graphite was oxidized to graphene oxide (GO) and its photocatalytic activity for hydrogen generation from water/methanol mixtures with visible or solar light was enhanced by the presence of dyes, in the absence of any noble metal. The most efficient tested photocatalyst was the one containing a tris(2,2-bipyridyl) ruthenium(II) complex incorporated in the interlayer spaces of a few layers of GO platelets with a moderate degree of oxidation. This photocatalyst was two orders of magnitude more efficient than a titania based photocatalyst containing Au, when the reaction is performed under 532 nm laser as excitation light. Doping G with nitrogen by pyrolysis of chitosan leads to a material that behaves as a semiconductor and exhibits high efficiency for the photocatalytic generation of hydrogen from water-methanol mixtures with similar efficiency using UV or visible light. This similar photocatalytic activity wis due to the fact that, in contrast to GO, N-doped G exhibits an almost “neutral” absorption spectrum. The main parameter controlling the residual amount of nitrogen and the resulting photocatalytic activity is the pyrolysis temperature that produces an optimal material when the thermal treatment is carried out at 900 °C. Furthermore, N-doped G was able to generate hydrogen also upon illumination of simulated sunlight. The use of G as co-catalyst of metal oxides semiconductors to enhance their photocatalytic activity has been extensively reported. Using alginate, a natural polysaccharide from algae, simultaneously as G precursor and as ceria nanoparticles template agent, a series of materials consisting of highly crystalline ceria nanoparticles embedded on a few layers G matrix has been prepared. Varying the weight percentage of ceria/alginate and the pyrolysis temperature, it was possible to prepare a ceria/G photocatalyst that exhibits about three times higher photocatalytic activity for water oxidation to oxygen than commercial ceria. Pyrolysis at 900 °C under inert atmosphere of alginate renders a graphitic carbon that upon ablation by exposure to a pulsed 532 nm laser (7 ns, 50 mJ pulse−1) in acetonitrile, water, and other solvents leads to the formation of multilayer graphitic quantum dots. The dimensions and the number of layers of these graphitic nanoparticles decrease along the number of laser pulses leading to G quantum dots (GQDs). Accordingly, the emission intensity of these GQDs increases along the number of laser shots, the maximum emission intensity appearing at about 500 nm in the visible region increasing in intensity along the reduction of the particle size. Transient absorption spectroscopy has allowed detection of a transient signal decaying in the microsecond time scale that has been attributed to the charge separation state. During the second part of the present thesis the photocatalytic hydrogenation of acetophenone by using titanium based semiconductors in batch and membrane reactors under UV and visible light has been studied. Different photocatalytic tests have been performed using ethanol or water and formic acid in a batch reactor in order to optimize the reaction parameters before to be applied in membrane reactors with different substrate addition mode. The use of a membrane reactor system for the photocatalytic hydrogenation of acetophenone in water solution with formic acid as hydrogen and electron donor was found to improve the efficiency of the photocatalytic system with respect to the use of batch reactor. The most efficient system for photocatalytic hydrogenation of acetophenone in terms of productivity, amount of phenylethanol produced and extraction of desired product was found to be the membrane reactor in which acetophenone was used as both organic phase and substrate. The presence of palladium enhances the visible light photocatalytic activity of TiO2 photocatalyst, that is not active alone. The productivity by using Pd/TiO2 photocatalyst under visible light increases five times more than using TiO2 under UV light
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    Impianto integrato a membrana per la produzione di idrogeno per PEM-PC
    (2014-06-10) Brunetti, Adele; Drioli, Enrico; Barbieri, Giuseppe; Aiello, Rosario
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    Produzione di Idrogeno dalla reazione di Steam Reforming dell’Etanolo in Reattori a Membrana
    (2014-04-16) Iulianelli, Adolfo; Basile, Angelo; Drioli, Enrico