Hydrogen production by enhanced methane reforming with membrane reactors or with CO2 capture materials

Pure hydrogen production from methane is a multi-step process run on a large scale for economic reasons. However, hydrogen can be produced in a one-pot continuous process for small scale applications, namely Low Temperature Steam Reforming. Here, Steam Reforming is carried out in a reactor whose walls are composed by a membrane selective toward hydrogen. Pd is the most used membrane material due to its high permeability and selectivity. However, Pd deteriorates at temperatures higher than 500°C, thus the operative temperature of the reaction has to be lowered. However, the employment of a membrane reactor may allow to give high yields thanks to hydrogen removal, which shifts the reaction toward the products. Moreover, pure hydrogen is produced. This work is concentrated on the synthesis of a catalytic system and the investigation of its performances in different processes, namely oxy-reforming, steam reforming and water gas shift, to find appropriate conditions for hydrogen production in a catalytic membrane reactor. The catalyst supports were CeZr and Zr oxides synthesized by microemulsion, impregnated with different noble metals. Pt, Rh and PtRh based catalysts were tested in the oxy reforming process at 500°C, where Rh on CeZr gave the most interesting results. On the opposite, the best performances in low temperature steam reforming were obtained with Rh impregnated on Zr oxide. This catalyst was selected to perform low temperature steam reforming in a Pd membrane reactor. The hydrogen removal given by the membrane allowed to increase the methane conversion over the equilibrium of a classical fixed bed reactor thanks to an equilibrium shift effect. High hydrogen production and recoveries were also obtained, and no other compound permeated through the membrane which proved to be hydrogen selective.

Development and Detailed Characterization of Innovative, High-Performance Membrane Materials for CO2 Capture Processes

The scope of this dissertation is to study the transport phenomena of small molecules in polymers and membranes for gas separation applications, with particular attention to energy efficiency and environmental sustainability. This work seeks to contribute to the development of new competitive selective materials through the characterization of novel organic polymers such as CANALs and ROMPs, as well as through the combination of selective materials obtaining mixed matrix membranes (MMMs), to make membrane technologies competitive with the traditional ones. Kinetic and thermodynamic aspects of the transport properties were investigated in ideal and non-ideal scenarios, such as mixed-gas experiments. The information we gathered contributed to the development of the fundamental understanding related to phenomenon like CO2-induced plasticization and physical aging. Among the most significant results, ZIF-8/PPO MMMs provided materials whose permeability and selectivity were higher than those of the pure materials for He/CO2 separation. The CANALs featured norbornyl benzocyclobutene backbone and thereby introduced a third typology of ladder polymers in the gas separation field, expanding the structural diversity of microporous materials. CANALs have a completely hydrocarbon-based and non-polar rigid backbone, which makes them an ideal model system to investigate structure-property correlations. ROMPs were synthesized by means of the ring opening metathesis living polymerization, which allowed the formation of bottlebrush polymers. CF3-ROMP reveled to be ultrapermeable to CO2, with unprecedented plasticization resistance properties. Mixed-gas experiments in glassy polymer showed that solubility-selectivity controls the separation efficiency of materials in multicomponent conditions. Finally, it was determined that plasticization pressure in not an intrinsic property of a material and does not represent a state of the system, but rather comes from the contribution of solubility coefficient and diffusivity coefficient in the framework of the solution-diffusion model.

Studio del metodo dell'assorbimento diretto della CO2 per l'analisi del radiocarbonio

L’attuale rilevanza rappresentata dalla stretta relazione tra cambiamenti climatici e influenza antropogenica ha da tempo posto l’attenzione sull’effetto serra e sul surriscaldamento planetario così come sull’aumento delle concentrazioni atmosferiche dei gas climaticamente attivi, in primo luogo la CO2. Il radiocarbonio è attualmente il tracciante ambientale per eccellenza in grado di fornire mediante un approccio “top-down” un valido strumento di controllo per discriminare e quantificare il diossido di carbonio presente in atmosfera di provenienza fossile o biogenica. Ecco allora che ai settori applicativi tradizionali del 14C, quali le datazioni archeometriche, si affiancano nuovi ambiti legati da un lato al settore energetico per quanto riguarda le problematiche associate alle emissioni di impianti, ai combustibili, allo stoccaggio geologico della CO2, dall’altro al mercato in forte crescita dei cosiddetti prodotti biobased costituiti da materie prime rinnovabili. Nell’ambito del presente lavoro di tesi è stato quindi esplorato il mondo del radiocarbonio sia dal punto di vista strettamente tecnico e metodologico che dal punto di vista applicativo relativamente ai molteplici e diversificati campi d’indagine. E’ stato realizzato e validato un impianto di analisi basato sul metodo radiometrico mediante assorbimento diretto della CO2 ed analisi in scintillazione liquida apportando miglioramenti tecnologici ed accorgimenti procedurali volti a migliorare le performance del metodo in termini di semplicità, sensibilità e riproducibilità. Il metodo, pur rappresentando generalmente un buon compromesso rispetto alle metodologie tradizionalmente usate per l’analisi del 14C, risulta allo stato attuale ancora inadeguato a quei settori applicativi laddove è richiesta una precisione molto puntuale, ma competitivo per l’analisi di campioni moderni ad elevata concentrazione di 14C. La sperimentazione condotta su alcuni liquidi ionici, seppur preliminare e non conclusiva, apre infine nuove linee di ricerca sulla possibilità di utilizzare questa nuova classe di composti come mezzi per la cattura della CO2 e l’analisi del 14C in LSC.

Chemical looping reforming from methane to syngas: investigation on CeO2 oxygen carrier lifetime and optimal process times

Emissions of CO2 are constantly growing since the beginning of industrial era. Interruption of the production of major emitters sectors (energy and agriculture) is not a viable way and reducing all the emission through carbon capture and storage (CCS) is not economically viable and little publicly accepted, therefore, it becomes fundamentals to take actions like retrofitting already developed infrastructure employing cleanest resources, modify the actual processes limiting the emissions, and reduce the emissions already present through direct air capture. The present thesis will deeply discuss the aspects mentioned in regard to syngas and hydrogen production since they have a central role in the market of energy and chemicals. Among the strategies discussed, greater emphasis is given to the application of looping technologies and to direct air capture processes, as they have been the main point of this work. Particularly, chemical looping methane reforming to syngas was studied with Aspen Plus thermodynamic simulations, thermogravimetric analysis characterization (TGA) and testing in a fixed bed reactor. The process was studied cyclically exploiting the redox properties of a Ce-based oxide oxygen carrier synthetized with a simple forming procedure. The two steps of the looping cycles were studied isothermally at 900 °C and 950° C with a mixture of 10 %CH4 in N2 and of 3% O2 in N2, for carrier reduction and oxidation, respectively. During the stay abroad, in collaboration with the EHT of Zurich, a CO2 capture process in presence of amine solid sorbents was investigated, studying the difference in the performance achievable with the use of contactors of different geometry. The process was studied at two concentrations (382 ppm CO2 in N2 and 5.62% CO2 in N2) and at different flow rates, to understand the dynamics of the adsorption process and to define the mass transfer limiting step.

Synthesis, Modification and Characterization of Polymeric Membranes for CO2 Separation

This doctorate focused on the development of dense polymeric membranes for carbon capture, mostly in post combustion applications, and for natural gas sweetening. The work was supported by the European Project NANOMEMC2 funded under H2020 program. Different materials have been investigated, that rely on two main transport mechanisms: the solution-diffusion and the facilitated transport. In both cases, proper nano-fillers have been added to the matrix, in order to boost the mechanical and permselective properties of the membranes. Facilitated transport membranes were based on the use of was polyvinylamine (PVAm), as main matrix with fixed-site carriers, and L-Arginine as mobile carrier; the filler, used mostly as reinforcer, was carboxymethylated nanocellulose (cNFC). Humid test showed interesting results, and especially the blend made of PVAm/cNFC/Arg in weight ratio 27,5/27,5/45 crossed the Robeson CO2/N2 upper bound, representing current state of the art membranes, with a CO2 permeability of 271 Barrer and CO2/N2 selectivity of 70. Solution diffusion membranes were based on Pebax®2533 matrix which was added with three different graphene oxide (GO)-based materials, namely pristine GO, Porous Graphene Oxide (PGO) and a GO functionalized with polyetheramine (PEAGO). All of them provided a modest but clear increment of permeability of the Pebax matrix, from plus 2% (GO) to plus 8% (PGO), with no change in selectivity. The gas tested with this type of composites were CO2 and N2, for Post combustion capture applications. Pebax®2533 was also chemically modified, obtaining the product called “Benzoyl-P2533”, that was fully characterized, and tested in term of permeation using five gas: CO2, N2, CH4, O2, and He. Modified material showed an increment of the overall permeability of the material of a fair 10% for all gases tested, apart from helium, that increased of almost 50%.

Economy and environment: Issues on transport externalities, CO2 responsibility and environmental Kuznets curve

In this thesis some of the most important issues presently debated on international sustainability are analysed. The thesis is composed of five independent studies that tackle organically the following issues: the maritime transport externalities, the environmental Kuznets curve, the responsibilities in the carbon dioxide emissions and the integrated approach that have to be used to translate the principles of sustainability into policy. The analysis will be instrumental to demonstrating that sustainability, being a matter of economy, society and environment, requires to be analysed in a transdisciplinary perspective. Using an integrated approach to analyse the relationships between economy and environment, this thesis highlight that sustainability management requires joint economic instruments, integrated analysis, societal behavioural changes as well as responsibilities shifting.

Un piano territoriale per la riduzione della concentrazione di CO2 nell'atmosfera e la produzione energetica da fonti rinnovabili per mezzo della filiera delle biomasse

Il progetto propone uno studio per verificare la fattibilita' di un piano territoriale (ideato per il bacino del Po ma di fatto estendibile a tutti i bacini fluviali) per la creazione di una filiera di colture bioenergetiche (biomasse) che, trasportate per mezzo della navigazione fluviale (uno dei mezzi di trasporto a minore emissione di CO2), alimentino una o piu' centrali a nuova tecnologia che associno alla produzione di calore (teleriscaldamento e raffreddamento) e di energia la separazione dei fumi. La CO2 catturata dalla crescita delle biomasse e recuperata dalla combustione, puo' quindi essere segregata nel sottosuolo di aree costiere subsidenti contrastando il fenomeno dell’abbassamento del suolo. Ricavando benefici in tutti i passaggi di attuazione del piano territoriale (lancio dell'agricoltura bioenergetica, rilancio della navigazione a corrente libera, avvio di una economia legata alla logistica del trasporto e dello stoccaggio delle biomasse, generazione di energia pulita, lotta alla subsidenza) il progetto, di fatto, consente di catturare ingenti quantitativi di CO2 dall'atmosfera e di segregarli nel sottosuolo, riducendo l'effetto serra. Nel corso del Dottorato e' stata sviluppata una metodologia di valutazione della sostenibilita' economica ed ambientale del progetto ad un bacino fluviale, che consta di una modulistica di raccolta dei dati di base e di una procedura informatizzata di analisi.

Trasporto di materia in membrane polimeriche e nanocomposite per la separazione di gas

Membrane-based separation processes are acquiring, in the last years, an increasing importance because of their intrinsic energetic and environmental sustainability: some types of polymeric materials, showing adequate perm-selectivity features, appear rather suitable for these applications, because of their relatively low cost and easy processability. In this work have been studied two different types of polymeric membranes, in view of possible applications to the gas separation processes, i.e. Mixed Matrix Membranes (MMMs) and high free volume glassy polymers. Since the early 90’s, it has been understood that the performances of polymeric materials in the field of gas separations show an upper bound in terms of permeability and selectivity: in particular, an increase of permeability is often accompanied by a decrease of selectivity and vice-versa, while several inorganic materials, like zeolites or silica derivates, can overcome this limitation. As a consequence, it has been developed the idea of dispersing inorganic particles in polymeric matrices, in order to obtain membranes with improved perm-selectivity features. In particular, dispersing fumed silica nanoparticles in high free volume glassy polymers improves in all the cases gases and vapours permeability, while the selectivity may either increase or decrease, depending upon material and gas mixture: that effect is due to the capacity of nanoparticles to disrupt the local chain packing, increasing the dimensions of excess free volume elements trapped in the polymer matrix. In this work different kinds of MMMs were fabricated using amorphous Teflon® AF or PTMSP and fumed silica: in all the cases, a considerable increase of solubility, diffusivity and permeability of gases and vapours (n-alkanes, CO2, methanol) was observed, while the selectivity shows a non-monotonous trend with filler fraction. Moreover, the classical models for composites are not able to capture the increase of transport properties due to the silica addition, so it has been necessary to develop and validate an appropriate thermodynamic model that allows to predict correctly the mass transport features of MMMs. In this work, another material, called poly-trimethylsilyl-norbornene (PTMSN) was examined: it is a new generation high free volume glassy polymer that, like PTMSP, shows unusual high permeability and selectivity levels to the more condensable vapours. These two polymer differ each other because PTMSN shows a more pronounced chemical stability, due to its structure double-bond free. For this polymer, a set of Lattice Fluid parameters was estimated, making possible a comparison between experimental and theoretical solubility isotherms for hydrocarbons and alcoholic vapours: the successfully modelling task, based on application of NELF model, offers a reliable alternative to direct sorption measurement, which is extremely time-consuming due to the relevant relaxation phenomena showed by each sorption step. For this material also dilation experiments were performed, in order to quantify its dimensional stability in presence of large size, swelling vapours.

Polymeric membranes for CO2 separation: effect of aging, humidity and facilitated transport

Polymeric membranes represent a promising technology for gas separation processes, thanks to low costs, reduced energy consumption and limited waste production. The present thesis aims at studying the transport properties of two membrane materials, suitable for CO2 purification applications. In the first part, a polyimide, Matrimid 5218, has been throughout investigated, with particular reference to the effect of thermal treatment, aging and the presence of water vapor in the gas transport process. Permeability measurements showed that thermal history affects relevantly the diffusion of gas molecules across the membrane, influencing also the stability of the separation performances. Subsequently, the effect of water on Matrimid transport properties has been characterized for a wide set of incondensable penetrants. A monotonous reduction of permeability took place at increasing the water concentration within the polymer matrix, affecting the investigated gaseous species to the same extent, despite the different thermodynamic and kinetic features. In this view, a novel empirical model, based on the Free Volume Theory, has been proposed to qualitatively describe the phenomenon. Moreover, according to the accurate representation of the experimental data, the suggested approach has been combined with a more rigorous thermodynamic tool (NELF Model), allowing an exhaustive description of water influence on the single parameters contributing to the gas permeation across the membrane. In the second part, the study has focused on the synthesis and characterization of facilitated transport membranes, able to achieving outstanding separation performances thanks to the chemical enhancement of CO2 permeability. In particular, the transport properties have been investigated for high pressure CO2 separation applications and specific solutions have been proposed to solve stability issues, frequently arising under such severe conditions. Finally, the effect of different process parameters have been investigated, aiming at the identification of the optimal conditions capable to maximize the separation performance.

Radiative neutron capture cross section on 238U at the n_TOF CERN facility: a high precision measurement

The aim of this work is to provide a precise and accurate measurement of the 238U(n,gamma) reaction cross-section. This reaction is of fundamental importance for the design calculations of nuclear reactors, governing the behaviour of the reactor core. In particular, fast neutron reactors, which are experiencing a growing interest for their ability to burn radioactive waste, operate in the high energy region of the neutron spectrum. In this energy region inconsistencies between the existing measurements are present up to 15%, and the most recent evaluations disagree each other. In addition, the assessment of nuclear data uncertainty performed for innovative reactor systems shows that the uncertainty in the radiative capture cross-section of 238U should be further reduced to 1-3% in the energy region from 20 eV to 25 keV. To this purpose, addressed by the Nuclear Energy Agency as a priority nuclear data need, complementary experiments, one at the GELINA and two at the n_TOF facility, were scheduled within the ANDES project within the 7th Framework Project of the European Commission. The results of one of the 238U(n,gamma) measurement performed at the n_TOF CERN facility are presented in this work, carried out with a detection system constituted of two liquid scintillators. The very accurate cross section from this work is compared with the results obtained from the other measurement performed at the n_TOF facility, which exploit a different and complementary detection technique. The excellent agreement between the two data-sets points out that they can contribute to the reduction of the cross section uncertainty down to the required 1-3%.

Solubility, diffusivity and permeability of gases in glassy polymers

Gas separation membranes of high CO2 permeability and selectivity have great potential in both natural gas sweetening and carbon dioxide capture. Many modified PIM membranes results permselectivity above Robinson upper bound. The big problem that should be solved for these polymers to be commercialized is their aging through time. In high glassy polymeric membrane such as PIM-1 and its modifications, solubility selectivity has more contribution towards permselectivity than diffusivity selectivity. So in this thesis work pure and mixed gas sorption behavior of carbon dioxide and methane in three PIM-based membranes (PIM-1, TZPIM-1 and AO-PIM-1) and Polynonene membrane is rigorously studied. Sorption experiment is performed at different temperatures and molar fraction. Sorption isotherms found from the experiment shows that there is a decrease of solubility as the temperature of the experiment increases for both gases in all polymers. There is also a decrease of solubility due to the presence of the other gas in the system in the mixed gas experiments due to competitive sorption effect. Variation of solubility is more visible in methane sorption than carbon dioxide, which will make the mixed gas solubility selectivity higher than that of pure gas solubility selectivity. Modeling of the system using NELF and Dual mode sorption model estimates the experimental results correctly Sorption of gases in heat treated and untreated membranes show that the sorption isotherms don’t vary due to the application of heat treatment for both carbon dioxide and methane. But there is decrease in the diffusivity coefficient and permeability of pure gases due to heat treatment. Both diffusivity coefficient and permeability decreases with increasing of heat treatment temperature. Diffusivity coefficient calculated from transient sorption experiment and steady state permeability experiment is also compared in this thesis work. The results reveal that transient diffusivity coefficient is higher than steady state diffusivity selectivity.