Analisi delle caratteristiche e delle performance di membrane polimeriche a microporosità intrinseca (PIM) per la cattura di CO2

In questo lavoro viene condotta un’analisi critica delle caratteristiche materiali e delle performance di una classe di polimeri recentemente sviluppata, i “Polimeri a Microporosità Intrinseca”, di grande interesse per lo sviluppo di membrane per la separazione di gas, specialmente nella Carbon Capture. Partendo dall’analisi del meccanismo di separazione di gas in membrane polimeriche dense si fornisce una overview sulle tecnologie assodate e innovative per la separazione di gas e per la CC. Le caratteristiche e le proprietà strutturali di rilievo dei polimeri vetrosi sono poi brevemente illustrate e le correlazioni empiriche note tra le suddette e le proprietà di trasporto di materia. Vengono quindi descritti i PIMs analizzando in primis la loro tipica struttura chimica, i processi di sintesi e le caratteristiche principali. Per il PIM-1, capostipite della categoria, il trasporto di gas viene approfondito con lo studio della variabilità delle proprietà quali la permeabilità, la diffusività e la solubilità di penetranti gassosi con i parametri operativi (p, T, composizione dei feed), considerando anche fenomeni tipici dei polimeri vetrosi quali l’aging e l’effetto dei solventi. Sono poi analizzate le proprietà di trasporto nei diversi PIMs, e confrontate con quelle di polimeri di comune utilizzo nelle separazioni in esame. La rielaborazione dei dati raccolti permette di confrontare le performance di una varietà di polimeri nella separazione di gas. In particolare l’analisi critica dei diagrammi permeabilità/selettività induce ad una valutazione approssimativa ma significativa delle possibili soluzioni tra cui optare per una data separazione di gas, considerando anche i parametri operativi tipici della stessa. Infine, vengono riportati e commentati dati di permeazione di miscele gassose in due diversi PIMs e nel polimero PTMSP, ponendo l’attenzione sulle reali condizioni operative con cui la tecnologia a membrane si deve confrontare in applicazioni reali

A Comparative Inherent Safety Assessment of Innovative CO2-based Production Processes of Dimethyl Ether and Methanol

Dimethyl ether (DME) and methanol are proposed as synthetic fuels prone to substitute present fossil propellants in the energy transition framework. Methanol and DME are traditionally synthesised starting from syngas but nowadays new production processes based on the efficient catalytic hydrogenation of CO2 have been introduced. Multiple catalysts, reaction conditions and reactor configurations have been tested to enhance the production performance of both fuels, especially for the case of DME. In fact, DME can be produced indirectly from CO2, i.e. after methanol synthesis and purification. Alternatively, it can be synthesised in a one-pot conversion mode by means of bifunctional catalysts directly receiving CO2. The latter route, avoiding several intermediate separation operations, appears promising from the process intensification viewpoint, thus favouring DME production with respect to methanol. Since safety plays an important role from the standpoint of societal acceptability, it needs to be considered in the selection of sustainable alternatives. This contribution aims to address an inherent safety assessment of the processes for methanol and DME production via CO2 hydrogenation. Inherent safety is evaluated through a consequence-based approach using specific Inherent Safety Key Performance Indicators, which proved to be effective in several applications to early process design. The results obtained shed light on the inherent safety performance of these alternative routes, thus helping decision-makers in accounting for process safety issues in the assessment of the sustainability of these alternative energy vectors and in the selection of the best technological alternative

Green Hydrogen Production Routes: an Inherent Safety Assessment

In the framework of energy transition, safety is a key requirement to be satisfied by novel process technologies. The aim of this study is to compare, from an inherent safety standpoint, three technologies for the production of green hydrogen via water splitting, powered by Renewable Energy Sources (RESs), in order to identify the inherently safest option and the critical equipment and/or operating conditions to be considered in the scale-up and industrialization of such technologies. The technologies considered for green hydrogen production are: alkaline electrolysis, proton exchange membrane electrolysis and reversible Solid Oxide Cells. The application of a consolidated methodology for inherent safety assessment based on Inherent Safety Key Performance Indicators (IS-KPIs) enabled to identify the most critical units within each process scheme and to select the inherently safest technological solution presently available for green hydrogen production

Analysis of an Integrated Energy System Aimed at the Offshore Production of Methanol

The results of the offshore integration of fossil and renewable energy sources (RESs) to produce an energy vector, namely methanol, are discussed. The methodology developed and hereby presented, allowed at first the selection of the best technology for offshore RESs exploitation, where a near-to-decommissioning platform is used as an energy hub. Based on the availability of natural gas from the depleted reservoir, the most suitable process for offshore methanol production was chosen among various alternative innovative processes. The optimal mix for energy production was then identified by varying the number of converters for each RES. Finally, the methanol production process was designed on the basis of the available electric power, including a backup system based on natural gas, to perform RESs valley filling and to achieve a steady state process

Optimized Renewable Energy Mixes: Facing Energy Scarcity in Remote Islands

The actual energy transition calls for the highest ever engagement of institutions and private sectors in the adoption of renewable energy systems in order to decarbonize all production chains. The high potential of renewable energy sources (RESs) in several locations worldwide is looked at as an important opportunity to both limit the energy supply issues and shift towards a greener society. On the other hand, it is also accompanied by the issues of resource variability, forecasting need and difficult management of the energy surpluses. The contemporary exploitation of multiple RESs in a hybrid renewable energy system (HRES) is a strategic initiative aimed at reducing the energy supply risk in a specific location, while decarbonizing the power generation facilities that satisfy specific energy requests. By means of systems optimally designed that valorize the RESs site-specific features and time trends, it is possible to comply with the identified energy demands while obtaining increased reliability. This contribution introduces an approach for the preliminary design of HRESs which is capable of accounting for the specific geographical constraints and the energy requests to be fulfilled. The approach is simulation-based, thus analyses the performance of all the possible combinations of renewable energy conversion technologies in terms of supply reliability and assesses their sustainability profile through key indicators. The application of the method is exemplified through a case study located on the island of Crete, Greece, for the valorization of the combined exploitation of offshore wind and wave energy. The most sustainable designs of the HRES in the site foresee the installation of 12 offshore wind turbines and maximum 10 wave energy converters for an overall system potentiality higher than 110 MW

Kinetic modelling and structure-reactivity study for the production of GVL from levulinic acid and its esters

This work is based on an experimental research activity in which direct hydrogenation reaction of biomass-derived compounds was performed to produce gamma-valerolactone (GVL), a relevant organic platform molecule in bio-refinery industry. After defining the best operative, levulinic acid (LA) and its alkyl esters (AL) were tested as starting substrates and a kinetic model was obtained from the data. The kinetic study was the starting point to compare the chemical reactivity of the four chosen substrates in the defined system in order to evaluate their advantages and disadvantages from the reaction point of view and taking into account their implications in a further applicative perspective. Finally, a discussion about a possible correlation between the kinetics and the chemical structures of the different substrates is presented

Sustainable exploitation of offshore renewable energy sources

Energy transition is the response of humankind to the concerning effects of fossil fuels depletion, climate change and energy insecurity, and calls for a deep penetration of renewable energy sources (RESs) in power systems and industrial processes. Despite the high potentials, low impacts and long-term availability, RESs present some limits which need to be overcome, such as the strong variability and difficult predictability, which result in scarce reliability and difficult applicability in steady-state processes. Some technological solutions relate to energy storage systems, equipment electrification and hybrid systems deployment, thus accomplishing distributed generation even in remote sites as offshore. However, all of these actions cannot disregard sustainability, which represents a founding principle for any project, bringing together economics, reliability and environmental protection. To entail sustainability in RESs-based innovative projects, previous knowledge and tools are often not tailored or miss the novel objectives. This research proposes three methodological approaches, bridging the gaps. The first contribute adapts literature-based indicators of inherent safety and energy efficiency to capture the specificities of novel process plants and hybrid systems. Minor case studies dealing with novel P2X processes exemplify the application of these novel indicators. The second method guides the conceptual design of hybrid systems for the valorisation of a RES in a site, by considering the sustainability performances of alternative design options. Its application is demonstrated through the comparison of two offshore sites where wave energy can be valorised. Finally, “OHRES”, a comprehensive tool for the sustainable optimisation of hybrid renewable energy systems is proposed. “OHRES” hinges on the exploitation of multiple RESs, by converting ex-post sustainability indicators into discrimination markers screening a large number of possible system configurations, according to the location features. Five case studies demonstrate “OHRES” versatility in the sustainable valorisation of multiple RESs

Application of the concept of Linear Free Energy Relationships to the hydrogenation of levulinic acid and its corresponding esters

International audienceBiomass valorization to chemicals, biofuels or materials will be more and more important during this century. Production of γ-valerolactone (GVL) from the hydrogenation of levulinic acid is a good illustration of this tendency. GVL can also be produced from alkyl levulinates hydrogenation. Can we find a relationship between the structure and the kinetics of this reaction? Can we predict the kinetics of any alkyl levulinates by knowing the kinetics of another alkyl levulinate? This paper has studied these two questions by developing a kinetic model including the effect of gas-liquid mass transfer. We have demonstrated that the kinetics of hydrogenation of levulinic acid, methyl, ethyl and butyl levulinates to GVL using Ru/C follow the Taft equation, which is derived from Linear Free Energy Relationships. This equation measures the effects of polar and steric on a reaction series. We have demonstrated that polar effect of the reaction series is the most significant effect. This relationship can predict the values of kinetic constants just by knowing their structure