Experimental investigation on CO2methanation process for solar energy storage compared to CO2-based methanol synthesis

The utilization of the captured CO2 as a carbon source for the production of energy storage media offers a technological solution for overcoming crucial issues in current energy systems. Solar energy production generally does not match with energy demand because of its intermittent and non-programmable nature, entailing the adoption of storage technologies. Hydrogen constitutes a chemical storage for renewable electricity if it is produced by water electrolysis and is also the key reactant for CO2 methanation (Sabatier reaction). The utilization of CO2 as a feedstock for producing methane contributes to alleviate global climate changes and sequestration related problems. The produced methane is a carbon neutral gas that fits into existing infrastructure and allows issues related to the aforementioned intermittency and non-programmability of solar energy to be overcome. In this paper, an experimental apparatus, composed of an electrolyzer and a tubular fixed bed reactor, is built and used to produce methane via Sabatier reaction. The objective of the experimental campaign is the evaluation of the process performance and a comparison with other CO2 valorization paths such as methanol production. The investigated pressure range was 2–20 bar, obtaining a methane volume fraction in outlet gaseous mixture of 64.75% at 8 bar and 97.24% at 20 bar, with conversion efficiencies of, respectively, 84.64% and 99.06%. The methanol and methane processes were compared on the basis of an energy parameter defined as the spent energy/stored energy. It is higher for the methanol process (0.45), with respect to the methane production process (0.41–0.43), which has a higher energy storage capability

Thermodynamic assessment and microscale Raman spectroscopy of binary CO2/CH4 hydrates produced during replacement applications in natural reservoirs

The present research deals with the micro – scale characterization of sI hydrates containing a binary mixture of methane and carbon dioxide. The application of replacement strategies in natural hydrate reservoirs, always leads to the formation of “mixed” hydrates, whose mechanical and chemical properties are different from those of pure CH4 and CO2 hydrates. As a function of the technique used for the process and due to the variability of the systems, a wide range of different compositions and morphologies can be obtained and the current literature must be expanded, in order to achieve a wide and accurate experimental database of CO2/CH4 hydrate properties. In this work, binary CO2/CH4 hydrates binary CO2/CH4 hydrates were produced in a small – scale reactor and then supercooled, in order to favour their extraction from the reactor and their stability at environmental conditions for a certain period of time. The gas hydrates, prepared with CO2 hydrates of pure water and with CH4 and CO2 mixtures, also in the presence of specific sands, were ex situ analysed by the use Raman-spectroscopy that confirmed the gas uptake in the hydrate structures by identification of the fingerprint of CH4 and CO2 occupancy in the hydrates. The characteristic of water inside the gas hydrates and the interaction between the host molecules and the lattice of water molecules was clarified. The different gas hydrates, analysed by Field Emission Scanning Electron Microscopy instrument equipped with “Coolstage head” under high vacuum condition, differed in morphology and surface features. The analysis of water Raman spectra of the different GHs permitted to describe the relation between symmetric and asymmetric OHs bands, but also provided information about the characteristics of water inside the different GHs, showing that the least ordered water structure was that of GHs containing sand, while the most ordered one was present on binary CO2/CH4 hydrates

May sediments affect the inhibiting properties of NaCl on CH4 and CO2 hydrates formation? an experimental report.

The equilibria of methane and carbon dioxide clathrate hydrates were measured in presence of a pure-quartz porous sand, with and without NaCl. Two different salt concentrations were tested: 0.030 and 0.037 wt%. Results were compared with phase equilibrium data already present in literature for these species. Despite salt, the porous medium was found to promote the process, mainly for the increased surface/volume ratio and for the improved heat transfer. In presence of salt, sand affected the process differently as a function of temperature: at values higher than 3 – 5 °C, it promoted the process, while for values lower than this range, but still greater than the ice-point, it acted as an inhibitor. However, these results can be considered true only for temperatures above the ice point. Due to similarity of ice water with clathrate hydrates, Raman microscale measurements were performed to gather information about the influence of sediments, salt, and temperature on OH-stretching vibrations of water. The obtained results allowed to clarify how the addition of NaCl, and or sediments to liquid water, under different temperature conditions (15 °C and −15 °C), influenced the water hydrogen bonds. Specifically, the changes of OH-stretching vibrations, when correlated with the NaCl concentrations, demonstrated that the presence of sediments partially inhibited the salt effects in the ice water probably due to hydrophilic interactions with the silanol groups of sediments. SEM measurements showed morphological information on sediments and on ice in different experimental conditions

The Effect of the Substrate on the Optic Performance of Retro-Reflective Coatings: An In-Lab Investigation

Retro-reflectivity is a promising surface capability, which has attracted the interest of researchers for building applications in order to counteract Urban Heat Island (UHI) effects. This work aims at studying the impact of the substrate material on the optic performance of retro-reflective (RR) coatings. Three types of substrate materials were investigated: smooth pine wood panels, rough plywood panels, and smooth acetate sheets. The RR coating samples were made by firstly adding a high reflective white paint onto the substrate material and a homogeneous RR glass beads layer on the top. As a reference case, also diffusive samples, without RR beads, were developed. Samples have been tested through a spectrophotometric and an angular reflectivity analysis. Results show that, despite a lower global reflectance of the RR samples with respect to the diffusive ones, the glass beads coating provides a good retro-reflective capability to all the diffusive samples. Additionally, the roughest RR sample exhibited the highest RR capability of up to 16%, with respect to the other smoother samples. Future developments may involve the optimum design of RR coatings, in terms of their optic performance by varying the substrate materials and roughness, the glass beads density and dimension

Intraspecific variability of leaf form and function across habitat types

: Trait-based ecology has already revealed main independent axes of trait variation defining trait spaces that summarize plant adaptive strategies, but often ignoring intraspecific trait variability (ITV). By using empirical ITV-level data for two independent dimensions of leaf form and function and 167 species across five habitat types (coastal dunes, forests, grasslands, heathlands, wetlands) in the Italian peninsula, we found that ITV: (i) rotated the axes of trait variation that define the trait space; (ii) increased the variance explained by these axes and (iii) affected the functional structure of the target trait space. However, the magnitude of these effects was rather small and depended on the trait and habitat type. Our results reinforce the idea that ITV is context-dependent, calling for careful extrapolations of ITV patterns across traits and spatial scales. Importantly, our study provides a framework that can be used to start integrating ITV into trait space analyses

Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds

We compare the Gaia DR2 and Gaia EDR3 performances in the study of the Magellanic Clouds and show the clear improvements in precision and accuracy in the new release. We also show that the systematics still present in the data make the determination of the 3D geometry of the LMC a difficult endeavour; this is at the very limit of the usefulness of the Gaia EDR3 astrometry, but it may become feasible with the use of additional external data. We derive radial and tangential velocity maps and global profiles for the LMC for the several subsamples we defined. To our knowledge, this is the first time that the two planar components of the ordered and random motions are derived for multiple stellar evolutionary phases in a galactic disc outside the Milky Way, showing the differences between younger and older phases. We also analyse the spatial structure and motions in the central region, the bar, and the disc, providing new insights into features and kinematics. Finally, we show that the Gaia EDR3 data allows clearly resolving the Magellanic Bridge, and we trace the density and velocity flow of the stars from the SMC towards the LMC not only globally, but also separately for young and evolved populations. This allows us to confirm an evolved population in the Bridge that is slightly shift from the younger population. Additionally, we were able to study the outskirts of both Magellanic Clouds, in which we detected some well-known features and indications of new ones

Water Salinity as Potential Aid for Improving the Carbon Dioxide Replacement Process’ Effectiveness in Natural Gas Hydrate Reservoirs

Natural gas hydrates represent a valid opportunity to counteract two of the most serious issues that are affecting humanity this century: climate change and the need for new energy sources, due to the fast and constant increase in the population worldwide. The energy that might be produced with methane contained in hydrates is greater than any amount of energy producible with known conventional energy sources; being widespread in all oceans, they would greatly reduce problems and conflicts associated with the monopoly of energy sources. The possibility of extracting methane and simultaneously performing the permanent storage of carbon dioxide makes hydrate an almost carbon-neutral energy source. The main topic of scientific research is to improve the recovery of technologies and guest species replacement strategies in order to make the use of gas hydrates economically advantageous. In the present paper, an experimental study on how salt can alter the formation process of both methane and carbon dioxide hydrate was carried out. The pressure–temperature conditions existing between the two respective equilibrium curves are directly proportional to the effectiveness of the replacement process and thus its feasibility. Eighteen formation tests were realized at three different salinity values: 0, 30 and 37 g/L. Results show that, as the salinity degree increases, the space between CO2 and CH4 formation curves grows. A further aspect highlighted by the tests is how the carbon dioxide formation process tends to assume a very similar trend in all experiments, while curves obtained during methane tests show a similar trend but with some significant differences. Moreover, this tendency became more pronounced with the increase in the salinity degree

Energy and Environmental Analysis of Membrane-Based CH4-CO2 Replacement Processes in Natural Gas Hydrates

Natural gas hydrates are the largest reservoir of natural gas worldwide. This paper proposes and analyzes the CH4-CO2 replacement in the hydrate phase and pure methane collection through the use of membrane-based separation. The investigation uses a 1 L lab reactor, in which the CH4 hydrates are formed in a quartz sand matrix partially saturated with water. CH4 is subsequently dissociated with a CO2 stream supplied within the sediment inside the reactor. An energy and environmental analysis was carried out to prove the sustainability of the process. Results show that the process energy consumption constitutes 4.75% of the energy stored in the recovered methane. The carbon footprint of the CH4-CO2 exchange process is calculated as a balance of the CO2 produced in the process and the CO2 stored in system. Results provide an estimated negative value, equal to 0.004 moles sequestrated, thus proving the environmental benefit of the exchange process