Modeling the extra-column volume in a small column setup for bulk gas adsorption

This study aims at highlighting the importance of an accurate characterization of the extra-column volume (ECV) and presents an experimental and computational protocol based on the characterization of the extra-column volume in terms of step-response experiments performed under various flow rates and pressures of 1bar, 5bar and 10bar. The experiments are interpreted by describing the extra-column volume with a compartment model that reflects the geometry of the physical setup and that involves a stagnant zone to account for the non-ideal flow behavior through the piping system. The use of a mathematical model combining the description of the adsorption column and of the ECV can successfully predict experimental CO2-H2 breakthrough profiles performed at different pressures on an activated carbon adsorbent. This work shows how the presence of non-negligible extra-column effects can be accounted for, for the determination of adsorption transport parameter

Structural Characterization of an Historical Building by Means of Experimental Tests on Full-Scale Elements

In order to properly design strengthening intervention of existing buildings, careful assessment of the structural behavior is certainly required. This is particularly important when dealing with historical constructions made of heterogeneous materials like masonry or stonework. In this context, this paper presents the results of knowledge process on a large monumental nineteenth century building located in Trieste. The traditional investigation approach considering a wide number of destructive tests for characterization of materials and evaluation of the structural details were not admissible due to the valuable cultural and historical importance of the building. Therefore, an alternative and not conventional investigation approach has been considered. After a wide historical research and a detailed structural survey, it has been possible to identify the main structural systems of the building. Then, to characterize the structural response, a limited number of nondestructive tests but on full-scale typological systems have been preferred to a larger number of destructive tests on specimens of the different materials. The selected experimental load tests have been conducted in order to assess the actual structural response of the main systems that constitute the building, thus allowing for a fine tuning of both the rehabilitation interventions and the numerical finite element models

Overcoming timescale and finite-size limitations to compute nucleation rates from small scale Well Tempered Metadynamics simulations

Condensation of a liquid droplet from a supersaturated vapour phase is initiated by a prototypical nucleation event. As such it is challenging to compute its rate from atomistic molecular dynamics simulations. In fact at realistic supersaturation conditions condensation occurs on time scales that far exceed what can be reached with conventional molecular dynamics methods. Another known problem in this context is the distortion of the free energy profile associated to nucleation due to the small, finite size of typical simulation boxes. In this work the problem of time scale is addressed with a recently developed enhanced sampling method while contextually correcting for finite size effects. We demonstrate our approach by studying the condensation of argon, and showing that characteristic nucleation times of the order of magnitude of hours can be reliably calculated, approaching realistic supersaturation conditions, thus bridging the gap between what standard molecular dynamics simulations can do and real physical systems.Comment: 9 pages, 7 figures, additional figures and data provided as supplementary information. Submitted to the Journal of Chemical Physisc

A model for enhanced coal bed methane recovery aimed at carbon dioxide storage: The role of sorption, swelling and composition of injected gas

Numerical simulations on the performance of CO2 storage and enhanced coal bed methane (ECBM) recovery in coal beds are presented. For the calculations, aone-dimensional mathematical model is used consisting of mass balances describing gas flow and sorption, and a geomechanical relationship to account for porosity and permeability changes during injection. Important insights are obtained regarding the gas flow dynamics during displacement and the effects of sorption and swelling on the ECBM operation. In particular, initial faster CH4 recovery is obtained when N2 is added to the injected mixture, whereas pure CO2 allows for a more effective displacement in terms of total CH4 recovery. Moreover, it is shown that coal swelling dramatically affects the gas injectivity, as the closing of the fractures associated with it strongly reduces coal's permeability. As a matter of fact, injection of flue gas might represent a useful option to limit this proble

Experimental and numerical evaluation of fiber-matrix interface behaviour of different FRCM systems

Abstract Fiber Reinforced Cementitious Matrix (FRCM) composites are a relatively new strengthening system family, whose mechanical behavior is strongly affected by the wide array of possible inorganic matrices and composites fabrics that can be used and coupled together. Structural tests highlighted that global capacity of the system is strongly affected by fabric-matrix adhesion mechanism. In the present paper, the experimental results of tensile and single-lap shear tests, aimed to define mechanical properties of four FRCM types, are discussed and compared. For each system type, the failure modes for both types of test have been physically identified and clarified. The following development of detailed finite element models, carefully reproducing the mechanical behavior of the different layers of the strengthening system, allowed for the proposal of a reliable shear stress-slip relation for the fiber-matrix interface. The experimental outcomes showed the relevant dispersion of the results in terms of performance, effectiveness and failure mechanisms exhibited by the different FRCM types while the numerical interpretation allowed for a better understanding of the reasons and the parameters behind them

Continuous chromatographic processes with a small number of columns: Comparison of simulated moving bed with Varicol, PowerFeed, and ModiCon

The Simulated Moving Bed process and its recent extensions called Varicol, PowerFeed and ModiCon are studied, in the case where a small number of columns are used, i.e. from three to five. A multiobjective optimization approach, using genetic algorithms and a detailed model of the multicolumn chromatographic process, is applied to optimize each process separately, and allow for comparison of the different operating modes. The non-standard SMB processes achieve better performance than SMB, due to the availability of more degrees of freedom in the operating conditions of the process, namely the way to carry out asynchronous switches for Varicol, and the different flow rates and feed concentration during the switching interval for PowerFeed and for ModiCon, respectively. We also consider the possibility of combining two non-standard operating modes in a new hybrid process, and evaluate also in this case the possible performance. Finally, a critical assessment of the results obtained and of the potential for practical implementation of the different techniques is reporte

Separation of Tröger's Base Enantiomers Through a Combination of Simulated Moving Bed Chromatography and Crystallization

This paper studies the coupling of simulated moving bed (SMB) chromatography with crystallization for the separation of Tröger's base enantiomers. SMB is used to achieve a certain level of enrichment and then evaporative crystallization of the extract and raffinate streams leads to the final product with the specified purity. The optimization of the combined process is based on thermodynamic data about adsorption isotherms of the two enantiomers in ethanol on microcrystalline cellulose triacetate (CTA) and about solubility of the two enantiomers in ethanol. The results, obtained using a genetic algorithm, prove that there is an optimal value of the purity achieved in the SMB that maximizes the productivity of the combined proces

Naphthalene crystal shape prediction from molecular dynamics simulations

We used molecular dynamics simulations to predict the steady state crystal shape of naphthalene grown from ethanol solution. The simulations were performed at constant supersaturation by utilizing a recently proposed algorithm [Perego et al., J. Chem. Phys., 142, 2015, 144113]. To bring the crystal growth within the timescale of a molecular dynamics simulation we applied Well-Tempered Metadynamics with a spatially constrained collective variable, which focuses the sampling on the growing layer. We estimated that the resulting steady state crystal shape corresponds to a rhombic prism, which is in line with experiments. Further, we observed that at the investigated supersaturations, the $\{00\bar{1}\}$ face grows in a two step two dimensional nucleation mechanism while the considerably faster growing faces $\{1\bar{1}0\}$ and $\{20\bar{1}\}$ grow new layers with a one step two dimensional nucleation mechanism