1,721,004 research outputs found
pVT Data Analysis for the Prediction of Vapor Sorption in Glassy Polymers through the Nonequilibrium PC-SAFT Model
Full text linkThe first implementation is presented for the Restrained Swelling (RS) version of the Nonequilibrium Thermodynamics for Glassy Polymers (NET-GP) approach, which counts on the PC-SAFT EoS to express the equilibrium properties of polymer-solute mixtures. Examples for application of the resulting model (NE-RS) PC-SAFT to the prediction of gas and vapor solubility in conventional glassy polymers are first discussed. Emphasis is put on the role of pVT properties for pure polymer species, as measured at both melt and glass conditions. The first application is then presented for the NE-RS approach to the analysis of gas and vapor solubility data in a polymer with intrinsic microporosity, for which pVT data in the melt phase cannot be measure and reliable values for the volumetric properties at glassy conditions are not available. In the latter analysis, both kinds of pVT properties are eventually retrieved from the best fit of the selected solubility data and the result for the polymer pVT characteristics are finally compared with those recently presented in the literature as obtained after the use of "Dry Glass Reference Perturbation Theory" (DGRPT), within the same NET-GP approach
Thermodynamic model for gas solubility in glassy polymers: Prediction of dual mode sorption parameters
No full textRelaxational behavior of glassy polymers: Experimental sorption and nonequilibrium thermodynamic model
No full textThermodynamic analysis of the solubility of gases and vapors in swelling glassy polymers: A predictive modeling approach
No full textAnalysis Tool for Gas and Vapor Solubility in Glassy Polymers: The Dual Nonequilibrium Lattice Fluid (d-NELF)
No full textIn view of the physically sounding ideas it is founded on, as well of its simplicity and stand-alone character, the dual-mode sorption model (DMS) has been almost universally used in past decades to analyze and compare gas sorption data in polymeric matrixes below the glass transition temperature. The elements the DMS analysis is based on are here revised with the help of results developed within the nonequilibrium lattice fluid (NELF) model to derive meaningful relations between DMS model parameters and equilibrium and nonequilibrium structure property characteristics of the NELF approach. The result is a stand-alone and simple-to-use new tool for the analysis of solubility data in glassy polymers which allows for the use of a limited amount of data to retrieve the nonequilibrium structure property characteristic of the polymer matrix. The model can then be used to compare the solubility of different gases in the same glassy polymer, based just on equilibrium binary interaction parameters, or to distinguish the gas or vapor solubility properties of different nonequilibrium structures in the same polymer species, based on pertinent values of excess-free volume and compressibility
Solute induced relaxation in glassy polymers: Experimental measurements and nonequilibrium thermodynamic model
No full textData for kinetics of mass uptake from vapor sorption experiments in thin glassy polymer samples are here interpreted in terms of relaxation times for volume dilation. To this result, both models from non-equilibrium thermodynamics and from mechanics of volume relaxation contribute. Different kind of sorption experiments have been considered in order to facilitate the direct comparison between kinetics of solute induced volume dilation and corresponding data from process driven by pressure or temperature jumps
Thixotropic behavior of reconstituted debris-flow mixture
Full text linkTime-dependent rheological properties and thixotropy of reconstituted debris-flows samples taken from channel bank deposits are examined using a commercial rheometer equipped with a vane rotor geometric system. Sweep tests and creep tests were carried out involving mixtures having different grain concentrations ranging between 50% and 58%. Different initial conditions of the mixtures were considered in order to analyze the effects of aging and rejuvenation (thixotropy) over a short period of time and long period of time. Tested slurries show viscosity bifurcation, yield stress and time-dependent behavior. According to the experimental results, three different regimes were identified: a lower shear rate regime, corresponding to a shear rate lower than the critical value; an intermediate banding shear rate regime characterized by static and dynamic yield stress level; and a higher shear rate regime where the flowing debris behaves as a non-Newtonian fluid characterized by a constant steady state ultimate apparent viscosity. In any case, the initial state of the mixture and the sediment concentration affects the ultimate steady state rheology and the time-dependent (thixotropy) slurries’ behavior
New Perspectives on Catalytic Hydrogen Production by the Reforming, Partial Oxidation and Decomposition of Methane and Biogas
Full text linkThe article provides a short review on catalyst-based processes for the production of hydrogen starting from methane, both of fossil origin and from sustainable processes. The three main paths of steam- and dry-reforming, partial oxidation and thermo-catalytic decomposition are briefly introduced and compared, above all with reference to the latest publications available and to new catalysts which obey the criteria of lower environmental impact and minimize the content of critical raw materials. The novel strategies based on chemical looping with CO2 utilization, membrane separation, electrical-assisted (plasma and microwave) processes, multistage reactors and catalyst patterning are also illustrated as the most promising perspective for CH4 reforming, especially on small and medium scale. Although these strategies should only be considered at a limited level of technological readiness, research on these topics, including catalyst development and process optimization, represents the crucial challenge for the scientific community
New hybrid unit operation for gas separation membranes application
No full textAn innovative membrane-based process for the separation of gaseous streams has been developed and tested at lab-scale. The new process can be conveniently carried out on the same modules currently employed for conventional gas separation membrane systems, and it relies on periodic swing of the downstream pressure, while upstream conditions are kept constant. Such new unit operation is run with no need of switching streams, and it allows to process constant flow rate and composition of both feed and retentate, while permeate is collected at assigned frequency, resulting in an overall on-average steady state process. An on-off control strategy over time of permeate collection produces alternate sorption/desorption steps in the membrane, associated to increase/decrease cycles of downstream pressure in the process, in a similar fashion to pressure swing adsorption (PSA). Indeed, consistently with the hybrid nature of the new process, the specific dynamic control of downstream pressure allows the exploitation of both resistive (permeation) and capacitive (adsorption) properties of the membrane, and the associated characteristics in terms of selectivity. By changing the duration of pressure swing period, the resistive or capacitive properties of the membrane can be conveniently tuned in order to explore different performances of the process, in terms of key component recovery and separation facto
Thermodynamic study on the feasibility of a new combined chemical looping process for syngas production
Full text linkMethane Chemical Looping mixed dry reforming - CLMDR (dry reforming and partial oxidation) is an integrate process that utilizes CO2 directly, in presence of carrier materials, for the production of syngas with tuneable H2/CO molar ratio. Herein Cerium oxide was selected as reference source of oxygen and its use in the CLMDR process was evaluated by means of thermodynamic tools of Aspen Plus process simulator. Crucial features such as reforming and regeneration operative temperature, oxygen to methane molar ratio and CO2 addition were investigated in order to identify the most suitable and effective conditions for process. Simulation results of the proposed metal oxide were compared on the basis of methane conversion and syngas purity. Relevantly, cerium-based oxide was found to be selective in syngas production even when CO2 was added to the reforming reactor. After the required thermodynamic validation, a fixed bed reactor on lab scale was specifically designed and fabricated, and cerium oxide oxygen carrier characterized by Thermogravimetric analysis. Thermodynamic results and experimental tests proved the solid/gas chemical reaction takes place with appreciable conversions, and they also demonstrated the stability of the oxygen carrier redox properties during several cycles, thus confirming the feasibility of this new process
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