Residence Time Distribution (RTD) theory is revisited and tracer technology discussed. The background of RTD following Danckwerts ideas is presented by introducing “distribution” functions for ...residence time, internal age and intensity function and how to experimentally obtain them with tracer techniques (curves C and F of Danckwerts). Compartment models to describe fluid flow in real reactors are reviewed and progressive modeling of chromatographic processes discussed in some detail. The shortcomings of Standard Dispersion Model (SDM) are addressed, the Taylor-Aris model discussed and the Wave Model of Westerterp’s group introduced. The contribution of Computational Fluid Dynamics (CFD) is highlighted to calculate RTD from momentum and mass transport equations and to access spatial age distribution and degree of mixing. Finally smart RTD and future challenges are discussed.
•Chitosan-based particles are gaining relevance as Pickering stabilizers.•Chitosan-based Pickering emulsions preparation methodologies are reviewed.•Food, skincare, environmental, and novel materials ...applications are discussed.•Challenges and future perspectives are highlighted.
Pickering emulsions, which are emulsions stabilized by solid particles, have gained increased research interest owing to their eco-friendliness and high stability. Among a wide range of solid particles, chitosan particles and chitosan-based particles have become attractive candidates as Pickering stabilizers due to their biodegradable, biocompatible and nontoxic properties. This review aims to provide an insight into the recent advances in the production and physicochemical properties of these systems. Moreover, this paper highlights the research progress in employing chitosan-based Pickering emulsions in different application areas, such as food and cosmetic applications, and environmental research. Chitosan-based Pickering emulsions have opened new avenues for the designing and production of innovative materials. The review also sheds light on the novel materials that are synthesized from these Pickering emulsion systems. Future research directions and opportunities on these promising Pickering systems are also addressed.
Cosmetics, like any product containing water and organic/inorganic compounds, require preservation against microbial contamination to guarantee consumer’s safety and to increase their shelf-life. The ...microbiological safety has as main goal of consumer protection against potentially pathogenic microorganisms, together with the product’s preservation resulting from biological and physicochemical deterioration. This is ensured by chemical, physical, or physicochemical strategies. The most common strategy is based on the application of antimicrobial agents, either by using synthetic or natural compounds, or even multifunctional ingredients. Current validation of a preservation system follow the application of good manufacturing practices (GMPs), the control of the raw material, and the verification of the preservative effect by suitable methodologies, including the challenge test. Among the preservatives described in the positive lists of regulations, there are parabens, isothiasolinone, organic acids, formaldehyde releasers, triclosan, and chlorhexidine. These chemical agents have different mechanisms of antimicrobial action, depending on their chemical structure and functional group’s reactivity. Preservatives act on several cell targets; however, they might present toxic effects to the consumer. Indeed, their use at high concentrations is more effective from the preservation viewpoint being, however, toxic for the consumer, whereas at low concentrations microbial resistance can develop.
The discovery of new materials with enhanced selectivity or capacity will boost adsorption applications, especially for environmental control. In particular, it was mentioned that metal-organic ...frameworks (MOF) with different tailored properties may be prepared for desired separations. To promote industrial application of MOF materials, up-scaling and process design still must be completely developed. In this work, we report adsorption equilibrium data of methane and carbon dioxide on Cu-MOF extrudates. The most important properties observed are the high-capacity for CO2 and the small nonlinearity of the isotherms. In this context, this adsorbent can be used for biogas upgrading to produce biomethane and reduce fossil-fuel CO2.
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•Analysis of the empirical pseudo first order model of Lagergreen for adsorption kinetics.•Comparison of the Lagergreen equation with the LDF model of Glueckauf.•A relation between ...the kinetic constants of both models is derived for linear systems.•The kinetic constants of both models exhibit very distinct dependency with temperature.
Adsorption processes can be modeled on the basis of phenomenological principles using conservation, equilibrium and transport kinetics equations. However many times an empirical approach is followed using pseudo first order and pseudo second order models to describe adsorption kinetics. In this short communication we discuss the use of Lagergreen model (pseudo first order kinetic model) and compare it with the linear driving force model of Glueckauf for a linear adsorption equilibrium isotherm. A relation between the kinetic constants of both models is derived, being possible to disclose they exhibit very distinct dependency with temperature whatever the porous structure of the adsorbent particle. In conclusion, care must be taken when using the short-cut approach of pseudo first order expressions, taking into account their theoretically inconsistent trends.
In this work, multicomponent breakthrough experiments (binary H2-CO2, ternary H2-CO2-CO and five-component H2-CO2-CO-CH4-N2) were performed under different operating conditions in activated carbon ...extrudates to validate the mathematical model. A 10 steps one-column VPSA experiment was also performed. These experiments allow experimental validation of adsorption equilibrium predicted by the multicomponent extension of the Virial isotherm and a fixed-bed mathematical model. In the VPSA experiment, a 99.981% hydrogen purity stream (with 63ppm of CO contamination) was obtained with a hydrogen recovery of 81.6% and an adsorbent productivity of 101molH2kgads−1day−1.
The mathematical model was also employed to assess the effect of operating conditions and the influence of step times and pressure equalizations in the PSA unit. It was verified that high-purity hydrogen (>99.99%) can be obtained using this adsorbent with recoveries higher than 75% and unit productivities of 160molH2kgads−1day−1.
Recently, there has been an increasing research interest in the development of Pickering emulsions stabilized with naturally derived biopolymeric particles. In this regard, plant gums, obtained as ...plant exudates or from plant seeds, are considered promising candidates for the development of non-toxic, biocompatible, biodegradable and eco-friendly Pickering stabilizers. The main objective of this review article is to provide a detailed overview and assess the latest advances in the formulation of Pickering emulsions stabilized with plant gum-based particles. The plant gum sources, types and properties are outlined. Besides, the current methodologies used in the production of plant gum particles formed solely of plant gums, or through interactions of plant gums with proteins or other polysaccharides are highlighted and discussed. Furthermore, the work compiles and assesses the innovative applications of plant gum-based Pickering emulsions in areas such as encapsulation and delivery of drugs and active agents, along with the utilization of these Pickering emulsions in the development of active packaging films, plant-based products and low-fat food formulations. The last part of the review presents potential future research trends that are expected to motivate and direct research to areas related to other novel food applications, as well as tissue engineering and environmental applications.
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•A volumetric unit was developed for measuring gas adsorption equilibria at mg scale.•The unit measures the kinetics of sorption by a piezometric method.•A simple LDF model has been ...developed to model uptake rate data.•The statistical analysis of the adsorption equilibria data was performed by RSM.
The screening of adsorbents (zeolites, MOFs, ACs, etc) requires the measurement of adsorption equilibria and kinetics at the milligram scale. In this regard, a volumetric apparatus (constant volume variable pressure – batch adsorber) has been developed for studying adsorption equilibria and kinetics of sorption. Its validation was accomplished by studying the adsorption equilibria of carbon dioxide (CO2), methane (CH4) and nitrogen (N2) and the kinetics of sorption of CO2 on commercial binder-free 4A zeolite. The data collected has an acceptable agreement with already published values by a gravimetric and breakthrough flow technique. The isotherms were modeled using Sips model from low pressure till 8 bar at 303, 343 and 373 K. The sorption kinetics of CO2 was measured from the uptake rate experiments and fitted with a solid-film linear-driving-force model (LDF). It was observed that the LDF mass transfer coefficients increase with pressure and temperature. Finally, the statistical analysis of the data was performed by Response Surface Methodology (RSM) to determine the interactions among process variables such as temperature and pressure in the respective gas adsorption equilibria data.
The surfactant-free nature and higher stability of Pickering emulsions make them preferable solutions over conventional emulsions for skin applications. In this work, Pickering emulsions stabilized ...by chitosan/gum Arabic (CH/GA) nanoparticles were tested as vehicles for trans-resveratrol topical delivery. Skin absorption was examined ex vivo using Franz diffusion cells and porcine skin. Pickering emulsions allowed higher cutaneous retention and lower permeation of resveratrol, in comparison with a control solution based on a 20% v/v ethanol. The total amount of resveratrol retained in the skin, 24 h after the application, was 11.60% and 10.82% of the applied dose for the tested Pickering emulsion-based formulations prepared with 0.5% and 1.5% w/v CH/GA nanoparticles, respectively. In contrast, resveratrol skin retention from the control solution was only 2.86%. Confocal laser scanning microscopy revealed enhanced skin deposition of Nile Red to deeper layers from the Pickering emulsion-based formulations. Moreover, Pickering emulsions led to trans-resveratrol photostability increase, as measured after exposure to UV for 4 h. These results show that the CH/GA Pickering emulsions are promising solutions for the topical delivery of trans-resveratrol and have the potential to be used as green cosmetic products.
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•Stable RSV-loaded chitosan/gum Arabic Pickering emulsions were developed.•Topical delivery of RSV from Pickering emulsions was assessed for the first time.•Entrapment of RSV in Pickering emulsions enhanced its retention in the skin.•Chitosan/gum Arabic Pickering emulsions improved the photostability of RSV.
In this work, the main results of a thermodynamic and kinetic study of glycerol ketalization to produce solketal in the presence of a solvent are presented. A catalyst and a solvent screening was ...carried out leading to the selection of Amberlyst-35 ion-exchange resin and ethanol as the most suitable materials for this reaction. A parametric study allowed one to determine reaction equilibrium and kinetic parameters in a batch reactor in the absence of external mass-transfer limitations. Regarding reaction thermodynamic equilibrium, a standard enthalpy of −20.1 ± 1.1 kJ mol–1 and a Gibbs free energy of 1.4 ± 0.3 kJ mol–1 were obtained. Reaction kinetics was studied assuming different reaction rate laws to fit the experimental data obtained: Pseudo-Homogeneous (PH), Langmuir–Hinshelwood–Hougen–Watson (LHHW), and Eley–Rideal (ER). The experimental results revealed that the reaction kinetics behavior could be accurately described by the LHHW reaction rate law, considering the presence of internal mass-transfer resistances. The activation energy for the overall reaction was found to be 69.0 ± 6.6 kJ mol–1.
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