Multiphase Microreactors Based on Liquid–Liquid and Gas–Liquid Dispersions Stabilized by Colloidal Catalytic Particles

Most of the surface reserves of copper minerals are oxidized while underground mining leads to rich silica–chalcopyrite–pyrite ore. Based on the challenges of the twenty-first century, the (bio)-hydrometallurgy processing is suggested as an alternative route to replace conventional techniques. However, the search for a sustainable metallurgy and/or more effective method to decrease impurities for efficient solvent extraction led to a comparative study of the removal performances of silica and solid colloidal particles from bioleachate solution by comparing the techniques using Shellsol set #2325 and Magnafloc set #1597, respectively. Three ratios (thinner/aqueous) or/and (coagulant /aqueous) of 1/2, 1, and 3/2 were assessed, along with the disengagement time and the required absorbed dose of Magnafloc 1597. The search for the alternative route also sought to ensure that the requirements in terms of concentration values at solvent extraction stage did not exceed 500 and 75 ppm, respectively. Findings show that the diluent/wash method is less efficient in terms of the removal performances of silica and solid colloidal particles from the bioleachate solution, but the phase disengagement time was similar, being comparatively around 150 s. The results of Magnafloc 1597 coagulation tests show removal performances of silica and colloidal particles from the bioleachate solution to be greater than 300 ppm, with a volume ratio of 1/1 for recovery rates of 68 and 58%, respectively, for SiO2 and colloidal solids in suspension. In comparison, the employment of Shellsol 2325 achieved silica removal efficiencies of 20.92 and 40%, respectively, of SiO2 and colloidal fine particles in suspension. A decreased phase separation time in aqueous continuity from 245 to 148 s has been recorded with a ratio of 1/1 (thinner or coagulant/aqueous). On the other hand, coagulant concentration of 300 ppm was retained. Hence, it could be assumed that the coagulation showed better results than the washing method.

Ultralong ZnO/Pt hierarchical structures for continuous-flow catalytic reactions

The equations which govern the ion distributions and velocities, the electrostatic potential and the hydrodynamic flow field around a solid colloidal particle in an applied electric field are reexamined. By using the linearity of the equations which determine the electrophoretic mobility, we show that for a colloidal particle of any shape the mobility is independent of the dielectric properties of the particle and the electrostatic boundary conditions on the particle surface. The mobility depends only on the particle size and shape, the properties of the electrolyte solution in which it is suspended, and the charge inside, or electrostatic potential on, the hydrodynamic shear plane in the absence of an applied field or any macroscopic motion.New expressions for the forces acting in the particle are derived and a novel substitution is developed which leads to a significant decoupling of the governing equations. These analytic developments allow for the construction of a rapid, robust numerical scheme for the solution of the governing equations which we have applied to the case of a spherical colloidal particle in a general electrolyte solution. We describe a computer program for the conversion of mobility measurements to zeta potential for a spherical colloidal particle which is far more flexible than the Wiersema graphs which have traditionally been used for the interpretation of mobility data. Furthermore it is free of the high zeta potential convergence difficulties which limited Wiersema's calculations to moderate values of ζ. Some sample computations in typical 1:1 and 2:1 electrolytes are exhibited which illustrate the existence of a maximum in the mobility at high zeta potentials. The physical explanation of this effect is given. The importance of the mobility maximum in testing the validity of the governing equations of electrophoresis and its implications for the colloid chemist's picture of the Stern layer are briefly discussed.

In the view of their ability to be uptaken by cells, colloidal particles can exert diverse physiological effects and are promising vehicles for the intracellular delivery of biologically active substances. Given that the modulation of biomaterial interfaces greatly facilitates the prediction and control of the corresponding cellular responses, the interfacial behavior of hydrophobic dye-modified gold (Au) nanoclusters (Au NCs) is rationally designed to develop Au NC-containing emulsions and control their biointerfacial interactions with cell membranes. The observed biological performance is indicative of a physical penetration mechanism. The amphiphilic Au NCs decrease the interfacial energy of two immiscible liquids and hinder droplet coalescence to facilitate the formation of emulsions thermodynamically stabilized by dipole-dipole and hydrophobic interactions. Moreover, the amphiphilic Au NCs are localized on the emulsion droplet surface and form segregated interfacial microdomains that adapt to the membrane structure and facilitate the traverse of the emulsions across the cell membrane via direct penetration. Fast penetration coupled with excellent photophysical performance endows the emulsions with multifluorescence tracing and efficient photothermal killing capabilities. The successful change of the interaction mode between NCs and biological objects and the provision of a universal formulation to modulate biointerfacial interactions are expected to inspire new bioapplications.

In recent years, there has been considerable interest in employing dispersed solid particles in the nanoscale range to enhance the friction and wear characteristics of liquid lubricants. Previous studies have suggested that tiny colloidal particles, under tribochemical conditions, deposit on rubbing surfaces influencing tribological characteristics of the contact. This article presents a study of the tribological behavior of stabilized silver nanoparticles dispersed in n-hexadecane. Friction and wear measurements are combined to investigate the extent to which colloidal solid particles influence a lubricated contact. It is shown that the silver nanoparticles studied contribute to reduce friction and wear only in the thin film regime. Nanoparticles help to reduce friction and wear down to a certain concentration value. Higher concentrations of nanoparticles do not bring any further contribution to reduce friction or wear, suggesting the existence of an optimum concentration of nanoparticles.

Wax deposition has always been an essential issue for flow assurance, especially in subsea pipelines. The coarse particles, which are usually measured in millimeters, will be carried out by oil flow during the deep-water oil fields production. However, due to insufficient understanding of the structure of wax deposits and the complexity of sandy crude oil deposition, the interaction between coarse particles and wax deposits in the pipeline have rarely been investigated. In this paper, the effect of coarse particles on the yield stress of wax deposits has been studied. The sample was mixed at reversible structure temperature so that the impact of shear history could be eliminated, and the rapid particle settlement at high temperature could be avoided. Experimental results have found that there is a critical fraction in coarse particle influences, below which a small number of coarse particles added will lead to a slight increase in bulk yield stress. On the contrary, a dramatic decrease in yield stress when exceeding the critical mass fraction and increasingly marked enhancement of yield stress as the fraction increases. This phenomenon has been explicated microscopically by the structural interaction between coarse particles and wax deposits. The interlock between wax crystals is the major contribution of the structure as the less particle fraction contains. Even though the silica sand is a typical non-colloidal particle, the asphaltene and resin could be absorbed on the surface of particles and forming a cluster of colloidal particles. As the fraction of particles slightly increased, the slip between colloidal particles and wax crystal interlock accelerates structural failure. Nevertheless, more particles involved the overall yield stress may depend on the friction and the adhesive force between solid particles. The subtle changes induced by coarse particles would have a harder deposit, which can hinder pig passing and affect pipeline pigging operations.

Evolution and critical roles of particle properties in Pickering emulsion: A review

Mass transfer enhancement and hydrodynamic performance with wire mesh coupling solid particles in bubble column reactor

Liquid foams are familiar from beer, frothed milk, or bubble baths; foams in general also play important roles in oil recovery, lightweight packaging, and insulation. Here a new class of foams is reported, obtained by frothing a suspension of colloidal particles in the presence of a small amount of an immiscible secondary liquid. A unique aspect of these foams, termed capillary foams, is the particle‐mediated spreading of the minority liquid around the gas bubbles. The resulting mixed particle/liquid coating can stabilize bubbles against coalescence even when the particles alone cannot. The coated bubbles are further immobilized by entrapment in a network of excess particles connected by bridges of the minority liquid. Capillary foams were prepared with a diverse set of particle/liquid combinations to demonstrate the generality of the phenomenon. The observed foam stability correlates with the particle affinity for the liquid interface formed by spreading the minority liquid at the bubble surface.

This chapter is dedicated to the topic of multi-phase reactors, characterized by reactions occurring in a liquid phase in which one or more of the reactants, coming from another gaseous or liquid phase, is dissolved. The catalyst promoting the reaction can be a component of the reacting mixture (e.g., gas–liquid reactors), a solid wetted by liquid phase (gas–liquid–solid reactors), or, more seldom, dissolved in another immiscible liquid (liquid–liquid or gas–liquid–liquid reactors). Modeling of such systems is challenging because chemical, physical, and fluid dynamic factors are all involved, sometimes giving place to peculiar phenomena. Occurrence of a reaction in the liquid phase containing the catalyst determines the occurrence of gradients at the interfaces, followed by a mass-transfer flow across the interface. The main theories presented in this chapter are two-film theory, surface renewal theory, and penetration theory. Examples presented in this chapter include the-oxidation of tetra-hydro-anthraquinol (THEAQH2) and o-cresol alkylation. The Matlab code associated with these examples is available online.

A method that controls the pore properties of porous materials with reasonable bounds by the use of emulsion stabilized by the solid particles, is presented. Small droplets of uniform size are created when two immiscible liquids are mixed in the presence of particles, and the particles added during emulsification, migrate to the droplet surface and get absorbed on it. The ratio of emulsified liquid and stabilizing particles determines the droplet size and the pore size and with this technique, a uniform droplet size distribution can be created. Density measurements of sintered samples show that the porosity is directly proportional to the suspension composition. In electrophoresis deposition, the particles of continuous phase deposit faster than the stabilized emulsion droplets, resulting in a layer of dense material on the deposition.

Optical second harmonic generation (SHG) has a high potential for studying surface properties of colloidal particles in situ with a high temporal resolution. In the past the SHG technique has been applied successfully to determine the surface potential of colloidal particles and emulsion droplets and to study adsorption processes at the interface of solid and liquid particles. However, in previous studies mainly monodisperse particles were used. Here we demonstrate that it is also possible to study adsorption processes on polydisperse particle systems with SHG by comparing in situ adsorption measurements on monodisperse and on polydisperse mixtures of polystyrene (PS) particles. In addition, the results suggest that SHG is also applicable for surface characterization of polydisperse samples at high particle concentrations, where absorption and scattering of the particles is dominant.

Measurement of real-time flow structures in gas–liquid and gas–liquid–solid flow systems using electrical capacitance tomography (ECT)

reactions have been used in the continuous flow reaction with a variety of immobilized palladium catalysts.To the best of our knowledge, the Hiyama cross-coupling reaction has never been used in a continuous micro-flow re-action, despite the many advantages of the silyl reagent such as its stability in air stable, nontoxicity and easy availability.

The enzymatic conversion of biomass-derived compounds represents a key step in the biorefinery flowsheet, allowing low-temperature high-efficiency reactions. β-Glucosidases are able to hydrolyze cellobiose into glucose. Wrinkled silica nanoparticles (WSNs) were demonstrated to be a good support for the immobilization of β-glucosidases, showing better performance than free enzymes in batch reaction; on the other hand, immobilized enzyme microreactors (IEMs) are receiving significant attention, because small quantities of reagents can be used, and favorable heat and mass transfer can be achieved with respect to conventional batch systems. In this work, we prepared, characterized, and tested structured enzymatic reactor compounds by a honeycomb monolith, a WSN washcoat, and β-glucosidases as the active phase. Powder and structured materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 physisorption, thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FT-IR). Structured catalysts were tested under both batch and continuous flow reaction conditions and compared to powder catalysts (batch reaction). The WSN washcoat was attached well onto the monolith walls, as suggested by the negligible weight loss after ultrasound treatment; the WSNs preserved their shape, porosity, and individual nature when deposited onto the monolith walls. The immobilized enzyme microreactors proved to be very efficient in hydrolysis of cellobiose to glucose, showing a complete conversion under continuous flow reaction at a batch-equivalent contact time equal to 120 min vs. 24 h obtained in the batch experiments. The apparent KM value showed a 20-fold decrease with respect to the batch process, due to the absence of external diffusive transport limitations.