Reactive Microemulsion Research Articles

Reactive flow of microemulsion-based EDTA fluid for carbonate stimulation

Traditional methods for stimulating carbonate formations primarily rely on the use of highly reactive acids, such as hydrochloric acid (HCl), to create wormholes. However, the limitations of this approach in certain scenarios have prompted the exploration of alternative strategies. In this study, we investigate the synergistic potential between microemulsion and ethylenediaminetetraacetic acid (EDTA) for stimulating carbonate formations. Microemulsion systems were formulated using a nonionic surfactant, sec-butanol as a cosurfactant, xylene as the oily phase, and an aqueous solution of EDTA as the water phase. The microemulsions were characterized by phase equilibrium and rheological behavior. Coreflooding and static dissolution experiments were performed. We employ microCT imaging to evaluate the change in porosity in static dissolution experiments. The results reveal that microemulsions containing EDTA presented remarkable stability and were able to significantly enhance carbonate rock permeability up to 85%, indicating that dissolution occurred and the rock was stimulated. Analyses of microCT images on static dissolution experiments of Indiana limestones in reactive microemulsions indicate an increase in porosity, confirming the dissolution process. These findings highlight the synergistic effect of EDTA in microemulsion media for enhancing the rock permeability of carbonate formation as an alternative as low reactive system.

Fast-track realization of reactive microemulsion systems – Systematic system analysis and tailored application of PSE methods

Despite the overarching necessity for sustainability, the realization of novel process concepts using innovative green reaction media, such as microemulsions is still hindered by their inherent complexity. To overcome this, a holistic guideline for the fast-track realization of microemulsion systems is presented and applied on a mini-plant for the hydroformylation of 1-dodecene in microemulsions. It combines a rigorous system analysis and identification of challenges for process design and operation. Here, critical unmeasurability of concentrations, small feasible operation regions, and a highly dynamic system behavior are identified. This is encountered by tailored PSE methods: a dynamic model for the complex three-phasic separation of microemulsions, the formulation of a concentration soft-sensor, as well as multi-rate moving horizon state estimation and subsequent dynamic real-time optimization. Applying those, stable operation of the mini-plant for up to 200 h is ensured together with a steady-state product yield of 38% and a product selectivity of 92%.

Back and forth invasion in the interaction of Turing and Hopf domains in a reactive microemulsion system

Pattern formation is studied numerically for a reactive microemulsion when two parts of the system with different droplet fractions are initially put into contact.

Optimization of process parameters for ruthenium nanoparticles synthesis by (w/o) reverse microemulsion

Taguchi OA factorial design method was used to identify the several factors that might affect the particle size of ruthenium nanoparticles prepared by the mixing of two reactive microemulsions. In the present work, the objective of evaluating the factors influencing the particle size had been improvised by studying two qualitative factors viz., effect of different reducing agents and effect of different co-surfactants. Using orthogonal experimental design and analysis technique, the system performance could be analyzed with more objective conclusion through only a small number of simulation experiments. Analysis of variance was carried out to identify the significant factors affecting the response and the best possible factor level combination was determined through. It was found that the formation of ruthenium nanoparticles, microemulsions were greatly influenced by the type of reducing agent used in the technique followed by water-to-surfactant molar ratio.

Nanostructured diffusion-limited-aggregation crystal pattern formation in a reactive microemulsion system

Nanostructured diffusion-limited-aggregation (DLA) crystal pattern formation in microemulsion consisting of water, styrene, cetyltrimethylammonium chloride (CTACl), potassium persulphate and an oscillating Belousov–Zhabotinsky (BZ) reactant is reported. A variety of spatiotemporal patterns like concentric wave, spatial (stripe) and chaotic patterns appear. A colloidal phase composed of numerous nano-sized particles has been observed. The solid phase nucleation has been found to occur in the colloidal phase and has been found to grow in a symmetric crystal pattern with the progress of the reaction finally exhibiting DLA structures. We show that the formation of a nanostructured DLA crystal pattern is governed by spatial structures emerging in the BZ microemulsion system. Without any spatial structure in the microemulsion system only hydrogel of high viscosity is formed. A nano-sized branched crystal pattern was formed with a particle diameter in the range of 60–100 nm, as evident by transmission electron microscope, powder x-ray diffraction and particle size analyser studies.

Role of interfacial elasticity of microemulsions on the morphology of TiO2 nanostructures: stiff templates versus flexible templates

The effects of temperature and interfacial elasticity on nanostructured titanium dioxide (TiO2) microemulsions templated materials have been investigated. The aim was to establish a simple and rapid selection of the best experimental conditions for achieving some required material property. TiO2 materials have been prepared through reactive microemulsion precipitation. The effect of microemulsion process parameters (temperature and oil phase density) on the final material characteristics has been investigated. The titania nanopowders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and N2 adsorption–desorption isotherms. The results obtained by different process conditions show that the nonpolar phase density and temperature of microemulsions have a great influence on the final characteristics of the obtained material. A reduction of the microemulsion oil density causes a significant decrease in the particle agglomeration and an augment of the material-specific surface area and pore volume. At the same time, rutile is favored over anatase phase. The increase of template microemulsion temperature produces, in some systems, a morphology change from granular to a bicontinuous structure.

Formation of Ruthenium Nanoparticles by the Mixing of Two Reactive Microemulsions

In this study, two reactants (ruthenium chloride and sodium borohydrate) were premicellized in two separate microemulsions and brought into contact through intermicellar exchange to conduct the reaction. As a result, ruthenium nanoparticles were formed. The overall reaction rate was governed by the intermicellar exchange rate. Particle size was controlled by varying surfactant concentration, water-to-surfactant molar ratio (ω), precursor (ruthenium chloride) concentration, and molar ratio of reducing agent-to-reagent (R). Dynamic light scattering and transmission electron microscopy were used to determine the size, size distribution, and structure of the synthesized ruthenium nanoparticles. The molar ratio ω was varied from 3 to 7; sizes of the particles were found to be in the range of 17.08–25.09 nm. The precursor (ruthenium chloride) concentration was varied in the range of 0.1–0.3 M; particle size was observed to decrease up to 0.2 M then increase due to particle agglomeration at higher precursor concentrations. Smaller nanoparticles were obtained at higher R values due to faster intramicellar nucleation and growth rate. Dispersion destabilization of colloidal ruthenium nanoparticles was detected by Turbiscan.

The hydrophobicity of silicone-based oils and surfactants and their use in reactive microemulsions

In this work, for the first time, the Hydrophilic-Lipophilic Difference (HLD) framework for microemulsion formulation has been applied to silicone oils and silicone alkyl polyether surfactants. Based on the HLD equations and recently introduced mixing rules, we have quantified the hydrophobicity of the oils according to the equivalent alkane carbon number (EACN). We have found that, in a reference system containing sodium dihexyl sulfosuccinate (SDHS) as the surfactant, 0.65 centistoke (cSt) and 3.0 cSt silicone oils behave like n-dodecane and n-pentadecane, respectively. Silicone alkyl polyether surfactants were found to have characteristic curvatures ranging 3.4-18.9, exceeding that of most non-ionic surfactants. The introduction of methacrylic acid (MAA) and hydroxyethyl methacrylate (HEMA) to the aqueous phase caused a significant negative shift in HLD, indicative of an aqueous phase that is less hydrophilic than pure water. The more hydrophobic surfactants (largest positive curvatures) were used in order to compensate for this effect. These findings have led to the formulation of bicontinuous microemulsions (μEs) containing silicone oil, silicone alkyl polyether and reactive monomers in aqueous solution. Ternary phase diagrams of these systems revealed the potential for silicone-containing polymer composites with bicontinuous morphologies. These findings have also helped to explain the phase behavior of formulations previously reported in literature, and could help in providing a systematic, consistent approach to future silicone oil based microemulsion formulation.

Study of the process parameters in the synthesis of TiO 2 nanospheres through reactive microemulsion precipitation

Spherical particles constituted by nanocrystals of titanium oxide TiO 2 have been prepared through reactive microemulsion precipitation. A water-in-oil microemulsion, added with a suitable emulsifier, has been used. The effect of the process parameters (water to oil ratio, type and amount of surfactant, concentration of precursor solution, mixing velocity) on the final characteristics has been investigated, in terms of structural phase and particle size. The titania nanopowders were characterized by means of X-ray diffraction, thermogravimetric and differential thermal analyses and scanning electron microscopy. The results obtained by different process conditions showed the development of both titania rutile and anatase spherical particles, with particle size ranging from tens to hundreds of nanometers.

Long-lasting dashed waves in a reactive microemulsion

In the Belousov-Zhabotinsky (BZ) reaction carried out in a reverse microemulsion with Aerosol OT as surfactant, the existence of two different sizes of droplets containing the BZ reactants leads to the emergence of segmented (dashed) waves. This bimodal distribution of sizes is stabilized by adding small amounts of the homopolymer poly(ethylene oxide) (PEO). Addition of PEO lengthens the period during which these patterns are observed, so that dashed waves can persist for 12-14 h, in contrast to the 2-3 h found in earlier studies without added polymer.

Modeling core–shell nanoparticle formation using three reactive microemulsions

Core and shell nanoparticle formation in reverse microemulsions has been formulated by taking the post-core method of synthesis, using population balance equations. The formation of core nanoparticle was done by a modified model [B. Viswanadh, Core and Shell Nanoparticle Formation by Using Water in Oil Microemulsions, M.Tech. Thesis, Department of Chemical Engineering, Indian Institute of Technology, Bombay, 2005] of Kumar et al. [A.R. Kumar, G. Hota, A. Mehra, K.C. Khilar, Modeling of nanoparticles formation by mixing of two reactive microemulsions, AIChE J. 50 (2004) 1556]. Formation of core and shell nanoparticles was followed there after by considering the probabilities of micelles of core nanoparticle formation, which were most significant. The study provides an insight into the effect of the concentration of reactants on the shell coating and shows that there exist nanoparticles which are completely coated, partially coated as well as particles with no coating too, with large fraction of partially coated nanoparticles.

Alternative Sol-Gel Routes for Synthesizing Gas Sensing Nanostructured Materials

Alternative sol-gel techniques, investigated in our laboratory with the aim to obtain nanostructured metal oxides powders with enhanced gas sensing properties, are reviewed. The synthesis of pure and doped In2O3 by a non aqueous sol-gel method and TiO2 by reactive microemulsion and gel-combustion, are described in detail. The morphological and microstructural characteristics are also described and related to the gas sensing characteristics of the synthesized nanopowders.

Decontamination of Radioactive Contaminants from Iron Pipes using Reactive Microemulsion of Organic Acid in Supercritical Carbon Dioxide

The ferrite fixed on the iron pipes was decontaminated by a reactive microemulsion in supercritical carbon dioxide (SC-CO2). The specimens were prepared by treating the iron pipes with steam at 1,273 K for 2 min. The specimen was not dissolved in 3 mol·dm−3 HNO3 because its surface was covered with ferrite, while the original iron pipe was easily dissolved. This difference was used for determination of the fraction of ferrite. The fraction of ferrite covering the iron pipes was 1.5±0.3 wt%. A microemulsion containing organic acid was prepared using a fluorinated reagent, pentade-cafluorooctanoic acid (PFOA), and a non-fluorinated surfactant, polyoxyethylene (2) nonylphenyl ether (NP-2) and citric acid. In the former system, PFOA acted as a surfactant as well as an acid. By observation of the phase equilibrium, the microemulsion was found to be stabilized when the molecular ratio of water to surfactant, the w value, was 5.0 for the PFOA+H2O+SC-CO2 system, and 8.7 for the NP-2+citric acid+SC-CO2 system at 25 MPa, and 323 or 353 K. Although the removal fractions of the ferrite were 0 and 1% for the PFOA and NP-2 system, respectively, at 25 MPa, 323 K, they increased to 92 and 56% at 25 MPa, 353 K.

Decontamination of Radioactive Contaminants from Iron Pipes using Reactive Microemulsion of Organic Acid in Supercritical Carbon Dioxide

The ferrite fixed on the iron pipes was decontaminated by a reactive microemulsion in supercritical carbon dioxide (SC-CO2). The specimens were prepared by treating the iron pipes with steam at 1,273 K for 2 min. The specimen was not dissolved in 3 mol·dm−3 HNO3 because its surface was covered with ferrite, while the original iron pipe was easily dissolved. This difference was used for determination of the fraction of ferrite. The fraction of ferrite covering the iron pipes was 1.5±0.3 wt%. A microemulsion containing organic acid was prepared using a fluorinated reagent, pentade-cafluorooctanoic acid (PFOA), and a non-fluorinated surfactant, polyoxyethylene (2) nonylphenyl ether (NP-2) and citric acid. In the former system, PFOA acted as a surfactant as well as an acid. By observation of the phase equilibrium, the microemulsion was found to be stabilized when the molecular ratio of water to surfactant, the w value, was 5.0 for the PFOA+H2O+SC-CO2 system, and 8.7 for the NP-2+citric acid+SC-CO2 system at 25 MPa, and 323 or 353 K. Although the removal fractions of the ferrite were 0 and 1% for the PFOA and NP-2 system, respectively, at 25 MPa, 323 K, they increased to 92 and 56% at 25 MPa, 353 K.

Complex patterns in reactive microemulsions: Self-organized nanostructures?

In a reverse microemulsion consisting of water, oil (octane), an anionic surfactant [aerosol OT (AOT)], and the reactants of the oscillating Belousov-Zhabotinsky (BZ) reaction, a variety of complex spatiotemporal patterns appear. These include traveling and standing waves, spirals that move either toward or away from their centers, spatiotemporal chaos, Turing patterns, segmented waves, and localized structures, both stationary and oscillatory. The system consists of nanometer-sized droplets of water containing the BZ reactants surrounded by a monolayer of AOT, swimming in a sea of oil, through which nonpolar BZ intermediates can diffuse rapidly. We present experimental and computational results on this fascinating system and comment on possible future directions for research.

Modeling of nanoparticles formation by mixing of two reactive microemulsions

AbstractA stochastic population balance model for the formation of nanoparticles, involving mixing of two micellized aqueous solutions containing the individual reactants, respectively, has been developed to study the effects of various parameters that influence the formation process of nanoparticles. Population balance equations have been formulated assuming a cooperative mode of intermicellar exchange in an attempt to explore the largest possible particles that can form in a given system. The proposed model essentially divides the entire population of micelles into different categories and formulates the equations describing the rate of change of the probabilities of different states of the micelles in each category. The effect of parameters, such as nucleation rate, intermicellar exchange rate, critical nucleation number, and concentration of the reactants on the particle sizes that can be obtained, has been investigated. The model predictions show a reasonable qualitative agreement with experimental data. © 2004 American Institute of Chemical Engineers AIChE J, 50:1556–1567, 2004