Emulsification using tubular metallic membranes

Tubular metallic membranes with pore diameters of 5 and 10 μm have been used in a cross-flow unit to prepare monodisperse oil-in-water emulsions (O/W) with span values as low as 0.67, significantly lower than for emulsions prepared with a rotor–stator homogenizer. The influence of typical operating parameters (continuous phase flow rate and transmembrane pressure) on droplet size distribution was studied. The smallest droplets were obtained at low transmembrane pressures and high continuous phase flow rates. The droplet production with tubular metallic membranes was higher than with other types of tubular membranes, such as SPG or ceramic.Experimental results were compared with those obtained in a stirred tank unit operating under similar conditions and using flat metallic membranes with the same pore diameter. Droplet size prediction models based on simple force balances were applied to compare theoretical and experimental droplet diameters. The droplet formation regime (dripping, jetting) was also studied for both types of membranes.     

一体式陶瓷外膜直接乳化法制备单分散水包油乳液

膜乳化法是靠膜两侧的压差使分散相通过微孔膜,以小液滴的形式分散在连续相中而形成乳状液的方法．与转一定体系、高压均化等传统制乳方法相比,膜乳化法所制得的乳液具有液滴尺寸均一、节能、剪应力小等特点,可应用于食品、医药、聚合物工业等领域．过去的十几年中,尽管在膜乳化方面进行了大量的工作,过程参数对乳滴尺寸的影响并未完全研究清楚．甚至在一些研究中,仅仅把平均乳滴直径作为分布参数．     

The membrane emulsification process—a review

Membrane emulsification has received increasing attention over the last 10 years, with potential applications in many fields. In the membrane emulsification process, a liquid phase is pressed through the membrane pores to form droplets at the permeate side of a membrane; the droplets are then carried away by a continuous phase flowing across the membrane surface. Under specific conditions, monodispersed emulsions can be produced using this technique. The purpose of the present paper is to provide a review on the membrane emulsification process including: principles of membrane emulsification, influence of process parameters and industrial applications. Small‐scale applications such as drug delivery systems, food emulsions, and the production of monodispersed microspheres are also included. Compared with conventional techniques for emulsification, membrane processes offer advantages such as control of average droplet diameter by average membrane pore size and lower energy input. Copyright © 2004 Society of Chemical Industry     

High throughput membrane emulsification using a single-pass annular flow crossflow membrane

Membrane emulsification has the potential to revolutionize the energy-efficient production of uniform emulsions and dispersions, relevant to diverse fields from pharmaceutical active ingredient controlled release particles to Fast Moving Consumer Goods. A novel highly robust single-pass continuous phase crossflow system has been developed providing dispersed phase concentrations up to 40% vol/vol and dispersed phase fluxes up to 5,730 L m⁻² hr⁻¹, from a single 100 mm long membrane tube. Extensive results of two oil-in-water systems (vegetable oil and PolyCaproLactone dissolved in DiChloroMethane) and one water-in-oil system (sodium silicate solution) are reported, using hydrophilic and hydrophobic membranes respectively. Mathematical models are validated enabling comprehensive engineering analysis of processes including predicted droplet size, membrane pressure drops, and energy requirement for dispersion production. Surfactant depletion, pore utilization, and droplet interaction at the membrane surface were investigated to provide a comprehensive analysis of the capabilities of novel annular-flow membrane emulsification for high throughput emulsion generation.     

Preparation of water-in-oil and ethanol-in-oil emulsions by membrane emulsification

In this work, water-in-oil emulsions (W/O) and ethanol-in-oil emulsions (E/O) emulsions were prepared successfully by membrane emulsification. The emulsifiers selected were PGPR and MO-750 for the W/O and E/O emulsions, respectively. For W/O emulsions prepared with an oil pre-filled membrane, the dispersed flux was lower and the droplet size sharper than that obtained with a water pre-filled membrane. On the contrary, for E/O emulsions prepared with the membrane pre-filled with oil, the dispersed phase (ethanol) rapidly pushed out the oil from the membrane pores. Therefore, the pre-treatment of the membrane had almost no effect on the dispersed phase flux and on the droplet size. The droplet size distribution of the E/O emulsion was close to that obtained with a classical homogenizer. The dispersed phase fluxes were high and no fouling was observed for our experimental conditions (1.6 l emulsion, 10 wt% ethanol). These results confirm that membrane emulsification could be an interesting alternative for the preparation of E/O emulsions for the purpose of biodiesel fuels, considering the scale-up ability of membranes and their potentiality for industrial processes.     

膜参数对乳化过程的影响

膜乳化法是近年来提出的一种新的乳化方法,可以制备出单分散性非常好的乳液,在各领域都有广泛的应用。但生产率低是制约该方法工业化的一个主要因素。对影响乳液形成的膜参数进行了讨论,并对膜的优化设计进行了探讨。     

Microstructure–performance relationships of hollow-fiber membranes with highly efficient separation of oil-in-water emulsions

The critical breakthrough pressure related to the membrane surface wettability and pore size is a key parameter determining membrane performance in particular applications, such as oil–water mixture separations. A series of hydrophilic polysulfone hollow-fiber membranes with different pore sizes were prepared and characterized to evaluate the separation performance of oil-in-water emulsions and to develop an optimum membrane for such emulsions. For the optimum membrane, the absolute value for the cosine of the surface oil droplet contact angle (0.72) was close to the ratio of the outer surface pore size to the oil droplet size (0.71); it was also similar to the absolute value of the cosine of the underwater oil contact angle on the polysulfone material (0.65). From the point of view of the surface wettability, theoretical calculations were performed to select a suitable membrane with the aim of reaching the maximum efficiency in practical oil–water mixture separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47615.     

Intensification of production of O/W emulsions using oscillatory woven metal micro-screen (WMMS)

Using high porosity woven metal micro-screen (WMMS), a novel design oscillatory emulsifier had been used for intensification of production of relatively narrow size distribution oil in water (O/W) emulsions. The average droplet size increased with increasing the dispersed phase flow and decreased with increasing both the oscillation frequency and amplitude. The emulsion polydispersity decreased with increasing both oscillation intensities as well as dispersed phase flux. Although the change in droplet size with oscillation was reasonably predicted using a simple torque balance model based on Stokes oscillatory flow, both the flow patterns and the surface phenomena are more complex, and the final droplet size is affected by interactions between different operating and physical parameters.     

Effect of dispersed phase feed time on the droplet size of Pickering emulsions produced in a stirred tank

The aim of this study was to investigate the effect of feed time of the oil phase on the average droplet size of Pickering emulsions produced in stirred tanks. Three types of impellers were tested: RT, up-pumping PBT (PBTU), and down-pumping PBT (PBTD). All the impellers were tested at two sizes, T/3 and T/2. All configurations were compared at constant tip speed, power per mass, and impeller Reynolds number. The droplet diameters were measured in Mastersizer® 3,000 (Malvern). The results showed that an increase in feed time causes a reduction in the average droplet size. At lower impeller speeds and higher feed times, the effect is more pronounced. It was found that some other geometric parameters also have an impact on the average droplet size.     

Effect of stretching on continuous oil/water separation performance of polypropylene hollow fiber membrane

In this work, polypropylene (PP) hollow fiber membranes were fabricated by thermal-induced phase separation method. The influence of cold-stretched and hot-stretched treatment on the morphology and permeability of the PP hollow fiber membranes was investigated. The results showed that there were cracks and crystalline particulate structures on the outer and inner surfaces of the stretched PP hollow fiber membranes, which were not isolated but linked together through fiber-like connections. Compared to the original PP hollow fiber membrane, the mean pore sizes, the porosities, the hydrophobicity and water entry pressure of the stretched PP hollow fiber membranes improved significantly. When applied in conjunction with a vacuum system, the PP hollow fiber membranes could continuously remove oils from water surface, and separate surfactant-free and surfactant-stabilized water-in-oil emulsions, as well. The initial kerosene fluxes of the hot-stretched PP hollow fiber membrane were higher than that of the membranes prepared from original PP hollow fibers or cold-stretched PP hollow fibers. The permeate fluxes of the hot-stretched PP hollow fiber membrane for all different emulsion separations were higher than those of the original PP hollow fiber membrane. There could be seen no emulsion droplet in the optical micrographs after separation, indicating that the water-in-oil emulsions were effectively separated in one-step method.     

Physico-chemical properties of heavy crude oil-in-water emulsions stabilized by mixtures of ionic and non-ionic ethoxylated nonylphenol surfactants and medium chain alcohols

This work describes the formulation and evaluation of concentrated, heavy oil-in-water emulsions stabilized by mixtures of ethoxylated surfactants and normal alcohols. The rheology, stability and droplet size of these emulsions were investigated as functions of the emulsification process parameters. The parameters investigated for this study include emulsifier agent composition, presence of additives, pH and salinity of the continuous aqueous phase, emulsification temperature, oil content and emulsion aging. The produced emulsions had viscosities ranging from 30 to 150 mPa s and represent a 30-fold reduction of the crude oil viscosity. Sauter mean diameters of the droplets ranged from 10 to 50 μm. The emulsions were produced by mixing the oil with an aqueous solution containing medium normal-chain alcohols and small quantities of a mixture of ethoxylated nonylphenol and ethoxylated amine surfactants. The presence of these alcohols led to a sharp decrease in the droplet size of the emulsion. This size decrease had a direct impact on the emulsions’ stability and apparent viscosity. The rheological parameters of the aged emulsions were also essentially constant over a 42-day period.     

Formation of O/W emulsions by static mixers for pharmaceutical applications

Oil-in-water (O/W) emulsions produced by static mixers in the laminar flow regime are characterized for their oil drop size spectra. The emulsions are used in the first process step for the production of microspheres for pharmaceutical applications by the emulsion extraction method. However, emulsion generation by static mixers in the laminar flow regime is rarely discussed in the scientific literature. Here we deduce a non-dimensional correlation for predicting the Sauter mean oil drop size as a function of the static mixer operation parameters and the liquid properties. First, the material properties of the organic and water phases are characterized. Second, the oil drop size spectra of the emulsions are measured by laser diffraction. Dimensional analysis is used to describe the relationship between the process parameters of the static mixer and the Sauter mean oil droplet size. Emulsion production experiments using SMX static mixers with two different diameters are carried out with the mixing of the two liquids taking place in the laminar flow regime. We provide results covering a wide range of all process parameters, which were identified influencing the droplet size of the emulsion. The correlation achieved is related to the non-dimensional drop-size based Ohnesorge number of the emulsification process and allows for the prediction of the mean oil droplet size with good accuracy, which is an essential information about the emulsion properties relevant for the pharmaceutical application.     

Droplet characteristics in the multi-staged high speed disperser with single inlet

Droplet characteristics in the cavity zone of a multi-staged high speed disperser with single inlet were studied in this paper. The influences of both the operating and structural parameters on the mean droplet diameter, size distribution and liquid flux distribution were quantitatively analyzed. The result showed that the mean droplet diameter decreased with the increase of rotational speed and the number of rotors;whilst there is little influence on the inlet flow rate. In the experimental range, the minimum value of mean droplet diameter is 0.57 mm, 0.48 mm, 0.41 mm in the two-staged, three-staged and four-staged rotors, respectively. The Rosin–Rammler(R–R) distribution could describe the droplet size distribution appropriately, and it became uniform with the increase of rotational speed and the number of rotor, while the inlet flow rate had little effect on the droplet size distribution. The liquid flux distribution curves were always unimodal. With the increase of rotational speed, the location of maximum liquid flux ratio moved from zone 3 to zone 4 and this value decreased from 22.1% to 18.1%. Using Coefficient of Variation(CV) to indicate the uniformity of liquid flux distribution, it was found that the CV decreases from 47.5% to 22.7%when the number of rotor increased from 2 to 4.     

Removal of Benzene/Toluene from Water by Vacuum Membrane Distillation in a PVDF Hollow Fiber Membrane Module

Abstract

Asymmetric polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared by a phase inversion method using dimethylacetamide (DMAc) and a mixture of water/LiCl as solvent and a nonsolvent additive, respectively. The prepared membranes were characterized by scanning electron microscopy (SEM) for observing its microstructures and by a gas permeation method for measuring its surface porosity, pore size, and pore size distribution. Wetting pressures of the dry hollow fiber membranes were also measured. Using the prepared PVDF hollow fiber membranes, a membrane module was fabricated for removal of benzene/toluene from water. Effects of various operating parameters such as downstream vacuum levels, feed temperatures, and feed flow rates on performances of the module were investigated experimentally. The benzene/toluene removal was achieved over 99% under an optimal operating condition. Mass transfer of benzene or toluene removal is controlled not only by the liquid phase resistance but also by the membrane and gas phase resistances. Benzene and toluene can be removed from water simultaneously with no adverse coupling effects.     

Preparation of Porous Calcium Alginate Membranes/Microspheres via an Emulsion Templating Method

Summary: A method is presented that can produce ordered macroporous alginate membranes and microspheres with a relatively narrow pore size distribution as compared to other existing porous alginate matrix generating procedures. The calcium alginate membranes and microspheres obtained were multiporous, and the pore size could readily be adjusted in the range of 1 to 10 µm by selecting appropriate initial emulsion parameters. A preliminary set of experiments was used to determine a range of conditions suitable for the formation of stable O/W emulsions consinsting of the alginate solution, liquid paraffin and surfactants. The obtained emulsions were characterized by size distribution measurements and optical microscopy. The emulsions were used to form alginate membranes and microspheres with diameters of 150–500 µm. Subsequent work was performed to remove liquid paraffin droplets, the dispersed phase of the emulsion which acted as template in the pore‐generating process, from the final alginate membranes and microspheres. The states of templates in hydrogels and the effect of template removal on the calcium alginate structures were thoroughly investigated.

Porous alginate membranes prepared via emulsion templating method.     

Thixotropic Behavior of Oil‐in‐Water Emulsions Stabilized with Ethoxylated Amines at Low Shear Rates

Oil‐in‐water (O/W) emulsification is a lubricating pipeline method based on the reduction of the energy frictional loss produced during viscous flow. The flow behavior of heavy O/W emulsions formulated with nonionic surfactants is described. The effects of pH and salinity of the aqueous phase on droplet diameter, stability, and apparent viscosity of O/W emulsions were evaluated. The low‐shear Couette flow of O/W emulsions displayed intense shear‐thinning and thixotropic behavior. Thixotropy was associated to the droplet deformation energy caused by shear rate changes. The droplet deformation and alignment led to the apparent viscosity reduction compared to the fluid at rest. Thixotropic behavior is supposed to balance between the breakdown and recovery of droplet ordered structures. Emulsion formulation parameters were influenced by the aqueous phase pH, enabling to manage the emulsion properties. The droplet mean diameter of < 18 µm resulted in very stable emulsions.     

Structure control of polyphenylene sulfide membrane prepared by thermally induced phase separation

Porous membranes were prepared through thermally induced phase separation (TIPS) of polyphenylene sulfide (PPS)/diphenyl ketone mixtures. The phase diagram of PPS/diphenyl ketone system was drawn by cloud point temperature and dynamic crystallization temperature. SEM images and porosity were used to characterize PPS membrane structures. According to the analysis of phase diagram, three main effecting factors including polymer concentration, cooling rate, and nucleating agent could control the pore structure and pore size for the preparation of symmetry and asymmetry membranes. The experimental results are coincident with the theory prediction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

连续相黏度对膜乳化结果的影响

Oil-in-water(o/w) emulsions were produced with a membrane emulsification system. The effect of the continuous phase viscosity on the emulsification was studied. The theoretical analyses show that the continuous phase viscosity influences not only the flow field of the continuous phase but also the interfacial tension. The droplet size distribution and disperse phase flux for different continuous phase viscosity were investigated experimentally at constant wall shear stress and constant volume flow rate of the continuous phase respectively.     

Open porous emulsion‐templated monoliths: Effect of the emulsion preparation conditions on the foam microstructure and properties

Highly open porous polymer foams were prepared via the polymerization of 10 : 1 styrene/divinylbenzene high‐internal‐phase emulsions (HIPEs) prepared under various emulsifying conditions. The effects of the emulsification stirring speed (SS) and rate of aqueous droplet‐phase addition on the HIPE equilibrium torque value, an approximate characterization of HIPE viscosity, and the microstructure and properties of the resulting HIPE polymer solid foams were investigated. SS was varied over the range 400–1200 rpm for aqueous‐droplet‐phase addition rates (AARs) of 0.53 and 1.3 mL/min. The microscopic results showed that at lower AARs, increasing SS decreased the weighted‐average cell diameter from 24.31 to 13.55 μm, whereas the cell size distribution was broadened, and the intercellular pore size varied irregularly in the range 0.76–1.42 μm. The average cell diameter and intercellular pore size for the solid foams prepared at higher AARs were greater than that of those prepared at lower AARs. The density of the foam materials ranged from 0.057 to 0.072 g/cm³, whereas their thermal conductivity varied from 0.649 to 0.705 W m^?1 °C^?1. The highest compressive stress–strain properties were found for the foam sample prepared with highest SS and a lower AAR. Adding electrolyte CaCl₂ to HIPE produced remarkable increases in the void diameter and intercellular pore size, especially at lower SS values. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010