Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - COMNACTSS (Controlling micro- and nano-channel transport with selective solvation)
Teaser
More than ever before, the better usage of existing water resources must be addressed in order to meet the world’s growing demand for clean water. This requires advances in water treatment technology. An industrial wastewater of emerging concern is so called produced water...
Summary
More than ever before, the better usage of existing water resources must be addressed in order to meet the world’s growing demand for clean water. This requires advances in water treatment technology. An industrial wastewater of emerging concern is so called produced water, a byproduct of oil and gas extraction processes. Produced water is a multi-phase oil/water mixture, whereby small oil droplets are difficult to separate by traditional methods. While membrane processes are increasingly being used for wastewater treatment due to their environmental friendliness, low cost, and energetic efficiency, their use is still limited by severe loss of membrane performance due to fouling (clogging). Considerable research has been carried out to improve membrane conductivity and selectivity and to prevent membranes from clogging. Almost always, the mixture to be separated also contains ions from dissolved salts.
The broad aim of this project was to explore how the dissolved ions affect the various membrane performance parameters and in particular, how the partitioning of ions between oil and water can be used to improve membrane performance.
Work performed
Before investigating the flow of salty mixtures through membrane pores, we started by studying the equilibrium (no-flow) state of a salty oil/water mixture when in contact with a pore. To our surprise, the presence of ions dramatically modified the equilibrium state, and we revealed a pore filling transition, whereby pores can be reversibly gated from oil-rich (poor conductor of ions and other solutes) to water-rich (good conductor) states by an external potential. This research was published in the journal Colloid and Interface Science Communications.
When small particulates (colloids) are also present in an oil/water mixture they adsorb extremely strongly to the oil/water interface. However, the recovery of particles from oil-water interface is an essential step for the realization of applications, such as in biofuel upgrade, “dry water†catalysis, and gas storage. We studied the interaction of an oil-dispersed colloidal particle with an oil-water interface and have shown it to be highly tunable from attractive to repulsive due the ions partitioning between the oil and water phases, thereby allowing to prevent colloids from attaching to interfaces by the proper choice of added salt . This research was published in the high-impact journal Physical Review Letters. Our theoretical predictions were affirmed by a subsequent work with our local experimental collaborators (group of prof. A. van Blaaderen), which was published in the journal Physical Chemistry Chemical Physics.
Pressure-driven membrane processes are by far the most widely used membrane technologies for water treatment applications. We studied the separation of a salt-free water/oil mixture at the single pore level in a pressure-driven process. When the water/oil mixture is near its critical point, we found a ten-fold increase in the separation efficiency of the mixture due to critical adsorption. We also uncovered a new adsorption regime at higher flow rates, where the mixture in the pore stratifies. This regime could be used to prevent the fouling of pores. Our findings were published in Physical Review Letters and where selected as an Editor’s suggestion and featured in an APS Focus article (https://physics.aps.org/articles/v10/2).
When ions are added to the oil/water mixture, we found that the ion partitioning can greatly modify the transport in the pore. When an external electric field parallel is applied parallel to the pore surface,
the partitioning of ions due to the adsorption of water (or oil) at the pore surface leads to a new type of flow, which we termed solvo-osmotic flow. The generated flow is comparable in magnitude to the ubiquitous electro-osmotic flow used in “Lab-on-a-Chip†devices, the separation and analysis of biological macromolecules, and in non-aqueous capillary electrophoresis. Solvo-osmotic flow differs qualitatively in its dependence on ionic strength compared to electro-osmotic flow and is also sensitive to temperature. Our findings offer a new way for controlling transport in membranes and microfluidic devices. This work was published in the Journal of Fluid Mechanics as a JFM Rapid paper.
During the action, I also worked on related projects with collaborators from Utrecht University (The Netherlands) Stuttgart University (Germany), Ben-Gurion University (Israel), which resulted in seven more publications in peer-reviewed international journals (Scientific Reports, Soft Matter and others).
I also presented my results in three international conferences (Complex Motion in Fluids, FOM@Physics, Droplets).
Final results
The theoretical framework that I developed during the action is a significant step forward in the description of charged multi-phase fluids. The study of the underlying equations and their numerical solution has only been done by one other group, and is in its infancy. Fifty billion barrels per year of produced water are generated worldwide. The treatment of this water and other polluted streams relies on using membranes. In turn, the rational design of membranes relies on our fundamental understanding of fluid transport at small scales. This action has advanced the knowledge on such transport and has laid down the theoretical and technical foundation for future studies.
Website & more info
More info: http://samins.github.io/.