Microfluidics for Energy & Environmental Applications
Using microfluidic techniques combined with optical diagnosis, we aim at exploring multiphase flow dynamics at various scales in energy and environmental-related applications. Specific examples are
a 1) CO2 diffusivity measurements into water2) Visualization of three-phase flow (CO2-water-solid precipitation) in porous media 3) CO2-Flooded Enhanced Oil Recovery 4) CO2 Capture by ethanolamine-nanoparticles 5) CO2 Hydration with Polymer-Nanoparticles 6) Biofuel – Improved Efficiency for Growth & Separation
1) CO2 Diffusivity Measurements
Measurements of accurate CO2 diffusivity to water are important to predict CO2 storage capacity as well as to secure safe/permanent storage strategies into geological saline formations. Images below are representatives of experimental setups and corresponding results.
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2) Visualization of Three-Phase Flow in Porous Media
<CO2 diffusion to brine>
Solid precipitations during CO2 injection in saline aquifers, porous geological formations filled with brine and several minerals, located 1-3 km underground, cause serious problems such as the increase of injection cost, the decrease of overall injectivity, and artificial earthquakes due to high pressure operations. Proper understanding of CO2 injection processes into porous media will help to resolve these hard questions. The video and images below are example experimental results including the chip fabrication procedure.
<CO2 injection to porous media>
<Fabrication of Porous Structures>
<Fluorescence Image of CO2 Injection> <Image Processed CO2 Injection> d d
<SEM Images of Precipitated Salt>
3) CO2-Flooded Enhanced Oil Recovery
Chemical enhanced oil recovery (EOR) is a successful method for increasing crude oil recovery. However, chemicals commonly used for enhanced oil recovery operations possess adverse biological impacts. To meet the legislative requirement and environmental protection demands, the performance of a highly biodegradable nonionic surfactant derived from tannic acid, a possible alternative, was evaluated using a microfluidic technology for the replacement of chemically synthesis surfactant by green chemistry products. Aqueous microdroplets containing the surfactant in crude oils were used for measurements of interfacial tension (IFT) reduction. The degree of interfacial tension reduction by sodium dodecyl sulfate (SDS), one of the most popular conventional surfactants, was also quantified for performance comparison. The potential of the biosurfactant for IFT reduction of light crude oil was superior to that of SDS. To evaluate the feasibility of the biosurfactant in improvement of recovery efficiency, surfactant-assisted flooding was tested under a random microfluidic network at the optimal concentrations, and the results were in good agreement with IFT reduction tests. The utilization of the polymer in a biosurfactant synthesis process effectively enhanced high sweep efficiency by decreasing a viscous fingering effect. The biosurfactant proved to be adequate and can sufficiently alleviate environmental concerns adopted by chemical flooding EOR.
4) CO2 Capture by Ethanolamine-Nanoparticles
5) CO2 Hydration with Polymer-Nanoparticles
This work shows the potential of nickel (Ni) nanoparticles (NPs) stabilized by polymers for accelerating carbon dioxide (CO2) dissolution into saline aquifers. The catalytic characteristics of Ni NPs were investigated by monitoring changes in diameter of CO2 microbubbles. An increase in ionic strength considerably reduces an electrostatic repulsive force in pristine Ni NPs, thereby decreasing their catalytic potential. This study shows how cationic dextran (DEX), nonionic poly(vinyl pyrrolidone) (PVP), and anionic carboxy methylcellulose (CMC) polymers, the dispersive behaviors of Ni NPs can be used to overcome the negative impact of salinity on CO2 dissolution. The cationic polymer, DEX was less adsorbed onto NPs surfaces, thereby limiting the Ni NPs’ catalytic activity. This behavior is due to a competition for Ni NPs’ surface sites between the cation and DEX under high salinity. On the other hand, the non/anionic polymers, PVP and CMC could be relatively easily adsorbed onto anchoring sites of Ni NPs by the monovalent cation, Na+. Considerable dispersion of Ni NPs by an optimal concentration of the anionic polymers improved their catalytic capabilities even under unfavorable conditions for CO2 dissolution. This study has implications for enhancing geologic sequestration into deep saline aquifers for the purposes of mitigating atmospheric CO2 levels.
6) Biofuel – Improved Efficiency for Growth & Separation