Carbon Separation and Utilization | Microfluidics and Energy Laboratory (MELab)

We are studying various interfacial gas (mainly CO₂) separation, carbon utilization, and carbon storage research under various temperature and pressure conditions. By leveraging microfluidic techniques, we have attempted to provide cost-effective, fast, and environmentally benign approaches for carbon dissolution (or capture) in aqueous solutions when compared with conventional largescale experiments. We hope that our findings help protect our environment and ecosystems with better strategies. Examples of our research topics include:

1) CO₂ diffusivity measurements into water 2) Visualization of three-phase flow (CO₂-water-solid precipitation) in porous media 3) CO₂ Capture by ethanolamine-nanoparticles 4) CO₂ Hydration with polymer-nanoparticles 5) Biofuel – Improved Efficiency for Growth & Separation

1) CO₂ Diffusivity Measurements

Measurements of accurate CO₂ diffusivity to water are important to predict geological CO₂ storage capacity as well as to secure safe/permanent storage strategies into 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

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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 examples of experimental results including the chip fabrication procedure.

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3) CO₂ Capture by Ethanolamine-Nanoparticles

In industrial post-carbon capture processes, monoethanolamine (MEA) has been mainly used as an absorption solvent. However, this approach generates significant amounts of toxic wastewater containing a heavy chemical difficult to treat and also raises concerns about acute corrosion of metal structures in the facility. To reduce the use of MEA in carbon capture, this work evaluates the catalytic performance of nickel nanoparticles (NiNPs) for CO₂ capture as a possible additive in an MEA solvent. We test the CO₂ absorption rate in MEA catalyzed by NiNPs in both limited and high mixing conditions to model real capturing processes in the packed column of industrial absorption reactors. For this purpose, a microreactor and a long serpentine microchannel are employed. The catalytic absorption performance of NiNPs for CO₂ in aqueous MEA is evaluated using CO₂ microbubbles by monitoring changes in size upon their time-dependent absorption. We find that the average CO₂ absorption rate with NiNPs is accelerated by 34% in the limited mixing condition in the microreactor. This increase is mainly due to NPs’ catalytic CO₂ absorption driven by a Brownian motion. On the other hand, in the high mixing condition in the long serpentine microchannel, the catalytic activity of NiNPs improves the average CO₂ absorption rate further to 54%. This improvement makes it possible to shorten the timescale for reaching CO₂ absorption equilibrium and therefore to reduce the size of the reactors significantly. The test results demonstrate that NiNPs serve as suitable additives in the MEA-based CO₂ absorption system.

4) 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 the 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 carboxymethylcellulose (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 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.

5) Biofuel – Improved Efficiency for Growth & Separation

For global energy sustainability, cutting-edge biodiesel production technologies have been extensively developed as scavenging methods of nonconventional energy. Despite its importance, the current extremely low-efficiency of microalgae cultivation and harvesting makes this energy resource expensive and non-competitive. The goal of this project is to develop an innovative scalable methodology that enables enhanced microalgae cultivation and harvesting for large-scale biodiesel production. The increased growth rate of microalgae permits better cultivation at higher efficiency over conventional technologies while the higher separation efficiency of solid microalgae from solvents guarantees cost-effective lipid harvesting.

Commercial Microalgae Growth

Buuble Microfluidics to Increase Growth Rate

COMSOL Simulation for Centrifugal Algae Separation