Jae W. Lee

Concurrent extraction and reaction for the production of biodiesel from wet microalgae.

This work addresses a reliable in situ transesterification process which integrates lipid extraction from wet microalgae, and its conversion to biodiesel, with a yield higher than 90 wt.%. This process enables single-step production of biodiesel from microalgae by mixing wet microalgal cells with solvent, methanol, and acid catalyst; and then heating them in one pot. The effects of reaction parameters such as reaction temperature, wet cell weight, reaction time, and catalyst volume on the conversion yield are investigated. This simultaneous extraction and transesterification of wet microalgae may enable a significant reduction in energy consumption by eliminating the drying process of algal cells and realize the economic production of biodiesel using wet microalgae.

Rheology of Hydrate Forming Emulsions

Results are reported on an experimental study of the rheology of hydrate-forming water-in-oil emulsions. Density-matched concentrated emulsions were quenched by reducing the temperature and an irreversible transition was observed where the viscosity increased dramatically. The hydrate-forming emulsions have characteristic times for abrupt viscosity change dependent only on the temperature, reflecting the importance of the effect of subcooling. Mechanical transition of hydrate-free water-in-oil emulsions may require longer times and depends on the shear rate, occurring more rapidly at higher rates but with significant scatter which is characterized through a probabilistic analysis. This rate dependence together with dependence on subcooling reflects the importance of hydrodynamic forces to bring drops or particles together.

In-situ transesterification of wet spent coffee grounds for sustainable biodiesel production

This work addresses in-situ transesterification of wet spent coffee grounds (SCGs) for the production of biodiesel. For in-situ transesterification process, the methanol, organic solvent and acid catalyst were mixed with wet SCG in one pot and the mixture was heated for simultaneous lipid extraction and transesterification. Maximum yield of fatty acid methyl esters (FAME) was 16.75wt.% based on the weight of dry SCG at 95°C. Comprehensive experiments were conducted with varying temperatures and various amounts of moisture, methanol, co-solvent and acid catalyst. Moderate polar and alcohol-miscible organic solvent is suitable for the high FAME yield. Unsaturated FAMEs are subject to oxidative cleavage by nitric acid and shorter chain (C6 and C10) FAMEs were mainly produced while sulfuric acid yielded long chain unsaturated FAMEs (C16 and C18). Utilization of wet SCGs as a biodiesel feedstock gives economic and environmental benefits by recycling the municipal waste.

Adsorption of surfactants on two different hydrates.

The interaction between surfactants and hydrates provides insight into the role of surfactants in promoting hydrate formation. This work aims at understanding the adsorption behavior of sodium dodecyl sulfate (SDS) on cyclopentane (CP) hydrates and its derivative surfactant on tetrabutylammonium bromide (TBAB) hydrates. Cyclopentane (CP) is a hydrophobic former whereas tetrabutylammonium bromide (TBAB) is a salt that forms semiclathrate hydrates. The adsorption on these two hydrates was studied by zeta potential and pyrene fluorescence measurements. CP hydrates have a negative surface charge in the absence of SDS, and it decreases to a minimum as the SDS concentration increases from 0 to 0.17 mM. Then, it increases with further increased SDS concentration. The adsorption density of DS (-) on CP hydrates reaches a saturated value at 1.73 mM SDS. The micropolarity parameter of the TBAB hydrate/water interface starts to increase rapidly at 0.17 mM SDS and levels off at 1.73 mM SDS. The presence of Br (-) in TBAB hydrate suspensions could compete with TBADS (from association of DS (-) and TBA (+)) and DS (-) for the adsorption on the hydrate surface, but they have a much stronger affinity for the hydrates than does Br (-). From the fluorescence measurements, it was found that the micropolarity of the hydrate/water interface is mainly dependent on the polarity of hydrate formers.

Investigation of Macroscopic Interfacial Dynamics between Clathrate Hydrates and Surfactant Solutions

Macroscopic interfacial interactions between cyclopentane (CP) hydrates and various surfactants droplets are examined in a CP/n-decane oil mixture. Initial contact force and subsequent z-axis dependent retraction force are measured utilizing a high-resolution microbalance integrated with a micrometer-precision stage. The resulting retraction force is utilized to determine the overall adhesion energy of the system. In addition, interfacial tensions and contact angles of the system are examined to further understand the effect of surface-active agents and substrates on the initial contact and retraction forces.

Concurrent production of biodiesel and chemicals through wet in situ transesterification of microalgae.

This work addresses an unprecedented way of co-producing biodiesel (FAEE) and valuable chemicals of ethyl levulinate (EL), ethyl formate (EF) and diethyl ether (DEE) from wet in situ transesterification of microalgae. EL, EF, and DEE were significantly produced up to 23.1%, 10.3%, and 52.1% of the maximum FAEE mass with the FAEE yield higher than 90% at 125 °C. Experiments to elucidate a detailed route of EL and EF synthesis were fulfilled and it was found that its main route to the production of EL and EF was the acid hydrolysis of algal cells and esterification with ethanol. To investigate the effect of reaction variables on the products yields, comprehensive experiments were carried out with varying temperatures, solvent and alcohol volumes, moisture contents and catalyst amounts. Coproduction of DEE, EL, EF and FAEE can contribute to elevating the economic feasibility of microalgae-based biodiesel supply chain.

Direct measurements of contact force between clathrate hydrates and water.

A method for precise and reproducible initial contact force measurements is introduced utilizing an apparatus fabricated with a microbalance and z-axis stage to study the interaction behavior between cyclopentane (CP) hydrate and water in a temperature controlled hydrocarbon environment. CP hydrate probes are prepared using hydrate slurries composed of 5 wt % CP and Wilhelmy rods. The CP hydrate probe is slowly brought into contact with water to determine the initial contact force. The effect of substrate morphology on the initial contact force is reported through employing aluminum substrates prepared using physical vapor deposition (PVD) and milling. Accurate and facile measurements are performed by applying a high-resolution microbalance with 0.1 microN resolution to provide repeatable and consistent results of initial contact force between hydrate and water.

Optimization of variables affecting the direct transesterification of wet biomass from Nannochloropsis oceanica using ionic liquid as a co-solvent

Ionic liquids have many applications, one of which entails their utilization as powerful solvents. In the present study, various experimental conditions of ionic liquid-mediated direct transesterification were investigated in terms of lipid-extracting ionic liquids, catalyst, reaction time, reaction temperature and volume of methanol to achieve effective FAME conversion with wet microalgal feedstock, Nannochloropsis oceanica. With ionic liquid, [Bmim][CF3SO3], highest fatty acid methyl ester (FAME) yield was shown. Among many experimental parameters, the two most critical factors to enhance FAME conversion were characteristic of ionic liquids and volume of methanol. Optimized ionic liquid-mediated direct transesterification of wet N. oceanica, compared with a control experiment using chloroform and methanol, increased the FAME conversion yield by 11-fold.

Highly effective Cs+ removal by turbidity-free potassium copper hexacyanoferrate-immobilized magnetic hydrogels

Potassium copper hexacyanoferrate-immobilized magnetic hydrogel (MHPVA) has been synthesized via a facile freeze/thaw crosslinking method. The citric acid coated Fe3O4 is embedded into the hydrogel matrix to facilitate the dispersion of nano-sized KCuHCF particles for Cs+ removal, followed by the rapid recovery of the composite in a magnetic field. The Cs+ adsorption behavior of the MHPVA is fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The MHPVA exhibits both high Cs+ adsorption capacity (82.8mg/g) and distribution coefficient (Kd) of 1.18×106mL/g (8.3ppm Cs+, V/m=1000mL/g). Sorption of above 90% Cs+ to the MHPVA is achieved in less than 3h of contact time. Moreover, the MHPVA reveals stable and high Cs+ removal efficiency across a wide pH range from 4 to 10. In terms of Cs+ selectivity, the MHPVA shows above 96% removal efficiency in the presence of 0.01M competing cations such as Mg2+, Ca2+, Na+, and K+ with 1ppm of Cs+. From a practical perspective, the MHPVA still exhibits stable and promising selective properties even in groundwater and seawater conditions and after 5days of contact time the used adsorbent is rapidly recovered leaving a turbidity-free aqueous environment.

Organically modified clay with potassium copper hexacyanoferrate for enhanced Cs+ adsorption capacity and selective recovery by flotation

The selective capture of mobile radioactive nuclides, such as 137Cs+, is crucial to the clean-up and remediation of contaminated environments. While remediation remains a challenging task, the current study considers novel organo-clay composites containing potassium copper hexacyanoferrate (KCuHCF) as a viable option for large-scale clean-up. A three-step synthesis has been demonstrated whereby pristine montmorillonite clay was readily modified to incorporate KCuHCF nanoparticles for enhanced and selective Cs+ removal from aqueous environments. Alkyldiamine (DT) was used as an organic modifier to intercalate the clay and provided chelating sites to anchor copper onto the clay matrix, from which KCuHCF nanoparticles were subsequently grown in situ via the coordination of hexacyanoferrate precursors with the immobilized copper ions. The organo-clay–HCF composite particles exhibited a superior Cs+ adsorption capacity (qm = 206 mg g−1), twice that of the pristine clay. The enhanced performance also extended to high Cs+ selectivity in seawater, with the organo-clay–HCF composites demonstrating Cs+ selectivity values in excess of 105 mL g−1, two orders of magnitude greater than the pristine clay. Organo modification of the clay particles reduced the particle wettability, thus facilitating the separation of Cs-loaded composite particles from aqueous environments by collector-less flotation. Batch flotation experiments showed recovery efficiencies of the Cs-loaded composite particles of up to 90%, which was in great contrast to the low recovery of less than 15% for the Cs-loaded pristine montmorillonite. The current study provides a new concept for the treatment of contaminated aqueous environments.