Sang Goo Jeon

Enhancement of CO2 Sorption Uptake on Hydrotalcite by Impregnation with K2CO3

The awareness of symptoms of global warming and its seriousness urges the development of technologies to reduce greenhouse gas emissions. Carbon dioxide (CO(2)) is a representative greenhouse gas, and numerous methods to capture and storage CO(2) have been considered. Recently, the technology to remove high-temperature CO(2) by sorption has received lots of attention. In this study, hydrotalcite, which has been known to have CO(2) sorption capability at high temperature, was impregnated with K(2)CO(3) to enhance CO(2) sorption uptake, and the mechanism of CO(2) sorption enhancement on K(2)CO(3)-promoted hydrotalcite was investigated. Thermogravimetric analysis was used to measure equilibrium CO(2) sorption uptake and to estimate CO(2) sorption kinetics. The analyses based on N(2) gas physisorption, X-ray diffractometry, Fourier transform infrared spectrometry, Raman spectrometry, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of enhanced CO(2) sorption. The equilibrium CO(2) sorption uptake on hydrotalcite could be increased up to 10 times by impregnation with K(2)CO(3), and there was an optimal amount of K(2)CO(3) for a maximum equilibrium CO(2) sorption uptake. In the K(2)CO(3)-promoted hydrotalcite, K(2)CO(3) was incorporated without changing the structure of hydrotalcite and it was thermally stabilized, resulting in the enhanced equilibrium CO(2) sorption uptake and fast CO(2) sorption kinetics.

Magnetophoretic harvesting of oleaginous Chlorella sp. by using biocompatible chitosan/magnetic nanoparticle composites

The consumption of energy and resources such as water in the cultivation and harvesting steps should be minimized to reduce the overall cost of biodiesel production from microalgae. Here we present a biocompatible and rapid magnetophoretic harvesting process of oleaginous microalgae by using chitosan-Fe3O4 nanoparticle composites. Over 99% of microalgae was harvested by using the composites and the external magnetic field without changing the pH of culture medium so that it may be reused for microalgal culture without adverse effect on the cell growth. Depending on the working volume (20-500 mL) and the strength of surface magnetic-field (3400-9200 G), the process of harvesting microalgae took only 2-5 min. The method presented here not only utilizes permanent magnets without additional energy for fast harvesting but also recycles the medium effectively for further cultivation of microalgae, looking ahead to a large scale economic microalgae-based biorefinement.

Effect of barium ferrite particle size on detachment efficiency in magnetophoretic harvesting of oleaginous Chlorella sp.

Microalgal biofuel is garnering many positive and promising reviews as a fuel for the next generation while research effort continues to improve the efficiency of its harvesting for commercial success. In this report, magnetophoretic harvesting of microalgae is conducted through a three-step process, which includes functionalization of magnetic particles by (3-aminopropyl)triethoxysilane (APTES), magnetic separation, and detachment of magnetic particles by increasing pH to higher than the isoelectric point. Detachment process is specifically focused and found that the use of larger magnetic particles is more efficient for detachment of magnetic particles from algae-particle conglomerates. The detaching efficiency improves from 12.5% to 85% when the particle size is increased from 108 nm to 1.17 μm. Smaller magnetic particles provide larger contact area to microalgae and form strong electrostatic binding to negatively-charged microalgae when pH is lower than the isoelectric point.

Rapid estimation of triacylglycerol content of Chlorella sp. by thermogravimetric analysis

A simple and reliable method based on thermogravimetric analysis has been developed for determining triacylglycerol content in Chlorella sp. KR-1. There are two decomposing steps during pyrolysis of the microalgal cells and the second step of weight loss may be attributed to degradation and volatilization of triacylglycerols. The second peak height in the temperature derivatives of weight loss increased with the triacylglycerol content of the microalgal cells and the peak was around 390°C regardless of the triacylglycerol contents. Based on these findings, a linear equation for determining triacylglycerol content was derived. The proposed method gives satisfactory results, showing small variance and a good interpolation capability.

Repeated use of stable magnetic flocculant for efficient harvest of oleaginous Chlorella sp.

In the present study, a simple magnetic-particle recycling strategy was developed for harvest of the oleaginous microalga Chlorella sp. KR-1. The method entails the flocculation of microalgal cells and bare-Fe3O4 magnetic particles (bMP) by electrostatic attraction and the subsequent recovery of the bMP from the harvested flocs by electrostatic repulsion below and above the isoelectric points (IEP), respectively. For 10 recycles, the bMP showed 94-99% and 90-97% harvest and recovery efficiencies, respectively. Furthermore, neither the use of bMP nor pH adjustment showed any adverse effect on the microalgal cell growth or the co-existing bacterial species, as confirmed from the subsequent medium-recycling test and denaturing gradient gel electrophoresis (DGGE) analysis.

Downstream integration of microalgae harvesting and cell disruption by means of cationic surfactant-decorated Fe3O4 nanoparticles

Microalgal biofuel, albeit an exciting potential fossil-fuel-replacement candidate, still requires the development of more advanced downstream processing technology for its price competitiveness. The major challenge in a microalgae-based biorefinery is the efficient separation of microalgae from low-concentration culture broth. The post-harvesting cell-disruption step necessary to render microalgae suitable for lipid extraction, moreover, further raises energy consumption and cost. For the mitigation of biorefinery complexity and costs, we suggest herein a new scheme that integrates the critical downstream processes (harvesting and cell disruption) by means of cationic surfactant-decorated Fe3O4 nanoparticles. The cationic surfactants’ quaternary ammonium heads play an important role in not only flocculating negatively charged microalgae but also weakening thick cell walls. In the present study, the harvesting efficiency and cell-damaging effects of three cationic surfactants — cetrimonium bromide (CTAB), cetylpyridinium chloride (CPC), and cetylpyridinium bromide (CPB) — were evaluated. The CTAB-decorated Fe3O4 nanoparticles, which were found to be the most effective, achieved a 96.6% microalgae harvesting efficiency at a dosage of 0.46 g particle per g cell. Next, for the purposes of magnetic nanoparticle recycling and high-purity microalgal biomass obtainment, microalgae detachment from microalgae-Fe3O4 flocs was performed by addition of an anionic surfactant, sodium dodecyl sulfate (SDS). The detached CTAB-decorated Fe3O4 nanoparticles showed a steady reuse efficiency of about 80%. Furthermore, microalgae harvesting by CTAB-decorated Fe3O4 nanoparticles could contribute to a great improvement in the total extracted lipid content and greener wet extraction without the additional energy-intensive cell-disruption step, thus demonstrating the cell-disruption ability of CTAB-decorated Fe3O4 nanoparticles.

High-Temperature CO2 Sorption on Hydrotalcite Having a High Mg/Al Molar Ratio.

Hydrotalcites having a Mg/Al molar ratio between 3 and 30 have been synthesized as promising high-temperature CO2 sorbents. The existence of NaNO3 in the hydrotalcite structure, which originates from excess magnesium nitrate in the precursor, markedly increases CO2 sorption uptake by hydrotalcite up to the record high value of 9.27 mol kg(-1) at 240 °C and 1 atm CO2.

High-temperature CO2 sorption on Na2CO3-impregnated layered double hydroxides

Layered double hydroxide (LDH), one of representative high-temperature CO2 sorbents, has many advantages, including stable CO2 sorption, fast sorption kinetics, and low regeneration temperature. However, CO2 sorption uptake on LDH is not high enough for practical use; thus it is usually enhanced by impregnation with alkali metals such as K2CO3. In this study, LDH was impregnated with Na2CO3, and analyses based on scanning electron microscopy, N2 gas physisorption, in situ X-ray diffraction, and Fourier transform infrared spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of CO2 sorption. Although the surface area of LDH decreased after Na2CO3 impregnation, CO2 sorption uptake was greatly enhanced by the additional basicity of Na2CO3. The crystal structure of Na2CO3 in the Na2CO3-impregnated LDH changed from monoclinic to hexagonal with increasing temperature, and the sorbed-CO2 was stored in the form of carbonate. Thermogravimetric analysis was used to measure CO2 sorption uptake at 200–600 °C. The sample of Na2CO3: LDH=0.35: 1 weight ratio had the largest CO2 sorption uptake among the tested sorbents, and the CO2 sorption uptake tended to increase even after 400 °C.

Magnetic-Nanoflocculant-Assisted Water-Nonpolar Solvent Interface Sieve for Microalgae Harvesting.

Exploitation of magnetic flocculants is regarded as a very promising energy-saving approach to microalgae harvesting. However, its practical applicability remains limited, mainly because of the problem of the postharvest separation of magnetic flocculants from microalgal flocs, which is crucial both for magnetic-flocculant recycling and high-purity microalgal biomasses, but which is also a very challenging and energy-consuming step. In the present study, we designed magnetic nanoflocculants dually functionalizable by two different organosilane compounds, (3-aminopropyl)triethoxysilane (APTES) and octyltriethoxysilane (OTES), which flocculate negatively charged microalgae and are readily detachable at the water-nonpolar organic solvent (NOS) interface only by application of an external magnetic field. APTES functionalization imparts a positive zeta potential charge (29.6 mV) to magnetic nanoflocculants, thereby enabling microalgae flocculation with 98.5% harvesting efficiency (with a dosage of 1.6 g of dMNF/g of cells). OTES functionalization imparts lipophilicity to magnetic nanoflocculants to make them compatible with NOS, thus effecting efficient separation of magnetic flocculants passing through the water-NOS interface sieve from hydrophilic microalgae. Our new energy-saving approach to microalgae harvesting concentrates microalgal cultures (∼1.5 g/L) up to 60 g/L, which can be directly connected to the following process of NOS-assisted wet lipid extraction or biodiesel production, and therefore provides, by simplifying multiple downstream processes, a great potential cost reduction in microalgae-based biorefinement.

Multifunctional Nanoparticle Applications to Microalgal Biorefinery

Microalgal feedstocks are leading candidates for application to large-scale production of sustainable biochemicals and biofuels, due to the inherent potentials of microalgae including high biomass and lipid productivities, carbon neutrality, a wide range of end products, and cultivation in nonarable lands. However, the overall process, starting from microalgae cultivation and ending in conversion to biofuels, entails complicated processes and, moreover, faces technological and economic challenges for commercialization. Recently, the application of multifunctional nanoparticles has been suggested as a potential tool to open commercialization of microalgae-based biofuels. In this context, this chapter will discuss the extensive research that has been conducted to improve process efficiency in microalgal biorefinery. Attention will be focused mainly on nanoparticle-aided microalgae harvesting, extraction, and conversion. With respect to microalgae harvesting, a diverse range of functionalized magnetic nanoparticles are utilized to enhance harvesting efficiency in a short time. Further, nanoparticles with multiple functions or recyclability are developed to reduce process costs. Aminoclay-conjugated nanoparticles are applied to increase lipid extraction yields through destabilization of cell walls or generation of hydroxyl radicals for cell disruption. Also, the various nanocatalysts for conversion yield enhancement and biodiesel upgrading are covered. It is hoped that this chapter of the current state of nanoparticle-based technology will prove a useful guide to future improvements in microalgal biorefinery.