Sun-A Choi

Acid-catalyzed hot-water extraction of lipids from Chlorella vulgaris.

Acid-catalyzed hot-water treatment for efficient extraction of lipids from a wet microalga, Chlorella vulgaris, was investigated. For an initial fatty acids content of 381.6mg/g cell, the extracted-lipid yield with no heating and no catalyst was 83.2mg/g cell. Under a 1% H2SO4 concentration heated at 120°C for 60min, however, the lipid-extraction yield was 337.4mg/g cell. The fatty acids content, meanwhile, was 935mg fatty acid/g lipid. According to the severity index formula, 337.5mg/g cell of yield under the 1% H2SO4 concentration heated at 150°C for 8min, and 334.2mg/g cell of yield under the 0.5% H2SO4 concentration heated at 150°C for 16min, were obtained. The lipids extracted by acid-catalyzed hot-water treatment were converted to biodiesel. The biodiesels fatty acid methyl ester (FAME) content after esterification of the microalgal lipids was increased to 79.2% by the addition of excess methanol and sulfuric acid.

Effect of nitric acid on pretreatment and fermentation for enhancing ethanol production of rice straw

In this study, nitric acid (HNO₃) was evaluated as an acid catalyst for rice straw pretreatment, and, after neutralization, as a sole nitrogen source for subsequent fermentation. Response surface methodology was used to obtain optimal pretreatment condition with respect to HNO₃ concentration (0.2-1.0%), temperature (120-160 °C) and reaction time (1-20 min). In a condition of 0.65% HNO₃, 158.8 °C and 5.86 min, a maximum xylose yield of 86.5% and an enzymatic digestibility of 83.0% were achieved. The sugar solution that contained nitrate derived from the acid catalyst supported the enhancement of ethanol yield by Pichia stipitis from 10.92 g/L to 14.50 g/L. The results clearly reveal that nitric acid could be used not only as a pretreatment catalyst, but also as a nitrogen source in the fermentation process for bioethanol production. It is anticipated that the HNO₃-based pretreatment can reduce financial burden on the cellulosic bioethanol industry by simplifying after-pretreatment-steps as well as providing a nitrogen source.

An integrated process for microalgae harvesting and cell disruption by the use of ferric ions

In this study, a simultaneous process of harvesting biomass and extracting crude bio-oil was attempted from wet microalgae biomass using FeCl3 and Fe2(SO4)3 as both coagulant and cell-disrupting agent. A culture solution of Chlorella sp. KR-1 was firstly concentrated to 20 g/L and then proceeded for cell disruption with the addition of H2O2. Optimal dosage were 560 and 1060 mg/L for FeCl3 and Fe2(SO4)3, showing harvesting efficiencies of more than 99%. Optimal extraction conditions were identified via the response surface method (RSM), and the extraction yield was almost the same at 120 °C for both iron salts but FAME compositions after transesterification was found to be quite different. Given iron salts were a reference coagulant in water treatment in general and microalgae harvesting in particular, the present approach of using it for harvesting and oil-extraction in a simultaneous manner can serve as a practical route for the microalgae-derived biodiesel production.

Hydrothermal nitric acid treatment for effectual lipid extraction from wet microalgae biomass.

Hydrothermal acid (combined with autoclaving and nitric acid) pretreatment was applied to Nannochloropsis salina as a cost-effective yet efficient way of lipid extraction from wet biomass. The optimal conditions for this pretreatment were determined using a statistical approach, and the roles of nitric acid were also determined. The maximum lipid yield (predicted: 24.6%; experimental: 24.4%) was obtained using 0.57% nitric acid at 120°C for 30min through response surface methodology. A relatively lower lipid yield (18.4%) was obtained using 2% nitric acid; however, chlorophyll and unsaturated fatty acids, both of which adversely affect the refinery and oxidative stability of biodiesel, were found to be not co-extracted. Considering its comparable extractability even from wet biomass and ability to reduce chlorophyll and unsaturated fatty acids, the hydrothermal nitric acid pretreatment can serve as one direct and promising route of extracting microalgae oil.

Changes in fatty acid composition of Chlorella vulgaris by hypochlorous acid

Hypochlorous acid treatment of a microalga, Chlorella vulgaris, was investigated to improve the quality of microalgal lipid and to obtain high biodiesel-conversion yield. Because chlorophyll deactivates the catalyst for biodiesel conversion, its removal in the lipid-extraction step enhances biodiesel productivity. When microalgae contacted the hypochlorous acid, chlorophyll was removed, and resultant changes in fatty acid composition of microalgal lipid were observed. The lipid-extraction yield after activated clay treatment was 32.7 mg lipid/g cell; after NaClO treatment at 0.8% available chlorine concentration, it was 95.2 mg lipid/g cell; and after NaCl electrolysis treatment at the 1 g/L cell concentration, it was 102.4 mg lipid/g cell. While the contents of all of the unsaturated fatty acids except oleic acid, in the microalgal lipid, decreased as the result of NaClO treatment, the contents of all of the unsaturated fatty acids including oleic acid decreased as the result of NaCl electrolysis treatment.

Effects of anionic surfactant on extraction of free fatty acid from Chlorella vulgaris.

Microalgal lipid with a high free fatty acid (FFA) content was directly extracted from Chlorella vulgaris, using SDBS, in an acid-catalyzed hot-water extraction process. The total fatty acid content of C. vulgaris was 296.0 mg/g cell. Under the 1.0% sulfuric acid, 0.4% SDBS conditions, the FFA content of the lipid increased to 96.7%, and the lipid-extraction yield was 248.4 mg/g cell. Under the 2.0% sulfuric acid, 0.2% SDBS conditions, the FFA content of the lipid was 96.1%, and the lipid-extraction yield was 266.0mg/g cell. Whereas the FAME content of the microalgal lipid extracted by hexane-methanol was 76.4% at the 10.0% sulfuric acid concentration, the FAME content of the high-FFA microalgal lipid was increased to 70.1% at a sulfuric acid concentration of only 0.1%. By combined sulfuric acid/SDBS treatment, high-FFA microalgal lipid was extracted in large yields; moreover, the amount of catalyst was remarkably reduced in the esterification of FFA.

Feasibility tests of –SO3H/–SO3−-functionalized magnesium phyllosilicate [–SO3H/–SO3− MP] for environmental and bioenergy applications

We have prepared a simple water-solubilized, transparent, and anionic clay. –SH-functionalized magnesium phyllosilicate [–SH MP] was easily oxidized into –SO3H/–SO3−-functionalized magnesium phyllosilicate [–SO3H/–SO3− MP] by treatment of 5.0% H2O2 at 60 °C for 24 hours, showing a pH of ∼2.0. These water-solubilized and anionic nanoparticles (NPs) were tested with organo-building blocks of –SO3H/–SO3− MP for removal of cationic pollutant dye (methylene blue) and heavy metals (Cd2+ and Pb2+). Furthermore, interactions of ubiquitous humic acid (HA) with –SO3H/–SO3− MP were removed due to an ion exchange mechanism. For bioenergy applications, glucose conversion from cellulose was tested, focusing on Bronsted acid-rich sites in –SO3H/–SO3− MP.