Mechanical cell disruption of microalgae for investigating the effects of degree of disruption on hydrocarbon extraction

Abstract

The colonial microalga, Botryococcus braunii, produces and stores hydrocarbons in membranes and in colonies. Although hydrocarbons in B. braunii could easily be extracted for biofuel production, yields are actually poor without energy-intensive pretreatment such as thermal drying. To develop extraction methods without drying, we applied the mechanical cell disruption to wet B. braunii using either a high-pressure homogenizer, a bead mill, or a circulating particle disruptor (Jet-Paster) and examined the relationships between the extent of cell and/or colony disruption and extracted hydrocarbon yields using n-hexane. When the number of particles over 20 μm classified as colonies, decreased after each treatment, the hydrocarbon yields of samples treated (over 20%) were much larger than those without treatments (under 5%). Thus, the colony disruption may increase hydrocarbon yields by enhancing n-hexane penetration to the colony. Although the degree of disruption on the Jet-Paster treatment was the lowest (2.2-9.3%) and that of sample treated by the homogenizer was the highest (27-55%), extracted hydrocarbon yields were improved in both treatments. The facts indicate that disrupting large colonies into small colonies improves hydrocarbon recovery, and the fractionation of cells is not needed for hydrocarbon extraction from B. braunii. Figure 4. Distributions of roundness of before and after cell disruption ((a-1), (b-1), and (c-1)) Untreated samples. (a-2) High-pressure homogenizer (30 MPa). (a-3) High-pressure homogenizer (80 MPa). (b-2) Bead mill (8 m/s). (b-3) Bead mill (14 m/s). (c-2) Jet-Paster (4800 rpm). (c-3) Jet-Paster (7200 rpm). S. TSUTSUMI ET AL.Asia-Pacific Journal of Chemical Engineering 460

Effect of Mechanical Pretreatment on Hydrocarbon Extraction from Concentrated Wet Hydrocarbon-Rich Microalga, Botryococcus braunii

“…A schematic representation of the JET PASTER is shown in Figure . The impulsive force caused by hydrodynamic cavitation and the shear force caused by rotation of the impeller drew the microalgae into the device . The rotational speed of the internal impeller was 4800 rpm, and algal samples were treated for 3 min.…”

“…Organic solvents such as n -hexane are frequently used for lipid extraction. ,,− This requires drying of the microalgal suspension, which consumes 80–90% of the total energy required for the entire conversion process. − As such, the amount of energy needed for biofuel production is greater than that produced . Hydrocarbon or lipid extraction from wet microalgae has been proposed to overcome this problem. − ,− Because common microalgae store lipids inside their cells, disrupting the cell wall prior to the extraction of lipids or other intracellular substances can increase the efficiency of this process. To this end, various methods such as application of mechanical force, ,,,− novel extraction solvents, ,,, and high temperature and water pressure have been investigated. ,− However, because the influence of pretreatment methods on the amount of extractable lipid varies due to several factors such as algal species, ,,, organic solvent used for extraction, ,, sample preparation method, , and moisture content (i.e., dry cell weight), it is difficult to determine the best pretreatment methods for microalgal lipid extraction.…”

“…Hydrocarbon or lipid extraction from wet microalgae has been proposed to overcome this problem. − ,− Because common microalgae store lipids inside their cells, disrupting the cell wall prior to the extraction of lipids or other intracellular substances can increase the efficiency of this process. To this end, various methods such as application of mechanical force, ,,,− novel extraction solvents, ,,, and high temperature and water pressure have been investigated. ,− However, because the influence of pretreatment methods on the amount of extractable lipid varies due to several factors such as algal species, ,,, organic solvent used for extraction, ,, sample preparation method, , and moisture content (i.e., dry cell weight), it is difficult to determine the best pretreatment methods for microalgal lipid extraction. Thus, the accumulation of knowledge regarding several pretreatment methods performed under the several algal conditions is necessary for future process design.…”

Investigation of the Wet Extraction of Hydrocarbons from a Heterotrophic Microalga, <i>Aurantiochytrium</i> sp. 18W-13a, by Cell Disruption Using a High-pressure Homogenizer

“…The hydrocarbon yield of the disrupted sample, extracted for 180 min, was only 72.7% of the hydrocarbons in cells could not be extracted in wet condition. In the previous study, the amount of hydrocarbon from wet algal cells disrupted using a high-pressure homogenizer cannot be extracted completely by using n-hexane 39) . This is because the proteins released due to cell disruption would interact with hydrocarbon droplets.…”

Current and novel approaches to downstream processing of microalgae: A review

“…cell disruption and energy efficiency were independent of cell density up to 25% solids (Yap et al, 2015); although this effect could be related with the ease of cell wall disruption it remains to be investigated. Treatment of the relatively tough B. braunii was also energy efficient (~0.04 kWh kg -1 ) when extraction of the hydrocarbon rich extracellular matrix was considered (Tsutsumi et al, 2017).…”