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
In
the present study, we investigated the effects of concentrating
a cell suspension of a hydrocarbon-rich microalga, Botryococcus
braunii, by membrane filtration on hydrocarbon recovery efficiency. B. braunii suspensions before and after filtration were
mechanically pretreated with a high-pressure homogenizer or a JET
PASTER high-speed mixer. Concentrating the suspension increased the
apparent viscosity of the sample and altered the particle size and
shape distributions. The increase of viscosity was derived from the
existence probability that was caused by shear forces in the pump
that introduced the suspension into the membrane filter and/or between
the membrane wall and algae. Homogenizer treatment decreased the sample
viscosity from 20 to 5 mPa·s due to the collapse of the bridge
between the algae and polysaccharides. The treatment also decreased
the hydrocarbon recovery efficiency from 60% to 15% because of the
release of intracellular substances that prevented hydrocarbon extraction.
In contrast, JET PASTER treatment increased the hydrocarbon recovery
efficiency by removing polysaccharides surrounding the colonies and
disrupting colonies, without disrupting the cells. Adding oleic acid
as a model intracellular substance to the concentrated sample before
extraction decreased the amount of extracted hydrocarbon. These results
demonstrate that concentrating the sample by filtration combined with
JET PASTER treatment can improve the hydrocarbon recovery efficiency
of B. braunii. In addition, an energy analysis was
performed in the present study. The energy consumption of the JET
PASTER treatment combined with filtration was 7.6 times as high as
the energy produced.
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