algal biofuel
TRANSCRIPT
CONT….
Energy crisis
Based on the current consumption of about 11.6 million
tons of crude oil per day, it is expected that the entire
resources can only suffice for a rather short time period.
Global warming and global climate changes
The use of oil can cause the risks of the rise of greenhouse
effect, which can result in all kinds of disasters to our
planet Earth and its inhabitants.
It is a biofuel consisting of monoalkyl esters that are derived from organic oils , plant or animal through the process of transesterification.
BIODIESEL PRODUCTION
FROM MICROALGAL OIL
A. The triglycerides methanol and catalyst are placed in a controlled reaction chamber to undergo transesterification.
B. The initial product is laced in a separator to remove the glycerin by product.
C. The excess methane ,oils removed from the methyl ester through evaporation.
Open Pond System Pond consist of closed loop
recirculation channel in which mixing and circulation are provided by paddle wheel.
Depth=0.2—0.5 Limitation= Loss of water due to
evaporation Unwanted algal &
microorganism growth.
.
Closed Photo bioreactor System(PBR)
Provide a controlled environment
Tubular shape & Flat shape
Biological &Physiological control
Reducing contamination level
Limitation=
High operating cost
ALGAE HARVESTING
The term algae harvesting refers to concentration of diluted algae suspension
until a thick algae paste is obtained.
Harvesting method is based upon size and properties of algae strain.
Harvesting of microalgae from algae cultivation pond or photobioreactors
employ several techniques:
FLOTATION
CENTRIFUGATION
FILTRATION
These processes are aided by cell flocculation. It causes the cells to become
aggregated into larger clumps which are more easily filtered and/or settle
more rapidly. It is done by addition of chemical flocculants or through
autoflocculation.
Filtration
Suitable for larger algal species with cell diameters >70 µm. For smaller
algal species membrane ultrafiltration can be employed.
Limitation is that biomass settles on the filter and eventually block filter
pores, which makes filtration less efficient, thus increasing energy
consumption.
In addition membrane replacement and pump operation increase operating
expenses therefore better suitable to handle smaller volumes.
Centrifugation
Method of separating algae from the medium by using a centrifuge to cause
the algae to settle to the bottom of a flask or tank.
Quick and effective method.
Limitation is very high energy consumption .
Flotation
It is performed using compressed air to inject air microbubbles at the
bottom of the culture medium, algae adhere to the microbubbles and
accumulate on the medium surface.
ALGAE OIL EXTRACTIONExtraction can be broadly classified into two categories:-
MECHANICAL METHOD
Expeller press
CHEMICAL METHOD
Hexane Solvent Method
Soxhlet extraction
Supercritical fluid Extraction
EXPELLER PRESS –
Algae is dried .
Oil content can be "pressed" out with an oil press
HEXANE SOLVENT METHOD –
Uses chemicals (such as hexane).
Can be harmful and explosive.
Cold press & hexane solvent = extract 95% of oil
SOXHLET EXTRACTION -
In this method, oils from the algae are extracted through repeated washing,
or percolation, with an organic solvent such as hexane , under reflux in a
special glassware.
The value of this technique is that the solvent is reused for each cycle.
SUPERCRITICAL FLUID EXTRACTION –
CO2 is liquefied under pressure and heated to the point that it has the
properties of both a liquid and gas.
This liquefied fluid then acts as the solvent in extracting the oil.
Can Extract almost 100% of the oils.
Expensive equipment.
Sodium ethanolate is used as catalyst, ethanol is reacted with the algal oil (
the triglyceride) to produce bio-diesel & glycerol. The end products of this
reaction are hence biodiesel, sodium ethanolate and glycerol.
End-mixture is separated as follows: Ether and salt water are added to the
mixture and mixed well. After sometime, the entire mixture get separated
into two layers, with the bottom layer containing a mixture of ether
and biodiesel. This layer is separated.
Biodiesel is in turn separated from ether by a vaporizer under a high
vacuum. As the ether vaporizes first, the biodiesel will remain. The
biodiesel from algae is now ready for use.
Mechanical method
Expeller Press
Chemical method
Hexane Solvent Method
Soxhlet Extraction
Supercritical Fluid Extraction
CONCLUSION
Algae are promising source for biodiesel production, as they can
perform photosynthesis, grow in heterotrophic conditions, grow
faster, do not require a special growth medium, and contain 50 % or
more of their mass as oil.
Carbon dioxide necessary for photosynthesis can be obtained from
stationary sources of environment air pollution such as fuel
combustion units, which would help to reduce emissions of
greenhouse gases.
Algal oil is similar to vegetable oil, the existing traditional biodiesel
production technologies can be easily adjusted to use this new raw
material.