Trip to Aban Offshore's lab
I took a trip to the lab facility of Aban Offshore Ltd. where they are currently doing work on commercial production of biofuels from algae. This is pretty much what I saw and learnt! :)
Algae is used as the source of fuel because it is rich in lipids,
carbohydrates and proteins. There are two types of algal strains used -
phycocyanin(blue), which is an anti cancer drug, and
haematococcus(yellow), which is valued for it's pigments. Algal strains
are first grown in nutrient media. The medium is essentially water and
contains little or no added nutrients. Algae is present in this medium
in the concentration of 1g/L. Harvesting this algae from the medium is
done by various methods depending on the scale. In lab scale, algal
solution is placed on a Whatmann filter paper and a vacuum pump is used
to remove the water. Larger scale harvesting is done by means of
filtering through a thin filtering sheet which is 5 microns thick. The
resultant sludge contains 80% water and 20% algal cells. This sludge is
used for the production of bio crude which is an alternative source of
fuel, supplementing crude oil found naturally. Algae is basically
unicellular, hence, difficult to extract. It passes freely through
filter papers. The method used to aggregate the cells is called
electroclarification. Algal cells have a negative charge on them. This
property of the algal cells is used in this process. The mixture
containing the cells along with the medium is passed through the
electroclarifier. It basically guns electrons into the solution and
makes the algae settle by neutralizing the charge on them. Algal
filaments are formed which settle at the bottom in the form of a sludge.
The sludge is passed through a machine called HTL (Hydro Thermal
Liquefier). This machine mimics the processes that animal and plant
remains undergo to get converted to crude oil, in lab scale. It is a
small reactor which supplies 350°C temperature and 200 bar pressure to
the reacting mixture to obtain bio crude. The lipids, proteins and
carbohydrates present in the algae are depolymerized into fatty acids,
amino acids and simple sugars. Further depolymerization also occurs and
the components are broken down into oxygen, carbon, hydrogen, nitrogen
and sulphur molecules. These are then repolymerized into hydrocarbons
which form biofuels. The lipid and carbohydrate rings are repolymerized
into hydrocarbon rings. Bio crude is obtained as a floating mass on the
surface of the water-protein mixture. Three distinct layers are formed.
The top layer is the bio crude which can be removed using a separating
funnel. The second layer is the water+nutrient medium. This may contain
some traces of the crude. This is extracted using an organic solvent
such as ethene or hexane. The rest of the water+nutrient medium is used
as medium again as it contains many nutrients. The third layer is the
sedimented algal mass. This may be dried and used as dry fuel, can be
used as inoculum, dried and used as protein supplements, etc. Problems
arise with the commercialization of bio crude. Firstly, the crude
obtained solidifies at room temperature. The nitrogen impurities present
in the crude increase the melting point of the oil. Methods have been
devised to eliminate the nitrogen content from the crude by digesting or
separating the protein content from the algal sludge. The proteins may
be used for other value added income purposes.
DISCLAIMER: Incomplete or half-accurate information is regretted
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