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