Assessment of a Dry and a Wet Route for the Production of Biofuels - Literature review Example

Microalgae are converted into energy both bio-chemically and thermo-chemically, which produce biodiesel and ethanol, and gas and oil respectively (Xu et al, 2011).

Recently, microalgae have been used to produce renewable energy through two techniques; the wet route and the dry route. Both routes have diesel production as their main target and, because it is in liquid form, it can be mixed with fossil diesel and applied in the transport industry. In the dry extraction route, Microalgae is cultured in the presence of makeup nutrients, water, carbon dioxide, and sunlight before undergoing the processes of flocculation, centrifugation, mechanical dehydration, thermal drying, and cell disruption, leading up to dry extraction (Xu et al, 2011).

Oil cake and lipids are produced at the dry extraction stage, in which the oil cake undergoes pyrolysis to form pyrolysis oil and biogas, as well as char that is shunted back into the pyrolysis stage (Xu et al, 2011). Lipids, on the other hand, are treated with methanol for trans-esterification to occur, producing glycerol and bio-diesel. In the process, water and carbon dioxide are also recycled from the mechanical dehydration stage. In the wet process, the microalgae are cultured in similar conditions to the dry process, after which they are flocculated, centrifuged, and mechanically dehydrated, leading up to wet extraction.

The products here are lipids and residues, of which the former is hydro-treated to form green diesel. The residues undergo supercritical gasification to produce hydrogen gas that is used in the hydro-treatment phase (Xu et al, 2011). In addition, supercritical gasification also produces water, carbon dioxide, and other gas products, of which the former two by-products are recycled in the microalgae culture. How It Was Applied To Solve A Particular Problem For a long time, there has been a need for less energy-intensive models of biofuel production from microalgae, particularly by reducing energy consumed during dewatering (Xu et al, 2011).

Thus, because the two routes discussed above do not consume significant energy in the dewatering process, they have been used in making the process of renewable energy production from microalgae more efficient. The ability of both routes to produce more efficiently bio-diesel was tested by comparing the energy balance of the wet and dry routes. It was found that both the dry and wet routes achieved large positive energy balances, while their energy output per unit area was higher than that achieved by sugar crops and vegetable oil crops.