Biodiesel Production from Algae

The process under analysis comprises three major sections: (1) Algae Cultivation; (2) Lipids Extraction and (3) Transesterification.

* Algae Cultivation. Initially, the microalgae are propagated in a scale-up system comprised of closed photobioreactors (PBR), covered ponds, and lined open ponds, until proper inoculum concentration is achieved. The microalgae cells are then inoculated in open raceway ponds, where algal biomass is grown until approximately proper density is achieved. After dewatering steps, the wet biomass is transferred to Lipids Extraction.

* Lipid Extraction. At this point, the wet biomass is submitted to a cell disruption pretreatment, in order to bring desired biomolecules outside the cell to facilitate lipids extraction itself. Such treatment consists in a high-pressure homogenization. The biomass is then directed to an extraction unit, in which hexane is used as organic solvent for further cell walls degradation and oil extraction. In this extraction unit, the cells are brought in contact (counter current) with a hexane stream, so that lipids in the feed migrate into the hexane forming an oil-hexane solution. The oil-hexane solution is then fed to a distillation column which yields a highly pure oil.

* Transesterification. The oil recovered and fresh methanol are fed to a two-stage mixer/settler unit, where they react in the presence of alkaline catalysts forming Biodiesel (fatty acid methyl esters) and glycerin. The methyl esters produced are separated from the glycerin, dissolved in methanol and water yielding high purity Biodiesel. Crude glycerin is also obtained as by-product.