Integrated protein extraction with bio-oil production for microalgal biorefinery

The economic feasibility of biofuel production from microalgae can benefit from the development of integrated processes that extract all valuable components from microalgal biomass. In this work, protein extraction of Chlorella vulgaris was integrated with bio-oil production using the protein-extracted microalgae. To extract the protein, the biomass was hydrolyzed at various pH, temperatures and times and then sonicated. This method recovered nearly 80% of the protein fraction from hydrolysis at pH 12 and 50 degrees C for 90 min. As a result, nitrogen content was 65.4% lower in protein-extracted microalgae and the bio-oil obtained from pyrolysis of the protein-extracted microalgae was of a higher quality than bio-oil from untreated microalgae. The bio-oil of protein-extracted microalgae had lower contents of acids, oxygenated, nitrogenated, and aromatic compounds but higher contents of alkanes and alkenes. While protein extraction improved the quality of the bio-oil, it did not increase the quantity produced. However, techno-economic analysis indicated that bio-oil production with an integrated hydrolysis process could produce profits from the extracted proteins. Therefore, the integration of effective and low-cost protein extraction into the bio-oil production process may contribute greatly to the development of the microalgal biorefinery concept.