In contrast to first generation biofuels, where edible plants were suggested to be grown to obtain oil, microalgae raise as a very promising source alternative to fossil fuels. For the first time, they have been used to make bio-bitumen. Some French public institutes (Centre National de la Recherche Scientifique, Université de Nantes, Ecole des Mines de Nantes) in partnership with the company AlgoSource Technologies, developed this bio-bitumen, whose characteristics are very close to the “real” bitumen used for roads. Their work is published in the journal ACS Sustainable Chemistry & Engineering.
Microalgae have long been known for their applications as colorants in cosmetics or as a food supplement. Their refining to produce, for example, biofuels, is an idea that has emerged in recent years. Today, the microalgae are part of promising alternatives to oil. With the development of efficient and effective processes, many products of the refining industry would become accessible.
As part of Algoroute program, Nantes & Orléans laboratories’ researchers produced bio-bitumen using microalgae residues, for instance, from the extraction of soluble algae proteins from the cosmetics industry. They used a method of hydrothermal liquefaction, where the microalgae waste is transform into a hydrophobic black viscous phase (organic-bitumen) with a similar appearance to oil bitumen. This process is carried out with a current conversion efficiency of 55%.
While the chemical composition of bio-bitumen is completely different from that of bitumen from oil, they still have similarities: the black color and rheological properties. Liquid above 100°C, the bio-bitumen enables to coat the mineral aggregate; viscoelastic -20°C to 60°C, ensures the cohesion of the granular structure, support loads and avoid mechanical stresses.
This innovation brings a new potential option for the road industry, now entirely dependent on oil. Until now, the bio-bitumen was mixed with agricultural oils (with the disadvantage of competing with human nutrition) or with paper industry’s wastes to improve their viscoelastic properties. Using microalgae, whose culture does not require the mobilization of arable land, is therefore an attractive solution.