Making chemicals from algal biomass waste

WASTE algal biomass left over after its oil is extracted for biofuels can be used as a source of carbon to make chemicals for producing pharmaceuticals, additives, and polyesters, according to new research.

Algae is a promising option for biofuels, as it can be easily grown in large tanks, so doesn’t compete with land for growing food, and is highly productive even in nutrient-limited conditions. Algal oil-based biofuels are already being used to make jet fuel. However, it is not only oil that the algae produce. Sho Yamaguchi and his colleagues at Tokyo Institute of Technology, Japan, instead examined whether the carbohydrates in the residue, mainly starch, could be utilised as well. They successfully made alkyl lactate, which can be used to make polyesters, and alkyl levulinate, a precursor for many pharmaceuticals, plasticisers and other compounds.

Yamaguchi and the team used starch extracted from freeze-dried samples of the alga Cyanidioschyzon merolae in their experiments. They tested a number of different catalysts to determine the best. For each experiment, the researchers placed 50 mg of the starch, 0.02 g of naphthalene, and 5 ml of methanol, along with the catalyst. The reactor was pressurised to 5 atm with argon and heated to 160?C for 24 hours.

Using a homogeneous Sn(OTf)₂ catalyst, the researchers obtained a 48% yield of alkyl levulinate. With SnBr₄, they achieved a 27% yield of alkyl lactate.

“The results of this study show that algae can be utilised not only for oil production, but also as a carbon resource for important chemicals. Therefore, we suggest the utilisation of algae biomass as a new alternative carbon resource to fossil fuels,” said the researchers.

They add that a better understanding of the mechanisms that lead to starch production in algae will improve yields further and advance algal biomass production. They will also look to optimise the catalysts.

Scientific Reports doi.org/b5x9