Catalytic transformation of the marine polysaccharide ulvan into rare sugars, tartaric and succinic acids

The green macroalga Ulva rigida represents a promising feedstock for biorefinary due to its fast growth and cosmopolitan distribution. The main component of the cell walls of U. rigida is a sulfated glucuronorhamnan polysaccharide known as ulvan. Herein it was found that due to the high (hydrogen)sulfate group content of ulvan, hydrothermal autohydrolysis at 130 degrees C renders a high percentage of rhamnose (78-79 % recovery from the initial content in the raw material), a rare sugar of high added value. In addition, acid catalysis by a triflate-based graphene oxide under oxygen-free conditions at 180 degrees C affords moderate amounts of tartaric acid (24-26 %). The same triflate-based graphene oxide catalyst under oxygen pressure yields remarkably high percentages of succinic acid (65 %). The catalyst preserves its activity for at least five consecutive reuses.

Automated summary

Ulva rigida, a green macroalga, is considered a promising feedstock for biorefinary due to its fast growth and widespread distribution. The cell walls of U. rigida contain a sulfated glucuronorhamnan polysaccharide called ulvan, which, due to its high sulfate content, can be efficiently recovered as rhamnose through hydrothermal autohydrolysis at 130 degrees C. Under different catalytic conditions, including triflate-based graphene oxide, significant amounts of tartaric acid and succinic acid can also be obtained. The catalyst shows good reusability, maintaining its activity for at least five consecutive cycles.