Levoglucosenone, furfural and levomannosan from mannan-rich feedstock: A proof-of-principle with ivory nut

Abstract

This work pioneers the thermocatalytic conversion of tagua seeds (or ivory nut) from the palm Phytelephas aequatorialis into key chemical building blocks, being levoglucosenone, furfural and levomannosan. Annually, ca. 100,000 metric ton of those seeds are produced in Ecuador. Mannan (a mannose-polymer similar to cellulose) is the main constituent in tagua. Thermocatalytic conversions were first explored on analytical scale to see if – and to which extent – e.g., levoglucosenone, was obtained from tagua, using catalysts with proven activity for cellulose conversion, being H3PO4 or ZnCl2. Non-catalytic fast pyrolysis led to levomannosan as main product (33.89 wt% ± 0.24 wt%), much like levoglucosan is the main product from cellulose pyrolysis. Catalytic fast pyrolysis using H3PO4 or ZnCl2 resulted in value-added levoglucosenone (max 6.64 wt% ± 0.27 wt%) and furfural (max 13.17 wt% ± 0.66 wt%) at the expense of levomannosan (between 12 wt.%–14 wt%). Validation experiments with a continuous fast pyrolysis auger reactor were successful and led to pyrolysis liquids with e.g., 3.69 wt% levoglucosenone, using H3PO4-infused ivory nut. Although further optimization should follow this work, the results showcased a fundamental “mannan to levoglucosenone and furfural” conversion and therefore the potential of mannan-rich feedstock for biorefining. Moreover, these results can be translated to other mannan-rich agricultural residues, like açaí seeds, which are a major residue in Brazil (1.1 million metric ton annually).