Processing spent yerba mate by pyrolysis to methoxyphenol-rich oil.

Drinking hot, concentrated infusions of yerba mate (Ilex paraguariensis) from gourds generates, only in Argentina, >220 Mt organic waste available annually for biorefining. Herein, we show that spent yerba mate (SYM) -the organic waste generated when the infusion becomes flavorless- has (bio)chemical features that make it particularly suitable for processing by pyrolysis, and we describe a custom-made device to run it. Extracting SYM with ethanol and acetic acid removed nearly all non-structural phenolics, caffein, and Ca, K, Mg and Mn minerals, without significant structural changes to the remaining fibrous biopolymers. The pre-treated SYM exhibited attractive traits: 83 % volatile matter, 18.7 kJ/kg HHV, 1.72 H/C, and 0.20 H/C. Pyrolysis at 550 °C yields 26 wt% bio-char and 29 wt% bio-oil, while pyrolysis with CuO at 350 °C lowers the bio-oil yield to 15 wt% but with enriched methoxyphenol content. Bio-based 2-MeTHF was used for the extraction of the latter pyrolysis oil yielding ∼6 wt% methoxyphenols (equivalent to ∼2 wt% from bio-oil and ∼0.2 wt% from biomass). These results show that processing SYM in a pyrolysis-based biorefinery model is not only feasible but also contributes positively to the development of the aromatic platform from renewable sources.