Processing spent yerba mate by pyrolysis to methoxyphenol-rich oil

Abstract

Drinking hot, concentrated infusions of yerba mate (Ilex paraguariensis) from gourds generates, only in Argentina, >220 kt 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/Ceff. 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.