Solid Phase Extraction of Bio-Oil Model Compounds and Lignin-Derived Bio-Oil Using Amine-Functionalized Mesoporous Silicas

Lignin-derived pyrolysis bio-oils are a rich source of alkylphenols that could find application if a feasible separation method could be developed. In this work, bio-oil model compounds and lignin-derived bio-oil were used to evaluate commercially available silica gel and normal phase amine-functionalized silica, as well as three different amine-functionalized mesoporous silicas, as adsorbents. The adsorption capacities of all materials at maximum retention of 12 bio-oil model compounds were compared. Catechol showed maximum retention (193.3 mg/g, 1.75 mmol/g) in the presence of the best mesoporous absorbent, while bulkier guaiacol and benzophenone did not show any retention. The best adsorbent was also applied for the separation of three groups of phenolic compounds present in the lignin-derived bio-oil, as determined by GC/MS analysis, namely, (i) methoxyphenols and alkylmethoxyphenols, (ii) phenol, alkylphenols, and hydroxyacids, and (iii) catechol. Adsorption studies showed that grafted triamine-functionalized mesoporous silica exhibited the best performance in separation of phenol-based compounds from bio-oils.