Analysis of the effect of temperature and reaction time on yields, compositions and oil quality in catalytic and non-catalytic lignin solvolysis in a formic acid/water media using experimental design

•The Pd, Rh and Ru catalysts give similar oil yields and oil qualities.•The alumina (AL) catalyzes de-polymerization and re-polymerization reactions.•Ru stabilizes the lignin monomers through HDO reactions.•The Mw of the oils depends on the T, reaction time and active acidity of the Al.•The H/C and O/C ratios are mainly dependent on the T and reaction time.

The catalytic solvolysis of Norway spruce (Picea abies L.) lignin in a formic acid/water media was explored at different temperatures and reaction times (283-397 °C and 21-700 min, respectively). Non-catalyzed experiments were compared with the effect of three different type of bifunctional catalysts (Pd/Al2O3, Rh/Al2O3 and Ru/Al2O3) and a solid Lewis acid (γ-Al2O3). We demonstrated that surface response methodology (RSM) and principal component analysis (PCA) were an adequate tool to: (i) evaluate the effect of the catalysts, temperature and reaction time in the oil yield, oil quality (H/C and O/C ratios, and Mw) and composition of the oil, (ii) establish the differences and/or similarities between the three bifunctional catalyst and (iii) to determine the role of the noble metal and the alumina support in the reaction system. In addition, the most active catalysts, Ru/Al2O3, and the optimum reaction conditions were determined (i.e. 340 °C and 6 h).

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