Microwave-Assisted Catalytic Conversion of Lignin to Liquid Products

Abstract

The catalytic pyrolysis of lignin under microwave (MW) irradiation in the presence of iron-containing systems deposited directly on the lignin surface from various precursors has been studied using iron acetylacetonate, diacetylferrocene, and potassium trioxalatoferrate(III) as the precursors. The study has been focused on the effect of the argon eluent gas flow rate (300–60 mL/min) on the yield of the liquid product fraction. The effect of the gaseous medium (Ar, H2/Ar, O2/Ar) on the yield of liquid products formed by MW treatment has been studied. It has been shown that a maximum yield of liquid products is achieved in a medium of the inert gas argon or in a hydrogen/argon mixture (33 or 36%), whereas this yield in an oxygen/argon mixture is twofold lower (17%). The gas chromatography–mass spectrometry method has been used to determine the qualitative composition of the liquid product fraction, which is mostly represented by phenol and anisol, the derivatives of the monomeric units of lignin (coumaryl and coniferyl alcohols). In studying the effect of the iron precursor deposited on the lignin surface, it has been found that the liquid yield increases twofold from 18 to 36 or 34% in the presence of iron acetylacetonate Fe(C5H7O2)3 or potassium trioxalatoferrate K3[Fe(C2O4)3] ⋅ 3H2O, respectively, at a feed gas flow rate of 300 mL/min and a temperature of 700°C.