Depolymerisation of organosolv lignin by supported Pt metal catalysts

Abstract

The conversion of lignocellulosic biomass into value-added chemicals and biofuels has been attracting the attention of researchers in recent years. Lignin is an abundant, natural polymer and a major component of lignocellulose comprising an aromatic structure with ether linkages, methoxy-, and hydroxyl groups. Therefore, it has great potential as a sustainable source to produce basic chemical products. In this study, precious metal-loaded hydrotalcite (HTC) catalysts for the depolymerization of organosolv lignin (OL) were investigated concerning minimizing coke formation and maximizing the value-added lignin oil fraction and lignin tar fraction. The influences of the catalyst support, the platinum loading as well as the loading with a second metal (Cu or Ni) were examined. The resulting depolymerization fractions (lignin oil, lignin tar, aqueous fraction, and coke) were determined gravimetrically. To compare the molecular mass distribution of the lignin oil and lignin tar fractions as well as the purchased OL, gel permeation chromatography (GPC) was used. The lignin oil fractions were analyzed quantitatively and qualitatively by gas chromatography-mass spectroscopy (GC–MS). Regarding the most suitable catalyst system (5%Pt-1%Ni/HTC), a design of experiment (DoE) was prepared to further minimize coke formation and maximize the value-added fractions (lignin oil and lignin tar). This optimization led to 18 wt% lignin oil fraction, 72 wt% lignin tar fraction, and 0.4 wt% coke formation.