Effects of mesostructured silica catalysts on the depolymerization of organosolv lignin fractionated from woody eucalyptus.

Isolated and purified organosolv eucalyptus wood lignin was depolymerized at different temperatures with and without mesostructured silica catalysts (i.e., SBA-15, MCM-41, ZrO2-SBA-15 and ZrO2-MCM-41). It was found that at 300°C for 1h with a solid/liquid ratio of 0.0175/1 (w/v), the SBA-15 catalyst with high acidity gave the highest syringol yield of 23.0% in a methanol/water mixture (50/50, wt/wt). Doping with ZrO2 over these catalysts did not increase syringol yield, but increased the total amount of solid residue. Gas chromatography-mass spectrometry (GC-MS) also identified other main phenolic compounds such as 1-(4-hydroxy-3,5-dimethoxyphenyl)-ethanone, 1,2-benzenediol, and 4-hydroxy-3,5-dimethoxy-benzaldehyde. Analysis of the lignin residues with Fourier transform-infrared spectroscopy (FT-IR) indicated decreases in the absorption bands intensities of OH group, CO stretching of syringyl ring and aromatic CH deformation of syringol unit, and an increase in band intensities associated with the guaiacyl ring, confirming the type of products formed.

Comparison of homogeneous and heterogeneous acid promoters in single-step aqueous-organosolv fractionation of eucalyptus wood chips.

Fractionation of lignocellulosic biomass is a primary step for converting multi-structure biomass to biofuels and other industrial products in integrated biorefinery processes. Here, the effects of homogeneous and heterogeneous acid promoters (HNO3-, HCl-, H2SO4-, and H3PO4-activated carbons) on Clean Fractionation (CF), a single-step aqueous-organosolv fractionation, of eucalyptus wood chips was studied and optimised. The optimised process contained 16.7% w/v biomass in a ternary mixture of methyl isobutyl ketone:methanol:water (25:42:33) with 5% AC-H3PO4 and incubated at 180 °C for 60 min. Under these conditions, 41.2 wt.% cellulose was obtained in enriched solid pulp with the average glucan content of 75.9%. The majority of the hemicelluloses was hydrolysed into the aqueous-methanol phase, which contained 17.8 wt.% monomeric xylose and xylooligomers while 13.7 wt.% lignin was separated into the organic phase. The heterogeneous acid-promoter process is a potent alternative to corrosive homogeneous acids for lignocellulose fractionation in integrated biorefineries.