Abstract
We optimized the solvolysis step in methanol for two-step lignin-first upgrading of woody biomass. Birchwood was first converted via sulfuric acid methanolysis to cellulose pulp and a lignin oil intermediate, which comprises a mixture of lignin oligomers and C5 sugars in the methanol solvent. The impact of reaction temperature (140–200 °C), acid loading (0.24–0.81 wt%, dry biomass), methanol/biomass ratio (2.3/1–15.8/1 w/w) and reaction time (2 h and 0.5 h) was investigated. At high biomass loadings (ratio < 6.3/1 w/w), operation at elevated pressure facilitates delignification by keeping methanol in the liquid phase. A high degree of delignification goes together to a large extent with C5 sugar release, mostly in the form of methyl xylosides. Gel permeation chromatography and heteronuclear single quantum coherence NMR of lignin fractions obtained at high acid (0.81 wt%) and low biomass (15.8/1 w/w) loading revealed extensive cleavage of β-O-4′ bonds during acidolysis at 180 °C for 2 h. At an optimized methanol/biomass ratio of 2.3/1 w/w and acid loading (0.24 wt%), more β-O-4′ bonds could be preserved, i.e., about 33% after 2 h and 47% after 0.5 h. The high reactivity of the extracted lignin fragments was confirmed by a second hydrogenolysis step. Reductive treatment with Pd/C under mild conditions led to disappearance of ether linkages and molecular weight reduction in the hydrotreated lignin oil.
Highlights
Concerns over anthropogenic climate change such as global warming are major drivers to accelerate the transition from fossil to renewable resources [1]
We optimized the acid solvolysis of birchwood towards the highest delignification degree by varying the methanol/biomass ratio, temperature and sulfuric acid concentration with retention of cellulose as another important aim
Acid solvolysis of birchwood was first conducted at a methanol/biomass ratio of
Summary
Concerns over anthropogenic climate change such as global warming are major drivers to accelerate the transition from fossil to renewable resources [1]. The development of alternative sustainable feedstocks for energy, chemicals and materials is regarded one of this century’s most important societal challenges [2,3] In this context, lignocellulosic biomass is a promising candidate because it is the most abundant renewable source of carbon on. 33 billion tonnes correspond to wood and wood processing wastes (i.e., chopped trees or sawmill dust), while 14 billion tonnes are classified as agricultural crops and waste materials (such as straw, corn husks or bagasse) [5]. Appropriate processing of these lignocellulosic feedstocks into biofuels and biochemicals can lead to more sustainable energy and chemical industries. The economic feasibility of biomass conversion processes depends strongly on the effectiveness of exploiting the principal lignocellulosic components
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