PhD defence Douwe Zijlstra: "Alcohol incorporation as a tool for efficient lignin extraction and utilization"

Promotors: Prof. P.J. Deuss and Prof. H.J. Heeres

Abstract: One of the key challenges for the development of a sustainable economically competitive alternative for the petrochemical industry is the full valorization of lignocellulosic biomass into high-value components. One current hurdle is the structural degradation of lignin during harsh commercial processes resulting in the cleavage of C-O bonds in the highly-abundant β-O-4 linking motif leading to a condensed C-C rich lignin streams. The use of milder extraction conditions combined with alcohol incorporation is studied in this thesis. Extractions at mild conditions (<100 °C) in alcohol/water mixtures result in excellent retention of the β-O-4 linking motifs combined with enhanced extraction efficiency due to the incorporation of alcohol at benzylic positions. The incorporation of the alcohol was shown to enhance the solubility of lignin in organic solvents and stability, which are favourable for the extraction efficiency and β-O-4 retention. Changing the alcohol/water mixture for an alcohol/acetone mixture showed further improvement in terms of extraction efficiency of lignin with modified β-O-4 linking motifs even at temperatures of 60 °C. An even bigger improvement was achieved by moving from batch to flow-through extractions which prevent secondary reactions and allow extractions to be run at higher temperature. Near quantitative delignification (>95%) was achieved with a mild butanosolv extraction at 120 °C with a 85% recovery yield of a lignin with an excellent β-O-4 retention, close to those found in the native lignin structure albeit modified with n-butanol. New chemical reaction pathways were explored with this structurally well-defined alcohol incorporated lignin showing high potential for multiple applications.

Dissertation