ISBN 9783843932608

978-3-8439-3260-8, Reihe Verfahrenstechnik

Lilia Adriana Zenker
Added-Value for the 2nd Generation Biorefinery: Isolation of Lignin and its Conversion into Nanoporous Materials

235 Seiten, Dissertation Technische Universität Hamburg-Harburg (2016), Softcover, A4

Zusammenfassung / Abstract

Lignin is one of the most abundant renewable materials on Earth and the only large-scale natural substance with a phenolic nature. A high-value (most likely) material use for lignin should be found, since the increasing focus of research based on natural resources will accelerate the development of pretreatment methods within the biorefinery and thus, will increase lignin availability. Without the inclusion of lignin in value-adding processes, the biorefinery will remain economically not viable. Since the properties of lignin are highly defined by its isolation method, understanding of the effect of pretreatment on the end-characteristics of isolated lignin fractions is extremely important. In this work, a comparison of promising chemical pretreatments applied to the same biomass source was performed. Solids pretreated with Organosolv (OS), Steam (SE) and Liquid-Hot-Water (LHW) were further enzymatically hydrolyzed. Best results for carbohydrate and lignin yield were found for the OS pretreatment followed close by the LHW and SE with similar results. OS, SE, AL and AS lignin fractions were obtained from each pretreatment and compared in their Klason lignin content, Mw and heat value. Lignin behavior during LHW pretreatment on the composition and yield of AL and AS lignin fractions was further investigated. Additionally, physicochemical characterization of the lignin fractions was performed using 31P NMAR, pyrolysis GC/MS, ASE, Soxhlet extraction, SEC and TGA techniques. Finally, lignin was used as a feedstock for the production of nanoporous materials (aerogels). AS lignin was successfully gelated by crosslinking with oligo(ethylene glycol)- and oligo(propylene glycol)- diglycidyl ethers of varying length. Stable gels were obtained at high concentration of lignin in solution, while larger amounts of crosslinker were needed when decreasing their molecular weight. After drying with scCO2, the aerogels obtained were light to dark brown and with porosities between 75 and 88%. The smallest density measured was 0.15 g cm-3 while the largest specific surface area obtained was 120 m2 g-1 aerogel. The aerogels were thermally stable with a decomposition temperature of around 250°C. The thermal and mechanical properties of the materials obtained indicate an affinity for their use as insulation materials.