Fractionation of three different lignins by thermal separation techniques—A comparative study. Issue 1 (28th September 2018)

• Record Type: Journal Article
• Authors: Rohde, Viktoria; Böringer, Sarah; Tübke, Beatrice; Adam, Christian; Dahmen, Nicolaus; Schmiedl, Detlef
• Is Part Of: Global change biology. Volume 11:Issue 1(2019)
• Page Start: 206
• Page End: 217
• Publication Date: 2018-09-28
• Subjects: Biomass energy -- Periodicals; Biomass energy -- Environmental aspects -- Periodicals; Energy crops -- Periodicals; 662.88
• DOI: 10.1111/gcbb.12546
• Languages: English
• ISSNs: 1757-1693

Abstract

Abstract: Separation of the heterogeneous lignin macromolecule in fractions with increased homogeneity, as well as different structural (molar mass) and functional (hydroxy groups, ‐OH) features is important in terms of its use as a chemical building block. For this purpose, three thermal separation techniques were investigated and compared: solvent extraction, successive precipitation and ultrafiltration. One important issue in this context is the utilization of organic solvents with low boiling points to ensure a simple and efficient recovery. In addition to a softwood Kraft lignin (Indulin AT) as reference lignin, two sulfur‐free Organosolv lignins from short rotation coppice ("poplar with bark") and from the energy grass Miscanthus × gigantheus were investigated. The lignins were separated into low, medium and high molecular weight fractions. Due to the different initial structural features and the associated varying solubility properties in such lignins, different organic solvents were needed for dissolution and precipitation of the individual lignin fractions. The polarity of the used solvent is one key factor regarding the yield of the soluble fraction and the success of molecular sorting into low, medium, and high molecular weight. Further structural features, for example the aliphatic OH‐group content increased with rising molecular weight of poplar, miscanthus, and Kraft lignin from minimum 0.72, 0.3, and 1.6 mmol/g to maximum 2.4, 1.6, and 2.8 mmol/g, respectively. The number of phenolic OH‐groups decreased from maximum 3.8, 4.3, and 4.2 to minimum 1.4, 2.7, and 2.9, respectively. The presented work illustrate options regarding the molecular sorting of several lignin types with three thermal techniques into fractions differing in key properties (yield, molecular weight, polydispersity, functional groups) for material applications. Abstract : The separation of the heterogeneous lignin macromolecule in fractions with increased homogeneity is an important intermediate step for the production of lignin‐based building blocks for various end applications. The three thermal separation techniques solvent extraction, successive precipitation, and ultrafiltration were investigated and compared regarding their suitability to fractionate two sulfur‐free Organosolv lignins of "poplar with bark" and Miscanthus × gigantheus and a softwood Kraft lignin as reference. The present work shows possibilities and methods for a molecular sorting of different lignin types in fractions of low, medium, and high molecular weight with different structural and functional properties.