Fast pyrolysis of sulfur-free lignin from alkaline pulping with a hot-water pretreatment stage

The pyrolytical conversion of birch (Betula pendula/pubescens) lignin fractions separated from hot-water pretreatment/sulfur-free delignification black liquors was investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Based on pyrolytical data, the main condensable compounds were organized into respective component groups, and the relative mass portions of the pyrolysis products (mainly monomer-related fragmented products) formed during pyrolysis of various feedstocks were determined. It could be concluded that relatively pure aromatic fractions, mainly of guaiacol and syringol origin, without carbohydrate impurities, could be produced by this integrated biorefinery approach, in which all biomass fractions can be utilized for manufacturing biobased chemicals and chemical precursors. It could be determined that the formation of the individual pyrolytical components was characteristically dependent on the utilized production conditions (i.e., alkali charge, temperature, pretreatment), creating the possibility for adjustment of the process parameters for pronounced production of desired product fractions. Hence, it could be concluded that this sulfur-free concept facilitated the environmentally friendly production of aromatics, without the need for removing sulfur or carbohydrates-derived impurities from the liquid feedstocks. The practical importance of the approach presented in this manuscript lies in the development of rapid and reliable characterization tools for various lignocellulosics-originated feedstocks possessing potential for thermochemical conversion and for creating novel biorefinery concept alternatives for producing aromatics and chemical precursors from currently underutilized feedstock, lignin.