Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2012
Publication Date: 12/20/2012
Citation: Nsimba, R.Y., Mullen, C.A., West, N., Boateng, A.A. 2013. Structure-property characteristics of pyrolytic lignins derived from fast pyrolysis of a lignin rich biomass extract. ACS Sustainable Chemistry & Engineering. 1:260-267. Interpretive Summary: Fast pyrolysis is a process involving the rapid heating of materials in the absence of oxygen, that can produce a liquid product (pyrolysis oil, bio-oil) from biomass such as wood, grasses and agricultural residues. Bio-oil is a liquid that has the potential to be refined into renewable gasoline and diesel fuels. As we move to a more bio-based fuel supply, bio-fuel plants (bio-refineries) will also produce coproducts such as chemicals and other bio-based materials. One potential source of such coproducts is the solid water insoluble fraction of pyrolysis bio-oil, called pyrolytic lignin, which can be easily separated from the liquid product. We extracted and used solvents to fractionate the pyrolytic lignins from the pyrolysis oil of a lignin rich wood byproduct. In order to determine the properties of the extracted materials, various analytical methods have been used for their characterization. Several fractions of the pyrolytic lignins isolated have different properties. The results suggest that most isolated lignin fractions possess high fuel value and contain chemical moieties that can be targeted in order to produce value-added chemicals. Further conversion of these chemicals might lead to structures that are similar to fuels like gasoline. This information will be important to those considering producing non-fuel coproducts from pyrolysis liquids and those considering refining these liquids into biofuels.
Technical Abstract: In this study, various fractions of pyrolytic lignin were isolated from the fast pyrolysis oil of Etek lignin, a residue of acidic processing of wood. Based on the solubility differences in selected solvents, the water insolubles of the pyrolysis oil were separated into various fractions (methanol-insoluble, water-immersed, dichloromethane-insoluble, and dichloromethane-soluble) with differing properties. A comparative study of the physicochemical characteristics amongst the isolated lignin fractions and the pure lignin extracted from the Etek lignin precursor (non-thermally altered lignin) was made using various analytical techniques including: elemental analysis, gel permeation chromatography, 31P-NMR of phosphitylated derivatives, ATR-FTIR, TGA, and scanning electron microscopy). The isolation/fractionation method employed led to production of lignin fractions with higher oxygen and lower carbon and hydrogen contents than that extracted from the Etek lignin leading to a decrease in their heating values. The results from GPC and 31P-NMR showed that the thermal pyrolysis of the Etek lignin produced decarboxylated pyrolytic lignins of varying molecular weight with higher concentration of condensed phenolic hydroxyl moieties, guaiacyl and alkyl hydroxyls than the lignin in the precursor, potentially resulting from the thermal cleavage of the C-O bonds. Their thermal stability parameters have shown that 120 degrees C is the temperature at which the isolated pyrolytic lignins begin to degrade. SEM photo micrographs show evidence of high minerals concentration in the methanol insoluble pyrolytic lignins with low lignin content, while the water immersed and the dichloromethane insoluble lignins exhibited similar surface topography, meaning that they are chemically identical. Information gathered from the various analytical techniques suggests that pyrolytic lignin fractions obtained from the fast pyrolysis of Etek lignin are potential starting materials for sustainable production of renewable chemicals and fuels.