Doctoral thesis: Characterisation of lignocellulose components by analytical pyrolysis gas chromatography mass spectrometry


VTT's Research Scientist Taina Ohra-aho presents her thesis in the field of bioproduct technology at the Aalto University on 20th December, 2017. The title of the thesis is "Characterisation of lignocellulose components by analytical pyrolysis gas chromatography mass spectrometry".

Analytical pyrolysis combined with gas chromatography mass spectrometry (Py-GC/MS) is a technique that can be used for the analysis of lignocellulose materials in situ. Pyrolysis degradation products provide information concerning the nature and origin of the initial sample.

The main aim of this thesis was to apply analytical pyrolysis for lignin and carbohydrate characterisation from various lignocellulosic plant materials. Isothermal pyrolysis was the main technique utilised. In addition, thermochemolysis, thermal desorption and fractionated pyrolysis were applied in order to provide better understanding of the changes observed in lignin structure and carbohydrate composition in various materials and processes.

In pyrolysis, hardwood lignin is degraded to guaiacyl and syringyl type pyrolysis degradation products with similar side chain structures, whereas carbohydrates form stable anhydrosugars. Lignin degradation products can be used to define the lignin composition and S/G ratio of the wood feedstocks. However, Py-GC/MS cannot be recommended for the comparison of carbohydrate composition between different wood species. Information on lignin structure and quantity was obtained directly from pulps by Py-GC/MS. Decrease of oxygenated lignin pyrolysis products and increase of short side chain structures were associated with beta-ether bond cleavage. Decrease of the short side chain structures as a function of delignification was interpreted to indicate leaching of the lignin products formed in cooking, and thus enrichment of native lignin in the residual pulp lignin.

Due to the more complex chemical structure of brewers spent grain than of wood, its lignin composition was characterised by Py-GC/MS and thermochemolysis. Thermochemolysis results demonstrated that Py-GC/MS leads to underestimation of native type syringyl structures and S/G ratios. In addition, thermochemolysis with TMAAc and TMAH reagents was applied as a means to differentiate between free fatty acids and esters, respectively. The results showed that thermochemolysis with alkaline TMAH can be used to determine total fatty acid contents from the aliphatic and aromatic esters. TMAAc can be used to distinguish between free acids and aliphaticesters, but not between aromatic esters and free acids.

In addition a thermal desorption method was developed to provide information on the odorous volatile organic compounds released from lignin. The method is applicable to the comparison of different lignin samples below their thermal degradation.


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