Influence of parameters on pyrolysis-GC/MS of lignin in the presence of tetramethylammonium hydroxide

Thermally assisted hydrolysis and methylation (THM) with tetramethylammonium hydroxide (TMAH) was performed on spruce milled wood lignin (MWL) in order to investigate THM parameters. The objective was the maximization of information on lignin structure. The main emphasis was laid on the formation of lignin monomer derivatives with intact propane side chain, as these fragments are thought to be indicators of favourable THM conditions. In the tested temperature range (310-710 °C) the lowest temperature of 310 °C was found to produce the highest yield of these monomers. The elution of unmethylated lignin monomers, such as phenols and methoxyphenols, was also minimized at 310 °C. In addition, a number of different TMAH to sample ratios were applied. The yield of the most lignin monomer derivatives was increased by using the highest tested TMAH concentration, whereas some unmethylated products, such as phenol, were unaffected. Methanol as solvent for TMAH was compared to an aqueous solution of TMAH of same concentration in respect of the influence on degradation product yields. The elution of 3,4-dimethoxybenzoic acid methyl ester increased and the yield of 3,4-dimethoxybenzaldehyde decreased when methanol was used. At last a prolonged incubation time of the TMAH-sample mixture was shown to be useful to enhance especially the yield of lignin monomer derivatives with intact propane side chain in case of application of a low TMAH to sample ratio.