Quantitative determination of fatty and resin acids in Kraft black liquors as their trimethylsilyl derivatives by gas chromatography

Abstract

Tall oil soap is an important byproduct of the Kraft pulping process used at papermaking facilities. Tall oil soap is comprised primarily of the sodium salts of unsaturated fatty acids and a variety of resin acids. These can be recovered from spent black liquor and sold as a feedstock for specialty chemicals manufacture. The ability to monitor the removal of soap from liquor at various stages of the recovery process is of extreme importance to the recovery operation. This paper describes a new procedure which has been developed for the analysis of residual tall oil components in black liquors. In this method, the liquor is extracted with methyl tert.-butyl ether (MTBE) under highly alkaline conditions. The extracted components are converted to their trimethylsilyl derivatives, and then analyzed by GC with on-column injection. Quantitation is performed through comparison to an internal standard. This new procedure provides many important advantages over the wet chemical method routinely used for monitoring residual soap levels. These include a more simplified extraction and analysis procedure, an increase in method precision, and detailed quantitative information regarding the type and distribution of components.