Dissolved lignin derivatives, separation

A study of dissolved lignin derivatives first requires their separation from each other. For this purpose gel permeation chromatography (GPC) is widely used. In this technique separation of lignin derivatives is based largely on the size and shape of the molecule, namely its hydrodynamic volume. 

A primary objective of wood pulping is to separate lignin from cellulose. Two chemical processes are commonly used to achieve this, namely the sulfite and the sulfate methods (Kraft-process). In the sulfite process, the lignin in wood is sulfo-nated with aqueous solutions of sulfites or hydrogen sulfites, with added SO2, at high temperatures, so that soluble lignin sulfonic acids are produced, which can be dissolved out of the wood. The sulfate method uses sodium hydroxide, sodium sulfide and sodium carbonate as basic pulping chemicals. It derived its name from the small amounts of sodium sulfate which are added to balance out alkali losses. 

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