Separators lignin

In order to separate lignin from carbohydrates, stronger reagents were used in the expts of Friese et al ( Refs 9 12) for the nitration of wood pulp, namely normal mixed acids. In this way nitrolignin with a higher N content was obtained. When nitric-sulfuric acids (1 2 ratio) were used, a prod contg 8.45% N was obtained with a yield of 55%... 

The difficulty encountered in separating lignin from the cellulose of wood without the intermediate use of hydrolytic conditions,43 as well as the fact that some workers have isolated uniform, lignin-cellulose complexes,44 has suggested the presence of a carbohydrate-lignin compound. 

The major part is used as firewood or timber only 13% is further processed by mechanical and chemical treatment. The common process to convert wood into wood pulp is the Kraft process, which uses a mixture of sodium hydroxide and sodium sulfide to separate lignin and cellulose. The resulting cellulose is predominantly used for the production of paper and board. Only a small percentage (4%, 4—5 million tonnes) is further processed chemically. 

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. 

Xylanases depolymerize hemicellulose and breaks the covalent bond between lignin and cellulose. The depolymerized hemicellulose and separated lignin may be removed exposing the celulosic fiber and increasing cellulose content. Cellulases are enzyme complexes including enzymes that attack the cellulose chains at random, that hydrolyze the cellulose chains from the end and that hydrolyze the cellulobiose into glucose [12]. Yilmaz [13] detected stronger effect of xylanases on fiber properties compared to that of cellulase enzymes. 

Animal feedstuffs (Table 2) are a natural by-product of vegetable oil manufacture because this latter results in a variety of residues such as palm fruit pulp fibre and Brazil nut or other kernel oil-cake. Most cellulosic fibre wastes can be converted by steam explosion (sudden release of steam pressure to separate lignin from cellulose) to a cellulose digestible by ruminants. The oil-cakes often have high protein and carbohydrate contents and can be used as a major component of nonruminant feeds. 

---