Lignins purification

The molecular weight of lignin in the wood, ie, of protolignin, is unknown. In addition to difficulties of isolation and purification, the polymer exhibits strong solvent, ionic, and associative effects in solution. An unequivocal method of measurement has not been developed. The polymer properties of lignin and its derivatives have been discussed (10,16). 

A large number of patents describe various procedures for the mainly continuous hydrolysis and oxidation processes, as weU as for the purification steps requited to obtain high grade vanillin. Lignin is degraded either with sodium hydroxide or with calcium hydroxide solution and simultaneously... 

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

A final are we should discuss is color removal. This is perhaps the most difficult impurity to remove from waters. In surface waters color is associated with dissolved or colloidal suspensions of decayed vegetation and other colloidal suspensions. The composition of this material is largely tannins and lignins, the components that hold together the cellulose cells in vegetation. In addition to their undesirable appearance in drinking water, these organics can cause serious problems in downstream water purification processes. For examples ... 

Synthetic examples include the poly(meth)acrylates used as flocculating agents for water purification. Biological examples are the proteins, nucleic acids, and pectins. Chemically modified biopolymers of this class are carboxymethyl cellulose and the lignin sulfonates. Polyelectrolytes with cationic and anionic substituents in the same macromolecule are called polyampholytes. 

The ubiquity of lignin in plant tissue presents an obstacle to the removal and purification of xylan. Lignin retards or prevents the complete solution of xylan either because of mechanical obstruction or perhaps by reason of attachment through as yet unidentified covalent bonds. Furthermore, lignin is partially soluble in the various aqueous alkaline solutions used for dissolving xylan and, consequently, poses a purification problem in various subsequent steps designed to isolate the pure polysaccharide. 

Various processes have been developed for hydrolyzing lignocellulose to its major constituents, i.e., to sugars and (partly) depolymerized lignin. The lignin is usually precipitated from the aqueous solution and either used as chemical feedstock or burned as process fuel. The aqueous sugar solution is then applied for fermentation to ethanol after neutralization and purification. 

Lignin peroxidases enzymes In-process control, semipreparative purification, comparison with conventional columns Anion Exchange disks [80]... 

These have been effectively used to remove lignin and hydrophobic metabolites from plant-derived samples. Bonded-phase mini-columns are also ideal for the prechromatographic purification of a perbenzoylated sugars, glycopeptides (and derived oligosaccharides), and peralkylated oligosaccharides. ... 

Fractionation by Stepwise Elution. Information obtained from the analytical separation was applied for a preparative purification. Lignin peroxidase concentrate was bound to a Q-Sepharose colunm (0= 5 cm, V = 1000 ml) after ultrafiltration and eluted stepwise with 0.08 M, 0.18 M and 0.28 M sodium acetate, pH 6.0. The fraction which was eluted with 0.28 M buffer (V= 3.91, 4400 U/1) was purified further. It was bound to Q-Sepharose and eluted with 0.18 M and 0.3 M sodium acetate. En rnie in the latter fraction was precipitated and dissolved in glycerol as previously described. The volume was 15 ml. 

Figure 2. Purification of lignin peroxidases by anion exchange chromatography. Enzyme activity (U/1) O Absorbance at 405 nm Absorbance at 280 nm.

Purification. One main peak was observed with detection at 405 nm, when purified lignin peroxidase was analyzed by Mono Q chromatography. The retention time of the main peak was 11.8 min and its area was 98.9% of the total peak area. Possibly the enzyme solution contains, however, two isoenzymes which have very similar properties. The Kj of the purified lignin peroxidase for veratryl alcohol was 139 on the basis of Eadie-Hofstee plot. 

This work also suggests other research and development directions needed to bring the price of ethanol down to an automotive fuel level. We need a lower capital cost hydrolysis process which can produce a concentrated sugar solution. We also need a fermentation process adaptable to concentrated sugar solutions to lower alcohol purification costs. Finally we need to recover and include by-product values - lignin, furfural, acids, methanol, etc. -in our income. 

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