Delignification processes

This process is somewhat ambiguously referred to as pulping, but should not be confused with the chemical delignification process... 

Several functional ligninase models that do not contain key structural elements of LiP or MnP are worth mentioning since they do not use dihydrogen peroxide in the delignification process. Among them, robust polyoxometallate catalysts have been shown [64] to work well with dioxygen, thus making this chemistry commercially attractive. 

Figure 7-32 illustrates the glucomannan and xylan losses during kraft pulping of pine wood. As can be seen, an appreciable portion of the lost xylan is actually not degraded but dissolves in the cooking liquor as a polysaccharide. The amount of dissolved xylan reaches a maximum around the midpoint of the delignification process. 

Salts added to aid phase separation, e.g. lithium sulfate, can act as catalysts in the delignification process. 

Supercritical fluids display attractive solvent characteristics which can be manipulated by either the pressure or temperature. Using supercritical fluids as reaction media, simultaneous reaction and separation are also achievable. This methodology has recently been applied to the reactive separation of wood constituents, especially lignin, by supercritical fluids (1-4). Delignification processes using supercritical fluids are of potential Industrial Importance (5,6) and there Is a need for the development of kinetic models which could permit a priori prediction of the rate of lignin removal. The present paper discusses such a model. 

The subdivision of this chapter follows the primary criterion based on whether lignins intervene only physically or also chemically in the manufacturing of synthetic pol5miers. The secondary criterion adopted here has to do with whether the lignins are used as such, that is, as recovered from industrial delignification processes, or after suitable chemical modifications. 

In a more prosaic, but inevitably relevant tone, lignins isolated from industrial or pilot delignification processes are cheap commodities and their direct use in the manufacture of novel materials is therefore particularly attractive, if the operation leads to a viable exploitation. 

The addition of less than 0.1% of anthraquinone can increase the cellulose yield and accelerate the delignification process, leading to better utilization of the... 

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