Lignin surface area, increasing

It is not clear, however, whether electron radiation would have beneficial effects upon the enzymatic hydrolysis of cellulose. It has been shown that the particle size reduction and surface area increase upon ball milling are probably more important than the reduction of crystallinity (19). Electron irradiation may not disrupt the shielding layer provided by the lignin to expose fresh cellulose to the action of large enzyme molecules. 

In alkaline hydrolysis, bases such as NaOH and NH3 are used for pretreatment The effects include increased porosity, larger internal surface area, a decrease of the degree of polymerization, separation of structural linkages between lignin and carbohydrates, and disruption of the lignin structure. 

Lignocellulosic substrates usually require significant pretreatment to disrupt the structure of cellulose and lignin molecules within the substrate. Substrates are often ground to particle sizes of 1-2 mm to increase the surface area for attack and to disrupt cell walls. In addition, the crystalline structure of cellulose may be disrupted by steaming under pressine. Sometimes the steaming is carried out in conjunction with chemical pretreatment with acid or alkali. 

Nano/microporous cellulose (NMC) prepared after removal of lignin from wood cellulose was found suitable for the development of cold pasteurization" processes acting as a biofilter for cell removal. It was also used successfully as biocatalyst in food fermentations acting as both cell immobilization carrier and as promoter of biochemical reactions, even at extremely low temperatures. The cumulative surface area of the NMC pores was found to be 0.8 to 0.89 m g" as indicated by porosimetry analysis. This surface is relatively small compared with other porous materials such as y-alumina however, using a natural organic material is attractive from the point of view that it is safer for bioprocess applications and is better accepted by consumers. The NMC/immobilized yeast biocatalyst increased the fermentation rate and was more effective at lower temperatures compared with free cells. Furthermore, the activation energy E, of fermentation was found to be 28% lower than that of free cells, indicating that it is an excellent material to promote the catalytic action of cells for alcoholic fermentation. 

APEX Increases accessible surface area Low formation of inhibitors Not efficient for raw materials with high lignin content High cost of large amounts of ammonia... 

CO2 explosion Increases accessible surface area Cost-effective Does not imply generation of toxic compounds Does not affect lignin and hemicelluloses Requires very high pressure... 

Alkali Remove hemicelluloses and lignin Increase surface area Low formation of inhibitors Slow Complex inhibitors Less effecrtive on softwoods... 

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