Lignin removal processes

Jain, R.K. Gupta, A. Dixit, A.K. Mathur, R.M. Kulkami, A.G. Enhanced biomethanation efficiency of black liquor througb lignin removal process in small agro based paper mills. Bioenergy... 

Alkaline delignification in the form of the Kraft or Sulfate process is now the most widely used method of lignin removal. It uses a mixture of sodium hydroxide and sodium sulfide—the latter being produced in the recovery process by the reduction of sodium sulfate... 

When autohydrolysed aspen was treated with cellulase enzyme, poor results were obtained. Based on a ton of dry wood, only about 300 lb of fermentable sugars were obtained, and the fermentation was very inefficient with low yields of ethanol. These results compare poorly with those shown in Figure 5 when autohy-drolysed-caustic extracted aspen was treated with cellulase enzyme, and then fermented. It would appear from these results that the caustic extraction step for lignin removal would be necessary if the enzymatic hydrolysis process were to be adopted and advisable when acid hydrolysis is used. 

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. 

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