Bleaching of Non-Wood Pulps: Can Sodium Hydroxide Be Replaced with Sodium Carbonate in the Alkaline Extraction of Non-wood Pulps?, 1990 Pulping Conference Proceedings

Use of sodium carbonate in the alkaline extraction of bamboo (Phyllostachys bambusoides) and eucalyptus (E. tereticornis) kraft pulps were examined. Sodium carbonate alone is not a viable alkaline extraction chemical. But a mixture of sodium carbonate and sodium hydroxide (5050) extracted these pulps as good as sodium hydroxide. In the alkaline extraction of bamboo and eucalyptus pulps with partial substitution of NaOH with Na2C03, the sodium hydroxide should be added first, followed by sodium carbonate. This would help in maintaining a high alkalinity during the initial delignification to maximize lignin removal. The pulps extracted with sodium hydroxide and sodium carbonate mixtures upon bleaching with hypochlorite and hydrogen peroxide gave pulps similar to that of sodium hydroxide extracted and bleached pulps. The total solids and COD values for the alkaline extraction stage effluent from sodium hydroxide alone and sodium hydroxide and sodium carbonate mixture extraction were higher than sodium carbonate extraction.