Wood delignification chemical process using ammonium magnesium bisulphite as the active reagent

Abstract

The present innovation consists of the use of a reagent solution (FINAL COOKING ACID) where ammonium magnesium bisulphite is the active chemical. This new process is particularly useful to those industrial plants where the cellulose pulp is obtained by the magnesium acid process. The present innovation consists of the introduction of ammonium ions in the cooking acid used in such plants (initial cooking acid). The final cooking acid is obtained by the reaction of the initial cooking acid with ammonium hydroxide. Experimental results show the superiority of the present innovation over the magnesium acid bisulphite pulping process which is expressed by production of cellulosic fibres with higher mechanico-physical index values, decrease in the percentage of uncooked material, increase in wood yield and less environmental impact.

1 . Chemical process for wood delignification characterised by the use of an aqueous unsaturated solution containing an ionic mixture of ammonium and magnesium bisulphite salts (herein called ammonium magnesium bisulphite reagent), fully dissociated: HSO 3   − +Mg 2+ +NH 4   + , a pH=2-4 kept through an excess of dissolved sulphur dioxide, where [SO2]=f(pH)], the percentage of total SO 2 , free plus combined forms, being kept within 4% to 7%, wherein the percentage of combined SO 2  is from 1.8% to 3.0%.  
     
     
         2 . Chemical process for wood delignification, according to  claim 1 , characterised by a Final Cooking Acid containing: % SO 2  Total 5-6, % SO 2  Combined 2.2-2.7 and a pH value between 2 and 4 at which the process must be run by the controlled addition of NH 4 OH to the initial cooking acid, whose pH is nearly 1.5.  
     
     
         3 . Chemical process for wood delignification, according to  claim 2 , which being applied to eucalyptus and taking a monocationic acid bisulphite process, namely magnesium, as reference, is characterised by a pulp production having cellulosic fibres with higher physical properties, mainly tensile Index end Tear Index respectively 25% and 15%, at least higher  
     
     
         4 . Chemical process for wood delignification, according to  claim 2 , which being applied to eucalyptus and taking a monocationic acid bisulphite process, namely magnesium, as reference, is characterised by a decrease in the percentage of uncooked material nearly 30% and an increase in the wood yield nearly 4-5%.  
     
     
         5 . Chemical process for wood delignification, according to  claim 2 , which taking a monocationic acid bisulphite process, namely magnesium, as reference, is characterised by the significant improvement of the environmental impact resulting from the lower amount of sulphur dioxide released to the air when the cook is discharged.  
     
     
         6 . Process for preparing the ammonium magnesium bisulphite reagent referred to in  claims 1  to  5 , characterised by having as reaction reagents the initial cooking acid and ammonium hydroxide, according to the equation:  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   INITIAL COOKING ACID: 
                   Mg(HSO 3 ) 2  (aq) + SO 2 (g) + 
                 
                     
                   AMMONIUM HYDROXIDE 
                   NH 4 OH(aq) = 
                 
                     
                   ADDITION: 
                 
                     
                   REACTION PRODUCT: 
                   NH 4 (HSO 3 )(aq) 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
               
            
           
         
       
       FINAL COOKING ACID COMPOSITION:  
       Mg(HSO 3 ) 2 +NH 4 (HSO 3 )+SO 2 (diss.), wherein the two salts are fully dissociated in aqueous unsaturated solution containing at pH=2-4 kept through an excess of dissolved sulphur dioxide, where [SO 2 =f(pH)], the percentage of total S 0   2 , free plus combined forms, being kept within 4% to 7%, wherein the percentage of combined SO 2  is from 1.8% to 3.0%.    
     
     
         7 . Process according to  claim 6 , characterised by a Final Cooking Acid containing: % SO 2  Total 5-6, % SO 2  Combined 2.2-2.7 and a pH value between 2 and 4 at which the process must be run by the controlled addition of NH 4 OH to the initial cooking acid, whose pH is nearly 1.5.″