Method and chemical compositions to improve efficiency of chemical pulping

Abstract

The invention provides methods and compositions for enhancing the digestion of pulp in a chemical pulping process. The method uses ultra-low, economically feasible dosages of BH applied right before the pulping process begins, in a stable alkaline solution fed into white liquor line, to improve the process by saving pulping chemicals, increasing pulp brightness and yield and reducing the kappa number.

1 . A method for digesting wood chips, the method comprising the addition of a composition to a lignin bearing substrate in a pulping process and then applying to the substrate a subsequent bleaching step, the composition comprising a small dosage of BH relative to the oven dried mass of substrate,
 wherein the BH is dosed at a point in the pulping process where there has been no black liquor in contact with the substrate, and where no more than 1% of hemicellulose originally present in the wood chip form of the substrate has been separated from the substrate, and optionally when the substrate is in contact with white liquor, the dose is in an amount high enough to selectively reduce at least 1% of the lignin alpha-carbonyl groups in substrate thereby making them more susceptible to subsequent easy quinone methide beta-O-4 bond splitting during pulping process, but not as high as it would substantially deactivate the chromophores in the lignin by itself,   wherein the bleaching step involves adding a dosage of bleach no greater than an amount insufficient to cause the resulting paper stock to have been substantially whitened in the absence of AQ but for the presence of the low dose BH, and   wherein the resulting paper stock is whitened.   
     
     
         2 . A method for digesting pulp, the method comprising the addition of a composition to pulp undergoing a delignification process, the composition comprising a small dosage of BH relative to the oven dried mass of the pulp. 
     
     
         3 . The method of  claim 2  wherein the composition is added to white liquor and fed to the digester with the liquor before the temperature ramping begins. 
     
     
         4 . The method of  claim 2  wherein the BH is in the form of an alkaline solution in water. 
     
     
         5 . The method of  claim 2  wherein the amount of BH relative to oven dried pulp is less than 0.1% on the active base. 
     
     
         6 . The method of  claim 2  in which the BH is sufficiently alkaline so it is stable under normal conditions and does not release hydrogen. 
     
     
         7 . The method of  claim 2  wherein the dosage of BH in an amount insufficient to be effective in bleaching the pulp. 
     
     
         8 . A method to improve soda or kraft pulping, the method comprises the step of adding a composition to pulp liquor comprising sodium borohydride in alkali prior to pulping, the method provides white liquor chemicals saving, decreased kappa number, lower rejects and higher yield of pulp. 
     
     
         9 . The method of  claim 8  in which the composition comprises 10-40% alkali and 5-25% borohydride. 
     
     
         10 . The method of  claim 8  further comprising adding a surfactant to the pulp. 
     
     
         11 . The method of  claim 8  further comprising adding a polysulfide to the pulp. 
     
     
         12 . The method of  claim 2  in which the small dosage is characterized as causing the BH to preferentially attack functional groups in lignin and passivate hemicelluloses. 
     
     
         13 . The method of  claim 12  in which the method excludes using BH in a dosage sufficient to bleach the pulp. 
     
     
         14 . The method of  claim 2  in which the dosage of BH is small enough for the process to be economically and regulatory viable, on the other hand providing sufficient economic benefits via saving of pulping chemicals. 
     
     
         15 . The method of  claim 2  excluding the use of a non-delignification pulp treatment process. 
     
     
         16 . The method of  claim 1  wherein the delignification process including a cooking step followed by a bleaching step, the bleaching step addressing residual lignin not removed or not having its chromophores deactivated by the delignification step.