Method and compositions for oxygen delignification of chemical pulp

Abstract

The present disclosure provides methods and compositions for improving the oxygen delignification process. The methods may include adding low doses of a borohydride stabilized in an alkaline solution to brownstock pulp. The methods may result in significant chemical savings, increased pulp brightness, increased pulp yield, and reduced kappa number.

What is claimed is: 
     
         1 . A method for pulp delignification in a kraft process comprising:
 adding a composition to a brownstock pulp, wherein the composition comprises a reducing agent in an alkaline solution, and wherein the composition is added after a pulp digestion stage and before an oxygen delignification process.   
     
     
         2 . The method of  claim 1 , wherein the reducing agent is a hydride donor. 
     
     
         3 . The method of  claim 1 , wherein the reducing agent is selected from the group consisting of lithium borohydride, sodium borohydride, potassium borohydride, and any combination thereof. 
     
     
         4 . The method of  claim 1 , wherein the reducing agent is added in an amount less than about 0.1% by weight relative to an oven dried amount of brownstock pulp. 
     
     
         5 . The method of  claim 1 , wherein the composition comprises an amount of about 1% to about 34% by weight of the reducing agent and an amount of about 1% to about 50% by weight of a base in water. 
     
     
         6 . The method of  claim 5 , wherein the base is selected from the group consisting of sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium carbonate, calcium carbonate, and any combination thereof. 
     
     
         7 . The method of  claim 1 , wherein the reducing agent comprises sodium borohydride, the composition comprises the sodium borohydride at a concentration of about 12% by weight, and the composition comprises sodium hydroxide at a concentration of about 40% by weight. 
     
     
         8 . The method of  claim 1 , wherein the alkaline solution comprises sodium hydroxide. 
     
     
         9 . The method of  claim 1 , wherein the alkaline solution has a pH in a range of about 10 to about 14. 
     
     
         10 . The method of  claim 1 , further comprising:
 forming a mixture comprising the composition and an alkaline liquor; and   adding the mixture to the brownstock pulp prior to a temperature increase in the oxygen delignification process.   
     
     
         11 . The method of  claim 1 , wherein the oxygen delignification process excludes adding peroxides. 
     
     
         12 . The method of  claim 1 , wherein the composition further comprises a surfactant. 
     
     
         13 . The method of  claim 1 , wherein the composition further comprises a phase transfer catalyst. 
     
     
         14 . The method of  claim 13 , wherein the phase transfer catalyst is selected from the group consisting of tetra-n-butylammonium bromide, methyltrioctylammonium chloride, benzyltrimethylammonium chloride, hexadecyltributylphosphonium bromide, and any combination thereof. 
     
     
         15 . The method of  claim 1 , wherein the composition further comprises a chelant. 
     
     
         16 . The method of  claim 15 , wherein the chelant is selected from the group consisting of diethylene-triamine-pentamethylene phosphonic acid (DTMPA), salts of DTMPA, diethylenetriaminepentaacetic acid (DTPA), salts of DTPA, ethylenediaminetetraacetic acid (EDTA), salts of EDTA, and any combination thereof. 
     
     
         17 . The method of  claim 1 , wherein the composition further comprises a polysulfide. 
     
     
         18 . The method of  claim 1 , further comprising:
 feeding the brownstock pulp and the composition into a reactor;   pressurizing the reactor with oxygen; and   increasing a temperature inside the reactor to about 80° C. to 110° C., wherein the method results in a decreasing amount of lignin in the brownstock pulp.   
     
     
         19 . The method of  claim 18 , further comprising:
 removing a pulp material from the reactor; and   bleaching the pulp material using a bleaching solution, wherein the bleaching solution has an enhanced effect on increasing pulp brightness, and wherein the bleaching the pulp is performed after the oxygen delignification process.   
     
     
         20 . A composition for brownstock pulp delignification comprising:
 a gas and an alkaline solution, wherein the gas is pressurized oxygen and the alkaline solution comprises a reducing agent and a base.