Metal substituted xerogels for improved peroxide bleaching of kraft pulps

Abstract

A novel process for bleaching cellulosic pulp is disclosed which provides improvements in pulp brightness and delignification without negatively impacting physical properties of the pulp. Specifically, a process is disclosed in which kraft pulp is treated with at least one of each of an oxidizing agent, an alkaline agent, and a metal substituted xerogel in a bleaching stage to improve brightness and delignification of softwood, hardwood, or recycled pulp. In a preferred embodiment, a process is disclosed which uses at least one metal substituted xerogel as a catalyst in an alkaline peroxide bleaching stage to improve kraft pulp brightness and delignification. Pulps bleached according to the process of the present invention are also disclosed.

We claim:  
     
         1 . A process for bleaching cellulosic pulp comprising treating said pulp with at least one oxidizing agent, at least one alkaline agent and at least one metal substituted xerogel, in amounts effective to improve brightness and delignification of said pulp.  
     
     
         2 . The process of  claim 1  wherein said pulp is a kraft pulp.  
     
     
         3 . The process of  claim 1  wherein said pulp has a consistency of from about 10% to about 20%.  
     
     
         4 . The process of  claim 3  wherein said pulp has a consistency of from about 10% to about 15%.  
     
     
         5 . The process of  claim 4  wherein said pulp has a consistency of about 10%.  
     
     
         6 . The process of  claim 1  wherein said treatment is practiced at a temperature of from about 60° C. to about 90° C.  
     
     
         7 . The process of  claim 6  wherein said temperature is from about 70° C. to about 90° C.  
     
     
         8 . The process of  claim 7  wherein said temperature is about 70° C.  
     
     
         9 . The process of  claim 1  wherein said treatment is practiced for a time of from about 60 minutes to about 180 minutes.  
     
     
         10 . The process of  claim 9  wherein said time is about 90 minutes.  
     
     
         11 . The process of  claim 1  wherein said treatment is practiced at a pH of from about 9 to about 12.5.  
     
     
         12 . The process of  claim 11  wherein said pH is about 12.2.  
     
     
         13 . The process of  claim 1  wherein said at least one alkaline agent is selected from NaOH, KOH, Na 2 CO 3 , Mg(OH) 2  and mixtures thereof.  
     
     
         14 . The process of  claim 11  wherein said alkaline agent is NaOH.  
     
     
         15 . The process of  claim 1  wherein said at least one metal substituted xerogel is an alkyl metal substituted xerogel.  
     
     
         16 . The process of  claim 15  wherein said alkyl metal substituted xerogel is selected from Al-Xgel, W-Xgel, Mn-Xgel, V-Xgel, Mn-Xgel, Li-Xgel, and Mo-Xgel, and mixtures thereof.  
     
     
         17 . The process of  claim 16  wherein said alkyl metal substituted xerogel is W-Xgel.  
     
     
         18 . The process of  claim 16  wherein said alkyl metal substituted xerogel is Al-Xgel.  
     
     
         19 . The process of  claim 16  wherein said alkyl metal substituted xerogel is Mn-Xgel.  
     
     
         20 . The pulp of  claim 1  wherein said pulp is selected from hardwood pulp, softwood pulp, and recycled pulp, and mixtures thereof.  
     
     
         21 . The process of  claim 20  wherein said pulp is softwood pulp.  
     
     
         22 . The process of  claim 1  wherein said at least one oxidizing agent is selected from oxygen, ozone, hydrogen peroxide, peracetic acid, peroxo monosulfate and mixtures thereof.  
     
     
         23 . The process of  claim 22  wherein said at least one oxidizing agent is hydrogen peroxide.  
     
     
         24 . The process of  claim 1  wherein the initial kappa number of said pulp is from about 20 to about 35.  
     
     
         25 . The process of  claim 24  wherein the initial kappa number of said pulp is from about 20 to about 30.  
     
     
         26 . The process of  claim 25  wherein the initial kappa number of said pulp is about 28.5.  
     
     
         27 . The process of  claim 1  wherein said treatment improves pulp brightness by at least about 30% .  
     
     
         28 . The process of  claim 1  wherein said treatment improves pulp delignification by at least about 38%.  
     
     
         29 . The process of  claim 1  wherein the amount of said at least one metal substituted xerogel is from about 0.05% to about 0.2% by weight of oven dry pulp.  
     
     
         30 . The process of  claim 29  wherein the amount of said at least one metal substituted xerogel is from about 0.05% to about 0.2% by weight of oven dry pulp.  
     
     
         31 . The process of  claim 30  wherein the amount of said at least one metal substituted xerogel is about 0.2% by weight of oven dry pulp.  
     
     
         32 . The process of  claim 1  wherein said pulp is recycled.  
     
     
         33 . The process of  claim 1  wherein the amount of said at least one oxidizing agent is from about 2% to about 4% by weight of oven dry pulp.  
     
     
         34 . The process of  claim 33  wherein the amount of said at least one oxidizing agent is about 2% by weight of oven dry pulp.  
     
     
         35 . The process of  claim 1  wherein the amount of said at least one alkaline agent is from about 2% to about 4% by weight of oven dry pulp.  
     
     
         36 . The process of  claim 35  wherein the amount of said at least one alkaline agent is about 2% by weight of oven dry pulp.  
     
     
         37 . A pulp treated in accordance with the process of  claim 1 .  
     
     
         38 . The process of  claim 1  further comprising, prior to bleaching, treating said cellulosic pulp with at least one treating agent to remove undesirable trace metal ions.  
     
     
         39 . The process of  claim 38  wherein said at least one treating agent is a chelating agent.  
     
     
         40 . The process of  claim 39  wherein said chelating agent is selected from nitrogenous polycarboxylic acids, nitrogenous polyalcohols, polycarboxylic acids and nitrogenous polyphosphonic acids.  
     
     
         41 . The process of  claim 40  wherein said chelating agent is selected from EDTA, DTPA, NTA, HEDTA, DTPMPA, or mixtures thereof.  
     
     
         42 . The process of  claim 39  wherein the amount of said chelating agent is from about 0.3% to about 0.8% per ton of oven dry pulp.  
     
     
         43 . The process of  claim 42  wherein the amount of said chelating agent is about 0.6% per ton of oven dry pulp.  
     
     
         44 . The process of  claim 39  wherein said chelating treatment is practiced at a pH of about 5.  
     
     
         45 . The process of  claim 38  wherein said treating agent is an acid.  
     
     
         46 . The process of  claim 38  wherein said pulp is washed between said chelating treatment and said bleaching treatment.  
     
     
         47 . A process for bleaching kraft pulp in an alkaline hydroxide stage comprising treating said pulp with hydrogen peroxide, sodium hydroxide, and at least one metal substituted xerogel in amounts effective to improve brightness and delignification of said pulp.  
     
     
         48 . The process of  claim 47  wherein said at least one metal substituted xerogel is selected from W-Xgel, Al-Xgel, Mn-Xgel, and mixtures thereof.  
     
     
         49 . The process of  claim 47  wherein said at least one metal substituted xerogel includes at least one recycled metal substituted xerogel.  
     
     
         50 . The process of  claim 1  wherein said at least one metal substituted xerogel includes at least one recycled metal substituted xerogel.  
     
     
         51 . The process of  claim 47  wherein said pulp is washed after said treatment.  
     
     
         52 . The process of  claim 47  wherein the amount of hydrogen peroxide is from about 2% to about 4%, the amount of sodium hydroxide is from about 2% to about 4%, and the amount of metal substituted xerogel is from about 0.05% to about 0.2%, all by weight of oven dry pulp.  
     
     
         53 . The process of  claim 52  wherein the amount of hydrogen peroxide is about 2%, the amount of sodium hydroxide is about 2%, and the amount of metal substituted xerogel is about 0.2%, all by weight of oven dry pulp.  
     
     
         54 . The process of  claim 1  wherein said process comprises at least one stage in a multistage bleaching sequence.