Ozone bleaching of low consistency pulp

Abstract

Provided is a process for bleaching pulp with ozone. The process involves preparing a slurry of cellulosic pulp having a consistency in fibers of from 1-5 weight %. Such a low consistency slurry is then mixed with ozone under high shear conditions. The ozone is then maintained in contact with the cellulosic fibers to effect bleaching of the fibers. The present process offers the advantages of bleaching using a low consistency slurry, with the added advantages of employing ozone.

1 - 21 . (cancelled).  
     
     
         22 . A process for bleaching pulp with ozone, comprising the steps of: 
 generating ozone onsite from oxygen in a pressurized ozone generator;    preparing a slurry of cellulosic pulp having a consistency in fibers of from 1 to less than 5 weight %;    adding the generated ozone to the cellulosic pulp under high shear mixing conditions; and    maintaining the added ozone in contact with the cellulosic fibers under the high shear mixing conditions for a period of time ranging from 0.01-4 seconds thereby consuming 87-99% of the ozone.    
     
     
         23 . The process for bleaching pulp of  claim 22 , wherein the ozone added to the pulp is in the range of from about 2-10 kg ozone/ton of pulp.  
     
     
         24 . The process for bleaching pulp of  claim 22 , wherein the ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         25 . The process for bleaching pulp of  claim 22 , wherein the generated ozone has a concentration in oxygen in the range of 5-20%.  
     
     
         26 . The process for bleaching pulp of  claim 22 , wherein the ozone generator is operated at a pressure in the range of from about 20-60 psig.  
     
     
         27 . The process for bleaching pulp of  claim 22 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         28 . The process for bleaching pulp of  claim 22 , wherein the ozone is maintained in contact with the cellulosic fibers under the high shear mixing conditions for a time period ranging from 0.1 to 4 seconds.  
     
     
         29 . The process for bleaching pulp of  claim 22 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 20 to 80° C.  
     
     
         30 . The process of  claim 22 , in which the generated ozone has a concentration in oxygen in the range of from 10-20%.  
     
     
         31 . The process of  claim 22 , wherein the ozone generator is operated at a pressure in the range of from about about 30-40 psig.  
     
     
         32 . The process of  claim 22 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         33 . The process of  claim 25 , wherein the ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         34 . The process of  claim 25 , wherein the ozone generator is operated at a pressure in the range of from about 20-60 psig.  
     
     
         35 . The process of  claim 25 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         36 . The process for bleaching pulp of  claim 25 , wherein the ozone is maintained in contact with the cellulosic fibers under the high shear mixing conditions for a time period ranging from 0.1 to 4 seconds.  
     
     
         37 . The process for bleaching pulp of  claim 25 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 20 to 80° C.  
     
     
         38 . The process of  claim 25 , in which the generated ozone has a concentration in oxygen of from 10-20%.  
     
     
         39 . The process of  claim 25 , wherein the ozone generator is operated at a pressure of from about about 30-40 psig.  
     
     
         40 . The process of  claim 25 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         41 . The process for bleaching pulp of  claim 28 , wherein the ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         42 . The process for bleaching pulp of  claim 28 , wherein the ozone generator is operated at a pressure in the range of from about 20-60 psig.  
     
     
         43 . The process for bleaching pulp of  claim 28 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         44 . The process for bleaching pulp of  claim 28 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 20 to 80° C.  
     
     
         45 . The process of  claim 28 , in which the generated ozone has a concentration in oxygen of from 10-20%.  
     
     
         46 . The process of  claim 28 , wherein the ozone generator is operated at a pressure of from about about 30-40 psig.  
     
     
         47 . The process of  claim 28 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         48 . The process for bleaching pulp of  claim 29 , wherein the ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         49 . The process for bleaching pulp of  claim 29 , wherein the ozone generator operates at a pressure in the range of from about 20-60 psig.  
     
     
         50 . The process for bleaching pulp of  claim 29 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         51 . The process of  claim 29 , in which the generated ozone has a concentration in oxygen of from 10-20%.  
     
     
         52 . The process of  claim 29 , wherein the ozone generator is operated at a pressure of from about about 30-40 psig.  
     
     
         53 . The process of  claim 29 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         54 . A process for bleaching pulp with ozone, comprising the steps of: 
 generating ozone onsite from oxygen in a pressurized ozone generator;    preparing a slurry of cellulosic pulp having a consistency in fibers of from 1 to less than 5 weight %;    adding the generated ozone to the cellulosic pulp under high shear mixing conditions; and    maintaining the added ozone in contact with the cellulosic fibers under the high shear mixing conditions for a period of time ranging from 0.01-10 seconds thereby consuming 87-99% of the ozone.    
     
     
         55 . The process for bleaching pulp of  claim 54 , wherein the ozone added to the pulp is in the range of from about 2-10 kg ozone/ton of pulp.  
     
     
         56 . The process for bleaching pulp of  claim 54 , wherein the ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         57 . The process for bleaching pulp of  claim 54 , wherein the generated ozone has a concentration in oxygen in the range of 5-20%.  
     
     
         58 . The process for bleaching pulp of  claim 54 , wherein the ozone generator is operated at a pressure in the range of from about 20-60 psig.  
     
     
         59 . The process for bleaching pulp of  claim 54 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         60 . The process for bleaching pulp of  claim 54 , wherein the period of time ranges from 0.1 to 4 seconds.  
     
     
         61 . The process for bleaching pulp of  claim 54 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 20 to 80° C.  
     
     
         62 . The process of  claim 54 , in which the generated ozone has a concentration in oxygen of from 10-20%.  
     
     
         63 . The process of  claim 54 , wherein the ozone generator is operated at a pressure of from about about 30-40 psig.  
     
     
         64 . The process of  claim 54 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         65 . A process for bleaching low consistency pulp with ozone, comprising the steps of: 
 a) preparing a low consistency slurry of cellulosic pulp, the pulp containing lignin, the low consistency slurry having a consistency in fibers of from 1 to less than 5 wt. %; and    b) adding ozone to the cellulosic pulp under high shear mixing conditions to react with the lignin and provide a slurry of ozone and pulp, wherein the ozone is added to the cellosic pulp at a pressure of from 30 psig to 110 psig and contact therebetween under the high shear mixing conditions is maintained for a period of time thereby consuming 87-99% of the added ozone during the high shear mixing conditions.    
     
     
         66 . The process of  claim 65 , comprising the additional steps of: 
 a) selecting 30 psig to 90 psig as the pressure of the ozone added during the high shear mixing conditions thereby consuming 87-94% of the amount of the added ozone at the expiration of the period of time; and    b) allowing the slurry of ozone and pulp to flow into a bottom of a tower and therefrom to a top of the tower, wherein by the time the flow of the slurry of ozone reaches the top of the tower 99% of the amount of the added ozone has been consumed.    
     
     
         67 . A process for bleaching low consistency pulp with ozone, comprising the steps of: 
 a) introducing a low consistency slurry of cellosic pulp into a pump, the low consistency slurry having a consistency in fibers of from 1 to less than 5 wt. %;    b) pumping the low consistency slurry to provide a flow of the low consistency slurry;    c) introducing ozone gas into the flow of the low consistency slurry to provide a combined flow of the ozone gas and the low consistency slurry;    d) mixing the ozone gas and the low consistency slurry in the combined flow under high shear mixing conditions, the ozone being introduced at a location between the pump and the mixer; and    e) allowing the mixed ozone gas and low consistency slurry to flow from the mixer to a bottom of a tower and therefrom up to a top of the tower, wherein: 
 1) the ozone gas introduced into the flow of the low consistency slurry is at a pressure of from 30-90 psig thereby consuming 86.9-93.4% of the amount of the ozone gas by the time the mixed ozone gas and low consistency slurry flows into the bottom of the container, and  
 2) by the time the mixed ozone gas and low consistency slurry flows to the top of the container 99.8% of the amount of the ozone introduced into the flow of the low consistency slurry has been consumed.  
   
     
     
         68 . A process for bleaching pulp with ozone, comprising the steps of: 
 generating ozone onsite from oxygen in a pressurized ozone generator operated at a pressure in the range of from about 20-60 psig, the generated ozone having a concentration in oxygen in the range of 5-20%;    preparing a slurry of cellulosic pulp having a consistency in fibers of from 1 to less than 5 weight %;    adding a charge of the generated ozone to the cellulosic pulp under high shear mixing conditions, the charge being in the range of from about 2-10 kg ozone/ton of pulp, a temperature of the pulp slurry just before undergoing the high shear mixing conditions being in the range of from 20 to 80° C.;    maintaining the added ozone in contact with the cellulosic fibers under the high shear mixing conditions for a period of time ranging from 0.01-10 seconds; and    at the expiration of the time period, allowing the mixed ozone and cellulosic pulp to flow into a bottom of a tower.    
     
     
         69 . The process for bleaching pulp of  claim 68 , wherein the charge of ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         70 . The process for bleaching pulp of  claim 68 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         71 . The process for bleaching pulp of  claim 68 , wherein period of time ranges from 0.1 to 4 seconds.  
     
     
         72 . The process of  claim 68 , in which the generated ozone has a concentration in oxygen of from 10-20%.  
     
     
         73 . The process of  claim 68 , wherein the ozone generator is operated at a pressure of from about about 3040 psig.  
     
     
         74 . The process of  claim 68 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         75 . The process of  claim 68 , wherein a pressure of the generated ozone added to the cellulosic pulp is in the range of from 30-110 psig thereby causing 87-99% of the ozone charge to be consumed at the expiration of the time period.  
     
     
         76 . The process of  claim 75 , wherein the charge of ozone added to the pulp is in the range of from about 5-6 kg ozone/ton of pulp.  
     
     
         77 . The process for bleaching pulp of  claim 75 , wherein the pulp slurry consistency is in the range of from 2-4 weight %.  
     
     
         78 . The process for bleaching pulp of  claim 75 , wherein period of time ranges from 0.1 to 4 seconds.  
     
     
         79 . The process of  claim 75 , in which the generated ozone has a concentration in oxygen of from 10-20%.  
     
     
         80 . The process of  claim 75 , wherein the ozone generator is operated at a pressure of from about about 30-40 psig.  
     
     
         81 . The process of  claim 75 , wherein a temperature of the pulp slurry just before undergoing the high shear mixing conditions is in the range of from 40 to 60° C.  
     
     
         82 . A process for bleaching low consistency pulp with ozone, comprising the steps of: 
 a) generating ozone onsite from oxygen in a pressurized ozone generator operated at a pressure in the range of from about 20-60 psig, the generated ozone having a concentration in oxygen in the range of 5-20%;    b) introducing a low consistency slurry of cellosic pulp into a pump, the low consistency slurry having a consistency in fibers of from 1 to less than 5 wt. %;    c) pumping the low consistency slurry to provide a flow of the low consistency slurry;    d) introducing ozone gas into the flow of the low consistency slurry to provide a combined flow of the ozone gas and the low consistency slurry, the ozone being added at a rage in the range of from about 2-10 kg ozone/ton of pulp;    e) mixing the ozone gas and the low consistency slurry in the combined flow under high shear mixing conditions for a period of time, the ozone being introduced at a location between the pump and the mixer, a temperature of the pulp slurry just before undergoing the high shear mixing conditions being in the range of from 20 to 80° C.; and    f) at the expiration of the period of time, allowing the mixed ozone gas and low consistency slurry to flow from the mixer to a bottom of a tower and therefrom up to a top of the tower, wherein: 
 1) the ozone gas introduced into the flow of the low consistency slurry is at a pressure of from 30-90 psig thereby consuming 86.9-93.4% of the amount of the ozone gas by the time the mixed ozone gas and low consistency slurry flows into the bottom of the container, and  
 2) by the time the mixed ozone gas and low consistency slurry flows to the top of the container 99.8% of the amount of the ozone introduced into the flow of the low consistency slurry has been consumed.