Pulp production utilizing bark-containing residues as raw material

Abstract

The present invention relates to a process for preparing pulp from one or more wood-based raw materials, including at least a residue of bark origin, by carrying out an alkaline treatment step on a bark-based raw material, recovering a solid residue after said alkaline treatment step, and cooking the resulting residue either alone or mixed with wood. The invention also relates to pulp prepared using said process.

1 - 16 . (canceled) 
     
     
         17 . A process for preparing pulp, the process comprising:
 carrying out an alkaline treatment step on a bark-based raw material;   recovering a solid bark-containing residue after said alkaline treatment step; and   cooking said solid bark-containing residue, alone or as a mixture with one or more further wood-based raw materials.   
     
     
         18 . The process of  claim 17 , wherein the bark-based raw material is selected from softwood species selected from pine, fir, beech or spruce, or from the hardwood species selected from birch, eucalyptus, acacia, poplar or willow, and wherein the bark-based raw material contains less than 5 w-% of other materials. 
     
     
         19 . The process of  claim 17 , wherein a pre-treatment on the bark-based raw material is carried out before the cooking, optionally before the alkaline treatment step, to remove, or at least to decrease the content of, inorganic compounds, the pre-treatment including washing the bark-based raw material with mineral acids, acids, or chelating agents, and separating and collecting solids for the alkaline treatment step. 
     
     
         20 . The process of  claim 17 , wherein the alkaline treatment step on the bark-based raw-material is carried out using one or more alkaline sodium compounds selected from the group consisting of sodium hydroxide (NaOH), sodium sulfide (Na 2 S) and sodium carbonate (NaCO 3 ) the bark-based raw material having an effective alkali content (EA) of 10-50%, based on the bark dry mass. 
     
     
         21 . The process of  claim 20 , wherein the effective alkali content (EA) is 14-30%. 
     
     
         22 . The process of  claim 17 , wherein the alkaline treatment step is carried out at a temperature of 80-190° C. 
     
     
         23 . The process of  claim 17 , wherein alkaline treatment step is carried out during a treatment time of 15-300 min. 
     
     
         24 . The process of  claim 17 , wherein a polyphenol-containing black liquor and a solid bark-containing residue are separated from each other after the alkaline treatment step on the bark-based raw material, and wherein the solid bark-containing residue is recovered and used in the cooking. 
     
     
         25 . The process of  claim 17 , wherein the cooking is carried out as a kraft pulping, by utilizing a white liquor having an effective alkali content (EA) of 10-50%, and a sulphidity of 30-50%, and by carrying out the cooking at a temperature of 80-190° C., and by maintaining these conditions for 15-300 min. 
     
     
         26 . The process of  claim 17 , wherein the solid bark-containing residue is mixed with wood chips before the cooking, and wherein the wood chips are obtained from hardwood species selected from birch, eucalyptus, acacia or willow, or from softwood species, selected from pine or spruce. 
     
     
         27 . The process of  claim 17 , wherein the solid bark-containing residue, optionally pre-treated to remove inorganic compounds, is mixed with wood chips before the cooking, in a concentration of 5-70 w-%. 
     
     
         28 . The process of  claim 27 , wherein the concentration is 20-40 w-%. 
     
     
         29 . The process of  claim 17 , wherein the cooking is followed by one or more bleaching steps. 
     
     
         30 . The process of  claim 17 , wherein a bark pulp is obtained from the cooking of the solid bark-containing residue, and wherein the bark pulp is mixed with a conventional wood pulp to form a mixed pulp. 
     
     
         31 . The process of  claim 30 , further comprising forming a paper product from said mixed pulp. 
     
     
         32 . The process of  claim 17 , wherein no hot-water extraction is performed. 
     
     
         33 . The process of  claim 17 , wherein the cooking yields a black liquor which is recycled to a subsequent cooking step. 
     
     
         34 . A pulp prepared by the process according to  claim 17 . 
     
     
         35 . The pulp of  claim 32 , wherein the pulp comprises up to 70 w-% of residue mixed with wood chips.