Method and chemical composition to improve efficiency of mechanical pulp

Abstract

The invention provides a composition of matter and a method, which enhance the process of mechanically pulping paper precursors. The composition of matter includes a small quantity of a reducing agent and a source of alkali. When added to the pulped material, e.g., wood chips, before or during mechanical pulping, the composition reduces the energy cost of the operation. In addition, not only does the composition also does not reduce the brightness of pulp, the composition can also enhance the effectiveness of subsequent bleaching processes.

1 . A composition that improves a mechanical papermaking process, the composition comprising:
 a base, and   a small quantity of a strong reductive chemical,   wherein when the composition is added to the papermaking process no later than when the mechanical pulping of wood chips occurs, the composition decreases the energy consumption of the mechanical pulping process but does not induce a net decrease in brightness of paper produced from the paper pulp when compared to paper similarly produced from similar paper pulp that did not have the composition added to its wood chips.   
     
     
         2 . The composition of  claim 1  in which the composition reduces the freeness of the resulting paper. 
     
     
         3 . The composition of  claim 1  wherein the base is selected from the list consisting of: an alkali metal hydroxide, an alkaline earth metal hydroxide, sodium hydroxide, magnesium hydroxide and any combination thereof and further comprise a chelating agent. 
     
     
         4 . The composition of  claim 1  in which the composition induces the resulting paper pulp to be more effectively bleached by peroxide or hydrosulfite bleaching. 
     
     
         5 . The composition of  claim 1  in which the reductive chemical is selected from the list consisting of: water soluble hydrosulfites, dithionites, sulfites, bisulfites, metabisulfites, formidinesulfinic acid, salts of formidinesulfinic acid, borohydrides, phosphines, phosphonium tertiary salts, an alkali, an alkaline earth metal hydrosulfite, borohydride, sodium hydrosulfite, sodium borohydride and any combination thereof. 
     
     
         6 . The composition of  claim 1  in which the chelating agent is a transitional metal ion chelant selected from the list consisting of: organic hydroxyacids, aminophosphonates, aminophosphates, aminocarboxylates, salts of DTPA, salts of EDTA, salts of DTMPA, and any combination thereof. 
     
     
         7 . The composition of  claim 1  in which composition is an aqueous solution or slurry capable of being applied by one method from the list of: being sprayed over wood chips, during soaking of wood chips, washing of wood chips, added in a refiner, and any combination thereof. 
     
     
         8 . The composition of  claim 1  in which the composition comprises 15-50% NaOH and 5-20% NaBH 4 . 
     
     
         9 . The composition of  claim 1  in which the base is only magnesium hydroxide in a dosage of 0.05-0.5%. 
     
     
         10 . The composition of  claim 1  in which the only reductive chemical in the composition is one selected from the list consisting of sodium borohydride and sodium hydrosulfite. 
     
     
         11 . A composition that improves a mechanical papermaking process, the composition comprising:
 magnesium hydroxide and optionally a chelating agent,   wherein when the composition is added to the papermaking process before or during the refining stage, the composition decreases the energy consumption of the mechanical pulping and increases the brightness of paper produced from the paper pulp when compared to paper similarly produced from similar paper pulp that did not have the composition added during the refining stage.   
     
     
         12 . A method of improving a mechanical pulping process, the method comprising:
 adding to pulp material prior to the conclusion of a mechanical pulping process a composition,   the composition comprising a base, a small quantity of a strong reductive chemical, and a chelating agent,   wherein the composition decreases the freeness of the resulting paper pulp and increases the brightness of the resulting paper pulp.   
     
     
         13 . The method of  claim 12  in which the composition is an aqueous solution or slurry capable of being added in according to one method selected from: being sprayed over wood chips, soaking of wood chips, washing of wood chips, added in a refiner, and any combination thereof. 
     
     
         14 . The method of  claim 12  wherein the composition is a synergistic mixture of magnesium hydroxide, sodium hydrosulfite and, optionally, sodium borohydride, sodium hydroxide, and a chelant. 
     
     
         15 . The method of  claim 14  further comprising the step of combining magnesium hydroxide with sodium hydrosulfite in a refiner which produces brighter mechanical pulp after subsequent peroxide or hydrosulfite bleaching. 
     
     
         16 . The method of  claim 12  in which the pulping process is one selected from the list consisting of TMP, RMP, GWD, and any combination thereof. 
     
     
         17 . The method of  claim 12  in which the composition has a component ratio of alkali:hydrosulfite:borohydrate:chelant as 1:0.15-0.65:0.01-0.1:0.01-0.1 by weight. 
     
     
         18 . The method of  claim 17  wherein the composition is applied at the rate 0.25-1% alkali by o.d. pulp. 
     
     
         19 . The method of  claim 12  wherein the composition enhances the brightening effects of subsequent bleaching of the pulp. 
     
     
         20 . The method of  claim 19  wherein the bleaching process is one selected from the list consisting of peroxide bleaching and hydrosulfite bleaching.