Methods for bleaching aqueous pulps and compositions for use in these methods

Abstract

The present invention relates to compositions for use in an aqueous pulp bleaching process, comprising one or more alkaline earth metal oxides and/or one or more alkaline earth metal hydroxides; one or more alkaline earth metal salts; and optionally, one or more pitch control additives. Methods and kits for the formation of said compositions, are also part of the invention, as is the use of said compositions, methods and kits.

1 . A method comprising:
 mixing an alkaline earth metal oxide or an alkaline earth metal hydroxide with a component selected from the group consisting of: a mineral acid, sulphur dioxide, carbon dioxide, an alkaline earth metal sulfate, an alkaline earth metal carbonate, another an alkaline earth metal salt and combinations thereof.   
     
     
         2 . A method according to  claim 1 , wherein the mixing step is performed within an aqueous pulp bleaching composition. 
     
     
         3 . A method according to  claim 2 , wherein the mixing step is performed by of adding sulphuric acid, sulphur dioxide, or carbon dioxide to a paper bleaching pulp comprising the alkaline earth metal oxide or alkaline earth metal hydroxide. 
     
     
         4 . A method according to  claim 1  comprising forming a composition that comprises
 (i) the one or more alkaline earth metal oxides or alkaline earth metal hydroxides; 
 (ii) the one or more alkaline earth metal salts; and 
 (iii) one or more pitch control additives. 
 
     
     
         5 . A method according to  claim 1 , wherein the mixing step takes place in the presence of a said control additive is selected from talc, micronized talc, bimodal talc, cationic talc, bentonite, zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, resin-decomposing enzymes, cationic polymers designed to capture and immobilise resins or resinous components on fibre surfaces, aluminium sulphate, polyaluminium chloride, and dispersing agents specifically designed for the dispersion of resins and resinous components, and mixtures thereof. 
     
     
         6 . A method according to  claim 1 , wherein the said alkaline earth metal is selected from magnesium, calcium, and mixtures thereof. 
     
     
         7 . A composition comprising
 (i) one or more alkaline earth metal oxides or alkaline earth metal hydroxides; and   (ii) one or more alkaline earth metal salts.   
     
     
         8 . A composition according to  claim 7 , further comprising a pitch control additive is selected from talc, micronized talc, bimodal talc, cationic talc, bentonite, zeolite, diatomaceous earth, cationic mica, hydrophobic carbonates, resin-decomposing enzymes, cationic polymers designed to capture and immobilise resins or resinous components on fibre surfaces, aluminium sulphate, polyaluminium chloride, and dispersing agents specifically designed for the dispersion of resins and resinous components, and mixtures thereof. 
     
     
         9 . A composition according to  claim 7 , wherein the alkaline earth metal is selected from magnesium, calcium, and mixtures thereof. 
     
     
         10 . A composition according to  claim 7 , wherein the composition is an aqueous slurry. 
     
     
         11 . A composition according to  claim 10 , wherein said aqueous slurry has a total solids content of from 10 to 75 wt. %, on the basis of the total weight of the slurry. 
     
     
         12 . A composition according to  claim 7 , wherein the weight ratio of (i) the one or more alkaline earth metal oxides or alkaline earth metal hydroxides and (ii) the one or more alkaline earth metal salts is from 1:10 to 100:1. 
     
     
         13 . A composition according to  claim 10 , further comprising at least one of the following additives: (a) dispersants; (b) fillers; (c) surfactants; (d) bleaching agents; (e) chelating agents; and (f) pH-buffering agents. 
     
     
         14 . A kit of ingredients comprising
 (i) one or more alkaline earth metal oxides or alkaline earth metal hydroxides stored in a first container, and   (ii) either one or both of an aqueous mineral acid solution stored in a second container and a sulphur dioxide and/or carbon dioxide stored in a third container.   
     
     
         15 . The method of  claim 1 , further comprising bleaching or delignification of a pulp. 
     
     
         16 . The method of  claim 15 , further comprising reducing pitch in the pulp. 
     
     
         17 . The method of  claim 15 , further comprising protecting the pulp from depolymerisation and/or degradation. 
     
     
         18 . The method of  claim 15 , further comprising an acidic bleaching step. 
     
     
         19 . The method of  claim 1 , further comprising adding the product of the mixing step to a pulp and bleaching the pulp, wherein the product of the mixing step is added to the pulp prior to any addition of other alkaline bleaching agents, such as water glass, sodium silicate, NaOH, and/or hydrogen peroxide. 
     
     
         20 - 25 . (canceled)