Groundwood pulp bleaching with sodium hydrosulfite in the presence of benzene polycarboxylates
Unlted States Patent 1 1 [111 3,874,993  
 Ellis 1 51 Apr. 1, 1975 1 GROUNDWOOD PULP BLEACHING WITH 2.707.145 4/1955 Sparrow et a1 162/71 SODIUM HYDROSULFITE IN THE 2,826,478 3/1958 Schucker 162/71 3,467,574 9/1969 West 162/71 X PRESENCE OF BENZENE 3,709,779 1/1923 Gupta 162/71 POLYCARBOXYLATES [75] Inventor: Leonard C. Ellis, Chesapeake, Va. OTHER PUBLICATIONS 73 A&#34; :V&#34;&#39;Ch&#39;lI., bslgnee gfigli wzf nc Gupta, et al., Pulp and Paper Magazine of Canada,  
  June 6, 1969, pages 77-84. [22] Filed: Mar. 18, 1974 Appl&#39; 452l32 Primary E.\&#39;aminerS. Leon Bashore Related U S, Application Data Assistant Examiner-Arthur L. Corbin [63] Continuation-impart of Scr. No. 295,422, Oct. 6, Anomey&#34; Agent or Flrm j Glbson Semmes 1972, abandoned.  
 [52] US. Cl. 162/71, 162/76 [51] Int. Cl. D2lc 9/10 [57] ABSTRACT Field of Search Groundwood pulp is bleached with sodium hydrosul- [5 5 fite in the presence of a chelating agent consisting of References Cited an alkali metal salt of benzene polycarboxylic acid. UNITED STATES PATENTS 15 Claims, No Drawings 2.264.103 11/1941 Tucker ZSZ/DIG. 11  
  GROUNDWOOD PULP BLEACHING WITH SODIUM HYDROSULFITE IN THE PRESENCE OF BENZENE POLYCARBOXYLATES This is a continuation-in-part of Patent application Ser. No. 295,422 filed Oct. 6, 1972 in the name of Leonard C. Ellis, now abandoned.  
 BACKGROUND OF THE INVENTION Eutrophication is a process characterized by an abundant accumulation of nutrients, such as carbon, nitrogen and phosphorus, in lakes and rivers that support a dense growth of algae and floating algae scums. The algae growths are odorous, clog filter treatment plants, and decay during the summer through an aerobic process which depletes the shallow waters of oxygen. Factors in the eutrophication of such waters are natural runoff, agricultural drainage, groundwater, sewage and waste effluents. Although there is no present adequate proof, it has been speculated phosphorus and nitrogen-containing components, especially in detergents, are the major contributors to the eutrophication process. If indeed true, then the decrease or elimination of such components from common usage should prove helpful in decreasing this effect. It is therefore an object of the present invention to improve groundwood pulp bleaching with sodium hydrosulfite through the use of auxiliary aids which are biodegradable and offer no nutrient value for algae.  
  Traces of heavy metals (e.g., ferric ions) in a groundwood bleach system are suspected of causing two major problems which seriously affect the brightness gain in a pulp bleaching operation. First, the groundwood pulp acts as a low capacity cationic exchanger with a great affinity for heavy metals such as iron which produces highly colored compounds in the pulp. Secondly, it is strongly suspected that metal ions in the bleaching system catalyze the decomposition of the hydrosulfite, resulting in the increased consumption of sodium hydrosulfite, to obtain a given pulp brightness. In addition, the paper manufactured in the presence of heavy metal ions shows large losses in brightness during storage.  
  To overcome the detrimental effects on the pulp bleaching, sequestering agents such as sodium tripolyphosphate (Na P O risodium nitrilotriacetate (NTA), and trisodium ethylenediaminetetracetate (EDTA) have been conventionally employed in the pulp bleaching industry to tie-up the metal ions. The greater popularity of such phosphates, in addition to economic factors, can probably be attributed to their multifunctional properties-sequestering ability, alkalinity, buffer capacity, and soil deflocculation. Only recently, however, these additives have come into disfavor because they are suspected of supplying vital nutrients in the eutrophication process, a situation under strong attack by the ecologists.  
 Known art in this field comprises:  
 A. V. Lamberti, Can. 853,647 (1970).  
 B. V. N. Gupta and D. B. Mutton, Pulp and Paper Magazine of Canada, T174, pp. 77-84, June 6, 1969.  
 PREFERRED EMBODIMENTS OF THE INVENTION As indicated, the alkali metal salts of the benzene polycarboxylic acids, which are phosphorus and nitrogen-free additives, have been found to be adequate sequestering agents for groundwood pulp bleaching with commercial grades of sodium hydrosulfite. It is common practice throughout the industry to use these commercial grades of sodium hydrosulfites at solution strengths of 0.2% to 15.0%. The sequestering agent acids include all benzene polycarboxylic acids from the dithrough the hexacarboxylic acids and the final salts derived therefrom include both the sodium and potassium salts. In the process the following conditions apply. To a groundwood pulp slurry of 5% or less consistency is added a commercial grade of sodium hydrosulfite such as a 1.0% sodium hydrosulfite in the amount of 3.0 to 50.0 lbs. per ton of pulp and a sequestering agent consisting of a 1.0% solution of an alkali metal salt of benzene polycarboxylic acid at 0.1 to 10.0 lbs., per ton of pulp the bleaching process being controlled at F. to 170 F. and the pH of the pulp slurry being controlled at 4.1 to 6.3.  
 EXAMPLE A sample of Great Northern groundwood pulp was bleached at 140F. for 60 minutes with approximately 20 pounds of sodium hydrosulfite per ton of pulp (OD). The pulp consistency was 3.25%. The effects of the sequestering agents were determined on systems into which 750 ppm Fe (III) were added on a pulp basis or 25 ppm Fe (III) on a water basis.  
  As noted in Table I, the alkali metal salts of the benzene dicarboxylic acids produced a brightness increase of 0.3 to 1.4 points over the non-sequestering standard when bleaching in the presence of 750 ppm Fe (III) on a pulp basis. The maximum increase for the tricarboxylate salts was 1.5 points, and for the tetracarboxylates, a 1.1 point increase was noted. The chelating effect of the additives on the undesirable metal ions will be obvious from reference to the notations of Table I.  
  Effective maximal-minimal quantities by weight of the additives per ton of pulp are as follows:  
 A. sodium hydrosulfite 3.0 to 50.0 lbs.  
  B. benzene carboxylate 0.1 to 10.0 lbs, the preferred quantity being at 1.0 to 5.0 lbs. per ton of the pulp. The variation in relative quantity by weight while not depicted in the TABLE I, will depend upon the source of groundwood pulp and mill conditions.  
 LABORATORY BLEACI-IING PROCEDURE A. After determining the moisture of the groundwood pulp sample, weigh out sufficient pulp to provide 12 grams on a dry pulp basis per bleach and then add sufficient water to make a heterogeneous mixture of 3.25% pulp. Blend the mixture for 10-15 seconds using a Waring blender.  
  B. Next, filter the blended pulp through a mesh screen and weigh the filter pad. Divide the pad of pulp into equal portions and place in 500 ml. Erlenmeyer flasks. Add the filtrate, treated appropriately with ferric ion, equally to each flask and then add additional make-up water to provide a total weight of 370 grams of mixture per flask.  
  C. Then de-aerate the pulp in the flask with a vacuum pump and place under an inert atmosphere.  
  D. While maintaining an inert atmosphere, add the auxiliary agent (e.g., disodium benzene 1,2- dicarboxylate) as a 1.0% solution. Maintain the nitrogen purge over the bleaching flask for a period of two minutes and then add a specified volume of 1% sodium hydrosulfite solution. Sti for 30 seconds.  
  E. Without exposing the treated pulp to air, remove the bleaching flask from the bleaching rig and stopper. Place the flask and its contents in a constant temperature bath set at the desired bleaching temperature.  
  F. At the conclusion of the bleaching period, adjust the pH of the pulp system to 4.5 and form a handsheet. Oven dry hand sheet and determine the brightness. Compare the brighteness of the bleached handsheet against the handsheet formed from the non-treated pulp sample.  
  Similar bleaching may be effected by either dry blending the salts of the benzene polycarboxylates with the sodium hydrosulfite; or adding said salts as a solid to the pulp slurry, before or during the addition of the sodium hydrosulfite; or adding said salts as a solution simultaneously as the hydrosulfite solution is added, the quantity of salt solution being limited only by its solubility.  
 TABLE I zene dicarboxylic acid (1,2).  
  4. The method according to claim 1, wherein the chelating agent comprises the alkali metal salts of benzene dicarboxylic acid (1,3).  
  5. The method according to claim 1, wherein the chelating agent comprises the alkali metal salts of benzene dicarboxylic acid (1,4).  
  6. The method according to claim 1, wherein the chelating agent consists of the alkali metal salts of benzene tricarboxylic acid.  
  7. The method according to claim 1, wherein the chelating agent consists of the alkali metal salts of benzene tricarboxylic acid 1,2,4).  
  8. The method according to claim 1, wherein the benzene polycarboxylate comprises the alkali metal salts of benzene tricarboxylic acid (1,3,5).  
  9. The method according to claim 1, wherein the chelating agent consists of the alkali metal salts of benzene GROUNDWOOD PULP BLEACHING WITH SODIUM HYDROS ULFITE IN THE PRESENCE OF BENZENE POLYCARBOXYLATES AT 140F. for ONE HOUR Weight Deviation Chelating Agent (lbs/ton Brightness from of pulp) Gain Standard None None 10.7 Standard Benzene Dicarboxylic 5.0 11.9 +1.2 Acid (1,2) 10.0 12.0 +1.3 Benzene Dicarboxylic 5.0 12.1 +1.4 Acid (1,3) 10.0 12.1 +1.4 Benzene DicarboXylic 5.0 1 1.3 +0.6 Acid (1,4) 10.0 11.0 +0.3 Benzene Tricarboxylic 5.0 10.6 0.1 Acid 1,2,4) 10.0 11.1 +0.4 Benzene Tricarboxylic 5 .0 12.2 +1.5 Acid (1,3,5) 10.0 12.2 +1.5 Benzene Tricarboxylic 5.0 l 1.2 +05 Acid (1,2,3) 10.0 11.2 +0.5 Benzene Tetracarboxylic 5.0 l 1.8 +1.1 Acid (1,2,3,5) 10.0 11.6 +0.9 Benzene Tetracarboxylic 5.0 l 1.2 +0.5 Acid (1,2,4,5) 10.0 11.2 +0.5  
 Great Northern groundwood pulp was bleached with 20.0 lbs. of a 987: commercial Sodium hydrosulfite 27: soda ash blend per ton of pulp in the presence of various benzene polycarhnxylates. The pulp was treated with 750 ppm iron on a pulp basis or ppm iron on a water basis.  
 &#39;The benzene polycarboxylates were addcd as 17: solutions adjusted to pH 5.3 to 5.5 with sodium I claim:  
  1. A method of bleaching groundwood pulp comprising the steps of:  
 A. preparing a groundwood pulp slurry at a consistency of less than 5.0% and agitating said slurry; B. adding to the pulp slurry a chelating agent consisting of an alkali metal salt of benzene polycarboxylic acid in an amount of 0.1 to 10.0 lbs. per ton of P p;  
 C. combining with the slurry a bleach water solution comprising sodium hydrosulfite in an amount of 3.0 to 50.0 lbs. per ton of pulp and;  
 D. maintaining the pH of the pulp slurry at 4.1 to 6.3  
 and the temperature thereof at 90F. 170F.  
  2. The method according to claim 1 wherein the chelating agent consists of the alkali metal salts of benzene dicarboxylic acid.  
  3. The method according to claim 1, in which the chelating agent comprises the alkali metal salts of bentetracarboxylic acid.  
  10. The method according to claim 1, wherein the chelating agent consists of the alkali metal salts of benzene tetracarboxylic acid (1,2,3,5).  
  11. The method according to claim 1, wherein the chelating agent comprises the alkali metal salts of benzene tetracarboxylic acid (1,2,4,5).  
  12. The method according to claim 1, wherein the chelating agent comprises the alkali metal salts of hen zene pentacarboxylic acid.  
  13. The method according to claim 1 wherein the chelating agent comprises the alkali metal salts of benzene hexacarboxylic acid.  
  14. The method according to claim 1, wherein the alkali metal salts of benzene polycarboxylic acids are sodium salts.  
  15. The method according to claim 1, wherein the alkali metal salts of benzene polycarboxylic acids are potassium salts.