Bleaching of wood pulp with a sequestering agent and hydrogen peroxide

Claim 1

THE METHOD OF BLEACHING WOOD PULP WHICH CONSISTS ESSENTIALLY IN ADDING TO A PULP SELECTED FROM THE GROUP CONSISTING OF MECHANICAL, CHEMICO-MECHANICAL, COLD SODA, NEUTRAL SULFITE AND UNBLEACHED SULFITE PULPS, INITIALLY CONTAINING LESS THAN 10 PERCENT SOLIDS, A SEQUESTERING AGENT TO ELIMINATE FREE METAL IONS IN AN AMOUNT OF 1 TO 2 POUNDS PER 100 POUNDS OF OVEN DRIED PULP, THICKENING THE PULP TO A SOLIDS CONCENTRATION OVER 10 PERCENT, FEEDING THE THUS TREATED PULP INTO A FIRST MIXER AND INTRODUCING INTO THE MIXER A 2 TO 25 PERCENT BY WEIGHT HYDROGEN PEROXIDE SOLUTION AT A PH OF ABOUT 4.0 TO 5.5 IN AN AMOUNT EQUIVALENT TO ABOUT 0.5 TO 2% EXPRESSED AS 100% H2O2, THOROUGHLY COMBINING ALL INGREDIENTS IN THE MIXER WHILE HEATING WITH LIVE STEAM TO A TEMPERATURE OVER 100*F., AND IN THE RANGE OF 110* TO 120*F., FEEDING THE THUS TREATED PULP TO A SECOND MIXER WHILE INTRODUCING THEREINTO AN AQUEOUS ALKALINE SOLUTION CONTAINING, CALCULATED AS NAOH, BETWEEN ABOUT 1.25 AND 1.8 PARTS OF ALKALI PER 100 PARTS OF OVEN DRIED PULP WITH SUFFICIENT SODIUM SILICATE TO EFFECT BUFFERING AT PH 10.5 TO 11 AND MAINTAINING THE ABOVE TEMPERATURE WITH STEAM, FEEDING THE WHOLE THROUGH A BLEACHING TOWER AND RETAINING IT THERE FOR NOT MORE THAN 90-120 MINUTES UNTIL BLEACHED AT ABOUT THE SAME TEMPERATURE, DISCHARGING THE CONTENTS OF THE TOWER AND ADDING SO2 IN AN AMOUNT TO NEUTRALIZE THE PULP AND TO REDUCE ITS PH TO AT LEAST 6.

Claim 2

THE METHOD OF BLEACHING WOOD PULP WHICH CONSISTS ESSENTIALLY IN ADDING TO A PULP SELECTED FROM THE GROUP CONSISTING OF MECHANICAL, CHEMICO-MECHANICAL, COLD SODA, NEUTRAL SULFITE AND UNBLEACHED SULFITE PULPS, INITIALLY CONTAINING LESS THAN 10 PERCENT SOLIDS, A SEQUESTERING AGENT TO ELIMINATE FREE METAL IONS IN AN AMOUNT OF 1 TO 2 POUNDS PER 100 POUNDS OF OVEN DRIED PULP, THICKENING THE PULP TO A SOLIDS CONCENTRATION OVER 10 PERCENT, FEEDING THE THUS TREATED PULP INTO A FIRST MIXER AND INTRODUCING INTO THE MIXER A 2 TO 25 PERCENT BY WEIGHT HYDROGEN PEROXIDE SOLUTION AT A PH OF ABOUT 4.0 TO 5.5 IN AN AMOUNT EQUIVALENT TO ABOUT 0.5 TO 2% EXPRESSED AS 100% H2O2, THOROUGHLY COMBINING ALL INGREDIENTS IN THE MIXER WHILE HEATING WITH LIVE STEAM TO A TEMPERATURE OVER 100*F., AND IN THE RANGE OF 110* TO 120*F., FEEDING THE THUS TREATED PULP TO A SECOND MIXER WHILE INTRODUCING THEREINTO AN AQUEOUS ALKALINE SOLUTION CONTAINING, CALCULATED AS NAOH, BETWEEN ABOUT 1.25 AND 1.8 PARTS OF ALKALI PER 100 PARTS OF OVEN DRIED PULP WITH SUFFICIENT SODIUM SILICATE TO EFFECT BUFFERING AT PH 10.5 TO 11 AND MAINTAINING THE ABOVE TEMPERATURE WITH STEAM, FEEDING THE WHOLE THROUGH A BLEACHING TOWER AND RETAINING IT THERE FOR NOT MORE THAN 90-120 MINUTES UNTIL BLEACHED AT ABOUT THE SAME TEMPERATURE, DISCHARGING THE CONTENTS OF THE TOWER AND ADDING SO2 IN AN AMOUNT TO NEUTRALIZE THE PULP AND TO REDUCE ITS PH TO AT LEAST 6.