Patent Application: US-63223005-A

Abstract:
polysulphide produced by oxidizing white liquor includes both active and inactive components . “ active ” polysulphide is the only component that increases pulp yield . the amount of active polysulphide formed when manganese oxides are used as catalysts in the generating process is increased by adding a co - catalyst . adding bismuth compounds and , in particular , bismuth oxide as a co - catalyst increases the total amount of polysulphide formed with all the manganese oxides and increases the amount of active polysulphide produced particularly when using the lower manganese oxides . the co - catalyst also increases the number of cycles in which the most active catalyst , manganese dioxide , can participate before losing efficiency . other elements in the same group and adjacent groups in the periodic table are active but these other elements are more soluble than bismuth and are toxic .

Description:
the process of this invention for , first , increasing the amount and proportion of active polysulphide in liquors generated by the oxidation of sulphide - containing liquor in the presence of manganese compounds and , second , maintaining the catalytic activity of the manganese compounds , is a process in which a co - catalyst , particularly a bismuth compound or compounds from metals of the same group or adjacent groups of the periodic table are used with the manganese compounds in the polysulphide generating process . in general , the co - catalyst is employed in a metal molar ratio of co - catalyst to manganese oxide of 1 : 1 to 1 : 10 ; preferably 1 : 1 to 1 : 5 , more preferably 2 : 3 to 2 : 5 and most preferably 1 : 2 ; more particularly these ratios are based on the metal component of the co - catalyst , for example , bi , and mn in the oxide forms . the manganese oxide may be employed , with advantage , in catalytic amounts , but also may be employed in higher amounts , for example stoichiometric amounts . suitable amounts of the manganese oxide are readily determined based on experiment and the prior literature . in particular , when the polysulphide is produced by oxidation of a white liquor and the manganese oxide is manganese dioxide , the manganese dioxide may suitably be employed in a catalytic amount of 0 . 1 to 2 . 0 g / l of the white liquor . in particular bismuth oxide ( bi 2 o 3 ) is applied at a metal molar bi 2 o 3 to mno 2 ratio of 1 to 2 with the mno 2 used for the generation of polysulphide by the oxidation of white liquor . manganese exists in several oxidation states and forms 4 major oxides — mn iv o 2 , mn iii 2 o 3 , mn iii / ii 3 o 4 and mn ii o . the manganese oxidation state affects the ratio of active polysulphide ( ps act ) to gravimeteric polysulphide ( ps gr ) with ps gr being the sum of ps act and inactive polysulphide ps inact . the higher the oxidation state of the manganese oxide the greater the amount of gravimetric and active polysulphide formed . tie active polysulphide concentration is lower and the inactive polysulphide concentration higher when using a catalytic rather than a stoichiometric amount of manganese compound which indicates that manganese compounds , when used as catalysts , are not effectively regenerated to the required oxidation state . the co - catalyst such as bi 2 o 3 increases the number of cycles or time that the catalyst retains its catalytic activity , in the production of oxidized white liquor containing active polysulphide . this discussion identifies the importance of the oxidation state of the oxide and the value of maintaining the oxide in the highest oxidation state possible . it has been found that bismuth compounds enhance the performance of manganese compounds in the polysulphide generation process . bi 2 o 3 was mixed with mno 2 in a 1 to 5 metal molar ratio . air was employed as oxidant to regenerate the catalyst . polysulphide was generated at 90 ° c . with magnetic stirring . mno 2 . ( 2 g / l ) was used catalytically and was regenerated constantly by bubbling air ( flow rate : 50 ml / min ) through the liquor with a sparger . the starting white liquor had an effective alkali ea concentration of 80 g / l and a sulphide concentration ( as na 2 o ) of 40 g / l . reaction time was either 120 or 240 minutes . the active polysulphide was measured by uv - vis analysis and the amount was determined by the peak intensity at 416 nm . the inactive polysulphide was determined as the difference between the amount of ps measured by gravimetric and by uv - vis ( spectrometric ) analyses . the table shows the results of applying the co - catalyst and the changes that occur as the polysulphide generation time is extended and the liquor is heat treated . heat treatment is the method of improving the ps act / ps gr ratio of polysulphide liquors produced by oxidation processes described in van heek et al ., 2004 . the liquor was heat treated at 90 ° c . for 120 min with no air and no stirring but in the presence of the catalyst . in the presence of bismuth oxide , the table shows that : after 120 minutes , the active polysulphide concentration is increased from 3 . 02 g / l to 3 . 87 g / l while the inactive polysulphide is decreased from 3 . 20 to 2 . 11 g / l ; after 240 minutes , the active polysulphide concentration is increased from 4 . 17 g / l to 5 . 23 g / l while the inactive polysulphide is decreased from 3 . 51 to 2 . 79 g / l ; and after heat treatment , the active polysulphide concentration is increased from 5 . 22 g / l to 6 . 10 g / l while the inactive polysulphide is decreased from 1 . 10 to 0 . 42 g / l ; bi 2 o 3 was mixed with mno 2 in a 1 to 5 metal molar ratio . oxygen was employed as oxidant to regenerate the catalyst . polysulphide was generated at 90 ° c . with magnetic stirring . mno 2 ( 2 g / l ) was used catalytically and was regenerated constantly by bubbling oxygen ( flow rate : 20 ml / min ) through the liquor with a sparger . the starting white liquor had an effective alkali ea concentration of 80 g / l and a sulphide concentration ( as na 2 o ) of 40 g / l . reaction time was either 120 or 240 minutes . tie active polysulphide was measured by uv - vis ( spectrometric ) analysis and the amount was determined by the peak intensity at 416 nm . the inactive polysulphide was determined as the difference between the amount of ps measured by gravimetric and by uv - vis analyses . the table shows the results of applying the co - catalyst and the changes that occur as the polysulphide generation time is extended and the liquor is heat treated . heat treatment is the method of improving the ps act / ps gr ratio of polysulphide liquors produced by oxidation processes described in van heek et al ., 2004 . the liquor was heat treated at 90 ° c . for 120 min with no air and no stirring but in the presence of the catalyst . in the presence of bismuth oxide , the table shows that : after 120 minutes , the , active polysulphide concentration is increased from 3 . 11 g / l to 4 . 01 g / l while the inactive polysulphide is decreased from 3 . 45 to 2 . 45 g / l ; after 240 minutes , the active polysulphide concentration is increased from 4 . 23 g / l to 5 . 31 g / l while the inactive polysulphide is decreased from 4 . 72 to 3 . 79 g / l ; and after heat treatment , the active polysulphide concentration is increased from 5 . 19 g / l to 5 . 92 g / l while the inactive polysulphide is decreased from 1 . 21 to 1 . 16 g / l ; bi 2 o 3 was mixed with mno 2 in different metal molar ratios . oxygen was employed as oxidant to regenerate the catalyst . polysulphide was generated at 90 ° c . with magnetic stirring . mno 2 ( 2 g / l ) was used catalytically and was regenerated constantly by bubbling oxygen ( flow rate : 20 ml / min ) through the liquor with a sparger . the starting white liquor had an effective alkali ea concentration of 80 g / l and a sulphide concentration ( as na 2 o ) of 40 g / l . reaction time was 120 minutes . the active polysulphide was measured by uv - vis analysis and the amount was determined by the peak intensity at 416 nm . the inactive polysulphide was determined as the difference between the amount of ps measured by gravimetric and by uv - vis ( spectrometric ) analyses . table 3 shows the results of applying different amounts of the co - catalyst . the optimum ratio of bi 2 o 3 to mno 2 under the conditions studied is 1 : 2 . this ratio gave 4 . 69 g / l of active polysulphide and 8 . 10 g / l of gravimetric polysulphide doubling the amount of bismuth to give a ratio of bi 2 o 3 to mno 2 of 1 : 1 only provided a marginal further improvement in active and gravimetric polysulphide concentrations . bi 2 o 3 , bi 2 s 3 or bi ( no 3 ) 3 . 5h 2 o was mixed with mno 2 in a 1 to 5 metal molar ratio . oxygen was employed as oxidant to regenerate the catalyst . polysulphide was generated at 90 ° c . with magnetic stirring . mno 2 ( 2 g / l ) was used catalytically and was regenerated constantly by bubbling oxygen ( flow rate : 20 ml / min ) through the liquor with a sparger . the starting white liquor had an effective alkali ea concentration of 80 g / l and a sulphide concentration ( as na 2 o ) of 40 g / l . reaction time was 120 minutes . the active polysulphide was measured by uv - vis analysis and the amount was determined by the peak intensity at 416 nm . the inactive polysulphide was determined as the difference between the amount of ps measured by gravimetric and by uv - vis ( spectrometric ) analyses . table 4 shows that similar results were obtained with all of these compounds . among the three bismuth compounds tested , bi 2 o 3 is preferred . the catalyst , mno 2 or , mno 2 combined with bi 2 o 3 in a 2 to 1 metal molar ratio , was reused three times by carefully removing the oxidized polysulphide liquor after reaction and adding the same amount of white liquor for the next reaction . oxygen was employed as oxidant to regenerate the catalyst . polysulphide was generated at 90 ° c . with magnetic stirring . mno 2 ( 2 g / l ) was used catalytically and was regenerated constantly by bubbling oxygen ( flow rate : 20 ml / min ) through the liquor with a sparger . the starting white liquor had an effective alkali ea concentration of 80 g / l and a sulphide concentration ( as na 2 o ) of 40 g / l . for each run the reaction time was 120 minutes . the active polysulphide was measured by uv - vis analysis and the amount was determined by the peak intensity at 416 nm . the inactive polysulphide was determined as the difference between the amount of ps measured by gravimetric and by uv - vis ( spectrometric ) analyses . table 5 shows bi helped to maintain the reactivity of mno 2 . comparing the first and the second run , the active polysulphide ( ps uv416 ) concentration decreased by 48 %, from 3 . 21 to 1 . 66 g / l , and the total amount of polysulphide ( ps gr ) decreased by 36 %, from 6 . 74 to 4 . 32 g / l , when no bi 2 o 3 was added . with bi 2 o 3 added , the active polysulphide concentration only decreased by 16 %, and the total amount of polysulphide decreased by 6 %. comparing the first and third run , the active polysulphide concentration decreased by 65 %, and the total amount of polysulphide decreased by 54 % when no bi 2 o 3 was added . with bi 2 o 3 added , the active polysulphide concentration only decreased by 23 %, and the total amount of polysulphide decreased by 13 %. this result is significant for polysulphide generating configurations where the catalyst is not reactivated by oxidation at high temperature . manganese oxides with different oxidation states : mno 2 , mn 2 o 3 or mn 3 o 4 was mixed with bi 2 o 3 in a 2 to 1 metal molar ratio . oxygen was employed as oxidant to regenerate the catalyst . polysulphide was generated at 90 ° c . with magnetic stirring . each manganese oxide compound ( 2 g / l ) was used catalytically and was regenerated constantly by bubbling oxygen ( flow rate : 20 ml / min ) through the liquor with a sparger . the starting white liquor had an effective alkali ea concentration of 80 g / l and a sulphide concentration ( as na 2 o ) of 40 g / l . reaction time was 120 minutes . the active polysulphide was measured by uv - vis analysis and the amount was determined by the peak intensity at 416 nm . the inactive polysulphide was determined as the difference between the amount of ps measured by gravimetric and by uv - vis ( spectrometry ). table 6 shows bismuth improves the performance of all the oxides particularly the lower oxide forms of manganese . with mno 2 , 1 . 58 g / l more active polysulphide and 1 . 54 g / l more gravimetric polysulphide were formed when bi 2 o 3 was added . with mn 2 o 3 , 2 . 33 g / l more active polysulphide and 2 . 94 g / l more gravimetric polysulphide were formed when bi 2 o 3 was added . with mn 3 o 4 ; 2 . 74 g / l of active polysulphide and 2 . 44 g / l of gravimetric polysulphide were formed when bi 2 o 3 was added . other heavy metals compounds in the same or adjacent groups in the periodic table , such as lead , antimony are active in the same way but not to the same extent as bismuth and suffer from the further drawbacks of higher solubility in sulphide liquors and toxicity . nickel also has activity but also has high solubility and toxicity . alfredsson , b ., samuelson , o . and sandstig , b . carboxyl end groups in sulfate and polysulfide pulps . svensk papperstidn . 66 ( 18 ): 703 ( 1963 ). clayton , d . w . and . salcai , a . multi - 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