Regeneration of chlorine dioxide for pulp treatment

Claim 2

The process of claim 1 wherein said alkali treatment is accomplished utilizing an aqueous sodium hydroxide solution.

Claim 3

A process for the production of a pulp of cellulosic fibrous material which comprises contacting a cellulosic fibrous material with a chlorine dioxide-containing material to provide a treated material, subjecting said treated material to caustic extraction to provide a pulp and a spent extraction solution, bleaching said pulp to provide a bleached pulp and a spent bleaching solution, oxidizing at least one of said spent extraction solution and said spent bleaching solution to form a material comprising alkali metal chloride and alkali metal carbonate, and subjecting said alkali metal carbonate to chlorination utilizing a chlorine-containing material selected from hydrogen chloride and chlorine, thereby converting said alkali metal carbonate to alkali metal chlorate and alkali metal chloride or alkali metal hypochlorite and alkali metal chloride when said gaseous material is chlorine and converting said alkali metal carbonate to alkali metal chloride when said gaseous material is hydrogen chloride.

Claim 4

A process for the production of a pulp of a cellulosic fibrous material which comprises forming chlorine dioxide by reduction in aqueous acid solution of an alkali metal chlorate, treating a cellulosic fibrous material with said chlorine dioxide to provide a treated material, forming an alkali metal hydroxide solution and chlorine by electrolysis of an aqueous alkali metal chloride solution, contacting said treated material with said alkali metal hydroxide solution to remove residual chlorine values and soluble organic materials from said treated material and to provide a pulp and a spent alkali metal hydroxide solution, oxidizing said spent alkali metal hydroxide solution to form a material comprising alkali metal chloride and alkali metal carbonate, and subjecting said alkali metal carbonate to chlorination utilizing a chlorine-containing material selected from hydrogen chloride and chlorine.

Claim 5

The process of claim 5 wherein said chlorine dioxide is generated by reaction of an aqueous solution of an alkali metal chlorate and hydrogen chloride in a reaction zone while simultaneously evaporating water from said aqueous solution.

Claim 6

The process of claim 6 wherein chlorine dioxide and chlorine are formed by reaction in a reaction zone of an alkali metal chlorate with hydrogen chloride in an aqueous reaction medium while simultaneously evaporating water from said medium to remove said chlorine dioxide and chlorine from said zone and deposit alkali metal chloride from said medium in said zone.

Claim 7

The process of claim 7 whErein said alkali metal chlorate is formed at least partly by electrolysis of an aqueous solution of an alkali metal chloride.

Claim 8

The process of claim 8 wherein said alkali metal chloride is constituted at least in part by said alkali metal chloride deposited in said reaction zone.

Claim 9

The process of claim 9 wherein said alkali metal chlorate is sodium chlorate and said alkali metal hydroxide is sodium hydroxide.

Claim 10

The process of claim 5 wherein said chlorine dioxide is generated together with chlorine by reaction of an aqueous solution of an alkali metal chloride and hydrogen chloride in a reaction zone and said chlorine dioxide and chlorine are removed from said reaction zone as a gaseous mixture with an inert gas.

Claim 11

The process of claim 11 wherein said inert gas is air.

Claim 12

The process of claim 11 wherein a spent reaction liquor containing alkali metal chloride, unreacted alkali metal chlorate and unreacted hydrogen chloride is removed from said reaction zone and said unreacted hydrogen chloride is utilized to achieve said chlorination whereby said alkali metal carbonate is converted to alkali metal chloride.

Claim 13

The process of claim 5 wherein said gaseous material is chlorine and alkali metal chlorate and alkali metal chloride are formed in said chlorination reaction from said alkali metal carbonate, said alkali metal chlorate and alkali metal chloride so formed being utilized respectively to form chlorine dioxide and alkali metal hydroxide.

Claim 14

The process of claim 5 wherein said chlorination is achieved utilizing chlorine and said chlorine is formed by said electrolysis of alkali metal chloride solution.

Claim 15

The process of claim 5 wherein said chlorination is achieved utilizing chlorine and alkali metal hypochlorite and alkali metal chloride are formed, said alkali metal hypochlorite and alkali metal chloride being utilized alternatively first to form alkali metal chlorate and subsequently to form chlorine dioxide, or to form alkali metal hydroxide.

Claim 16

A process for the production of a pulp of cellulosic fibrous material which comprises forming an aqueous solution of alkali metal chlorate and hydrogen by electrolysis of an aqueous alkali metal chloride solution, forming chlorine dixoide and chlorine by reaction in an aqueous solution of hydrogen chloride and an alkali metal chlorate in a reaction zone while simultaneously evaporating water from said solution to remove said chlorine dioxide and chlorine from said reaction zone and to deposit alkali metal chloride in said zone, said alkali metal chlorate being constituted partially by said alkali metal chlorate formed by electrolysis, removing said alkali metal chloride from said zone, forming an aqueous alkali metal hydroxide solution, hydrogen and chlorine by electrolysis of an aqueous solution of an alkali metal chloride, contacting a cellulosic fibrous material with said chlorine dixoide to provide a chlorine dioxide treated material, recovering residual chlorine values of said chlorine dioxide and removing soluble organic materials from said chlorine dioxide-treated material by contacting said chlorine dioxide-treated material with said alkali metal hydroxide solution to provide a pulp and a spent alkali metal hydroxide solution, oxidizing said spent solution to form carbon dioxide and a material comprising alkali metal chloride and alkali metal carbonate, forming an aqueous solution containing said alkali metal carbonate and said alkali metal chloride, subjecting said alkali metal carbonate to chlorination utilizing part of said chlorine to form alkali metal chlorate and alkali metal chloride, forming said hydrogen chloride by reaction between the remainder of said chlorine and part of said hydrogen formed in said electrolysis of alkali metal chloride to form alkali metal hydroxide, and passing said latter alkali metal chlorate and alkali metal chloride to said reaction zone.

Claim 17

The process of claim 17 wherein said alkali metal is sodium.

Claim 18

The process of claim 17 including The steps of washing said chlorine dioxide-treated material and said pulp and forwarding the spent wash water from said steps with said spent solution to said oxidizing step.

Claim 19

The process of claim 17 including the steps of washing said chlorine dioxide-treated material and said pulp, the spent wash water from washing said pulp being utilized as the wash water for said chlorine dioxide-treated material, and passing the spent wash water from washing said chlorine dioxide-treated material with said spent solution to said oxidizing step.

Claim 20

The process of claim 17 wherein said cellulosic fibrous material is wood.

Claim 21

A process for the production of a pulp of cellulosic fibrous material which comprises forming an aqueous solution of alkali metal chlorate and hydrogen by electrolysis of an aqueous alkali metal chloride solution, forming chlorine dioxide and chlorine by reaction in an aqueous solution of hydrogen chloride and an alkali metal chlorate constituted at least partially by said alkali metal chlorate formed by electrolysis, in a reaction zone while simultaneously evaporating water from said solution to remove said chlorine dioxide and chlorine from said reaction zone as a gaseous mixture with said evaporated water, and to deposit alkali metal chloride in said zone, removing said alkali metal chloride from said zone, forming an aqueous alkali metal hydroxide solution, hydrogen and chlorine by electrolysis of an aqueous solution of an alkali metal chloride, separating an aqueous solution of chlorine dioxide from said gaseous mixture, contacting a cellulosic fibrous material with said chlorine dioxide to provide a chlorine dioxide-treated material, washing said latter material with a first wash water to provide a first spent wash water, subjecting the resulting washed material to caustic extraction with said alkali metal hydroxide solution to remove residual chlorine dioxide values and soluble organic materials from said washed material and to provide a pulp and a spent extraction solution containing residual alkali metal hydroxide values, washing said pulp with a second wash water to provide a second spent wash water, bleaching said latter washed pulp with a bleaching agent constituted by chlorine from said gaseous mixture to provide a bleached pulp and a spent bleaching agent, washing said bleached pulp with a third wash water to provide a bleached and washed pulp and a third spent wash water, said third spent wash water constituting said second wash water and said second spent wash water constituting said first wash water, mixing said spent bleaching agent and said first spent wash water with said spent extraction solution whereby chlorine values in said first spent wash water and said sepnt extraction solution react with part of said residual alkali metal hydroxide to provide a waste liquor, oxidizing said waste liquor to form carbon dioxide and a material comprising alkali metal chloride and alkali metal carbonate, forming an aqueous solution containing said alkali metal chloride and alkali metal carbonate, subjecting said alkali metal carbonate to chlorination utilizing part of said chlorine formed by electrolysis of alkali metal chloride to form alkali metal hydroxide to convert said alkali metal carbonate to alkali metal chlorate and alkali metal chloride, and forming said hydrogen chloride by reaction between the remainder of said chlorine and part of said hydrogen formed in said electrolysis of alkali metal chloride to form alkali metal hydroxide.

Claim 22

In a process of forming a white liquor, including the steps of forming a green liquor from a solid mass containing sodium carbonate and sodium chloride and an aqueous material, causticizing said green liquor to form a white liquor containing sodium hydroxide, sodium chloride and uncausticized sodium carbonate, and concentrating said white liquor to deposit therefrom sodium chloride and sodium carbonate and to provide concentrated white liquor, the improvement which comrpises forming an aqueous solution from tHe deposited sodium chloride and sodium carbonate, and reacting said sodium carbonate in said aqueous solution with a chlorine-containing material selected from chlorine and hydrogen chloride.

Claim 23

The process of claim 23 wherein said solid mass additionally contains sodium sulphide and said green liquor contains said sodium sulphide.

Claim 24

The process of claim 23 wherein said solid mass is formed by fractionating a smelt containing sodium sulphide, sodium chloride and sodium carbonate to separate said sodium sulphide from said smelt, said smelt being formed in the recovery of spent chemicals from the pulping of cellulosic fibrous material.

Claim 25

The process of claim 25 wherein said fractionation is achieved by contacting said smelt with said concentrated white liquor to dissolve said sodium sulphide from said smelt into said white liquor.

Claim 26

The process of claim 25 wherein said fractionation is achieved by contacting said smelt with water to dissolve preferentially sodium sulphide from said smelt.

Claim 27

The process of claim 25 wherein said fractionation is achieved by dissolving said smelt in water, and evaporating the resulting solution to deposit said solid mass containing sodium chloride and sodium carbonate therefrom.

Claim 28

A process for the production of a pulp of a cellulosic fibrous material which comprises pulping said cellulosic fibrous material with a pulping liquor, separating pulped material from spent pulping liquor, forming a sodium chloride- and sodium carbonate-containing smelt from said spent pulping liquor, forming a sodium chloride- and sodium carbonate-containing white liquor from said smelt, concentrating said white liquor to deposit therefrom sodium chloride and sodium carbonate, forming an aqueous solution of the deposited sodium chloride and sodium carbonate, reacting said sodium carbonate in said aqueous solution with a chlorine-containing gaseous material selected from chlorine and hydrogen chloride thereby forming a reaction product consisting of sodium chlorate and sodium chloride when said gaseous material is chlorine and sodium chloride when said gaseous material is hydrogen chloride, forming sodium chlorate by electrolysis of an aqueous solution of sodium chloride, forming an aqueous solution in a reaction zone of sodium chlorate, sodium chloride and sulphuric acid, generating a gaseous mixture of chlorine dioxide and chlorine from said aqueous solution and removing said mixture from said reaction zone, subjecting said pulp after removal of said spent pulping liquor to a bleaching operation which includes bleaching with one or more of said gaseous mixture of chlorine dioxide and chlorine, and utilizing said reaction product of said sodium carbonate and said chlorine-containing gaseous material and said deposited sodium chloride in at least one of the formation of said sodium chlorate and the formation of said gaseous mixture of chlorine dioxide and chlorine.

Claim 29

The process of claim 25 wherein said aqueous solution in said reaction zone is maintained at its boiling point and said reaction zone is subjected to a sub-atmospheric pressure, whereby said gaseous mixture of chlorine dioxide and chlorine is removed from said reaction zone by steam formed from said aqueous solution.

Claim 30

The process of claim 25 wherein spent chemicals are recovered from said bleaching operation and wherein said sodium chloride- and sodium carbonate-containing white liquor is formed by dissolving said smelt in an aqueous material including said spent chemicals to provide a green liquor and causticizing a substantial proportion of the sodium carbonate content of said green liquor.