US3574052A - Chemical pulping and bleaching in an enclosed reaction zone,by reduction of chlorate - Google Patents

Abstract

A PROCESS FOR THE TREATMENT OF CELLULOSIC MATERIAL IN SUBDIVIDED FORM INCLUDING THE STEPS OF FIRSTLY PROVIDING AN ENCLOSED REACTION ZONE FOR THE TREATMENT OF THE CELLULOSIC MATERIALS; SECONDLY PROVIDING A REACTANT LIQUOR PHASE IN THE REACTION ZONE; THIRDLY PROVIDING A SUPERPOSED GAS PHASE OVER THE REACTANT LIQUOR IN THE REACTION ZONE; AND FOURTHLY AGITATING THE CELLULOSIC MATERIAL IN THE ENCLOSED REACTION ZONE. THE IMPROVEMENT INVOLVES USING AS THE REACTANT LIQUOR PHASE, AN AQUEOUS LIQUOR COMPRISING A LIQUOR SOLUBLE CHLORATE AND A REDUCING AGENT FOR THE CHLORATE, THE REDUCING AGENT BEING PRESENT IN 0.1 TO 2.0 MOLAR EXCESS BASED UPON THE AMOUNT OF CHLORATE USED. BECAUSE OF THE SERIES OF STEPS CARRIED OUT AND THE PARTICULAR COMPOSITION OF THE REACTANT PHASE, THE GAS PHASE SUPERPOSED OVER THE REACTANT LIQUOR IN THE ENCLOSED REACTION ZONE CONTAINS EVOLVED CHLORINE DIOXIDE AND/OR CHLORINE THUS PREVENTING ANY ENCRUSTATION WHICH MAY FORM ON THE OUTER WALLS OR SURFACES OF THE CELLULOSIC MATERIALS.

Description

FIPSEU? CHEMICAL PULPING AND BLEACHING IN AN ENCLOSED REACTION ZONE, BY REDUCTION OF CHLORATE Gothe Oscar Westerlund and Kin Seto, Vancouver, British Columbia, Canada, assignors to Chemech Engineering Ltd., Vancouver, British Columbia, Canada No Drawing. Filed July 7, 1967, Ser. No. 651,712 Claims priority, application Canada, Feb. 28, 1967,

Int. (:1. 1521c 3/06 US. Cl. 162-64 22 Claims ABSTRACT OF THE DISCLOSURE A process for the treatment of cellulosic material in subdivided form including the steps of firstly providing an enclosed reaction zone for the treatment of the cellulosic materials; secondly providing a reactant liquor phase in the reaction zone; thirdly providing a superposed gas phase over the reactant liquor in the reaction zone; and fourthly agitating the cellulosic material in the enclosed reaction zone. The improvement involves using as the reactant liquor phase, an aqueous liquor comprising a liquor soluble chlorate and a reducing agent for the chlorate, the reducing agent being present in 0.1 to 2.0 molar excess based upon the amount of chlorate used. Because of the series of steps carried out and the particular composition of the reactant phase, the gas phase superposed over the reactant liquor in the enclosed reaction zone contains evolved chlorine dioxide and/or chlorine thus preventing any encrustation which may form on the outer walls or surfaces of thc cellulosic materials.

This invention relates to the treatment of cellulosic materials in subdivided form. In one aspect, it relates to the pulping and/or bleaching of wood chips or sawdust. In another aspect, it relates to the delignification and subsequent 'bleaching of lignocellulosic fibrous materials.

It is now well known that both chlorine gas and chlorine, dioxide are effective agents both for the delignification of cellulosic materials and for the treatment of unpulped wood materials. (See U.S. Patent No. 1,843,467 issued Feb. 2, 1932 to J. Traquair et al.)

One known process for bleaching of wood pulp involves preoxidizing the pulp fibers with chlorine dioxide. (See a paper by Singh and Andrews, delivered at the International Pulp & Paper Conference, Murray Bay, Quebec, June 22-25, 1965.) Another known procedure involves the addition of chlorine dioxide to the chlorination stage in a wood pulp bleaching process. (See a paper by Rapson and Anderson, delivered at the International Pulp & Paper Conference, Murray Bay, Quebec; also Canadian Patent No. 552,007 issued Jan. 21, 1958 to Stone and Matarese.)

Another process heretofore suggested involved the addi tion of chlorate at the chlorination stage of a wood pulp bleaching procedure, allegedly to produce stronger pulp. (See US. Patent No. 2,903,326 issued Sept. 8, 1959 to I. B. Heitman and Canadian Patent No. 586,838 issued Nov. 10, 1959 to J. B. Heitman.)

Another process comprises bleaching a cellulosic material using a first chlorination stage, followed by several stages using hypochlorite and/or chlorine dioxide as subsequent alkali treating and bleaching stages.

Another process suggested was a low temperature disincrustation procedure involving impregnation of fibrous materials with chlorateand then reacting the moist material with gaseous hydrogen chloride. (See Canadian Patent No. 546,718 issued Sept. 24, 1957 to Ladislav I. Rys.)

Another process suggested was a delignification of ice pulping material with a chlorate employing a catalyst for the reduction reaction. (See Canadian Patent No. 550,735 issued Dec. 24, 1957 to Paola Marpillero.) Another similar procedure in the preparation of cellulose involves employing a catalyst in the chlorate solution. (See Canadian Patent No. 283,573 issued Sept. 25, 1928 to Arthur Franz.)

Yet another process involves bleaching cellulosic materials employing both a chlorine generator and a chlorine dioxide generator in conjunction with the bleaching stages. (See Canadian Patent No. 452,351 issued Nov. 2, 1948 to Harry N. Tatomer.)

However, it was reported by Rapson (TAPPI 42, 642- 49) that activated chlorate failed to result in desirable advantages in the bleaching of pulp when compared to chlorine dioxide.

An object of one broad aspect of this invention is the provision of an improved cellulosic material treating procedure.

An object of another aspect of this invention is the provision of a pulping process which can yield high grade pulp when applied to various wood species.

An object of yet another aspect of this invention is the provision of a process which may be controlled to yield either a partially bleached wood pulp or a fully bleached wood pulp.

An object of yet another aspect of this invention'is the provision of a process which may be used as a secondary pulping process.

An object of still another aspect of this invention is the provision of a process for the delignification of lignocellulosic materials.

An object of a further aspect of this invention is the provision of a process for the bleaching of cellulosic materials.

An object of yet a further aspect of this invention is the provision of a one step process for the pulping and bleaching of wood in subdivided form.

An object of yet another aspect of this invention is the provision of a multistep process for the pulping of wood in sub-divided form and the subsequent further bleaching of the so-produced wood pulp.

An object of an ancillary aspect of this invention is the provision of a process which may be used for the pulping of wood in sub-divided form, while permitting the recov cry of chemicals and products from the pulping solution.

By one broad aspect of this invention a process is pro vided for the treatment of cellulosic materials in subdivided form which comprises the steps of (1) providing an enclosed reaction zone; (2) providing a reactant liquor phase in the reaction zone; (3) providing a superposed gas phase over the reactant liquor in the reaction zone; and (4) agitating cellulosic material in the reaction zone; wherein (a) the reactant liquor phase comprises an aqueous liquor comprising a water soluble chlorate and a. reducing agent for the chlorate, the reducing agent being present in 0.1 to 2.0 molar excess based on the amount of chlorate; and (b) the gas phase containing evolved chloride dioxide and/ or chlorine.

In a preferred aspect of the invention the agitation step is conducted at a temperature of less than C. at pressures between atmospheric and up to 11 atmospheres and a pH of less than 4.

The reducing agent may be acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid.

In one preferred embodiment the reactant liquor phase comprises an aqueous liquor comprising a water soluble chlorate, a water soluble chloride and an acid reducing agent for the chloride which is acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid,

In another embodiment the reactant liquor comprises a water soluble chlorate, an organic reducing agent which is either oxalic acid or methanol and an acid. reducing agent for the chlorate which is acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid.

By yet another embodiment of the invention, the reactant liquor phase comprises an aqueous liquor comprising a water soluble metal chlorate, sulfur dioxide, and an acid reducing agent for the chlorate which is acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid or nitric acid.

Basically, then, this invention resides in the use, as a pulping, or bleaching or delignifying liquor, of a solution of a reducible chlorate and a reducing agent for the chlorate, whereby to form chlorine dioxide, in situ. There are many such procedures for converting chlorate to chlorine dioxide which are within the scope of the present invention. Among them are the following non-limiting examples:

(A) REDUCTION OF A METAL CHLORATE WITH AN ACID- Many metal chlorates are useful in such procedure. Among the metal chlorates which are within the scope herein are the chlorates of e.g. ammonium, sodium, calcium, potassium, lithium and magnesium. It is preferred that the metal chlorate be a water soluble metal chlorate, e.g. an alkali metal chlorate, preferably sodium chlorate.

Among the acids which may be used in this procedure are organic acids, e.g. acetic acid and inorganic acids, e.g. hydrochloric acid, sulphuric acid, phosphoric acid, and nitric acid. Particularly preferred is hydrochloric acid.

A particularly advantageous procedure is that described and claimed in Canadian patent application Ser. No. 972,150, represented by the following equations:

NaClO +2HCl ClO /2Cl +NaCl+H O (l) or at higher acidity;

NaClO 6HCl 3Cl +NaCl+ 3H O (2) (B) REDUCTION OF A METAL CHLORATE WITH AN ACID IN THE PRESENCE OF A METAL CHLORIDE Many metal chlorates are useful in such procedure. Among the metal chlorates which are within the scope herein are the chlorates of e.g. sodium, potassium and calcium. It is preferred that the metal chlorate be a water soluble metal chlorate, e.g. an alkali metal chlorate, preferably sodium chlorate.

Among the acids which may be used in this procedure are organic acids, e.g. acetic acid and inorganic acids, e.g. hydrochloric acid, sulphuric acid, phosphoric acid, and nitric acid. Particularly preferred is sulphuric acid.

Among the metal chlorides which are within the scope herein are the chlorides of e.g. sodium, potassium, calcium, magnesium and ammonium. It is preferred that the metal chloride be water soluble, e.g., an alkali metal chlo ride, preferably sodium chloride.

A particularly advantageous procedure is disclosed and claimed in Canadian Patent No. 452,351 issued Nov. 2, 1948 to H. N. Tatomer, represented by the following equation:

(C) REDUCTION OF A CHLORATE WITH AN ORGANIC REDUCING AGENT IN THE PRES- ENCE OF AN ACID Many metal chlorates aer useful in such procedure. Among the metal chlorates which are within the scope herein are the chlorates of e.g. sodium, potassium, calcium, magnesium and ammonium. However, sodium chlorate is preferred.

Among the acids which may be used in this procedure are organic acids, e.g., acetic acid and oxalic acid and inorganic acids, e.g. hydrochloric acid, sulphuric acid, phosphoric acid, and nitric acid. Particularly preferred is sulphuric acid.

Among the organic reducing agents which are within the scope herein are e.g. methanol, and oxalic acid. Particularly preferred is methanol.

A particularly advantageous procedure is disclosed and claimed in Canadian Patent No. 434,213 issued Apr. 16, 1946 to C. A. Hampel et al. represented by the following equation:

(D) REDUCTION OF A METAL CHLORATE WITH SULPHUR DIOXIDE IN THE PRESENCE OF AN A-CID Many metal chlorates are useful in such procedure. Among the metal chlorates which are within the scope herein are the chlorates of e.g. sodium, potassium and calcium. It is preferred that the metal chlorate be a water soluble metal chlorate, e.g. an alkali metal chlorate, preferably sodium chlorate.

Among the acids which may be used in this procedure are organic acids, e.g. acetic acid and inorganic acids, e.g. hydrochloric acid, sulphuric acid, phosphoric acid, and nitric acid. Particularly preferred is sulphuric acid.

A particularly advantageous procedure is that disclosed and claimed in Canadian Patent No. 533,803 issued Nov. 27, 1956 to F. H. Dole represented by the following equation:

H2504 2NnClO3+SOz 2CIOz-I-NMSO4 A particularly preferred reagent chlorate liquor is the product produced by the electrolysis of chlorides. While the chloride may be any water soluble metal chloride, for example sodium, potassium, calcium and magnesium, it is preferred that the chloride be sodium chloride. The reagent liquor Will then contain NaClO NaCl, NaOCl, and HOCl. It may also contain dichromate if it is not treated to recover that compound.

The process herein described may be carried out in one step or in several stages. In addition it may be conducted as a batch process or as a continuous process.

It has been found that the size of the wood chips significantly affected the treatment time required for pulping. As the size of the wood chips increased from 2 mm. thickness x 4 mm. width x 6 mm. length to 3 mm. thickness x 12 mm. width x 25 mm. length, it was found that the pulping time, under similar conditions of pulping reagent and reaction temperature, was increased from 10 to 30 times.

The following examples are given to illustrate aspects of the present invention. In all cases, the reaction vessel was a laboratory combined digester and bleaching apparatus comprising a 1 inch diameter glass tube, 24 inches long.

Example I Wood chips were immersed in a chlorate electrolytic cells electrolyte containing up to:

650 g.p.l. NaClO 150 g.p.l. NaCl,

3 g.p.l. total NaOCl and HOCl, and 3 g.p.l. Na Cr O To this solution was added methanol in a ratio of approximately 1 part to 7 parts chlorate. 36 N sulphuric acid was then added at a controlled feed rate in order to prevent too sudden a temperature rise and too large an excess of the formation of chlorine dioxide and/or chlorine. The temperature of the reaction was approximately C., and the pressure was at or about atmospheric.

It was found that fast pulping resulted (a Kappa Number of less than 10 in less than 15 minutes) and that there was substantial bleaching (a GE. brightness above 60).

These results were achieved when a substantial excess (i.e. about 0.1 to 2:0 molar excess) of reagent chemicals were used compared to the requirements for slow pulpinn. This resulted in chlorine dioxide and/or chlorine being present in the vapor phase above the pulping liquor. Such bleaching agents are preferably drawn oil to be used in a second stage, or in several other stages for further bleaching and/or pulping.

Example H Example I was repeated, except that the temperature was increased to 120-130 C. The produced gases (C10, and/or C1 were constantly bled otf. Similar Kappa numbers and GE. Brightness numbers were achieved in a few minutes e.g. 2 minutes time.

It is observed that at such higher temperatures the unreacted methanol vaporized. Such vaporized methanol may be condensed and returned to the system.

Example III Example I was repeated except that the acid used was dilute sulphuric acid, of 6 N. The pulped product has substantially the same characteristics except that the reaction time was increased to about 10 hours.

Examples IV, V and VI ture was necessary in order to avoid undigested and discolored cores of the wood chips. The temperature should preferably be less than 120 C. if the pH is below 2.

Examples VII-XII Example XIX Western Hemlock and Spruce Wood Chips were immersed in a solution containing g.p.l. of sodium chlorate acidified to pH 2 with muriatic acid and then additional acid to an amount equal to the stoichiometry ratio of HCl versus NaClO for production of two moles chlorine dioxide and one mole chlorine. The solution releases chlorine dioxide and chlorine when the temperature is raised above 30 C.

The pulp produced had a Kappa Number equal to 24 and GE. Brightness of 54 after about two hours timeat 70 C. and 100 p.s.i.g. The amount of bleaching agent was almost fully reacted in the pulping process and the amount of bleaching agent in the vapor phase was negligible. The residual chlorate in the treatment liquor was below 0.5 g.p.l.

Conventional bleaching sequences after the above pulping process resulted in fully bleached pulp 90 GE.

brightness and higher with minimum degradation of the pulp.

. Example XX Example XIX was repeated, but the reaction temperature was increased to 150 C. and pressure maintained was up to p.s.i.g. It was found that, for the same degree of pulping,.a significantly shorter treatment time,

i.e., about 45 minutes, was necessary. However, this re sulted in lower pulp yields.

Examples XXI and XXII Examples XXIII and XXIV Examples XIX and XX were repeated, except that the wood chips were subjected to a pre-steam treatment. It was found that the amount of chemicals required were reduced.

Examples XXV and XXVI Examples XIX and XX were repeated, except that the wood chips were pre-treated with alkali. It was found that the amount of chemicals was reduced.

Examples XXVII and XXVIII Examples XIX and XX were repeated, except that the wood chips 'were pre-treated with sulphur dioxide. The excess sulphur dioxide may be used as a reducing agent for the chlorate. It was found that the amount of chemicals required was reduced.

In any of the above twenty-eight examples, the treatment solution may be resaturated with chlorate and makeup acid added while .controlling the water balance by means of released vapor. The solution in the pulp may then be removed. Thus, the dissolved wood products could be concentrated and values recovered.

' The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1'. A process for the treatment of cellulosic materials in sub-divided form, which process comprises the steps of:

(1) providing an enclosed reaction zone; (2) providing a reactant liquor phase in said reaction zone;

(3) providing a superposed gas phase over said reactant liquor in said reaction zone; and

(4) agitating said subdivided cellulosic material in said enclosed reaction zone; wherein (a) said reactant liquor phase comprises an aqueous liquor comprising a water soluble chlorate and a reducing agent for said chlorate, said reducing agent being present in 0.1 to 2.0.molar excess, based on the amount of chlorate and (b) said gas phase contains evolved chlorine dioxide and/ or chlorine.

2. The process of claim 1 wherein the said agitation step (4) is conducted at a temperature of less than C., at a pressure between atmospheric and up to 11 atmospheres and at a pH of less than 4.

3. The process of claim 1 including the preliminary step of subjecting the sub-divided cellulosic material to a steam pre-treatin-g step.

4. The process of claim 1 including the preliminary step of subjecting the sub-divided cellulosic material to an alkali pretreating step.

5. The process of claim 1 including the preliminary step of subjecting the sub-divided cellulosic material to a pretreatment with sulphur dioxide.

6. The process of claim 1 wherein said reducing agent is selected from a group consisting of acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid.

7. The process of claim 6 wherein said metal chlorate comprises sodium chlorate andwherein said acid comprises hydrochloric acid.

8. The process of claim 7 wherein said agitation reaction (4) is conducted at a temperature of less than 150 C., at pressures between atmospheric and up to 11 atmospheres, and at a pH of less than 4.

9. The process of claim 1 wherein said reactant liquor phase comprises an aqueous liquor comprising a water soluble metal chlorate, a water soluble metal chloride, and an acid reducing agent for said chlorate, selected from the group consisting of acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid.

10. The process of claim 9 wherein the metal chlorate comprises sodium chlorate, wherein the metal chloride comprises sodium chloride and wherein the acid comprises sulfuric acid.

11. The process of claim 10 wherein said agitation reaction (4) is conducted at a temperature of less than 150 C., at pressures between atmospheric and up to 11 atmospheres, and at a pH of less than 4.

12. The process of claim 1 wherein said reactant liquor phase comprises a water soluble chlorate, an organic reducing agent selected from the group consisting of oxalic acid and methanol, and an acid reducing agent for said chlorate selected from a group consisting of acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid.

13. The process of claim 12 wherein the chlorate comprises hypochlorous acid, wherein the organic reducing agent comprises methanol and wherein the acid reducing agent comprises sulfuric acid.

14. The process of claim 13 wherein said agitating step (4) is conducted at a temperature of less than 150 C., at pressures between atmospheric and up to 11 atmospheres, and at a-pH of less than 4.

15. The process of claim 1 wherein said reactant liquor phase comprises an aqueous liquor comprising a water soluble metal chlorate, sulfur dioxide, and an acid reducing agent for said chlorate, selected from the group consisting of acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid and nitric acid.

16. The process of claim 15 wherein the metal chlorate comprises sodium chlorate and wherein the acid comprises sulfuric acid.

117. The process of claim 16 wherein said agitation step (4) is conducted at a temperature of 150 C. at pressures between atmospheric up to 11 atmospheres, and at a pH of less than 4.

.18. The process of claim 1 including the step of withdrawing excess gaseous chlorine dioxide and/or chlorine from the superposed gas phase over said reactant liquor in said reaction zone.

19. The process of claim 9 including the step of withdrawing excess gaseous chlorine dioxide and/or chlorine from the superposed gas phase over said reactant liquor in said reaction zone.

20. The process of claim 12 including the step of withdrawing excess gaseous chlorine dioxide and/or chlorine from the superposed gas phase over said reactant liquor in said reaction zone.

21. The process of claim 15 including the step of withdrawing excess gaseous chlorine dioxide and/or chlorine from the superposed gas phase over said reactant liquor in said reaction zone.

22. The process of claim 18 wherein the withdrawn gaseous chlorine dioxide and/ or chlorine is employed for further treatment of the cellulosic material.

References Cited UNITED STATES PATENTS 1,828,338 10/ 1931 Neumann 162-73 2,065,396 12/ 1936 Richter 162--64 2,203,205 6/ 1940 Rawling 162-88 2,730,426 1/ 1956 Becker 162-66 FOREIGN PATENTS 452,351 11/1948 Canada.

533,803 11/1956 Canada.

546,718 9/1957 Canada.

8. LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner US. Cl. X.R.