US2928825A - Catalysis of the ageing of alkali cellulose - Google Patents

Description

Mgrh 15, 1960 B. LEoPoLD ETAL CATALYSIS OF THE AGEING OF ALKALI CELLULOSE Filed Sept. 2, 1958 Hmoo e o m .Emoo e Qn ...moo e QN Hmoo .EE o. 5,58

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CATALYSIS OF THE AGEING F ALKALI CELLULOSE Bengt Leopold, Donald B. Mutton, and William R. Saxton, all of Hawkesbury, Ontario, Canada, assrgnors to Canadian International, Paper Company, Montreal, Quebec, Canada, a corporation of Canada Application September 2, l1958, Serial No. 758,446

8 Claims. (Cl. 260-233) This invention relates broadly to the depolymerization of cellulose. More particularly, the invention 1s concerned with the catalytic ageing or depolymerization of .alkali cellulose obtained from various cellulosic materials such as wood, refined cotton, etc., to decrease its viscosity. The invention finds its greatest application 1n the viscose ture. The invention is also of particular value in ageing or depolymerizing alkali cellulose for production of cellophane, cellulose` ethers, or any other cellulosic products in the manufacture of which alkali cellulose is an intermediate product.

The manufacture of viscose rayon and cellophane employs solutions of cellulose. In order to obtain solutions of low enough viscosity to handle conveniently, the molecular weight of the cellulose must be reduced considerably from its original value in the wood, cotton or other cellulosic material from which it is obtained. This cellu- .lose depolymerization is carried out mainly in the case of wood during the cooking of the wood, the bleaching of the pulp, and the ageing of the alkali cellulose. Depolymerization by bleaching is expensive to the pulpvmanufacturer since it consumes large quantities of chemicals which are not'inexpensive and it reduces yield. Ageing of alkali cellulose may require a considerable'length of time and itis expensive and inefcient for the rayon manumerization during ageingcould be increased suiciently, then all or rnost of the degradation now carried out during the bleaching and ageing steps could be performed -during the ageing period alone, and even the ageingztime could be reduced. This would enable the rayon manu- -facturer to save time and reduce costs and the pulp manu- -facturer to reduce chemical costs as well as to sell higher viscosity pulps which might yield improved rayon yarn of caustic soda as'a steeping liquid. To effect necessary .economy it is essential to reuse the caustic steeping solu- 4tions for treating subsequent batches of pulp. When the -transition metal catalyst is relatively soluble in the steepq ing alkali, variable amounts of the catalyst are retained by the steeping liquid when separated from the alkali cellulose. This leads to large variations in ageing reactivity imparted to the `alkali cellulose subsequently produced with the result that viscosity control is difcult.

This is especially true in the case of cobalt compounds which are much moreactive catalysts than compounds of manganese or iron. f

We have discovered that in accordance with the present If the rate of depoly-v 2,928,825 Patented Mar. 15,

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invention certain organic complexes or chelate com pounds of cobalt are not lonly substantially completely insoluble in water and steeping caustic, but what is more important and unexpected, these complexes retain the ability to catalyze the ageing of alkali cellulose. These alkali-insoluble complexes not only catalyze the ageing o'f alkali cellulose, but they are retained bythe alkali cellulose and do not contaminate the steeping caustic. Consequently, the present invention vmakes itv possible lto effectivelycatalyze the ageing of the alkali cellulosewithout contaminating the steeping caustic, thereby permitting .reuse of the steeping caustic without the concomitant variations in ageing reactivity which have plaguedthe Vprior art. Since the steeping caustic, after separation from the cellulose, contains substantially no catalytic cobalt complex or chelate compound, it can be reused with the next batch of cellulose to which an exact amount of catalyst has been added to produce controlled ageing'of the cellulose. During the research investigation which resulted in the present invention it was found that only certain organic complexes or chelate compounds'of cobalt are substantially insoluble in steeping caustic and yet retain the ability to catalyze the ageing or depolymerization of alkali cellulose.

lThe process of the invention provides greater control over the degree of an rate of depolymerization. This control is important since too much depolymerization results in weakened rayon fiber strength.

It is an object of the present invention to provide improvements in the depolymerization of cellulose.

It is also an object of the present invention to provide an improved process for the controlled depolymerization of cellulose in the manufacture of viscose rayon and cellophane.

which are substantially insoluble in steeping alkali and yet catalyze the ageing of alkali cellulose and which d0 not contaminate the steeping alkali.

The foregoing objects, as well as others,.wi1l be apparent to those skilled in the art from the present description, taken in conjunction with the accompanying coordinate diagram illustrating the effect of varying amounts of one of the cobalt complex catalysts on the ageing of Yalkali cellulose.

In accordance with the process of the present invention for depolymerizing cellulose, a small amount of an alkaliinsoluble cobalt complex or coordinate compounds as hereinafter dened is brought into the presence of cellulose, such as wood pulp, and steeping alkali to catalyze cellulose depolymerization. Since such processes as the viscose process and the manufacture of cellulose ethers involve conversion of cellulose into alkali cellulose, usually by steeping sheets of cellulose in an equeous caustic soda solution containing from about 17 to 25% of caustic soda, it is desirable for use in that process to ,add the cobalt complex catalyst to the cellulose prior to the steeping operation. After the cellulose has been steeped sufliciently in the alkali to substantially convert the cellulose to alkali cellulose, the alkali cellulose is separated from the steeping alkali by draining and pressing. The

'alkali cellulose, after comminution, is permitted t0 age essere@ cpbalt complex is sprayed or striped on to the formed pulp sheet as it passes into the drier on the pulp machine or into the cutter. Alternatively, dilute solutions of .the cobalt complexes in an organic liquid, such as chloro` folim, may be employed. In accordance with another method, lthe cobalt complex may be formed in situ on rthe cellulose by adding a soluble salt of cobalt, such as YAcobalt chloride, with, the insolubilizing organic complexing agent, the latter being added in excess of the ,stoichiometric amounts necessary to react with and complex substantially all the cobalt chloride.

Although any amount of cobalt complex catalyst may be added Yto the cellulose, it is usually necessary to add only very small amounts, because of the high catalytic activity of these complexes. In addition, we have found vthat increasing the amount of cobalt catalyst added to the cellulose has progressively less effect on the rate of ageing, so that normally there is little additional advantage in adding more than p.p.m. of cobalt on the weight of bone dry cellulose. Similarly there is no lower limit to the amount of cobalt catalyst which may be applied to the cellulose. We have found, however, that the ,lower the catalyst concentration, the more sensitive is the rate of ageing to small variations in the'catalyst concentration. For these reasons, we usually prefer to ern ploy between 0.5 and 3 p.p.m. of cobalt on the weight of boue dry cellulose. As those skilled in the art will recognize, the optimum amount of catalyst will vary .somewhat depending upon the original pulp viscosity .andthe desired viscosity of the aged alkali cellulose, as well as time and temperature of ageing.

It is well known that cobalt forms coordinate compounds or complexes with a wide variey of anions and neutral molecules. The essential feature of a coordinated group is that it contains an electron pair which it can share with the metal ion in the formation of a more or less covalent bond. Cobalt usually has a coordination nurnberof V6 and can thus form 6 essentially covalent -bondsvwith coordinated groups. In the case of simple cobalt salts, ythe coordinated groups are usually water molecules, 6 in number.

The cobalt complexes of the present invention are formed with bifunctional organic reagents which form more than one covalent bond with the cobalt ion. When the positive charges of the cobalt `ion have been neutralized by coordinate groups, the Aresulting complex is electrically neutral and is no longer Ian electrolyte. These characteristics of the cobalt complexes of the present invention are responsible for their Ainsolubility in water and alkaline solutions.

The cobalt ion is capable of existing in the bivalent or trivalent state. In its simple salts, such as the chloride, the cobalt is almost always bivalent. Most complexes or coordinated compounds of cobalt usually occur with a trivalent cobalt ion. The cobalt complexes of the cpresent invention appear to occur -as mixtures of the complexes formed by bivalent and trivalent cobalt with the organic complexing agent.

While no precise valence can be ascribed to the cobalt in the complex, the complexes of the invention may be characterized in terms of their alkali insolubility vand from the fact that they are produced by reacting a water-soluble salt or cobalt,

Ysuch as cobalt chloride, with a stoichiometric excess of the organic complexing agent.

the following structural formula:

wherein n is a number between 2 and3; "R is an'alkyl,

-cycloalkyl or aryl group.

VExamples of the cobalt complexes of the invention arethe complexes of cobaltwith Qthy1xanthate, Vbutyl- `vxzmthatc, methylxanthate, cyclohexylxanthate and phenylxanthate.

In order more clearly to disclose the nature of the present invention, the following examples illustrating the invention are disclosed. It should be understood, however, that this is done solely by way of example and is intended neither todelineate the scope of the invention nor limit the ambit of the appended claims. In the examples which follow, and throughout the specification, the quantities of materials are expressed in terms of parts by weight, unless otherwise specified, and cobalt concentrations are expressed in terms of p.p.m. of cobalt per weight of bone-dry cellulose.

EXAMPLE 1 vthe cobalt complex suspension were 4required per square foot of pulp. The pulp sheets were then air-dried in an atmosphere of 65% relative humidity. The dried pulp Y was steepedrfor 45 minutes at room temperature (22 C.) in the customary manner in a caustic soda steeping liquor containing 216.5 gms. of sodium hydroxide per liter of solution Aand containing also 5 gms. per liter of hemieellulose. The resulting alkali cellulose sheets were then drained and pressed to expel the Vsteeping liquor to give a cellulose content of 32%. The sheets were shredded and the alkali cellulose crumbs were aged for 24 hours at 22 C. Thecrumbs were then xanthated with 39% of carbon disulfide based on the weight of cellulose in the alkalicellulose by reacting for 21A hours at 26 C. in the absence of air. The resultingxanthate was then mixed with dilute sodium hydroxide solution to give a viscose having a composition of about 7% cellulose and 6% sodium hydroxide. The resulting viscose had a Vspinning viscosity of 26.1 seconds when measured by the falling ball method. A sample of identical pulp but without the ycobalt addition, processed in an analogous manner, required 65% .more ageing time to give the same viscose spinning viscosity. The tensile and durability properties of rayon produced from the viscose of the example and of thecontrol were equivalent.

lcaustic by cobalt complex in the example was determined. The caustic drained and pressed from thepulp `was reused torsteep further batches of control pulp, su-

cient fresh .caustic being added to replace the caustic Control batches of alkali cellulose employing the used caustic were ,-then aged and made into viscose as described and .the spinning viscosity/measured. It was found that, when caustic from Athe batch treated with cobalt complex was reused, the .spinning viscosity of the second batch of .viscose was substantially the same as that obtained when caustic which had at no time been treated with cobalt -complex was used for steeping. vThis indicated that the Ycobalt complex catalyst was completely retained by the -alkalicellulose and none of the complex contaminated the'recovered steeping caustic. On the other hand, when caustic usedto steep a batch of pulp containing the same amount of cobalt in the form of cobalt chloride was reused, the spinning viscosity of the viscose was less than half that obtainedwhen caustic from the above example, employingthecobalt complex of the invention, was reused. This indicated the high degree of contamination of thersteeping caustic when employing an alkali-soluble cobaltsaln such as cobalt chloride.

EXAMPLE 2 `The foregoing example was repeated, except that varyweer ing'- amounts of cobalt ethylxanthate complex varying p.p.m. of cobalt on pulp Time (hours) 0 0. 5 5. 0

EXAMPLE 3 The procedure of Example l was repeated employing the same wood pulp and alkali steeping liquor except that the 3 p.p.m. of cobalt was provided by the cobalt phenylxanthate complex of Example 8 herei-nbelow. When the catalyzed alkali cellulose crumbs were xanthated and converted to viscose, it was found that the ageing time was reduced by 60%. When tested, the 'used steeping liquor was found to be substantially free from cobalt contamination.

EXAMPLE4 The procedure of Example 1 was repeated employing the same wood pulp and alkali steeping liquor except that the 3 p.p.m. of cobalt was provided by the cobalt butylxanthate complex of Example 9. When the catalyzed alkali cellulose crumbs were xanthated and converted to viscose, it was found that the ageing time was reduced by 75%. When tested the used steeping liquor was found to be substantially free from cobalt contamination.

EXAMPLE 5 The procedure of Example l was repeated employing the same wood pulp and alkali steeping liquor except that the 3 p.p.m. of cobalt Was provided by the cobalt methylxanthate complex of Example 10. When the catalyzed alkali cellulose crumbs were xanthated and converted to viscose, it was found that the ageing time was reduced by 55%. When tested, the used steeping liquor was found to be substantially free from cobalt contamination.

EXAMPLE 6 The procedure of Example 1 was repeated employing the same wood pulp and alkali steeping liquor except that the 3 p.p.m. of cobalt was provided by the cobalt cyclohexylxanthate complex of Example 11. When the catalyzed alkali cellulose crumbs were xanthated and converted to viscose, it was found that the ageing time was reduced by 55%. When tested, the used steeping liquor was found to be substantially free from cobalt contamination.

The preparation of the alkali-insoluble cobalt organic complexes employed in the foregoing examples is described in Examples 7-11 which follow:

EXAMPLE 7 COBALT ETHYLXANTHATE COMPLEX Pure potassium ethylxanthate (1.37 gm.), which is commercially available, was dissolved in 100 ml. of water EXAMPLE 8 COBALT PHENYLXANTHATE COMPLEX To a solution of 25 gm. of phenol in 100 ml. of methyl alcohol were added 18 gm. of potassium hydroxide. The mixture was refluxed for half an hour. Carbon disulphide (20 ml.) was added and refluxing was continued on the steam bath for four hours. After standing overnight, the

mixture was filtered and cooled. Ether ml.) was added, and the precipitated potassium phenyl xanthate was ltered off. The product'was washed with ether and dried in the vacuum desiccator.

The substantially pure potassium phenyl xanthate (1.70 gm.) was dissolved in 100 ml. of water and mixed with a solution of 1 gm. of sodium carboxymethyl cellulose in 100 ml. of water. Tov this solution was added, with very vigorous stirring, a solution of 0.41 gm. of cobalt chloride hexahydrate in 50 ml. of water. (The molarratio of potassium phenyl xanthate to cobalt was 5:1 in order to ensure complete reaction of the cobalt.) A very line g'reen suspension was formed of cobalt phenyl xanthate complex.

EXAMPLE 9 COBALT BUTYLXANTHATE COMPLEX A mixture of 100 gm. of n-butyl alcohol and 18 gm. of potassium hydroxide pellets was reluxed for one hour and the residual solid was removed by decanting. Carbon disulphide (36 gm.) was added slowly and with constant shaking. The mixture was cooled in an ice bath and the potassium butylxanthate which separated was filtered ott and Washed with several 25 ml. portions of dry ether. The product was dried in a vacuum desiccator over silica gel.

The substantially pure potassium butylxanthate (1.61 gm.) was dissolved in 100 ml. of water and mixed with a solution of 1 gm. of sodium carboxymethyl cellulose in 100 ml. of water. To this solution was added, with very vigorous stirring, a solution of 0.41 gm. of cobalt chloride hexahydrate in 50 ml. of water. (The molar ratio of potassium butylxanthate to cobalt was 5:1 in order to ensure complete reaction of the cobalt.) A very tine green suspension was formed of cobalt butylxanthate complex.

EXAMPLE 10 COBALT METHYLXANTHATE COMPLEX Methyl alcohol (100 ml.) was refluxed with 25 gm. of potassium hydroxide pellets for 30 minutes and the solution was decanted from any undissolved solid. Carbon disulphide (35 ml.) was added slowly with constant shaking. The mixture was cooled in an ice bath and the resulting crystals of potassium methylxanthate were filtered oi and washed with dry ether. The product was dried in the vacuum desiccator.

The substantially pure potassium methylxanthate (1.25 gm.) was dissolved in 100 ml. of water and mixed with a solution of 1 gm. of sodium carboxymethyl cellulose in 100 ml. of Water. To this solution was added, with very vigorous stirring, a solution of 0.41 gm. of cobalt chloride hexahydrate in 50 ml. of water. (The molar ratio of potassium methylxanthate to cobalt was 5:1 in order to ensure complete reaction of the cobalt.) A very tine green suspension was formed of cobalt methylxanthate complex.

7 EXAMPLE 1l COBALT CYCLOHEXYLXANTHATE COMPLEX l Cyclohexanol (100Y m13 was refluxd with l8 of potassium hydroxide pellets for one hour and the solution was cooled and lteredto remove any undissolved solid. Carbonr disulphide (28.5 ml.) was added slowly with con-v stant shaking. The mixture was cooled in an ice Vbath and the resulting crystals of potassium cyclohexyl xanthate were filtered olf and washed with dry ether. The product was dried in the vacuum desiccator.

The substantially pure potassium cyclohexyl xanthate (1.67 gm.) was dissolved in 100 ml. of water and mixed with a solution of l gm. of sodium carboxymethyl cellulose in 100V ml. of water. To this solution was added, with very vigorous stirring, a solution of 0.41 gm. of cobalt chloride hexahydrate in 50 ml. of water. (The molar ratio of potassium cyclohex-yl xanthate to cobalt was 5:1 in order to ensure complete reaction of the cobalt.) A very line green suspension was formed of cobalt cyclohexyl xanthate complex. Y v

The terms and expressions which :have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

1^. In the ageing of alkali cellulose the improvement which'comprises catalyzing the ageing of the alkali cellulose with an alkali-insoluble cobalt coordinate compound comprising a cobalt xanthate complex selected fromV the class consisting of cobalt complexes of alkyl, cycloalkyl and aryl xanthates.

2. In the viscose process the improvement which com prises ageing the alkali cellulose in the presence of an alkaliiinsolble cobalt coordinate compound comprising4 a cobalt'xanthate'complex selected from the class con-1 sisting ofcobalt complexes of alkyl, cycloalkyl and aryl Xanthate's'. Y

3. In the `ageing of alkali cellulose, the improvement which comprises ageing alkali cellulose in the presence of an' organic cobalt complex having the following struc-V wherein n is a number between 2 and 3, R is a member selected from the class consisting of alkyl, cycloalkyl and aryl groups.

Y 4. Theimprovement in ageing alkali cellulose which comprises ageing l'the alkali cellulose in the presence of cobalt ethyl'xanthate complex.

5.` The improvement.

ageing alkali cellulose which'` comprises ageing the alkali cellulose in the presence of References Cited in the tile of kthis patent UNITED STATES PATENTS 2,682,536 Mitchell .Tune 29, 1954 2,768,968 Reppe Oct. 30, 1956A 2,841,579 Villefroy et al. July l, 1958

Claims (1)

1. IN THE AGEING OF ALKALI CELLULOSE THE IMPROVEMENT WHICH COMPRISES CATALYZING THE AGEING OF THE ALKALI CELLULOSE WITH AN ALKALI-INSOLUBLE COBALT COORDINATE COMPOUND COMPRISING A COBALT XANTHATE COMPLEX SELECTED FROM THE CLASS CONSISTING OF COBALT COMPLEXES OF ALKYL, CYCLOALKYL AND ARYL XANTHATES.

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