US2928826A - Catalysis of the ageing of alkali cellulose - Google Patents

Description

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CATALYSIS OF THE AGEING F ALKALI CELLULGSE Bengt Leopold, Donald B. Mutton, and William R. Saxton, Hawkesbury, Ontario, Canada, assignors to Canadian international Paper Company, Montreal, Quebee, Canada, a corporation of Canada No Drawing. Application September 2, 1958 Serial No. 758,590

2 Claims. (Cl. 260-233) process for producing rayon by providing improvements in the ageing of the alkali cellulose in viscose manufacture. 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 inter mediate 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 cellulose 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 pulp manufacturer 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 it is expensive and inefficient for the rayon manufacturer to increase that time. If the rate of depolymerization during ageing could be increased sufiiciently, then all or most of the degradation new carried out during the bleaching and ageing steps could be performed during the ageing period alone, and even the ageing time could be reduced. This would enable the rayon manufacturer to save time and reduce costs and the pulp manufacturer to reduce chemical costs as Well as to sell higher viscosity pulps which might yield improved rayon yarn and cord.

It is known that the transition metals, such as iron, manganese and cobalt, particularly the latter, catalyze the ageing of alkali cellulose. The prior art is limited to employing water-soluble and alkali-soluble compounds of these metals. These compounds are particularly soluble in steeping caustic, especially in the presence of hemicellulose. It is general practice to employ caustic solutions containing between about 17 and 25% by weight of caustic soda as a steeping liquid. To effect necessary economy it is essential to reuse the caustic steeping solutions for treating subsequent batches of pulp. When the transition metal catalyst is relatively soluble in the steeping 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 diflicult. This is especially true in the case of cobalt compounds which are much more active catalysts than compounds of manganese or iron.

We have discovered that in accordance with the present 2,928,826 Patented Mar. :15 1960 2 invention an organic complex or chelate compound of cobalt is not only substantially completely insoluble in water and steeping caustic, but what is more important and unexpected, this complex retains the ability to catalyze the ageing of alkali cellulose. This alkali-insoluble complex not only catalyzes the ageing of alkali cellulose but it is retained by the alkali cellulose and does not conterminate the steeping caustic. Consequently, the present invention makes it possible to effectively catalyze the ageing of the alkali cellulose without contaminating the steeping caustic, thereby permitting reuse of the steeping caustic without the concomitant variations in ageing reactivity which have plagued the prior art. Since the steeping caustic, after separation from the cellulose, contains substantially no catalytic cobalt complex or ch'elate 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 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.

It is a further object of the present invention to provide an organic coordinate compound or complex of cobalt and S-hydroxyquinoline, which is substantially insoluble in steeping alkali and yet catalyzes the ageing of alkali cellulose, and which does not contaminate the steeping alkali.

The foregoing objects, as well as others, will be apparent to those skilled in the art from the present description.

In accordancewith the process of the present invention for depolymerizing cellulose, a small amount of an alkali-insoluble cobalt complex or coordinate compound with S-hydroxyquinoline 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 aqueous 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 sufficiently 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 to age until the desired degree of depolymerization has been attained. The aged alkali cellulose is then in con dition for xanthation and conversion to viscose in accordance with well established procedures or it may be employed for other desired purposes which require aged or depolymerized alkali cellulose.

Additions of the cobalt complex to the cellulose may be made by any suitable method. In one preferred method of application a dilute aqueous suspension of the cobalt S-hydroxyquinoline complex is spr'ayedor 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 complex in an organic liquid, such as chloroform, may be employed. In accordance with another method, the cobalt complex may be formed in situ on the cellulose by adding a soluble salt of cobalt, such as cobalt chloride, with the S-hydrbxyquinoline complexing agent, the latter being added in excess of the stoichiometric amount necessary to react with and complex substantially all the cobalt chloride.

.Although any amount of cobalt complex catalyst may be added to the cellulose, it is usually necessary to add only very small amounts, because of the high catalytic activity of this complex. In addition, we have found that increasing the amount of cobalt catalyst added to the cellulose has progressively less efiect on the rate of ageing, so that normally there is little additional advantage in adding more than 5 ppm. 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 employ between -0.5 and 3 ppm. of cobalt on the weight of bone dry cellulose. As those skilled in the art will recognize, the optimum amount of catalyst will vary somewhat depending upon the original pulp viscosity and the 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 variety of anions and neutral molecules. nated 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 number of 6 and can thus form 6 essentially covalent bonds with coordinated groups. In the case of simple cobalt salts, the coordinated groups are usually water molecules, 6 in number. The cobalt complex of the present invention is formed with S-hydroxyquinoline which forms more than one covalent bond with the cobalt ion. When the positive charges of the cobalt ion have been neutralized by coordinate groups, the resulting complex is electrically neutral and is no longer an electrolyte. These characteristics of the cobalt complex of the present invention are responsible for their insolubility 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 complex of the present invention appears to occur as mixtures of the complexes formed by bivalent and trivalent cobalt with 8-hydroxyquinoline. While no precise valence can be ascribed to the cobalt in the complex, the complex may be characterized in terms of its alkali insolubility and from the fact that it is produced by reacting a water-soluble salt of cobalt, such as cobalt chloride, with a stoichiometric excess of the S-hydroxyquinoline complexing agent.

In order more clearly to disclose the nature of the present invention, the following examples illustrating the invention are disclosed. It shouldbe understood, however, that this is done solely by way of example and is intended neither to delineate 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 A web of Kipawa Tancell tire cord grade of sulphite wood pulp was spotted uniformly with a dilute chloro- The essential feature of a coordiform solution of the cobalt S-hydroxyquinoline complex 4 V of Example 2 hereinbelow, in sufficient amount to deposit about 4.2 p.p.m. of cobalt on the pulp. The cobalt solution was of such concentration and the pulp was of such thickness and moisture content that about 10 to 15 drops of the cobalt complex solution were required per square foot of pulp; The pulp sheets were then air-dried in an atmosphere of 65% relative humidity. The dried pulp was steeped for 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 and containing also 5 gms. per liter of hemicellulose. The resulting alkali cellulose sheets were then drained and pressed to expel the steeping 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. The crumbs were then xanthated with 39% of carbon disulfide based on the weight of cellulose in the alkali cellulose by reacting for 2% hours at 26 C. in the absence of air. The resulting xanthate was then mixed with dilute sodium hydroxide solution to give a viscose having a composition of about 7% cellulose and 6% sodium hyroxide. The resulting viscose had a spinning viscosity of 47.3 seconds when measured by the falling ball method. A sample of identical pulp but without the cobalt addition, processed in an analogous manner, required 50% 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 the control were equivalent. The extent of any contamination of the used steeping caustic by cobalt in the example was determined. The caustic drained and pressed from the pulp was reused to steep further batches of control pulp, sufiicient fresh caustic being added to replace the caustic taken up by the previous batch of cellulose. 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 the 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. This indicated that the cobalt complex catalyst was completely retained by the alkali cellulose and none of the complex contaminated the recovered steeping caustic. On the other hand, when caustic used to steep a batch of pulp containing the same amount of cobalt in the form of cobalt chloride was reused, the spinning viscosity was less than half that obtained when caustic from the above example, employing the cobalt complex of the invention, was reused. This indicated the high degree of contamination of the steeping caustic when employing an alkali soluble cobalt salt, such as cobalt chloride.

Example 2 The cobalt 8-hydroxyquinoline complex employed in Example 1 was prepared as follows:

S-hydroxyquinoline is available commercially. A solution of 1.25 gm. of the reagent in 50 ml. of alcohol was added with vigorous stirring to ml. of an aqueous for the complex of divalent cobalt is 17.0% cobalt, for

trivalent 12.0% cobalt.

The terms and expressions which have been employed are used as .terms of description and not of limitation, and i is not intended, in the use of such terms and a 6 expressions, to exclude any equivalents of the features prises ageing alkali cellulose in the presence of the alkalishown and described or portions thereof, but it is recoginsoluble coordinate compound, cobalt 8-hydroxyquinonized that various modifications are possible within the line, scope of the invention claimed.

What is claimed is: 5 References Cited in the file of this patent 1. In the ageing of alkali cellulose the improvement which comprises catalyzing the ageing of alkali cellulose UNITED STATES PATENTS with the alkali-insoluble coordinate compound, cobalt 2, 8 ,536 Mltchell June 29, 1954 8-hydroxyquinoline. 2,841,579 Villefroy et al. July 1, 1958 2. In the viscose process, the improvement which com- 10

Claims (1)

1. IN THE AGEING OF ALKALI CELLULOSE THE IMPROVEMENT WHICH COMPRISES CATALYZING THE AGEING OF ALKALI CELLULOSE WITH THE ALKALI-INSOLUBLE COORDINATE COMPOUND, COBALT 8-HYDROXYQUINOLINE.