US1997153A - Manufacture of alpha cellulose - Google Patents

Description

"\ l 4 i i I l I i a o m Li J. S. POU

v MANUFACTURE OF ALPHA CELLULOSE Filed Febf23, 1934 April 9, 1935.

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Patented A r. s, 1935 PA-TENT ol-F cE MANUFACTURE OF ALPHA CELLULOSE,

Jose Sala Pou, Barcelona, Spain Application 3 Claims.

I have filed an application in Spain on the 21st October, 1933.

4 The present invention relates to the manufacture of alpha cellulose, andmore particularly to 5 a process for manufacturing this product from bamboo canes in a form suitable for the production of cellulose esters as substitutes for cotton pulp and its derivatives. 7

The plants of the order Graminacete, species -of'bamb'oos', have fibres possessing special characteristics, a fact which has already been known to paper manufacturers; but the said fibres have.

not hitherto been used for the manufacture of super-alpha celluloses capable of competing in the market with the super-alpha celluloses derived from cotton.

The nature of the plants, which are different in their constitution from wood, leads to the assump: -tion of the possibility of the formation of a cellulosic compound which being less lignified, may give characteristics more similar 'to the polymerization ofthe cotton molecule. On the otherhand, the greater percentage of lignine which the plants contain ascompared to the other plants of the order Graminaceae, allows also ofthe bamboos producing a cellulose in the form of 'filaments having fibro-vascular fascicles of a bleaching chlorine and which can be with difficulty eliminated by the latter unless the chlorine is used in proportions which always produce considerable oxidation ofthe fibres. Moreover, the peptins can be easily rendered soluble by alkaline hydrates at temperatures in the neighbourhoodv of degrees.

In view of the simplicity with which the peptins are eliminated theidea has been conceived to use in place of a continuousprocess, a fractional process which at a first boiling at a presv sure of 0.5 atmosphere in an alkaline lye containing 1.5 per cent of the corresponding alkali, in the proportion of 1 :5 between the weight of the material treated and the weight of the bath, elim- February23, 1934, Serial No. 712,628 In-Spain October 21, .1933

inates the peptins; This quantity of hydrate is sufiicient for converting them into the form of a soluble salt which remains in solution. The combination of sugars, starches and peptins formed, owing to the excess of alkali which remains in the bath without reacting, cannot be abstracted, as otherwise it would be precipitated and would stain the cellulose fibre to such an extent that-it would be difiicult to clean it.

The alkaline hydrates, even at the low temperal tures at which the operation is carried out, always exerta hydrolyzing effect on the hemi-celluloses which accompany the alpha cellulose, and the oxidizing molecules of-the hydrates always exercise some hydrolytic action' also on the alpha i celluloses. For that reason it has been considered advisable to introducein the first stage a reducing element such as-an alkaline sulphite or sulphites, which combining with-oxygen, prevents the said hydrolyzing effect andleaves the elimi- 2 nation of the lignine and of the semi-celluloses to the second stage of the process, so that the first stage thereof serves only for the elimination of the above-mentioned substances.

The combined'action of the alkaline hydrates 2 and of the alkaline sulphites must take place at the temperature and pressure indicated and within a period of time of two to four hours. As soon as this first stage of the operation is completed, the pulp is washed first with hot water and then a two or three times with cold water. Into the autoclave in which the operation is carried out, anew lye which contains per litre 45 grammes of alkaline hydrate, 20 grammes of sulphide of sodium and 5 grammes of sulphite of sodium is 3 then introduced.

The first object aimed at by the use of this lye is to avoid theeifects of hydrolyzation which have been provided for in the first stage. Sodiumsulphide and sulphite are intended to attain this 4 object. For the same purpose the lye in the form of sodium sulphide and caustic soda, could also be-combined in any proportion which may be con- 'sidered suitable for combining the said products with the lignine. 4 The highly beneficial reducing effect of the sodium sulphide for obtaining super-alphas may be assumed'to' be represented by the following equation:

NazS+HzO=NarS+HOH=NaOH1=NaHS This reaction, which, as indicated is reversible, is a. hydrolysis which gives sodium sulphohydrate, and this product forms the reducing atmosphere 6 which prevents the effect of oxidation on the alpha cellulose. I

The acid contents of the lignine or the lignitic acids are neutralized by the alkaline hydrate or by the hydrolysis of the NazS to NaOH, giving soluble soda compounds.

The NaHS combines with alcohols (to form mercaptans) and with phenols, the result of the reaction being by weight, with regard to the sulphide, as follows:

i Per cent Combined with the lignine after the hydrolysis 51.8 Retained by volatile organic substances 15.0 Remaining unaltered as NazS 15.8 Eliminated in the form of sulphate 17.8

This oxidation of sulphide in order to pass to sulphate takes place at the expense of active oxygen which would have produced oxidizing action on the alpha celluioses.

The temperatures applied for the elimination of the lignine start at 140 degrees C., but in some kinds of old bamboos, that is to say, bamboos which arein the advanced period of lignification, or inthe bamboos which grow in shallow soils which prevent the roots of the plant from penetrating deeply into the earth and where the rainy periods are veryrare or the'rain is scarce between the stage of first growth of the stem and the stage of second growth in which latter the branches and the leaves appear, asa result of ,which there is a lack of moisture in the roots and therefore in the plant, with the consequent quick drying up of the starches in the fundamental porenchyma of the plant, on the said alimentary substances being eliminated for the normal development of the cellulose until its maximum uniform growth is reached, there takes place a premature ageing, so

that a premature kind of very much condensed lignine is produced which strongly envelops the fibres in the ligneous fibro-vascular sheafs or faggots, and which is difiicult to eliminate by the industrial processes for the elimination of the said product, and in such cases it is necessary to use high temperatures of degrees C. which produce on the other hand a serious hydrolysis of the alpha cellulose.

In spite of the reducing atmosphere which the sulphide produces, it has been found difficult to avoid these actions, and in order to avoid also such high temperatures, and it has been attempted to find some solvent for the lignine. A' suitable solvent has been finally found among the ethers of the phenols. As an example of this solvent, may be used guayacol, that is to say monomethyl ether of the phenol which is found in cellulose. The guayacol quickly dissolves the coating of lignine gelatinized by the hydrate and allows new portions of the lye to attack rapidly new zones of lignine. Owing to the action of the guayacol it is possible, even in cases where old.

bamboos or bamboos'grown in bad conditions are used, to do without varying the times and the pressures required for the operation, and in these pressure of 8 atmospheres.

After the completion of the boiling, a. further washing operation with hot water is carried out. When guayacol has been used, the first water is emulsified with a benzol in the proportion to the quantity of the guayacol used, plus 50% by weight of this body. .After twice washing with hot water, the product is washed two or three times with cold water, and thereupon bleached with a hypochlorite solution of one half to one degree B. This cellulose thus obtained is washed and submitted to the action of a HFl bath of half percent. In this way the remains of the silica are eliminated, and the residue of ashes can be reduced to 0.3%. After this bath, the product is washed in plenty of water, and the bleached cellulose is subjected to the action of a solution of bisulphite of soda of 2 B. at a temperature which may vary between 60 degrees C. at atmospheric pressure and '120 degrees C. at a pressure of one atmosphere. This operation eliminates the quantities of oxiand hydrocellulose, and the rest of the lignine that may still be left. After this bath, the cellulose is washed in plenty of water and may be submitted if desired to the action of'a solution of peroxide of sodium or of peroxide of hydrogen for the purpose of improving its whiteness.

The cellulose obtained by this process from the bamboos has exceptional characteristics which are in no way inferior to the characteristics of cotton.

For carrying out the reactions and operations above set forth it is preferred to employ an installation comprising a combination of elements, by means of which the whole process according to the invention can be carried out automatically from the commencement up to the delivery of the cellulose without the necessity for manual operations.

A preferred constructional arrangement of such an installation is illustrated by way of example in the only figure .of the accompanying drawing.

Referring to the drawing:

The cut bamboos afterhaving been left to dry in the field for a period of forty days, are exposed to the action of running water, either in a river or in suitable pools for a period of time which varies from 7 to 15 days.

The bamboos prepared in this way are introduced into a grinding mill l constituted by four pairs of cylinders or rollers, two of which are provided with grooves or flutes, and these two rollers owing to the action of hydraulic pressure applied to them, flatten and break the joints or knots of the bamboos. The other two pairs of rollers are provided with teeth arranged in zigzag shape and are also subjected to strong by draulic pressure, their object being to cut the bamboos. This operation is of the greatest importance, inasmuch as, the uniformity of the boiling depends on the elimination of the air from the perforated vessels, since the said air may cause the mass to fioatin the boiling lye, which would retard by at least one hour the time of immersion.

The bamboo stems having been cut to portions of about one square centimetre section and completely disintegrated, drop into a pit which is 10- cated in front of buckets 2 which lift the cut stems up to the hopper 3. The said hopper is so dimensioned that its capacity is the same as that of the autoclave 4 with which it is associated. The said autoclave receives the new lye which is supplied from 18, and which has been mixed in a well ill provided with an agitator, with the regenerated iyes coming from the tank 26.

As soon as the cut bambro and the lye have been introduced in the said manner into the autoclave, steam is admitted from a steam generator 20 the said steam being used. for indirect heating so as to avoid any dilution of the bath. This point, though it is not of much importance in the production of cellulose intended for the manufacture of paper, is important in the case of those super-alpha celluloses in which variations to the extent of one tenth percent in the lye are liable to produce variations of more than two percent in the contents of the alpha. At the proper moment, the top valve of the apparatus is opened, and a circulating pump with which it is provided, is started, for the purpose of enabling the air contained in the mass consisting of lye and bamboo tobe expelled. This operation is of great importance as it avoids the oxidation of the cellulose by the oxygen of the air. As soon as this operation is finished, the temperature is raised until the pressure previously stated is reached and is maintained during the period of time also stated, whereupon the lye is discharged through a valve and sent for recovery or recuperation. The mass contained in the autoclave, is thereupon washed once with hot water and three times withcold water.

This first stage of boiling of the bamboo being finished, the lye by means of which the second operation or stage is carried out, is introduced into the autoclave, the same precautions being taken with regard to the air as were adopted in the previous operation, and a continuous circulation being kept up during theboiling operationby means of the pump already referred to.

As soon as the operation is finished and after the washing operations which follow those with emulsioned benzol, the lye is returned to the well 5 from which it passes together with the first two washing waters, to a tank 2| serving for the reception of the lyes which are to be treated for recovery or recuperation.

The lyes from the tank 2| are conveyed to a. multiple action evaporator 22 which is fed with the steam coming from the steam generator 20 andv afterwards pass to the rotary oven 23 in which they are calcined and from the latter pass to thekpit 24 from which an Archimedean screw raises them to the caustifying vessels 25. from which they pass to settling tanks 26.

As soon. as the lyes have been conveyed to the recovery units, the cellulose is returned to the well 5 in which it is diluted with water and washed therewith, being stirred for the purpose by a powerful agitating device. The pulp which is thus formed, is conveyed by means of a pump to a thickener or concentrator 6 which in its turn after having eliminated the water, delivers the pulp to a disintegrator-deflbrator of the kind known under the name of cone breaker. This disintegrator is sufiicient for the purpose in asmuch as the material to be treated is thoroughly boiled pulp which does not normally contain any knots (since it has been ground in the mill I); but in cases in which, owing to some defect in the grinding mill, the knots of the bamboos had not already been sufliciently ground, it would be necessary to interpose between the well 5 and the concentrator 6, one or more rotary purifiers working with one millimetre pitch.

On being discharged from the cone breaker, the pulp is introduced into one or more washing and bleaching vats or machines 8 to which is supplied a solution of sodium hypochlorites supplied from decanting devices 30. From the said washing and bleaching machine or machines 8 the cellulose passes to a vat 9 where it is treated with hydrofluoric acid of the above-mentioned concentration. This vat is lined inside with a plastic material having for its basis rubber, in order to render it proof against the action of the acid which comes from a supply unit 29.

The cellulose passes from the vat I to a vat III in which it is washed with plenty of water until the last traces of the acid are removed and from the said vat the cellulose passes to a concentrator II from which it is here conveyed by a pump into an autoclave l2.

The cellulose is introduced into the autoclave l2 through the bottom part of the latterand is forced to circulate through several inclined planes arranged in the interior of the said autoclave, arid at the proper time the corresponding solution of sodium sulphlte is introduced. The bath is thereupon heated by means of steam coming from the steam generator 20 and passing through a closed coil arranged at the bottom of the apparatus. In these conditions, the pressure rises to one atmosphere, and the pulp is extracted from the upper part of the autoclave by a pump provided with a special pressure-relief device. On its discharge from the said pump, the pulp passes into a vat I3 in which it is thoroughly washed. The sulphlte used in the last named lye is supplied from a unit 21.

The pulp contained in the vat l3, after having been treated in the latter, passes to the vat I where it is treated with a solution which is prepared in a unit 28-and which is composed of sodium peroxides or hydrogen peroxides, and on leaving the vat M, the pulp passes through a long sand-removing device l5, from the latter to a centrifugal purifier l5 and finally to a pulp press i1.

The pulp thus obtained which contains from 97 to 98% of alpha cellulose is of a magnificent white colour, and its fibres are 7 to 8 millimetres long. This super-alpha cellulose with such exceptional characteristics, extracted from bamboos, is obtained in a proportion of 35 to 40% of the dry 'plant and is more particularly suitable for the esterification as well as for the manufacture of papers, particularly of papers for documents, ledgers and bank notes. Moreover in view of the exceptional absorption capacity which this fibre possesses, it can be used in place of cotton for the hygienic and sanitary purposes for which the latter is employed.

The product obtained by the process hereinbefore described, has the following characteristics:

Viscosity equal to that of pure normal cotton in a cupro-ammoniacal solution of 0.5%

, subsequent use may also vary and generally the process, installation and product may be modified in various ways without departing from the scope of the invention.

I claim:

1. A process for the manufacture of alpha cellulose from bamboos, comprising in steps: drying out bamboo in the open air; exposing the cut and dried bamboo to the action of running water; grinding said bamboo to form a kind of tow; boiling said tow in an autoclave with a lye composed of alkaline hydrates and a reducing agent at a pressure of .5 to 1 atmosphere; washing said tow in the autoclave first'with hot water and then with cold water; subjecting the bamboo pulp thus produced in the same autoclave to the action of a second lye containing alkaline hydrate, sodium sulphide, sodium sulphite and guayacol for one hour at 156 C. and 4.8 atmospheres pressure, and for a few hours at 143 C. and 3 atmospheres pressure; washing the pulp in the autoclave first with water emulsified with benzol and then three times with cold water; discharging the pulp into a tank fitted with an agitator and diluting it with water; passing the pulp through a thickener and then through a disintegrator-de'fibrator; subjecting the pulp to the oxidizing action of sodium hypochlorite lye, washing it in plenty of water and subjecting it then to the action of a bath of hydrofluoric acid and again washing with ample water; passing the pulp through a thickener and then into an autoclave in which it is mixed with a suitable quan tity of sodium sulphite at 60 C. and 2 atmospheres pressure and then washed; and bleaching the pulp with hydrogen peroxide or sodium peroxide, washing it, and converting it into solid form.

2. A process for the manufacture of alpha cellulose from bamboos,-comprising in steps: drying cut bambooin the open air; exposing the cut and dried bamboo to the action of running water; grinding said bamboo to form a kind of tow; boiling said tow in an autoclave with a lye composed of alkaline hydrates and a reducing agent at a pressure of -.5 to 1 atmosphere; washing said tow in the autoclave first with hot water and then with cold water; subjecting the bamboo pulp thus produced in the same autoclave to the action of a second lye containing alkaline hydrate, sodium sulphide, sodium sulphite and guayacol for one hour at 156 C. and 4.8 atmospheres pressure, and for a few hours at 143 C. and 3 atmospheres pressure; washing the pulp in the autoclave first with water emulsified with benzol and then three times with cold water; discharging the pulp into a tank fitted with an agitator and diluting it with water; passing the pulp through a rotary purifier having a pitch of 1 millimetre for removing any bamboo knots which have still been left unground during the previous mechanical action to which the pulp has been submitted; passing the pulp through a thickener and then through a disintegrator-defibrator; subjecting the pulp to the oxidizing action of sodium hypochlorite lye, washing it in plenty of water and subjecting it then to the actionof a bath of hydrofluoric acid and again washing with ample water; passing the pulp through a thickener and then into an autoclave in which it is mixed with a suitable quantity of sodium sulphite at 60 C. and 2 atmospheres pressure and then washed; and bleaching the pulp with hydrogen peroxide or sodium peroxide, washing it, and converting it into solid form;

3. A process for the manufacture of alpha cellulose from bamboos, in a form suitable for conversion to cellulose esters as substitutes for catton pulps and derivatives comprising in steps: drying the cut bamboo in the field in the open air for forty days; exposing the-cut and dried bamboo to the action of running water in a river for from"? to 15 days; grinding said bamboo to form a kind of tow; boiling said tow in a autoclave for a period of 2 to 3 hours with a circulating lye, the ratio between the amount of the tow and the lye being 1:5, and the lye being composed of alkaline hydrates together with 1.5 to 2 percent of a reducing element, the boiling operation taking place at a pressure of .5 to 1 atmosphere and the temperature corresponding thereto; washing said tow in the same autoclave first with hot water and then three times with cold water; subjecting the bamboo pulp thus produced in the same autoclave to the action of a second lye containing per litre 45 grammes of alkaline hydrate, 20 grammes of sodium sulphide and 5 grammes of sodium sulphite together with a suitable quantity of guayacol, the lye being caused to circulate through the bamboo pulp for 1 hour at 156 C. and 4.8 atmospheres pressure, and then for 2 to 3 hours at 143 C. and 3 atmospheres pressure; washing the pulp in the autoclave first with water emulsified with benzol in the proportion of one-and-a-half times the weight of the guayacol and then three times with cold water; discharging the pulp into a bleaching the pulp with hydrogen peroxide or sodium peroxide, washing it, and converting it into the usual known solid form.

JOSE SALA POU.

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