US1918250A - Method of producing alpha cellulose - Google Patents

Description

?atented .luly 18, 1933 v PATENT OFFICE JOAQUIN JULIO DE LA BOZA, SR, 01:- 'IU'INUCU, CUBA METHOD OI PRODUCING ALPHA CELLULOSE No Drawing. Application filed June 28,

This invention relates to fibrous material produced from sugar cane fiber and to the method of manufacturing the same; the said material being soft, strong, of very high al- 5 pha content, low ash content, and exceptional quality and color; and being adapta le for use in various manufactures, especially for the production of high quality cellulose derivatives.

The invention has for an object to provide a method in which sugar cane fiber may be given a first treatment of an acid nature, at medium to high density, at a temperature substantially above 98 C., and at a pressure substantially greater than atmosphere; after which the material may be washed with Water; and after which Washing the material may be given a treatment of an alkaline nature sufiicient to convert the fiber into cellu- 0 lose pulp of more than ninety-five percent alpha content, said alkaline treatment being conducted at medium to high density, at a temperature substantially above 100 (1., and at a pressure substantially above atmosphere.

Another object consists in providing certain improvements in the method whereby advantageous results are attained.

This application is a continuation in part of my pending application, Serial No. 398,077, filed October 10,1929.

I believe that I have created a method of producing the above named material, which method is commercially economical and practical and does not decrease the natural resistance of the fibrous element of the sugar cane. Although the cellulose obtained by this method can be employed in various manufactures, it is, owing to its exceptional purity, resistance and light color, particularly well adaptable to the manufacture of the better qualities of cellulose derivatives, explosives, artificial silks, photograph films, pyroxylin products, absorbents and analogous products, in which it is very desirable to employ a cellulose of a content of more than ninety-five percent alpha, very low in ash and very pure. 1

It should be noted that the manufacture of sugar from cane is commonly accompanied by a treatment which has as its object the 1930. Serial No. 464,717.

separation of the sucrose juice from the fibrous part of the cane as, for instance, by crushing between rollers or treatment in diffusers, and that the said industry thus supplies a great quantity of fibrous material in a form that is generally inefficiently employed and in some cases entirely wasted. This material is commonly known as bagasse. My invention is adapted to the attainment of the economic industrial achievement which reside in the utilization of this large amount of fi rous material in a commercially advantageous and highly remunerative manner. I

Generallyspeaking, my method includes a first treatment of the fiber with a mixture of water and sulphur dioxide, at a density between medium and big at a temperature between 98 and 120 (1. (preferably about 110 0.), and at a pressure substantially higher than atmosphere, for a comparatively short period; said treatment being followed by washing with water (preferably hot), and thereafter by a second treatment with an aqueous alkaline solution of medium concentration, at a density between medium and high, at a temperature above 100 C. (preferably not higher than 140 (1.), and at a; pressure substantially greater than atmosphere. The first, or acid treatment, is calculated to partially or wholly eliminate, or transform so as to nullify their injurious effects, the sucrose, invert and other sugars, pentosans and similar carbohydrates, together with coloring and mineral matters, as well as other undesirable substances that would not be satisfactorilyseliminated by the alkaline treatment. The said acid treatment further prepares thematerial to satisfactory action by the subsequent treatment. The washing, which follows the acid treatment, and is preferably performed several times with hot water (although warm or cold water maybe satisfactorily used), is calculated to remove quantities of substances which are in condition to beeliminated by solution or separation by water at that stage of the method. The alkaline treatment is calculated to renon der soluble various coloring and mineral 1 material 5 convert the material into cellulose pulp and adapt it for the final customar steps employed in the manufacture of cel ulose, lead-.

ing to the product with'minimum loss of reslstance, maximum alpha content, minimum ash content, light color, high purity, and

maximum yield.

In following the preferred manner of carrying out my invention, the sugar cane fiber obtained from the crushing rollers or difl'users is weighed and thereafter conveyed by a belt, or other suitable means, to a shredding or combining apparatus for the purpose of tearing-apart or separating the fibrous bundles, ithy fibres and the like. If the as already been shredded, as is done in some cases in the manufacture of sugar, this step may naturally be eliminated.

From the shredder the material is passed to a screening device, which may he rotary, the

object of said device being to separate dust,

powder, fibrous materials, trash, etc., and a large proportion of the shorter and more absorbent, fibers freed from each other by the previous treatment, from the longer and stronger fibers which form the outer portion of the cane. The screening device may have openings, for instance, of from one-sixteenth of an inch to three-eighths of an inch or more, according to the condition of the fibrous material and the object desired, and the larger fibers which do not pass through the said openings are either transported direct from the screen to thefirst treatment'of the method or stored under suitable conditions until 40 the appointed time for subjecting the same to treatment.

The first treatment of the; said selected fibrous material, according to my invention, is preferably carried out in a closed vessel in which the fibrous material is mixed with water and sul hur dioxide in proportion, for example, 0 five hundred to one thousand or more pounds of water and a proximately fifteen to fifty or more oun s of sul hur dioxide for each one hun red pounds 0 the fiber calculated on a bone dry basis; said treatment being conducted at a temperature between 98 and 120 CL, and preferabl; at about 110 C.; for a period of from, say, one

to four hours. It may be noted that the concentration of the acid mixture and the degree of temperature depends a preciably upon the mechanical treatment that the material has previously received, particularly from 69 the point of view of freeing the same from ggst and cut, pulverized, damaged, or short The use of sulphur dioxide calls for a closed vessel which is resistant to high pres- 6 sure as well as to the chemical action enr v endered and, although a standard di ester or making pulp from wood by the su phite process which is of sufficient strength to withstand the pressure developed by this step of my method can be used, I prefer a vessel especially desi ed for this purpose which will have better heat and liquor circulation and which will be easier to charge and dis- 1 charge and generally more adaptable such, for instance, as the vessel disclosed in my United States patent application, Serial No. 414,610. I prefer to use a rotating vessel in order to obtain more uniform cooking of the material. In any event the vessel should 'be provided with suitable valves, vents, thermometer, and other uipment, the provision of which is well within the skill of the calling; and it should benoted that said equipment should be arranged and protected against the pressure and chemical action involved.

ment preferably at medium to high density, that is to sa ten percent or more of the total charge of her, water, and sulphur dioxide may be fiber figured as bone dry. After the fibrous material has been charged" into the vessel, the cover is tightly closed and the relief valve, which is preferably located on the'cover, is opened so' as to vent a consider- The material is subjected to this acid treatable amount of the air contained within the vessel. This condition may be augmented by means of a vacuum pump, or the like, so as,

more completely to eliminate air from the vessel. Thereupon, after venting the air or creating a partial vacuum within the vessel, the water and sulphur dioxide are passed into the vessel either together or so arately, and the charge is promptly heate by the direct or indirect application of steam, or in any other approved manner, until a tem rature substantially in excess of 98 C. 15 attained. Another procedure might be to introduce into the vessel, from a suitable storage ieservoir, or the like, acid and water which have been heated and placed under pressure in the reservoir; after which heat could be applied to the treatingvessel for the purpose of maintaining the temperature during treatment at the desired degree.

As previously indicated, the tem erature and period of time employed depen considerably upon the'character and condition of the material, but I have found that, ordinarily, a temperature of 110 C. maintained for a period of from one to four hours is adequate for leading to the production of a product of over ninet -five percent alpha content. In general, prefer to use the highest temperature practicable without damaging the cellulose and within the limits hereinabove recited, it naturally being understood that the higher the temperature the more complete and rapid the effect. However, care must be observed not to injure the fiber, lower the yield, or produce other undesirable results which may arise from too intensive conditions of treatment. Ordinarily a temperature above 115 is to be 6 avoided, and any temperature above 120 C.

remaining in the fiber can be largely elimi-' is very dangerous.

The acid mixture employed in this first treatment should be free from added or combined base, especially calcium, since the presence of such base or bases is detrimental to the quality of the product substantially in proportion to the quantity of base present. This acid treatment with water and sulphur dioxide carried out as above is very important, since it eliminates certain very objectionable substances, such as sugars, pentosans and similar carbohydrates, iron, manganese and other metals, which would not be eliminated by the subsequent treatment; and since it also partially eliminates or transforms other substances so that they may readily be eliminated by the subsequent treatment. The said acid treatment is not calculated to be sufiicient to reduce the material to cellulose pulp but only to effect the above mentioned and allied objects, although the fiber is very considerably softened by the treatment, and considerable reduction in its dry weight is effected. The said acid may be employed by using a mixture of sulphur dioxide (S0 and water (H O) which mixture contains the desired quantity of sulphur dioxide; or by using an aqueous solution of sulphurous acid (H 50 which contains part of the sulphur dioxide required, and adding the remainder of the sulphur dioxide in an desired form.

At the end of the said aci treatment, the gas is first released and may be recovered by reabsorption or in any other approved manner, after which the material is washed one or more times with water and then removed from the vessel in order to finish the washmg and squeezing; or. the material may be removed from the treating vessel withoutany washing therein, and then suitably washed and compressed in any approved apparatus. Hot, warm,- or cold water may be used for washing, it being understood that hot water is generally to be preferred and that the more thorough the washing the more improved the quality of the product. The waterused for washing should be the purest readily obtainable, particularly with respect to its content of minerals, such as iron, manganese, calcium, etc., and colormg matters. After the washing, the liquid nated by squeezing or pressure, for instance, in a two or three roll mill or' the like, thus leaving the material comparatively freeof acid and at a concentration of twenty-five to fifty percent or more dry fiber, depending largely on the pressure applied and other conditions of the particular treatment. I

prefer to press the fiber to a very substantial extent so as to, for example, bring it to a concentration of approximately fifty to sixty percent dryfiber. In addition to the recovery of the gas above indicated, certain desirable substances may be recovered from the liquid of the acid cook in a well understood manner.

Following the acid treatment and the washing, the material is given an alkaline treatment, preferably with a. mixture of water and sodium hydroxide. This alkaline treatment should be conducted in a closed vessel fitted to withstand the pressure and protected against the chemical action involved in the treatment. I prefer to use a vessel of the t pe of the kraft rotating digester, which has been suitably protected as above indicated. The placingof the valves, reliefs, and kindred equipment may be somewhat different from that generally provided in the said with a solution of sodium hydroxide dissolved in water, which solution contains preferably not over eighteen pounds of sodium hydroxide per one hundred pounds of fiber.

and, usually, not over sixteen pounds of sodium hydroxide per one hundred pounds fiber. The matori a1 is subjected to the said alkaline treatment at a temperature of from approximately100 to approximately 140 C., maintained for a period of approximately one to three hours, or more. A period of from one to two and one-half hours at approximately'140 C. maximum temperature, with a medium density, gives good results.

'Temperatures up to 170 C. may be used but the advantage of such high temperature is doubtful because, although it shortens the period of time, the cellulose is apt to be con siderably attacked and injured. The density of the charge, i. e., the ratio of fiber to solution, may also depend ,upon the type of cooking vessel employed since a. higher density is possible when a rotating digester of the kraft type is used. Generally a ratio of three to five parts of solution to one part of fiber is satisfactory. In general, the higher the density of the solution the lower the temperature required to achieve best results, and, if too high a temperature be employed with a verydense solution, the fiber will be considerably attacked. 1

The fibrous material and the water and sodium hydroxide may be introduced into the vessel in a manner corresponding to that described in connection with the acid treatment,

the cover applied to the vessel and the vents and the like closed and, thereupon, the charge heated by the direct or indirect application of steam, or in any other approved way, until the desired temperature is reached and the treatment continued at the said temperature for the selected period.

At the end of this alkaline treatment the material may be discharged from the vessel by its own pressure, or by gravity, or in any other approved manner, to a blow pit, vat,

tank, or the like; and from there it may be conveyed to a suitable Washing apparatus where it may be thoroughly washed with water and thereafter bleached and finally treated, all as well understood in this art. In some cases bleaching will be found to be unnecessary as the product is of alight color, but, if an absolutely white product is desired, bleaching is indicated. The final product will be found to be cellulose having more than ninety-five percent alpha content, very low ash content, and very white color.

In preparation of the mixture of sodium hydroxide and water for the above described treatment, it will frequently be found practical to employ a substantial quantity of the so called black liquor derived from the application of this alkaline treatment to previous batches of material, and the successive use of the said liquor will permit great economy and be of consequence in relation to a profit able commercial operation. At least a part of the chemical ingredients used in the alkaline treatment may be recovered by the usual processes of concentration and burning to powder and regenerating the alkali therefrom, all as is well understood.

It should be pointed out as a characteristic of this procedure that neither of the treatments described is, of itself, adequate to produce a fully pulped fiber. True, the alkaline treatment accomplishes this pulping, but that is because of the effect of the preceding acid treatment which has so acted upon the fibrous material as to render it very soft and sus:

, ceptible to pulping by the alkaline treatment, which latter treatment is of such a mild nature that it'would not, of itself, pulp the fibrous material if it had not been subject to the previous acid treatment.

With reference to either or both the acid and alkaline treatments, instead of conduct ing the material and the chemical mixture separately into the vessel, I may mix the material and chemical prior to introduction into the vessel, as fully explained in my said pending application, Serial No. 398.677.

Although I have described the separation of the longer fibers and their treatment owing to the fact that from said material it is easier to obtain the highest quality of alpha cellulose with the greatest. yield, themethodQis also applicable to the treatment of the whole of the fiber without such separation and,

damaged with respect to its adaptability to the manufacture of sugar as, for instance, by

-inversion, or by fires in the field. Such damaged sugar cane, even though it may be unsuitable for the production of sugar, includes fibrous material which is well adapted for treatment by my above described method whereby the uninjured fibers can be separated and the intended product obtained. Furthermore, this method is adapted to the treatment of sugar cane before it has been processed for the extraction of the juice and, in brief, my invention is fitted to obtain the desired product from sugar cane in any form or condition as long as it contains a reasonable percentage of uninjured fiber.

Therefore, when, in the claims, I refer to sugar cane fiber, I intend to cover the treatment of such fiber in any form or condition suitable to the application of my method. Finally, when I refer-to sulphur dioxide and to sodium hydroxide, I intend to cover not only the said specific acid and alkali but also others having a similar effect in my method; though I prefer, for the acid treatment, a mixture of sulphur dioxide and water, and, for the alkaline treatment, a mixture of sodium hydroxide and water.

It will be understood that various changes may be resorted to in the steps of the method, in the materials and in the apparatus, without departing from the spirit and scope of my invention; and hence I do not intend to be limited to the details herein set forth, except as they may be included in the claims.

What Iclaim is '1. A method oftreating sugar cane fiber to produce cellulose of high alpha content, low ash content, light color, and great purity, which includes; passing the fiber into a vessel, closing the vessel, creating a partial vacuum in the vessel, injecting into the vessel a mixture ofsulphur dioxide and water, treating the fiber with said mixture in said vessel within directly applied heat at a temperature of approximately110' to 120 0., and, subsequently, treating the fiber with a mixture of sodium hydroxide and water in a closed vessel at a temperature of approximately sel, closing the vessel creating apartial vacuum in the vessel, injecting into the vessel :1

mixture of sulphur dioxide and water,'treatcane which has been subjected to successive ingv the fiber with said mixture in said vesbaseless acid and alkali treatments and is in sel with indirectly applied heat at a tempersoft and strong condition, of more than ature of approximately 110 to120 0., and, ninety-five per cent alpha content, of less 5 subsequently, treating the fiber with a mixthan two tenths of one per cent ash content,

ture of sodium hydroxide and water in a roof substantially white color, and substantating closed vessel at a temperature of aptially entirely free of all constituents other proximately 120 to 140 C. than cellulose which would hamper the use 3. Amaterial adapted for the manufacture of the material for the manufacture of said 10 of high quality cellulose derivatives, said mahigh quality cellulose derivatives. 5

terial comprising the fibrous part of sugar JOAQUIN JULIO DE LA ROZA, SR.

CERTIFICATE or coamacnon hem No, 1,918,250, .July 18, 1933.

JOAQUIN JULIO de la ROZA, sn.

it is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 4,. line 119, claim l, for "within directly" read "with indirectly"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 24th day of October, A. D. 1933.

F. M. Hopkins (seal) I Acting Commissioner of Patents.

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