US975387A - Method of treating bagasse. - Google Patents

Description

UNITED STATES PrlTENT OFFICE.

THOMAS J. HUTCHINSON, OF MANCHESTER, ENGLM METHOD OF TREATING BAGASSE.

No Drawing.

To all 'UF/lO/IL 1Y4 'nnrg/ com-(m.

lie it known that l, 'lnoinas J. llu'rcnixsox, analytical and consulting chemist, a subject of llis Majesty the [ting o't' l lngland, and resident of illanchester, l lnglantl, whose post-ollice address is No. 54 Arcade Chambers, ls lanclu-ster, England. have invented certain new and usetul lniprovcments in Methods ol li.'eating llagasse, of which the following is a full. true, and (-oncise specification.

l\'l v invention relates to a process ol. treating bagasse with the object to separate therefrom. a n'iaxinnnn portion of its papermaking contents with the least ex ease of materials and time 1nd of a quality suitable for making a co1nn'ierciall useful bagasse paper.

The invention rests on the discovery 1 have made that a bagasse cellulose excellently adapted for paper-making as well. as for other purposes may be obtained by subjecting the bagasse to mild digestive action and sufi icient washing, conducted in such manner as to avoid the re-combination of the dissolved gummyor disassociated noncellulose constituents of the bagasse with the pure cellulose thereof, will be hereinafter more fully described.

In its simplest form the process comprises two main steps or stages, the first resulting in a cellulose product of substantial purity resembling in appearance the original un treated bagasse but which can be compactly shipped in dry form and used as a papermaking fiber, and the second stage resulting in a paper-makers half-stuff which may be converted into a commercially useful paper in substantially the same manner as halfstutl made from other materials, and such paper is found to possess all the desired qualities of texture and toughness, being also cheaply produced because of the abundance and. cheapness ot' bagasse and the mildness of the process by which it is derived.

One of the primary considerations in the successful production of paper halt-stuff from bagasse is the cost. of the treatment of the raw material in proportion to the yield of paper-making cellulose. While the cellulose forms by far the greater part of the composition of the bagasse, its form or organization is such that the application of ordinary reduction processes results in such extended loss by decomposition and impoverishment of material as to render the pro- Spccification of Letters Patent.

Patented Nov. 8, 1910.

Application filed September 8, 1908. Serial No. 452,142.

duction of halt-stud or paper on such basis wholly inipracticable trom the economical and commercial standpoint.

The present improved process is essentially characterized by the employn'ient of extremely mild or brief digestive treatment and o'l very low ttunperatnres and pressures, lower than have been used in any actual paper making process of which I am aware, so that the cost of the treatment is correspondingly small, while the cellulose yield is higher than can be obtained by the use of the ordinary or any method involving more prolonged and drastic action. The ratio of the cost of treatment to the cellulose yield is ample to establish the new process as a commercially practicable and profitable means for making paper from bagasse. I am enabled to accomplish such results with mildly active solutions, working under low pressure and temperature, by reason of the manner in which I conduct the process. Briefly stated I subject the bagasse to a series of partial digestions, in the mild solution, following each digestive treatment with a particularly thorough washing with water. Thereby, the dissolved impurities (being impurities only from the paper-making standpoint) are removed from the remaining material before they can recombine therewith and such remaining material goes into the next mild digestion treatment devoid of such matters and otherwise as clean as possible. The second treatment, though mild, operates most efiectively under these conditions to dissolve still more of the socalled impurities which in turn are likewise removed before they can recombine and so on, so that the delicate cellulose of bagasse is thus ultimately deprived of all its non-.

paper making associates without ever itself being subjected to the action of alkali of suflicient strength to injure it. The removal of dissolved impurities so that they do not become fixed in the cellulose of the remaining mass enables the weak solutions to perform effectively the impurity dissolving effect of stronger solutions and improves the character of the resulting fibers, as well as the amount of yield. While, theoretically, a great number of mild digestions, each followed by immediate thorough washing, will thus give the highest proportion of yield of pure cellulose, obvious commercial consid erations, particularly that of the time consumed, make it desirable that the number of treatments be reduced, even though it be at the expense of some increase in the strength of the alkali employed, and for this reason I prefer to conduct the process in two main steps or stages. The first step or stage results in the cellulose product above referred to as being suitable to be shipped as a papermaking fiber, and such stage may comprise a single digestive treatment, but preferably comprises two mild digestive treatments each followed by thorough washings, constituting a. fractional digestion treatment. The second step or stage, results in halfstufl', and consists of a short final digestive treatment calculated to complete the mechanical disintegration but still with the use of very mild solution or solutions and little or no pressure.

In carrying out my process I may use either air-dried bagasse or the wet freshly crushed bagasse in the condition in which it comes from the crushing rolls, and I prefer the latter because of the greater convenience in handling it. For the first stage of my )IOCGSS when cm 910 'in but a sin 'le di esa b b tive treatment, I proceed as follows: I place afquantity of the bagasse in a closed receptacle together with .an alkaline solution composed either of carbonate of soda or caustic soda or a mixture of both of these alkalies in. water, and then boil the mass under a moderate pressure for about an hour. In treating the ordinary or average grades of bagasse, the solution should contain an amount of carbonate of soda or of caustic soda approximately equal in weight to ten per cent. of the weight of the bagasse (air dried), and if a mixture of both alkalies is employed, a satisfactory proportion is two and a half per cent. of caustic soda with seven and a half per cent. of carbonate of soda taken with like reference to the Weight of the bagasse, but the percentage of alkali in the solution may be varied somewhat, depending upon the character of the charge under treatment, and the kind of alkali, also, may be adapted to the same condition.

The operator will understand that ba-f gasse in which the tissues are more refraetory must be treated with a stronger alkaline solution, and will therefore ascertain .whether the carbonate or caustic soda will give the best results, but in any case the solution employed is distinctively a weak solution as compared with-the strengths of solutions commonly employed in the production of half-stuff from Wood and other substances, and in practicing my process it is always best to use the weakestsolution which suffices to remove the gummy constituents or impurities in about the time mentioned; The boiling of the mass in the solution is preferably carried on at a pressure which gives a boiling point of about 100 C. or slightly higher, and while it is llill'JOI'ttlllt that the boiling be done at some pressure, it is advisable that it should not be allowed to exceed ten pounds for any considerable period. On the question of temperature and pressure, also, the. operator n'iust exercise his judgment, taking into considcration that as a general rule the stronger the alkali the less ten'iperature is required, and, in any event, the temperature and pressure are to be kept, as low as col'isistent with the strrngth of the alkaline solution and the character of the charge. During the boiling operation it is also desirable that the solution be caused to flow or percolate through the mass uniforn'ily in the same direction and that the mass be not agitated or disturbed during this stage, as otherwise b'al l ing of the fibrous mass and consequent. imperfect reduction is found to result.

The purpose of the mild treatment carried on as above indicated is to dissolve or disassociate from the cellulose the pectosans, fats, lignins, minerals and other similar and gummy in'ipuritics, without, however, affecting the Clltll'tlCtQl of the cellulose itself, and this first. stage. of my process is completed when such undesired constituents have been liberated from the cellulose to such an extent. that the reater part of them may be removed by rinsing. lVith the proportions as above git-en, this condition may be expected to arise in about an hours time as above stated and may be observed either by analytical tests-the cellulose showing itself in substantially unaffected condition and combined with very little of the other constituents, preferably not more than about five per cent.-or, after some experience, by the appearance and feeling of the mass itself, the material still retaining its original shape without material mechanical disinteg-ation, and the fibers remaining in a clean but not fully disintegrated condition.

In carrying out the preferred process in .which the first main stage thereof comprises [two digestive treatments, 2. digestion, I place the bagasse 1n the recepe. fractional tacle and treat it for about thirty'minutes with a solutioncontaining about from 2% to 5 per cent. of sodium carbonate at about 100 C. or up to and under a steam pressure of ten pounds. The liquid is then run off and the charge is further treated for about thirty minutes with a solution of from 5 per cent. to 7% per cent. of caustic soda at about the same temperature or steam pressure. Between the two stages the material should be washed for the purpose above explained by running water through it. It is not nossible to sufficiently remove the di gesting liquor by expressing it from the fiber without thorough Washing.

After treatment in the manner above indicated, the cellulose must be again thoroughly Washed either in the receptacle in which it has been boiled, or after removing it therefrom in any suitable manner in order to remove all of the gummy constituents that have been disassociated during the previous stage of the process and to prevent said liberated impurities becoming again fixed in the cellulose. A convenient type of washing machine which may be used, is one which is somewhat similar in general principle to a known machine for wasl'iing wool. It has two or more compartments with sieves or perforated walls and the washing liquid flows through such machine in the reverse direction to the travel of the material being washed. The material being washed is always so treated that it is not packed or crushed and is transferred from one compartment to another of the machine, by suitable rakes, which allow it to remain in its open shredded condition. The washed product thus obtained contains substantially all the cellulose of the original bagasse, in a vital and unimpaired condition and constitutes a material suitable to be dried and stored, or shipped, and from which a paper half-stuff can be readily obtained by a second chemical treatment of simple nature, which constitutes the second main stage of the process. This treatment consists in boiling the washed or washed and dried mass for about one hour at a temperature not exceeding 100 C., with a solu tion containing from about two and a half to five per cent. by weight of caustic soda taken with reference to the weight of the cellulose. The effect of this second treatment is to disintegrate and complete the reduction of the bagasse and at the same time to liberate such remaining gummy materials or impurities as may still be associated with the cellulose, but by reason of its mildness as well as the low temperature at which it is carried on, this treatment has no depreciative effect upon the .cellulose itself, and the latter is therefore obtainable at the conclusion of the proeess,and after washingin a practically pure state, unaffected by the caustic action of the .alkali. I believe the remarkable purity and vitality of the cellulose fibers of my productto be due as above stated to the removal of the digesting liquor in which most of the gummy constituents have been dissolved, before the process of reduction has reached a stage in which the impurities contained dissolved in that liquor can become fixed in the cellulose fibers. The said fibers do not, therefore, require severe and injurious treatment to complete their purification, such as has hitherto been the case with fibers that have been so impregnated and which then become brittle and dead as a consequence of the caustic action and heating.

The cellulose of the pith of bagasse is extremely susceptible to the action of strong alkali or alkaline salts under high temperatures, more so than other a parently analogous plants and the resuft of the severe treatment, such as has been hitherto given to bagasse, has been that the cellulose of the plth has been almost totally reduced and dissolved, while the remaining cellulose, that from the fibers and rind, has become brittle and discolored and has deteriorated through gummy and other ii'npurities which have been only incompletely removed, becoming again fixed in the cellulose as a result of the severe and prolonged treatment. The mild treatn'ient given to the bagasse ac cording to my invention is of such a nature, is contlnued only to such an extent, and comprises washing operations so arranged, that the impurities of the pith cellulose are removed without injury to such cellulose, while the impurities are effectually removed not from the pith alone but also from the other tissues as well, without deterioration of the cellulose of such tissues.

In its preferred form my process is conducted with a somewhat stronger solution or solutions for the operations constituting the first stage of the process than for the subsequent operation which results in'halfstuff, as I find it desirable to remove the gummy constituents as completely as possible without injuring the cellulose, in the first instance, but it will be understood that the less the amount of impurities removed in the first operation, the stronger will he the solution required for the final reduction to half-stuff, and in some cases it may be that substantially equal strength for both operations will be most serviceable, depending upon the kind of paper desired and the fancy of the operator, but such solutions will not vary substantially from the percentages hereinabove indicated and in the trade are weak solutions.

The apparatus suitable for use in treating bagasse according to my invention may consistsimply of a receptacle such as may be already found in pulp making establishments, provided wlth means for heating it to the required temperature under the proper pressure and for keeping up a circulation through the mass without, however, agitating it.

Having described my invention, what I claim and desire to secure by United States Letters Patent is:

1. A process of obtaining paper-making cellulose from bagasse, which consists in a. succession of mild digestive treatments of the bagasse, each treatment being terminated when a portion of the non-cellulose constituents'have been disassociated from the pure bagasse cellulose and before the latter becomes appreciably impaired by such treatment, and being followed by the immediate removal of such disassociated con stituents by washing, substantially as de scribed.

2. A process of obtaining cellulose suitable for aper-malting from bagasse, which consists n1 subjecting the bagiuse to mild digestive and reducing treatment under moderate heat and pressure for the purpose and with the result of liberating a portion of its non-cellulose constituents without injuriously atl'ccting the cellulose, or decomposing any substantial amount: thereof, washing such liberated constituents out of the mass before the cellulose fibers become recmnbined or im 'n'cgnated therewith and thereafter repeating such mild digestive tleat'n'icnt and washing upon the resultant product until the said non-cellulose constituents have been sutlicicntly removed.

3. A process of producing half-stutt from bagasse which consists in digesting the bagassc for about one hour in a solution or solutioi'is containing less than ten per cent. of alkali, taken with reference to the. weight of the bagasse, and under a pressure above atmosphere of approxin'iately ten pounds or less, until the greater part. of the constituents not cellulose has become disassociated from the bagasse and removable by washing, washing out said constituents and thereafter further digesting the mass in a mild digestive solution.

at. A process of obtaining cellulose suitable for paper-malting from bagasse, which consists in mildly digesting the bagasse under moderate heat. and pressure in a suitable reducing solution or solutions for such period of time, depending upon the effect thereof upon the bagasse, as will sutficc to disassociate or liberate therefrom a portion of the non-cellulose constituents without impairing or destroying any substantial part of the cellulose of the bagas-se and then separating such liberated constituents out of the mass by thorough washing and before the said cellulose becomes recombined or impregnated with said non-cellulose constituents.

A process of obtaining cellulose suitable for paper-making from bagasse, which 2510 consists in digesting the bagasse in a mildly active solution or solutions of moderate temperature and under a pressure above atmosphere of approximately ten pounds or less, continuing such treatment until a portion of 'i5'5 the non-cellulose constituents are disassociated from the bagasse cellulose but before the same become appreciably recombined or impregnated therein and then Washing the said liberated constituents out of the mass before such recombination or impregnation ing a portion of the non-cellulose constituents thereof, but Without. decomposing or injuriously att'ecting the cellulose, second, subjecting the resultant product to a further treatment in a clean. mildly reducing solution to liberate a further portion of said non-cellulose constituents, but without injuriously affecting the cellulose, and third, preventing reconibination of such liberated impurities with the cellulose of the remaining mass by washing with water.

7. A process of obtaining cellulose snitable for pa1' -r-mal ing from bagasse, which consists in digesting the bagasse in a mild alkaline solution for about one-half hour at a pressure above atmosphere of approximately 10 lbs. or less, washing the mass, further digesting the mass in a similar solution and under a similar pressure fo about half an hour and further washing the mass.

8. A process of producing half-stufl' from lmgasse, which consists in fractionally digesting the bagasse in a suitable reducing solution or solutions undermoderate heatand pressure substantially as set forth, continuing such treatment to a point where the greater part of the non-cellulose constituents has become disassociated or dissolved therefrom but without permitting the cellulose of the bagasse to become impregnated with the said dissolved constituents, washing the bagasse to remove said non-cellulose constituents, thereby leaving in the remaining mass substantially all the cellulose of the whole bagasse and thereafter further digesting the washed mass in a clean reducing solution until reduced to the condition of half-stuff.

J. A process of producing halfstuif from bagasse, which consists in fractionally digesting the bagasse in mild solutions until its non-cellulose constituents have become disassociated therefrom to such extent that, of the remaining combined mass about five per cent. will consist of such constituent-s, washing the said disassociated constituents out of the mass to leave therein all the cellu lose of the whole bagasse and then further digesting the washed mass until reduced to the condition of half-stuff.

10. The process of obtaining cellulose from bagasse, which consists in passing a mild digestive solution in one directlon through the bagasse under pressure of ap proximately ten pounds or less until the cellulose becomes disassociated from the remaining constituents, and then Washing said constituents outof the same.

In testimony whereof, I have signed my name to the specification in the presence of 125 two subscribing Witnesses.

TI-IOS. J. HUTCHINSON. VVitnesses Gno'. HEYS, FRANK A. HEYS.