US2932600A

US2932600A - Process for the production of pulp from bagasse

Info

Publication number: US2932600A
Application number: US338910A
Authority: US
Inventors: Edward L Powell
Original assignee: Brown and Root Inc
Current assignee: Brown and Root Inc
Priority date: 1953-02-25
Filing date: 1953-02-25
Publication date: 1960-04-12
Anticipated expiration: 1977-04-12

Description

Edward L. Powell, Lookout Mountain,

No. 188,265, filed October 3, 1950,

United States Patent PROCESS FOR THE PRODUCTION OF PULP FROM BAGASSE Tenn., assignor to grown and Root, Inc., Houston, Tex., a corporation of exas 1 No Drawing. Application February 25, 1953 SEl'lfllNO. 338,910

2 Claims. (Cl. 162-58) The present invention relates to processes for producing purified cellulose for chemical consumption and more particularly is directed to the production of pulp from bagasses for use as chemical pulp, paper pulp and the like in subsequent manufacturing processes. This application is a continuation in part of my application Serial entitled Process for the Production of Bulk From Bagasse, now abandoned.

Presently available sources of raw materials for the production of pulp include wood, straw and cotton linters. Due to the large volume of pulp now being used industrially, these sources are rapidly becoming inadequate and it has become necessary to find new sources of raw materials. One such source, which is readily available in ample quantities,is the bagasse which is a necessary waste product in the production of sugar from sugar cane. Bagasse is present in many areas of the World, chiefly in the tropical and lower temperate zones. Since it is a waste product and is available throughout the world in large quantities, it constitutes a fruitful new source of pulp, where its use as a fuel can, if necessary, be partially or completely replaced by more conventional fuels.

Bagasse results from the crushing of sugar cane in the production of sugar, in which the cane is shredded and the shreds are passed between heavy rolls for squeezing out the saccharine juices from the plant tissues. The residue resulting from the sugar extraction process is a coarse, fibrous mass which is commercially known as bagasse and has generally been used as a fuel burned in the steam boilers of the sugar plantations.

The treatment of bagasse to render its fibers suitable for use as a commercial pulp must vary, depending primarily upon the end use to be made of the product.

The bagasse consists essentially of plant tissue containing cellulose fibers, as well as hemicelluloses, pentosans, pectins and gums. The chemical analysis of bagasse is given on page 171 of The Chemurgic Digest for May 31, 1945. To provide a purified cellulose suitable as a commercial pulp, these hemicelluloses or non-cellulosic components of the bagasse may be present in very small amounts or may be removed entirely from the fibers. For this purpose, known processes have treated the bagasse fibers at some stage during processing with mineral or organic acids, but these processes have been proven to be costly to carry out and theresulting pulp cannot economically compete with other less expensive pulps, particularly wood pulp made from southern pine.

It is, therefore, one object of my invention to produce a commercial pulp from bagasse, and particularly a pulp which can be'produced at a very low cost, making the pulp commercially desirable.

Another object of my invention is to produce a purified cellulose from bagasse without employing inorganic or organic acids, the process being carried out economically, producing a pulp with a low mineral content and characterized by the high whiteness of its appearance.

A further object is ,to provide a process for the production of pulp-from bagasse in which the bulk of the incrustants present in the bagasse are removed from it by steam distillation, rather than by an alkaline treatment.

Still another object of my invention is to provide a process for the production of pulp from bagasse including a pre-hydrolysis treatment in a cooking vessel under steam pressure, a partial venting of the cooking vessel to effect steam distillation of incrustants from the bagasse, followed immediately by an alkaline extraction without completely removing the steam pressure and without washing the bagasse between the pre-hydrolysis and the alkaline extraction steps.

The foregoing and other objects, features and advantages of this invention will be apparent from the following description, it being understood that the detailed description is merely illustrative of the invention, which is defined in the claims.

In carrying out the process, relatively long fibered fractions of bagasse are selected and are separated from the pith and from the short fibers of the crushed sugar cane by such known processes as wet shredding, dry shredding, flotation, or screening of the coarse fibrous mass of crushed cane. In this manner, the selected fibers, which form about 50% of the entire mass, are obtained. The selected fibers are partially fibrillated, as distinguished from relatively coarse bundles of the crushed cane mass. The bagasse fibers so selected have a moisture content of 75% or below.

The depithed, long fibers just described result in a product of a quality slightly higher than that obtained in using whole bagasse. They are used to advantage in producing pulp in geographical areas in which the rest of the bagasse, including the pith and. the short fibers, is needed for use as fuel.- 7

On the other hand, in areas where fuelis more readily available and is cheaper, all of the bagasse can be used in producing pulp, with a consequent higher yield.

Because bagasse fiber is a very bulky material, it was discovered that, to produce an economical return, it would be necessary to use either ponderous equipment or very rapid processing cycles. In order to avoid the use of very heavy and expensive equipment, it was deemed more practical to accelerate the processing cycles. It was found that this can be done by using a rotary digester as the cooking vessel, which makes possible the use of a lower liquor-to-fiber ratio. As a consequence, the time and the quantity of heat required to bring the vessel up to pressure are much lower than would otherwise be the case. Such a rotary vessel must be one capable of steam operating pressures up to'150 pounds per square inch.

The bagasse, either in the form of whole bagasse or of depithed fibers, is placed in the cooking vessel, which is then closed and rotated. Live steam is introduced into the vessel until the proper pressure, about to p.s.i, is reached. The vessel is rotated continuously for a period of about thirty minutes to one hour, during which time the steam pressure is maintained. The latent acidity of the vapors created is sufficient to effect the required degree of prehydrolysis.

The rotation of the vessel is stopped and it is then partially vented down to a pressure of between 50 and 60 p.s.i. During this partial venting or blow-oil, substantially all of the liquefied incrustants are removed by an effective steam distillation. Although under some circumstances it may be desirable to vent the vessel completely, it is not considered essential to do so. With only a partial venting, considerable time may he saved in the whole pulp production cycle.

Under the conditions of this process, in which no actual mineral, or other acid is added it is not necessary to wash the fiber between the pre-hydrolysis treatment and assaeoo the alkaline extraction step. This, also, saves time in the process and, in addition, saves material because, in any washing process, there is'necessarily some loss of material. Yield values have been consistently higher in the use of my process than in the use of other'methods, largely due to the elimination of the use of applied acids and of this washing step.

After the .vessel'has been vented down to the lower pressure, a caustic, such as-a2 .or' 3% solution of sodium, potassiumor calcium hydroxide, in a weight ratio of 5 to 1, based on the weight of the fiberas originally placed in the vessel, is pumped into thevessel under the necessary pressure. Introducing the caustic into the same vessel under pressure further shortens the time cycle, since it is not then necessary to build the steam pressure up again all the way from atmospheric pressure. Of course, where the vessel has beencompletely vented, such pressure on the caustic is not needed. Rotation of-the vessel 'is begun again and steam is introduced into the vessel to a pressure ofabout 100 to 125 p.'s.i., rotation of the vessel being continued for a period of about thirty minutes -t o onehour. -Any incrustants remaining after the partial (qr-complete venting of the vessel are saponified or otherwise solubi-lized in the alkaline treatment. The vessel is again vented and thefibers are removed from it.

The .pre-steamed, alkaline extracted, mass is next washed directly with water, which also keeps the yields at' an economicallysound value. It is then agitated to breakup fiber bundles and screened. Because of the purity of the fiber j'at'this point, it is not necessary to have a preliminary chlorination step. Previously used processes requires two-stage bleaching, comprising a preliminary chlorination, followed by bleaching with other conventional bleaching agents, such as calcium or sodium hypochloriteyand then followed by a secondary alkaline extraction step. 1 Such processes are expensive, from both standpoints of materials used and yield. By contrast, in my;process, calcium or sodium hypochlorite is the only required bleaching agent and'the resulting yield is'appreciablyhigher. The bleach is followed by'a conventional washing.

-Depending upon the type of, pulp to be obtained from the bagasse, that is, for example, whether an acetate type pulp which can be used in the manufacture of cellulose acetate is desired or a pulp for the manufacture of viscose film or filaments, or cellulose nitrate, or a paper pulp, the

steam-hydrolysis step may be varied as to either pressure or time of treatment or both.v In general, the longer the timeand thehigher the steam pressure, the lower will be the pentosan content and the higher will he the alpha cellulose content of the resulting pulp product.

Similarly, the alkaline extraction step may be varied 'with' respect to caustic content, liquor ratio, steam pres-.

sure, and time, or all four of these factors, depending upon the desired end use of'the product. I

"By theuse of my invention, several advantages are enjoyed. The use of a rotary vessel etfectsan appreciable savingin'timeand in quantity of heat required. With =the'useof'a rotating vessel, a superior degree'of uniform- -'-ity ofsproduct'is achieved. Elimination of any added acid veifects an economy inmaterials. The partial ventingor blow-otf of the vessel after the pre-hydrolysis treatment effects a steam distillation of the incrustants which because a washing cycle is eliminated, increases theyield of the process. The partial venting also saves an appreciable amount of time and of fuel, since, in the subsequent alkaline extraction step, it is not necessary to raise the steam pressure up all the way from atmospheric pressure. Moreover, due to. the eliminationof any. added. acid, no washing is needed between thepre-"hydrolysis 'and the alkaline extraction steps. This means a further saving of time and ahigher yield, since there isno loss of material in washing. The elimination ofi a preliminary Lchlorination step effects a further saving in time and materials. Finally, since the treated material is of high purity, only a single-stage bleach is required, "further saving time and materials.

I claim:

1. A process for producing purified cellulose pulp from bagasse consisting of agitating and treating bag'asse with steam under pressure of to 125,p.s.i. .for aperiodof thirty minutes to one hour, rapidly relieving thepressure to one-half or less than'half its highest value, adding'to the materials. 2 to 3 percent caustic solution intheproportion of 5 partssolution to 1 part bagasse, by weight,

then agitating and cooking thematerial with live :steam.

under pressureof 100 to psi. for a 'periodof thirty minutes toonehour.

.2. A processfor producing purified cellulosepulpl from bagasse consisting of agitating. and treating 'bagasse with steam under pressure of 100m 125 p.s.i.v for aperiod of thirty. minutes to onehour, rapidly and .only partially. relieving-the pressure down to 50.10 60 psi, adding .to the material under pressure a 2 to 3 percent caustic solution in the proportion of 5 parts solution to l part bagass e, by weight, then agitatingand cooking the material with live steam under pressure off-100 to 125 .p.s.i. for. a period of thirty minutes to one hour.

References Cited in the file of thispatent" UNITEDSTATES PATENTS 109,742 Keen "Nov. 29, 1870 117,683 Riddell Aug.l 1, 1871 811,419 'Manns "Jan. 30, 1906 1,235,220 Marsden July 31, 1917 1,679,441 Nanji Aug. 7, 1928 1,729,772 Forsyth Oct.' 1,. 1929 1,739,683 Lucas .4 Dec. 17,1929 1,782,869 De La Roza Nov.,25, 1930 1,813,184 McQuiston et al. ..-'July 7, 1931 1,831,032 Richter Nov. 10, 1931 1,931,933 Nicoll .Oct. 24, 1933 1,993,148 De Cew Mar. 5, 1935 2,049,676 Tomlinson Q. Aug. 4, 1936 2,161,763 Jones Jnne6, 1939 2,530,244 Jensen Nov. 14, 1950 2 ,560,638 Dreyfus July..17, 1951 2,583,994 Briggs Jan. 29,. 1952 2,640,774 Ross et al. June 2 1953 OTHER REFERENCES

Claims

1. A PROCESS FOR PRODUCING PURIFIED CELLULOSE PULP FROM BAGASSE CONSISTING OF AGITATING AND TREATING BAGASSE WITH STEAM UNDER PRESSURE OF 100 TO 125 P.S.I. FOR A PERIOD OF THIRTY MINUTES TO ONE HOUR, RAPIDLY RELIEVING THE PRESSURE TO ONE-HALF OR LESS THAN HALF ITS HIGHEST VALUE, ADDING TO THE MATERIAL A 2 TO 3 PERCENT CAUSTIC SOLUTION IN THE PROPORTION OF 5 PARTS SOLUTION TO 1 PART BAGASSE, BY WEIGHT, THEN AGITATING AND COOKING THE MATERIAL WITH LIVE STEAM UNDER PRESSURE OF 100 TO 125 P.S.I. FOR A PERIOD OF THIRTY MINUTES TO ONE HOUR.