US2607680A - Apparatus and method for processing vegetable fibers - Google Patents

Description

Aug. 19, 1952 c. B. wElss ET AL 2,607,680

APPARATUS AND METHOD F OR PROCESSING VEGETABLE FIBERS Filed Feb. 17, 1947 2 SHEETS-SHEET 1 vim l "T 5mm sumv BLACK )LIQUOR FRESH CAUSTI G VENT VEN T SQUEEZER. uunno.3

MIXER UNIT No.3.

4a? m n A q I\ I n BLACK LIQUOR I \'I '\:'-q vI \v' \VAV l \VI V \'I v v o um FRESH cAusm- 159 o 5 O COOMNG UNIT CHEMICALS WATER o I Q STEAM METERNO STOCK NSCHARGE o SCRAPER J4 FINAL SQUEEZER I FTT 55 l J2 H "533; 3/1/- M I I BLACK u UOR J8 ROTARY DISCHARGE I To 91 VALVE 1 0 m 5115A" saws STOCK TO WASHER YWWWMS a g 4 CZaremeflWws' 'arlesWhia-am warm, at; GM *w m 1 Ways A 1952 c. B. wElss 12 1- AL v 2,607,630

APPARATUS AND METHOD FOR PROCESSING VEGETABLE FIBERS- rla MIXER UNIT "0.! STOCK FROM B LE DRSINTEGRATOR OR WET CLEANING OJVERFLOW WATER 44 W WATER T0 BALE msm'rEeRATOR I SURGE TANKVK To sawen BLACK uquuR T0 BALE DISINTEGRATOR cbuosusm 10 BLACK uquoR 43 STOCK PUMP TO SEWER vunp gf F.

v v dlzrewefi. 7152s 'arlesmezzre,

Patented Aug. 19,1952

' UNITED STATES PATENT I OFFICE APPAnA'rus Anp METHOD FoR rnooii's's 1 i ING VEGETABLE FIBERS I Clarence B. Weiss and Charles W. Dean, Memphis, Tenn, assignors to Buckeye Go'tt'o'n Oil- C'ompany,.'M'emphis, Tenn., a' corporation of Ohio - ApplicationFebruary 17, 1947, Serial non'zzaosi This invention relates to improvements in the treatment of vegetable fibers to "produce a purified cellulos'e suitable for'use'i'n the various fields to which cellulose is adapted, and especially for the preparation of cellulose derivatives. It is an object of th invention to provide'an im step. 'Itis also desirable to'emplcy substantially fresh alkali in the final step and to use in an earlier stage the partially spent liquor derived from the final step. Such treatment not only has-the advantages which might be expected with countercurrent-processing, such as more or less complet utilization ofcaustic, reduction of processing. time, and simplification of equipment, but enhances the purity and color'of the finished product.

.Batchv and semi-continuous processes are not readily adaptable.to.multi-stepiprocessing of the character described, and continuous processing embodying the conventional counter-flow principle offers mechanical difliculties owing to the nature of. the material 7 being treated It is therefore proposed, as partof' the instant invention, to .conduct the alkaline treatment by causing a. liquid suspension of fibers to flow continuously through a. closed system including two or more treatment'zonesinv which elevated pressures and temperaturesmay be maintained, the

alkaline agent flowing. with the fibers in each of the treatment zones, and being expressed fromthe :fibers on discharge from each zone for return and. re-use in a preceding treatment zone. For. convenience, this method may be described as stepwise countercurrent' treatment, the fiber' being progressively treated with fresher alkali as the purity of'thefiber increases. We .have found that in thepractice of the invention in this manner, it is possible: to exhaust or substantially exhaust the alkaline agent, so that the-black liquor withdrawnfiat-the conclusion of the; first processing step is practically spent and 2' Claims. (01. 92-7) may be discarded without substantial loss of free caustic. I

It is a feature of the invention that most of the suspending liquid is expelled from the stock before introduction of the stock into each of the several treatment zones. "Consequently the stock is quickly and uniformly permeatedby the treating liquidadded to the partially dewatered stock'in each zone. Thisaccounts. in large measure, for T the exceptional uniformity of product and the substantialreduction in processing time achieved byour method. M

It will be perceived that expulsion of liqu'id under pressure, as described, permits elfective treatment of the fibers with a small amount of liquid capable of absorptionby the fibers; such small percentages of treatment liquid are highly economical, but must be expressed from. the fibers to allow absorption by the fibers of the liquid inthe succeeding stage of treatment.

The squeezing of the lint ers incident to the expulsion of liquid therefrom is also found to assist greatly in the removal of hull bran and of foreign particles, such as pieces of bells, leaves, cotton stalk, etc.; hus we have found that while such particles are: swollen with caustic, they maybe readily broken down by the application of pressure, disolved in the treatment liquid, and thus removed from the linter's.', Sim-. ilarly, waxes andwaxlike products may be more readily removedfromthe fibers if the latter are pressed and twisted while swollen with hot caustic.

Thus by continuously processing cotton linters 1n the manner described, we have been able "to produce cellulose ofremarkably uniform viscosity, regardless of substantial variation in they inventionmay be achieved by the typical practice. hereinafterset forth"; it being understood that no limitation of the scope of is intended by the useof describe thesame. v tus, suitable for such practice of "the invention,

the invention a specifie .language te- One embodiment" creepe s is illustrated in the accompanying drawings, in

which:

Figures 1 and 1a are a diagrammatic representation of a system suitable for the processing of cotton linters and like fibers, Figure 1a being a continuation of Figure 1. a

A suspension of linters in water or other liquid is fed by a pump to a head box H in which is maintained a constant supply of the suspension, any excess being returned to a bale disintegrator or other preliminary apparatus. From the head box the linters suspension is subsequent treatment stage may be constituted delivered to a thickener i2, which may -be ofconventional construction; in which the consistency of the suspension is 'increased, the drained liquid being withdrawn through outlet I5. Discharge conduit I8 of thickener l2 delivers the partially dewatered stock into the inlet end of a device 20, called for convenience ,a squeezer, which functions to compress the stock, thereby expelling liquid from the linters, excess liquid being withdrawn through outlet 22 and combinedwith-liquid from outlet l5 of the thickener for return to the bale disintegrator.

The expression of liquid from the fibrous material prior to treatment with the alkaline agent is important to effective practice of the invention, and a squeezer similar to that shown at 28 is associated with each step of the process, re-

leasing entrained liquid for re-use in a preceding treatment zon and delivering to the succeeding zoneacoricentrated stock from which the impurities dissolvedin the precedingzone have been largely removed, such stock being readily dispersible in and capable of reacting quickly with the fresher reagent. While various devices for compressing fibrous slurry to extract liquid are available for this purpose, it is preferable to employ a squeezer constructed and functioning similarly to that shown in our copending application for U. S. Letters Patent, Serial No. 729,056, filed concurrently herewith. In such a squeezer, the discharge of fibrous material is resisted by the frictional drag of the denser material near the outlet end, the compacted fibers plugging the outlet of the squeezer and thereby offering the resistance tomovement which is required for expulsion of liquid from the incoming stock. The fibrous plug also functions. as a barrier to prevent discharge of steam from the system, as hereinafter explained.

Thus as shown schematically in the accompanying drawings, the stock is fed by a screw conveyor 23 from the inlet end toward the outlet end of the squeezer, the screw working in a perforated cylinder 24 through which liquid may be expressed. The conveyor terminates short of the rear end of the cylinder to permit the formation adjacent the squeezer outlet of a plug of compacted fiber, this fibrous plug being gradually extruded at the outlet end and discharging downwardly through outlet conduit 25, the plug being continually replenished by the feeding of fresh fiber against its forward face. A picker device (not shown) efiectively disintegrates the fibrous plug, eliminating knots or lumps, facilitating the formation of a suspension in the succeeding treatment zone, and promoting intimate contact between the treating agent and the individual fibers.

From squeezer 2B the fibers are discharged into an elongated casing defining a cooking chamber, called for convenience a mixer 28, affording the first of a series of at least two treatment zones,

bya cylindrical compartment or casing having a screw conveyor 38, whereby the stock or suspension is agitated while being fed continuously from the inlet toward the outlet end of the mixer, the conveyor being so constructed and designed that the material remains in the mixer for the requisite period of time. This period may vary widely, but is preferably chosen, with due regard to other processing conditions, so that the operation in the first mixer is substantially limited to the removal, or partial removal, of incrusting materials and the like. a a

At the discharge end of the ,first mixer 28, the partially purified material is discharged through conduit 3 I into a second squeezer unit 32,-which may be-similar in structure and function to squeezer 28 hereinbefore described. The

liquid issuing from outlet pipe 34 of squeezer 32,

comprising completely spent zblackliquor, flows through a conduit comprising surge tank 36 and condenser'31, and may then be discarded. A pressure relief valve is located in the passage connecting the surge tank with the condenser. Th fibrous stock issuing from squeezer 32 is discharged into the inlet end of second mixer 38.. Partially spent liquor from the succeeding stage, and steam for establishing the desired conditions; of temperature and pressure, are admitted to,

mixer 38 through the outlet end of squeezer 32.

as hereinbefore described with reference to mixer 28 and queezer 20.

The stock is fed continuously in mixer 38 from the inlet toward the outlet end, forrexample by means of a screw conveyor; and is discharged at the outlet end of the mixer 'into a third squeezer 40, constructed similarly. to the'squeezers hereinbefore described; The treatment applied to the fiber in mixer 38 is essentially similar to that efiected in mixer 28, the purification of the fiber being continued substantially'to completion by the use of alkaliof greaterstrength and freshness than that employed in;the first stage. The partially spent liquor discharged from outlet 4| of squeezer 40 is passed through asurge tank 42 and a pump 43, being returned to the inlet end of mixer 28 by pipe 44. "The squeezed stock, together with fresh caustic and steam'is discharged from the'outlet .end of squeezer 40 into a third mixer 48- which'constitutes part of the third and final treatmentzone; 'As hereinbefore explained, the conditions established in the final zone are conducive to more intense or more extensive treatment and are so selected as to alter and improve the characteristics of the fiber, adequate purification havingbeen eifected in the preceding zone or zones byathe ,use of the'partially spent liquor derived from the final zone. For instance, a substantially higher temperature may be maintained in the final zone, whereby reduction of viscosity of ithecellulose product is facilitated; We prefer; however, tosupply steam of uniform pressure, withina range of 60 to 200 pounds per square inch to each zone, and to prochambers. or zones.

anoweeo vide for a substantially longer period of treatment in the final Jzone. Thusif the .perio'dof treat mentin-eachof the earlier zones is 6 minutes, the material may remain inithefinal zone for about 10. minutes, giving a total time for treatmentfof 22 'minut'esfo'r the three zones. Treate mentitimes may be easily regulated to establish satisfactory :processingconditions by adjustment of speed of thelscrew conveyors .in the -several mixers, and byiinterrupting the conveyor flights to retard the feedingrate, in theiknownmanner.

The minimum treatment. time in each 'of the purifying zones shouldnot be less than one minute. Treatment for about 4 minutes in each purifying zone is usually suific'ient in a system employing two such zones and "a final viscosity regulating zone; Treatment for a long'e'r'period of time will not "adversely affect the quality of the pulp, but. may unnecessarily increase consumption of caustic. In thefinal or viscosity regulating zone, at least 5 minutes should be allowed, the maximum period being: about 90 minutes. The treatment periods will, of course, vary with change in caustic concentration and temperature, and it is'ne'cessary to correlate these several factors to 'obtain optimum results.

The initial supply of alkali, as 'introducedinto the final stage in solution in an appropriate amount of water, will be determined largely by the grade of the linters being processed and the amount of impurities .contained therein. Thus 100 pounds of linters may require from 5 to 12 pounds of sodium hydroxide for adequate purification and viscosity reduction, 6 to 8 pounds usually being adequate for grades of linters most commonly treated. Excessive caustic usage over that used up in the chemical reactions which occur is obviously uneconomical, whereas an inadequate caustic usage will not result in adequate purification of the linters. Thus for proper viscosity control in processing a given grade of linters. it isnecessary to correlate only the factors of time and temperature, increasing either factor effecting. greater reduction in viscosity in the final stage and promoting the purifying action in the earlier stages.

To provide for an extended treatment time in the last zone, mixer 48, which may be constructed similarly to the preceding'mixers, discharge'sinto a cooking unit 50, having a capacity substantially greater than the capacity of the mixers, mixer 48 andcooking unit 50 affording in effect a continuous treatment chamber having a capacity substantially greater than that of. the preceding By altering the level of 'material in unit 50, the treatment time may easily be regulated; this-may be-efiected by controlling the rateoi withdrawal ofamaterials from the. unit for example by adjusting the speed of operation of the final squeezer 55. The cooking unit may comprise-an elongatedtank orcylinder throughwhich the stool: moves continuously by gravity, and in a relatively quiescent state, being fed into the upper end and withdrawnfrom the, lower end of the unit. To facilitate'withdrawal'of stock, a scraper or other conventional discharging device 52 may be provided in the lower end of the cooking unit. It will be noted that the conjoint use of mixer 48 and cooking unit 50 in the last processing stage contributes materially to the production of pulp of uniform viscosity, the mixer insuring effective contact of the agent with the fibers to initiate the reaction promptly and uniformly, and unit 50 providing for accurate adjustment of the duration of the reaction.

6 The stock is delivered to the :final squeezer '55 through the -outletwconduit 15:4, and thence through :a rotary di'schargevalve .516 to storage for subsequent processing. .flEhe-black liquor discharged from :outlet 2518 .ro'f jsquee'zer 55' is returned through a surge :t'ank 59 "and a pump *6 I to supply'linet'. .for:delivery:into itheinlet'end introduced. The -materials-fedinto the mixtank are suitablyheated;preferably by--steam,; and the mix isqdeliveredpthrough :a pump 66 and a meteringjdevice 5,637, to the inlet .end of mixer -48 of therfinal stage. -A-ny alkaline agent of a concentrationsuitable for the treatment of vegetable fibers may be employed, the commonly used sodium hydroxide being the preferred agent. By Way-of example -we may use-as the agent 2.5% caustic solution in amountsufiicient to establish a liquor to lint ratio of about 2.4:1 to 3.2:'1 in the several treatment zones. Concentration of caustie; is usually reducedfin the last zone to about 1.0% .to,2.0%, and in .theisecond zone to about 0.5% to 1.0%,; the liquor discharged from the first zone will .preierably contain not ever a small fraction of 1% of "caustic.

. These and otnertonainons and "factors involvedlinthe practiceofj the invention may vary widelyfin accordance with prior practice in'this field, provided that 'the selected conditions are such vas to promote .pu'rifi'o'a'tion of the 'ifiber in the preliminary treatmentzoneor zones, and improvement of-fibe'r characteristics, including viscosity, in'the final-zone.

"It will 'be'obser-ved that the process is contin'uous'throughout, and'that it lends itself par 'ticularly well to the production of cellulose of uniform viscosity. Thus, on initiating treatment of a batch of cotton linters, the'viscosity of 'the final product may be determined'from'a sample, regulation of the'viscosity being readily-effected by adjustment of operating conditions in the final treatment zone, preferably by varying the time of treatment in that zone, as hereinbefore indicated. Any conventional method of determining viscosity may be employed, for instance the method described in detail in Industrial and Engineering Chemistry. 'volfi23, page 136, 193-1.

For example, an average batch of linters, processed in three steps for-periods of 4 minutes, 4 minutes'and 30 minutes, respectively, employing in the last'step a 1% caustic solution and a liquorto lint ratio of 'l .-5:'l,-'th'e steam pressure ingeach'stagebeing '100 pounds'per square inch, will'yield'cellulose having a viscosity of the order of 3,000 seconds. if the'steam pressure is increased to 200"pounds per square inch, -'the viscosity of the cellulose vv-ill be rfedu'cedto about seconds. Howeven'if'the "processing time in the final stage be decreased from-30 minutes to about Gmi'nutes; and'steam a't 200 pounds per square inch be employed, "the final'viscosity will. be increased to 3,000 seconds. It is thus apparent that the viscosity of the final product may be varied over a wide range by appropriate selection of processing conditions, and that these conditions may be quite readily adjusted to yieldv any desired product.

It will be appreciated that satisfactory practice of the invention may be effected with the use of'only two stages, or that the number of puri- 7 fying or preliminary stages .may be increased. Benefits of the invention are obviously not realized, however, unlessthere; are provided at least two treatment-zones, the treating liquor being withdrawn,- at least in large part, from the fibrous material at the dischargeend of each such zone forreturn to-a-preceding. zone .or, in the case of the first zone, to waste.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent isz- 1. In apparatus for use in the continuous alkaline treatment of cotton linters in the preparation of cellulose, aclose'd system comprising a plurality of elongated, generally horizontal cooking casings afiording a succession of alkaline treatment zones, each casing having an inlet passage and a remotely located outlet passage, a conveyor in each casing for causing a suspension of linters in an alkaline liquid agent to flow continuously through each Of said casingsin succession from the inlet to the outlet passage thereof, a cooking tank afiording a final alkaline treatment zone, having an inlet passage and-a remotely located outlet passage, a squeezer associated with each outlet passage for'receiving and continuously compressing discharged linters to expel most of the liquid therefrom, each squeezer save that associated with the cooking tank communicating with the inlet passage of the succeeding casing to deliver thereto compressed linters, conduits continuously delivering expressed liquid from each squeezer save that associatedfwith the first casing to the inlet passage of 'a'preceding casing, a conduit continuously delivering to'the inlet passage of the cooking tank a fresh alkaline liquid agent, whereby the linters aretreated in the successive casings and cooking tank with a liquid agent of progressively increasing freshness, and steam pipes introducing in each of said casings and said cooking tank steam at a pressure of from 60 to 200 pounds per square inch, said cooking tank having a capacity substantially greater than that of the preceding casings, whereby the treatment time in said cooking tank is substantially greater.

2. In a process for the alkaline treatment of cotton linters in the preparation of cellulose, the steps which comprise feeding a slurry of cotton linters in a liquid into and through a compression zone, continuously mechanically compressing the linters in said zone to an extent sufficient to expel therefrom most of the liquid and to form the linters into a dense plug, continuously extruding the fibrous plug so formed from the compression Zone, disintegrating the plug as it is extruded, and discharging the fibrous particles derived from the plug into a first alkaline treatment zone containing an aqueous caustic solution, mixing the solution and the fibers to effect uniform impregnation of the fibers with the solution while continuously feeding the fibers through and out of said firsttreatment zone, maintaining in said first treatment zone a temperature corresponding to that of saturated steam of from 60 to 200 pounds pressure, delivering the fibers from said firsttreatment zone into a second 00111-1 pressionzone, compressing the fiberstin said second compression zoneto an extent sufiicient'. to expel. therefrom most .of nthe. solution entrained in the fibersv and to.form;the fibers into a dense plug, continuously.extrudingflthe fibrous plug so formed from thesecond compression zone, dis-. charging the fibrous particles. derived from the last named plug into a second alkaline treatment zone' containing an aqueous caustic solution, mixing the solution and the fibers to effect uniform impregnation of the fibers with the solution while continuously feedingthe. fibers through and out of said second treatment .zone, maintaining in saidsecond treatment "zone a temperature cor.- responding to that of saturated steam of from 60 to 200 pounds pressure, delivering the fibers from said second treatment zone into a third compression zone, compressing the fibers in said third compression zone to an extent sufiicient to expel therefrom most of the. solution entrained in the fibers into a dense plug, continuously extruding said last named plug from the third compression zone, and continuously returning the solutionexpelled from the fibers in said third compression zone to said first alkaline treatment zone. to provide the aqueous caustic solution therein.

CLARENCE B. WEISS. CHARLES W. DEAN.

REFERENCES CITED UNITED STATES PATENTS Name Date:v 1

Number 848,484 Newnham Mar. 26, 1907 1,048,853 Muntzing Dec. 31, 1912 1,505,934 Olier Aug. 19, 1924 1,632,802 ,Richter 'June 21, 1927 1,679,336 Dunbar July 31, 1928 1,683,262 Richter et a1 Sept. 4, 1928 1,690,954 Spencer 'Nov. 6, 1928 1,842,649 Bassett Jan; 26, 1932 1,915,812 Wollenberg June 27, 1933 1,933,609 Wagner Nov. 7, 1933 1,954,012 Lemberger Apr. 10,1934 2,007,348 Scharmann Jul 9, 1935 2,059,435 Brownlee Nov. 3, 1936 2,063,367 Roza Dec. 8, 1936 2,089,992 Campbell et al. Aug. 17, 1937 2,178,266 lomili'o Oct. 31, 1939 2,263,903 Pomilio Nov. 25, 1941 2,355,091 McDonald Aug. 8, 1944 V FOREIGN PATENTS Number 'Country Date 559,909 Great Britain 1 Mar. 10, 1944 537,038 France 1 .May 13, 1922 86,206 Sweden Apr. 28, 1936 OTHER REFERENCES

Claims (1)

1. IN APPARATUS FOR USE IN THE CONTINUOUS ALKALINE TREATMENT OF COTTON LINTERS IN THE PREPARATION OF CELLULOSE, A CLOSED SYSTEM COMPRISING A PLURALITY OF ELONGATED, GENERALLY HORIZONTAL COOKING CASINGS AFFORDING A SUCCESSION OF ALKALINE TREATMENT ZONES, EACH CASING HAVING AN INLET PASSAGE AND A REMOTELY LOCATED OUTLET PASSAGE, A CONVEYOR IN EACH CASING FOR CAUSING A SUSPENSION OF LINTERS IN AN ALKALINE LIQUID AGENT TO FLOW CONTINUOUSLY THROUGH EACH OF SAID CASTINGS IN SUCCESSION FROM THE INLET TO THE OUTLET PASSAGE THEREOF, A COOKING TANK AFFORDING A FINAL ALKALINE TREATMENT ZONE, HAVING AN INLET PASSAGE AND A REMOTELY LOCATED OUTLET PASSAGE, A SQUEEZER ASSOCIATED WITH EACH OUTLET PASSAGE FOR RECEIVING AND CONTINUOUSLY COMPRESSING DISCHARGED LINTERS TO EXPEL MOST OF THE LIQUID THEREFROM, EACH SQUEEZER SAVE THAT ASSOCIATED WITH THE COOKING TANK COMMUNICATING WITH THE INLET PASSAGE OF THE SUCCEEDING CASING TO DELIVER THERETO COMPRESSED LINTERS, CONDUITS CONTINUOUSLY DELIVERING EXPRESSED LIQUID FROM EACH SEQEEZER SAVE THAT ASSOCIATED WITH THE FIRST CASING TO THE INLET PASSAGE OF A PRECEDING CASING, A CONDUIT CONTINUOUSLY DELIVERING TO THE INLET PASSAGE OF THE COOKING TANK A FRESH ALKALINE LIQUID AGENT, WHEREBY THE LINTERS ARE TREATED IN THE SUCCESSIVE CASINGS AND COOKING TANK WITH A LIQUID AGENT OF PROGESSIVELY INCREASING FRESHNESS, AND STEAM PIPES INTRODUCING IN EACH OF SAID CASTINGS AND SAID COOKING TANK STEAM AT A PRESSURE OF FROM 60 TO 200 POUNDS PER SQUARE INCH, SAID COOKING TANK HAVING A CAPACITY SUBSTANTIALLY GREATER THAN THAT OF THE PRECEDING CASTINGS, WHEREBY THE TREATMENT TIME IN SAID COOKING TANK IS SUBSTANTIALLY GREATER.

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