US2381965A - Solvent extraction of solid materials - Google Patents

Description

Aug. 14,

N. E. BERRY SOLVENT EXTRACTION OF SOLID MATERIALS 2 Sheets-Sheet 1 Filed May 8. 1941 AW 14 1945 N. E. BERRY 2,381,965;

SOLVENT EXTRACTION OF SOLID MATEREEALS Filed May 8, 1941 2 Sheets-Sheet 2 7 JaL IE/v7 /A/ LAET Ms ree/Az F550 Marne/,9L omc/mea;

MH rf@ fnl. F5515 DI d Exrfic T104/ 324529 ENEL Pstesieanug. 14, 194s 'y soLvEN'r Ex'rmio'rloN or soLm MATERIALS vNorton E. Berry, Summit, N. J asaignor to General Foods Corporation, New York, N. Y.r a corporation of Delaware Application Mayv s, 1941, sensi No. 392,590 4 claims. (ci. :za-210) This invention relates to the solvent extraction of solid materials and is directed to the provision of an improvedrsystem of countercurrent liquidsolid extraction adapted for the treatment of such materials ascacao beans, soy ibeans, coffee beans,

iligar beet cossettes, coarse mineral sands and the It is generally recognized in the operation ofv any'liquid-solid extraction system, whether of the single or multiple liquid phase type, that the eiliciency of the extraction is'increasedas the velocity of movement of the solvent relative tothe material extracted is increased. For this reason it is considered good practice in batch procedures to employ some form of agitation and in continuous processes to employ the highest velocity of solvent ow feasible underthe conditions obtaining in each particular case. However, there are practical and economic considerations which normally limit the velocities obtainable in countercurrent procedures'of the typel now in use, and in a great many instances, as, where a hish degree of extraction is desired, these limitations entail a serious loss jin efficiency of the extraction l continuous liquid-solid 'extraction system of greater eciency than the countercurrent extraction procedures heretofore employed.- I

A further object of the invention is to provide a countercurrent liquid-solid extraction process wherein lesser quantities of solvent are required to obtain given velocities of movement of solvent relative to the material extracted than have been required with the procedures heretofore employed. 1

I have found that the above objects can be at.- tained by imparting an alternating forward and backward movement to the body of solvent in l contact with the Amaterial while maintaining a desired net forward flow of solvent throughv the extraction apparatus countercurrently to the material. Compared with the 'velocity obtainable with a unidirectional movement :of solvent through thematerial at the same netiilow, the

..actuaiygloeity of movement of the solvent may thus be madeconsiderably'greater not only in the forward butin the backward direction. Hence an increased velocity of movement of solvent relavSii tive to the material being extracted is. obtainable with any given quantity j'of solvent, and con-- versely, any givenr velocity of movement of sol\ vent is obtainable with a lesser quantity ofsolvent than required when unidirectional movement of solvent through the material 'is employed.- Thefrequency and extent .of the alternating movement of the solvent relative to the material can be adjusted to suit conditions infany particular. case, but the extent 'of movement in each direction shoum not bes'o great as to interre with proper countercurrent operation.

Any suitable method and apparatus can be employed to eifect the desired alternation ofthe direction of movement of solvent.' Assuming for example a normal countercurrent flow of solvent and solid material into and out of the extraction apparatus, the body of solvent in the apparatus may be moved baclr"` and forth lthrough the material being extracted by means of a suitable pumping device. Alternatively the relative extent of movement of the body of solvent intheziorward and reverse directions may be regulated so a predetermined quantity of solvent is discharged from the apparatus during each cycle, the 'quan-'- tity discharged being of course compensated by the introduction of an equivalent quantity of fresh solvent at the inlet end of the apparatus. .'In both cases the level of solvent in the apparatus will vary but since the magnitudeof the reversals is preferably made small,I such-variation is not objectionable and in fact-provides a convenient means of regulating the reversal of ilow.

The last-mentioned procedure has the advan- --tage that it can be performed without .material changeoi existing equipment, and hence 'it may conveniently be used to illustrate the operation of the invention, but lt will be understood that the methods and apparatus specifically described in the following examples are for purposes of illustration only. f

-In the accompanying drawings: i

Fig.' 1 is a schematic showing of an apparatus suitable for practicing the invention in connection with tlm countercurrent extraction of solid materials lighter than the solvent; and

Figs. 2,. 3, and 4 are schematlcshowings of three different forms vof apparatus suitable for practicing the invention in 'connection with the countbrcurrent @extraction vof solid materials heavier than the solvent, the passage of thematerlal through the solvent being eifected by gravity in Fig'. 2 and by screw propulsion in each of Fits. Band 4. I

Pig. 1 illustrates the applica n of the inven- A tion to the method of countercurrent extraction of caiein from green coiee beans disclosed in the co-pending application of T. M. Rector, Serial No. 373,039, led January 3, V1941. In accordance with this method, the beans are passed upwardly under the action of buoyancy through a vertical column of downwardly moving caifein solvent.

Referring to this ligure, the extracting apparatus is shown as comprising a heat insulated vessel I through which the coffee passes upwardly and the solvent downwardly in countercurrent relation, the vessel preferably being of cylindrical form and having a coned bottom II. Centrally fitted through the coned bottom II is an injector pipe I2 connected to a pump I3 `having its input connected by a pipe I4 with a hopper I5, into which the coffee to be extracted is continuously fed in any suitable manner. Solvent from the `vessel lll is continuously introduced through the pipe I6 into the hopper I5, from which it flows through the pipe Il to the pump I3, which pumps it back into the vessel I0 through the injector pipe I2. The introduction of solvent into the hopper I5 is controlled by a float valve I1, to maintain a desired level I8 therein, and the coiee and solvent in the hopper I5 form a slurry which can be readily pumped through the pipe I2 into the vessel Ill. The pipe I6 preferably communicates-With the vessel I0 below the outlet of injector pipe I2 to insure by the rising and falling solvent level 29 in the vessel I0, as by means' of a float operatedl switch 30 responsive to thesolvent level and controlling the pump driving motor. As shown, the operating arm 3l of the switch has an aperture 32 through which a vertical rod 33 carrying actuating blocks 34 on either slide of the operating against any return passage of coifee therethrough. I'he coffee introduced in the vessel I0 being lighter than the solvent rises against the bottom I9 of the column of beans 20 which substantially fills the vessel I0 and due toits buoyancy extends above the level of the solvent. Colee from the top of the column of beans 20 is discharged through a side chute 2| by a rotary raking mechanism 22. Fresh solvent is intro- .duced into the top of the vessel I0 through the hollow shaft 23 of the raking mechanismA and an associated rotating sprayer 24, and spent solvent is discharged from the bottom of the vessel by a pipe 25.

As described in the aforesaid Rector applica.. tion, the above apparatus is adapted for the continuous countercurrent extraction of caffein from the coffee beans at a constant rate of solvent flow through the vessel I0. 'I'he present invention additionally provides for the back and forth movement of the body of solvent within the vessel to increase the velocity of movement of the solvent through the coiee beans. This result is accomplished in the form shown by alternately withdrawing from and returning to the vessel I0 a portion of the solvent therein, the frequency arm 3l is freely movable. The lower end of rod 33 is attached to a noat 35 in a oat chamber or vessel 36 that is connected by a pipe 3l to the vessel I0. Hence the level of solvent in the vessels Ill and 36 is the same. When this level rises to a desired point 'as indicated by the dotted line 38, the upward movement ofthe oat 35 closes the switch 30 and starts the operation o the pump 26. When the solvent level falls to a suitable point as indicated by the dotted line 39, the downward movement of the iioat 25 opens the switch 30 and stops the pump 26 so that the solvent pumped into the storage vessel 28 runs back by gravity into the vessel I0, the pump being of suitable type or suitably arranged to permit the return iiow. Thus it is apparent that solvent is alternately transferred from the vesseltl into the vessel 28 and returned from the vessel 28 into the vessel I0, which maintains alternate downward and upward movement of the body of solvent in the vessel I0.

The rates at which solvent is alternately removed from the vessel I0 by the pump 26 and returned to the vessel lll by gravity are preferably made to exceed considerably the normal rate of solvent flow through the apparatus, so that high velocities of movement'of the solvent are maintained in the vessel IIJ in both directions of movement of the solvent. However, the quantitles of solvent alternately removed from the vessel I0 by the pump 26 and returned to the vessel I0 by gravity yare made comparatively small by suitable adjustment of the switch blocks 34 so that the alternate downward and upward movement of the solvent takes place over comparatively small distances and does not interfere with the desired countercurrent operation.

It will be seen that they withdrawal of spent solvent from the apparatus at a rate equal to the rate of'introduction of `fresh solvent can take place regardless of the alternate upward and downward movement of solvent inthe vessel IB as described above, so thatthe desired net forward ilow of solvent through the apparatus is maintained. Preferably, however, this net forward flowl is combined with the withdrawal of solvent from the vessel I0 by the pump 26 in order to avoid unnecessary duplication of equipment. To this end the storage vessel 2B is provided with an overflow pipe 40 through which spent solvent overflows from the vessel 28 and is discharged from the apparatus on each pumping cycle of the pump 26. The quantity of solvent returned to the vessel I0 is thus less than that withdrawn on each cycle of operation by an In ycarrying out the above described operation, solvent leaving the vessel I0 through the pipe 25 is delivered by an intermittentlypperated pump 26 and a pipe 21 to a storage'chamber or vessel 28, from which it iows back into thev vessel I0 when the pump stops to cause the periodic reversal of movement of the body of solvent in the vessel. The intermittent operation of the pump 26 is conveniently controlled amount which is equal to the quantity of fresh solvent introduced into the vessel I@ through the hollow shaft 23 and sprayer 2t during the cycle. In operation, when solvent reaches the level '3S in the vessel Ill, pump 26 begins to pump sol= vent into the storage vessel 28. The solvent in the latter vessel rises to the level .el of the overflow d0 and thereafter overows until the lower level 3Q is reached in the vessel lll. At this point pump 26 stops and solvent flows back into the vessel l0 while the level of solvent in the storage vessel 28 falls to the point 62. Meanwhile the assises j vessel through pipe 45. Solvent is withdrawn solvent level inthe vessel Il rises again to the point Il. due to the return oi solvent from the storage vessel 2l and the introduction of fresh solvent, whereupon' the pump 26 starts again and the cycle isrepeated. The average rates of introduction ot fresh solvent into the vessel II and discharge of spent solvent through the overilow Il are always equal, so if desired the introduction of fresh solvent may vary from time to time' or be intermittent without eect on the operation. Preferably the operation should be such that the lower limit 42 in the storage vessel 2l is kept above the upper level Il in the vessel Ili,

even i! the supply of fresh solvent should fail.

It will be seen that there is a substantially iloating column or mass of coiee in the vessel Il, untreated collec being continuously supplied to the bottom of the columnby the injector pipe l2 while treated coiiee is continuously discharged trom'the top of the column by the raking mechanism 22. Because of its inertia, thetendency o( the column of coffee to, rise and fall with varlauoos in the solvent level' ls relatively ought,

when the upward and downward movement of the solvent-ifs erected at luga velocity and for short periods, and" consequently the velocity of movement of the solvent through and relative to the mass of -coiifee'isrelatively high and the emciency oi extraction is accordingly increased. 0n the other hand; the extraction is carried'out without increasing the quantity ot solvent necessary to maintain the desired net forward ow of solvent' through the apparatus as determined bythe average rate of introduction of fresh solvent into the vessel l.. Moreover, because o! the high-velocity alternating movement of solvent maintained inthe vessel Il, the amount of solventused may he reduced if desired without sacrifice oi'` eihciency.

' three forms of apparatus shown diagramlEl' leavellitattlletopthrt'lughltnoverowpirlcli.v

. tion through a conduit 6l.

from the extraction vessel by a pipe il and an intermittently operated pump Iii and delivered to an elevated storage vessel 52, from which the solvent returns to the extraction vessel by gravity when the pump'stops. The operation o! the pump can be controlled conveniently by the rise and fall of solvent in the storage vessel. In the form shownl a iloat operated switch 53 similar tothe 'switch Sil'of Fig. l controls the pump 'driving motor and is operated by a iloat- 54 in response to variations of the solvent level in the vessel 52. When the solvent level reaches the desired maximum indicated by dotted line I5, the switch 'it is operated to stop the pump. The solvent then ilows out of the vessel by gravity until the desired'minimum level indicated by dotted line i6 is reached, whereupon the switch is operated to start the pump and the cycle is repeated. 'Ihe pump 5| and conduit 50 should be proportioned to provide the desired rate of ilow and velocity of movement of the solvent, and the e vol e of solvent withdrawnand frequency of alternation can be regulated by 'adjusting the position of the switch blocksy 5l and 58.

'The rate at which solvent lis alternately removed and returned through the conduit ,.'l`

should be large in comparison with the rate of introduction of fresh solvent through the pipe M. The level 59 of spent solvent in the vessel I3 varies between an upper limit to determined by overflow pipe l5 and a lower -limit il the distance between these limits being small as compared to the height of the vessel 43 and being dependent upon the amolmt of fresh solvent introduced and the amount of solvent withdrawn by the pump 5i. Since the volume of solvent withdrawn by the pump is equal to the volume returned by gravity, the amount of spent solvent discharged throughv the overilow pipe It is always equal to the amount of fresh solvent introduced through pipe 4l.

Fig. 3 illustrates a U-shaped extraction vesselcomprising a horizontal section i2 and vertical sections 6l and il each provided with a screw for conveying the solid material which is continuously introduced into the top of vertical4 section II and continuously discharged from vertical section Il through a chute. 6I.. Freshsolvext is introduced intothe top of vertical section ll through a pipe il and spent solvent is removed from sec- 'rl outlet eomlult tl le eolinected through a pump ll-to a storage vessel Il provided with ,an overllowpipe "Il, Controllingthepump II is a door opts-atea swlten ll oetuated by the level of'l solventinadlamberllconnectedtothevertical eeeaoonbyanlnels. Rleeortnesolventlevel] iltoadeaircdupperlimitlistartsthepuml.-

whileV tall-o! the level-M to a desired lower limit 16 stops the pump Il. Spent solvent is thus 4al- Aternatelytransferredbythepunillilirolntlle1 to the storage-vessel and returned bylravltyfrom thelatterto theextraction vessel.

'Intisoperatlontheleveiotspentsolventin'the' venel Il varies between upper and lower limitsv l1 aindlllndtotheellentthfrehsolventlsintraducen ummh the pille GI. spent solvent will be' discharged through the overilow pipe lo.

` naalllustrateesull mother'mle eremo-action4 :params to which the invention may be applied.

llllallmnathevesselaverticallegllr.

.ducedaniaconnectinginclinedscrewcarrying vnl vsechnnllitllroughwhichthlematerialisconveyed tori chute ll. Freshsolventisintroduced near the upper end o leg Bil through a. pipe 32 and spent solvent is discharged from the leg 1S through an overow pipe B3. As in the case of the apparatus previously described means are provided for establishing an alternating low-amplitude high-velocity movement of the body of solvent in the' extraction vessel, such means comprising a pipe 84, pump 85 andstorage vessel 8S provided with a lioat switch l1 controlling the operation of the pump. However, in this case, withdrawal of solvent from the extraction vessel takes place by gravity until the solvent level in the storage veel reaches the upper limit 88. At this point the :doat switch 81 starts the pump and solvent is forced back` into the extraction vessel until the level in the storage 'vessel drops to the lower limit 89, when the pumpl is stopped and the cycle is repeated.

Rrom the foregoing description it will be appement that the invention provides increased velocity oi movement of the solvent in contact with the solid numerici and accordingly increased efciencxrv of extraction, without .the quantity of solvent required. In cases where it ls important to extract the material tothe greatest possible extent, as in decaieinating coffee, for instance, the invention makes possible the extraction of a greater `proportion of the calein content than has heretofore heen practicable within economical limitations of commercial operation. In other cases invention may he 'employed to provide more emcient and economical extraction. resulting in sa in time or extraction, quantity oi solvent, etc. L

It will be understood that the procedures speciilcally described above, as well as the forms of apparatus illustrated in the drawings, are by way of example only and that other applicaiions oi the invention. as well as variations in the details of the method and apparatus, will readily suggest themselves to those skilled in the art. Accordingly reference should he had to the ap- Banded claims for a deilnltion of the limits of the What is claimed isz' l. Apparatus for continuous solvent extraction of solid material comprising an extraction chamber, means for owing material to he extracted through seid chamber, means for feeding `solvent to anddischarsme it from said chamber cmmtercurrently to the now of said material, means for p, conduit, and mams actuated by the ilnw ed said solventintoamioutofoneofsaidto control the operation of the pimp.

2- Apparatus for continuous solvent 1 of solid material comprising an on chamber, means :for llowing material-.to he through Said Chamber, means for a if .l toand r: it frornsaid i countercurrently to the How ci said rial, means ier alternately from and f to said chambers. portion oi ilowingsolventeomp ing a storage chamber connected to said tion chamber by a conduit, a p in said am duit, and means actuated by the new ci said scivent into and out of said tion to control .the operation of the p.

3. Apparatus for continuous solvent extraction of solid material comprising an im tion ber, means for flowing material to he extracted through said cher,- means for www solvent tu and I .1. it .from said chamber countereurrently to the dow oi said material, means for alternately withdrawing imm and reg tu said chamber a portion of il solvent cornprising a storage chamber connected to said estraction chamber hy a commitn a. p in said conduit, and means acti-atm hy the dow o said solvent into and" out of said storage her in control the operation el the u.

4. Apparatus for continuous solvent extraction of solid material comprising an extraction chamber, means for iowing material te .he extracted through said chamber, means :for i suivent to and discharging it from said her y@muntercurrently to the iiow of said material, means ier alternatew withdrawing imm and to said chamber a portion oi iimving solvent eemprising a storage chamber connected to said eatraction chamber by a conduit, said chambers Soeing disposed w that solvent nous conduit hy gravity in one direch'on, a pump in saiz conduit for owing solvent therethrough in opposite direction, and means aetuated hy the iioiv of said solvent inte and out of one ci said charnbers to control the operation ci said pump.

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