LANTS I I
Filtration-Extraction of Cottonseed E . L. D'AQUIN, H. L. E. VIX, J. J . SPADARO, A. V. GRACI, JR., P. H. EAVES, C. G. REUTHER, E. J. McCOURTNEY, A. J. CROVETTO, AND E. A. GASTROCK
JR.,
L. J. MOLAISON,
Southern Regional Research Laboratory, New Orleans, La.
N. B. KNOEPFLER,
National Cottonseed Producfs Association, Dallas, rex.
T
HE development of a satisfactory, simplified process for
filtration. Also indicated was a high tonnage capacity per square foot of filter area. These oonsiderations pointed t o the selection of the standardtype, continuous, horizontal, rotary vacuum filter in preference t o the disk and drum types (10, 11, IS). Also, the horizontal type permits efficient countercurrent, displacement washing, efficient drainage of the original slurry and of the cake after each stage of multiple washing, allowing minimum filtrate holdup, and provides for continuously clearing the screen. In addition, the final spent marc (solvent-damp cake) was of the nonsticky and free-flowing type that could be continuously discharged by means of a scroll. The use of a horizontal vacuum filter t o conduct countercurrent washing is not a new or radical application. However, the combined operations of extracting a solid material for a desirable component and subsequent countercurrent washing is not a usual commercial practice and, in fact, is an innovation in oilseeds extraction technology. It was necessary, before accurate performance data on the pilot plant filter could be obtained, t o determine the respective screen a r e a required for best placement of slurry feed and washes and for drainage of the initial slurry and of the cake after each of the washes. Vacuum and blowback requirements were then established, and observations were made relative t o cover blinding, blowback performance, and cake discharge over extended periods. The filter (Figure 1) used in the work reported here has been described previously (8). The only alteration from standard is enclosure in an adequately vapor-tight hood. The filter is of alliron construction, and consists essentially of an annular, rotating pan, containing wedge-shaped screen sections, each of which has outlet ports t o a common centrally located multiport valve below the pan. The valve is so constructed as to lend itself t o a variety of filtrate separations, which makes i t particularly adaptable t o countercurrent washings. A typical combination of the valve filtrate outlets t o attain the countercurrent washing procedure for the four separations used in this process is shown in Figure 2. The filter pan is turned by a variable-speed drive between 1 and 3 minutes per revolution. The scroll which discharges the cake from the pan is shown in Figure 3. It is of triple-flight, standard pitch construction, and revolves a t 70 r.p.m. The filter medium used for the initial pilot plant runs was a 20 X 250 mesh, stainless steel Dutch twill wire screen. This was later replaced by a plain Dutchscreenof 24 X IlOmesh, whichcosts less, is more sturdy, and permits satisfactory fines retention and faster filtration rates than with the finer-mesh screen. B y means of blowback nitrogen gas, introduced continuously at a point immediately underneath the filter section onto which the slurry is deposited, the oncoming slurry is mixed with the
direct solvent extraction of cottonseed, yielding meal and oil of high quality, is definitely desired by the cottonseed industry, particularly by the small- and medium-sized mills, before there is further expansion of conventional processes. Direct solvent extraction in immersion-type extractors presents a serious fines problem ( 1 , I%, 16). Moreover, the maintenance of consistently low residual lipides in the extracted flakes has proved difficult (14). Percolation extractors, such as the basket, cell, and band types, present the problem of obtaining relatively rapid and efficient percolation of solvent and oil-solvent mixtures through thick material beds. The pilot plant development of a simplified solvent process, called filtration-extraction (8),is described here; it apparently overcomes most of the usual problems with direct solvent extraction and is applicable under the conditions met in the smaller aa well as in larger mills. The principal unit of equipment is a continuous, horizontal vacuum filter. The oil extraction step consists of a flake-miscella mixing-soaking operation followed by high-capacity vacuum filtration and countercurrent washing. Another departure of the process from conventional solvent extraction is that i t embodies a mild precooking of the flakes. Development of the process on a pilot plant scale is based on a batch extraction made in the laboratory (18). The data reported here supplement pilot plant data reported previously ( 7 4 , which included some preliminary runs with cottonseed.
Process Combines Soaking to Extract Oil and Horizontal Vacuum Filter to Remove Miscella The fast settling characteristics of the slurry of miscella (oilsolvent mixture) and cooked flakes demonstrated in the prepilot plant studies indicated that larger scale filtration and washing should be conducted on a horizontal plane and that vacuum should be used in preference to pressure. Also, the earlier studies indicated t h a t the filter medium should be solid, monofilamental material, such as metal or saran, rather than multifilament yarns, such as cotton ducks. I n the previous work rapid filtration (high mass velocities) of the initial slurry and of the three countercurrent washes was obtained with Et horizontal screen and a filter cake up t o 4 inches thick and under vacuum of less than 5 inches of mercury. These results indicated t h a t the cake was satisfactory with regard t o particle-size distribution, porosity, noncompressibility, and other considerations given in the literature (2, 4, 10) and that its specific resistance was considerably below the minimum of 5 x 1011 feet per pound (a cake 1/8 inch thick can be formed in 5 minutes or less a t a vacuum of 20 inches of mercury), which is recommended by Grace (10) for satisfactory industrial vacuum 241
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 45, No. 1
The slurry is transferred t o the filter by means of an inclined, 3-inch tubular screw conveyor (Figure 3, top left), powered by a hydraulic-type variable-speed drive. Four 10-gallon vertical receivers are mounted below the filter t o collect the separate filtrates from the respective outlets of the multiport filter valve. They are connected a t the top t o a header through which vacuum is applied by means of a wet-seal pump, which uses hexane as the sealing liquid. -4separate centrifugal pump handles the filtrate from each receiver. This asscmbly is shown in Figure 5 . The system for application of continuous blowback gas comprises a nitrogen gas cylinder, a variable pressure reducing valve, A rotameter, and a pressure gage. &4ll equipment units are rlectrically grounded. Electrical equipment is Class I, Group D. The pressure filters used for polishing the miscella, the continuous evaporators, and steam-stripping column for oil recovery, and the continuous screw-type desolventizers for meal recovery have been previously described (6). Conversion of the continuous solvent-extraction pilot plant a t the Southern Regional Research Laboratory t o filtration-extraction was relatively simple. It required merely replacing the scrcw-type immersion extractor by the filter, with mixing conveyor and accessories.
Flakes A r e Cooked M i l d l y and Cooled for Extraction Cottonseed of three different histories was used: Current prime seed (A) with a free fatty acid content of 0.53%, from Greenwood, Miss., which was received and processed in November 1951; current prime seed (B) with a free fatty acid of 0.80%, also from Greenwood, Miss. , received and processed in January 1952; and current subquality seed (C) with a free fatty acid of 5.2%, which was received from Alagnolia, hliss., and processed in November 1951. Figure
1. Continuous Rotary Horizontal Pilot Plant Filter,
f
%Foot Diameter
SCROLL
layer of meal (1/16 t o 1/8 inch thick) passing underneath the discharge scroll. This operation helps to keep the filter medium clean. Vacuum is applied t o the system through a common header connecting the four filtrate receivers, described later.
Mixing Conveyor .and Filter Convert Plant from Solvent-Extraction to Filtration-Extraction The hullers, meats separator shaker screens, purifier, hull beater, flaking rolls, and five-high cooker which were used for the material preparation are small-size, conventional-type, such as currently used in cottonseed mills. The five-high, steam-jacketed cooker is equipped with vents, atomizing sprays, steam ejectors, and indicating and recording instruments t o control as closely as possible the moisture and temperature of the flakes in each cooker ring. Open drying trays constructed of '/a-inch mesh wire are used t o cool the cooked flakes. A simple, paddle-type mixing conveyor (Figure 4) was constructed in which t o mix thoroughly the slurry of cooked flakes and miscella. It consists of a vapor-tight, standard U-trough, 1 foot in diameter by 12 feet long, having a shaft with adjustable flat paddles set at 7 degrees t o the centerline. The shaft is turned by a l/*-hp. hydraulic-type variable-speed drive, capable of any speed between 0 and 25 r.p.m. The speed used depends on the filter feed rate, the angle of paddles, and the slurry characteristics. A screw-type feeder ( 6 ) ,built in the laboratory shops, 4 inches in diameter, with variable-speed drive and plug-type vapor seal mechanism feeds the cooked material t o the mixing conveyor.
Figure
9. Arrangement of M u l t i p o r t V a l v e Outlets in Horizontal Rotary Filter
The material was prepared for extraction under the conditions indicated in Table I. The cottonseed was first cleaned and delinted. The meats preparation equipment was operated so as t o produce a mixture of whole and fine meats having a moisture content ranging from 6.8 t o 8.7% and containing some hulls. I n none of these runs was moisture added t o meats t o improve flake formation ( 1 7 )or t o flakes prior to cooking. T o prepare flakes for the first run the meats were rolled through corrugated rolls (one pair high) spaced a t 0.016 inch and then through smooth rolls (one pair high) set t o produce flakes 0.004 t o
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1953
Table I. Run No. Cottonseed Free fatty acid, yo Lb. processed Meatsfraction. lb. Meats fraction, moisFlaktt?io?fs type Flake feed' rate to cooker, lb./hr. Cooking conditions Total time, min. Temperature, O F. Ring: 1st 2nd 3rd 4th 5th Moisture, 7' Ring: 1st 5th Cooling and reforming conditions Time cooled. min. Temp. after cooling,
F.
Material Preparation Data 1
2
3
4
B
B
B
1600 1010
5 C 0.80 0.80 0.80 5.20 1300 1000 1400 1600 1052 619 891 738
6.8 l-Higha
8.2 5-High
8.6 5-High
8 7 5-High
7.2 5-High
260
260
260
260
A 0.53
260 60
60
60
60
60
208 215 216 213 223
202 211 214 217 222
203 211 214 217 222
200 214 218 219 223
210 215 218 218 223
25.8 12.7
15.5 8.4
17.5 11.8
18.2 8.9
15.4 6.4
15
10
10
15
12
135
135
135
140
140
None
None
Rolls for reforming, 5-Highb I-High0 1-HighC type a 1 pair high cracking, 1 pair high flaking. b Two bottom rolls only. e 1 pair high flaking.
0.007 iach thick. For the remaining four runs the meats were flaked through five-high rolls (top two corrugated) set t o produce flakes in the same thickness range. For all five runs, flakes were fed to the cooker at a rate of 260 ounds per hour and cooked for 12 minutes in each of the five fettles-a total cooking time of I hour. Cooking conditions were comparable except for the moisture added in the first ring for run 1, 25.8'%, as against 15 t o 18% for the other four runs. The purpose in adjusting the moisture content t o a relatively high level is t o accomplish moist cooking as the temperature is raised t o about 210' to 215' F. in the second ring which facilitates binding of the bulk of the free gossypol with the protein components of the meal (17'). I n the first ring, the temperatures for the runs ranged from 200" to 210" F. I n successive rings, temperatures were gradually increased t o about 223" F. in the last ring. Moisture contents were reduced during cooking t o a range of 6.4
-- --..
249
The cooked material is fed t o the continuous mixing conveyor where it is slurried with the No. 2 filtrate under gentle agitation for 15 t o 20 minutes. During this soaking period the greater part of the oil goes into solution as concentrated miscella. Coats and Karnofsky (3) have shown that the rate of solution of the oil from raw cottonseed flakes soaked in hexane miscella is relatively independent of the concentration of the extracting solution and is mainly a matter of soaking time. The same is true of cooked, re-rolled flakes, but the action is significantly more rapid and complete. The slurry is continuously deposited on the revolving pan of the filter, where, in from 1 t o 2 minutes, the bulk of the concentrated, or full, miscella is drained off by vacuum and the remainder, with some additional oil, is extracted by the use of three successive countercurrent washes and drains, the first, two with progressively weaker miscella and the third with hexane. The initial or most concentrated filtrate, which is drawn through the first three outlets of the filter valve to a receiver below, is the final miscella and is continuously pumped to the oil recovery system. The deposited cake, after the initial drain, moves forward onto a blanked-off outlet directly below the first spray, or wash, which is allowed t o pool before it is drawn through the next two valve outlets t o the second receiver. This filtrate is the second most concentrated miscella and is pumped t o the mixing conveyor for slurrying. Similarly, the second wash is applied, pooled, and drained, and the filtrate of this wash is used as the first wash. The third and last wash is hexane, the filtrate of which is used as the second wash. After the final wash is drained off, the fast-moving scroll discharges the marc into a chute which empties into the desolventizers below.
Filter Operates with 1-Inch Cake, Pan Speed of 1.6 Min./Rev., and Vacuum of 1.5 to 6 Inches H g Operation data for five pilot-plant runs are included in Table
11. The operating time per run, which ranged between 2 and 3 hours, represents the actual time the filter was in operation to process the specified pounds of material.
tn 12 7 %
The &,-cooked flakes were cooled from about 223" to 140' F. by spreading on the open trays for 10 to 20 minutes. T h e moisture content decreased as much as 2oJ, during this operation. The batch scale studies had shown that the best results with filtration-extraction were obtained with cooked material. A secondary reason for cooking, particularly by the techniques described, is t o produce meal of improved nutritional quality. It had also been indicated t h a t the cooked flakes should be re-rolled after cooling. Re-rolling flattens out small agglomerates (Figure 6) which may form in the cooker, caused by hulls curling around meats particles and hindering efficient extraction. T h e cooled flakes were re-rolled for runs 1 t o 3, using rolls (one pair high) except in run 1, where only the bottom smooth rolls of the fivehigh set were used. The combination of these operations resulted in t h e production of crisp, granularlike material from which t h e oil could readily be extracted. Bulk densities were as follows: Flakes t o the cooker, 22 pounds per cubic foot unpacked and 27 pounds packed; cooled cooked flakes t o the slurrying conveyor, 36 pounds unpacked and 47 pounds packed; final desolventized extracted meal, 42 pounds unpacked and 46 pounds packed. Samples of the following were taken for each run: cottonseed, meats before and after flaking, flakes in top ring, flakes after cooking, after cooling, and after reforming.
Cooled Flakes A r e Soaked in Second Most Concentrated Miscella, Then Washed on Filter Figure 7 is a flow diagram of t h e over-all process, including both the DreDaration and the extraction Dhases. The filtration-ex* traction phase is illustrated specifically in Figure 8.
Table II. Filtration-Extraction Data Run No. 1 2 3 4 5 Cooked material processed, lb. 910 709 509 525 575 300 300 300 300 300 Feed rate, lb./hr. 10.1 10.4 9.9 8.8 7 6 Moisture, % 29.9 Lipides, % 27.2 28.1 29.0 31 7 1 1:l 1.1:l Solvent-flake ratio 1.1:l 1.1:l 1.1:1 Slurry temperature, F. 91 87 83 82 28.0 Solids in slurry, % 3i:3 31.1 25.7 28 0 Filter pan speed, min./rev. 1.9 1.4 1.4 1.4 1 4 1 0 0.8 1.0 1.0 Cake thickness, inches 1 .o 0.9 0.9 0.9 1.0 0.9 Wash rates, gal./min. Vacuum required, inches mer3.5 cury 6.0 6.0 3.0 1 5 Lipides in filtrate, % 26.0 22.1 24.5 25.3 1st 25 8 2nd 11.8 11.6 9.7 9.1 10 7 1 5 2.1 1.3 3rd 3.7 0.7 0.5 0.6 0 3 0.5 4th 0.4 0.21 Pines in first filtrate. % 0.17 0 30 0.13 0.25 28.4 Solvent in marc, % ' 22.1 24 8 21.3 27.8 Residual lipides in desolvent1.02 ized meal yo 0.90 0.66 0.83 1 49
The prepared material with a n oil content by weight of 27 t o 32'% was fed t o the mixing conveyor trough at a rate of 300 pounds per hour. The second filtrate miscella, containing about 10% oil (9.1 t o ll.S%), was introduced simultaneously at the solids feed end of t h e trough, t o form a slurry of about 26 t o by weight. Slurry temperatures did not exceed about YO" F. The speed of t h e mixer conveyor was maintained at from 5 t o 8 r.p.m. The feed rate t o the filter for all runs was the equivalent in slurry form of 5 Dounds of cooked. cooled material Der minute. The speed of the %inch slurry feed.conveyor was regilated t o 50
250
Figure
INDUSTRIAL AND ENGINEERING CHEMISTRY
3.
Top V i e w of Filter Showing M a r c Discharge Scroll
t o 60 r.p.m. t o dclivcr slurry to the filter pan at a rate equal t o the combined rate of the flakcs and the No. 2 filtrate dclivcred t o the mixer. The filter was operated with a cakr thickricss of 1 inch, pan speeds of 1.4 to 1.9 min. per rev., arid with vacuum requirements of 1.5 to 6.0 inches of mercury. The cake thickness was controlled by the speed of the pan. The solvent-to-flake ratio throughout was 1 1 to 1. The vacuum capacity employed ranged between 3 and 10 cubic feet per minute (volume a t the vacuum) per square foot of filtering area. The blowback gas rate ranged between 0.2 and 0.5 cubic feet per minute per square foot of filtering area. Periodic readings were taken of wash rates, blowback gas rates, vacuum, and cake thickness. Samples mere taken periodically for analysis of the following: feed material t o slurry mixer; slurry; hexane; filtrates; filter cake before and after each wash; final discharged marc: and h a 1 desolventized meal.
seed which had not been re-rolled. The residual lipidcs for run 5 , on flakes from subquality seed, mas l.570. These results indicate t h a t for prime seed the slight gain in oil rccovery may probably not justify the expense of the re-rolling step Rerolling of subquality seed would probably also not be justified, since it is generally recognized that there is an economic level for residual oil content depending on the particular cottonseed and its grade, below which the increase in oil recovery would be offset by the lowering of the quality of the oil with respect t o the r e h i n g loss and refined and bleached color. The residual lipides would be further reduced when hull material is added t o the meal t o adjust the proteincontent to41%, the standard for most commercially produced meals. The extent of the reduction would drprnd, of course, on the oil content of the hull material. For thc meals produced in the runs repoited, the reduction could be significant, since the protein contents (not tabulated) ranged between 48 and 51%. Data in Table I11 show that thc major portion of the lipides was removed during the initial blurry filtration and during the first Rash-only 1.2 to 2.9% remaining in the cake after t h e first wash. The low lipides and solvent contents of the cake aftcr carh \\ash indicate the high efficitncy of drainage and washing that was obtainable by the UEC of vacuum. Thorough drainage following the final wash is of especial importance, since the retained solvent contains some lipides. The concentration of lipides in the first filtrate (final miscella) averaged about 25% (Table 11),in comparison with 15 to 20% usually obtained in final miscellas in conmercial direct extraction operations. In the three filtrates used in the countercurrent washing, the concentrations of lipides fall off markedly, as noted. The higher concentration 111 the final miscella means that lesv solvent must be evaporated, thereby reducing steam consumption as \vel1 as size of equipment required. With meats originally of higher lipides content and where the hull rontcnt of the material feed stream can be reduced, the niiscella concentration with filtration-extraction could be increased. AIiscclla concentrations as high as 28% have bcen achieved in other pilot-plant runs, with filtration-extraction, to be reported elsewhere, where the solvent-to-flake ratio was only 1.0 t o 1. These iesults indicated that there is considerable leeway for efficimt operation and evtraction at still lower ratios with only a nominal sacrifice in exti action efficiencv and that further advantages would hc realized hv the use of heated solvent. I n the
Extraction Results Compare Favor-
ably with Conventional Processes Tables I1 and I11 give data on extraction; Table IV, data on filter capacity; and Tables V and VI contain analytical data indicating the quality of the oil and meal products. Residual lipides contents in the desolventized extracted cake (Table 11) are in the desirable low range, averaging 0.8% for runs 1 t o 3, on re-rolled, cooked flakes from prime seed, compared to 1.02% for run 4 on flakes from prime
Vol. 45, No. 1
Figure
4.
Slurry M i x i n g Conveyor at Left of Filter
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 1953
Table 111.
2
1 Lipides,
%
Hexane,
%
Table IV.
3 4 Lip- Hex- Lip- Hexides, ane, ides, ane,
Lipides,
Hexane,
10.3 1.2 0.8 0.6
25.2 12.0 2 8 . 1 25.6 1.526.4 0.9 2 5 . 9 31.0 22.1 0.9 21.3
%
11.7 28.3 2.131.0 1 . 1 34.0 0 . 9 27.8
Before 1st wash After 1st wash After 2nd wash After 3rd wash
%
%
%
%
%
14.7 30.9 1,936.1 0 . 9 32.9 0 . 8 28.4
Filter Capacities
(Basis 1250 lb. meats-hulls mixture per ton of cottonseed) Tons Cottonseed per 24 Hours Pilot plant filter Commercial filter" (3 ft. diam., (10ft. diam., Feed Rate. 3.5 sq. ft.) 65.0 sq. ft.) Lb./iMin. 110 5 6 220 12 10 335 18 15 445 24 20 Capacities calculated on basis of filtering area.
Table V.
Run S o . 1 2 3 4
5 a
Refining Loss",
%
2.1 4.6 5.0 4.2 15.6
Lovibond Color Refined Bleached Y-R Y-R 36-5.8 20-1.2 35-5.3 20-1.6 35-7.4 20-1.6 15-1.7 35-5.3 35-8.3 35-2.7
A.O.C.S. official hydraulic refinihg method was used; all foots were firm.
Run No.
Lipides.
1
0.90 0.66 0.83 1.02 1.49
5
Data on Crude Oils
Crude Oil Free Free gossypol, fatty acid % 0.74 0.013 1.10 0.012 0.008 0.93 0.97 0.009 5.23 0.089
Table VI.
2 3 4
25% solvent requires the evaporation of only one third as much solvent per pound of solvent-free meal as a marc containing 50% solvent. Moreover, any reduction in size of the marc desol5 ventizing unit is of particular significance because Lip- Hexides, ane, this type of equipment is relatively large and ex% % pensive t o fabricate. Secondly, the lowcr marc 13 2 26.7 2:b29.8 solvent content should result in a reduction in the 1 . 7 32.4 residual lipides of the final meal since solvent re1 . 5 24.8 tained in the marc contains lipides. The solvent-to-flake ratio in filtration-extraction, 1.1 t o 1 bv weiaht (Table II)-amreciablv less than the ratio of about i.8 to-1 used in cottonseed processing plants employing direct solvent extraction-is attributed t o the high extractability of the cooked material, the efficiency of the displacement washing, the effectiveness of the vacuum drainage between washes, and the thorough drainage of the final marc. The low solvent requirement coupled with the short slurry holdup time for extraction permits smaller equipment and should decrease solvent losses as well as enhance the safety features of the process. While no particular effort has been directed so far to determine the minimum solvent-to-flake ratio obtainable t h a t would be commensurate with practiral operation and efficient oil extraction, as this development work moves further along, i t should b e possible t o achieve much lower ratios through the uw of improved preparation techniques, higher solvent temperatures, and recircu1at:on and flooding of wash liquids on the filter Also, for cottonseed, it should be pointcd out t h a t reduction in the hull content of the meats stream may not necessarily make possible a. lower solvent-to-flake ratio, but the solvent-to-whole Beed ratio should bc lower. Vacuum requirements as t o degrec and volumetric rate are in the desirable low operating range'and could have been reduced to some extent in all the runs without adversely affecting operation efficiency. Vacuum requirements will vary with the method of material preparation, the amount of blowback gas applied, with cake thickness, and with the type and size. of the filter screen. In runs 4 and 5 , in which the material was not reformed and therefore contained less fines, the vacuum required was only 3.0 and 1.5 inches of mercury, respectively. It should be pointed out t h a t the vacuum can be varied as desired t o attain a condition t h a t a n operator may consider advantageous. As a n example, the extraction efficiency can be improved, if desirable, b y decreasing the system vacuum, as this increases the pooling of wash liquid on the cake. Rlowback requirements, as t o volumetric rate and pressure (less than 1 pound per square inch) were also in the desirable low range and will vary with the material characteristics, the degree of vacuum required, the type of screen, and size of screen openings. Although nitrogen was used as the blowback gas in this investigation, i t is realized t h a t in translation t o commercial scale, i t would be more practical t o use the hexane-saturated air from the filter hood; however, gas from a noncombustible gas generator, concentrated miscella, or possibly superheated hexane vapors could also be used.
Residual Lipides and Hexane Content of Cake on Filter ar Various Stages
Run No.
a
251
yo
Data on Desolventized Meals
Moisture, % 4.8 5.1 6.0 5 3 5.1
GoSsYPol, % Free Total 0 030 1.17 0.033 1.33 0.027 1.32 0.028 1.28 0.050 1.25
Nitro en Solubfes, Thiamine, % P.P.M. 25 7 38 1 15:6 34.3 17 0 44.7 41.3
.. .*
batch-type investigations using unheated solvent, ratios as low as 0.85 t o 1 have been employed successfully, yielding miscella with as high as 32% oil content. The fines content (0.13 t o 0.30% b y weight) in the first filtrates (Table 11) is considered low for direct solvent extraction and is especially low, considering t h a t the miscella is filtered through a cake of only 1-inch thickness. The fines form a much more porous bed in a polishing filter than do fines from uncooked material and can be filtered more readily. The concentration of fines in the second, third, and fourth filtrates averaged 0.07, 0.03, and 0.03y0 by weight, respectively. It is probable t h a t the fines problem can be reduced considerably or eliminated by permitting a longer slurry settling time for formation of the original cake on the filter and by circulating the first filtrate miscella back t o the cake on the filter for refiltrationa well-known technique used commercially-and draining it off just ahead of the first wash. The wash sprays could be moved back one space and a fifth filtrate receiver installed, or the first wash eliminated. As shown in Table 111, the elimination of one wash would leave only about 0.2% more residual lipides in the cake. Either method would be feasible; the one chosen would depend mainly on economical considerations. Solvent content of marc t o the dryers ranged from 22 t o 28% (Table 11), as compared to the 45 t o 55% obtained commercially. This lower solvent content is significant for two reasons. First, i t should result in a n appreciable saving in steam consumption and in smaller desolventizing equipment, since a marc containing
Filter Capacity. Table IV gives filter capacities obtained with the filter used in this investigation (3 feet in diameter), with the corresponding capacities for a commercial filter (10 feet in diameter), extrapolated on the basis of filtering area. Since these figures are calculated on the basis of 1250 pounds of meah-hulls mixture fed t o the filter per ton of whole cottonseed, i t is obvious that greater capacities than shown in the tabulation should result where the particular seed and mills separating equipment will permit better purification of meats, up t o a point of diminishing returns as determined by the maximum allowance of oil loss in the hull stream. T h e more hulls t h a t can be removed from the meats stream, the less the material that must be handled by the rolls, cooker, slurry-mixer, filter, and desolventizers, and t h e lower the requirement of solvent per ton of whole seed for extrac-
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The free gossypol contents in the crude oils are low, showing t h a t the cooking procedure advocated herein for filtration-extraction was adequate for chemically combining or binding the bulk of the free gossypol in the meal. I t is common knowledge in the industry that crude oils of low gossypol content usually exhibit only slight color reversion on storage a t 100" F. for as long as 30 days. Additional refining data, not included in the table, were obtained on hydraulically pressed crude oils prepared from separate portions of the cooked flakes from each of the pilot plant filtration-extraction runs for comparison with the filtration-extractcd oils. The latter and the corresponding hydraulic oils were closely comparable in refining loss and in refined a.nd bleached color, both as prepared and after 14 days of storage a t 100" F. Table VI gives essential quality data pertaining t o the final (desolvent'ized) meals. The values for free gossypol (0.027 to 0.033%) are appreciably lower than those normally obtained in commercial hydraulic pressing operations with prime seed. This lower free gossypol content is attributed to more effective rolling and t o the use of higher moisture contents of the flakes during cooking, The free gossypol content would be further reduced by adding hull material to the meal t o adjust the protein content to 41%. Nitrogen solubility and the thiamine contents of the meals are higher than normally obtained in hydraulic pressing. These results are attributable to the shorter cooking time and to the lower cooking teniperaturo.
Figure
5.
Filtrate Receiver Assembly
tor. The additional hulls removed would, of c o u r s ~he , addrd t o the extracted meal for adjustment t o 41y0 protein content. The maximum capacity a t M hich the pilot plant filter \?as operated was equivalent to a rate of 24 tons of cottonseed per 24-hour day. The factor that limited the pilot plant capasit3 Kith properly prepared material was the actual physical handling of the large liquid volumes required for the higher material feed rate on such a small filter area. These higher rates would not necessarily be recommended for commercial practice. For example, for a 150-ton-per-day plant, the 10-foot filter might be desired in place of, say, a 6-foot filter with a filtering area of 25 square feet (calculated capacity 170 tons) since a smaller cake thickness could be used and the difference in cost of the two filters is relatively small. This would give leewav for operating above plant capacity, if desired, or to obtain highest possible capacities with oil-bearing materials having inferior extractability properties or having lower filterability characteristics-for example, materials that contain excessive fincs or that have not been properly prepared for extraction.
Short Moist Cook at Low Temperatures Improves Product Quality Analysee of the crude oil produced for free fatty acid and free gossypol contents wi'h refining data are given in Table V. Bleachable prime oils werc obtained from the prime seed, and the oils produced from the subquality seed refined and bleached t o just beyond the upper limits for prime color of 7.5 red and 2.5 red, respectively. The low bleach colors are of particular iniportance since oil refiners consider bleach color the best single criterion of cottonseed oil quality.
Figure 6. O n 1 4 - M e s h Fraction of Typical C o o k e d Unreformed Material Showing Hulls Curled around M e a t s Particles
These analytical values for any givcn cottonseed m e d arc being correlated with rcsults in feeding experiments to establish whether such chemical tests can bo used t o indicate the nutritional value of a meal for livestock.
Cost Estimates for Commercial Installation Indicate Advantageous Investment Rates The interest manifested by the oilseed crushing industry when the details of the filtration-extraction process were first made available indicated the need for a cost analysis as early as possible. A preliminary cost study ( 1 5 ) of the application of the process t o cottonseed, based on the available pilot plant development and material balance data on filtration-extraction and on the quotations of equipment manufacturers for conventional commercial
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1953
costs and also provide information necessary for detailed designs to meet the requirements of particular situations. At least two equipment fabricators are reportedly preparing engineering evaluations of the process in contemplation of bidding on commercial-sized installations.
COTTONSEEO LINTERS HULLS
FLAKES
I
1
MILD COOKING
I
CONDITIONING
Development Work Promises Successful Application to Other Oilseeds
1
AGITATION WITH SOLVENT OR MISCELLA
I
I
CONTiNUOUS HORIZONTAL
Figure
7.
253
Flow Diagram of Process for Cottonseed
equipment units for the remainder of the plant (exclusive of office buildings, control laboratory, and steam-generating plant), indicates t h a t the over-all investment cost for a completely installed plant for processing 100 tons of cottonseed a day would be somewhat lower than that of a comparable conventional direct solvent extraction plant. Comparative cost data from private sources (not given in the study) indicate t h a t the estimated installed cost for only the extraction and desolventization equipment would be approximately 15% lower than for a conventional direct extraction plant. The cost of converting a direct solvent-extraction plant would be the cost of replacing the extractor unit and accessories with the slurry-mixer, filter, and accessories. The equipment costs, not including installation costs for these, are given in the cost study. On converting a n existing screw-press or hydraulic-press mill t o filtration-extraction, the filtration-extraction equipment would replace the pressing equipment. The estimated costs listed in the cost study (16)under “Filtration-Extraction Unit” would represent t h e approximate probable conversion costs for installations of 50,200, and 400 tons capacity.
While the process development work has been mainly with cottonseed, favorable results have been obtained on a limited number of preliminary pilot plant runs on soybeans and on raw and converted rice bran. Some other oil-bearing materials t h a t have been investigated on a preliminary, batch scale with promising results include peanuts, flaxseed, and tung press-cake. These small scale tests, which have been specifically designed for extrapolation t o the pilot plant scale, have correlated satisfactorily in the work done so far with cottonseed, soybeans, and rice bran. For processing oil-bearing materials other than cottonseed, the indications are that optimal preparation and extraction conditions will not be critical, but will be somewhat different from one material to another. Versatility of the filtration-extraction process for handling other oilseeds is of particular importance t o cottonseed oil mills that supplement their seasonal operation by processing soybeans, peanuts, and other oleaginous crops that are becoming available in larger and larger volume in the Southern area. While the process as described operates satisfactorily under the described operating conditions, there is, as with any process in its early Rtage of technological development, latitude for
d
SLURRY MIXER-CONVEYOR
NO.PWASH
Low Solvent Requirements Should Reduce Operating Costs Detailed data are not yet available for estimating operating costs. Lower utility costs are indicated by the fact t h a t compared to conventional direct solvent extraction, only one third as much solvent may have t o be removed by the meal desolventizers, and only one half as much by the oil recovery equipment. Also, the absence of critical operating conditions, the indicated ease of control of the filtration-extraction operations, and the resulting lower supervision and operating costs anticipated indicate t h a t considerable savings could be expected. These factors should also ensure low down-time and greater uniformity of products. Experimental operation of a commercial direct solvent extraction plant which is being adapted t o filtration-extraction should provide a &mer basis for estimating investment and operating
Figure
8.
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