Modeling the solvent extraction of oilseeds

A computer model and an experimental procedure for generating data needed in the model have been developed for the oilseed extraction process. The experiments are relatively simple and are performed with a bench-top extractor. Experimental results and modeling calculations are presented for the extraction of cottonseed using hexane, isopropanol and ethanol. The calculations show that in an alcohol extraction using a chill separation, isopropanol’s greater oil miscibility allows for a lower solvent-to-feed ratio than does ethanol. Using the latter solvent, however, achieves lower residual lipids in the extracted meal because recycled ethanol contains less oil than recycled isopropanol. Presented in part at the AOCS meeting in Honolulu, HI, in 1986.     

Supercritical carbon dioxide extraction of cottonseed with co-solvents

Extraction of cottonseed lipids with supercritical carbon dioxide (SC-CO₂) was conducted with and without a cosolvent, ethanol or 2-propanol (IPA). At 7000 psi and 80°C, the reduced pressure, temperature and density of SC-CO₂ was at 6.5, 1.17 and 1.85, respectively; the specific gravity was 0.87. Under these conditions, CO₂ is denser than most liquid extraction agents such as hexane, ethanol and IPA. The extraction of cottonseed with SC-CO₂ gave a yield of more than 30% (moisture-free basis). This is comparable to yields obtained by the more commonly used solvent, hexane. The crude cottonseed oil extracted by SC-CO₂ was visually lighter than refined cottonseed oil. This was substantiated by colorimetric measurements. No gossypol was detected in the crude oil. However, crude oil extracted by SC-CO₂, to which less than 5% of ethanol or IPA as co-solvent was added, containedca. 200 ppm of gossypol, resulting in the typical dark color of cottonseed crude oil with gossypol. CO₂ extracted a small amount of cottonseed phosphatides, about one-third of that extracted by pure ethanol, IPA or hexane. A second extraction with 100% ethanol or IPA after the initial SC-CO₂ extraction produced a water-soluble lipid fraction that contained a significant amount of gossypol, ranging between 1500 and 5000 ppm. Because pure gossypol is practically insoluble in water, this fraction is believed to be made up of gossypol complexed with polysaccharides and phosphatides. Partially presented at the AOCS 1993 Annual Meeting & Expo in Anaheim, California.     

Ethanol extraction of oil,gossypol and aflatoxin from cottonseed

Commercial processing of cottonseed requires hexane to extract and recover edible oil. Gossypol and aflatoxin are not removed from extracted meals. A bench-top extraction process with 95% (vol/vol) aqueous ethanol (EtOH) solvent has been developed that extracts all three of the above materials with a much less volatile solvent. In this process, cottonseed is pretreated and extracted with ambient 95% EtOH to remove gossypol and then extracted with hot 95% EtOH to extract oil and aflatoxin. Membranes and adsorption columns are used to purify the various extract streams, so that they can be recycled directly. A representative extracted meal contained a total gossypol content of 0.47% (a 70% reduction) and 3 ppb aflatoxin (a 95% reduction). Residual oil content was approximately 2%. Although the process is technically feasible, it is presently not economical unless a mill has a continual, serious aflatoxin contamination problem. However, if a plant cannot meet the hexane emission standards under the Clean Air Act of 1990, this process could provide a safer solvent that may expand the use and increase the value of cottonseed meal as a feed for nonruminants. Presented in part at the AOCS annual meeting, Toronto, Canada, May 1992.     

Cottonseed oil

Research on the effects of genetics and growing location on cottonseed has shown that oil and fatty acid composition could be improved if geneticists and agronomists would strive for improved seed quality as vigorously as they do for improved fiber quality. Breeding of glandless or gossypol-free cottonseed was a genetic breakthrough. Glandless varieties are now available that produce yields having the quality of fiber and seed equivalent to those of glanded cultivars. Oil, food-grade lecithin and meal byproducts are readily processed from glandless cottonseeds because of the absence of gossypol. Major research programs on cottonseed processing include: (a) testing alternative screw-press and extrusion operations for efficient direct solvent oil extraction; (b) developing alternative solvent extraction systems with ethanol, isopropanol and supercritical fluids; (c) using gas chromatographic/mass spectrophotometric techniques to characterize enzymatic and nonenzymatic mechanisms that produce secondary oxidation off-flavor products; and (d) controlling hexane losses in solvent extraction systems.     

An aqueous ethanol extraction process for cottonseed oil

A bench-top process for the extraction of cottonseed flakes with aqueous ethanol has been developed. The process consists of cottonseed meat flaking, drying and extraction with boiling, aqueous ethanol (95% by volume) at atmospheric pressure. The resulting miscella is chilled, producing free oil, emulsified oil and mucilaginous gum. The heterogeneous solution is processed through a phase separator where free and emulsified oil and gum are separated from oil-lean miscella. The oil and gum phases are treated with caustic soda and centrifuged to produce semirefined oil containing about 4% volatiles. The miscella phase, containing about 3.3% lipid-like material and 1% petroleum ether insolubles, is reheated and recycled to the extractor. After the marc is pressed foots are added, and it is desolventized to produce a meal having a residual oil content less than 1%. Although not yet otpimized, the process shows potential for scaleup to pilot plant processing and adaptability to current oil mill solvent operations. Presented at the AOCS annual meeting, Chicago, May 1983.     

A new method of detoxification of cottonseed by means of mixed solvent extraction

For several decades, scientists in the field of vegetable oils tried unsuccessfully to detoxify cottonseed by a practical method. By using 20-30% (by wt) of ethyl alcohol (90% in vol) with commercial hexane as a mixed solvent, we were able to extract effectively both gossypol and oil from cottonseed prepressed cake or flakes. Free gossypol in meal was reduced to ca. 0.013-0.04%; total gossypol was reduced to 0.32-0.55%; residual oil was reduced to ca. 0.5% or less. Any aflatoxin present also can be eliminated by this process. The detoxified cottonseed meal can be used as animal feed. Cottonseed protein can be used to substitute for soy protein. The extracted oil is of better quality than that obtained by the usual hexane extraction method, and gossypol is a valuable byproduct.     

Pilot plant studies on extracting cottonseed with methylene chloride

The practical feasibility of using methylene chloride to extract oil, aflatoxin and gossypol simultaneously from cottonseed flakes was demonstrated in a 56-hr experimental run using a pilot-scale, continuous extractor. Nine different trials varying in extraction time, solvent:flake ratio, flake preparation method and blending with 5% ethanol were evaluated. Residual oil contents were lower than typically achieved in extraction with hexane. Aflatoxin contents of the meals were reduced by 73–92% of the level in cottonseed meats, making possible the upgrading of a large portion of cottonseed meal that otherwise would exceed current action levels. Because gossypol also was extracted, it was possible to produce cottonseed meal that was well suited for use in poultry feeds, especially when a blend of 5% ethanol in methylene chloride was used. Meal desolventized easily, and residual levels of methylene chloride were generally less than 12 ppm. The oil was refined and bleached to acceptable quality standards, and no residual aflatoxin was detected in alkali-refined oil.     

Alcoholic extraction of vegetable oils. V. Pilot plant extraction of cottonseed by aqueous ethanol

Summary Cottonseed flakes were extracted by aqueous ethanol in a countercurrent pilot plant unit to determine the effect of operating variables and the optimum operating conditions. This investigation has shown that direct extraction of cottonseed, using aqueous ethanol as a solvent, is a feasible process in the type of equipment developed previously in this laboratory. The optimum operating conditions for the ethanol extraction of cottonseed have been established. The pilot plant extractions have shown that in this process a prime quality of crude oil and lightcolored meal of good quality, with negligible free gossypol content, are obtained. Presented at the spring meeting, American Oil Chemists' Society, April 29-May 1, 1957, New Orleans, La.     

Hexane and heptane as extraction solvents for cottonseed: A laboratory-scale study

For many years, commercial-grade hexane has been the preferred solvent for extracting oil from cottonseed. Recent environmental and health concerns about hexane may limit the use of this solvent; therefore, the need for a replacement solvent has become an important issue. Heptane is similar to hexane, but does not have the environmental and health concerns associated with the latter. On a laboratory scale, delinted, dehulled, ground cottonseed was extracted with hexane and heptane. The solvent-to-meal ratio was 10:1 (vol/wt). The yield and quality of the oil and meal extracted by heptane were similar to that extracted by hexane. Extraction temperature was higher for heptane than for hexane. A higher temperature and a longer time were required to desolventize miscella from the heptane extraction than from the hexane extraction. Based on these studies, heptane offers a potential alternative to hexane for extracting oil from cottonseed.     

Alternative hydrocarbon solvents for cottonseed extraction: Plant trials

Hexane has been used for decades to extract oil from cottonseed and is still the solvent of choice for the edible-oil industry. Due to increased regulations as a result of the 1990 Clean Air Act and potential health risks, the edible-oil extraction industry urgently needs an alternate hydrocarbon solvent to replace hexane. Based on laboratory-scale extraction tests, two hydrocarbon solvents, heptane and isohexane, were recommended as potential replacements for hexane. A cottonseed processing mill with a 270 MT/day (300 tons/day) capacity agreed to test both solvents with their expander-solvent process. Extraction efficiencies of isohexane and heptane, judged by extraction time and residual oil in meal, refined and bleached color of miscella refined oil, and solvent loss, were comparable to that of hexane. However, fewer problems were encountered with the lower-boiling isohexane than with the higher-boiling heptane. With isohexane, the daily throughput increased more than 20%, and natural gas consumption decreased more than 40% as compared to hexane.     

Degossypolized cottonseed flour—the liquid cyclone process

Predictions can be made safely that glanded cottonseed is likely to be with us for quite some time. Worldwide, 20 to 22 million metric tons of glanded cottonseed are produced annually. Hence a workable process for the removal of pigment glands is needed urgently if food-grade products are to be made from cottonseed. A brief history of the development of the Liquid Cyclone Process for the preparation of degossypolized cottonseed flour is outlined. Gossypol is removed in pigment glands via liquid cyclones, thus giving the development its name. The process consists of several unique operations including adequate drying of the meats prior to flaking, fluidizing of the flakes using commercial hexane, comminuting the fluidized slurry in a stone mill and adjusting the solids content of the milled slurry for proper separation of the fine flour from the glands, hulls and coarse meal in the cyclones. Finally, the flour is defatted and washed with hexane on a rotary vacuum filter, dried and desolventized under mild conditions to maintain protein quality. It is visualized that the above operations can be incorporated in a satellite plant operated in conjunction with a parent solvent extraction cottonseed oil mill. Sanitary conditions of the satellite plant will meet the exacting standards of the better food processing plants. Raw material specifications as well as type of plant needed and potential markets are discussed. One of 21 papers presented at the Symposium, “Oilseed Processors Challenged by World Protein Need,” ISF-AOCS World Congress, Chicago, September 1970. Deceased. So. Market. Nutr. Res. Div., ARS, USDA.     

The fatty acid composition of cottonseed oil at various stages of solvent extraction

The variation in the fatty acid composition of the glyceride portion of cottonseed oil at various stages of solvent extraction has been investigated. Prime cottonseed meats were flaked and extracted in glassware rate extraction apparatus, using commercial hexane up to different degrees of extractions. The fatty acid composition of cottonseed oil obtained after extracting the flakes to different residual oil contents was determined by gas-liquid partition chromatography. No difference was found.     

Factors affecting oil extraction/water adsorption in sequential extraction processing of corn

The sequential extraction process (SEP) uses ethanol to extract oil and protein from cracked, flaked, and dried corn, and the dried corn simultaneously dehydrates the ethanol. Value-added co-products are possible, potentially making production of fuel ethanol more economical. The effects of solvent-to-corn (S/C) ratio, corn moisture content (MC), and number of extraction stages on ethanol drying, oil recovery, and protein loss during the simultaneous oil extraction/water adsorption step of SEP were evaluated. Extractions were carried out by using both aqueous ethanol and ethanol/hexane blends at 56°C. The S/C ratios tested were 3∶1, 2∶1 (control), 1.5∶1, and 1∶1 (w/w). More anhydrous ethanol, greater oil yields, and less co-extracted protein were obtained with higher S/C ratios. Less anhydrous ethanol and lower moisture adsorption capacities were obtained when the corn MC was ≥1.12%. Oil yields gradually decreased with drier corn, whereas protein loss increased when corn MC was <1.12%. Reducing the number of extraction stages from seven (original SEP) to five did not affect ethanol drying capability, oil yields, and protein co-extracted with oil. Using ethanol/hexane blends resulted in more anhydrous ethanol, higher oil yields, and less protein co-extracted with oil.     

Acidic ethanol extraction of cottonseed

Ethanol (EtOH) is being evaluated as an alternate solvent to hexane for the extraction of glanded cottonseed. Hot EtOH, needed for efficient oil and aflatoxin extraction, binds gossypol to protein. However, this binding can be minimized by acidifying aqueous EtOH with a tribasic acid, such as phosphoric or citric. While this solvent extracts oil and gossypol, it does not affect EtOH’s ability to extract aflatoxin. The defatted cottonseed meals produced from this process contained 0.03% total gossypol (which is lower than meal prepared by most other processes) and the aflatoxin content was reduced from 69 to 2.9 ppb. These are preliminary results and additional research is needed to determine commercial feasibility. The removal of essentially all gossypol from an extracted meal has the potential to expand the use of cottonseed meal as a feed, increasing its value to both the cotton farmer and the seed processor. Presented in part at the 40th Oilseed Processing Clinic, March 4, 1991, New Orleans, LA.     

Solvent extraction of cottonseed meats

In the experimental countercurrent extraction of flaked cottonseed meats by trichloroethylene the residual oil content of the extracted flakes decreased with: first, a decrease in the final oil content of the final miscella; second, decrease in the flake moisture down to 8.64%; third, decrease in flake thickness; fourth, increase in temperature; and fifth, increase in extraction time. For the batch of cottonseed meats used the following equation was developed: whereR is percent residual extractables,b is flake thickness in feet,D is meat diameter in feet,ϑ is extraction time in hours,μ in viscosity, lb. per ft. hr.,ρ is density, lb. per cu. ft., andt is extraction temperature in degrees F. Not enough data were secured by extraction with hexane to check the equation developed for trichloroethylene extraction. Hexane is a poorer solvent for cottonseed oil than trichloroethylene. The amount of oil remaining in the meal is affected to a greater extent by the miscella concentration in hexane extraction than in trichloroethylene extraction.     

Influence of operation variables on quality parameters of olive husk oil extracted with CO<Subscript>2</Subscript>: Three-step sequential extraction

Supercritical CO₂ extraction is a viable alternative process for the extraction of high-quality oil from olive husk (also known as olive pomace), a residue obtained in the production of olive oil. We analyzed the effect of pressure (100–300 bar), temperature (40–60°C), solvent flow (1–1.5 L/min), and particle size (0.30–0.55 mm) on four important quality parameters of the oil extracted with CO₂: tocopherol concentration, extinction coefficients at 232 and 270 nm, and saponification value. Response surface methodology was used to obtain mathematical expressions related to the operating variables and parameters studied. Results from these experiments were also used to design a three-step sequential CO₂ extraction procedure to obtain a higher-quality extract. The optimal operational sequence consisted of a first extraction step at 75 bar for 1 h using 1% (vol/vol) ethanol modifier, followed by a second extraction stage at 350 bar for 2.5 h without ethanol and a third step, also at 350 bar, for 2.5 h but using ethanol. These extraction conditions obtained an intermediate fraction of oil with 64% yield and all normal parameters according to European Commission food legislation. This fraction is suitable without any further refining. On the contrary, the oils obtained by hexane extraction and by conventional supercritical CO₂ extraction at optimal conditions are suitable for human consumption after further refining. This last finding may result in improved economics of the sequential CO₂ extraction process compared to the conventional extraction method with hexane.     

Composition of oils extracted from potato chips by supercritical fluid extraction

To determine effects of two extraction procedures on oil compositions, tocopherols, monoacylglycerol, diacylglycerol, triacylglycerol, free fatty acids, polymers and polar components were determined in oils after extraction from potato chips by either supercritical carbon dioxide or hexane. Potato chips were fried in cottonseed oil or low linolenic acid soybean oil and sampled after 1, 10 and 20 h of oil use. Both extraction methods recovered comparable amounts of oil from the potato chips. Compositions of triacylglycerol and non‐triacylglycerol components including tocopherols, monomer, polymer, monoacylglycerol, diacylglycerol were similar for samples of chips fried in either oil except for the δ‐tocopherol data for potato chips fried in the low linolenic acid soybean oil used for 10 h of frying. There were some differences between the composition of low linolenic acid soybean oil extracted from the potato chips compared to the fryer oil at the 20 h sampling time. These results showed that the supercritical carbon dioxide extraction gave similar results to hexane extraction in yield and composition of oils from potato chips.     

Phase equilibrium data pertaining to the extraction of cottonseed oil with ethanol and 2-propanol

Summary Basic phase relation data have been obtained relative to the extraction of cottonseed oil with ethanol and 2-propanol, especially as affected by water in the solvent. Mutual solubility diagrams have been constructed for cottonseed oil with ethanol and 2-propanol of various aqueous concentrations. Tie-line data at 30° C. have been obtained for the ternary ethanol-cotton-seed oil-water and 2-propanol-cottonseed oil-water systems. These combined data will be of assistance in the selection of the most desirable temperatures and moisture concentrations in the solvent extraction of cottonseed with these alcohols. Comparison with results previously published for soybean oil suggests that the mutual solubility data for cottonseed oil and aqueous ethanols are applicable to other vegetable oils over a wide range of iodine values. In general, the results indicate that 2-propanol is the more desirable solvent since complete miscibility with the oil can be attained at temperatures below its normal boiling point even at moisture contents as high as 10% by weight whereas ethanol can tolerate only about 1.5% of water. High moisture contents result in more effective separation of the oil from the solvent when the miscella is cooled after extraction. Constant boiling aqueous ethanol and 2-propanol present the disadvantage of requiring greater than atmospheric pressure during extraction in order to attain complete miscibility with the oil. One of the laboratories of the Bureau of Agricultural and Industrial Chemistry, Agricultural Research Administration, U. S. Department of Agriculture.     

Cottonseed extraction with mixtures of acetone and hexane

Cottonseed flakes were extracted with mixtures of n-hexane and acetone, with the concentration of acetone varying between 10 and 75%. Adding small amounts of acetone (≤25%) to n-hexane significantly increased the extraction of free and total gossypol from cottonseed flakes. Sensory testing detected no difference in the odor of cottonseed meals produced either by extraction with 100% n-hexane or by extraction with a 10∶90 (vol/vol) mixture of acetone/hexane. More than 80% of the free gossypol was removed by the 10∶90 mixture of acetone/hexane, whereas pure n-hexane extracted about 47% of the free gossypol from cottonseed flakes. A solvent mixture containing 25% acetone removed nearly 90% of the free gossypol that was removable by extraction with pure acetone; the residual meal had only a minimal increase in odor. In contrast, cottonseed meals produced by extraction with pure acetone had a much higher odor intensity. The composition of the cottonseed crude oil was insignificantly affected by the acetone concentration of the extraction solvent. The results indicate that mixtures of acetone and n-hexane can be used as extraction solvents to produce cottonseed crude oil without the concomitant development of odorous meals.     

Extraction of cottonseed oil using subcritical water technology

This work represents the extraction of cottonseed oil using subcritical water. The extraction efficiencies of different range temperatures (180–280°C), having mean particle size range from 3 mm to less than 0.5 mm, water:seed ratios of 0.5:1, 1:1, and 2:1, and extraction times in the range of 5–60 min were all investigated. The composition of the extracted oil, using the subcritical water, was analyzed by gas‐liquid chromatography and compared with that extracted using traditional hexane extraction. The results showed that the optimum temperature, mean particle size, water:seed ratio, and extraction time were 270°C, <0.5 mm, 2:1, and 30 min, respectively. In addition the extracted oil was identical to that extracted using the traditional hexane method. © 2010 American Institute of Chemical Engineers AIChE J, 2011