Search

Supercritical fluid extraction has recently become a reality in the petroleum, coal and food industries and is rapidly increasing in importance as its advantages become known. Advantages of carbon dioxide as a supercritical fluid include its low toxicity, low cost, lack of flammability, lack of reactivity, wide range of solvent properties at different pressures and temperatures, and improved properties of separated components in certain cases. Disadvantages of such extractions include high capital costs for batch extraction and lack of engineering hardware technology for continuous operation. In the supercritical CO2 extraction of oil from soybeans, equilibrium solubility and high flow rates are readily achieved in a short-path batch reactor. The oil has a lighter color, less iron and ca. 1/10 of the phosphorus contained in hexane-extracted oil. The lower phosphorus content results in lower refining losses. During extraction, some fractionation is observed to take place, with some more polar and/or higher molecular weight compounds having a tendency to increase in the later fractions. In a long cylindrical batch extractor, the flakes perform much like the stationary phase of a chromatographic column. The same advantages that result from extraction of soybeans also apply to the extraction of oil from cottonseed and corn germ. Cottonseed oil obtained by supercritical CO2 extraction has a lower gossypol content and requires less alkali for refining. In the extraction of wheat germ and bran, the oil has a lighter color, a milder odor and less unsaponifiables than that obtained by hexane. Free fatty acid contents were comparable, but tocopherol was higher in the supercritical CO2 extract.

Moisture level and particle size of soybeans, peanuts and cottonseed were correlated with the extraction rate and yield of oil when extracted with supercritical carbon dioxide (SC-CO2) at a constant temperature (50 C) and pressure (8000 psig). The rate of extraction and ultimate oil yields were quite low with cracked soybeans. However, good extraction rates and nearly theoretical oil yields were obtained from ground or thinly flaked (

Dry-milled corn germ, soybean and cottonseed flakes were extracted (at 70-90 C and 12,000 psi) with supercritical carbon dioxide (SC-CO2) to yield crude oils. Oxidative stability of the crude oils was determined and compared to similar products obtained by conventional expeller and/or prepress solvent extraction. Under Schall oven storage conditions (60 C), SC-CO2-extracted oils undergo rapid deterioration and fail to show the normal induction period observed with conventional expeller and solvent-extracted crude oils. The levels of tocopherols found in SC-CO2-extracted oils are comparable to those obtained by expeller or solvent extraction, while phospholipids present in significant amounts in conventional crude oils are essentially absent from SC-CO2-processed crudes. The addition of phosphatides to SC-CO2-extracted crude oils improves oxidative stability, which suggests that both tocopherols and phospholipids are required to stabilize crude oils against autoxidation. Heating of SC-CO2-extracted crude oils to deodorization temperatures improves oxidative stability. The destruction of fat hydroperoxides under these conditions probably accounts for improved oxidative stability. A combination of heat and the addition of citric acid and phenolic antioxidants resulted in further improvement of oxidative stability.

Full-fat soyflakes are readily extracted with supercritical carbon dioxide (SC-CO2) at pressures of 3,000~10,000 psig and 50 C. Under these conditions, SC-CO2 has the density of a liquid and the diffusivity of a gas. Therefore, equilibrium solubility is readily achieved in a short-path batch extractor which permits high gas flow rates. Soybean oil extracted with SC-CO2 is lighter in color and contains less iron and about one-tenth the phosphorus of hexane-extracted crude oil from the same beans. The lower phosphorus content is reflected in a chromatographic refining loss of 0.6% compared to 1.9% for hexane crude. Refined oils from hexane and SC-CO2 extraction had equivalent odor and flavor scores initially and after 4 days' storage at 60 C. Carbon dioxide, an ideal solvent for extraction of food products, is low-cost and readily available from fermentation processes and could free over 20 million gallons of costly hexane per year for essential energy uses.

Selective hydrogenation of soybean oil to reduce linolenic acid is accomplished better with copper than with nickel catalysts. However, the low activity of copper catalysts at low pressure and the high cost of batch equipment for high-pressure hydrogenation has precluded their commercial use so far. To evaluate continuous systems as an alternative, soybean oil was hydrogenated in a 120 ft × 1/8 in. tubular reactor with copper catalyst. A series of hydrogenations were performed according to a statistical design by varying processing conditions: oil flow (0.5 L/hr, 1.0 L/hr and 2.0 L/hr), reaction temperature (180 C and 200 C), hydrogen pressure (1,100 psig and 4,500 psig) and catalyst concentration (0.5% and 1.0%). An iodine value (IV) drop of 8–43 units was observed in the products whereas selectivity varied between 7 and 9. Isomerization was comparable to that observed with a batch reactor. Analysis of variance for isomerization indicated interaction between catalyst concentration and hydrogen pressure and between catalyst concentration and temperature. The influence of pressure on linolenate selectivity was different for different temperatures and pressure. Hydrogenation rate was significantly affected by pressure, temperature and catalyst concentration.

Full-fat soybean flakes were extracted with supercritical carbon dioxide (SC-CO2) at pressures of 10,600–12,400 psi, temperatures from 80–100°C, and moisture levels of 5–13.5%. Conditions could be selected to produce defatted soybean meals with nitrogen solubility indices greater than 70% and flavor scores greater than 6.5 on a scale of 1 to 10 (1 = strong and 10 = bland). The usual grassy-beany and bitter flavors of hexane-defatted soybean flours were only minimally detectable in the optimally SC-CO2-extracted materials. Bland, defatted soybean meal prepared by SC-CO2 extraction was further processed into high-quality protein concentrates and isolates that were stable when stored under adverse conditions.

Selective hydrogenation of soybean oil with copper catalyst at 50 psig or less is characterized as a relatively slow reaction requiring higher catalyst concentrations than the less selective but rapid nickel-catalyzed reactions used in most commercial practice. Hydrogenations of soybean oil have been performed which included a high-pressure scan (500, 1000, and 3000 psig), at selected temperatures (110, 130, 150, and 170 C), and at specific catalyst concentrations (0.05, 0.1, 0.2, and 0.4% copper). Selectivities, relative reaction rates, and geometric and positional isomerization have been determined as an evaluation of the effects of high pressure on the kinetics of the reaction. The experimental results indicate that an appropriate selection of pressure, temperature, and catalyst concentration can permit: (a) a significant increase in the rate of reaction while retaining the high linolenic acid selectivity of copper catalysts, (b) use of lower concentrations of copper catalyst while maintaining the higher reaction rate, and (c) elimination of conjugated diene as a measureable product in the hydrogenated oil.

The use of Cr(CO)6 was investigated to convert polyunsaturated fats intocis unsaturated products. With methyl sorbate, the same order of selectivity for the formation ofcis-3-hexenoate was demonstrated for Cr(CO)6 as for the arene-Cr(CO)3 complexes. With conjugated fatty esters, the stereoselectivity of Cr(CO)6 toward thetrans, trans diene system was particularly high in acetone. However, this solvent was not suitable at elevated temperatures required to hydrogenatecis, trans- andcis, cis-conjugated dienes (175 C) and nonconjugated soybean oil (200 C). Reaction parameters were analyzed statistically to optimize hydrogenation of methyl sorbate and soybean oil. To achieve acceptable oxidative stability, it is necessary to reduce the linolenate constituent of soybean oil below 1–3%. When this is done commercially with conventional heterogenous catalysts, the hydrogenated products contain more than 15%trans unsaturation. By hydrogenating soybean oil with Cr(CO)6 (200 C, 500 psi H2, 1% catalyst in hexane solution), the product contains less than 3% each of linolenate andtrans unsaturation. Recycling of Cr(CO)6 catalyst by sublimation was carried through three hydrogenations of soybean oil, but, about 10% of the chromium was lost in each cycle by decomposition. The hydrogenation mechanism of Cr(CO)6 is compared with that of arene-Cr(CO)3 complexes.

Methyl formylstearate, containing soluble rhodium complex from rhodium-catalyzed hydroformylation of methyl oleate, is oxidized in an emulsion to methyl carboxystearate. The reaction is carried out in a closed system at 20–25 C in the presence of either air or oxygen (1–3 atm). Conversion to methyl carboxystearate is 87–89% in 2–3 hr; when catalytic amounts of calcium acetate are present, 93–95% is converted. The principal byproduct of oxidation is methyl formyloxystearate, formation of which is suppressed by calcium acetate. Distillation of crude methyl carboxystearate yields a residue containing soluble rhodium (and calcium acetate if used), which after calcining in the presence of a refractory support produces an effective hydroformylation catalyst. Recovery and regeneration of this catalyst provide an economically feasible batch process for methyl carboxystearate.

Liquid C-18 saturated monocarboxylic acids, which are termed “cylic acids” because they contain a ring structure, have been prepared by the action of excess sodium hydroxide on linseed oil in ethylene glycol at elevated temperatures, followed by distillation and hydrogenation of the resulting free fatty acid monomers and by separation of the straight-chain components by low-temperature crystallization from acetone. In a survey of other possible catalysts and reaction conditions, cyclic acid yields were improved from the previously reported 32.4 g to 43.5 g of cyclic acid per 100 g of linseed fatty acids by removing water from the starting materials and using the monosodium derivative of ethylene glycol as catalyst. The corresponding amount of polymer formed decreased because of a decrease in hydroxylation and subsequent polyester formation.

Liquid C-18 saturated monocarboxylic acids that fail to crystallize at −70°C. have been prepared from linseed oil, linolenic acid, and tung oil. Heating one part of linseed oil in three parts of glycol (weight-volume ratio) at 295°C. for 1 hr. with 25% excess sodium hydroxide, followed by distillation and hydrogenation of the resulting free fatty acid monomers and separation of the straight-chain components by low temperature crystallization from acetone, yielded these liquid acids.

We have studied the reaction of 1,1-dichloro-2,2-difluoro-, chlorotrifluoro-, and tetrafluoro-ethylenes and also hexafluoropropylene withcis,trans andtrans,trans isomers of conjugated methyl octadecadienoate. Reactions gave 50-82% yields of cycloaddition products. The pre-ponderance of products with a cyclobutane struc-ture and a double bonda,β to the cyclobutane ring was shown by IR and NMR spectra. Reactions were carried out in diluent with hy-droquinone inhibitor at autogenous pressure and a temperature of 200C for 5 hr. The distilled adducts are colorless liquids with viscosities rang-ing from 11 to 19 centistokes at 100F. These products and their hydrogenated derivatives ex-hibit low pour points (down to -76F) and may be useful as low-temperature plasticizers or lubricant additives.

8-(4-n-Hexylcyclohex-2-enyl)octanoic acid obtained by the addition of ethylene totrans,trans-9,11-octadecadienoic acid was treated with 28% hydrogen peroxide in acetic or formic acid to give the hydroxyacetoxy or-formoxy derivative. Saponification of the hydroxyacetoxy derivative yielded two crystalline glycols. The hydroxyformoxy fatty acid was converted in one step either to the glycol ester, methyl 8-(4-n-hexyl-2,3-dihydroxycyclohexyl)octanoate, by reaction with anhydrous hydrochloric acid in methanol or to the acetone derivative of the glycol ester by treatment with dimethoxypropane and anhydrous hydrochloric acid in methanol. Epoxidation of the C20 cyclohexene fatty methyl ester gave the oxirane derivative. A ring opening reaction of the diol acid with periodic acid yielded 9,12-diformylstearic acid.

Methyl oleate was hydroformylated to methyl formylstearate at 120 C and 850–900 psig with a 1:1 mol mixture of hydrogen and carbon monoxide. In the presence of triphenylphosphite, an activated rhodium-on-alumina catalyst produced an essentially quantitative conversion in about 40 min. Filtration followed by distillation yielded methyl formylstearate. The solubilized rhodium catalyst was concentrated in the distillation residue. The residue was resupported on the spent support in a gas-fired rotary kiln. The process was repeated 9 times without significant loss of catalyst activity. Assuming the catalyst can be recycled repeatedly to the process without affecting the efficiency of operation, a preliminary estimate based on a hypothetical plant producing 2 million 1b of methyl formylstearate annually places the processing costs, not including cost for methyl oleate, at about 13.7 cents per pound.

Methyl 8-(4-n-hexylcyclohex-2-enyl) octanoate obtained by esterifying the adduct of ethylene andtrans,trans-9,11-octadecadienoic acid was ozonized in methanol as a participating solvent. The resultant cyclic methoxyhemiperacetal was reduced with powdered zinc to the dialdehyde, methyl 9,12-diformylstearate, which was isolated as the tetramethyldiacetal. This dialdehyde readily air-oxidizes to give methyl 9,12-dicarboxystearate. Heating the cyclic methoxyhemiperacetal slowly from 25 to 100 C in vacuo results in an unusual decomposition reaction which gives hydrogen and methyl 9 (12)-carbomethoxy-12(9)-carboxystearate as the primary products and methyl 9 (12)-carbomethoxystearate as the major by-product. Treatment of the cyclic hemiperacetal with hydrogen peroxide in formic acid gave unexpectedly dihydroxystearic acid as one of the products.

Crude oils were extracted from wet- and dry-milled corn germs with supercritical carbon dioxide (SC-CO2) at 50–90 C and 8,000–12,000 psi and were characterized for color, free fatty acids, phosphorus, refining loss, unsaponifiable matter, tocopherol and iron content. They were compared with commercial products. Extraction of wetmilled germ with SC-CO2 has some advantages over the conventional prepress solvent method commonly used in the industry. For example, SC-CO2 extraction of wet-milled germ at 50 C and 8,000 psi yields crude oil with a lower refining loss and a lighter color. After laboratory processing, a light-colored, bland salad oil is obtained. Crude, refined, bleached and deodorized oils from SC-CO2-extracted dry-milled germ appear equivalent to those obtained by expeller pressing.

An adiabatic reactor was constructed to simulate conditions that lead to storage-damaged soybeans. The heart of the system is an electronic temperature controller that causes the reactor temperature to closely follow intrinsic heating of the soybeans. Using moisture concentrations between 17% and 20%, we observed intrinsic heating ranging from 47 C to 52 C after 3–13 weeks. Quality of the extracted oil was determined by analyses for triglyceride (TG) composition, total phosphorus (P), peroxide value and free fatty acid (FFA). Higher FFA and lower P and linolenic acid concentrations in the damaged beans compared with undamaged beans agree with the literature and indicate reliability of the adiabatic reactor for further studies, e.g., the effect of enzymatic activity on the quality of resulting soybean oil.

Extraction of flaked cottonseed with supercritical carbon dioxide at temperatures of 50-80 C and pressures of 8,000-15,000 psi yields an improved etude cottonseed oil compared to those obtained by con­ ventional solvent or expeller processes. Improvements include lighter initial color, less refining loss and lighter refined bleached colors. Ctude cottonseed oils obtained by supercritical fluid extraction re­ quire less refining lye and show less tendency to undergo color fixation while in storage. INTRODucnON Recently, there has been much interest in the use of super­ critical fluid (SCF) for the extraction of oilseeds, and previous reports from this laboratory have described work with soybeans and corn germ (1-3). This report extends the work to cottonseed and details some preliminary observa­ tions on the composition, processing and organoleptic properties of oils obtained by extraction of cottonseed flakes with supercritical carbon dioxide (SC-C02). Cotton­ seed oil generally is considered to be more difficult to process than the other common vegetable oils, because it contains somewhat higher levels of free fatty acids and is more intensely colored as the result of the presence of gossypol and related pigments that are carried along during solvent extraction or expeller pressing.

The crude oil extracted from soy flakes with supercritical carbon dioxide (SCCO2) was characterized for color, free fatty acid, phosphorus, neutral oil loss, unsaponifiable matter, tocopherol and iron content and compared to a commercial hexane-extracted sample of crude degummed oil. Characterization and processing studies indicate that SCCO2 extraction yields a product comparable to a hexane-extracted degummed oil. However, hexane-extracted degummed soybean oils exhibit better oxidative stability because phosphatides, which are natural antioxidants, are essentially absent in SCCO2-extracted oils.

A laboratory-scale continuous deodorizer, based on a modified Snyder distillation column, was constructed and tested for the deodorization of alkali-refined and bleached vegetable oils. Soybean oil extracted with supercritical carbon dioxide and without further processing also was deodorized to a finished edible oil. Results of taste panel evaluations of the finished oils show that the quality of oils deodorized over a temperature range of 194–260 C is equivalent to commercial salad oils. Oil flow rates are 1 to 2 ml/min, and contact time is about 5 min; a vacuum of 0.5 to 1.0 mm Hg is maintained with countercurrent steam flow of 1 to 5% of the oil weight. Small samples of oil (250–1000 ml) are readily accommodated in this equipment, and the deodorization conditions more nearly simulate commercial practice than do traditional small-scale batch deodorizers.

Methods are described to determine metallic rhodium on small smaples of either carbon or alumina catalyst supports. After the catalysts were digested with hot mineral acids, the solutions were analyzed by an established colorimetric method and results were compared with those from an atomic absorption procedure. Statistical analysis showed that the two methods were equal in precision with a combined standard deviation of 0.08 for a 5.0% rhodium catalyst.

Saturated C18- and C20-cyclic alcohols have been prepared by catalytic hydrogenation of methyl esters from cyclized linseed monomeric acids, purified saturated C18-cyclic acids, ethylene adduct of conjugated soybean fatty acids, and ethylene adduct of conjugated octadecadienoic acids. The cyclic alcohols have also been prepared from free acids of crude cyclic linseed, cyclic linseed monomeric, and ethylene adduct of 9,11,t,t,-octadecadienoic. Conversion of esters and acids was 88–99% by hydroxyl determination; by gas-liquid chromatographic analysis, almost quantitative Hydrogenations were carried out with 10%, by weight, copper chromite catalyst, an initial hydrogen pressure of 2,100 psi, and a temperature of 280C for 3–5 hr. Preliminary evaluations indicate that saturated C18- and C20-cyclic alcohols have a potential use in cosmetic formulations.

Monoalkyl esters of linseed-oil-derived C18-saturated cyclic acids (HCal), described in earlier work, showed promise as lubricant base stocks for turbine aircraft as set forth in the military specification MIL-L-7808E. These esters, however, did not exhibit the increased oxidative stability and higher viscosity required by the more recent specification MIL-L-23699.

Monomeric fatty acids derived from the alkali treatment of linseed oil at temperatures above 200C contain cyclic (1,2-disubstituted cyclohexadiene) and straight-chain fatty acids. Hydrogenation converts cyclic to liquid, saturated cyclic acids that can be recovered in a pure state by crystallization. During hydrogenation (palladium catalyst) some of the unsaturated cyclic acids form aromatic fatty acids by loss of hydrogen and under some conditions are not subsequently hydrogenated. It was necessary to establish conditions for complete hydrogenation since color and oxidative stability at high temperature are inversely related to aromatic content. Previously, the preparation of cyclic acids free of aromatic acids was by hydrogenation in the presence of a high concentration of acetic acid. A further study of reaction variables established conditions to make saturated cyclic fatty acids free of aromatic without acetic acid. Factors favoring the elimination of aromatic acids include a high catalyst concentration, high temperature and pressure, good hydrogen dispersion in the liquid and good agitation.