J. P. Friedrich

Supercritical CO2 extraction of lipid-bearing materials and characterization of the products

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.

Effect of moisture and particle size on the extractability of oils from seeds with supercritical CO2

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 (<0.010″) seeds. Moisture levels between 3% and 12% had little effect on extracability. Oil composition was not influenced by either parameter. Scanning electron microscopy was used to study seed structure before and after extraction with SC-CO2. Micrographs of SC-CO2-extracted seeds were similar to hexane-extracted seeds.

Oxidative stability of seed oils extracted with supercritical carbon dioxide 1

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.

Characterization and processing of cottonseed oil obtained by extraction with supercritical carbon dioxide

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 crude cottonseed oil compared to those obtained by conventional solvent or expeller processes. Improvements include lighter initial color, less refining loss and lighter refined bleached colors. Crude cottonseed oils obtained by supercritical fluid extraction require less refining lye and show less tendency to undergo color fixation while in storage.

Properties and processing of corn oils obtained by extraction with supercritical carbon dioxide

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.

Processing characteristics and oxidative stability of soybean oil extracted with supercritical carbon dioxide at 50 C and 8,000 psi

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.

Estimation of supercritical fluid-liquid solubility parameter differences for vegetable oils and other liquids from data taken with a stirred autoclave

Fujishiro and Hildebrand developed a procedure for determining the solubility parameter difference between the components of a partially miscible binary mixture, knowing the molar volumes of the components and the composition of each phase. Using this procedure, the solubility parameter differences between supercritical carbon dioxide (SCCO2) and each of three vegetable oils and four hydrogen bonding liquids have been determined. For the vegetable oils the solubility parameter differences at 72 C over the pressure range 5,000–10,000 psi were low, of the order of 2.0, and decreased only slightly with increasing pressure. For the hydrogen-bonding liquids at 52 C, over the same pressure range, the solubility parameter differences were much larger, of the order of 4 to 7 units, and independent of pressure except for ethylene glycol for which the difference increased from 5.7 to 6.7 from 5,000 to 10,000 psi.

Selective hydrogenation of soybean oil: X. Ultra high pressure and low pressure1

Soybean oil was partially hydrogenated with copper-chromite catalyst at 170 C and up to 30,000 psig hydrogen pressure. Catalyst activity increased with increase in pressure up to 15,000 psig. The linolenate selectivity (SLn) of the reaction remained essentially unchanged over 50–1000 psig pressure range. A SLn of 5.5 to 5.6 was achieved at 15,000 to 30,000 psig pressure range. This value is somewhat lower than the selectivity at 50–1000 psig, but much higher than that obtained with nickel catalysts. Geometric isomerization increased as pressure increased up to 200 psig; above this pressure, the percenttrans remained the same up to 500 psig.trans Isomer content decreased when the pressure was increased to 30,000 psig. cis,trans Isomerization of linoleate was greater at 1000 psig and 15,000 psig than at 50 psig. At 15,000 psig, part of the linoleate in soybean oil was hydrogenated directly without prior conjugation, whereas at low pressures, all of the double bonds first conjugate prior to hydrogenation. This difference in mechanism might explain the lower selectivities obtained at high pressures. Conjugated diene isomers were found in the products up to 200 psig. Above this pressure conjugated diene was not measurable. No significant differences were found in the double bond distribution oftrans monoenes even though the amount oftrans monoene formed decreased as pressure was increased to 30,000 psig.

cis-bond-producing hydrogenation of polyunsaturates catalyzed by polymer-complexed Cr(CO)3 catalysts

Abstractcis-Bond-producing chromium carbonyl catalysts were prepared by complexing conventional or macroreticular, styrene-divinylbenzene copolymers or cross-linked poly (vinyl benzoate) with Cr(CO)6. With one exception, these polymer-Cr(CO)3 catalysts were as selective as the corresponding homogeneous arene-Cr(CO)3 complexes for the formation ofcis-monoenes from methyl sorbate and from conjugated, polyunsaturated fatty esters in cyclohexane. Although several of the polymer catalysts were very active when fresh, they all lost activity on recycling. They could not be recycled more than two times before a marked decrease in activity occurred due to loss of Cr, as shown by elemental analysis and infrared absorption in the recovered catalyst. Thermal analysis indicated instability of the polymer complexes at hydrogenation temperatures.

Laboratory continuous deodorizer for vegetable 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.