Soybeans degumming

Fig. 2. Flow sheet of lecithin producing unit. Crude soybean oil is heated in the preheater, 1, to 80°C, mixed with 2% water in the proportion control unit, 2, and intensively agitated in 3. The mixture goes to a dweUing container, 4, and is then centrifuged after a residence time of 2—5 min. The degummed oil flows without further drying to the storage tanks. The lecithin sludge is dried in the thin-film evaporator, 6, at 100°C and 6 kPa (60 mbar) for 1—2 min and is discharged after cooling to 50—60°C in the cooler, 8. 9 and 10 are the condenser and vacuum pump, respectively.

The total commercial lecithin potential if all vegetable oils were degummed worldwide would be 552,000 t (Table 7). Although soybean, sunflower, and rape lecithins are available in the market, the principal commercial interest is only in soybean lecithin. The aimual worldwide production is 130,000 t (Table 8). 

The process involves reacting the degummed oil with an excess of methyl alcohol in the presence of an alkaline catalyst such as sodium or potassium methoxide, reaction products between sodium or potassium hydroxide and methyl alcohol. The reaction is carried out at approximately 150°F under pressure of 20 psi and continues until trans-esterification is complete. Glycerol, free fatty acids and unreacted methyl alcohol are separated from the methyl ester product. The methyl ester is purified by removal of residual methyl alcohol and any other low-boiling-point compounds before its use as biodiesel fuel. From 7.3 lb of soybean oil, 1 gallon of biodiesel fuel can be produced. See FIGURE 12-5. 

From a technical standpoint, phospholipids (e.g., from soybean) are composed mainly of lecithin, cephalin, or phosphatidylinositol. These complex mixtures (2-3% in soybean oil) are hydrated during the degumming step, removed, and dried. These products are sold as commercial lecithin used in margarines, confections, and shortenings where a fat-soluble emulsifier is required. 

In commercial formulations, phospholipids are not available as pure products. Mostly they are obtained as a by-product of the process of refining vegetable oils, during the so-called degum-ming step (3,4), from which a liquid-to-pasty product is obtained that is referred to as lecithin. Lecithin contains about 65% phospholipids plus about 30% residual neutral lipids and minor amounts of glycolipids. For historical reasons, most commercially available lecithins are derived from soybean oil, but lecithins of other oils could be used as well. From this discussion it follows that the determination and quantification of phospholipids is of importance both to control how efficiently the phospholipids have been removed from vegetable oils and to control the quality of the lecithin. For this purpose it is important to know not only the total amount of phospholipids but also the amount of the different types of phospholipids present, because it is well known that the functional properties of the various phospholipids differ widely (2-8). 

Haas et al. [18] developed a computer model to estimate the capital and operating costs of a moderately sized industrial biodiesel production facility with a capacity of 33.5 ktonne (10 million gallons) using degummed soybean oil as... 

Candida antarctica (Novozym 435) MethanoP Degumming soybean Free 94% Watanabe et al,... 

Watanabe, Y., Pinsirodom, P., Nagao, T., Yamauchi, A., Kobayashi, T., Nishida, Y., Takagi, Y., and Shimada, Y. 2002. Conversion of degummed soybean oil to biodiesel fuel with immobilized Candida antarctica lipase. J. Mol. Catal. B Enzym., 17, 151-155. 

To prevent hydration and precipitation of phosphatides during storage and shipping, the phosphorous content of crude soybean oil must be reduced to less than 0.02 percent (200 ppm) before entering the trade. This usually is accomplished by water degumming. 

Mid-1980s—Degummed, alkali-refined cottonseed and soybean oils used in pesticide aerial spays. 

Crude soybean oil has limited uses as sprays. Spray nozzles are in danger of clogging by phospholipids, which also leave repeatedly sprayed surfaces sticky. Generally, once-refined oil (degummed, alkali-neutralized,... 

Erickson, D. R., Degumming and lecithin processing and utilization, in Practical Handbook of Soybean Processing and Utilization, D. R. Erickson (Ed.), pp. 174-183, AOCS, Champaign, IL, 1995. 

Phospholipids (Figure 3) are constituents of membranes and are only minor components of oils and fats, sometimes responsible for cloudiness. They are usually removed during degumming, the residue from soybean oil processing being a source of phospholipids used as food emulsifiers. The term lecithin is used very loosely for such material, and it may variously mean phosphatidylcholine, mixed glycerophospholipids, or cmde phospholipid extracts from various sources. Where possible, more specific nomenclature or the source and purity should be used (14). 

Cmde oils generally contain phospholipids that are removed during the degum-ming stage of refining as a crude mixture (lecithin). This valuable product is the basis of the phospholipid industry, and phospholipids are used extensively in food products, in animal feeds, and in industrial processes. The major members are phosphatidylcholines, phosphatidylethanolamines, and phosphatidylinositols and are accompanied by smaller proportions of other phospholipids. Soybean oil (3.2%), rapeseed oil (2.5%), and sunflower seed oil (1.5%) contain the proportions of total phospholipids indicated in parentheses and are the main sources of commercial lecithins, especially soya lecithin. Palm oil contains little or no phospholipids (7-9). 

USA-ASTM standard for 100% pure biodiesel is similar in many respects (146), but it is written for the use of soybean oil as the main starting material. Canola oil for methyl ester production must either be degummed (<20 mg/kg of phosphorus), or in addition, must be alkali refined and bleached, depending on the methyl ester production process requirements (148). 

Some soybean extraction plants also degum their oil before shipping to centralized refineries. There is not sufficient market to make it profitable to recover all of the soybean phosphatides and market them as soy lecithin. The gums are added back to the meal in the toaster to evaporate the water. The gums contribute to the metabolizable energy content of the meal and the soybean crusher can get meal prices for crude phosphatides. 

The quality of crude soybean oil inhuences the efficacy of degumming. Phospholipids can exist in a hydratable form, which can be readily removed by addihon... 

Recently, polymeric ultrafiltration membranes were used for degumming crude soybean oil and removing phospholipids from the crude oil/hexane miscella (168). Crude soybean oil also can be de-acidified by methanol extraction of the free fatty acids and the extract separated into fatty acids and solvent by a membrane filter (169). A surfactant-aided membrane degumming also has been applied to crude soybean oil, and the degummed oil contained 20-58 ppm of phosphorus (170). Supercritical carbon dioxide extraction was shown to be an effective means of degumming (171). In this process, soybean oil countercurrently contacted supercritical carbon dioxide at 55 MPa and 75°C. The phosphorus content of the oil was reduced from 620 ppm to less than 5 ppm. Ultrasonic degumming was also successfully used to reduce the gum content of soybean oil (172). 

TABLE 16. Trading Specifications for Crude Degummed, Once-Refined and Fuiiy Refined Soybean Oiis (228). 

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