Phosphoric acid degumming

The phosphoric acid and water are added to the warmed (65°C/150°F) crude oil stream, pass through a high-shear mixer, and are pumped to the stirred hydration tank. Details of the process, using an Alfa Laval (Lund, Sweden) PX-90 centrifuge rated at 33,000 kg/hr for degumming, are shown in Fig. 34.18.7 After degumming, the crude oil is vacuum dried to <0.3 percent moisture... 

The objective in acid degumming is to chelate the calcium and magnesium ions and render the nonhydratable phosphatide forms hydratable. In addition to phosphoric acid, citric and malic acids are effective, as well as eth-ylenediaminetetraacetic acid (EDTA). Acid-treated phosphatides are not used for production of commercial lecithins. Extensive reviews on oil degumming have been prepared.106 107 Lurgi, a German equipment manufacturer, has developed an EnzyMax process that cleaves the nonhydratable phosphatides with a phospholipase B at the triglyceride s second carbon to produce a lysophosphatide that is insoluble in oil and is removed by centrifuging.108... 

A typical fat refining plant (Alfa-Laval process) for the acid washing of fats and oils is illustrated in Fig. 36.8.8 The triglyceride is degummed to remove phosphatides and other impurities such as mucilage, proteinaceous matter, and trace metals by acid washing with citric or phosphoric acids, and then is sent to a bleaching plant where it is dehydrated and treated with an activated clay for the removal of color bodies, heavy metals, chlorophyll, and polyethylene (Fig. 36.9).6... 

In the most recent development, acid and aqueous sodium hydroxide, rather than acid and water are being used, especially with lower quality oils (acid-caustic degumming). This represents an intermediate between acid-water degumming and alkali refining. It obviates the need for cooling, similar to the practice in alkali refining. Phosphoric acid rather than an organic acid is preferred in this case. Phosphatides as well as some of the other impurities are removed, and if sufficient, alkali is applied to saponify the free fatty acids, fully refined oil is obtained. 

Degumming. Crude coconut oil is continuously heated to 80-90°C, and 85% phosphoric acid at a range of 0.05-0.10% by volume of feedstock is dispersed in the oil via an in-line static mixer. The mixture is conveyed into a coagulation tank and agitated for 20-30 min. 

An expired U.S. patent describes molecular distillation of WGO (47). Initially, WGO was degummed by using phosphoric acid and water. Bleaching was carried out with activated clay followed by distillation using a centrifugal molecular distillation unit. Free fatty acids were removed at 140-200°C and below 50 mTorr. It was claimed in the same patent that a Vitamin E concentrate was prepared from purified WGO by a second-stage molecular distillation process carried out at 220-300°C and pressures less than 25 mTorr (47). 

Fluidization with phosphoric acid is not recommended because darkening of the product and hydrolysis may occur. Degumming with acetic anhydride results in fluidized lecithins possibly because PE is acetylated by the reagent. Nonedible lecithins may be fluidized by the addition of acidulated and dried soapstock. 

Most seed oils contain 0.2-0.8% nonhydratable phospholipids (5), specifically the magnesium (Mg) and calcium (Ca) salts of phospholipids, which cannot be removed by water degumming. For many years, a common way for nonlecithin producers to degum edible oil was to treat the oil with 0.02-1% of concentrated phosphoric acid at 70-90°C, after water degumming. Then, without the removal of any precipitated solids, the oil is caustically refined. Phosphoric acid chelates the Ca and Mg in the oil so that the nonhydratable phospholipids are converted into the hydratable form. The phosphoric acid pretreatment produces a darker lecithin with lower purity (5). 

In the acid degumming process, the oil is treated with citric acid, though phosphoric acid has also been used by some oil processors to reduce the cost. Mixing the oil and citric acid is done in the same manner as in the water degumming process. The oil is sometimes heated to a slightly higher temperature and residence times of 60-90 min have been used by processors. 

Acid degumming of sunflower oil is not generally required because of the low concentration of the phospholipids in the oil. Some processors degum poor quality sunflower oil with citric acid treatment. The results are satisfactory. However, this is not commonly followed in the sunflower processing industry. Some processors also pre-treat crude sunflower oil with phosphoric acid or citric acid before chemical refining. This is a common practice for refining most vegetable oils. 

For the short-mix process, the oil temperature is raised to 80—90°C (175—195°F) before the addition of the caustic soda. A break between the neutral oil and soapstock takes place immediately, reducing the losses due to emulsification. The contact time between the caustic and oil is reduced to a 30-sec maximum, which helps to reduce the saponification losses. Because it is standard in Europe to degum solvent-extracted oils and to condition the oils with phosphoric acid before refining, the excess caustic treatment can be eliminated or reduced substantially. The oil is finally washed with demineralized water to help remove the traces of soap remaining in the oil and dried with processes similar to the systems used for the long-mix caustic refining process. 

The hot oil may be cooled to 82 C and proceed directly to degumming by first being thoroughly mixed with 1 % or 2% of hot (82°C) condensate water. Some processors also add a small (variable) amount of phosphoric acid to... 

Oil that has been degummed with acid and water to a phosphorus concentration of less than 50 ppm can be prepared for steam refining by bleaching. Usually, a small amount of phosphoric acid (0.05-0.1 %) is used on the oil prior to the addition of bleaching clay to assist in the removal of the phosphatides. Also, it may be necessary to use somewhat more clay than is required in the bleaching of alkali-refined oil. Contact time and contact... 

---