Degumming with membranes

Membrane degumming. Membrane separation has also been evaluated as an alternative process to conventional oil refining processing. Ultrafiltration (UF) and nanofiltration (NF) membranes separate phospholipids almost completely, and FFAs, pigments, and other components can also be removed with the phospholipids to a certain extent. Less effort is required in the later processing steps. 

The process developed by Gupta (19-22) processed crude oils with a combination of UF membrane separation and silica gel column percolation. The soybean and rapeseed-hexane miscellas were passed through various UF membranes. The solvent was removed from the permeate, and the degummed oil was then treated with bleaching clay, silica, and/or acid and finally was steam deodorized to produce refined, bleached, and deodorized oil. The color readings of the oils obtained... 

Semi-pilot plant scale trials with crude oils containing 220-580 ppm phosphorous (28) show that nonaqueous UF separations might be used to degum and partially decolorize cmde domestic oils before physical refining. No permeates from two commercially available membranes contained phosphorous, thus indicating complete removal of hydratable and nonhydratable phospholipids (28). 

Lecithin, a mixture of phosphatidyl choline, phosphaddyl ethanolamine, and phosphatidyl inositol, is used as a surfactant in many food, pharmaceutical, and cosmetic products. Lecithin is a product of soy bean oil degumming operations. It is obtained from the hexane extract of flaked soy beans which contains the seed oil and a portion of the phosphatides that are initially present in the soy bean membrane. The exhact is seated with water at 80 °C, and the phosphatides are hydrated rendering them oil insoluble which makes it easy to filler them from the oil. This oil insoluble fraction is termed cmde lecithin and consists of about 70% phosphatides and 30% oil. De-oiled lecithin is obtained by treating the cmde lecithin with acetone. Lecithin is insoluble in acetone and the oil is, and a separation into a 90 to 9r phosphatides fraction can be achieved quite readily. The prior... 

The effect of pressure on rise of the permeate flux, decreases after a certain time of filtration previously reported by Wu and Lee [24] enter into agreanent with the results obtained by Kim et al. [21] in degumming of crude soybean oil by a PI UF membrane. According to these authors, the gel layer represented by the precipitation of solute on the membrane surface makes the permeate flux independent of pressure, and an increase in pressure resulted in a layer of solute denser and thicker. Initially, with the increase in the work pressure, the rate of permeation of oil miscella in hexane increased. However, up to 3 kg cm , the rate of permeation of miscella tended to become constant, which is a behavior usually observed in UF membranes. This trend was observed in three concentrations of miscella analyzed (20%, 30%, and 40%, m m ). This is attributed to the fact that the phospholipid layer due to the polarization of concentration retained on the membrane surface can control the permeation rate above the critical pressure. From this stage, therefore, the permeation rate is not more related to a function of the pressure. 

Pagliero et al. [53] evalnated the recovery of solvent in miscella degummed snnflower oil/hexane with concentrations of oil between 25% and 45% (w/w). Manbranes were synthesized from PVDF, prepared by the process of phase inversion, and evaluated for their flow and selectivity toward the oil. Tests were performed in a 400 mL filtration unit, with an effective area of membrane equal to 31.66.10 m and agitation of 750 rpm. The best separation was achieved at pressures between 4 and 6 bar, and a tanperature of 50 C and 25% oil in miscella (w/w), corresponding to a flow of 30 L m h. 

Membrane degumming can be performed either with the miscella, generally 20%-30% of crude oil in hexane, m/m, and with the crude oil without the addition or removal of solvent. 

In a study of the degumming of crude sunflower and soybean oils, with no added solvent, using polymeric UF membrane with a molar weight cutoff of 15 kDa. Koris and Vatai [69] obtained at an operational pressure of 5 bar, a temperature of 60°C, and a flow rate of 0.3 m h-, 77%, and 73.5% of the retention of phospholipids in sunflower and soybean oils, respectively. 

In an experiment with miscella degumming of soybean oil in hexane, 25% m m-, using UF membranes made from PVDF, PES, and PS, Ochoa et al. [70] found that the stability of membranes in organic liquids is influenced by both the type of polymer and the average pore size. Small-pore membranes become more stable, while that for the type of polymer, the results showed that PVDF is more stable in hexane than PES and PS membranes. 

Degumming — Hexane-resistant UF membranes (PA, PS, PVDF, PI, PAN, or inorganic) with a MWCO of 20,000 Da and molecular sizes of 20-200 nm. 

Austrian patent 3 562 28 is concerned with refining in miscella. Degumming is achieved by membrane ultrafiltration of the miscella which is then refined by passing it through a silica or aluminium oxide column. If necessary the oil can be bleached in miscella after which the solvent is distilled off and the oil deodorized. UK Patent application 2 118 568A also uses membrane ultrafiltration of a miscella. In this case a phosphatide solute and ammonia or other specified neutralizing chemical are added to the miscella before ultrafiltration. 

The membrane separation process was initially conducted in degumming vegetable oil and then was adapted for the recovery of carotenoids. Dense polymeric membranes are employed in this system and are very effective in the separatirm of xanthophylls, phospholipids, and chlorophyll, with retention of 80-100 %, producing an oil rich in carotenes [72,73]. This process, however, requires an additional step of hydrolysis or transesterification. Chiu, Coutinho, and Gruigalves examined the membrane technology as an alternative to concentrate carotenoids from crude palm oil in detriment of ethyl esters. A flat sheet polymeric membrane constituted by polyethersulfone was used and obtained a retention rate of 78.5 % [74]. Damoko and Cheryan obtained similar results using nanofiltration with 2.76 MPa and 40 °C in red palm methyl esters [75]. Whereas Tsui and Cheryan combined ultraiiltration with nanofiltration to separate zein and xanthophylls from ethanolic com extract [76]. 

---