Refining soapstock processing

In the process, miscella leaves the extractor at about 30-35 percent oil and is concentrated to approximately 65 percent oil by evaporation. The FFA in the concentrate then is reacted with alkali (sodium hydroxide solution) to produce soaps that are removed with other water-soluble compounds by centrifugation. Next, the solvent is removed from the miscella-refined oil by further evaporation, and the soapstock is spread on the meal in the DT to recover its solvent. Hexane vapors from the miscella and the DT are condensed, and the solvent is recycled to the extractor for reuse. The noncondensable gases are passed through a mineral oil stripper to recover the last traces of hexane. 

The recovery of fatty acids from soapstocks by a continuous process has been described soapstocks obtained from degumming and alkali refining operations are subjected to a saponification step followed by controlled acidification for cost efficiency and pollution control.Ila,b... 

In the batch refining process, the separation of the water phase containing soap-stock from the oil is by gravity. Some amount of neutral oil is lost by saponification and by occlusion in soapstock. 

Continuous refining process, on the other hand, offers the following major advantages over the batch-type operation (1) saponification of neutral oil is minimized due to a short contact time of 30-45 s between oil and sodium hydroxide (2) the time consumed for the separation of the aqueous soapstock and wash water from the oil is reduced considerably by passage through centrifugal separators. 

Process control Proper processing conditions (dosage of processing aids, temperature, pressure/vacuum, flow rate, etc.) must be closely adhered to and monitored to ensure the oil is processed correctly and to minimize undesirable side reactions. In order to assess process efficiency, the oil losses through spent clay or soapstock (as in the case of alkaline refining only) must also be monitored. 

Two coproducts are originated in the sunflower-seed oil extraction process meal and hulls. Sodium soapstock is obtained as a byproduct of alkali refining of the... 

If the plant acidulates soapstock and/or washwater, the resulting acidulation waste will contain sufficient residual heat and acidity to affect the entire waste stream pH and temperature, which obviously assumes an alkali refining process rather than a physical refinery. This process will produce an acidulation effect on residual oils. These oils can then be readily removed in a gravity separation process. 

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 deodorized product, if properly pretreated and bleached, will be as stable and as high in quality as an alkali refined product. In some cases, a physically refined oil will show more flavor and oxidative stability than the alkali refined product. Physical refining has reduced processing losses by as much as 2%. As a result of eliminating alkali refining, many effluent problems are solved. Effluent is cleaner as a result of the elimination of soapstock production, acidulation, and reduced oil losses. The acidulation process accounts for the majority of the effluent from a refinery and is the most difficult to clean up. 

KT21. Soapstock is recovered via the alkaline refinement process of oilseeds and contains phosphorus lipids, hydrateable and nonsaponifiable compounds, soaps of FFA, vitamins A and E, as well as carotenoid pigments. In their work, condensed corn-soluble basal medium was initially fed with biodiesel glycerol water but when the dissolved oxygen level rose above 10%, the medium was fed with sunflower soapstock. A shift in the monomer compositions from 3-hydroxydecanoate to 3-hydroxyoctanoate was observed when the medium was fed with sunflower soapstock. The final PHA also contained 3-hydroxytetradecanoate and 3-hydroxytetradecenoate monomers with a CDW and PHA content of 17 g/1 and 17%, respectively. 

The advantages of physical compared to chemical refining are improved product yield in many cases reduced refining costs both in plant and processing elimination of soapstock splitting reduction of effluent treatment costs. 

Pardun (1979) has described two methods for the continuous refining of soybean oil using ammonia. The first treats water-degummed oil with aqueous ammonia followed by weak (0.5 m) caustic soda, and in the second, crude undegummed oil is treated with citric or formic acid solution followed, without gum separation, by neutralization with ammonia. The soapstock is separated and the ammonia boiled off, leaving, in the second case, a by-product of lecithin enriched with fatty acids. These processes avoid the environmental hazards of the splitting of soapstock with mineral acids. The oil from both processes is washed, dried, bleached and deodorized according to normal practice. 

---