Steam refining

P. W. Sleggs, "Steam Refining of Castor Oil," Meeting of the International Castor Oil Association, New York, presented Dec. 6, 1990. 

Bitumens [8052-42-4], extracts of steam-refined and air-refined (Vol. 35, Suppl. 7 1987)... 

In mice skin-painting studies, skin tumors were produced by steam-refined petroleum bitumens, an air-refined bitumen in toluene, two cracking residue bimmens, and a pooled mixmre of steam- and air-blown petroleum bitumens. In contrast, standard roofing petroleum asphalts produced no tumors. 

Typical properties of alkah-refined, bleached canola oil and of acid-water-degummed, acid pretreated, bleached canola oil ready for hydrogenation or steam refining/deodorization are given in Table 16. With the exception of the concentration of free fatty acids, the two process routes produce the same bleached oil quality. 

The main feature in physical refining of crude oils is the application of steam distillation to remove the free fatty acids and volatile components from the oil. The technical feasibility of physical refining depends largely on the pretreatment stages for the removal of phosphatides, color bodies, metal ions, and nonvolatile impurities. Without an effective pretreatment, steam refining may fail to produce an oil of color and stability characteristics comparable to the classically refined product (23). 

Steam refining/ Removes free fatty acids and other Distillate—a source of free... 

Refining Cost. Crude palm oil can be further processed by refining. Presently, most of the palm products obtained in the market are processed using physical or steam refining. Crude or processed palm products may also undergo fractionation where the solid and the liquid portions are separated. The total cost of refining a ton of palm oil is about 25.92 while the cost of fractionation is about 5.55 per ton. 

Excessive losses may occur in refining of rice oil. A 5% FFA crude oil has losses ranging from 12% to 40% by the cup method. The cause of high refining losses is unknown. It is assumed the losses are caused by the presence of partial esters, oxidized components, and waxes, as well as high FFA acidity (8). Steam refining is practiced by various refineries in Japan and the United States (2). 

Physical refining, also called steam refining, combines deacidihcation with deodorization. Physical refining is more efficient for high FFA oils giving better yields of neutrahzed oil than alkali refining (2). 

Removal of all phospholipids and gums is a necessary part of the steam-refining process. However, this process has not yet been developed to the point where it can produce refined soybean oil that meets U.S. competitive requirements. Studies have been carried out to fulfill this objective (112, 113). 

Steam refining Vacuum-stripping process in which acid oil is treated to remove both free fatty acids and malodorous compounds to obtain fully refined oil. 

In literature, the distinction between deodorization and steam refining is rarely and certainly not consistently made. As the process is best known as deodorization, it is used as general term in this chapter as well. 

Principles of Deodorization/Steam Refining The stripping medium requirements during deodorization/steam refining are described by the following mathematical equation ... 

In case of steam refining, the partial pressure of the fatty acids must be taken into account and omitting the term (Va — Vq) would lead to a considerable overestimation of the stripping medium requirements. 

The simplified Equation 10 is also known as the Bailey Equation. It states that the amount of steam required for deodorization or steam refining is directly proportional to the amount of oil and the absolute pressure in the deodorizer and inversely proportional to the vapor pressure of the pure volatile component at the process temperature and the overall vaporization efficiency E. 

The efficiency of deodorization/steam refining is usually quantified by the stripping of free fatty acids (FFA). As a result of their relatively low volatility, an efficient... 

Figure 3. Effect of (a) temperature and (b) pressure on FFA removal during deodorization/ steam refining of soybean oil. Conditions (a) 3 mbar, 0.5% sparge steam/h, varying temperature (b) 230°C, 0.5% sparge steam/h, varying pressure.

Free sterols are slightly less volatile than tocopherols (Figure 2). Deodorization of soybean oil under varying process conditions (temperature 220-260°C, low pressure 1.5 mbar and 1.5% steam) resulted in a 10-35% reduction of the total sterol content (20). This sterol reduction is totally attributed to the free sterol fraction because esterified sterols are not volatile under the conditions prevailing inside the deodorizer. In case of steam refining, an increase of the steryl ester content can sometimes be observed, probably because of a heat-promoted esterification reaction between free sterols and fatty acids (20). This phenomenon will not take place during deodorization of chemically neutralized oil because the initial FFA concentration is much lower in that case. 

Although severe process conditions are required (low pressure 1-2 mbar high temperature up to 250°C), steam refining is the most suitable and economical process to lower the cholesterol content of animal fats (e.g., milkfat and tallow). 

Improvement of the deodorizer design by the installation of baffles and demisters in the vapor chimneys has significantly reduced entrainment losses to 0.1-0.2% in chemical refining. For steam refining, an additional loss directly proportional to the FFA content has to be taken into account. For most oils (soybean oil, pahn oil, etc.), NOL is exclusively due to mechanical carry-over. However, in lauric oils, part of the NOL is a consequence of effective evaporation of volatile short-chain mono- and diacylglycerols (30). (Table 13). This distillation loss of NOL is inherently due to the deodorization conditions, but is not affected by the deodorizer design. 

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