Soapstock acid oil

Soapstock acid oil, a concentrated by-product of the soybean oil rehning process based on fatty acid salts, was proposed by Soares et al. as a raw material for the production of biodiesel via acid heterogeneous catalysts using ethanol. The esterihcation reaction was conducted in a packed-bed bioreactor containing a lipase-rich fermented solid (sugarcane bagasse and sunflower seed meal fermented by Burkholderia cepacia) with a configuration that avoided inhibition of the catalyst by the presence of ethanol (Soares et al., 2015). 

Hydrolyzed vegetable oil (HVO) or acid oil is a by-product of alkali refining of crude corn oil, and is obtained by acidulating alkaline soapstock. HVO must contain at least 92% total fatty acids. It is used to control dust and as an energy source in beef and poultry rations. 

BDF is produced currently by a chemical process with an alkaline catalyst, which has some drawbacks, such as the energy-intensive nature of the process, the interference of the reaction by free fatty acids (FFAs) and water, the need for removal of alkaline catalyst from the product, the difficulty in recovering glycerol, and the treatment of alkaline wastewater. To overcome these problems, the processes using ion-exchange resins (Shibasaki-Kitakawa et al., 2007), supercritical MeOH (Kusdiana and Saka, 2004), MeOH vapor (Ishikawa et al, 2005), and immobilized lipases (Mittelbach, 1990 Nelson et al, 1996 Selmi and Thomas, 1998) have been proposed. In this paper, enzyme processes for production of BDF from waste edible oil, waste FFAs, and acid oil recovered from soapstock are described. In addition, applications of the element reactions to the oil and fat industry are introduced. 

Vegetable oils are refined through pressing/extraction, degumming, alkali deacidification, decolorization, and deodorization. Alkali deacidification byproduces soapstock. Acidulation of soapstock prepares acid oil which contains FFAs, acylglycerols, and other lipophilic compounds. It is reproduced currently as FFAs, which are used as raw materials for production of soaps, lubricants, and paints. But the demand for FFAs is almost in saturation. Hence, conversion of acid oil to BDF is expected to avoid an oversupply of the industrial FFAs and subsequent price decrease. 

An enzymatic process cannot be adopted for industrial production of BDF, if immobilized lipase cannot be used for long period. Studies on the stability of immobilized C. antarctica lipase revealed that it was the most stable when the reaction was conducted with 5 to 8 mol MeOH for total FAs in acid oil prepared from soapstock (Watanabe et al., 2007). The phenomenon, that there is the optimum region of MeOH concentration, may be explained as follows ... 

Most manufacturers use soapstock to spray on meal for animal feed, or ship the material to acidulators. Some seed oil producers treat soapstock on site with sulfuric acid at a temperature of 90-95 °C to produce acidulated soapstock (Dijkstra and Segers, 2007). Acidulated soapstock is very dark in color with a strong, rancid, burned odor from the free fatty acids and neutral oils. Free fatty acid content varies and can be in excess of 90%. Moisture content as well as unsaponifiables can be substantial and the pH (based on samples provided to Stepan Company) may vary from 3 to 4.5. An example of a typical analysis of an acid oil sample is listed below (Table 6.2). 

Stirred, and a measured amount of sodium hydroxide solution is introduced by spraying on the surface of the oil. An excess of 5-10% sodium hydroxide over the stoichiometric requirement is added to ensure appropriate neutralization of free fatty acids. In this stage, hydrated gums migrate to the water phase. Heating and stirring are stopped when soap breaks are formed. A break forms as soap coagulates with some occluded neutral oil, excess sodium hydroxide, and other impurities. The aqueous soapstock is allowed to settle and subsequently drawn off for acidulation with sulfuric acid to recover a mixture of fatty acids, occluded neutral oil, and other impurities. The mixture is called acid oil. 

One of the major uses of acid oil from soapstock and the distillates from physical refining is in the manufacture of animal feeds. The fatty components increase the caloric density of the feed. 

By-products. Chemical Refining. The neutralization of free fatty acid in the crude pahn oil with caustic soda results in the formation of soapstock, which is treated with dilute sulfuric acid of pH 2.0-3.5 at 110-130°C for 30 min. A by-product called palm acid oil is then separated from the aqueous phase by centrifugation followed by hot-water washing. It consists mainly of free fatty acids, neutral oil, and partial glycerides. A small amount of unsaponifiable matter is also present. Characteristics and properties of palm acid oil (derived from chemical refining of crude pahn oil, stearin, and olein) are given in Table 35 (55). 

Sodium soapstock may also be subjected to treatment with mineral acids, freeing the constiment fatty acids upon decomposition of the soaps. The product thus obtained, having a very low water content, is called acid oil. Storage and transportation requirements are the same as for crude oil. 

Both acid oil and the free fatty acids obtained in the physical refining may be incorporated in the manufacture of soap. In view of its high linoleic acid content (in particular when originating in the refining of regular sunflower oil), soapstock does not make a fatty material of good properties for the manufacture of toilet soap. To this end, it is blended in relatively low proportions with other more appropriate fatty materials. It is used in cattle producer countries also producing sunflower oil as a means to reduce the titer of beef tallow or of the beef tallow/coconut oil blend. 

Methods 2 and 3 above do not produce any wastes other than from handhng losses however, they are often not the most economical method of deahng with soapstock as the value of the acid oil is not reahzed. 

Haas, M.J. S. Bloomer K. Scott. Simple, high-efficiency synthesis of fatty acid methyl esters from soapstock./. Am. Oil Chem. Soc. 2000, 77, 373-379. 

In a typical batch operation, soapstock and wash-water from a refining run is charged to a vat and heated to about 70°C, if required. Concentrated sulfuric acid is then added to the soapstock until a "split" is obtained (pH of less than 3). Depending on the tendency of the acidulated soapstock to produce emulsions there may be a water layer with low fat concentration in the bottom of the vat, an emulsion layer above, and a layer of free acid oil at the top. 

The soapstock and water washes are combined and split using mineral acid, usually sulphuric acid. The oil phase, known as acid oil is settled, and in some cases washed, to achieve the required specification and is sold as a by-product. The aqueous phase is run off to the effluent system. 

The crude oil from which gums are taken for lecithin production still contains nonhydratable phosphatides, but can be treated with a chelating agent before alkali neutralization and will be removed with the soapstock by centrifugation. Provision must be made for the added acid in calculating the amount of neutralizing alkali added. 

Rice bran oil is reported to lower serum cholesterol by reducing LDL and VLDL without changing the level of HDL. This effect seems not to be related to fatty acid or triacylglycerol composition but to the unsaponifiable fraction and probably to the oryzanols (1.5-2.0% of the oil). These can be isolated in concentrated form from rice bran oil soapstock but have not yet been accepted for food use (46-51). 

The free fatty acids (FFA) of crude coconut oil are neutralized with dilute sodium hydroxide solution resulting in the formation of soap RCOOH + Na OH RCOO Na" + H2O. The soap and other impurities in the water phase are collectively called soapstock. 

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