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Pretreatment of Soap Raw Materials

As the user’s requirements for the quality of soap are improved, the quality requirements for oils and fats in production are also relatively strict, especially for the manufacture of soap and oil, the quality requirements have exceeded the level of edible oil.

In natural animal and plant oils, in addition to fatty acid glycerides, they also contain insoluble solid impurities, such as sand mud, fodder powder, and other insoluble solid impurities, which are suspended or precipitated in the oil. Free fatty acids, phospholipids, pigments, proteins and other impurities that are dissolved or emulsified in oils.

In order to meet the requirements of soap making, the grease must be pretreated. The modern oil treatment method includes four processes of degumming, deacidification, decolorization and deodorization, and if necessary, hydrotreating.

  • Degumming

Degumming refers to the removal of phospholipids, proteins and other colloids and mucus in fats and oils. The presence of colloid reduces the use and stability of the grease and affects other processes in refining, resulting in a decrease in the quality of the soap product. The modern degumming method is to treat the oil with phosphoric acid, the colloid is condensed by phosphoric acid, and the heavy metal in the oil can also form phosphate precipitate with phosphoric acid. In industrial production, the wool is first filtered to remove insoluble impurities such as sediment and cellulose, heated to 40 to 50 in a heat exchanger, fed to a mixer and mixed with phosphoric acid, and then decomposed to the reactor to coagulate the gum. The oil containing the agglomerates is mixed with the hot water, so that the colloidal impurities such as the agglomerates are absorbed as small micelles, and then the grease and the agglomerates are separated by a centrifuge. The oil phase is sent to a vacuum dryer for dehydration-degassing treatment, and the degummed grease is removed after removing moisture and air.

  • Deacidification

Deacidification refers to the process of removing free fatty acids and pigments from oils and fats. If the fatty acid neutralizes the soap, the oil is hydrolyzed to fatty acids and glycerol, so there is no need to remove free fatty acids before hydrolysis. However, soaps prepared by the saponification method must remove free fatty acids before the oil is bleached, otherwise the bleaching effect of the clay will be affected. The free fatty acid can be removed by alkali refining, or it can be distilled off while deodorizing the fat. Here, the treatment method for the deacidification of the oil alkali refining is introduced. The basic principle of the method is: RCOOH NaOH RCOONa 15%) The oil is treated, and the free fatty acids in the oil are neutralized into soap. The soap has a certain adsorption effect, and can adsorb other impurities such as proteins and pigments. Therefore, alkali refining can be either deacidified or decolored. In the alkali refining, the concentration of the lye and the amount of the lye should be strictly controlled so as not to cause saponification of the oil. Modern soap making plants generally use a continuous alkali refining process, in which the oil is mixed with a theoretically calculated amount of 115% to 150% of the lye in the mixer at a temperature at which the oil melts into a liquid state. The soap solution produced by the neutralization adsorbs a certain amount of impurities and is separated by a centrifuge and stored in a soap tank. The deacidified oil is then passed to another mixer and washed with hot water to remove residual lye and soap from the oil. The washing water is separated into a sewage treatment tank by a centrifuge to be recycled, and the oil is then introduced into a vacuum dryer to remove moisture and gas to obtain a deacidified essential oil. The method has a short action time on the oil and the lye, and the centrifuge is separated by the separation of the soap foot and the washing water. Therefore, the treatment efficiency is high, the separation effect is good, and the grease loss is low.

  • Decolorizing

Natural animal and vegetable oils and oils may entrain pigments or produce pigments when they are not stored properly. Although some of them are removed after alkali refining, the color still does not reach the light color soap, especially the quality requirements of white soap, so it is still necessary Decolorization treatment. There are two types of methods for decolorization: chemical methods and physical adsorption methods. The chemical decolorization method is to use the oxidation and reducing agent to remove the pigment in the oil and fat, and is only used for treating the low-quality oil for producing the laundry soap; the physical adsorption method is to adsorb the pigment in the oil and fat with the active white clay, and is suitable for the treatment of the soap. Quality grease. The main component of the activated clay is SiO or the like and contains crystal water. The amount of clay used is 3% to 5% of fats and oils. To produce high-grade soap, especially for white soap, it is necessary to add 0.2% to 0.3% activated carbon to the activated clay to improve the decolorization effect. The temperature of decolorization depends on the type of oil and the color-removing requirements, and is generally between 105 and 130. The grease is first heated to the specified temperature during the decolorization operation. A part of the fat is mixed with the quantitative activated clay to form a slurry, and the slurry mixture and the remaining oil are mixed into the bleaching pot under vacuum to be mixed, so that the oil is decolored at a high temperature for several hours. Then, the adsorbed white clay and the oil and fat mixture are subjected to pressure filtration to separate the two, that is, the decolorized oil is obtained. The filtered clay cake still contains 18% to 22% of oil and fat, and the oily white clay is boiled in water to float the oil, so that the oil content of the waste clay can be reduced to 3.5% to 5%. Recycling this part of the grease, the oil is darker in color and can be used to make industrial soaps that do not require high color.

  • Deodorization

Natural animal and vegetable oils often have special odors, such as suffocation of beef and sheep oil. These odors will affect the odor of soaps, especially soaps, for which deodorization must be carried out on the fat and oil raw materials from which the soap is made. The odor of the oil is higher than that of the oil. The high temperature and high vacuum are often used to distill the superheated steam to remove the odorous substances in the oil. The higher the temperature, the shorter the deodorization takes. In addition to lowering the boiling point of odorants, the role of high vacuum is to protect the oil from oxidation by air at high temperatures. The modern deodorization unit has a vacuum of only 400 to 600 Pa, and the deodorization tower is made of stainless steel and belongs to a conventional distillation column. If the quality of the oil is good (free fatty acids are less than 5%), it is possible to remove the acid by vacuum distillation instead of deacidification by vacuum distillation. At this time, the combination of deacidification and deodorization is completed in the same set of equipment, which greatly simplifies the process and improves economic efficiency.