The refining process of almond oil
The refining process of almond oil generally needs to go through four steps of degumming (degumming, deacidification, decolorization, deodorization) and fractionation, and through refining, it can reach the standards required for all levels of oil.
1. Degumming
The purpose of degumming is to remove all gums in almond oil and produce valuable by-products, while phospholipids in gums will affect deodorization and decolorization during steam distillation, and can also chelate with metal ions to increase the oxygen sales process. , affecting the stability of the oil, in order to obtain almond oil products that meet the requirements, it is necessary to carry out a degumming process.
2. Deacidification
Deacidification is the process of neutralizing free fatty acids in almond oil by adding alkali, and it is the most critical process in the oil refining process. The principle is: after adding alkali, free fatty acids become water-soluble salts and are removed. In actual operation, a certain amount of excess alkali needs to be added to complete the alkali refining. The amount of alkali added, alkali concentration, temperature, crude oil quality, and stirring time and speed all affect the effect of alkali refining. Neutralization and deacidification is a process that has a great impact on product quality and price. If there is a problem with the neutralization process, it will bring difficulties to the various processes after decolorization and reduce product quality and yield.
3. Decolorization
Color is one of the important qualities of almond oil, so decolorization is an essential part of oil refining. Decolorization is not to remove all pigments, but to improve the color of almond oil, improve the quality of oil, and provide qualified raw oil for further refining. In addition to removing pigments in oil, decolorization can also reduce phospholipid content, peroxide value, soap content and metal ion content, thereby improving oil color, flavor and oxidative stability, and further refining and hydrogenation of oil. , Deodorization provides good conditions.
At present, the most commonly used method for oil decolorization is activated clay adsorption decolorization method, that is, using clay, a substance with strong selective adsorption, to remove pigments soluble in oil under certain conditions or disperse in oil with colloidal particles. Pigments and other impurities. After metering, the oil is preheated to 80~90℃, all the oil is pre-mixed with activated clay, and then sent to the decolorization tower for decolorization. The mixing of oil and activated clay is carried out under normal pressure, and all pre-mixing is carried out at a lower temperature, which avoids the oxidation of oil caused by heating to the greatest extent, thereby ensuring the quality of oil products.
The separation of oil and waste clay after decolorization is by filtration. In China, two forms of vertical leaf filter and plate and frame filter are often used for continuous oil decolorization in China. When the vertical leaf filter is filtration, the separated medium is completely enclosed during the whole process. After filtration, dry the grease in the filter cake with dry steam, which can reduce the amount of residual oil in the filter cake and reduce the oxidation of grease.
In the decolorized clean oil obtained by the above-mentioned primary filtration, a certain amount of waste clay will inevitably remain due to the filter equipment or operation. If it is directly sent to the deodorization, it will accelerate the oxidation of the oil and pollute the deodorization equipment. , detrimental to the quality of the final oil product. Therefore, in actual production, the decolorized clear oil that is initially filtered generally needs to be safely filtered to ensure the color and quality of the final oil product. The factors that affect the decolorization effect are:
(1) Decolorization temperature: the best effect is around 110. In order to prevent the condensed water from entering the filter cake and affecting the drying of the filter cake and automatic slag unloading, the temperature of the filter medium should be guaranteed to be above 105 °C.
(2) Decolorization time: The effective decolorization time of oil should be controlled within 20~30min to ensure the decolorization effect.
(3) Absolute pressure: the absolute pressure in the decolorizer should be reduced to 9.3~6.6kPa, that is, vacuum decolorization, which can effectively remove the air in it. Appropriate effective stirring blades can improve the decolorization effect and calculate the effective decolorization time.
4. Deodorization
Deodorization is mainly to remove odorous substances in oil. The principle is to use the difference in volatility between odorous substances and triglycerides to remove odorous substances under high temperature and vacuum conditions. Deodorization can not only remove the odorous substances in the oil, improve the flavor of the edible oil, but also increase the smoke point of the oil. There are batch, semi-continuous and continuous methods for oil deodorization. The former is used for small-scale production (below 12t), especially for lauric acid type oils. The semi-continuous and continuous deodorization process has good effect, short production cycle and low energy loss. The semi-continuous type can easily switch raw materials, prevent possible short circuit of grease, and ensure product quality. The continuous type does not require batch feeding and discharge of grease from each tank, and does not require intermittent heating and cooling.
The processing capacity is large and the operation is simple. For the sake of safety and hygiene, with the popularization of continuous deodorization process, in terms of the choice of heat medium for deodorization process, compared with steam and electric heating, heat transfer oil as a carrier is more economical and safe, and its application is becoming more and more extensive. Some research results show that in a specially designed deodorization pot, the vacuum degree of almond oil complete deodorization is 260Pa, the temperature is 200℃, and the steam consumption is 3%~8% of the quality of almond oil.
In conventional deodorizers, the pressure of the cooling pipe is often too high due to the high oil temperature at the beginning of the cooling stage, resulting in violent vibration of the coil and the pot, which is very dangerous. In order to avoid this problem, in the design of the process and equipment, high temperature water and pump force should be used for forced cooling in the initial stage.
5. Fraction
In order to increase the content of unsaturated fatty acids such as oleic acid in the product, reduce the content of saturated fatty acids, especially stearic fatty acids, and remove wax, etc., the process of separation according to the different freezing points of different substances is called fractionation. Generally, it is frozen at -5°C for 48h, and then centrifuged to increase the oleic acid content. Diatomite can greatly improve the filtration speed of frozen oil and improve product quality in the process of fractionation.
