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Pure triglycerides are colorless when they are liquid, but in common vegetable oils, they show different colors because they contain different amounts and qualities of pigments. Most pigments are non-toxic, but they will affect the appearance of grease. There are also by-products that are not conducive to the quality of fats and oils, including certain harmful substances that are not conducive to food safety and hygiene, such as polycyclic aromatic hydrocarbons caused by pollution, oxidative deterioration substances, and so on. Therefore, the grease must be decolorized. The most widely used in industrial production is the adsorption decolorization method.

The adsorption and decolorization of grease is to use certain substances with strong selective adsorption of pigments to adsorb pigments or other impurities under certain conditions, and then remove the adsorbent through filtering equipment to achieve the purpose of grease decolorization. In addition to the adsorbents introduced in the previous issues, the factors affecting adsorption and decolorization also have the following key factors in the operation process:

1. Oil quality

The natural pigments of oils are relatively easy to remove, but the new pigments formed during storage or oxidation of oils are difficult to remove, such as degradation products of proteins and phospholipids (usually dark brown), free fatty acids and iron ions The iron soap produced by the function is difficult to remove due to the low selectivity of the adsorbent. Therefore, it is very important to avoid oxidation of grease during storage and processing.

2. Operating temperature

The increase in temperature makes the movement of molecules more intense, and accelerates the diffusion speed of the outside/inside in the liquid phase around the adsorbent, thereby increasing the adsorption efficiency. However, as the adsorption speeds up, the side reaction-the oxidation of fats and oils will also speed up, so there is an optimal temperature T. The optimal temperature T depends on the type, characteristics and operating pressure of grease, adsorbent.

3. Operating pressure

In the process of adsorption and decolorization of grease, in addition to adsorption, there is also a side reaction-thermal oxidation reaction. This side reaction will produce new pigments and affect the stability of the oil.

At present, the common decolorization reactions in various countries are negative pressure decolorization. In the process of negative pressure decolorization, due to the low operating pressure, the amount of oxides introduced is small, and the effect of thermal oxidation side reactions is very small, thereby reducing the production of new pigments in oils.

Different types of oils and adsorbents have inconsistent decolorization effects under different pressure conditions. For example, adsorbents with high activity and low-saturation grease are suitable for decolorization under negative pressure, while adsorbents with low activity, such as natural bleaching soil, and grease with high saturation are suitable for decolorization under normal pressure, because of low-activity adsorbents The catalytic oxidation performance is low, and the degree of adsorption and fading exceeds the generation of new pigments.

4. Reaction time

The length of the reaction time depends on the adsorption equilibrium, and it only needs to be stirred sufficiently, and the time to reach the adsorption equilibrium does not need to be too long. Although the degree of adsorption and decolorization will deepen with the extension of the reaction time, excessive extension of the time will also cause the chroma to rise, the acid value to rise, and the fat to oxidize.

Fats adsorbed at high temperatures may also undergo fatty acid double bond conjugation, so the reaction time can be controlled at 20 minutes during the decolorization process.

5. Stirring intensity

Adsorption is carried out on the surface of the adsorbent, which is a heterogeneous reaction. Good mixing, uniform contact, establish adsorption equilibrium as soon as possible, so as to avoid local long-term contact causing oil oxidation. In negative pressure decolorization, the stirring intensity should not produce splashing oil; in normal pressure decolorization, the stirring intensity should not be too high to reduce the occurrence of oxidation reactions.

To sum up, we can find the reason for the deterioration of the decolorization effect in the process, and we may start from the above five points and analyze the problem in combination with the actual situation. Only by analyzing the nature of the problem can the problem be truly solved. 

The above wonderful content is the sharing of The influence of operation process on adsorption decolorization by Henan Zhongxing Grain and Oil Machinery Co., Ltd.