Oil is closely related to human life. Oil, protein and sugar together form the nutritional basis of human life, it is an indispensable part of human food and an important raw material for food industry and light industry. Human has been eating, using oil for thousands of years. In the 20th century, oil processing technology developed rapidly. There are two types of oil processing methods: refining and modification.

Overview of oil refining and deep processing

1) Oil refining
Oil refining, also known as refinery, is a general term for a series of processes to remove impurities from crude oil, and refers to the process of removing impurities in oil. It studies the physical and chemical properties of oil and its companions, according to the quality requirements of refined oils and the property differences between oil and impurities, appropriate technological measures are taken to separate the oils and impurities, thereby improving the practical safety and storage stability of oil. Oil refining mainly includes degumming, deacidification, decolorization, deodorization, dewaxing and other processes.

2) Oil modification
Oil modification refers to a process of changing the natural form and performance of oil by proper process with refined oil as raw material. It studies some special properties of oil, and through changing the structure and composition of oil, it achieves the purpose of increasing the variety of oil, improving the nutrition and use performance of oil, and expanding the use of oil. Oil deep processing mainly includes oil fractionation, oil hydrogenation, oil transesterification, and oil modulation and so on.

2. Significance of oil refining and modification
Oil is an important substance that constitutes organism of various animals and plants, and participates in the life activities of organism. It is also one of the main substances stored in animals and plants. There are 5 aspects of its function in the human body:

It is an important high-energy heat source for the human body (Oil supplies more than twice as much calorie as protein or carbohydrate of the same mass);

It provides functional material for cells and cell membranes;

It provides essential fatty acids to the body;

It provides the body with a variety of oil-soluble vitamins;

It controls the body’s blood lipid content.

However, crude oil produced by any method contains a variety of substances, which affect the quality and flavor of oil, and even make it inedible with toxicity. Moreover, the single oil generally has some deficiencies in some aspects, which is not conducive to its function. Therefore, it is of great significance to refine and modify crude oil.

Methods of oil refining and modification

1. Methods and principles of oil refining
Oil refining can take different methods according to the nature and quantity of impurities in crude oil, the use of refined oil and quality requirements. There are many methods of oil refining, which are usually divided into the following three categories according to the different process, equipment, auxiliary materials and operation process used in oil refining.

1) Mechanical method

Mechanical method includes sedimentation, filtration, centrifugal separation, etc. It is mainly used to separate mechanical and some colloidal impurities suspended in oil.

2) Chemical method

Chemical method mainly includes acid refining, alkali refining, oxidation, esterification and so on. There are obvious chemical reactions when this method is used. Acid refining is the acid treatment to remove pigment and gelatinized impurities; alkali refining is the alkali treatment to remove free fatty acids in crude oil; oxidation is mainly used for decolorization; esterification method is not used much, mainly for adding glycerol to make free fatty acids in oil form triglyceride, which reduces the content of free fatty acids

3) Physical and chemical method
Physical and chemical method mainly includes hydration, adsorption, steam distillation, liquid-liquid extraction and so on. This method is used without obvious chemical reactions but is different from mechanical method. Hydration is mainly used to remove colloidal impurities such as phospholipids in crude oil; adsorption is mainly used for decolorization; steam distillation is mainly used to remove odorous substances and free fatty acids in crude oil; liquid-liquid extraction is suitable for deacidification of dark oil with high acid value and is a promising deacidification method.

Enzymatic degumming technology and nanometer degumming/alkali refining technology
Enzymatic degumming is the use of modern biological engineering technology in oil refining. The principle of enzymatic degumming is to use the biologically produced phospholipase PLC to selectively interact with phospholipid bonds in phospholipids, cut phospholipid bonds, and triglyceride in the phospholipid structure is converted into diglyceride, and the obtained diglyceride is dissolved in the oil, and finally remains in the oil, and the phospholipid bond after the cleavage is converted into a phospholipid salt into the aqueous phase, so that the comprehensive yield of the oil is improved.

Nanometer neutralization and degumming is also a newly developed oil processing technology. The mesoscopic environment of nanometer reaction is modulated by nanometer scale, which is embodied in the reaction medium, carrier interface, etc. Nanoreactors should generally be nanomaterials or materials with nanostructures. They provide a nanoscale space, limiting the reaction to the nanospace range. The product with special structures and properties can be obtained by controlling the size of the nanometer reactor, materials and other factors (separation of phospholipids from neutral oils).

The above methods are difficult to separate in practice and the actual refining process is often a combination of several methods. For example, alkali refining is a typical chemical method, but during alkali refining, soapstock generated by alkali and free fatty acids will adsorb pigments, mucus and proteins, so that they can be separated from oil with soapstock. Soapstock adsorption is a physical and chemical process. After adsorption of impurities, oil soap separation or centrifugal separation is a mechanical method. So alkaline refining is not only a chemical refining process, but also a process of physical chemical and mechanical refining.

2. Methods of oil deep processing

1) Methods of oil modification
There are mainly three methods of oil modification: oil fractionation, oil hydrogenation and transesterification. They are also the three main processes for producing food-specific oil. Oil hydrogenation is the hydrogenation or supersaturation of the double bonds of unsaturated fatty acids in triglyceride molecules under the action of catalysts, thereby improving the melting point of oil and increasing its antioxidant capacity. Transesterification is the change (rearrangement) of fatty acids in the position of triglycerides under the action of catalysts. Hydrogenation and transesterification are irreversible chemical changes in the fatty acid composition under the action of catalysts.

Fractionation is based on melting points differences of different fatty acid triglycerides in and oil, crystallization of high melting point components through cooling, and filtration or centrifugation to obtain components with different melting points.

Fractionation is a completely reversible physical modification method based entirely on molecular thermodynamics. Hydrogenation, transesterification and fractionation have their advantages and disadvantages. As trans acids are harmful to human health, We will introduce three modification methods in a future articles.

2) Methods of oil modulation
The methods of oil modulation include blending, emulsifying, quenching kneading and homogenizing. According to the functional requirements of various oil products, several raw materials and other ingredients are proportionally blended and then processed in whole or in part by these methods. (As shown in the figure below is the powder oil of oil deep-processing product)

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