Crude oil generally refers to oils and fats which are extracted from plant oils from leaching or pressing processes，which contain some undesirable (or industrial) impurities.The main component of crude oil is a mixture of triglycerides (commonly known as neutral oil).In addition to neutral oil, the crude oil also contains non glycerides (collectively known as impurities), and their types, properties and state can be divided into three major categories: mechanical impurities, fat soluble impurities and water-soluble impurities.
1.Method of oil refining
According to the operation characteristics and the raw materials selected, the method of oil refining can be roughly divided into three methods: mechanical method, chemical method and physical chemistry method. In general, it is necessary to precipitate the crude oil first.
The gum soluble impurities in crude oil not only affect the stability of oil, but also affect the technological effect of oil refining and deep processing. Therefore, the gum soluble impurities must be removed at first.
The degumming methods include degumming, acid degumming, adsorption degumming, thermal degumming and degumming by chemical reagents. The most common application of the oil industry is the hydration degumming and the acid degumming.The refining of edible oils is mostly dehydration by hydration, and strong acid and acid degumming are used for refining industrial oils.
Generally, the operation of degumming and degumming of oil is used. The hydrophilic degumming is a kind of oil degumming method, which uses the hydrophilic property of phosphatidylcholine and other colloidal impurities, and gives a certain amount of water, such as hot water or dilute alkali, salt, phosphoric acid, and so on.
The main equipment of degumming can be divided into a hydrator, a separator, a desiccator and a desictator according to the process effect, and can be divided into intermittent and continuous type according to the consistency of production.
3.Alkali refining and deacidification
The crude oil contains a certain amount of free fatty acids. The process of removing these fatty acids is called deacidification. The commonly used methods of deacidification are alkali refining, chemical refining, steam distillation and physical refining. Alkali refining deacidification is to neutralize the crude oil or degummed oil by adding alkaline aqueous solution.
All kinds of oils have different colors because they contain different pigments. It can be decolorized according to the use of oil. The methods of decolorization of oils include sunlight decolorization (also known as oxidation), chemical decolorization, heating and adsorption. At present, adsorption method is the most widely used. Some substances with strong adsorption capacity (acidic soil, bleached soil and activated carbon) are added to oil, and the pigment and other impurities (protein, mucus, resin and soap etc.) are adsorbed in the heating condition.
Process: Intermittent decolorization refers to the process in which oil and adsorbent are decolorized through one adsorption equilibrium in a batch state.
The decolorization oil is transferred into the decolorization tank through the storage tank. After heating and drying under the vacuum, the adsorbent is fully touched with the adsorbent inhaled by the adsorbent tank to complete the adsorption equilibrium, and then the adsorbent is separated by the cooling of the oil pump pump into the filter press. After filtering, the decolorized oil is pumped into the tank, transferred to the deodorization process by vacuum suction or oil pump, and the absorbent cake in the filter press is transferred to the treatment tank to recover residual oil.
Pure glycerin three fatty acid esters are colorless and odorless, but natural oils have their own special odors (also known as stink). Odors, such as solvent, soap and soil, can also be produced during oil production. The process of removing the peculiar smell (flavor substance) of oil is called “deodorization” of oils and fats. The deodorization of the leaching oil is very important. Before deodorization, hydration, alkali refining and decolorization must be done first to create a good deodorizing condition, which is conducive to the removal of residual solvents and other odors in oils and fats. There are many ways to deodorization, such as vacuum steam deodorization, gas blowing, hydrogenation and polymerization. At present, the vacuum steam deodorization method is the most widely used and the best effect at home and abroad.
Vacuum steam deodorization is a process to remove the flavoring substances in the deodorizer by superheated steam (vacuum). The principle of vacuum steam deodorization is that water vapor is saturated through the oil containing flavour components, vapor-liquid contact, and the odor group volatilized from water vapor, and removed according to its partial pressure ratio.
After the above operation processes, the oil obtained is refined oil.