1. Cold pressed dewaxing
The principle is to directly cool the oil to the low temperature required for the precipitation of wax, and then separate the wax oil by pressure filtration to obtain dewaxed oil and crude wax respectively.
2. Urea dewaxing
Some substances, after reacting with paraffin wax, form complexes that are insoluble in petroleum products, so that paraffin wax can be removed from the petroleum. Substances that can produce insoluble complexes with paraffin wax include urea, sulfur veins, selenium veins, and hoof veins.
Currently only urea is used in the dewaxing process in industry. The principle of urea dewaxing is to use urea and wax hydrocarbon components to perform addition action to generate solid complexes, and the complexes are separated from solid-liquid and then urea is recovered to obtain crude wax.
The basic advantage of the process of urea dewaxing to prepare micro crystal wax is that it is not necessary to take freezing when preparing low freezing point oil from the corresponding raw oil. However, this process is very complicated both in terms of technology and process, resulting in a narrow application area, such as dewaxing of jet fuel and diesel.
3. Extraction and dewaxing
The solubility of easily setting components and low freezing point components in some solvents is different. According to this principle, the easily condensable and low freezing point components can be separated by the extraction method.
The process of dewaxing by extraction method is called "extraction dewaxing". The process of preparing micro crystalline wax by extraction and dewaxing is mainly divided into two types of high temperature processes.
That is, the temperature of the process is higher than the melting point of the separated paraffin, that is, at the temperature of the process, most of the easily condensable components in the raw oil exist in a crystalline state.
4. Preparation of micro crystalline wax by bacterial dewaxing
The waxy hydrocarbon components can be biotransformed during the fermentation and reproduction of some bacteria such as Candida lipolytica, and then the process of dewaxing by solid-liquid separation is called bacterial dewaxing.
This technology can not only obtain deoiled wax and dewaxed oil, but also obtain biological protein feed. The use of bacterial dewaxing is very limited, only some light and low viscosity oils such as transformer oil are used, and the use efficiency of micro crystalline wax prepared by its equipment is very low.
5. Adsorption dewaxing
The dewaxing of petroleum products can also be based on the different adsorbability of easily coagulating components and low freezing point components. At the same time, various adsorbents can have different effects on petroleum products due to their different properties.
Adsorption dewaxing is to selectively adsorb the waxy hydrocarbon components of the oil under the action of molecular sieves to achieve the effect of dewaxing to prepare micro crystalline wax.
6. Catalytic dewaxing
High freezing point n-alkanes can undergo selective hydrogenation and isomerization reactions with hydrogen under catalytic action. These two types of reactions convert the normal paraffins with high freezing point into small molecules and isoparaffins with low freezing point on the basis of keeping other hydrocarbons basically unchanged.
Through this kind of catalytic dewaxing method to prepare micro crystalline wax, on the one hand, the freezing point of dewaxed oil can be reduced under high temperature and high pressure, and the quality of oil products has also been greatly improved; on the other hand, the toughness, strength and transmittance of the wax divided into small molecules have been greatly improved.
7. Solvent dewaxing
Solvent dewaxing is to add a large amount of selective solvent to the oil, freeze and crystallize it, and then mechanically separate the wax and oil to obtain dewaxed oil and crude wax, respectively.