Newbie’s question: Why is it necessary to dewax crude oil? How are there several ways to dewax?

I’ve never seen crude oil dewaxing, nor do I know how it’s done. As for diesel oil dewaxing, 0# diesel can be transformed into -10# after dewaxing······

It’s not dewaxing directly from crude oil; rather, it’s done on straight-run distillate oils. Generally, this involves separating the lubricant components from the paraffin components. Nowadays, homobenzene dewaxing is commonly used. The functions of wax are... numerous.

I read it written this way in the book, but I don’t understand it; thank you very much! ! !

Petroleum refining process – Petroleum product purification – Molecular sieve dewaxing: A process that utilizes the selective adsorption properties of molecular sieves to remove n-paraffins from fractions such as gasoline, jet fuel, and diesel. Therefore, it is both an important means for refining petroleum products in refineries and a key production method for liquid paraffin (see petroleum waxes). Molecular sieve dewaxing units were initially used to increase the octane rating of gasoline; later, they were applied to lower the freezing point of jet fuel and to produce liquid paraffin wax, as well as to manufacture diesel with a low pour point. China built molecular sieve dewaxing units in the 1960s; the existing units are mainly used to produce liquid paraffin wax (as a raw material for detergents). 　　Among the hydrocarbons contained in fractions such as gasoline, kerosene, and diesel, n-alkanes have the lowest octane number and the highest freezing point; their molecular diameter (4.9Å) is smaller than that of isoparaffins, cycloparaffins, and aromatic compounds. Therefore, by using 5A molecular sieve (with a micropore size of 5.2A), normal alkanes can be selectively adsorbed from mixed hydrocarbons, thereby achieving separation. 　　Molecular sieve dewaxing is a process of gas-solid adsorption and desorption. The adsorption and desorption operations in industrial processes are carried out in two or more adsorbers. Different desorbents require different operating conditions; taking an industrial process using water vapor as a desorbent as an example, the feed material heated to 190–240°C is vaporized and then fed into an adsorption tank where the n-alkanes are adsorbed. After adsorption, desorption is carried out by blowing superheated steam at 365–375°C to remove the n-alkanes. The steam consumption per ton of raw material is approximately 4 tons. After operating for a period of time, coking forms on the surface of the molecular sieve, reducing its activity, and it needs to be regenerated by burning with air. The advantage of using water vapor as a desorption agent is its ease of operation, but wastewater treatment is troublesome. In addition to water vapor, hydrogen, light alkanes, ammonia, etc. can also be used as desorbents. Their advantage is that they avoid wastewater pollution problems. 　　In recent years, new technologies have been developed in which both adsorption and desorption take place in the liquid phase; using liquid ammonia for liquid-phase desorption saves energy compared to desorption with water vapor.

Wax removal is relative to its application; for example, if diesel contains a high amount of wax, its freezing point drops, making it unsuitable for use in low-temperature areas. From this perspective, it can be concluded that there is no need to remove wax from crude oil, unless there are special requirements.

I’ve never seen dewaxing of crude oil 1, but dewaxing of side-stream oil is quite common! For more details, you can check out oil refining

Regarding the dewaxing process mentioned by the original poster, I personally understand it as a process step in lubricant production. The quality requirements for lubricant base oils specify a certain freezing point; a high wax content leads to a high freezing point of the lubricant base oil and poor flowability at low temperatures, hence dewaxing is necessary. The removed wax is generally divided into fully refined wax and semi-refined wax, with the main difference between the two being their oil content. The removed wax can be exported and sold as a finished product after hydrorefining. There are physical and chemical methods for dewaxing. Physical methods include solvent dewaxing (the most widely used currently), adsorption dewaxing, cold pressing dewaxing, urea dewaxing, and bacterial dewaxing ； Chemical methods include hydrodewaxing and catalytic dewaxing.

There are several methods of dewaxing: 1. Molecular sieve dewaxing, which is mainly used to remove lighter fractions such as kerosene and diesel; the wax obtained in this process is liquid paraffin； 2. Cold pressing dewaxing, used for fractions such as first-line and regular fourth-line fractions that have a low wax content and low viscosity ； The resulting wax paste, after being subjected to sweating, yields semi-refined paraffin ； 3. Co-phenol dewaxing: This is a process used in the production of lubricants from paraffin-based crude oils, with paraffin as the by-product ； 4. Hydrodesulfurization (pour point reduction), which involves the cracking of large molecular weight n-alkanes; it is also used in the lubricant production process.

What the original poster should be aware of is the dewaxing process in the production of lubricants. For lubricants to function at low temperatures, such as in the northeast where temperatures can drop to minus 20 degrees, it is essential that they do not solidify under such conditions; therefore, all lubricants require a low pour point. Wax, in the everyday sense, is a solid at normal temperatures; for example, the candles we use regularly indicate that wax has a relatively high freezing point (it freezes at high temperatures). Crude oil undergoes atmospheric and vacuum distillation; the vacuum wax oil obtained as a result is a mixture of wax and oil, which is used in the production of lubricants. To separate the wax from the oil, dewaxing is required. The most common method used in refineries is paraffin dewaxing, though there are also other methods such as urea dewaxing and bacterial dewaxing.

Crude oil dewaxing involves testing the wax content in crude oil; wax content is an indicator used to evaluate crude oil