Hydroisomerization dewaxing technology

In simple terms, hetero-dewaxing involves using a catalyst to convert straight-chain molecules into branched ones in order to lower the freezing point, while hydrocracking achieves the same goal by breaking rings and long chains. Relatively speaking, the former maintains a constant overall density, while the latter has a lower molecular weight and yields more light oil

Can heterogeneous and refined catalysts be loaded into the same reactor simultaneously?

Comparative Analysis of the Reaction Mechanisms of Isomerization Dewaxing Technology and Hydrocracking Technology I. Reaction Mechanism of Isomerization Dewaxing Technology Isomerization dewaxing technology is a method specifically used for producing high-quality lubricant base oils. Its core reaction mechanism involves the isomerization of large-molecule n-alkanes into isoparaffins with the same molecular weight or slightly lower molecular weights, under the action of a catalyst. This process primarily occurs in a hydrogen-rich environment, with the catalytic reaction being achieved through a metal-acid bifunctional mechanism. 1.1 Basic reaction process In a typical isomerization dewaxing process, the feed oil is first mixed with hydrogen, and then fed into a reactor equipped with a catalyst. Inside the reactor, n-alkane molecules undergo a series of processes such as adsorption, reaction, and desorption at the active sites of the catalyst. Specifically, under the action of a catalyst, long-chain normal alkanes undergo carbon skeleton rearrangement to form branched isomeric alkanes, with the molecular weight remaining essentially unchanged. 1.2 Catalyst System Isomerization dewaxing catalysts are typically composed of precious metal components (such as platinum and palladium) supported on a molecular sieve carrier. Molecular sieves possess a unique pore structure and acidity, which provide an appropriate environment for the isomerization of n-alkanes. Precious metals can promote the activation of hydrogen, thereby accelerating the reaction rate. For example, the Pt/SAPO-11 catalyst exhibits excellent performance in the isomerization of n-alkanes due to its regular pore structure and acidic properties. 1.3 Process conditions Isomerization dewaxing is typically carried out under mild conditions, with typical operating parameters of a temperature of 280–380°C and a pressure of 3–8 MPa. These relatively mild conditions help maintain a high yield and high viscosity index for the lubricant base oil, while also achieving a low pour point. II. Reaction mechanism of hydrocracking technology Hydrocracking is an important petroleum refining process that converts heavy oils into lighter oils such as gasoline, kerosene, and diesel, and its reaction mechanism differs significantly from that of isomerization dewaxing. 2.1 Basic reaction mechanism Hydrocracking follows a normal carbocation reaction mechanism and proceeds according to the β-scission rule. During the reaction, the large tertiary carbocation undergoes cleavage at the β-position to yield an isomeric olefin and a small primary carbocation; the olefin is then hydrogenated to form an isomeric alkane. This mechanism results in hydrocracking products being rich in isomeric alkanes. 2.2 Parallel Multi-Reactions Hydrocracking is essentially a combination of hydrogenation and catalytic cracking processes, accompanied by the following reactions: Hydrogenation reaction: Saturates olefins and removes impurities such as sulfur, nitrogen, and oxygen. Cracking reaction: Breaks down heavy oil molecules into smaller ones. Isomerization reaction: Creates branched structures to improve the properties of the products. 2.3 Catalyst System Hydrocracking catalysts are typically composed of hydrogenation components (such as sulfides of W, Mo, and Ni) and acidic components (such as amorphous silica-alumina or molecular sieves). Compared to heterogeneous dewaxing catalysts, hydrocracking catalysts need to possess both hydrogenation and cracking functions. 2.4 Process Conditions The conditions for hydrocracking reactions are more stringent; high temperatures (350–450°C) and high pressures (10–20 MPa) are usually required. Such harsh conditions are favorable for the cracking of heavy oil molecules, but they may also result in a broader product distribution. III. Main differences between the two technologies
Comparison dimension | Heterogeneous dewaxing technology | Hydrocracking technology
Main purpose | To produce lubricant base oils with high viscosity index and low pour point | To convert heavy oils into light oils (gasoline, kerosene, diesel)
Reaction mechanism | Selective isomerization, with little change in molecular weight | Complex reactions including hydrogenation, cracking, and isomerization
Catalyst type | Noble metal (Pt, Pd)/zeolite bifunctional catalysts | Hydrogenation components (W, Mo, Ni)/acidic component catalysts
Operating conditions | Milder (280–380°C, 3–8 MPa) | More stringent (350–450°C, 10–20 MPa)
Product characteristics | Lubricant base oils with high viscosity index and low pour point | Wide range of light oils, rich in isoparaffins
Hydrogen consumption | Relatively low | Higher, due to the need for extensive hydrogenation reactions

IV. Technical applications and synergistic effects
Although the two technologies differ in terms of reaction mechanism and purpose, they are often used together in actual industrial production. For example, hydrocracking tail oil can be used as a raw material for isomerodewaxing, thereby further improving its properties as a base oil for lubricants. This combined process enables the production of high-quality base oils for categories II and III using the all-hydrogen method. Furthermore, from the perspective of technological development, heterogeneous dewaxing technology focuses more on the selective transformation of specific molecular structures, whereas hydrocracking technology emphasizes the overall transformation of heavy oils and the control of product distribution. This difference reflects their distinct positions and roles in the petroleum refining industry chain.