How is the conversion rate of hydrocracking feedstock calculated?

Hydrocracking is essentially a combination of hydrogenation and catalytic cracking processes. On the one hand, it enables heavy crude oils to be converted into lighter oils such as gasoline, kerosene, and diesel through catalytic cracking reactions; on the other hand, it prevents the formation of large amounts of coke. It also removes impurities such as sulfur, nitrogen, and oxygen from the feedstock, as well as saturating the olefins. Hydrocracking features high yields of light oils and excellent product quality. (1) Chemical reactions in hydrocracking: The direction and extent of the reactions of hydrocarbons under hydrocracking conditions depend on the composition of the hydrocarbons, the properties of the catalyst, and the operating conditions. The main types of reactions that occur include cracking, hydrogenation, isomerization, cyclization, desulfurization, denitration, deoxygenation, and demetallization. ① Hydrocracking of alkanes. Under hydrocracking conditions, alkanes primarily undergo C-C bond cleavage reactions as well as hydrogenation of the resulting unsaturated fragments; in addition, isomerization reactions can also occur. ② Hydrocracking of naphthenes. During hydrocracking, the reactions of naphthenes are influenced by factors such as the number of rings, the length of side chains, and the properties of the catalyst. Monocyclic cycloalkanes generally undergo reactions such as isomerization, chain scission, and dealkylation of side chains ； Bicyclic naphthenes and polycyclic naphthenes are first isomerized into pentacyclic derivatives, and then the rings are broken. ③ Hydrocracking of olefins. Under hydrocracking conditions, olefins are easily hydrogenated to form saturated hydrocarbons; in addition, reactions such as polymerization and cyclization also occur. ④ Hydrocracking of aromatic hydrocarbons. For aromatic hydrocarbons with side chains containing three or more carbon atoms, the side chain first breaks off to form the corresponding aromatic and alkanic hydrocarbons; in some cases, the aromatic hydrocarbons may also undergo hydrogenation to form cycloalkanes. The hydrocracking of bicyclic and polycyclic aromatic hydrocarbons occurs in stages: first, one of the aromatic rings is hydrogenated to form naphthoaromatic hydrocarbons; then the naphthene ring breaks apart to yield alkylaromatic hydrocarbons, after which the reaction continues. ⑤ Hydrocracking of non-hydrocarbon compounds. Under hydrocracking conditions, non-hydrocarbon compounds containing sulfur, nitrogen, and oxygen heteroatoms undergo hydrogenation to produce corresponding hydrocarbons as well as hydrogen sulfide, ammonia, and water. (2) Hydrocracking catalysts Hydrocracking catalysts are bifunctional catalysts composed of a metal hydrogenation component and an acidic support. Such catalysts are required to possess not only hydrogenation activity but also cracking activity and isomerization activity. ① Oxides or sulfides of several metal elements from groups B and VII (such as Fe, Co, Ni, Cr, Mo, W), as well as precious metal elements such as Pt and Pd. The hydrogenation active component of the catalyst. Similar to hydrogenation refining catalysts, the hydrogenation active component of hydrocracking catalysts is also mainly the support of type Ⅵ ② catalysts. The supports for hydrocracking catalysts are of acidic and weakly acidic types. Acidic carriers include aluminum silicate, magnesium silicate, molecular sieves, etc., while weakly acidic carriers include alumina and activated carbon, etc. The support of the catalyst serves the following functions: increasing the effective surface area of the catalyst ； Provide an appropriate pore structure ； Provides acidic centers ； Increase the mechanical strength of the catalyst ； Improve the thermal stability of the catalyst ； Increase the catalyst’s resistance to poisons ； Reduce the amount of metal components used, thereby lowering costs. ③ Pre-sulfurization of the catalyst. The active component of hydrocracking catalysts exists in the form of oxides, and its activity is higher only when it is in the form of sulfides; therefore, such catalysts need to be pre-sulfurized before use. Pre-sulfidization involves reacting its active components with H2S at a certain temperature, thereby converting them from oxides to sulfides. The effect of presulfurization depends on the presulfurization conditions, with a typical temperature range of 280–300°C. (3) Factors affecting petroleum fraction hydrogenation The main factors influencing the hydrogenation processes of petroleum fractions (hydrofining and hydrocracking) include reaction pressure, reaction temperature, feedstock properties, and catalyst performance. ① Reaction pressure. The effect of reaction pressure is manifested through the hydrogen partial pressure, which in turn is determined by the operating pressure, hydrogen-to-oil ratio, purity of the recycled hydrogen, and the gasification rate of the feedstock. The reactions of hydrodesulfurization of sulfur-containing compounds and hydrosaturation of olefins proceed rapidly, achieving high conversion rates even at low pressures ； The hydrogenation denitration reaction of nitrogen-containing compounds proceeds at a slow rate; therefore, it is necessary to increase the reaction pressure (i.e., extend the reaction time) and reduce the space velocity in order to achieve a certain level of denitration. For aromatic hydrocarbon hydrogenation reactions, increasing the reaction pressure not only improves the conversion rate but also enhances the reaction rate. ② Reaction temperature. Raising the reaction temperature accelerates the reaction rates of hydrorefining and hydrocracking. Within the typical reaction pressure ranges, the reaction temperature for hydrorefining generally does not exceed 420°C, while the reaction temperature for hydrocracking is usually between 260°C and 400°C. Of course, the specific hydrogenation reaction temperature needs to be determined reasonably based on the properties of the raw materials, the requirements for the product, and the performance of the catalyst. ③ Airspeed. Air velocity reflects the processing capacity of the device. Industrially, higher space velocities are desired, but the space velocity is constrained by the reaction temperature. Depending on catalyst activity, feedstock properties, and reaction depth, the space velocity varies over a wide range (0.5–10 h-1). Heavy oils and oils obtained through secondary processing generally use lower space velocities; during hydrorefining, reducing the space velocity can increase the desulfurization rate, denitration rate, and olefin saturation rate. ④ Hydrogen-to-oil ratio. Increasing the hydrogen-to-oil ratio can raise the hydrogen partial pressure, which is beneficial not only for the hydrogenation reaction but also helps to suppress the condensation reactions that lead to carbon deposition; however, it increases power consumption and operating costs. Furthermore, the hydrogenation process is an exothermic reaction, and a large amount of recycled hydrogen can increase the heat capacity of the reaction system, thereby reducing the magnitude of changes in reaction temperature. During hydrorefining, the heat of reaction is not significant, allowing for a lower hydrogen-to-oil ratio to be used ； During hydrocracking, the heat effect is significant and hydrogen consumption is high, allowing for a higher hydrogen-to-oil ratio to be used. (4) Hydrocracking process flow: The vast majority of current hydrocracking processes use fixed-bed reactors. Depending on the properties of the feedstock, the requirements for the products, and the volume of material to be processed, hydrocracking units generally operate according to two types of processes: single-stage hydrocracking and two-stage hydrocracking. In addition to fixed-bed hydrocracking, there are also processes such as fluidized-bed hydrocracking and slurry-bed hydrocracking. ① Fixed-bed first-stage hydrocracking process. Hydrocracking is primarily used to produce liquefied gas from crude gasoline, as well as aviation kerosene and diesel from vacuum wax oil and deasphalted oil. In a single-reactor hydrocracking unit, the hydrorefining of the feed oil and the hydrocracking take place in the same reactor; the upper part of the reactor is used for refining, while the lower part is used for cracking. The flowchart is shown in the figure below. A schematic diagram of a hydrocracking process is shown, taking the first-stage hydrocracking of Daqing straight-run diesel fractions (330–490°C) as an example. The crude oil is pressurized to 16.0 MPa by a pump, mixed with fresh hydrogen and recycled hydrogen for heat exchange, then fed into a heater for heating, before entering the reactor for reaction. The feed temperature of the reactor is 370–450°C, and the feedstock reacts at a reaction temperature of 380–440°C, with a space velocity of 1.0 h-1 and a hydrogen-to-oil volume ratio of approximately 2500. The reaction products and raw materials are heat-exchanged to around 200°C, and softened water is added to dissolve substances such as NH3 and H2S in order to prevent the formation of hydrates that could block the pipes; after that, the mixture is cooled to 30–40°C before being fed into the high-pressure separator. Cyclic hydrogen is separated at the top, pressurized by a compressor, and then returned to the system for use ； Oil is produced at the bottom; after the pressure is reduced to 0.5 MPa, it enters the low-pressure separator where water is removed and some of the dissolved gases (fuel gas) are released. The produced oil is heated and then fed into a stabilizer column, where liquefied gas is distilled off at a pressure of 1.0–1.2 MPa. The liquid at the bottom of the column is heated to 320°C and sent to a fractionation column, from which light gasoline, aviation kerosene, low-viscosity diesel, and residue oil are obtained. Hydrocracking can be operated in three ways: single-pass feed, partial recycle of tail oil, and full recycle of tail oil. ② Fixed-bed two-stage hydrocracking process: The two-stage hydrocracking unit consists of two reactors, each equipped with catalysts of different properties. The first reactor is primarily used for the refining of crude oil, with highly active catalysts being employed to preprocess the crude oil ； The second reactor is primarily used for hydrocracking reactions; cracking and isomerization reactions take place on catalysts with high cracking activity, in order to produce as much gasoline and intermediate distillates as possible. There are two operating schemes for two-stage hydrocracking: refining in the first stage and hydrocracking in the second stage ； In the first stage, in addition to refining, partial cracking is also carried out, while in the second stage hydrocracking takes place. The two-stage hydrocracking process has a high degree of adaptability to feedstocks and is relatively flexible in operation. ③ Fixed-bed series hydrocracking process: A fixed-bed series hydrocracking unit consists of two reactors connected in series, with different catalysts filled in each reactor; the first reactor is equipped with a hydrogenation catalyst that exhibits good activity for desulfurization and denitration, while the second reactor uses a molecular sieve hydrocracking catalyst that is resistant to ammonia and hydrogen sulfide. The other parts are the same as those in a hydrocracking process. Compared to the same hydrocracking process, the advantage of the series process is that it is possible to produce gasoline, aviation kerosene, or diesel to the greatest extent possible simply by changing the operating conditions. ④ Boiling bed hydrocracking: The boiling bed hydrocracking process utilizes the flow velocity of fluids to move catalyst particles of a certain size, thereby creating a three-phase bed of gas, liquid, and solid. This allows hydrogen, feed oil, and catalyst to come into full contact with each other, enabling the hydrocracking reaction to take place. This process can handle feedstocks with high metal content and residual carbon levels (such as vacuum residue), and enables the deep conversion of heavy oil. However, the operating temperature of this process is relatively high, generally ranging from 400 to 450°C. ⑤ Suspension bed hydrocracking process: The suspension bed hydrocracking process can be used with very low-quality feedstocks, and its principle is similar to that of the bubbling bed. The basic process involves pre-mixing the fine-powdered catalyst with the raw materials, which are then fed into the reactor along with hydrogen and flow from bottom to top, where the hydrocracking reaction takes place. The catalyst remains suspended in the liquid phase and exits the reactor from the top along with the reaction products.

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The last edit to this post was made by zhangyong6404 on 2009-8-2 at 21:28. In reports on hydrocracking, the conversion rate of crude oil feedstock is generally expressed as a volume percentage, such as 60–70(v)%. The calculation of hydrogen consumption is rather complicated; hydrogen usage affects the investment and costs associated with the equipment. It can be divided into chemical hydrogen consumption, dissolved hydrogen consumption, emitted hydrogen consumption, and leaked hydrogen consumption. For more details, refer to Chapter 4 of the \"Operation Guide for Hydrocracking Units\". Here’s a free link for you: http://zhangyong6404.qupan.com/4037069.html

Why isn’t there a specific calculation formula?

.... Just look at the formula for conversion rate; then you won’t have to ask whether it’s the conversion rate based on mass or that based on amount of substance. For substances in the same system, divide the masses together. Volume. Moles are all the same