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According to U.S. magazine Hydrocarbon Processing, hydrocracking is the most important catalytic conversion unit in refineries, offering flexibility both in processing crude oil and in the distribution of products. In recent years, several systems have brought this flexibility to a very high level. Some refineries use hydrocracking units to process difficult-to-process crude oils, while others modify the operating parameters of their hydrocracking units in order to seek opportunities in the markets for lubricant base oils and petrochemical feedstocks. These refineries achieved differentiated operation of their hydrocracking units, all of which improved economic efficiency. Refining companies still face unstable profit levels and an uncertain future. Although oil prices are currently low and refineries can achieve reasonable profits, the market competition for bulk petroleum products is fierce. Demand for traditional petroleum products such as gasoline, jet fuel, and diesel is expected to continue declining, and some **newly built, efficient refineries in Asia and the Middle East have intensified market competition. Some refineries have chosen to adopt measures to enhance their competitiveness. Currently, some refineries are using the flexibility of hydrocracking units to enhance their competitiveness through the following approaches: First, refineries process inexpensive, heavy-quality crude oil. Refineries that process highly acidic crude oil face risks related to the reliability of their units and unplanned shutdowns, especially with regard to atmospheric and vacuum distillation units; these issues have now been resolved. For refineries that process low-quality heavy crude oil, the large amount of aromatics poses a significant challenge to the quality of the distillate oils produced, as well as to the production of high-quality lubricant base oils. The combination of hydrocracking and hydrotreating of distillate oils has led to the development of advanced process flows. Specially designed catalysts can be used to reduce the density and aromatic content of diesel, causing significant changes in boiling points and improving cold flow properties, thus making it possible to process high-aromatic crude oils without any problems. For refineries that process low-quality, heavy crude oils rich in metals, large amounts of metals such as iron, nickel, vanadium, magnesium, sodium, and calcium can cause various problems including severe coking; however, significant progress has been made in metal removal technologies recently. Choosing the appropriate catalyst and using a protective bed catalyst can ensure that the highly active catalyst functions properly. For refineries that process low-quality, heavy high-nitrogen crude oil, the high nitrogen content places significant strain on the pretreatment catalysts in the hydrocracking units, and it affects the processing capacity of these units. However, hydrogenation pretreatment catalysts with improved activity have been successfully developed, as well as hydrocracking catalysts with better activity and selectivity. When these two catalysts are combined to treat difficult-to-process crude oil using a pretreatment catalyst, it ensures that there is no significant loss in product yield or in the operating cycle of the plant. II. Hydrocracking units for processing non-standard feedstocks: Processing non-standard feedstocks involves adding certain cracking components to the conventional hydrocracking feedstock, namely vacuum gas oils produced by delayed coking, solvent deasphalting, fluidized bed hydrocracking, and (in the near future) slurry bed hydrocracking. These feedstocks (including coker heavy gas oil and deasphalted oil) are difficult to process due to their high levels of nitrogen, Kestenbaum residue, and metals. Some crude oils have an \"inhibiting\" effect due to having undergone cracking, which makes them more difficult to process. The advent and performance of new-generation catalysts are key to processing these feedstocks economically and efficiently, whether in newly built hydrocracking units or in upgraded existing ones. III. Hydrocracking to produce lubricant base oils or feedstocks for cracking (for the production of ethylene). Although medium-distillate oil is usually a product of higher value, in certain regions products that offer better economic benefits are lubricant base oils or cracking feedstocks; as a result, some refineries have taken advantage of these market opportunities. In the market for lubricant base oils, one of the reasons is the shift from Class I base oil products produced using solvent refining technology to Class II/III base oils produced using isomerization dewaxing/hydrogenation followed by refining technology. Demand for Category I base oils is expected to decline significantly, especially in Europe and North America. Some production facilities for Category I base oils have already been shut down, and all new facilities are for Category II/III base oils. Importantly, Category II/III base oils are generally produced from the tail oil from hydrocracking units. Of course, base oil of Category III needs to be produced using hydrocracking tail oil with a high conversion rate, because only such tail oil can yield base oil with a high viscosity index of 120–130. It is expected that in the future, all lubricant base oils will be supplied with raw materials from hydrocracking units. To produce base oils for lubricants, it is necessary to have a thorough understanding of the properties of the unconverted oil at the bottom of the distillation column in hydrocracking units, particularly its viscosity index and the contents of aromatics, sulfur, and nitrogen. The process flow of the hydrocracking unit and the proper selection of catalyst systems are key to achieving the highest yields of high-quality base oil products. In terms of producing cracking feedstocks, ethane has long been the best material for cracking to produce ethylene. Although it remains the best raw material for producing ethylene today, due to limitations in its sources, it is necessary to diversify these sources by using liquefied gas, naphtha, hydrogenated vacuum gas oil, and more recently, unconverted tail oil from hydrocracking. If the raw material is heavier, the ethylene yield will decrease, and other unwanted products will increase. However, the price of raw materials has dropped. Similar to the refining industry, the petrochemical industry also has its own economic cycles; for integrated refining/petrochemical companies, the key to long-term success lies in the flexibility of their feedstocks. Hydrocracking has important advantages here. Since hydrogen is selectively added to the unconverted product, it may also result in some loss of yield. However, the higher the hydrogen content, the higher the yield of ethylene obtained from pyrolysis, and this is what gives value to this type of feedstock. Many modern cracking units are designed to process a variety of feedstocks, from ethane to naphtha to hydrocracking tail oil. The integration between the hydrocracking unit at Shell’s Pernis refinery and the cracking unit at the nearby Moerdijk petrochemical plant illustrates this point. Towards the end of the operating cycle of the hydrocracking unit in 2013, the unit’s technical experts concluded that replacing the catalyst with a new one would help increase the yield of high-value middle distillate oils. However, any such change has an adverse effect on Shell’s petrochemical plant in nearby Moerdijk, as that plant also uses hydrocracking tail oil as a feedstock for its cracking units. If the new catalyst causes a decrease in the hydrogen content of the hydrocracking tail oil, the ethylene yield of the cracking unit or the operating cycle of the cracking furnace will be severely affected. Technical experts hope that the new catalyst used will maintain the quality of the hydrocracking tail oil unchanged, while also increasing the yield of middle-distillate oils. This type of integrated enterprise **increases the complexity of replacing catalysts; the ultimately approved approach is to enhance the value of such integration, so as to increase profits for both refineries and petrochemical plants.** The project team’s assessment after installing the new catalyst showed that the company’s total profit increased by $5 million per year. IV. Combination approaches for producing cracking feedstocks or lubricant base oils via hydrocracking. Currently, there are four techniques that utilize the flexibility of hydrocracking units to produce cracking feedstocks or lubricant base oils, thereby increasing the overall profitability of the plant: the first is the combination of high-vacuum vacuum distillation and hydrocracking. Maximizing the yield of vacuum gas oil through vacuum distillation not only provides more feedstock for hydrocracking but also reduces the size of the residue processing unit, thereby cutting costs. Practice has shown that the latest generation of vacuum distillation technology, high-vacuum vacuum distillation, not only enables the production of large quantities of vacuum gas oil but also keeps the levels of heavy metals (nickel and vanadium), residue, and C7 asphaltenes (the most important) within acceptable ranges for hydrocracking units. Data show that the modified high-vacuum vacuum distillation unit increases the yield of vacuum gas oil by approximately 2%, and it also helps to extend the operating cycle of the unit from 3 years to 4 years. The investment required for the renovation is low, with a payback period of less than 1 year. Furthermore, the scope of the modifications is limited; it mainly involves installing new spray nozzles, new packing for the oil washing layer, and new stripping tray plates. The modification can be completed in a short time, during the refinery’s regular major maintenance period. The second is the delayed coking-hydrocracking combination. It is generally believed that delayed coking is one of the most effective technologies for processing residue oil, but coker heavy gas oil can affect the processing in downstream units. Some believe that processing coker heavy gas oil from hydrocracking units together with vacuum gas oil can affect the raw materials used to produce lubricant base oils. In fact, the latest hydrocracking technologies can process coker heavy gas oil together with vacuum gas oil to produce high-quality clean fuels or raw materials for lubricant base oils. The delayed coking-hydrocracking combination is a very effective approach that allows for the elimination of fuel oil production while also providing refineries with the flexibility to process crude oil. Since hydrocracking units can process high-nitrogen, high-aromatic feedstocks obtained from crude oil switched in refineries, delayed coking units can process highly difficult-to-process residue oils. Third is the solvent deasphalting-hydrocracking combination. The combination of solvent deasphalting and hydrocracking of deasphalted oil is the least capital-intensive scheme for residue conversion, especially compared to direct hydrocracking of residue. Due to the high content of metals and residue, the conventional approach is to subject deasphalted oil to catalytic cracking. Reduced pressure gas oil contains about 1–2 ppm of metals and about 0.5–1.0% by weight of residue, whereas deasphalted oil typically contains 15–30 ppm of metals and about 6–10% by weight of residue. With a well-designed catalyst system, along with pretreatment and cracking catalysts, it is relatively easy to handle these impurities. Deasphalted oil is a relatively \"clean\" hydrocracking feedstock, with an extremely low content of C7 asphaltenes compared to vacuum gas oil. Industrial data show that the asphaltenic content in deasphalted oil C7 is only 10 ppm, whereas that in vacuum gas oil C7 is as high as 700 ppm. The key is to have a good understanding of the catalysts used for deasphalting oil. Compared to the demetallization of atmospheric residue, the demetallization of deasphalted oil is faster and easier. The designed reaction conditions must involve slow demetallization in order to maximize the metal deposited on the catalyst. The selection of catalysts is also important, both for the pretreatment catalyst and the cracking catalyst, as it is necessary to achieve a balance between selectivity and activity, in order to suit the properties of the deasphalted oil, including its large hydrocarbon molecules. Advanced solvent deasphalting units can produce deasphalted oil with high yields and minimal impurities sent on to downstream processing. The impact of impurities on the operation of hydrocracking units varies significantly; C7 asphaltenes have the greatest impact, followed by metals, residue, and nitrogen, while sulfur has the least impact. Fourth is the hydrocracking-isomerization dewaxing combination. The production process for lubricant base oils is rapidly shifting from solvent refining to isomerization dewaxing. The improvement in the quality of base oil does not depend on the use of specific crude oils; an increase in the yield of base oil also makes it easier to produce high-quality Class III base oil that meets market demands. The combination of hydrocracking and isomerization dewaxing is consistent with the strategy used by refineries to process difficult-to-process crude oils, with hydrocracking being the key and viable unit. Typically, atmospheric residue oil is fed into a high-vacuum vacuum distillation unit, where deep flashing is used to obtain the maximum amount of vacuum gas oil suitable as a hydrocracking feedstock. The conversion rate of hydrocracking can be carefully adjusted to balance product quality and yield, while the isomerization dewaxing/hydroprocessing unit can produce base oil products of Class II or III as required. If there is a sufficient demand for the heavier 500N base oil, deasphalted oil can be added (this is the production method used by Hyundai Oil Company in South Korea). Type II brightening oils can also be produced using the processing route for deasphalted oil; such products are not yet available on the market. However, as more facilities for producing Type I base oils shut down and there is a lack of traditional brightening oils, demand for these products will arise.