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HYDROTREATING AND SOLVENT DEASPHALTING
Publication date:3Q 2018
Hydrotreating and Solvent Deasphalting
Hydrotreating (HT) is a process that has become synonymous with removing impurities from petroleum feedstocks. By mixing hydrogen and feedstocks under controlled conditions in the presence of a catalyst, contaminants in the form of sulfur-, nitrogen-, and oxygen-containing compounds, as well as metals, can be removed. When the catalyst is designed to remove a specific class of compounds, that fact is reflected in the name of the process, e.g., hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodenitrogenation (HDN), and hydrodearomatization (HDA)/hydrogenation (HYD).
Hydrotreating is suitable for removing contaminants from feedstreams or product streams. For the feedstocks intended for other refinery processes—catalytic cracking, hydrocracking, catalytic reforming, and isomerization—HT protects the sensitive (and costly) catalysts from contamination. To meet product specifications, refiners rely on HT to perform posttreatment in order to meet mandated specifications such as gasoline benzene, sulfur, and also olefins (for European and Californian standards). HDS of diesel is required to satisfy ultra-low sulfur requirements. To a lesser extent, HT may be used to produce 0.1 wt% sulfur bunker fuel oil for the 2020 International Maritime Organization (IMO) mandate. Furthermore, hydrotreaters play a key role in processing unconventional (resid and renewable) feeds to produce more diesel while helping meet stricter environmental regulations. Hydrotreating is not without drawbacks: the capital investment is significant; operating costs (catalysts and hydrogen) can be high; and product quality may be adversely affected by the potential saturation of aromatics and olefins.
Companies and licensers continue to research on and release highly active HDS catalysts that allow for high HDS conversion while limiting the weighted average bed temperature (WABT) of their reactors. Furthermore, the ongoing shale boom and natural gas supply in the US have led to cheaper hydrogen production for refineries, which has opened the door for increased diesel production by increasing the volume swell of a particular unit. New offerings allow for saturation of aromatics in feeds like LCO in order to decrease diesel density and therefore increase the potential gains of incoming crude. Improvement to diesel quality has also been addressed through hydrodewaxing (HDW), which can improve the cloud point and pour point for better cold flow properties. Numerous companies have released technologies which aim to efficiently and effectively dewax a diesel stream through the use of selective catalysts.
Another challenge for refiners comes from the Tier III gasoline standard, in the US which calls for 10 ppm sulfur in gasoline, which is a third of the previous standard. This change greatly impacts the production of FCC gasoline, as it accounts for around a third of the gasoline blending pool, and is the main contributor of sulfur in the final gasoline product. Different refiners and licensers offer technologies and recommendations when deciding between FCC pretreatment and FCC posttreatment. Both options can reduce sulfur levels to meet the new standards, but at a cost. Pretreatment requires reactors to operate at higher severities, which can decrease catalyst cycles by as much as 40%. Companies are releasing and carrying out research into highly active FCC pretreat catalysts that can produce low-sulfur FCC feeds while maintaining desired cycle lengths. Meanwhile, posttreatment of FCC naphtha can lead to olefin saturation and significant octane loss as a result. New offerings and current research aim to find ways to increase HDS activity while decreasing olefin saturation by making the HDS process more selective.
Additionally, the hydrotreating section features the latest trends and technology offerings, including:
Solvent extraction and deasphalting processes—or solvent deasphalting (SDA) as it is commonly known—use hydrocarbons such as propane, butanes, pentanes, or a mixture of these to extract light, paraffinic components from heavy residue streams. Regardless of the level of impurities in the feedstock, these processes effectively produce deasphalted (DAO) or demetallized oil (terms that are used interchangeably). DAO product quality and yield are dependent upon the solvent that is selected for the process; i.e., the quality (metals, sulfur, nitrogen and Conradson carbon levels) of the products—which can be used as lubricating oil base stock or cracker feedstock—decreases with increasing yield and with the use of heavier solvents. Asphalt or pitch from the solvent deasphalter is in the form of a highly-viscous liquid. Previously, this low-value stream was commonly used as a blending component for residual fuel oils. More recently, the conversion of liquid pitch into solid form has been achieved to improve potential end uses of heavy byproducts.
Given the upcoming implementation of the IMO 0.5%-sulfur bunker specification in Jan. 2020, there has been significant focus by global refineries to invest in new technologies that minimize bottoms output, which were typically blended into the bunker pool. SDA technology can be applied in a number of areas in the refinery. Due to its versatility, relatively low capital and operating costs, and low energy requirements, solvent deasphalting can also be integrated in a number of flexible configurations with a range of refinery processing units that will treat the high-quality DAO, intermediate-quality resin, or low-quality pitch: coker, visbreaker, gasifier, resid FCC, resid hydrocracker, etc. Ultimately, refinery liquid yields are improved and production of low-value pitch is significantly reduced or eliminated. Integration opportunities also offer benefits in terms of heat and power consumption and can enhance control of product quality to meet the unique product slate specifications for a particular refiner.
There is also increased interest in applying SDA units upstream to upgrade heavy oil, particularly in Canada. Upgrading heavy oil with solvent deasphalting makes it pipeline and refinery ready while decreasing the use of diluents. Overall, as the worldwide supply of heavy and extra-heavy crude oil increases resulting in an increased quantity of heavy asphaltenes passing through the refinery, plant operators can utilize solvent deasphalting technology as a flexible and robust tool to maintain and/or increase liquid yields and optimize plant economics while processing these discounted heavier feeds.
Additionally, the solvent deasphalting section features the latest trends and technology offerings, including:
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Keywords: hydrogen, hydrotreating, middle distillates, diesel, ULSD, heavy oil, tight oil, fixed-bed, single-stage, two-stage, two-stage with recycle, jet fuel, kerosene, gasoil, gas oil, coker gas oil, coker naphtha, DAO, VGO, HVGO, LCO, resid hydrotreating, renewable hydrotreating, renewable jet fuel, renewable diesel, biodiesel, dewaxing, cold flow properties, cloud point, pour point, cetane, Tier III, gasoline, FCC pretreatment, FCC posttreatment, hydrocracker pretreatment, HDS, hydrodesulfurization, hydrodemetallization, HDM, hydrodenitrogenation, HDN, hydrodearomatization, HDA, hydrogenation, HYD, deasphalted oil, DAO, deoiled asphalt, demetallized oil, DOA, pitch, residue upgrading, bottom of the barrel, opportunity crudes, heavy oil, asphaltenes, solvent recovery, supercritical solvent extraction, gasification, IGCC, residual fuel oil, bunker fuels, marine fuels, asphaltene pelletization, solvent selection, three-product SDA, resin, solvent-to-oil ratio, integration