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HYDROTREATING AND ALKYLATION
Publication date:3Q 2014
Hydrotreating and Alkylation
Hydrotreating refers to catalytic processes with the primary purpose of removing sulfur, nitrogen, metals, and coke precursors from oil streams while saturating the olefins, aromatics, and polynuclear aromatics (PNAs) that are present. It is distinct from hydrocracking, where the intent is to reduce the boiling temperature of the feed. The term hydroprocessing may refer to either hydrotreating or hydrocracking or even to processes in which both removal of contaminants-and reduction of boiling range occur.
As oil becomes more difficult to access and process, the supply of energy may struggle to keep pace with demand. Along with demand growth, tighter environmental regulations for on-road fuels and an increased focus on reducing CO2 emissions from industrial sources will force refiners to alter operations, and these alterations could be a challenge as capital and operating budgets continue to decline. Hydrotreaters will help refiners cope with this changing market, as these units offer the ability to upgrade unconventional (resid and renewable) feeds to produce more diesel while helping meet stricter environmental regulations.
New, more stringent standards with regard to sulfur content within transportation fuels has been a major driver for hydrotreating technology over the past year. As more countries continue to adopt Euro V standards, which calls for 10 ppm sulfur within diesel, refiners seek to improve the production of ultra-low sulfur diesel (ULSD). Companies and licensers continue to research on and release highly active hydrodesulfurization (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 the 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 due to olefin saturation. 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:
Isoparaffin alkylation comprises the reaction of isobutane with C3-C5 olefins in the presence of an acid catalyst to produce a high-quality gasoline blendstock product. The product is known as alkylate made up of a mixture of iso-heptanes and iso-octanes with high-octane, low-sulfur, and low-vapor pressure. In the US, alkylate is responsible for about 11-13% of the total gasoline pool, depending on regional demand and seasonal factors.
One of the primary drivers for increasing alkylate demand in the US is the increasing use of high-RVP ethanol in the gasoline pool, that forces producers to seek out lower-RVP blending components. The need to balance high volumes of ethanol blending with less-volatile fuel components is particularly emphasized during the spring and summer months, when more-stringent limitations on gasoline RVP levels are mandated. Additionally, the ongoing shale boom in the US has created opportunities for operators of alkylation units as the shale boom is providing abundant stocks of cheap butane. Furthermore, the paraffinic nature of tight oils is resulting in a FCC gasoline product that is seeing on average an 8-10 point reduction in octane value meaning refiners will need to account for that octane loss with a high-octane gasoline blending pool component like alkylate.
Outside of the US the ongoing transition to more stringent transportation (e.g., Euro V) standards for motor gasoline in developing areas such as China and Russia will be a main factor in higher alkylation capacity in these countries in the future. Like the US, increased use of high-RVP ethanol in the gasoline pool will also result in higher demand for alkylate.
Alkylation can be carried out non-catalytically using high temperature and pressure, although refiners prefer low-temperature, acid-catalyzed processes to provide better alkylate yields. In the 1960s, approximately three times more alkylate was produced using sulfuric acid (H2SO4) as the catalyst than was produced with hydrofluoric acid (HF) catalyst. Since then, the trend in alkylation shifted to favor the use of HF, followed by a return to sulfuric acid. In North America, approximately the same volume of alkylate is produced from both types of units. Given the safety concerns associated with liquid acid alkylation, the installation of new units in North America and Europe has essentially stopped as refiners look to avoid catastrophic accidents and the high insurance premiums associated with these units. According to UOP, revamping existing liquid alkylation units has become more popular for refiners looking to increase liquid acid alkylation capacity.
Alternatives to conventional liquid acid technologies (e.g., solid acid or ionic liquid catalysts) may become viable in certain situations in the near future. Solid acid catalysts, in particular, offer improved performance in terms of plant safety. Aside from safety considerations, solid acids will be of interest where liquid acid regeneration facilities are not economically feasible. Catalyst supply and toxic mitigation costs can also be decreased by implementing alternative systems, and it is estimated that the elimination of either HF or H2SO4 from a refinery alkylation unit in favor of an alternative, less-toxic catalyst may provide a potential savings of $250MM/y. In the coming years, commercialization of these technologies as well as further improvement of conventional operations will help to shape the role of alkylation.
Additionally, the alkylation 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, alkylation, alkylate, gasoline, MTBE, ethanol, naphtha, reformate, octane, MON, RON, RVP, Reid Vapor Pressure, liquid acid, sulfuric acid, hydrofluoric acid, H2SO4, HF, solid acid, ionic liquid, revamp, butylene, propylene, amylene, tight oil, isobutane, NGLs, 1-butene, 2-butene, isooctane, indirect alkylation, oxidative dehydrogenation, butane dehydrogenation, renewable alkylation