HYDROCARBON PUBLISHING COMPANY
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A member of the Hydrocarbon Analytics Group
Publication date:3Q 2014
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: 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