Patent Application
20140171702
The technical field generally relates to methods and apparatuses for forming low-aromatic high-octane product streams from aromatic-rich streams, and more particularly relates to methods and apparatuses for increasing alkyl-cyclopentane concentrations in toluene-rich streams.
Aromatics such as benzene and toluene are naturally-occurring constituents of crude oil and of many petroleum products. Aromatics have been added to gasoline blending to increase the gasoline's octane number, e.g., Research Octane Number (RON). However, due to harmful biological and environmental effects of aromatics, standards have been enacted to regulate their content in fuels such as gasoline. For example, certain standards may limit gasoline to concentrations of no more than 35 wt % aromatics. At the same time, fuel standards continue to require high octane numbers for gasoline.
The demand for distillates as fuel has been increasing and is forecasted to continue to grow strongly. Specifically, consumption of diesel and middle distillate components is projected to be the primary driver for oil consumption growth over the next decade. Industrial production of distillates is primarily supported by hydrocracking processes, rather than by fluid catalytic cracking (FCC). The growing demand for diesel and other distillates has led to the construction of refineries that rely on hydrocracking units designed to maximize production of distillates rather than fluid catalytic cracking units. Furthermore, new refineries often lack fluid catalytic cracking units altogether.
Blending of aromatic-rich streams into other hydrocarbon streams during processing of gasoline fuel blends is easily accomplished in refineries with fluid catalytic cracking units, as the fluid catalytic cracking process provides a source of moderately high octane and moderate aromatic blend material to compensate for the addition of aromatics. However, in refineries that rely on hydrocracking units and that lack fluid catalytic cracking units, the ratio of heavy naphtha reformate streams, high in aromatics, to light naphtha isomerate streams, void of aromatics, produced by hydrocracking is too high to provide economical gasoline blending with the required low aromatic levels and high octane numbers. For example, the gasoline range naphthas that come from crude units and hydrocracking units typically have a heavy naphtha reformate (C7+) to light naphtha isomerate (C5s and C6s) ratio of 2:1. The heavy naphtha reformate typically has a toluene concentration of 70-75 wt %. While it has been possible to blend the heavy naphtha and light naphtha to reach the minimum octane requirement, such blends typically cannot meet the required low aromatic concentration.
Therefore, there is a growing need in refineries that lack fluid catalytic cracking units, as well as in other processing schemes, for processing capabilities that reduce toluene levels in gasoline blends. Further, there is a growing need in those refineries for processing capabilities that increase octane numbers in gasoline blends. A method that both reduces toluene levels and avoids significant octane loss would provide a source for additional gasoline production.
Accordingly, it is desirable to provide novel methods and apparatuses for increasing alkyl-cyclopentane concentrations in aromatic-rich streams. It is also desirable to provide methods and apparatuses for processing hydrocarbon streams into gasoline blends. Also, it is desirable to provide such methods and apparatuses that operate economically. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
Methods and apparatuses for increasing an alkyl-cyclopentane concentration in an aromatic-rich stream and methods for processing hydrocarbons are provided. In one exemplary embodiment, a method for increasing an alkyl-cyclopentane concentration in an aromatic-rich stream includes saturating aromatics in the aromatic-rich stream to form methylcyclohexane. Further, the method includes isomerizing the methylcyclohexane to form alkyl-cyclopentanes. The method dehydrogenates residual methylcyclohexane to form aromatics in a product stream. The product stream includes aromatics and alkyl-cyclopentanes.
In another embodiment, a method for processing hydrocarbons is provided. The method for processing hydrocarbons includes providing a toluene-rich stream. Further, the method includes converting toluene in the toluene-rich stream into methylcyclohexane. In the method, a portion of the methylcyclohexane is converted into alkyl-cyclopentanes.
In another embodiment, an apparatus for increasing an alkyl-cyclopentane concentration in a toluene-rich stream is provided. The apparatus includes a saturation zone configured to receive the toluene-rich stream and to saturate toluene therein to form a saturated stream comprising toluene and methylcyclohexane. The apparatus also includes an isomerization zone configured to receive the saturated stream and to isomerize the methylcyclohexane therein to form an isomerized stream comprising toluene, methylcyclohexane and alkyl-cyclopentanes. The apparatus further includes a dehydrogenation zone configured to receive the isomerized stream and to dehydrogenate the methylcyclohexane therein to form a product stream comprising toluene and alkyl-cyclopentanes.
Embodiments of methods and apparatuses for increasing alkyl-cyclopentane concentrations in hydrocarbon streams will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the methods or apparatuses for increasing alkyl-cyclopentane concentrations in aromatic-rich streams. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
Methods and apparatuses for processing hydrocarbons, and more particularly, for increasing alkyl-cyclopentane concentrations in aromatic-rich streams are provided herein. The methods and apparatuses enable hydrocarbon product streams to be obtained with low levels of aromatics, such as no more than about 35 wt % aromatics, while achieving high octane numbers, such as a RON of about 95. The low aromatic concentration and high octane number is achieved by converting a portion of the aromatics to high octane number alkyl-cyclopentanes to increase the alkyl-cyclopentane concentration of the gasoline blend while simultaneously decreasing the aromatic concentration. In an exemplary embodiment, the portion of aromatics is converted to dimethylcyclopentane, as dimethylcyclopentane has an unusually high octane number in comparison to other C7 species. Certain embodiments convert a portion of a toluene content to high octane number alkyl-cyclopentanes to increase the alkyl-cyclopentane concentration of the gasoline blend while simultaneously decreasing the toluene concentration.
In an embodiment, and as shown in
The apparatus 10 includes a processing zone 16, a saturation zone 18, an isomerization zone 20, and a dehydrogenation zone 22. As shown, the processing zone 16 receives the hydrocarbon stream 12. Suitable hydrocarbon streams 12 include natural gasoline, straight run naphtha, and refined feedstocks. The processing zone 16 may comprise a fractionation unit, a hydrocracking unit, a reforming unit, or other processing unit that forms an aromatic-rich stream 30, such as a toluene-rich stream. For example, the processing unit 16 may be a fractionation unit for fractionating the aromatic-rich stream 30 from a catalytic reformate. Or, the processing zone 16 could include a toluene extraction unit forming a toluene-rich stream 30, though such a unit may be uneconomical for the purposes described herein. The phrases “aromatic-rich” and “toluene-rich” as used herein are not intended to require any minimum concentration of aromatics or toluene in the referenced stream other than above zero. As such, “aromatic-rich” and “toluene-rich” may be interpreted as “aromatic-containing” and “toluene-containing” herein. However, economic use of the apparatus and method is envisioned as being supported at higher aromatic, or specifically, toluene concentrations. In certain embodiments, the aromatic-rich stream may comprise over 70 wt % aromatics [based on the total weight of the stream 30], such as about 80-85 wt % aromatics. Likewise, a toluene-rich stream may comprise over 70 wt % toluene [based on the total weight of the stream 30], such as about 80-85 wt % toluene.
As shown in
Saturation zone 18 is configured to saturate or hydrogenate toluene or other aromatics in the aromatic-rich stream 30 with hydrogen from a hydrogen stream 31 to form cyclohexanes. More specifically, saturation zone 18 is configured to partially saturate the aromatic-rich stream 30 by saturating or hydrogenating a portion of the toluene or other aromatics therein to cyclohexanes. During an exemplary saturation/hydrogenation process toluene is converted to methylcyclohexane as illustrated:
As shown in
Because the saturation reaction is highly exothermic, the heat release may require special treatment. For example, the saturation zone 18 may include sequential stages with inter stage cooling. Alternatively, the saturation zone 18 may utilize a recycle/diluent to manage heat. Or the saturation zone 18 may use a temperature controlled saturation reactor, such as a liquid cooled reactor, a steam generating reactor, or other known systems.
In a saturation zone using more than one saturation reactor in series, particularly those using adiabatic saturation reactors connected in series, it will normally be necessary to control the temperature rise across each catalyst bed in order to avoid hot spot formation and to obviate the risk of temperature runaways occurring. It is typically disadvantageous to operate with too high an exit temperature from the catalyst bed because high exit temperatures often result in increased formation of by-products. One way of controlling the temperature rise across a catalyst bed of an adiabatic reactor is recycle product liquid to absorb heat. Another way is to increase the amount of hydrogen in the circulating gas or to allow inert gases, such as nitrogen, to build up in the recirculating gas. In this way the extra gas acts as a heat sink to absorb the exothermic heat of reaction. However, the size of the gas conduits and the size of the gas recycle compressor must be increased to allow for the increased gas flow and the capital costs of the plant are increased. Use of a plurality of adiabatic reactors in series with injection of cold shots of gas between reactors is another solution. Inter-bed cooling is another method of limiting the temperature rise across an adiabatically operated catalyst bed.
By partially saturating the aromatic-rich stream 30, the saturation zone 18 forms a saturated stream 32 comprised of toluene or other aromatics and methylcyclohexane. In an exemplary embodiment, high toluene or other aromatics saturation is achieved, such as about 90% or more. In other embodiments, a lower saturation may be achieved, particularly in cases where maximum octane is to be maintained.
In
While 1,1 dimethylcyclopentane is illustrated, other dimethylcyclopentanes may be formed. Formation of alkyl-cyclopentanes is favored at high temperatures, such as above 200° C. Operating conditions within the isomerization zone 20 are selected to maximize the production of alkyl-cyclopentanes from methylcyclohexanes introduced therein, and may be selected to maximize the production of dimethylcyclopentane or of a particular dimethylcyclopentane. Operating conditions within the isomerization zone 20 are dependent upon various factors including, but not limited to, feed severity and catalyst type, and those of skill in the art are readily able to identify appropriate operating conditions within the isomerization zone 20 to maximize formation of alkyl-cyclopentanes in general and dimethylcyclopentanes specifically from the isomerization of methylcyclohexane.
The isomerization catalyst can be a conventional paraffin isomerization catalyst or a lower acidity metal-containing catalyst. For example, the isomerization catalyst can comprise a Group VIII metal, such as platinum or palladium, on a porous inorganic oxide support, for example alumina, silica/alumina or an alumino-silicate such as a zeolite. Suitable isomerization catalysts comprise sulfated zirconia, platinum on chloride alumina and platinum on a zeolite. Suitable zeolites include faujasite, mordenite and synthetic alumino-silicates.
As a result of isomerization, the isomerization zone 20 forms an isomerized stream 34 comprising alkyl-cyclopentanes, toluene or other aromatics and methylcyclohexane. In an exemplary embodiment, the isomerized stream 34 includes no more than about 35 wt % residual methylcyclohexane.
As shown in
This reaction is performed over a catalyst, such as a mono-functional dehydrogenation catalyst. Mono and bi-metallic platinum catalysts may be used. The dehydrogenation reaction is endothermic and may be heated through heat exchange with streams from the saturation zone 18. During dehydrogenation, substantially all of the methylcyclohexane is converted to toluene. Further, a hydrogen stream 36 is formed and exits the dehydrogenation zone 22. The hydrogen stream 36 may be recycled for use as the hydrogen stream 31 entering the saturation zone 18.
As a result of the dehydrogenation step, the product stream 14 is formed by the dehydrogenation zone 22 and contains alkyl-cyclopentanes, such as dimethylcyclopentane, and toluene or other aromatics. The product stream 14 may also contain residual methylcyclohexane. As described herein, the product stream 14 includes an increased concentration of alkyl-cyclopentanes as compared to the aromatic-rich stream 30. For example, the product stream 14 may include over 30 wt % alkyl-cyclopentanes, such as over 50 wt % alkyl-cyclopentanes, or for example over 60 wt % alkyl-cyclopentanes. In an exemplary embodiment, the product stream 14 includes about 65 wt % alkyl-cyclopentanes and about 35 wt % toluene or other aromatics. Such a stream has an octane number (RON) of about 95 and meets the gasoline standard of no more than 35 wt % aromatics. Of course, the exact composition of the product stream 14 is dependent on the composition of the aromatic-rich stream 30 and on processing conditions in the saturation zone 18, isomerization zone 20 and dehydrogenation zone 22, which can be manipulated to reach a desired toluene or other aromatics and alkyl-cyclopentane concentration. Nevertheless, the apparatus 10 and method described herein can provide for the economical production of the product stream 14 appropriate for use as gasoline with a required low aromatic content, such as lower than 35 wt %, and high octane number, such as higher than 90 or about 95. In an embodiment with an initial amount X of toluene or other aromatics in the aromatic-rich stream, the apparatus and method can form the product stream with about 0.65× dimethylcyclopentane and about 0.35× toluene or other aromatics.
Referring to
As shown, a combined saturation/isomerization zone 50 receives the aromatic-rich stream 30 and a hydrogen stream 31. The combined saturation/isomerization zone 50 includes a bifunctional catalyst that catalyzes both the saturation/hydrogenation of toluene or other aromatics to form methylcyclohexane and the isomerization of methylcyclohexane to alkyl-cyclopentanes, such as dimethylcyclopentane. As shown, the combined saturation/isomerization zone 50 forms an isomerized stream 34. In an exemplary embodiment, the combined saturation/isomerization zone 50 forms an isomerized stream 34 comprising about 65 wt % alkyl-cyclopentanes, such as dimethylcyclopentane, and about 35 wt % methylcyclohexane and toluene or other aromatics.
As shown in
As a result of the dehydrogenation step, the product stream 14 is formed by the dehydrogenation zone 22 and contains alkyl-cyclopentanes, such as dimethylcyclopentane, and toluene. The product stream 14 may also contain residual methylcyclohexane. As described herein, the product stream 14 includes an increased concentration of alkyl-cyclopentanes as compared to the aromatic-rich stream 30. For example, the product stream 14 may include over 30 wt % alkyl-cyclopentanes, such as over 50 wt % alkyl-cyclopentanes, or for example over 60 wt % alkyl-cyclopentanes. In an exemplary embodiment, the product stream 14 includes about 65 wt % alkyl-cyclopentanes and about 35 wt % toluene. Such a stream has an octane number of about 95 and meets the gasoline standard of no more than 35 wt % aromatics. Of course, the exact composition of the product stream 14 is dependent on the composition of the aromatic-rich stream 30 and on processing conditions in the combined saturation/isomerization zone 50 and dehydrogenation zone 22 which can be manipulated to reach a desired toluene or other aromatics and alkyl-cyclopentane concentration. As described, the apparatus 10 and method can provide for the economical production of the product stream 14 for use as gasoline with a required low aromatic content and high octane number.
As described herein, an apparatus and method for increasing an alkyl-cyclopentane concentration in an aromatic-rich stream have been provided. In exemplary embodiments, an apparatus and method have been described for increasing a dimethylcyclopentane concentration in an aromatic-rich stream. The apparatus and method described above are particularly well-suited for the formation of a gasoline product stream that has both a low aromatic level, such as less than 35 wt %, and a high octane number, such as at least about 95.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment or embodiments. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope set forth in the appended claims.
