The technical field generally relates to methods and apparatuses for adsorption and desorption and more particularly relates to methods and apparatuses for separating a desorbent from different streams that include the desorbent.
Adsorption/desorption is a common separation technique that is employed for separation of various molecules from a mixed stream that includes the molecules to be adsorbed along with other molecules. Adsorption/desorption is particularly useful to separate certain molecules from the mixed stream that may otherwise be difficult to separate through other separation techniques, such as fractionation. For example, adsorption/desorption is commonly used to separate isomers of certain hydrocarbon compounds, such as C5 to C8 hydrocarbons, whereas fractionation is not effective to separate the isomers. Adsorption/desorption is also commonly used to remove contaminants that are present at low concentrations from various feed streams.
Adsorption generally involves collection of molecules from the mixed stream on a surface of an adsorbent material that adsorbs the molecules selectively over other molecules in the mixed stream. A desorbent stream that can be readily separated from the adsorbed molecules, such as through fractionation, is employed to remove the adsorbed molecules from the adsorbent material. Portions of the mixed stream that are not adsorbed by the adsorbent material remain in a raffinate stream after adsorption.
Various adsorption/desorption techniques allow for continuous adsorption and desorption. For example, countercurrent flow of the mixed stream over a solid adsorbent material is one technique that is commonly employed to effectuate adsorption and desorption. In this technique, desorbents are used that are effective to desorb the adsorbed molecules from the solid adsorbent material, and the desorbent also dilutes the portions of the mixed stream that remain after adsorption of the molecules from the mixed stream. As a result, an extract stream and a raffinate stream are produced. The extract stream includes the adsorbed molecules and the desorbent, and the raffinate stream includes portions of the mixed stream that remain after adsorption of the molecules from the mixed stream along with the desorbent.
The desorbent is generally separated from the extract stream and the raffinate stream to recover the desorbent for further use. Due to different compositional makeup of the extract stream and the raffinate stream, the extract stream and the raffinate stream are generally fractionated through separate fractionation techniques to separate the individual compounds therefrom. Separate fractionation columns and associated units such as receiver vessels and overhead pumps are thus required for fractionating the extract stream and the raffinate stream. This duplication of hardware increases the cost of adsorption/desorption assemblies and decreases the efficiencies of such systems.
Accordingly, it is desirable to provide methods and apparatuses for separating desorbent from an extract stream and a raffinate stream that enable duplication of fractionation equipment to be minimized. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
Methods and apparatuses for separating desorbent from an extract stream and a raffinate stream are provided. In an embodiment, a method of separating desorbent from an extract stream and a raffinate stream includes fractionating a first stream in a first fractionation zone into a first fractionation overhead stream and a first fractionation bottom stream. The first stream includes an extract stream from an adsorption zone, and the first fractionation overhead stream includes a desorbent. A second stream that is different from the first stream is fractionated in a second fractionation zone into a second fractionation overhead stream and a second fractionation bottom stream. The second fractionation zone is in liquid isolation from and in vapor communication with the first fractionation zone. The second stream includes a raffinate stream from the adsorption zone, and the second fractionation overhead stream includes the desorbent. The first fractionation bottom stream is removed from the first fractionation zone and the second fractionation bottom stream is removed from the second fractionation zone separate from the first fractionation bottom stream. The first fractionation overhead stream from the first fractionation zone and the second fractionation overhead stream from the second fractionation zone are combined to produce a combined fractionation overhead stream that includes the desorbent.
In another embodiment, a method of separating desorbent from multiple streams includes providing a split fractionation column that includes an internal partition. The internal partition defines a first fractionation zone and a second fractionation zone in liquid isolation from and in vapor communication with the first fractionation zone. A first stream is fractionated in the first fractionation zone into a first fractionation overhead stream and a first fractionation bottom stream. The first stream includes an extract stream from an adsorption zone, and the first fractionation overhead stream includes a desorbent. A second stream different from the first stream is fractionated in a second fractionation zone into a second fractionation overhead stream and a second fractionation bottom stream. The second fractionation zone is in liquid isolation from and in vapor communication with the first fractionation zone. The second stream includes a raffinate stream from the adsorption zone, and the second fractionation overhead stream includes the desorbent. The first fractionation bottom stream is removed from the first fractionation zone and the second fractionation bottom stream is removed from the second fractionation zone separate from the first fractionation bottom stream. The first fractionation overhead stream from the first fractionation zone and the second fractionation overhead stream from the second fractionation zone are combined to produce a combined fractionation overhead stream that includes the desorbent.
In another embodiment, an apparatus for separating desorbent from multiple streams includes an adsorption zone for receiving a feed stream and for selectively adsorbing a component from the feed stream to produce an extract stream and a raffinate stream. The apparatus further includes a split fractionation column that includes an internal partition. The internal partition defines a first fractionation zone and a second fractionation zone in liquid isolation from and in vapor communication with the first fractionation zone. The first fractionation zone is in fluid communication with the adsorption zone for receiving a first stream that includes the extract stream from the adsorption zone. The second fractionation zone is also in fluid communication with the adsorption zone for receiving the second stream that includes the raffinate stream from the adsorption zone.
The various embodiments 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 various embodiments or the application and uses thereof. 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 separating desorbent from multiple streams are provided herein. In particular, the methods and apparatuses are provided for separating desorbent from multiple streams that each include the desorbent, where the desorbent is used to desorb components that are adsorptively separated from a mixed stream of chemical compounds (and that also include other components from which the desorbent is to be separated). Desorbents that can be separated from the multiple streams in accordance with the methods and apparatuses described herein include any desorbents that have a lower vapor pressure than substantially all of the other components that are present in the multiple streams from which the desorbent is separated. This allows the multiple streams to be fractionated with the desorbent separated in fractionation overhead streams as a result of fractionation.
The desorbent can be removed from the multiple streams while minimizing duplication of fractionation equipment by fractionating the individual streams in respective fractionation zones that are in liquid isolation from each other, but that are also in vapor communication with each other. In this manner, the fractionation overhead streams from the respective fractionation zones are combined while the fractionation bottom streams from the respective fractionation zones are kept separate, thereby at least avoiding duplication of separate overhead receivers, pumps, or other overhead-handling equipment that would otherwise be required if the fractionation overhead streams from the respective fractionation zones were to be separated. Further, a split fractionation column can be employed, with the respective fractionation zones included in the split fractionation column and separated by at least one internal partition to maintain liquid separation between the respective fractionation zones, thus avoiding duplication of separation fractionation columns for the respective fractionation zones.
In an embodiment, and as shown in
In an embodiment and as shown in
Suitable feed streams 42 that are separated in the adsorption zone 40 are not limited and may include any feed stream 42 from which components can be separated through adsorption. In an embodiment, the component that is separated from the feed stream 42 through adsorption is a hydrocarbon component, i.e., one or more compounds that include only carbon and hydrogen atoms. Examples of hydrocarbon components that may be separated from feed streams 42 through adsorption may be chosen from, but are not limited to, an aromatic component, a linear paraffin component, or an olefin component. Specific examples of aromatic hydrocarbons that may be separated from feed streams 42 through adsorption include para-xylene or meta-xylene (which may be separated from mixed C8 aromatic isomers including ortho-xylene and ethylbenzene in the feed stream 42); and para-cymene or meta-cymene (which may be separated from other cymene isomers in the feed stream 42). Linear paraffins may be separated from branched or cyclic hydrocarbons through adsorption, and olefins may be separated from paraffins through adsorption. In another embodiment, the component that is separated from the feed stream 42 through adsorption is an organic component that is different from the aforementioned hydrocarbon component. Examples of organic components that may be separated from the feed stream 42 include carbon-containing compounds that also contain one or more heteroatoms such as, but not limited to, nitrogen, oxygen, sulfur, and/or halogen, and such organic compounds may be separated from other hydrocarbons that are present in the feed stream 42. For example, para-cresol or meta-cresol may be separated from other cresol isomers in the feed stream 42. As another example, fructose may be separated from mixed sugars in the feed stream 42. In another embodiment, the component that is separated from the feed stream 42 through adsorption is an inorganic component such as, for example, a metal or metal-containing compound. Adsorption of all of the aforementioned components from feed streams 42 is known in the art, and appropriate adsorption materials for separating the aforementioned components from feed streams 42 are known to those of skill in the art.
Referring to
As alluded to above, the extract stream 14 and the raffinate stream 20 both include the desorbent. In particular, after desorbing the adsorbed compound from the adsorption zone 40 to produce the extract stream 14 and the raffinate stream 20, the desorbent remains with the adsorbed component in the extract stream 14. The desorbent also dilutes the unadsorbed component and remains with the unadsorbed component in the raffinate stream 20. As such, the desorbent is present in both the extract stream 14 and the raffinate stream 20 that are produced by the adsorption zone 40. The first stream 12 and the second stream 18 are substantially free of compounds that have a higher vapor pressure than the desorbent, thereby enabling the desorbent to be separated from both the first stream 12 and the second stream 18 through fractionation without contaminating the separated desorbent with other compounds. It is to be appreciated that compounds that have the higher vapor pressure than the desorbent can be removed from the feed stream 42 in upstream separation units (not shown) prior to separation in the adsorption zone 40 such that the extract stream 14 and the raffinate stream 20 are substantially free of such compounds, with only trace amounts, e.g., less than about 1 weight % based on the total weight of the extract stream 14 and the raffinate stream 20, of the compounds that have higher vapor pressure than the desorbent possibly present in the extract stream 14 and the raffinate stream 20. Further, although not shown, a purge steam may be employed to separate co-boiling contaminants from the desorbent, where the co-boiling contaminants have a substantially similar vapor pressure as the desorbent, to avoid accumulation of the co-boiling contaminants in the desorbent.
Referring to
In an embodiment and as shown in
The first fractionation overhead stream 22 and the second fractionation overhead stream 34 are substantially free of compounds that have a higher vapor pressure than the desorbent, and the first fractionation overhead stream 22 and the second fractionation overhead stream 34 generally include substantially pure desorbent, e.g., at least 90 wt %, such as at least 99 wt %, of desorbent is present based on the total weight of the fractionation overhead streams 22, 34. As such, the first fractionation overhead stream 22 and the second fractionation overhead stream 34 are combined to produce the combined fractionation overhead stream 38 that includes the desorbent, and combination of the first fractionation overhead stream 22 and the second fractionation overhead stream 34 avoids duplication of equipment for separate processing of the first fractionation overhead stream 22 and the second fractionation overhead stream 34. In an embodiment and as shown in
While the first fractionation overhead stream 22 and the second fractionation overhead stream 34 are combined, the first fractionation bottom stream 24 is maintained separate from the second fractionation bottom stream 36. Such separation is accomplished, for example, by the internal partition 52 in the split fractionation column 50. The first fractionation bottom stream 24 and the second fractionation bottom stream 36 are separately removed from the first fractionation zone 16 and the second fractionation zone 32, respectively, and may be provided to further downstream processes (not shown) for use as end products, as a reactant stream for other processes, and/or for further separation of compounds contained therein.
The combined fractionation overhead stream 38 including the desorbent can be used for any purpose for which the particular desorbent that is contained therein is generally used, for example as an end product, as a reactant stream for other processes within the apparatus 10, and/or for again desorbing the adsorbed component from the adsorption zone 40. In an embodiment and as shown in
As described in detail above and as shown in
In an embodiment, the second stream 18 includes the raffinate stream 20 from the different adsorption stage 328 than the adsorption stage 28 that produces the extract stream 14 that is included in the first stream 12. For example, as shown in
In the embodiment of the method and apparatus 310 shown in
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, 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 invention 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 of the invention. 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 of the invention as set forth in the appended claims.