Patent Application
20150119613
The present invention relates generally to processes for treating pyrolysis gasoline, and more specifically to processes for treating pyrolysis gasoline to remove dienes and olefins prior to downstream processing to remove benzene, toluene and xylene isomers (commonly referred to as BTX processing).
The treatment of pyrolysis gasoline to remove dienes and olefins prior to downstream BTX processing for high value para-xylene (PX) remains a challenge. Currently, the process requires two steps and the high heat of reaction needed for these steps require high effluent recycle rates to maintain the resulting temperature rise at an acceptable delta temperature performance. The key steps include: (1) a first stage to saturate di-olefins; and (2) a second stage to hydrotreat the remaining olefins and aromatics to remove sulfur and nitrogen species down to a level of less than 0.5 ppm to make the net product stream acceptable for further processing in a downstream aromatics complex for high value PX production. The current technology is limited in that heat control in the first and second stages requires high selectivity catalysts to be used in the lead stage, followed by careful heat management in the second stage to reduce recycle rates to minimize utilities consumption and capital costs.
Briefly, in certain embodiments, the present process is a process for treating pyrolysis gasoline that includes introducing a pyrolysis gasoline stream into a first stage reactor and performing a fractionation process on the pyrolysis gasoline stream after being routed through the first stage reactor. After performing the fractionation process, the resultant stream is split into a first stream and a second stream. Next, the first stream is routed to a first portion of a second stage reactor and the second stream is routed to a second portion of the second stage reactor. Preferably, the first stage reactor is a di-olefin reactor, and the second stage reactor is a hydrotreater reactor.
Alternatively, in certain embodiments, the present process relates to a process for treating pyrolysis gasoline that includes routing a pyrolysis gasoline stream to a di-olefin reactor and then routing a first recycle liquid stream to the di-olefin reactor. The process of these embodiments also includes performing a fractionation process on the pyrolysis gasoline stream after being routed through the di-olefin reactor. Next, after performing the fractionation process, the resultant stream is split into a first stream and a second stream. The first stream is routed to a first portion of a hydrotreater reactor, and the second stream is routed to a second portion of the hydrotreater reactor. Additionally, preferably, a second recycle liquid stream is routed to the second portion of the hydrotreater reactor.
As an additional alternative, embodiments of the present process also relate to a process for treating pyrolysis gasoline that includes routing a pyrolysis gasoline stream containing a full range of C5 to C10 hydrocarbons to a first stage reactor and separating the C5 hydrocarbons and the C10 hydrocarbons from the pyrolysis gasoline stream after being routed through the first stage reactor. After separating, a liquid effluent stream containing C6 to C9 hydrocarbons is routed to a second stage reactor.
These and other embodiments are described in the following Detailed Description of the Invention.
A preferred embodiment of the present invention is described herein with reference to the drawing wherein:
In certain embodiments, the present invention relates to a process for treating pyrolysis gasoline that utilizes a high selectivity di-olefin saturation catalyst consisting of a shell impregnated palladium (Pd) system or a Pd layered sphere system in the lead stage of a two stage reactor system, such that once through hydrogen (H2) can be processed without excessive heat generation due to secondary saturation of olefins or aromatics. This first stage of the process is followed by a second stage where a high selectivity catalyst is used to selectively saturate the remaining olefins, and to hydrotreat the sulfur and nitrogen species without aromatics saturation. In the second stage, the catalyst could consist of a combination of a Ni—Mo catalyst and a Co—Mo catalyst in a system in which the ratio of Ni—Mo to Co—Mo of between 20% to 80% Ni—Mo catalyst and between 30% to 70% Co—Mo catalyst.
Further, as described more fully below, a split feed reactor can be used in the second stage. Under such a configuration, a gas phase only recycle stream is required to manage the heat, and the need for a liquid phase recycle stream is either eliminated, or, if desired, it could possibly be included as a back-up only for added process flexibility.
By using a high selectivity catalyst in the lead stage, the fractionation process can be performed between the first and second stages, enabling the achievement of a high yield with minimum recycle. Examples of the high selectivity catalyst include an egg shell type catalyst, ECS (engineered catalyst support or layer sphere system), and conventional uniformly impregnated Pd catalysts, such as PF-4. The egg shell type catalyst provides somewhat better selectivity than the ECS catalyst, and both the egg shell type catalyst and the ECS type catalyst provide better performance than the conventional uniformly impregnated Pd catalyst, PF-4.
Further, the use of a split feed reactor in the second stage allows the additional heat sink required in a liquid recycle to be eliminated, resulting in further capital and utilities cost reduction.
An example of an embodiment of the present process will now be described. More specifically,
The feed stream 10 of
After receiving make-up hydrogen from the make-up hydrogen stream 16A, if necessary, the pyrolysis gasoline stream 10 is directed to a first stage reactor 18, which in this embodiment is a di-olefin reactor that is used for removing di-olefins from the pyrolysis gasoline with a catalyst. Preferably, the catalyst used in the di-olefin reactor 18 is a high selectivity di-olefin saturation catalyst. For example, a high selectivity di-olefin saturation catalyst consisting of a shell impregnated palladium (Pd) system or a Pd layered sphere could be used. Alternatively, the catalyst could include engineered catalyst support (ECS). Sufficient performance could also be obtained with a conventional PF-4 catalyst, which is a spherical R-9 catalyst with 0.4% Pd, 0.5% Li that has been reduced and cold sulfided, although catalysts with an eggshell Pd profile are preferred for certain embodiments.
The first stage reactor 18 may be of any desired type, but one example of a specific embodiment of a two bed reactor that can be used in the present process is disclosed in Application Serial No. ______ [GBC Docket No. 5066.115488; UOP No. H0041208-8200], which is assigned to the same Assignee as the present application, and which is hereby incorporated by reference it its entirety into the present application.
After the pyrolysis gasoline has been routed through the first stage reactor 18, a fractionation process can be performed upon the pyrolysis gasoline stream. Dashed box 20 of
Another resultant stream 28 from the surge drum 24, which stream is preferably in a vapor phase, is routed to a depentanizer column 30, or other similar component, for removing pentane and lighter fractions from the pyrolysis gasoline stream. After processing within the depentanizer column 30, the removed C5 hydrocarbons will be in stream 32, which stream can be further processed if desired, and a vent gas stream 34 will also result. Further, the processed pyrolysis gasoline, which now lacks the C5 hydrocarbons, is routed via stream 36 to a rerun column 38 for the removal of the C9+ hydrocarbons, which exit column 38 via stream 40. Stream 40 can be further processed, as desired. As an alternative, the C9 hydrocarbons can also be removed, if desired, such that resultant stream 42 is a pyrolysis gasoline stream containing C6 to C8 hydrocarbons.
The resultant stream 42 from the rerun column 38, which in this embodiment is a pyrolysis gasoline stream containing C6 to C9 hydrocarbons (as the C5 and C9+ hydrocarbons have been removed during the fractionation process 20), is then split into a first stream 44A and a second stream 44B. Preferably, streams 44A and 44B are both liquid phase streams.
Both stream 44A and stream 44B are routed to a second stage reactor 46, which in this embodiment is preferably a hydrotreater reactor with two catalyst beds (such as an upper bed in a first portion of the reactor and a lower bed in a second portion of the reactor). In certain embodiments, the catalyst(s) and process parameters of reactor 46 are selected such that the remaining olefins and aromatics are selectively saturated, and the sulfur and nitrogen species are hydrotreated without their aromatics being saturated. The same catalyst may be used in both portions of the second stage reactor 46, or different catalysts could be used in each portion. Further, a mix of two, or more, different catalysts could be used in each portion of reactor 46, whereby either the same ratio of components of the catalyst are used in both portions of reactor 46, or different ratios of the same components are used in each of the two portions of reactor 46. Finally, it also contemplated that a reactor with more than two beds, and/or with more than two feeds, could also be used as reactor 46.
In one exemplary embodiment, the catalyst in both the first and second portions of second stage reactor 46 comprises a catalyst that is a combination of a Ni—Mo catalyst and a Co—Mo catalyst, where there is between 20-30% of the Ni—Mo component and between 70-80% of the Co—Mo component. As mentioned above, the catalyst for the first and second portions could be the same (such as a 30/70% split for Ni—Mo/Co—Mo) or two different formulations could be used (such as a 30/70% of Ni—Mo/Co—Mo for the first portion and a 20/80% split of Ni—Mo/Co—Mo for the second portion, or vice-versa).
Preferably, the second make-up hydrogen stream 16B (mentioned above) is configured to be combined with stream 44A prior to the combined stream 45 entering the second stage reactor 46. The amount of make-up hydrogen needed can be determined and controlled in any desired manner.
In the
If the optional liquid phase stream 54A is provided, it can be used as a liquid recycle feed into the first portion of the second stage reactor 46. More specifically, stream 54A, if provided, is combined with stream 44A and make-up hydrogen stream 16B to form combined stream 45, which is then directed into the first portion of the second phase reactor 46.
The stream 54B from the separator 50, via stream 52, is routed to a debutanizer 58, where it is processed to form a stream 60, which contains the C4 hydrocarbons, and a stream 62, which contains the C6 to C8 hydrocarbons. Preferably, the stream 62 is a liquid phase stream and the stream 60 is a vapor phase stream
Returning to the separator 50 of
Some of the advantages of the new scheme described above include the following:
(1) Hydrogen is processed Once-Through in a first stage di-olefin reactor.
(2) The make-up hydrogen can be added to both the first and the second stage reactor sections in the current process, while some previous processes only added the make-up hydrogen in the first stage reactor.
(3) The fractionation process of the current process is moved to between the first and second stages. Moving the fractionation process enables for only hydrotreating the C6 to C8 (or C9) cut, and lowers the feed rate to the second stage.
(4) The split feed to the second stage reactor eliminates the need for liquid recycle to control the delta T across the reactor (but such liquid recycle can still be provided, if desired for certain embodiments).
(5) With the current process, better aromatic retention can be expected due to controlled hydrogen addition and reduced operating severity in both the first and second stage reactors.
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 is 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.
