Process for the utilization of C.SUB.5 .hydrocarbons with integrated pygas treatment

Abstract

Methods and systems for treating pygas are disclosed. Methods include depentanizing the pygas to produce a C.sub.5 stream and a C.sub.6+ stream before hydrotreating the C.sub.6+ stream, to integrate the processing of pygas with the production of isoprene, piperylene, and dicyclopentadiene. Systems include a depentanizer added before a pygas hydrotreatment unit.

Claims

1. A process for treating pygas, the process comprising the steps of: a) depentanizing the pygas to produce a C.sub.5 stream and a C.sub.6+ stream; b) contacting the C.sub.6+ stream with a first catalyst to form one or more hydrotreatment products; c) separating the C.sub.5 stream to form a product stream and a raffinate stream, wherein the raffinate stream includes remaining C.sub.5 and C.sub.4 hydrocarbons; d) separating the raffinate stream to produce a C.sub.4 raffinate stream and a C.sub.5 raffinate stream; and e) contacting the C.sub.5 raffinate stream with a second catalyst to produce alkanes; wherein the first and/or second catalyst comprises a hydrogenation catalyst; and wherein the second catalyst comprises a C.sub.5 or C.sub.4/C.sub.5 hydrogenation catalyst.

2. The process of claim 1, wherein the second catalyst comprises a C.sub.5 hydrogenation catalyst.

3. The process of claim 1, wherein the product stream comprises isoprene, piperylene, and dicyclopentadiene.

4. The process of claim 1, wherein the contacting the C.sub.6+ stream further comprises deoctanizing the hydrotreatment products to form a benzene, toluene, and/or xylene stream and a C.sub.9+ hydrocarbon stream.

5. The process of claim 1, wherein the contacting the raffinate stream further comprises cracking the alkanes to produce feedstock.

6. The process of claim 1, further comprising contacting the raffinate stream with a sulfur removal unit to remove sulfur containing compounds from the raffinate stream prior to contacting step d).

7. The process of claim 1, further comprising contacting the C.sub.6+ stream with a sulfur removal unit to remove sulfur containing compounds from the C.sub.6+ stream prior to contacting step b).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 depicts a method for recovering isoprene, piperylene, and dicyclopentadiene from pygas according to one exemplary embodiment of the disclosed subject matter.

(2) FIG. 2 depicts a system for recovering isoprene, piperylene, and dicyclopentadiene from pygas according to another exemplary embodiment of the disclosed subject matter.

DETAILED DESCRIPTION

(3) The presently disclosed subject matter provides methods and systems for recovering C.sub.5 hydrocarbons from pygas. The presently disclosed subject matter also provides methods for recovering isoprene and cyclopentadiene from pygas. For the purpose of illustration and not limitation, FIG. 1 is a schematic representation of an exemplary method according to a non-limiting embodiment of the disclosed subject matter.

(4) In certain embodiments, a method 100 for recovering isoprene and cyclopentadiene from pygas includes depentanizing the pygas to produce a C.sub.5 stream and a C.sub.6+ stream. The pygas of the presently disclosed subject matter can originate from various sources, for example other chemical processes, e.g., ethylene production or the cracking of naphtha, butanes, or gas oil. The pygas can include alkanes, alkenes, alkynes, aromatics, naphthenes, alkyl aromatics, and polyaromatics. For example, the pygas can include cyclopentadiene and/or dicyclopentadiene.

(5) As used herein, the term about or approximately means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, about can mean a range of up to 20%, up to 10%, up to 5%, and or up to 1% of a given value.

(6) In certain embodiments, the method can include separating a C.sub.5 stream from the pygas 101. In certain embodiments, the C.sub.5 fraction can be recovered from the pygas by distillation, i.e., in a fractional distillation column. The distillation column can be a depentanizer column. The C.sub.5 fraction can include aliphatic and aromatic hydrocarbons, e.g., pentanes, pentenes, pentynes, cyclopentanes, cyclopentenes, and/or cyclopentadiene. In certain embodiments, a stream containing C.sub.6+ hydrocarbons is also recovered, e.g., by distillation.

(7) In certain embodiments, the method can further include contacting the C.sub.6+ hydrocarbon stream with a first catalyst to form hydrotreatment products 102. For example, the C.sub.6+ stream can be contacted with a catalyst, e.g., in a hydrotreatment reactor. In certain embodiments, the catalyst is any hydrogenation catalyst known in the art. In certain embodiments, the catalyst can include nickel, platinum, and/or palladium supported on alumina or the like. In certain embodiments, the C.sub.6+ hydrocarbon stream can be introduced into or contacted with a sulfur removal unit (e.g., a sulfur removal adsorption bed, amine treatment unit, etc.) to remove sulfur containing compounds (e.g., mercaptains, carbon sulfides, hydrogen sulfide, etc.) from the stream prior to coming into contact with the first catalyst. In certain embodiments, the method can further include recovering benzene, toluene, and/or xylene from the hydrotreatment products, e.g., in a distillation column. The distillation column can be a deoctanizer column. In certain embodiments, the method can further include recovering C.sub.9+ hydrocarbons from the hydrotreatment products, e.g., in a distillation column. The distillation column can be the same deoctanizer column and can operate from between about 80 C. to about 200 C. of temperature and pressures from between about 1 bar to about 10 bars.

(8) In certain embodiments, the method 100 can further include separating the C.sub.5 stream to form a product stream and a raffinate stream 103. For example, a product stream can be recovered from the C.sub.5 stream by separation, i.e., in a separations unit via a series of separations, including, but not limited to, extractive distillation. The product stream can include chemicals such as isoprene, piperylene and cyclopentadiene. In certain embodiments, the cyclopentadiene is dimerized to dicyclopentadiene (DCPD).

(9) In certain embodiments, the raffinate stream includes the remaining C.sub.5 and/or C.sub.4 hydrocarbons. In certain embodiments, the C.sub.4 hydrocarbons can be recovered from the raffinate stream, e.g., in a hydrotreatment reactor. The C.sub.4 hydrocarbons can be recycled to a cracker furnace. Alternatively, in other embodiments, the C.sub.4 hydrocarbons are not separated from the raffinate stream and the raffinate stream is contacted with a second catalyst to produce alkanes 104. In certain embodiments, the raffinate stream can be introduced into or contacted with a sulfur removal unit (e.g., a sulfur removal adsorption bed, amine treatment unit, etc.) to remove sulfur containing compounds (e.g., mercaptains, carbon sulfides, hydrogen sulfide, etc.) from the stream prior to coming into contact with the second catalyst. In certain embodiments the second catalyst is a C.sub.4/C.sub.5 hydrogenation catalyst. Hydrogenation catalysts can include, but are not limited to, nickel, palladium and platinum on an aluminum support or the like. In certain embodiments, the alkanes are further processed to obtain feedstock, e.g., in a cracker furnace.

(10) The presently disclosed subject matter further provides systems for processing pygas. The system can include one or more distillation columns, e.g., depentanizer and/or deoctanizer columns, and one or more reactors which can include one or more catalysts. For the purpose of illustration and not limitation, FIG. 2 is a schematic representation of an exemplary system according to a non-limiting embodiment of the disclosed subject matter.

(11) In certain embodiments, a system 200 for recovering dicyclopentadiene from pygas includes a pygas stream 201. To preserve the C.sub.5 valuable chemicals, a depentanizer column 202 is placed before the hydrotreatment reactor 204, C.sub.5 hydrocarbons are separated in the overhead stream from the C.sub.6+ hydrocarbons of pygas in the depentanizer column. The depentanizer column can be a distillation column. Although not show in FIG. 2, in certain embodiments, a sulfur removal unit can be coupled to the depentanizer column 202 such that the pygas is first treated to remove (e.g., reduce) sulfur containing compounds prior to entering depentanizer column 202. Additionally, or alternatively, a sulfur removal unit can be coupled to the depentanizer column 202 and the hydrotreatment reactor 204 to remove (e.g., reduce) sulfur containing compounds from the C.sub.6 stream 203 prior to entering the hydrotreatment reactor 204.

(12) The bottom stream of the depentanizer column is removed as C.sub.6+ hydrocarbons 203. In certain embodiments, the depentanizer column's overhead stream is coupled to a separations unit 208 for separating the C.sub.5 stream to recover isoprene, piperylene and cyclopentadiene 213 from the stream. In certain embodiments, the cyclopentadiene 213 is dimerized to dicyclopentadiene (DCPD) as a final product. In certain embodiments, the separations unit 208 is also coupled to a hydrogenation reactor 210 for separating the remains of the C.sub.5 stream (referred to as raffinate) 209 before C.sub.4 is recycled back 212 to the cracker 211. In certain embodiments, the reactor 210 includes a catalyst. In other embodiments the catalyst can be a C.sub.4 hydrogenation catalyst or a C.sub.4/C.sub.5 hydrogenation catalyst that is capable of hydrogenating mixed raffinate streams of C.sub.4-C.sub.5 hydrocarbons. In certain embodiments, the reactor 210 is a three bed deep hydrogenation reactor that converts all hydrocarbons to alkanes. Although not shown in FIG. 2, in certain embodiments, a sulfur removal unit can be coupled to and positioned between the separations unit 208 and the hydrogenation reactor 210 to remove (e.g., reduce) sulfur containing compounds from the C.sub.5 stream prior to entering the hydrogenation reactor 210. In certain embodiments, the outlet stream of this reactor 210 can be coupled to the cracker furnaces 211 without the need for another depentanizer column.

(13) Coupled as used herein refers to the connection of a system component to another system component by any means known in the art. The type of coupling used to connect two or more system components can depend on the scale and operability of the system. For example, and not by way of limitation, coupling of two or more components of a system can include one or more joints, valves, fitting, coupling, transfer lines or sealing elements. Non-limiting examples of joints include threaded joints, soldered joints, welded joints, compression joints and mechanical joints. Non-limiting examples of fittings include coupling fittings, reducing coupling fittings, union fittings, tee fittings, cross fittings and flange fittings. Non-limiting examples of valves include gate valves, globe valves, ball valves, butterfly valves, needle valves and check valves.

(14) In certain embodiments, a system 200 includes processing of the C.sub.6+ hydrocarbons of pygas, extracted from depentanizer column bottom 203. In certain embodiments, the depentanizer column bottom is coupled to a pygas hydrotreatment unit 204 which includes a catalyst. In further embodiments, the pygas hydrotreatment unit 204 can be coupled to a deoctanizer for separating a C.sub.9+ hydrocarbon stream 206 and a benzene, toluene, and/or xylene stream 207. The deoctanizer column can be a distillation column.

(15) The distillation columns, e.g., a depentanizer or deoctanizer, for use in the presently disclosed subject matter can be any type known in the art to be suitable for fractional distillation. The one or more distillation columns can be adapted to continuous or batch distillation. The one or more distillation columns can be coupled to one or more condensers and one or more reboilers. The one or more distillation columns can be stage or packed columns, and can include plates, trays and/or packing material. The one or more distillation columns can be coupled to one or more transfer lines. The one or more distillation columns can be made of any suitable material including, but not limited to, aluminum, stainless steel, carbon steel, glass-lined materials, polymer-based materials, nickel-base metal alloys, cobalt-based metal alloys or combinations thereof. The presently disclosed systems can further include additional components and accessories including, but not limited to, one or more gas exhaust lines, cyclones, product discharge lines, reaction zones, heating elements and one or more measurement accessories. The one or more measurement accessories can be any suitable measurement accessory known to one of ordinary skill in the art including, but not limited to, pH meters, flow monitors, pressure indicators, pressure transmitters, thermos-wells, temperature-indicating controllers, gas detectors, analyzers and viscometers. The components and accessories can be placed at various locations within the system.

(16) The methods and systems of the presently disclosed subject matter provide advantages over certain existing technologies. Exemplary advantages include a decrease in capital and separation energy costs due to the saving of an additional depentanizer column. Also, due to the separation of valuable chemicals from the C.sub.5 stream, there is less hydrogen required for the hydrogenation reactor. In addition, when the C.sub.4/C.sub.5 hydrogenation catalyst is a three bed hydrogenation reactor which can perform deep hydrogenation, the C.sub.4/C.sub.5 hydrocarbons recycled to the cracker are totally hydrogenated and therefore have a low tendency to form coke in the cracker. The diversion of a C.sub.5 hydrocarbon stream from the hydrotreater reactor also offloads the pygas reactor capacity by about 25-40% allowing an aromatics plant to process more aromatics using the same reactor unit. Another benefit of the presently disclosed subject matter is that the same depentanizer column used after pygas hydrotreatment unit can be used upstream without modification. Yet another benefit of the presently disclosed subject matter is that the C.sub.4/C.sub.5 hydrogenation reactor can be a 3 stage reactor which can perform deep hydrogenation of C.sub.5 unsaturated hydrocarbons. This is unlike pygas hydrogenation which usually utilizes one or two stage reactors to avoid hydrogenating aromatic products. The deep hydrogenation of C.sub.5 and C.sub.4 hydrocarbons ensures that only alkanes are recycled to cracker. This reduces coke formation in cracker tubes and gives longer cycle time.

(17) In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

(18) It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.