Process For Separating Benzene From A Reactor Effluent (Patent Application UOP)

CATEGORY: BENZENE 
Process For Separating Benzene From A Reactor Effluent (Patent Application UOP)
United States Patent Application 20150251978
September 10, 2015
Assignee: UOP LLC
Abstract
A process for separating benzene from a reactor effluent in which the reactor effluent is passed to a first separation zone to separate the effluent into a bottom benzene lean stream and an overhead stream. The bottom benzene lean stream does not need to be processed further to remove benzene. The overhead stream may be cooled and is passed to a second separation zone in which it is separated into a bottom benzene rich stream and a second overhead stream. The bottom benzene rich stream contains at least 80% of the benzene from the reactor effluent. The operating temperature of the first separation zone is greater than the operating temperature of the second separation zone.
Description
BACKGROUND OF THE INVENTION
[0001] The demand for clean and safe transportation fuel is increasing worldwide. This increased demand is, in part, a result of government regulations in various countries which attempt to reduce and/or eliminate certain chemicals that are typically contained in the transportation fuel. These government regulations can impose challenges on fuel refiners and producers to provide transportation fuel which contains lower amounts of the specified chemicals in order to comply with the various governmental regulations.
[0002] In the United States, a recent example of this is the Mobile Source Air Toxics 2 (MSAT2) benzene control program. Benzene is a byproduct of one or more chemical reactions in the reforming process associated with the refining of light petroleum distillate. Beginning in 2011, the MSAT2 regulations limit the level of benzene, a known carcinogen, in gasoline sold in the United States to an average of 0.62% of the total liquid volume of the gasoline.
[0003] It is believed that a typical reforming process might result in a reformate that has approximately 10% or less by weight of benzene. Generally, in a reforming process light petroleum distillate is contacted with catalyst in the presence of hydrogen at high temperatures to produce a high-octane liquid effluent that is rich aromatic compounds. Typically, there are a series of reactors in which the feedstock passes. After a reactor effluent from the last reactor is cooled, it is typically sent to a separator where a part of overhead vapor can be compressed and recycled to the reactor. The remaining reactor effluent can be sent to a product recovery section which includes passing the reactor effluent through various processing units and separating units some of which are designed to remove the benzene from the reactor effluent.
[0004] While current processes may be successful at obtaining appropriate benzene levels in separation steps of the entire process, the current methods require large amounts of heat and energy input. Additionally such methods typically also require large equipment sizes.
[0005] Additionally, competition in the gasoline refining industry constantly demands development of more energy efficient processing technology and methods--especially technology and methods that can competitively meet the current requirements.
[0006] Finally, beyond the current standards, future government regulations may further limit the amount of benzene in gasoline to an even lower level--creating a greater challenge for refiners and producers.
[0007] Therefore, it would be desirable to have a process that can effectively and efficiently separate benzene from a reactor effluent.
SUMMARY OF THE INVENTION
[0008] Accordingly, in an embodiment of the present invention, a method for separating benzene from a reactor effluent is provided in which a reactor effluent is recovered from a reaction zone. The reactor effluent includes at least benzene. The reactor effluent is passed to a first separation zone to separate the reactor effluent into an overhead stream and a bottom stream. It is contemplated that the reactor effluent is cooled prior to passing from the reactor effluent to the first separation zone.
[0009] The first separation zone has an operating temperature. In some embodiments of the present invention, it is contemplated that the operating temperature of the first separation zone is between 65.degree. C. to 130.degree. C., and preferably between 85.degree. C. to 110.degree. C.
[0010] In some embodiments of the present invention, a temperature of the reactor effluent as it is passed to the first separation zone is measured. Based upon the temperature of the reactor effluent, the operating temperature of the first separation zone may be adjusted.
[0011] The overhead stream from the first separation zone is recovered from the first separation zone and cooled to produce a cooled overhead stream. The cooled overhead stream is passed to a second separation zone to separate the cooled overhead stream into a benzene rich bottom stream and a second overhead stream.
[0012] The second separation zone has an operating temperature lower than the operating temperature of the first separation zone. It is preferred that the operating temperature of the second separation zone is approximately ambient temperature.
[0013] The benzene rich bottom stream from the second separation zone may be recovered and passed to a debutanizer or a recontact zone or both.
[0014] It is further contemplated to recover the second overhead stream from the second separation zone and pass it to a recontact zone. In the recontact zone, the second overhead stream is separated into a recontact light stream and a recontact bottom stream. The recontact bottom stream may be recovered from the recontact zone and passed to a debutanizer.
[0015] In other embodiments of the present invention, a method for separating benzene from a reactor effluent is provided in which a naphtha feedstock is reacted in the presence of a catalyst in a reaction zone to produce a reactor effluent. Again, the reactor effluent includes at least benzene. The reactor effluent is recovered from the reaction zone and passed to a first separation zone.
[0016] In the first separation zone, the reactor effluent is separated into an overhead stream and a bottom stream. Again, the first separation zone may have an operating temperature between 65.degree. C. to 130.degree. C., and preferably between 85.degree. C. to 110.degree. C., and an operating pressure between approximately 345 to 689 KPa (approximately 50 to 100 psi). In a preferred embodiment of the present invention, a temperature of the reactor effluent is measured, and an operating temperature of the first separation zone is controlled and adjusted based upon the temperature of the reactor effluent.
[0017] The bottom stream includes mostly hydrocarbons containing seven carbons or more. The bottom stream is recovered from the first separation zone.
[0018] The overhead stream from the first separation zone includes mostly hydrocarbons containing six carbons or less. The overhead stream is also recovered from the first separation zone and may be cooled to a temperature of approximately 40.degree. C. to produce a cooled overhead stream. Thereafter, the cooled overhead stream is passed to a second separation zone.
[0019] In the second separation zone, the cooled overhead stream is separated into a benzene rich bottom stream and a second overhead stream. In some embodiments, the first separation zone has an operating temperature that is higher than the operating temperature of the second separation zone. The second separation zone may have an operating temperature that is an ambient temperature
[0020] It is further contemplated that the second overhead stream is recovered from the second separation zone and passed to a recontact zone. In the recontact zone, the second overhead stream is compressed and separated into a recontact light stream and a recontact bottom stream. The recontact zone may have an operating pressure between approximately 2760 to 3450 KPa (approximately 400 to 500 psi). The recontact bottom stream may be recovered from the recontact zone and passed to a debutanizer. Additionally, the recontact light stream may also be recovered from the recontact zone and passed to a hydrogen purification unit.
[0021] In one or more embodiments of the present invention, the benzene rich bottom stream includes approximately 80% of a total benzene amount in the reactor effluent. It is contemplated that the bottom stream of the first separation zone includes less than 15% of a total benzene amount in the reactor effluent and preferably between approximately 5 to 10% of a total benzene amount in the reactor effluent.
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