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US-12623987-B2 - Removal of C3 lights from LPG feedstock to butane isomerization unit

US12623987B2US 12623987 B2US12623987 B2US 12623987B2US-12623987-B2

Abstract

Systems and methods for processing a C 3 and C 4 hydrocarbon mixture have been disclosed. The C 3 and C 4 hydrocarbon mixture is first processed in an isomerization unit to isomerize n-butane to form isobutane. The resulting effluent stream from the isomerization unit comprising primarily isobutane and C 3 hydrocarbons, collectively, is flowed into a separation unit configured to separate the effluent stream to form a C 3 stream comprising C 1 to C 3 hydrocarbons and a C 4 stream comprising primarily isobutane. The isobutane in the C 4 stream is further dehydrogenated to form isobutene, which is further flowed into an MTBE synthesis unit as a feedstock for producing MTBE.

Inventors

  • Vijay Dinkar BODAS
  • Guillermo LEAL CANELON
  • Mohammed Bismillah ANSARI

Assignees

  • SABIC GLOBAL TECHNOLOGIES B.V.

Dates

Publication Date
20260512
Application Date
20210716
Priority Date
20200717

Claims (17)

  1. 1 . A method of processing a hydrocarbon mixture, the method comprising: processing a first hydrocarbon mixture comprising propane, n-butane, and isobutane in an isomerization unit at a temperature of 125 to 175° C. to isomerize the n-butane to produce isobutane; separating a mixture from the isomerization unit by a de-isobutanizer to produce and form an isomerization unit effluent comprising propane, isobutane, or combinations thereof and an unreacted n-butane stream; separating a second hydrocarbon mixture comprising propane, n-butane, and isobutane in a second separation unit to produce an overhead stream comprising primarily propane and isobutane, collectively, and a first C4 stream comprising n-butane; cracking the first C4 stream and/or the unreacted n-butane stream in a first steam cracking unit to produce propylene, ethylene, and benzene; combining the overhead stream and the isomerization unit effluent to form a combined stream; separating the combined stream to form a C3 stream comprising primarily propane and a second C4 stream comprising isobutane; dehydrogenating the isobutane of the second C4 stream in a dehydrogenation unit to produce isobutene in a dehydrogenation unit effluent; and reacting, in an etherification unit, the isobutene of the dehydrogenation unit effluent with an alkanol in the presence of a catalyst to produce an alkyl tert-butyl ether in a product stream.
  2. 2 . The method of claim 1 , further comprising: steam-cracking the C3 stream in a first second steam cracking unit.
  3. 3 . The method of claim 2 , wherein the steam cracking of the second C3 stream is performed at a temperature of 750 to 900° C. and a steam cracker residence time of 0.1 to 0.5 s.
  4. 4 . The method of claim 1 , wherein the isomerization unit comprises an isomerization catalyst comprising Pt/AlCl 3 /Al 2 O 3 , Pt/AlCl 3 /zeolite, Pt/SO 4 2− —ZrO 2 , SO 4 2− /ZrO 2 —Al 2 O 3 , or combinations thereof.
  5. 5 . The method of claim 1 , wherein the reaction conditions in the isomerization unit include an isomerization pressure of 20 to 30 bar.
  6. 6 . The method of claim 1 , wherein the isomerization unit effluent comprises 95 to 99.5 wt. % isobutane.
  7. 7 . The method of claim 1 , wherein the dehydrogenation unit effluent comprises 35 to 65 wt. % isobutene.
  8. 8 . The method of claim 1 , wherein the first hydrocarbon mixture and/or the second hydrocarbon mixture comprises liquefied petroleum gas.
  9. 9 . The method of claim 1 , wherein the first hydrocarbon mixture comprises 60 to 80 wt. % n-butane and 20 to 30 wt. % isobutane.
  10. 10 . The method of claim 1 , wherein the etherification unit further produces a recycle stream comprising isobutane.
  11. 11 . The method of claim 10 , further comprising: flowing the recycle stream into the dehydrogenation unit.
  12. 12 . The method of claim 1 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.
  13. 13 . The method of claim 1 , wherein the alkanol comprises methanol, ethanol, or combinations thereof.
  14. 14 . The method of claim 13 , wherein the alkyl tert-butyl ether comprises MTBE, ETBE, or combinations thereof.
  15. 15 . The method of claim 5 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.
  16. 16 . The method of claim 4 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.
  17. 17 . The method of claim 1 , wherein the dehydrogenation unit comprises a dehydrogenation catalyst comprising chromia/alumina, Pt/alumina, or combinations thereof.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a national phase under 35 U.S.C. § 371 of International Application No. PCT/IB2021/056455, filed Jul. 16, 2021, which claims the benefit of priority to European Patent Application No. 20186357.8, filed Jul. 17, 2020, the entire contents of which are hereby incorporated by reference in their entirety. FIELD OF INVENTION The present invention generally relates to a process of producing alkyl tert-butyl ether. More specifically, the present invention relates to a process of producing alkyl tert-butyl ether using liquefied petroleum gas as a feedstock. BACKGROUND OF THE INVENTION MTBE is an organic compound that is used as an additive in gasoline to enhance the octane number of the gasoline. Since about 1970, MTBE has been synthesized by etherification of isobutylene by reaction with methanol in the presence of an acidic catalyst. Isobutylene used for MTBE synthesis can be obtained from C4 hydrocarbons. Generally, isobutylene and methanol are fed into a fixed bed reactor to produce an MTBE containing effluent. The effluent is then fed to a reaction column to react isobutylene remaining in the effluent with additional methanol to produce more MTBE. One of the sources for the C4 hydrocarbons used in the MTBE production process can include liquefied petroleum gas, which includes primarily C4 and C3 hydrocarbons. The liquefied petroleum gas is processed in an isomerization unit and then by a dehydrogenation unit to produce isobutylene. The effluent stream from the dehydrogenation unit(s) is then flowed to an MTBE synthesis unit to react with methanol for producing MTBE. However, the reaction efficiency in the isomerization unit(s) and/or dehydrogenation unit(s) is relatively low when liquefied petroleum gas is used as the feedstock, resulting in high production cost for MTBE. Overall, while systems and methods for producing MTBE from a C4 and C3 hydrocarbon mixture (e.g., liquefied petroleum gas) exist, the need for improvements in this field persists in light of at least the aforementioned drawback for the conventional systems and methods. BRIEF SUMMARY OF THE INVENTION A solution to at least the above mentioned problem associated with the systems and methods for producing MTBE from a C4 and C3 hydrocarbon mixture (e.g., liquefied petroleum gas) has been discovered. The solution resides in a method for processing a hydrocarbon mixture that includes C4 and C3 hydrocarbons. The method includes processing the hydrocarbon mixture in an isomerization unit to produce isobutane, separating an effluent from the isomerization unit to form a C3 stream comprising propane and a C4 stream comprising isobutane, and dehydrogenating the isobutane, in the C4 stream, in a dehydrogenation unit, to produce isobutene. An effluent from the dehydrogenation unit is further flowed into an etherification unit for producing alkyl tert-butyl ether. This can be beneficial for at least reducing the inert portion in the feed stream flowed into the isomerization unit and/or the dehydrogenation unit, thereby increasing the reaction efficiency for dehydrogenating isobutane. Furthermore, the disclosed method can reduce or eliminate the large amount of propane in the effluent stream of the dehydrogenation unit, resulting in a feed stream with higher concentration of isobutene being flowed into the MTBE synthesis unit. Hence, the disclosed method is capable of increasing the reaction efficiency in the etherification unit, and reducing the amount of gas that is recycled back to the dehydrogenation unit, resulting in reduced production cost for alkyl tert-butyl ether. Therefore, the systems and methods of the present invention provide a technical solution to at least some of the problems associated with the conventional systems and methods for alkyl tert-butyl ether production as mentioned above. Embodiments of the invention include a method of processing a hydrocarbon mixture. The method comprises processing a hydrocarbon mixture comprising propane, n-butane, and isobutane in an isomerization unit under reaction conditions sufficient to isomerize the n-butane to produce isobutane and form an isomerization unit effluent comprising propane, isobutane, or combinations thereof. The method further comprises separating the isomerization unit effluent to form a C3 stream comprising propane and a C4 stream comprising isobutane. The method further comprises steam cracking the propane of the C3 stream under reaction conditions sufficient to produce propylene. The method further comprises dehydrogenating the isobutane of the C4 stream in a dehydrogenation unit to produce isobutene in a dehydrogenation unit effluent. The method further comprises reacting, in an etherification unit, the isobutene of the dehydrogenation unit effluent with an alkanol in the presence of an etherification catalyst under reaction conditions sufficient to produce alkyl tert-butyl ether in an etherification unit effluent. Embodi