Front-end hydrogenation and absorption process for ethylene recovery

• US 5,220,097 A
• Filed: 02/19/1992
• Issued: 06/15/1993
• Est. Priority Date: 02/19/1992
• Status: Expired due to Term

• Current Assignee: Advanced Extraction Technologies, Inc., Kinetics Technology International
• Original Assignee: Advanced Extraction Technologies, Inc., Kinetics Technology International
• Inventors: Mullins, Don W., Mehra, Yuv R., Lam, Wilfred K.
• Primary Examiner(s): McFarlane, Anthony
• Assistant Examiner(s): Phan, Nhat
• Application Number:
  US07/836,911
• Time in Patent Office: 482 Days
• Field of Search: 585/809, 585/802, 585/833, 585/259, 62/24, 62/17
• US Class Current: 585/809
• CPC Class Codes: C10G 5/04 with liquid absorbents
• CPC Class Codes: C10G 70/041 by distillation
• CPC Class Codes: C10G 70/06 by gas-liquid contact

Abstract

A continuous process is described for contacting an olefins-containing feed gas stream, freed of CO₂ and sulfur compounds, in a front-end heat-pumped depropanizer to remove the C₄₊ compounds, selectively hydrogenating the overhead stream to significantly reduce the acetylene and diolefins content, dehydrating the reactor effluent to remove traces of moisture, feeding the dehydrated stream to an intercooled and reboiled demethanizing absorber to produce a rich solvent containing ethylene and heavier hydrocarbons, feeding the absorber overhead stream to an auto refrigerated recovery unit to remove hydrogen, methane, and CO as overhead to a fuel gas system, separating the rich solvent in a solvent regenerator into an overhead stream of ethylene and heavier hydrocarbons and a bottom lean solvent stream for recycle to the demethanizing absorber, combining the overhead of the solvent regenerator with the bottoms of the demethanizer in the auto refrigerated recovery unit, and feeding the combined stream to a deethanizer which produces an overhead stream that is split into ethylene as product and ethane for recycling to the cracker.

Claims

1. A process for recovering ethylene from a stream of feedstock gases selected from the group consisting of cracked hydrocarbon gases and refinery off-gases, comprising removing at least 75% of said ethylene in a solvent-based, demethanizing absorber, prior to an auto refrigerated recovery unit which recovers the remainder of said ethylene from said feedstock gases.

2. The process of claim 1, wherein said demethanizing absorber removes 75-95% of said ethylene from said feedstock gases.

3. The process of claim 1, wherein said absorber is preceded by a selective catalytic hydrogenation reactor which substantially reduces acetylenes and diolefins in said gases.

4. The process of claim 3, wherein said reactor is preceded by a front-end depropanizer which receives said feedstock gases and removes C₄₊ hydrocarbons therefrom.

5. The process of claim 4, wherein chilling and phase separation is interposed between said reactor and said absorber, producing a liquid stream which is recycled t said depropanizer.

6. A process for recovering ethylene from a cooled, sweetened, and compressed hydrocarbon gas stream containing hydrogen, methane, carbon monoxide, ethane, ethylene, acetylene, and C₃ and heavier hydrocarbons characteristic of ethylene plant cracked gas and/or a refinery off gas stream, said process comprising:

A. feeding said hydrocarbon gas stream to a heat-pumped depropanizer and producing therefrom a bottom stream of C₄₊ hydrocarbons and an overhead stream of C₃ and lighter hydrocarbons;

B. feeding said overhead stream to a selective hydrogenation reactor to produce a reactor effluent stream containing reduced amounts of acetylene and diolefins;

C. feeding said reactor effluent stream to a dehydrator to remove trace quantities of water formed in the reactor;

D. feeding the dried reactor effluent stream produced by said Step C through at least one cooler and separating said stream into a vapor stream and a liquid stream that is recycled to said depropanizer;

E. feeding said vapor stream to an intercooled and reboiled demethanizing absorber and producing therefrom a bottom stream of rich solvent containing most of said ethylene and heavier hydrocarbons present in said vapor stream and an overhead stream containing said hydrogen, said methane, said carbon monoxide, and the remainder of said ethylene and heavier hydrocarbons;

F. feeding said overhead stream to a auto refrigerated recovery unit which is cryogenically cooled and producing therefrom an overhead stream of hydrogen, methane, and carbon monoxide having less than 0.5% of said ethylene and a bottom stream containing substantially all of the remainder of the said ethylene and heavier hydrocarbons;

G. feeding said rich solvent of Step E to a solvent regenerator and obtaining therefrom a bottom stream of lean solvent which is recycled to the top of said demethanizing absorber and an overhead hydrocarbon stream of said ethylene and heavier hydrocarbons;

H. combining said overhead hydrocarbon stream of step G with said bottom stream from said auto refrigerated recovery unit of step F and feeding said combined stream to a deethanizer which produces a bottom stream of propylene and heavier hydrocarbons and an overhead stream of ethylene and ethane; and

I. feeding said overhead stream of said ethylene and ethane to a C2 splitter and producing therefrom a bottom stream of ethane and an overhead stream of ethylene as product.

7. The process of claim 6, wherein said bottom stream of propylene and heavier hydrocarbons from said deethanizer is fed to a C3 splitter which produces propylene and propane.

8. The process of claim 7, wherein said hydrocarbon gas feed stream is a cracked gas stream, and said ethane and said propane are recycled for cracking.

9. A process of claim 6, wherein said hydrocarbon gas feed stream is a refinery off-gas stream, and said ethane and propane are used as fuel.

10. The process of claim 6, wherein said hydrocarbon gas feed stream is a refinery off-gas stream, and said ethane and propane are disposed of as products.

11. The process of claim 6, wherein said hydrocarbon gas feed stream is a cracked gas stream and said ethane and propane are used as fuel.

12. The process of claim 6, wherein said hydrocarbon gas feed stream is a cracked gas stream and said ethane and propane are disposed of as products.

14. The process of claim 9, wherein said hydrocarbon gas feed stream is a cracked gas stream and said ethane is recycled for cracking.

13. A process for recovering ethylene from a cracked, cooled, sweetened and compressed hydrocarbon gas stream containing hydrogen, methane, carbon monoxide, ethylene, ethane, acetylene, and C₃ and heavier hydrocarbons characteristic of an ethylene plant cracked gas and/or a refinery off gas stream which comprises:

A. feeding said hydrocarbon gas stream to a deethanizer fractionation column and producing therefrom a bottom stream of C₃ + hydrocarbons and an overhead stream of C₂ and lighter hydrocarbons plus a small fraction of C₃ hydrocarbons;

B passing said overhead stream through a compressor to produce a compressed overhead stream;

C. passing said compressed overhead stream through a cooler and/or heater to achieve the required inlet condition for said selective hydrogenation reactor to produce a reactor effluent stream containing reduced amounts of acetylenes and diolefins;

D. passing said reactor effluent stream through a drier to remove trace quantities of water formed in the reactor;

E. passing said dried reactor effluent stream through at least one cooler and separating said effluent stream into a liquid stream that is recycled to said deethanizer column and a vapor stream;

F. feeding said vapor stream to an intercooled and reboiled demethanizing absorber and producing therefrom a bottom stream of rich solvent containing most of said ethylene and heavier hydrocarbons present in said vapor stream and an overhead stream containing said hydrogen, said methane, said carbon monoxide, and some C₂ and heavier hydrocarbons;

G. feeding said overhead stream of Step F to an auto refrigerated recovery unit which is cryogenically cooled and producing therefrom an overhead stream of hydrogen, methane, and carbon monoxide having less than 0.5% of said ethylene and a bottom stream containing substantially all of the remainder of said ethylene and heavier hydrocarbons;

H. feeding said rich solvent to a solvent regenerating column and obtaining therefrom a bottom stream of lean solvent which is recycled to the top of said demethanizing absorber column and an overhead hydrocarbon stream of said ethylene and heavier hydrocarbons; and

I. combining said overhead hydrocarbon stream of Step H with said bottom stream of Step G and feeding said combined stream to a C₂ splitter column and producing therefrom a bottom stream of ethane and an overhead stream of ethylene as product.

15. The process of claim 13, wherein said hydrocarbon gas feed stream is a refinery off-gas stream and said ethane and propane are used as fuel.

16. The process of claim 13, wherein said hydrocarbon gas feed stream is a refinery off-gas stream and said ethane and propane are disposed of as products.

17. In a process for recovery of olefins from hydrocarbon gases containing olefins by a demethanizing absorber with a preferential physical solvent, the improvement comprising:

A. pretreating said olefin-containing gases through a heat-pumped front-end deethanizer or a heat-pumped front-end depropanizer;

B. subsequently compressing an overhead stream from said deethanizer or said depropanizer; and

C. selectively catalytically hydrogenating said compressed gases to significantly reduce the acetylene and diolefins content thereof before feeding said gases to said demethanizing absorber.

18. In a process for producing ethylene from a gas stream selected from the group consisting of refinery off-gases and cracked hydrocarbon gases containing ethylene, the improvement comprising sequentially feeding respective overhead streams from a front-end heat-pumped depropanizer to a selective front-end catalytic acetylene hydrogenation reactor, from said reactor to a dehydrator, from said dehydrator to a chilling and phase separation unit which produces a reflux stream, from said chilling and phase separation unit to an intercooled and reboiled demethanizing absorber which produces a rich solvent bottom stream containing 75% to 95% of said ethylene, and from said absorber to an auto refrigerated recovery unit that produces an overhead fuel gas stream, containing no more than about 0.5% of the ethylene in said overhead stream from said chilling and phase separation unit to said demethanizing absorber, and a bottom stream that contains the remaining 5% to 25% of said ethylene, said bottom stream being combined with an overhead stream from a solvent regenerator, to which is fed said rich solvent bottom stream from said demethanizing absorber, to form a demethanized ethylene stream that is fed to a deethanizer which produces an overhead stream for feeding to a C₂ splitter column that produces ethylene product.

19. A process that:

(a) provides a means for reducing the concentration of acetylenes and diolefins in a feed gas stream to an absorber having intercooling and reboiling, (b) reduces the costs of recovering solvent from an overhead stream produced by said absorber, and (c) reduces the costs of ethylene recovery while utilizing said absorber, said process comprising;

A. treating a gas stream, selected from the group consisting of refinery off-gases and cracked hydrocarbon gases containing ethylene, in a heat-pumped deethanizer or depropanizer and coupling said deethanizer or depropanizer with a front-end catalytic acetylene hydrogenation reactor which produces an overhead effluent gas stream as said feed gas stream to said absorber;

B. feeding said overhead effluent gas stream from said reactor to said absorber which produces a bottom stream of rich solvent, containing 75% to 95% of the ethylene in said overhead effluent gas stream, and an overhead gas stream containing the remaining 5% to 25% of said ethylene;

C. feeding said overhead gas stream from said absorber to an auto refrigerated recovery unit to produce an overhead fuel gas stream containing no more than 0.5% of said ethylene in said overhead effluent gas stream and a bottom stream containing said 5% to 25% of said ethylene;

D. feeding said bottom stream of Step B to a solvent regenerator to produce a bottom stream of lean solvent which is recycled to said absorber and an overhead stream which contains said 75% to 95% of said ethylene; and

E. combining said bottom stream of Step C with said overhead stream of Step D to form an ethylene product stream.

20. The process of claim 19, wherein said auto refrigerated recovery unit requires no external cryogenic refrigeration for condensation of compounds in said bottom stream of Step C.