Tail gas utilization for mixed alcohols production
It has been discovered that mixed-alcohol production can utilize the waste tail gas stream from the pressure-swing adsorption section of an industrial hydrogen plant. Some variations provide a process for producing mixed alcohols, comprising: obtaining a tail-gas stream from a methane-to-syngas unit (e.g., a steam methane reforming reactor); compressing the tail-gas stream; separating the tail-gas stream into at least a syngas stream, a CO 2 -rich stream, and a CH 4 -rich stream; introducing the syngas stream into a mixed-alcohol reactor operated at effective alcohol synthesis conditions in the presence of an alcohol-synthesis catalyst, thereby generated mixed alcohols; and purifying the mixed alcohols to generate a mixed-alcohol product. Other variations provide a process for producing clean syngas, comprising: obtaining a tail-gas stream from a methane-to-syngas unit; compressing the tail-gas stream; separating the tail-gas stream into at least a syngas stream, a CO 2 -rich stream, and a CH 4 -rich stream; and recovering a clean syngas product.
1. A process for producing mixed alcohols, said process comprising:
(a) obtaining a tail-gas stream from a methane-to-syngas unit, wherein said tail-gas stream comprises CO 2 , CO, H 2 , and CH 4 ;
(b) compressing said tail-gas stream;
(c) separating said tail-gas stream into at least a syngas stream, a H 2 -rich stream, a CO 2 -rich stream, and a CH 4 -rich stream;
(d) introducing said syngas stream into a mixed-alcohol reactor operated at effective alcohol synthesis conditions and in the presence of an alcohol-synthesis catalyst, thereby generated mixed alcohols and a reactor off-gas; and
(e) purifying said mixed alcohols to generate a mixed-alcohol product, wherein said purifying includes one or more of sulfur removal, dehydration, and distillation.
2. The process of claim 1 , wherein said tail-gas stream is an output of a first pressure-swing adsorption unit.
3. The process of claim 1 , wherein said CO 2 -rich stream is compressed and used in enhanced oil recovery.
4. The process of claim 1 , wherein said CO 2 -rich stream is sequestered in a geological formation.
5. The process of claim 1 , wherein said CH 4 -rich stream is utilized as a fuel for heating said methane-to-syngas unit.
6. The process of claim 1 , wherein said H 2 -rich stream is recovered and sold.
7. The process of claim 1 , wherein said H 2 -rich stream is combined with hydrogen produced from said methane-to-syngas unit.
8. The process of claim 1 , wherein said H 2 -rich stream is utilized as a fuel for heating said methane-to-syngas unit.
9. The process of claim 1 , wherein step (c) further generates a N 2 stream that is released to the atmosphere.
10. The process of claim 1 , wherein step (c) utilizes an amine-based system, a cryogenic system, a membrane-separation system, a second pressure-swing adsorption unit, or a combination thereof.
11. The process of claim 1 , wherein in step (d), said alcohol-synthesis catalyst is a metal sulfide catalyst.
12. The process of claim 1 , wherein said reactor off-gas is recycled to step (c).
13. The process of claim 12 , wherein said reactor off-gas is treated in a H 2 S removal unit prior to recycling to step (c).
14. A system for producing mixed alcohols, said system comprising:
a tail-gas compression sub-system configured to receive a tail-gas stream from a methane-to-syngas unit, wherein said tail-gas stream comprises CO 2 , CO, H 2 , and CH 4 , and wherein said tail-gas compression sub-system is configured to form a compressed tail-gas stream;
a tail-gas separation sub-system in flow communication with said tail-gas compression sub-system, wherein said tail-gas separation sub-system is configured to separate said compressed tail-gas stream into at least a syngas stream, a H 2 -rich stream, a CO 2 -rich stream, and a CH 4 -rich stream;
a mixed-alcohol reaction sub-system configured to receive at least a portion of said syngas stream, and wherein said mixed-alcohol reaction sub-system is configured to generate mixed alcohols;
a mixed-alcohol purification sub-system configured to receive said mixed alcohols, wherein said mixed-alcohol purification sub-system contains a sulfur-removal unit, a dehydration unit, a distillation unit, or a combination thereof, and wherein said mixed-alcohol purification sub-system is configured to purify said mixed alcohols to generate purified mixed alcohols; and
a system outlet configured for recovering a mixed-alcohol product.
15. The system of claim 14 , wherein said tail-gas separation sub-system includes an amine-based unit, a cryogenic unit, a membrane-separation unit, a pressure-swing adsorption unit, or a combination thereof.
16. The system of claim 14 , wherein said mixed-alcohol reaction sub-system contains a metal sulfide catalyst.