Gas separation: processes – Liquid contacting – Inorganic gas – liquid particle – or solid particle sorbed
Reexamination Certificate
2000-03-30
2002-03-05
Smith, Duane (Department: 1724)
Gas separation: processes
Liquid contacting
Inorganic gas, liquid particle, or solid particle sorbed
C423S220000, C423S437100
Reexamination Certificate
active
06352576
ABSTRACT:
FIELD OF THE INVENTION
The field of this invention is selective absorption of CO
2
gas.
INTRODUCTION
In many applications where mixtures of two or more gaseous components are present, it is often desirable to selectively remove one or more of the component gases from the gaseous stream. Of increasing interest in a variety of industrial applications, including power generation, chemical synthesis, natural gas upgrading, and conversion of methane hydrates to hydrogen and CO
2
, is the selective removal of CO
2
from multicomponent gaseous streams.
An example of where selective CO
2
removal from a multicomponent gaseous stream is desirable is the processing of synthesis gas or syngas. Syngas is a mixture of hydrogen, carbon monoxide and CO
2
that is readily produced from fossil fuels and finds use both as a fuel and as a chemical feedstock. In many applications involving syngas, the carbon monoxide is converted to hydrogen and additional CO
2
via the water-gas shift process. It is then often desirable to separate the CO
2
from the hydrogen to obtain a pure H
2
stream for subsequent use, e.g. as a fuel or feedstock.
As man made CO
2
is increasingly viewed as a pollutant, another area in which it is desirable to separate CO
2
from a multicomponent gaseous stream is in the area of pollution control. Emissions from industrial facilities, such as manufacturing and power generation facilities, often include CO
2
. In such instances, it is often desirable to at least reduce the CO
2
concentration of the emissions. The CO
2
may be removed prior to combustion in some cases and post combustion in others.
A variety of processes have been developed for removing or isolating a particular gaseous component from a multicomponent gaseous stream. These processes include cryogenic fractionation, selective adsorption by solid adsorbents, gas absorption, and the like. In gas absorption processes, solute gases are separated from gaseous mixtures by transport into a liquid solvent. In such processes, the liquid solvent ideally offers specific or selective solubility for the solute gas or gases to be separated.
Gas absorption finds widespread use in the separation of CO
2
from multicomponent gaseous streams. In CO
2
gas absorption processes that currently find use, the following steps are employed: (1) absorption of CO
2
from the gaseous stream by a host solvent, e.g. monoethanolamine; (2) removal of CO
2
from the host solvent, e.g. by steam stripping; and (3) compression of the stripped CO
2
for disposal, e.g. by sequestration through deposition in the deep ocean or ground aquifers.
Although these processes have proved successful for the selective removal of CO
2
from a multicomponent gaseous stream, they are energy intensive. For example, using the above processes employing monoethanolamine as the selective absorbent solvent to remove CO
2
from effluent flue gas generated by a power plant often requires 25 to 30% of the available energy generated by the plant. In most situations, this energy requirement, as well as the additional cost for removing the CO
2
from the flue gas, is prohibitive.
Accordingly, there is continued interest in the development of less energy intensive processes for the selective removal of CO
2
from multicomponent gaseous streams. Ideally, alternative CO
2
removal processes should be simple, require inexpensive materials and low energy inputs, and be low in cost for separation and sequestration of the CO
2
. Of particular interest would be the development of a process which provided for efficient CO
2
separation at low temperature (e.g. 0 to 10° C.) from low CO
2
partial pressure multicomponent gaseous streams.
Relevant Literature
Patents disclosing methods of selectively removing one or more components from a multicomponent gaseous stream include: U.S. Pat. Nos. 3,150,942; 3,359,744; 3,479,298; 3,838,553; 4,253,607; 4,861,351; 5,397,553; 5,434,330; 5,562,891; 5,600,044 and 5,700,311.
Other publications discussing CO
2
clathrate formation include Japanese unexamined patent application 3-164419; Austvik & Loken, “Deposition of CO
2
on the Seabed in the Form of Clathrates, ” Energy Convers. Mgmt. (1992) 33: 659-666; Golumb et al., “The Fate of CO
2
Sequestered in the Deep Ocean,” Energy Convers. Mgmt. (1992) 33: 675-683; Morgan et al., “Hydrate Formation from Gaseous CO
2
and water,” Environmental Science and Technology (1999) 33: 1448-1452; Nishikawa et al., “CO
2
Clathrate Formation and its Properties in the Simulated Deep Ocean,” Energy Convers. Mgmt. (1992) 33:651-657; Saji et al., “Fixation of Carbon Dioxide by Clathrate-Hyrdrate,” Energy Convers. Mgmt. (1992) 33: 643-649; Spencer, “A preliminary Assessment of Carbon Dioxide Mitigation Options,” Annu. Rev. Energy Energy Environ. (1991) 16: 259-273; Spencer & North, “Ocean Systems for Managing the Global Carbon Cycle,” Energy Convers. Mgmt. (1997) 38 Suppl.: 265-272; and Spencer & White, “Sequestration Processes for Treating Multicomponent Gas Streams,” Proceedings of 23
rd
Coal and Fuel Systems Conference, Clearwater, Fla. (March 1998).
SUMMARY OF THE INVENTION
Methods are provided for the selective removal of CO
2
from a multicomponent gaseous stream to provide a CO
2
depleted gaseous stream having at least a reduction, e.g. 20%, in the concentration of CO
2
relative to the untreated multicomponent gaseous stream. In practicing the subject methods, the multicomponent gaseous stream is contacted with an aqueous fluid, e.g. CO
2
nucleated (or structured) water, under conditions of selective CO
2
clathrate formation to produce a CO
2
clathrate slurry and CO
2
depleted gaseous stream. A feature of the subject invention is that a CO
2
hydrate promoter is employed, where the CO
2
hydrate promoter is included in the multicomponent gaseous stream and/or the aqueous fluid. The CO
2
hydrate promoter serves to reduce the minimum CO
2
partial pressure required for formation of CO
2
containing hydrates (i.e. CO
2
hydrates) as compared to a control using pure CO
2
gas and water. The subject methods find use in a variety of applications where it is desired to selectively remove CO
2
from a multicomponent gaseous stream.
DETAILED DESCRIPTION OF THE INVENTION
Methods are provided for the selective removal of CO
2
from a multicomponent gaseous stream to provide a CO
2
depleted gaseous stream having at least a reduction, e.g. 30 to 90%, in the concentration of CO
2
relative to the untreated multicomponent gaseous stream. In practicing the subject methods, the multicomponent gaseous stream is contacted with an aqueous fluid, e.g. CO
2
nucleated (or structure) water, under conditions of selective CO
2
clathrate formation to produce a CO
2
clathrate slurry and CO
2
depleted gaseous stream. A feature of the subject invention is that a CO
2
hydrate promoter is employed, where the CO
2
hydrate promoter is included in the multicomponent gaseous stream and/or the aqueous fluid. The CO
2
hydrate promoter serves to reduce the minimum CO
2
partial pressure required for formation of CO
2
containing hydrates as compared to a control using pure CO
2
and water. The subject methods find use in a variety of applications where it is desired to selectively remove CO
2
from a multicomponent gaseous stream.
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patent: 5277038 (1994-01-01), Carr
patent: 5364611 (1994-11-01), Iijima et al.
patent: 5397553 (1995-03-01), Spencer
patent: 5434330 (1995-07-01), Hnatow et al.
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patent: 5562891 (1996-10-01), Spencer et al.
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patent: 3-164419 (1991-07-01), None
Austvick et al. (19
Currier Robert P.
Spencer Dwain F.
Bozicevic, Field & Francis
Field Bret E.
Greene Jason M.
Smith Duane
The Regents of the University of California
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