Methods for removing oxyanions from water according to the following steps: (i) dissolving an oxyanion precipitating compound into the aqueous source to result in precipitation of an oxyanion salt of the oxyanion precipitating compound; and (ii) removing the oxyanion salt from the water containing the oxyanion to result in water substantially reduced in concentration of the oxyanion; wherein the oxyanion precipitating compound has the following composition:

##STR00001##

wherein A is a ring-containing moiety and X.sup.m is an anionic species with a magnitude of charge m. The invention employs bis-iminoguanidinium compounds according to Formula (1a) as well as neutral precursor compounds according to Formula (1), which can be used for removing undesirable species from aqueous solutions or air, such as removal of sulfate from water and carbon dioxide from air.

Solvent absorption processes for separating components of an impure feed gas are disclosed. The processes involve two stages of gas purification. The acid gases including hydrogen sulfide, carbon dioxide and other sulfur compounds are simultaneously removed from the feed gas by contact with a physical solvent in two stages. The subject matter disclosed provides improved processes to reduce the operating costs of the system.

The invention provides a process for regenerating a liquid absorbent, comprising: contacting the liquid absorbent with a hydrophobic medium, wherein the liquid absorbent comprises at least one amine of Formula (I) and degradation product thereof comprising at least one imine of Formula (II), wherein each Ar is independently an aromatic group and each R is independently selected from hydrogen, an organyl group and NH.sub.2; and selectively extracting the degradation product into or through the hydrophobic medium. ##STR00001##

A class of water lean, organic solvents that can bind with various acid gasses to form acid gas bound molecules having a high degree of intramolecular hydrogen bonding which enables their use as regenerable solvents for acid gas capture. Unlike the other devices described in the prior art, the present invention takes advantage of shortened distances between the portions of the molecule that form hydrogen bonds within the structures when loaded with an acid gas so as to create a molecule with a higher internal bonding affinity and a reduced proclivity for agglomeration with other molecules.

The present disclosure relates to electrochemical target species (e.g., carbon dioxide) capture and release with a redox-active amine. Associated systems and articles are also described.

Methods for removing oxyanions from water according to the following steps: (i) dissolving an oxyanion precipitating compound into the aqueous source to result in precipitation of an oxyanion salt of the oxyanion precipitating compound; and (ii) removing the oxyanion salt from the water containing the oxyanion to result in water substantially reduced in concentration of the oxyanion; wherein the oxyanion precipitating compound has the following composition:

##STR00001##

wherein A is a ring-containing moiety and X.sup.m is an anionic species with a magnitude of charge m. The invention employs bis-iminoguanidinium compounds according to Formula (1a) as well as neutral precursor compounds according to Formula (1), which can be used for removing undesirable species from aqueous solutions or air, such as removal of sulfate from water and carbon dioxide from air.

A process for absorbing carbon dioxide from a gas stream containing carbon dioxide, including the steps of contacting the gas stream with an aqueous composition including a substituted heteroaromatic compound having a six-membered heteroaromatic ring with from 1 to 3 nitrogen atoms in the heteroaromatic ring and at least one substituent wherein at least one of the substituents is of formula R.sup.1NH.sub.2 wherein R.sup.1 is selected from C1 to C6 alkylene and ethers of formula R.sup.2OR.sup.3 wherein R.sub.2 and R.sub.3 are C.sub.1 to C.sub.3 alkylene

A process for removing sulfur dioxide from a feed gas stream, which comprises (i) contacting the feed gas stream with an aqueous lean absorbing medium comprising a chemical solvent comprising a regenerable absorbent, a physical solvent, and one or more heat stable salts. The regenerable absorbent is an amine. The ratio of the wt % of the physical solvent over that of the regenerable absorbent is 0.5 to 2.5. The ratio of the wt % of heat stable salts over that of the regenerable absorbent is 0.29 to 0.37. The pH of the lean absorbing medium is 6 or less. With the process SO2 can be selectively removed. When the absorbing medium is stripped, a reduced amount of energy is required as compared to known processes.

A carbon dioxide recovery system includes an absorption tower in which carbon dioxide is absorbed into an absorbing solution then the absorbing solution is output to a regeneration tower in which carbon dioxide is released from the absorbing solution. The regeneration tower outputs the absorbing solution from which carbon dioxide has been released and an exhaust gas included released carbon dioxide and water vapor. In a condensing section the exhaust gas is separated into dioxide gas stream and a condensed water stream. In a mixing section the condensed water is mixed with an amine to a replenishment amine aqueous solution in which the amine is dissolved in the condensed water. In a replenishment section the absorbing solution is mixed with the replenishment amine aqueous solution.

A class of water lean, organic solvents that can bind with various acid gasses to form acid gas bound molecules having a high degree of intramolecular hydrogen bonding which enables their use as regenerable solvents for acid gas capture. Unlike the other devices described in the prior art, the present invention takes advantage of shortened distances between the portions of the molecule that form hydrogen bonds within the structures when loaded with an acid gas so as to create a molecule with a higher internal bonding affinity and a reduced proclivity for agglomeration with other molecules.