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.

An absorbent composition includes an amino-siloxane having structure (I): wherein R is independently at each occurrence a C.sub.1-C.sub.6 aliphatic or aromatic radical; R.sup.2 is independently at each occurrence a C.sub.2-C.sub.10 aliphatic or aromatic radical; R.sup.3 is independently at each occurrence a hydrogen atom or a C.sub.1-C.sub.6 aliphatic or aromatic radical; R.sup.4 is independently at each occurrence a C.sub.1-C.sub.18 aliphatic or aromatic radical or R.sup.5, wherein R.sup.5 comprises structure (II): wherein X is independently at each occurrence an oxygen atom or a sulfur atom; w is between 0 and 5; y is between 0 and 10; and z is between 0 and 10; wherein, when R.sup.4 is R.sup.5 comprising the structure (II), a sum of w, y, and z is greater than or equal to 0, and, when R.sup.4 is not R.sup.5, a sum of w, y, and z is greater than or equal to 1.

##STR00001##

The embodiments provide an acidic gas absorbent, an acidic gas removal method, and an acidic gas removal apparatus. The absorbent absorbs an acidic gas in a large amount and hardly diffuses in air. The acidic gas absorbent according to the embodiment comprises an amine compound having a sulfonyl group and two or more amino groups.

A method for removing carbon dioxide from a gaseous source, the method comprising: (i) contacting said gaseous source with an aqueous solution of a carbon dioxide sorbent that reacts with carbon dioxide to form an aqueous-soluble carbonate or bicarbonate salt of said carbon dioxide sorbent; (ii) contacting the aqueous solution from step (i) with a bis-iminoguanidine carbon dioxide complexing compound, which is different from the carbon dioxide sorbent, to result in precipitation of a carbonate or bicarbonate salt of said carbon dioxide complexing compound and regeneration of the carbon dioxide sorbent; and (iii) removing the precipitated carbonate or bicarbonate salt from the aqueous solution in step (ii) to result in a solid form of said carbonate or bicarbonate salt of the carbon dioxide complexing compound. The method may further include a step (iv) of regenerating the carbon dioxide complexing compound by subjecting the precipitated salt to sufficient heat and/or vacuum.

A gas treatment device uses a gas to be treated which contains an acid compound that dissolves into water to produce acid and a treatment liquid which absorbs the acid compound to phase-separate, to separate an acid compound from the gas to be treated. The gas treatment device includes an absorber which brings the gas to be treated into contact with the treatment liquid; a regenerator 14 which heats the treatment liquid contacting the gas to be treated to separate an acid compound; and a liquid feeding portion which feeds the treatment liquid contacting the gas to be treated in the absorber to the regenerator. In the absorber, the treatment liquid contacting the gas to be treated phase-separates into a first phase portion having a high acid compound content and a second phase portion having a low acid compound content. The liquid feeding portion is configured to introduce, into the regenerator, the treatment liquid with the phase-separated first phase portion and second phase portion mixed.

To provide an aldehyde scavenger and a method for removing aldehydes by using the same, for quickly and continuously capturing aldehydes. An aldehyde scavenger comprising at least one O-substituted hydroxylamine or at least one chemically acceptable salt thereof, is used against an aldehyde generation source.

The invention relates to a process for removing hydrogen sulfide and carbon dioxide from a feed gas stream. H2S in the feed gas stream is converted to elemental sulfur in a Claus unit. At least a part of the gas stream obtained is contacted with an aqueous lean absorbing medium in an absorption zone at a pressure between 0.9 and 2 bara. The aqueous lean absorbing medium used comprises one or more amines chosen from: a polyamine in the absence of tertiary amine functionalities having a pKa sufficient to neutralize carbamic acid, the polyamine having at least one primary amine functionality having a pKa smaller than 10.0 at 25 C., a polyamine in the absence of tertiary amine functionalities having a pKa sufficient to neutralize carbamic acid, the polyamine having at least one secondary amine functionality having a pKa for each sorbing nitrogen smaller than 10.0 at 25 C. The process is improved as compared to a process involving Claus off-gas treatment with (activated) MDEA. Effective CO2 removal is achieved while at the same time a simplified line-up with less equipment can be used.

The embodiments provide an acidic gas absorbent, an acidic gas removal method using the absorbent, and an acidic gas removal apparatus using the absorbent. The absorbent absorbs an acidic gas in a large amount and is hardly diffused. The acidic gas absorbent according to the embodiment comprises an amine compound represented by the following formula (1):

##STR00001##

[In the formula, each R.sup.1 is independently hydrogen, an alkyl group, or a primary or secondary amino-containing aminoalkyl group provided that at least one of R.sup.1s is the aminoalkyl group, each R.sup.2 is independently hydrogen, an alkyl group, hydroxy, amino, hydroxyamino, or a primary or secondary amino-containing aminoalkyl group, the alkyl or aminoalkyl group contained in R.sup.1 or R.sup.2 has a straight-chain or branched-chain skeleton and may be substituted with hydroxy or carbonyl, and p is 2 to 4.]

A carbon dioxide absorbent composition is disclosed. Based on 100 parts by weight of the carbon dioxide absorbent composition, the carbon dioxide absorbent composition includes 5 to 45 parts by weight of sodium 2-[(2-aminoethyl)amino]ethanesulfonate. Moreover, a method for capturing carbon dioxide using the carbon dioxide absorbent composition is disclosed.

A system and a process for capturing Carbon Dioxide (CO.sub.2) from flue gases are disclosed. The process comprises feeding a flue gas comprising CO.sub.2 to at least one Rotary Packed Bed (RPB) absorber rotating circularly. A solvent may be provided through an inner radius of the RPB absorber. The solvent may move towards an outer radius of the RPB absorber. The solvent may react with the flue gas in a counter-current flow. The process further includes passing the flue gas through at least one of a water wash and an acid wash to remove traces of the solvent present in the flue gas. Finally, the solvent reacted with the CO.sub.2 may be thermally regenerated for re-utilizing the solvent back in the process.