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 C.sub.1 to C.sub.6 alkylene and ethers of formula —R.sup.2—O—R.sup.3— wherein R.sup.2 and R.sup.3 are C.sub.1 to C.sub.3 alkylene.

A scrubbing solution for removing contaminants, including particularly hydrogen sulfide, from a fluid. The scrubbing solution includes at least one scrubbing reagent which has a primary or secondary amine and an acid, which may be phosphoric acid. The fluid being scrubbed is passed through the scrubbing solution. The contaminants react with the scrubbing reagent securing them in the scrubbing solution. The fluid being scrubbed and the scrubbing solution are then separated. The scrubbing solution is heated and, if the scrubbing solution is under pressure, the pressure is reduced. The acid facilitates thorough removal of the contaminants, and especially the hydrogen sulfide, from the scrubbing solution. The scrubbing solution is then ready for reuse. Because the scrubbing solution is rendered substantially free of hydrogen sulfides, it can absorb other sulfide contaminants that might not otherwise be absorbed.

A composite amine absorbent according to the present invention is an absorbent for absorbing CO.sub.2 or H.sub.2S, or both of CO.sub.2 and H.sub.2S in a gas. The absorbent is obtained by dissolving (1) a linear monoamine, (2) a diamine, and (3) propylene glycol alkyl ether, for example, represented by the following chemical formula (I) in water. In the composite amine absorbent, the components complexly interact, and the synergistic effect thereof provides good absorbability of CO.sub.2 or H.sub.2S, or both of CO.sub.2 and H.sub.2S and good releasability of CO.sub.2 or H.sub.2S absorbed during regeneration of the absorbent. Furthermore, the amount of water vapor in a reboiler 26 used during regeneration of the absorbent in a CO.sub.2 recovery unit 12 can be reduced.
R.sup.1—O—(R.sup.2—O).sub.n—R.sup.3  (I)

Disclosed herein is a method and system for CO.sub.2 removal from a gas stream using a diamine solvent having a Formula I
R.sup.1(R.sup.2)N-L.sup.1-NH—R.sup.3  Formula I.
With respect to Formula I, each of R.sup.1 and R.sup.2 independently is aliphatic, cycloaliphatic, or R.sup.1 and R.sup.2 together with the nitrogen to which they are attached, form a heterocyclyl ring; L.sup.1 is aliphatic, cycloaliphatic, or L.sup.1 and R.sup.1 together with the nitrogen to which they are attached form a heterocyclyl ring; and R.sup.3 is aliphatic, cycloaliphatic, cycloalkylalkyl, or alkoxyalkyl. And/or the compound may have a viscosity of less than 75 cP at a CO.sub.2-loading of 40 mol % and at a temperature of 40° C.

An aqueous solvent composition is provided, comprising a nucleophilic component having one or more sterically unhindered primary or secondary amine moieties, a Brønsted base component having one or more basic nitrogen moieties, a water-soluble organic solvent, and water. A biphasic composition is provided, comprising one or more carbamate compounds, one or more conjugate acids of Brønsted base, a water-soluble organic solvent, and water. A biphasic CO.sub.2 absorption process is also provided, utilizing the biphasic solvent composition.

Disclosed herein is a method and system for CO.sub.2 removal from a gas stream using a diamine solvent having a Formula I

R.sup.1(R.sup.2)N−L.sup.1−NH—R.sup.3  Formula I.

With respect to Formula I, each of R.sup.1 and R.sup.2 independently is aliphatic, cycloaliphatic, or R.sup.1 and R.sup.2 together with the nitrogen to which they are attached, form a heterocyclyl ring; L.sup.1 is aliphatic, cycloaliphatic, or L.sup.1 and R.sup.1 together with the nitrogen to which they are attached form a heterocyclyl ring; and R.sup.3 is aliphatic, cycloaliphatic, cycloalkylalkyl, or alkoxyalkyl. And/or the compound may have a viscosity of less than 75 cP at a CO.sub.2-loading of 40 mol % and at a temperature of 40° C.

A method and apparatus for continuously treating acid gases including recovering absorbent chemicals by introducing streams leaving a regenerator and/or leaving an absorber into a static mixing zone wherein supplemental washing water is added to recover absorbent chemicals. Improvements to the prior art methods are provided where one or more absorbent chemical recovery units are included to increase the amount of recovered absorbent chemicals exiting the regenerator and/or exiting the absorber are increased and/or maximized. Absorbent chemical recovery units can include mixing units where liquid is added to the stream of sour gas and absorbent chemical to mix with and absorb the absorbent chemical from the stream.

Provided is a composition for removal of a sulfur-containing compound in a liquid or gas, wherein the sulfur-containing compound is at least one selected from the group consisting of hydrogen sulfide and a compound containing an —SH group, and the composition contains an aldehyde and a polyvalent amine represented by the general formula (1).

The acid gas removal system for removing acidic gases from gaseous hydrocarbons (10) removes sour gases, such as hydrogen sulfide (H.sub.2S) and carbon dioxide (CO.sub.2), from an input gaseous stream. The system (10) includes a contactor (12) for contacting the input gaseous stream with an absorption liquid solvent (ALS), and a stripper (24) for recycling the absorption liquid solvent (ALS) and removing acidic gases (AG) therefrom, but with the addition of a pair of plate-plate heat exchangers (22, 26). The first heat exchanger (22) heats the used absorption liquid solvent (UALS) output from the contactor (12) prior to injection into the stripper (24). The used absorption liquid solvent (UALS) is heated via heat exchange with the acidic gases (AG) output from the stripper (24). The second heat exchanger (26) cools the recycled absorption liquid solvent (RALS) before injection back into the contactor (12).

Systems and methods for at least partially removing carbon dioxide (CO.sub.2) from a feed gas comprising CO.sub.2 are generally provided.