BACKGROUND

Power generating processes that are based on combustion of carbon-containing fuel typically produce carbon dioxide (CO2) and other exhaust gases as byproducts. The exhaust gases may be harmful to the environment, such as by contributing to the greenhouse effect and global warming. It may be desirable to capture or otherwise separate the CO2from the gas stream exhausted to the environment to reduce the CO2emissions and/or to utilize CO2in the power generation process or in other processes.

Conventional absorbent solvents used to capture a target gas, such as CO2or other exhaust gases, experience increased viscosity when exposed to the target gas. The increased viscosity of the solvent has several disadvantages. For example, the absorbent solvents may form solids or very high viscosity oils upon reacting with CO2. The increased viscosity reduces the mass transfer of CO2into the solvent, such that the absorbent solvent reacts with less CO2than is theoretically possible. Furthermore, materials that form solid CO2reaction products may not readily fit into existing CO2capture process schemes which are designed for flowable liquids.

In order to avoid the issues associated with the increased viscosity of the absorbent solvent upon reaction, some conventional absorbent solvents dilute the concentration of the absorbent composition in the solvent using a carrier fluid, such as water. Although using a carrier fluid can reduce the viscosity of the reaction product, the reduced concentration of the absorbent composition also reduces the performance of the absorbent solvent by decreasing the amount of CO2that can be absorbed, referred to herein as CO2uptake. Moreover, the use of the carrier fluid also increases the energy consumption of the process relative to not using the carrier fluid, due to the energy required for heating and evaporation of the carrier fluid.

BRIEF DESCRIPTION

In an embodiment, an absorbent composition is provided that includes an amino-siloxane having structure (I):


wherein R1is independently at each occurrence a C1-C6aliphatic or aromatic radical; R2is independently at each occurrence a C2-C10aliphatic or aromatic radical; R3is independently at each occurrence a hydrogen atom or a C1-C6aliphatic or aromatic radical; R4is independently at each occurrence a C1-C18aliphatic or aromatic radical or R5, wherein R5comprises 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 R4is R5comprising the structure (II), a sum of w, y, and z is greater than or equal to 0, and, when R4is not R5, a sum of w, y, and z is greater than or equal to 1.

In another embodiment, an absorbent composition is provided that includes an amino-siloxane having structure (III):


wherein R1is independently at each occurrence a C1-C6aliphatic or aromatic radical; R2is independently at each occurrence a C2-C10aliphatic or aromatic radical; R3is independently at each occurrence a hydrogen atom or a C1-C6aliphatic or aromatic radical; R4is independently at each occurrence a C1-C18aliphatic or aromatic radical or R5, wherein R5comprises structure (IV):


wherein X is independently at each occurrence an oxygen atom or a sulfur atom; and n is between 1 and 6, such that the structure (III) includes a ring-shaped core comprising between three and eight alternating pairs of silicon and oxygen atoms.

In an embodiment, a method of reducing an amount of target gas in a process stream is provided that includes contacting the process stream containing the target gas with an absorbent composition comprising an amino-siloxane having structure (I):


wherein R1is independently at each occurrence a C1-C6aliphatic or aromatic radical; R2is independently at each occurrence a C2-C10aliphatic or aromatic radical; R3is independently at each occurrence a hydrogen atom or a C1-C6aliphatic or aromatic radical; R4is independently at each occurrence a C1-C18aliphatic or aromatic radical or R5, wherein R5comprises 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 R4is R5comprising the structure (II), a sum of w, y, and z is greater than or equal to 0, and, when R4is not R5, a sum of w, y, and z is greater than or equal to 1.

