Carbon Capture and Storage (CCS) is a way of mitigating greenhouse gas emissions from burning fossil fuels, power plants, and industrial processes. This could be a potentially significant tool to manage global warming. Aqueous amine-based solvents are used to separate and capture CO2 in commercial CCS processes. One way to further improve CCS is to increase the absorption efficiency is by lowering the surface tension of the solvent so it can better wet the absorber packing material and increase gas/liquid (CO2/solvent) contact. One approach to decrease the surface tension of the amine solvent is by incorporating small amount of surfactant-like compounds, such as commercially available Tween (a non-ionic amphipathic surfactant), as an emulsifier to generate controlled micro-bubbles and increase turbulence within the solvent leading to increased CO2 absorption efficiency. However, it is a challenge to analyze and monitor the concentration and degradation of these surfactant additives in the complex high pH, high carbon-loaded (C/N ∼ 0.5) amine solvent matrix. Due to the structural heterogeneity of surfactants such as Tween and their polar head group and non-polar fatty acid tail, the sample matrix complexity and instrumentation capabilities, it has been a challenge to develop a suitable analytical approach for these surfactants. The development of an indirect method for the analysis of Tween in carbon-loaded amine solutions has been developed in this work. The modified method involves base hydrolysis induced cleavage at the ethylene oxide subunits and hydrolysis of fatty acid ester bond resulting free fatty acids followed by BF3 methylation and GC-MS analysis. Solid phase extraction prior to methylation or derivatization enhances the concentration of fatty acids by removing interfering matrix components. The results show that in carbon-loaded amine samples the base hydrolysis of Tween worked significantly well to liberate the fatty acids. The GC-MS quantification of all fatty acids is used in determining the amount of the Tween surfactant present in the complex samples from the UK CAER small bench carbon capture unit.

Determination of surfactants in high pH CO2 capture solvents by hydrolysis, derivatization, and GC-MS analysis

ACS Fall 2021

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